In this work we present three studies in protein engineering. While all three protein classes that have been targeted for engineering tasks are very different, the studies have a focus on scaling-up the throughput in protein engineering.
\r\n\r\nThe first study concerns machine learning (ML) based antibody humanization techniques. Achieving a reduction of patient anti-drug antibody responses in clinical trials is the goal of antibody humanization. To measure this however, one needs to pass significant scientific, bureaucratic, and financial hurdles, which is very rarely done and especially never at scale. Most existing ML-based antibody humanization techniques claim that they work without providing any experimental evidence. We developed Mousify as an in silico antibody humanization platform to place existing models into one framework for wet-laboratory validation. We demonstrate that even the best models have a fundamental flaw in that they only generate a single antibody. We use Mousify and Markov chains to show that using ML-based antibody humanization models for library generation is not only feasible but produces both stable and functional variants. Learning the lessons from our wet-laboratory experiments, we then developed a variational autoencoder model with properties that hopefully improve the outcomes of antibody humanization experiments.
\r\n \r\nIn the second study, we outline our plans and initial results to develop a bioelectrocatalytic system for the conversion of N2 to ammonia using nitrogenase. Most of the world\u2019s ammonia is used for agricultural purposes and is produced via the environmentally damaging Haber-Bosch process. Engineering nitrogenase for the bioelectrocatalytic production of ammonia is not trivial and a high throughput is not guaranteed. We present preliminary results in how throughput can be increased through diazotrophic pre-selection of nitrogenase variants, as well as a quest to find the ideal starting point for engineering using a combination of ancestral sequence reconstruction and generative protein language models.
\r\n\r\nIn the third and final study we present a directed evolution campaign to evolve protoglobins for the enantioselective catalytic formation of cis-trifluoromethyl substituted cyclopropanes, the first such reaction in both the chemical and biological world. Not only is the enzyme ApePgb LQ capable of efficiently performing carbene insertions into double-bonds, but it also shows a much more diverse substrate scope than similar enantioselective formations of trans-trifluoromethyl substituted cyclopropanes. After demonstrating that ApePgb LQ reactions can be increased to a 1-mmol scale, we investigated the nature of protoglobin cis-selectivity using various computational methods.
" }, { "name": "Yu, Jing", "degree": "PhD", "year": "2025", "title": "Safe and Scalable Learning-Based Control: Theory and Application in Sustainable Energy Systems", "advisor": "Doyle, John Comstock; Wierman, Adam C.", "url": "https://resolver.caltech.edu/CaltechThesis:08192024-223132153", "creators": [ { "name": { "family": "Yu", "given": "Jing" }, "id": "Yu-Jing", "orcid": "0000-0003-1318-0189", "display_name": "Yu, Jing" } ], "advisors": [ { "name": { "family": "Doyle", "given": "John Comstock" }, "id": "Doyle-J-C", "orcid": "0000-0002-1828-2486", "role": "co-advisor", "display_name": "Doyle, John Comstock" }, { "name": { "family": "Wierman", "given": "Adam C." }, "id": "Wierman-A-C", "orcid": "0000-0002-5923-0199", "role": "co-advisor", "display_name": "Wierman, Adam C." } ], "committee": [ { "name": { "family": "Low", "given": "Steven H." }, "id": "Low-S-H", "orcid": "0000-0001-6476-3048", "role": "chair", "display_name": "Low, Steven H." }, { "name": { "family": "Doyle", "given": "John Comstock" }, "id": "Doyle-J-C", "orcid": "0000-0002-1828-2486", "role": "member", "display_name": "Doyle, John Comstock" }, { "name": { "family": "Wierman", "given": "Adam C." }, "id": "Wierman-A-C", "orcid": "0000-0002-5923-0199", "role": "member", "display_name": "Wierman, Adam C." }, { "name": { "family": "Yue", "given": "Yisong" }, "id": "Yue-Yisong", "orcid": "0000-0001-9127-1989", "role": "member", "display_name": "Yue, Yisong" } ], "option_major": [ "cds" ], "doi": "10.7907/bgar-0602", "abstract": "From intelligent transportation systems to the smart grid, the next generation of cyber-physical systems (CPS) will substantially transform our society. It is vital that these systems are scalable and robust to uncertainties, with contextual awareness and fast adaptation. This dissertation presents progress towards addressing key challenges arising in the control of large-scale CPS, with a special focus on applications in sustainable energy systems.
\r\n\r\nLarge-scale CPS such as the smart grid often consist of numerous interconnected and heterogeneous subsystems that must coordinate to achieve global objectives by exchanging information over a communication network. \r\nTherefore, the first part of this thesis focuses on developing control algorithms that handle crucial design requirements emerging from scalability and communication constraints, such as disturbance localization, communication delay conformation, and distributed implementation.
\r\n\r\nSustainable energy systems are crucial for reducing greenhouse gas emissions and mitigating climate change. However, the inherent unpredictability and large uncertainties associated with renewable generation pose significant challenges for maintaining system stability and safety. Traditional control approaches, while robust and effective for known system models, often fall short when faced with the dynamic and uncertain nature of modern power systems. In the second part of the thesis, we address this challenge by integrating machine learning techniques with model-based control methods using uncertainty sets constructed from real-time data. In particular, we will introduce and provide convergence guarantees for a classic uncertainty set estimation method. Building on these uncertainty sets, we combine learning and control techniques to tackle core CPS control problems, such as adversarial stability certification for linear time-varying systems as well as networked systems under communication constraints where the system models are unknown.
\r\n\r\nThe final part of this thesis applies the developed methodologies to address the voltage control problem in power distribution networks with unknown grid topologies. We will combine online learning techniques and a robust predictive controller to achieve provably finite-time convergence to safe voltage limits, despite uncertainties in network topology and load variations. Our case study on a Southern California Edison 56-bus distribution system demonstrates the effectiveness of this approach in nonlinear, partial observation, and partial control settings.
" }, { "name": "Sun, Yuchun", "degree": "PhD", "year": "2024", "title": "3D Micro-Architected Materials for Batteries", "advisor": "Greer, Julia R.", "url": "https://resolver.caltech.edu/CaltechTHESIS:04162024-184348195", "creators": [ { "name": { "family": "Sun", "given": "Yuchun" }, "id": "Sun-Yuchun", "orcid": "0000-0002-7028-3523", "display_name": "Sun, Yuchun" } ], "advisors": [ { "name": { "family": "Greer", "given": "Julia R." }, "id": "Greer-J-R", "orcid": "0000-0002-9675-1508", "role": "advisor", "display_name": "Greer, Julia R." } ], "committee": [ { "name": { "family": "Faber", "given": "Katherine T." }, "id": "Faber-K-T", "orcid": "0000-0001-6585-2536", "role": "chair", "display_name": "Faber, Katherine T." }, { "name": { "family": "See", "given": "Kimberly" }, "id": "See-Kimberly", "orcid": "0000-0002-0133-9693", "role": "member", "display_name": "See, Kimberly" }, { "name": { "family": "West", "given": "William C." }, "id": "West-W-C", "orcid": "0000-0001-6417-8930", "role": "member", "display_name": "West, William C." }, { "name": { "family": "Greer", "given": "Julia R." }, "id": "Greer-J-R", "orcid": "0000-0002-9675-1508", "role": "member", "display_name": "Greer, Julia R." } ], "option_major": [ "matsci" ], "doi": "10.7907/y6bt-xb40", "abstract": "Additive manufacturing (AM) enables three-dimensional micro-patterning of battery electrode materials, permitting complex structural designs beyond those of traditional slurry electrodes. We demonstrate two novel AM approaches for architecting electrode materials in lithium-ion batteries. First, we introduce a process for fabricating 3D micro-architected cathodes utilizing gel infusion additive manufacturing, and demonstrate this technique with lithium cobalt oxide (LCO). This method combines VP-based 3D printing with subsequent ion infusion and calcination processes. It starts with the printing of a blank organogel structure using a customized acrylate-based photoresin. This organogel is then converted into a hydrogel, infused with lithium and cobalt precursors, and finally subjected to calcination to form the LCO structure. This technique achieves 3D micro-architected LCO lattices with beam diameters of 45 \u03bcm, and maintains the designed architecture with tunable microstructures. By fabricating 3D micro-architected LiNi0.33Mn0.33Co0.33O2 (NMC111) through a very similar process, we demonstrate the potential for this gel infusion additive manufacturing method to engineer a variety of cathode materials for lithium-ion batteries in 3D.
\r\n\r\nWe also develop a fabrication method to create 3D lithium anodes supported by micro-architected carbon scaffold. By pyrolyzing 3D printed polymer microlattices, mechanically robust carbon electrodes are produced. Their micro-scale features and flexible structural control make them suitable as scaffolds for lithium-metal anodes. Surface functionalization and lithium electrodeposition are explored for dense lithium nucleation and uniform epitaxial growth on the carbon framework, resulting in micro-architected lithium/carbon anodes. With the rapid development of high-resolution AM techniques in recent decades, these approaches to additively manufacture cathode and anode materials provide promising pathways to build batteries with customizable 3D designs, and pursue higher energy and power densities for different applications.
" }, { "name": "Zeichner, Sarah Soojin", "degree": "PhD", "year": "2024", "title": "Fates of Carbon", "advisor": "Eiler, John M.", "url": "https://resolver.caltech.edu/CaltechTHESIS:01022024-183348243", "creators": [ { "name": { "family": "Zeichner", "given": "Sarah Soojin" }, "id": "Zeichner-Sarah-Soojin", "orcid": "0000-0001-8897-7657", "display_name": "Zeichner, Sarah Soojin" } ], "advisors": [ { "name": { "family": "Eiler", "given": "John M." }, "id": "Eiler-J-M", "orcid": "0000-0001-5768-7593", "role": "advisor", "display_name": "Eiler, John M." } ], "committee": [ { "name": { "family": "Fischer", "given": "Woodward W." }, "id": "Fischer-W-W", "orcid": "0000-0002-8836-3054", "role": "chair", "display_name": "Fischer, Woodward W." }, { "name": { "family": "Sessions", "given": "Alex L." }, "id": "Sessions-A-L", "orcid": "0000-0001-6120-2763", "role": "member", "display_name": "Sessions, Alex L." }, { "name": { "family": "Grotzinger", "given": "John P." }, "id": "Grotzinger-J-P", "orcid": "0000-0001-9324-1257", "role": "member", "display_name": "Grotzinger, John P." }, { "name": { "family": "Eiler", "given": "John M." }, "id": "Eiler-J-M", "orcid": "0000-0001-5768-7593", "role": "member", "display_name": "Eiler, John M." } ], "option_major": [ "geochem" ], "doi": "10.7907/vy9f-k705", "abstract": "This thesis investigates the organic matter relevant to the oldest rocks on the Earth and in the Solar System, along with novel methods for exploring the composition of that organic matter. Chapter II describes a novel method for using a gas chromatography-Orbitrap mass spectrometer system to simultaneously analyze multiple isotopic properties from multiple compounds within a complex mixture. This method is ideal for the study of environmental or extraterrestrial samples and was integral to the study described in Chapter III. Chapters III and IV highlight new isotopic properties that can be measured in extraterrestrial samples to constrain processes of abiotic organic molecule formation: These processes have direct implications for where the carbon on Earth comes from. Chapter III details the measurement of \u00b9\u00b3C, D, and double-\u00b9\u00b3C contents of five polycyclic aromatic hydrocarbons in samples returned by the Hayabusa2 spacecraft mission to the Ryugu asteroid. The findings of this study support the formation of aromatic hydrocarbons---arguably the most abundant molecules in the Milky Way galaxy and other galaxies---through low-temperature reactions within molecular clouds in the interstellar medium. Chapter IV characterizes the position-specific carbon isotopic compositions of three structurally-distinct amino acids-- \u03b1-alanine, \u03b2-alanine and aspartic acid--from the Murchison meteorite, which provide constraints for how they were synthesized abiotically within the meteorite parent body. Chapters V-VI of this thesis relate to organic molecules on the early Earth. Chapter V is a scholarly review of prior data documenting the carbon isotope contents of organic carbon in Archean rocks. It also includes a model for the evolution of the carbon isotopic composition of organic matter as it goes through the rock cycle (i.e., diagenesis, catagenesis, metagenesis and metamorphism), which is then used to re-interpret carbon isotope data based on extant biology and models of metabolic evolution. Chapter VI uses sedimentological experiments to demonstrate that water-soluble organic compounds may have led to the rise of mud deposition concurrent with the evolution of land plants." }, { "name": "Beery, Sara Meghan", "degree": "PhD", "year": "2023", "title": "Where the Wild Things Are: Computer Vision for Global-Scale Biodiversity Monitoring", "advisor": "Perona, Pietro", "url": "https://resolver.caltech.edu/CaltechTHESIS:04242022-005200355", "creators": [ { "name": { "family": "Beery", "given": "Sara Meghan" }, "id": "Beery-Sara-Meghan", "orcid": "0000-0002-2544-1844", "display_name": "Beery, Sara Meghan" } ], "advisors": [ { "name": { "family": "Perona", "given": "Pietro" }, "id": "Perona-P", "orcid": "0000-0002-7583-5809", "role": "advisor", "display_name": "Perona, Pietro" } ], "committee": [ { "name": { "family": "Yue", "given": "Yisong" }, "id": "Yue-Yisong", "orcid": "0000-0001-9127-1989", "role": "chair", "display_name": "Yue, Yisong" }, { "name": { "family": "Bouman", "given": "Katherine L." }, "id": "Bouman-K-L", "orcid": "0000-0003-0077-4367", "role": "member", "display_name": "Bouman, Katherine L." }, { "name": { "family": "Belongie", "given": "Serge J." }, "id": "Belongie-S-J", "orcid": "0000-0002-0388-5217", "role": "member", "display_name": "Belongie, Serge J." }, { "name": { "family": "Perona", "given": "Pietro" }, "id": "Perona-P", "orcid": "0000-0002-7583-5809", "role": "member", "display_name": "Perona, Pietro" } ], "option_major": [ "cms" ], "doi": "10.7907/m4mt-2q51", "abstract": "We require a real-time, modular earth observation system that unites efforts across research groups in order to provide the necessary information necessary for global-scale impact in sustainability and conservation in the face of climate change. The development of such systems requires collaborative, interdisciplinary approaches that translate diverse sources of raw information into accessible scientific insight. For example, we need to monitor species in real time and in greater detail to quickly understand which conservation efforts are most effective and take corrective action. Current ecological monitoring systems generate data far faster than researchers can analyze it, making scaling up impossible without automated data processing. However, ecological data collected in the field presents a number of challenges that current methods, like deep learning, are not designed to tackle. These include strong spatiotemporal correlations, imperfect data quality, fine-grained categories, and long-tailed distributions. Our work seeks to overcome these challenges, and this thesis includes methods which can learn from imperfect data, systematic frameworks and benchmarks for measuring and overcoming performance drops due to domain shift, and the development and deployment of efficient human-AI systems that have made significant real-world conservation impact." }, { "name": "Chen, Zhewei", "degree": "PhD", "year": "2023", "title": "Engineering Conditional Guide RNAs for Cell-Selective Regulation of CRISPR/Cas9", "advisor": "Pierce, Niles A.", "url": "https://resolver.caltech.edu/CaltechTHESIS:12022022-010002116", "creators": [ { "name": { "family": "Chen", "given": "Zhewei" }, "id": "Chen-Zhewei", "orcid": "0000-0002-7422-095X", "display_name": "Chen, Zhewei" } ], "advisors": [ { "name": { "family": "Pierce", "given": "Niles A." }, "id": "Pierce-N-A", "orcid": "0000-0003-2367-4406", "role": "advisor", "display_name": "Pierce, Niles A." } ], "committee": [ { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "orcid": "0000-0002-5785-7481", "role": "chair", "display_name": "Murray, Richard M." }, { "name": { "family": "Rothemund", "given": "Paul W. K." }, "id": "Rothemund-P-W-K", "orcid": "0000-0002-1653-3202", "role": "member", "display_name": "Rothemund, Paul W. K." }, { "name": { "family": "Hay", "given": "Bruce A." }, "id": "Hay-B-A", "orcid": "0000-0002-5486-0482", "role": "member", "display_name": "Hay, Bruce A." }, { "name": { "family": "Pierce", "given": "Niles A." }, "id": "Pierce-N-A", "orcid": "0000-0003-2367-4406", "role": "member", "display_name": "Pierce, Niles A." } ], "option_major": [ "bioeng" ], "doi": "10.7907/cajs-d417", "abstract": "CRISPR/Cas9 is a versatile platform for implementing diverse modes of genetic perturbation such as gene silencing, induction, deletion, or replacement. This technology is popularly used in developmental biology to probe genetic circuitry via constitutive gene knockdown. Global gene silencing could introduce artifacts in the study of developmental regulatory pathways, and this motivates the development of cell-selective gene editing. Our lab has recently created conditional guide RNAs (cgRNA) that enable CRISPR/Cas9 systems to silence a desired gene Y conditioned on the detection of an RNA transcript X inside of a cell. cgRNA systems were discovered via insertion and deletion mutations that systematically explored the structure function of the guide RNA. Nucleic acid engineering software (NUPACK) was used to generate orthogonal libraries of cgRNA molecules that executed both ON \u2192 OFF logic (conditional inactivation by an RNA trigger) and OFF \u2192 ON logic (conditional activation by an RNA trigger). A dCas9-based RFP silencing assay in bacteria was developed and used to show these cgRNA sequences were functional and could detect short exogenous trigger sequences in an orthogonal and doseresponsive manner. Subsequent studies on cgRNA structure and function enabled us to engineer next-generation systems that have fewer constraints on the trigger sequence or structure. These next-generation cgRNAs were tested against short synthetic mRNA transcripts, truncated sub-sequences of endogenous mRNAs, and full-length endogenous mRNAs. Synthetic mRNA transcripts were used to study the effect of protein translation on trigger RNA binding. cgRNAs were capable of detecting synthetic sequences embedded in the 3\u2032 UTR of fluorescent protein mRNAs. cgRNAs could also detect short synthetic mRNAs or truncated subsequences from endogenous mRNAs. However, the detection of native full-length endogenous mRNAs remained challenging because we cannot reliably predict the local structure of sub-sequences within a long RNA transcript. High-throughput cgRNAscreening may prove necessary for finding accessible binding sites onmRNA transcripts. Nevertheless, cgRNA functionalities could be useful in developmental biology by enabling precision perturbation of regulatory events, linking guide RNA activity to an RNA marker X correlated to a specific cell type or temporal expression pattern. This work opens the possibility for future applications such as cell-selective gene therapies.
" }, { "name": "Cole, Elijah Henry John", "degree": "PhD", "year": "2023", "title": "Visual and Spatial Representation Learning with Applications in Ecology", "advisor": "Perona, Pietro", "url": "https://resolver.caltech.edu/CaltechTHESIS:06072023-210232983", "creators": [ { "name": { "family": "Cole", "given": "Elijah Henry John" }, "id": "Cole-Elijah-Henry-John", "orcid": "0000000166230966", "display_name": "Cole, Elijah Henry John" } ], "advisors": [ { "name": { "family": "Perona", "given": "Pietro" }, "id": "Perona-P", "orcid": "0000-0002-7583-5809", "role": "advisor", "display_name": "Perona, Pietro" } ], "committee": [ { "name": { "family": "Perona", "given": "Pietro" }, "id": "Perona-P", "orcid": "0000-0002-7583-5809", "role": "member", "display_name": "Perona, Pietro" }, { "name": { "family": "Yue", "given": "Yisong" }, "id": "Yue-Yisong", "orcid": "0000-0001-9127-1989", "role": "chair", "display_name": "Yue, Yisong" }, { "name": { "family": "Bouman", "given": "Katherine L." }, "id": "Bouman-K-L", "orcid": "0000-0003-0077-4367", "role": "member", "display_name": "Bouman, Katherine L." }, { "name": { "family": "Belongie", "given": "Serge J." }, "id": "Belongie-S-J", "orcid": "0000-0002-0388-5217", "role": "member", "display_name": "Belongie, Serge J." } ], "option_major": [ "cms" ], "doi": "10.7907/xp2k-es46", "abstract": "Machine learning has the potential to empower scientists, physicians, and other human experts working to solve problems of societal importance. To realize this goal, we need algorithms that can distill useful knowledge from real-world data. However, most machine learning research focuses on benchmarks that seldom reflect real-world challenges, such as learning from limited, noisy, or weak supervision. This thesis develops new benchmarks, algorithms, and problem settings that link fundamental machine learning research to impactful applications in ecology. In Part I, we provide context and motivation for our work. How and why should machine learning researchers work with domain experts on real-world problems? What is the appeal of ecology specifically Part II focuses on visual representation learning with an emphasis on label efficiency. We discuss the strengths and limitations of self-supervised learning, the relationship between concept specificity and representation learning, and multi-label learning with minimal labeled data. Part III covers our work in the emerging field on spatial representation learning. In particular, we consider the problem of modeling the spatial distribution of plant and animal species. We review this important ecological problem from a machine learning perspective before showing how deep learning can transform the way these models are applied (using spatial models to assist image classifiers) and developed (jointly learning spatial distributions and representations). Finally, Part IV concludes and highlights opportunities for future work." }, { "name": "Dove, Lilian Aja", "degree": "PhD", "year": "2023", "title": "Impacts of Zonal Asymmetry on Southern Ocean Dynamics and Biogeochemistry", "advisor": "Thompson, Andrew F.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05302023-201452585", "creators": [ { "name": { "family": "Dove", "given": "Lilian Aja" }, "id": "Dove-Lilian-Aja", "orcid": "0000-0001-8346-0034", "display_name": "Dove, Lilian Aja" } ], "advisors": [ { "name": { "family": "Thompson", "given": "Andrew F." }, "id": "Thompson-A-F", "orcid": "0000-0003-0322-4811", "role": "advisor", "display_name": "Thompson, Andrew F." } ], "committee": [ { "name": { "family": "Adkins", "given": "Jess F." }, "id": "Adkins-J-F", "orcid": "0000-0002-3174-5190", "role": "chair", "display_name": "Adkins, Jess F." }, { "name": { "family": "Fu", "given": "Xiaojing" }, "id": "Fu-Xiaojing", "orcid": "0000-0001-7120-704X", "role": "member", "display_name": "Fu, Xiaojing" }, { "name": { "family": "Gray", "given": "Alison R." }, "id": "Gray-Alison-R", "role": "member", "display_name": "Gray, Alison R." }, { "name": { "family": "Gierach", "given": "Michelle Marie" }, "id": "Gierach-M-M", "role": "member", "display_name": "Gierach, Michelle Marie" }, { "name": { "family": "Thompson", "given": "Andrew F." }, "id": "Thompson-A-F", "orcid": "0000-0003-0322-4811", "role": "member", "display_name": "Thompson, Andrew F." } ], "option_major": [ "envreng" ], "doi": "10.7907/qnah-sc58", "abstract": "The Southern Ocean is a key region for the ventilation and formation of intermediate and deep water masses. Interactions of the Southern Ocean\u2019s Antarctic Circumpolar Current (ACC) with bathymetry can result in the diversion and compaction of frontal currents, resulting in standing meanders associated with enhanced mesoscale eddy kinetic energy (EKE) and submesoscale vertical velocities. As a result, standing meanders are thought to shape uptake and sequestration of heat and carbon across the ACC. In this thesis, I use observations from remote sensing and various autonomous underwater vehicles to investigate how physical mechanisms, from the submesoscale to the basin scale, shape the biogeochemical properties and tracer distributions of the Southern Ocean.
\r\n\r\nProcesses at the ocean's submesoscale can play a vital role in exchanging water across the base of the mixed layer, contributing to water mass ventilation. Data from over 20,000 profiles from biogeochemical-Argo floats across the ACC highlight that the high EKE regions associated with standing meanders have relatively reduced apparent oxygen utilization (AOU) values below the base of the mixed layer. This result, as well as larger AOU variance in deep potential density classes, suggests there is enhanced ventilation occurring in standing meanders. Further investigation suggests the observed increased ventilation is due to both along-isopycnal stirring and enhanced exchange across the base of the mixed layer by vertical velocities at the submesoscale, highlighting the importance of standing meanders in shaping temporal and spatial variability of biogeochemical cycles and air-sea exchange.
\r\n\r\nObservations with horizontal scales of 2-4 kilometers in the standing meander associated with Crozet Plateau show that submesoscale processes are indeed ubiquitous. In this region, processes on the submesoscale to mesoscale spectrum play a role in enhancing surface frontal gradients and heightening tracer variability at depth. A separate field program provided novel observations at the submesoscale in Drake Passage during wintertime. The Polar Front, one of the major fronts of the ACC, is shown to be eddy-suppressing, suggesting that along-isopycnal submesoscale processes contribute to ventilation at the front. These spatial variations in stratification may additionally impact carbon fluxes between the atmosphere, surface mixed layer, and interior ocean. This thesis presents evidence that ventilation is a heterogeneous process across the Southern Ocean, with contributions from processes at physical scales that are undersampled by current observational programs.
" }, { "name": "Dowling, Jacqueline Anne", "degree": "PhD", "year": "2023", "title": "Long-Duration Energy Storage in Reliable Wind and Solar Electricity Systems", "advisor": "Lewis, Nathan Saul", "url": "https://resolver.caltech.edu/CaltechTHESIS:06042023-203620894", "creators": [ { "name": { "family": "Dowling", "given": "Jacqueline Anne" }, "id": "Dowling-Jacqueline-Anne", "orcid": "0000-0001-5642-8960", "display_name": "Dowling, Jacqueline Anne" } ], "advisors": [ { "name": { "family": "Lewis", "given": "Nathan Saul" }, "id": "Lewis-N-S", "orcid": "0000-0001-5245-0538", "role": "advisor", "display_name": "Lewis, Nathan Saul" } ], "committee": [ { "name": { "family": "Gray", "given": "Harry B." }, "id": "Gray-H-B", "orcid": "0000-0002-7937-7876", "role": "chair", "display_name": "Gray, Harry B." }, { "name": { "family": "Hunt", "given": "Melany L." }, "id": "Hunt-M-L", "orcid": "0000-0001-5592-2334", "role": "member", "display_name": "Hunt, Melany L." }, { "name": { "family": "Kornfield", "given": "Julia A." }, "id": "Kornfield-J-A", "orcid": "0000-0001-6746-8634", "role": "member", "display_name": "Kornfield, Julia A." }, { "name": { "family": "Lewis", "given": "Nathan Saul" }, "id": "Lewis-N-S", "orcid": "0000-0001-5245-0538", "role": "member", "display_name": "Lewis, Nathan Saul" } ], "option_major": [ "chemistry" ], "doi": "10.7907/gyzn-4n98", "abstract": "Several U.S. states mandate zero-carbon electricity systems based primarily on renewable technologies, such as wind and solar. Reliable and affordable electricity systems based on these variable resources may depend on the ability to store large quantities of low-cost energy over long timescales. This thesis combines techno-economic analysis with materials chemistry to advance long-duration energy storage in reliable wind and solar electricity systems. Our macro-energy model incorporated multi-decadal weather datasets and revealed unique long-duration energy storage roles, such as seasonal and multi-year storage, that increase the affordability of wind- and solar-based electricity, informing technology investments and policy. We find that low-cost energy storage, such as underground hydrogen, is valuable even if the charge/discharge cost is expensive. In U.S. wind and solar systems, hydrogen energy storage and conversion capital cost improvements are more valuable than efficiency improvements. Low-cost earth-abundant catalysts may be acceptable replacements for precious metal catalysts in proton exchange membrane electrolyzers despite lower efficiency for storage applications in wind and solar systems. We synthesized earth-abundant manganese antimony oxide catalysts via a new chemical vapor deposition route and assessed their long-term electrochemical durability for oxygen evolution. Multi-day tests confirmed the activity-stability tradeoff across the Mn:Sb composition space." }, { "name": "Kerkovius, Jeffrey Kevan", "degree": "PhD", "year": "2023", "title": "Total Synthesis of Lupin Alkaloids, Diterpenoid Alkaloids, and Progress Towards the Myrsinane Diterpenes", "advisor": "Reisman, Sarah E.", "url": "https://resolver.caltech.edu/CaltechTHESIS:06012023-171716967", "creators": [ { "name": { "family": "Kerkovius", "given": "Jeffrey Kevan" }, "id": "Kerkovius-Jeffrey-Kevan", "orcid": "0000-0001-5692-0285", "display_name": "Kerkovius, Jeffrey Kevan" } ], "advisors": [ { "name": { "family": "Reisman", "given": "Sarah E." }, "id": "Reisman-S-E", "orcid": "0000-0001-8244-9300", "role": "advisor", "display_name": "Reisman, Sarah E." } ], "committee": [ { "name": { "family": "Stoltz", "given": "Brian M." }, "id": "Stoltz-B-M", "orcid": "0000-0001-9837-1528", "role": "chair", "display_name": "Stoltz, Brian M." }, { "name": { "family": "Agapie", "given": "Theodor" }, "id": "Agapie-T", "orcid": "0000-0002-9692-7614", "role": "member", "display_name": "Agapie, Theodor" }, { "name": { "family": "Nelson", "given": "Hosea M." }, "id": "Nelson-H-M", "orcid": "0000-0002-4666-2793", "role": "member", "display_name": "Nelson, Hosea M." }, { "name": { "family": "Reisman", "given": "Sarah E." }, "id": "Reisman-S-E", "orcid": "0000-0001-8244-9300", "role": "member", "display_name": "Reisman, Sarah E." } ], "option_major": [ "chemistry" ], "doi": "10.7907/y6rd-nm97", "abstract": "The interplay between total synthesis and methodology is a driver of innovation in organic synthesis. Challenging bond formations in complex systems necessitate the development ever more robust new reactions, which intern can enable more efficient syntheses. The need for powerful synthetic organic chemistry can\u2019t be understated because of its utility in applications such as medicine, petrochemicals, plastics, and agrichemicals.
\r\n\r\nHerein, we present how total synthesis drives innovation in organic chemistry. First, a novel cyclization reaction between pyridine and glutaryl chloride is discussed, which has enabled the synthesis of seven lupin alkaloids. Next, the development of a convergent fragment coupling tactic based upon the semi-pinacol rearrangement is evaluated for its generality inspired by the total synthesis of several C19 diterpenoid alkaloids. Lastly, a convergent fragment coupling approach is applied to the total synthesis of falcatin A based upon a Mukaiyama Michael tandem Mukaiyama aldol reaction.
" }, { "name": "Li, Tongxin", "degree": "PhD", "year": "2023", "title": "Learning-Augmented Control and Decision-Making: Theory and Applications in Smart Grids", "advisor": "Low, Steven H.; Wierman, Adam C.", "url": "https://resolver.caltech.edu/CaltechThesis:07202022-040725024", "creators": [ { "name": { "family": "Li", "given": "Tongxin" }, "id": "Li-Tongxin", "orcid": "0000-0002-9806-8964", "display_name": "Li, Tongxin" } ], "advisors": [ { "name": { "family": "Low", "given": "Steven H." }, "id": "Low-S-H", "orcid": "0000-0001-6476-3048", "role": "advisor", "display_name": "Low, Steven H." }, { "name": { "family": "Wierman", "given": "Adam C." }, "id": "Wierman-A-C", "orcid": "0000-0002-5923-0199", "role": "co-advisor", "display_name": "Wierman, Adam C." } ], "committee": [ { "name": { "family": "Yue", "given": "Yisong" }, "id": "Yue-Yisong", "orcid": "0000-0001-9127-1989", "role": "chair", "display_name": "Yue, Yisong" }, { "name": { "family": "Low", "given": "Steven H." }, "id": "Low-S-H", "orcid": "0000-0001-6476-3048", "role": "member", "display_name": "Low, Steven H." }, { "name": { "family": "Wierman", "given": "Adam C." }, "id": "Wierman-A-C", "orcid": "0000-0002-5923-0199", "role": "member", "display_name": "Wierman, Adam C." }, { "name": { "family": "Mazumdar", "given": "Eric V." }, "id": "Mazumdar-Eric", "orcid": "0000-0002-1815-269X", "role": "member", "display_name": "Mazumdar, Eric V." } ], "option_major": [ "cms" ], "doi": "10.7907/cdf6-0w78", "abstract": "Achieving carbon neutrality by 2050 does not only lead to the increasing penetration of renewable energy, but also an explosive growth of smart meter data. Recently, augmenting classical methods in real-world cyber-physical systems such as smart grids with black-box AI tools, forecasts, and ML algorithms has attracted a lot of growing interest. Integrating AI techniques into smart grids, on the one hand, provides a new approach to handle the uncertainties caused by renewable resources and human behaviors, but on the other hand, creates practical issues such as reliability, stability, privacy, and scalability, etc. to the AI-integrated algorithms.
\r\n\r\nThis dissertation focuses on solving problems raised in designing learning-augmented control and decision-making algorithms.
\r\n \r\nThe results presented in this dissertation are three-fold. We first study a problem in linear quadratic control, where imperfect/untrusted AI predictions of system perturbations are available. We show that it is possible to design a learning-augmented algorithm with performance guarantees that is aggressive if the predictions are accurate and conservative if they are imperfect. Machine-learned black-box policies are ubiquitous for nonlinear control problems. Meanwhile, crude model information is often available for these problems from, e.g., linear approximations of nonlinear dynamics. We next study the problem of equipping a black-box control policy with model-based advice for nonlinear control on a single trajectory. We first show a general negative result that a naive convex combination of a black-box policy and a linear model-based policy can lead to instability, even if the two policies are both stabilizing. We then propose an adaptive \u03bb-confident policy, with a coefficient \u03bb indicating the confidence in a black-box policy, and prove its stability. With bounded nonlinearity, in addition, we show that the adaptive \u03bb-confident policy achieves a bounded competitive ratio when a black-box policy is near-optimal. Finally, we propose an online learning approach to implement the adaptive \u03bb-confident policy and verify its efficacy in case studies about the Cart-Pole problem and a real-world electric vehicle (EV) charging problem with data bias due to COVID-19.
\r\n\r\nAggregators have emerged as crucial tools for the coordination of distributed, controllable loads. To be used effectively, an aggregator must be able to communicate the available flexibility of the loads they control, known as the aggregate flexibility to a system operator. However, most existing aggregate flexibility measures often are slow-timescale estimations and much less attention has been paid to real-time coordination between an aggregator and an operator. In the second part of this dissertation, we consider solving an online decision-making problem in a closed-loop system and present a design of real-time aggregate flexibility feedback, termed the maximum entropy feedback (MEF). In addition to deriving analytic properties of the MEF, combining learning and control, we show that it can be approximated using reinforcement learning and used as a penalty term in a novel control algorithm--the penalized predictive control (PPC) that enables efficient communication, fast computation, and lower costs. We illustrate the efficacy of the PPC using a dataset from an adaptive electric vehicle charging network and show that PPC outperforms classical MPC. We show that under certain regularity assumptions, the PPC is optimal. We illustrate the efficacy of the PPC using a dataset from an adaptive electric vehicle charging network and show that PPC outperforms classical model predictive control (MPC). In a theoretical perspective, a two-controller problem is formulated. A central controller chooses an action from a feasible set that is determined by time-varying and coupling constraints, which depend on all past actions and states. The central controller's goal is to minimize the cumulative cost; however, the controller has access to neither the feasible set nor the dynamics directly, which are determined by a remote local controller. Instead, the central controller receives only an aggregate summary of the feasibility information from the local controller, which does not know the system costs. We show that it is possible for an online algorithm using feasibility information to nearly match the dynamic regret of an online algorithm using perfect information whenever the feasible sets satisfy some criterion, which is satisfied by inventory and tracking constraints.
\r\n\r\nThe third part of this dissertation consists of examples of learning, inference, and data analysis methods for power system identification and electric charging. We present a power system identification problem with noisy nodal measurements and efficient algorithms, based on fundamental trade-offs between the number of measurements, the complexity of the graph class, and the probability of error. Next, we specifically consider prediction and unsupervised learning tasks in EV charging. We provide basic data analysis results of a public dataset released by Caltech and develop a novel iterative clustering method for classifying time series of EV charging rates.
" }, { "name": "L\u00f3pez G\u00f3mez, Ignacio", "degree": "PhD", "year": "2023", "title": "A Unified Data-Informed Model of Turbulence and Convection for Climate Prediction", "advisor": "Schneider, Tapio", "url": "https://resolver.caltech.edu/CaltechTHESIS:11152022-215747755", "creators": [ { "name": { "family": "L\u00f3pez G\u00f3mez", "given": "Ignacio" }, "id": "L\u00f3pez-G\u00f3mez-Ignacio", "orcid": "0000-0002-7255-5895", "display_name": "L\u00f3pez G\u00f3mez, Ignacio" } ], "advisors": [ { "name": { "family": "Schneider", "given": "Tapio" }, "id": "Schneider-T", "orcid": "0000-0001-5687-2287", "role": "advisor", "display_name": "Schneider, Tapio" } ], "committee": [ { "name": { "family": "Callies", "given": "Joern" }, "id": "Callies-J", "orcid": "0000-0002-6815-1230", "role": "chair", "display_name": "Callies, Joern" }, { "name": { "family": "Stuart", "given": "Andrew M." }, "id": "Stuart-A-M", "orcid": "0000-0001-9091-7266", "role": "member", "display_name": "Stuart, Andrew M." }, { "name": { "family": "Teixeira", "given": "Joao" }, "id": "Teixeira-Joao", "role": "member", "display_name": "Teixeira, Joao" }, { "name": { "family": "Schneider", "given": "Tapio" }, "id": "Schneider-T", "orcid": "0000-0001-5687-2287", "role": "member", "display_name": "Schneider, Tapio" } ], "option_major": [ "envreng" ], "doi": "10.7907/042m-9686", "abstract": "Resolving atmospheric turbulent and convective processes in global climate simulations is, and will remain for decades, an intractable computational problem. The strong influence of these processes on cloud formation and maintenance makes the task of modeling turbulence and convection one of the grand challenges in climate modeling, due to the outsized effect of clouds on climate. Current operational climate models fail to represent atmospheric turbulence and convection accurately and consistently across dynamical regimes and vertical levels; errors in the representation of these processes explain about half of the spread in climate projections. This dissertation seeks to reduce such representation errors by improving a recently proposed unified framework for modeling turbulence and convection, known as the extended eddy-diffusivity mass-flux scheme, in several ways. First, the framework is rederived by systematically coarse-graining the governing fluid equations, highlighting the assumptions about atmospheric motion that are necessary to yield the scheme. New terms related to turbulent entrainment processes are shown to arise from the derivation. Second, a generalized formulation of turbulent diffusion consistent with the framework is presented. This novel formulation is shown to accurately represent turbulent processes under statically stable and unstable conditions, including regimes with sharp lapse rate inversions such as the stratocumulus-topped boundary layer. Finally, a methodology to calibrate free parameters within the model from indirect data is proposed. The methodology, based on Kalman filtering, is shown to be efficient at calibrating imperfect black-box models from noisy data, and in its regularized unscented version approximately quantifies parametric uncertainty. The resulting unified data-informed model of turbulence and convection is shown to accurately represent a range of low-cloud regimes that are associated with the largest biases in current operational climate models. The response of the model to realistic climate perturbations is also shown to be consistent with the resolved climate response, although structural errors in the amount of condensate are still important at realistic vertical resolutions." }, { "name": "Quine, Cullen Mackenzie", "degree": "PhD", "year": "2023", "title": "Tunability of Gas Adsorption Enthalpies in Carbonaceous Materials for Energy-Related Applications", "advisor": "Fultz, Brent T.; Ahn, Channing C.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05292023-054311609", "creators": [ { "name": { "family": "Quine", "given": "Cullen Mackenzie" }, "id": "Quine-Cullen-Mackenzie", "orcid": "0000-0002-7301-0969", "display_name": "Quine, Cullen Mackenzie" } ], "advisors": [ { "name": { "family": "Fultz", "given": "Brent T." }, "id": "Fultz-B-T", "orcid": "0000-0002-6364-8782", "role": "advisor", "display_name": "Fultz, Brent T." }, { "name": { "family": "Ahn", "given": "Channing C." }, "id": "Ahn-C-C", "role": "co-advisor", "display_name": "Ahn, Channing C." } ], "committee": [ { "name": { "family": "Fultz", "given": "Brent T." }, "id": "Fultz-B-T", "orcid": "0000-0002-6364-8782", "role": "member", "display_name": "Fultz, Brent T." }, { "name": { "family": "Schwab", "given": "Keith C." }, "id": "Schwab-K-C", "orcid": "0000-0001-8216-4815", "role": "chair", "display_name": "Schwab, Keith C." }, { "name": { "family": "Wang", "given": "Zhen-Gang" }, "id": "Wang-Zhen-Gang", "orcid": "0000-0002-3361-6114", "role": "member", "display_name": "Wang, Zhen-Gang" }, { "name": { "family": "Stadie", "given": "Nicholas" }, "id": "Stadie-P-Nicholas", "orcid": "0000-0002-1139-7846", "role": "member", "display_name": "Stadie, Nicholas" }, { "name": { "family": "Ahn", "given": "Channing C." }, "id": "Ahn-C-C", "role": "member", "display_name": "Ahn, Channing C." } ], "option_major": [ "matsci" ], "doi": "10.7907/r5ad-1j85", "abstract": "Carbonaceous materials provide a porous, high surface area framework for the adsorption of gases through physisorption. Physisorption operates through van der Waals forces, resulting in highly reversible, densified gas storage. The density of adsorbed gas species approaches the bulk liquid density, providing a method to increase the volumetric energy density of hydrogen and natural gas at conditions where the adsorbate is a non-liquid in the bulk phase. This dissertation explores the tunability of the strength of gas adsorption to surfaces of carbon adsorbents, known as the enthalpy of adsorption. Two methods are studied: modification of the surface atomic composition and microstructural changes to the carbon porosity. Applications are considered for both energy storage and carbon capture applications.
\r\n\r\nThe first chapter presents a brief overview of the energy storage field, with emphasis on non-conventional methods to store gases efficiently. Chapter 2 provides the thermodynamic and statistical mechanical derivations used throughout this work, and the assumptions that go into the models used to analyze adsorption data. Chapter 3 reports work on a copper-modified commercial carbon MSC-30 for hydrogen storage, which exhibits an activated dissociative chemisorption desorption feature around ambient temperature. Chapter 4 presents the densification of a novel architected carbon structure, zeolite-templated carbon, for adsorbed natural gas storage. Through the pelletization process, the pore morphology of the underlying adsorbent framework is compressed, resulting in increased adsorption enthalpies with applied pelletization pressure. Chapter 5 focuses on the tunability of pore structure through potassium hydroxide activation, and the resulting adsorption properties pertinent to carbon dioxide capture from a simulated flue-gas stream. The last chapter provides insight into the work as a whole and identifies areas of future work that would improve the fundamental understanding and broader impact of adsorbent materials.
" }, { "name": "Tribby, Ariana Linnae", "degree": "PhD", "year": "2023", "title": "Inference of Global Methane Emissions from Oil and Gas Production", "advisor": "Wennberg, Paul O.", "url": "https://resolver.caltech.edu/CaltechTHESIS:06022023-045855497", "creators": [ { "name": { "family": "Tribby", "given": "Ariana Linnae" }, "id": "Tribby-Ariana-Linnae", "orcid": "0000-0002-6435-4575", "display_name": "Tribby, Ariana Linnae" } ], "advisors": [ { "name": { "family": "Wennberg", "given": "Paul O." }, "id": "Wennberg-P-O", "orcid": "0000-0002-6126-3854", "role": "advisor", "display_name": "Wennberg, Paul O." } ], "committee": [ { "name": { "family": "Seinfeld", "given": "John H." }, "id": "Seinfeld-J-H", "orcid": "0000-0003-1344-4068", "role": "chair", "display_name": "Seinfeld, John H." }, { "name": { "family": "Wennberg", "given": "Paul O." }, "id": "Wennberg-P-O", "orcid": "0000-0002-6126-3854", "role": "member", "display_name": "Wennberg, Paul O." }, { "name": { "family": "Blake", "given": "Geoffrey A." }, "id": "Blake-G-A", "orcid": "0000-0003-0787-1610", "role": "member", "display_name": "Blake, Geoffrey A." }, { "name": { "family": "Flagan", "given": "Richard C." }, "id": "Flagan-R-C", "orcid": "0000-0001-5690-770X", "role": "member", "display_name": "Flagan, Richard C." } ], "option_major": [ "chemistry" ], "doi": "10.7907/pjn3-az83", "abstract": "Atmospheric methane plays a significant role in warming the climate. Characterizing its sources and sinks is important for future climate and air quality impacts. Global methane background trends suggest a sustained increase in emissions since 2007. There is no debate that reducing anthropogenic (human-driven) emissions can lead to short-term decreases in atmospheric methane, posing an attractive avenue towards mitigating climate change. Yet, effective policy to limit emissions from energy-related activities relies on accurate emission estimates, and historically, it has been challenging to diagnose both the magnitude and origin of methane leaks from a wide range of facilities and components across production, transmission, storage, and distribution systems. We present a novel Bayesian hierarchical model to improve methane emission estimates on global and regional scales from oil and gas processes. We also present methods to optimize time and cost of model simulations of certain trace gases, including several of which have important climate implications. Finally, we present our efforts in characterizing fossil methane from burgeoning oil production in Oklahoma and Texas using long term ground-based remote-sensing observations combined with Stochastic Time-Inverted Larangian Transport modeling.
" }, { "name": "Versaw, Brooke Ann", "degree": "PhD", "year": "2023", "title": "Thermally and Mechanically Responsive Platforms for Functional Polymeric Materials", "advisor": "Robb, Maxwell J.", "url": "https://resolver.caltech.edu/CaltechTHESIS:04272023-220317123", "creators": [ { "name": { "family": "Versaw", "given": "Brooke Ann" }, "id": "Versaw-Brooke-Ann", "orcid": "0000-0002-6200-7203", "display_name": "Versaw, Brooke Ann" } ], "advisors": [ { "name": { "family": "Robb", "given": "Maxwell J." }, "id": "Robb-M-J", "orcid": "0000-0002-0528-9857", "role": "advisor", "display_name": "Robb, Maxwell J." } ], "committee": [ { "name": { "family": "Stoltz", "given": "Brian M." }, "id": "Stoltz-B-M", "orcid": "0000-0001-9837-1528", "role": "chair", "display_name": "Stoltz, Brian M." }, { "name": { "family": "Reisman", "given": "Sarah E." }, "id": "Reisman-S-E", "orcid": "0000-0001-8244-9300", "role": "member", "display_name": "Reisman, Sarah E." }, { "name": { "family": "Agapie", "given": "Theodor" }, "id": "Agapie-T", "orcid": "0000-0002-9692-7614", "role": "member", "display_name": "Agapie, Theodor" }, { "name": { "family": "Robb", "given": "Maxwell J." }, "id": "Robb-M-J", "orcid": "0000-0002-0528-9857", "role": "member", "display_name": "Robb, Maxwell J." } ], "option_major": [ "chemistry" ], "doi": "10.7907/2hwm-af78", "abstract": "Connecting a polymer\u2019s reactivity or properties to its working environment is a grand challenge in polymer chemistry. Research towards this goal is driven both by a fundamental interest in mimicking nature\u2019s ability to create surfaces that adapt to their surroundings and a practical desire to tailor the properties of materials to the wide-ranging contexts where they find use. This thesis investigates the development of polymers that exhibit productive changes in physical properties or chemical reactivity under an applied environmental stimulus." }, { "name": "Werner, Lucien Desloge", "degree": "PhD", "year": "2023", "title": "Uncertainty and Decentralization: Two Themes in an Energy Transformation", "advisor": "Low, Steven H.; Wierman, Adam C.", "url": "https://resolver.caltech.edu/CaltechTHESIS:06122023-232029846", "creators": [ { "name": { "family": "Werner", "given": "Lucien Desloge" }, "id": "Werner-Lucien-Desloge", "orcid": "0000-0003-1613-1702", "display_name": "Werner, Lucien Desloge" } ], "advisors": [ { "name": { "family": "Low", "given": "Steven H." }, "id": "Low-S-H", "orcid": "0000-0001-6476-3048", "role": "advisor", "display_name": "Low, Steven H." }, { "name": { "family": "Wierman", "given": "Adam C." }, "id": "Wierman-A-C", "orcid": "0000-0002-5923-0199", "role": "co-advisor", "display_name": "Wierman, Adam C." } ], "committee": [ { "name": { "family": "Yue", "given": "Yisong" }, "id": "Yue-Yisong", "orcid": "0000-0001-9127-1989", "role": "chair", "display_name": "Yue, Yisong" }, { "name": { "family": "Murray", "given": "Richard M." }, "id": "Murray-R-M", "orcid": "0000-0002-5785-7481", "role": "member", "display_name": "Murray, Richard M." }, { "name": { "family": "Low", "given": "Steven H." }, "id": "Low-S-H", "orcid": "0000-0001-6476-3048", "role": "member", "display_name": "Low, Steven H." }, { "name": { "family": "Wierman", "given": "Adam C." }, "id": "Wierman-A-C", "orcid": "0000-0002-5923-0199", "role": "member", "display_name": "Wierman, Adam C." } ], "option_major": [ "cms" ], "doi": "10.7907/scmm-p028", "abstract": "Over the last two decades, the rapidly decreasing units costs of solar, wind, and energy storage technologies have launched a fundamental transformation in how electric power is produced, distributed, and consumed. Proliferation of these technologies has effected a shift towards a more decentralized, flexible, and sustainable energy system that can meet the growing demand for energy while reducing greenhouse gas emissions from fossil fuels. The work in this thesis studies two principal themes in this transformation: uncertainty and decentralization.
\r\n\r\nUncertainty is a key challenge in the modern grid resulting from the weather dependence of variable renewables and volatile loads like electric vehicles distributed throughout the grid. Electricity markets, whose function is to regulate the precise balance of supply and demand across the system, face a pressing need for dispatch mechanisms that account for uncertainty while providing participation incentives for generators and loads. We introduce a framework for multi-stage market dispatch and pricing under a general description of forecast uncertainty that enables system operators to explicitly incorporate uncertainty into market-clearing prices. In related work, we study mechanisms that guarantee feasibility of multi-interval dispatch under robust uncertainty and provide participation incentives for shiftable demand response in forward multi-interval markets.
\r\n\r\nThe trend towards a more decentralized energy system stems from the inherent modularity of distributed energy resources (DERs), such as solar and storage, as well as the persistent growth in end-use loads. This evolution presents significant challenges to system operators who typically lack the tools and processes for managing a complex, distributed power system. To fill this gap, we introduce and implement a Microgrid Operating System (OS), a software platform for monitoring, modeling, and optimizing microgrids and distribution systems. The Microgrid OS is a central layer that links DER hardware, such as batteries, solar, and flexible loads, to energy applications like cost minimization, emissions reduction, and wholesale market participation. The core functions it provides are data acquisition and processing, system modeling and learning, and optimization and control. We present key modules of the Microgrid OS in the context of several implementation projects in microgrids, commercial buildings, and distribution networks.
" }, { "name": "Zhang, Yi", "degree": "PhD", "year": "2023", "title": "Application of Heterojunction Ni-Sb-SnO\u2082 Anodes for Electrochemical Water Treatment", "advisor": "Hoffmann, Michael R.", "url": "https://resolver.caltech.edu/CaltechTHESIS:03132023-113800696", "creators": [ { "name": { "family": "Zhang", "given": "Yi" }, "id": "Zhang-Yi", "orcid": "0000-0002-9062-5201", "display_name": "Zhang, Yi" } ], "advisors": [ { "name": { "family": "Hoffmann", "given": "Michael R." }, "id": "Hoffmann-M-R", "orcid": "0000-0001-6495-1946", "role": "advisor", "display_name": "Hoffmann, Michael R." } ], "committee": [ { "name": { "family": "Sessions", "given": "Alex L." }, "id": "Sessions-A-L", "orcid": "0000-0001-6120-2763", "role": "chair", "display_name": "Sessions, Alex L." }, { "name": { "family": "Frankenberg", "given": "Christian" }, "id": "Frankenberg-Christian", "orcid": "0000-0002-0546-5857", "role": "member", "display_name": "Frankenberg, Christian" }, { "name": { "family": "See", "given": "Kimberly" }, "id": "See-Kimberly", "orcid": "0000-0002-0133-9693", "role": "member", "display_name": "See, Kimberly" }, { "name": { "family": "Gschwend", "given": "Philip M." }, "id": "Gschwend-Philip-M", "orcid": "0000-0002-9497-4492", "role": "member", "display_name": "Gschwend, Philip M." }, { "name": { "family": "Hoffmann", "given": "Michael R." }, "id": "Hoffmann-M-R", "orcid": "0000-0001-6495-1946", "role": "member", "display_name": "Hoffmann, Michael R." } ], "option_major": [ "envreng" ], "doi": "10.7907/dmrd-w489", "abstract": "Clean water supply and adequate sanitation services are critical for public health as well as for food production. Small-scale decentralized treatment represents an attractive alternative that can provide necessary water treatment in many parts of the developing world where centralized wastewater treatment facilities are not practical owing to financial, geographical, or political constraints. Electrochemical oxidation (EO) is a suitable technique for decentralized treatment settings since it does not require the addition of auxiliary chemicals and offers fast reaction kinetics and modular treatment capacity. EO is considered a versatile technology since it can degrade a wide array of contaminants and inactivate waterborne pathogens. The chemical composition of the anode, where EO takes place, is a key factor that controls reactive species production and thus treatment efficiency and energy consumption. Ideal anodes for wastewater treatment should have high overpotential for oxygen evolution (\u201cnonactive\u201d anodes) and favor complete organics oxidation through direct electron transfer and/or reactions with potent oxidants such as hydroxyl radical and ozone. Common nonactive anodes including antimony-doped tin oxide (Sb-SnO\u2082), lead oxide (PbO\u2082), and boron-doped diamond (BDD) have attracted wide research interests. The work presented in this thesis centered around a newly designed heterojunction Ni-Sb-SnO\u20822-based anode (NAT/AT) and its various applications in decentralized water and wastewater treatment. Direct treatment using NAT/AT has proved to be efficient for chemical oxygen demand removal, trace organic compound degradation, and microbial disinfection. Detailed investigation into pharmaceutical degradation kinetics and transformation products further established NAT/AT as a potential treatment alternative for the control of pharmaceuticals and their metabolites in hospital wastewaters. NAT/AT is also capable of synthesizing ferrates (e.g., FeO\u2084\u00b2\u207b) in circumneutral conditions, the high oxidation state iron species that represents another group of powerful oxidants well-suited for decentralized treatment purposes. In an additional effort to tackle high concentrations of ammonium often present in latrine wastewaters, functionalized metal-organic framework (MOF), a class of materials featuring high porosity, abundant active sites, and highly tunable physical and chemical properties, was used to recover the ammonium nitrogen. Various modifications of MOF-808, a highly water stable MOF, were designed and synthesized to achieve urea hydrolysis, ammonium capture, and real-time ammonium sensing in sequence. In combination, the described works provide a powerful toolkit that can be used in treating various waste streams before discharge and/or reuse." }, { "name": "Zott, Michael David", "degree": "PhD", "year": "2023", "title": "Strategic Applications of Electrochemistry in Ammonia Oxidation and Alkyl Halide Reduction", "advisor": "Peters, Jonas C.", "url": "https://resolver.caltech.edu/CaltechTHESIS:04282023-205948012", "creators": [ { "name": { "family": "Zott", "given": "Michael David" }, "id": "Zott-Michael-David", "orcid": "0000-0003-0535-0512", "display_name": "Zott, Michael David" } ], "advisors": [ { "name": { "family": "Peters", "given": "Jonas C." }, "id": "Peters-J-C", "orcid": "0000-0002-6610-4414", "role": "advisor", "display_name": "Peters, Jonas C." } ], "committee": [ { "name": { "family": "Hadt", "given": "Ryan G." }, "id": "Hadt-Ryan-G", "orcid": "0000-0001-6026-1358", "role": "chair", "display_name": "Hadt, Ryan G." }, { "name": { "family": "Peters", "given": "Jonas C." }, "id": "Peters-J-C", "orcid": "0000-0002-6610-4414", "role": "member", "display_name": "Peters, Jonas C." }, { "name": { "family": "Chan", "given": "Garnet K." }, "id": "Chan-G-K", "orcid": "0000-0001-8009-6038", "role": "member", "display_name": "Chan, Garnet K." }, { "name": { "family": "Fu", "given": "Gregory C." }, "id": "Fu-G-C", "orcid": "0000-0002-0927-680X", "role": "member", "display_name": "Fu, Gregory C." }, { "name": { "family": "Gray", "given": "Harry B." }, "id": "Gray-H-B", "orcid": "0000-0002-7937-7876", "role": "member", "display_name": "Gray, Harry B." } ], "option_major": [ "chemistry" ], "doi": "10.7907/4fr8-7r78", "abstract": "This thesis describes the strategic application of electrochemistry in the development of catalytic systems for two challenging processes: alkyl halide reduction and ammonia oxidation. In the case of alkyl halide reduction, the ability to precisely tune electrochemical potential favored the use of electrochemistry as compared to chemical reagents. By contrast, for ammonia oxidation, electrochemistry was specifically targeted due to motivations in the eventual development of ammonia fuel cell technology. The first chapter introduces these and other advantages of electrochemistry, as well as details regarding the thermodynamic potentials and kinetic barriers associated with alkyl halide reduction or ammonia oxidation. The second chapter details our development of photoelectrochemical methodology to employ a strongly luminescent dicopper system for outer-sphere, single-electron transfer reduction of benzyl chlorides. The third chapter marks the beginning of our work in molecular iron-mediated ammonia oxidation catalysis, in which we develop our hypothesis that catalyst structures featuring cis-labile coordination sites should mediate ammonia oxidation. We disclose the first iron electrocatalyst ([(TPA)Fe(MeCN)\u2082]\u00b2\u207a) as well as a framework for the analysis of metrics such as overpotential, catalytic rate, and catalyst stability. The fourth chapter introduces a hypothesis for catalyst improvement\u2014favoring low-spin electronic structures\u2014and a model system for testing: ([(BPM)Fe(MeCN)\u2082]\u00b2\u207a). Using this second-generation catalyst, improved stability, enhanced activity, and lowered overpotential were observed. The fifth chapter explores the validity of the cis-labile and low-spin hypotheses via Hammett-type substituent studies on both the [(TPA)Fe(MeCN)\u2082]\u00b2\u207a and the [(BPM)Fe(MeCN)\u2082]\u00b2\u207a platforms. This study resulted in the development of a further enhanced molecular electrocatalyst for ammonia oxidation and revealed mechanistic information pertinent to the development of future catalytic systems." }, { "name": "Gu, Alan Yalun", "degree": "PhD", "year": "2022", "title": "Aqueous Aerosols in Atmospheric Chemistry and Airborne Diseases", "advisor": "Hoffmann, Michael R.", "url": "https://resolver.caltech.edu/CaltechTHESIS:04142022-025410011", "creators": [ { "name": { "family": "Gu", "given": "Alan Yalun" }, "id": "Gu-Alan-Yalun", "orcid": "0000-0001-8095-3634", "display_name": "Gu, Alan Yalun" } ], "advisors": [ { "name": { "family": "Hoffmann", "given": "Michael R." }, "id": "Hoffmann-M-R", "orcid": "0000-0001-6495-1946", "role": "advisor", "display_name": "Hoffmann, Michael R." } ], "committee": [ { "name": { "family": "Wennberg", "given": "Paul O." }, "id": "Wennberg-P-O", "orcid": "0000-0002-6126-3854", "role": "chair", "display_name": "Wennberg, Paul O." }, { "name": { "family": "Gray", "given": "Harry B." }, "id": "Gray-H-B", "orcid": "0000-0002-7937-7876", "role": "member", "display_name": "Gray, Harry B." }, { "name": { "family": "Goddard", "given": "William A., III" }, "id": "Goddard-W-A-III", "orcid": "0000-0003-0097-5716", "role": "member", "display_name": "Goddard, William A., III" }, { "name": { "family": "Hoffmann", "given": "Michael R." }, "id": "Hoffmann-M-R", "orcid": "0000-0001-6495-1946", "role": "member", "display_name": "Hoffmann, Michael R." } ], "option_major": [ "chemeng" ], "doi": "10.7907/4spy-az88", "abstract": "Aqueous atmospheric aerosols are small droplets (typically smaller than 5 \u03bcm) suspended in the air that are comprised of water and water-soluble components. These aerosols provide an air-water interfacial reaction environment on their surfaces, and act as a medium for airborne disease transmission. In this thesis, Chapters II and V explore atmospherically relevant reactions on the aqueous aerosol surface using an online mass spectrometry, while Chapter III investigates the SARS-CoV-2 airborne transmission considering suspended virus-laden aerosols as the transmission media. Spinning off this SARS-CoV-2 work, Chapter IV describes a newly developed quantitative RNA amplification test kit for COVID-19, with an emphasis on the amplification result photo recognition component." }, { "name": "Saccone, Max Anthony", "degree": "PhD", "year": "2022", "title": "Vat Photopolymerization Additive Manufacturing of Functional Materials: from Batteries to Metals and Alloys", "advisor": "Greer, Julia R.", "url": "https://resolver.caltech.edu/CaltechTHESIS:06062022-211326081", "creators": [ { "name": { "family": "Saccone", "given": "Max Anthony" }, "id": "Saccone-Max-Anthony", "orcid": "0000-0003-3846-2908", "display_name": "Saccone, Max Anthony" } ], "advisors": [ { "name": { "family": "Greer", "given": "Julia R." }, "id": "Greer-J-R", "orcid": "0000-0002-9675-1508", "role": "advisor", "display_name": "Greer, Julia R." } ], "committee": [ { "name": { "family": "Manthiram", "given": "Karthish" }, "id": "Manthiram-Karthish", "orcid": "0000-0001-9260-3391", "role": "chair", "display_name": "Manthiram, Karthish" }, { "name": { "family": "See", "given": "Kimberly" }, "id": "See-Kimberly", "orcid": "0000-0002-0133-9693", "role": "member", "display_name": "See, Kimberly" }, { "name": { "family": "Kornfield", "given": "Julia A." }, "id": "Kornfield-J-A", "orcid": "0000-0001-6746-8634", "role": "member", "display_name": "Kornfield, Julia A." }, { "name": { "family": "Greer", "given": "Julia R." }, "id": "Greer-J-R", "orcid": "0000-0002-9675-1508", "role": "member", "display_name": "Greer, Julia R." } ], "option_major": [ "chemeng" ], "doi": "10.7907/v3cn-8h28", "abstract": "In recent years, additive manufacturing (AM), also known as 3D printing, has emerged as a uniquely powerful tool for rapid prototyping and for creating complex, high value structures. Vat polymerization (VP) is an AM technique which forms parts through light-initiated polymerization, capable of achieving both high resolution and high throughput. While VP has been utilized to fabricate a wide variety of polymeric materials, fabricating functional materials such as ceramics, metals, and inorganic composites has remained a challenge. This thesis focuses on developing fabrication methods for a range of functional materials, from battery active materials to metals and ceramics, via vat polymerization additive manufacturing, taking advantage of chemical reactions within an AM part after fabrication to form target materials in situ.
\r\n\r\nWe demonstrate the use of emulsions to introduce aqueous active material precursors into organic photopolymer resins to create architected lithium sulfide/carbon composites for use as lithium-sulfur battery cathodes. Such architected cathode materials are promising for mitigating mechanical degradation in high volume-change battery materials such as the sulfur cathode. We additionally performed nanome- chanical experiments on lithium sulfide powders to determine how lithium sulfide yields, deforms, and fails in the context of volume-change-induced stress during battery cycling. Because lithium sulfide is present as a discharge product in all lithium sulfur batteries, these nanomechanical particle compressions have bearing on the entire field, beyond the realm of 3D architected cathodes.
\r\n\r\nWe additionally demonstrate the use of organogel templates to streamline the AM process by enabling the fabrication of many materials starting with a single resin composition, followed by infiltration of appropriate metal precursors and post-processing heat treatment to convert the polymer/precursor matrix to the target metal via calcination and reduction reactions. We fabricate and characterize copper, nickel, silver, cobalt, cupronickel alloys, tungsten, and more to highlight the wide-ranging versatility of achievable materials and microstructures.
" }, { "name": "Went, Cora Margaret", "degree": "PhD", "year": "2022", "title": "Two-Dimensional Transition Metal Dichalcogenides for Ultrathin Solar Cells", "advisor": "Atwater, Harry Albert", "url": "https://resolver.caltech.edu/CaltechTHESIS:04082022-171550192", "creators": [ { "name": { "family": "Went", "given": "Cora Margaret" }, "id": "Went-Cora-Margaret", "orcid": "0000-0001-7737-3348", "display_name": "Went, Cora Margaret" } ], "advisors": [ { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "orcid": "0000-0001-9435-0201", "role": "advisor", "display_name": "Atwater, Harry Albert" } ], "committee": [ { "name": { "family": "Hsieh", "given": "David" }, "id": "Hsieh-David", "orcid": "0000-0002-0812-955X", "role": "chair", "display_name": "Hsieh, David" }, { "name": { "family": "Yeh", "given": "Nai-Chang" }, "id": "Yeh-Nai-Chang", "orcid": "0000-0002-1826-419X", "role": "member", "display_name": "Yeh, Nai-Chang" }, { "name": { "family": "Refael", "given": "Gil" }, "id": "Refael-G", "role": "member", "display_name": "Refael, Gil" }, { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "orcid": "0000-0001-9435-0201", "role": "member", "display_name": "Atwater, Harry Albert" } ], "option_major": [ "physics" ], "doi": "10.7907/xrxk-3q08", "abstract": "Ultrathin solar cells, with absorber layers less than one micron thick, have the potential to use orders of magnitude less high-quality semiconducting material than current silicon solar cells. This could be advantageous in applications that require high power output per unit weight, such as vehicle-integrated photovoltaics, or where reducing the capital cost of solar cell manufacturing is important. Transition metal dichalcogenides are a promising candidate for the semiconducting absorber layer of ultrathin solar cells due to their intrinsically passivated surfaces and their high absorption per unit thickness.
\r\n\r\nThis thesis explores two-dimensional transition metal dichalcogenides for ultrathin photovoltaics. We start with the simplest type of solar cell, which collects carriers via a Schottky junction formed by sandwiching the absorber layer between two metal contacts with different work functions. To enable this geometry and avoid Fermi-level pinning, we develop a new process for gently transferring van der Waals metal contacts onto transition metal dichalcogenides. We measure an open-circuit voltage of 250 mV and a power conversion efficiency of 0.5% in Schottky-junction solar cells. To improve upon this efficiency, we next make carrier-selective contact solar cells, which employ wide bandgap semiconductors to selectively collect electrons on one side and holes on the other side of the absorber layer. We measure an open-circuit voltage of 520 mV and a power conversion efficiency greater than 2% in devices based on perovskite solar cell geometries, with PTAA and C60 as selective contact layers. We demonstrate that short carrier lifetimes limit the voltage in these solar cells to 750 mV, well below the detailed balance voltage limit. This motivates a more thorough understanding of the carrier dynamics at play, and we use a new pump-probe optical microscopy technique, stroboSCAT, to spatiotemporally track heat and carrier evolution in transition metal dichalcogenides. When paired with a kinetic model, we show that this technique can be used to measure lifetimes and other important material parameters even in materials with low radiative efficiencies.
\r\n\r\nWe conclude by outlining future research directions towards achieving power conversion efficiencies greater than 10% in transition metal dichalcogenide solar cells.
" }, { "name": "Ford, Rachel Rae", "degree": "PhD", "year": "2021", "title": "Controlling the Dynamics of Microstructure Formation in Mixed-Matrix Polymeric-Particle Membranes", "advisor": "Kornfield, Julia A.; Diallo, Mamadou S.", "url": "https://resolver.caltech.edu/CaltechTHESIS:04192021-200916929", "creators": [ { "name": { "family": "Ford", "given": "Rachel Rae" }, "id": "Ford-Rachel-Rae", "orcid": "0000-0001-9844-1557", "display_name": "Ford, Rachel Rae" } ], "advisors": [ { "name": { "family": "Kornfield", "given": "Julia A." }, "id": "Kornfield-J-A", "orcid": "0000-0001-6746-8634", "role": "advisor", "display_name": "Kornfield, Julia A." }, { "name": { "family": "Diallo", "given": "Mamadou S." }, "id": "Diallo-Mamadou-S", "role": "co-advisor", "display_name": "Diallo, Mamadou S." } ], "committee": [ { "name": { "family": "Goddard", "given": "William A., III" }, "id": "Goddard-W-A-III", "orcid": "0000-0003-0097-5716", "role": "chair", "display_name": "Goddard, William A., III" }, { "name": { "family": "Grubbs", "given": "Robert H." }, "id": "Grubbs-R-H", "orcid": "0000-0002-0057-7817", "role": "member", "display_name": "Grubbs, Robert H." }, { "name": { "family": "Wei", "given": "Lu" }, "id": "Wei-Lu", "role": "member", "display_name": "Wei, Lu" }, { "name": { "family": "Kornfield", "given": "Julia A." }, "id": "Kornfield-J-A", "orcid": "0000-0001-6746-8634", "role": "member", "display_name": "Kornfield, Julia A." }, { "name": { "family": "Diallo", "given": "Mamadou S." }, "id": "Diallo-Mamadou-S", "role": "member", "display_name": "Diallo, Mamadou S." } ], "option_major": [ "chemistry" ], "doi": "10.7907/fqgq-vd04", "abstract": "Polymer membranes are increasingly important in energy generation, water purification, and resource recovery. Control over chemistry, morphology, and mechanical properties gives organic polymers unparalleled advantages for membrane technology\u2014but only if these complementary functions can be married into a cohesive material. Herein I have sought to expand upon the chemical tools for integrating diverse polymers into multifunctional membrane materials, making them easily tunable to various applications. To overcome a fundamental challenge in polymer science\u2014namely, that polymers with different functions often do not mix\u2014the functional polymer is grown in situ in a solution containing a preformed scaffold polymer, a method pioneered by co-advisor Mamadou Diallo. The hierarchical structure of the resulting mixed matrix polymeric-particle (M2P2) membrane is governed by the kinetic competition between polymerization and phase separation of the functional polymer from the scaffold polymer. This competition is quenched by immersion in a nonsolvent, which rapidly solidifies the material to trap the metastable structure formed during synthesis.
\r\n\r\nIn my quest to understand how these competing processes interact to inform multifunctional membrane design, I developed a general method for studying transient structure using ultra-small angle neutron scattering (Chapter II), working closely with Kornfield Group alumnus Dr. Joey Kim. I then investigated the synergistic effects of incorporating different functional polymer architectures in M2P2 membranes (Chapter III), working with fellow graduate student Orland Bateman. By combining low-generation dendrimers with randomly hyperbranched oligomers bearing similar chemical functionality, we can systematically tune the characteristic length of domains formed during synthesis. In the final chapter I discuss the main conclusions and describe future directions for understanding structure during processing in M2P2 membranes. My thesis ultimately provides a broadly relevant platform for membrane design and synthesis, one in which the favorable properties of different polymers may be combined to strike a balance between function, stability, and ease of fabrication.
" }, { "name": "Lee, Sebastian James Rice", "degree": "PhD", "year": "2021", "title": "Combining High- and Low-Level Electronic Structure Theories for the Efficient Exploration of Potential Energy Surfaces", "advisor": "Miller, Thomas F.", "url": "https://resolver.caltech.edu/CaltechTHESIS:10292020-175326058", "creators": [ { "name": { "family": "Lee", "given": "Sebastian James Rice" }, "id": "Lee-Sebastian-James-Rice", "orcid": "0000-0001-7006-9378", "display_name": "Lee, Sebastian James Rice" } ], "advisors": [ { "name": { "family": "Miller", "given": "Thomas F." }, "id": "Miller-T-F", "orcid": "0000-0002-1882-5380", "role": "advisor", "display_name": "Miller, Thomas F." } ], "committee": [ { "name": { "family": "Chan", "given": "Garnet K." }, "id": "Chan-G-K", "orcid": "0000-0001-8009-6038", "role": "chair", "display_name": "Chan, Garnet K." }, { "name": { "family": "Miller", "given": "Thomas F." }, "id": "Miller-T-F", "orcid": "0000-0002-1882-5380", "role": "member", "display_name": "Miller, Thomas F." }, { "name": { "family": "Hadt", "given": "Ryan G." }, "id": "Hadt-Ryan-G", "orcid": "0000-0001-6026-1358", "role": "member", "display_name": "Hadt, Ryan G." }, { "name": { "family": "Okumura", "given": "Mitchio" }, "id": "Okumura-M", "orcid": "0000-0001-6874-1137", "role": "member", "display_name": "Okumura, Mitchio" } ], "option_major": [ "chemistry" ], "doi": "10.7907/saf3-j798", "abstract": "The efficient exploration and characterization of potential energy surfaces paves the way for the theoretical elucidation of complex chemical processes. A potential energy surface arises from the application of the Born-Oppenheimer approximation when solving the Schr\u00f6dinger equation for a molecular system. The extraction of energies and nuclear gradients from the Schr\u00f6dinger equation is typically cost-prohibitive, which has inspired a plethora of approximations. In this thesis, we present the development of embedding and machine learning methodologies that provide fast and accurate energies and nuclear gradients for different chemical classes by combining high- and low-level electronic structure theories. If a chemical change occurs in a spatially localized region, embedding strategies offer an effective approach for balancing accuracy and computational cost. We first consider embedded mean-field theory (EMFT), which seamlessly combines different mean-field theories for different subsystems to describe the whole molecular system. We analyze the errors in EMFT calculations that occur when subsystems employ different atomic-orbital basis sets. These errors can be alleviated by a Fock-matrix correction scheme or by following general basis set recommendations. Systems exhibiting a more complicated electronic structure require a systematically improvable level of theory for the subsystems, which can be realized by projection-based embedding. Projection-based embedding enables the description of a small part of a molecular system at the level of a correlated wavefunction method while the remainder of the system is described at the mean-field level. We go on to derive and numerically demonstrate the analytical nuclear gradients for projection-based embedding. If description of the entire system at the high level of theory is deemed necessary, molecular-orbital-based machine learning (MOB-ML) calculations offers a framework to predict accurate correlation energies at the cost of obtaining molecular orbitals. We go on to present the derivation, implementation, and numerical demonstration of MOB-ML analytical nuclear gradients. We demonstrate the developed methodologies by exploring potential energy surfaces of organic and transition-metal containing molecules.
" }, { "name": "Lee, Zachary Jordan", "degree": "PhD", "year": "2021", "title": "The Adaptive Charging Network Research Portal: Systems, Tools, and Algorithms", "advisor": "Low, Steven H.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05282021-174411678", "creators": [ { "name": { "family": "Lee", "given": "Zachary Jordan" }, "id": "Lee-Zachary-Jordan", "orcid": "0000-0002-5358-2388", "display_name": "Lee, Zachary Jordan" } ], "advisors": [ { "name": { "family": "Low", "given": "Steven H." }, "id": "Low-S-H", "orcid": "0000-0001-6476-3048", "role": "advisor", "display_name": "Low, Steven H." } ], "committee": [ { "name": { "family": "Wierman", "given": "Adam C." }, "id": "Wierman-A-C", "orcid": "0000-0002-5923-0199", "role": "chair", "display_name": "Wierman, Adam C." }, { "name": { "family": "Bouman", "given": "Katherine L." }, "id": "Bouman-K-L", "orcid": "0000-0003-0077-4367", "role": "member", "display_name": "Bouman, Katherine L." }, { "name": { "family": "Chandrasekaran", "given": "Venkat" }, "id": "Chandrasekaran-V", "role": "member", "display_name": "Chandrasekaran, Venkat" }, { "name": { "family": "Low", "given": "Steven H." }, "id": "Low-S-H", "orcid": "0000-0001-6476-3048", "role": "member", "display_name": "Low, Steven H." } ], "option_major": [ "eleceng" ], "doi": "10.7907/8eqg-e110", "abstract": "Millions of electric vehicles (EVs) will enter service in the next decade, generating gigawatt-hours of additional energy demand. Charging these EVs cleanly, affordably, and without excessive stress on the grid will require advances in charging system design, hardware, monitoring, and control. Collectively, we refer to these advances as smart charging. While researchers have explored smart charging for over a decade, very few smart charging systems have been deployed in practice, leaving a sizeable gap between the research literature and the real world. In particular, we find that research is often based on simplified theoretical models. These simple models make analysis tractable but do not account for the complexities of physical systems. Moreover, researchers often lack the data needed to evaluate the performance of their algorithms on real workloads or apply techniques like machine learning. Even when promising algorithms are developed, they are rarely deployed since field tests can be costly and time-consuming.
\r\n \r\nThe goal of this thesis is to develop systems, tools, and algorithms to bridge these gaps between theory and practice.
\r\n\r\nFirst, we describe the architecture of a first-of-its-kind smart charging system we call the Adaptive Charging Network (ACN). \r\nNext, we use data and models from the ACN to develop a suite of tools to help researchers. These tools include ACN-Data, a public dataset of over 80,000 charging sessions; ACN-Sim, an open-source simulator based on realistic models; and ACN-Live, a platform for field testing algorithms on the ACN. Finally, we describe the algorithms we have developed using these tools. For example, we propose a practical and robust algorithm based on model predictive control, which can reduce infrastructure requirements by over 75%, increase operator profits by up to 3.4 times, and significantly reduce strain on the electric power grid. Other examples include a pricing scheme that fairly allocates costs to users considering time-of-use tariffs and demand charges and a data-driven approach to optimally size on-site solar generation with smart EV charging systems.
" }, { "name": "Teh, Ying Shi", "degree": "PhD", "year": "2021", "title": "Understanding Imperfections and Instabilities in Crystals via Physics-Based and Data-Driven Models", "advisor": "Bhattacharya, Kaushik", "url": "https://resolver.caltech.edu/CaltechTHESIS:04202021-184720643", "creators": [ { "name": { "family": "Teh", "given": "Ying Shi" }, "id": "Ying-Shi-Teh", "orcid": "0000-0003-1743-4158", "display_name": "Teh, Ying Shi" } ], "advisors": [ { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "orcid": "0000-0003-2908-5469", "role": "advisor", "display_name": "Bhattacharya, Kaushik" } ], "committee": [ { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "orcid": "0000-0002-2912-0001", "role": "chair", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Ortiz", "given": "Michael" }, "id": "Ortiz-M", "orcid": "0000-0001-5877-4824", "role": "member", "display_name": "Ortiz, Michael" }, { "name": { "family": "Daraio", "given": "Chiara" }, "id": "Daraio-C", "orcid": "0000-0001-5296-4440", "role": "member", "display_name": "Daraio, Chiara" }, { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "orcid": "0000-0003-2908-5469", "role": "member", "display_name": "Bhattacharya, Kaushik" } ], "option_major": [ "mecheng" ], "doi": "10.7907/kd3n-eq78", "abstract": "In crystals, atoms are arranged in a periodic manner in space. However in reality, imperfections and instabilities exist and this repeated arrangement is never perfect. The coupling between crystal defects, lattice instabilities, other defects like domain walls and domain patterns, and material properties generates interesting phenomena that can be leveraged on for future materials design. Nevertheless, the coupling of different scales and processes also makes the modeling and understanding of these materials an open challenge. This thesis examines these various aspects of crystalline solids through the development of both physics-based and data-driven computational models at the appropriate length scales.
\r\n\r\nAbove-bandgap photovoltaic (PV) effect has been observed experimentally in multi-domain ferroelectric perovskites, but the underlying working mechanisms are not well understood. The first part of the thesis presents a device model to study the role of ferroelectric domain walls in the observed PV effect. The model accounts for the intricate interplay between ferroelectric polarization, space charges, photo-generation, and electronic transport. When applied to bismuth ferrite, results show a significant electric potential step across both 71\u00b0 and 109\u00b0 domain walls, which in turn contributes to the PV effect. The domain-wall-driven PV effect is further shown to be additive in nature, allowing for the possibility of generating the above-bandgap voltage.
\r\n\r\nIn the second part, we present a lattice model incorporating random fields and long-range interactions where a frustrated state emerges at a specific composition, but is suppressed elsewhere. The model is motivated by perovskite solid solutions, and explains the phase diagram in such materials including the morphotropic phase boundary (MPB) that plays a critical role in applications for its enhanced dielectric, piezoelectric, and optical properties. Further, the model also suggests the possibility of entirely new phenomena by exploiting MPBs.
\r\n\r\nThe final part of the thesis focuses on constructing data-driven models from first principles calculations, particularly density functional theory (DFT) for studying crystalline materials. Specifically we propose an approach that exploits machine learning to approximate electronic fields in crystalline solids subjected to deformation. When demonstrated on magnesium---a promising light weight structural material---our model predicts the energy and electronic fields to the level of chemical accuracy, and it even captures lattice instabilities. This DFT-based machine learning approach can be very useful in methods that require repeated DFT calculations of unit cell subjected to strain, especially multi-resolution studies of crystal defects and strain engineering that is emerging as a widely used method for tuning material properties.
" }, { "name": "Yu, Weilai", "degree": "PhD", "year": "2021", "title": "Stability of Photo-Electrochemical Interface for Solar Fuels", "advisor": "Lewis, Nathan Saul", "url": "https://resolver.caltech.edu/CaltechTHESIS:03172021-221106133", "creators": [ { "name": { "family": "Yu", "given": "Weilai" }, "id": "Yu-Weilai", "orcid": "0000-0002-9420-0702", "display_name": "Yu, Weilai" } ], "advisors": [ { "name": { "family": "Lewis", "given": "Nathan Saul" }, "id": "Lewis-N-S", "orcid": "0000-0001-5245-0538", "role": "advisor", "display_name": "Lewis, Nathan Saul" } ], "committee": [ { "name": { "family": "Gray", "given": "Harry B." }, "id": "Gray-H-B", "orcid": "0000-0002-7937-7876", "role": "chair", "display_name": "Gray, Harry B." }, { "name": { "family": "Lewis", "given": "Nathan Saul" }, "id": "Lewis-N-S", "orcid": "0000-0001-5245-0538", "role": "member", "display_name": "Lewis, Nathan Saul" }, { "name": { "family": "See", "given": "Kimberly" }, "id": "See-Kimberly", "orcid": "0000-0002-0133-9693", "role": "member", "display_name": "See, Kimberly" }, { "name": { "family": "Okumura", "given": "Mitchio" }, "id": "Okumura-M", "orcid": "0000-0001-6874-1137", "role": "member", "display_name": "Okumura, Mitchio" } ], "option_major": [ "chemistry" ], "doi": "10.7907/2z16-d005", "abstract": "Photoelectrochemical (PEC) water splitting is a promising approach to convert renewable solar energy to clean hydrogen (H2) fuels in one simple step. Although \u2162-\u2164 semiconductors are attractive candidates as light-absorbers in tandem solar-fuel devices, their long-term stability for the hydrogen-evolution reaction (HER) in either acidic or alkaline aqueous electrolytes needs to be established. Chapter 2-5 of this thesis first aims at revealing the underlying corrosion chemistry for a variety of \u2162-\u2164 semiconductors specifically under the HER conditions, offering a rational understanding towards the stability of semiconductor photoelectrode.
\r\n \r\nIn Chapter 2, we start from p-InP and reveal its susceptibility to cathodic photocorrosion forming metallic In0, which however can be completely mitigated by the presence of Pt catalyst due to kinetic stabilization. We also show that the resulting PEC performance of p-InP/Pt electrodes is sensitive to the changes in surface stoichiometry, whereas an InOx-rich surface developed in KOH caused a substantial degradation in the current density-potential (J-E) behavior. In Chapter 3, we discovered that a non-stoichiometric and As0-rich surface of p-GaAs, resulting from a galvanic corrosion by Pt, led to mid-gap surface states as well as a complete loss in photoactivity. In Chapter 4-5, we demonstrate similar kinetic stabilization applied to both p-InGaP2/Pt and pn+-InGaP2/Pt photocathodes for the HER at both pH 0 and pH 14. Additionally, we found that the corrosion of underlying GaAs substrates for the pn+-InGaP2/Pt photocathodes at positive potentials caused damage of structural integrity as well as instability in electrode performance. Altogether these works underscore the mutual dependence of the physical and electrochemical stability of semiconductor photoelectrodes during the HER, which also need to be considered separately. Moreover, both catalytic kinetics and surface stoichiometry are crucial factors for defining long-term corrosion chemistry for semiconductor photoelectrode.
\r\n \r\nIn Chapter 6-7, we further explore solar fuels beyond H2, namely electrochemical N2-to-NH3 conversion. We first establish a new analytical method to isotopically quantify the concentrations of 15NH3 in aqueous solutions with a high sensitivity and a low limit-of-detection of <1 \u03bcM. Further we applied this advanced method to rigorously verify the electrocatalytic activity of a CoMo electrode for reducing N2(g) to NH3. We show that the additional ammonia detected in electrolyte was instead attributed to the corrosion of N impurities present in the CoMo electrode under cathodic bias, thus giving false positive results. These works emphasize the importance of both rigorous product analysis and experiment design in further catalyst development.
" }, { "name": "Chadwick, Austin John", "degree": "PhD", "year": "2020", "title": "Mechanics of River Avulsions on Lowland River Deltas", "advisor": "Lamb, Michael P.", "url": "https://resolver.caltech.edu/CaltechTHESIS:02032020-134346875", "creators": [ { "name": { "family": "Chadwick", "given": "Austin John" }, "id": "Chadwick-Austin-John", "orcid": "0000-0002-2552-0083", "display_name": "Chadwick, Austin John" } ], "advisors": [ { "name": { "family": "Lamb", "given": "Michael P." }, "id": "Lamb-M-P", "orcid": "0000-0002-5701-0504", "role": "advisor", "display_name": "Lamb, Michael P." } ], "committee": [ { "name": { "family": "Avouac", "given": "Jean-Philippe" }, "id": "Avouac-J-P", "orcid": "0000-0002-3060-8442", "role": "chair", "display_name": "Avouac, Jean-Philippe" }, { "name": { "family": "Grotzinger", "given": "John P." }, "id": "Grotzinger-J-P", "orcid": "0000-0001-9324-1257", "role": "member", "display_name": "Grotzinger, John P." }, { "name": { "family": "Thompson", "given": "Andrew F." }, "id": "Thompson-A-F", "orcid": "0000-0003-0322-4811", "role": "member", "display_name": "Thompson, Andrew F." }, { "name": { "family": "Lamb", "given": "Michael P." }, "id": "Lamb-M-P", "orcid": "0000-0002-5701-0504", "role": "member", "display_name": "Lamb, Michael P." } ], "option_major": [ "geol" ], "doi": "10.7907/97C1-JG94", "abstract": "Lowland deltas are home to over 0.5 billion people and some of the most biodiverse ecosystems on Earth. Deltas are highly dynamic landscapes, and at the largest scale grow through repeated construction of depositional lobes punctuated by river avulsions \u2013 abrupt shifts in river course to the shoreline. River avulsions have been responsible for dangerous floods and civil unrest over human history, but also counter land loss due to sea-level rise and coastal subsidence by nourishing wetlands with sediment. Despite the central role avulsions play on lowland deltas, the processes controlling their location and frequency remain poorly understood compared to steeper environments such as alluvial fans. This thesis is focused on the mechanics of river avulsions on lowland deltas, and the factors controlling their location and frequency. Chapter 1 addresses the origin of a preferential avulsion site on river deltas, using a novel modeling framework that unites previous work to incorporate backwater hydrodynamics, river-mouth progradation, relative sea-level rise, variable flood regimes, and cycles of lobe construction, abandonment, and reoccupation. Chapter 2 focuses on changes to avulsion frequency caused by relative sea-level rise, incorporating a combination of theory, field data, and numerical modeling. Chapter 3 explores general model predictions for avulsion location and timing during climate change, including rising and falling sea level, imbalances in upstream water and sediment supply, and the magnitude and frequency of storm events. Finally, Chapter 4 presents a scaled laboratory experiment where models and theory for lowland delta avulsion mechanics were put to the test. The work presented in this thesis offers new tools to predict river avulsions on densely populated lowland deltas, and allows for comparison with existing models of coastal restoration that fail to account for river avulsion mechanics and the hydrodynamics of lowland rivers.
" }, { "name": "Chalkley, Matthew J.", "degree": "PhD", "year": "2020", "title": "Proton-Coupled Electron Transfer in Nitrogen Fixation", "advisor": "Peters, Jonas C.", "url": "https://resolver.caltech.edu/CaltechTHESIS:02052020-203503014", "creators": [ { "name": { "family": "Chalkley", "given": "Matthew J." }, "id": "Chalkley-Matthew-J", "orcid": "0000-0002-0484-7335", "display_name": "Chalkley, Matthew J." } ], "advisors": [ { "name": { "family": "Peters", "given": "Jonas C." }, "id": "Peters-J-C", "role": "advisor", "display_name": "Peters, Jonas C." } ], "committee": [ { "name": { "family": "Agapie", "given": "Theodor" }, "id": "Agapie-T", "role": "chair", "display_name": "Agapie, Theodor" }, { "name": { "family": "Gray", "given": "Harry B." }, "id": "Gray-H-B", "role": "member", "display_name": "Gray, Harry B." }, { "name": { "family": "Miller", "given": "Thomas F." }, "id": "Miller-T-F", "role": "member", "display_name": "Miller, Thomas F." }, { "name": { "family": "Peters", "given": "Jonas C." }, "id": "Peters-J-C", "role": "member", "display_name": "Peters, Jonas C." } ], "option_major": [ "chemistry" ], "doi": "10.7907/FE9D-9K14", "abstract": "This thesis focuses on the management of protons and electrons in the formation of X\u2212H bonds. In our pursuit of better understanding this process, we have been particularly interested in the nitrogen fixation reaction (N2-to-NH3) because of the high number of protons and electrons involved in this conversion (6) and the significant difficulty of functionalizing N2. The first chapter introduces the important themes of this thesis: (i) multiple bonding, (ii) proton-coupled electron transfer, (iii) overpotential in N2 fixation, and (iv) selectivity in N2 fixation. The second chapter discusses the bonding of an iron complex with a small molecule (NO) and how this bonding is key to activating the small molecule for reactivity. The third chapter looks at how employing a new proton and electron source allows an Fe catalyst to achieve improved selectivity and turnover number for the reduction of N2 to NH3 despite a lowered overpotential relative to previous reactions. It also raises the hypothesis that this is possible due to proton-coupled electron transfer mediated by a metallocene. The fourth chapter studies the effect of acid strength on N2 fixation selectivity and demonstrates circumstantial evidence for the involvement of a decamethylcobaltocene (Cp*2Co) in the formation of N\u2212H bonds via proton-coupled electron transfer. It also highlights how the addition of co-catalytic [Cp*2Co]+ to electrochemical experiments with our Fe catalyst enabled truly electrocatalytic N2 fixation for the first time. The fifth chapter provides both atomistic detail on the protonation reactivity of Cp*2Co and experimentally verifies the prediction that this species would be an extremely strong hydrogen-atom donor. It also develops a conceptual framework to explain the uniquely weak C\u2212H bonds both homolytic and heterolytic that result from metallocene protonation and discusses their potential to play a role in not only the hydrogen evolution reaction (HER), but also the N2 fixation reaction. In the final chapter, we develop a synthetic route to a base appended cobaltocene. We demonstrate that this second-generation cobaltocene can, unlike the first generation, serve as a net hydrogen-atom donor under electrocatalytic conditions. As a demonstration of the utility of this, we use the base-appended cobaltocene for the selective, proton-coupled reduction of ketones to pinacols via a rate-determing concerted proton-electron transfer.
" }, { "name": "Finke, Cody Enslin", "degree": "PhD", "year": "2020", "title": "An Experimental and Economic Analysis of Electrochemical Technologies to Reduce Greenhouse Gas Emissions", "advisor": "Hoffmann, Michael R.", "url": "http://resolver.caltech.edu/CaltechTHESIS:07132019-171515484", "creators": [ { "name": { "family": "Finke", "given": "Cody Enslin" }, "id": "Finke-Cody-Enslin", "orcid": "0000-0002-1343-1737", "display_name": "Finke, Cody Enslin" } ], "advisors": [ { "name": { "family": "Hoffmann", "given": "Michael R." }, "id": "Hoffmann-M-R", "role": "advisor", "display_name": "Hoffmann, Michael R." } ], "committee": [ { "name": { "family": "Adkins", "given": "Jess F." }, "id": "Adkins-J-F", "role": "chair", "display_name": "Adkins, Jess F." }, { "name": { "family": "Hoffmann", "given": "Michael R." }, "id": "Hoffmann-M-R", "role": "member", "display_name": "Hoffmann, Michael R." }, { "name": { "family": "Gray", "given": "Harry B." }, "id": "Gray-H-B", "role": "member", "display_name": "Gray, Harry B." }, { "name": { "family": "Peters", "given": "Jonas C." }, "id": "Peters-J-C", "role": "member", "display_name": "Peters, Jonas C." } ], "option_major": [ "envreng" ], "doi": "10.7907/msvc-8t85", "abstract": "Global warming and the related problem of water scarcity are predicted to cause widespread environmental, humanitarian, and economic challenges. New technologies may be able to reduce greenhouse gas emissions enough to prevent many of the worst consequences of climate change However, in order to be competitive in the market, new, low emissions technologies much be affordable. In this thesis I present work on building a technology to lower the cost of decentralized, electrochemical wastewater treatment technologies by improving maintenance. I also show that atomic layer deposition of TiO2 can be used to tune the catalytic activity and stability of multiple electrocatalysts for both the chlorine and oxygen evolution reactions (two of the most widely used electrochemical reactions used to make chlorine gas and in electroplating metals respectively). With more development, this phenomenon has the potential to be used to reduce the cost of many electrochemical systems. I modeled the techno-economics of a low-cost industrial hydrogen production technology and found the first process, to my knowledge, which is able to make industrially relevant quantities of hydrogen at a large scale. I conclude by urging researchers who are trying to solve environmental problems to consider both the potential for the cost of the entire technology to be competitive with existing technologies and to determine what the most effective way to reduce costs are. Finally, I propose that cogeneration of hydrogen and other chemicals may be a viable strategy to producing large quantities of inexpensive, clean hydrogen.
" }, { "name": "Huang, Jinglin Alice", "degree": "PhD", "year": "2020", "title": "Investigations of Different Methods to Promote Drug Mixing in the Eye", "advisor": "Gharib, Morteza", "url": "https://resolver.caltech.edu/CaltechTHESIS:12122019-162434400", "creators": [ { "name": { "family": "Huang", "given": "Jinglin Alice" }, "id": "Huang-Jinglin-Alice", "orcid": "0000-0003-0760-4950", "display_name": "Huang, Jinglin Alice" } ], "advisors": [ { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "advisor", "display_name": "Gharib, Morteza" } ], "committee": [ { "name": { "family": "Tai", "given": "Yu-Chong" }, "id": "Tai-Yu-Chong", "orcid": "0000-0001-8529-106X", "role": "chair", "display_name": "Tai, Yu-Chong" }, { "name": { "family": "Gao", "given": "Wei" }, "id": "Gao-Wei", "orcid": "0000-0002-8503-4562", "role": "member", "display_name": "Gao, Wei" }, { "name": { "family": "Petrasek", "given": "Danny" }, "id": "Petrasek-Danny", "role": "member", "display_name": "Petrasek, Danny" }, { "name": { "family": "Schwartz", "given": "Daniel M." }, "id": "Schwartz-Daniel-M", "role": "member", "display_name": "Schwartz, Daniel M." }, { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "member", "display_name": "Gharib, Morteza" } ], "option_major": [ "medeng" ], "doi": "10.7907/741T-MN38", "abstract": "Age-related macular degeneration (AMD) is the leading cause of central vision loss in the developed world. In the case of wet AMD, it can be managed through serial intravitreal injections of anti-vascular endothelial growth factor (anti-VEGF) agents. However, sometimes the treatment is ineffective. Given that half-life time of the drug is limited, one possible cause of the ineffective treatment is inefficient drug mixing in the eye. Here, we focus on the understanding of drug mixing in vitreous chamber and parameters that could potentially influence mixing profiles. Both movement-driven method and thermal-driven method are explored. The in-vitro study outcomes will not only be useful for achieving fundamental understandings of fluid dynamics in the eye, but also helpful in developing a better strategy for intravitreal injection and improving the quality of care for patients." }, { "name": "Moon, Jaeyun", "degree": "PhD", "year": "2020", "title": "Thermal Conduction in Amorphous Materials and the Role of Collective Excitations", "advisor": "Minnich, Austin J.", "url": "https://resolver.caltech.edu/CaltechTHESIS:01162020-015608435", "creators": [ { "name": { "family": "Moon", "given": "Jaeyun" }, "id": "Moon-Jaeyun", "orcid": "0000-0001-8199-5588", "display_name": "Moon, Jaeyun" } ], "advisors": [ { "name": { "family": "Minnich", "given": "Austin J." }, "id": "Minnich-A-J", "role": "advisor", "display_name": "Minnich, Austin J." } ], "committee": [ { "name": { "family": "Bhattacharya", "given": "Kaushik" }, "id": "Bhattacharya-K", "role": "chair", "display_name": "Bhattacharya, Kaushik" }, { "name": { "family": "Fultz", "given": "Brent T." }, "id": "Fultz-B-T", "role": "member", "display_name": "Fultz, Brent T." }, { "name": { "family": "Daraio", "given": "Chiara" }, "id": "Daraio-C", "role": "member", "display_name": "Daraio, Chiara" }, { "name": { "family": "Minnich", "given": "Austin J." }, "id": "Minnich-A-J", "role": "member", "display_name": "Minnich, Austin J." } ], "option_major": [ "mecheng" ], "doi": "10.7907/Z23D-Z566", "abstract": "The atomic vibrations and thermal properties of amorphous dielectric solids are of fundamental and practical interest. For applications, amorphous solids are widely used as thermal insulators in thermopile and other detectors where low thermal conductivity directly sets the sensitivity of the detector. Amorphous solids are of fundamental interest themselves because the lack of atomic periodicity complicates theoretical development. As a result, the lower limits of thermal conductivity in solids as well as the nature of the vibrational excitations that carry heat remain active topics of research.
\r\n\r\nIn this thesis, we use numerical and experimental methods to investigate the thermal conduction in amorphous dielectrics. We begin by using molecular dynamics to investigate the thermal conductivity of amorphous nanocomposites. We find that mismatching the vibrational density of states of constituent materials in the composite is an effective route to achieve exceptionally low thermal conductivity in fully dense solids.
\r\n\r\nWe then transition to examining the properties of the atomic vibrations transporting heat in amorphous solids. For decades, normal mode methods have been used extensively to study thermal transport in amorphous solids. These methods naturally assume that normal modes are the fundamental vibrational excitations transporting heat. We examine the predictions from normal mode analysis that are now able to be tested against experiments, and we find that the predictions from these methods do not agree with experimental observations. For instance, normal mode methods predict that the low frequency normal modes are scattered by anharmonic interactions as in single crystalline solids. However, temperature dependent thermal conductivity measurements demonstrate a typical glassy temperature dependence inconsistent with normal modes scattering through anharmonic interactions. These discrepancies suggest that normal modes are not the fundamental heat carriers in amorphous dielectrics.
\r\n\r\nTo identify the actual heat carriers, we draw on fundamental concepts from many- body physics and inelastic scattering theory that dictate that the excitation energies of a many-body interacting system are given by the poles of the single-particle Green's function. The imaginary part of this function is proportional to the dynamic structure factor that is directly measured in inelastic scattering experiments. Collective excitations of a given energy and wavevector can thus be identified from peaks in the dynamic structure factor; their damping is given by the broadening of the peak. Using these concepts from many-body physics, the physical picture that emerges is that heat is carried in large part by a gas of weakly interacting collective excitations with a cutoff frequency that depends on the atomic structure and composition of the glass.
\r\n\r\nWe test this picture using numerical and experimental inelastic scattering measurements on amorphous silicon, a commonly studied amorphous solid. We observe collective excitations up to 10 THz, well into the thermal spectrum, and far higher than previous inelastic scattering measurements on other glasses. Our numerical and experimental evidence also confirms that the collective excitations are damped by structural disorder rather than anharmonic interactions and that they dominate the thermal conduction in amorphous silicon. Subsequent analysis shows that these high frequency acoustic excitations are supported in amorphous silicon due to a large sound velocity and monatomic composition, suggesting that other monatomic amorphous solids with large sound velocities may also support these thermal excitations.
\r\n\r\nOverall, our results provide strong evidence that the heat carriers in amorphous dielectrics are collective excitations rather than normal modes. This change in physical picture advances our understanding of atomic dynamics in glasses and also provides a foundation for realizing dielectric solids with ultralow thermal conductivity.
" }, { "name": "Naviaux, John David", "degree": "PhD", "year": "2020", "title": "Chemical and Physical Mechanisms of Calcite Dissolution in Seawater", "advisor": "Adkins, Jess F.", "url": "https://resolver.caltech.edu/CaltechTHESIS:11062019-135828667", "creators": [ { "name": { "family": "Naviaux", "given": "John David" }, "id": "Naviaux-John-David", "orcid": "0000-0002-0681-3163", "display_name": "Naviaux, John David" } ], "advisors": [ { "name": { "family": "Adkins", "given": "Jess F." }, "id": "Adkins-J-F", "role": "advisor", "display_name": "Adkins, Jess F." } ], "committee": [ { "name": { "family": "Thompson", "given": "Andrew F." }, "id": "Thompson-A-F", "role": "chair", "display_name": "Thompson, Andrew F." }, { "name": { "family": "Adkins", "given": "Jess F." }, "id": "Adkins-J-F", "role": "member", "display_name": "Adkins, Jess F." }, { "name": { "family": "Menemenlis", "given": "Dimitris" }, "id": "Menemenlis-D", "role": "member", "display_name": "Menemenlis, Dimitris" }, { "name": { "family": "Hoffmann", "given": "Michael R." }, "id": "Hoffmann-M-R", "role": "member", "display_name": "Hoffmann, Michael R." } ], "option_major": [ "envreng" ], "doi": "10.7907/DA32-MY55", "abstract": "Calcium carbonates are among the most abundant and reactive minerals on Earth, and their dissolution/preservation in the ocean helps to regulate changes in atmospheric pCO2. The chemistry of the oceans has varied significantly over the past several billion years, and it is changing at an unprecedented rate today in response to anthropogenic burning of fossil fuels. The excess CO2 from human activities is acidifying the oceans and decreasing the saturation state (\u03a9 = ([Ca2+][CO32-])/Ksp') of marine carbonates, increasing their propensity to dissolve. Despite its importance, the rate of carbonate dissolution in seawater is still described by a purely empirical expression, and the physical and chemical mechanisms setting the overall kinetics remain unknown. This stands in contrast to calcite dissolution in freshwater, where fully coupled surface-solution models have been identified. The lack of mechanistic understanding in seawater limits our ability to predict how carbonate dissolution kinetics, and therefore the buffering capacity of the ocean, are affected by changes in chemistry. This thesis advances our knowledge of the physical and chemical mechanisms responsible for carbonate dissolution by making new measurements in seawater both in the lab and in-situ.
\r\n \r\nI first probe the activation energy of the reaction in seawater by dissolving 13C-labeled CaCO3 across the full range of \u03a9 at 5, 12, 21, and 37\u00b0C. I find that a surface-based framework is required to explain the strong non-linearity of the data near equilibrium. In this framework, dissolution proceeds by the retreat of pre-existing steps for 0.9<\u03a9<1, defect-assisted etch pit formation for 0.75<\u03a9<0.9, and homogenous etch pit formation for 0<\u03a9<0.75. I provide the first seawater estimates of kinetic coefficients (\u03b2), nucleation site densities (ns), and step edge free energies (\u03b1) for each mechanism, as well as the activation energy for detachment from steps (\u03f5step) and the kinetic energy barrier to etch pit initiation (\u03f5init).
\r\n\r\nNext, I use a custom designed in-situ reactor to measure calcite dissolution rates across a transect of the North Pacific. I find that the same surface mechanisms and \"critical\" \u03a9s identified in lab also govern the dissolution of calcite in the open ocean. In-situ dissolution rates are ~4x slower than in the lab, but I use a combination of chemical spike experiments and measurements in archived seawater to show that this discrepancy can be explained by the presence of dissolved organic carbon in-situ. I propose an empirical rate equation that describes all previous in-situ measurements of inorganic calcite dissolution rates.
\r\n \r\nChanges in the relation between dissolution rate and \u03a9 can be explained by the activation of different surface processes, but the surface theory cannot account for much of the near-equilibrium dissolution behavior and temperature dependence. I therefore continue on in this thesis to combine the latest speciation models with dissolution measurements in artificial seawater of varying sulfate concentrations. I find that low sulfate solutions suppress dissolution rates by two orders of magnitude near equilibrium, while dissolution rates in the same solutions are enhanced far-from-equilibrium. Using these results, I fit a mechanistic model of dissolution that couples surface and solution processes. The model satisfies the principle of microscopic reversibility, provides an excellent estimate of calcite solubility product in seawater, and explains near equilibrium (\u03a9 > 0.75) dissolution rates in 0, 14, and 28 mM [SO42-] seawater at 21\u00b0C. The model cannot explain dissolution rates for \u03a9 < 0.75 when etch pits begin opening homogenously across the surface, so I suggest areas of improvement for future models.
\r\n\r\nPrevious work has demonstrated that calcite dissolution rates are enhanced in the presence of the enzyme carbonic anhydrase (CA). In the final chapter of this thesis, I evaluate the mechanism of CA rate enhancement by comparing the catalytic effects of freely dissolved CA, CA immobilized within hydrogels, and CA chemically bound onto porous silica beads. At the same time, I design and test a fluidized bed reactor and demonstrate its efficacy as a carbon capture device by attaching it directly to the Caltech cogeneration power plant smokestack. I find that dissolution rates within the reactor are only enhanced when CA is freely dissolved, strongly suggesting that the catalytic mechanism is direct proton transfer from the enzyme to the calcite surface.
" }, { "name": "Taeb, Armeen", "degree": "PhD", "year": "2020", "title": "Latent-Variable Modeling: Algorithms, Inference, and Applications", "advisor": "Chandrasekaran, Venkat", "url": "https://resolver.caltech.edu/CaltechTHESIS:09222019-132051506", "creators": [ { "name": { "family": "Taeb", "given": "Armeen" }, "id": "Taeb-Armeen", "orcid": "0000-0002-5647-3160", "display_name": "Taeb, Armeen" } ], "advisors": [ { "name": { "family": "Chandrasekaran", "given": "Venkat" }, "id": "Chandrasekaran-V", "role": "advisor", "display_name": "Chandrasekaran, Venkat" } ], "committee": [ { "name": { "family": "Hassibi", "given": "Babak" }, "id": "Hassibi-B", "orcid": "0000-0002-1375-5838", "role": "chair", "display_name": "Hassibi, Babak" }, { "name": { "family": "Stuart", "given": "Andrew M." }, "id": "Stuart-A-M", "orcid": "0000-0001-9091-7266", "role": "member", "display_name": "Stuart, Andrew M." }, { "name": { "family": "Pachter", "given": "Lior S." }, "id": "Pachter-L", "orcid": "0000-0002-9164-6231", "role": "member", "display_name": "Pachter, Lior S." }, { "name": { "family": "Doyle", "given": "John Comstock" }, "id": "Doyle-J-C", "orcid": "0000-0002-1828-2486", "role": "member", "display_name": "Doyle, John Comstock" }, { "name": { "family": "Chandrasekaran", "given": "Venkat" }, "id": "Chandrasekaran-V", "role": "member", "display_name": "Chandrasekaran, Venkat" } ], "option_major": [ "eleceng" ], "doi": "10.7907/YRF1-7W29", "abstract": "Many driving factors of physical systems are often latent or unobserved. Thus, understanding such systems crucially relies on accounting for the influence of the latent structure. This thesis makes advances in three aspects of latent-variable modeling: inference, algorithms, and applications. Specifically, we develop and explore latent-variable techniques that a) ensure interpretable and statistically significant models, b) can be efficiently optimized to identify best fit to data, and c) provide useful insights in real-world applications. The specific contributions of this thesis are:
\r\n\r\n1. We employ a latent-variable graphical modeling technique to develop the first state-wide statistical model of the California reservoir network. With this model, we precisely characterize the system-wide behavior of the network to hypothetical drought conditions, and proposed guidelines for more sustainable reservoir management.
\r\n\r\n2. Motivated by the previous application, we provide a geometric framework to assess the extent to which our latent variable model has learned true or false discoveries about the relevant physical phenomena. Our approach generalizes the classical notions of true and false discoveries in mathematical statistics that rely on the discrete structure of the decision space to settings where the decision space is continuous and more complicated. We highlight the utility of this viewpoint in problems involving subspace selection and low-rank estimation.
\r\n\r\n3. We propose a convex optimization procedure to fit a latent-variable graphical model for generalized linear models. This framework provides a flexible approach to model non-Gaussian variables including Poisson, Bernoulli, and exponential variables. A particularly novel aspect of our formulation is that it incorporates regularizers that are tailored to the type of latent variables.
\r\n\r\n4. We describe a computationally efficient framework to learn a latent-variable model with high-dimensional and non-iid data. This framework is based on factoriable precision operators that decouple the component associated with the observational dependencies and the component associated to interdependencies among the variables.
\r\n\r\n5. We propose a convex optimization technique to provide semantics to latent variables of a factor model. This approach is based on linking auxiliary variables -- chosen based on domain expertise -- to these latent variables.
" }, { "name": "Vyatskikh, Andrey", "degree": "PhD", "year": "2020", "title": "Additive Manufacturing of 3D Nano-Architected Metals and Ceramics", "advisor": "Greer, Julia R.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05252020-134146453", "creators": [ { "name": { "family": "Vyatskikh", "given": "Andrey" }, "id": "Vyatskikh-Andrey", "orcid": "0000-0002-6917-6931", "display_name": "Vyatskikh, Andrey" } ], "advisors": [ { "name": { "family": "Greer", "given": "Julia R." }, "id": "Greer-J-R", "role": "advisor", "display_name": "Greer, Julia R." } ], "committee": [ { "name": { "family": "Shapiro", "given": "Mikhail G." }, "id": "Shapiro-M-G", "role": "chair", "display_name": "Shapiro, Mikhail G." }, { "name": { "family": "Faber", "given": "Katherine T." }, "id": "Faber-K-T", "role": "member", "display_name": "Faber, Katherine T." }, { "name": { "family": "Gao", "given": "Wei" }, "id": "Gao-Wei", "role": "member", "display_name": "Gao, Wei" }, { "name": { "family": "Greer", "given": "Julia R." }, "id": "Greer-J-R", "role": "member", "display_name": "Greer, Julia R." } ], "option_major": [ "medeng" ], "doi": "10.7907/pdz2-dd59", "abstract": "Additive manufacturing (AM) represents a set of manufacturing processes that create complex 3D parts out of polymers, metals, and ceramics. AM of metals and ceramics is widely used to produce parts for aerospace, automotive, and medical applications. At the micro- and nano-scales, AM is poised to become the enabling technology for efficient 3D microelectromechanical systems (MEMS), 3D micro-battery electrodes, 3D electrically small antennae, micro-optical components, and photonics. Today, the minimum feature size for most commercially available metal and ceramic AM is limited to ~20-50 \u03bcm. Currently, no established processes can reliably produce complex 3D metal and ceramic parts with sub-micron features.
\r\n\r\nIn this thesis, we first demonstrate a nanoscale metal AM process that can produce ~300 nm features out of nanocrystalline, nanoporous nickel using synthesized hybrid organic-inorganic materials, two-photon lithography, and pyrolysis. We study microstructure and mechanical properties of as-fabricated nickel architectures and compare their structural strength to established AM processes. We then show how this process can be extended to other metals and metalloids, including Mg, Ge, Si, and Ti.
\r\n\r\nThis study extends further into nanoscale AM of transparent, high refractive index materials for micro-optics and photonic crystals. We develop an AM process to 3D print fully dense nanocrystalline rutile titanium dioxide (TiO\u2082) with feature dimensions down to ~120 nm. We carefully study and model the relationship between feature dimensions and process parameters to achieve a <2% variation in critical dimensions. We then use this understanding of the process to fabricate and study 3D dielectric photonic crystals with a full photonic bandgap in the infrared.
\r\n\r\nFinally, a microscale AM process of titanium dioxide is demonstrated for photocatalytic water treatment. We show how synthesized hybrid organic-inorganic materials can be applied for stereolithography to print TiO\u2082 architectures with 100 \u03bcm features. We use the developed 3D printing process to investigate the effect of 3D architecture on the efficiency of photocatalytic water treatment.
\r\n\r\nThis work establishes a versatile and efficient pathway to create three-dimensional nano-architected metals and ceramics and to investigate their properties for applications in 3D MEMS, micro-optics, photonics, and photocatalysis.
\r\n" }, { "name": "Dhandapani, Chandru", "degree": "PhD", "year": "2019", "title": "Using the Force: Applications and Implications of Turbulence Forcing Terms in Direct Numerical Simulations", "advisor": "Blanquart, Guillaume", "url": "https://resolver.caltech.edu/CaltechTHESIS:06102019-185605511", "creators": [ { "name": { "family": "Dhandapani", "given": "Chandru" }, "id": "Dhandapani-Chandru", "orcid": "0000-0002-7319-557X", "display_name": "Dhandapani, Chandru" } ], "advisors": [ { "name": { "family": "Blanquart", "given": "Guillaume" }, "id": "Blanquart-G", "orcid": "0000-0002-5074-9728", "role": "advisor", "display_name": "Blanquart, Guillaume" } ], "committee": [ { "name": { "family": "Meiron", "given": "Daniel I." }, "id": "Meiron-D-I", "orcid": "0000-0003-0397-3775", "role": "chair", "display_name": "Meiron, Daniel I." }, { "name": { "family": "Pullin", "given": "Dale Ian" }, "id": "Pullin-D-I", "role": "member", "display_name": "Pullin, Dale Ian" }, { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "member", "display_name": "Colonius, Tim" }, { "name": { "family": "Blanquart", "given": "Guillaume" }, "id": "Blanquart-G", "orcid": "0000-0002-5074-9728", "role": "member", "display_name": "Blanquart, Guillaume" } ], "option_major": [ "aeronautics" ], "doi": "10.7907/FH31-4468", "abstract": "Most energy requirements of modern life can be fulfilled by renewable energy sources, but it is impossible in the near future to provide an alternative energy source to combustion for airplanes. That being said, combustion in aviation can be made more sustainable by using alternative jet fuels, which are made from renewable sources like agricultural wastes, solid wastes, oils, and sugars. These alternative fuels can be used in commercial flights only after a long certification process by the Federal Aviation Agency (FAA) and ASTM International. Unfortunately, in over 50 years of fuel research, only five fuels have been certified.\r\nThis research project aims to speed up the certification process with quicker testing of alternative fuels. Engine testing and even laboratory testing require large amounts of time and fuel. Simulations can make the process much more efficient, but accurately simulating highly turbulent flames in such complex geometries would need large amounts of computational resources. The goal of this thesis is to create an efficient computational framework, that can replicate different engine-like turbulent flow conditions in simple geometries with numerical tractability.
\r\n\r\nThe central idea is to decompose the flow field into ensemble mean and fluctuating quantities. The simulations then resolve only the fluctuations using simple computational domains, while emulating the effect of the mean flow using \"forcing\" terms. These forcing terms are calculated first for incompressible turbulence, and this method is later extended to turbulent reacting flows. In incompressible turbulence, Direct Numerical Simulations (DNS) performed on simple triply periodic cubic domains reasonably capture the statistically stationary shear turbulence, that is observed in free shear flows. The simulations are also performed in cuboidal domains, that are longer in one direction and with an inflow/outflow along it. Both changes are observed to not have a significant impact on the turbulence statistics. Finally, shear convection is applied to the turbulence simulations with inflow/outflow, which has a significant impact on the turbulence. These simulations accurately capture the turbulence anisotropy in free-shear flows.
\r\n\r\nThe study is extended to DNS of highly turbulent n-heptane-air flames performed under different flow conditions. Turbulent flames involve two-way coupling between fluid mechanics and combustion. The effects of the flame on the turbulence and the impact of the turbulent flow conditions on the flame behavior are analyzed. The focus is placed on the effects of turbulence production, shear convection, and pressure gradients. The anisotropy produced in the turbulence due to the different flow conditions and the flame are also compared and contrasted. While the global behavior and flow anisotropy were affected by these conditions, the local chemistry effects were unaffected, and depend only on the laminar flame properties and turbulence intensity. These findings can help predict turbulent flame behavior, and can expedite the search and testing of sustainable alternatives to conventional jet fuels.
" }, { "name": "Guo, Linqi", "degree": "PhD", "year": "2019", "title": "Impact of Transmission Network Topology on Electrical Power Systems", "advisor": "Low, Steven H.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05312019-191005982", "creators": [ { "name": { "family": "Guo", "given": "Linqi" }, "id": "Guo-Linqi", "orcid": "0000-0001-5771-2752", "display_name": "Guo, Linqi" } ], "advisors": [ { "name": { "family": "Low", "given": "Steven H." }, "id": "Low-S-H", "role": "advisor", "display_name": "Low, Steven H." } ], "committee": [ { "name": { "family": "Wierman", "given": "Adam C." }, "id": "Wierman-A-C", "role": "chair", "display_name": "Wierman, Adam C." }, { "name": { "family": "Chandrasekaran", "given": "Venkat" }, "id": "Chandrasekaran-V", "role": "member", "display_name": "Chandrasekaran, Venkat" }, { "name": { "family": "Doyle", "given": "John C." }, "id": "Doyle-J-C", "role": "member", "display_name": "Doyle, John C." }, { "name": { "family": "Low", "given": "Steven H." }, "id": "Low-S-H", "role": "member", "display_name": "Low, Steven H." } ], "option_major": [ "cms" ], "doi": "10.7907/EN8K-W872", "abstract": "Power system reliability is a crucial component in the development of sustainable infrastructure. Because of the intricate interactions among power system components, it is often difficult to make general inferences on how the transmission network topology impacts performance of the grid in different scenarios. This complexity poses significant challenges for researches in the modeling, control, and management of power systems.
\r\n\r\nIn this work, we develop a theory that aims to address this challenge from both the fast-timescale and steady state aspects of power grids. Our analysis builds upon the transmission network Laplacian matrix, and reveals new properties of this well-studied concept in spectral graph theory that are specifically tailored to the power system context. A common theme of this work is the representation of certain physical quantities in terms of graphical structures, which allows us to establish algebraic results on power grid performance using purely topological information. This view is particularly powerful and often leads to surprisingly simple characterizations of complicated system behaviors. Depending on the timescale of the underlying problem, our results can be roughly categorized into the study of frequency regulation and the study of cascading failures.
\r\n\r\nFast-timescale: Frequency Regulation. We first study how the transmission network impacts power system robustness against disturbances in transient phase. Towards this goal, we develop a framework based on the Laplacian spectrum that captures the interplay among network topology, system inertia, and generator/load damping. This framework shows that the impact of network topology in frequency regulation can be quantified through the network Laplacian eigenvalues, and that such eigenvalues fully determine the grid robustness against low frequency perturbations. Moreover, we can explicitly decompose the frequency signal along scaled Laplacian eigenvectors when damping-inertia ratios are uniform across the buses. The insights revealed by this framework explain why load-side participation in frequency regulation not only makes the system respond faster, but also helps lower the system nadir after a disturbance, providing useful guidelines in the controller design. We simulate an improved controller reverse engineered from our results on the IEEE 39-bus New England interconnection system, and illustrate its robustness against high frequency oscillations compared to both the conventional droop control and a recent controller design.
\r\n\r\nWe then switch to a more combinatorial problem that seeks to characterize the controllability and observability of the power system in frequency regulation if only a subset of buses are equipped with controllers/sensors. Our results show that the controllability/observability of the system depends on two orthogonal conditions: (a) intrinsic structure of the system graph, and (b) algebraic coverage of buses with controllers/sensors. Condition (a) encodes information on graph symmetry and is shown to hold for almost all practical systems. Condition (b) captures how buses interact with each other through the network and can be verified using the eigenvectors of the graph Laplacian matrix. Based on this characterization, the optimal placement of controllers and sensors in the network can be formulated as a set cover problem. We demonstrate how our results identify the critical buses in real systems using a simulation in the IEEE 39-bus New England interconnection test system. In particular, for this testbed a single well chosen bus is capable of providing full controllability and observability.
\r\n\r\nSteady State: Cascading Failures. Cascading failures in power systems exhibit non-monotonic, non-local propagation patterns which make the analysis and mitigation of failures difficult. By studying the transmission network Laplacian matrix, we reveal two useful structures that make the analysis of this complex evolution more tractable: (a) In contrast to the lack of monotonicity in the physical system, there is a rich collection of monotonicity we can explore in the spectrum of the Laplacian matrix. This allows us to systematically design topological measures that are monotonic over the cascading event. (b) Power redistribution patterns are closely related to the distribution of different types of trees in the power network topology. Such graphical interpretation captures the Kirchhoff's Law in a precise way and naturally suggests that we can eliminate long-distance propagation of system disturbances by forming a tree-partition.
\r\n\r\nWe then show that the tree-partition of transmission networks provides a precise analytical characterization of line failure localizability. Specifically, when a non-bridge line is tripped, the impact of this failure only propagates within well-defined components, which we refer to as cells, of the tree-partition defined by the bridges. In contrast, when a bridge line is tripped, the impact of this failure propagates globally across the network, affecting the power flow on all remaining transmission lines. This characterization suggests that it is possible to improve the system robustness by switching off certain transmission lines, so as to create more, smaller components in the tree-partition; thus spatially localizing line failures and making the grid less vulnerable to large-scale outages. We illustrate this approach using the IEEE 118-bus test system and demonstrate that switching off a negligible portion of transmission lines allows the impact of line failures to be significantly more localized without substantial changes in line congestion.
\r\n\r\nUnified Controller on Tree-partitions. Combining our results from both the fast-timescale and steady state behaviors of power grids, we propose a distributed control strategy that offers strong guarantees in both the mitigation and localization of cascading failures in power systems. This control strategy leverages a new controller design known as Unified Controller (UC) from frequency regulation literature, and revolves around the powerful properties that emerge when the management areas that UC operates over form a tree-partition. After an initial failure, the proposed strategy always prevents successive failures from happening, and regulates the system to the desired steady state where the impact of initial failures are localized as much as possible. For extreme failures that cannot be localized, the proposed framework has a configurable design that progressively involves and coordinates across more control areas for failure mitigation and, as a last resort, imposes minimal load shedding. We compare the proposed control framework with the classical Automatic Generation Control (AGC) on the IEEE 118-bus test system. Simulation results show that our novel control greatly improves the system robustness in terms of the N-1 security standard, and localizes the impact of initial failures in majority of the load profiles that are examined. Moreover, the proposed framework incurs significantly less load loss, if any, compared to AGC, in all of our case studies.
" }, { "name": "Jhalani, Vatsal A.", "degree": "PhD", "year": "2019", "title": "Light Emission and Ultrafast Carrier Dynamics in III-V Semiconductors from First Principles", "advisor": "Bernardi, Marco", "url": "https://resolver.caltech.edu/CaltechTHESIS:06062019-155629104", "creators": [ { "name": { "family": "Jhalani", "given": "Vatsal A." }, "id": "Jhalani-Vatsal-A", "orcid": "0000-0003-0866-0858", "display_name": "Jhalani, Vatsal A." } ], "advisors": [ { "name": { "family": "Bernardi", "given": "Marco" }, "id": "Bernardi-Marco", "orcid": "0000-0001-7289-9666", "display_name": "Bernardi, Marco" } ], "committee": [ { "name": { "family": "Minnich", "given": "Austin J." }, "id": "Minnich-A-J", "orcid": "0000-0002-9671-9540", "role": "chair", "display_name": "Minnich, Austin J." }, { "name": { "family": "Bernardi", "given": "Marco" }, "id": "Bernardi-Marco", "orcid": "0000-0001-7289-9666", "role": "member", "display_name": "Bernardi, Marco" }, { "name": { "family": "Faraon", "given": "Andrei" }, "id": "Faraon-A", "orcid": "0000-0002-8141-391X", "role": "member", "display_name": "Faraon, Andrei" }, { "name": { "family": "Goddard", "given": "William A., III" }, "id": "Goddard-W-A-III", "orcid": "0000-0003-0097-5716", "role": "member", "display_name": "Goddard, William A., III" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/9E0D-KX54", "abstract": "The III-V semiconductors are a broad class of technologically important materials which have seen immense research interest in academia and industry due to their electronic, optoelectronic, and photovoltaic properties. In particular, GaN and the III-nitride family of wide bandgap semiconductors have emerged as promising candidates for the next generation of high-efficiency power electronics and light-emitting devices. Their device operation and macroscopic properties are governed by the dynamics of charge carriers and their microscopic scattering processes. Near room temperature, the carriers are scattered by lattice vibrations (phonons) at ultrafast timescales of order fs-ps. Microscopic understanding of carrier dynamics is challenging due to both the ultrafast time scale at play and to the presence of defects, interfaces, and impurities affecting transport and spectroscopy measurements. Typical theoretical treatments of carrier dynamics and light emission employ empirical models to interpret and fit experimental results. Over the last few years, so-called first-principles (or \"ab initio\") methods to accurately compute ultrafast carrier dynamics, transport, and light emission have seen a rapid rise. These approaches do not employ parameters from experiments, and using only the structure of the material as input, together with quantum mechanics and condensed matter theory, are enabling accurate predictions of carrier dynamics in a wide range of materials and are shedding light on microscopic details such as which electronic states, phonon modes and dissipative processes are responsible for the observed charge transport and light emission properties.
\r\n\r\n\r\nHere, we present first-principles calculations of different aspects of ultrafast carrier dynamics and light emission in III-V semiconductors of technological relevance, focusing on GaN, a key material for solid-state light emission technology. We first present a study of the ultrafast nonequilibrium dynamics of excited (so-called \"hot\") carriers in GaN, with a focus on electron-phonon scattering and the nanometer scale transport of carriers in GaN light emitting devices (LEDs). Using cutting-edge first-principles methods developed in this work, we find an asymmetry between the time scale of hot electron and hole thermalization which provides a possible explanation on a major open problem in the efficiency and energy losses of GaN LEDs. We then develop and apply a new rigorous first-principles approach for computing light emission and the radiative recombination lifetimes in bulk crystals, nanomaterials and isolated systems. Our approach is based on the Bethe-Salpeter equation (BSE), and it accurately includes excitons, namely electron-hole states bound by the Coulomb interaction that play a key role in light-matter interactions. Using this method, we carry out benchmark calculations of radiative lifetimes in GaAs and GaN. In GaN, our computed radiative lifetimes are in excellent agreement with experiment (within a factor of two), and our calculations further highlight the importance of including excitonic effects and spin-orbit coupling to obtain accurate radiative. We also employ a model to account for exciton thermal dissociation at high temperature, finding excellent agreement with spectroscopic measurements. Lastly, we discuss ongoing work on computing the intrinsic (phonon-limited) mobility in bulk GaN from first principles, focusing on efforts to include piezoelectric electron-phonon interactions, which are important for acoustic phonon modes in GaN. We compute the electron and hole mobilities in GaN and obtain excellent agreement with experiment. Our calculations shed light on which phonon modes scatter the carriers, providing new microscopic insight into charge carrier dynamics in GaN and related III-V semiconductors.
" }, { "name": "Reed, Christopher John", "degree": "PhD", "year": "2019", "title": "Activation of Nitric Oxide and Water by Transition Metal Clusters Relevant to Active Sites in Biology", "advisor": "Agapie, Theodor", "url": "https://resolver.caltech.edu/CaltechTHESIS:06072019-140931627", "creators": [ { "name": { "family": "Reed", "given": "Christopher John" }, "id": "Reed-Christopher-John", "orcid": "0000-0002-8774-5106", "display_name": "Reed, Christopher John" } ], "advisors": [ { "name": { "family": "Agapie", "given": "Theodor" }, "id": "Agapie-T", "role": "advisor", "display_name": "Agapie, Theodor" } ], "committee": [ { "name": { "family": "Peters", "given": "Jonas C." }, "id": "Peters-J-C", "role": "chair", "display_name": "Peters, Jonas C." }, { "name": { "family": "Dougherty", "given": "Dennis A." }, "id": "Dougherty-D-A", "role": "member", "display_name": "Dougherty, Dennis A." }, { "name": { "family": "Gray", "given": "Harry B." }, "id": "Gray-H-B", "role": "member", "display_name": "Gray, Harry B." }, { "name": { "family": "Agapie", "given": "Theodor" }, "id": "Agapie-T", "role": "member", "display_name": "Agapie, Theodor" } ], "option_major": [ "chemistry" ], "doi": "10.7907/QWMZ-HA45", "abstract": "This dissertation discusses the synthesis, characterization, and reactivity of site-differentiated tetranuclear clusters containing Fe and Mn with NO and H2O-derived ligands. The motivation of this work was to conduct a detailed examination of structure-property relationships in well-defined molecular systems focused on unique features of multinuclear systems, such as bridging ligands, neighboring metal identity, and cluster oxidation state. Reactivity towards NO and H2O-derived ligands was targeted due to their relevance to biological multinuclear transition metal active sites that promote multi-electron small molecule transformations.
\r\n\r\nChapter 2 discusses the synthesis of Fe-nitrosyl clusters bearing an interstitial \u03bc4-F atom. These clusters were prepared to compare their reactivity to previously synthesized [Fe33OFeNO] clusters with an analogous structure. A redox series of the [Fe3FFe] and [Fe3FFeNO] clusters were accessed, with the nitrosyl clusters displaying five cluster oxidation states, from FeII3{FeNO}8 to FeIII3{FeNO}7. Overall, the weaker bonding of the F- ligand resulted in attenuation of the activation and reactivity of the {FeNO}7, relative to the corresponding \u03bc4-O clusters. Furthermore, the ability of distal Fe oxidation state changes to influence the activation of NO was decreased, demonstrating lower cooperativity between metals in clusters linked by a weaker \u03bc4-atom This represents a rare case where the effects of bridging atom ligands could be compared in isostructural multinuclear complexes and decoupled from changes in metal ion coordination number, oxidation states, or geometry.
\r\n\r\nChapter 3 describes the synthesis of site-differentiated heterometallic clusters of [Fe3OMn], displaying facile ligand substitution at the five-coordinate Mn. This system was able to coordinate H2O and thermodynamic parameters of the proton and electron transfer processes from the MnII\u2013OH2 to form a MnIII\u2013OH moiety were studied. The oxidation state distribution of the neighboring Fe centers had a significant influence on these thermodynamic parameters, which was similar to the analogous parameters for mononuclear Mn systems, demonstrating that oxidation state changes in neighboring metals of a cluster can perturb the reactivity of a Mn\u2013OHx unit nearly as much as an oxidation state change at the Mn\u2013OHx. Subsequent experiments attempted to find spectroscopic or electrochemical evidence for formation of a terminal Mn-oxo in this system; however, that was not obtained, even in relatively extreme conditions. This established a lower limit for the bond dissociation enthalpy of the MnIII\u2013OH of ca. 93 kcal/mol, which makes formation of a terminal Mn-oxo cluster unfavorable in most organic solvents, due to expected facile hydrogen atom abstraction of a solvent C\u2013H bond.
\r\n\r\nThe insights obtained on the reactivity of these tetranuclear metal-hydroxide clusters was applied towards stabilizing a terminal metal-oxo in a multinuclear complex, as outlined in Chapter 4. Through the use of pendant hydrogen bond donors with tert-butyl-aminopyrazolate ligands, tetranuclear Fe clusters bearing terminal-hydroxide and -oxo ligands could be stabilized and structurally characterized. A similar thermodynamic analysis of the FeIII\u2013OH bond dissociation enthalpy was conducted, which demonstrated FeIII-oxo clusters could be accessed with a range of reactivity at the terminal-oxo ligand, based on the redox distribution of the neighboring Fe centers. The kinetics of C\u2013H activation for the [FeII2FeIII2]-oxo cluster redox state were analyzed, demonstrating a strong dependence of the C\u2013H bond pKa on the rate of proton coupled electron transfer.
\r\n\r\nLastly, Chapter 5 describes the synthesis and reactivity of tetranuclear Fe clusters bearing unsubstituted pyrazolate ligands, focusing on attempts to observe evidence for a terminal Fe-oxo or Fe-imido motif. Clusters bearing a labile trifluoromethanesulfonate ligand at the five-coordinate Fe center could be prepared, and would react with oxygen atom transfer reagents to produce a terminal Fe-hydroxide cluster, which, upon dehydration, led to isolation of an octanuclear \u03bc2-O cluster. The pathway for Fe-hydroxide formation was investigated, but could not conclusively determine whether reactivity occurred from a transient terminal Fe-oxo. Similarly, the reduced tetra-iron cluster, in the [FeII3FeIII], redox state was prepared, and demonstrated reactivity towards electron deficient aryl azides. Isolation of aryl amide clusters (Fe-NHAr) was observed, suggesting, again, formation of a reactive Fe-imido which decomposes through formal hydrogen atom abstraction. Efforts to stabilize either of these Fe=O/NR multiply-bonded species through a more acidic Fe were investigated by synthesizing the corresponding pyrazolate bridged \u03bc4-F clusters. The [FeII4] cluster also displayed reactivity towards oxygen atom transfer reagents, and produced a similar octanuclear \u03bc2-O cluster, but the observation of \u03bc4-F substitution with oxygen to produce \u03bc4-O clusters with a terminal F ligand likely precluded formation of a reactive terminal-oxo cluster. Instead, thermodynamically favorable cluster rearrangement to the [Fe3OFe] structure dominates.
" }, { "name": "Zhao, Hao", "degree": "PhD", "year": "2019", "title": "Essays on Economics of Groundwater Resource Management", "advisor": "Rosenthal, Jean-Laurent", "url": "https://resolver.caltech.edu/CaltechTHESIS:05312019-084004761", "creators": [ { "name": { "family": "Zhao", "given": "Hao" }, "id": "Zhao-Hao", "orcid": "0000-0002-9110-589X", "display_name": "Zhao, Hao" } ], "advisors": [ { "name": { "family": "Rosenthal", "given": "Jean-Laurent" }, "id": "Rosenthal-J-L", "role": "advisor", "display_name": "Rosenthal, Jean-Laurent" } ], "committee": [ { "name": { "family": "Shum", "given": "Matthew S." }, "id": "Shum-M-S", "role": "chair", "display_name": "Shum, Matthew S." }, { "name": { "family": "Ledyard", "given": "John O." }, "id": "Ledyard-J-O", "role": "member", "display_name": "Ledyard, John O." }, { "name": { "family": "Ewens", "given": "Michael J." }, "id": "Ewens-M-J", "role": "member", "display_name": "Ewens, Michael J." }, { "name": { "family": "Rosenthal", "given": "Jean-Laurent" }, "id": "Rosenthal-J-L", "role": "member", "display_name": "Rosenthal, Jean-Laurent" } ], "option_major": [ "socsci" ], "doi": "10.7907/WXTB-7828", "abstract": "This thesis examines groundwater management regimes in California and discusses how to implement an optimal aquifer management scheme.
\r\n\r\nChapter 2 examines the effectiveness of adjudication, a legal settlement among groundwater pumpers, in managing groundwater basins in Southern California. As a form of self-governance, adjudication generally leads to higher water level in the adjudicated basins than the unregulated ones. However, its rigid rules impair dynamic efficiency. Compared with the competitive pumpers, pumpers in the adjudicated basins actually have a less counter-cyclical extraction pattern in response to surface water availability.
\r\n\r\nChapter 3 examines how surface water trading intensifies groundwater depletion in California's Central Valley. A surface water market only mitigates the groundwater over-extraction problem when pumping costs are very high, while market failure arises when the pumping costs are low. I build an agricultural water use model to connect the efficacy of the surface water market with crop patterns response to surface water supply variation. The data suggest that the Central Valley is in a low pumping cost regime where the farmers pump groundwater to replace whatever surface water they sell. Therefore, the surface water trade is inefficient because it depletes groundwater resources and should be curtailed until the commons problem is addressed.
\r\n\r\nChapter 4 studies optimal groundwater aquifer management. I solve the dynamic optimization problem for groundwater extraction by a social planner when when farmers are heterogeneous and the surface water supply is uncertain. To implement the optimal pumping plan, the farmers must be allocated pumping rights each period equal to the socially optimal extraction. An incentive compatibility issue arises if farmers have heterogeneous access to groundwater. Those who overlie the deepest part of the aquifer might delay regulation because they will get more water as others exit. A larger amount of farmers must be included in the decision set to resolve this political conflict.
\r\n" }, { "name": "Dou, Nicholas Gang", "degree": "PhD", "year": "2018", "title": "Thermal Transport in Three-Dimensional Nanoarchitected Materials", "advisor": "Minnich, Austin J.", "url": "https://resolver.caltech.edu/CaltechTHESIS:06022018-070416991", "creators": [ { "name": { "family": "Dou", "given": "Nicholas Gang" }, "id": "Dou-Nicholas-Gang", "orcid": "0000-0001-8199-5588", "display_name": "Dou, Nicholas Gang" } ], "advisors": [ { "name": { "family": "Minnich", "given": "Austin J." }, "id": "Minnich-A-J", "role": "advisor", "display_name": "Minnich, Austin J." } ], "committee": [ { "name": { "family": "Blanquart", "given": "Guillaume" }, "id": "Blanquart-G", "role": "chair", "display_name": "Blanquart, Guillaume" }, { "name": { "family": "Greer", "given": "Julia R." }, "id": "Greer-J-R", "role": "member", "display_name": "Greer, Julia R." }, { "name": { "family": "Hunt", "given": "Melany L." }, "id": "Hunt-M-L", "role": "member", "display_name": "Hunt, Melany L." }, { "name": { "family": "Minnich", "given": "Austin J." }, "id": "Minnich-A-J", "role": "member", "display_name": "Minnich, Austin J." } ], "option_major": [ "mecheng" ], "doi": "10.7907/TPC8-VH59", "abstract": "Materials that simultaneously possess ultralow thermal conductivity, high stiffness, and damage tolerance are highly desirable for engineering applications. However, this combination of properties has never been demonstrated in a single material because thermal and mechanical properties are coupled in most fully dense and porous solids. A new class of lattice materials with nanoscale features, called nanolattices, can fill this void in the material property space by virtue of their architecture and nanoscale dimensions. Extensive work on nanolattice mechanical properties report their excellent stiffness-to-density ratio and recoverability from large compressive strains. In contrast, the framework for studying their thermal properties has not been established. Our work develops the computational and experimental tools necessary to study heat conduction in nanoarchitected materials and applies those tools to prove the viability of octet-truss nanolattices as multifunctional thermal insulators.
\r\n\r\nWe implement significant improvements to a phonon Monte Carlo method to solve the Boltzmann transport equation (BTE) in highly complex geometries like the octet-truss. No prior works solve the BTE in a domain as intricate as a nanolattice, so we create a geometry representation scheme that can model any arbitrary 3-D body. Our enhanced variance-reduced Monte Carlo code incorporates this scheme, allowing us to predict the thermal conductivity of nanolattices and analyze the phonon transport behavior in them. Results suggest that hollow-beam silicon nanolattices indeed reach ultralow thermal conductivities. Based on Monte Carlo and finite element simulations, we develop a predictive thermal conductivity model that accounts for both diffusive and radiative phonon transport in nanolattices.
\r\n\r\nWe also devise custom modifications to the 3\u03c9 method to experimentally measure the thermal conductivity of additively manufactured nanolattices. Since the serial fabrication process of nanolattices makes it costly to cover large areas, we design a specialized 3\u03c9 sample that minimizes the required structure size while maintaining good experimental sensitivity. We derive a new thermal model to account for conductive losses through the heater line in our novel sample geometry. 3\u03c9 measurements and compression tests of hollow-beam alumina nanolattices show that they combine ultralow thermal conductivity with excellent mechanical stiffness and resilience, which proves that nanolattices occupy a previously unreachable region in material property space. Our work provides motivation to further investigate and improve the thermal properties of architected materials.
\r\n" }, { "name": "Matson, Benjamin David", "degree": "PhD", "year": "2018", "title": "Interplay of Proton Transfer, Electron Transfer and Proton-Coupled Electron Transfer in Transition Metal Mediated Nitrogen Fixation", "advisor": "Peters, Jonas C.", "url": "https://resolver.caltech.edu/CaltechTHESIS:02232018-152758526", "creators": [ { "name": { "family": "Matson", "given": "Benjamin David" }, "id": "Matson-Benjamin-David", "orcid": "0000-0001-5733-0893", "display_name": "Matson, Benjamin David" } ], "advisors": [ { "name": { "family": "Peters", "given": "Jonas C." }, "id": "Peters-J-C", "role": "advisor", "display_name": "Peters, Jonas C." } ], "committee": [ { "name": { "family": "Agapie", "given": "Theodor" }, "id": "Agapie-T", "role": "chair", "display_name": "Agapie, Theodor" }, { "name": { "family": "Miller", "given": "Thomas F." }, "id": "Miller-T-F", "role": "member", "display_name": "Miller, Thomas F." }, { "name": { "family": "Hsieh-Wilson", "given": "Linda C." }, "id": "Hsieh-Wilson-L-C", "role": "member", "display_name": "Hsieh-Wilson, Linda C." }, { "name": { "family": "Peters", "given": "Jonas C." }, "id": "Peters-J-C", "role": "member", "display_name": "Peters, Jonas C." } ], "option_major": [ "chemistry" ], "doi": "10.7907/Z9MS3R0Z", "abstract": "Mitigation of the hydrogen evolution reaction (HER) is a key challenge in selective small molecule reduction catalysis, including the nitrogen (N2) reduction reactions (N2RR) using H+/e- currency. Here we explore, via DFT calculations, three iron model systems, P3EFe (E = B, Si, C), known to mediate both N2RR and HER, but with different selectivity depending on the identity of the auxiliary ligand. It is shown that the respective efficiencies of these systems for N2RR trend with the predicted N\u2013H bonds strengths of two putative hydrazido intermediates of the proposed catalytic cycle, P3EFe(NNH2)+ and P3EFe(NNH2). Bimolecular proton-coupled electron transfer (PCET) from intermediates with weak N\u2013H bonds is posited as a major source of H2 instead of more traditional scenarios that proceed via metal hydride intermediates and proton transfer/electron transfer (PT/ET) pathways.
\r\n\r\nStudies on our most efficient molecular iron catalyst, [P3BFe]+, reveal that the interaction of acid and reductant, Cp*2Co, is critical to achieve high efficiency for NH3, leading to the demonstration of electrocatalytic N2RR. Stoichiometric reactivity shows that Cp*2Co is required to observe productive N\u2013H bond formation with anilinium triflate acids under catalytic conditions. A study of substituted anilinium triflate acids demonstrates a strong correlation between pKa and the efficiency for NH3, which DFT studies attribute to the kinetics and thermodynamics of Cp*2Co protonation. These results contribute to the growing body of evidence suggesting that metallocenes should be considered as more than single electron transfer reagents in the proton-coupled reduction of small molecule substrates and that ring-functionalized metallocenes, believed to be intermediates on the background HER pathway, can play a critical role in productive bond-forming steps.
" }, { "name": "Ren, Xiaoqi", "degree": "PhD", "year": "2018", "title": "Optimizing Resource Management in Cloud Analytics Services", "advisor": "Wierman, Adam C.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05312018-080301508", "creators": [ { "name": { "family": "Ren", "given": "Xiaoqi" }, "id": "Ren-Xiaoqi", "orcid": "0000-0002-1121-9046", "display_name": "Ren, Xiaoqi" } ], "advisors": [ { "name": { "family": "Wierman", "given": "Adam C." }, "id": "Wierman-A-C", "role": "advisor", "display_name": "Wierman, Adam C." } ], "committee": [ { "name": { "family": "Wierman", "given": "Adam C." }, "id": "Wierman-A-C", "role": "chair", "display_name": "Wierman, Adam C." }, { "name": { "family": "Low", "given": "Steven H." }, "id": "Low-S-H", "role": "member", "display_name": "Low, Steven H." }, { "name": { "family": "Chandy", "given": "K. Mani" }, "id": "Chandy-K-M", "role": "member", "display_name": "Chandy, K. Mani" }, { "name": { "family": "Yue", "given": "Yisong" }, "id": "Yue-Yisong", "role": "member", "display_name": "Yue, Yisong" } ], "option_major": [ "compsci" ], "doi": "10.7907/K62Y-FV39", "abstract": "The fundamental challenge in the cloud today is how to build and optimize machine learning and data analytical services. Machine learning and data analytical platforms are changing computing infrastructure from expensive private data centers to easily accessible online services. These services pack user requests as jobs and run them on thousands of machines in parallel in geo-distributed clusters. The scale and the complexity of emerging jobs lead to increasing challenges for the clusters at all levels, from power infrastructure to system architecture and corresponding software framework design.
\r\n\r\nThese challenges come in many forms. Today's clusters are built on commodity hardware and hardware failures are unavoidable. Resource competition, network congestion, and mixed generations of hardware make the hardware environment complex and hard to model and predict. Such heterogeneity becomes a crucial roadblock for efficient parallelization on both the task level and job level. Another challenge comes from the increasing complexity of the applications. For example, machine learning services run jobs made up of multiple tasks with complex dependency structures. This complexity leads to difficulties in framework designs. The scale, especially when services span geo-distributed clusters, leads to another important hurdle for cluster design. Challenges also come from the power infrastructure. Power infrastructure is very expensive and accounts for more than 20% of the total costs to build a cluster. Power sharing optimization to maximize the facility utilization and smooth peak hour usages is another roadblock for cluster design.
\r\n\r\nIn this thesis, we focus on solutions for these challenges at the task level, on the job level, with respect to the geo-distributed data cloud design and for power management in colocation data centers.
\r\n\r\nAt the task level, a crucial hurdle to achieving predictable performance is stragglers, i.e., tasks that take significantly longer than expected to run. At this point, speculative execution has been widely adopted to mitigate the impact of stragglers in simple workloads. We apply straggler mitigation for approximation jobs for the first time. We present GRASS, which carefully uses speculation to mitigate the impact of stragglers in approximation jobs. GRASS's design is based on the analysis of a model we develop to capture the optimal speculation levels for approximation jobs. Evaluations with production workloads from Facebook and Microsoft Bing in an EC2 cluster of 200 nodes show that GRASS increases accuracy of deadline-bound jobs by 47% and speeds up error-bound jobs by 38%.
\r\n\r\nMoving from task level to job level, task level speculation mechanisms are designed and operated independently of job scheduling when, in fact, scheduling a speculative copy of a task has a direct impact on the resources available for other jobs. Thus, we present Hopper, a job-level speculation-aware scheduler that integrates the tradeoffs associated with speculation into job scheduling decisions based on a model generalized from the task-level speculation model. We implement both centralized and decentralized prototypes of the Hopper scheduler and show that 50% (66%) improvements over state-of-the-art centralized (decentralized) schedulers and speculation strategies can be achieved through the coordination of scheduling and speculation.
\r\n\r\nAs computing resources move from local clusters to geo-distributed cloud services, we are expecting the same transformation for data storage. We study two crucial pieces of a geo-distributed data cloud system: data acquisition and data placement. Starting from developing the optimal algorithm for the case of a data cloud made up of a single data center, we propose a near-optimal, polynomial-time algorithm for a geo-distributed data cloud in general. We show, via a case study, that the resulting design, Datum, is near-optimal (within 1.6%) in practical settings.
\r\n \r\nEfficient power management is a fundamental challenge for data centers when providing reliable services. Power oversubscription in data centers is very common and may occasionally trigger an emergency when the aggregate power demand exceeds the capacity. We study power capping solutions for handling such emergencies in a colocation data center, where the operator supplies power to multiple tenants. We propose a novel market mechanism based on supply function bidding, called COOP, to financially incentivize and coordinate tenants' power reduction for minimizing total performance loss while satisfying multiple power capping constraints. We demonstrate that COOP is \"win-win\", increasing the operator's profit (through oversubscription) and reducing tenants' costs (through financial compensation for their power reduction during emergencies).
" }, { "name": "Sherrott, Michelle Caroline", "degree": "PhD", "year": "2018", "title": "Active Infrared Nanophotonics in van der Waals Materials", "advisor": "Atwater, Harry Albert", "url": "https://resolver.caltech.edu/CaltechTHESIS:01262018-171457982", "creators": [ { "name": { "family": "Sherrott", "given": "Michelle Caroline" }, "id": "Sherrott-Michelle-Caroline", "orcid": "0000-0002-7503-9714", "display_name": "Sherrott, Michelle Caroline" } ], "advisors": [ { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "role": "advisor", "display_name": "Atwater, Harry Albert" } ], "committee": [ { "name": { "family": "Greer", "given": "Julia R." }, "id": "Greer-J-R", "role": "chair", "display_name": "Greer, Julia R." }, { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "role": "member", "display_name": "Atwater, Harry Albert" }, { "name": { "family": "Rossman", "given": "George Robert" }, "id": "Rossman-G-R", "role": "member", "display_name": "Rossman, George Robert" }, { "name": { "family": "Minnich", "given": "Austin J." }, "id": "Minnich-A-J", "role": "member", "display_name": "Minnich, Austin J." } ], "option_major": [ "matsci" ], "doi": "10.7907/Z9J964M8", "abstract": "Two-dimensional van der Waals materials have recently been introduced into the field of nanophotonics, creating opportunities to explore novel physics and realize first-of-their kind devices. By reducing the thickness of these materials, novel optical properties emerge due to the introduction of vertical quantum confinement. Unlike most materials, which suffer from a reduction in quality as they are thinned, layered van der Waals materials have naturally passivated surfaces that preserve their performance in monolayer form. Moreover, because the thickness of these materials is below typical charge carrier screening lengths, it is possible to actively control their optical properties with an external gate voltage. By combining these unique properties with the subwavelength control of light-matter interactions provided by nanophotonics, new device architectures can be realized.
\r\n\r\nIn this thesis, we explore van der Waals materials for active infrared nanophotonics, focusing on monolayer graphene and few-layer black phosphorus. Chapter 2 introduces gate-tunable graphene plasmons that interact strongly with their environment and can be combined with an external cavity to reach large absorption strengths in a single atomic layer. Chapter 3 builds on this, using graphene plasmons to control the spectral character and polarization state of thermal radiation. In Chapter 4, we complete the story of actively controlling infrared light using graphene-based structures, introducing graphene into a resonant gold structure to enable active control of phase. By combining these resonant structures together into a multi-pixel array, we realize an actively tunable meta-device for active beam steering in the infrared. In Chapters 5 and 6, we present few layer black phosphorus (BP) as a novel material for active infrared nanophotonics. We study the different electro-optic effects of the material from the visible to mid-infrared. We additionally examine the polarization-dependent response of few-layer BP, observing that we can tune its optical response from being highly anisotropic to nearly isotropic in plane. Finally, Chapter 7 comments on the challenges and opportunities for graphene- and BP-integrated nanophotonic structures and devices.
" }, { "name": "Thompson, Niklas Bjarne", "degree": "PhD", "year": "2018", "title": "A Synthetic Nitrogenase: Insights into the Mechanism of Nitrogen Fixation by a Single-Site Fe Catalyst", "advisor": "Peters, Jonas C.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05292018-165300346", "creators": [ { "name": { "family": "Thompson", "given": "Niklas Bjarne" }, "id": "Thompson-Niklas-Bjarne", "orcid": "0000-0003-2745-4945", "display_name": "Thompson, Niklas Bjarne" } ], "advisors": [ { "name": { "family": "Peters", "given": "Jonas C." }, "id": "Peters-J-C", "role": "advisor", "display_name": "Peters, Jonas C." } ], "committee": [ { "name": { "family": "Agapie", "given": "Theodor" }, "id": "Agapie-T", "role": "chair", "display_name": "Agapie, Theodor" }, { "name": { "family": "Fu", "given": "Gregory C." }, "id": "Fu-G-C", "role": "member", "display_name": "Fu, Gregory C." }, { "name": { "family": "Chan", "given": "Garnet K." }, "id": "Chan-G-K", "role": "member", "display_name": "Chan, Garnet K." }, { "name": { "family": "Peters", "given": "Jonas C." }, "id": "Peters-J-C", "role": "member", "display_name": "Peters, Jonas C." } ], "option_major": [ "chemistry" ], "doi": "10.7907/T4WQ-TM68", "abstract": "Nitrogen fixation, specifically the conversion of molecular nitrogen into ammonia, is a fundamental reaction necessary to support life. Our group has recently discovered the first family of well-defined iron complexes that catalyze the conversion of dinitrogen to ammonia. This thesis details mechanistic study of the nitrogen fixation chemistry these complexes. Chapter 1 presents an abbreviated overview of catalytic nitrogen fixation, which places our work in a larger context. Chapter 2 details the synthesis and nitrogen fixation activity of a series of cobalt complexes that are homologous to the known iron-based catalysts. The central goal of this work was to provide a structure-function study of the isostructural cobalt and iron complexes, in which the nature of the transition metal ion was changed in a fashion that predictably modulated the electronics of the system. Chapter 3 details in situ mechanistic studies of nitrogen fixation catalyzed by the iron complexes under the originally-reported reaction conditions. In this study, we were able to achieve a nearly order-of-magnitude improvement of catalyst turnover. Study of the reaction dynamics evidence a single-site mechanism for dinitrogen reduction, which is corroborated by in situ monitoring of catalytic reaction mixtures using freeze-quench M\u00f6ssbauer spectroscopy. In Chapter 4, we study the key N-N bond cleavage step in the catalytic cycle for nitrogen fixation. In this chapter, we demonstrate that sequential reduction and low-temperature protonation of an iron catalyst results in the formation of ammonia and a terminal Fe(IV) nitrido complex. This result provides a compelling proposal for the mechanism of the catalytic nitrogen fixation reaction. Finally, in Chapter 5 we present spectroscopic and computational studies detailing the electronic structures of a redox series of Fe(NNR2) complexes that model key catalytic intermediates occurring prior to the N-N bond cleavage step. We evidence one-electron redox non-innocence of the \u201cNNR2\u201d ligand, which resembles that of the classically non-innocent ligand, NO, and may have mechanistic implications for the divergent nitrogen fixation activity of the some of the iron complexes studied by our group.
" }, { "name": "Hunter, Bryan Michael", "degree": "PhD", "year": "2017", "title": "Fuels and Materials from Sunlight and Water", "advisor": "Gray, Harry B.", "url": "https://resolver.caltech.edu/CaltechTHESIS:06022017-112043547", "creators": [ { "name": { "family": "Hunter", "given": "Bryan Michael" }, "id": "Hunter-Bryan-Michael", "orcid": "0000-0001-8559-9304", "display_name": "Hunter, Bryan Michael" } ], "advisors": [ { "name": { "family": "Gray", "given": "Harry B." }, "id": "Gray-H-B", "role": "advisor", "display_name": "Gray, Harry B." } ], "committee": [ { "name": { "family": "Barton", "given": "Jacqueline K." }, "id": "Barton-J-K", "role": "chair", "display_name": "Barton, Jacqueline K." }, { "name": { "family": "Gray", "given": "Harry B." }, "id": "Gray-H-B", "role": "member", "display_name": "Gray, Harry B." }, { "name": { "family": "Rossman", "given": "George Robert" }, "id": "Rossman-G-R", "role": "member", "display_name": "Rossman, George Robert" }, { "name": { "family": "Rees", "given": "Douglas C." }, "id": "Rees-D-C", "role": "member", "display_name": "Rees, Douglas C." } ], "option_major": [ "chemistry" ], "doi": "10.7907/Z9FQ9TNB", "abstract": "The urgency to develop new technologies that harness energy and natural feedstocks in a sustainable fashion has never been more apparent. With global power consumption growing at an exponential rate, only one resource is truly capable of powering the planet: the sun. Sunlight is reliable, clean, and free.
\r\n\r\nSignificant resources have been pledged to develop and refine solar energy devices that convert photons into electricity (i.e. photovoltaics), but the sun\u2019s intermittency and the poor overlap of solar irradiance with global power demand a different strategy. In light of these limitations, we have proposed a device which converts solar energy into reduced chemical fuels (e.g. dihydrogen or methane) that can be indefinitely stored and easily transported. In principle, the only required inputs are sunlight, an earth-abundant feedstock such as carbon dioxide, protons (H+), and reducing equivalents (e-). The source of these protons and electrons must be abundant and ubiquitous\u2014we chose water.
\r\n\r\nDespite the 2-billion-year history of plants performing water oxidation to produce molecular oxygen, protons, and electrons (Photosystem II), our understanding of this complex 4H+/4e- process has been severely limited. Only recently have high-performing, earth-abundant heterogeneous electrocatalysts been reported that can be scaled up to make functioning devices.
\r\n\r\nThis dissertation describes progress on both the synthetic and mechanistic fronts in developing earth-abundant heterogeneous water oxidation catalysts for solar-driven water splitting. We have synthesized nanoparticulate Ni-Fe catalysts with the highest measured activity on flat electrodes to date. We carefully characterized these materials spectroscopically to determine that edge-site iron was active in catalysis. We then undertook novel in-situ spectroelectrochemical techniques in non-aqueous media to identify the active iron species, which is surprisingly a cis-dioxo-iron(VI) corner site. The data also indicate that geminal iron-oxo coupling may be the operative mechanism of O-O bond formation, a new scheme with potential biological relevance.
\r\n\r\nFinally, we have expanded our goal to include sustainably reducing other feedstocks, such as carbon dioxide and hydrocarbons. In doing so, we aim to make pharmaceuticals, polymers, and other high-value products from sunlight and water.
" }, { "name": "Johnson, Samantha Jo Iva", "degree": "PhD", "year": "2017", "title": "Computational Investigation of Small Molecule Catalysis by Cobalt, Rhodium, and Iridium Molecular Catalysts ", "advisor": "Goddard, William A., III", "url": "https://resolver.caltech.edu/CaltechTHESIS:12082016-154933538", "creators": [ { "name": { "family": "Johnson", "given": "Samantha Jo Iva" }, "id": "Johnson-Samantha-Jo-Iva", "orcid": "0000-0001-6495-9892", "display_name": "Johnson, Samantha Jo Iva" } ], "advisors": [ { "name": { "family": "Goddard", "given": "William A., III" }, "id": "Goddard-W-A-III", "role": "advisor", "display_name": "Goddard, William A., III" } ], "committee": [ { "name": { "family": "Goddard", "given": "William A., III" }, "id": "Goddard-W-A-III", "role": "chair", "display_name": "Goddard, William A., III" }, { "name": { "family": "Gray", "given": "Harry B." }, "id": "Gray-H-B", "role": "member", "display_name": "Gray, Harry B." }, { "name": { "family": "Faber", "given": "Katherine T." }, "id": "Faber-K-T", "role": "member", "display_name": "Faber, Katherine T." }, { "name": { "family": "Greer", "given": "Julia R." }, "id": "Greer-J-R", "role": "member", "display_name": "Greer, Julia R." }, { "name": { "family": "Persson", "given": "Petter" }, "id": "Persson-Petter", "role": "member", "display_name": "Persson, Petter" } ], "option_major": [ "matsci" ], "doi": "10.7907/Z9TD9V9K", "abstract": "Global energy demands are predicted to increase through 2040. In the spirit of meeting these demands, work focusing on increasing the efficiency of existing energy technologies, as well as improving energy storage is necessary. This work takes a catalytic approach to these challenges, focusing on Co, Rh, and Ir catalysts with pincer and bipyridine ligands. Density functional theory (DFT) can be used in order to gain a deeper understanding of how these catalysts behave. In the realm of improving existing technologies, the mechanism for oxidation of methane to methanol by Phebox Ir (Phebox = bis(oxazolinyl)phenyl) is investigated with a focus on understanding how subtle substitutions to the ligand can help or hinder this reaction. It is shown that in this catalyst, two unwanted intermediates on the potential energy surface (an IrIV state leading to catalyst deactivation and an IrV state leading to over-oxidation) can potentially be avoided by adding trifluoromethyl groups to the ligand. For production of fuels from solar energy, two reactions are studied. Experimentally, CO2 reduction to formate by (POCOP)Ir (POCOP = C6H3-2,6-[OP(tBu)2]2) has been shown to selectively occur at moderate potentials. The mechanism by which this catalyst reduces CO2 is elucidated. In particular, the impressive product selectivity afforded this catalyst for formate over hydrogen production is rooted in kinetics: high barriers for protonation inhibit the creation of H2 adducts. In addition to this, substitutions to the ligand and metal center are investigated to further illuminate the relationship between kinetics and thermodynamics. Hydrogen evolution in Cp*Rh(bpy) (bpy = 2,2'-bipyridine, Cp* = pentamethylcyclopentadienyl) is investigated, centering on unexpected protonation at the Cp* ligand rather than the metal center. This state is on the path for hydrogen evolution in the case of using weak acids, but in the presence of strong acids, the path through the traditional hydride is most likely. Finally, the attachment of these catalysts to electrode surfaces is discussed with the aim of making molecular catalysts a more viable option in industry It is shown that chlorine present in the attachment process enables easy catalyst dissociation from the surface. Several non-halogen options are discussed as replacements. Throughout the thesis two themes emerge: the constant interaction between thermodynamics and kinetics to control mechanistic paths and products, and the ability of small modifications to have huge impacts on catalytic cycles. " }, { "name": "Ravichandran, Navaneetha Krishnan", "degree": "PhD", "year": "2017", "title": "Theoretical and Experimental Investigation of Phonon Boundary Scattering in Thin Silicon Membranes", "advisor": "Minnich, Austin J.", "url": "https://resolver.caltech.edu/CaltechTHESIS:01172017-145551495", "creators": [ { "name": { "family": "Ravichandran", "given": "Navaneetha Krishnan" }, "id": "Ravichandran-Navaneetha-Krishnan", "display_name": "Ravichandran, Navaneetha Krishnan" } ], "advisors": [ { "name": { "family": "Minnich", "given": "Austin J." }, "id": "Minnich-A-J", "role": "advisor", "display_name": "Minnich, Austin J." } ], "committee": [ { "name": { "family": "Hunt", "given": "Melany L." }, "id": "Hunt-M-L", "role": "chair", "display_name": "Hunt, Melany L." }, { "name": { "family": "Minnich", "given": "Austin J." }, "id": "Minnich-A-J", "role": "member", "display_name": "Minnich, Austin J." }, { "name": { "family": "Blanquart", "given": "Guillaume" }, "id": "Blanquart-G", "role": "member", "display_name": "Blanquart, Guillaume" }, { "name": { "family": "Faraon", "given": "Andrei" }, "id": "Faraon-A", "role": "member", "display_name": "Faraon, Andrei" } ], "option_major": [ "mecheng" ], "doi": "10.7907/Z9SJ1HK2", "abstract": "The thermal transport properties of thin semiconductor membranes play an important role in the performance of many technologies like micro-electronics and solid-state energy conversion. The dominant resistance to heat flow in thin membranes is offered by the scattering of thermal phonons at the membrane boundaries. In this dissertation, we examine the nature of microscopic phonon boundary scattering processes and their effect on the thermal conductivity of the thin membranes using a pump-probe experimental technique and computationally efficient solutions of the phonon Boltzmann transport equation (BTE).
\r\n\r\nFirst, we investigate the boundary scattering-limited thermal transport in nanostructures using an efficient variance-reduced Monte Carlo (MC) solution of the BTE to elucidate the impact of specular and diffuse phonon boundary scattering events on the thermal conductivity of the nanostructures. To directly measure the relative frequency of these two boundary scattering events, called the phonon specularity parameter, we design, implement and characterize a non-contact laser-based pump-probe experiment called the transient grating (TG) to perform phonon mode-dependent measurements of the specularity parameter in suspended free-standing thin silicon membranes. We describe the phenomenon of quasiballistic heat conduction, which enables the phonon mode-dependent measurements of the specularity parameter, and derive a transfer function based on the BTE with ab-initio phonon properties as inputs, to connect the specularity parameter with the experimentally measured thermal conductivity of the thin membranes.
\r\n\r\nFinally, we present the methodology adopted to invert the BTE transfer function to extract the phonon specularity parameter from the thermal conductivity measurements in the TG experiment, while rigorously accounting for the experimental uncertainties. We find that the observed magnitudes and trends of the thermal conductivity of the thin membranes cannot be explained by the 50-year old Ziman's model for the phonon specularity parameter and the Fuchs-Sondheimer theory of phonon boundary scattering. We also find that the partially specular boundary scattering picture of phonon boundary interactions works well for one of the membranes, enabling a direct measurement of the mode-dependent phonon specularity parameter for the first time in an experiment. We discuss the possibility of phonon mode conversion at the boundaries of a few membranes for which the partially specular phonon boundary scattering picture fails to explain the observed thermal conductivity trends. Considering the importance of understanding phonon boundary scattering to engineer and improve nanoscale device performance, we expect that the new experimental and computational tools developed in this work will advance a variety of nanoscale energy applications and further our understanding of nanoscale heat transport.
" }, { "name": "Subhas, Adam Vinay", "degree": "PhD", "year": "2017", "title": "Chemical Controls on the Dissolution Kinetics of Calcite in Seawater", "advisor": "Adkins, Jess F.", "url": "https://resolver.caltech.edu/CaltechTHESIS:06092017-091849904", "creators": [ { "name": { "family": "Subhas", "given": "Adam Vinay" }, "id": "Subhas-Adam-Vinay", "orcid": "0000-0002-7688-6624", "display_name": "Subhas, Adam Vinay" } ], "advisors": [ { "name": { "family": "Adkins", "given": "Jess F." }, "id": "Adkins-J-F", "role": "advisor", "display_name": "Adkins, Jess F." } ], "committee": [ { "name": { "family": "Sessions", "given": "Alex L." }, "id": "Sessions-A-L", "role": "chair", "display_name": "Sessions, Alex L." }, { "name": { "family": "Berelson", "given": "William M." }, "id": "Berelson-W-M", "role": "member", "display_name": "Berelson, William M." }, { "name": { "family": "Eiler", "given": "John M." }, "id": "Eiler-J-M", "role": "member", "display_name": "Eiler, John M." }, { "name": { "family": "Adkins", "given": "Jess F." }, "id": "Adkins-J-F", "role": "member", "display_name": "Adkins, Jess F." } ], "option_major": [ "geochem" ], "doi": "10.7907/Z93X84P3", "abstract": "Calcium carbonate minerals are abundant on the earth\u2019s surface. Delivery of alkalinity to the oceans is balanced by the production and burial of calcium carbonate in marine sediments, which results in a large reservoir of sedimentary calcium carbonate both in the ocean and in terrestrial rocks. Alkalinity also provides oceanic buffering capacity, which today results in about 60 times more dissolved carbon dioxide in the world oceans than is present as carbon dioxide gas in the atmosphere. Because calcium carbonate formation removes alkalinity from the oceans, calcium carbonate precipitation leads to the outgassing of carbon dioxide from the ocean into the atmosphere. Likewise, the dissolution of calcium carbonate adds alkalinity to the oceans, leading to an increased buffering capacity and a drawdown of atmospheric carbon dioxide concentration.
\r\n\r\nCalcium carbonate precipitation in the form of calcite and aragonite is almost exclusively mediated by biological organisms such as corals, coccoliths, and foraminifera, which use these minerals as components in their shells. calcium carbonate is overproduced by organisms in the ocean relative to the flux of alkalinity delivered to the oceans by rivers. Thus, a significant portion of calcium carbonate must be dissolved back into seawater for the ocean alkalinity cycle to come into steady state. Because of the link between alkalinity and carbon dioxide, the ocean alkalinity cycle has a direct effect on atmospheric carbon dioxide concentration especially on timescales less than 100,000 years.
\r\n\r\nHow fast calcium carbonate dissolves back into seawater is thus a crucial rate in determining the response of the oceanic system to perturbations in either alkalinity or carbon dioxide input to the ocean-atmosphere system. We are testing the kinetics of this system with the large amount of carbon dioxide emitted from fossil fuel burning, about one third of which has dissolved into the surface ocean. This process is known as ocean acidification, as carbon dioxide is an acid, soaking up buffering capacity and dropping ocean pH. This carbon dioxide will eventually be neutralized through the dissolution of carbonate rich deep-sea sediments, but the process will take a long time. This thesis makes new measurements calcite dissolution in seawater, in an attempt to build an understanding of the chemical processes responsible for dissolution kinetics.
\r\n\r\nI first introduce the new method, in which carbon-13 labeled calcium carbonate is dissolved in undersaturated seawater. Mass loss is directly traced by measuring the appearance of carbon-13 in seawater over time. The dissolution rate of calcite is a highly nonlinear function of calcite saturation state.
\r\n\r\nNext, I show that this tracer can tell us about the balance of precipitation and dissolution at the mineral surface. I use this balance to constrain mass fluxes due to precipitation and dissolution as a function of saturation state. I also show that the enzyme Carbonic Anhydrase (CA), which rapidly equilibrates carbon dioxide and carbonic acid, greatly enhances the rate of calcite dissolution especially near equilibrium. A model of dissolution is presented in which CA is most effective in the region where dissolution proceeds via etch pit nucleation at surface defects.
\r\n\r\nThe dissolution behavior of biogenic carbonates is also investigated using the carbon-13 method. I cultured coccoliths, foraminifera, and soft corals in carbon-13-labeled seawater so that their skeletons incorporated the carbon-13 tracer. These skeletons were then used in dissolution experiments. I show that both magnesium and organic matter contained within the calcite lattice have large effects on the dissolution behavior of biogenic carbonates. Magnesium content generally increases dissolution rate, and it is hypothesized that highly soluble magnesium-rich phases are preferentially removed from dissolving carbonates. Organic content generally decreases dissolution rate. It is hypothesized that organic matrices within the calcite lattice promote re-precipitation reactions, due to the balance of dissolution and precipitation rates in our data, and their promotion of precipitation during biomineralization.
\r\n\r\nI then analyze in 2- and 3-dimensions dissolved foraminiferal tests to locate where and how mass is being lost. It is shown that dissolution proceeds along specific layers, that are consistent with the size and location of Mg-rich carbonate spherules that are initially deposited during chamber formation. Surface topography generation of foraminiferal tests shows that sub-micron features are formed rapidly and then quickly eroded into larger pits and channels. These larger channels then propagate and cover the test surface at higher amounts of mass loss.
\r\n\r\nFinally, the involvement of CA in carbonate dissolution necessitates the measurement of CA activity in the environment, especially in carbonate-rich ecosystems such as reefs, carbonate-rich sediments, and carbonate-rich marine particles. To this end, I survey a number of available techniques for measuring CA activity. In the end, it is shown that the most effective method is based on measuring the depletion of oxygen-18 from carbon-13- and oxygen-18-labeled DIC, as measured by membrane inlet mass spectrometry (MIMS). This method is promising and shows about 0.1 nM CA present in unfiltered surface seawater collected from San Pedro Basin.
" }, { "name": "Toutov, Anton Alexandrovich", "degree": "PhD", "year": "2017", "title": "Alkaline Salts of Sodium and Potassium: from C\u2013X Reduction to C\u2013H Functionalization and Beyond", "advisor": "Grubbs, Robert H.", "url": "https://resolver.caltech.edu/CaltechTHESIS:10172016-133616811", "creators": [ { "name": { "family": "Toutov", "given": "Anton Alexandrovich" }, "id": "Toutov-Anton-Alexandrovich", "orcid": "0000-0002-6561-0462", "display_name": "Toutov, Anton Alexandrovich" } ], "advisors": [ { "name": { "family": "Grubbs", "given": "Robert H." }, "id": "Grubbs-R-H", "role": "advisor", "display_name": "Grubbs, Robert H." } ], "committee": [ { "name": { "family": "Reisman", "given": "Sarah E." }, "id": "Reisman-S-E", "role": "chair", "display_name": "Reisman, Sarah E." }, { "name": { "family": "Agapie", "given": "Theodor" }, "id": "Agapie-T", "role": "member", "display_name": "Agapie, Theodor" }, { "name": { "family": "Stoltz", "given": "Brian M." }, "id": "Stoltz-B-M", "role": "member", "display_name": "Stoltz, Brian M." }, { "name": { "family": "Virgil", "given": "Scott C." }, "id": "Virgil-S-C", "role": "member", "display_name": "Virgil, Scott C." }, { "name": { "family": "Grubbs", "given": "Robert H." }, "id": "Grubbs-R-H", "role": "member", "display_name": "Grubbs, Robert H." } ], "option_major": [ "chemistry" ], "doi": "10.7907/Z9VM499F", "abstract": "The discovery and contemplations of Gilbert N. Lewis (1875\u20131946) regarding the concept of electron pair acceptors has led to an improved fundamental understanding of molecular interactions. Lewis\u2019s recognition that acidic character can exist in substances not containing hydrogen (i.e.,\r\nBr\u00f8nsted acids) led to the classification of a new group of reagents and catalysts for organic synthesis: Lewis acids. Over the last half-century, the application of these reagents and catalysts has in turn led to the discovery of a plethora of new chemical reactions, enabling previously unknown\r\ntransformations. It has also been appreciated that electron pair donors (i.e., Lewis bases) are characterized by analogous and opposite behavior. Perhaps most intriguing is that in certain cases Lewis bases are capable of modifying simultaneously the electrophilic and nucleophilic character of\r\nthe substance to which they are coordinated. It is also known that neutral tetravalent silicon can act as a Lewis acid for a variety of nucleophiles (i.e., Lewis bases) generating pentavalent Si species; these adducts are observed to have enhanced electrophilicity at Si and enhanced electron density at the ligands bound to silicon. In the case of organosilanes wherein at least one of the groups on silicon is a hydrogen (i.e., a hydrosilane), the reaction with Lewis bases can lead to pentavalent adducts with weakened Si\u2013H bonds wherein the H has enhanced hydridic character. This property has been exploited by researchers in a number of ways, perhaps most prevalently in the development of hydrosilanes as mild reducing agents for the reduction of carbonyl compounds or for the mechanistically-related carbonyl hydrosilylation reaction.
\r\n\r\nThis thesis details the discovery and development of fundamentally new chemical reactivity of silanes enabled by their interaction with basic salts of certain alkali metals (and includes some, but certainly not all of the work that I have performed in this area). First, it was found that specific combinations of hydrosilanes with basic alkali metal salts \u2013 in particular KOt-Bu \u2013 under certain conditions form exceptionally powerful reductive couples capable of selectively cleaving strong aromatic C\u2013O and C\u2013S bonds with exceptional effectiveness and novel selectivity. Second, I found that certain modifications and elaborations of this chemical system lead to dramatic changes in the operative reaction manifold: from C\u2013X bond cleavage to E\u2013Si bond formation. I determined that this concept of activating hydrosilanes with alkaline salts of the alkali metals can be harnessed for the mild and efficient construction of a wide array of E\u2013Si bond classes by catalytic crossdehydrogenative coupling. Surprisingly, these challenging chemistries all occur in the absence of transition metal species, providing new horizons and opportunities for investigating Earth-abundant elements as catalysts and reagents for a host of applications.
" }, { "name": "Araya, Daniel Borsodi", "degree": "PhD", "year": "2016", "title": "Aerodynamics of Vertical-Axis Wind Turbines in Full-Scale and Laboratory-Scale Experiments", "advisor": "Dabiri, John O.", "url": "https://resolver.caltech.edu/CaltechTHESIS:12022015-023535926", "creators": [ { "name": { "family": "Araya", "given": "Daniel Borsodi" }, "id": "Araya-Daniel-Borsodi", "display_name": "Araya, Daniel Borsodi" } ], "advisors": [ { "name": { "family": "Dabiri", "given": "John O." }, "id": "Dabiri-J-O", "orcid": "0000-0002-6722-9008", "role": "advisor", "display_name": "Dabiri, John O." } ], "committee": [ { "name": { "family": "McKeon", "given": "Beverley J." }, "id": "McKeon-B-J", "orcid": "0000-0003-4220-1583", "role": "chair", "display_name": "McKeon, Beverley J." }, { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "member", "display_name": "Colonius, Tim" }, { "name": { "family": "Leonard", "given": "Anthony" }, "id": "Leonard-A", "role": "member", "display_name": "Leonard, Anthony" }, { "name": { "family": "Dabiri", "given": "John O." }, "id": "Dabiri-J-O", "orcid": "0000-0002-6722-9008", "role": "member", "display_name": "Dabiri, John O." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/Z9VD6WC2 ", "abstract": "Within a wind farm, multiple turbine wakes can interact and have a substantial effect on the overall power production. This makes an understanding of the wake recovery process critically important to optimizing wind farm efficiency. Vertical-axis wind turbines (VAWTs) exhibit features that are amenable to dramatically improving this efficiency. However, the physics of the flow around VAWTs is not well understood, especially as it pertains to wake interactions, and it is the goal of this thesis to partially fill this void. This objective is approached from two broadly different perspectives: a low-order view of wind farm aerodynamics, and a detailed experimental analysis of the VAWT wake.
\r\n\r\nOne of the contributions of this thesis is the development of a semi-empirical model of wind farm aerodynamics, known as the LRB model, that is able to predict turbine array configurations to leading order accuracy. Another contribution is the characterization of the VAWT wake as a function of turbine solidity. It was found that three distinct regions of flow exist in the VAWT wake: (1) the near wake, where periodic blade shedding of vorticity dominates; (2) a transition region, where growth of a shear-layer instability occurs; (3) the far wake, where bluff-body oscillations dominate. The wake transition can be predicted using a new parameter, the dynamic solidity, which establishes a quantitative connection between the wake of a VAWT and that of a circular cylinder. The results provide insight into the mechanism of the VAWT wake recovery and the potential means to control it.
" }, { "name": "Cahn, Jackson Kenai Blender", "degree": "PhD", "year": "2016", "title": "Engineering, Predicting, and Understanding Nicotinamide Cofactor Specificity", "advisor": "Arnold, Frances Hamilton; Mayo, Stephen L.", "url": "https://resolver.caltech.edu/CaltechTHESIS:01212016-225223309", "creators": [ { "name": { "family": "Cahn", "given": "Jackson Kenai Blender" }, "id": "Cahn-Jackson-Kenai-Blender", "display_name": "Cahn, Jackson Kenai Blender" } ], "advisors": [ { "name": { "family": "Arnold", "given": "Frances Hamilton" }, "id": "Arnold-F-H", "orcid": "0000-0002-4027-364X", "role": "advisor", "display_name": "Arnold, Frances Hamilton" }, { "name": { "family": "Mayo", "given": "Stephen L." }, "id": "Mayo-S-L", "orcid": "0000-0002-9785-5018", "role": "co-advisor", "display_name": "Mayo, Stephen L." } ], "committee": [ { "name": { "family": "Tirrell", "given": "David A." }, "id": "Tirrell-D-A", "orcid": "0000-0003-3175-4596", "role": "chair", "display_name": "Tirrell, David A." }, { "name": { "family": "Shan", "given": "Shu-ou" }, "id": "Shan-Shu-ou", "orcid": "0000-0002-6526-1733", "role": "member", "display_name": "Shan, Shu-ou" }, { "name": { "family": "Dougherty", "given": "Dennis A." }, "id": "Dougherty-D-A", "orcid": "0000-0003-1464-2461", "role": "member", "display_name": "Dougherty, Dennis A." }, { "name": { "family": "Arnold", "given": "Frances Hamilton" }, "id": "Arnold-F-H", "orcid": "0000-0002-4027-364X", "role": "member", "display_name": "Arnold, Frances Hamilton" }, { "name": { "family": "Mayo", "given": "Stephen L." }, "id": "Mayo-S-L", "orcid": "0000-0002-9785-5018", "role": "member", "display_name": "Mayo, Stephen L." } ], "option_major": [ "chemistry" ], "doi": "10.7907/Z9QV3JJ8", "abstract": "Oxidoreductases, the enzymes that catalyze the transfer of electrons between molecules, represent the largest group of enzymes in metabolism, and the vast majority of these enzymes use the functionally-equivalent cofactors nicotinamide adenine dinucleotide (NAD) or nicotinamide adenine dinucleotide phosphate (NADP) for the storage and transport of the electrons. Understanding the interactions of these proteins with their cofactors is therefore crucial to the engineering of biological pathways and systems that involve these enzymes. In particular, because cells tightly regulate the levels of oxidized and reduced NAD and NADP, it is often valuable to engineer the specificity of enzymes to better integrate them into particular metabolic contexts.
\r\n\r\nThe first section of this thesis focuses on this specificity, taking as a model system the ketol-acid reductoisomerase (KARI) enzyme family. Prior to the work described here, all known members of the KARI enzyme family displayed a strict specificity for NADP over NAD. However, the use of these enzymes in a constructed pathway for the production of medium-chain alcohols created a clear need for NAD-specific KARIs to improve yields. Chapter 1 briefly summarizes the prior state of the art in nicotinamide cofactor specificity engineering before describing how a previous switching of the KARI from E. coli was extended to create a simple recipe for the specificity reversal of any KARI enzyme. Chapter 2 then uses the insights into cofactor specificity in KARIs afforded by the engineering in Chapter 1 to search databases of KARI sequences and predict naturally NAD-specific KARIs, resulting in the discovery of extremophilic NAD-utilizing KARIs with properties that outstrip those of the best engineered enzymes. Chapter 3 extends this prediction approach into another enzyme family, xylose reductases, and discusses its strengths and limitations across diverse enzyme folds and families.
\r\n\r\nThe next section of the thesis diverges from the topic of cofactor specificity engineering to briefly explore three structural questions which arise from the study of KARIs. Chapter 4 covers an analysis of several new KARI crystal structures, including those obtained during the efforts described in Chapters 1 and 2. From a comprehensive comparison of these structures, two topics are addressed: (1) the effect of insertions and deletions in the cofactor specificity loop on the binding geometry of NAD and NADP, and (2) the conformational motions involved in the binding of cofactor, substrate, and metal ions. Based on a pair of structures from Chapter 4, Chapter 5 experimentally explores the structural evolution of the KARI enzyme family\u2019s two distinct structural classes, replicating in a class I KARI the structural duplication that produced the class II KARI fold, and demonstrating a remarkable retention of enzymatic activity. Chapter 6 explores a curious sensitivity to mutations observed around the adenine moiety of several KARIs, and extends this observation to a range of other NADP- and NAD-dependent enzymes, with implications both for engineering these proteins and for understanding protein evolution more generally.
\r\n\r\nThe third and final section discusses the development of a general method for the cofactor specificity reversal of any NAD(P)-utilizing enzyme. Chapter 7 explains the approach used and how it represents a new paradigm in protein engineering, as well as covering the thorough experimental validation to which the method was subjected. This method was developed into a web applet (CSR-SALAD) for public use, and Chapter 8 discusses the development and use of this tool. This third section represents the culmination of the preceeding work, drawing from an understanding of the sequence and structural determinants of cofactor binding as explored in the preceeding six chapters to create the heuristic picture of specificity which informed the comprehensive engineering approach.
" }, { "name": "Duvvuri, Subrahmanyam", "degree": "PhD", "year": "2016", "title": "Non-Linear Scale Interactions in a Forced Turbulent Boundary Layer", "advisor": "McKeon, Beverley J.", "url": "https://resolver.caltech.edu/CaltechTHESIS:02292016-143116051", "creators": [ { "name": { "family": "Duvvuri", "given": "Subrahmanyam" }, "id": "Duvvuri-Subrahmanyam", "display_name": "Duvvuri, Subrahmanyam" } ], "advisors": [ { "name": { "family": "McKeon", "given": "Beverley J." }, "id": "McKeon-B-J", "orcid": "0000-0003-4220-1583", "role": "advisor", "display_name": "McKeon, Beverley J." } ], "committee": [ { "name": { "family": "Gharib", "given": "Morteza" }, "id": "Gharib-M", "orcid": "0000-0003-0754-4193", "role": "chair", "display_name": "Gharib, Morteza" }, { "name": { "family": "Pullin", "given": "Dale Ian" }, "id": "Pullin-D-I", "role": "member", "display_name": "Pullin, Dale Ian" }, { "name": { "family": "Colonius", "given": "Tim" }, "id": "Colonius-T", "orcid": "0000-0003-0326-3909", "role": "member", "display_name": "Colonius, Tim" }, { "name": { "family": "McKeon", "given": "Beverley J." }, "id": "McKeon-B-J", "orcid": "0000-0003-4220-1583", "role": "member", "display_name": "McKeon, Beverley J." } ], "option_major": [ "aeronautics" ], "doi": "10.7907/Z9Z31WKP ", "abstract": "This thesis explores the dynamics of scale interactions in a turbulent boundary layer through a forcing-response type experimental study. An emphasis is placed on the analysis of triadic wavenumber interactions since the governing Navier-Stokes equations for the flow necessitate a direct coupling between triadically consist scales. Two sets of experiments were performed in which deterministic disturbances were introduced into the flow using a spatially-impulsive dynamic wall perturbation. Hotwire anemometry was employed to measure the downstream turbulent velocity and study the flow response to the external forcing. In the first set of experiments, which were based on a recent investigation of dynamic forcing effects in a turbulent boundary layer, a 2D (spanwise constant) spatio-temporal normal mode was excited in the flow; the streamwise length and time scales of the synthetic mode roughly correspond to the very-large-scale-motions (VLSM) found naturally in canonical flows. Correlation studies between the large- and small-scale velocity signals reveal an alteration of the natural phase relations between scales by the synthetic mode. In particular, a strong phase-locking or organizing effect is seen on directly coupled small-scales through triadic interactions. Having characterized the bulk influence of a single energetic mode on the flow dynamics, a second set of experiments aimed at isolating specific triadic interactions was performed. Two distinct 2D large-scale normal modes were excited in the flow, and the response at the corresponding sum and difference wavenumbers was isolated from the turbulent signals. Results from this experiment serve as an unique demonstration of direct non-linear interactions in a fully turbulent wall-bounded flow, and allow for examination of phase relationships involving specific interacting scales. A direct connection is also made to the Navier-Stokes resolvent operator framework developed in recent literature. Results and analysis from the present work offer insights into the dynamical structure of wall turbulence, and have interesting implications for design of practical turbulence manipulation or control strategies." }, { "name": "Farivar, Masoud", "degree": "PhD", "year": "2016", "title": "Optimization and Control of Power Flow in Distribution Networks", "advisor": "Hassibi, Babak; Low, Steven H.", "url": "https://resolver.caltech.edu/CaltechTHESIS:12092015-021431773", "creators": [ { "name": { "family": "Farivar", "given": "Masoud" }, "id": "Farivar-Masoud", "orcid": "0000-0001-7298-3526", "display_name": "Farivar, Masoud" } ], "advisors": [ { "name": { "family": "Hassibi", "given": "Babak" }, "id": "Hassibi-B", "role": "advisor", "display_name": "Hassibi, Babak" }, { "name": { "family": "Low", "given": "Steven H." }, "id": "Low-S-H", "role": "co-advisor", "display_name": "Low, Steven H." } ], "committee": [ { "name": { "family": "Hassibi", "given": "Babak" }, "id": "Hassibi-B", "role": "chair", "display_name": "Hassibi, Babak" }, { "name": { "family": "Low", "given": "Steven H." }, "id": "Low-S-H", "role": "member", "display_name": "Low, Steven H." }, { "name": { "family": "Wierman", "given": "Adam C." }, "id": "Wierman-A-C", "role": "member", "display_name": "Wierman, Adam C." }, { "name": { "family": "Chandrasekaran", "given": "Venkat" }, "id": "Chandrasekaran-V", "role": "member", "display_name": "Chandrasekaran, Venkat" }, { "name": { "family": "Chen", "given": "Lijun" }, "id": "Chen-Lijun", "role": "member", "display_name": "Chen, Lijun" } ], "option_major": [ "eleceng" ], "doi": "10.7907/Z9JW8BSM", "abstract": "Climate change is arguably the most critical issue facing our generation and the next. As we move towards a sustainable future, the grid is rapidly evolving with the integration of more and more renewable energy resources and the emergence of electric vehicles. In particular, large scale adoption of residential and commercial solar photovoltaics (PV) plants is completely changing the traditional slowly-varying unidirectional power flow nature of distribution systems. High share of intermittent renewables pose several technical challenges, including voltage and frequency control. But along with these challenges, renewable generators also bring with them millions of new DC-AC inverter controllers each year. These fast power electronic devices can provide an unprecedented opportunity to increase energy efficiency and improve power quality, if combined with well-designed inverter control algorithms. The main goal of this dissertation is to develop scalable power flow optimization and control methods that achieve system-wide efficiency, reliability, and robustness for power distribution networks of future with high penetration of distributed inverter-based renewable generators.
\r\n\r\nProposed solutions to power flow control problems in the literature range from fully centralized to fully local ones. In this thesis, we will focus on the two ends of this spectrum. In the first half of this thesis (chapters 2 and 3), we seek optimal solutions to voltage control problems provided a centralized architecture with complete information. These solutions are particularly important for better understanding the overall system behavior and can serve as a benchmark to compare the performance of other control methods against. To this end, we first propose a branch flow model (BFM) for the analysis and optimization of radial and meshed networks. This model leads to a new approach to solve optimal power flow (OPF) problems using a two step relaxation procedure, which has proven to be both reliable and computationally efficient in dealing with the non-convexity of power flow equations in radial and weakly-meshed distribution networks. We will then apply the results to fast time- scale inverter var control problem and evaluate the performance on real-world circuits in Southern California Edison\u2019s service territory.
\r\n\r\nThe second half (chapters 4 and 5), however, is dedicated to study local control approaches, as they are the only options available for immediate implementation on today\u2019s distribution networks that lack sufficient monitoring and communication infrastructure. In particular, we will follow a reverse and forward engineering approach to study the recently proposed piecewise linear volt/var control curves. It is the aim of this dissertation to tackle some key problems in these two areas and contribute by providing rigorous theoretical basis for future work.
" }, { "name": "Lionetti, Davide", "degree": "PhD", "year": "2016", "title": "Heterometallic Complexes as Models of Enzymatic Active Sites", "advisor": "Agapie, Theodor", "url": "https://resolver.caltech.edu/CaltechTHESIS:09282015-080838463", "creators": [ { "name": { "family": "Lionetti", "given": "Davide" }, "id": "Lionetti-Davide", "display_name": "Lionetti, Davide" } ], "advisors": [ { "name": { "family": "Agapie", "given": "Theodor" }, "id": "Agapie-T", "role": "advisor", "display_name": "Agapie, Theodor" } ], "committee": [ { "name": { "family": "Bercaw", "given": "John E." }, "id": "Bercaw-J-E", "role": "chair", "display_name": "Bercaw, John E." }, { "name": { "family": "Gray", "given": "Harry B." }, "id": "Gray-H-B", "role": "member", "display_name": "Gray, Harry B." }, { "name": { "family": "Dougherty", "given": "Dennis A." }, "id": "Dougherty-D-A", "role": "member", "display_name": "Dougherty, Dennis A." }, { "name": { "family": "Agapie", "given": "Theodor" }, "id": "Agapie-T", "role": "member", "display_name": "Agapie, Theodor" } ], "option_major": [ "chemistry" ], "doi": "10.7907/Z98G8HMT", "abstract": "This dissertation describes studies on two multinucleating ligand architectures: the first scaffold was designed to support tricopper complexes, while the second platform was developed to support tri- and tetrametallic clusters.
\r\n\r\nIn Chapter 2, the synthesis of yttrium (and lanthanide) complexes supported by a tripodal ligand framework designed to bind three copper centers in close proximity is described. Tricopper complexes were shown to react with dioxygen in a 1:1 [Cu3]/O2 stoichiometry to form intermediates in which the O\u2013O bond was fully cleaved, as characterized via UV-Vis spectroscopy and determination of the reaction stoichiometry. Pre-arrangement of the three Cu centers was pivotal to cooperative O2 activation, as mono-copper complexes reacted differently with dioxgyen. The reactivity of the observed intermediates was studied with various substrates (reductants, O-atom acceptors, H-atom donors, Br\u00f8nsted acids) to determine their properties. In Chapter 3, the reactivity of the same yttrium-tricopper complex with nitric oxide was explored. Reductive coupling to form a trans-hyponitrite complex (characterized by X-ray crystallography) was observed via cooperative reactivity by an yttrium and a copper center on two distinct tetrametallic units. The hyponitrite complex was observed to release nitrous oxide upon treatment with a Br\u00f8nsted acid, supporting its viability as an intermediate in nitric oxide reduction to nitrous oxide.
\r\n\r\nIn Chapter 4, a different multinucleating ligand scaffold was employed to synthesize heterometallic triiron clusters containing one oxide and one hydroxide bridges. The effects of the redox-inactive, Lewis acidic heterometals on redox potential was studied by cyclic voltammetry, unveiling a linear correlation between redox potential and heterometal Lewis acidity. Further studies on these complexes showed that the Lewis acidity of the redox-inactive metals also affected the oxygen-atom transfer reactivity of these clusters. Comparisons of this reactivity with manganese systems, collaborative efforts to reassign the structures of related manganese oxo-hydroxo clusters, and synthetic attempts to access related dioxo clusters are also described.
\r\n\r\nIn Appendix A, ongoing efforts to synthesize new clusters supported by the same multinucleating ligand platform are described. Studies of novel approaches towards ligand exchange in tetrametallic clusters and incorporation of new supporting and bridging ligand motifs in trinuclear complexes are presented.
" }, { "name": "Shaner, Matthew Reed", "degree": "PhD", "year": "2016", "title": "An Experimental and Technoeconomic Study of Silicon Microwire Arrays for Fuel Production Using Solar Energy", "advisor": "Lewis, Nathan Saul; Atwater, Harry Albert", "url": "https://resolver.caltech.edu/CaltechTHESIS:05312016-151045544", "creators": [ { "name": { "family": "Shaner", "given": "Matthew Reed" }, "id": "Shaner-Matthew-Reed", "orcid": "0000-0003-4682-9757", "display_name": "Shaner, Matthew Reed" } ], "advisors": [ { "name": { "family": "Lewis", "given": "Nathan Saul" }, "id": "Lewis-N-S", "role": "co-advisor", "display_name": "Lewis, Nathan Saul" }, { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "role": "co-advisor", "display_name": "Atwater, Harry Albert" } ], "committee": [ { "name": { "family": "Lewis", "given": "Nathan Saul" }, "id": "Lewis-N-S", "role": "chair", "display_name": "Lewis, Nathan Saul" }, { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "role": "member", "display_name": "Atwater, Harry Albert" }, { "name": { "family": "Flagan", "given": "Richard C." }, "id": "Flagan-R-C", "role": "member", "display_name": "Flagan, Richard C." }, { "name": { "family": "Davis", "given": "Mark E." }, "id": "Davis-M-E", "role": "member", "display_name": "Davis, Mark E." } ], "option_major": [ "chemeng" ], "doi": "10.7907/Z98C9T7Z", "abstract": "Direct solar energy conversion is one of few sustainable energy resources able to wholly satisfy global energy demand; however, utility scale adoption and reliance are currently limited by the lack of a cost effective energy storage technology. The production of fuel from sunlight (solar fuels) enables solar energy storage in chemical bonds, a volumetrically and gravimetrically dense form compatible with current infrastructure worldwide. Hydrogen production via water splitting is a first generation solar fuel targeted herein that is currently used for hydrocarbon up-grading and fertilizer production and could further be utilized in combustion cycles and/or fuel cells for electricity and heat production and transportation.
\r\n\r\nThis thesis presents achievements that form the foundation for Si microwire array based solar water splitting devices beginning with a tandem junction device design using Si microwire arrays as the architectural motif and one of many active components. Si microwire arrays have potential advantages over two dimensional planar device architectures such as minimized resistance losses, lower semiconductor material usage, and embedment in a polymeric membrane enabling a flexible device.
\r\n\r\nExperimental fabrication and characterization of this tandem junction device design was realized in the form of a np+-Si microwire array coated by either tungsten oxide (WO3) or titanium dioxide (TiO2) as the second tandem semiconductor. The Si/TiO2 device demonstrated the highest performance with an expected solar-to-hydrogen efficiency of 0.39%. To achieve these demonstrations new processing methods were needed and developed for formation of the np+-Si microwire array homojunction and formation of a low resistance contact between the p+-Si and second semiconductor using sputtered tin- doped indium oxide (ITO) and spray pyrolyzed fluorine-doped tin oxide (FTO).
\r\n\r\nAnother achievement includes demonstration of the longest known (>2200 hours) photoanode stability for water oxidation using a np+-Si microwire array coated with an in-house developed amorphous TiO2 protection layer and NiCrOx electrocatalyst. Additionally, the Si microwire array architecture was used to enable decoupling of semiconductor light absorption and catalytic activity, two performance metrics that ideally are maximized simultaneously. However, all previous demonstrations have shown anti-correlation between these performance metrics because planar architectures are subject to a trade-off where adding electrocatalyst increases catalytic activity, but decreases semiconductor light absorption and vice versa.
\r\n\r\nFinally, a techno-economic analysis of solar water splitting production facilities was performed to assess economic competitiveness because this is the ultimate metric by which all energy production technologies are currently evaluated. This analysis suggests that a hydrogen production facility that is cosmetically similar to current solar panel installations with hydrogen collection from distributed tilted panels is unlikely to achieve cost competitiveness with fossil fuel derived hydrogen due to the balance of systems costs alone. A cost of CO2 greater than ~$800 (ton CO2)-1 was estimated to be necessary for the least expensive base-case solar-to-hydrogen system to reach price parity with hydrogen derived from steam reforming of methane priced at $3 (MM BTU)-1 ($1.39 (kg H2)-1). Direct CO2 reduction systems were also explored and resulted in even larger challenges than hydrogen production. Accordingly, major facility wide breakthroughs are required to obtain viable economic costs for solar hydrogen production, but the barriers to achieve cost-competitiveness with existing large-scale thermochemical processes for CO2 reduction are even greater.
" }, { "name": "Webb, Michael Anthony", "degree": "PhD", "year": "2016", "title": "Path-Integral and Coarse-Graining Strategies for Complex Molecular Phenomena", "advisor": "Miller, Thomas F.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05252016-213050706", "creators": [ { "name": { "family": "Webb", "given": "Michael Anthony" }, "id": "Webb-Michael-Anthony", "orcid": "0000-0002-7420-4474", "display_name": "Webb, Michael Anthony" } ], "advisors": [ { "name": { "family": "Miller", "given": "Thomas F." }, "id": "Miller-T-F", "role": "advisor", "display_name": "Miller, Thomas F." } ], "committee": [ { "name": { "family": "Miller", "given": "Thomas F." }, "id": "Miller-T-F", "role": "chair", "display_name": "Miller, Thomas F." }, { "name": { "family": "Wang", "given": "Zhen-Gang" }, "id": "Wang-Zhen-Gang", "role": "member", "display_name": "Wang, Zhen-Gang" }, { "name": { "family": "Brady", "given": "John F." }, "id": "Brady-J-F", "role": "member", "display_name": "Brady, John F." }, { "name": { "family": "Eiler", "given": "John M." }, "id": "Eiler-J-M", "role": "member", "display_name": "Eiler, John M." } ], "option_major": [ "chemeng" ], "doi": "10.7907/Z90Z7172", "abstract": "Molecular simulation provides a powerful tool for connecting molecular-level processes to physical observables. However, the facility to make those connections relies upon the application and development of theoretical methods that permit appropriate descriptions of the systems or processes to be studied. In this thesis, we utilize molecular simulation to study and predict two phenomena with very different theoretical challenges, beginning with (1) lithium-ion transport behavior in polymers and following with (2) equilibrium isotope effects with relevance to position-specific and clumped isotope studies. In the case of ion transport in polymers, there is motivation to use molecular simulation to provide guidance in polymer electrolyte design, but the length and timescales relevant for ion diffusion in polymers preclude the use of direct molecular dynamics simulation to compute ion diffusivities in more than a handful of candidate systems. In the case of equilibrium isotope effects, the thermodynamic driving forces for isotopic fractionation are often fundamentally quantum mechanical in nature, and the high precision of experimental instruments demands correspondingly accurate theoretical approaches. Herein, we describe respectively coarse-graining and path-integral strategies to address outstanding questions in these two subject areas." }, { "name": "Brown, David Ross", "degree": "PhD", "year": "2015", "title": "Enhanced Thermoelectric Performance at the Superionic Phase Transitions of Mixed Ion-Electron Conducting Materials", "advisor": "Snyder, G. Jeffrey", "url": "https://resolver.caltech.edu/CaltechTHESIS:08112014-121653693", "creators": [ { "name": { "family": "Brown", "given": "David Ross" }, "id": "Brown-David-Ross", "display_name": "Brown, David Ross" } ], "advisors": [ { "name": { "family": "Snyder", "given": "G. Jeffrey" }, "id": "Snyder-G-J", "role": "advisor", "display_name": "Snyder, G. Jeffrey" } ], "committee": [ { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "role": "chair", "display_name": "Atwater, Harry Albert" }, { "name": { "family": "Snyder", "given": "G. Jeffrey" }, "id": "Snyder-G-J", "role": "member", "display_name": "Snyder, G. Jeffrey" }, { "name": { "family": "Johnson", "given": "William Lewis" }, "id": "Johnson-W-L", "role": "member", "display_name": "Johnson, William Lewis" }, { "name": { "family": "Minnich", "given": "Austin J." }, "id": "Minnich-A-J", "role": "member", "display_name": "Minnich, Austin J." } ], "option_major": [ "appliedphys" ], "doi": "10.7907/Z9B56GNM", "abstract": "The quality of a thermoelectric material is judged by the size of its temperature de- pendent thermoeletric-figure-of-merit (zT ). Superionic materials, particularly Zn4Sb3 and Cu2Se, are of current interest for the high zT and low thermal conductivity of their disordered, superionic phase. In this work it is reported that the super-ionic materials Ag2Se, Cu2Se and Cu1.97Ag0.03Se show enhanced zT in their ordered, normal ion-conducting phases. The zT of Ag2Se is increased by 30% in its ordered phase as compared to its disordered phase, as measured just below and above its first order phase transition. The zT \u2019s of Cu2Se and Cu1.97Ag0.03Se both increase by more than 100% over a 30 K temperatures range just below their super-ionic phase transitions. The peak zT of Cu2Se is 0.7 at 406 K and of Cu1.97Ag0.03Se is 1.0 at 400 K. In all three materials these enhancements are due to anomalous increases in their Seebeck coefficients, beyond that predicted by carrier concentration measurements and band structure modeling. As the Seebeck coefficient is the entropy transported per carrier, this suggests that there is an additional quantity of entropy co-transported with charge carriers. Such co-transport has been previously observed via co-transport of vibrational entropy in bipolaron conductors and spin-state entropy in NaxCo2O4. The correlation of the temperature profile of the increases in each material with the nature of their phase transitions indicates that the entropy is associated with the thermodynamcis of ion-ordering. This suggests a new mechanism by which high thermoelectric performance may be understood and engineered." }, { "name": "Liu, Yiyang", "degree": "PhD", "year": "2015", "title": "Palladium-Catalyzed Decarboxylative and Decarbonylative Transformations in the Synthesis of Fine and Commodity Chemicals", "advisor": "Stoltz, Brian M.", "url": "https://resolver.caltech.edu/CaltechTHESIS:05292015-170352881", "creators": [ { "name": { "family": "Liu", "given": "Yiyang" }, "id": "Liu-Yiyang", "display_name": "Liu, Yiyang" } ], "advisors": [ { "name": { "family": "Stoltz", "given": "Brian M." }, "id": "Stoltz-B-M", "role": "advisor", "display_name": "Stoltz, Brian M." } ], "committee": [ { "name": { "family": "Reisman", "given": "Sarah E." }, "id": "Reisman-S-E", "role": "chair", "display_name": "Reisman, Sarah E." }, { "name": { "family": "Stoltz", "given": "Brian M." }, "id": "Stoltz-B-M", "role": "member", "display_name": "Stoltz, Brian M." }, { "name": { "family": "Agapie", "given": "Theodor" }, "id": "Agapie-T", "role": "member", "display_name": "Agapie, Theodor" }, { "name": { "family": "Grubbs", "given": "Robert H." }, "id": "Grubbs-R-H", "role": "member", "display_name": "Grubbs, Robert H." } ], "option_major": [ "chemistry" ], "doi": "10.7907/Z9NZ85NC", "abstract": "Decarboxylation and decarbonylation are important reactions in synthetic organic chemistry, transforming readily available carboxylic acids and their derivatives into various products through loss of carbon dioxide or carbon monoxide. In the past few decades, palladium-catalyzed decarboxylative and decarbonylative reactions experienced tremendous growth due to the excellent catalytic activity of palladium. Development of new reactions in this category for fine and commodity chemical synthesis continues to draw attention from the chemistry community.
\r\n\r\nThe Stoltz laboratory has established a palladium-catalyzed enantioselective decarboxylative allylic alkylation of \u03b2-keto esters for the synthesis of \u03b1-quaternary ketones since 2005. Recently, we extended this chemistry to lactams due to the ubiquity and importance of nitrogen-containing heterocycles. A wide variety of \u03b1-quaternary and tetrasubstituted \u03b1-tertiary lactams were obtained in excellent yields and exceptional enantioselectivities using our palladium-catalyzed decarboxylative allylic alkylation chemistry. Enantioenriched \u03b1-quaternary carbonyl compounds are versatile building blocks that can be further elaborated to intercept synthetic intermediates en route to many classical natural products. Thus our chemistry enables catalytic asymmetric formal synthesis of these complex molecules.
\r\n\r\nIn addition to fine chemicals, we became interested in commodity chemical synthesis using renewable feedstocks. In collaboration with the Grubbs group, we developed a palladium-catalyzed decarbonylative dehydration reaction that converts abundant and inexpensive fatty acids into value-added linear alpha olefins. The chemistry proceeds under relatively mild conditions, requires very low catalyst loading, tolerates a variety of functional groups, and is easily performed on a large scale. An additional advantage of this chemistry is that it provides access to expensive odd-numbered alpha olefins.
\r\n\r\nFinally, combining features of both projects, we applied a small-scale decarbonylative dehydration reaction to the synthesis of \u03b1-vinyl carbonyl compounds. Direct \u03b1-vinylation is challenging, and asymmetric vinylations are rare. Taking advantage of our decarbonylative dehydration chemistry, we were able to transform enantioenriched \u03b4-oxocarboxylic acids into quaternary \u03b1-vinyl carbonyl compounds in good yields with complete retention of stereochemistry. Our explorations culminated in the catalytic enantioselective total synthesis of (\u2013)-aspewentin B, a terpenoid natural product featuring a quaternary \u03b1-vinyl ketone. Both decarboxylative and decarbonylative chemistries found application in the late stage of the total synthesis.
" }, { "name": "Narang, Prineha", "degree": "PhD", "year": "2015", "title": "Light-Matter Interactions in Semiconductors and Metals: From Nitride Optoelectronics to Quantum Plasmonics", "advisor": "Atwater, Harry Albert; Lewis, Nathan Saul", "url": "https://resolver.caltech.edu/CaltechTHESIS:06052015-164458210", "creators": [ { "name": { "family": "Narang", "given": "Prineha" }, "id": "Narang-Prineha", "orcid": "0000-0003-3956-4594", "display_name": "Narang, Prineha" } ], "advisors": [ { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "role": "advisor", "display_name": "Atwater, Harry Albert" }, { "name": { "family": "Lewis", "given": "Nathan Saul" }, "id": "Lewis-N-S", "role": "co-advisor", "display_name": "Lewis, Nathan Saul" } ], "committee": [ { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "role": "chair", "display_name": "Atwater, Harry Albert" }, { "name": { "family": "Goddard", "given": "William A., III" }, "id": "Goddard-W-A-III", "role": "member", "display_name": "Goddard, William A., III" }, { "name": { "family": "Refael", "given": "Gil" }, "id": "Refael-G", "role": "member", "display_name": "Refael, Gil" }, { "name": { "family": "Schwab", "given": "Keith C." }, "id": "Schwab-K-C", "role": "member", "display_name": "Schwab, Keith C." }, { "name": { "family": "Lewis", "given": "Nathan Saul" }, "id": "Lewis-N-S", "role": "member", "display_name": "Lewis, Nathan Saul" } ], "option_major": [ "appliedphys" ], "doi": "10.7907/Z9513W4S", "abstract": "This thesis puts forth a theory-directed approach coupled with spectroscopy aimed at the discovery and understanding of light-matter interactions in semiconductors and metals.
\r\n\r\nThe first part of the thesis presents the discovery and development of Zn-IV nitride materials.The commercial prominence in the optoelectronics industry of tunable semiconductor alloy materials based on nitride semiconductor devices, specifically InGaN, motivates the search for earth-abundant alternatives for use in efficient, high-quality optoelectronic devices. II-IV-N2 compounds, which are closely related to the wurtzite-structured III-N semiconductors, have similar electronic and optical properties to InGaN namely direct band gaps, high quantum efficiencies and large optical absorption coefficients. The choice of different group II and group IV elements provides chemical diversity that can be exploited to tune the structural and electronic properties through the series of alloys. The first theoretical and experimental investigation of the ZnSnxGe1\u2212xN2 series as a replacement for III-nitrides is discussed here.
\r\n\r\nThe second half of the thesis shows ab\u2212initio calculations for surface plasmons and plasmonic hot carrier dynamics. Surface plasmons, electromagnetic modes confined to the surface of a conductor-dielectric interface, have sparked renewed interest because of their quantum nature and their broad range of applications. The decay of surface plasmons is usually a detriment in the field of plasmonics, but the possibility to capture the energy normally lost to heat would open new opportunities in photon sensors, energy conversion devices and switching. A theoretical understanding of plasmon-driven hot carrier generation and relaxation dynamics in the ultrafast regime is presented here. Additionally calculations for plasmon-mediated upconversion as well as an energy-dependent transport model for these non-equilibrium carriers are shown.
\r\n\r\nFinally, this thesis gives an outlook on the potential of non-equilibrium phenomena in metals and semiconductors for future light-based technologies.
" }, { "name": "Ning, Xin", "degree": "PhD", "year": "2015", "title": "Imperfection Insensitive Thin Shells", "advisor": "Pellegrino, Sergio", "url": "https://resolver.caltech.edu/CaltechTHESIS:05212015-174045815", "creators": [ { "name": { "family": "Ning", "given": "Xin" }, "id": "Ning-Xin", "display_name": "Ning, Xin" } ], "advisors": [ { "name": { "family": "Pellegrino", "given": "Sergio" }, "id": "Pellegrino-S", "orcid": "0000-0001-9373-3278", "role": "advisor", "display_name": "Pellegrino, Sergio" } ], "committee": [ { "name": { "family": "Kochmann", "given": "Dennis M." }, "id": "Kochmann-D-M", "orcid": "0000-0002-9112-6615", "role": "chair", "display_name": "Kochmann, Dennis M." }, { "name": { "family": "Pellegrino", "given": "Sergio" }, "id": "Pellegrino-S", "orcid": "0000-0001-9373-3278", "role": "member", "display_name": "Pellegrino, Sergio" }, { "name": { "family": "Ravichandran", "given": "Guruswami" }, "id": "Ravichandran-G", "orcid": "0000-0002-2912-0001", "role": "member", "display_name": "Ravichandran, Guruswami" }, { "name": { "family": "Beck", "given": "James L." }, "id": "Beck-J-L", "role": "member", "display_name": "Beck, James L." } ], "option_major": [ "space" ], "doi": "10.7907/Z91J97P9", "abstract": "The buckling of axially compressed cylindrical shells and externally pressurized spherical shells is extremely sensitive to even very small geometric imperfections. In practice this issue is addressed by either using overly conservative knockdown factors, while keeping perfect axial or spherical symmetry, or adding closely and equally spaced stiffeners on shell surface. The influence of imperfection-sensitivity is mitigated, but the shells designed from these approaches are either too heavy or very expensive and are still sensitive to imperfections. Despite their drawbacks, these approaches have been used for more than half a century.
\r\n\r\nThis thesis proposes a novel method to design imperfection-insensitive cylindrical shells subject to axial compression. Instead of following the classical paths, focused on axially symmetric or high-order rotationally symmetric cross-sections, the method in this thesis adopts optimal symmetry-breaking wavy cross-sections (wavy shells). The avoidance of imperfection sensitivity is achieved by searching with an evolutionary algorithm for smooth cross-sectional shapes that maximize the minimum among the buckling loads of geometrically perfect and imperfect wavy shells. It is found that the shells designed through this approach can achieve higher critical stresses and knockdown factors than any previously known monocoque cylindrical shells. It is also found that these shells have superior mass efficiency to almost all previously reported stiffened shells.
\r\n\r\nExperimental studies on a design of composite wavy shell obtained through the proposed method are presented in this thesis. A method of making composite wavy shells and a photogrametry technique of measuring full-field geometric imperfections have been developed. Numerical predictions based on the measured geometric imperfections match remarkably well with the experiments. Experimental results confirm that the wavy shells are not sensitive to imperfections and can carry axial compression with superior mass efficiency.
\r\n\r\nAn efficient computational method for the buckling analysis of corrugated and stiffened cylindrical shells subject to axial compression has been developed in this thesis. This method modifies the traditional Bloch wave method based on the stiffness matrix method of rotationally periodic structures. A highly efficient algorithm has been developed to implement the modified Bloch wave method. This method is applied in buckling analyses of a series of corrugated composite cylindrical shells and a large-scale orthogonally stiffened aluminum cylindrical shell. Numerical examples show that the modified Bloch wave method can achieve very high accuracy and require much less computational time than linear and nonlinear analyses of detailed full finite element models.
\r\n\r\nThis thesis presents parametric studies on a series of externally pressurized pseudo-spherical shells, i.e., polyhedral shells, including icosahedron, geodesic shells, and triambic icosahedra. Several optimization methods have been developed to further improve the performance of pseudo-spherical shells under external pressure. It has been shown that the buckling pressures of the shell designs obtained from the optimizations are much higher than the spherical shells and not sensitive to imperfections.
\r\n" }, { "name": "Usiskin, Robert Ezra", "degree": "PhD", "year": "2015", "title": "Surface Activity and Bulk Defect Chemistry of Solid Oxide Fuel Cell Cathodes", "advisor": "Haile, Sossina M.", "url": "https://resolver.caltech.edu/CaltechTHESIS:10032014-161017442", "creators": [ { "name": { "family": "Usiskin", "given": "Robert Ezra" }, "id": "Usiskin-Robert-Ezra", "display_name": "Usiskin, Robert Ezra" } ], "advisors": [ { "name": { "family": "Haile", "given": "Sossina M." }, "id": "Haile-S-M", "role": "advisor", "display_name": "Haile, Sossina M." } ], "committee": [ { "name": { "family": "Haile", "given": "Sossina M." }, "id": "Haile-S-M", "role": "chair", "display_name": "Haile, Sossina M." }, { "name": { "family": "Fultz", "given": "Brent T." }, "id": "Fultz-B-T", "role": "member", "display_name": "Fultz, Brent T." }, { "name": { "family": "Faber", "given": "Katherine T." }, "id": "Faber-K-T", "role": "member", "display_name": "Faber, Katherine T." }, { "name": { "family": "Rossman", "given": "George Robert" }, "id": "Rossman-G-R", "role": "member", "display_name": "Rossman, George Robert" } ], "option_major": [ "matsci" ], "doi": "10.7907/Z91N7Z3N", "abstract": "In the first half of this thesis, a new robotic instrument called a scanning impedance probe is presented that can acquire electrochemical impedance spectra in automated fashion from hundreds of thin film microelectrodes with systematically varied properties. Results from this instrument are presented for three catalyst compositions that are commonly considered for use in state-of-the-art solid oxide fuel cell cathodes. For (La0.8Sr0.2)0.95MnO3+\u03b4 (LSM), the impedance spectra are well fit by a through-the-film reaction pathway. Transport rates are extracted, and the surface activity towards oxygen reduction is found to be correlated with the number of exposed grain boundary sites, suggesting that grain boundaries are more surface-active than grains. For La0.5Sr0.5CoO3-\u03b4 (LSC), the surface activity degrades ~50x initially and then stabilizes at a comparable activity to that of previously measured Ba0.5Sr0.5Co0.8Fe0.2O3-\u03b4 films. For Sr0.06Nb0.06Bi1.87O3 (SNB), an example of a doped bismuth oxide, the activity of the metal-SNB boundary is measured.
\r\n\r\nIn the second half of this thesis, SrCo0.9Nb0.1O3-\u03b4 is selected as a case study of perovskites containing Sr and Co, which are the most active oxygen reduction catalysts known. Several bulk properties are measured, and synchrotron data are presented that provide strong evidence of substantial cobalt-oxygen covalency at high temperatures. This covalent bonding may be the underlying source of the high surface activity.
\r\n" }, { "name": "Weitekamp, Raymond Andrew", "degree": "PhD", "year": "2015", "title": "Multifunctional Materials: Bottom-Up and Top-Down", "advisor": "Grubbs, Robert H.; Atwater, Harry Albert", "url": "https://resolver.caltech.edu/CaltechTHESIS:06042015-140901217", "creators": [ { "name": { "family": "Weitekamp", "given": "Raymond Andrew" }, "id": "Weitekamp-Raymond-Andrew", "display_name": "Weitekamp, Raymond Andrew" } ], "advisors": [ { "name": { "family": "Grubbs", "given": "Robert H." }, "id": "Grubbs-R-H", "role": "co-advisor", "display_name": "Grubbs, Robert H." }, { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "role": "co-advisor", "display_name": "Atwater, Harry Albert" } ], "committee": [ { "name": { "family": "Tirrell", "given": "David A." }, "id": "Tirrell-D-A", "role": "chair", "display_name": "Tirrell, David A." }, { "name": { "family": "Miller", "given": "Thomas F." }, "id": "Miller-T-F", "role": "member", "display_name": "Miller, Thomas F." }, { "name": { "family": "Gray", "given": "Harry B." }, "id": "Gray-H-B", "role": "member", "display_name": "Gray, Harry B." }, { "name": { "family": "Grubbs", "given": "Robert H." }, "id": "Grubbs-R-H", "role": "member", "display_name": "Grubbs, Robert H." }, { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "role": "member", "display_name": "Atwater, Harry Albert" } ], "option_major": [ "chemistry" ], "doi": "10.7907/Z90C4SSB", "abstract": "This thesis is thematically separated into two complimentary approaches to advanced materials synthesis: bottom-up and top-down. Part I will discuss the self-assembly of photonic crystals, a unique class of periodic nanostructured materials featuring resonant optical response. Chapter 1 will introduce the concepts of self-assembly, specifically in the context of colloidal crystals and block copolymer nanostructures. Chapter 2 summarizes many years of work towards the goal of utilizing brush block copolymers as paintable photonic crystals. We employed 2D colloidal crystals as resonant light-trapping elements to improve the performance of thin-film solar cells; this work is described in Chapter 3. Part II of the thesis is centered around the concept of functional lithography: the ability to directly pattern materials with tailored physical properties and chemically active interfaces. We will briefly provide a history of photolithography in Chapter 4, and outline some of the limitations of the incumbent lithographic methods. The discovery of latent reactivity in ruthenium vinyl ether complexes, and the subsequent development of PhotoLithographic Olefin Metathesis Polymerization (PLOMP), are discussed in Chapter 5. This discovery has since blossomed into a true platform technology. We will discuss improvements to the functional group tolerance of PLOMP, as well as a few of our efforts to use PLOMP towards specific applications in Chapter 6. In the final Chapter 7 we document our attempts to activate PLOMP resists via multiphoton absorption, towards 3D printing of chemically functional microstructures." }, { "name": "Kosten, Emily Dell", "degree": "PhD", "year": "2014", "title": "Optical Designs for Improved Solar Cell Performance", "advisor": "Atwater, Harry Albert", "url": "https://resolver.caltech.edu/CaltechTHESIS:05222014-154510725", "creators": [ { "name": { "family": "Kosten", "given": "Emily Dell" }, "id": "Kosten-Emily-Dell", "display_name": "Kosten, Emily Dell" } ], "advisors": [ { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "role": "advisor", "display_name": "Atwater, Harry Albert" } ], "committee": [ { "name": { "family": "Atwater", "given": "Harry Albert" }, "id": "Atwater-H-A", "role": "chair", "display_name": "Atwater, Harry Albert" }, { "name": { "family": "Roukes", "given": "Michael Lee" }, "id": "Roukes-M-L", "role": "member", "display_name": "Roukes, Michael Lee" }, { "name": { "family": "Cross", "given": "Michael Clifford" }, "id": "Cross-M-C", "role": "member", "display_name": "Cross, Michael Clifford" }, { "name": { "family": "Schwab", "given": "Keith C." }, "id": "Schwab-K-C", "role": "member", "display_name": "Schwab, Keith C." } ], "option_major": [ "physics" ], "doi": "10.7907/8Y5H-AM79", "abstract": "The solar resource is the most abundant renewable resource on earth, yet it is currently exploited with relatively low efficiencies. To make solar energy more affordable, we can either reduce the cost of the cell or increase the efficiency with a similar cost cell. In this thesis, we consider several different optical approaches to achieve these goals. First, we consider a ray optical model for light trapping in silicon microwires. With this approach, much less material can be used, allowing for a cost savings. We next focus on reducing the escape of radiatively emitted and scattered light from the solar cell. With this angle restriction approach, light can only enter and escape the cell near normal incidence, allowing for thinner cells and higher efficiencies. In Auger-limited GaAs, we find that efficiencies greater than 38% may be achievable, a significant improvement over the current world record. To experimentally validate these results, we use a Bragg stack to restrict the angles of emitted light. Our measurements show an increase in voltage and a decrease in dark current, as less radiatively emitted light escapes. While the results in GaAs are interesting as a proof of concept, GaAs solar cells are not currently made on the production scale for terrestrial photovoltaic applications. We therefore explore the application of angle restriction to silicon solar cells. While our calculations show that Auger-limited cells give efficiency increases of up to 3% absolute, we also find that current amorphous silicion-crystalline silicon heterojunction with intrinsic thin layer (HIT) cells give significant efficiency gains with angle restriction of up to 1% absolute. Thus, angle restriction has the potential for unprecedented one sun efficiencies in GaAs, but also may be applicable to current silicon solar cell technology. Finally, we consider spectrum splitting, where optics direct light in different wavelength bands to solar cells with band gaps tuned to those wavelengths. This approach has the potential for very high efficiencies, and excellent annual power production. Using a light-trapping filtered concentrator approach, we design filter elements and find an optimal design. Thus, this thesis explores silicon microwires, angle restriction, and spectral splitting as different optical approaches for improving the cost and efficiency of solar cells. " }, { "name": "Abrecht, David Gregory", "degree": "PhD", "year": "2013", "title": "Thermodynamic Properties of Organometallic Dihydrogen Complexes for Hydrogen Storage Applications", "advisor": "Fultz, Brent T.", "url": "https://resolver.caltech.edu/CaltechTHESIS:12102012-132511810", "creators": [ { "name": { "family": "Abrecht", "given": "David Gregory" }, "id": "Abrecht-David-Gregory", "display_name": "Abrecht, David Gregory" } ], "advisors": [ { "name": { "family": "Fultz", "given": "Brent T." }, "id": "Fultz-B-T", "role": "advisor", "display_name": "Fultz, Brent T." } ], "committee": [ { "name": { "family": "Fultz", "given": "Brent T." }, "id": "Fultz-B-T", "role": "chair", "display_name": "Fultz, Brent T." }, { "name": { "family": "Tirrell", "given": "David A." }, "id": "Tirrell-D-A", "role": "member", "display_name": "Tirrell, David A." }, { "name": { "family": "Davis", "given": "Mark E." }, "id": "Davis-M-E", "role": "member", "display_name": "Davis, Mark E." }, { "name": { "family": "Wang", "given": "Zhen-Gang" }, "id": "Wang-Zhen-Gang", "role": "member", "display_name": "Wang, Zhen-Gang" } ], "option_major": [ "chemeng" ], "doi": "10.7907/z9057cvb", "abstract": "The mechanism and thermodynamic properties of hydrogen binding to the solid-state complexes [M(CO)dppe2][BArF24] (M = Mn, Re, Tc) and [M'Hdppe2][NTf2] (M' = Fe, Ru, Os) were investigated experimentally and computationally over the temperature range 298K-373K and pressure range 0-2800 torr, based on the Sieverts method. The bulk absorption behavior was found to be accurately described by Langmuir isotherms. Enthalpy and entropy values of ΔH° = -52.2 kJ/mol and ΔS° = -99.6 J/mol-K were obtained experimentally for hydrogen absorption onto [Mn(CO)dppe2][BArF24] from the Langmuir equilibrium constant, and values obtained from electronic structure calculations using the LANL2DZ-ECP basis set were found to successfully reproduce both the pressure-temperature-composition behavior and the thermodynamic values to within 5% of those obtained through experiment. Results from simulations for all complexes yielded large enthalpy values similar to metal hydride formation enthalpies for all complexes studied, and the substitution of the metal center reproduced qualitative binding strength trends of 5d>3d>4d consistent with those previously reported for the group 6 metals.
\r\n\r\nX-ray diffraction patterns and Mössbauer spectra were taken to determine the thermal decomposition pathway for [FeH(η2-H2)dppe2][NTf2]. Simulations at the B3LYP/TZVP level of theory and experimental Mössbauer spectra confirmed the direct thermal decomposition from singlet-state [FeH(η2-H2)dppe2][NTf2] to triplet-state [FeHdppe2][NTf2] under vacuum conditions at 398K. Evaluation of the partial quadrupole splitting values of Q(H2) = -0.245 mm/s from Mössbauer spectroscopy significantly differ from typical values obtained for hydrides, indicating an underutilized mechanism for identification of dihydrogen ligands. Singlet-state thermodynamic values from simulation were consistent with experimental observations for Ru and Os, and ruthenium complexes were found to have thermodynamic properties within appropriate ranges for hydrogen storage applications. Simulated thermodynamic values for Fe complexes were found to significantly underestimate experimental behavior, demonstrating the importance of the magnetic spin state of the molecule to hydrogen binding properties.
" }, { "name": "Smith, Matthew Alexander", "degree": "PhD", "year": "2013", "title": "Non-Contiguous Protein Recombination", "advisor": "Arnold, Frances Hamilton", "url": "https://resolver.caltech.edu/CaltechTHESIS:04102013-164733450", "creators": [ { "name": { "family": "Smith", "given": "Matthew Alexander" }, "id": "Smith-Matthew-Alexander", "display_name": "Smith, Matthew Alexander" } ], "advisors": [ { "name": { "family": "Arnold", "given": "Frances Hamilton" }, "id": "Arnold-F-H", "orcid": "0000-0002-4027-364X", "role": "advisor", "display_name": "Arnold, Frances Hamilton" } ], "committee": [ { "name": { "family": "Tirrell", "given": "David A." }, "id": "Tirrell-D-A", "orcid": "0000-0003-3175-4596", "role": "chair", "display_name": "Tirrell, David A." }, { "name": { "family": "Marcus", "given": "Rudolph A." }, "id": "Marcus-R-A", "orcid": "0000-0001-6547-1469", "role": "member", "display_name": "Marcus, Rudolph A." }, { "name": { "family": "Phillips", "given": "Robert B." }, "id": "Phillips-R", "orcid": "0000-0003-3082-2809", "role": "member", "display_name": "Phillips, Robert B." }, { "name": { "family": "Arnold", "given": "Frances Hamilton" }, "id": "Arnold-F-H", "orcid": "0000-0002-4027-364X", "role": "member", "display_name": "Arnold, Frances Hamilton" } ], "option_major": [ "bioeng" ], "doi": "10.7907/4B8E-ZH08", "abstract": "Swapping sequence elements among related proteins can produce chimeric proteins with novel behaviors and improved properties such as enhanced stability. Although homologous mutations are much more conservative than random mutations, chimeras of distantly-related proteins have a low probability of retaining fold and function. Here, I introduce a new tool for protein recombination that identifies structural blocks that can be swapped among homologous proteins with minimal disruption. This non-contiguous recombination approach enables design of chimeras and libraries of chimeras with less disruption than can be achieved by swapping blocks of sequence. Less disruption means that one can generate libraries with higher fractions of functional enzymes and enables recombination of more distant homologs.
\r\n\r\nUsing this new tool I design and construct many functional chimeric cellulases. I illustrate the structurally conservative nature of this recombination by creating a functional prokaryotic-eukaryotic chimera and solving its structure. I also show how non-contiguous recombination can be used to efficiently identify stabilizing mutations that have been incorporated into homologs in nature.
" } ]