This text describes in some detail the design and operational history of an instrument used as the front-end receiver for a fast, broadband, high-resolution spectrometer for the 1.3 millimeter wavelength atmospheric window. Using only a single superconductor-insulator-superconductor (SIS) tunnel junction as its heterodyne detector, the receiver\u2019s novel design achieved then unprecedented RF and IF bandwidths and incorporated several innovations which have since been widely adopted within the millimeter and submillimeter wave research communities. Although intended as a relatively simple technology demonstrator and starting point for more refined and sophisticated designs, the receiver turned out to be a useful astronomical instrument in its own right, and it was deployed as a de facto facility instrument for several years at the Caltech Submillimeter Observatory. Also described are the author\u2019s contributions to another important aid to research and design efforts: the SuperMix software library for the analysis and optimization of high-frequency circuitry, especially developed to aid in the design of systems involving SIS and other superconducting elements. Finally, the text may serve as a useful introduction to the theory behind and methodology for modeling and design of SIS heterodyne mixers.
", "doi": "10.7907/357d-6535", "publication_date": "2021", "thesis_type": "phd", "thesis_year": "2021" }, { "id": "thesis:9002", "collection": "thesis", "collection_id": "9002", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:06052015-153743425", "type": "thesis", "title": "Toward Understanding Astrophysical Phenomena", "author": [ { "family_name": "Luan", "given_name": "Jing", "clpid": "Luan-Jing" } ], "thesis_advisor": [ { "family_name": "Goldreich", "given_name": "Peter Martin", "clpid": "Goldreich-P-M" } ], "thesis_committee": [ { "family_name": "Prince", "given_name": "Thomas A.", "clpid": "Prince-T-A" }, { "family_name": "Ott", "given_name": "Christian D.", "clpid": "Ott-C-D" }, { "family_name": "Chen", "given_name": "Yanbei", "clpid": "Chen-Yanbei" }, { "family_name": "Goldreich", "given_name": "Peter Martin", "clpid": "Goldreich-P-M" } ], "local_group": [ { "literal": "TAPIR" }, { "literal": "Astronomy Department" }, { "literal": "div_pma" } ], "abstract": "Fast radio bursts (FRBs), a novel type of radio pulse, whose physics is not yet understood at all. Only a handful of FRBs had been detected when we started this project. Taking account of the scant observations, we put physical constraints on FRBs. We excluded proposals of a galactic origin for their extraordinarily high dispersion measures (DM), in particular stellar coronas and HII regions. Therefore our work supports an extragalactic origin for FRBs. We show that the resolved scattering tail of FRB 110220 is unlikely to be due to propagation through the intergalactic plasma. Instead the scattering is probably caused by the interstellar medium in the FRB's host galaxy, and indicates that this burst sits in the central region of that galaxy. Pulse durations of order ms constrain source sizes of FRBs implying enormous brightness temperatures and thus coherent emission. Electric fields near FRBs at cosmological distances would be so strong that they could accelerate free electrons from rest to relativistic energies in a single wave period. When we worked on FRBs, it was unclear whether they were genuine astronomical signals as distinct from 'perytons', clearly terrestrial radio bursts, sharing some common properties with FRBs. Recently, in April 2015, astronomers discovered that perytons were emitted by microwave ovens. Radio chirps similar to FRBs were emitted when their doors opened while they were still heating. Evidence for the astronomical nature of FRBs has strengthened since our paper was published. Some bursts have been found to show linear and circular polarizations and Faraday rotation of the linear polarization has also been detected. I hope to resume working on FRBs in the near future. But after we completed our FRB paper, I decided to pause this project because of the lack of observational constraints.
\r\n\r\n\r\nThe pulsar triple system, J0733+1715, has its orbital parameters fitted to high accuracy owing to the precise timing of the central ms pulsar. The two orbits are highly hierarchical, namely Porb,1 << Porb,2, where 1 and 2 label the inner and outer white dwarf (WD) companions respectively. Moreover, their orbital planes almost coincide, providing a unique opportunity to study secular interaction associated purely with eccentricity beyond the solar system. Secular interaction only involves effect averaged over many orbits. Thus each companion can be represented by an elliptical wire with its mass distributed inversely proportional to its local orbital speed. Generally there exists a mutual torque, which vanishes only when their apsidal lines are parallel or anti-parallel. To maintain either mode, the eccentricity ratio, e1/e2, must be of the proper value, so that both apsidal lines precess together. For J0733+1715, e1 << e2 for the parallel mode, while e1 >> e2 for the anti-parallel one. We show that the former precesses ~ 10 times slower than the latter. Currently the system is dominated by the parallel mode. Although only a little anti-parallel mode survives, both eccentricities especially e1 oscillate on ~ 103yr timescale. Detectable changes would occur within ~ 1\\yr. We demonstrate that the anti-parallel mode gets damped ~ 104 times faster than its parallel brother by any dissipative process diminishing e1. If it is the tidal damping in the inner WD, we proceed to estimate its tidal quantity parameter (Q) to be ~ 106, which was poorly constrained by observations. However, tidal damping may also happen during the preceding low-mass X-ray binary (LMXB) phase or hydrogen thermal nuclear flashes. But, in both cases, the inner companion fills its Roche lobe and probably suffers mass/angular momentum loss, which might cause e1 to grow rather than decay.
\r\n\r\n\r\nSeveral pairs of solar system satellites occupy mean motion resonances (MMRs). We divide these into two groups according to their proximity to exact resonance. Proximity is measured by the existence of a separatrix in phase space. MMRs between Io-Europa, Europa-Ganymede and Enceladus-Dione are too distant from exact resonance for a separatrix to appear. A separatrix is present only in the phase spaces of the Mimas-Tethys and Titan-Hyperion MMRs and their resonant arguments are the only ones to exhibit substantial librations. When a separatrix is present, tidal damping of eccentricity or inclination excites overstable librations that can lead to passage through resonance on the damping timescale. However, after investigation, we conclude that the librations in the Mimas-Tethys and Titan-Hyperion MMRs are fossils and do not result from overstability.
\r\n\r\n\r\nRubble piles are common in the solar system. Monolithic elements touch their neighbors in small localized areas. Voids occupy a significant fraction of the volume. In a fluid-free environment, heat cannot conduct through voids; only radiation can transfer energy across them. We model the effective thermal conductivity of a rubble pile and show that it is proportional the square root of the pressure, P, for P\u2264 \u03b53\u03bc where \u03b5 is the material's yield strain and \u03bc its shear modulus. Our model provides an excellent fit to the depth dependence of the thermal conductivity in the top 140 cm of the lunar regolith. It also offers an explanation for the low thermal inertias of rocky asteroids and icy satellites. Lastly, we discuss how rubble piles slow down the cooling of small bodies such as asteroids.
\r\n\r\n\r\nElectromagnetic (EM) follow-up observations of gravitational wave (GW) events will help shed light on the nature of the sources, and more can be learned if the EM follow-ups can start as soon as the GW event becomes observable. In this paper, we propose a computationally efficient time-domain algorithm capable of detecting gravitational waves (GWs) from coalescing binaries of compact objects with nearly zero time delay. In case when the signal is strong enough, our algorithm also has the flexibility to trigger EM observation before the merger. The key to the efficiency of our algorithm arises from the use of chains of so-called Infinite Impulse Response (IIR) filters, which filter time-series data recursively. Computational cost is further reduced by a template interpolation technique that requires filtering to be done only for a much coarser template bank than otherwise required to sufficiently recover optimal signal-to-noise ratio. Towards future detectors with sensitivity extending to lower frequencies, our algorithm's computational cost is shown to increase rather insignificantly compared to the conventional time-domain correlation method. Moreover, at latencies of less than hundreds to thousands of seconds, this method is expected to be computationally more efficient than the straightforward frequency-domain method.
", "doi": "10.7907/Z97942NB ", "publication_date": "2015", "thesis_type": "phd", "thesis_year": "2015" }, { "id": "thesis:2058", "collection": "thesis", "collection_id": "2058", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-05252006-181025", "primary_object_url": { "basename": "mpan.pdf", "content": "final", "filesize": 4672868, "license": "other", "mime_type": "application/pdf", "url": "/2058/1/mpan.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "Slices of Theoretical Astrophysics: Solar System Dynamics and Relativistic Explosions", "author": [ { "family_name": "Pan", "given_name": "Margaret Whei-Jie", "clpid": "Pan-Margaret-Whei-Jie" } ], "thesis_advisor": [ { "family_name": "Sari", "given_name": "Re'em", "clpid": "Sari-R" } ], "thesis_committee": [ { "family_name": "Kamionkowski", "given_name": "Marc P.", "clpid": "Kamionkowski-M-P" }, { "family_name": "Brown", "given_name": "Michael E.", "clpid": "Brown-M-E" }, { "family_name": "Scoville", "given_name": "Nicholas Zabriskie", "clpid": "Scoville-N-Z" }, { "family_name": "Goldreich", "given_name": "Peter Martin", "clpid": "Goldreich-P-M" }, { "family_name": "Sari", "given_name": "Re'em", "clpid": "Sari-R" } ], "local_group": [ { "literal": "TAPIR" }, { "literal": "Astronomy Department" }, { "literal": "div_pma" } ], "abstract": "This thesis presents studies in two distinct areas of theoretical astrophysics: dynamics of planetary systems and relativistic fluid flows from shocks emerging from stellar envelopes. The first pertains to the early solar system, planet formation, and extrasolar planets; the second is related to extreme explosions like gamma-ray bursts and supernovae.
\r\n\r\nWe present two investigations of the dynamics and population evolution of small solar system bodies. First, we explore the dynamics of mean-motion resonances for a test particle moving in a highly eccentric long-period orbit in the restricted circular planar three-body problem --- a scenario relevant to the scattered Kuiper belt and the formation of the Oort cloud. We find an infinite number of analogues to the Lagrange points; a simple explanation for the presence and absence of asymmetric librations in particular mean-motion resonances; and a criterion for the onset of chaotic motion at large semimajor axes.
\r\n\r\nSecond, we study the size distribution of Kuiper belt objects (KBOs), which is observed to be a broken power law. We apply a simple mass conservation argument to the KBO collisional cascade to get the power-law slope for KBOs below the break; our result agrees well with observations if we assume KBOs are held together by self-gravity rather than material strength. We also explain the location and time evolution of the break in the size distribution.
\r\n\r\nWe also present investigations of the flow which results when a relativistic shock propagates through and then breaks out of a stellar envelope with a polytropic density profile. This work informs predictions of the speed of and energy carried by the relativistic ejecta in supernovae and perhaps in gamma-ray bursts. We find the asymptotic solution for the flow as the shock reaches the star's edge and find a new self-similar solution for flow of hot fluid after the shock breakout. Since the post-breakout flow acclerates by converting its thermal energy into bulk kinetic energy, the fluid in the flow eventually cools to non-relativistic temperatures. We derive a second new self-similar solution which includes the cold portions of the flow. This second solution gives an exact relation between the terminal Lorentz factor of each fluid element and the Lorentz factor it acquired upon being shocked before breakout.
", "doi": "10.7907/40AE-N743", "publication_date": "2006", "thesis_type": "phd", "thesis_year": "2006" }, { "id": "thesis:2065", "collection": "thesis", "collection_id": "2065", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-05252006-223939", "primary_object_url": { "basename": "thesis_liu.pdf", "content": "final", "filesize": 1682415, "license": "other", "mime_type": "application/pdf", "url": "/2065/1/thesis_liu.pdf", "version": "v2.0.0" }, "type": "thesis", "title": "Interaction of Magnetic Field and Flow in the Outer Shells of Giant Planets", "author": [ { "family_name": "Liu", "given_name": "Junjun", "clpid": "Liu-Junjun" } ], "thesis_advisor": [ { "family_name": "Stevenson", "given_name": "David John", "clpid": "Stevenson-D-J" }, { "family_name": "Goldreich", "given_name": "Peter Martin", "clpid": "Goldreich-P-M" }, { "family_name": "Ingersoll", "given_name": "Andrew P.", "clpid": "Ingersoll-A-P" } ], "thesis_committee": [ { "family_name": "Ingersoll", "given_name": "Andrew P.", "orcid": "0000-0002-2035-9198", "clpid": "Ingersoll-A-P" }, { "family_name": "Stevenson", "given_name": "David John", "orcid": "0000-0001-9432-7159", "clpid": "Stevenson-D-J" }, { "family_name": "Goldreich", "given_name": "Peter Martin", "clpid": "Goldreich-P-M" }, { "family_name": "Sari", "given_name": "Re'em", "orcid": "0000-0002-1084-3656", "clpid": "Sari-R" }, { "family_name": "Schneider", "given_name": "Tapio", "orcid": "0000-0001-5687-2287", "clpid": "Schneider-T" } ], "local_group": [ { "literal": "TAPIR" }, { "literal": "Astronomy Department" }, { "literal": "div_gps" } ], "abstract": "This study of the interaction of magnetic field and flow in the outer shells of giant planets consists of three parts.
\r\n\r\nPart one: The atmospheres of Jupiter and Saturn exhibit strong and stable zonal winds. Busse suggested that they might be the surface expression of deep flows on cylinders. However, the deep flow hypothesis experiences difficulty when account is taken of the electrical conductivity of molecular hydrogen as measured in shockwave experiments. The deep zonal flow of an electrically conducting fluid would produce a toroidal magnetic field, an associated poloidal electrical current, and Ohmic dissipation. In steady state, the total Ohmic dissipation cannot exceed the planet's net luminosity. If we assume that the observed zonal flow penetrates along cylinders until it is truncated to (near) zero at some spherical radius, the upper bound on Ohmic dissipation constrains this radius to be no smaller than 0.95 Jupiter radius and 0.87 Saturn radius. The truncation of the cylindrical flow in the convective envelope requires an appropriate force to break the Taylor-Proudman constraint. We have been unable to identify any plausible candidate. Thus we conclude that deep-seated cylindrical flows do not exist.
\r\n\r\nPart two: A fluid shell with sufficient electrical conductivity and azimuthal velocity shear outside of the dynamo generation region can attenuate the non-axisymmetric component of the magnetic field. However, the interaction of the axisymmetric component of the magnetic field and the zonal flow is able to reduce the magnitude of zonal flow. The dimensionless number characterizing this reduction is the Chandrasekhar number. The smaller Saturnian field may allow a larger velocity shear and a greater attenuation of the non-axisymmetric field, thereby providing a possible explanation for the nearly axisymmetric field.
\r\n\r\nPart three: Combining the study for the attenuation effect produced by the semi-conducting layer and the observation of the magnetic field by Galileo and Voyager, we find the possible outer boundary of the dynamo generation zone is at 0.86 Jupiter radius. The magnetic fields generated in the outer shell are dictated by a length scale comparable to the scale height of electrical conductivity, which is much smaller than the radius of the planet.
", "doi": "10.7907/4PVM-0G30", "publication_date": "2006", "thesis_type": "phd", "thesis_year": "2006" }, { "id": "thesis:1971", "collection": "thesis", "collection_id": "1971", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-05232005-155338", "primary_object_url": { "basename": "main.pdf", "content": "final", "filesize": 2036830, "license": "other", "mime_type": "application/pdf", "url": "/1971/2/main.pdf", "version": "v4.0.0" }, "type": "thesis", "title": "Adventures in Theoretical Astrophysics", "author": [ { "family_name": "Farmer", "given_name": "Alison Jane", "clpid": "Farmer-Alison-Jane" } ], "thesis_advisor": [ { "family_name": "Goldreich", "given_name": "Peter Martin", "clpid": "Goldreich-P-M" } ], "thesis_committee": [ { "family_name": "Cohen", "given_name": "Judith G.", "clpid": "Cohen-J-G" }, { "family_name": "Kamionkowski", "given_name": "Marc P.", "clpid": "Kamionkowski-M-P" }, { "family_name": "Goldreich", "given_name": "Peter Martin", "clpid": "Goldreich-P-M" }, { "family_name": "Sari", "given_name": "Re'em", "clpid": "Sari-R" }, { "family_name": "Sargent", "given_name": "Wallace L. W.", "clpid": "Sargent-W-L-W" } ], "local_group": [ { "literal": "TAPIR" }, { "literal": "Astronomy Department" }, { "literal": "div_pma" } ], "abstract": "This thesis is a tour of topics in theoretical astrophysics, unified by their diversity and their pursuit of physical understanding of astrophysical phenomena.
\r\n\r\nIn the first chapter, we raise the possibility of the detection of white dwarfs in transit surveys for extrasolar Earths, and discuss the peculiarities of detecting these more massive objects.
\r\n\r\nA population synthesis calculation of the gravitational wave background from extragalactic binary stars is then presented. In this study, we establish a firm understanding of the uncertainties in such a calculation and provide a valuable reference for planning the Laser Interferometer Space Antenna mission.
\r\n\r\nThe long-established problem of cosmic ray confinement to the Galaxy is addressed in another chapter. We introduce a new wave damping mechanism, due to the presence of background turbulence, that prevents the confinement of cosmic rays by the resonant streaming instability.
\r\n\r\nWe also investigate the spokes in Saturn's B ring, an electrodynamic mystery that is being illuminated by new data sent back from the Cassini spacecraft. In particular, we present assessments of the presence of charged dust near the rings, and the size of currents and electric fields in the ring system. We make inferences from the Cassini discovery of oxygen ions above the rings. In addition, the previous leading theory for spoke formation is demonstrated to be unphysical.
\r\n\r\nIn the final chapter, we explain the wayward motions of Prometheus and Pandora, two small moons of Saturn. Previously found to be chaotic as a result of mutual interactions, we account for their behavior by analogy with a parametric pendulum. We caution that this behavior may soon enter a new regime.
", "doi": "10.7907/JJKJ-J144", "publication_date": "2005", "thesis_type": "phd", "thesis_year": "2005" }, { "id": "thesis:3744", "collection": "thesis", "collection_id": "3744", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-09242008-095607", "type": "thesis", "title": "Collisional Processes Involving Icy Bodies in the Solar System", "author": [ { "family_name": "Stewart", "given_name": "Sarah Toby", "orcid": "0000-0001-9606-1593", "clpid": "Stewart-Sarah-Toby" } ], "thesis_advisor": [ { "family_name": "Ahrens", "given_name": "Thomas J.", "clpid": "Ahrens-T-J" }, { "family_name": "Yung", "given_name": "Yuk L.", "orcid": "0000-0002-4263-2562", "clpid": "Yung-Y-L" } ], "thesis_committee": [ { "family_name": "Ingersoll", "given_name": "Andrew P.", "orcid": "0000-0002-2035-9198", "clpid": "Ingersoll-A-P" }, { "family_name": "Ahrens", "given_name": "Thomas J.", "clpid": "Ahrens-T-J" }, { "family_name": "Yung", "given_name": "Yuk L.", "orcid": "0000-0002-4263-2562", "clpid": "Yung-Y-L" }, { "family_name": "Brown", "given_name": "Michael E.", "orcid": "0000-0002-8255-0545", "clpid": "Brown-M-E" }, { "family_name": "Goldreich", "given_name": "Peter Martin", "clpid": "Goldreich-P-M" }, { "family_name": "Kamb", "given_name": "W. Barclay", "clpid": "Kamb-W-B" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "1. The Shock Hugoniot of Solid Ice:
\r\n\r\nWe present a complete description of the solid ice Hugoniot based on new shock wave experiments conducted at an initial temperature of 100 K and previously published data obtained at 263 K. We identify five regions on the solid ice Hugoniot: (1) elastic shock waves, (2) ice Ih deformation shocks, transformation shocks to (3) ice VI, (4) ice VII, and (5) liquid water. In each region, data obtained at different initial temperatures are described by a single Us - Δup shock equation of state. The dynamic strength of ice Ih is strongly dependent on temperature. The Hugoniot Elastic Limit varies from 0.05 to 0.62 GPa, as a function of temperature and peak shock stress. We estimate the entropy and temperature along the 100 and 263 K Hugoniots and derive the critical pressures for shock-induced incipient (IM) and complete (CM) melting upon release. On the 100 K Hugoniot, the critical pressures are about 4.5 and between 5-6 GPa for IM and CM, respectively. On the 263 K Hugoniot, the critical pressures are 0.6 and 3.7 GPa for IM and CM, lower than previously suggested. Shock-induced melting of ice will be widespread in impact events.
\r\n\r\n2. Rampart Crater Formation on Mars:
\r\n\r\nWe present a model for the fluidization of Martian rampart crater ejecta blankets with liquid water based on the shock physics of cratering onto an ice-rich regolith. We conducted simulations of crater formation on Mars, explicitly accounting for the equations of state and shock-induced melting criteria for both the silicate and ice components and using strength models constrained by the observed transition diameter DTr from simple to complex craters on Mars, where DTr = 8 km corresponds to an effective yield strength of 107 Pa.
\r\n\r\nFor the observed size range of rampart craters (diameters D ≾ 30 km) and typical asteroidal impact conditions (silicate impactors, D ≾ 1 km, at 10 km s-1), we find that the hemispherical volume where subsurface ice is partially melted by the impact shock has a radius of about 15 projectile radii (rp), much larger than previous predictions of about 6 rp. The radius of the final crater is comparable to the radius of partial melting and more than half the ice within the excavated material is melted. Thus, the amount of shock-melted water incorporated into the continuous ejecta blanket is within a factor of two of the near-surface ground ice content.
\r\n\r\nWe find that fluidized ejecta blankets may form in the current climate with mean surface temperatures of 200 K. Decreasing the effective yield strength of the modeled materials, e.g., by increasing the ice content or porosity, modifies the impact-induced flow in the excavated cavity, resulting in deeper projectile penetration, steeper ejection angles, higher crater rim uplift, and reduced final crater diameter. The volume fraction of shock-melted water in the ejecta blanket increases with distance from the crater rim. The horizontal flow velocities during emplacement of fluidized ejecta (~ 10 - 1000 m s-1) is nearly constant in the continuous ejecta blanket and within the range of large terrestrial landslides. Therefore, ground-hugging debris flow conditions are achieved. The ejecta blanket properties from impacts into a Martian regolith containing 20-40%vol near-surface ice are consistent with the fraction of liquid water inferred from models of ejecta flow rheologies which produce rampart morphologies, about 10-30% liquid water by volume [Ivanov, B. A., Solar System Research, 30, 43-58, 1996].
\r\n\r\nWe present a model for the formation of different rampart ejecta morphologies which may be used in conjunction with an ejecta blanket debris flow model to map the distribution of ground ice. In addition, we find that formation of single or multiple-rampart ejecta blankets does not require pre-existing liquid water in the Martian crust. We estimate the minimum water content in observed rampart ejecta blankets to be equivalent to a global layer of water 0.6 m thick. Based on the crater sampling efficiency, the implied global Martian ice content, within the upper 2 km of the crust, is equivalent to a global layer of water 100 m deep. This result is comparable to other estimates of HM2O content in the Martian crust.
\r\n", "doi": "10.7907/0V4Q-VF61", "publication_date": "2002", "thesis_type": "phd", "thesis_year": "2002" }, { "id": "thesis:4106", "collection": "thesis", "collection_id": "4106", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-10162001-185319", "primary_object_url": { "basename": "thesis.pdf", "content": "final", "filesize": 40626495, "license": "other", "mime_type": "application/pdf", "url": "/4106/1/thesis.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "The Discovery and Characterization of Methane-bearing Brown Dwarfs and the Definition of the T Spectral Class", "author": [ { "family_name": "Burgasser", "given_name": "Adam Jonathan", "orcid": "0000-0002-6523-9536", "clpid": "Burgasser-Adam-Jonathan" } ], "thesis_advisor": [ { "family_name": "Janda", "given_name": "Kenneth C.", "clpid": "Janda-K-C" }, { "family_name": "Porter", "given_name": "Frank C.", "orcid": "0000-0003-1948-8889", "clpid": "Porter-F-C" } ], "thesis_committee": [ { "family_name": "Brown", "given_name": "Michael E.", "orcid": "0000-0002-8255-0545", "clpid": "Brown-M-E" }, { "family_name": "Soifer", "given_name": "B. Thomas", "clpid": "Soifer-B-T" }, { "family_name": "Kirkpatrick", "given_name": "J. Davy", "clpid": "Kirkpatrick-J-D" }, { "family_name": "Hillenbrand", "given_name": "Lynne A.", "clpid": "Hillenbrand-L-A" }, { "family_name": "Goldreich", "given_name": "Peter Martin", "clpid": "Goldreich-P-M" }, { "family_name": "Janda", "given_name": "Kenneth C.", "clpid": "Janda-K-C" }, { "family_name": "Porter", "given_name": "Frank C.", "orcid": "0000-0003-1948-8889", "clpid": "Porter-F-C" } ], "local_group": [ { "literal": "Astronomy Department" }, { "literal": "div_pma" } ], "abstract": "I present the discovery of 18 T dwarfs, brown dwarfs exhibiting CH4 absorption analogous to Gliese 229B, identified in the Two Micron All Sky Survey. Follow-up spectroscopic observations reveal the presence of strong H2O and CH4 bands in these objects, as well as broadened Na I and K I absorption in the red optical; fine lines of K I, Cs I, and Rb I; and FeH absorption at 9896 \u00ae Three objects are analyzed in detail; the widely-separated companion brown dwarf Gliese 570D, the coolest known brown dwarf with Teff = 810+/-45 K; the active T dwarf 2MASS 1237+6526, whose unique and steady H alpha emission may be the result of Roche-lobe overflow accretion from a closely-separated companion; and 2MASS 0559-1404, the brightest T dwarf currently known, which appears to be overluminous but unresolved in HST images. The variation in spectral features amongst these objects and those identified by the Sloan Digital Sky Survey have been used to derive a near-infrared spectral classification scheme, tied to the observed strengths of H2O and CH4 bands, color ratios, and K-band spectral morphology. The grid of subclasses segregates the currently known population into seven distinct groups, ranging from T1 V to T8 V. I show that the possible presence of CH4 in the L7 V DENIS 0205-1159AB argues for few subtypes between the latest known L dwarfs and the earliest T dwarfs. One peculiar object, 2MASS 0937+2931, has a highly suppressed K-band peak, likely due to increased H2 opacity in a high-gravity or low-metallicity atmosphere. Examination of absolute brightness and effective temperature across the L/T transition indicates rapid evolution of spectral features, possibly linked to heterogenous cloud coverage as condensibles rain out of the photosphere. Finally, I have used the T dwarf search samples to constrain the substellar field mass function. Through rigorous analysis of selection biases and Monte Carlo simulations, I show that my results are consistent with a power-law mass function scaling as 0.5 [less than] alpha [less than] 1.0, consistent with young stellar cluster surveys but significantly less than current estimates in the field.
", "doi": "10.7907/KECQ-7R18", "publication_date": "2002", "thesis_type": "phd", "thesis_year": "2002" }, { "id": "thesis:6796", "collection": "thesis", "collection_id": "6796", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:01302012-162107660", "primary_object_url": { "basename": "Lithwick_y_2002.pdf", "content": "final", "filesize": 28809074, "license": "other", "mime_type": "application/pdf", "url": "/6796/1/Lithwick_y_2002.pdf", "version": "v5.0.0" }, "type": "thesis", "title": "Topics in MHD Turbulence", "author": [ { "family_name": "Lithwick", "given_name": "Yoram", "orcid": "0000-0003-4450-0528", "clpid": "Lithwick-Yoram" } ], "thesis_advisor": [ { "family_name": "Goldreich", "given_name": "Peter Martin", "clpid": "Goldreich-P-M" }, { "family_name": "Readhead", "given_name": "Anthony C. S.", "orcid": "0000-0001-9152-961X", "clpid": "Readhead-A-C-S" } ], "thesis_committee": [ { "family_name": "Goldreich", "given_name": "Peter Martin", "clpid": "Goldreich-P-M" }, { "family_name": "Blandford", "given_name": "Roger D.", "clpid": "Blandford-R-D" }, { "family_name": "Phinney", "given_name": "E. Sterl", "orcid": "0000-0002-9656-4032", "clpid": "Phinney-E-S" }, { "family_name": "Scoville", "given_name": "Nicholas Zabriskie", "orcid": "0000-0002-0438-3323", "clpid": "Scoville-N-Z" }, { "family_name": "Readhead", "given_name": "Anthony C. S.", "orcid": "0000-0001-9152-961X", "clpid": "Readhead-A-C-S" } ], "local_group": [ { "literal": "TAPIR" }, { "literal": "Astronomy Department" }, { "literal": "div_pma" } ], "abstract": "I consider two topics in MHD turbulence. First, I work out the theory of compressible MHD turbulence, including kinetic effects. I use this theory to understand features of interstellar scintillation that have hitherto been unexplained. Second, I work out the theory of imbalanced weak MHD turbulence.", "doi": "10.7907/FP3Q-EZ29", "publication_date": "2002", "thesis_type": "phd", "thesis_year": "2002" }, { "id": "thesis:3767", "collection": "thesis", "collection_id": "3767", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-09252008-090426", "primary_object_url": { "basename": "Adelberger_kl_2002.pdf", "content": "final", "filesize": 73056574, "license": "other", "mime_type": "application/pdf", "url": "/3767/1/Adelberger_kl_2002.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "Star Formation and Structure Formation between Redshifts 1 < z < 4", "author": [ { "family_name": "Adelberger", "given_name": "Kurt Ludvig", "clpid": "Adelberger-Kurt-Ludvig" } ], "thesis_advisor": [ { "family_name": "Steidel", "given_name": "Charles C.", "orcid": "0000-0002-4834-7260", "clpid": "Steidel-C-C" } ], "thesis_committee": [ { "family_name": "Sargent", "given_name": "Wallace L. W.", "clpid": "Sargent-W-L-W" }, { "family_name": "Djorgovski", "given_name": "George", "orcid": "0000-0002-0603-3087", "clpid": "Djorgovski-G" }, { "family_name": "Goldreich", "given_name": "Peter Martin", "clpid": "Goldreich-P-M" }, { "family_name": "Martin", "given_name": "D. Christopher", "orcid": "0000-0002-8650-1644", "clpid": "Martin-D-Christopher" }, { "family_name": "Steidel", "given_name": "Charles C.", "orcid": "0000-0002-4834-7260", "clpid": "Steidel-C-C" } ], "local_group": [ { "literal": "Astronomy Department" }, { "literal": "div_pma" } ], "abstract": "The universe of galaxies beyond redshift one has finally become relatively easy to observe. While only a handful of galaxies with redshifts z > 1 were known 10 years ago, more than 2000 have spectroscopic redshifts today. These surveys are beginning to provide us with a detailed view of the first half of cosmic history. Their creation and interpretation is the subject of this thesis. Chapter 1 describes efficient techniques that can be used to locate galaxies at 1 \u227e z \u227e 5 among the numerous foreground and background objects in deep optical images. Chapter 2 characterizes the effects of dust obscuration on the resulting large high-redshift samples. The remainder of the thesis attemtps to place star-forming high-redshift galaxies into a larger cosmological context. Chapter 3 investigates the spatial clustering of galaxies at z ~ 3, finds it to be strong, and shows that this suggests a close link between rapidly star-forming galaxies and massive virialized objects in the underlying distribution of dark matter. Chapter 4 analyses the curious spatial association of high-redshift galaxies with inter-galactic hydrogen and metals, and finds some evidence that the numerous supernova explosions in young galaxies may profoundly affect the evolution of the universe's baryons.", "doi": "10.7907/F2SF-4J89", "publication_date": "2002", "thesis_type": "phd", "thesis_year": "2002" }, { "id": "thesis:6967", "collection": "thesis", "collection_id": "6967", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:04242012-142706141", "primary_object_url": { "basename": "Dyudina_ua_2002.pdf", "content": "final", "filesize": 30330221, "license": "other", "mime_type": "application/pdf", "url": "/6967/1/Dyudina_ua_2002.pdf", "version": "v5.0.0" }, "type": "thesis", "title": "Light Scattering in the Clouds on Jupiter", "author": [ { "family_name": "Dyudina", "given_name": "Ulyana Anatolyevna", "clpid": "Dyudina-Ulyana-Anatolyevna" } ], "thesis_advisor": [ { "family_name": "Ingersoll", "given_name": "Andrew P.", "orcid": "0000-0002-2035-9198", "clpid": "Ingersoll-A-P" } ], "thesis_committee": [ { "family_name": "Goldreich", "given_name": "Peter Martin", "clpid": "Goldreich-P-M" }, { "family_name": "Brown", "given_name": "Michael E.", "orcid": "0000-0002-8255-0545", "clpid": "Brown-M-E" }, { "family_name": "Ingersoll", "given_name": "Andrew P.", "orcid": "0000-0002-2035-9198", "clpid": "Ingersoll-A-P" }, { "family_name": "Yung", "given_name": "Yuk L.", "orcid": "0000-0002-4263-2562", "clpid": "Yung-Y-L" } ], "local_group": [ { "literal": "Astronomy Department" }, { "literal": "div_gps" } ], "abstract": "We construct maps of jovian cloud properties from images taken simultaneously by the Galileo solid state imaging system (SSI) and the near-infrared mapping spectrometer (NIMS) at 26 visible and near infrared wavelengths, ranging from 0.41 to 5.2 \u00b5m. Three regions - the Great Red Spot (GRS), a 5-micron Hot Spot, and one of the White Ovals - are studied. We perform a principal component analysis (PCA) on the multispectral images. PCA shows that the pixel-to-pixel variations at the different wavelengths are highly correlated, and that 91% of the variance in the data can be summarized using only three maps. The three maps are combined into one color map, which indicates different 26-wavelength spectra as different colors. Using the representative spectra for each color we compare different areas on the map qualitatively. We find that in the GRS there is a red chromophore which is associated with clouds that block 5-\u00b5m emission. At the hot spot and white oval regions there is no chromophore associated with clouds. Most of the bright, optically thick clouds blocking thermal emission are also extended vertically to the upper troposphere. Some of the bright, optically thick clouds blocking thermal emission are deep and do not extend vertically to the upper troposphere. A small convective stormlike cloud to the northwest of the GRS is unusually reflective at long wavelengths (4\u00b5m) and might indicate large particles.
\r\n\r\nWe study lightning on Jupiter and the clouds illuminated by the lightning. The Galileo SSI lightning images have a resolution of 25 km/pixel and are able to resolve the diffuse spots of light scattered in the clouds, which have full widths at half maximum in the range 90-160 km. We compare the lightning images with the images produced by our 3D Monte Carlo light scattering model. The model reproduces non isotropic non-conservative scattering of the photons in the non-homogeneous opacity distribution. We derive that some of the observed scattering patterns are produced in a 3D cloud rather than in a plane-parallel cloud layer, suggesting deep convection. For the six flashes studied, the clouds above the lightning are optically thick (\u0393 > 5). Lightning is as deep as the bottom of the water cloud. Jovian flashes are more regular\r\nand circular than the largest terrestrial flashes observed from space.
", "doi": "10.7907/N7JD-N925", "publication_date": "2002", "thesis_type": "phd", "thesis_year": "2002" }, { "id": "thesis:2430", "collection": "thesis", "collection_id": "2430", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-06042002-125011", "primary_object_url": { "basename": "thesis020605.pdf", "content": "final", "filesize": 5424798, "license": "other", "mime_type": "application/pdf", "url": "/2430/1/thesis020605.pdf", "version": "v2.0.0" }, "type": "thesis", "title": "Optical Pulse-Phased Observations of Faint Pulsars with a Phase-Binning CCD Camera", "author": [ { "family_name": "Kern", "given_name": "Brian Daniel", "clpid": "Kern-Brian-Daniel" } ], "thesis_advisor": [ { "family_name": "Martin", "given_name": "D. Christopher", "orcid": "0000-0002-8650-1644", "clpid": "Martin-D-Christopher" }, { "family_name": "Djorgovski", "given_name": "George", "orcid": "0000-0002-0603-3087", "clpid": "Djorgovski-G" } ], "thesis_committee": [ { "family_name": "Goldreich", "given_name": "Peter Martin", "clpid": "Goldreich-P-M" }, { "family_name": "Steidel", "given_name": "Charles C.", "orcid": "0000-0002-4834-7260", "clpid": "Steidel-C-C" }, { "family_name": "Martin", "given_name": "D. Christopher", "orcid": "0000-0002-8650-1644", "clpid": "Martin-D-Christopher" }, { "family_name": "Harrison", "given_name": "Fiona A.", "orcid": "0000-0003-2992-8024", "clpid": "Harrison-F-A" }, { "family_name": "Kulkarni", "given_name": "Shrinivas R.", "orcid": "0000-0001-5390-8563", "clpid": "Kulkarni-S-R" }, { "family_name": "Djorgovski", "given_name": "George", "orcid": "0000-0002-0603-3087", "clpid": "Djorgovski-G" } ], "local_group": [ { "literal": "Astronomy Department" }, { "literal": "div_pma" } ], "abstract": "We have constructed a phase-binning CCD camera optimized for optical observations of faint pulsars. The phase-binning CCD camera combines the high quantum efficiency of a CCD with a pulse-phased time resolution capable of observing pulsars as fast as 10 ms, with no read noise penalty. The phase-binning CCD can also operate as a two-channel imaging polarimeter, obtaining pulse-phased linear photopolarimetric observations.\r\n\r\nWe have used this phase-binning CCD to make the first measurements of optical pulsations from an anomalous X-ray pulsar. We measured the optical pulse profile of 4U 0142+61, finding a pulsed fraction of 27%, many times larger than the pulsed fraction in X-rays. From this observation, we concluded that 4U 0142+61 must be a magnetar, an ultramagnetized neutron star (B > 10^14 G). The optical pulse is double-peaked, similar to the soft X-ray pulse profile.\r\n\r\nWe also used the phase-binning CCD to obtain the photometric and polarimetric pulse profiles of PSR B0656+14, a middle-aged isolated rotation-powered pulsar. The optical pulse profile we measured significantly disagrees with the low signal-to-noise profile previously published for this pulsar. Our results show that the optical flux is entirely pulsed, with optical peaks at phases 0.2 and 0.8 with respect to the radio peak, and a bridge of emission between the peaks. The significance of the detection of pulsed polarized flux is low, but the position angles match the extrapolation of the radio polarization profile. The optical data, both photometric and polarimetric, are consistent with the polar cap model of pulsar magnetospheric emission. The fit of the optical data with the competing emission model, the outer gap model, has not yet been determined.\r\n\r\nWe have developed a number of statistical tools, both to estimate the errors in our measurements and to identify systematic errors present in the pulse profiles. The statistical tools, when applied to the data presented here, show that the systematic errors are negligible, bolstering the claims of significance of these results.", "doi": "10.7907/XP9W-WM62", "publication_date": "2002", "thesis_type": "phd", "thesis_year": "2002" }, { "id": "thesis:3180", "collection": "thesis", "collection_id": "3180", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-08212001-163318", "type": "thesis", "title": "A Measurement of the Angular Power Spectrum of the Cosmic Microwave Background with a Long Duration Balloon-Borne Receiver", "author": [ { "family_name": "Crill", "given_name": "Brendan Patrick", "orcid": "0000-0002-4650-8518", "clpid": "Crill-Brendan-Patrick" } ], "thesis_advisor": [ { "family_name": "Lange", "given_name": "Andrew E.", "clpid": "Lange-A-E" } ], "thesis_committee": [ { "family_name": "Lange", "given_name": "Andrew E.", "clpid": "Lange-A-E" }, { "family_name": "Readhead", "given_name": "Anthony C. S.", "orcid": "0000-0001-9152-961X", "clpid": "Readhead-A-C-S" }, { "family_name": "Blake", "given_name": "Geoffrey A.", "orcid": "0000-0003-0787-1610", "clpid": "Blake-G-A" }, { "family_name": "Goldreich", "given_name": "Peter Martin", "clpid": "Goldreich-P-M" } ], "local_group": [ { "literal": "div_pma" } ], "abstract": "This thesis describes BOOMERANG; a balloon-borne telescope and receiver designed to map the Cosmic Microwave Background (CMB) at a resolution of 10' from the Long Duration Balloon (LDB) platform. The millimeter-wave receiver employs new technology in bolometers, readout electronics, cold re-imaging optics, millimeter-wave filters, and cryogenics to obtain high sensitivity to CMB anisotropy. Sixteen detectors observe in 4 spectral bands centered at 90, 150, 240 and 400 GHz. The wide frequency coverage, the long flight duration, the optical design and the observing strategy all provide strong rejection of systematic effects. We report the in-flight performance of the instrument during a short test flight from Palestine, Texas, that mapped 230 square degrees and during a 10.5 day stratospheric balloon flight launched from McMurdo Station, Antarctica, that mapped ~ 2000 square degrees of the sky. The Antarctic data yielded a measurement of the angular power spectrum of the CMB between 50 < \u2113 < 600 which shows a peak at \u2113peak = 197 \u00b1 6 (1\u03c3 error). A maximum likelihood estimation of cosmological parameters within the cold dark matter (CDM) paradigm of structure formation indicates that the universe is flat with a precision of ~ 6% and that the density of baryons in the universe may be slightly higher than previously thought. The combination of observations of large scale structure (LSS) and the BOOMERANG power spectrum implies the presence of both dark matter and dark energy, or the existence of Einstein's cosmological constant.
", "doi": "10.7907/GVJ5-GC44", "publication_date": "2001", "thesis_type": "phd", "thesis_year": "2001" }, { "id": "thesis:8219", "collection": "thesis", "collection_id": "8219", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:05052014-152343905", "primary_object_url": { "basename": "Maron_j_2001.pdf", "content": "final", "filesize": 13543876, "license": "other", "mime_type": "application/pdf", "url": "/8219/1/Maron_j_2001.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "Magnetohydrodynamic Turbulence", "author": [ { "family_name": "Maron", "given_name": "Jason L.", "clpid": "Maron-Jason-L" } ], "thesis_advisor": [ { "family_name": "Janda", "given_name": "Kenneth C.", "clpid": "Janda-K-C" } ], "thesis_committee": [ { "family_name": "Goldreich", "given_name": "Peter Martin", "clpid": "Goldreich-P-M" }, { "family_name": "Blandford", "given_name": "Roger D.", "clpid": "Blandford-R-D" }, { "family_name": "Pullin", "given_name": "Dale Ian", "clpid": "Pullin-D-I" }, { "family_name": "Sargent", "given_name": "Wallace L. W.", "clpid": "Sargent-W-L-W" }, { "family_name": "Janda", "given_name": "Kenneth C.", "clpid": "Janda-K-C" } ], "local_group": [ { "literal": "Astronomy Department" }, { "literal": "div_pma" } ], "abstract": "We simulate incompressible, MHD turbulence using a pseudo-spectral code. Our\r\nmajor conclusions are as follows.
\r\n\r\n1) MHD turbulence is most conveniently described in terms of counter propagating\r\nshear Alfv\u00e9n and slow waves. Shear Alfv\u00e9n waves control the cascade dynamics. Slow\r\nwaves play a passive role and adopt the spectrum set by the shear Alfv\u00e9n waves. Cascades\r\ncomposed entirely of shear Alfv\u00e9n waves do not generate a significant measure\r\nof slow waves.
\r\n\r\n2) MHD turbulence is anisotropic with energy cascading more rapidly along k\u22a5 than\r\nalong k\u2225, where k\u22a5 and k\u2225 refer to wavevector components perpendicular and parallel\r\nto the local magnetic field. Anisotropy increases with increasing k\u22a5 such that excited\r\nmodes are confined inside a cone bounded by k\u2225 \u221d k\u03b3\u22a5 where \u03b3 less than 1. The opening\r\nangle of the cone, \u03b8(k\u22a5) \u221d k-(1-\u03b3)\u22a5, defines the scale dependent anisotropy.
\r\n\r\n3) MHD turbulence is generically strong in the sense that the waves which comprise it\r\nsuffer order unity distortions on timescales comparable to their periods. Nevertheless,\r\nturbulent fluctuations are small deep inside the inertial range. Their energy density is less than that of the background field by a factor \u03b82 (k\u22a5)\u226a1.
\r\n\r\n4) MHD cascades are best understood geometrically. Wave packets suffer distortions\r\nas they move along magnetic field lines perturbed by counter propagating waves.\r\nField lines perturbed by unidirectional waves map planes perpendicular to the local\r\nfield into each other. Shear Alfv\u00e9n waves are responsible for the mapping's shear and\r\nslow waves for its dilatation. The amplitude of the former exceeds that of the latter\r\nby 1/\u03b8(k\u22a5) which accounts for dominance of the shear Alfv\u00e9n waves in controlling\r\nthe cascade dynamics.
\r\n\r\n5) Passive scalars mixed by MHD turbulence adopt the same power spectrum as the\r\nvelocity and magnetic field perturbations.
\r\n\r\n6) Decaying MHD turbulence is unstable to an increase of the imbalance between\r\nthe flux of waves propagating in opposite directions along the magnetic field. Forced\r\nMHD turbulence displays order unity fluctuations with respect to the balanced state\r\nif excited at low k by \u03b4(t) correlated forcing. It appears to be statistically stable to\r\nthe unlimited growth of imbalance.
\r\n\r\n7) Gradients of the dynamic variables are focused into sheets aligned with the magnetic\r\nfield whose thickness is comparable to the dissipation scale. Sheets formed by\r\noppositely directed waves are uncorrelated. We suspect that these are vortex sheets\r\nwhich the mean magnetic field prevents from rolling up.
\r\n\r\n8) Items (1)-(5) lend support to the model of strong MHD turbulence put forth by\r\nGoldreich and Sridhar (1995, 1997). Results from our simulations are also consistent\r\nwith the GS prediction \u03b3 = 2/3. The sole not able discrepancy is that the 1D power\r\nlaw spectra, E(k\u22a5) \u221d k-\u221d\u22a5, determined from our simulations exhibit \u221d \u2248 3/2, whereas\r\nthe GS model predicts \u221d = 5/3.
\r\n\r\n\r\n\r\n", "doi": "10.7907/x455-kq95", "publication_date": "2001", "thesis_type": "phd", "thesis_year": "2001" }, { "id": "thesis:6351", "collection": "thesis", "collection_id": "6351", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:04252011-131341033", "primary_object_url": { "basename": "Jenet_fa_2001.pdf", "content": "final", "filesize": 12083275, "license": "other", "mime_type": "application/pdf", "url": "/6351/1/Jenet_fa_2001.pdf", "version": "v6.0.0" }, "type": "thesis", "title": "High Time Resolution Observations of Radio Pulsars: The First Detection of Coherent Emission", "author": [ { "family_name": "Jenet", "given_name": "Fredrick August", "clpid": "Jenet-Fredrick-August" } ], "thesis_advisor": [ { "family_name": "Prince", "given_name": "Thomas A.", "orcid": "0000-0002-8850-3627", "clpid": "Prince-T-A" } ], "thesis_committee": [ { "family_name": "Prince", "given_name": "Thomas A.", "orcid": "0000-0002-8850-3627", "clpid": "Prince-T-A" }, { "family_name": "Blandford", "given_name": "Roger D.", "clpid": "Blandford-R-D" }, { "family_name": "Goldreich", "given_name": "Peter Martin", "clpid": "Goldreich-P-M" }, { "family_name": "Harrison", "given_name": "Fiona A.", "orcid": "0000-0003-2992-8024", "clpid": "Harrison-F-A" } ], "local_group": [ { "literal": "Astronomy Department" }, { "literal": "div_pma" } ], "abstract": "Recent advances in recording technology and computational power have made possible the development of a wide bandwidth digital recording system for radio astronomy. A prototype 50 MHz bandwidth system along with two production systems with 10-50 MHz bandwidth have been designed and built at Caltech. Signal processing techniques have been developed in order to remove various artifacts introduced into the signal by the digitization process. These techniques along with various pulsar signal processing algorithms have been successfully implemented in a suite of highly portable analysis programs designed to run on multi-purpose parallel supercomputers, networked workstations, and stand-alone workstations. The single pulse radio emission properties of the bright millisecond pulsar PSR J0437-4715 have been studied using standard analysis methods. New techniques have been developed in order to study the single pulse properties of \"weak\" or low-intensity pulsars. These techniques have been used to analyze the pulse-to-pulse amplitude and pulse shape variations of the fastest millisecond pulsar PSR B1937+21. Techniques have also been developed in order to search for the presence of coherent non-Gaussian emission statistics. Such statistics have been detected in pulsars B0823+26, B0950+08, and B1133+16. This is the first time such a phenomenon has been observed.\r\n", "doi": "10.7907/frka-dh94", "publication_date": "2001", "thesis_type": "phd", "thesis_year": "2001" }, { "id": "thesis:4431", "collection": "thesis", "collection_id": "4431", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-11072001-160517", "primary_object_url": { "basename": "01title_page.pdf", "content": "final", "filesize": 35117, "license": "other", "mime_type": "application/pdf", "url": "/4431/1/01title_page.pdf", "version": "v2.0.0" }, "type": "thesis", "title": "Low Order Model of Martian Circulation and Interannual Variability of Global Dust Storms", "author": [ { "family_name": "Pankine", "given_name": "Alexey Anatolyevich", "clpid": "Pankine-Alexey-Anatolyevich" } ], "thesis_advisor": [ { "family_name": "Ingersoll", "given_name": "Andrew P.", "orcid": "0000-0002-2035-9198", "clpid": "Ingersoll-A-P" }, { "family_name": "Muhleman", "given_name": "Duane Owen", "clpid": "Muhleman-D-O" } ], "thesis_committee": [ { "family_name": "Murray", "given_name": "Bruce C.", "clpid": "Murray-B-C" }, { "family_name": "Ingersoll", "given_name": "Andrew P.", "orcid": "0000-0002-2035-9198", "clpid": "Ingersoll-A-P" }, { "family_name": "Albee", "given_name": "Arden Leroy", "clpid": "Albee-A-L" }, { "family_name": "Goldreich", "given_name": "Peter Martin", "clpid": "Goldreich-P-M" }, { "family_name": "Stevenson", "given_name": "David John", "orcid": "0000-0001-9432-7159", "clpid": "Stevenson-D-J" } ], "local_group": [ { "literal": "Astronomy Department" }, { "literal": "div_gps" } ], "abstract": "The main theme of this work is the development of a simplified model of the martian circulation suitable for conducting computationally fast long term simulations of the martian climate system. In particular, we are looking for causes of the irregular occurrence of the martian global dust storms (GDSs). The low-order model (LOM) is constructed by Galerkin projection of a 2D (zonally averaged) general circulation model (GCM) onto a truncated set of basis functions. The resulting low-order model consists of twelve coupled nonlinear ordinary differential equations (ODEs). The forcing of the model is described by simplified physics based on Newtonian cooling and Rayleigh friction. The atmosphere and surface are coupled: atmospheric heating depends on the dustiness of the atmosphere, and the surface dust source depends on the strength of the atmospheric winds. Parameters of the model are tuned to fit output of the NASA Ames GCM.
\r\n\r\nThe model performance is examined for different seasons and dust opacities and it is found that the simulated mean meridional circulation and temperature fields compare well with the more sophisticated GCM. The time of occurence and duration of the global dust storms produced by the model compare well with observations by Viking Landers (VLs). The intensity of the meridional circulation as simulated by the LOM during northern summer is stronger than that predicted by the GCM. The situation can be improved if the Rayleigh friction varies seasonally. The LOM uncoupled from the dust source can be further simplified to form the Lorenz system with forcing.
\r\n\r\nThe model is applied to the problem of interannual variability of martian global dust storms. Basic hypotheses of the intrinsic and of the extrinsic irregularity of the martian climate system are tested. The intrinsic irregularity hypothesis implies that the system under consideration is chaotic, so that small variations in initial conditions make the behavior of the system essentially unpredictable. Different paths taken by the system in state space would correspond to years with and without a GDS. The extrinsic irregularity hypothesis, on the other hand, implies that without noise the system behaves periodically, but stochastic forcing of the system causes it to behave irregularly. It is concluded that the observed variability of GDSs is more easily explained by extrinsic irregularity. The stochastic forcing (``noise') could be provided by transient weather systems or some surface process, like size sorting or redistribution of the sand particles in the ``active' (i.e., storm generating) zones on the surface. The results are very sensitive to the value of the saltation threshold, which hints at the possible feedback between saltation threshold and dust storm activity. According to this hypothesis, the saltation threshold has adjusted its value so that dust storms are barely able to occur.
", "doi": "10.7907/MGSA-ZT98", "publication_date": "2001", "thesis_type": "phd", "thesis_year": "2001" }, { "id": "thesis:3670", "collection": "thesis", "collection_id": "3670", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-09202008-105312", "primary_object_url": { "basename": "Kuchner_mj_2001.pdf", "content": "final", "filesize": 7392327, "license": "other", "mime_type": "application/pdf", "url": "/3670/1/Kuchner_mj_2001.pdf", "version": "v4.0.0" }, "type": "thesis", "title": "Exozodiacal Dust", "author": [ { "family_name": "Kuchner", "given_name": "Marc Jason", "clpid": "Kuchner-Marc-Jason" } ], "thesis_advisor": [ { "family_name": "Hoffmann", "given_name": "Michael R.", "orcid": "0000-0001-6495-1946", "clpid": "Hoffmann-M-R" } ], "thesis_committee": [ { "family_name": "Blake", "given_name": "Geoffrey A.", "orcid": "0000-0003-0787-1610", "clpid": "Blake-G-A" }, { "family_name": "Goldreich", "given_name": "Peter Martin", "clpid": "Goldreich-P-M" }, { "family_name": "Scoville", "given_name": "Nicholas Zabriskie", "orcid": "0000-0002-0438-3323", "clpid": "Scoville-N-Z" }, { "family_name": "Sargent", "given_name": "Anneila Isabel", "orcid": "0000-0002-4633-5098", "clpid": "Sargent-A-I" }, { "family_name": "Hoffmann", "given_name": "Michael R.", "orcid": "0000-0001-6495-1946", "clpid": "Hoffmann-M-R" } ], "local_group": [ { "literal": "Astronomy Department" }, { "literal": "div_pma" } ], "abstract": "Besides the sun, the most luminous feature of the solar system is a cloud of \"zodiacal\" dust released by asteroids and comets that pervades the region interior to the asteroid belt. Similar clouds of dust around other stars\u2014exozodiacal clouds\u2014may be the best tracers of the habitable zones of extra-solar planetary systems. This thesis discusses three searches for exozodiacal dust:
\r\n\r\nWe also discuss the interaction of dust with planets. We used the COBE DIRBE Sky and Zodi Atlas and the IRAS Sky Survey Atlas to search for dynamical signatures of three different planets in the solar system dust complex:
\r\n\r\nThis thesis studies disks in three astrophysical contexts: (1) protoplanetary disks; (2) the Edgeworth-Kuiper Belt; and (3) planetary rings.
\r\n\r\nWe derive hydrostatic, radiative equilibrium models of passive protoplanetary disks surrounding T Tauri and Herbig Ae/Be stars. Each disk is encased by an optically thin layer of superheated dust grains. This layer is responsible for up to ~70% of the disk luminosity at wavelengths between ~5 and 60 \u03bcm. The heated disk flares and absorbs more stellar radiation at a given stellocentric distance than a flat disk would. Spectral energy distributions are computed and found to compare favorably with the observed flattish infrared excesses of several young stellar objects. Spectral features from dust grains in the superheated layer appear in emission if the disk is viewed nearly face-on.
\r\n\r\nWe present the results of a pencil-beam survey of the Kuiper Belt using the Keck 10-m telescope. Two new objects are discovered. Data from all surveys are pooled to construct the luminosity function from mR = 20 to 27. The cumulative number of objects per square degree, \u2211(< mR, is such that log10\u2211(< mR = 0.52(mR - 23.5). The luminosity function is consistent with a power-law size distribution for which the smallest objects possess most of the surface area but the largest bodies contain most of the mass. To order-of-magnitude, 0.2M\u2d32 and 1 x 1010 comet progenitors lie between 30 and 50 AU. The classical Kuiper Belt appears truncated at a distance of 50 AU.
\r\n\r\nWe propose that rigid precession of narrow eccentric planetary rings surrounding Uranus and Saturn is maintained by a balance of forces due to ring self-gravity, planetary oblateness, and interparticle collisions. Collisional impulses play an especially dramatic role near ring edges. Pressure-induced accelerations are maximal near edges because there (1) velocity dispersions are enhanced by resonant satellite perturbations, and (2) the surface density declines steeply. Remarkably, collisional forces felt by material in the last ~100 m of a ~10 km wide ring can increase equilibrium masses up to a factor of ~100. New ring surface densities are derived which accord with Voyager radio measurements.
\r\n", "doi": "10.7907/8B2W-8V06", "publication_date": "2000", "thesis_type": "phd", "thesis_year": "2000" }, { "id": "thesis:3275", "collection": "thesis", "collection_id": "3275", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-08292008-130426", "primary_object_url": { "basename": "Murphy_tw_2000.pdf", "content": "final", "filesize": 16977876, "license": "other", "mime_type": "application/pdf", "url": "/3275/1/Murphy_tw_2000.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "Ultraluminous Infrared Galaxies: Power Sources and Ages Along the Merger Sequence", "author": [ { "family_name": "Murphy", "given_name": "Thomas Williams, Jr.", "orcid": "0000-0003-1591-6647", "clpid": "Murphy-Thomas-Williams-Jr" } ], "thesis_advisor": [ { "family_name": "Soifer", "given_name": "B. Thomas", "clpid": "Soifer-B-T" } ], "thesis_committee": [ { "family_name": "Soifer", "given_name": "B. Thomas", "clpid": "Soifer-B-T" }, { "family_name": "Neugebauer", "given_name": "Gerry", "clpid": "Neugebauer-G" }, { "family_name": "Scoville", "given_name": "Nicholas Zabriskie", "clpid": "Scoville-N-Z" }, { "family_name": "Goldreich", "given_name": "Peter Martin", "clpid": "Goldreich-P-M" } ], "local_group": [ { "literal": "Astronomy Department" }, { "literal": "div_pma" } ], "abstract": "Ultraluminous infrared galaxies (ULIRGs) are the most luminous galaxies in the local universe, with power outputs above 10\u00b9\u00b2 times that of our sun. Almost all ULIRGs are found to be associated with collisions between large, gas-rich galaxies. With most of the energy output emerging at far-infrared wavelengths, these galaxies are understood to be extremely dusty. As such, the nature of the power source within the dust shroud is not clearly understood. The two most likely explanations involve either a massive burst of star formation or the presence of an active galactic nucleus (AGN) in the form of a dust-enshrouded quasar.
\r\n\r\nThis work presents two separate approaches to investigating the nature of ultraluminous infrared galaxies. The first is a spectrosciopic survey of 33 ULIRGs in the near-infrared band around a wavelength of 2 microns, where dust extinction is much less severe than in visible light. The aim of this study is to search for evidence of buried AGN, as indicated by velocity-broadened hydrogen recombination lines as well as the presence of the high excitation [Si VI] emission line. This survey finds that signs of AGN are rare in ULIRGs, with the most natural conclusion being that the majority of ULIRGs are powered by starburst phenomena.
\r\n\r\nThe second approach presented involves the design, construction, and use of a novel instrument built specifically to study the spatial and kinematical properties of gas within the morphologically complex ULIRGs. A single long slit is generally not capable of capturing the rich phenomenology found in the complex environments of ULIRGs. Data from the Palomar Integral Field Spectrograph reveals that several ULIRGs are found to exist at times very early in the galaxy encounter process. The possibility that ultraluminous activity may develop so early in the merger history suggests a non-trivial luminosity evolution among galaxy mergers, wherein the less powerful class of luminous infrared galaxies may represent a different phase of the same overall phenomenon.
\r\n", "doi": "10.7907/JR80-9T40", "publication_date": "2000", "thesis_type": "phd", "thesis_year": "2000" }, { "id": "thesis:3596", "collection": "thesis", "collection_id": "3596", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-09172008-111737", "primary_object_url": { "basename": "Behr_bb_2000.pdf", "content": "final", "filesize": 5366317, "license": "other", "mime_type": "application/pdf", "url": "/3596/1/Behr_bb_2000.pdf", "version": "v4.0.0" }, "type": "thesis", "title": "A New Spin on Horizontal-Branch Stars: Anomalous Abundances and Rapid Rotation Rates", "author": [ { "family_name": "Behr", "given_name": "Bradford B.", "clpid": "Behr-Bradford-B" } ], "thesis_advisor": [ { "family_name": "McCarthy", "given_name": "James K.", "clpid": "McCarthy-James-K" } ], "thesis_committee": [ { "family_name": "Cohen", "given_name": "Judith G.", "orcid": "0000-0002-8039-4673", "clpid": "Cohen-J-G" }, { "family_name": "Blandford", "given_name": "Roger D.", "clpid": "Blandford-R-D" }, { "family_name": "Djorgovski", "given_name": "George", "orcid": "0000-0002-0603-3087", "clpid": "Djorgovski-G" }, { "family_name": "Goldreich", "given_name": "Peter Martin", "clpid": "Goldreich-P-M" }, { "family_name": "McCarthy", "given_name": "James K.", "clpid": "McCarthy-James-K" } ], "local_group": [ { "literal": "Astronomy Department" }, { "literal": "div_pma" } ], "abstract": "High-resolution spectroscopy of blue horizontal-branch stars in metal-poor globular clusters reveals remarkable differences in photospheric composition and rotation rate between cooler and hotter stars. For the cooler stars (Teff < 11000 K), the derived abundances are in good agreement with the canonical cluster metallicities, and we confirm the range of v sin i rotation velocities, some as high as 40 km s-1, previously reported in the literature. In the hotter stars, however, metals are enhanced by factors of 100 or more, and helium is depleted by as much as two orders of magnitude. In addition, the hot stars are almost exclusively slow rotators, with v sin i < 8 km s-1. The anomalous abundances are due to atomic diffusion mechanisms \u2014 gravitational settling of helium, and radiative levitation of metals - in the stable, non-convective atmospheres of these hot stars. The enhanced metal content in the stellar photospheres can alter the emergent spectral energy distributions, creating the photometric \"gaps\" observed in the clusters' color-magnitude diagrams. We discuss the connections between rotation and the diffusion mechanisms, and explore potential implications regarding the internal structure and evolution of these stars.", "doi": "10.7907/rdxg-qg24", "publication_date": "2000", "thesis_type": "phd", "thesis_year": "2000" }, { "id": "thesis:15067", "collection": "thesis", "collection_id": "15067", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:11292022-160931702", "primary_object_url": { "basename": "Showman_AP_1999.pdf", "content": "final", "filesize": 55782739, "license": "other", "mime_type": "application/pdf", "url": "/15067/1/Showman_AP_1999.pdf", "version": "v2.0.0" }, "type": "thesis", "title": "I. Dynamics at the Galileo Probe Site on Jupiter and II. Orbital and Thermal Evolution of Ganymede", "author": [ { "family_name": "Showman", "given_name": "Adam Peter", "clpid": "Showman-Adam-Peter" } ], "thesis_advisor": [ { "family_name": "Ingersoll", "given_name": "Andrew P.", "orcid": "0000-0002-2035-9198", "clpid": "Ingersoll-A-P" }, { "family_name": "Stevenson", "given_name": "David John", "orcid": "0000-0001-9432-7159", "clpid": "Stevenson-D-J" } ], "thesis_committee": [ { "family_name": "Stevenson", "given_name": "David John", "orcid": "0000-0001-9432-7159", "clpid": "Stevenson-D-J" }, { "family_name": "Ingersoll", "given_name": "Andrew P.", "orcid": "0000-0002-2035-9198", "clpid": "Ingersoll-A-P" }, { "family_name": "Brown", "given_name": "Michael E.", "orcid": "0000-0002-8255-0545", "clpid": "Brown-M-E" }, { "family_name": "Goldreich", "given_name": "Peter Martin", "clpid": "Goldreich-P-M" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "The low abundances of water and H\u2082S measured by the Galileo probe at Jupiter sug\u00adgest that the probe entered a downdraft where dry air from above cloud top advects to 10 bars or deeper. I use basic physical constraints to extract dynamical informa\u00adtion from three aspects of Galileo probe data. First, I suggest that to remain dry, the downdraft must be underlain by a stable layer which inhibits mixing of volatiles from below; this requires the downdraft to be mechanically forced. Second, on rapidly rotating planets, the Coriolis and centripetal forces caused by winds usually balance the horizontal pressure-gradient force (which gives information about horizontal den\u00adsity differences). Therefore, I use the known winds versus depth at the probe site to infer horizontal density differences between the probe site and its surroundings. Under reasonable assumptions, these densities are consistent with a downdraft at the probe site. Third, I use ideas of horizontal mixing and column stretching to explain how the observed vertical profiles of ammonia, H\u2082S, and water vapor can be produced in a downdraft. Finally, I discuss some apparent inconsistencies between these sim\u00adple models. I also describe preliminary efforts to explore the origin, stability, and evolution of the downdrafts using the shallow water equations.
\r\n\r\nThe differences between Ganymede and Callisto have led to speculation that Gany\u00admede's history was shaped by tidal heating from an orbital resonance. Using the numerical model developed by Malhotra (1991, Icarus 94, 399), I demonstrate that Io, Europa, and Ganymede could have passed through either of two (previously un\u00adexplored) Laplace-like resonances en route to the current Laplace resonance. Un\u00adder reasonable conditions, these resonances produce great enough tidal heating in Ganymede to be geophysically significant. I also coupled the orbital evolution to an internal model of Ganymede to explore the effect of the resonance on Ganymede's interior. If Ganymede's tidal Q decreases strongly with temperature, the coupling can lead to massive, short-lived heating episodes which can melt much of the icy interior. Such heat pulses require the initial ice temperature to be extremely cold (>200 K), however, so they may be unlikely.
", "doi": "10.7907/q4n0-9s68", "publication_date": "1999", "thesis_type": "phd", "thesis_year": "1999" }, { "id": "thesis:4634", "collection": "thesis", "collection_id": "4634", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-11222004-140151", "type": "thesis", "title": "I. Observations and Photochemical Modeling of the Venus Middle Atmosphere. II. Thermal Infrared Spectroscopy of Europa and Callisto", "author": [ { "family_name": "Mills", "given_name": "Franklin Perry", "clpid": "Mills-Franklin-Perry" } ], "thesis_advisor": [ { "family_name": "Yung", "given_name": "Yuk L.", "clpid": "Yung-Y-L" } ], "thesis_committee": [ { "family_name": "Yung", "given_name": "Yuk L.", "clpid": "Yung-Y-L" }, { "family_name": "Burnett", "given_name": "Donald S.", "clpid": "Burnett-D-S" }, { "family_name": "Brown", "given_name": "Michael E.", "clpid": "Brown-M-E" }, { "family_name": "Okumura", "given_name": "Mitchio", "clpid": "Okumura-M" }, { "family_name": "Goldreich", "given_name": "Peter Martin", "clpid": "Goldreich-P-M" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "The evolution of our solar system remains one of the most fascinating questions since ancient astronomers first realized that the \"stars\" which do not twinkle are planets. In the modern era, the future evolution of the Earth has become a topic that may arise even in lay conversations. For example, the effects of changes in the earth's climate and the ozone layer are debated in policy and economic discussions as well as in scientific forums. One method for assessing our understanding of the Earth's atmosphere is to examine the atmospheres of the other terrestrial planets. The atmospheres of Venus and Mars share some common features with that of the Earth, but there are important differences. These differences are important because they force us to examine the often implicit assumptions that lie within the tunable parameters that exist in all models. Consequently, studies of the atmospheric chemistry on Venus and Mars can provide a test of the degree to which our understanding of the fundamental physical and chemical principles that govern the Earth's atmosphere is correct.
\r\n\r\nThe chemistry of the Martian atmosphere has been \"solved\" to the extent that modern photochemical models [e.g., Nair et al. 1994] can reproduce the primary observable characteristics to within a factor of 2 - 3 using the results from laboratory studies of photochemical reaction rates. The chemistry of the Venus atmosphere, however, remains an \"unsolved\" problem in that the differences between the most recent generation of models [Yung and DeMore 1982] and some of the existing observations are greater than a factor of 10. The first part of this dissertation (Chapters 1, 2, and 3) combines several lines of research that focused on how the discrepancy between models and observations of the Venus atmosphere can be reduced. (The appendices for Chapter 2 are in Chapter 5.) The results provide a better understanding of the current photochemical processes in the Venus atmosphere and can serve as a baseline for future studies of its evolution.
\r\n\r\nThe intervening chapter reports observations of Europa and Callisto in the 8-l3μm wavelength region. Those observations provide constraints on the composition and/ or physical state of the surficial material on the two satellites.
\r\n\r\nPart I (Observations and Photochemical Modeling of the Venus Middle Atmosphere)
\r\n\r\nThe primary photochemical cycle of the Venus middle atmosphere (within and above the upper cloud layer) is the photolysis of C02 to form CO and oxygen atoms on the dayside followed by the reformation of C02 from CO and oxygen, primarily via catalytic reactions. Previous photochemical models-using ClOx, SOx, NOx, and HOx radicals to catalyze the reformation of C02-could qualitatively explain the stability of Venus' C02 atmosphere. Despite the powerful catalytic reactions introduced, however, none of the previous models could quantitatively explain either the low column abundance of molecular oxygen or the intense nightside air glow in the 02(a1Δ) band. The most comprehensive of the previous models, that by Yung and DeMore [1982], predicted a column abundance of molecular oxygen that was a factor of ~30 larger than the upper limit obtained the following year [Trauger and Lunine 1983], and it predicted a nightside airglow that was about three-quarters of the observed intensity. These discrepancies suggested that significant gaps remained in our understanding of the dominant chemical processes in the Venus middle atmosphere.
\r\n\r\nIn the fifteen years since these studies, new observations have provided further insight into the current state of the Venus atmosphere, and our understanding of chlorine and sulfur chemistry has improved as a result of laboratory and field studies related to the terrestrial stratosphere. One idea that had been proposed is that the abundance of 02 in the Venus atmosphere might vary by as much as a factor of 10 over time scales of years. This proposal was based on observations of S02 and SO at the top of the Venus clouds which showed a monotonic decrease in the abundances of both species from 1980 to 1995 with S02 declining by a factor of 10 and SO by a factor of 5. An alternate proposal was that rapid reactions on aerosol particles, such as
\r\n\r\nHOCl + HCl +aerosol-+ H20 + Cl2 + aerosol
\r\n\r\nwhich converts Cl from a relatively nonreactive form, HCl, to a potentially highly reactive form, Cl2, could greatly enhance the effectiveness of the chlorine catalytic reactions that oxidize CO to C02.
\r\n\r\nThis project has attempted to reconcile the differences between observations and photochemical models with regard to the oxygen budget of the Venus middle atmosphere. To examine the potential temporal variability of the 02 abundance, we attempted to detect molecular oxygen on the dayside of Venus using the Ultra-High Resolution Facility at the Anglo-Australian Telescope on 23 January 1995. We observed the 763.6325 and 763.2165 nm 02 lines at a spectral resolving power, λ⁄⁄λ, of 600000 with a square, 1.5 arc-second field of view. These observations reveal no evidence for 02 above the Venus cloud tops within our detection limit which is equivalent to a uniform vertical mixing ratio of 3 ppm. Our upper limit on the abundance of 02 in the Venus middle atmosphere is comparable to that obtained by Traub and Carlton [1974] and is a factor of ten larger (less stringent) than that obtained by Trauger and Lunine [1983] (2σ = 0.3 ppm). Within the obvious limitations imposed by the relative sensitivities of the non-detections, we find no evidence for an increase in the abundance of 02 in association with the observed decreases in S02 and SO abundances.
\r\n\r\nThe parallel branch to new observations was development of a new photochemical model for the Venus middle atmosphere that incorporates the most recent chemical kinetic rates and photoabsorption cross sections. Our one-dimensional, steady-state photochemical model can reproduce (within measurement uncertainty and temporal⁄spatial variability) the retrieved SO profile [Na et al. 1994], the retrieved S02 abundance and scale height at the cloud top [Na et al. 1994], the retrieved CO profile [Clancy and Muhleman 1991], and the observed \"global average\" 02 (a1Δ) airglow [Crisp et al. 1996] using only gas-phase chemistry if we adjust key reaction rates within their assessed one standard deviation uncertainties. Our predicted column abundance for 02 is a factor of 10 smaller than than from previous models. Our results suggest SClx and ClSOx compounds may be important in the chemistry of the upper cloud layer, and we find that Reaction G10 is not an important source of Cl2 above the cloud top.
\r\n\r\nThe current observational upper limit can be reconciled with the predictions from our photochemical model if one examines the absorption produced by our predicted 02 distribution instead of the column abundance. Our model predicts that most of the 02 in the Venus atmosphere will be located between 85 and 95 km altitude, several scale heights above the cloud top (~70-75 km altitude) and, thus, above the region in which multiple scattering is important. Radiative transfer model calculations indicate that the absorption due to our predicted 02 distribution is equivalent to that produced for a uniform vertical distribution of 02 with mixing ratio of 0.3 ppm, the two standard deviation upper limit from the observations. If the equilibrium constant for ClCO is adjusted by two standard deviations and the temperatures at 85 - 95 km altitude are decreased by ~15-20 K (two standard deviations), the predicted 02 absorption will lie below the observed one standard deviation upper limit.
\r\n\r\nPart II (Thermal Infrared Spectroscopy of Europa and Callisto)
\r\n\r\nThe trailing hemispheres of Europa and Callisto were observed and a 9- 13 μm spectrum of Europa with better spectral resolution and better signal-to-noise than was previously possible has been derived. The ratio spectrum of the two satellites has a signal-to-noise ratio of approximately 30 and spectral resolving power of approximately 50. The ratio spectrum was combined with the average Voyager 1 spectrum of Callisto from Spencer [1987a] to obtain a 9- 13 μm spectrum of Europa with signal-to-noise that is a factor of 10 better than that in the average Voyager spectrum of Europa in Spencer [1987a]. No emissivity features due to water ice are apparent at the 3% level in our Europa spectrum. The disk-integrated, effective color temperature ratio for the two satellites is consistent with previous ground-based, broadband, thermal infrared photometry. One possible explanation for the absence of features in the thermal infrared spectra of Europa (at the 3% level) and Callisto (at the 1% level) is if the surfaces of both satellites have significant abundances of small particles (≲50 micrometer in size). This explanation is consistent with most of the published observations by Galileo.
\r\n", "doi": "10.7907/NWPG-E852", "publication_date": "1998", "thesis_type": "phd", "thesis_year": "1998" }, { "id": "thesis:5338", "collection": "thesis", "collection_id": "5338", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:10302009-110303489", "primary_object_url": { "basename": "Mahajan_s_1998.pdf", "content": "final", "filesize": 8955378, "license": "other", "mime_type": "application/pdf", "url": "/5338/1/Mahajan_s_1998.pdf", "version": "v5.0.0" }, "type": "thesis", "title": "Order of Magnitude Physics: A Textbook with Applications to the Retinal Rod and the Density of Prime Numbers", "author": [ { "family_name": "Mahajan", "given_name": "Sanjoy Sondhi", "clpid": "Mahajan-Sanjoy-Sondhi" } ], "thesis_advisor": [ { "family_name": "Phinney", "given_name": "E. Sterl", "orcid": "0000-0002-9656-4032", "clpid": "Phinney-E-S" } ], "thesis_committee": [ { "family_name": "Phinney", "given_name": "E. Sterl", "orcid": "0000-0002-9656-4032", "clpid": "Phinney-E-S" }, { "family_name": "Frautschi", "given_name": "Steven C.", "clpid": "Frautschi-S-C" }, { "family_name": "Hopfield", "given_name": "John J.", "clpid": "Hopfield-J-J" }, { "family_name": "Goldreich", "given_name": "Peter Martin", "clpid": "Goldreich-P-M" }, { "family_name": "Mead", "given_name": "Carver", "orcid": "0000-0003-4051-0462", "clpid": "Mead-C-A" } ], "local_group": [ { "literal": "TAPIR" }, { "literal": "Astronomy Department" }, { "literal": "div_pma" } ], "abstract": "I develop tools to amplify our mental senses: our intuition and reasoning abilities. The first five chapters\u2014based on the Order of Magnitude Physics class taught at Caltech by Peter Goldreich and Sterl Phinney\u2014form part of a textbook on dimensional analysis, approximation, and physical reasoning. The text is a resource of intuitions, problem-solving methods, and physical interpretations. By avoiding mathematical complexity, order-of-magnitude techniques increase our physical understanding, and allow us to study otherwise difficult or intractable problems. The textbook covers: (1) simple estimations, (2) dimensional analysis, (3) mechanical properties of materials, (4) thermal properties of materials, and (5) water waves.
\r\n\r\nAs an extended example of order-of-magnitude methods, I construct an analytic model for the flash sensitivity of a retinal rod. This model extends the flash-response model of Lamb and Pugh with an approximate model for steady-state response as a function of background light Ib. The combined model predicts that the flash sensitivity is proportional to Ib-1.3. This result roughly agrees with experimental data, which show that the flash sensitivity follows the Weber-Fechner behavior of Ib-1 over an intensity range of 100. Because the model is simple, it shows clearly how each biochemical pathway determines the rod's response.
\r\n\r\nThe second example is an approximate model of primality, the square-root model. Its goal is to explain features of the density of primes. In this model, which is related to the Hawkins' random sieve, divisibility and primality are probabilistic. The model implies a recurrence for the probability that a number n is prime. The asymptotic solution to the recurrence is (log n)-1, in agreement with the prime-number theorem. The next term in the solution oscillates around (log n)-1 with a period that grows superexponentially. These oscillations are a model for oscillations in the density of actual primes first demonstrated by Littlewood, who showed that the number of primes \u2264 n crosses its natural approximator, the logarithmic integral, infinitely often. No explicit crossing is known; the best theorem, due to to Riele, says that the first crossing happens below 7 x 10370. A consequence of the square-root model is the conjecture that the first crossing is near 1027.
\r\n", "doi": "10.7907/8MJZ-A984", "publication_date": "1998", "thesis_type": "phd", "thesis_year": "1998" }, { "id": "thesis:3736", "collection": "thesis", "collection_id": "3736", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-09232008-142919", "primary_object_url": { "basename": "Wu_y_1998.pdf", "content": "final", "filesize": 8367380, "license": "other", "mime_type": "application/pdf", "url": "/3736/1/Wu_y_1998.pdf", "version": "v4.0.0" }, "type": "thesis", "title": "Excitation and Saturation of White Dwarf Pulsation", "author": [ { "family_name": "Wu", "given_name": "Yanqin", "orcid": "0000-0003-0511-0893", "clpid": "Wu-Yanqin" } ], "thesis_advisor": [ { "family_name": "Hoffmann", "given_name": "Michael R.", "orcid": "0000-0001-6495-1946", "clpid": "Hoffmann-M-R" } ], "thesis_committee": [ { "family_name": "Goldreich", "given_name": "Peter Martin", "clpid": "Goldreich-P-M" }, { "family_name": "Hoffmann", "given_name": "Michael R.", "orcid": "0000-0001-6495-1946", "clpid": "Hoffmann-M-R" }, { "family_name": "Cohen", "given_name": "Judith G.", "orcid": "0000-0002-8039-4673", "clpid": "Cohen-J-G" }, { "family_name": "Cohen", "given_name": "Marshall H.", "clpid": "Cohen-M-H" }, { "family_name": "McCarthy", "given_name": "James K.", "clpid": "McCarthy-James-K" }, { "family_name": "Phinney", "given_name": "E. Sterl", "orcid": "0000-0002-9656-4032", "clpid": "Phinney-E-S" } ], "local_group": [ { "literal": "Astronomy Department" }, { "literal": "div_pma" } ], "abstract": "Variable hydrogen white dwarfs (DAV) pulsate in a number of low-order gravity-modes with periods from 100 s to 1200 s and amplitudes no larger than a few percent. We answer two questions in this thesis: the driving for these pulsations, and the saturation of their amplitudes.
\r\n\r\nThe surface convection zone in these stars, which adjusts its entropy level instantaneously during the pulsation, can drive the observed modes. This mechanism (called 'convective driving') was discovered by Brickhill but has been largely neglected so far. We find that modes with periods shorter than the thermal adjustment time of the convection zone can become overstable, but those with very short periods are hardly visible at the surface. As the star cools and the convection zone deepens, longer period modes can be excited. The driving rates increase sharply with period. We relate these to the time-scale of mode variability. We include complications arising from nonadiabaticity in the radiative interior and turbulent damping at the convective-radiative boundary. The former limits the driving and damping rates for strongly nonadiabatic modes, and relates the phase and amplitude of surface horizontal velocity in a gravity-mode to those of its flux variation. The turbulent damping results from the horizontal velocity shear below the convection zone, inside which there is little velocity shear and negligible damping. This suppresses the amplitudes of long period modes to below detection. The width of the theoretical DAV instability strip is about 1000 K.
\r\n\r\nThe growth of an overstable mode can be saturated by parametric instability, where energy transfers resonantly into two damped modes of roughly half its frequency. This occurs above a critical amplitude which depends on the 3-mode coupling coefficient and the nonadiabatic damping rates. The critical amplitudes all fall below a few percent, with longer period modes having larger surface amplitudes. Combined with the amplitude limits due to turbulent damping, our estimates compare well with observations. Other types of mode couplings are needed to explain the observed 'mode selection'.
\r\n\r\nFinally, we show that the combination frequencies found in pulsation power spectra are produced by the time-varying convection zone which nonlinearly affects mode visibility.
", "doi": "10.7907/nc60-8v65", "publication_date": "1998", "thesis_type": "phd", "thesis_year": "1998" }, { "id": "thesis:8666", "collection": "thesis", "collection_id": "8666", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:09292014-084326709", "primary_object_url": { "basename": "Labrador.pdf", "content": "final", "filesize": 45698731, "license": "other", "mime_type": "application/pdf", "url": "/8666/1/Labrador.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "Measurement of the Galactic Cosmic Ray Antiproton Flux from 0.25 GeV to 3.11 GeV with the Isotope Matter Antimatter Experiment (IMAX)", "author": [ { "family_name": "Labrador", "given_name": "Allan Wayne", "orcid": "0000-0001-9178-5349", "clpid": "Labrador-Allan-Wayne" } ], "thesis_advisor": [ { "family_name": "Prince", "given_name": "Thomas A.", "orcid": "0000-0002-8850-3627", "clpid": "Prince-T-A" }, { "family_name": "Mewaldt", "given_name": "Richard A.", "orcid": "0000-0003-2178-9111", "clpid": "Mewaldt-R-A" }, { "family_name": "Stone", "given_name": "Edward C.", "orcid": "0000-0002-2010-5462", "clpid": "Stone-E-C" } ], "thesis_committee": [ { "family_name": "Prince", "given_name": "Thomas A.", "orcid": "0000-0002-8850-3627", "clpid": "Prince-T-A" }, { "family_name": "Goldreich", "given_name": "Peter Martin", "clpid": "Goldreich-P-M" }, { "family_name": "Mewaldt", "given_name": "Richard A.", "orcid": "0000-0003-2178-9111", "clpid": "Mewaldt-R-A" }, { "family_name": "Newman", "given_name": "Harvey B.", "orcid": "0000-0003-0964-1480", "clpid": "Newman-H-B" }, { "family_name": "Stone", "given_name": "Edward C.", "orcid": "0000-0002-2010-5462", "clpid": "Stone-E-C" } ], "local_group": [ { "literal": "Astronomy Department" }, { "literal": "Space Radiation Laboratory" }, { "literal": "div_pma" } ], "abstract": "The intensities and relative abundances of galactic cosmic ray protons and antiprotons have been measured with the Isotope Matter Antimatter Experiment (IMAX), a balloon-borne magnet spectrometer. The IMAX payload had a successful flight from Lynn Lake, Manitoba, Canada on July 16, 1992. Particles detected by IMAX were identified by mass and charge via the Cherenkov-Rigidity and TOP-Rigidity techniques, with measured rms mass resolution \u22640.2 amu for Z=1 particles.
\r\n\r\nCosmic ray antiprotons are of interest because they can be produced by the interactions of high energy protons and heavier nuclei with the interstellar medium as well as by more exotic sources. Previous cosmic ray antiproton experiments have reported an excess of antiprotons over that expected solely from cosmic ray interactions.
\r\n\r\nAnalysis of the flight data has yielded 124405 protons and 3 antiprotons in the energy range 0.19-0.97 GeV at the instrument, 140617 protons and 8 antiprotons in the energy range 0.97-2.58 GeV, and 22524 protons and 5 antiprotons in the energy range 2.58-3.08 GeV. These measurements are a statistical improvement over previous antiproton measurements, and they demonstrate improved separation of antiprotons from the more abundant fluxes of protons, electrons, and other cosmic ray species.
\r\n\r\nWhen these results are corrected for instrumental and atmospheric background and losses, the ratios at the top of the atmosphere are p̅/p=3.21(+3.49, -1.97)x10\u207b\u2075 in the energy range 0.25-1.00 GeV, p̅/p=5.38(+3.48, -2.45)x10\u207b\u2075 in the energy range 1.00-2.61 GeV, and p̅/p=2.05(+1.79, -1.15)x10\u207b\u2074 in the energy range 2.61-3.11 GeV. The corresponding antiproton intensities, also corrected to the top of the atmosphere, are 2.3(+2.5, -1.4) x10\u207b\u00b2 (m\u00b2 s sr GeV)\u207b\u00b9, 2.1(+1.4, -1.0)x10\u207b\u00b2 (m\u00b2 s sr GeV)\u207b\u00b9, and 4.3(+3.7, -2.4) x10\u207b\u00b2 (m\u00b2 s sr GeV)\u207b\u00b9 for the same energy ranges.
\r\n\r\nThe IMAX antiproton fluxes and antiproton/proton ratios are compared with recent Standard Leaky Box Model (SLBM) calculations of the cosmic ray antiproton abundance. According to this model, cosmic ray antiprotons are secondary cosmic rays arising solely from the interaction of high energy cosmic rays with the interstellar medium. The effects of solar modulation of protons and antiprotons are also calculated, showing that the antiproton/proton ratio can vary by as much as an order of magnitude over the solar cycle. When solar modulation is taken into account, the IMAX antiproton measurements are found to be consistent with the most recent calculations of the SLBM. No evidence is found in the IMAX data for excess antiprotons arising from the decay of galactic dark matter, which had been suggested as an interpretation of earlier measurements. Furthermore, the consistency of the current results with the SLBM calculations suggests that the mean antiproton lifetime is at least as large as the cosmic ray storage time in the galaxy (~10\u2077 yr, based on measurements of cosmic ray \u00b9\u2070Be). Recent measurements by two other experiments are consistent with this interpretation of the IMAX antiproton results.
\r\n", "doi": "10.7907/92WC-0T91", "publication_date": "1997", "thesis_type": "phd", "thesis_year": "1997" }, { "id": "thesis:18855", "collection": "thesis", "collection_id": "18855", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:07092026-180732446", "primary_object_url": { "basename": "Taylor_MJ_1996.pdf", "content": "final", "filesize": 40591744, "license": "other", "mime_type": "application/pdf", "url": "/18855/1/Taylor_MJ_1996.pdf", "version": "v2.0.0" }, "type": "thesis", "title": "Oligonucleotide-Directed Alkylation of Double Stranded DNA: a Product and Kinetic Analysis", "author": [ { "family_name": "Taylor", "given_name": "Matthew Jabez", "clpid": "Taylor-Matthew-Jabez" } ], "thesis_advisor": [ { "family_name": "Goldreich", "given_name": "Peter Martin", "clpid": "Goldreich-P-M" } ], "thesis_committee": [ { "family_name": "Rees", "given_name": "Douglas C.", "orcid": "0000-0003-4073-1185", "clpid": "Rees-D-C" }, { "family_name": "Dervan", "given_name": "Peter B.", "orcid": "0000-0001-8852-7306", "clpid": "Dervan-P-B" }, { "family_name": "Dougherty", "given_name": "Dennis A.", "orcid": "0000-0003-1464-2461", "clpid": "Dougherty-D-A" }, { "family_name": "Myers", "given_name": "Andrew G.", "orcid": "0000-0001-9602-6915", "clpid": "Myers-A-G" }, { "family_name": "Goldreich", "given_name": "Peter Martin", "clpid": "Goldreich-P-M" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "This thesis research focuses on providing a better understanding of a methodology\r\ndeveloped in the group of Professor Peter B. Dervan for the sequence-specific alkylation of\r\ndouble stranded DNA. It was previously reported from this group that an oligonucleotide\r\nequipped with an electrophilic bromoacetyl moiety could be used to cleave yeast\r\nchromosome III (340 kilobase pairs) at a single site in high yield. Attachment of the\r\nnondiffusible electrophile to the 5-position of a thymine at the 5'-end of a pyrimidine\r\noligodeoxyribonucleotide affords sequence-specific alkylation of a guanine two base pairs\r\nto the 5'-side of a local triple-helical complex. Warming and base treatment then produces\r\ncleavage at this site. We have identified the products of this reaction. Consistent with an\r\nalkylation / depurination mechanism is the formation of phosphate termini in the\r\noligonucleotide products, and identification of the oligonucleotide-guanine conjugate\r\nproduced in the reaction was achieved, demonstrating that this reaction for cleavage of\r\ndouble helical DNA is atom-specific for the N7-position of guanine in duplex DNA.
\r\n\r\nLimitations in specificity for these systems will be due, in part, to the rate\r\nenhancement achieved upon covalent attachment of the electrophile to the DNA-binding\r\nligand. We now understand this in quantitative terms following a comparison of the rate of\r\nbimolecular reaction of 2-bromoacetamide at the N7-position of guanine in duplex DNA to\r\nthe rate of unimolecular reaction at N7 of guanine mediated by triple helix formation.\r\nEmploying a polyacrylamide gel assay, these rate constants were determined and provide\r\ndata indicating a maximum rate enhancement upon localization of bromoacetyl by triple\r\nhelix formation of ten-million fold. The work described here has given us a detailed\r\nunderstanding of this system, which couples sequence-specific recognition one million\r\ntimes more specific than restriction enzymes with atom-specific reactivity ten million times\r\nfaster than its bimolecular counterpart, and represents a foundation for development of\r\nfuture systems of this class.
\r\n\r\nPart two of this thesis describes our efforts to extend oligonucleotide-directed\r\nalkylation to double stranded RNA. Because it has been shown that only RNA single\r\nstrands bind double-helical RNA by triple helix formation, an N-bromoacetyloligoribonucleotide\r\nwas synthesized. Described is the synthesis of the\r\nphosphoramidite necessary for the synthesis of this novel RNA-electrophile conjugate. In\r\ncollaboration with Jean-Francois Mouscadet, a postdoctoral fellow in the Dervan group, it\r\nwas found that triplex helix mediated alkylation of double stranded RNA occurred with\r\nonly modest efficiency. It is likely that solutions to this problem will be attained only\r\nthrough long-term efforts beyond the scope of this thesis.
\r\n\r\nPart three describes our attempts to determine an x-ray crystal structure of a triple-helical\r\ncomplex. In collaboration with Professor Doug Rees at Caltech, various triple-helical\r\ncomplexes of the pyrimidine\u2022purine\u2022pyrimidine type were prepared on a ten\r\nmicromole scale and crystallography experiments were performed. Single crystals were\r\nobtained which diffracted to high resolution, and analysis of these crystals indicated a\r\nstoiciometry consisted with triple-helical complexes. No solution of any of the complexes\r\ngiving x-ray quality crystals were obtained. Documented in this work is methodology for\r\nthe synthesis and purification of 5-i'odo-2'-deoxyuridine-containing oligonucleotides. At\r\nthis time, no high resolution x-ray crystal structure of these complexes has been reported,\r\nhighlighting the continued importance of efforts in this area.
", "doi": "10.7907/61av-hm22", "publication_date": "1996", "thesis_type": "phd", "thesis_year": "1996" }, { "id": "thesis:7472", "collection": "thesis", "collection_id": "7472", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:02112013-110255064", "primary_object_url": { "basename": "Betts 1994.pdf", "content": "final", "filesize": 50949690, "license": "other", "mime_type": "application/pdf", "url": "/7472/1/Betts 1994.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "Thermal and visible studies of Mars using the Termoskan data set", "author": [ { "family_name": "Betts", "given_name": "Bruce Harold", "clpid": "Betts-B-H" } ], "thesis_advisor": [ { "family_name": "Murray", "given_name": "Bruce C.", "clpid": "Murray-B-C" } ], "thesis_committee": [ { "family_name": "Goldreich", "given_name": "Peter Martin", "clpid": "Goldreich-P-M" }, { "family_name": "Ingersoll", "given_name": "Andrew P.", "clpid": "Ingersoll-A-P" }, { "family_name": "Muhleman", "given_name": "Duane Owen", "clpid": "Muhleman-D-O" }, { "family_name": "Murray", "given_name": "Bruce C.", "clpid": "Murray-B-C" }, { "family_name": "Paige", "given_name": "David", "clpid": "Paige-P" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "In February and March, 1989, the Termoskan instrument on board the Phobos '88\r\nspacecraft of the USSR acquired the highest spatial resolution thermal data ever obtained\r\nfor Mars, ranging in resolution from 300 m to 3 km per pixel. It simultaneously obtained\r\nbroad band visible channel data. The panoramas cover a large portion of the equatorial\r\nregion from 30\u00b0S to 6\u00b0N. New and unique analyses facilitated by Termoskan are\r\npresented here. In addition, this thesis describes the instrument, data, and validation.\r\nTermoskan thermal data shows good temperature agreement with Viking IRTM.\r\nHowever, conversion of Termoskan visible data to bolometric albedo is problematic.
\r\n\r\nUtilizing the Termoskan data, I recognized a new feature on Mars: ejecta blanket\r\ndistinct in the thermal infrared (EDITH). Virtually all of the more than 100 such features\r\ndiscovered in the Termoskan data are located on the plains near Valles Marineris. I\r\ncompiled a data base of 110 EDITH and non-EDITH craters ranging in diameter from 4.2\r\nkm to 90.6 km. EDITHs have a startlingly clear dependence upon terrains of Hesperian\r\nage, and show almost no other correlations within the data base. The Hesperian terrain\r\ndependence cannot be explained by either atmospheric or impactor variations. Wind\r\npatterns or locally available aeolian material cannot provide a single overall explanation for\r\nthe observed variations. I postulate that most of the observed EDITHs are due to\r\nexcavation of thermally distinctive Noachian age material from beneath a relatively thin\r\nlayer of younger, more consolidated Hesperian volcanic material. The plausibility of this\r\ntheory is supported by much geological evidence for relatively thin near-surface Hesperian\r\ndeposits overlying massive Noachian megabreccias on the EDITH-rich plains units. I\r\nsuggest that absence of thermally distinct ejecta blankets on Noachian and Amazonian\r\nterrains is due to absences of distinctive near-surface layering. Thermally distinct ejecta blankets are excellent locations for future landers and remote sensing because of relatively dust free surface exposures of material excavated from depth.
\r\n\r\nAlso included in the thermal images are observations of several major channel and\r\nvalley systems including significant portions of Shalbatana, Ravi, Al-Qahira, and Ma'adim\r\nValles, the channel south of Hydraotes Chaos, channel material in Eos Chasma, and small\r\nportions Simud, Tiu, and Ares Valles and channel material in Gangis Chasma.\r\nSimultaneous broad band visible data exists for all but Ma'adim Vallis. I find that most of\r\nthe channels and valleys have higher inertias than their surroundings, consistent with\r\nprevious thermal studies of martian channels. I show for the first time that thermal inertia\r\nboundaries closely match all flat channel floor boundaries. Using Viking albedos,\r\nTermoskan temperatures, and thermal modelling, I derive lower bounds on typical channel\r\nthermal inertias ranging from 8.4 to 12.5 (10^(-3) cal cm^(-2) s^(-1/2) K^(-1). Lower bounds on\r\ninertia differences with the surrounding heavily cratered plains range from 1.1 to 3.5.\r\nAtmospheric and geometric effects are not sufficient to cause the inertia enhancements. I\r\nagree with previous researchers that localized, dark, high inertia areas within channels are\r\nlikely aeolian in nature. However, thermal homogeneity and strong correlation of thermal\r\nboundaries with the channel floor boundaries lead me to favor non-aeolian overall\r\nexplanations. Small scale aeolian deposition or aeolian deflation may, however, play some\r\nrole in the inertia enhancement Channel floor inertia enhancements are strongly\r\nassociated with channels showing fretted morphologies such as wide, flat floors and steep\r\nscalloped walls. Therefore, I favor fretting processes over catastrophic flooding for\r\nexplaining the inertia enhancements. Fretting may have emplaced more blocks on channel\r\nfloors or caused increased bonding of fines due to increased availability of water.\r\nAlternatively, post-channel formation water that may have been preferentially present due\r\nto the low, flat fretted floors may have enhanced bonding of original fines or dust fallout\r\nThe coupling of both EDITHs and channel inertias to morphology is unlike most sharp\r\nMartian inertia variations which are decoupled from observed surface morphology.
\r\n\r\nTermoskan observed morning limb brightening in the thermal channel, but not in\r\nthe visible channel. The thermal morning limb brightening is likely due to a water ice or\r\ndust haze that is warmer than the surface at the time of the observations. A water ice haze\r\nwith a scale height of 5 km could match the observations. Visible scattering is observed to\r\nbe significant on morning and evening limbs out to 60 or 70 km. Localized high altitude\r\nstratospheric clouds are observed in the visible channel.
\r\n\r\nThe Termoskan data show that the highland-lowland boundary in the Aeolis\r\nQuadrangle appears strongly correlated with a high-low thermal inertia boundary. The\r\nsharpness of that boundary varies from less than 4 km to more than 50 km. In all cases,\r\ninertias continue to decrease gradually for many tens of km into the lowlands. Several\r\nother large scale thermal boundaries are also observed in the data.
\r\n\r\nTermoskan observed fine thermal structure on the flanks of Arsia Mons and\r\nelsewhere, which represent examples of interesting and significant thermal variations seen\r\nat the limit of Termoskan's spatial resolution. Sharp variations and boundaries imply there\r\ncannot be global scale dust blanketing deeper than about one centimeter, if that.
\r\n\r\nTermoskan obtained the first ever thermal images of Phobos' shadow on the\r\nsurface of Mars, along with simultaneous visible images. The best observed shadow\r\noccurrence was on the flanks of Arsia Mons. For this occurrence, I combined the\r\nobserved decrease in visible illumination of the surface with the observed decrease in\r\nbrightness temperature to calculate thermal inertias of the Martian surface. Most of the\r\nderived inertias fall within the range 0.9 to 1.4, corresponding to 5 to 10 micron dust\r\nparticles for a homogeneous surface. Dust at the surface is consistent with previous\r\ntheories of Tharsis as a current area of dust deposition. Shadow derived inertias are\r\nsensitive to mm depths, whereas diurnally derived inertias are sensitive to cm depths. The\r\nshadow derived inertias are very similar to Haberle and Jakosky [1991] atmospherically\r\ncorrected Palluconi and Kieffer [1981] Viking IRTM diurnally derived inertias. Thus, if\r\nnear surface layering exists at all in this region, it is not very significant.
\r\n\r\n\r\n", "doi": "10.7907/M9T5-G181", "publication_date": "1994", "thesis_type": "phd", "thesis_year": "1994" }, { "id": "thesis:3440", "collection": "thesis", "collection_id": "3440", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-09102008-105723", "primary_object_url": { "basename": "Roth_j_1994.pdf", "content": "final", "filesize": 9915525, "license": "other", "mime_type": "application/pdf", "url": "/3440/1/Roth_j_1994.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "Constraints upon the cosmological density parameter from Tully-Fisher observations of IRAS galaxies", "author": [ { "family_name": "Roth", "given_name": "Joshua", "clpid": "Roth-J" } ], "thesis_advisor": [ { "family_name": "Mould", "given_name": "Jeremy R.", "clpid": "Mould-J-R" } ], "thesis_committee": [ { "family_name": "Mould", "given_name": "Jeremy R.", "clpid": "Mould-J-R" }, { "family_name": "Sargent", "given_name": "Wallace L. W.", "clpid": "Sargent-W-L-W" }, { "family_name": "Goldreich", "given_name": "Peter Martin", "clpid": "Goldreich-P-M" }, { "family_name": "Djorgovski", "given_name": "George", "clpid": "Djorgovski-G" } ], "local_group": [ { "literal": "Astronomy Department" }, { "literal": "div_pma" } ], "abstract": "Mapping galaxy peculiar velocities, or departures from the uniform expansion of the universe, on megaparsec scales promises to indicate whether number density fluctuations in galaxy counts trace density fluctuations in the underlying matter (to within some factor b), and, if so, to constrain the cosmological density parameter \u03a9, which dictates whether space will expand forever or one day collapse. To sample the peculiar velocity field to distances approaching that of the Hydra-Centaurus complex (but in all directions) we have extracted an all sky, quasi volume limited sample to 4000 km sec-1 from the 1.9 Jy 60 micron IRAS redshift survey of Michael Strauss and collaborators. These objects enjoy distance predictions as functions of \u03b2 \u2261 \u03a90.6/b derived from iterative correction of their redshifts for mutual peculiar gravity, which scales with \u03b2. Our volume limited sample most efficiently probes the cosmic flowfield and enjoys objective and uniform selection criteria whose effects upon inferred quantities can be probed with simulations.
\r\n\r\nWe have sought to measure relative distances to the 251 objects in this sample judged a priori suitable for use in the Tully-Fisher (luminosity - linewidth) relation. The requisite neutral hydrogen radio spectra and near infrared CCD photometry have been obtained for about one half of these objects. Methods of reducing the radio and CCD data are explained in detail. Isophotal I band magnitudes are reproduced by independent observations to ~ 0.05 magnitudes precision. Errors and biases in neutral hydrogen linewidths at low signal to noise ratio are quantified.
\r\n\r\nThe I band magnitude and 21 cm. linewidth data imply a Tully-Fisher (TF) relation at each value of \u03b2 from 0.05 to 2.00 used by Strauss et al. to iterate the IRAS redshift catalog. The \u03b2 value producing minimum apparent TF scatter is investigated as a diagnostic with extensive Monte Carlo simulations. Such simulations suggest that, if the \u03b2 knob setting producing minimum apparent TF scatter were found to equal unity, ~ 100 galaxy distance moduli to ~ 0.5 magnitudes precision would constrain the actual value of \u03b2 to lie within the range 0.7 \u2272 \u03b2 \u2272 1.3 at a ~ 95% confidence level.
\r\n\r\n'\u03b2 response profiles' (apparent TF scatter versus \u03b2) observed in various subsets of our provisional database are presented. Our provisional database yields minimum apparent TF scatter at a \u03b2 value of ~ 0.9. Excising the apparently problematic Virgo cluster region yields a response profile favoring \u03b2 values of ~ 0.6 \u00b1 0.2, or \u03a9 ~ 0.4 \u00b1 0.3. Excising data points disfavored by statistical estimates of leverage upon \u03b2 likewise favors low values of \u03b2 ~ 0.5. Limitations to our current data analysis which preclude our asserting strong constraints upon the density parameter at present are discussed in detail.
\r\n", "doi": "10.7907/G8Y2-6V10", "publication_date": "1994", "thesis_type": "phd", "thesis_year": "1994" }, { "id": "thesis:2644", "collection": "thesis", "collection_id": "2644", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-06182008-135507", "primary_object_url": { "basename": "Leroy_ss_1994.pdf", "content": "final", "filesize": 8359682, "license": "other", "mime_type": "application/pdf", "url": "/2644/1/Leroy_ss_1994.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "Convectively generated internal gravity waves in Venus's middle atmosphere : momentum transport and radio scintillations", "author": [ { "family_name": "Leroy", "given_name": "Stephen Sylvain", "clpid": "Leroy-Stephen-Sylvain" } ], "thesis_advisor": [ { "family_name": "Ingersoll", "given_name": "Andrew P.", "clpid": "Ingersoll-A-P" } ], "thesis_committee": [ { "family_name": "Yung", "given_name": "Yuk L.", "clpid": "Yung-Y-L" }, { "family_name": "Ingersoll", "given_name": "Andrew P.", "clpid": "Ingersoll-A-P" }, { "family_name": "Goldreich", "given_name": "Peter Martin", "clpid": "Goldreich-P-M" } ], "local_group": [ { "literal": "Astronomy Department" }, { "literal": "div_gps" } ], "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nThis work is divided into two papers. Firstly, we theoretically calculate how gravity waves are emitted from the neutrally buoyant dry convection in Venus's middle atmosphere and investigate whether such waves play a significant role in supporting the superrotation of Venus's atmosphere. Secondly, we attempt to explain the radio scintillations seen in the occultations of many spacecraft, particularly Pioneer Venus, as caused by convectively generated gravity waves. Below are the abstracts of the two papers presented in this thesis.\r\n\r\nPaper I:\r\n\r\nWe calculate the emission of internal gravity waves from neutrally buoyant dry convection embedded within a stable atmosphere with static stability and zonal winds varying in height. We apply this theory to Venus's middle atmosphere to investigate whether these waves can help support the superrotation of Venus's atmosphere. Furthermore, we model the radio scintillation data obtained for Venus as caused by such internal gravity waves. The emission mechanism is similar to that suggested for driving the gravity modes of the Sun. We assume a background atmosphere on which we have superimposed linear wave propagation. Waves are damped by reabsorption by the convection, wavebreaking in the stable atmosphere, critical layer absorption, and by wave radiation to space. Wavebreaking is imposed wherever the waves become convectively unstable. Inertial effects are neglected and plane parallel geometry is assumed. Propagation of the waves is handled using a second order WKBJ approximation. A complete three dimensional ensemble of waves is retained.\r\n\r\nWe show that both westward and eastward propagating waves exert strong accelerations on the mean flow. The westward propagating carry enough momentum to support the westward superrotation between the convection and the cloud-tops; however, the bulk of the wave momentum flux is critically absorbed and deposited within a kilometer of the convection because most of the waves propagate slowly in the horizontal. The eastward propagating waves are found to exert large decelerations above the zonal wind maximum. The decelerations are larger than 20 m [...] day [...], similar to wave drag in the Earth's mesosphere.\r\n\r\nIn the course of evaluating our model, we have found that dry convection must have \"penetrative\" mixed layers above and below it. This arises from wavebreaking of gravity waves immediately after their generation. The effect of the penetrative layer is to filter wave emission and to create a discontinuity in the background temperature lapse rate dT/dz. The latter may be observable in atmospheres.\r\n\r\nPaper II:\r\n\r\nWe simulate radio scintillations as they would appear in Pioneer Venus radio occultation data assuming that the index of refraction fluctuations in Venus's atmosphere responsible for the scintillations are directly caused by gravity wave fluctuations. We assume that the gravity waves are created by a global convection layer between 50 and 55 km altitude in Venus's atmosphere and propagate vertically. Associated with the gravity waves are density fluctuations which create the index of refraction variations. We compare the simulated scintillations with data and argue that this theory for the radio scintillations is preferable to the theory that the scintillations are caused by clear air turbulence in Venus's atmosphere.\r\n\r\nWe show that these gravity waves can explain the shape and amplitude of the radio scintillation variance spectra in frequency. The shape of the simulated radio scintillation variance spectra in frequency is nearly a direct result of a saturated spectrum of breaking gravity waves. This saturated spectrum is the spectrum of breaking gravity waves in the vertical wavenumber. On the other hand, the overall amplitude is subject to parameters such as the intensity of the convection, the angle between the zonal winds and the beam path, and the zonal wind profile at polar latitudes. Limits can be placed, though, on the intensity of the convection which generates the waves and on the angle between the radio beam path and the winds in Venus's atmosphere. We find that the convection in Venus's middle atmosphere, even in polar regions, must transport 1 W/[...] to create gravity waves strong enough to break. This result is dependent on the amplitude of the zonal winds at polar latitudes.\r\n", "doi": "10.7907/msgs-7b48", "publication_date": "1994", "thesis_type": "phd", "thesis_year": "1994" }, { "id": "thesis:7382", "collection": "thesis", "collection_id": "7382", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:01082013-145722103", "primary_object_url": { "basename": "Reisenegger_ta_1993.pdf", "content": "final", "filesize": 18339616, "license": "other", "mime_type": "application/pdf", "url": "/7382/1/Reisenegger_ta_1993.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "Hydrodynamics of neutron star interiors and laboratory superfluids", "author": [ { "family_name": "Reisenegger", "given_name": "Tassilo Andreas", "clpid": "Reisenegger-T-A" } ], "thesis_advisor": [ { "family_name": "Goldreich", "given_name": "Peter Martin", "clpid": "Goldreich-P-M" } ], "thesis_committee": [ { "family_name": "Goldreich", "given_name": "Peter Martin", "clpid": "Goldreich-P-M" }, { "family_name": "Blandford", "given_name": "Roger D.", "clpid": "Blandford-R-D" }, { "family_name": "Kulkarni", "given_name": "Shrinivas R.", "clpid": "Kulkarni-S-R" } ], "local_group": [ { "literal": "Astronomy Department" }, { "literal": "div_pma" } ], "abstract": "This thesis contains the following papers:
\r\n\r\n1) A new class of g-modes in neutron stars (Astrophys. J., 395, 240 (1992)):\r\nIn the fluid core of a neutron star, the ratio of the number densities of charged\r\nparticles (protons and electrons) to neutrons is an increasing function of the mass\r\ndensity. This composition gradient stably stratifies the matter, giving rise to g-modes\r\nwith periods ranging upward from a few milliseconds. Some of these modes\r\nare computed and their damping mechanisms are discussed.
\r\n\r\n2) Magnetic field decay in isolated neutron stars (Astrophys. J., 395, 250\r\n(1992)): We investigate mechanisms that promote the loss of magnetic flux from\r\nan isolated neutron star. Ambipolar diffusion involves a drift of the magnetic field\r\nand charged particles relative to the neutrons, opposed by frictional drag. Variants\r\nof it include both the buoyant rise and the dragging by superfluid neutron vortices\r\nof magnetic flux tubes. The charged particle flux decomposes into a solenoidal\r\nand an irrotational component. The irrotational component perturbs the chemical\r\nequilibrium, generating pressure gradients that effectively choke it. The solenoidal\r\ncomponent can transport magnetic flux from the outer core to the crust on a short\r\ntimescale. Flux that threads the inner core is permanently trapped unless particle\r\ninteractions can rapidly smooth departures from chemical equilibrium. We speculate\r\nthat Hall drift may lead to a turbulent cascade of the magnetic field in the\r\nsolid crust, terminated by ohmic dissipation at small scales.
\r\n\r\n3) The spin-up problem in helium II (To appear, J. Low Temp. Phys., 92 (1/2)\r\n(July 1993)): The laminar spin-up of helium II is studied by solving the linearized\r\ntwo-fluid equations in a simple case. No direct interactions between vortex lines\r\nand container walls are included. Two mechanisms are identified for the transfer\r\nof angular momentum from the container to the interior fluid. Both involve a\r\npoloidal secondary flow. An analytic expression for the spin-up time is found.
\r\n", "doi": "10.7907/1FTJ-0J14", "publication_date": "1993", "thesis_type": "phd", "thesis_year": "1993" }, { "id": "thesis:933", "collection": "thesis", "collection_id": "933", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-03112009-141429", "primary_object_url": { "basename": "Svitek_t_1992.pdf", "content": "final", "filesize": 9657969, "license": "other", "mime_type": "application/pdf", "url": "/933/1/Svitek_t_1992.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "Martian water frost : control of global distribution by small-scale processes", "author": [ { "family_name": "Svitek", "given_name": "Tomas", "clpid": "Svitek-T" } ], "thesis_advisor": [ { "family_name": "Murray", "given_name": "Bruce C.", "clpid": "Murray-B-C" } ], "thesis_committee": [ { "family_name": "Murray", "given_name": "Bruce C.", "clpid": "Murray-B-C" }, { "family_name": "Ingersoll", "given_name": "Andrew P.", "clpid": "Ingersoll-A-P" }, { "family_name": "Albee", "given_name": "Arden Leroy", "clpid": "Albee-A-L" }, { "family_name": "Kamb", "given_name": "W. Barclay", "clpid": "Kamb-W-B" }, { "family_name": "Stevenson", "given_name": "David John", "clpid": "Stevenson-D-J" }, { "family_name": "Muhleman", "given_name": "Duane Owen", "clpid": "Muhleman-D-O" }, { "family_name": "Goldreich", "given_name": "Peter Martin", "clpid": "Goldreich-P-M" }, { "family_name": "Yung", "given_name": "Yuk L.", "clpid": "Yung-Y-L" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "This thesis analyzes the small\u2014scale physical processes occurring in the Martian water polar frosts. The small\u2014scale processes are considered from the point of view of how they control the global distribution and behavior of water on Mars. The analysis of the small\u2014scale properties of the surface frost is essential in efforts to find solutions for some outstanding, contradictory observations, to interpret correctly remote sensing observations, to model the surface\u2014frost thermal balance, and to implement the boundary conditions and parameterizations used in the global models of the volatiles' behavior on Mars. Two different problems are investigated in this thesis:\r\n\r\nThe effect of surface roughness on frost temperature and morphology is studied in Chapter 2 and 3. The investigation of the temperature/roughness feedback leads to the following suggestion: There is a natural tendency of volatile surfaces to develop spontaneously small-scale roughness in a sublimation\u2014dominated environment. The evidence for this claim consists of the model of a rough\u2014surface thermal balance, and of the terrestrial analogs of differential sublimation structures. Such a phenomenon can be tested by the Mars Observer and has important implications for the behavior of water frost on Mars.\r\n\r\nViking Lander 2 winter\u2014frost observations are described in Chapter 4. This study suggests that winter water frost occurred there in two forms: a) thin, almost continuous, early frost, and b) much thicker, patchy, later frost with local cold\u2014trapping of water vapor playing the crucial role. This conclusion is based on the correlation of multiple data sets (from both Viking Orbiter and Lander) and on the combined models of the physical processes occurring on a small scale \u2014 below the resolution of remote sensing. The evidence consists of the frost\u2014surface coverage and color transitions, and of the calculation of the vertical and horizontal water\u2014vapor transport near the surface. Again, this phenomenon can be confirmed or rejected by a set of observations from the Mars Observer.\r\n\r\nThe inherent rough\u2014surface morphology and the frost cold\u2014trapping must be a general property of at least some forms of the seasonal and residual frosts. Both effects must be considered in order to understand the global observations of the Martian frost and the surface environment of Mars in general.\r\n", "doi": "10.7907/EDK8-3457", "publication_date": "1992", "thesis_type": "phd", "thesis_year": "1992" }, { "id": "thesis:2662", "collection": "thesis", "collection_id": "2662", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-06202007-132612", "primary_object_url": { "basename": "Coppi_ps_1991.pdf", "content": "final", "filesize": 17984809, "license": "other", "mime_type": "application/pdf", "url": "/2662/1/Coppi_ps_1991.pdf", "version": "v2.0.0" }, "type": "thesis", "title": "Radiative processes in active galactic nuclei", "author": [ { "family_name": "Coppi", "given_name": "Paolo Severo", "clpid": "Coppi-Paolo-Severo" } ], "thesis_advisor": [ { "family_name": "Blandford", "given_name": "Roger D.", "clpid": "Blandford-R-D" }, { "family_name": "Phinney", "given_name": "E. Sterl", "clpid": "Phinney-E-S" } ], "thesis_committee": [ { "family_name": "Goldreich", "given_name": "Peter Martin", "clpid": "Goldreich-P-M" }, { "family_name": "Thorne", "given_name": "Kip S.", "clpid": "Thorne-K-S" }, { "family_name": "Phinney", "given_name": "E. Sterl", "clpid": "Phinney-E-S" } ], "local_group": [ { "literal": "TAPIR" }, { "literal": "Astronomy Department" }, { "literal": "div_pma" } ], "abstract": "A study of processes relevant to the electron-positron pair plasmas thought to exist in Active Galactic Nuclei is undertaken. The processes considered include: Compton scattering, pair annihilation, two photon pair production, synchrotron emission, e-e bremsstrahlung, and Coulomb scattering. Approximations used in the past to treat these processes in the context of a kinetic code are examined, and improvements are presented. A two-moment scattering formalism is presented to allow for important energy dispersion effects in scattering. This improved treatment of microphysical processes is implemented in a time-dependent, kinetic code incorporating Klein-Nishina effects on both the pair and photon distributions, relativistic thermal Comptonization, and synchrotron reabsorption.\r\n\r\nThe effects of pair plasma reprocessing on the emergent radiation spectrum are examined. Time-varying and stationary spectra are computed. Good qualitative agreement with previous calculations is found, except when the differences are attributable to the improved treatment of the microphysics. These differences can be substantial, particularly in the \"photon-starved\" regime where the effects of Coulomb scattering by suprathermal pairs off thermal pairs significantly modify the spectra. The spectral response of the pair plasma to variations in the particle injection is found to depend sensitively on the plasma parameters. A transitional spectrum may look very different from the spectra of either the stationary initial or final states. The highest energies (gamma-rays) are found to respond most rapidly to changes and should vary more than the X-rays. Pair plasmas can produce soft X-ray excesses. This happens under conditions independently favored by current pair plasma-Compton reflection models of the hard X-ray spectrum.\r\n", "doi": "10.7907/GDMQ-Q829", "publication_date": "1991", "thesis_type": "phd", "thesis_year": "1991" }, { "id": "thesis:2690", "collection": "thesis", "collection_id": "2690", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-06222007-113504", "primary_object_url": { "basename": "Han_m_1991.pdf", "content": "final", "filesize": 26453265, "license": "other", "mime_type": "application/pdf", "url": "/2690/1/Han_m_1991.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "The I-band Tully-Fisher relation and large-scale motions in the universe", "author": [ { "family_name": "Han", "given_name": "Mingsheng", "clpid": "Han-M" } ], "thesis_advisor": [ { "family_name": "Mould", "given_name": "Jeremy R.", "clpid": "Mould-J-R" } ], "thesis_committee": [ { "family_name": "Mould", "given_name": "Jeremy R.", "clpid": "Mould-J-R" }, { "family_name": "Goldreich", "given_name": "Peter Martin", "clpid": "Goldreich-P-M" }, { "family_name": "Blandford", "given_name": "Roger D.", "clpid": "Blandford-R-D" }, { "family_name": "Phinney", "given_name": "E. Sterl", "clpid": "Phinney-E-S" } ], "local_group": [ { "literal": "Astronomy Department" }, { "literal": "div_pma" } ], "abstract": "The ultimate goal of this thesis is to better understand the large-scale motions in the universe on scales beyond the Local-Supercluster, and also to better understand the Tully-Fisher relation as a distance indicator. Sixteen clusters of galaxies in redshifts range from 3000-10000 kms(-1) are studied as test points of the large-scale velocity field, using the I-band Tully-Fisher relation as distance indicator. A complete observational procedure and techniques of measuring cluster distance using the Tully-Fisher relation is investigated in detail, which involves many general topics in the photometric studies of galaxies. Major discussions and results in the thesis are summarized as:\n\n1. CCD surface photometry is described in detail. Errors and various effects (extinction, cosmological and seeing) on surface photometry are discussed. I-band surface photometry is carried out for some 280 galaxies in the thesis sample.\n\n2. The problem of internal absorption in spiral galaxies is investigated; new magnitude and isophotal-diameter corrections for internal absorption are derived.\n\n3. Different techniques for deriving cluster distances using Tully-Fisher relation are compared; distance bias due to sample selection effects is discussed at length; a Maximum-Likelihood method is given which is able to handle the sample selection effects.\n\n4. Global photometric properties of the cluster galaxies are examined; the problem of second parameter in the TF relation is investigated; a physical explanation for the TF relation and its dispersion is proposed.\n\n5. The peculiar velocity field as traced by the sample clusters is found to be highly non-random, and appears to be a coherent flow towards the general direction of the Great Attractor, with a flow amplitude of some 400~600 kms(-1) at the position of the Local Group.", "doi": "10.7907/85nr-2g69", "publication_date": "1991", "thesis_type": "phd", "thesis_year": "1991" }, { "id": "thesis:8797", "collection": "thesis", "collection_id": "8797", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:03202015-092027205", "primary_object_url": { "basename": "Bent-al-1990.pdf", "content": "final", "filesize": 20363896, "license": "other", "mime_type": "application/pdf", "url": "/8797/1/Bent-al-1990.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "Source Characteristics of Recent and Historic Earthquakes in Central and Southern California: Results from Forward Modeling", "author": [ { "family_name": "Bent", "given_name": "Allison Lyn", "clpid": "Bent-Allison-Lyn" } ], "thesis_advisor": [ { "family_name": "Helmberger", "given_name": "Donald V.", "clpid": "Helmberger-D-V" }, { "family_name": "Kanamori", "given_name": "Hiroo", "orcid": "0000-0001-8219-9428", "clpid": "Kanamori-H" } ], "thesis_committee": [ { "family_name": "Kanamori", "given_name": "Hiroo", "orcid": "0000-0001-8219-9428", "clpid": "Kanamori-H" }, { "family_name": "Goldreich", "given_name": "Peter Martin", "clpid": "Goldreich-P-M" }, { "family_name": "Helmberger", "given_name": "Donald V.", "clpid": "Helmberger-D-V" }, { "family_name": "Harkrider", "given_name": "David G.", "clpid": "Harkrider-D-G" }, { "family_name": "Tanimoto", "given_name": "Toshiro", "clpid": "Tanimoto-T" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "The long- and short-period body waves of a number of moderate earthquakes occurring in central and southern California recorded at regional (200-1400 km) and teleseismic (> 30\u00b0) distances are modeled to obtain the source parameters-focal mechanism, depth, seismic moment, and source time history. The modeling is done in the time domain using a forward modeling technique based on ray summation. A simple layer over a half space velocity model is used with additional layers being added if necessary - for example, in a basin with a low velocity lid.
\r\n\r\nThe earthquakes studied fall into two geographic regions: 1) the western Transverse Ranges, and 2) the western Imperial Valley. Earthquakes in the western Transverse Ranges include the 1987 Whittier Narrows earthquake, several offshore earthquakes that occurred between 1969 and 1981, and aftershocks to the 1983 Coalinga earthquake (these actually occurred north of the Transverse Ranges but share many characteristics with those that occurred there). These earthquakes are predominantly thrust faulting events with the average strike being east-west, but with many variations. Of the six earthquakes which had sufficient short-period data to accurately determine the source time history, five were complex events. That is, they could not be modeled as a simple point source, but consisted of two or more subevents. The subevents of the Whittier Narrows earthquake had different focal mechanisms. In the other cases, the subevents appear to be the same, but small variations could not be ruled out.
\r\n\r\nThe recent Imperial Valley earthquakes modeled include the two 1987 Superstition Hills earthquakes and the 1969 Coyote Mountain earthquake. All are strike-slip events, and the second 1987 earthquake is a complex event With non-identical subevents.
\r\n\r\nIn all the earthquakes studied, and particularly the thrust events, constraining the source parameters required modeling several phases and distance ranges. Teleseismic P waves could provide only approximate solutions. P\u2099\u2097 waves were probably the most useful phase in determining the focal mechanism, with additional constraints supplied by the SH waves when available. Contamination of the SH waves by shear-coupled PL waves was a frequent problem. Short-period data were needed to obtain the source time function.
\r\n\r\nIn addition to the earthquakes mentioned above, several historic earthquakes were also studied. Earthquakes that occurred before the existence of dense local and worldwide networks are difficult to model due to the sparse\r\ndata set. It has been noticed that earthquakes that occur near each other often produce similar waveforms implying similar source parameters. By comparing recent well studied earthquakes to historic earthquakes in the same\r\nregion, better constraints can be placed on the source parameters of the historic events.
\r\n\r\nThe Lompoc earthquake (M=7) of 1927 is the largest offshore earthquake to occur in California this century. By direct comparison of waveforms and amplitudes with the Coalinga and Santa Lucia Banks earthquakes, the focal\r\nmechanism (thrust faulting on a northwest striking fault) and long-period seismic moment (10\u00b2\u2076 dyne cm) can be obtained. The S-P travel times are consistent with an offshore location, rather than one in the Hosgri fault zone.
\r\n\r\nHistoric earthquakes in the western Imperial Valley were also studied. These events include the 1942 and 1954 earthquakes. The earthquakes were relocated by comparing S-P and R-S times to recent earthquakes. It was found that only minor changes in the epicenters were required but that the Coyote Mountain earthquake may have been more severely mislocated. The waveforms as expected indicated that all the events were strike-slip. Moment estimates were obtained by comparing the amplitudes of recent and historic events at stations which recorded both. The 1942 event was smaller than the 1968 Borrego Mountain earthquake although some previous studies suggested the reverse. The 1954 and 1937 earthquakes had moments close to the expected value. An aftershock of the 1942 earthquake appears to be larger than previously thought.
", "doi": "10.7907/wyry-7c13", "publication_date": "1990", "thesis_type": "phd", "thesis_year": "1990" }, { "id": "thesis:3433", "collection": "thesis", "collection_id": "3433", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-09102008-084535", "type": "thesis", "title": "Outflows in High Mass Star-Forming Regions", "author": [ { "family_name": "Barsony", "given_name": "Mary Anne", "clpid": "Barsony-Mary-Anne" } ], "thesis_advisor": [ { "family_name": "Scoville", "given_name": "Nicholas Zabriskie", "clpid": "Scoville-N-Z" } ], "thesis_committee": [ { "family_name": "Scoville", "given_name": "Nicholas Zabriskie", "clpid": "Scoville-N-Z" }, { "family_name": "Blake", "given_name": "Geoffrey A.", "clpid": "Blake-G-A" }, { "family_name": "Goldreich", "given_name": "Peter Martin", "clpid": "Goldreich-P-M" }, { "family_name": "Libbrecht", "given_name": "Kenneth George", "clpid": "Libbrecht-K-G" } ], "local_group": [ { "literal": "Owens Valley Radio Observatory (OVRO)" }, { "literal": "Astronomy Department" }, { "literal": "div_pma" } ], "abstract": "In the last decade, observations of star-forming regions in the millimeter wavelength range have led to the discovery of supersonic molecular outflows from embedded infrared sources, a heretofore unsuspected, but now generally accepted, phase in the star formation process. In order to better understand the outflow phenomenon in high mass (i.e., high luminosity) pre-main sequence stars, the three sources S87, LkH\u03b1101, and S106 were chosen for closer study. Observations from the recently completed Owens Valley Radio Observatory's millimeter wave interferometer afford us the highest spatial-resolution, molecular line (CS J=2\u21921 and 13CO J=1\u21920) maps of these sources to date. The OVRO maps were combined with data from the 14 m FCRAO millimeter wave radio telescope, the VLA, IRAS, and the Palomar 5 m and 1.5 m optical telescopes.
\r\n\r\nA synthesis of the data reveals that although all three pre-main sequence objects are the sources of powerful, ionized stellar winds, only one, S87/IRS1, currently drives a bipolar molecular outflow. The inferred mass loss rates in the winds of S87/IRS1, LkH\u03b1101, and S106 IR are 1.8 x 10-5, 1.7 x 10-6, 1.1 x 10-5 M\u2609 yr-1, with corresponding wind velocities of 160, 350, and 200 km s-1. In all cases the wind velocities are lower, and the mass loss rates higher, than for main sequence stars of the same spectral types. Radiation pressure is inadequate to drive these winds, which can be anisotropic in their velocity fields.
\r\n\r\nThe existence of massive, large-scale (r \u2248 1016 cm) disks, necessary for numerous proposed molecular outflow models, can now be ruled out. Only one of the many proposed molecular outflow models is consistent with the new observations (K\u00f6nigl 1982).
\r\n\r\nAlthough the observed winds can disperse a good portion of the cloud cores they inhabit, they cannot completely destroy these cores. Consequently, outflows from pre-main sequence stars alone cannot account for the dispersal of molecular clouds, as some investigators have suggested.
\r\n\r\nTwo glaring and intriguing problems remain to be solved in this field: the origin of the supersonic turbulence observed throughout a molecular cloud, and the driving mechanism of the powerful, ionized winds found in the high-mass, pre-main sequence stars.
\r\n", "doi": "10.7907/FDFC-0Q12", "publication_date": "1989", "thesis_type": "phd", "thesis_year": "1989" }, { "id": "thesis:5302", "collection": "thesis", "collection_id": "5302", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:10162009-112521312", "type": "thesis", "title": "I. Episodic Volcanism of Tidally Heated Satellites with an Application to Io. II. Thermal State of an Ice Shell on Europa. III. Polar Wander of a Synchronously Rotating Satellite with Application to Europa", "author": [ { "family_name": "Ojakangas", "given_name": "Gregory Wayne", "clpid": "Ojakangas-Gregory-Wayne" } ], "thesis_advisor": [ { "family_name": "Stevenson", "given_name": "David John", "clpid": "Stevenson-D-J" }, { "family_name": "Ingersoll", "given_name": "Andrew P.", "clpid": "Ingersoll-A-P" } ], "thesis_committee": [ { "family_name": "Ingersoll", "given_name": "Andrew P.", "clpid": "Ingersoll-A-P" }, { "family_name": "Goldreich", "given_name": "Peter Martin", "clpid": "Goldreich-P-M" }, { "family_name": "Hager", "given_name": "Bradford H.", "clpid": "Hager-B-H" }, { "family_name": "Stevenson", "given_name": "David John", "clpid": "Stevenson-D-J" } ], "local_group": [ { "literal": "Astronomy Department" }, { "literal": "div_gps" } ], "abstract": "Two examples of planetary bodies that may have coupled thermal and dynamical evolutions are investigated. The work is presented in three individual papers.
\r\n\r\nThe first example is that of a tidally heated satellite in an orbital resonance, for which the tidal dissipation rate is a strongly increasing function of the internal temperature. For such a satellite, a feedback mechanism exists between the orbital and thermal energies, which may lead to periodic variations in tidal heating within the satellite and its orbital eccentricity. A simple model of this mechanism is presented in the first paper and is applied specifically to Io.
\r\n\r\nThe second example is that of an ice shell on Europa, which is decoupled from the silicate core by a layer of liquid water. In the second paper, the spatially varying thickness that such a shell would have in thermal equilibrium with tidal dissipation within it, surface solar insolation and heat flow from the core is calculated for reasonable rheological laws for ice. The contribution of these variations in ice thickness to Europa's inertia tensor is estimated, and the implications for nonsynchronous rotation of Europa are discussed. In the third paper, a detailed dynamical model is developed, which demonstrates that such a shell may exhibit large\u2014scale polar wander as it approaches thermal equilibrium, because of the destabilizing effect of the variations in ice thickness on the inertia tensor of the shell.
\r\n\r\nThe abstracts of the three papers are reproduced below.
\r\n\r\nEpisodic Volcanism of Tidally Heated Satellites with Application to Io
\r\n\r\nA simple model of the coupled thermal and orbital evolution of a tidally heated satellite in an orbital resonance is presented and applied specifically to Io. The model quantitatively demonstrates how a feedback mechanism between the orbital and thermal energy of such a satellite can lead to periodic variations in surface heatflow and orbital eccentricity. The convective heatflow and (k/Q) of the satellite are parameterized as local power laws of the temperature, where Q is the quality factor and k is the second-degree tidal potential Love number. The time evolution of the model is determined by two nonlinear equations: an equation governing the orbital eccentricity, and a simple heat-balance equation determining the temperature. A linear stability analysis reveals that the time-independent solution is unstable if n > m + p, where n and m are the exponents in the power laws for (k/Q) and convective heatflow, respectively, and p is the ratio of the convective cooling time scale to the time scale for equilibration of the eccentricity. Numerical integration of the nonlinear equations reveals behavior in qualitative agreement with this relation. Laboratory data on near-solidus peridotites suggest 20 \u227e n \u227e 30, and parameterized convection schemes suggest m ~ 10. Since p is of order unity, it follows that tidally heated satellites are probably in the unstable regime if they are operating near the solidus. It is thus probable that Io has no thermal steady state. The model is made more realistic by (1) arresting the reduction of (k/Q) at low temperature, and (2) arresting the growth of temperature at the mantle solidus and allowing volcanism to remove the excess heat. When the second modification is included, the unstable regime becomes periodic. In addition, a global k substantially larger than the elastic value is possible for a mostly solid Io because the body may begin to behave viscously when the tidal period is longer than, or comparable to, the Maxwell time. This requires a solid-state viscosity of \u227e 4 x 10\u00b9\u2075 Pa s, which may be achievable with a small amount of partial melt. The model can easily be adjusted to pass through Io's current observed heatflow (1-2 W m\u207b\u00b2) and eccentricity (~ 0.004) for reasonable choices of parameters (Q/k)min ~ 100, (Q/k)max ~ few x 10\u00b3 solidus viscosity ~ 10\u00b9\u2075\u201310\u00b9\u2077 Pas, and QJ within the required dynamical bounds. The periods of high heatflow and acceptable eccentricity typically have duration of ~ 20-20 myr, separated in time by ~ 80-100 myr. Spatial heterogeneities in Io's thermal structure are likely to make the behavior more complicated. The model predicts that Io's mean motion may be currently increasing, a possibility suggested by recent estimates of \u1e45\u2081 from eclipse data. Since Europa's eccentricity mimics that of Io, the model also implies that the tidal stresses in Europa's ice shell may have recently been large enough to produce the observed fracturing. The episodic heating mechanism may be responsible for the resurfacing of Enceladus < 10\u2079 years ago.
\r\n\r\nThermal State of an Ice Shell on Europa
\r\n\r\nWe consider a model of Europa consisting of an ice shell that is decoupled from a silicate core by a layer of liquid water. The thickness of the shell is calculated as a function of colatitude and longitude, assuming that a state of conductive equilibrium exists with the incident annual average solar insolation, tidal dissipation within the shell, and heat flow from the core. Ice thickness profiles are calculated for each of two plausible rheological behaviors for ice: the Maxwell rheology and the generalized flow law rheology. In both cases the strong temperature\u2014dependence of the dissipation rate is explicitly included as well as the temperature\u2014dependence of the thermal conductivity of ice. Because of the strong temperature dependence of the dissipation rate, nearly all of the tidal dissipation is concentrated in the lowermost few kilometers of the shell. Even though the effective Q of the greater part of the shell is >> 100 in our models, average shell thicknesses do not exceed 25 km. Thus, if the total thickness of H\u2082O which mantles Europa is \u2273 25 km, none of the models admit the possibility of a completely frozen H\u2082O layer. The total dissipation rates in our models are comparable to those of a constant Q model with Q ~ 10. The thickness profiles are relatively insensitive to heat flow from the core. The second degree spherical harmonic components of the ice thickness are given and the resulting contributions to the quantities (B-A)/C and (B-C)/A of Europa are estimated. Although the contribution to (B-A)/C is perhaps larger than the permanent value needed to prevent nonsynchronous rotation, its dependence on the shell's orientation relative to synchroneity suggests that very slow nonsynchronous rotation will persist, with reorientation of the shell relative to the satellite-planet direction occurring on a timescale \u2273 the thermal diffusion timescale for the shell (~10\u2077 yr). The existence of a significant \"fossil\" bulge on the shell due to long-term elastic behavior of its outer, coldest regions would eliminate nonsynchronous rotation. Since the contribution to ((B-C)/A) of the thickness variations in most of our models is > 0, Europa may experience polar wander as thermal equilibrium is approached, if the above is the most important permanent contribution to ((B-C)/A). The magnitudes of the principal moment differences are insensitive to the details of the parameterization of the tidal dissipation.
\r\n\r\nPolar Wander of a Synchronously Rotating Satellite with Application to Europa
\r\n\r\nAn ice shell on Europa that is decoupled from the silicate core by a layer of liquid water has a thermal-equilibrium thickness profile that varies with position over its surface, because of spatial variations in the surface temperature and tidal dissipation within the ice (see previous paper). The second spherical harmonic degree components of these thickness variations and of any fossil rotational and tidal bulges present on the shell contribute to the inertia tensor of the body. The problem is that of a planetary elastic lithosphere that is topographically loaded from below. Following the development of Willemann and Turcotte (1981) we develop equations describing the variations in the inertia tensor of a body, which are caused by the addition of second harmonic degree topography to the base of the crust. Applied to the case of an ice shell on Europa, it is found for many choices of parameters that a state of thermal equilibrium for the shell will involve an orientation of Europa's principal axes of inertia (when the hydrostatic bulges are relaxed), which is unusual for a synchronously rotating satellite. Specifically, the intermediate and maximum principal moments are reversed. To reach the preferred orientation for synchronous satellites, a thermal equilibrium ice shell must execute a net reorientation of ninety degrees about the satellite\u2014planet direction. We present a simple model of a rigid, synchronously rotating satellite in a circular orbit for which the difference between the intermediate and maximum principal moments is linear in time, passing through zero when t = 0. The model demonstrates that the expected reorientation is indeed dynamically favored.
\r\n\r\nWe then consider a more realistic model, including the effects of various torques which act to couple the motions of the core, shell, and liquid water layer, as well as the effect of viscous dissipation which arises in the shell due to the predicted polar wander. It is found that the Poincar\u00e9 torque, gravitational coupling, and the torque due to viscous shear in the liquid water layer are unable to induce significant motion of the core during polar wander of the shell. However, the Poincar\u00e9 torque exerted on the liquid water layer by the shell is believed to cause the liquid water layer to reorient in coincidence with the shell. The model suggests that viscous friction in the shell eliminates the possibility that polar wander will occur unless preexisting fractures (e.g., due to tidal stresses (Crawford and Stevenson, 1988)) extend from the surface to a depth where the ice behaves viscously on the polar wander time scale. If the temperature Tf at the base of the fractured region is as high as ~ 140-145 K, the model indicates that polar wander occurs on a time scale of 10\u2076-10\u2075 y (shorter as Tf increases) after the sign of the difference between the maximum and intermediate principal moments reverses. In the absence of dissipation, polar wander would occur in ~ few x 10\u00b3 y. Polar wander must occur on a time scale significantly shorter than ~ 10\u2077 y, or the thickness profile of the ice will be in continuous equilibrium with its thermal environment regardless of its orientation, and the mechanism driving the polar wander will be virtually eliminated. It is likely that events of large scale polar wander occur episodically, separated in time by periods on the order of the time scale for thermal diffusion through the shell (~ 10\u2077 y), although a state of slow, continuous drifting of the pole is also possible. The time scale of viscous flow of topography at the base of the ice is also near 10\u2077 y. If dissipation in the shell due to polar wander is a few orders of magnitude smaller than our simple model suggests, polar wander as described here is a much more effective means for fracturing the ice than is tidal flexing, and it may contribute to producing the observed global fracture systems in Europa's ice.
\r\n", "doi": "10.7907/RMD6-XM66", "publication_date": "1988", "thesis_type": "phd", "thesis_year": "1988" }, { "id": "thesis:3410", "collection": "thesis", "collection_id": "3410", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-09092008-111823", "type": "thesis", "title": "Magnetic Fields and Supergranule Velocity Fields on the Quiet Sun", "author": [ { "family_name": "Wang", "given_name": "Haimin", "orcid": "0000-0002-5233-565X", "clpid": "Wang-Haimin" } ], "thesis_advisor": [ { "family_name": "Zirin", "given_name": "Harold", "clpid": "Zirin-H" } ], "thesis_committee": [ { "family_name": "Zirin", "given_name": "Harold", "clpid": "Zirin-H" }, { "family_name": "Libbrecht", "given_name": "Kenneth George", "clpid": "Libbrecht-K-G" }, { "family_name": "Goldreich", "given_name": "Peter Martin", "clpid": "Goldreich-P-M" }, { "family_name": "Phinney", "given_name": "E. Sterl", "clpid": "Phinney-E-S" }, { "family_name": "Oke", "given_name": "J. Beverly", "clpid": "Oke-J-B" } ], "local_group": [ { "literal": "Astronomy Department" }, { "literal": "div_pma" } ], "abstract": "I have carried out detailed study on the quiet sun magnetic fields and super-granule velocity fields. This thesis consists of 6 themes. 1. I studied the statistical properties of quiet sun magnetic fields, including size distribution, evolution, flux budget of magnetic flux elements, and the magnetic diffusion constant. From the observations, I derived that the magnetic diffusion constant is \u2264150 km\u00b2/sec in the quiet region. I found that cancelling features and Ephemeral Regions are major sources of magnetic flux disappearance and replenishment. 2. I studied the supergranule velocity fields. Supergranule vertical velocities have a r.m.s. speed of 0.03 km/s. By observing the evolution of individual supergranule cells, I found that the average lifetime of supergranules is \u226550 hours. 3. I measured the contrast of faculae near the solar limb. The measurements show no obvious contrast increase or decrease near the solar limb. The observation fits neither the \"hot wall\" nor \"hot cloud\" fluxtube model. 4. I measured the separation velocities of new bipoles. The observed values are several times smaller than the values estimated by the theory of magnetic buoyancy. 5. I applied the local correlation tracking technique to BBSO Videomagnetogram data and detected an approximate radial intranetwork flow pattern. 6. I studied the relationship between magnetic fields and convection velocity fields. I found that ephemeral regions have a light tendency to emerge at or near the boundaries of supergranules; supergranules have the same scale, correlation lifetime and mean horizontal speed in the enhanced network region as in the mixed polarity quiet sun; the velocity of moving magnetic features that surround sunspots is consistent with the direct Doppler measurement.", "doi": "10.7907/1cja-6j65", "publication_date": "1988", "thesis_type": "phd", "thesis_year": "1988" }, { "id": "thesis:3407", "collection": "thesis", "collection_id": "3407", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-09092008-090628", "type": "thesis", "title": "Excitation and Damping of Solar P-Modes", "author": [ { "family_name": "Kumar", "given_name": "Pawan", "clpid": "Kumar-Pawan" } ], "thesis_advisor": [ { "family_name": "Goldreich", "given_name": "Peter Martin", "clpid": "Goldreich-P-M" } ], "thesis_committee": [ { "family_name": "Goldreich", "given_name": "Peter Martin", "clpid": "Goldreich-P-M" }, { "family_name": "Franklin", "given_name": "Joel N.", "clpid": "Franklin-J-N" }, { "family_name": "Libbrecht", "given_name": "Kenneth George", "clpid": "Libbrecht-K-G" }, { "family_name": "Phinney", "given_name": "E. Sterl", "clpid": "Phinney-E-S" }, { "family_name": "Thorne", "given_name": "Kip S.", "clpid": "Thorne-K-S" } ], "local_group": [ { "literal": "Astronomy Department" }, { "literal": "div_pma" } ], "abstract": "I have carried out detailed analysis of the interaction of acoustic radiation with homogeneous turbulence in order to understand the excitation of solar p-modes by turbulent convection. The most significant outcome of this investigation is the finding that, for certain types of forced turbulences, the absorption of acoustic waves is no greater than a free turbulence, whereas the emission is always enhanced by a factor M\u207b\u00b2, where M is the Mach number of the turbulence. Turbulent convection in the sun is an example of this kind of turbulence. This leads to the conclusion that energies in solar p-modes, due to their interaction with the convection, should be approximately equal to the thermal energy in a resonant eddy. This is found to be in good agreement with the observations. The ideas developed in the above work have been applied to explain the recently observed absorption of acoustic waves by sunspots as well. Work has also been carried out to determine the probability distribution function for the time averaged energy of stochastically excited modes. We hope to learn about the nature of the excitation and damping processes for the solar modes by comparing this theoretically determined distribution with the observations.
\r\n\r\nIn an effort towards resolving the overstability question of solar p-modes, I have investigated the effectiveness of 3-mode couplings, the most plausible process for limiting the amplitudes of overstable modes. The 3-mode coupling mechanism is also a good candidate for exciting fundamental modes which are found to be linearly stable, but are observed to have energies comparable to p-modes of similar frequencies. The issue of mode stability remains inconclusive due to the unknown energies of modes with period ~3.5 minutes. However, we find the fundamental modes to be damped as a result of mode couplings and hence they require excitation by a mechanism other than the overstability.
\r\n", "doi": "10.7907/q6y2-3263", "publication_date": "1988", "thesis_type": "phd", "thesis_year": "1988" }, { "id": "thesis:7484", "collection": "thesis", "collection_id": "7484", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:02202013-103037890", "primary_object_url": { "basename": "Rudy 1987.pdf", "content": "final", "filesize": 28898031, "license": "other", "mime_type": "application/pdf", "url": "/7484/1/Rudy 1987.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "Mars: High Resolution VLA Observations at Wavelengths of 2 and 6 cm and Derived Properties", "author": [ { "family_name": "Rudy", "given_name": "Donald James", "clpid": "Rudy-Donald-James" } ], "thesis_advisor": [ { "family_name": "Ingersoll", "given_name": "Andrew P.", "clpid": "Ingersoll-A-P" } ], "thesis_committee": [ { "family_name": "Ingersoll", "given_name": "Andrew P.", "clpid": "Ingersoll-A-P" }, { "family_name": "Albee", "given_name": "Arden Leroy", "clpid": "Albee-A-L" }, { "family_name": "Goldreich", "given_name": "Peter Martin", "clpid": "Goldreich-P-M" }, { "family_name": "Murray", "given_name": "Bruce C.", "clpid": "Murray-B-C" }, { "family_name": "Muhleman", "given_name": "Duane Owen", "clpid": "Muhleman-D-O" } ], "local_group": [ { "literal": "Astronomy Department" }, { "literal": "div_gps" } ], "abstract": "Observations of Mars at wavelengths of 2 and 6cm were made using the VLA in its A configuration. Two seasons were observed; late spring in the northern hemisphere (LS ~ 60\u00b0) and early summer in the southern summer (LS ~ 300\u00b0). The sub-earth latitudes were 25\u00b0N and 25\u00b0S, for each of these seasons respectively. So the geometry for viewing the polar region was optimal in each case. Whole-disk brightness temperatures were estimated to be 193.2 K \u00b1 1.0 at 2 cm and 191.2 K \u00b1 0.6 at 6 cm for the northern data set and 202.2 K \u00b1 l.0 at 2 cm and 195.4 K \u00b1 0.6 at 6 cm for the southern data set (formal errors only). Since measurements of the polarized flux were taken at the same time, whole-disk effective dielectric constants could be estimated and from these, estimates of sub-surface densities could be made. The results of these calculations at 2cm yielded whole-disk effective dielectric constants of 2.34 \u00b1 0.05 and 2.02 \u00b1 0.03 which imply sub-surface densities of 1.24 g cm-3 \u00b1 0.06 and 1.02 g cm-3 \u00b1 0.05 for the north and south, respectively. The same calculations at 6 cm yielded effective densities of 1.45 g cm-3 \u00b1 0.10 and 1.31 g cm-3 \u00b1 0.07 from effective dielectric constants of 2.70 \u00b1 0.09 and 2.48 \u00b1 0.06 for the north and south data sets, respectively.
\r\n\r\nFrom the mapped data these parameters were also estimated as a function of latitude between latitudes of 15\u00b0S and 60\u00b0N for the north data set; and between latitudes of 30\u00b0N and 60\u00b0S for the south data set. A region in which the brightness temperature behaves in an anomalous manner was discovered in both data sets. This region lies between about 10\u00b0S and 40\u00b0S. Here the brightness temperatures at both wavelengths in both data sets appears lower, by 4 K to 8 K, than a nominal model would predict. In addition to the effective dielectric constant and sub-surface density the radio absorption length of the sub-surface was estimated. The radio absorption length for most of these latitudes was about 15 wavelengths with formal errors on the order of 5 or 10 wavelengths. This is true for both data sets. The estimation of the effective dielectric constant at most latitudes was between 2 and 3.5 with only slight differences between the two different wavelengths. The two data sets show the same relative trends, but are off by a scaling factor.
\r\n\r\nThese estimates of the dielectric constant lead to estimation of the sub-surface densities as a function of latitude. Most calculations of the sub-surface density yielded results between 1 and 2 g cm-3 with errors on the order of 0.5 g cm-3. These results seem to imply that the sub-surface is not much different than the surface as observed by the Viking and Mariner missions. In line with this, an examination of the correlation of the dielectric constant at each wavelength with the thermal inertia, determined by the Viking infrared measurements, shows a relatively strong correlation, at both wavelengths, for the North data set. The South data set, however, shows little to nocorrelation between the radio parameters and the thermal inertia. Since the South data set is primarily composed of latitudes which contain the anomalous region, it is not suprising that the South data set shows no correlation.
\r\n\r\nIn addition, the thermal-radiative model used to estimate the above parameters was used to estimate the variability of the whole-disk brightness temperature of Mars. This was done in an effort to establish a background for those astronomers wishing to use Mars as a calibration source. The parameters investigated for their effect on the whole-disk brightness temperature of Mars were: the sub-earth longitude, the sub-earth latitude, the sub-earth time of day, the dielectric constant, and the radio absorption length. A nominal model was first created which established the variation of the brightness temperature as a function of season and radio absorption length. A nominal value of 2.2 was used for the dielectric constant, and the sub-earth latitude was set at 0\u00b0N and the sub-earth longitude was set at 75\u00b0W. The sub-earth time of day was held at noon for this nominal model. This is equivalent to a 0\u00b0 phase angle. The most important geometric factor was the sub-earth latitude. The error in estimating the whole-disk brightness temperature of Mars by using the wrong sub-earth latitude can be as large as 5 to 10%. The charts presented will be useful to estimate the whole-disk brightness temperature which the thermal model would predict. It is believed that the error in this estimate is less than or equal to 5 K.
\r\n", "doi": "10.7907/3g59-p796", "publication_date": "1987", "thesis_type": "phd", "thesis_year": "1987" }, { "id": "thesis:4554", "collection": "thesis", "collection_id": "4554", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-11142006-131417", "primary_object_url": { "basename": "Kirk_rl_1987.pdf", "content": "final", "filesize": 17917757, "license": "other", "mime_type": "application/pdf", "url": "/4554/1/Kirk_rl_1987.pdf", "version": "v2.0.0" }, "type": "thesis", "title": "I. Thermal Evolution of Ganymede and Implications for Surface Features. II. Magnetohydrodynamic Constraints on Deep Zonal Flow in the Giant Planets. III. A Fast Finite-Element Algorithm for Two-Dimensional Photoclinometry", "author": [ { "family_name": "Kirk", "given_name": "Randolph Livingstone", "clpid": "Kirk-Randolph-Livingstone" } ], "thesis_advisor": [ { "family_name": "Goldreich", "given_name": "Peter Martin", "clpid": "Goldreich-P-M" } ], "thesis_committee": [ { "family_name": "Goldreich", "given_name": "Peter Martin", "clpid": "Goldreich-P-M" }, { "family_name": "Stevenson", "given_name": "David John", "orcid": "0000-0001-9432-7159", "clpid": "Stevenson-D-J" }, { "family_name": "Ingersoll", "given_name": "Andrew P.", "orcid": "0000-0002-2035-9198", "clpid": "Ingersoll-A-P" }, { "family_name": "Murray", "given_name": "Bruce C.", "clpid": "Murray-B-C" }, { "family_name": "Kirschvink", "given_name": "Joseph L.", "orcid": "0000-0001-9486-6689", "clpid": "Kirschvink-J-L" } ], "local_group": [ { "literal": "Astronomy Department" }, { "literal": "div_gps" } ], "abstract": "The work is divided into three independent papers:
\r\n\r\nPAPER I:
\r\n\r\nThermal evolution models are presented for Ganymede, assuming a mostly differentiated initial state of a water ocean overlying a rock layer. The only heat sources are assumed to be primordial heat (provided by accretion) and the long-lived radiogenic heat sources in the rock component. As Ganymede cools, the ocean thins, and two ice layers develop, one above composed of ice I, and the other below composed of high-pressure polymorphs of ice. Subsolidus convection proceeds separately in each ice layer, its transport of heat calculated using a simple parameterized convection scheme and the most recent data on ice rheology. The model requires that the average entropy of the deep ice layer exceed that of the ice I layer. If the residual ocean separating these layers becomes thin enough, then a Rayleigh-Taylor-like (\"diapiric\") instability may ensue, driven by the greater entropy of the deeper ice and merging the two ice mantles into a single convective layer. This instability is not predicted by linear analysis but occurs for plausible finite amplitude perturbations associated with large Rayleigh number convection. The resulting warm ice diapirs may lead to a dramatic \"heat pulse\" at the surface and to fracturing of the lithosphere, and may be directly or indirectly responsible for resurfacing and grooved terrain formation on Ganymede. The timing of this event depends rather sensitively on poorly known rheological parameters but could be consistent with chronologies deduced from estimated cratering rates. Irrespective of the occurrence or importance of the heat pulse, we find that lithospheric fracturing requires rapid stress loading (on a timescale \u227e 104) years). Such a timescale can be realized by warm ice diapirism, but not directly by gradual global expansion. In the absence of any quantitative and self-consistent model for the resurfacing of Ganymede by liquid water, we favor resurfacing by warm ice flows,which we demonstrate to be physically possible, a plausible consequence of our models, compatible with existing observations, and a hypothesis testable by Galileo. We discuss core formation as an alternative driver for resurfacing, and conclude that it is less attractive. We also consider anew the puzzle of why Callisto differs so greatly from Ganymede, offering several possible explanations. The models presented do not provide a compelling explanation for all aspects of Ganymedean geological evolution, since we have identified several potential problems, most notably the apparently extended period of grooved terrain formation (several hundred million years), which is difficult to reconcile with the heat pulse phenomenon.
\r\n\r\nPAPER II:
\r\n\r\nThe observed zonal flows of the giant planets will, if they penetrate below the visible atmosphere, interact significantly with the planetary magnetic field outside the metalized core. The appropriate measure of this interaction is the Chandrasekhar number Q = (H2)/(4\u03c0\u03c1\u03bd\u03b12\u03bb) (where H = radial component of the magnetic field, \u03bd = eddy viscosity, \u03bb = magnetic diffusivity, \u03b1-1 = lengthscale on which \u03bb varies); at depths where Q \u2273 1 the velocity will be forced to oscillate on a small lengthscale or decay to zero. We estimate the conductivity due to semiconduction in H2 (Jupiter, Saturn) and ionization in H2O (Uranus, Neptune) as a function of depth; the value \u03bb \u2243 1010 cm2s-1 needed for Q = 1 is readily obtained well outside the metallic core (where \u03bb \u2243 102 cm2s-1).
\r\n\r\nThese assertions are quantified by a simple model of the equatorial zonal jet in which the flow is assumed uniform on cylinders concentric with the spin axis, and the viscous and magnetic torques on each cylinder are balanced. We solve this \"Taylor constraint\" simultaneously with the dynamo equation to obtain the velocity and magnetic field in the equatorial plane. With this model we reproduce the widely differing jet widths of Jupiter and Saturn (though not the flow at very high or low latitudes) using \u03bd = 2500 cm2s-1, consistent with the requirement that viscous dissipation not exceed the specific luminosity. A model Uranian jet consistent with the limited Voyager data can also be constructed, with appropriately smaller \u03bd, but only if one assumes a two-layer interior. We tentatively predict a wide Neptunian jet.
\r\n\r\nFor Saturn (but not Jupiter or Uranus) the model has a large magnetic Reynolds number where Q = 1 and hence exhibits substantial axisymmetrization of the field in the equatorial plane. This effect may or may not persist at higher latitudes. The one-dimensional model presented is only a first step. Variation of the velocity and magnetic field parallel to the spin axis must be modeled in order to answer several important questions, including: 1) What is the behavior of flows at high latitudes, whose Taylor cylinders are interrupted by the region with Q \u2273 1? 2) To what extent is differential rotation in the envelope responsible for the spin-axisymmetry of Saturn's magnetic field?
\r\n\r\nPAPER III:
\r\n\r\nIt is shown that the problem of two-dimensional photoclinometry (PC) -- the reconstruction of a surface z(x,y) from a brightness image B(x,y) -- may be formulated in a natural way in terms of finite elements. The resulting system of equations is underdetermined as a consequence of the lack of boundary conditions for z, but a unique solution may be chosen by minimizing a function S expressing the \"roughness\" of the surface. An efficient PC algorithm based on this formulation is presented, requiring ~ 10.66 (four-byte) memory locations and ~104 floating multiplications/additions per pixel, and incorporating: 1) Minimization of the roughness by the penalty method, which yields the smallest set of equations. 2) Iterative solution of the nonlinear equations by Newton's method. 3) Solution of the linearized equations by an inner iterative cycle of successive over-relaxation, which takes advantage of the extreme sparseness of the system. 4) Multigridding, in which the solutions to the smaller problems obtained by reducing the resolution are used recursively to greatly speed convergence at the higher resolutions, and 5) A rapid noniterative initial estimate of z obtained by exploiting the special symmetry of the equations obtained in the first linearization.
\r\n\r\nThe algorithm is extensively demonstrated on 200 by 200 pixel synthetic \"images\" generated from digital topographic data for northern Utah over a range of phase angles. Rms error in the solution is ~ 22 m, out of ~ 660 m total relief. The error is dominated by \"stripes\" with the same azimuth as the light source, resulting from use of the roughness criterion in lieu of boundary conditions; the rms error along profiles parallel to the stripes is only ~ 2-8 m, depending on the phase angle. Satisfactory solutions are obtained even in the presence of quantization error, noise, and moderate blur in the image.
\r\n\r\nApplications of the PC algorithm to both remote sensing and photomicrography are sketched; a photoclinometric map of a low-relief Precambrian era fossil is presented as an example of the latter. Prospects for dealing with photometrically inhomogeneous surfaces, and an extension of the method to the analysis of side-looking radar data (\"radarclinometry\") are also discussed.
", "doi": "10.7907/T5PT-S948", "publication_date": "1987", "thesis_type": "phd", "thesis_year": "1987" }, { "id": "thesis:10448", "collection": "thesis", "collection_id": "10448", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:09222017-142706466", "primary_object_url": { "basename": "Romani_RW_1987.pdf", "content": "final", "filesize": 70003746, "license": "other", "mime_type": "application/pdf", "url": "/10448/1/Romani_RW_1987.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "Neutron Stars Observations as Astrophysical Probes", "author": [ { "family_name": "Romani", "given_name": "Roger William", "orcid": "0000-0001-6711-3286", "clpid": "Romani-Roger-William" } ], "thesis_advisor": [ { "family_name": "Blandford", "given_name": "Roger D.", "clpid": "Blandford-R-D" } ], "thesis_committee": [ { "family_name": "Blandford", "given_name": "Roger D.", "clpid": "Blandford-R-D" }, { "family_name": "Goldreich", "given_name": "Peter Martin", "clpid": "Goldreich-P-M" }, { "family_name": "Tombrello", "given_name": "Thomas A.", "clpid": "Tombrello-T-A" }, { "family_name": "Readhead", "given_name": "Anthony C. S.", "orcid": "0000-0001-9152-961X", "clpid": "Readhead-A-C-S" } ], "local_group": [ { "literal": "TAPIR" }, { "literal": "div_pma" } ], "abstract": "Several aspects of observations of neutron stars and compact extragalactic radio sources are considered, with particular regard to their use in constraining certain astrophysical phenomena.
\r\n\r\nA theoretical treatment of the pulse arrival time analysis of millisecond pulsars is made; we consider how a detailed timing analysis can be used to quantitatively probe noise processes affecting the pulsar period and the propagation of the radiation. The intrinsic noise may be used to study the neutron star interior, while propagation effects due to gravitational perturbations of the neutron star and interstellar refraction of the emitted radio waves provide probes of the pulsar environment and the intervening plasma. In addition, important constraints on the background of cosmological gravitational radiation can be derived from timing such pulsars.
\r\n\r\nWe consider the thermal X-rays emitted from a warm (105K \u2272 Teff \u2272 3 x 106 K) neutron star, either cooling from its initial formation or heated by internal dissipation, accretion, etc. Constructing model atmospheres appropriate to such stars with various effective temperatures and elemental abundances, we calculate their emergent spectra and the bolometric correction for observation bands of various X-ray satellites. We conclude that the present limits on neutron star surface flux are even more constraining than those derived assuming that the spectra are blackbody and examine how this effects models of neutron star interiors, formation and cooling. We also examine the consequences of similar X-ray observations for neutron star models of various gamma-ray stars.
\r\n\r\nThe refraction of radio waves from pulsars and other compact sources by interstellar plasma is also studied. We show how pulsar observations, in particular, can be used to characterise the large scale inhomogeneities in the ionized ISM and compute a number of observable effects for various electron density perturbation spectra. It is shown how similar refraction can account for the low and intermediate frequency variation of compact extragalactic radio sources. We argue that the observations indicate that more power is present in the large scale fluctuations than previously believed. In addition, single ~1014 cm scale clouds in a previously unrecognized dense, ionised phase of the ISM can apparently dominate the refractive scintillation for some lines of sight.
", "doi": "10.7907/txfg-q107", "publication_date": "1987", "thesis_type": "phd", "thesis_year": "1987" }, { "id": "thesis:7452", "collection": "thesis", "collection_id": "7452", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:01292013-151449809", "primary_object_url": { "basename": "Friedson_aj_1987.pdf", "content": "final", "filesize": 33130951, "license": "other", "mime_type": "application/pdf", "url": "/7452/1/Friedson_aj_1987.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "I. Meridional Energy Balance of Uranus. II. Viscosity of Rock-Ice Mixtures. III. The Thermosphere of Titan", "author": [ { "family_name": "Friedson", "given_name": "Andrew James", "orcid": "0000-0002-7712-0583", "clpid": "Friedson-Andrew-James" } ], "thesis_advisor": [ { "family_name": "Ingersoll", "given_name": "Andrew P.", "orcid": "0000-0002-2035-9198", "clpid": "Ingersoll-A-P" } ], "thesis_committee": [ { "family_name": "Yung", "given_name": "Yuk L.", "orcid": "0000-0002-4263-2562", "clpid": "Yung-Y-L" }, { "family_name": "Goldreich", "given_name": "Peter Martin", "clpid": "Goldreich-P-M" }, { "family_name": "Ingersoll", "given_name": "Andrew P.", "orcid": "0000-0002-2035-9198", "clpid": "Ingersoll-A-P" }, { "family_name": "Muhleman", "given_name": "Duane Owen", "clpid": "Muhleman-D-O" }, { "family_name": "Stevenson", "given_name": "David John", "orcid": "0000-0001-9432-7159", "clpid": "Stevenson-D-J" } ], "local_group": [ { "literal": "Astronomy Department" }, { "literal": "div_gps" } ], "abstract": "Part I:
\r\n\r\nThe seasonal meridional energy balance and thermal structure of the atmosphere of Uranus is investigated using a two-dimensional radiative-convective-dynamical model. Diurnal-average temperatures and heat fluxes are calculated as a function of pressure, latitude, and season. In addition to treating radiation and small-scale convection in a manner typical of conventional radiative-convective models, the dynamical heat fluxes due to large-scale baroclinic eddies are included and parameterized using a mixing length formulation (Stone, 1972; Ingersoll and Porco, 1978). The atmosphere is assumed to be bounded below by an adiabatic, fluid interior with a single value of potential temperature at all latitudes. The internal heat flux is found to vary with latitude and season. The total internal power and the global enthalpy storage rate are seen to oscillate in phase with a period of 1/2 Uranian year. On an annual-average basis, equatorward heat transport can take place in both the atmosphere and the convective interior. For a weak internal heat source, the meridional transport takes place predominantly in the atmosphere. If the internal heat source is larger, a greater share of the transport is taken up by the interior. For a value of the internal heat near the current upper limit for Uranus (~27% of the absorbed sunlight), about 1/3 of the equatorward heat transport at mid-latitudes occurs in the interior. For a given internal heat source, placing the peak of the solar heating at high altitudes or depositing the solar energy into a narrow altitude range favors heat transport by the atmosphere over the interior. Deep penetration of sunlight favors transport by the interior. For the time corresponding to the Voyager 2 Uranus encounter, the effective temperature at the south (sunlit) pole is calculated to be ~1.5 K higher than that at the equator. Horizontal contrasts of the mean 450-900 mbar temperature are found to be less than \u2264 1.5 K, in fair agreement with Voyager 2 IRIS results (Hanel et al., 1986), but the model fails to reproduce the local minimum in this temperature seen at 30\u00b0S. Nevertheless, it is concl uded that meridional heat transport in the atmosphere is efficient in keeping seasonal horizontal temperature contrasts below those predicted by radiative-convective models (Wallace, 1983).
\r\n\r\nPart II:
\r\n\r\nTheory and experiments are used to establish lower and upper bounds on the ratio of actual viscosity to pure ice viscosity for a suspension of rock particles in a water ice matrix. For typical conditions encountered in icy satellites, this ratio is of order ten or possibly larger, depending on unknown factors such as the particle size distribution. It is shown that even this modest increase in viscosity may be enough to have caused a failure of solidstate convective self-regulation early in the evolution of a homogeneous, rock-water ice satellite, provided the satellite is large enough and sufficiently silicate-rich. The criteria for this failure are satisfied by Ganymede and are marginal for Callisto, if the silicates are hydrated. Failure of self-regulation means that the viscosity is too high for the interior to remain completely solid and eliminate the heat production of long-lived radioisotopes by solid state convection. Partial melting of the ice then occurs. It is further shown that satellites of this size may then undergo runaway differentiation into a rock core and almost pure ice mantle, because the gravitational energy release is sufficient to melt nearly all the ice, and the Rayleigh-Taylor instability time scale is short. (Although the high pressure phases of ice melt, the resulting water quickly refreezes at a higher level.) We conjecture that these results explain the striking surface dissimilarity of Ganymede and Callisto, if these satellites accreted cold and undifferentiated. Ganymede may have gone supercritical (melted and differentiated) because of a failure of self-regulation, whereas Callisto remained undifferentiated to the present day. Like all proposed explanations for the Ganymede-Callisto dichotomy, this conjecture cannot be quantified with confidence, because of inadequate or incomplete observations, theory and experimental data.
\r\n\r\nPart III:
\r\n\r\nThe diurnal variation of the vertical structure of Titan's thermosphere is calculated through simultaneous solution of the equations of heat transfer and hydrostatic equilibrium. The temperature and density profiles are found above the mesopause. The dynamical response of the thermosphere to heating is for the most part neglected. Nevertheless, we are able to draw some interesting qualitative and quantitative conclusions regarding the vertical structure. Heating of the upper thermosphere occurs primarily through absorption of solar Lyman \u03b1 radiation by methane, with an additional amount of heating (\u2264 20%) due to low-energy magnetospheric electron precipitation. The heat is conducted downward to the mesopause, where it is removed by IR cooling due principally to acetylene. The mesopause is found to occur where the density is 2.2 x 1012 cm-3 (736 km) and has a temperature of ~110 K. The exospheric temperature is unlikely to exceed 225 K in the course of a Titan day. The diurnally averaged exospheric temperature is in the range 187-197 K, depending on the amount of magnetospheric electron heating that is included in the model. The amplitude of the diurnal variation is found to be \u2264 28 K. We find that the vertical extent of the hydrogen cloud is too large to be explained in terms of simple thermal escape of hydrogen from a ~225 K exosphere and conclude that other processes must be important for populating or heating the neutral torus.
", "doi": "10.7907/65ch-hj35", "publication_date": "1987", "thesis_type": "phd", "thesis_year": "1987" }, { "id": "thesis:7455", "collection": "thesis", "collection_id": "7455", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:01302013-101810609", "primary_object_url": { "basename": "Wenkert_d_1986.pdf", "content": "final", "filesize": 28024085, "license": "other", "mime_type": "application/pdf", "url": "/7455/1/Wenkert_d_1986.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "Empirical Relations Between the Earth's Radiation Budget, Cloudiness, and Various Meteorological Parameters", "author": [ { "family_name": "Wenkert", "given_name": "Daniel", "orcid": "0009-0000-4203-7141", "clpid": "Wenkert-Daniel" } ], "thesis_advisor": [ { "family_name": "Ingersoll", "given_name": "Andrew P.", "orcid": "0000-0002-2035-9198", "clpid": "Ingersoll-A-P" } ], "thesis_committee": [ { "family_name": "Muhleman", "given_name": "Duane Owen", "clpid": "Muhleman-D-O" }, { "family_name": "Ingersoll", "given_name": "Andrew P.", "orcid": "0000-0002-2035-9198", "clpid": "Ingersoll-A-P" }, { "family_name": "Goldreich", "given_name": "Peter Martin", "clpid": "Goldreich-P-M" }, { "family_name": "Epstein", "given_name": "Samuel", "clpid": "Epstein-S" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "I have investigated the effect of variation of meteorological variables, cloudiness, and surface variables (such as albedo and continentality) on the reflected solar and emitted terrestrial radiation leaving the top of the atmosphere. The investigation was empirical and used the radiometric data from the scanner channels of the Earth Radiation Budget (ERB) instrument on Nimbus 7, cloudiness variables from analyses done by L. Stowe et al. on data from the Temperature and Humidity Infrared Radiometer (THIR) on Nimbus 7, and meteorological data from the FGGE (First GARP Global Experiment) Level III-b global weather analyses. The data were analysed on time scales of one day and spatial scales of about 450 km.
\r\n\r\nThis investigation had three main goals. The first goal was to determine the effect of cloudiness on the net radiation for various surface and atmospheric conditions during the period investigated (12 June to 18 June 1979). The second goal was to determine whether or not this type of linear analysis on a data set of synoptic time and space scales could be used for a reasonable and empirically accurate parameterization of radiation to be used in simple energy balance climate models (which are valid at vastly larger time and space scales than this data set). The third goal was to compare the regressions determined from this data set between radiation, cloudiness, and weather with the internal statistics developed in a Global Circulation Mode l (GCM), with the idea that eventually this type of linear analysis could be used as a constraint on GCMs used by the atmospheric science community.
\r\n", "doi": "10.7907/5TWR-Z031", "publication_date": "1986", "thesis_type": "phd", "thesis_year": "1986" }, { "id": "thesis:5720", "collection": "thesis", "collection_id": "5720", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:04162010-092926816", "primary_object_url": { "basename": "Paige_da_1985.pdf", "content": "final", "filesize": 7612070, "license": "other", "mime_type": "application/pdf", "url": "/5720/1/Paige_da_1985.pdf", "version": "v5.0.0" }, "type": "thesis", "title": "The Annual Heat Balance of the Martian Polar Caps from Viking Observations", "author": [ { "family_name": "Paige", "given_name": "David Abbey, Jr.", "orcid": "0009-0001-6122-9904", "clpid": "Paige-David-Abbey-Jr" } ], "thesis_advisor": [ { "family_name": "Ingersoll", "given_name": "Andrew P.", "orcid": "0000-0002-2035-9198", "clpid": "Ingersoll-A-P" } ], "thesis_committee": [ { "family_name": "Stevenson", "given_name": "David John", "orcid": "0000-0001-9432-7159", "clpid": "Stevenson-D-J" }, { "family_name": "Murray", "given_name": "Bruce C.", "clpid": "Murray-B-C" }, { "family_name": "Morgan", "given_name": "James J.", "clpid": "Morgan-J-J" }, { "family_name": "Muhleman", "given_name": "Duane Owen", "clpid": "Muhleman-D-O" }, { "family_name": "Goldreich", "given_name": "Peter Martin", "clpid": "Goldreich-P-M" }, { "family_name": "Zurek", "given_name": "Richard W.", "clpid": "Zurek-Richard-W" }, { "family_name": "Ingersoll", "given_name": "Andrew P.", "orcid": "0000-0002-2035-9198", "clpid": "Ingersoll-A-P" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "This thesis presents the first measurements of the annual heat budgets of the polar caps of Mars from spacecraft observations. The primary motivation for this work is to understand why seasonal CO2 frost deposits at the north pole of Mars disappear in the summer, whereas seasonal CO2 deposits near the south pole do not. This behavior is not expected to first order because both Martian poles receive the same total amount of sunlight at the top of the atmosphere over the course of a year. Understanding why the Martian north and south polar caps behave in an asymmetric fashion is important because the vapor pressures of permanent polar CO2 deposits determine the planet-wide surface pressures of CO2 gas, which is the dominant constituent of the Martian atmosphere.
\r\n\r\nAnnual radiation budgets for the core regions of the north and south polar caps are determined from solar reflectance and infrared emission observations obtained by the Infrared Thermal Mappers (IRTMs) aboard the two Viking orbiters. The results show that the absence of CO2 frost at the north pole during summer is primarily due to an asymmetry in the rates of CO2 frost sublimation at surface in the north and south during spring. Further analysis traces this difference to seasonal frost reflectivities being approximately 20% lower in the north than in the south during late spring. It is shown that seasonal frost deposits at the poles demonstrate a remarkable tendency to not become darker when contaminated with dust, and to become brighter with increasing rates of solar illumination. Since peak solar illumination rates are presently higher at the south pole than the north pole because of the large eccentricity of Mars' orbit, the tendency for the frost to become brighter with increasing rates of solar illumination explains the asymmetry. The tendency for the frost to not become darker when contaminated by dust explains why the seasonal behavior of the Martian polar caps is highly repeatable from year to year despite interannual variations in the occurrence of Martian global dust storms.
\r\n\r\nIt is suggested that the unexpected properties of Martian seasonal frost deposits revealed by the results of this study are caused by the tendency for dust particles within the frost to absorb solar radiation, sublimate the solid CO2 that supports them and sink into the frost. If the current behavior of Martian CO2 frost is an indicator to past events, then interactions between dust and frost have exerted a powerful stabilizing influence on the Martian climate system.
", "doi": "10.7907/DPB3-P589", "publication_date": "1985", "thesis_type": "phd", "thesis_year": "1985" }, { "id": "thesis:3395", "collection": "thesis", "collection_id": "3395", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-09082008-150750", "primary_object_url": { "basename": "Fillmore_ja_1985.pdf", "content": "final", "filesize": 3975765, "license": "other", "mime_type": "application/pdf", "url": "/3395/1/Fillmore_ja_1985.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "A Study on the Formation and Dynamics of Galaxies", "author": [ { "family_name": "Fillmore", "given_name": "James Arthur", "clpid": "Fillmore-James-Arthur" } ], "thesis_advisor": [ { "family_name": "Goldreich", "given_name": "Peter Martin", "clpid": "Goldreich-P-M" } ], "thesis_committee": [ { "family_name": "Goldreich", "given_name": "Peter Martin", "clpid": "Goldreich-P-M" }, { "family_name": "Sargent", "given_name": "Wallace L. W.", "clpid": "Sargent-W-L-W" }, { "family_name": "Blandford", "given_name": "Roger D.", "clpid": "Blandford-R-D" }, { "family_name": "Schmidt", "given_name": "Maarten", "clpid": "Schmidt-M" } ], "local_group": [ { "literal": "Astronomy Department" }, { "literal": "div_pma" } ], "abstract": "The first half of this thesis is a study on the growth of perturbations in the early universe which might lead to galaxies, clusters of galaxies, or regions void of galaxies.
\r\n\r\nThe growth of self-similar perturbations in an Einstein-deSitter universe with cold, collisionless particles is investigated. Three classes of solutions are obtained; one each with planar, cylindrical, and spherical symmetry. The solutions follow the development of structure in both the linear and nonlinear regimes.
\r\n\r\nSelf-similar spherical voids which develop from initially underdense regions are also investigated. The character of each solution depends upon the initial density deficit. Steep perturbations result in voids bounded by overdense shells with sharp edges.
\r\n\r\nThe second half of this thesis details solutions of steady-state axisymmetric models of elliptical and disk galaxies, and considers which observable properties can be used as diagnostics of the kinematic configuration of the spheroidal component of these systems.
\r\n\r\nTwo component mass models are fitted to surface brightness measurements and used to fit kinematic models to the velocity data. The models with constant mass-to-light ratios and isotropic velocity dispersions adequately fit the inner regions of spiral galaxies with three caveats:
\r\n\r\n(i) Several galaxies show significant differences between the two sides of the major axis in both their rotation rate and velocity dispersion. While the differences might be caused by non-axisymmetric potentials, variations in the line-of-sight extinction are a more likely cause.
\r\n\r\n(ii) The inner segment (R \u2264 1 kpc) of the emission line (gas) rotation curve falls below the predicted circular velocity derived from the stellar velocities. We rule out a variation in the mass-to-light ratio as a cause for this discrepancy because M/L would have to significantly decrease at small radii; this trend is opposite to typical expectations of M/L. Significant emission from gas produced by stellar mass loss, particularly planetary nebulae, which is not yet settled into the disk might explain this observation.
\r\n\r\n(iii) Some of the bulges are flatter than one would expect from their rotation rate assuming isotropic random motions, but this additional flattening could be caused by the disk potential.
\r\n\r\nSelf-consistent solutions of the stellar hydrodynamic equations for systems with isodensity surfaces which are concentric oblate spheroids and have constant mass-to-light ratios are presented. Various kinematic configurations are constructed to develop observational diagnostics which can distinguish these configurations. Because the inclination and true flattening of each elliptical is indeterminable, several kinematically distinct configurations are indistinguishable. Observations can uniquely characterize only those galaxies which lie at certain kinematic extremes.
\r\n", "doi": "10.7907/b70x-qk59", "publication_date": "1985", "thesis_type": "phd", "thesis_year": "1985" }, { "id": "thesis:3328", "collection": "thesis", "collection_id": "3328", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-09042008-105047", "primary_object_url": { "basename": "Sahai_r_1985.pdf", "content": "final", "filesize": 3296227, "license": "other", "mime_type": "application/pdf", "url": "/3328/1/Sahai_r_1985.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "Circumstellar Shells of Late-Type Stars: a Study at Millimeter and Infrared Wavelengths", "author": [ { "family_name": "Sahai", "given_name": "Raghvendra", "orcid": "0000-0002-6858-5063", "clpid": "Sahai-Raghvendra" } ], "thesis_advisor": [ { "family_name": "Scoville", "given_name": "Nicholas Zabriskie", "orcid": "0000-0002-0438-3323", "clpid": "Scoville-N-Z" } ], "thesis_committee": [ { "family_name": "Goldreich", "given_name": "Peter Martin", "clpid": "Goldreich-P-M" }, { "family_name": "Neugebauer", "given_name": "Gerry", "clpid": "Neugebauer-G" }, { "family_name": "Phillips", "given_name": "Thomas G.", "clpid": "Phillips-T-G" }, { "family_name": "Wannier", "given_name": "Peter G.", "clpid": "Wannier-P-G" }, { "family_name": "Scoville", "given_name": "Nicholas Zabriskie", "orcid": "0000-0002-0438-3323", "clpid": "Scoville-N-Z" } ], "local_group": [ { "literal": "Astronomy Department" }, { "literal": "div_pma" } ], "abstract": "This thesis describes an investigation of the physical conditions and molecular abundances in mass-loss envelopes around late-type stars based on millimeter and near infrared spectroscopy, concentrating on the high mass loss, carbon-rich star IRC +10216.
\r\n\r\nThe first part of this thesis is a multi-transition study of the rotational spectrum of SiS from the IRC +10216 envelope. The observational results are described in Chapter 2. A general numerical model to calculate the excitation and radiative transfer for rotation and vibration-rotation lines in circumstellar envelopes is developed in Chapter 3.
\r\n\r\nApplying this model to fit the observed SiS lines from IRC +10216 (Chapter 4), we find that the undissociated abundance [SiS]/[H2] in the shielded inner regions of the circumstellar shell is ~2.4 x 10-7, roughly a factor of 100 smaller than that predicted previously by chemical models. The SiS density falls steeply with radius, reaching one-half the undissociated abundance at r = 9 x 1016 cms. We show that a) Si, not S depletion is responsible for the low SiS abundance, and b) most of the available Si has probably been used up in forming SiC grains in the cool IRC +10216 atmosphere.
\r\n\r\nVariations in the 13 \u00b5m infrared flux over the 644 day light-cycle of IRC +10216 produce observable changes in some of the SiS lines. Sharp cusps in the J = 5-4 line wings, observed with the Onsala 20 m antenna, are explained in terms of weak maser emission at maximum light. The model predicts a different shape for this line at minimum light, in excellent agreement with a recent Onsala observation. Line coincidences, involving 13 \u00b5m transitions of HCN and C2H2 (not considered in the model), may be responsible for poor fits to some of the SiS rotational spectrum.
\r\n\r\nA sensitive search for SiS J = 7-6 and J = 6-5 lines in other carbon-rich, oxygen-rich, and S-type circumstellar shells was also conducted (Chapter 2). Three new SiS sources, CIT 6, CRL 2688 and IRC +20370, all of which are carbon-rich were detected, in agreement with the chemical equilibrium models predicting SiS to be significantly more abundant in a carbon-rich environment than in an oxygen-rich environment.
\r\n\r\nThe second part of the thesis (Chapters 5 and 6) deals with the investigation of physical conditions in the inner (r ~ 2\") envelope of IRC +10216 -- a scale size that has never been observed previously. We have devised a new observational technique, employing an annular aperture (size 2 - 3.45\") to measure extended emission from resonant-scattered photons in the 4.6 \u00b5m CO vibration-rotation band from IRC +10216. In addition to the expected emission up to the expansion velocity of the envelope, both CO and 13CO show evidence of high velocity features in the blue wing of the line, beyond the 15 km s-1 expansion velocity (Chapter 5).
\r\n\r\nIn order to derive physical quantities from the many P and R branch lines present in the infrared spectra, we develop an analytical model to calculate the excitation of these lines due to radiative pumping by thermal emission from circumstellar dust (Chapter 6). The lines are optically thick, and trapping of line radiation has been included. The model emission intensity is found to vary in a simple manner with radius, velocity, J value of the lower state, and the kinetic temperature (which we expect characterises the populations of the V = 0 rotational levels). Our model shows the V = 1 rotational level populations to be in equilibrium with the kinetic temperature despite being excited by infrared radiation.
\r\n\r\nWe derive the following results for the IRC +10216 inner envelope:
\r\n\r\ni) The kinetic temperature at radius r = 2\" is ~ 244 K, roughly twice the extrapolation of the Kwan and Hill (1977) thermodynamic model. This measurement forces revision of analyses of infrared absorption lines in which the radial information was derived assuming a temperature profile (known a priori).
\r\n\r\nii) The gas density in the inner regions of the envelope is characterised by a minimum mass loss rate of
\r\n\r\n[Equation; see abstract in scanned thesis for details].
\r\n", "doi": "10.7907/yfv7-n741", "publication_date": "1985", "thesis_type": "phd", "thesis_year": "1985" }, { "id": "thesis:3474", "collection": "thesis", "collection_id": "3474", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-09112008-091427", "primary_object_url": { "basename": "Hernquist_l_1985.pdf", "content": "final", "filesize": 10276056, "license": "other", "mime_type": "application/pdf", "url": "/3474/1/Hernquist_l_1985.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "Thermal and Magnetic Properties of Neutron Stars", "author": [ { "family_name": "Hernquist", "given_name": "Lars Eric", "orcid": "0000-0001-6950-1629", "clpid": "Hernquist-Lars-Eric" } ], "thesis_advisor": [ { "family_name": "Blandford", "given_name": "Roger D.", "clpid": "Blandford-R-D" } ], "thesis_committee": [ { "family_name": "Blandford", "given_name": "Roger D.", "clpid": "Blandford-R-D" }, { "family_name": "Goldreich", "given_name": "Peter Martin", "clpid": "Goldreich-P-M" }, { "family_name": "Tombrello", "given_name": "Thomas A.", "clpid": "Tombrello-T-A" }, { "family_name": "Stevenson", "given_name": "David John", "orcid": "0000-0001-9432-7159", "clpid": "Stevenson-D-J" } ], "local_group": [ { "literal": "TAPIR" }, { "literal": "div_pma" } ], "abstract": "The interaction of the magnetic field with the heat flux in neutron stars is investigated.
\r\n\r\nIt is proposed that the magnetic field develops as a result of thermal processes in the liquid and solid phases of neutron star envelopes. Necessary conditions for the growth to occur are derived and it is shown that surface fields comparable to those observed would result. The magnetization of neutron stars in binary systems (which have magnetic properties differing substantially from those of isolated pulsars) can be explained by thermal processes associated with accretion flows.
\r\n\r\nIn order to study magnetic effects on neutron star cooling a number of subsidiary issues are considered.
\r\n\r\nThe thermal structure of unmagnetized neutron star envelopes is examined using approximate analytical models. From the results it is possible to justify a number of simplifying assumptions and extend them to the magnetized case. For example, it is shown that an accurate treatment of photon transport is not required in order to determine the relation between the heat flux and the core temperature of neutron stars.
\r\n\r\nThe effect of the field on the magnetic properties of the electron gas in neutron star crusts is considered. It is shown that the gas is unstable to the formation of domains of alternating magnetization. It is further argued that the domain structure will have a negligible influence on the heat flux because of the small free energy associated with the domains.
\r\n\r\nThe influence of the field on the electron transport properties of neutron star envelopes is examined in detail. Accurate expressions are derived for all components of the relevant transport tensors, taking into account quantum mechanical and relativistic effects. In addition, allowance is made for arbitrary degree of degeneracy and scattering mechanism.
\r\n\r\nFinally, these results are used to study the thermal structure of magnetized neutron star envelopes. It is shown that the enhancement in the heat flux due to quantum effects is almost completely canceled by the suppression of the heat flux due to geometrical effects. Thus the magnetic field is expected to play only a minor role in neutron star cooling, contrary to earlier claims.
\r\n", "doi": "10.7907/ajp7-kr29", "publication_date": "1985", "thesis_type": "phd", "thesis_year": "1985" }, { "id": "thesis:3405", "collection": "thesis", "collection_id": "3405", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-09092008-083654", "primary_object_url": { "basename": "Filippenko_av_1984.pdf", "content": "final", "filesize": 9870292, "license": "other", "mime_type": "application/pdf", "url": "/3405/1/Filippenko_av_1984.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "Physical Conditions in Low-Luminosity Active Galactic Nuclei", "author": [ { "family_name": "Filippenko", "given_name": "Alexei Vladimir", "orcid": "0000-0003-3460-0103", "clpid": "Filippenko-Alexei-Vladimir" } ], "thesis_advisor": [ { "family_name": "Sargent", "given_name": "Wallace L. W.", "clpid": "Sargent-W-L-W" } ], "thesis_committee": [ { "family_name": "Sargent", "given_name": "Wallace L. W.", "clpid": "Sargent-W-L-W" }, { "family_name": "Cohen", "given_name": "Marshall H.", "clpid": "Cohen-M-H" }, { "family_name": "Oke", "given_name": "J. Beverly", "clpid": "Oke-J-B" }, { "family_name": "Goldreich", "given_name": "Peter Martin", "clpid": "Goldreich-P-M" }, { "family_name": "Mould", "given_name": "Jeremy R.", "orcid": "0000-0003-3820-1740", "clpid": "Mould-J-R" } ], "local_group": [ { "literal": "Astronomy Department" }, { "literal": "Caltech Distinguished Alumni Award" }, { "literal": "div_pma" } ], "abstract": "Physical conditions in the nuclei of emission-line galaxies are investigated by analyzing their continua and optical emission lines.
\r\n\r\nThe strength and shape of the nonstellar continuum is derived for nine Seyfert galaxies. As in QSOs, it is described by a power law with slope ~ -1.1, and in the most luminous objects it flattens at blue and UV wavelengths. Even at minimum brightness it has no short-wavelength cutoff near 1 \u03bcm, eliminating the possibility that the near-infrared flux is dominated by thermal emission from hot dust grains.
\r\n\r\nA detailed analysis at optical and X-ray energies demonstrates that gas in the nucleus of NGC 7213 is photoionized by nonstellar radiation, even though it also exhibits the spectral characteristics of galaxies thought to be heated by shocks. After careful removal of the strong stellar component, it is shown how these \"shock\" features are actually more consistent with photoionization. The key is a large range of densities (~ 103-107cm-3) in the narrow-line clouds, and a fairly low ionization parameter.
\r\n\r\nSimilar studies of three additional galaxies confirm these results and strengthen the hypothesis that gas in LINERs (\"low ionization nuclear emission-line regions\") is photoionized rather than shock-heated. A tight correlation is found between the width of forbidden lines and their critical density. Moreover, much of the ionizing radiation is probably produced by a hot (T ~ 104-105 K) accretion disk.
\r\n\r\nA sensitive survey indicates that ~ 30-40% of LINERS exhibit weak, broad H\u03b1 emission. The emission-line intensity ratios are consistent with photoionization by a nonstellar continuum, indicating the presence of activity similar to (but much milder than) that of QSOs in a significant fraction of all nearby galaxies.
\r\n\r\nRelative intensities of emission lines in the narrow-line X-ray galaxy NGC 7314 are typical of type 2 Seyferts, but their widths (FWHM ~ 120-150 km s-1) are remarkably small. Thus, nonstellar radiation need not be associated with rapid motions among the narrow-line clouds. The profile of the broad H\u03b1 emission suggests that gas flows ballistically away from the nucleus. Dust, which heavily reddens radiation from broad-line clouds, is probably located within or near the clouds themselves.
\r\n", "doi": "10.7907/34v9-vc35", "publication_date": "1984", "thesis_type": "phd", "thesis_year": "1984" }, { "id": "thesis:11210", "collection": "thesis", "collection_id": "11210", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:10012018-103419193", "type": "thesis", "title": "Photochemical Modeling of the Earth's Stratosphere", "author": [ { "family_name": "Froidevaux", "given_name": "Lucien", "orcid": "0000-0002-0681-1483", "clpid": "Froidevaux-Lucien" } ], "thesis_advisor": [ { "family_name": "Muhleman", "given_name": "Duane Owen", "clpid": "Muhleman-D-O" } ], "thesis_committee": [ { "family_name": "Muhleman", "given_name": "Duane Owen", "clpid": "Muhleman-D-O" }, { "family_name": "DeMore", "given_name": "William B.", "clpid": "DeMore-William-B" }, { "family_name": "Epstein", "given_name": "Samuel", "clpid": "Epstein-S" }, { "family_name": "Goldreich", "given_name": "Peter Martin", "clpid": "Goldreich-P-M" }, { "family_name": "Yung", "given_name": "Yuk L.", "orcid": "0000-0002-4263-2562", "clpid": "Yung-Y-L" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "We have helped develop a one-dimensional photochemical model of the Earth's stratosphere, in order to provide an up-to-date comparison with mid-latitude observations. This work focuses on the present state of the stratosphere, and includes studies of the radiation field (absorption and scattering), the important partitioning and vertical distribution of halo-carbons and their products, as well as certain intriguing discrepancies related to light and heavy ozone.
\r\n\r\nWe briefly comment on the detection by J. R. Herman and J. E. Mentall of a 10% ratio of total scattered flux to direct solar flux at a wavelength of about 200 nm and an altitude of 40 km. This ratio is over a factor of two higher than our theoretical results and cannot be explained without the existence of a scattering component not included in the model. We also explicitly demonstrate the first-order effects of the inclusion of sphericity (spherical shell atmosphere) on the stratospheric photochemistry at solar zenith angles close to 90\u00b0. The resulting changes in model concentrations for short-lived radicals such as O, OH, ClO, and NO are largest in the lower stratosphere, but relatively small compared to current observational uncertainties.
\r\n\r\nWe propose that a significant overestimate of the molecular oxygen absorption cross sections in the important spectral window from about 200 to 220 nm is in large part responsible for the discrepancy between observed and modeled vertical profiles of some halocarbons (CFCl3 in particular), as well as for the long-standing problem of simultaneously fitting N2O, CH4, CF2Cl2, and CFCl3 profiles with a single eddy diffusion model. Recent measurements of atmospheric transmission by J. R. Herman and coworkers seem to support this idea. The use of their proposed reduction in O2 cross sections leads to significant decreases in the CFCl3 concentration above about 20 km, with smaller reductions in N2O, CF2Cl2 and HNO3. The concentrations of CH4, H2, and CO are not significantly altered. Changes in other gases (including ozone) are also discussed, as well as the effect on eddy diffusion coefficients obtained from measurements of N2O or CH4 profiles in the stratosphere. Accurate determinations of these small O2 absorption cross sections are needed, since they affect the vertical distribution of halo-carbons in the stratosphere, and the lifetime of these species has an impact on ozone depletion estimates.
\r\n\r\nIn terms of the halocarbon decomposition products in the stratosphere, our model vertical distribution of ClO is shown to provide a reasonably good fit to the mean of available observations. As discussed by others, changes in certain rate constants affecting HOx in the lower stratosphere have led to decreases in model ClO concentrations by over a factor of three in the lower stratosphere, thus improving the shape of the vertical profile. In addition, the amount of upper stratospheric ClO has increased due to recent changes in the kinetics (reactions O + HO2, O + ClO, and possibly OH + HCl). The diurnal variation of ClO observed from the ground (microwave emission) by P. Solomon and coworkers is consistent with our model results in terms of the maximum day-to-night decrease in column abundance above about 30 km. However, the observed mid-morning increase is slower than theoretical values, while the predicted afternoon decrease might be too slow, even if one considers the uncertainties in photochemical data. This could indicate the existence of missing chemistry in the models. Although the different observations show somewhat contradictory results. Other observations (balloon-borne microwave spectroscopy and infrared laser radiometry) are also discussed in relation to our model. To first-order, indirect evidence for the breathing cycle between ClO and ClONO2 seems to have been established. The mean observed HCl mixing ratio profile decreases somewhat faster towards the lower stratosphere than model profiles, a discrepancy which has previously been noted, particularly at high latitudes. Measurements of ethane in the lower stratosphere seemed to indicate that the atomic chlorine concentration was three to five times lower than predicted, but more recent data do not show such a discrepancy.
\r\n\r\nThe fluorine products consist mostly of HF and COF2. We show that the main uncertainty for this system is the value of the quantum yield (as a function of wavelength) for COF2 photodissociation, which translates into a factor of three or more uncertainty in the ratio of HF to COF2 concentrations in the upper stratosphere. If this quantum yield has an average value close to 0.25, a better model fit to observations of HF and [HF]/[HCl] is obtained than if the value is close to unity. Simultaneous stratospheric measurements of COF2 and HF, as well as ClO and HCl, would greatly enhance our ability to test photochemical models of these halocarbon products.
\r\n\r\nFinally, we stress that, although generally good agreement is found between our model and observations of HOx, NOx, and ClOx species (involved in catalytic cycles destroying ozone), the mean observed mid-latitude ozone abundance from about 35 to 50 km is up to 50 or 60% greater than current model results. Certain observations of a 10 to 15% daytime increase in ozone concentration in the 30 to 40 km region are also puzzling, if real. We explore the model sensitivity to various input parameters and point out that, given the present uncertainties in photochemical laboratory data, no reasonable change in one or even three or four of these parameters can eliminate the ozone discrepancy. There might well be some missing chemistry in relation to the effectiveness of the loss processes for odd oxygen, or a (less likely) unknown significant O3 source. We have to understand the present upper stratospheric ozone distribution, before estimates of possible future ozone depletion can be made with confidence. We also discuss our understanding of heavy ozone photochemistry, which might be related to a light ozone photochemical source. Fast isotopic exchange processes between O and O2 will dominate the heavy odd oxygen chemistry, and we do not find any significant heavy ozone enhancement possibilities in the stratosphere, unless unusually large fractionation processes exist. The in situ mass spectrometer observations of a 40% enhancement in 18O32O2 near 30 km by K. Mauersberger remain a mystery, and further data collection -- possibly via infrared or microwave spectroscopy as well -- should be undertaken if this potentially significant discrepancy is to be understood.
", "doi": "10.7907/hzdt-5z21", "publication_date": "1984", "thesis_type": "phd", "thesis_year": "1984" }, { "id": "thesis:3404", "collection": "thesis", "collection_id": "3404", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-09092008-083043", "primary_object_url": { "basename": "Lichten_sm_1984.pdf", "content": "final", "filesize": 5636116, "license": "other", "mime_type": "application/pdf", "url": "/3404/1/Lichten_sm_1984.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "Turbulence and Mass Motion in Galactic Molecular Clouds", "author": [ { "family_name": "Lichten", "given_name": "Stephen Morris", "clpid": "Lichten-Stephen-Morris" } ], "thesis_advisor": [ { "family_name": "Wannier", "given_name": "Peter G.", "clpid": "Wannier-P-G" } ], "thesis_committee": [ { "family_name": "Phillips", "given_name": "Thomas G.", "clpid": "Phillips-T-G" }, { "family_name": "Oke", "given_name": "J. Beverly", "clpid": "Oke-J-B" }, { "family_name": "Goldreich", "given_name": "Peter Martin", "clpid": "Goldreich-P-M" }, { "family_name": "Wannier", "given_name": "Peter G.", "clpid": "Wannier-P-G" } ], "local_group": [ { "literal": "Owens Valley Radio Observatory (OVRO)" }, { "literal": "Astronomy Department" }, { "literal": "div_pma" } ], "abstract": "The main subject of this thesis is the origin and maintenance of supersonic gas motions in dense molecular clouds.
\r\n\r\nIn Chapters 1 and 2, we interpret and model millimeter wavelength CO line profiles whose broad wings and self-reversals provide clues about the nature of the observed supersonic motions. Broad molecular line wings provide evidence for high-velocity bipolar gas flows powered by strong stellar winds. The self-reversed CO line profiles are due in part to radiative transfer effects in molecular clouds which, in some cases, are expanding or contracting; Monte Carlo simulations of radiative transfer, however, demonstrate that cloud fragmentation may be responsible for some observed properties of the line profiles. The detection of broad-wing sources in quiescent, dark nebulae, shows that energetic outflows are common in a wide range of molecular clouds.
\r\n\r\nIn Chapter 3, our high resolution maps of molecular and atomic line emission across molecular cloud edges show that these clouds are embedded in warm H I halos which appear in emission against the galactic H I background. We also find that molecular cloud internal motions may be correlated with the H I halo temperature; however, the halo masses are much less than those of the molecular clouds and exert only a limited influence on internal cloud kinematics.
\r\n\r\nThe statistical and autocorrelation analyses of Chapters 4 and 5 show that molecular clouds are clumpy and contain hundreds of turbulent fragments whose relative velocities are supersonic, but whose internal velocity dispersions are not. Shock dissipation processes, clump collisions, and gas compression have major roles in molecular cloud kinematics. Our observations indicate that turbulent energy is supplied at small scales, as opposed to the dissipationless energy transfer from large to small scales which is known to occur in incompressible fluids with high Reynolds numbers. Energetic outflows from embedded young stars may break apart, fragment, and compress portions of molecular clouds, and may be capable of originating and sustaining the supersonic turbulence. Additional observational and theoretical studies of cloud clumpiness and of the rate of energy transfer from stellar outflows to ambient molecular material, are required before this mechanism for cloud support can be evaluated.
\r\n", "doi": "10.7907/wbm2-9x67", "publication_date": "1984", "thesis_type": "phd", "thesis_year": "1984" }, { "id": "thesis:4438", "collection": "thesis", "collection_id": "4438", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-11072005-081513", "primary_object_url": { "basename": "Trimberger_sm_1983.pdf", "content": "final", "filesize": 7180994, "license": "other", "mime_type": "application/pdf", "url": "/4438/1/Trimberger_sm_1983.pdf", "version": "v2.0.0" }, "type": "thesis", "title": "Automated Performance Optimization of Custom Integrated Circuits", "author": [ { "family_name": "Trimberger", "given_name": "Stephen Mathias", "orcid": "0009-0006-5482-3362", "clpid": "Trimberger-Stephen-Mathias" } ], "thesis_advisor": [ { "family_name": "Kajiya", "given_name": "James Thomas", "clpid": "Kajiya-J-T" } ], "thesis_committee": [ { "family_name": "Kajiya", "given_name": "James Thomas", "clpid": "Kajiya-J-T" }, { "family_name": "Mead", "given_name": "Carver", "orcid": "0000-0003-4051-0462", "clpid": "Mead-C-A" }, { "family_name": "Seitz", "given_name": "Charles L.", "clpid": "Seitz-C-L" }, { "family_name": "Goldreich", "given_name": "Peter Martin", "clpid": "Goldreich-P-M" }, { "family_name": "Lewicki", "given_name": "George W.", "clpid": "Lewicki-G-W" } ], "local_group": [ { "literal": "div_eng" } ], "abstract": "The complexity of integrated circuits requires a hierarchical design methodology that allows the user to divide the problem into pieces, design each piece independently, and assemble the pieces into the complete system. The design hierarchy brings out composition problems, problems that are a property of the assembly as a whole, not of one single instance in the hierarchy.
\r\n\r\nRecent research has produced tools that automate part of the composition task - the logical connection of the pieces. However, these tools do not ensure that signals driven over these connections will be driven sufficiently to give reasonable cycle speed of the resulting chips. It is easily possible to specify an assembly in which a small-sized gate is required to drive an enormous load. Parasitic capacitance of the wiring made automatically by the logical connection tool can be the dominant source of delay, so assembly tools can actually worsen the performance of the circuit and hide this fact from the designer.
\r\n\r\nWhen required to make large circuits, automated layout tools such as PLA generators can blindly make layouts that give abysmally poor performance. Here again, the delay is in a part of circuit that the designer did not specify, so it is hidden. Finding and correcting these problems is a difficult and time-consuming task in integrated circuit design, and one that consumes vastly more people's time and computer time than the simple assembly of the chip.
\r\n\r\nThe task of guaranteeing that circuits meet performance specifications has been left mainly to the designer. Computer aided design has provided analysis tools, tools that tell the designer the performance statistics of the current design. It is then the designer's burden to interpret the performance statistics and use them as guides to make changes in the circuit.
\r\n\r\nThis thesis views performance optimization as an electrical composition task. Poor performance as a result of mismatched loads on devices is a problem of composition and should be corrected by the composition tool. Such a tool is presented in this thesis -- a program that automatically sizes transistors in a symbolic description of a chip to match the load the transistors are driving. The results are encouraging: they show that delays can be cut by a factor of two in many current designs.
", "doi": "10.7907/8YDZ-G637", "publication_date": "1983", "thesis_type": "phd", "thesis_year": "1983" }, { "id": "thesis:4825", "collection": "thesis", "collection_id": "4825", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-12072004-143533", "primary_object_url": { "basename": "Zwiebach_b_1983.pdf", "content": "final", "filesize": 5895459, "license": "other", "mime_type": "application/pdf", "url": "/4825/1/Zwiebach_b_1983.pdf", "version": "v2.0.0" }, "type": "thesis", "title": "Use of Superspace Geometry to Find All Supergravity Theories: Case of N = 4 and SO(4) Symmetry", "author": [ { "family_name": "Zwiebach", "given_name": "Barton", "orcid": "0000-0001-6504-3210", "clpid": "Zwiebach-Barton" } ], "thesis_advisor": [ { "family_name": "Gell-Mann", "given_name": "Murray", "clpid": "Gell-Mann-M" } ], "thesis_committee": [ { "family_name": "Gell-Mann", "given_name": "Murray", "clpid": "Gell-Mann-M" }, { "family_name": "Schwarz", "given_name": "John H.", "orcid": "0000-0001-9861-7559", "clpid": "Schwarz-J-H" }, { "family_name": "Peck", "given_name": "Charles W.", "clpid": "Peck-C-W" }, { "family_name": "Goldreich", "given_name": "Peter Martin", "clpid": "Goldreich-P-M" } ], "local_group": [ { "literal": "div_pma" } ], "abstract": "The main subject of this thesis is the study of the N = 4 supergravity theories. Superspace geometry is used to search for all N = 4 supergravities with at least SO(4) global symmetry. It is found that the general solution to the unconstrained Bianchi Identities, with the field content of N = 4 supergravity, are equivalent to the known SO(4) and SU(4) supergravities up to field redefinitions. Therefore the field content determines uniquely the N = 4 theories and further constraints are not necessary.
\r\n\r\nThe SO(4) supergravity is gauged with two coupling constants and a new theory with positive cosmological constant and spontaneous breaking of the four supersymmetries is found. The presence of scalar fields in the kinetic term of the vectors is seen to make the values of the physical gauge coupling constants depend on the choice of vacuum.
", "doi": "10.7907/PC47-EM20", "publication_date": "1983", "thesis_type": "phd", "thesis_year": "1983" }, { "id": "thesis:4069", "collection": "thesis", "collection_id": "4069", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-10132005-145503", "primary_object_url": { "basename": "Jewitt_d_1983.pdf", "content": "final", "filesize": 12757025, "license": "other", "mime_type": "application/pdf", "url": "/4069/1/Jewitt_d_1983.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "I. Physical Studies of Distant Comets. II. Morphologies of Planetary Nebulae", "author": [ { "family_name": "Jewitt", "given_name": "David Clifford", "orcid": "0000-0003-0262-8160", "clpid": "Jewitt-David-Clifford" } ], "thesis_advisor": [ { "family_name": "Yung", "given_name": "Yuk L.", "orcid": "0000-0002-4263-2562", "clpid": "Yung-Y-L" } ], "thesis_committee": [ { "family_name": "Yung", "given_name": "Yuk L.", "orcid": "0000-0002-4263-2562", "clpid": "Yung-Y-L" }, { "family_name": "Goldreich", "given_name": "Peter Martin", "clpid": "Goldreich-P-M" }, { "family_name": "Westphal", "given_name": "James A.", "clpid": "Westphal-J-A" }, { "family_name": "Searle", "given_name": "Leonard", "clpid": "Searle-Leonard" }, { "family_name": "Soifer", "given_name": "B. Thomas", "clpid": "Soifer-B-T" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "Part 1:
\r\n\r\nBroadband observations of comets P/Stephan-Oterma (1980g), Bowell (1980b) and Panther (1980u) in the visual (0.5 \u227e \u03bb(\u00b5m) \u227e 0.9) and infrared (1.2 \u227e \u03bb(\u00b5m) \u227e 20) wavelength regions are reported together with measurements in the 1.5 to 2.4 \u00b5m wavelength range having 5% spectral resolution. The visual data indicate the existence of solid grains in extended halos around the nuclei of the three comets. The visual photometric profiles of comets P/Stephan-Oterma and Panther are interpreted as evidence that grains around Panther and those close to the nucleus of P/Stephan-Oterma are sublimating. Broadband near infrared and thermal infrared measurements of comet Panther suggest the presence of 2 to 4 \u00b5m radius particles in the coma. The particles within a 5.8 x 106 diameter region centered on the comet have a total cross section of 108m2 and a near infrared geometric albedo of about 14%. Comet Bowell presents a total cross section of 3 x 108m2 within a 1.2 x 107m region centered on the comet and its coma grains also have an albedo of 14%.
\r\n\r\nThe near infrared spectrum of P/Stephan-Oterma is a featureless solar-reflection continuum. The near infrared spectra of Bowell and Panther exhibit features which are similar in the two comets. The spectral features are not due to H2O, CH4 or CO2 ices nor to emissions from gases released from the nuclei nor to reflection from mineral grains of known composition in the comae. The spectrum of solid ammonia provides the best match to the near infrared; it is nevertheless significantly different from the comet spectra.
\r\n\r\nThe synthesis of the visual data with the infrared data is attempted in terms of a model involving a mantle of volatile material on the nuclei of Bowell and Panther, but not on P/Stephan-Oterma. The composition of the mantle cannot be exactly specified from the existing data but a complex molecule incorporating the N-H bond may be present.
\r\n\r\nPart 2:
\r\n\r\nAn extensive series of observations of comet Bowell at optical and infrared wavelengths is summarized and interpreted in terms of a model of the outgassing of the nucleus. The observations indicate that the optical coma consists of large grains. The outer edge of the coma is expanding from the nucleus at 0.9 \u00b1 0.2 ms-1: extrapolation of the expansion suggests that the coma was ejected from the nucleus when the comet was at a heliocentric distance R ~ 10 AU. At this distance, water ice sublimation would be negligible. Models of the brightness of the comet as a function of R are compared with the measured brightness variation. Between R = 5.3 and 3.4 AU, the apparent cometary brightness changed by a factor of less than 20. Models which account for the equilibrium sublimation of volatiles from the nucleus predict much larger brightness variations. In particular, the models confirm that the sublimation of water ice does not control the activity of comet Bowell. The observations are consistent with the presence of an inert nucleus surrounded by a dissipating grain coma ejected impulsively at R ~ 10 AU. Strong OH production observed near R = 3.4 AU could be a result of the photodissociation of water molecules released from the coma grains by sublimation. However, near infrared spectra of the grains show no evidence for the presence of OH. Instead, several absorptions similar to the overtones of NH bond vibrations are observed. It is noted that the outgassing properties of the comet are similar to those of proton-bombarded laboratory ice specimens. Both the impulsive coma ejection and the peculiar near infrared spectrum may result from the presence of unstable compounds produced in the nucleus by cosmic ray bombardment. The activity of comet Bowell is quite unlike that exhibited by comets at small R, but may be representative of the properties of the distant comets.
\r\n\r\nPart 3:
\r\n\r\nThe spatial distribution of [CI] 9823, 9850 \u00c5 emission in NGC 6720 is reported. Like [01], the [CI] radiation appears enhanced in the region of the bright filaments. A few percent of the carbon atoms in the filaments are neutral. This neutral fraction is consistent with ionization equilibrium calculations made under the assumption of complete shielding of direct stellar radiation by hydrogen. The observed carbon lines are excited by photoelectrons produced from hydrogen by the nebular diffuse radiation field. The [CI] observations confirm that the filaments in NGC 6720 are regions of locally enhanced shielding.
\r\n\r\nPart 4:
\r\n\r\nThe preliminary results of a CCD survey designed to detect and investigate faint halos around planetary nebulae are described. A TI 800 x 800 pixel CCD was used to take deep exposures of 44 planetary nebulae. The exposures were mostly obtained through an Ha filter at the Cassegrainian focus of the Palomar 1.5 m telescope. Spatial resolutions of 1 to 2 arcsecond were obtained across 400 arcsecond wide fields. The images, which are in many cases considerably deeper than any previously taken, reveal numerous planetary nebula halos. About 2/3 of the studied nebulae possess extensive outer halos. In some nebulae the mass in the halo is comparable to the mass contained in the primary HII region. We have used the data to place constraints on the mode of origin of the halos. It is likely that the halos originate either by dynamical separation of a single ejected shell of gas, or by the ejection of two or more such shells from the central star. It is less likely that the halos are caused by excitation of the pre-planetary stellar wind and highly improbable that the halos represent reflection nebulae.
", "doi": "10.7907/f9ge-m194", "publication_date": "1983", "thesis_type": "phd", "thesis_year": "1983" }, { "id": "thesis:16226", "collection": "thesis", "collection_id": "16226", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:10312023-202011054", "primary_object_url": { "basename": "Pechmann_JB_1983.pdf", "content": "final", "filesize": 66438934, "license": "other", "mime_type": "application/pdf", "url": "/16226/1/Pechmann_JB_1983.pdf", "version": "v2.0.0" }, "type": "thesis", "title": "Thermal Tides in the Atmosphere of Venus", "author": [ { "family_name": "Pechmann", "given_name": "Judith Burt", "clpid": "Pechmann-Judith-Burt" } ], "thesis_advisor": [ { "family_name": "Goldreich", "given_name": "Peter Martin", "clpid": "Goldreich-P-M" } ], "thesis_committee": [ { "family_name": "Ingersoll", "given_name": "Andrew P.", "orcid": "0000-0002-2035-9198", "clpid": "Ingersoll-A-P" }, { "family_name": "Muhleman", "given_name": "Duane Owen", "clpid": "Muhleman-D-O" }, { "family_name": "Yung", "given_name": "Yuk L.", "orcid": "0000-0002-4263-2562", "clpid": "Yung-Y-L" }, { "family_name": "Harkrider", "given_name": "David G.", "clpid": "Harkrider-D-G" }, { "family_name": "Goldreich", "given_name": "Peter Martin", "clpid": "Goldreich-P-M" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "The daily variation in the absorption of sunlight by the atmosphere provides the forcing for thermal tides. In this thesis the response of the Venus atmosphere as a function of height and latitude to the diurnal and semidiurnal components of the forcing is calculated using a linearized primitive equation model. We specify the atmospheric mean state using data from the Pioneer Venus probes and orbiter, and solve for the first order tidal perturbation. Our forcing function is based on data returned by the solar flux radiometer on the Pioneer Venus sounder probe. The perturbation variables are discretized horizontally by spherical harmonics and vertically by finite elements. A semi\u00ad implicit time-stepping algorithm is used.
\r\n\r\nThe model results for Venus thermal tides are in agreement with the solar-fixed component of diurnal and semidiurnal brightness temperature fluctuations determined from Pioneer Venus orbiter infrared radiometer (OIR) data. Contrary to the prediction of classical tidal theory, the observed semidiurnal brightness temperature maxima occur before the forcing maxima from about 60 to 80 km. In the model, this phase lead is due to a long vertical wavelength (~30 km) from the cloud tops to 80 km. Also, the data unexpectedly show that the semidiurnal amplitude is larger than the diurnal over much of the region observed, even though the diurna1 forcing is about twice as great. The model's diurnal temperature amplitude is larger than that observed in the brightness temperature. However, convolution with the OIR weighting functions results in model brightness temperature amplitudes which are as small as the observed values because the vertical wavelength of the\r\ndiurnal tide is shorter than the width of the weighting functions.
\r\n\r\nThe success of the model increases our confidence in our knowledge of the mean state of the Venus atmosphere and provides us with the opportunity to determine the importance of energy and angular momentum transport by the tides. The zonally averaged vertically integrated tidal energy flux is significant compared to the zonally averaged imbalance in incoming solar radiation and outgoing infrared radiation from equatorial to mid-latitudes. However, the tides do not in general tend to reduce the imbalance by transporting heat poleward. The mean meridional circulation driven by this imbalance and the tidal energy flux consists of stacked direct and indirect Hadley cells. The angular momentum transport is upward and poleward in the direct cells. Since the transport is not upward at all altitudes, some other processes must be involved in maintaining the large shear in the mean zonal wind. The vertical transport by the tides is small compared to that of the mean circulation. However, the tides do transport a significant amount of angular momentum equatorward from mid-latitudes.
", "doi": "10.7907/5cd0-3q63", "publication_date": "1983", "thesis_type": "phd", "thesis_year": "1983" }, { "id": "thesis:3390", "collection": "thesis", "collection_id": "3390", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-09082008-132748", "type": "thesis", "title": "The Structure and Evolution of Interacting Binary Galaxies", "author": [ { "family_name": "Borne", "given_name": "Kirk Daniel", "orcid": "0000-0001-5608-255X", "clpid": "Borne-Kirk-Daniel" } ], "thesis_advisor": [ { "family_name": "Gunn", "given_name": "James E.", "clpid": "Gunn-J-E" } ], "thesis_committee": [ { "family_name": "Oke", "given_name": "J. Beverly", "clpid": "Oke-J-B" }, { "family_name": "Gunn", "given_name": "James E.", "clpid": "Gunn-James-E" }, { "family_name": "Sargent", "given_name": "Wallace L. W.", "clpid": "Sargent-W-L-W" }, { "family_name": "Goldreich", "given_name": "Peter Martin", "clpid": "Goldreich-P-M" } ], "local_group": [ { "literal": "Astronomy Department" }, { "literal": "div_pma" } ], "abstract": "A numerical code has been constructed for the study of the evolution of interacting binary galaxies. This \"multiple three-body\" algorithm (MTBA) essentially involves N concurrent three-body integrations; it is the sum of the interactions of the perturber with each of the N particles comprising the primary \"galaxy\" that determines the binary orbital evolution. MTBA incorporates a violent relaxation phase that allows the particles to redistribute themselves in the gravitational field of the perturber prior to the full binary orbital evolution calculation. This redistribution is important for systems with an initially strong tidal potential; their predicted merger times are 50-100% larger than previously estimated. Tabulated merger times for both circular and elliptical orbits demonstrate that typical close binary galaxies will merge in about twice their initial binary orbital periods, roughly 109 years. This timescale depends strongly on the binary separation, weakly on its mass ratio, and less on initial galaxy rotation than has heretofore been suggested.
\r\n\r\nA specific interacting binary simulation is described in detail in the first paper. Surface brightness maps, structural parameters, and rotation properties are described at various times during the evolution, followed by a discussion of the properties of the merger remnant. Many of the results reported here are consistent with those obtained from the larger, more expensive N-body simulations.
\r\n\r\nFor the second paper, MTBA is altered so that each \"galaxy\" is represented by a configuration of test particles. Simulated tidal interactions between these \"galaxies\" are matched to the measured properties of real binaries in an effort to determine the physical state of each observed pair. The catalog of isolated galaxy pairs prepared by Karachentsev has been culled for its E-E constituents. CCD pictures and long-slit spectroscopic observations have been obtained at KPNO for the most photometrically distorted of these systems. Such pairs very likely represent strongly interacting, physically associated, binary elliptical galaxies. Radial variations of rotation velocity and velocity dispersion are extracted from the spectroscopic data for each of the two galaxies in a given pair. The combined spectroscopic and photometric data for that binary can be reproduced by an appropriate projection of a particular numerical simulation of the system. Some constraints can be placed on the masses of the galaxies, their internal dynamical configurations, and the properties of their relative orbit, including the three-dimensional orientation of the pair. Detailed results are presented for two pairs, K99 and K564. NGC 1587, the brighter component of K99, has the highest rotation rate known for an E2 galaxy, with a value vrot/\u03c3 = 0.6.
", "doi": "10.7907/8PH6-6R18", "publication_date": "1983", "thesis_type": "phd", "thesis_year": "1983" }, { "id": "thesis:7461", "collection": "thesis", "collection_id": "7461", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:02042013-113709002", "primary_object_url": { "basename": "Gladstone-gr-1983.pdf", "content": "final", "filesize": 23291604, "license": "other", "mime_type": "application/pdf", "url": "/7461/1/Gladstone-gr-1983.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "Radiative Transfer and Photochemistry in the Upper Atmosphere of Jupiter", "author": [ { "family_name": "Gladstone", "given_name": "George Randall", "clpid": "Gladstone-George-Randall" } ], "thesis_advisor": [ { "family_name": "Muhleman", "given_name": "Duane Owen", "clpid": "Muhleman-D-O" } ], "thesis_committee": [ { "family_name": "Muhleman", "given_name": "Duane Owen", "clpid": "Muhleman-D-O" }, { "family_name": "Goldreich", "given_name": "Peter Martin", "clpid": "Goldreich-P-M" }, { "family_name": "Yung", "given_name": "Yuk L.", "orcid": "0000-0002-4263-2562", "clpid": "Yung-Y-L" }, { "family_name": "Ingersoll", "given_name": "Andrew P.", "orcid": "0000-0002-2035-9198", "clpid": "Ingersoll-A-P" }, { "family_name": "Burnett", "given_name": "Donald S.", "orcid": "0000-0001-9521-8675", "clpid": "Burnett-D-S" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "The upper atmosphere of Jupiter, from the tropopause to well above the homopause, is investigated as to its compositional structure and vertical mixing parameters. Constraints are obtained through the study of the radiative transfer of ultraviolet resonance lines and continuum radiation. These constraints and others are then used in the modeling of the hydrocarbon photochemistry of Jupiter.
\r\n\r\nA direct finite difference numerical solution for the equation of radiative transfer is developed for use in planetary atmospheres. The procedure uses a plane-parallel atmosphere, and can treat partial frequency redistribution (for use in the radiative transfer of optically thick resonance lines), inhomogeneity, external or internal sources, and various boundary conditions. Isotropic scattering is assumed, but in the case of no frequency redistribution, a Rayleigh phase function may be used. A program utilizing this solution is tested against more powerful and elaborate methods. This program is then applied to the Lyman-\u03b1 aurora of Jupiter, and detailed line profiles are presented.
\r\n\r\nUsing this program, a study is made of the UV reflection spectrum of Jupiter as measured by the International Ultraviolet Explorer. Detailed modeling reveals the mixing ratios of C2H2, C2H6, and C4H2 to be (1.0 \u00b1 0.1) x 10-7, (6.6 \u00b1 5.3) x 10-6, and (2.9 \u00b1 2.0) x 10-10, respectively in the pressure region between \u223c 3 and 40 mbar. Upper limits in this pressure region for the mixing ratios of C2H4 and NH3 were determined to be (3.9 \u00b1 4.93.9) x 10-10 and (4.2 \u00b1 6.74.2 x 10-9, respectively. An upper limit to the optical depth of dust above the tropopause, assuming it is well mixed, is 0.2 \u00b1 0.30.2 and an upper limit on the dayglow emission by the Lyman bands of H2 is 1.4 \u00b1 2.41.4 kiloRayleighs. Comparison with Voyager results suggests that the scale height of C2H2 in the region 150-10 mbar is approximately twice that of the bulk atmosphere, consistent with the IUE observation of cosine-like limb darkening in the north-south direction on Jupiter in the UV.
\r\n\r\nThe resonant scattering of the solar He I 584 \u00c5 emission line by the upper Jovian atmosphere is investigated next. The observed intensity of this scattered line depends directly on the eddy diffusion for vertical mixing (Kh) and the temperature (Th) at the homopause. Using the temperature profile determined by the Voyager UVS experiment, a value of Kh = 1.3 x 106 cm2s-1 \u00b1 30% is obtained. If the temperature profile was the same during the Pioneer 10 encounter with Jupiter, then Kh \u2248 1 x 108 cm2 s-1 at that time. The He 584 \u00c5 brightness is found not to depend strongly on the gradients of either the eddy diffusion or temperature profiles. A semi-analytical expression for computing the He 584 \u00c5 brightness for a constant-K, constant-T atmosphere is derived and compared with calculations by other authors. It is speculated that the apparent decrease in Kh by two orders of magnitude between the Pioneer and Voyager encounters may be the result of an increase in the pole-to-equator circulation in the thermosphere, perhaps driven by the solar cycle.
\r\n\r\nThe above results are used as constraints for a one-dimensional photochemical-diffusive model of the hydrocarbon chemistry in Jupiter's upper atmosphere. The important chemical cycles and pathways among the C and C2 species are outlined and it is shown that the amount of methane dissociation resulting from acetylene photochemistry is comparable to the amount that is due to direct photolysis. Profiles for the major observed hydrocarbon species are calculated and their sensitivity to eddy diffusion profile, chemistry, and solar UV flux is examined. A best fit to the eddy diffusion profile of the upper atmosphere during the Voyager encounters is found to be given by K = 1.3 x 106(2.17 x 1013/n)0.5 cm2 s-1 (where n is the total number density), which implies a vertical mixing time at the tropopause of ~ 50 years. It is shown that polyacetylene formation driven by acetylene photochemistry in the models presented here is capable of producing the observed abundance of Danielson dust in the stratosphere of Jupiter. The disk-averaged Lyman-\u03b1 albedo of the the preferred model is calculated to be ~ 8 kiloRayleighs, almost a factor of two lower than the Voyager observed value of ~ 14 kiloRayleighs. This may indicate the need for an increased flux of atomic hydrogen from the thermosphere over the already present source from EUV and soft electron dissociation of H2. Such a flux is available from the auroral regions if there exists a pole-to-equator flow in the thermosphere as postulated earlier. Finally, a brief consideration of the auroral chemistry concludes that more lab studies of ion-neutral and ion-electron recombination reactions are needed before a meaningful study of that problem may be undertaken.
", "doi": "10.7907/pzzp-2209", "publication_date": "1983", "thesis_type": "phd", "thesis_year": "1983" }, { "id": "thesis:3677", "collection": "thesis", "collection_id": "3677", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-09212004-110904", "primary_object_url": { "basename": "Porco_cc_1983.pdf", "content": "final", "filesize": 5964354, "license": "other", "mime_type": "application/pdf", "url": "/3677/1/Porco_cc_1983.pdf", "version": "v4.0.0" }, "type": "thesis", "title": "Voyager Observations of Saturn's Rings. 1. The Eccentric Rings at 1.29, 1.45, 1.95 and 2.27 R\u209b. 2. The Periodic Variation of Spokes", "author": [ { "family_name": "Porco", "given_name": "Carolyn C.", "clpid": "Porco-Carolyn-C" } ], "thesis_advisor": [ { "family_name": "Muhleman", "given_name": "Duane Owen", "clpid": "Muhleman-D-O" } ], "thesis_committee": [ { "family_name": "Goldreich", "given_name": "Peter Martin", "clpid": "Goldreich-P-M" }, { "family_name": "Stevenson", "given_name": "David John", "orcid": "0000-0001-9432-7159", "clpid": "Stevenson-D-J" }, { "family_name": "Sargent", "given_name": "Wallace L. W.", "clpid": "Sargent-W-L-W" }, { "family_name": "Muhleman", "given_name": "Duane Owen", "clpid": "Muhleman-D-O" }, { "family_name": "Ingersoll", "given_name": "Andrew P.", "orcid": "0000-0002-2035-9198", "clpid": "Ingersoll-A-P" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "Part 1:
\r\n\r\nFive major eccentric features in the rings of Saturn are studied. These are the outer A and B ring edges at 1.95 and 2.27 R\u209b and three narrow ringlets at 1.29, 1.45, and 1.95 R\u209b. Data acquired by four Voyager experiments - Imaging Science (ISS), Radio Science (RSS), Ultraviolet Spectrometer (UVS), and Photopolarimeter(PPS) - were used in this investigation.
\r\n\r\nThe shapes and kinematics of the A and B ring outer edges are determined by their proximity to strong low-order Lindblad resonances. The data for the A ring edge are consistent with a 7-lobed distortion rotating with the mass-weighted mean angular velocity of the co-orbital satellite system. The B ring edge has a double-lobed figure which rotates with the mean motion of Mimas.
\r\n\r\nThe Saturnian ringlets are narrow (mean widths vary from ~ 10-60 km) and have eccentricities of order 10-4. All have sharp edges, normal optical depths \u03c4 ~ 1-2, and are embedded in essentially empty gaps (\u03c4 < 0.05). The Titan ring at 1.29 R\u209b and the Huygens ring at 1.45 R\u209b exhibit positive linear width-radius relations; the Maxwell ring at 1.95 R\u209b does not. The kinematics of the Huygens ring are determined solely by Saturn's non-spherical gravity field. The kinematics of the Titan ring are apparently completely determined by its interaction with Titan. At present, the most plausible model for the Maxwell ring involves the superposition of two components: one which is freely precessing and the other which is forced by Mimas and the elliptical B ring. Masses, mean surface mass densities, and specific opacities have been calculated for the Titan and Huygens rings.
\r\n\r\nPart 2:
\r\n\r\nThe discovery of a periodic variation in spoke activity in Saturn's rings from the analysis of Voyager images is reported. A Fourier power spectrum was computed using a data set generated by quantifying spoke activity observed on the morning (western) half of the rings in Voyager images spanning ~ 12 Saturn rotations and in Voyager 2 images spanning ~ 90 Saturn rotations. The period from Voyager 1 data is 631 \u00b1 22 min; from Voyager 2, 640.6 \u00b1 3.5 min. The latter result suggests that the fundamental modulation in spoke activity is due to the rotation of Saturn's magnetic field, the period of which is 639.4 min. Maximum spoke activity observed anywhere on the rings is most likely to be associated with the region of the magnetic field responsible for the most intense emission of the Saturn Kilometric Radiation (SKR). Passage of this region through Saturn's shadow may play a significant role in the creation and/or rejuvenation of spokes.
\r\n", "doi": "10.7907/q3z6-ca90", "publication_date": "1983", "thesis_type": "phd", "thesis_year": "1983" }, { "id": "thesis:11856", "collection": "thesis", "collection_id": "11856", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:10242019-095223820", "type": "thesis", "title": "Near Infrared Studies of Reflection Nebulae", "author": [ { "family_name": "Sellgren", "given_name": "Kristen", "orcid": "0000-0003-0817-2862", "clpid": "Sellgren-Kristen" } ], "thesis_advisor": [ { "family_name": "Neugebauer", "given_name": "Gerry", "clpid": "Neugebauer-G" } ], "thesis_committee": [ { "family_name": "Soifer", "given_name": "B. Thomas", "clpid": "Soifer-B-T" }, { "family_name": "Cohen", "given_name": "Judith G.", "orcid": "0000-0002-8039-4673", "clpid": "Cohen-J-G" }, { "family_name": "Goldreich", "given_name": "Peter Martin", "clpid": "Goldreich-P-M" }, { "family_name": "Houck", "given_name": "James R.", "clpid": "Houck-James-R" }, { "family_name": "Porter", "given_name": "Frank C.", "orcid": "0000-0003-1948-8889", "clpid": "Porter-F-C" }, { "family_name": "Neugebauer", "given_name": "Gerry", "clpid": "Neugebauer-G" } ], "local_group": [ { "literal": "div_pma" } ], "abstract": "Near infrared studies have been made of the extended emission from, and stellar clusters within, three visual reflection nebulae, NGC 7023, 2023, and 2068. The extended emission from each nebula consists of a smooth continuum from 1.25 to 4.8 \u03bcm, which can be described by a greybody with a color temperature of ~1000 K, and strong emission features at 3.3 and 3.4 \u03bcm. The spectrum is the same in all three sources, and is independent of position over regions 0.4-0.9 pc in diameter within each source. The 2.2 \u03bcm surface brightness distributions in NGC 7023 and 2023 agree well with the distributions of visual reflected light. The continuum emission cannot be explained by free-free emission, reflected light, fluorescent processes, field stars, or thermal emission from grains in equilibrium with the stellar radiation field.
\r\n\r\nA model is proposed in which the extended emission is due to thermal emission from very small grains (radius ~10 \u00c5) which are briefly heated to ~1000 K by absorption of an ultraviolet photon. This model explains the agreement between near infrared and visual surface brightness distributions, and the constancy of the energy distribution with offset from the central stars. The numbers of 10 \u00c5 sized grains required by the observations are in agreement with the numbers expected from an extrapolation of the grain size distribution of Mathis, Rumpl, and Nordsieck (1977) to smaller grain sizes.
\r\n\r\nClusters of young stars found associated with the reflection nebulae NGC 7023, 2023, and 2068 have also been studied at near infrared wavelengths. At least 30-60 % of the stars found at 2.2 \u03bcm are pre-main sequence objects, as indicated by their infrared excesses, hydrogen line emission, or irregular variability. The spatial distributions and observed luminosity functions of these young open clusters are derived, and the inferred mass function and star formation efficiencies are discussed.
", "doi": "10.7907/8dpe-n502", "publication_date": "1983", "thesis_type": "phd", "thesis_year": "1983" }, { "id": "thesis:945", "collection": "thesis", "collection_id": "945", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-03132009-081222", "type": "thesis", "title": "Stability of Spherically Symmetric, Charged Black Holes and Multipole Moments for Stationary Systems", "author": [ { "family_name": "G\u00fcrsel", "given_name": "Halis Yekta", "clpid": "G\u00fcrsel-Halis-Yekta" } ], "thesis_advisor": [ { "family_name": "Thorne", "given_name": "Kip S.", "orcid": "0000-0002-9475-4318", "clpid": "Thorne-K-S" } ], "thesis_committee": [ { "family_name": "Thorne", "given_name": "Kip S.", "orcid": "0000-0002-9475-4318", "clpid": "Thorne-K-S" }, { "family_name": "Frautschi", "given_name": "Steven C.", "clpid": "Frautschi-S-C" }, { "family_name": "Whitcomb", "given_name": "Stanley E.", "clpid": "Whitcomb-S-E" }, { "family_name": "Goldreich", "given_name": "Peter Martin", "clpid": "Goldreich-P-M" } ], "local_group": [ { "literal": "TAPIR" }, { "literal": "Astronomy Department" }, { "literal": "div_pma" } ], "abstract": "This dissertation is written in two parts. Part I deals with the question of stability of a spherically symmetric, charged black hole against scalar, electromagnetic, and gravitational perturbations. It consists of two papers written in collaboration with Igor D. NoVikov, Vernon D. Sandberg and A. A. Starobinsky. In these papers we describe the dynamical evolution of these perturbations on the interior of a Reissner-Nordstrom black hole. The instability of the hole's Cauchy horizon is discussed in detail in terms of the energy densities of the test fields as measured by a freely falling observer approaching the Cauchy horizon. We conclude that the Cauchy horizon of the analytically extended Reissner-Nordstrom solution is highly unstable and not a physical feature of a realistic gravitational collapse. Part II of this dissertation addresses two problems closely connected with muitipole structure of stationary, asymptotically flat spacetimes. It consists of two papers written in collaboration with Kip S. Thorne despite the fact that his name does not appear on one of them. The first one (Paper III in this thesis) shows the equivalence of the moments defined by Kip S. Thorne and the moments defined by Robert Geroch and Richard Hansen. The second (Paper IV in this thesis) proves a conjecture by Kip S. Thorne: In the limit of \"slow\" motion, general relativistic gravity produces no changes whatsoever in the classical Euler equations of rigid body motion. We prove this conjecture by giving an algorithm for generating rigidly rotating solutions of Einstein's equations from nonrotating, static solutions.
\r\n", "doi": "10.7907/e9t6-dr05", "publication_date": "1983", "thesis_type": "phd", "thesis_year": "1983" }, { "id": "thesis:3320", "collection": "thesis", "collection_id": "3320", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-09032008-131405", "type": "thesis", "title": "The Orientation and Sizes of Molecular Clouds in the Galaxy", "author": [ { "family_name": "Redman", "given_name": "Russell Ormond", "clpid": "Redman-Russell-Ormond" } ], "thesis_advisor": [ { "family_name": "Wannier", "given_name": "Peter G.", "clpid": "Wannier-P-G" } ], "thesis_committee": [ { "family_name": "Phillips", "given_name": "Thomas G.", "clpid": "Phillips-T-G" }, { "family_name": "Goldreich", "given_name": "Peter Martin", "clpid": "Goldreich-P-M" }, { "family_name": "Schmidt", "given_name": "Maarten", "clpid": "Schmidt-M" }, { "family_name": "Wannier", "given_name": "Peter G.", "clpid": "Wannier-P-G" } ], "local_group": [ { "literal": "Astronomy Department" }, { "literal": "div_pma" } ], "abstract": "In Part I of this dissertation, a technique is introduced to investigate the shapes and orientations of molecular clouds. The clouds are shown to be roughly bar-shaped with their long axes normally aligned within thirty degrees of the axis of the spiral arm in which the cloud is embedded. The long axis is typically three times longer than the two shorter axes, although all axial ratios from one to five appear to be present. These results appear to be independent of cloud size over the range from 15 parsecs to 175 parsecs for the maximum apparent cloud dimension.
\r\n\r\nIn Part II, the size distribution of the CO clouds is measured. Most of the mass of molecular gas in the galaxy resides in the largest clouds, with semimajor axes slightly larger than 100 pc long. The largest cloud sizes appear to be about the same over the entire molecular disk. These very large clouds must have been formed full sized from the intercloud gas, since they cannot have been assembled from smaller clouds. In deriving this distribution a simple and effective technique was developed to resolve the kinematic distance ambiguity.
\r\n\r\nThe concentration of the mass of molecular gas into the largest clouds, and the alignment of the clouds along the spiral arms, both indicate that the clouds are very young. They must be formed directly from the intercloud medium, probably behind a spiral arm shock wave, and cannot grow over long periods of time from smaller clouds. The mechanism forming the clouds from the intercloud gas must have a prefered scale length. Examples of such mechanisms are the Parker magnetic instability, or the collapse of a slowly accumulating dust lane. Similarly, the clouds must be dispersed rapidly at the ends of their lives.
\r\n", "doi": "10.7907/p0pn-sw91", "publication_date": "1982", "thesis_type": "phd", "thesis_year": "1982" }, { "id": "thesis:8670", "collection": "thesis", "collection_id": "8670", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:10072014-083229203", "primary_object_url": { "basename": "Cook_wr_1981.pdf", "content": "final", "filesize": 32111784, "license": "other", "mime_type": "application/pdf", "url": "/8670/1/Cook_wr_1981.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "Elemental Composition of Solar Energetic Particles", "author": [ { "family_name": "Cook", "given_name": "Walter Richardson, III", "clpid": "Cook-Walter-Richardson-III" } ], "thesis_advisor": [ { "family_name": "Vogt", "given_name": "Rochus E.", "clpid": "Vogt-R-E" } ], "thesis_committee": [ { "family_name": "Vogt", "given_name": "Rochus E.", "clpid": "Vogt-R-E" }, { "family_name": "Buffington", "given_name": "Andrew", "clpid": "Buffington-Andrew" }, { "family_name": "Goldreich", "given_name": "Peter Martin", "clpid": "Goldreich-P-M" }, { "family_name": "Walker", "given_name": "Robert Lee", "clpid": "Walker-R-L" } ], "local_group": [ { "literal": "div_pma" } ], "abstract": "The Low Energy Telescopes on the Voyager spacecraft are used to measure the elemental composition (2 \u2264 Z \u2264 28) and energy spectra (5 to 15 MeV /nucleon) of solar energetic particles (SEPs) in seven large flare events. Four flare events are selected which have SEP abundance ratios approximately independent of energy/nucleon. The abundances for these events are compared from flare to flare and are compared to solar abundances from other sources: spectroscopy of the photosphere and corona, and solar wind measurements.
\r\n\r\nThe selected SEP composition results may be described by an average composition plus a systematic flare-to-flare deviation about the average. For each of the four events, the ratios of the SEP abundances to the four-flare average SEP abundances are approximately monotonic functions of nuclear charge Z in the range 6 \u2264 Z \u2264 28. An exception to this Z-dependent trend occurs for He, whose abundance relative to Si is nearly the same in all four events.
\r\n\r\nThe four-flare average SEP composition is significantly different from the solar composition determined by photospheric spectroscopy: The elements C, N and O are depleted in SEPs by a factor of about five relative to the elements Na, Mg, Al, Si, Ca, Cr, Fe and Ni. For some elemental abundance ratios (e.g. Mg/O), the difference between SEP and photospheric results is persistent from flare to flare and is apparently not due to a systematic difference in SEP energy/nucleon spectra between the elements, nor to propagation effects which would result in a time-dependent abundance ratio in individual flare events.
\r\n\r\nThe four-flare average SEP composition is in agreement with solar wind abundance results and with a number of recent coronal abundance measurements. The evidence for a common depletion of oxygen in SEPs, the corona and the solar wind relative to the photosphere suggests that the SEPs originate in the corona and that both the SEPs and solar wind sample a coronal composition which is significantly and persistently different from that of the photosphere.
", "doi": "10.7907/04wf-f966", "publication_date": "1981", "thesis_type": "phd", "thesis_year": "1981" }, { "id": "thesis:10773", "collection": "thesis", "collection_id": "10773", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:03132018-124306975", "primary_object_url": { "basename": "Nadeau_D_1981.pdf", "content": "final", "filesize": 52415053, "license": "other", "mime_type": "application/pdf", "url": "/10773/1/Nadeau_D_1981.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "High Spectral Resolution Observations of the Molecular Hydrogen Emission in the Orion Molecular Cloud", "author": [ { "family_name": "Nadeau", "given_name": "Daniel", "clpid": "Nadeau-Daniel" } ], "thesis_advisor": [ { "family_name": "Neugebauer", "given_name": "Gerry", "clpid": "Neugebauer-G" } ], "thesis_committee": [ { "family_name": "Davis", "given_name": "Leverett", "clpid": "Davis-Leverett" }, { "family_name": "Goldreich", "given_name": "Peter Martin", "clpid": "Goldreich-P-M" }, { "family_name": "Phillips", "given_name": "Thomas G.", "clpid": "Phillips-T-G" }, { "family_name": "Soifer", "given_name": "B. Thomas", "clpid": "Soifer-B-T" }, { "family_name": "Neugebauer", "given_name": "Gerry", "clpid": "Neugebauer-G" } ], "local_group": [ { "literal": "div_pma" } ], "abstract": "Observations of line profiles of the vibrationally excited H2 gas in the Orion molecular cloud are presented. The \u03bd = 1 \u2192 0 S(1), \u03bd = 1 \u2192 0 S(0) and \u03bd = 2 \u2192 1 S(1) lines, emitted at a wavelength near 2 \u03bcm, have been observed with a spectral resolution of 20 km s-1. The region has been mapped extensively in the \u03bd = 1 \u2192 0 S(1) line with a spatial resolution of 10\" and 5\", and the line has been monitored at a few positions over a period of 15 months. The profiles of the \u03bd = 1 \u2192 0 S(0) and \u03bd = 2 \u2192 1 S(1) lines have been compared at two positions.
\r\n\r\nThe mapping measurements show variations from the periphery where the profiles are narrow, symmetric and have a peak velocity equal to that of the molecular cloud, to the center of the region of emission where the profiles are wide, asymmetric and blueshifted. The line profiles do not appear to vary with time or with the energy of the upper level of the transition.
\r\n\r\nThe results are interpreted by a model of a radially expanding flow of gas. From a study of H2 excitation behind a shock front and in a magnetic precursor ahead of a shock wave, it is concluded that the high velocity emission comes from the high velocity gas in the flow, and the low velocity emission comes from gas in the molecular cloud surrounding the flow, with density inhomogeneities contributing to the detailed profiles. Finally the H2 emission is compared to the CO and H2O maser emission and lo the infrared continuum sources.
\r\n\r\nAn instrument which incorporates a piezoelectrically scanned Fabry-P\u00e9rot interferometer, an InSb detector cooled to ~ 55 K, a rotary chopper, and an offset guider has been built to make these observations. Its operation is described in an appendix.
", "doi": "10.7907/mz32-5279", "publication_date": "1981", "thesis_type": "phd", "thesis_year": "1981" }, { "id": "thesis:10394", "collection": "thesis", "collection_id": "10394", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:08282017-145742321", "primary_object_url": { "basename": "Wisdom_jl_1981.pdf", "content": "final", "filesize": 19568200, "license": "other", "mime_type": "application/pdf", "url": "/10394/1/Wisdom_jl_1981.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "1. The Origin of the Kirkwood Gaps: A Mapping for Asteroidal Monitor Near the 3/1 Commensurability. 2. The Resonance Overlap Criterion and the Onset of Stochastic Behavior in the Restricted Three-Body Problem", "author": [ { "family_name": "Wisdom", "given_name": "Jack Leach", "clpid": "Wisdom-Jack-Leach" } ], "thesis_advisor": [ { "family_name": "Goldreich", "given_name": "Peter Martin", "clpid": "Goldreich-P-M" } ], "thesis_committee": [ { "family_name": "Goldreich", "given_name": "Peter Martin", "clpid": "Goldreich-P-M" }, { "family_name": "Thorne", "given_name": "Kip S.", "clpid": "Thorne-K-S" }, { "family_name": "Cohen", "given_name": "Donald S.", "clpid": "Cohen-D-S" }, { "family_name": "Zachariasen", "given_name": "Fredrik", "clpid": "Zachariasen-F" } ], "local_group": [ { "literal": "TAPIR" }, { "literal": "Astronomy Department" }, { "literal": "div_pma" } ], "abstract": "Paper 1:
\r\n\r\nA mapping of the phase space onto itself with the same low order resonance structure as the 3/1 commensurability in the planar elliptic three-body prob\u00adlem is derived. This mapping is approximately one thousand (1000) times faster than the usual method of numerically integrating the averaged equations of motion (as used by Schubart, Froeschl\u00e9 and Scholl in their studies of the asteroid belt). This mapping exhibits some very surprising behavior that might provide the key to the origin of the gaps. A test asteroid placed in the gap may evolve for a million years with low eccentricity (< 0.05) and then suddenly jump to large eccentricity (> 0.3) becoming a Mars crosser. The asteroid can then be removed by a close encounter with Mars. To test this hypothesis a dis\u00adtribution of 300 test asteroids in the neighborhood of the 3/1 commensurability was evolved for two million years. When the Mars crossers are removed the dis\u00adtribution of initial conditions displays a gap at the location of the 3/1 Kirkwood gap. While this is the first real demonstration of the formation of a gap, the gap is too narrow. The planar elliptic mapping is then extended to include the incli\u00adnations and the secular perturbations of Jupiter's orbit. The two million year evolution of the 300 test asteroids is repeated using the full mapping. The resulting gap is somewhat larger yet still too small. Finally the possibility that over longer times more asteroids will become Mars crossers is tested by studying the evolution of one test asteroid near the border of the gap for a much longer time. A jump in its eccentricity occurs after 18 million years indicating that indeed it may simply be a matter of time for the full width of the gap to open.
\r\n\r\nPaper 2:
\r\n\r\nThe resonance overlap criterion for the onset of stochastic behavior is applied to the planar circular-restricted three-body problem with small mass ratio (\u00b5). Its predictions for \u00b5 = 10-3, \u00b5 = 10-4 and \u00b5 = 10-5 are compared to the transitions in the numerically determined Kolmogorov-Sinai entropy and found to be in remarkably good agreement. In addition, an approximate scaling law for the onset of stochastic behavior is derived.
", "doi": "10.7907/s1r9-ff38", "publication_date": "1981", "thesis_type": "phd", "thesis_year": "1981" }, { "id": "thesis:2597", "collection": "thesis", "collection_id": "2597", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-06142007-142536", "type": "thesis", "title": "Some Topics in Theoretical High-Energy Physics", "author": [ { "family_name": "Wolfram", "given_name": "Stephen", "clpid": "Wolfram-Stephen" } ], "thesis_advisor": [ { "family_name": "Frautschi", "given_name": "Steven C.", "clpid": "Frautschi-S-C" }, { "family_name": "Field", "given_name": "Richard D.", "clpid": "Field-R-D" } ], "thesis_committee": [ { "family_name": "Field", "given_name": "Richard D.", "clpid": "Field-R-D" }, { "family_name": "Frautschi", "given_name": "Steven C.", "clpid": "Frautschi-S-C" }, { "family_name": "Goldreich", "given_name": "Peter Martin", "clpid": "Goldreich-P-M" }, { "family_name": "Feynman", "given_name": "Richard Phillips", "clpid": "Feynman-R-P" }, { "family_name": "Sciulli", "given_name": "Frank J.", "clpid": "Sciulli-F-J" } ], "local_group": [ { "literal": "div_pma" } ], "abstract": "This thesis discusses various aspects of theoretical high-energy physics. The first two sections describe methods for investigating QCD effects in e\u207ae\u207b annihilation to hadrons. The third section presents some predictions for various features of QCD jets. The fourth section shows that any fermions in the standard weak interaction model must have masses \u227e100 GeV. In the fifth section, the abundances of any new absolutely stable heavy particles which should have been produced in the early universe are estimated, and found to be inconsistent with observational limits. Finally, the sixth section describes the development of a baryon excess in the very early universe due to B, CP violating interactions.\r\n", "doi": "10.7907/S6JE-QF83", "publication_date": "1980", "thesis_type": "phd", "thesis_year": "1980" }, { "id": "thesis:3331", "collection": "thesis", "collection_id": "3331", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-09042008-141513", "primary_object_url": { "basename": "Cimerman_m_1980.pdf", "content": "final", "filesize": 2558298, "license": "other", "mime_type": "application/pdf", "url": "/3331/1/Cimerman_m_1980.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "A Study of Hydroxyl Masers in the Circumstellar Envelopes of Long Period Variable Stars", "author": [ { "family_name": "Cimerman", "given_name": "Menachem", "clpid": "Cimerman-Menachem" } ], "thesis_advisor": [ { "family_name": "Cohen", "given_name": "Marshall H.", "clpid": "Cohen-M-H" }, { "family_name": "Wannier", "given_name": "Peter G.", "clpid": "Wannier-P-G" } ], "thesis_committee": [ { "family_name": "Cohen", "given_name": "Marshall H.", "clpid": "Cohen-M-H" }, { "family_name": "Goldreich", "given_name": "Peter Martin", "clpid": "Goldreich-P-M" }, { "family_name": "Wannier", "given_name": "Peter G.", "clpid": "Wannier-P-G" }, { "family_name": "Scoville", "given_name": "Nicholas Zabriskie", "orcid": "0000-0002-0438-3323", "clpid": "Scoville-N-Z" } ], "local_group": [ { "literal": "Astronomy Department" }, { "literal": "div_pma" } ], "abstract": "The 18 cm wavelength maser radiation from long period variable (LPV) stars is emitted by hydroxyl (OH) molecules in the expanding circumstellar envelopes. The four possible transitions within the ground state of the OH molecule are divided into two groups: mainlines at 1665 and 1667 MHz and satellite lines at 1612 and 1720 MHz. Three of these lines are observed in maser radiation from LPV stars: the 1612 MHz line and the mainlines. The observed properties of the 1612 MHz radiation are easier to interpret than those of the mainlines due to the quantum mechanical symmetries of the OH molecule. This investigation tackles the problem of the OH mainline masers, first by radio observations of two LPV sources with unique OH properties, and then by a theoretical analysis.\r\n\r\nThe U Ori OH masers were monitored following the drastic events in these masers in early 1974. The events consisted of the sudden appearance of strong 1612 MHz radiation, coincident with the disappearance of the 1667 MHz radiation. They are interpreted in light of the monitored evolution of the 1612 MHz radiation, the decline in its output level, and the subsequent re-emergence of a 1667 MHz line. The conclusion is that the events are the outcome of a short-lived disturbance in the stellar photosphere, most likely a shock-wave, which affected the maser through radiative coupling between the photosphere and the OH molecules.\r\n\r\nObservations of the OH maser in W Hya are presented, which suggest an explanation of their unique polarization characteristics. The maser lines may be formed at a distance of ~ 10[superscript 14] cm from the stellar surface in the presence of a magnetic field of ~ 9 milligauss. This magnetic field is coupled to the ionized component of the outflowing circumstellar envelope. In the W Hya case the magnetic field is evident in the strong polarization, Zeeman pattern and differential magnetorotation. However, it may exist unnoticed in other OH sources, and contribute to the pumping mechanism.\r\n\r\nThe pumping of OH masers in late-type-variables by direct stellar radiation of 2.8\u03bc is studied. Two pumping schemes are suggested based on line coincidences between OH V=0-1 transitions and strong H[subscript 2]0 \u03c5[subscript 3] transitions. The water molecules perturb the stellar radiation by absorption, and thus cool the coinciding OH transition. It is demonstrated that this cooling is capable of producing strong OH masers in the circumstellar envelopes of late-type-variables. This model can account for the existence of mainline (\u0394F=0) OH masers, which is hard to explain otherwise.", "doi": "10.7907/zsta-x423", "publication_date": "1980", "thesis_type": "phd", "thesis_year": "1980" }, { "id": "thesis:3676", "collection": "thesis", "collection_id": "3676", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-09212004-110141", "type": "thesis", "title": "I. Small Angle Scattering of Radiation. II. Molecular Emission Lines Around Evolved Stars", "author": [ { "family_name": "Alcock", "given_name": "Charles", "clpid": "Alcock-Charles" } ], "thesis_advisor": [ { "family_name": "Goldreich", "given_name": "Peter Martin", "clpid": "Goldreich-P-M" } ], "thesis_committee": [ { "family_name": "Goldreich", "given_name": "Peter Martin", "clpid": "Goldreich-P-M" }, { "family_name": "Blandford", "given_name": "Roger D.", "clpid": "Blandford-R-D" }, { "family_name": "Garmire", "given_name": "Gordon Paul", "clpid": "Garmire-G-P" }, { "family_name": "Wannier", "given_name": "Peter G.", "clpid": "Wannier-P-G" } ], "local_group": [ { "literal": "Astronomy Department" }, { "literal": "div_pma" } ], "abstract": "This dissertation is in two Parts. Part I consists of a paper on the effect of small angle scattering on a pulse of radiation, and an analysis of the particular case of X-rays scattering off interstellar grains. Part II concerns the excitation of SiO emission lines around evolved stars. There are two papers, the first on 'thermal' emission lines and the second on maser emission lines. Each paper has its own abstract.
\r\n\r\nPart I: We have analyzed in detail the general problem of the propagation of a pulse of radiation through a uniform medium containing small angle scatterers. Simple expressions for the first moment of the arrival time delay and for the second and fourth moments of the arrival angle of the pulse photons are given, valid for any optical depth. Using the first two of these we find a simple method of distance determination. Joint and individual distribution functions for arrival time and angle are derived in the small and large optical depth limits. An exponential tail in the arrival time distribution is characteristic in both limits. The analysis has been applied to a burst of x-rays from a source near the galactic center propagating through the dust of the interstellar medium. The grains responsible for interstellar reddening can have very little observable effect. However, the observed lengths, energy dependence, and variability of the burst tails can be readily accounted for by a population of large ~3\u03bc grains. We derive useful constraints on the grain distribution from observations of the burst tails.
\r\n\r\nPart II (i): We have investigated the excitation of the microwave lines in the ground vibrational state of the SiO molecule in the expanding envelope of cool Mira-type stars. The rotational levels are excited when an SiO molecule absorbs an 8\u03bc photon and is left in the lowest excited vibrational state; the spontaneous decay of the excited vibrational state preferentially leaves the molecule with a higher rotational quantum number than it had before. In all of the cases investigated the majority of the microwave transitions were optically thick, and photon trapping causes the excitation temperature to increase with optical depth in such a way that the antenna temperature measured by a distant observer is proportional to the flux of SiO leaving the star, to the square root of the ambient 8\u03bc flux and inversely to the square of the asymptotic velocity. We have analysed the reported detection of J = 1 \u2192 2, v = 0 emission from three Miras and VY CMa, and find that the flux of SiO leaving the stars is very low. This indicates that either they are losing very little mass, or more probably that grain formation very effectively removes a large fraction of gaseous SiO molecules.
\r\n\r\nPart II (ii): We have investigated the excitation of the microwave lines in the excited vibrational states of the SiO molecules in the expanding envelopes of cool Mira-type stars. The excited vibrational states are populated principally by the absorption of 8\u03bc photons. The inversions occur when the gas temperature exceeds the excitation temperature of the vibrational levels, and upward vibrational collisions selectively populate higher rotational levels. The masers are all saturated. We discuss the line profiles, and show how the profile is determined by the velocity gradient and the ambient radiation field.
\r\n\r\nThe SiO abundance required for the masers is large. We discuss this in the light of our earlier calculation that the abundance is low in the outer envelope, and argue that grain formation is an efficient process.
\r\n", "doi": "10.7907/9NC1-B853", "publication_date": "1978", "thesis_type": "phd", "thesis_year": "1978" }, { "id": "thesis:3231", "collection": "thesis", "collection_id": "3231", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-08262008-113619", "type": "thesis", "title": "The Structure of Hydroxyl Masers and Circumstellar Envelopes of Long Period Variable Stars", "author": [ { "family_name": "Reid", "given_name": "Mark Jonathan", "orcid": "0000-0001-7223-754X", "clpid": "Reid-Mark-Jonathan" } ], "thesis_advisor": [ { "family_name": "Muhleman", "given_name": "Duane Owen", "clpid": "Muhleman-D-O" } ], "thesis_committee": [ { "family_name": "Muhleman", "given_name": "Duane Owen", "clpid": "Muhleman-D-O" }, { "family_name": "Goldreich", "given_name": "Peter Martin", "clpid": "Goldreich-P-M" }, { "family_name": "Neugebauer", "given_name": "Gerry", "clpid": "Neugebauer-G" }, { "family_name": "Preston", "given_name": "George W.", "clpid": "Preston-G-W" }, { "family_name": "Cohen", "given_name": "Marshall H.", "clpid": "Cohen-M-H" } ], "local_group": [ { "literal": "Owens Valley Radio Observatory (OVRO)" }, { "literal": "Astronomy Department" }, { "literal": "div_pma" } ], "abstract": "Long period variable stars with envelopes of circumstellar dust and gas often exhibit strong hydroxyl (OH) maser emission. This emission is characterized by two emission line complexes typically separated by 20 km/s. While the OH maser spectra suggest well defined dynamical properties of the circumstellar material, the crucial observations required to determine these properties have been lacking. This thesis is primarily concerned with determining the radial velocity of the central star and the spatial distribution of the maser emission in the circumstellar material.
\r\n\r\nThe radial velocity of the central star can be determined by a statistical analysis of spectral line velocities in an ensemble of stars. Such an analysis is presented in Chapter I for optical emission and absorption lines and for radio OH maser emission lines. The results indicate that, contrary to currently accepted theories, the optical absorption line velocities and the high velocity OH emission line velocities are red-shifted with respect to the stellar radial velocity. This argues against models of the OH emission which involve shock fronts or emission from the limb of a spherically expanding circumstellar shell.
\r\n\r\nThe spatial distribution of the maser emission can be determined from radio interferometric observations. Spectral-line very long baseline (VLB) interferometric observations of the OH maser emission in long period variable stars such as IRC+F10011, U Ori and R Aql are presented in Chapter II. The primary result of these observations is that the apparent sizes of the OH maser components in long period variable stars are greater than or about 5 x 1015 cm. These large apparent sizes argue strongly against either gravitational collapse or rotation as the dominant dynamical process in the circumstellar envelope. Analysis of data obtained on IRC+10011 and VY CMa (discussed in Chapter III) indicate that the two emission complexes probably are separated by distances less than, or comparable to, the extent of the emission in either complex. These and other findings suggest that OH emission from long period variable stars comes from a series of concentric, inhomogeneous, circumstellar shells expanding from the central star. The origin of these shells is probably a result of condensation of dust followed by radiative acceleration away from the star during the stellar light cycle.
\r\n\r\nA direct Fourier inversion of VLB data is presented in Chapter III for the 1612 MHz OH emission of VY CMa. This is the first attempt at such an analysis procedure for any VLB observations. This work demonstrates that Fourier inversion of spectral-line VLB data, even with very limited u-v coverage, is more efficient and less biased than direct model fitting for the resolution of complex source structures.
\r\n", "doi": "10.7907/4EGT-TW53", "publication_date": "1976", "thesis_type": "phd", "thesis_year": "1976" }, { "id": "thesis:14017", "collection": "thesis", "collection_id": "14017", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:12072020-234014838", "primary_object_url": { "basename": "Lagus_PL_1974.pdf", "content": "final", "filesize": 30518048, "license": "other", "mime_type": "application/pdf", "url": "/14017/1/Lagus_PL_1974.pdf", "version": "v2.0.0" }, "type": "thesis", "title": "The Equations of State of Hydrogen and Argon: Applications to the Jovian Interior", "author": [ { "family_name": "Lagus", "given_name": "Peter Leonard", "clpid": "Lagus-Peter-Leonard" } ], "thesis_advisor": [ { "family_name": "Ahrens", "given_name": "Thomas J.", "clpid": "Ahrens-T-J" } ], "thesis_committee": [ { "family_name": "Archambeau", "given_name": "Charles B.", "clpid": "Archambeau-C-B" }, { "family_name": "Goldreich", "given_name": "Peter Martin", "clpid": "Goldreich-P-M" }, { "family_name": "Muhleman", "given_name": "Duane Owen", "clpid": "Muhleman-D-O" }, { "family_name": "Anderson", "given_name": "Donald L.", "clpid": "Anderson-D-L" }, { "family_name": "Ahrens", "given_name": "Thomas J.", "clpid": "Ahrens-T-J" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "Hugoniot data for solid argon (initially at 77\u00b0K and l bar) and solid hydrogen (initially at 5\u00b0K and 1 bar) have been obtained to 143 kbar and 6.4 kbar respectively utilizing a propellant gun. The argon data (at volumes of 15.28, 14.84 and 14.64 cc/mole) are in fair agreement with previous shock data, and in excellent agreement with recent theoretically predicted Hugoniots. The hydrogen data (at volumes of 17.10, 15.32, 15.27, 15.11 cc/mole) are compared with Hugoniots calculated from published isothermal compression data. For both argon and hydrogen, the present data are consistent with the assumption that \u03b3/V is constant. Furthermore, to compressions of V/V\u2080 \u2243 0.65, no gross inconsistencies exist between shock-wave and isothermal compression measurements in solid hydrogen.
\r\n\r\nA simple equation of state (E0S) for molecular hydrogen based on a spherically averaged De Boer-type repulsion potential which explicitly includes the zero point energy reproduces experimental pressure-volume data between 5 kbar and 370 kbar. This molecular equa\u00adtion of state when combined with recent metallic equations of state implies a molecular to metallic phase transition pressure of 1.9 \u00b1 0.4 Mbar at 0\u00b0K.
\r\n\r\nA thermally expanded model of Jupiter which incorporates this molecular equation of state, recent metallic hydrogen and helium equa\u00adtions of state, and a van der Waals-type atmosphere yields a model with a hydrogen abundance of x = 0.57. However, the interior temperatures are everywhere above the melting temperature of metallic hydrogen.
", "doi": "10.7907/zzpq-2876", "publication_date": "1974", "thesis_type": "phd", "thesis_year": "1974" } ]