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: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: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:3593", "collection": "thesis", "collection_id": "3593", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-09172008-092907", "primary_object_url": { "basename": "Krasnopolsky_r_2000.pdf", "content": "final", "filesize": 6686386, "license": "other", "mime_type": "application/pdf", "url": "/3593/1/Krasnopolsky_r_2000.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "Hydromagnetic astrophysical outflows", "author": [ { "family_name": "Krasnopolsky", "given_name": "Ruben", "clpid": "Krasnopolsky-R" } ], "thesis_advisor": [ { "family_name": "Blandford", "given_name": "Roger D.", "clpid": "Blandford-R-D" }, { "family_name": "Goldreich", "given_name": "Peter Martin", "clpid": "Goldreich-P-M" } ], "thesis_committee": [ { "family_name": "Unknown", "given_name": "Unknown" } ], "local_group": [ { "literal": "TAPIR" }, { "literal": "Astronomy Department" }, { "literal": "div_pma" } ], "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\n\r\nThe launching, acceleration and stability of MHD outflows were studied numerically in two and three dimensions using a parallelized version of the ZEUS code.\r\n\r\nThe launching from Keplerian accretion disks was investigated using time-dependent simulations, to determine parameter dependence and stability to 3D perturbations. The most critical factors controlling the cold outflows from the disk surface were found to be the poloidal magnetic field profile and the mass discharge rate: together they determine the acceleration of gas away from the disk, and the location of the Alfven surface, which, in turn, fixes the angular momentum loss and the asymptotic speed. The flows were found to be remarkably stable in 3D against perturbations of the initial conditions, at least in the formation region of the jet before the Alfven surface. This is surprising in the context of previous studies.\r\n\r\nIntermittent flows are found when the mass discharge rate is too large for a given magnetic field profile. This may be relevant to some observed episodic sources. This intermittency can be suppressed if the mass loading has the angular dependence suggested by the magnetocentrifugal mechanism, namely that the discharge is a function of the angle \u03b8 between the poloidal fieldline threading the disk and the rotation axis, turning off when \u03b8[...]30\u00b0. The mechanism of intermittency sets up a maximum mass loading to the observed smooth jets, may explain those that are pulsed, and shows a possible transition back and forth between both regimes. The result presented here may be compared to some recently published papers which suggest that intermittency could occur if the mass loading is too small: here it occurs when it is too large. If both results are generic, mass loading is bracketed for steady flows.\r\n\r\nLaunching from disks was simulated using a cold disk and atmosphere. The number of boundary conditions that was imposed on the disk surface is what is necessary and sufficient to take into account information propagating upstream from the fast and Alfven critical surfaces, avoiding over-determination of the flow and unphysical effects, such as numerical \"boundary layers\" that otherwise isolate the disk from the flow, produce impulsive accelerations and confuse the connection between the disk parameters and the flow.\r\n\r\nThe solar wind provides another example of an MHD outflow, using the high solar latitude observations by the satellite Ulysses. The simulations performed here allowed an estimate of the mean value of the azimuthal velocity, which is not directly accessible to measurement, and is necessary to estimate the torque of the solar wind. The Alfven point was found to be located at ~11R[...]. Similar outflows from faster rotators were simulated, and found to be collimated along the rotational axis.\r\n", "doi": "10.7907/j2ak-0b24", "publication_date": "2000", "thesis_type": "phd", "thesis_year": "2000" }, { "id": "thesis:3600", "collection": "thesis", "collection_id": "3600", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-09172008-151500", "primary_object_url": { "basename": "Chiang_e_2000.pdf", "content": "final", "filesize": 5991255, "license": "other", "mime_type": "application/pdf", "url": "/3600/1/Chiang_e_2000.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "Circumstellar and circumplanetary disks", "author": [ { "family_name": "Chiang", "given_name": "Eugene", "clpid": "Chiang-E" } ], "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": "Phinney", "given_name": "E. Sterl", "clpid": "Phinney-E-S" }, { "family_name": "Sargent", "given_name": "Anneila Isabel", "clpid": "Sargent-A-I" }, { "family_name": "Blake", "given_name": "Geoffrey A.", "clpid": "Blake-G-A" }, { "family_name": "Brown", "given_name": "Michael E.", "clpid": "Brown-M-E" } ], "local_group": [ { "literal": "Astronomy Department" }, { "literal": "div_pma" } ], "abstract": "This 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:18908", "collection": "thesis", "collection_id": "18908", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:08282026-223733233", "primary_object_url": { "basename": "Mecozzi_S_1997.pdf", "content": "final", "filesize": 70218772, "license": "other", "mime_type": "application/pdf", "url": "/18908/1/Mecozzi_S_1997.pdf", "version": "v2.0.0" }, "type": "thesis", "title": "Electrostatic Forces in Aqueous Media and the Nature of the Cation-\u03c0 Interaction", "author": [ { "family_name": "Mecozzi", "given_name": "Sandro", "orcid": "0000-0003-0828-1399", "clpid": "Mecozzi-Sandro" } ], "thesis_advisor": [ { "family_name": "Dougherty", "given_name": "Dennis A.", "orcid": "0000-0003-1464-2461", "clpid": "Dougherty-D-A" }, { "family_name": "Goldreich", "given_name": "Peter Martin", "clpid": "Goldreich-P-M" } ], "thesis_committee": [ { "family_name": "Imperiali", "given_name": "Barbara", "orcid": "0000-0002-5749-7869", "clpid": "Imperiali-B" }, { "family_name": "Gray", "given_name": "Harry B.", "orcid": "0000-0002-7937-7876", "clpid": "Gray-H-B" }, { "family_name": "Carreira", "given_name": "Erick Moran", "orcid": "0000-0003-1472-490X", "clpid": "Carreira-E-M" }, { "family_name": "Dougherty", "given_name": "Dennis A.", "orcid": "0000-0003-1464-2461", "clpid": "Dougherty-D-A" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "The forces responsible for the molecular recognition of organic\r\ncompounds in aqueous media are mainly hydrophobic and electrostatic\r\nforces. It has been known for some time that water-solvated positively\r\ncharged organic compounds, such as N-methylquinolinium and\r\nadamantyl trimethylammonium, are bound by cyclophane receptors, in\r\naqueous media, more strongly than neutral organic molecules. The origin\r\nof this interaction can be found in the attraction between the cation and\r\nthe electron-rich face of the aromatics in the host. This intermolecular\r\nforce has been called the cation-1t interaction. We report our findings on\r\nthe nature of this interaction. We performed a series of high level ab initio\r\ncomputational studies on the binding of the sodium cation to the \u03c0 face of\r\neleven aromatic molecules. Binding energies were evaluated at the 6-\r\n31G**//6-31G** level. We then replaced the sodium cation in the\r\noptimized complex with a dummy probe atom and evaluated the\r\nelectrostatic potential at that point. This procedure allowed us to calculate\r\nthe electrostatic contribution to the binding. A plot of the electrostatic\r\npotentials vs. the binding energies showed that the electrostatic\r\ncomponent of the cation-1t interaction is highly variable. However, across\r\nthe series of examined molecules, essentially 100% of the variation in\r\nbinding energy is reflected in the electrostatic term. All other factors,\r\nincluding induced dipole interactions, charge transfer, and dispersion\r\nforces, are absorbed in a constant term worth ca. 12 kcal/mol in the\r\nprototype aromatics considered in this study. These results prompted us to\r\nuse electrostatic potential surfaces of aromatics as a qualitative and semi-quantitative\r\nguide for cation-\u03c0 interactions. We report the electrostatic\r\npotential surfaces for seventeen different \u03c0 systems. We found that the\r\ntrend found in the binding of sodium cation to the \u03c0 surface of the\r\naromatic can be easily reproduced by simple visual inspection of these\r\nsurfaces. We evaluated the electrostatic potential surfaces with ab initio\r\nand semi-empirical calculations and we found that AM1 surfaces can\r\nreproduce the trends found in the ab initio surfaces. We then report a\r\nseries of AM1 electrostatic potential surfaces for a larger series of aromatic\r\nsystems, and show their relevance to medicinal and biological issues.
\r\n\r\nThe synthesis of a neutral water-soluble cyclophane receptor is then\r\nreported. This molecule originated from previous studies on a similar\r\nreceptor bearing four peripheral carboxylates. The uncertain importance of\r\nthese carboxylates on the binding of cations inspired us to make its neutral\r\nwater-soluble analog. We report the binding affinities of this host for some\r\nneutral and positively charged guests. The absence of the external negative\r\ncharges results in a decrease of approximately 1.5 kcal/mol in selected\r\nguests.
\r\n\r\nFinally, synthetic approaches to the synthesis of two new\r\ncyclophane receptors are reported. In one case we added four more\r\nperipheral negative charges to the host, and in the other case we made a\r\nwater-soluble cyclophane with only one carboxylate adjacent to the\r\nbinding cavity. The former receptor was designed to study long-range\r\nelectrostatic interactions in aqueous media, while the latter host was\r\ndesigned to study short-range electrostatic interactions.
", "doi": "10.7907/vpy4-bb38", "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:18880", "collection": "thesis", "collection_id": "18880", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:08042026-202912516", "primary_object_url": { "basename": "Priestley_ES_1996.pdf", "content": "final", "filesize": 50321557, "license": "other", "mime_type": "application/pdf", "url": "/18880/1/Priestley_ES_1996.pdf", "version": "v2.0.0" }, "type": "thesis", "title": "Energetics of Triple Helix Formation by Oligonucleotides Containing Nonnatural Bases", "author": [ { "family_name": "Priestley", "given_name": "Eldon Scott", "orcid": "0000-0001-8390-1143", "clpid": "Priestley-Eldon-Scott" } ], "thesis_advisor": [ { "family_name": "Goldreich", "given_name": "Peter Martin", "clpid": "Goldreich-P-M" }, { "family_name": "Dervan", "given_name": "Peter B.", "orcid": "0000-0001-8852-7306", "clpid": "Dervan-P-B" } ], "thesis_committee": [ { "family_name": "Myers", "given_name": "Andrew G.", "orcid": "0000-0001-9602-6915", "clpid": "Myers-A-G" }, { "family_name": "Rees", "given_name": "Douglas C.", "orcid": "0000-0003-4073-1185", "clpid": "Rees-D-C" }, { "family_name": "Imperiali", "given_name": "Barbara", "orcid": "0000-0002-5749-7869", "clpid": "Imperiali-B" }, { "family_name": "Dervan", "given_name": "Peter B.", "orcid": "0000-0001-8852-7306", "clpid": "Dervan-P-B" } ], "local_group": [ { "literal": "div_chem" } ], "abstract": "Oligonucleotide directed triple helix formation is a powerful chemical approach to\r\nthe sequence specific recognition of duplex DNA. In this approach, pyrimidine\r\noligonucleotides bind homopurine duplex sequences by formation of T\u00b7AT and C+GC\r\nbase triplets. Likewise, purine oligonucleotides also bind homopurine sequences by\r\nformation of G\u00b7GC and either A\u00b7AT or T\u00b7AT triplets. The two motifs differ in that the\r\nthird strand oligonucleotide binds parallel to the homopurine duplex strand in the\r\n\"pyrimidine motif\" and antiparallel in the \"purine motif.\" This approach currently lacks\r\ngenerality, since there are no third strand bases available for highly specific, high affinity\r\nrecognition of CG and TA base pairs in either structural motif. In addition, the pyrimidine\r\nmotif suffers from pH dependent triplex stability introduced by the C+GC base triplets,\r\nwhile the purine motif suffers from competing aggregation due to G quartet formation by\r\nthe G-rich third strand. In principle, these problems may be addressed by the development\r\nof nonnatural bases with the desired properties.
\r\n\r\nThis thesis describes the application of quantitative DNase footprinting methods to\r\ndetermine the energetics of triple helix formation by oligonucleotides containing nonnatural\r\nbases. Chapter One provides an introduction to current research on triple helix formation.\r\nChapter Two describes an NMR study of an intramolecular triplex containing the\r\nnonnatural base P, which provides pH independent recognition of GC base pairs. Chapter\r\nThree describes the quantitation of the specificity and sequence composition effects for\r\ntriple helix formation by oligonucleotides containing P, using DNase footprinting. The\r\nspecificity assay has proven particularly useful for initial characterization of a variety of\r\nnovel bases. In Chapter Four, the synthesis and binding studies of the desmethyl derivative\r\nof P are reported. The results indicate that removal of the methyl group has a small\r\ndetrimental effect on triple helix formation. Chapter Five describes an investigation of the\r\nspecificity of the novel base 2-pyrimidinone. Chapter Six introduces the nonnatural base\r\nN7-deoxyguanosine, which is shown to be a replacement for P as a base for pH\r\nindependent GC recognition, since it shows slightly improved affinity and is synthetically\r\nmore accessible. Chapter Seven describes attempts to develop a new structural motif for\r\ntriple helix formation based on N7-substituted purine nucleosides.
", "doi": "10.7907/ja6x-c417", "publication_date": "1996", "thesis_type": "phd", "thesis_year": "1996" }, { "id": "thesis:4843", "collection": "thesis", "collection_id": "4843", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-12072007-081017", "primary_object_url": { "basename": "Willette_gt_1994.pdf", "content": "final", "filesize": 4011220, "license": "other", "mime_type": "application/pdf", "url": "/4843/1/Willette_gt_1994.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "Stochastic excitation of the solar oscillations by turbulent convection", "author": [ { "family_name": "Willette", "given_name": "Gregory Thomas", "clpid": "Willette-G-T" } ], "thesis_advisor": [ { "family_name": "Goldreich", "given_name": "Peter Martin", "clpid": "Goldreich-P-M" } ], "thesis_committee": [ { "family_name": "Unknown", "given_name": "Unknown" } ], "local_group": [ { "literal": "Astronomy Department" }, { "literal": "div_eng" } ], "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\n\r\nThe thesis topic is the stochastic excitation of the solar p-modes by turbulent convection, and the work consists of four parts: three theoretical sections and one observational. In the first section of the thesis, an explicit calculation of the acoustic radiation of a buoyant oscillating bubble is presented as a model for the excitation of the solar p-modes. The central scientific issue addressed in this work is the cancellation of monopole and dipole radiation fields in an anisotropic medium, first pointed out by Goldreich and Kumar (1990). When the bubble oscillation frequency is small compared to the acoustic cutoff, the monopole and dipole disturbances cancel to the quadrupole order in the far field. The second section deals with the role of convective structures in a wide number of problems, including the creation of acoustic disturbances, the transport of heat and magnetic fields, and the penetration of flows into stable layers of the atmosphere (overshoot). A model of plume convection is developed to discuss these issues. It is argued that the scaleheight-sized flows (the only energetically significant ones) are properly characterized as coherent, entropy-preserving plumes, in contradistinction to the picture of amorphous parcels of fluid suggested by the Mixing Length Theory, and in spite of the large Reynolds numbers typical in astrophysical convection. The third section of the thesis is an analysis of high-resolution surface velocity data taken with a magneto-optical filter on the 10 inch telescope at Big Bear Solar Observatory. Estimates are obtained for the frequencies and amplitudes of the solar oscillations of high spherical harmonic degree ([...] 2000). The observed mode energies follow a Boltzmann distribution [...], as is predicted in the stochastic excitation model. In the final section of the thesis, a derivation of the variational principle for an incompressible fluid is presented. The Lagrange and Hamiltonian densities are calculated to third order in the displacement field, and these results suitable to study the non-linear interactions among incompressible modes.\r\n", "doi": "10.7907/7nmq-8a04", "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: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: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: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: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: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:849", "collection": "thesis", "collection_id": "849", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-03032006-160754", "type": "thesis", "title": "1. Tidal Synchronization of the Rotation of Early Main Sequence Stars in Close Binaries. 2. The Rings of Uranus: Results of the 1978 April 10 Occultation. 3. On the Resonance Theory of the Rings of Uranus", "author": [ { "family_name": "Nicholson", "given_name": "Philip David", "orcid": "0000-0003-2275-4463", "clpid": "Nicholson-Philip-David" } ], "thesis_advisor": [ { "family_name": "Goldreich", "given_name": "Peter Martin", "clpid": "Goldreich-P-M" } ], "thesis_committee": [ { "family_name": "Unknown", "given_name": "Unknown" } ], "local_group": [ { "literal": "Astronomy Department" }, { "literal": "div_gps" } ], "abstract": "Part 1:
\r\n\r\nThe rotational synchronization of an early type main sequence star in a close binary system has been attributed to radiative damping of the dynamical component of the tide raised in the star by its companion (Zahn, 1975, 1977). An investigation of the dynamical tide is presented here, which includes the heretofore neglected effects of stellar rotation. Foremost among these effects is the splitting of the tidal response into a set of modes whose latitudinal structures are controlled by the solutions of Laplace's tidal equation.
\r\n\r\nAn approximate analytic expression is derived for the rate of tidal energy dissipation associated with each of these modes, which in turn determines the rate of synchronization of the star's rotation with its orbital motion. This analytic result is supported by a numerical analysis of the dynamical tide raised in a 5 M\u2299 star. Combination of analytic and numerical results yields synchronization timescales for stars in the mass range 2 M\u2299 - 10 M\u2299. These timescales are a factor of 10 shorter than those obtained by Zahn, and are in good agreement with the observational data concerning synchronism among early type stars in close binaries. It is suggested, however, that the final stages of synchronization are controlled by another mechanism: the slow stellar expansion which accompanies the later stages of main sequence evolution.
\r\n\r\nPart 2:
\r\n\r\nObservations of the 1978 April 10 stellar occultation by the rings of Uranus are presented. Nine rings were observed and their radii and widths are calculated. Rings \u03b7, \u03b3, and \u03b4 are found to be most likely circular and coplanar, in agreement with previous analyses; the remaining rings are either non-circular or slightly inclined. The width of the \u03f5 ring is a linear function of its radius from the center of Uranus, projected onto the satellites' orbital plane; this suggests that it forms one continuous non-circular ring. The optical depth profile of the \u03f5 ring has not changed significantly since 1977 March. A model of this ring which fits all available observations adequately is that of a uniformly precessing Keplerian ellipse coplanar with the satellites' orbits. This model permits predictions of the radius and width of the \u03f5 ring for future occultations. The precession rate is used to determine J2 for Uranus, on the assumption that precession is caused solely by the planetary oblateness and not by satellite-ring interactions.
\r\n\r\nPart 3:
\r\n\r\nA three-body resonance model proposed to account for the rings of Uranus is quantitatively analyzed and found to be unacceptable on several grounds. Calculation of the strengths of two-body and three-body resonances involving all known satellites of Uranus, and which fall in the neighborhood of the rings, reveals that the strongest resonances are the 4:1 and 5:1 resonances with Miranda, and the three-body resonances involving Miranda and Ariel. Resonances invoked by the proposed model are much weaker. Despite the fact that four of these relatively strong resonances approximately coincide with rings 5, \u03b1, \u03b3, and \u03f5, they are too weak to explain the observed widths of the rings. Finally, the simple ring model of densely packed particles librating about a resonance is shown to be secularly unstable.
", "doi": "10.7907/xtcv-p562", "publication_date": "1979", "thesis_type": "phd", "thesis_year": "1979" }, { "id": "thesis:3377", "collection": "thesis", "collection_id": "3377", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-09082004-115311", "type": "thesis", "title": "Molecular Clouds and Star Formation", "author": [ { "family_name": "Sargent", "given_name": "Anneila Isabel", "clpid": "Sargent-Anneila-Isabel" } ], "thesis_advisor": [ { "family_name": "Goldreich", "given_name": "Peter Martin", "clpid": "Goldreich-P-M" } ], "thesis_committee": [ { "family_name": "Unknown", "given_name": "Unknown" } ], "local_group": [ { "literal": "Astronomy Department" }, { "literal": "Caltech Distinguished Alumni Award" }, { "literal": "div_pma" } ], "abstract": "Observations of the J = 1 \u2192 0 transition of 12CO were made in and around the region occupied by the young OB association Cepheus OB3 to determine the connection between newly formed stars and molecular clouds. An extended (20 pc x 60 pc) molecular cloud was detected and mapped, and additional observations of 13CO and H2CO were made at selected positions. The total mass of the cloud is 5 x 103 M\u2609. A range of velocities is seen over the cloud complex. This is comparable with the stellar velocities in the association.
\r\n\r\nWithin the molecular cloud are found three regions in which different stages of star formation are identified. In one an embedded star may be present. Another appears to be collapsing on a time scale of ~3 x 105 years to form a new subgroup of the OB association. The mass of this region, 500 M\u2609, is sufficient to produce only the number of O and B stars typically found in association subgroups, suggesting that lower mass stars must form under different conditions. The third displays signs of enhanced density and is probably the precursor of a star forming region. All three regions are situated in that part of the molecular cloud which is closest to the association stars.
\r\n\r\nThe membership and ages of the subgroups of the Cepheus OB3 association have been re-examined, and their places of origin determined. Ages of 1-3 x 105 years and 5-7 x 105 years are found for younger and older subgroups respectively. Their birthplaces are not coincident but are situated at that end of the cloud where star formation still appears to be taking place. The younger subgroup appears to have formed closer to the active regions than did the older subgroup, so that there is a well-defined age sequence across the association which continues into the cloud.
\r\n\r\nThere is currently little direct interaction between the stars and the molecular cloud, although a few younger subgroup stars still lie close to or within the complex. The absence of primeval gas in the environs of the older subgroup is attributed to the unusually high velocity of separation between these stars and the cloud.
\r\n\r\nIt appears that the younger and still-forming subgroups of Cepheus OB3 are created in a different way from the older subgroup. However, the way in which star formation is initiated in this association remains uncertain.
\r\n", "doi": "10.7907/XZSK-2H71", "publication_date": "1978", "thesis_type": "phd", "thesis_year": "1978" }, { "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:10392", "collection": "thesis", "collection_id": "10392", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:08252017-145131867", "primary_object_url": { "basename": "Kwan_JYK_1973.pdf", "content": "final", "filesize": 24975678, "license": "other", "mime_type": "application/pdf", "url": "/10392/1/Kwan_JYK_1973.pdf", "version": "v2.0.0" }, "type": "thesis", "title": "Polarization Properties of Astrophysical Masers", "author": [ { "family_name": "Kwan", "given_name": "John Ying-Kuen", "clpid": "Kwan-John-Ying-Kuen" } ], "thesis_advisor": [ { "family_name": "Goldreich", "given_name": "Peter Martin", "clpid": "Goldreich-P-M" } ], "thesis_committee": [ { "family_name": "Unknown", "given_name": "Unknown" } ], "local_group": [ { "literal": "TAPIR" }, { "literal": "Astronomy Department" }, { "literal": "div_pma" } ], "abstract": "Observed interstellar OH and H2O maser lines at 18 cm and\r\n1.35 cm exhibit unusual polarization properties. The OH emitters with the\r\nhighest brightness temperatures, usually associated with H II regions, almost\r\nalways show a high degree of circular polarization. The H2O maser line,\r\non the other hand, is rarely polarized, and then only linearly polarized.
\r\n\r\nThe preference for circular polarization in the brightest OH\r\nsources was attributed by Litvak to the mechanism of parametric down-conversion.\r\nIn this process the higher-frequency components of a Zeeman\r\nsplit maser line are down-converted to lower-frequency components and to\r\nan electron cyclotron wave. This mechanism is shown to be too weak to be\r\nof importance in astrophysical masers.
\r\n\r\nThe polarization properties of the OH and H2O masers are related \r\nto the physical conditions in the maser clouds. It is found that the magnetic\r\nfield, the plasma, and trapped infrared lines in maser sources play an\r\nimportant role in determining the polarization on the emitted radiation.
", "doi": "10.7907/906J-2N21", "publication_date": "1973", "thesis_type": "phd", "thesis_year": "1973" }, { "id": "thesis:874", "collection": "thesis", "collection_id": "874", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-03042009-085737", "primary_object_url": { "basename": "Ward_wr_1973.pdf", "content": "final", "filesize": 8967564, "license": "other", "mime_type": "application/pdf", "url": "/874/1/Ward_wr_1973.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "I. The Formation of Planetesimals. II. Tidal Friction and Generalized Cassini's Laws in the Solar System", "author": [ { "family_name": "Ward", "given_name": "William Roger", "clpid": "Ward-William-Roger" } ], "thesis_advisor": [ { "family_name": "Goldreich", "given_name": "Peter Martin", "clpid": "Goldreich-P-M" } ], "thesis_committee": [ { "family_name": "Unknown", "given_name": "Unknown" } ], "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\nIn Part 1, four stages in the accretion of planetesimals are described. The initial stage is the condensation of dust particles from the gaseous solar nebula as it cools. These dust particles settle into a thin disk which is gravitationally unstable. A first generation of planetesimals, whose radii range up to ~10\u207b\u00b9 kilometer, form from the dust disk by direct gravitational collapse to solid densities on a time scale of order one year. The resulting disk, composed of first generation planetesimals, is still gravitationally unstable and the planetesimals are grouped into clusters containing approximately 10\u2074 members. The contraction of these clusters is controlled by the rate at which gas drag damps their internal rotational and random kinetic energies. On a time scale of a few thousand years, the clusters contract to form a second generation of planetesimals having radii of the order of a few kilometers. Further coalescence of planetesimals proceeds by collisions which seem capable of producing objects with a growth rate of ~15 cm. yr\u207b\u00b9 at one A.U. The final stage of accretion during which planet-sized objects form is not considered here.
\r\n\r\nIn Part 2 of this thesis, an investigation of a dynamical problem which has considerable application to the solar system is undertaken. The evolution of the obliquity of an object is determined when under the influence of three phenomena: (1) the precession of the object's orbit plane, (2) the precession of the object's spin axis, and (3) tidal friction. In the absence of tidal friction, it is concluded that if the period for precession of the spin axis is much shorter than the orbit precession period, the obliquity of the object will remain very nearly constant in spite of the movement of the orbit normal. It is further concluded, that since the obliquity is not changed by the motion of the orbit plane, the decay of the obliquity towards zero by tidal friction is not significantly altered by this motion. These results are applied to Mercury, Venus, Iapetus, Triton, as well as the equatorial satellites of Mars, Jupiter, Saturn, and Uranus. The final spin states of these objects satisfy a generalization of Cassini's laws for the moon.
", "doi": "10.7907/kqm5-4r97", "publication_date": "1973", "thesis_type": "phd", "thesis_year": "1973" }, { "id": "thesis:9912", "collection": "thesis", "collection_id": "9912", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:09062016-085609385", "primary_object_url": { "basename": "Strange_dlp_1972.pdf", "content": "final", "filesize": 14749505, "license": "other", "mime_type": "application/pdf", "url": "/9912/1/Strange_dlp_1972.pdf", "version": "v2.0.0" }, "type": "thesis", "title": "Radiative Processes in an Intense Magnetic Field", "author": [ { "family_name": "Strange", "given_name": "Donald Lionel Patrick", "clpid": "Strange-Donald-Lionel-Patrick" } ], "thesis_advisor": [ { "family_name": "Goldreich", "given_name": "Peter Martin", "clpid": "Goldreich-P-M" } ], "thesis_committee": [ { "family_name": "Unknown", "given_name": "Unknown" } ], "local_group": [ { "literal": "div_pma" } ], "abstract": "Three astrophysical problems relating to the intense magnetic fields associated with neutron stars (i.e. 1012 gauss) and white dwarfs (i.e. 108 gauss) are studied.
\r\n\r\n(1) The radiation rate for non-relativistic bremsstrahlung in 1012 gauss is computed by both quantum-mechanical and classical methods. The main features of this emissivity are a 1/pz dependence (magnetic field in the z-direction) characteristic of a one-dimensional momentum space, a larger flux perpendicular to \u0496 than parallel to it, and a net left-handed polarization in the flux parallel to \u0496.
\r\n\r\n(2) The electron energy levels and orbits for hydrogen in 1012 gauss are calculated with variational techniques. The ground state binding energy is found to be 200 ev. The other levels divide into a set of tightly bound states (binding energies 100 to 200 ev) and a double-set of hydrogen-like levels (0 to 13 ev). The overall electron density of the atom is elongated along the magnetic field direction. The thermal ionization fraction of a neutral hydrogen plasma is computed using an appropriately modified Saha equation, and is found to be 90%. Finally, high Z atoms are investigated via the Thomas-Fermi approximation with the result that the definitive equation is
\r\n\r\nX11 = X1/2x1/2
\r\n\r\ngiving an atomic radius of
\r\n\r\nR = 4 x 10-5 Z1/5 \u04962/5 cm.
\r\n\r\n(3) Cyclotron emission and absorption in a magnetic field of 108 gauss is studied as a possible mechanism for the observed degree of circular polarization in the optical emission from white dwarfs. A few simple models explain some of the quantitative and qualitative aspects of the polarization data.
\r\n\r\n", "doi": "10.7907/TDYS-3Y25", "publication_date": "1972", "thesis_type": "phd", "thesis_year": "1972" }, { "id": "thesis:1665", "collection": "thesis", "collection_id": "1665", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-05072008-142808", "primary_object_url": { "basename": "Keeley_da_1970.pdf", "content": "final", "filesize": 4725152, "license": "other", "mime_type": "application/pdf", "url": "/1665/1/Keeley_da_1970.pdf", "version": "v2.0.0" }, "type": "thesis", "title": "Static and Dynamical Models of Long-Period Variable Stars", "author": [ { "family_name": "Keeley", "given_name": "Douglas Allan", "clpid": "Keeley-Douglas-Allan" } ], "thesis_advisor": [ { "family_name": "Goldreich", "given_name": "Peter Martin", "clpid": "Goldreich-P-M" } ], "thesis_committee": [ { "family_name": "Unknown", "given_name": "Unknown" } ], "local_group": [ { "literal": "Astronomy Department" }, { "literal": "div_pma" } ], "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nThe parameters of the models were M=1 and 1.3M[...], M[subscript B] = -3.8 to -5, and T[subscript e] = 2200[...]K. The equation of state included a detailed calculation of ionization equilibrium and the dissociation of H2, OH, CO, and H2O. The opacity of CO, OH, and H2O was included. The dynamical calculations show that large-amplitude pulsation can occur in convective models. The opacity mechanism causes strong driving of the pulsation in the region outside the hydrogen ionization zone, and the [gamma]-mechanism results in very low dissipation in the hydrogen zone. The phase relation between the bolo-metric luminosity and the radius variations is similar to that of Cepheids. The static models have large ionization and dissociation zones, which cause the pulsation parameter Q=P[subscript days](p/p[...])[...] to become greater than 0.15 in some models. The fundamental periods range from 180 days to greater than 2000 days; the overtone periods are about [...] as long. The positions of many observed stars in the theoretical HR diagram suggest that their periods should be associated with the overtone periods of the models.", "doi": "10.7907/NTN2-HH47", "publication_date": "1970", "thesis_type": "phd", "thesis_year": "1970" }, { "id": "thesis:1566", "collection": "thesis", "collection_id": "1566", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-05012008-103453", "primary_object_url": { "basename": "Defouw_rj_1970.pdf", "content": "final", "filesize": 3662222, "license": "other", "mime_type": "application/pdf", "url": "/1566/1/Defouw_rj_1970.pdf", "version": "v2.0.0" }, "type": "thesis", "title": "Thermal Instability and the Convective Stability of Stellar Chromospheres", "author": [ { "family_name": "Defouw", "given_name": "Richard John", "clpid": "Defouw-Richard-John" } ], "thesis_advisor": [ { "family_name": "Goldreich", "given_name": "Peter Martin", "clpid": "Goldreich-P-M" } ], "thesis_committee": [ { "family_name": "Unknown", "given_name": "Unknown" } ], "local_group": [ { "literal": "TAPIR" }, { "literal": "Astronomy Department" }, { "literal": "div_pma" } ], "abstract": "It is generally believed that stellar chromospheres are stable against convection since the Schwarzschild criterion indicates stability when temperature increases with height. It is shown, however, that the Schwarzschild criterion does not apply to chromospheres because it ignores the possibility of thermal instability. In the absence of a magnetic field, thermally unstable regions of a chromosphere will be overstable if the temperature inversion is sufficiently steep. This overstability may explain the origin of a certain class of oscillations in the solar chromosphere. Thermally unstable regions containing magnetic fields are monotonically unstable for all values of the temperature gradient. It is suggested that this monotonic instability of magnetic regions is responsible for spicule formation in the solar chromosphere. Elementary considerations of thermal balance predict that the temperature gradient should diverge at levels of marginal stability. The chromospheric region of spicule formation should therefore be bounded below by an abrupt temperature jump.
\r\n\r\nThe above results are derived by analyzing the stability of a simple model chromosphere in which all neutral hydrogen atoms are assumed to be in the ground state. Although the model chromosphere emits only free-bound radiation, its thermal instability is caused by the same ionization effects which lead to instability in plasmas emitting line radiation. Thermally unstable regions of a stellar chromosphere, although not represented in detail by the model, should behave in a similar fashion.
\r\n", "doi": "10.7907/QDN8-FH95", "publication_date": "1970", "thesis_type": "phd", "thesis_year": "1970" } ]