322 Works

Spectroscopy and Kinetics of Atmospheric and Astrochemical Reactions

Joseph Peter Herman Messinger
The reactions between reactive radicals and other neutral compounds have long been known to be important in atmospheric chemistry and astrochemistry. This work uses pulsed-laser photolysis cavity ringdown spectroscopy and laser-induced fluorescence to measure the rate constants and branching ratios of chemical reactions over a wide range of temperatures and pressures relevant to both polluted atmospheres, and the interstellar medium. This includes studying the OH + NO₂ reaction in the 253 – 333 K range,...

Non-Covalent Interactions in Aqueous Media: Molecular Recognition Studies Through Circular Dichroism and Self-Assembly of Discrete Aggregates

Jonathan Eric Forman
The application of circular dichroism (CD) spectroscopy to the study of molecular recognition phenomena in chiral water-soluble cyclophane hosts is described. The CD method produces results that complement and expand upon previous NMR studies. This includes allowing the measurement of larger binding constants by allowing studies to be carried out at lower concentrations. Using the excitonic chirality method, these studies have provided a means of assigning the absolute stereochemistry of the ethenoanthracene building blocks used...

Cooperative Oligonucleotide-Directed Triple Helix Formation at Adjacent DNA Sites

Natalia Colocci
Cooperative interactions between DNA-binding ligands are essential for their sequence specificity, binding affinity, and biological activity. Oligonucleotides can bind cooperatively to adjacent sites on double-helical DNA by triple helix formation. The study of the cooperative binding of oligonucleotides to DNA by triple helix formation is important as it provides useful information for the development of new methods leading to the sequence-specific recognition of DNA. As a first step towards this goal, the thermodynamics of the...

Boundary Integral Equation Methods for Simulation and Design of Photonic Devices

Emmanuel Garza Gonzalez
This thesis presents novel boundary integral equation (BIE) and associated optimization methodologies for photonic devices. The simulation and optimization of such structures is a vast and rapidly growing engineering area, which impacts on design of optical devices such as waveguide splitters, tapers, grating couplers, and metamaterial structures, all of which are commonly used as elements in the field of integrated photonics. The design process has been significantly facilitated in recent years on the basis of...

Scanning Tunneling Microscopy and Spectroscopy of Silicon and Carbon Surfaces

Shenda Mary Baker
Scanning Tunneling Microscopy (STM) investigations and additional surface analyses were performed on carbon and silicon surfaces. A number of anomalies have been observed on highly oriented pyrolytic graphite (HOPG), including large corrugations, distorted images, large range of tip motion and the absence of defects. A mechanism involving direct contact between tip and sample or contact through a contamination layer to provide an additional conduction pathway is proposed. This model of point-contact imaging provides an explanation...

Hunting for Hidden Explosions: Exploring the Transient Infrared Sky with the Spitzer Space Telescope

Jacob Edmund Jencson
The study of time-variable astronomical phenomena is undergoing an explosive renaissance ushered in by recent advancements in capabilities to monitor the sky from radio to gamma rays. The infrared region of the electromagnetic spectrum provides a unique window to uncover a vast array of stellar eruptions and explosions that are otherwise obscured; however, the dynamic infrared sky has remained largely unexplored. To uncover these hidden cosmic explosions, I undertook a systematic search in the infrared...

Suspension Mechanics: I. Inertial and Non-Newtonian Migration of Neutrally Buoyant Rigid Spheres in Two-Dimensional Unidirectional Flows. II. The Effect of Viscoelasticity on the Creeping Motion of a Train of Neutrally Buoyant Newtonian Drops through a Circular Tube

Bosco Po-Wai Ho
The lateral migration of neutrally buoyant rigid spheres in two-dimensional unidirectional flows was studied theoretically. The cases of both inertia-induced migration in a Newtonian fluid and normal stress-induced migration in a second-order fluid were considered. Analytical results for the lateral velocities were obtained, and the equilibrium positions and trajectories of the spheres compared favorably with the experimental data available in the literature. The effective viscosity was obtained for a dilute suspension of spheres which were...

Information Scrambling in Quantum Many-Body Systems

Yongliang Zhang
A closed quantum system never forgets its initial state, but the encoded information can get scrambled and become inaccessible without measuring a large fraction of all the system degrees of freedom. This scrambling can be diagnosed by studying the spatial spreading of initially local operators under the Heisenberg time evolution, and the decay of the out-of-time-ordered correlators (OTOC). What insights can OTOCs provide to understand the dynamics of quantum many-body systems? What are the characteristic...

Surface Reconstruction from Distributed Angle Measurements

Thibaud Talon
This thesis presents an innovative solution to the shape measurement of large structures for space applications. The current state-of-the-art heavily relies on optical solutions such as cameras or lasers to recover the shape of a surface. Because of the impracticality of placing a system in front of a large structure flying in space, new solutions need to be developed. The proposed solution is to embed angular sensors (such as sun sensors) directly on the surface....

Silicon-Directed Carbon-Carbon Bond Forming Reactions

Katherine Widdowson
It is shown that O-silyl ketene N,O-acetals react with aldehydes, without catalysis, to form aldol-type products with high diastereoselectivity. For example, the prolinolderived O-silyl ketene N,O-acetal 7 reacts with benzaldehyde to form the anti aldol product 9 with > 98% diastereoselectivity. Mechanistic studies are presented which support a scheme involving formation of trigonal bipyrarnid (tbp) G, pseudorotation to form tbp Tboat, and rate-determining C-C bond formation to produce 9. [Formula. See abstract in scanned thesis...

Visually Mediated Control of Flight in Drosophila: Not Lost in Translation

Michael Bernard Reiser
Flying insects exhibit stunning behavioral repertoires that are largely mediated by the visual control of flight. For this reason, presenting a controlled visual environment to tethered insects has been and continues to be a powerful tool for studying the sensory control of complex behaviors. The work presented in this dissertation concerns several robust behavioral responses exhibited by Drosophila that shed light on some of the challenges of visual navigation. To address questions of visual flight...

Mechanics of Ultra-Thin Composite Coilable Structures

Christophe Leclerc
Coilable structures are thin-shell structures that can be coiled around a hub by flattening their cross-section. They are attractive for multiple space applications as they allow efficient packaging and deployment of large planar structures. Reducing the shell thickness enables smaller coiling radius and more efficient packaging. This thesis investigates TRAC structures, a type of coilable structure, made of ultra-thin composite materials. A design using a laminate made of glass fiber plainweave fabric and carbon fiber...

Phonon Thermodynamics and Elastic Behavior of GaN and GaAs at High Temperatures and Pressures

Jane Elizabeth Herriman
The work herein studies how high temperatures and pressure impact the properties of four materials: two phases of Gallium Nitride (GaN) and two phases of Gallium Arsenide (GaAs). The particular phases we study are the wurtzite and zinc blende phases of each chemical composition. The properties we study concern (1) the phonon thermodynamics and (2) the elastic behavior. In particular, phonons were calculated at simultaneously elevated temperature and pressure, and elastic constants were calculated as...

On the influence of radial components of blade forces in axial turbomachines

Thorbjorn Karlsson
The flow of an incompressible inviscid fluid through a turbomachine with infinite number of blades is investigated in this paper in order to determine the effects of radial forces resulting from the twist of the blades on the flow through the machine. Prandtl's method of replacing blade rows by distributed vorticity is used and the mathematical problem is treated from that point of view. The flow through the annulus between hub and outer casing of...

Methods for Computational Enzyme Design and Application to the Chorismate-Prephenate Rearrangement

Jonathan Kyle Lassila
The Claisen rearrangement of chorismate to prephenate has become an important model system for developing understanding of enzymatic catalysis as well as for computational treatment of enzyme active sites. This thesis presents general methods for the computational design of enzyme active sites and applies these methods to the design of catalysts for the chorismate-prephenate rearrangement. The computational methods described allow the incorporation of transition-state structures and other small molecules into protein design calculations. These design...

The Many Facets of Cosmic Explosions

Alicia Margarita Soderberg
Over the past few years, long-duration gamma-ray bursts (GRBs) including the subclass of X-ray flashes (XRFs) have been revealed to be a rare variety of Type Ibc supernova (SN Ibc). While all these events result from the death of massive stars, the electromagnetic luminosities of GRBs and XRFs exceed those of ordinary Type Ibc SNe by many orders of magnitude. The observed diversity of stellar death corresponds to large variations in the energy, velocity and...

Function and Regulation of the Strongylocentrotus purpuratus gatae Gene

Pei Yun Lee
The Strongylocentrotus purpuratus gatae is orthologous to vertebrate gata4/5/6 genes. gatae is expressed throughout embryogenesis, beginning in the 15 h blastula in presumptive mesoderm cells, and at mesenchyme blastula, in endoderm and mesoderm cells of the veg2 lineage. During gastrulation, gatae is expressed in the midgut, hindgut and mesoderm, while in the pluteus expression it is limited to the midgut and coelomic pouches. Perturbation of gatae expression resulted in the lowered RNA levels for many...

Crystal to Glass Transition and its Relation to Melting

Mo Li
This work contributes to the understanding of thermodynamic aspects and microscopic mechanisms of the crystal to glass transition and its relationship to melting. The topological order to disorder transition was investigated primarily in a model system consisting of Lennard-Jones binary solid solutions via molecular dynamics simulations. Under constant temperature and pressure, thermodynamic properties and structures of the solid solutions are mainly determined by solute/solvent atomic size difference and solute concentration. At a critical atomic size...

Computational Studies of Orphan G Protein-Coupled Receptors

Jiyoung Heo
G protein-coupled receptors (GPCRs) play an essential role in cell communications and sensory functions. Consequently, they are involved in wide variety of diseases and are targets for many drug therapies. Particularly important is the large number of orphan GPCRs, which may play important, albeit unknown, functions in various cells. To understand their respective physiological roles, it is important to identify their endogenous ligands, and to find small molecule ligands that would serve as selective agonists...

Deep Learning in Unconventional Domains

Michael William (Milan0 Cvitkovic
Machine learning methods have dramatically improved in recent years thanks to advances in deep learning (LeCun et al., 2015), a set of methods for training high-dimensional, highly-parameterized, nonlinear functions. Yet deep learning progress has been concentrated in the domains of computer vision, vision-based reinforcement learning, and natural language processing. This dissertation is an attempt to extend deep learning into domains where it has thus far had little impact or has never been applied. It presents...

On-Chip Photonic Devices for Coupling to Color Centers in Silicon Carbide

Chuting Wang
Optical quantum networks are important for global use of quantum computers, and secure quantum communication. Those networks require storage devices for synchronizing or making queues of processing transferred quantum information. Practical quantum information networks should minimize loss of transmitted data (photons) and have high efficiency mapping when writing data on memories (solid state qubits). This requires strong light-matter interaction that is enabled by coupling qubits to optical cavities. The first half of the thesis focuses...

I. Regional Variations in Upper Mantle Compressional Velocities beneath Southern California. II. Post-Shock Temperatures: Their Experimental Determination, Calculation, and Implications

Susan Ann Raikes
The establishment in Southern California of a large seismographic network provides an unique opportunity for studying the seismic velocity variations within a tectonically active region that includes a major plate boundary, whose surface expression is the San Andreas Fault. In the first part of this thesis, the compressional velocity within the upper mantle beneath Southern California is investigated through observations of the dependence of teleseismic P-delays at all stations of the array on the distance...

Spectroscopy of Reactive Molecules and Clusters

Matthew Stanley Johnson
This thesis presents spectroscopic investigations of reactive molecules and clusters. The techniques of laser excited fluorescence, infrared predissociation spectroscopy, and photoelectron spectroscopy were employed to investigate systems relating to fundamental cluster chemistry, ion solvation, and atmospheric ozone depletion. An instrument was developed to investigate van der Waals complexes of refractory elements. A pulsed laser ablation cluster source harnessed the cooling power of a supersonic free jet to condense weakly bound neutral clusters. Laser excited fluorescence...

Higher-Order RNA and DNA Hubs Shape Genome Organization in the Nucleus

Sofia Agustina Quinodoz
Although the entire genome is present within the nucleus of every cell, distinct genes need to be accessed and expressed in different cellular conditions. Accordingly, the nucleus of each cell is a highly organized arrangement of DNA, RNA, and protein that is dynamically assembled and regulated in different cellular states. These dynamic nuclear structures are largely arranged around functionally related roles and often occur across multiple chromosomes. These include large nuclear bodies (i.e., nucleolus, nuclear...

Decision Making Under Threat: An Ecological Framework

Song Qi
Humans, like other animals, have evolved a set of neural circuits whose primary function is survival. In the case of predation, these circuits include "reactive fear" circuits involved in fast escape decisions, and "cognitive fear" circuits that are involved in more complex processing associated with slow strategic escape. In the context of flight initiation distance (FID), using neuroimaging combined with computational modeling, we support this differentiation of fear circuits by showing that fast escape decisions...

Registration Year

  • 2020
    322

Resource Types

  • Text
    322

Affiliations

  • California Institute of Technology
    322