8,089 Works

Dynamics of Electron-Molecule Collisions

Marco Aurelio Pinheiro Lima
We have developed a multichannel formulation for low-energy electron-molecule collisions based on the Schwinger variational method. An important feature of this formulation is that it is capable of dealing with some important aspects of electron-molecule collisions such as electronically inelastic scattering and nonlinear targets. The formulation also allows for the inclusion of a substantial number of closed electronic channels to represent polarization effects, which are very important at low-impact energies. To assess the accuracy with...

Proton-Coupled Electron Transfer in Nitrogen Fixation

Matthew J. Chalkley
This thesis focuses on the management of protons and electrons in the formation of X−H bonds. In our pursuit of better understanding this process, we have been particularly interested in the nitrogen fixation reaction (N2-to-NH3) because of the high number of protons and electrons involved in this conversion (6) and the significant difficulty of functionalizing N2. The first chapter introduces the important themes of this thesis: (i) multiple bonding, (ii) proton-coupled electron transfer, (iii) overpotential...

Ultraviolet Radiation of Hypervelocity Stagnation Flows and Shock/Boundary-Layer Interactions

Nelson Javier Yanes
Shock/boundary-layer interactions can induce flow distortion, create flow separation with loss of control authority, and result in high thermal loads. Correct prediction of the flow structure and heating loads is vital for vehicle survival. However, a recent NATO workshop revealed severe underprediction of thermal loads and discrepancies in the location of separation by simulations of high enthalpy air flows. Due to the coupling between thermochemistry and fluid mechanics, a substantial effort has been placed on...

Investigating the Evolution of Surface Water on Mars through Spectroscopy of Secondary Minerals

Ellen Kathleen Leask
Despite its current arid climate, Mars’ surface preserves a wide variety of morphologies and minerals that point to a water-rich past. However, the mechanisms and timing of this environmental change are not yet well understood. In this dissertation, we explore a variety of water-related minerals through visible-shortwave infrared (VSWIR) reflectance spectroscopy to better understand the environmental conditions at the time of their formation, and trace the evolution of surface water on Mars over time. We...

On the Index of Refraction of Spatially Periodic Plasma

C. H. Papas
A knowledge of the change produced in the index of refraction of a uniform plasma by the spontaneous generation of coagula or inhomogeneities is essential to the use of electromagnetic waves as a diagnostic tool. The general problem is a difficult one to handle, but certain non-trivial cases are mathematically tractable. One of these, which is also of some practical import, occurs when the inhomogeneities are periodically distributed throughout the plasma. Here this special case...

Comments on Philippe de la Hire’s Memoir on Arch Abutment Design (1712)

John F. Hall
Philippe de la Hire (1640-1718), a multi-disciplinary French scientist, is generally credited as being the first person to apply the principles of statics to the analysis and design of arches. Prior efforts employed geometric design rules that were based on experience. Thus, de la Hire plays an important role in the transition to scientifically based methods for civil engineering structures. Therefore, it is of historical interest to understand de la Hire’s approach and perspective.

Political Networks

Deborah Elizabeth (Betsy) Sinclair
This dissertation examines the degree to which relationships between individuals determine their political behavior. The dissertation finds, through theoretical and experimental examination, that the political context within which an individual exists affects their preferences. Additionally, using a series of canonical data-sets the correlation between context and preferences is revealed to be a consequence of the information voters obtain via horizontal voter-to-voter communication. The dissertation is divided into five sections, each of which uses a distinct...

Progress toward the Development of a Single Molecule Transistor with Graphene Electrodes

Emma Rose Schmidgall
Single molecule transistors are useful for studying both the charge and spin states of molecules. These devices consist of a nanogap with three contacts for the source, drain, and gate. Current versions use metallic contacts for the source and drain, which remain essentially three dimensional. It is thought that graphene contacts for the source and drain, which would he atomically tlat, would enable the observation of more molecular charge states due to reduced screening between...

Laser Offset Stabilization for Broadly Tunable TeraHertz (THz) Frequency Generation

Kevin Cossel
Spectroscopy and imaging in the terahertz region promises to be useful for a wide variety of applications. For remote sensing, terahertz spectroscopy could help in the identification of explosives and narcotics. In astronomy, terahertz imaging should provide new information about the composition of the interstellar medium and about the processes by which stars and planets are born. In chemistry and molecular biology, terahertz spectroscopy provides new rotational or rovibrational spectra of molecules and is useful...

Role of Conformational Changes in G Protein-Coupled Receptor Activation

Caitlin Eileen Scott
Transmembrane signal transduction is achieved by activation of G protein-coupled receptors (GPCRs) like the human cannabinoid type 1 (CB1) receptor, the human cannabinoid type 2 (CB2) receptor, and the human mu-opioid receptor. These receptors exist in the membrane in an ensemble of conformations each of which might bind to different signaling molecules and cause different physiological effects. Understanding the structural basis of their activation will eventually help us in designing drugs that target these receptors...

Extensional tectonics in the Basin and Range province and the geology of the Grapevine Mountains, Death Valley region, California and Nevada

Nathan Alan Niemi
Geologic mapping provides structural and stratigraphic observations which lead to new insights into the magnitude, timing, and rate of Cenozoic extensional tectonism in the Death Valley region of the Basin and Range province in the western United States. Detailed mapping of the Grapevine Mountains, in northeastern Death Valley, yields new information on the structural evolution of the Titus Canyon anticline, a west-vergent fold of the Cordilleran thrust belt. The Grapevine Mountains contain the longest exposure...

Energetic Protons in the Magnetosphere of Neptune

Mark Dixon Looper
The Cosmic Ray Subsystem aboard Voyager 2 measured large fluxes of trapped energetic protons and electrons in the inner magnetosphere of Neptune during the 1989 flyby; the protons above 1.9 MeV observed by the Low Energy Telescopes are analyzed in this thesis. Proton events are extracted from pulse-height distributions dominated by low-energy electron pileup noise, and fluxes are calculated with corrections for discriminator deadtime. Theoretical models for satellite absorption of charged particles are adapted to...

Mechanics of River Avulsions on Lowland River Deltas

Austin John Chadwick
Lowland deltas are home to over 0.5 billion people and some of the most biodiverse ecosystems on Earth. Deltas are highly dynamic landscapes, and at the largest scale grow through repeated construction of depositional lobes punctuated by river avulsions – abrupt shifts in river course to the shoreline. River avulsions have been responsible for dangerous floods and civil unrest over human history, but also counter land loss due to sea-level rise and coastal subsidence by...

Airships: A New Horizon for Science

Sarah H. Miller, Robert Fesen, Lynne A. Hillenbrand, Jason Rhodes, Gil Baird, Geoffrey A. Blake, Jeff Booth, David E. Carlile, Riley Duren, Frederick G. Edworthy, Brent Freeze, Randall R. Friedl, Paul F. Goldsmith, Jeffery L. Hall, Scott E. Hoffman, Scott E. Hovarter, Rebecca M. Jensen-Clem, Ross M. Jones, Jens Kauffmann, Alina Kiessling, Oliver G. King, Nick P. Konidaris, Timothy L. Lachenmeier, Steven D. Lord, Jessica Neu … & Thomas Zambrano
The "Airships: A New Horizon for Science" study at the Keck Institute for Space Studies investigated the potential of a variety of airships currently operable or under development to serve as observatories and science instrumentation platforms for a range of space, atmospheric, and Earth science. The participants represent a diverse cross-section of the aerospace sector, NASA, and academia. Over the last two decades, there has been wide interest in developing a high altitude, stratospheric lighter-than-air...

Theoretical Studies of Intramolecular Dynamics and Energy Redistribution

Gregory Alan Voth
By virtue of various theoretical techniques, the fundamental mechanisms responsible for intramolecular vibrational energy redistribution (IVR) in isolated molecules are studied in this thesis. One such mechanism, the nonlinear resonance, is examined in some detail for several systems. In particular, nonlinear stretch-bend resonances in a series of isotopically substituted methanes are predicted to have a large effect on the spectral properties of those molecules. By using a semiclassical analysis, the general properties of stretch-bend interactions...

Wide Field-of-view Microscopes and Endoscopes for Time-lapse Imaging and High-throughput Screening

Chao Han
Wide field-of-view (FOV) microscopy is of high importance to biological research and clinical diagnosis where a high-throughput screening of samples is needed. This thesis presents the development of several novel wide FOV imaging technologies and demonstrates their capabilities in longitudinal imaging of living organisms, on the scale of viral plaques to live cells and tissues. The ePetri Dish is a wide FOV on-chip bright-field microscope. Here we applied an ePetri platform for plaque analysis of...

Graph Clustering: Algorithms, Analysis and Query Design

Ramya Korlakai Vinayak
A wide range of applications in engineering as well as the natural and social sciences have datasets that are unlabeled. Clustering plays a major role in exploring structure in such unlabeled datasets. Owing to the heterogeneity in the applications and the types of datasets available, there are plenty of clustering objectives and algorithms. In this thesis we focus on two such clustering problems: Graph Clustering and Crowdsourced Clustering. In the first part, we consider the...

I. On the initial value problems of radiation and scattering of water waves by immersed obstacles. II. Gravity waves due to a point disturbance in a stratified flow

Chiang Chung Mei
I. Some initial value problems are studied regarding the radiation and scattering of gravity waves by finite bodies in an infinitely deep ocean. Emphasis is placed on the case where a finite number of thin plates lie on a vertical line, for which the general solution is obtained by transforming the boundary value problem to one of the Riemann-Hilbert type. Explicit investigations are made for the large time behavior of the free surface elevation for...

Composite Grid Construction and Applications

Geoffrey Samuel Chesshire
For many problems that involve the discrete representation of a function on a two-dimensional region, a single rectangular grid is inappropriate. However, any compact region with a smooth boundary can be discretised using a composite grid, which provides boundary-fitted coordinates and allows stretched coordinates for boundary layers and internal layers wherever these are needed. We have developed interactive software for specifying composite grids, and general-purpose subroutines for using them in discretising PDE boundary-value problems. The...

I. Reactions of non-activated aryl halides with strong basic and nucleophilic agents. II. Evidence for cyclohexene as an intermediate in the coupling reaction of phenyllithium with 1-chlorocyclohexene. III. Reactions of non-activated aryl halides with strong bases at high temperatures. IV. The synthesis of some four-membered ring compounds

Franco Scardiglia
NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document. Part I. Previous studies have shown that non-activated aryl halides are aminated by alkali amides in liquid ammonia by the way of a benzyne intermediate. Nucleophilic substitution products are formed with some strong bases and aryl halides in liquid ammonia, provided alkali amides are present. A study of the mechanism and the scope of such reactions...

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...

Resonance Cones and Mode Conversion in a Warm Magnetized Bounded Plasma

Crockett Lane Grabbe
The warm plasma resonance cone structure of the quasistatic field produced by a gap source in a bounded magnetized slab plasma is determined theoretically. This is initially determined for a homogeneous or mildly inhomogeneous plasma with source frequency lying between the lower hybrid frequency and the plasma frequency. It is then extended to the complicated case of an inhomogeneous plasma with two internal lower hybrid layers present, which is of interest to radio frequency heating...

Akt Phosphorylation of Drosophila Heat-Shock Factor: A Signature for Stress Resistance

Sarina Mohanty
The heat-shock response is vital to cellular homeostasis. Drosophila melanogaster heat-shock factor (dHSF) is the primary transcriptional activator in the stress response pathway for induction of heat-shock-mediated gene transcription. This work investigates the potential for dHSF to undergo post-translational modification by phosphorylation and lysine tagging, specifically, direct phosphorylation by kinases and covalent-lysine tagging by ubiquitin, acetyl, and SUMO groups. Direct phosphorylation of, and binding to, dHSF was demonstrated by Akt/PKB kinase. Knock-down of this kinase...

Search for scalar leptons at LEP with the L3 detector

Lei Xia
In this thesis, I present a search for scalar leptons in e+e- annihilation using the L3 detector at LEP. Data collected in 1999 and 2000, at center-of-mass energies between 192 GeV and 208 GeV, was used in this analysis. This work covered the scalar lepton searches in both SUGRA and GMSB models. To achieve this analysis, a parametrized selection was developed to handle the different event signatures in SUGRA models. Improvement of the L3 simulation...

Local-to-Global in Multi-Agent Systems

Concetta Pilotto
The thesis presents performance analysis and simulation results for algorithms that compute global functions out of local interactions on multi-agent systems. We focus on optimization problems; this is because many problems can be formulated in terms of designing algorithms which optimize some global function subject to local constraints. We model the environment as an adversary of the system. The environment is able to attack the system, modifying the system in arbitrary ways: some agents and/or...

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