Theses/Dissertations - Physics

Permanent URI for this collectionhttps://hdl.handle.net/2104/4793

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Development of a digital optical diagnostic system for the CASPER GEC rf reference cell.
(2006-05-11T20:09:16Z) Boesse, Carolyn M.; Hyde, Truell Wayne.; Physics.; Baylor University. Dept. of Physics.
The development and implementation of a completely digital optical analysis system for dusty plasma research has been completed. This system minimizes data loss during acquisition and processing and allows image data to be acquired much more quickly and efficiently than in previous analog methods. The automated camera-lens system has been shown to be successful in imaging plasma discharge regions at a sufficient acquisition rate with multiple images to provide ease of analysis concerning position and velocity of particles and ordering of the crystal lattice. Analysis techniques have been improved due primarily to uncompromised raw data with Matlab providing a unique analysis toolset for processing data via PIV and PTV algorithms. PIV algorithms have been shown to have the advantage of greatly reducing computation time and the ability to calculate particle velocities when individual particles are not resolvable, while PTV algorithms provide more specific information about dust grain interactions and more precise velocity calculations.
Fabrication of a single layer organic photovoltaic device based on an indium-tin-oxide/copper phthalocyanine/aluminum heterostructure.
(2007-01-18T17:27:30Z) Jayasinghe, Aroshan.; Park, Kenneth Taesung, 1965-; Physics.; Baylor University. Dept. of Physics.
An ultra high vacuum chamber was designed and constructed for the purpose of fabricating organic photovoltaic devices. Thermal vapor deposition of copper phthalocyanine as the active layer and aluminum as the cathode onto a substrate of indium-tin-oxide coated glass was tested in ultra high vacuum conditions. Auger electron spectroscopy was used to analyze the surface properties of the different layers. It was possible to prepare the electrodes to the necessary quality, but the vapor deposition of the organic active layer proved to be unsuccessful. The conductivity of the deposited copper phthalocyanine was much higher than anticipated. Two possible mechanisms for this increase in conductivity are polymerization of the molecules and the formation of stacked assemblies. The residual copper phthalocyanine left in the crucible was examined with a scanning electron microscope and evidence of both mechanisms was observed.
Strange quark contribution to the nucleon.
(2007-02-07T19:30:49Z) Darnell, Dean; Wilcox, Walter, 1954-; Morgan, Ronald Benjamin, 1958-; Physics.; Baylor University. Dept. of Physics.
The strangeness contribution to the electric and magnetic properties of the nucleon has been under investigation experimentally for many years. Lattice Quantum Chromodynamics (LQCD) gives theoretical predictions of these measurements by implementing the continuum gauge theory on a discrete, mathematical Euclidean space-time lattice which provides a cutoff removing the ultra-violet divergences. In this dissertation we will discuss effective methods using LQCD that will lead to a better determination of the strangeness contribution to the nucleon properties. Strangeness calculations are demanding technically and computationally. Sophisticated techniques are required to carry them to completion. In this thesis, new theoretical and computational methods for this calculation such as twisted mass fermions, perturbative subtraction, and General Minimal Residual (GMRES) techniques which have proven useful in the determination of these form factors will be investigated. Numerical results of the scalar form factor using these techniques are presented. These results give validation to these methods in future calculations of the strange quark contribution to the electric and magnetic form factors.
Gravitational collapse and formation of black holes in the Brans-Dicke theory of gravity with (2+1) dimensions.
(2008-03-03T17:23:59Z) Wu, Rui.; Wang, Anzhong.; Physics.; Baylor University. Dept. of Physics.
In this thesis, the gravitational collapse of the Brans-Dicke scalar field and formation of black holes in 2+1 Gravity is examined. In contrast to general relativity, there are two conformally related frames in the Brans-Dicke theory: the Jordan frame and the Einstein frame. All the self-similar solutions are first re-derived in three dimensional Brans-Dicke theory, and then their local and global properties are studied by paying particular attention to the formation of black holes due to the gravitational collapse of the scalar field.
Investigation into compactifed dimensions: Casimir energies and phenomenological aspects.
(2009-01-07T22:13:03Z) Obousy, Richard K.; Cleaver, Gerald B.; Physics.; Baylor University. Dept. of Physics.
A central theme in this dissertation is the notion of the quantum vacuum. To a particle physicist, the term 'vacuum' means the ground state of a theory. In general, this ground state must obey Lorentz invariance, at least with regards to 3 spatial dimensions, meaning that the vacuum must look identical to all observers. At all energies probed by experiments to date, the universe is accurately described as a set of quantum fields. If we take the Fourier transform of a free quantum field, each mode of a fixed wavelength behaves like a simple harmonic oscillator. A quantum mechanical property of a simple harmonic oscillator is that the ground state exhibits zero-point fluctuations as a consequence of the Heisenberg Uncertainty Principle. These fluctuations give rise to a number of phenomena; however, two are particularly striking. First, the Casimir Effect, which will be examined in detail in this dissertation is arguably the most salient manifestation of the quantum vacuum. In its most basic form it is realized through the interaction of a pair of neutral parallel conducting plates. The presence of the plates modifies the quantum vacuum, and this modification causes the plates to be pulled toward each other. Second is the prediction of a vacuum energy density, which is an intrinsic feature of space itself. Many attempts have been made to relate this vacuum energy to the cosmological constant Lambda, which is a common feature in modern cosmology; however, calculations are typically plagued either by divergences or by ridiculously high predictions which are far removed from observation. This chapter will first provide a brief historical review of the vacuum and then discuss in detail some of the attempts to explain the vacuum in the language of Quantum Field Theory (QFT).
Total electron scattering cross sections of Tetrafluoromethane, Trifluoromethane, Hexafluoroethane, and Octafluorocyclobutane in the energy range 0.10 to 4.50 keV.
(2009-04-01T16:48:49Z) Palihawadana, Prasanga D.; Ariyasinghe, Wickramasinghe M.; Physics.; Baylor University. Dept. of Physics.
The total electron scattering cross sections of Tetrafluoromethane, Trifluoromethane, Hexafluoroethane, and Octafluorocyclobutane are measured in the energy range 0.10 to 4.50 keV using the linear transmission technique. The measured experimental cross sections are compared with other experimental and theoretical cross sections available in the literature. A simple empirical formula is also developed by using the present measurements to predict the cross sections of linear fluorocarbons as a function of the electron energy and the number of atoms in the target molecule. This empirical formula is used to calculate the total cross sections of linear fluorocarbons in the energy range 0.30 to 3.50 keV. Those empirically calculated cross sections are compared to the present experimental cross sections and other experimental and theoretical cross sections available in the literature.
Characteristic measurements within a GEC rf Reference Cell.
(2010-10-08T16:15:25Z) Creel, James Ruell.; Hyde, Truell Wayne.; Physics.; Baylor University. Dept. of Physics.
Since its introduction, the GEC rf Reference Cell has provided a baseline for comparison among various experiments performed within the complex (dusty) plasma community. The GEC cell, while providing for data comparison between systems due to its standardized design, does not exist without some variation between cells. In this work, two GEC rf Reference Cells located within the CASPER Hypervelocity Impacts & Dusty Plasmas Lab will be utilized to examine variations in operating parameters. Both standard analysis and Langmuir probe techniques will be employed in an attempt to gain insight into the experimental workings of a standard GEC rf Reference Cell.
Surface embedded green function method applied to Ag(111).
(2010-10-08T16:20:56Z) Katz, David A. (David Alan), 1982-; Benesh, Gregory Allen, 1953-; Physics.; Baylor University. Dept. of Physics.
Theoretical self-consistent calculations utilizing the Surface Embedded Green Function (SEGF) method have been performed on the Ag(111) surface. Analysis of the surface energetics reveal an energy minimum in the low temperature limit at an outerlayer contraction of 0.5% which agrees well with low energy electron diffraction and ion scattering studies. The predicted Ag(111) work function of 4.75 eV is in excellent agreement with the experimental value from photoelectron measurements. Furthermore, a surface state is predicted to exist at 0.15 eV below Ef, in very good agreement with a state observed experimentally in photoelectron spectroscopy at 0.12 eV below Ef.. The best agreement with experiment across this diverse set of surface phenomena is obtained with the current implementation of the SEGF method.
Nanomanipulator perturbation of dust crystals in a GEC rf plasma cell.
(2010-10-08T16:24:26Z) Murphree, Jay Michael.; Hyde, Truell Wayne.; Physics.; Baylor University. Dept. of Physics.
The vast majority of observable matter is composed of complex plasma. Even with its prevalence, the interactions between the plasma's constituents are not fully understood. In many cases, clouds of dust grains from and can even display organized, crystal-like, structures. Understanding the interparticle forces involved within these dust crystals will greatly advance the understanding of complex plasmas as a whole. Perturbing and observing the crystal's reaction is a practical and powerful method of examining these forces. In this paper, a new versatile system for controlled dust manipulation, the S100 nanomanipulator, is examined. Two experiments were conducted with this probe to characterize the response of both the plasma and a dust crystal. First, the dust was exposed to the probe to determine the length scale of interaction between the two. Next, a Langmuir probe was used to find the extent of the wake field produced.
Investigation of low Higgs models in Weakly Coupled Free Fermionic Heterotic String Theory.
(2010-10-08T16:25:07Z) Pechan, Kristen.; Cleaver, Gerald B.; Physics.; Baylor University. Dept. of Physics.
Superstring phenomenology explores classes of vacua which can reproduce the Standard Model at low energy. We consider Weakly Coupled Free Fermionic Heterotic String Theory (WCFFHST) which produces four dimensional Standard-like Models and allows for their SO(10) embedding. In the models herein, we explore the removal of extra Higgs representations via free fermion boundary conditions directly at the string level, rather than in the low energy effective field theory. We focus on the flat direction analysis of four models with reduced number of Higgs, after flat direction analysis of a three generation reduced Higgs model revealed no stringent F- and D-flat solutions to all order in the superpotential. Flat direction analysis of the four models presented herein shows the lack of D- and F-flat solutions to all order is not a general property of low Higgs models, as stringent flat directions appear to all order for three of our four models.
A search for the standard model Higgs boson produced in association with a W boson.
(2011-05-12T15:29:39Z) Frank, Martin J., 1983-; Dittmann, Jay R.; Physics.; Baylor University. Dept. of Physics.
We present a search for a standard model Higgs boson produced in association with a W boson using data collected with the CDF II detector from proton/antiproton collisions at a center of mass energy of 1.96 TeV. The search is performed in the WH channel where the W boson decays leptonically and the Higgs boson decays to a bottom/antibottom quark pair. The two quarks usually fragment into two jets, but sometimes a third jet can be produced via gluon radiation, so we have increased the standard two-jet sample by including events that contain three jets. We reconstruct the Higgs boson using two or three jets depending on the kinematics of the event. We find an improvement in our search sensitivity using the larger sample together with this multijet reconstruction technique. Our data show no evidence of a Higgs boson, so we set 95% confidence level upper limits on the WH production rate. We set limits between 3.36 and 28.7 times the standard model prediction for Higgs boson masses ranging from 100 to 150 GeV/c^2.
Search for anomalous production of photon + jets + missing transverse energy in proton-antiproton collisions at a center of mass energy of 1.96 TeV using the CDF II detector.
(2011-05-12T15:37:21Z) Hewamanage, Samantha K.; Dittmann, Jay R.; Physics.; Baylor University. Dept. of Physics.
A model-independent signature-based search for physics beyond the Standard Model is performed in the photon + jets + missing transverse energy channel in proton-antiproton collisions at a center of mass energy of 1.96 TeV using the CDF II detector. Events with a photon + jets are predicted by the Standard Model and also by many theoretical models beyond the Standard Model. In the Standard Model, the main mechanisms for photon + jets production include quark-antiquark annihilation and quark-gluon scattering. No intrinsic missing transverse energy is present in any of these Standard Model processes. In this search, photon + ≥1 jet and photon + ≥2 jet events are analyzed with and without a minimum requirement on the missing transverse energy. Numerous mass distributions and kinematic distributions are studied and no significant excess over the background prediction is found. All results indicate good agreement with expectations of the Standard Model.
Initial systematic investigations of the weakly coupled free fermionic heterotic string landscape statistics.
(2011-09-14) Renner, Timothy, 1984-; Cleaver, Gerald B.; Physics.; Baylor University. Dept. of Physics.
A C++ framework was constructed with the explicit purpose of systematically generating string models using the Weakly Coupled Free Fermionic Heterotic String (WCFFHS) method. The software, optimized for speed, generality, and ease of use, has been used to conduct preliminary systematic investigations of WCFFHS vacua. Documentation for this framework is provided in the Appendix. After an introduction to theoretical and computational aspects of WCFFHS model build- ing, a study of ten-dimensional WCFFHS models is presented. Degeneracies among equivalent expressions of each of the known models are investigated and classified. A study of more phenomenologically realistic four-dimensional models based on the well known “NAHE” set is then presented, with statistics being reported on gauge content, matter representations, and space-time supersymmetries. The final study is a parallel to the NAHE study in which a variation of the NAHE set is systematically extended and examined statistically. Special attention is paid to models with “mirroring” — identical observable and hidden sector gauge groups and matter representations.
Electric neutron polarizability and eigenspectrum subtraction techniques for disconnected quark loops.
(2011-09-14) Guerrero, Victor Xavier.; Wilcox, Walter, 1954-; Physics.; Baylor University. Dept. of Physics.
I present an analysis for the mass shift of the neutron in order to obtain the neutron electric polarizability. Neutron electric polarizability can be studied by implementing a static electric field on the lattice. The implementation of this field, though, is non-trivial and the "proper" form for lattice implementation is studied and the various techniques are presented. Separately, I present the development of new techniques to calculate disconnected quark loops; a quantity that is necessary for many different analyzes but has been shown to be computationally intensive. These new techniques, which use Z(N) noise, utilize the eigenspectrum of the quark matrix to reduce statistical error found in disconnected operators.
Orbifold branes in string theory and their applications to cosmology.
(2011-09-14) Devin, Michael J.; Wang, Anzhong.; Physics.; Baylor University. Dept. of Physics.
This dissertation contains two distinct compactification schemes of 10-dimensional string theory, as well as some of the implications of one of these schemes for string cosmology. The first half of this work begins with a brief overview of cosmology and goes through constructing and then analyzing the first model, inspired by the work of Santos and Wang. The second part consists of an attempt to construct similar models using the the popular warped conifold compactification scheme, as well as an appendix with a variant of the first model and its derivation. The work concludes with the observation that the latter attempt does not admit solutions of the same form, and that the variant model in the appendix is degenerate to previously studied KK-type models.
Effects of laser light on argon plasma in a GEC rf reference cell.
(2011-09-14) Price, Alexander Thomas.; Hyde, Truell Wayne.; Physics.; Baylor University. Dept. of Physics.
Since lasers have become so powerful in dusty plasma research, it is important to determine the manner in which a laser will affect the plasma. In this work, a Verdi ™ G-Series optically pumped semiconductor laser was used in conjunction with a Langmuir probe to determine the effect (if any) that the laser has on the plasma. A Langmuir probe was used to measure and monitor various plasma parameters in a dusty argon plasma. Measurements were taken with the laser immediately beneath the probe at various plasma pressures, plasma powers, and laser powers.
Charging of aggregate grains in astrophysical environments.
(2011-12-19) Ma, Qianyu.; Matthews, Lorin Swint.; Physics.; Baylor University. Dept. of Physics.
Plasma is a gas in which a portion of particles are ionized. Dust is a ubiquitous component of the universe, and when present in plasma, can form dusty plasma system. Dust in the plasma is generally charged due to the constant collisions with free moving electrons and ions. Cosmic dust can also be charged by other means such as UV and X-ray radiation, and secondary electron emission due to the impact of energetic electrons and ions. The presence of charged dust particles alters the properties of the plasma. The charge on dust grains also affects their dynamics, and influences the coagulation rate. Most previous work assumes that cosmic dust is spherical in shape. However, remote observations and in-situ measurements indicate that cosmic dust is likely to have an aggregate structure. This study examines the charging of aggregate grains in different astrophysical environments. A 3D numerical model employing a self-consistent iterative approach to compute the aggregate charge is introduced. Different size distributions for cosmic dust grains are used in the simulation. The results are compared with previous work on spherical grains, and it is shown that the charging of aggregates differ significantly from that of spheres. Models on predicting charge based on the aggregate structure are proposed, and implications and consequences for future research are discussed.
Studies on the missing energy measurement and supersymmetry search in 7 TeV proton-proton collisions.
(2012-11-29) Scarborough, Tara A.; Hatakeyama, Kenichi.; Physics.; Baylor University. Dept. of Physics.
The main theme of the research presented in this thesis is the search for Supersymmetry, one of the most likely and well-motivated extensions of the standard model of particle physics, in 7 TeV proton-proton collisions delivered by the world's most energetic accelerator — the Large Hadron Collider (LHC). In the Supersymmetry search, the key observable is the "missing transverse energy" (Emiss), which T indicates the signal of the lightest stable supersymmetric particles. These lightest supersymmetric particles are also candidates for the constituents of dark matter ob- served in astronomical observations. The research presented in this thesis consists of two major parts: (1) improving the measurement of the missing transverse energy, and (2) searching for Supersymmetry with an emphasis on the study of fake Emiss T events and on the interpretation of real Emiss events using a framework called the "simplified model".
Impact of microphysical interactions on aggregate morphologies.
(2012-11-29) Perry, Jonathan D.; Matthews, Lorin Swint.; Physics.; Baylor University. Dept. of Physics.
Coagulation of (sub)micron-sized dust particles occurs in a variety of envi- ronments; such as the interstellar medium, protoplanetary disks, Earth's upper atmosphere and industrial processes. Understanding the physics of collisions and interparticle interactions of dust grains within this size regime is essential to in- derstanding such environments. To gain detailed insight into the parameters which enhance or inhibit coagulation it is beneficial to employ numerical methods to grow aggregates where the degrees of freedom may be tuned to a multitude of possible parameter sets. Two of the possible numerical methods which may be employed are pair-wise simulations or N-body simulations. This work expands upon previous numerical methods by examination of the combined e ects of electrostatic and magnetostatic interactions. E ffects of these interactions, alone and in combination, are examined based upon collision probabil- ities as well as the resulting aggregate structures. Also examined are the variations induced by employing ellipsoidal monomers during aggregation.
Fundamental physics within complex plasmas.
(2012-11-29) Douglass, Angela Michelle.; Hyde, Truell Wayne.; Physics.; Baylor University. Dept. of Physics.
In this work, both experimental and numerical methods are used to investigate several of the fundamental processes and assumptions commonly found in an earth-based radio-frequency (RF) complex plasma discharge. First the manner in which the dust particle charge varies with the particle’s height above the powered electrode is investigated. Knowledge of the dust particle charge is required to understand nearly all complex plasma experiments since it affects the dust particle’s levitation height and particle-particle interactions. A fluid model which includes effects due to ion flow and electron depletion (which are significant dust charging effects within the sheath where the particles levitate) is employed to determine the plasma parameters required to calculate the dust particle charge. Second, the levitation limits of the dust particles and the structure of the sheath are investigated. The CASPER GEC RF reference cell is used to perform two experiments: one to measure the dust levitation height as a function of applied RF voltage and one to determine the electric force profile. The fluid model is then used to interpret the experimental results. This study provides a better understanding of the sheath structure, particle behavior within the sheath, and provides a new, in situ experimental method for locating the approximate height of the sheath edge in any dusty plasma system. Finally, both molecular dynamics (MD) simulations and an experiment are employed to determine the physical processes that a complex plasma system goes through as it rapidly transitions from a liquid to solid state.

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