UNT Theses and Dissertations - 380 Matching Results

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Computer Simulations of Mechanical Behavior of Polymer Liquid Crystals

Description: In this dissertation molecular dynamics simulations of behavior of polymer liquid crystals (PLC's) under tensile deformation have been performed. PLC's composed of random or block copolymers of rigid and flexible segments have been studies. Systems of fully flexible chains have been simulated for comparison. Stress-strain relations and fracture mechanics have been investigated.
Date: December 1991
Creator: Blonski, Slawomir
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The Concept of Collision Strength and Its Applications

Description: Collision strength, the measure of strength for a binary collision, hasn't been defined clearly. In practice, many physical arguments have been employed for the purpose and taken for granted. A scattering angle has been widely and intensively used as a measure of collision strength in plasma physics for years. The result of this is complication and unnecessary approximation in deriving some of the basic kinetic equations and in calculating some of the basic physical terms. The Boltzmann equatio… more
Date: May 2004
Creator: Chang, Yongbin
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A Continuously Sensitive Cloud Chamber

Description: A continuous cloud chamber would be a valuable asset to laboratory work in nuclear and atomic physics. For this reason the construction and investigation of a continuously sensitive diffusion cloud chamber has been undertaken. It is the purpose of this paper to report the design and operating characteristics of such a chamber.
Date: 1951
Creator: Hughes, James E.
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Cooperation-induced Criticality in Neural Networks

Description: The human brain is considered to be the most complex and powerful information-processing device in the known universe. The fundamental concepts behind the physics of complex systems motivate scientists to investigate the human brain as a collective property emerging from the interaction of thousand agents. In this dissertation, I investigate the emergence of cooperation-induced properties in a system of interacting units. I demonstrate that the neural network of my research generates a series o… more
Date: August 2013
Creator: Zare, Marzieh
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Core-Shell Based Metamaterials: Fabrication Protocol and Optical Properties

Description: The objective of this study is to examine core-shell type plasmonic metamaterials aimed at the development of materials with unique electromagnetic properties. The building blocks of metamaterials under study consist of gold as a metal component, and silica and precipitated calcium carbonate (PCC) as the dielectric media. The results of this study demonstrate important applications of the core-shells including scattering suppression, airborne obscurants made of fractal gold shells, photomodific… more
Date: December 2017
Creator: De Silva, Vashista C
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Criticality in Cooperative Systems

Description: Cooperative behavior arises from the interactions of single units that globally produce a complex dynamics in which the system acts as a whole. As an archetype I refer to a flock of birds. As a result of cooperation the whole flock gets special abilities that the single individuals would not have if they were alone. This research work led to the discovery that the function of a flock, and more in general, that of cooperative systems, surprisingly rests on the occurrence of organizational collap… more
Date: May 2012
Creator: Vanni, Fabio
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Cross-Section at 15.6 and 16.1 MeV

Description: The intent of this investigation is the determination of the values of the Cs-133 (n,2n)Cs-132 cross-section at neutron energies of 15.6 and 16.1 MeV. Neutrons of this energy are produced with comparative ease by means of the D-T reaction, in which deuterons of energy 500 and 750 keV, respectively, are impingent upon a tritium target.
Date: May 1969
Creator: Pepper, George H.
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Cross Section Measurements in Praseodymium-141 as a Function of Neutron Bombarding Energy

Description: Using the parallel disk method of activation analysis, the (n,2n) reaction cross section in 141-Pr was measured as a function of neutron energy in the range 15.4 to 18.4 MeV. The bombarding neutrons were produced from the 3-T(d,n)4-He reaction, where the deuterons were accelerated by the 3-MV Van de Graff generator of the North Texas Regional Physics Laboratory in Denton, Texas.
Date: May 1971
Creator: Marsh, Stephen Addison
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Crystalline Polymorphism of Nitrates

Description: The purpose of this study was to investigate the polymorphism of a group of related compounds. Special emphasis was placed upon the temperature at which transitions occurred and a possible correlation of these temperatures with other properties of the compounds.
Date: 1951
Creator: Shepherd, Jimmie G.
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A Decay Scheme for 164 Ho

Description: The present investigation was prompted by several considerations. In previous studies there was considerable variance with regard to the reported values for the half-lives of the isomeric and ground states in 164 Ho. There was also considerable variance with regard to the values reported for the branching ratios and the relative intensities of the transitions. Thus a further study of the problem was needed.
Date: December 1972
Creator: Guertin, James
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Decoherence, Master Equation for Open Quantum Systems, and the Subordination Theory

Description: This thesis addresses the problem of a form of anomalous decoherence that sheds light into the spectroscopy of blinking quantum dots. The system studied is a two-state system, interacting with an external environment that has the effect of establishing an interaction between the two states, via a coherence generating coupling, called inphasing. The collisions with the environment produce also decoherence, named dephasing. Decoherence is interpreted as the entanglement of the coherent superposit… more
Date: August 2005
Creator: Giraldi, Filippo
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Deep Minima and Vortices for Positronium Formation in Positron-Hydrogen and Positron-Helium Collisions

Description: This dissertation work is a study of positronium formation for positron-hydrogen and positron-helium collisions in the Ore gap (the energy region between the threshold for ground-state positronium formation and the first excitation level of the target atom) using variational K-matrices. We have fitted the K-matrices using multichannel effective range theories and using polynomials. Using the variational K-matrices and their fits, we have located zeros in the positronium-formation scattering amp… more
Date: May 2021
Creator: Alrowaily, Albandari Wanes
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Defect Modulated Properties of Molybdenum Disulfide Monolayer Films

Description: In this dissertation work, the study focuses on large areal growth of MoS2 monolayers and a study of the structural, optical and electrical properties of such monolayers before and after transfer using a polymer-lift off technique. This work will discuss the issue of contact resistance and the effect of defects (both intrinsic and extrinsic) on the overall quality of the monolayer films. The significance of this dissertation work is that a reproducible strategy for monolayer MoS2 film growth an… more
Date: May 2022
Creator: Jiang, Yan
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Degenerate Four Wave Mixing of Short and Ultrashort Light Pulses

Description: This dissertation presents experimental and theoretical studies of transient degenerate four wave mixing (DFWM) in organic dyes. Chapter 1 is an introduction to DFWM. Chapter 2 describes DFWM experiments that were performed in the gain medium of a dye laser. Chapter 3 presents the theory of DFWM of short pulses in three level saturable media. Chapter 4 presents DFWM experiments of femtosecond pulses in the saturable absorber of a passively modelocked ring dye laser. Chapter 5 presents the theor… more
Date: August 1984
Creator: McMichael, Ian C. (Ian Charles)
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Degradation Mechanisms and Dynamics of Silicon Telluride: A Guide to the Effective Fabrication and Characterization of Silicon Telluride-Based Devices

Description: Silicon telluride (Si2Te3) and many other tellurium containing compounds show emergent Raman peaks located at ~120 cm-1 and ~140 cm-1 as they age. The origin of these two emergent peaks is controversial in the literature and has been attributed to myriad causes such as the intrinsic Raman modes of the telluride materials, surface oxidation, defects, double resonances, and tellurium precipitates. The controversial nature of these peaks has led to the misidentification of highly degraded materia… more
Date: December 2023
Creator: Hathaway, Evan Allen
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Density Profile of a Quantized Vortex Line in Superfluid Helium-4

Description: The density amplitude of an isolated quantum vortex line in superfluid 4He is calculated using a generalized Gross-Pitaevskii (G-P) equation. The generalized G-P equation for the order parameter extends the usual mean-field approach by replacing the interatomic potential in the ordinary G-P equation by a local, static T matrix, which takes correlations between the particles into account. The T matrix is a sum of ladder diagrams appearing in a diagrammatic expansion of the mean field term in an … more
Date: May 1975
Creator: Harper, John Howard
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Design and Testing of a Corona Column and a Closed Gas Distribution System for a Tandem Van de Graaff Voltage Generator

Description: The purpose of this study had been to design and test a corona column and an insulating gas distribution system for a small tandem Van de Graaff. The intent of this paper is to describe the gas handling system and to compare experimentally the effects of corona electrode shape on the corona current carried between adjacent sections of the column.
Date: June 1962
Creator: Gray, Thomas Jack
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Design, Construction, and Application of an Electrostatic Quadrupole Doublet for Heavy Ion Nuclear Microprobe Research

Description: A nuclear microprobe, typically consisting of 2 - 4 quadrupole magnetic lenses and apertures serving as objective and a collimating divergence slits, focuses MeV ions to approximately 1 x 1 μm for modification and analysis of materials. Although far less utilized, electrostatic quadrupole fields similarly afford strong focusing of ions and have the added benefit of doing so independent of ion mass. Instead, electrostatic quadrupole focusing exhibits energy dependence on focusing ions. A heav… more
Date: December 2017
Creator: Manuel, Jack Elliot
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