You limited your search to:
Partner:
UNT Libraries
Department:
Department of Physics
Degree Discipline:
Physics
 Absolute Beta Counting Using Thick Sources
 The problem with which we shall concern ourselves in this paper is the selfscattering and selfabsorption of beta particles by the source. digital.library.unt.edu/ark:/67531/metadc96872/
 Accelerator Mass Spectrometry Studies of Highly Charged Molecular Ions
 The existence of singly, doubly, and triply charged diatomic molecular ions was observed by using an Accelerator Mass Spectrometry (AMS) technique. The mean lifetimes of 3 MeV boron diatomic molecular ions were measured. No isotopic effects on the mean lifetimes of boron diatomic molecules were observed for charge state 3+. Also, the mean lifetime of SiF^3+ was measured. digital.library.unt.edu/ark:/67531/metadc279004/
 Analysis of Biological Materials Using a Nuclear Microprobe
 The use of nuclear microprobe techniques including: Particle induced xray emission (PIXE) and Rutherford backscattering spectrometry (RBS) for elemental analysis and quantitative elemental imaging of biological samples is especially useful in biological and biomedical research because of its high sensitivity for physiologically important trace elements or toxic heavy metals. The nuclear microprobe of the Ion Beam Modification and Analysis Laboratory (IBMAL) has been used to study the enhancement in metal uptake of two different plants. The roots of corn (Zea mays) have been analyzed to study the enhancement of iron uptake by adding Fe (II) or Fe (III) of different concentrations to the germinating medium of the seeds. The Fe uptake enhancement effect produced by lacing the germinating medium with carbon nanotubes has also been investigated. The aim of this investigation is to ensure not only high crop yield but also Ferich food products especially from calcareous soil which covers 30% of world’s agricultural land. The result will help reduce iron deficiency anemia, which has been identified as the leading nutritional disorder especially in developing countries by the World Health Organization. For the second plant, Mexican marigold (Tagetes erecta), the effect of an arbuscular mycorrhizal fungi (Glomus intraradices) for the improvement of leadphytoremediation of lead contaminated soil has been investigated. Phytoremediation provides an environmentally safe technique of removing toxic heavy metals (like lead), which can find their way into human food, from lands contaminated by human activities like mining or by natural disasters like earthquakes. The roots of Mexican marigold have been analyzed to study the role of arbuscular mycorrhizal fungi in enhancement of lead uptake from the contaminated rhizosphere. digital.library.unt.edu/ark:/67531/metadc700099/
 Analyzing Magnet System for the Electrostatic Accelerator
 This thesis describes the design and construction of a linear accelerator, specifically, a positiveion source, a high voltage supply, an accelerating column, and the necessary associated vacuum system. digital.library.unt.edu/ark:/67531/metadc130409/
 Anderson Localization in TwoChannel Wires with Correlated Disorder: DNA as an Application
 This research studied the Anderson localization of electrons in twochannel wires with correlated disorder and in DNA molecules. It involved an analytical calculation part where the formula for the inverse localization length for electron states in a twochannel wire is derived. It also involved a computational part where the localization length is calculated for some DNA molecules. Electron localization in twochannel wires with correlated disorder was studied using a singleelectron tightbinding model. Calculations were within secondorder Bornapproximation to secondorder in disorder parameters. An analytical expression for localization length as a functional of correlations in potentials was found. Anderson localization in DNA molecules were studied in singlechannel wire and twochannel models for electron transport in DNA. In both of the models, some DNA sequences exhibited delocalized electron states in their energy spectrum. Studies with twochannel wire model for DNA yielded important link between electron localization properties and genetic information. digital.library.unt.edu/ark:/67531/metadc5204/
 Angular Dependence of the Stopping Processes and the Yields of Ioninduced Electron Emission from Channeled MEV Protons in <100> Silicon Foils
 The present work reports the experimental evidence of anomalous energy loss, energy straggling, and the corresponding ioninduced electron emission yields of channeled protons in silicon. digital.library.unt.edu/ark:/67531/metadc279025/
 The Angular Distribution and Total Flux of Neutrons Obtained from the DeuteriumTritium Reaction
 Monoenergetic neutrons have been produced with the lowvoltage CockroftWalton accelerator at North Texas State College using two different reactions. It is the purpose of this paper to report the angular distribution and total flux of the neutrons obtained from the T(D,n) reaction. digital.library.unt.edu/ark:/67531/metadc107901/
 The Angular Distribution of the DeuteriumDeuterium Neutrons with 100 Kev Deuterons
 It is the purpose of this paper to present the experimental techniques used in obtaining. 3.25 MeV neutrons from the H2(d,n)He3 reaction, as well as an analysis of the experimental data. digital.library.unt.edu/ark:/67531/metadc107904/
 Anisotropic Relaxation Time for Solids with Ellipsoidal Fermi Surfaces
 Many solids have Fermi surfaces which are approximated as ellipsoids. A comprehensive solution for the magnetoconductivity of an ellipsoid is obtained which proves the existence of a relaxation time tensor which can be anisotropic and which is a function of energy only. digital.library.unt.edu/ark:/67531/metadc278322/
 Anomalous Behavior in the Rotational Spectra of the v₈=2 and the v₈=3 Vibrations for the ¹³C and ¹⁵N Tagged Isotopes of the CH₃CN Molecule in the Frequency Range 1795 GHz
 The rotational microwave spectra of the three isotopes (^13CH_3^12C^15N, ^12CH_3^13C^15N, and ^13CH_3^13C^15N) of the methyl cyanide molecule in the v_8=3, v_8=2, v_7=1 and v_4=1 vibrational energy levels for the rotational components 1£J£5 (for a range of frequency 1795 GHz.) were experimentally and theoretically examined. Rotational components in each vibration were measured to determine the mutual interactions in each vibration between any of the vibrational levels investigated. The method of isotopic substitution was employed for internal tuning of each vibrational level by single and double substitution of ^13C in the two sites of the molecule. It was found that relative frequencies within each vibration with respect to another vibration were shifted in a systematic way. The results given in this work were interpreted on the basis of these energy shifts. Large departure between experimentally measured and theoretically predicted frequency for the quantum sets (J, K=±l, ϑ=±1), Kϑl in the v_8=3 vibrational states for the ^13c and ^15N tagged isotopes of CH_3CN showed anomalous behavior which was explained as being due to Fermi resonance. Accidently strong resonances (ASR) were introduced to account for some departures which were not explained by Fermi resonance. digital.library.unt.edu/ark:/67531/metadc330976/
 Antiferromagnetic Ordering in PicrylAminoCarbazyl
 The purpose of the experiment was to investigate other paramagnetic salts to determine whether the W. B. perchlorate type peak was more common than previously suspected. An organic salt, picrylnaminocarbazyl, was chosen. digital.library.unt.edu/ark:/67531/metadc163864/
 Application of the Finite Element Method to Some Simple Systems in One and Two Dimensions.
 The finite element method (FEM) is reviewed and applied to the onedimensional eigensystems of the isotropic harmonic oscillator, finite well, infinite well and radial hydrogen atom, and the twodimensional eigensystems of the isotropic harmonic oscillator and the propagational modes of sound in a rectangular cavity. Computer codes that I developed were introduced and utilized to find accurate results for the FEM eigensolutions. One of the computer codes was modified and applied to the onedimensional unbound quantum mechanical system of a square barrier potential and also provided accurate results. digital.library.unt.edu/ark:/67531/metadc3087/
 Application of the Wigner Formalism to a Slightly Relativistic Quantum Plasma
 A slightly relativistic fermion gas is described by the dynamical theory obtained from the Wigner distribution function. The problem is approached in a selfconsistent manner including the twobody Darwin Hamiltonian. The goal is to find the departures from equilibrium and dispersion relations for wave propagation in the gas. digital.library.unt.edu/ark:/67531/metadc130850/
 Approach to Quantum Information starting from Bell's Inequality (Part I) and Statistical Analysis of Time Series Corresponding to Complex Processes (Part II)

Access: Use of this item is restricted to the UNT Community.
I: Quantum information obeys laws that subtly extend those governing classical information, making possible novel effect such as cryptography and quantum computation. Quantum computations are extremely sensitive to disruption by interaction of the computer with its environment, but this problem can be overcome by recently developed quantum versions of classical errorcorrecting codes and faulttolerant circuits. Based on these ideas, the purpose of this paper is to provide an approach to quantum information by analyzing and demonstrating Bell's inequality and by discussing the problems related to decoherence and errorcorrecting. II: The growing need for a better understanding of complex processes has stimulated the development of new and more advanced data analysis techniques. The purpose of this research was to investigate some of the already existing techniques (Hurst's rescaled range and relative dispersion analysis), to develop a software able to process time series with these techniques, and to get familiar with the theory of diffusion processes. digital.library.unt.edu/ark:/67531/metadc3092/  Automatic Frequency Control of Microwave Radiation Sources
 Resonant cavity controlled klystron frequency stabilization circuits and quartzcrystal oscillator frequency stabilization circuits were investigated for reflex klystrons operating at frequencies in the Xband range. The crystal oscillator circuit employed achieved better than 2 parts in 10 in frequency stability. A test of the functional properties of the frequency standard was made using the Stark effect in molecules. digital.library.unt.edu/ark:/67531/metadc504304/
 Backscattering from Prolate Spheroids at Microwave Frequencies
 This thesis examines backscattering from prolate spheroids at microwave frequencies. digital.library.unt.edu/ark:/67531/metadc107919/
 Ballistic Deposition: Global Scaling and Local Time Series.
 Complexity can emerge from extremely simple rules. A paradigmatic example of this is the model of ballistic deposition (BD), a simple model of sedimentary rock growth. In two separate ProbleminLieuof Thesis studies, BD was investigated numerically in (1+1)D on a lattice. Both studies are combined in this document. For problem I, the global interface roughening (IR) process was studied in terms of effective scaling exponents for a generalized BD model. The model used incorporates a tunable parameter B to change the cooperation between aggregating particles. Scaling was found to depart increasingly from the predictions of KardarParisiZhang theory both with decreasing system sizes and with increasing cooperation. For problem II, the local single column evolution during BD rock growth was studied via statistical analysis of time series. Connections were found between single column time series properties and the global IR process. digital.library.unt.edu/ark:/67531/metadc4392/
 Boundary Scattering of Electrons in Thin Cadmium Single Crystals
 In the present investigation, zinc was plated onto a cadmium crystal to determine the effect on the scattering parameter. digital.library.unt.edu/ark:/67531/metadc130996/
 Brownian Movement and Quantum Computers

Access: Use of this item is restricted to the UNT Community.
This problem in lieu of thesis is a discussion of two topics: Brownian movement and quantum computers. Brownian movement is a physical phenomenon in which the particle velocity is constantly undergoing random fluctuations. Chapters 2, 3 and 4, describe Brownian motion from three different perspectives. The next four chapters are devoted to the subject of quantum computers, which are the signal of a new era of technology and science combined together. In the first chapter I present to a reader the two topics of my problem in lieu of thesis. In the second chapter I explain the idea of Brownian motion, its interpretation as a stochastic process and I find its distribution function. The next chapter illustrates the probabilistic picture of Brownian motion, where the statistical averages over trajectories are related to the probability distribution function. Chapter 4 shows how to derive the Langevin equation, introduced in chapter 1, using a Hamiltonian picture of a bath with infinite number of harmonic oscillators. The chapter 5 explains how the idea of quantum computers was developed and how stepbystep all the puzzles for the field of quantum computers were created. The next chapter, chapter 6, discus the basic quantum unit of information namely, the so called qubit and its properties. Chapter 7 is devoted to quantum logic gates, which are important for conducting logic operation in quantum computers. This chapter explains how they were developed and how they are different from classical ones. Chapter 8 is about the quantum algorithm, Shor's algorithm. Quantum algorithm in quantum computers enables one to solve problems that are hard to solve on digital computers. The last chapter contains conclusions on Brownian movement and the field of quantum computers. digital.library.unt.edu/ark:/67531/metadc4660/  A Calculation of the KaonNeutron Scattering Cross Section
 The purpose of this investigation was to study the scattering processes of K+ mesons with neutrons. In order to do such a study one must first make certain basic assumptions about the type of interaction involved and then proceed to calculate physically meaningful qualities which describe the processes. Thus, the problem is this: assuming the validity of Feynman's rules for these strongly interacting particles, calculate the differential and total scattering cross sections for the interaction of scalar K+ mesons and neutrons. digital.library.unt.edu/ark:/67531/metadc130687/
 Carbon Contamination Measurements in Single Silicon Crystals
 The intent of this investigation was to directly measure the amount of carbon contamination in a single silicon crystal and, in so doing, develop a mathematical procedure that would be applicable to other contaminants in other substances. digital.library.unt.edu/ark:/67531/metadc131331/
 Carbon KShell XRay and AugerElectron Cross Sections and Fluorescence Yields for Selected Molecular Gases by 0.6 To 2 .0 MeV Proton Impact
 Absolute Kshell xray cross sections and Augerelectron cross sections are measured for carbon for 0.6 to 2.0 MeV proton incident on CH₄, nC₄H₁₀ (nButane), iC₄H₁₀ (isobutane), C₆H₆ (Benzene), C₂H₂ (Acetylene), CO and CO₂. Carbon Kshell fluorescence yields are calculated from the measurements of xray and Augerelectron cross sections. Xray cross sections are measured using a variable geometry end window proportional counter. An alternate method is described for the measurement of the transmission of the proportional counter window. Auger electrons are detected by using a constant transmission energy Π/4 parallel pi ate electrostatic analyzer. Absolute carbon Kshell xray cross sections for CH₄ are compared to the known results of Khan et al. (1965). Augerelectron cross sections for proton impact on CH₄ are compared to the known experimental values of RΦdbro et al. (1979), and to the theoretical predictions of the first Born and ECPSSR. The data is in good agreement with both the first Born and ECPSSR, and within our experimental uncertainties with the measurements of RΦdbro et al. The xray cross sections, Augerelectron cross sections and fluorescence yields are plotted as a function of the Pauling charge, and show significant variations. These changes in the xray cross sections are compared to a model based on the number of electrons present in the 2s and 2p sub shells of these carbon based molecules. The changes in the Augerelectron cross sections are compared to the calculations of Matthews and Hopkins. The variation in the fluorescence yield is explained on the basis of the multiconfiguration DiracFock model. digital.library.unt.edu/ark:/67531/metadc331849/
 Carbon Nanotube/Microwave Interactions and Applications to Hydrogen Fuel Cells.

Access: Use of this item is restricted to the UNT Community.
One of the leading problems that will be carried into the 21st century is that of alternative fuels to get our planet away from the consumption of fossil fuels. There has been a growing interest in the use of nanotechnology to somehow aid in this progression. There are several unanswered questions in how to do this. It is known that carbon nanotubes will store hydrogen but it is unclear how to increase that storage capacity and how to remove this hydrogen fuel once stored. This document offers some answers to these questions. It is possible to implant more hydrogen in a nanotube sample using a technique of ion implantation at energy levels ~50keV and below. This, accompanied with the rapid removal of that stored hydrogen through the application of a microwave field, proves to be one promising avenue to solve these two unanswered questions. digital.library.unt.edu/ark:/67531/metadc5796/  Chaos and Momentum Diffusion of the Classical and Quantum Kicked Rotor
 The de BroglieBohm (BB) approach to quantum mechanics gives trajectories similar to classical trajectories except that they are also determined by a quantum potential. The quantum potential is a "fictitious potential" in the sense that it is part of the quantum kinetic energy. We use quantum trajectories to treat quantum chaos in a manner similar to classical chaos. For the kicked rotor, which is a bounded system, we use the Benettin et al. method to calculate both classical and quantum Lyapunov exponents as a function of control parameter K and find chaos in both cases. Within the chaotic sea we find in both cases nonchaotic stability regions for K equal to multiples of π. For even multiples of π the stability regions are associated with classical accelerator mode islands and for odd multiples of π they are associated with new oscillator modes. We examine the structure of these regions. Momentum diffusion of the quantum kicked rotor is studied with both BB and standard quantum mechanics (SQM). A general analytical expression is given for the momentum diffusion at quantum resonance of both BB and SQM. We obtain agreement between the two approaches in numerical experiments. For the case of nonresonance the quantum potential is not zero and must be included as part of the quantum kinetic energy for agreement. The numerical data for momentum diffusion of classical kicked rotor is well fit by a power law DNβ in the number of kicks N. In the anomalous momentum diffusion regions due to accelerator modes the exponent β(K) is slightly less than quadratic, except for a slight dip, in agreement with an upper bound (K2/2)N2. The corresponding coefficient D(K) in these regions has three distinct sections, most likely due to accelerator modes with period greater than one. We also show that the local Lyapunov exponent of the classical kicked rotor has a plateau for a duration that depends on the initial separation and then decreases asymptotically as O(t1lnt), where t is the time. This behavior is consistent with an upper bound that is determined analytically. digital.library.unt.edu/ark:/67531/metadc4824/
 Characterization and Field Emission Properties of Mo2C and Diamond Thin Films Deposited on Mo Foils and Tips by Electrophoresis
 In this dissertation M02C and diamond films deposited by electrophoresis on flat Mo foils and tips have been studied to determine their suitability as field emission tips. digital.library.unt.edu/ark:/67531/metadc278393/
 Characterization, Properties and Applications of Novel Nanostructured Hydrogels.

Access: Use of this item is restricted to the UNT Community.
The characterization, properties and applications of the novel nanostructured microgel (nanoparticle network and microgel crystal) composed of polyNisopropylacrylanmidecoallylamine (PNIPAMcoallylamine) and PNIPAMcoacrylic acid(AA) have been investigated. For the novel nanostructured hydrogels with the two levels of structure: the primary network inside each individual particle and the secondary network of the crosslinked nanoparticles, the new shear modulus, drug release law from hydrogel with heterogeneous structure have been studied. The successful method for calculating the volume fraction related the phase transition of colloid have been obtained. The kinetics of crystallization in an aqueous dispersion of PNIPAM particles has been explored using UVvisible transmission spectroscopy. This dissertation also includes the initial research on the melting behavior of colloidal crystals composed of PNIPAM microgels. Many new findings in this study area have never been reported before. The theoretical model for the columnar crystal growth from the top to bottom of PNIPAM microgel has been built, which explains the growth mechanism of the novel columnar hydrogel colloidal crystals. Since the unique structure of the novel nanostructured hydrogels, their properties are different with the conventional hydrogels and the hardspherelike system. The studies and results in this dissertation have the important significant for theoretical study and valuable application of these novel nanostructured hydrogels. digital.library.unt.edu/ark:/67531/metadc5605/  Charge Collection Studies on Integrated Circuit Test Structures using HeavyIon Microbeams and MEDICI Simulation Calculations
 Ion induced charge collection dynamics within Integrated Circuits (ICs) is important due to the presence of ionizing radiation in the IC environment. As the charge signals defining data states are reduced by voltage and area scaling, the semiconductor device will naturally have a higher susceptibility to ionizing radiation induced effects. The ionizing radiation can lead to the undesired generation and migration of charge within an IC. This can alter, for example, the memory state of a bit, and thereby produce what is called a "soft" error, or Single Event Upset (SEU). Therefore, the response of ICs to natural radiation is of great concern for the reliability of future devices. Immunity to soft errors is listed as a requirement in the 1997 National Technology Roadmap for Semiconductors prepared by the Semiconductor Industry Association in the United States. To design more robust devices, it is essential to create and test accurate models of induced charge collection and transport in semiconductor devices. A heavy ion microbeam produced by an accelerator is an ideal tool to study charge collection processes in ICs and to locate the weak nodes and structures for improvement through hardening design. In this dissertation, the Ion Beam Induced Charge Collection (IBICC) technique is utilized to simulate recoil effects of ions in ICs. These silicon or light ion recoils are usually produced by the elastic scattering or inelastic reactions between cosmic neutrons or protons and the lattice atoms in ICs. Specially designed test structures were experimentally studied, using microbeams produced at Sandia National Laboratories. A new technique, Diffusion Time Resolved IBICC, is first proposed in this work to measure the average arrival time of the diffused charge, which can be related to the first moment (or the average time) of the arrival carrier density at the junction. A 2D device simulation tool, the MEDICI code, and heavyion microbeams are used to calculate and measure charge collection and relative arrival time on stripelike test junctions. The MEDICI simulation is in qualitative and sometimes even quantitative agreement with the microbeam measurements. The amount of charge collection and the magnitude of average arrival time for diffused charge collection can be crucial to understanding and mitigating radiation induced circuit malfunctions during normal IC operations. digital.library.unt.edu/ark:/67531/metadc2469/
 Charge State Dependence of LShell XRay Production Cross Sections of ₂₈Ni, ₂₉Cu, ₃₀Zn, ₃₁Ga, and ₃₂Ge by Energetic Oxygen Ions
 Charge state dependence of Lshell xray production cross sections have been measured for 414 MeV ¹⁶O^q (q=3⁺8⁺) ions incident on ultraclean, ultrathin copper, and for 12 MeV ¹⁶O^q (q=3⁺8⁺) on nickel, zinc, gallium and germanium solid foils. Lshell xray production cross section were measured using target foils of thickness ≤0.6 μg/cm² evaporated onto 5 μg/cm² carbon backings. Oxygen ions at MeV energies and charge state q were produced using a 3MV 9SDH2 National Electrostatics Corporation tandem Pelletron accelerator. Different charge states, with and without Kvacancies, were produced using a post acceleration nitrogen striping gas cell or ¹²C stripping foils. Lshell xrays from ultrathin ₂₈Ni, ₂₉Cu,₃₀Zn,₃₁Ga, and ₃₂Ge targets were measured using a Si(Li) xray detector with a FWHM resolution of 135 eV at 5.9 keV. The scattered projectiles were detected simultaneously by means of silicon surface barrier detectors at angle of 45° and 169° with respect to the beam direction. The electron capture (EC) as well as direct ionization (DI) contributions were determined from the projectile charge state dependence of the target xray production cross sections under single collision conditions. The present work was undertaken to expand the measurements of Lshell xray production cross sections upon selected elements with low Lshell binding energies by energetic ¹⁶O^q (q=3⁺,4⁺,5⁺,6⁺,7⁺,8⁺) incident ions. Collision systems chosen for this work have sufficiently large Z₁/Z₂ ratios (0.250.28) so that EC may noticeably contribute to the xray production enhancement. In this region, reliable experimental data are particularly scarce, thus, fundamental work in this area is still necessary. DI and EC cross section measurements were compared with the ECPSSR and the first Born theories over the range of 0.25 <Z₁/Z₂ < 0.29 and 0.38 < v₁/v₂_L <0.72. The ECPSSR theoretical predictions (including DI and EC) are in closer agreement with the data than the first Born's. digital.library.unt.edu/ark:/67531/metadc277981/
 Charge State Dependence of MShell XRay Production in 67Ho by 212 MeV Carbon Ions
 The charge state dependence of Mshell xray production cross sections of 67HO bombarded by 212 MeV carbon ions with and without Kvacancies are reported. The experiment was performed using an NEC 9SDH2 tandem accelerator at the Ion Beam Modification and Analysis Laboratory of the University of North Texas. The high charge state carbon ions were produced by a postaccelerator stripping gas cell. Ultraclean holmium targets were used in ionatom collision to generate Mshell x rays at energies from 1.05 to 1.58 keV. The xray measurements were made with a windowless Si(Li) xray detector that was calibrated using radiative sources, particle induced xray emission (PIXE), and the atomic field bremsstrahlung (AFB) techniques. digital.library.unt.edu/ark:/67531/metadc278725/
 Charge State Distributions in Molecular Dissociation
 The present work provides charge state fractions that may be used to generate TEAMS relative sensitivity factors for impurities in semiconductor materials. digital.library.unt.edu/ark:/67531/metadc278340/
 Charged Particle Transport and Confinement Along Null Magnetic Curves and in Various Other Nonuniform Field Configurations for Applications in Antihydrogen Production
 Comparisons between measurements of the groundstate hyperfine structure and gravitational acceleration of hydrogen and antihydrogen could provide a test of fundamental physical theories such as CPT (charge conjugation, parity, timereversal) and gravitational symmetries. Currently, antihydrogen traps are based on MalmbergPenning traps. The number of antiprotons in MalmbergPenning traps with sufficiently low energy to be suitable for trappable antihydrogen production may be reduced by the electrostatic space charge of the positrons and/or collisions among antiprotons. Alternative trap designs may be needed for future antihydrogen experiments. A computational tool is developed to simulate charged particle motion in customizable magnetic fields generated by combinations of current loops and current lines. The tool is used to examine charged particle confinement in two systems consisting of dual, levitated current loops. The loops are coaxial and arranged to produce a magnetic null curve. Conditions leading to confinement in the system are quantified and confinement modes near the null curve and encircling one or both loops are identified. Furthermore, the tool is used to examine and quantify charged particle motion parallel to the null curve in the large radius limit of the dual, levitated current loops. An alternative to new trap designs is to identify the effects of the positron space in existing traps and to find modes of operation where the space charge is beneficial. Techniques are developed to apply the Boltzmann density relation along curved magnetic field lines. Equilibrium electrostatic potential profiles for a positron plasma are computed by solving Poisson's equation using a finitedifference method. Equilibria are computed in a model Penning trap with an axially varying magnetic field. Also, equilibria are computed for a positron plasma in a model of the ALPHA trap. Electric potential wells are found to form selfconsistently. The technique is expanded to compute equilibria for a twospecies plasma with an antiproton plasma confined by the positron space charge. The twospecies equilibria are used to estimate timescales associated with threebody recombination, losses due to collisions between antiprotons, and temperature equilibration. An equilibrium where the threebody recombination rate is the smallest is identified. digital.library.unt.edu/ark:/67531/metadc849779/
 Coherent Resonant Interaction and Harmonic Generation in Atomic Vapors
 This work examines the use of higher order multiphoton resonances in higher harmonic generation together with judicious exploitation of coherent interaction properties to achieve efficient harmonic generation. A detailed experimental study on third harmonic generation in two photon resonant coherent interaction and a theoretical study on four photon resonant coherent interaction have been conducted. Two photon resonant coheren propagation in lithium vapor (2S4S and 2S3D interaction) has been studied in detail as a function of phase and delay of the interacting pulse sequence. Under coherent lossless propagation of 90 phase shifted pulse pair, third harmonic generation is enhanced. A maximum energy conversion efficiency of 1% was measured experimentally. This experiment shows that phase correlated pulse sequence can be used to control multiphoton coherent resonant effects. A larger two photon resonant enhancement does not result in more efficient harmonic generation, in agreement with the theoretical prediction. An accurate (to at least 0.5 A°) measurement of intensity dependent Stark shift has been done with the newly developed "interferometric wavemeter." Stark shifts as big as several pulse bandwidths (of picosecond pulses) result in a poor tuning of multiphoton resonance and become a limiting factor of resonant harmonic generation. A complete theory has been developed for harmonic generation in a four photon resonant coherent interaction. A numerical application of the theory to the Hg atom successfully interprets the experimental observations in terms of the phase dependent stimulated Raman scattering. With the intensity required for four photon resonant transition, the calculation predicts a dramatic Stark shift effect which completely destroys the resonance condition. This model provides a basis for the development of future schemes for efficient higher order coherent upconversion. digital.library.unt.edu/ark:/67531/metadc332243/
 Complex Numbers in Quantum Theory
 In 1927, Nobel prize winning physicist, E. Schrodinger, in correspondence with Ehrenfest, wrote the following about the new theory: “What is unpleasant here, and indeed directly to be objected to, is the use of complex numbers. Psi is surely fundamentally a real function.” This seemingly simple issue remains unexplained almost ninety years later. In this dissertation I elucidate the physical and theoretical origins of the complex requirement. I identify a freedom/constraint situation encountered by vectors when, employed in accordance with adopted quantum representational methodology, and representing angular momentum states in particular. Complex vectors, quite simply, provide more available adjustable variables than do real vectors. The additional variables relax the constraint situation allowing the theory’s representational program to carry through. This complex number issue, which lies at the deepest foundations of the theory, has implications for important issues located higher in the theory. For example, any unification of the classical and quantum accounts of the settled order of nature, will rest squarely on our ability to account for the introduction of the imaginary unit. digital.library.unt.edu/ark:/67531/metadc804988/
 Complexity as a Form of Transition From Dynamics to Thermodynamics: Application to Sociological and Biological Processes.
 This dissertation addresses the delicate problem of establishing the statistical mechanical foundation of complex processes. These processes are characterized by a delicate balance of randomness and order, and a correct paradigm for them seems to be the concept of sporadic randomness. First of all, we have studied if it is possible to establish a foundation of these processes on the basis of a generalized version of thermodynamics, of nonextensive nature. A detailed account of this attempt is reported in Ignaccolo and Grigolini (2001), which shows that this approach leads to inconsistencies. It is shown that there is no need to generalize the KolmogorovSinai entropy by means of a nonextensive indicator, and that the anomaly of these processes does not rest on their nonextensive nature, but rather in the fact that the process of transition from dynamics to thermodynamics, this being still extensive, occurs in an exceptionally extended time scale. Even, when the invariant distribution exists, the time necessary to reach the thermodynamic scaling regime is infinite. In the case where no invariant distribution exists, the complex system lives forever in a condition intermediate between dynamics and thermodynamics. This discovery has made it possible to create a new method of analysis of nonstationary time series which is currently applied to problems of sociological and physiological interest. digital.library.unt.edu/ark:/67531/metadc4209/
 Complexity as Aging NonPoisson Renewal Processes
 The search for a satisfactory model for complexity, meant as an intermediate condition between total order and total disorder, is still subject of debate in the scientific community. In this dissertation the emergence of nonPoisson renewal processes in several complex systems is investigated. After reviewing the basics of renewal theory, another popular approach to complexity, called modulation, is introduced. I show how these two different approaches, given a suitable choice of the parameter involved, can generate the same macroscopic outcome, namely an inverse power law distribution density of events occurrence. To solve this ambiguity, a numerical instrument, based on the theoretical analysis of the aging properties of renewal systems, is introduced. The application of this method, called renewal aging experiment, allows us to distinguish if a time series has been generated by a renewal or a modulation process. This method of analysis is then applied to several physical systems, from blinking quantum dots, to the human brain activity, to seismic fluctuations. Theoretical conclusions about the underlying nature of the considered complex systems are drawn. digital.library.unt.edu/ark:/67531/metadc3706/
 A Comprehensive Model for the Rotational Spectra of Propyne CH₃CCH in the Ground and V₁₀=1,2,3,4,5 Vibrational States
 The energy states of C₃ᵥ symmetric top polyatomic molecules were studied. Both classical and quantum mechanical methods have been used to introduce the energy states of polyatomic molecules. Also, it is shown that the vibrationrotation spectra of polyatomic molecules in the ground and excited vibrational states can be predicted by group theory. A comprehensive model for predicting rotational frequency components in various v₁₀ vibrational levels of propyne was developed by using perturbation theory and those results were compared with other formulas for C₃ᵥ symmetric top molecules. The v₁₀=1,2,3 and ground rotational spectra of propyne in the frequency range 1770 GHz have been reassigned by using the derived comprehensive model. The v₁₀=3 and v₁₀=4 rotational spectra of propyne have been investigated in the 70 GHz, and 17 to 52 GHz regions, respectively, and these spectral components assigned using the comprehensive model. Molecular constants for these vibrationally excited states have been determined from more than 100 observed rotational transitions. From these experimentally observed components and a model based upon first principles for C₃ᵥ symmetry molecules, rotational constants have been expressed in a form which enables one to predict rotational components for vibrational levels for propyne up to v₁₀=5. This comprehensive model also appears to be useful in predicting rotational components in more highly excited vibrational levels but data were not available for comparison with the theory. Several techniques of assignment of rotational spectra for each excited vibrational state are discussed. To get good agreement between theory and experiment, an additional term 0.762(J+1) needed to be added to Kℓ=1 states in v₁₀=3. No satisfactory theoretical explanation of this term has been found. Experimentally measured frequencies for rotational components for J→(J+1)=+1 (0≤J≤3) in each vibration v₁₀=n (0≤n≤4) are presented and compared with those calculated using the results of basic perturbation theory. The v₉=2 rotational spectrum of the propyne molecule was introduced in Appendix A to compare the rotational spectra of the same molecule in different vibrational levels v₉ and v₁₀. digital.library.unt.edu/ark:/67531/metadc332026/
 A Computer Analysis of Complex GammaRay Spectra
 The purpose of this investigation was to provide a method for determining the relative intensities of all gamma rays in a particular spectrum, and thereby determine the relative transition probabilities. digital.library.unt.edu/ark:/67531/metadc130612/
 The Concept of Collision Strength and Its Applications
 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 equation has a fivefold integral collision term that is complicated. Chandrasekhar and Spitzer's approaches to the linear FokkerPlanck coefficients have several approximations. An effective variablechange technique has been developed in this dissertation as an alternative to scattering angle as the measure of collision strength. By introducing the square of the reduced impulse or its equivalencies as a collision strength variable, many plasma calculations have been simplified. The fivefold linear Boltzmann collision integral and linearized Boltzmann collision integral are simplified to threefold integrals. The arbitrary order linear FokkerPlanck coefficients are calculated and expressed in a uniform expression. The new theory provides a simple and exact method for describing the equilibrium plasma collision rate, and a precise calculation of the equilibrium relaxation time. It generalizes bimolecular collision reaction rate theory to a reaction rate theory for plasmas. A simple formula of high precision with wide temperature range has been developed for electron impact ionization rates for carbon atoms and ions. The universality of the concept of collision strength is emphasized. This dissertation will show how Arrhenius' chemical reaction rate theory and Thomson's ionization theory can be unified as one single theory under the concept of collision strength, and how many important physical terms in different disciplines, such as activation energy in chemical reaction theory, ionization energy in Thomson's ionization theory, and the Coulomb logarithm in plasma physics, can be unified into a single one  the threshold value of collision strength. The collision strength, which is a measure of a transfer of momentum in units of energy, can be used to reconcile the differences between Descartes' opinion and Leibnitz's opinion about the "true'' measure of a force. Like Newton's second law, which provides an instantaneous measure of a force, collision strength, as a cumulative measure of a force, can be regarded as part of a law of force in general. digital.library.unt.edu/ark:/67531/metadc4530/
 A Continuously Sensitive Cloud Chamber
 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. digital.library.unt.edu/ark:/67531/metadc97019/
 Cooperationinduced Criticality in Neural Networks
 The human brain is considered to be the most complex and powerful informationprocessing 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 cooperationinduced properties in a system of interacting units. I demonstrate that the neural network of my research generates a series of properties such as avalanche distribution in size and duration coinciding with the experimental results on neural networks both in vivo and in vitro. Focusing attention on temporal complexity and fractal index of the system, I discuss how to define an order parameter and phase transition. Criticality is assumed to correspond to the emergence of temporal complexity, interpreted as a manifestation of nonPoisson renewal dynamics. In addition, I study the transmission of information between two networks to confirm the criticality and discuss how the network topology changes over time in the light of Hebbian learning. digital.library.unt.edu/ark:/67531/metadc283813/
 A Correction Factor for the First Born Approximation
 This thesis looks at a Schroedinger equation and the Born approximation. digital.library.unt.edu/ark:/67531/metadc130574/
 Criticality in Cooperative Systems
 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 collapses. In this study, I used cooperative systems based on selfpropelled particle models (the flock models) which have been proved to be virtually equivalent to sociological network models mimicking the decision making processes (the decision making model). The critical region is an intermediate condition between a highly disordered state and a strong ordered one. At criticality the waiting times distribution density between two consecutive collapses shows an inverse power law form with an anomalous statistical behavior. The scientific evidences are based on measures of information theory, correlation in time and space, and fluctuation statistical analysis. In order to prove the benefit for a system to live at criticality, I made a flock system interact with another similar system, and then observe the information transmission for different disturbance values. I proved that at criticality the transfer of information gets the maximal efficiency. As last step, the flock model has been shown that, despite its simplicity, is sufficiently a realistic model as proved via the use of 3D simulations and computer animations. digital.library.unt.edu/ark:/67531/metadc271910/
 CrossSection at 15.6 and 16.1 MeV
 The intent of this investigation is the determination of the values of the Cs133 (n,2n)Cs132 crosssection at neutron energies of 15.6 and 16.1 MeV. Neutrons of this energy are produced with comparative ease by means of the DT reaction, in which deuterons of energy 500 and 750 keV, respectively, are impingent upon a tritium target. digital.library.unt.edu/ark:/67531/metadc131110/
 Cross Section for the 165/Ho (n, 2n) 164/Ho Reaction at 15.6 MeV
 It was the purpose of this investigation to bring together the ideas and procedures involved in the measurement of (n, 2n) reaction cross sections. Some of the inherent properties of the material under investigation (Holium) are involved in determining these relationships. digital.library.unt.edu/ark:/67531/metadc131148/
 Cross Section Measurements in Praseodymium141 as a Function of Neutron Bombarding Energy
 Using the parallel disk method of activation analysis, the (n,2n) reaction cross section in 141Pr was measured as a function of neutron energy in the range 15.4 to 18.4 MeV. The bombarding neutrons were produced from the 3T(d,n)4He reaction, where the deuterons were accelerated by the 3MV Van de Graff generator of the North Texas Regional Physics Laboratory in Denton, Texas. digital.library.unt.edu/ark:/67531/metadc131376/
 Crystalline Polymorphism of Nitrates
 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. digital.library.unt.edu/ark:/67531/metadc97053/
 DD and DT Neutron Excitation of Energy Levels in Cs133
 The purpose of this experiment was to make positive assignment of the Cs133 energy levels excited by the inelastic scattering of neutrons. digital.library.unt.edu/ark:/67531/metadc130455/
 A Decay Scheme for 164 Ho
 The present investigation was prompted by several considerations. In previous studies there was considerable variance with regard to the reported values for the halflives 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. digital.library.unt.edu/ark:/67531/metadc131582/
 Decoherence, Master Equation for Open Quantum Systems, and the Subordination Theory
 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 twostate 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 superposition of these two states with the environment. The joint action of inphasing and dephasing generates a Markov master equation statistically equivalent to a random walker jumping from one state to the other. This model can be used to describe intermittent fluorescence, as a sequence of "light on" and "light off" states. The experiments on blinking quantum dots indicate that the sojourn times are distributed with an inverse power law. Thus, a proposal to turn the model for Poisson fluorescence intermittency into a model for nonPoisson fluorescence intermittency is made. The collisionlike interaction of the twostate system with the environment is assumed to takes place at random times rather than at regular times. The time distance between one collision and the next is given by a distribution, called the subordination distribution. If the subordination distribution is exponential, a sequence of collisions yielding no persistence is turned into a sequence of "light on" and "light off" states with significant persistence. If the subordination function is an inverse power law the sequel of "light on" and "light off" states becomes equivalent to the experimental sequences. Different conditions are considered, ranging from predominant inphasing to predominant dephasing. When dephasing is predominant the sequel of "light on" and "light off" states in the time asymptotic limit becomes an inverse power law. If the predominant dephasing involves a time scale much larger than the minimum time scale accessible to the experimental observation, thereby generating persistence, the resulting distribution becomes a MittagLeffler function. If dephasing is predominant, in addition to the inverse power law distribution of "light off" and "light on" time duration, a strong correlation between "light on" and "light off" state is predicted. digital.library.unt.edu/ark:/67531/metadc4812/
 Design and Construction of a Positive RadioFrequency Ion Source for the Production of Negative Ions
 It is the purpose of this paper to present a detailed account of the design and construction of this positiveion source and associated equipment. digital.library.unt.edu/ark:/67531/metadc108015/