You limited your search to:
Partner:
UNT Libraries
Degree Discipline:
Physics
Collection:
UNT Theses and Dissertations
 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/
 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/
 Design and Testing of a Coincidence System
 This paper is concerned with the design, testing and performance of a coincidence system, the proposed North Texas State College accelerator. digital.library.unt.edu/ark:/67531/metadc108113/
 Design and Testing of a Corona Column and a Closed Gas Distribution System for a Tandem Van de Graaff Voltage Generator
 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. digital.library.unt.edu/ark:/67531/metadc163849/
 Design and Testing of a Positive Ion Accelerator and Necessary Vacuum System
 This thesis is a study of the design and testing of a positive ion accelerator and necessary vacuum system. digital.library.unt.edu/ark:/67531/metadc163830/
 Detection of the Resonant Vibration of the Cellular Membrane Using Femtosecond Laser Pulses
 An optical detection technique is developed to detect and measure the resonant vibration of the cellular membrane. Biological membranes are active components of living cells and play a complex and dynamic role in life processes. They are believed to have oscillation modes of frequencies in the range of 1 to 1000 GHz. To measure such a highfrequency vibration, a linear laser cavity is designed to produce a train of femtosecond pulses of adjustable repetition rate. The method is then directly applied to liposomes, "artificial membrane", stained with a liphophilic potential sensitive dye. The spectral behavior of a selection of potential sensitive dyes in the membrane is also studied. digital.library.unt.edu/ark:/67531/metadc331235/
 A Determination of the Bothe Depression Factor for Discs in Water
 The purpose of this work is to determine experimentally the depression of the neutron density by a detecting foil. The depression factor is known as the "selfshading" of the foil. digital.library.unt.edu/ark:/67531/metadc130255/
 A Determination of the Fine Structure Constant Using Precision Measurements of Helium Fine Structure
 Spectroscopic measurements of the helium atom are performed to high precision using an atomic beam apparatus and electrooptic laser techniques. These measurements, in addition to serving as a test of helium theory, also provide a new determination of the fine structure constant α. An apparatus was designed and built to overcome limitations encountered in a previous experiment. Not only did this allow an improved level of precision but also enabled new consistency checks, including an extremely useful measurement in 3He. I discuss the details of the experimental setup along with the major changes and improvements. A new value for the J = 0 to 2 fine structure interval in the 23P state of 4He is measured to be 31 908 131.25(30) kHz. The 300 Hz precision of this result represents an improvement over previous results by more than a factor of three. Combined with the latest theoretical calculations, this yields a new determination of α with better than 5 ppb uncertainty, α1 = 137.035 999 55(64). digital.library.unt.edu/ark:/67531/metadc31547/
 Deterministic Brownian Motion
 The goal of this thesis is to contribute to the ambitious program of the foundation of developing statistical physics using chaos. We build a deterministic model of Brownian motion and provide a microscpoic derivation of the FokkerPlanck equation. Since the Brownian motion of a particle is the result of the competing processes of diffusion and dissipation, we create a model where both diffusion and dissipation originate from the same deterministic mechanism  the deterministic interaction of that particle with its environment. We show that standard diffusion which is the basis of the FokkerPlanck equation rests on the Central Limit Theorem, and, consequently, on the possibility of deriving it from a deterministic process with a quickly decaying correlation function. The sensitive dependence on initial conditions, one of the defining properties of chaos insures this rapid decay. We carefully address the problem of deriving dissipation from the interaction of a particle with a fully deterministic nonlinear bath, that we term the booster. We show that the solution of this problem essentially rests on the linear response of a booster to an external perturbation. This raises a longstanding problem concerned with Kubo's Linear Response Theory and the strong criticism against it by van Kampen. Kubo's theory is based on a perturbation treatment of the Liouville equation, which, in turn, is expected to be totally equivalent to a firstorder perturbation treatment of single trajectories. Since the boosters are chaotic, and chaos is essential to generate diffusion, the single trajectories are highly unstable and do not respond linearly to weak external perturbation. We adopt chaotic maps as boosters of a Brownian particle, and therefore address the problem of the response of a chaotic booster to an external perturbation. We notice that a fully chaotic map is characterized by an invariant measure which is a continuous function of the control parameters of the map. Consequently if the external perturbation is made to act on a control parameter of the map, we show that the booster distribution undergoes slight modifications as an effect of the weak external perturbation, thereby leading to a linear response of the mean value of the perturbed variable of the booster. This approach to linear response completely bypasses the criticism of van Kampen. The joint use of these two phenomena, diffusion and friction stemming from the interaction of the Brownian particle with the same booster, makes the microscopic derivation of a FokkerPlanck equation and Brownian motion, possible. digital.library.unt.edu/ark:/67531/metadc279262/
 A DeuteriumDeuterium Type Neutron Source
 In view of the advantages of its type, the decision to construct a neutron source of the particle accelerator type was made. The purpose of this thesis is to survey the problems encountered in the construction of the source. digital.library.unt.edu/ark:/67531/metadc96980/
 The Dielectric Constant of Galvinoxyl
 The molecules in many substances are know to undergo at characteristic temperatures a change in their rotational freedom in the solid state, signifying either a change in structure of the material of the onset of limited rotation of the molecule about some symmetry axis. The purpose of this research was to determine from dielectric constant measurements over the 100°K420°K temperature range whether or not the organic free radical galvinoxyl and its diamagnetic parent molecule, dihydroxydiphenylmethane, undergo any such transitions. digital.library.unt.edu/ark:/67531/metadc163926/
 Dielectric Relaxation of Aqueous Solutions at Microwave Frequencies for 335 GHz. Using a Loaded Microwave Cavity Operating in the TM010 Mode
 The frequency dependence and temperature dependence of the complex dielectric constant of water is of great interest. The temperature dependence of the physical properties of water given in the literature, specific heat, thermal conductivity, electric conductivity, pH, etc. are compared to the a. c. (microwave) and d. c. conductivity of water with a variety of concentration of different substances such as HC1, NaCl, HaS04, etc. When each of these properties is plotted versus inverse absolute temperature, it can be seen that each sample shows "transition temperatures". In this work, Slater's perturbation equations for a resonant microwave cavity were used to analyze the experimental results for the microwave data. digital.library.unt.edu/ark:/67531/metadc279039/
 Dipole Moments of Diphenyl Compounds with Conjugated Double Bonds
 This thesis is a continuation of a study of molecular moments begun by Joseph T. Fielder. In his paper he discussed the theory and the equipment necessary for such a study. It is the purpose of this paper to set forth modifications of his equipment, to present data obtained with this modified equipment, and to interpret this data. digital.library.unt.edu/ark:/67531/metadc83668/
 Dipole Moments of Olefenic Diesters
 It is the purpose of this paper to present experimental data for the determination of the dielectric constant and the dipole moments for a series of olefenic diesters of the cis and trans configurations. digital.library.unt.edu/ark:/67531/metadc96944/
 Dipole Moments of Olefinic Esters
 It is the purpose of this thesis to investigate the applicability of the Debye equation to measurements dipole moments of polar compounds in dilute solutions of nonpolar solvents more fully than has been done by previous workers at this institution. digital.library.unt.edu/ark:/67531/metadc107828/
 Dispersion of the Nonlinear Refractive Index of CS₂ in the Spectral Range of 911 μm
 The nonlinear refractive index (n2) of room temperature liquid CS2 in the wavelength range of 9 to 11 micrometers is measured. A line tunable hybrid C02 TEA laser and amplifier system is used for the experiments. In these measurements the well known photoacoustic method is utilized to observe the onset of whole beam selffocusing. The photoacoustic signal in a CS2 cell, much longer than the confocal parameter, is monitored. The departure of the acoustic signal from linear growth marks the critical power for the onset of nonlinearity. It is experimentally verified that the phenomenon is power dependent as expected from selffocusing theory. The value of n2 is then calculated from the theoretical model of self focusing. Measurements of the onaxis irradiance transmitted through the nonlinear material as well as the measurements of beam distortion are used to verify the validity of the photoacoustic method. In all the measurements the onaxis intensity was smaller than the calculated threshold intensity for stimulated Brillouin scattering. The back reflection was monitored to make sure that stimulated Brillouin scattering was not playing a role in the phenomenon. digital.library.unt.edu/ark:/67531/metadc332448/
 Distribution of Nighttime Fregion Molecular Ion Concentrations and 6300 Å Nightglow Morphology
 The purpose of this study is twofold. The first is to determine the dependence of the molecular ion profiles on the various ionospheric and atmospheric parameters that affect their distributions. The second is to demonstrate the correlation of specific ionospheric parameters with 6300 Å nightglow intensity during periods of magnetically quiet and disturbed conditions. digital.library.unt.edu/ark:/67531/metadc278620/
 The Diurnal Variation of Cosmic Radiation
 The primary purpose of this investigation was to study the diurnal variation of cosmicray intensity. digital.library.unt.edu/ark:/67531/metadc163872/
 A Dynamic and Thermodynamic Approach to Complexity.
 The problem of establishing the correct approach to complexity is a very hot and crucial issue to which this dissertation gives some contributions. This dissertation considers two main possibilities, one, advocated by Tsallis and coworkers, setting the foundation of complexity on a generalized, nonextensive , form of thermodynamics, and another, proposed by the UNT Center for Nonlinear Science, on complexity as a new condition that, for physical systems, would be equivalent to a state of matter intermediate between dynamics and thermodynamics. In the first part of this dissertation, the concept of KolmogorovSinai entropy is introduced. The Pesin theorem is generalized in the formalism of Tsallis nonextensive thermodynamics. This generalized form of Pesin theorem is used in the study of two major classes of problems, whose prototypes are given by the Manneville and the logistic map respectively. The results of these studies convince us that the approach to complexity must be made along lines different from those of the nonextensive thermodynamics. We have been convinced that the Lévy walk can be used as a prototype model of complexity, as a condition of balance between order and randomness that yields new phenomena such as aging, and multifractality. We reach the conclusions that these properties must be studied within a dynamic rather than thermodynamic perspective. The second part focuses on the study of the heart beating problem using a dynamic model, the socalled memory beyond memory, based on the Lévy walker model. It is proved that the memory beyond memory effect is more obvious in the healthy heart beating sequence. The concepts of fractal, multifractal, wavelet transformation and wavelet transform maximum modulus (WTMM) method are introduced. Artificial time sequences are generated by the memory beyond memory model to mimic the heart beating sequence. Using WTMM method, the multifratal singular spectrums of the sequences are calculated. It is clear that the sequence with strong memory beyond memory effect has broader singular spectrum.200308 digital.library.unt.edu/ark:/67531/metadc4276/
 The Dynamic Foundation of Fractal Operators.
 The fractal operators discussed in this dissertation are introduced in the form originally proposed in an earlier book of the candidate, which proves to be very convenient for physicists, due to its heuristic and intuitive nature. This dissertation proves that these fractal operators are the most convenient tools to address a number of problems in condensed matter, in accordance with the point of view of many other authors, and with the earlier book of the candidate. The microscopic foundation of the fractal calculus on the basis of either classical or quantum mechanics is still unknown, and the second part of this dissertation aims at this important task. This dissertation proves that the adoption of a master equation approach, and so of probabilistic as well as dynamical argument yields a satisfactory solution of the problem, as shown in a work by the candidate already published. At the same time, this dissertation shows that the foundation of Levy statistics is compatible with ordinary statistical mechanics and thermodynamics. The problem of the connection with the KolmogorovSinai entropy is a delicate problem that, however, can be successfully solved. The derivation from a microscopic Liouvillelike approach based on densities, however, is shown to be impossible. This dissertation, in fact, establishes the existence of a striking conflict between densities and trajectories. The third part of this dissertation is devoted to establishing the consequences of the conflict between trajectories and densities in quantum mechanics, and triggers a search for the experimental assessment of spontaneous wavefunction collapses. The research work of this dissertation has been the object of several papers and two books. digital.library.unt.edu/ark:/67531/metadc4235/
 Dynamical Friction Coefficients for Plasmas Exhibiting NonSpherical Electron Velocity Distributions
 This investigation is designed to find the net rate of decrease in the component of velocity parallel to the original direction of motion of a proton moving through an electron gas exhibiting a nonspherical velocity distribution. digital.library.unt.edu/ark:/67531/metadc130480/
 EEG, Alpha Waves and Coherence
 This thesis addresses some theoretical issues generated by the results of recent analysis of EEG time series proving the brain dynamics are driven by abrupt changes making them depart from the ordinary Poisson condition. These changes are renewal, unpredictable and nonergodic. We refer to them as crucial events. How is it possible that this form of randomness be compatible with the generation of waves, for instance alpha waves, whose observation seems to suggest the opposite view the brain is characterized by surprisingly extended coherence? To shed light into this apparently irretrievable contradiction we propose a model based on a generalized form of Langevin equation under the influence of a periodic stimulus. We assume that there exist two different forms of time, a subjective form compatible with Poisson statistical physical and an objective form that is accessible to experimental observation. The transition from the former to the latter form is determined by the brain dynamics interpreted as emerging from the cooperative interaction among many units that, in the absence of cooperation would generate Poisson fluctuations. We call natural time the brain internal time and we make the assumption that in the natural time representation the time evolution of the EEG variable y(t) is determined by a Langevin equation perturbed by a periodic process that in this time representation is hardly distinguishable from an erratic process. We show that the representation of this random process in the experimental time scale is characterized by a surprisingly extended coherence. We show that this model generates a sequence of damped oscillations with a time behavior that is remarkably similar to that derived from the analysis of real EEG's. The main result of this research work is that the existence of crucial events is not incompatible with the alpha wave coherence. In addition to this important result, we find another result that may help our group, or any other research group working on the analysis of brain's dynamics, to prove or to disprove the existence of crucial events. We study the diffusion process generated by fluctuations emerging from the same model after filtering out the alpha coherence, and we study the recursion to the origin. We study the survival probability of this process, namely the probability that up to a given time no recrossing of the origin occurs. We find that this is an inverse power law with a power that depends on whether or not crucial events exist. digital.library.unt.edu/ark:/67531/metadc28389/
 The Effect of Average Grain Size on Polycrystalline Diamond Films
 The work function of hydrogenterminated, polycrystalline diamond was studied using ultraviolet photoelectron spectroscopy. Polycrystalline diamond films were deposited onto molybdenum substrates by electrophoresis for grain sizes ranging from 0.3 to 108 microns. The work function and electron affinity were measured using 21.2 eV photons from a helium plasma source. The films were characterized by xray photoelectron spectroscopy to determine elemental composition and the sp2/sp3 carbon fraction. The percentage of (111) diamond was determined by xray diffraction, and scanning electron microscopy was performed to determine average grain size. The measured work function has a maximum of 5.1 eV at 0.3 microns, and decreases to 3.2 eV at approximately 4 microns. Then the work function increases with increasing grain size to 4.0 eV at 15 microns and then asymptotically approaches the 4.8 eV work function of single crystal diamond at 108 microns. These results are consistent with a 3component model in which the work function is controlled by singlecrystal (111) diamond at larger grain sizes, graphitic carbon at smaller grain sizes, and by the electron affinity for the intervening grain sizes. digital.library.unt.edu/ark:/67531/metadc3164/
 Effect of Sample Geometry on Magnetomorphic Oscillations in the Hall Effect in Cadium at LiquidHelium Temperatures
 This thesis presents observations on sizeeffect oscillations in the Hall effect in an oriented single crystal of highly pure cadmium at liquidhelium temperatures. All measurements were made in transverse magnetic field. digital.library.unt.edu/ark:/67531/metadc130799/
 The Effects of Cesium Deposition and Gas Exposure on the Field Emission Properties of Single Wall and Multiwall Carbon Nanotubes
 The effects of Cs deposition on the field emission (FE) properties of singlewalled carbon nanotube (SWNT) bundles were studied. In addition, a comparative study was made on the effects of O2, Ar and H2 gases on the field emission properties of SWNT bundles and multiwall carbon nanotubes (MWNTs). We observed that Cs deposition decreases the turnon field for FE by a factor of 2.1  2.9 and increases the FE current by 6 orders of magnitude. After Cs deposition, the FE current versus voltage (IV) curves showed nonFowlerNordheim behavior at large currents consistent with tunneling from adsorbate states. At lower currents, the ratio of the slope of the FE IV curves before and after Cs deposition was approximately 2.1. Exposure to N2 does not decrease the FE current, while exposure to O2 decreases the FE current. Our results show that cesiated SWNT bundles have great potential as economical and reliable vacuum electron sources. We find that H2 and Ar gases do not significantly affect the FE properties of SWNTs or MWNTs. O2 temporarily reduces the FE current and increases the turnon voltage of SWNTs. Full recovery of these properties occurred after operation in UHV. The higher operating voltages in an O2 environment caused a permanent decrease of FE current and increase in turnon field of MWNTs. The ratios of the slopes before and after O2 exposure were approximately 1.04 and 0.82 for SWNTs and MWNTs, respectively. SWNTs compared to MWNTs would appear to make more economical and reliable vacuum electron sources. digital.library.unt.edu/ark:/67531/metadc3110/