Latest content added for Digital Library Partner: UNT Librarieshttps://digital.library.unt.edu/explore/partners/UNT/browse/?fq=str_degree_discipline:Physics&start=20&fq=untl_collection:UNTETD2015-08-21T05:42:39-05:00UNT LibrariesThis is a custom feed for browsing Digital Library Partner: UNT LibrariesTemporal Complexity and Stochastic Central Limit Theorem2015-08-21T05:42:39-05:00https://digital.library.unt.edu/ark:/67531/metadc700093/<p><a href="https://digital.library.unt.edu/ark:/67531/metadc700093/"><img alt="Temporal Complexity and Stochastic Central Limit Theorem" title="Temporal Complexity and Stochastic Central Limit Theorem" src="https://digital.library.unt.edu/ark:/67531/metadc700093/small/"/></a></p><p>Complex processes whose evolution in time rests on the occurrence of a large and random number of intermittent events are the systems under study. The mean time distance between two consecutive events is infinite, thereby violating the ergodic condition and activating at the same time a stochastic central limit theorem that explains why the Mittag-Leffler function is a universal property of nature. The time evolution of these complex systems is properly generated by means of fractional differential equations, thus leading to the interpretation of fractional trajectories as the average over many random trajectories, each of which fits the stochastic central limit theorem and the condition for the Mittag-Leffler universality. Additionally, the effect of noise on the generation of the Mittag-Leffler function is discussed. Fluctuations of relatively weak intensity can conceal the asymptotic inverse power law behavior of the Mittag-Leffler function, providing a reason why stretched exponentials are frequently found in nature. These results afford a more unified picture of complexity resting on the Mittag-Leffler function and encompassing the standard inverse power law definition.</p>Relaxation Time Measurements for Collision Processes in the Surface Layers of Conductors and Semiconductors Near 10 Ghz2015-06-24T09:39:17-05:00https://digital.library.unt.edu/ark:/67531/metadc663566/<p><a href="https://digital.library.unt.edu/ark:/67531/metadc663566/"><img alt="Relaxation Time Measurements for Collision Processes in the Surface Layers of Conductors and Semiconductors Near 10 Ghz" title="Relaxation Time Measurements for Collision Processes in the Surface Layers of Conductors and Semiconductors Near 10 Ghz" src="https://digital.library.unt.edu/ark:/67531/metadc663566/small/"/></a></p><p>This thesis represents one phase of a joint effort of research on the properties of liquids and solids. This work is concerned primarily with the microwave properties of solids. In this investigation the properties exhibited by conductor and semiconductor materials when they are subjected to electromagnetic radiation of microwave frequency are studied. The method utilized in this experiment is the perturbation of a resonant cavity produced by introduction of a cylindrically shaped sample into it.</p>Microwave Line Widths of the Asymmetric Top Formic Acid Molecule2015-06-24T09:39:17-05:00https://digital.library.unt.edu/ark:/67531/metadc663604/<p><a href="https://digital.library.unt.edu/ark:/67531/metadc663604/"><img alt="Microwave Line Widths of the Asymmetric Top Formic Acid Molecule" title="Microwave Line Widths of the Asymmetric Top Formic Acid Molecule" src="https://digital.library.unt.edu/ark:/67531/metadc663604/small/"/></a></p><p>This work consisted of an experimental investigation of the formic acid (HCOOH) molecule's rotational spectrum. Measurements of line widths were obtained for J = 5, 12, 13, 19, and 20 for a pressure range from 1 to 10 microns. A linear behavior between Av and p was observed as predicted by theory. The line width parameter Avp was observed to depend on the quantum number J. Hard sphere collision diameters b1 were calculated using the obtained AvP values. These deduced hard sphere values were found to be larger than the physical size of the molecule. This result was found to be in general agreement with other investigation in which long range forces (dipole-dipole) dominate.</p>Effects of Discharge Tube Geometry on Plasma Ion Oscillations2015-06-24T09:39:17-05:00https://digital.library.unt.edu/ark:/67531/metadc663636/<p><a href="https://digital.library.unt.edu/ark:/67531/metadc663636/"><img alt="Effects of Discharge Tube Geometry on Plasma Ion Oscillations" title="Effects of Discharge Tube Geometry on Plasma Ion Oscillations" src="https://digital.library.unt.edu/ark:/67531/metadc663636/small/"/></a></p><p>This study considers the effect, on plasma ion oscillations, of various lengths of discharge tubes as well as various cross sections of discharge tubes. Four different gases were used in generating the plasma. Gas pressure and discharge voltage and current were varied to obtain a large number of signals.
A historical survey is given to familiarize the reader with the field. The experimental equipment and procedure used in obtaining data is given. An analysis of the data obtained is presented along with possible explanations for the observed phenomena. Suggestions for future study are made.</p>A Technique for Increasing the Optical Strength of Single-Crystal NaCl and KCl Through Temperature Cycling2015-05-10T06:16:59-05:00https://digital.library.unt.edu/ark:/67531/metadc504009/<p><a href="https://digital.library.unt.edu/ark:/67531/metadc504009/"><img alt="A Technique for Increasing the Optical Strength of Single-Crystal NaCl and KCl Through Temperature Cycling" title="A Technique for Increasing the Optical Strength of Single-Crystal NaCl and KCl Through Temperature Cycling" src="https://digital.library.unt.edu/ark:/67531/metadc504009/small/"/></a></p><p>This thesis relates a technique for increasing the optical strength of NaCl and KCl single-crystal samples. The 1.06-μm pulsed laser damage thresholds were increased by factors as large as 4.6 for a bulk NaCl single-crystal sample. The bulk laser damage breakdown threshold (LDBT) of the crystal was measured prior to and after heat treatment at 800*C using a Nd:YAG laser operating at 1.06 μm. Bulk and surface LDBTs were also studied on samples annealed at 400° C. These samples showed differences in damage morphology on both cleaved and polished surfaces, and the cleaved surfaces had improved damage thresholds. However, neither the polished surfaces nor the bulk showed improved threshold at the lower annealing temperature.</p>Automatic Frequency Control of Microwave Radiation Sources2015-05-10T06:16:59-05:00https://digital.library.unt.edu/ark:/67531/metadc504304/<p><a href="https://digital.library.unt.edu/ark:/67531/metadc504304/"><img alt="Automatic Frequency Control of Microwave Radiation Sources" title="Automatic Frequency Control of Microwave Radiation Sources" src="https://digital.library.unt.edu/ark:/67531/metadc504304/small/"/></a></p><p>Resonant cavity controlled klystron frequency stabilization circuits and quartz-crystal oscillator frequency stabilization circuits were investigated for reflex klystrons operating at frequencies in the X-band 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.</p>The Classical Limit of Quantum Mechanics2015-05-10T06:16:59-05:00https://digital.library.unt.edu/ark:/67531/metadc504591/<p><a href="https://digital.library.unt.edu/ark:/67531/metadc504591/"><img alt="The Classical Limit of Quantum Mechanics" title="The Classical Limit of Quantum Mechanics" src="https://digital.library.unt.edu/ark:/67531/metadc504591/small/"/></a></p><p>The Feynman path integral formulation of quantum mechanics is a path integral representation for a propagator or probability amplitude in going between two points in space-time. The wave function is expressed in terms of an integral equation from which the Schrodinger equation can be derived. On taking the limit h — 0, the method of stationary phase can be applied and Newton's second law of motion is obtained. Also, the condition the phase vanishes leads to the Hamilton - Jacobi equation. The secondary objective of this paper is to study ways of relating quantum mechanics and classical mechanics. The Ehrenfest theorem is applied to a particle in an electromagnetic field. Expressions are found which are the hermitian Lorentz force operator, the hermitian torque operator, and the hermitian power operator.</p>A Calculation of the Excitation Spectrum of Superfluid Helium-42015-05-10T06:16:59-05:00https://digital.library.unt.edu/ark:/67531/metadc504576/<p><a href="https://digital.library.unt.edu/ark:/67531/metadc504576/"><img alt="A Calculation of the Excitation Spectrum of Superfluid Helium-4" title="A Calculation of the Excitation Spectrum of Superfluid Helium-4" src="https://digital.library.unt.edu/ark:/67531/metadc504576/small/"/></a></p><p>The Hartree-Fock-Bogoliubov theory of homogeneous boson systems at finite temperatures is rederived using, a free energy variational principle. It is shown that a t-matrix naturally emerges in the theory. Phenomenological modifications are made (1) to remove the energy gap at zero momentum, and (2) to eliminate the Hartree-Fock-like terms, which dress the kinetic energy of the particle. A numerical calculation of the energy spectrum is made over a temperature range of 0.00 to 3.14 K using the Morse dipole-dipole-2 potential and the Frost-Musulin potential. The energy spectrum of the elementary excitations is calculated self-consistently. It has a phonon behavior at low momentum and a roton behavior at higher momentum, so it is in qualitative agreement with the observed energy spectrum of liquid He II. However, the temperature dependence of the spectrum is incorrectly given. At the observed density of 0.0219 atoms A-3, the depletion of the zero-momentum state at zero temperature is 40.5% for the Morse dipole-dipole-2potential, and 43.2% for the Frost- Musulin potential. The depletion increases gradually until at 3.14 K the zero momentum density becomes zero discontinuously, which indicates a transition to the ideal Bose gas.</p>Microwave Properties of Liquids and Solids, Using a Resonant Microwave Cavity as a Probe2015-05-10T06:16:59-05:00https://digital.library.unt.edu/ark:/67531/metadc504294/<p><a href="https://digital.library.unt.edu/ark:/67531/metadc504294/"><img alt="Microwave Properties of Liquids and Solids, Using a Resonant Microwave Cavity as a Probe" title="Microwave Properties of Liquids and Solids, Using a Resonant Microwave Cavity as a Probe" src="https://digital.library.unt.edu/ark:/67531/metadc504294/small/"/></a></p><p>The frequency shifts and Q changes of a resonant microwave cavity were utilized as a basis for determining microwave properties of solids and liquids. The method employed consisted of varying the depth of penetration of a cylindrical sample of the material into a cavity operating in the TM0 1 0 Mode. The liquid samples were contained in a thin-walled quartz tube. The perturbation of the cavity was achieved by advancing the sample into the cavity along the symmetry axis by employing a micrometer drive appropriately calibrated for depth of penetration of the sample. A differentiation method was used to obtain the half-power points of the cavity resonance profile at each depth of penetration. The perturbation techniques for resonant cavities were used to reduce the experimental data obtained to physical parameters for the samples. The probing frequency employed was near 9 gHz.</p>K-Shell Ionization Cross Sections of Selected Elements from Ag to La for Proton Bombardment from 0.6 to 2.0 MeV2015-05-10T06:16:59-05:00https://digital.library.unt.edu/ark:/67531/metadc504034/<p><a href="https://digital.library.unt.edu/ark:/67531/metadc504034/"><img alt="K-Shell Ionization Cross Sections of Selected Elements from Ag to La for Proton Bombardment from 0.6 to 2.0 MeV" title="K-Shell Ionization Cross Sections of Selected Elements from Ag to La for Proton Bombardment from 0.6 to 2.0 MeV" src="https://digital.library.unt.edu/ark:/67531/metadc504034/small/"/></a></p><p>The K-shell x-ray and ionization cross sections are measured for protons on Ag, Cd, Sn, Sb, Te, Ba, and La over the ion energy range of 0.6 to 2.0 MeV. The data are compared to the predictions of the PWBA, the PWBA with corrections for binding energy and/or Coulomb deflection, the BEA, and the constrained BEA predictions. In general, the non-relativistic PWBA with binding energy correction gives the best overall agreement with the measurements of proton-induced x-ray processes for the K-shell of the elements studied in this work. The data further suggest the need for relativistic PWBA treatment of the interactions in the K-shell for the range of binding energies represented by the elements investigated in this work.</p>