UNT Libraries - 8 Matching Results

Search Results

Results: 1 - 8
open access

A Calculation of the Excitation Spectrum of Superfluid Helium-4

Description: 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 M… more
Date: May 1974
Creator: Goble, Gerald W.
Item Type: Refine your search to only Thesis or Dissertation
open access

Density Profile of a Quantized Vortex Line in Superfluid Helium-4

Description: The density amplitude of an isolated quantum vortex line in superfluid 4He is calculated using a generalized Gross-Pitaevskii (G-P) equation. The generalized G-P equation for the order parameter extends the usual mean-field approach by replacing the interatomic potential in the ordinary G-P equation by a local, static T matrix, which takes correlations between the particles into account. The T matrix is a sum of ladder diagrams appearing in a diagrammatic expansion of the mean field term in an … more
Date: May 1975
Creator: Harper, John Howard
Item Type: Refine your search to only Thesis or Dissertation
open access

K-Shell Ionization Cross Sections of Selected Elements from Ag to La for Proton Bombardment from 0.6 to 2.0 MeV

Description: 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 o… more
Date: May 1974
Creator: Khelil, Najat Arafat
Item Type: Refine your search to only Thesis or Dissertation
open access

Measurement of the Rate Coefficients for the Bimolecular and Termolecular Charge Transfer Reactions of He₂⁺ with Ne, Ar, N₂, CO, CO₂, and CH₄

Description: The problem with which this investigation is concerned is that of measuring the rate coefficients for termolecular charge transfer reactions of He2+ in atmospheric pressure afterglows with the minority reacting species. Of particular interest was the discovery that the presence of a third body can change an improbable charge transfer reaction involving He+2 into a very probable one, as in the case of the reaction with argon. For example, in Tables II and II it was shown that less than a 300 tor… more
Date: May 1977
Creator: Lee, Francis Wha-Pyo
Item Type: Refine your search to only Thesis or Dissertation
open access

The Role of Defects in the Quantum Size Effect

Description: This investigation is a theoretical study of the influence of defects of finite volume on the electrical conductivity in the quantum size effect regime. Correction terms to existing equations are derived, and a physical explanation of the results is given. Many macroscopic properties of films exhibit an oscillatory dependence on thickness when the thickness is comparable to the de Broglie wavelength of an electron at the Fermi surface. This behavior is called the quantum size effect. In very th… more
Date: December 1974
Creator: Malone, Farris D.
Item Type: Refine your search to only Thesis or Dissertation
open access

Room Temperature Gold-Vacuum-Gold Tunneling Experiments

Description: An experiment has been completed which demonstrated quantum mechanical tunneling of electrons between two gold electrodes separated in vacuum. The tunneling current between the gold electrodes has been measured, for fixed voltages of 0.1 and 0.01 volts, as the electrode spacing was varied from a distance of approximately 2.0 nm down to a point where the electrodes touched. Current-voltage characteristics for fixed electrode spacing in the direct tunneling region have also been measured. Numeric… more
Date: August 1978
Creator: Teague, E. C. (Edgar Clayton), 1941-
Item Type: Refine your search to only Thesis or Dissertation
open access

A Theoretical Investigation of Bound Roton Pairs in Superfluid Helium-4

Description: The Bogoliubov theory of excitations in superfluid helium is used to study collective modes at zero temperature. A repulsive delta function shell potential is used in the quasiparticle excitation energy spectrum to fit the observed elementary excitation spectrum, except in the plateau region. The linearized equation of motion method is used to obtain the secular equation for a collective mode consisting of a linear combination of one and two free quasiparticles of zero total momentum. It is sho… more
Date: August 1974
Creator: Cheng, Shih-ta
Item Type: Refine your search to only Thesis or Dissertation
Back to Top of Screen