69 Matching Results

Search Results

Results: 1 - 24 next
open access

10 microsecond time resolution studies of Cygnus X-1

Description: Time variability analyses have been applied to data composed of event times of X-rays emitted from the binary system Cygnus X-1 to search for unique black hole signatures. The X-ray data analyzed was collected at ten microsecond time resolution or better from two instruments, the High Energy Astrophysical Observatory (HEAO) A-1 detector and the Rossi X-ray Timing Explorer (XTE) Proportional Counter Array (PCA). HEAO A-1 and RXTE/PCA collected data from 1977--79 and from 1996 on with energy sens… more
Date: June 1, 1997
Creator: Wen, H.C.
Partner: UNT Libraries Government Documents Department
open access

Advances and applications of dynamic-angle spinning nuclear magnetic resonance

Description: This dissertation describes nuclear magnetic resonance experiments and theory which have been developed to study quadrupolar nuclei (those nuclei with spin greater than one-half) in the solid state. Primarily, the technique of dynamic-angle spinning (DAS) is extensively reviewed and expanded upon in this thesis. Specifically, the improvement in both the resolution (two-dimensional pure-absorptive phase methods and DAS angle choice) and sensitivity (pulse-sequence development), along with effect… more
Date: June 1, 1993
Creator: Baltisberger, J. H.
Partner: UNT Libraries Government Documents Department
open access

Application of a-Si:H radiation detectors in medical imaging

Description: Monte Carlo simulations of a proposed a-Si:H-based current-integrating gamma camera were performed. The analysis showed that the intrinsic resolution of such a camera was 1 {approximately} 2.5 mm, which is somewhat better than that of a conventional gamma camera, and that the greater blurring, due to the detection of scattered {gamma}-rays, could be reduced considerably by image restoration techniques. This proposed gamma camera would be useful for imaging shallow organs such as the thyroid. Pr… more
Date: June 1, 1995
Creator: Lee, Hyoung-Koo
Partner: UNT Libraries Government Documents Department
open access

Atomic holography with electrons and x-rays: Theoretical and experimental studies

Description: Gabor first proposed holography in 1948 as a means to experimentally record the amplitude and phase of scattered wavefronts, relative to a direct unscattered wave, and to use such a {open_quotes}hologram{close_quotes} to directly image atomic structure. But imaging at atomic resolution has not yet been possible in the way he proposed. Much more recently, Szoeke in 1986 noted that photoexcited atoms can emit photoelectron of fluorescent x-ray wavefronts that are scattered by neighboring atoms, t… more
Date: June 1, 1997
Creator: Len, P. M.
Partner: UNT Libraries Government Documents Department
open access

Calculations of Bottom Quark Production at Hadron Colliders

Description: This thesis studies Monte Carlo simulations of QCD heavy flavor production processes (p{bar p} {yields} Q({anti Q})X) at hadron colliders. ISAJET bottom quark cross-sections are compared to the O({alpha} {sub s}{sup 3}) perturbative calculation of Nason, Dawson, and Ellis. These Monte Carlo cross-sections are computed from data samples which use different parton distribution functions and physics parameters. Distributions are presented in the heavy quark`s transverse momentum and rapidity. Corr… more
Date: June 29, 1991
Creator: Kuebel, D.
Partner: UNT Libraries Government Documents Department
open access

Computed tomography and optical remote sensing: Development for the study of indoor air pollutant transport and dispersion

Description: This thesis investigates the mixing and dispersion of indoor air pollutants under a variety of conditions using standard experimental methods. It also extensively tests and improves a novel technique for measuring contaminant concentrations that has the potential for more rapid, non-intrusive measurements with higher spatial resolution than previously possible. Experiments conducted in a sealed room support the hypothesis that the mixing time of an instantaneously released tracer gas is inverse… more
Date: June 1, 1995
Creator: Drescher, A.C.
Partner: UNT Libraries Government Documents Department
open access

Control of nonlinear systems using periodic parametric perturbations with application to a reversed field pinch

Description: In this thesis, the possibility of controlling low- and high-dimensional chaotic systems by periodically driving an accessible system parameter is examined. This method has been carried out on several numerical systems and the MST Reversed Field Pinch. The numerical systems investigated include the logistic equation, the Lorenz equations, the Roessler equations, a coupled lattice of logistic equations, a coupled lattice of Lorenz equations, the Yoshida equations, which model tearing mode fluctu… more
Date: June 1, 1998
Creator: Mirus, Kevin A.
Partner: UNT Libraries Government Documents Department
open access

The dE/dx capabilities of the D0 tracking system

Description: The D0 forward tracking system has been extensively calibrated using electron and pion beams in the energy range from 10 GeV to 150 GeV in the neutrino area fixed target beam line at Fermilab. The forward tracking system provides a spatial resolution of 200 {mu}m and a two hit separation of 2.5 mm at 90% efficiency. The chamber provides 32 samples of pulse height information for a given track equivalent to a dE/dx resolution of 12.7%. The energy loss response of the chamber to low energy-beam h… more
Date: June 1, 1992
Creator: Rajagopalan, S.
Partner: UNT Libraries Government Documents Department
open access

Decision making in a non-profit engineering environment

Description: A conceptual management framework is developed and applied in a science and engineering organization located within a non-profit, public institution. The goal of this research is to select a set of projects whose combined contributions to the organization`s strategic interests satisfy sponsor desires and can be completed within existing time and resource constraints. The development of the rationale for project selection and implementation within the plutonium facility at Los Alamos National La… more
Date: June 1, 1997
Creator: Christensen, D.C.
Partner: UNT Libraries Government Documents Department
open access

Design, synthesis, characterization and study of novel conjugated polymers

Description: After introducing the subject of conjugated polymers, the thesis has three sections each containing a literature survey, results and discussion, conclusions, and experimental methods on the following: synthesis, characterization of electroluminescent polymers containing conjugated aryl, olefinic, thiophene and acetylenic units and their studies for use in light-emitting diodes; synthesis, characterization and study of conjugated polymers containing silole unit in the main chain; and synthesis, … more
Date: June 24, 1997
Creator: Chen, W.
Partner: UNT Libraries Government Documents Department
open access

Development and Application of a Mass Spectrometric System to Study Volatile Components of Fluid Inclusions

Description: A quadrupole mass spectrometric system coupled with mechanical decrepitation was constructed and calibrated to study fluid inclusions from an active geothermal system. Fluid inclusions in Salton Sea Scientific Drilling Project well cores and ejects from flow tests were analyzed. Ion currents from selected mass/charge ratio numbers were measured for gases from ruptured inclusions in epidote, calcite, and hematite vein minerals from different depths. Water, carbon dioxide, hydrogen sulfide, sulfu… more
Date: June 1, 1992
Creator: Sloan, R. C., Jr.
Partner: UNT Libraries Government Documents Department
open access

Development of a Database Guide for Institutional Research in a Theological Seminary

Description: This study sought to create a guideline to assist theological seminaries build a longitudinal database for institutional research. The study used the National Center for Higher Education Management (NCHEMS) data element dictionary as the base document for the study.
Date: June 1997
Creator: Bratton, Terry L. (Terry Lee)
Partner: UNT Libraries
open access

Differential utilization of allochthonous and autochthonous carbon by aquatic insects of two shrub-steppe desert spring-streams: A stable carbon isotope analysis and critique of the method

Description: The purpose of this study is to assess whether the carbon supporting stream food webs comes principally from terrestrial sources or is produced within the stream. Lacking data to resolve the allochthonous/autochthonous issue with any finality, stream ecologists have alternately postulated that stream carbon was principally autochthonous or principally allochthonous. Others argued that autochthonous and allochthonous carbon resources cannot be separated and that the allochthonous/autochthonous d… more
Date: June 1, 1993
Creator: Mize, A. L.
Partner: UNT Libraries Government Documents Department
open access

Direct observation of resonance effects in laser cluster interactions

Description: Time resolved dynamics of high intensity laser interactions with atomic clusters have been studied with both theoretical analysis and experiment. A short-pulse Ti:sapphire laser system, which could produce 50 mJ of energy in a 50 fs pulse, was built to perform these experiments. The laser used a novel single grating stretcher and was pumped, in part, by a custom Nd:YLF laser system, including 19 mm Nd:YLF amplifiers. It was found that there is an optimal pulse width to maximize absorption for a… more
Date: June 1, 1999
Creator: Zweiback, J
Partner: UNT Libraries Government Documents Department
open access

Donor spectroscopy at large hydrostatic pressures and transport studies in compound semiconductors

Description: In the first part of this work, the author describes studies of donors in AlSb and in GaAs at large hydrostatic pressures, two materials in which the conduction band minimum is not parabolic, but has a camel`s back shape. These donors were found to display only one or two absorption lines corresponding to ground to bound excited state transitions. It is shown that due to the non-parabolic dispersion, camel`s back donors may have as few as one bound excited state and that higher excited states a… more
Date: June 1, 1997
Creator: Hsu, L.
Partner: UNT Libraries Government Documents Department
open access

The electrical conductivity of sodium polysulfide melts

Description: The sodium polysulfide melt has been described by a macroscopic model. This model considers the melt to be composed of sodium cations, monosulfide anions, and neutral sulfur solvent. The transport equations of concentrated-solution theory are used to derived the governing equations for this binaryelectrolyte melt model. These equations relate measurable transport properties to fundamental transport parameters. The focus of this research is to measure the electrical conductivity of sodium polysu… more
Date: June 1, 1992
Creator: Wang, Meihui
Partner: UNT Libraries Government Documents Department
open access

Field simulation of axisymmetric plasma screw pinches by alternating-direction-implicit methods

Description: An axisymmetric plasma screw pinch is an axisymmetric column of ionized gaseous plasma radially confined by forces from axial and azimuthal currents driven in the plasma and its surroundings. This dissertation is a contribution to detailed, high resolution computer simulation of dynamic plasma screw pinches in 2-d {ital rz}-coordinates. The simulation algorithm combines electron fluid and particle-in-cell (PIC) ion models to represent the plasma in a hybrid fashion. The plasma is assumed to be … more
Date: June 1, 1996
Creator: Lambert, M.A.
Partner: UNT Libraries Government Documents Department
open access

Fundamental studies of hydrogen chemisorption on supported monometallic and bimetallic catalysts using microcalorimetry

Description: Highly dispersed transition metal catalysts are used in numerous commercial processes such as hydrocarbon conversions. For example, the use of Pt supported on acidic alumina or silica-alumina for reforming of naphtha in the production of gasoline is well known. Another use of supported catalysts is in automobile emission control where supported Pt-Rh bimetallic catalysts are used. Supported Ru can be used in Fischer-Tropsch synthesis for the production of higher hydrocarbons from synthesis gas.… more
Date: June 24, 1997
Creator: Narayan, R.L.
Partner: UNT Libraries Government Documents Department
open access

Generation and characterization of superradiant undulator radiation

Description: High-power, pulsed, coherent, far-infrared (FIR) radiation has many scientific applications, such as pump-probe studies of surfaces, liquids, and solids, studies of high-T{sub c} superconductors, biophysics, plasma diagnostics, and excitation of Rydberg atoms. Few sources of such FIR radiation currently exist. Superradiant undulator radiation produced at the SUNSHINE (Stanford UNiversity SHort INtense Electron-source) is such a FIR source. First proposed in the mm-wave spectral range by Motz, s… more
Date: June 1, 1997
Creator: Bocek, D.
Partner: UNT Libraries Government Documents Department
open access

Genetic algorithms applied to nonlinear and complex domains

Description: The dissertation, titled ''Genetic Algorithms Applied to Nonlinear and Complex Domains'', describes and then applies a new class of powerful search algorithms (GAS) to certain domains. GAS are capable of solving complex and nonlinear problems where many parameters interact to produce a ''final'' result such as the optimization of the laser pulse in the interaction of an atom with an intense laser field. GAS can very efficiently locate the global maximum by searching parameter space in problems … more
Date: June 1, 1999
Creator: Barash, D & Woodin, A E
Partner: UNT Libraries Government Documents Department
open access

Genetic algorithms applied to nonlinear and complex domains

Description: The dissertation, titled ''Genetic Algorithms Applied to Nonlinear and Complex Domains'', describes and then applies a new class of powerful search algorithms (GAS) to certain domains. GAS are capable of solving complex and nonlinear problems where many parameters interact to produce a final result such as the optimization of the laser pulse in the interaction of an atom with an intense laser field. GAS can very efficiently locate the global maximum by searching parameter space in problems whic… more
Date: June 1, 1999
Creator: Barash, D & Woodin, A E
Partner: UNT Libraries Government Documents Department
open access

The Growth of Thin Epitaxial Copper Films on Ruthenium (0001)and Oxygen-Precovered Ruthenium (0001) as studied by x-rayphotoelectron diffraction. University of California, Davis, Department of Physics, Ph.D. Thesis

Description: In the first part of this dissertation, the variation of mean emitter depths with direction for core photoelectron emission from single crystals, including the effects of both isotropic inelastic scattering and single and multiple elastic scattering was theoretically studied. The mean emitter depth was found to vary by as much as ±30% with direction. In the second part of this dissertation, x-ray photoelectron diffraction (XPD) was used to study the structure and growth mechanisms of Cu … more
Date: June 1, 1997
Creator: Ruebush, Scott Daniel
Partner: UNT Libraries Government Documents Department
open access

Hydrogen local vibrational modes in semiconductors

Description: Following, a review of experimental techniques, theory, and previous work, the results of local vibrational mode (LVM) spectroscopy on hydrogen-related complexes in several different semiconductors are discussed. Hydrogen is introduced either by annealing in a hydrogen ambient. exposure to a hydrogen plasma, or during growth. The hydrogen passivates donors and acceptors in semiconductors, forming neutral complexes. When deuterium is substituted for hydrogen. the frequency of the LVM decreases b… more
Date: June 1, 1997
Creator: McCluskey, M. D.
Partner: UNT Libraries Government Documents Department
open access

An implementation of SISAL for distributed-memory architectures

Description: This thesis describes a new implementation of the implicitly parallel functional programming language SISAL, for massively parallel processor supercomputers. The Optimizing SISAL Compiler (OSC), developed at Lawrence Livermore National Laboratory, was originally designed for shared-memory multiprocessor machines and has been adapted to distributed-memory architectures. OSC has been relatively portable between shared-memory architectures, because they are architecturally similar, and OSC generat… more
Date: June 1, 1995
Creator: Beard, P. C.
Partner: UNT Libraries Government Documents Department
Back to Top of Screen