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open access

Design and construction of a imaging instrument for studying ion emission from pure ion emitters

Description: The development of new ion sources is important in the area of surface analysis to make it easier to perform more sensitive and accurate analyses. In surface analysis a primary ion beam composed of a single species can help when predicting and interpreting the results. Therefore, much interest and effort has been focused on producing pure ion emitters. An instrument has been designed and constructed to view the current densities of the ions being emitted from pure ion emitters. The instrument e… more
Date: September 1, 1993
Creator: Olson, J. E.
Partner: UNT Libraries Government Documents Department
open access

On the hypothesis that quantum mechanism manifests classical mechanics: Numerical approach to the correspondence in search of quantum chaos

Description: Quantum manifestation of classical chaos has been one of the extensively studied subjects for more than a decade. Yet clear understanding of its nature still remains to be an open question partly due to the lack of a canonical definition of quantum chaos. The classical definition seems to be unsuitable in quantum mechanics partly because of the Heisenberg quantum uncertainty. In this regard, quantum chaos is somewhat misleading and needs to be clarified at the very fundamental level of physics.… more
Date: September 1, 1993
Creator: Lee, Sang-Bong
Partner: UNT Libraries Government Documents Department
open access

Enhanced algorithms for stochastic programming

Description: In this dissertation, we present some of the recent advances made in solving two-stage stochastic linear programming problems of large size and complexity. Decomposition and sampling are two fundamental components of techniques to solve stochastic optimization problems. We describe improvements to the current techniques in both these areas. We studied different ways of using importance sampling techniques in the context of Stochastic programming, by varying the choice of approximation functions… more
Date: September 1, 1993
Creator: Krishna, A. S.
Partner: UNT Libraries Government Documents Department
open access

Fatigue crack growth in lithium hydride

Description: Subcritical fatigue crack growth, from cyclic tensile loading, was demonstrated in warm pressed Polycrystalline lithium hydride. Experiments were performed with cyclic tension-tension crack opening (mode I) loads applied to a pre-cracked compact type specimen in an argon environment at a temperature of 21C (70F). The fatigue crack growth was found to occur between 7.56 {times} 10{sup {minus}ll} M/cycle (2.98 {times} l0{sup {minus}9} in/cycle) and 2.35 {times} l0{sup {minus}8} m/cycle (9.24{time… more
Date: September 1, 1993
Creator: Healy, Thomas E.
Partner: UNT Libraries Government Documents Department
open access

Circular magnetic x-ray dichroism in rare earth compounds

Description: This report discusses the following topics: Circular magnetic x-ray dichroism at the ER L{sub 3} Edge; angular dependence of circular magnetic x-ray dichroism in rare earth compounds: and circular magnetic x-ray dichroism in crystalline and amorphous GDFE{sub 2}.
Date: September 30, 1993
Creator: Jonathan, L.
Partner: UNT Libraries Government Documents Department
open access

Applications of highly spin-polarized xenon in NMR

Description: The main goal of the work presented in this thesis is produce highly spin-polarized xenon to create much greater signal intensities (up to 54,000 times greater) so as to allow studies to be made on systems with low surface area and long spin-lattice relaxation times. The spin-exchange optical pumping technique used to create high nuclear spin polarization is described in detail in chapter two. This technique is initially applied to some multiple-pulse optically detected NMR experiments in low m… more
Date: September 1, 1993
Creator: Long, H. W.
Partner: UNT Libraries Government Documents Department
open access

The dynamics of interacting nonlinearities governing long wavelength driftwave turbulence

Description: Because of the ubiquitous nature of turbulence and the vast array of different systems which have turbulent solutions, the study of turbulence is an area of active research. Much present day understanding of turbulence is rooted in the well established properties of homogeneous Navier-Stokes turbulence, which, due to its relative simplicity, allows for approximate analytic solutions. This work examines a group of turbulent systems with marked differences from Navier-Stokes turbulence, and attem… more
Date: September 1, 1993
Creator: Newman, D. E.
Partner: UNT Libraries Government Documents Department
open access

Nuclear magnetic relaxation studies of semiconductor nanocrystals and solids

Description: Semiconductor nanocrystals, small biomolecules, and {sup 13}C enriched solids were studied through the relaxation in NMR spectra. Surface structure of semiconductor nanocrystals (CdS) was deduced from high resolution {sup 1}H and {sup 13}C liquid state spectra of thiophenol ligands on the nanocrystal surfaces. The surface coverage by thiophenol was found to be low, being 5.6 and 26% for nanocrystal radii of 11.8 and 19.2 {angstrom}. Internal motion is estimated to be slow with a correlation tim… more
Date: September 1, 1993
Creator: Sachleben, J. R.
Partner: UNT Libraries Government Documents Department
open access

Submillimeter residual losses in high-{Tc} superconductors

Description: Bolometry was used obtain accurate submillimeter residual loss data for epitaxial films of YBa{sub 2}Cu{sub 3}O{sub 7} (YBCO), Tl{sub 2}Ca{sub 2}Ba{sub 2}Cu{sub 3}O{sub 10}, Tl{sub 2}CaBa{sub 2}Cu{sub 2}O{sub 8} (TCBCO), and Ba{sub 0.6}K{sub 0.4}BiO{sub 3} (BKBO). We were able to fit the absorptivity measured for Nb films to an Eliashberg strong coupling calculation; excellent agreement resulted between parameters from best fits and measured Residual Resistivity Ratio. Microwave surface resista… more
Date: September 1, 1993
Creator: Miller, D.
Partner: UNT Libraries Government Documents Department
open access

Disassembly of hot nuclear matter formed in Au-induced reactions near the Fermi energy

Description: Complex fragment emission has been studied in the 60 MeV/A {sup 197}Au + {sup 12}C, {sup 27}Al, {sup 51}V, {sup nat}Cu, and {sup 197}Au reactions. Velocity spectra, angular distributions and cross sections have been constructed for each target from the inclusive data. Coincidence data including 2-, 3-, 4-, and 5-fold events have also been examined. Furthermore neutron multiplicity distributions have been obtained for the above reactions by utilizing a novel neutron calorimetric approach.
Date: September 1, 1993
Creator: Delis, D. N.
Partner: UNT Libraries Government Documents Department
open access

Measurement of tau lepton branching fractions

Description: We present {tau}{sup {minus}} lepton branching fraction measurements based on data from the TPC/Two-Gamma detector at PEP. Using a sample of{tau}{sup {minus}} {yields} {nu}{sub {tau}}K{sup {minus}}{pi}{sup +}{pi}{sup {minus}} events, we examine the resonance structure of the K{sup {minus}}{pi}{sup +}{pi}{sup {minus}} system and obtain the first measurements of branching fractions for {tau}{sup {minus}} {yields} {nu}{sub {tau}}K{sub 1}{sup {minus}}(1270) and {tau}{sup {minus}} {yields} {nu}{sub … more
Date: September 30, 1993
Creator: Nicol, N. A.
Partner: UNT Libraries Government Documents Department
open access

The Mirrortron experiment: A proof of principle test for a method of generating high transient potentials

Description: The Mirrortron is a concept in which heavy ions are accelerated by a large local transient space potential that is produced in a hot electron plasma. The purpose of this experiment is to begin a proof of principle experiment to investigate the feasibility of producing this space potential and its associated electric field. If a large magnetic field is suddenly generated in a hot electron plasma with a loss-cone distribution, then potentials on the order of the electron temperature are expected.… more
Date: September 1, 1993
Creator: Douglass, S. R.
Partner: UNT Libraries Government Documents Department
open access

Application of an Electrochemical Quartz Crystal Microbalance to the study of electrocatalytic films

Description: The EQCM was used to study the deposition and composition of electrodeposited pure PbO{sub 2} and Bi-doped PbO{sub 2} active toward anodic oxygen-transfer reactions. Within the doped films, Bi is incorporated as Bi{sup +5} in the form of BiO{sub 2}A, where A is ClO{sub 4}{sup {minus}} or NO{sub 3}{sup {minus}}. For deposition of these 2 materials, changes in hydration between the Au oxide and the depositing film resulted in higher mass-to-charge ratios. XRD and XPS were used to study the films;… more
Date: September 1, 1993
Creator: Gordon, J. S., Jr.
Partner: UNT Libraries Government Documents Department
open access

CCM Continuity Constraint Method: A finite-element computational fluid dynamics algorithm for incompressible Navier-Stokes fluid flows

Description: As the field of computational fluid dynamics (CFD) continues to mature, algorithms are required to exploit the most recent advances in approximation theory, numerical mathematics, computing architectures, and hardware. Meeting this requirement is particularly challenging in incompressible fluid mechanics, where primitive-variable CFD formulations that are robust, while also accurate and efficient in three dimensions, remain an elusive goal. This dissertation asserts that one key to accomplishin… more
Date: September 1, 1993
Creator: Williams, P. T.
Partner: UNT Libraries Government Documents Department
open access

Quantitative evaluation of material composition of composites using x-ray energy-dispersive NDE technique

Description: This technique worked well for determining the thickness and densities for composite components having the higher linear attenuation coefficient; it accurately determined thickness of epoxy-resin and Al metal, and the denisty of bone, to {le} 4% in the graphite-epoxy, bone-plexiglas, and Al-Al corrosion composites. Accuracy is dictated by the magnitude and uncertainty of the linear attenuation coefficient. Use of Ge detector and multichannel analyzer are limited by inspection time (1 day for po… more
Date: September 1, 1993
Creator: Ting, J.
Partner: UNT Libraries Government Documents Department
open access

The incongruent melting and melt textured solidification process of Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8}

Description: The melting and solidification was studied using in-situ high temperature XRD from melting point to 900{degree}C in 0.2, 0.1, 0.02 atm O{sub 2} and pure N{sub 2}. The incongruent melting point of Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8} was lowered by decreasing the partial O{sub 2} pressure from 870C (in .2 atm O{sub 2}) to 830C (in pure N{sub 2} atmosphere). As temperature was increased the incongruent melting of Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8} followed a phase sequence in which (Ca, Sr)Cu… more
Date: September 1, 1993
Creator: Polonka, J.
Partner: UNT Libraries Government Documents Department
open access

Reduction of plyatomic ion interferences in indictively coupled plasma mass spectrometry with cryogenic desolvation

Description: A desolvation scheme for introducing aqueous and organic samples into an argon inductively coupled plasma is described; the aerosol generated by nebulizer is heated (+140 C) and cooled ({minus}80 C) repeatedly, and the dried aerosol is then injected into the mass spectrometer. Polyatomic ions are greatly suppressed. This scheme was validated with analysis of seawater and urine reference samples. Finally, the removal of organic solvents by cryogenic desolvation was studied.
Date: September 1, 1993
Creator: Alves, L. C.
Partner: UNT Libraries Government Documents Department
open access

Thermally-generated reactive intermediates: Trapping of the parent ferrocene-based o-quinodimethane and reactions of diradicals generated by hydrogen-atom transfers

Description: Ferrocenocyclobutene is prepared by flash vacuum pyrolysis (FVP) of the N-amino-2-phenylaziridine hydrazone of 2-methylferrocenealdehyde. In the second section of this dissertation, a series of hydrocarbon rearrangements were observed. FVP of o-allyltoluene at 0.1 Torr (700--900 C) gives 2-methylindan and indene, accompanied by o-propenyltoluene. FVP of 2-methyl-2`-vinylbiphenyl gives 9-methyl-9,10-dihydrophenanthrene, which fits the proposed mechanism. However, FVP of 2-(o-methylbenzyl)styrene… more
Date: September 1, 1993
Creator: Ferguson, J. M.
Partner: UNT Libraries Government Documents Department
open access

Chaos and simple determinism in reversed field pinch plasmas: Nonlinear analysis of numerical simulation and experimental data

Description: In this dissertation the possibility that chaos and simple determinism are governing the dynamics of reversed field pinch (RFP) plasmas is investigated. To properly assess this possibility, data from both numerical simulations and experiment are analyzed. A large repertoire of nonlinear analysis techniques is used to identify low dimensional chaos in the data. These tools include phase portraits and Poincare sections, correlation dimension, the spectrum of Lyapunov exponents and short term pred… more
Date: September 1, 1993
Creator: Watts, C. A.
Partner: UNT Libraries Government Documents Department
open access

Mean carrier transport properties and charge collection dynamics of single-crystal, natural type IIa diamonds from ion-induced conductivity measurements

Description: Ion-induced conductivity has been used to investigate the detector characteristics of diamond detectors. Both integrated-charge, and time-resolved current measurements were performed to examine the mean carrier transport properties of diamond and the dynamics of charge collection under highly-localized and high-density excitation conditions. The integrated-charge measurements were conducted with a standard pulse-counting system with {sup 241}Am radioactivity as the excitation source for the det… more
Date: September 1, 1993
Creator: Han, S. S.
Partner: UNT Libraries Government Documents Department
open access

Localization from near-source quasi-static electromagnetic fields

Description: A wide range of research has been published on the problem of estimating the parameters of electromagnetic and acoustical sources from measurements of signals measured at an array of sensors. In the quasi-static electromagnetic cases examined here, the signal variation from a point source is relatively slow with respect to the signal propagation and the spacing of the array of sensors. As such, the location of the point sources can only be determined from the spatial diversity of the received s… more
Date: September 1, 1993
Creator: Mosher, J. C.
Partner: UNT Libraries Government Documents Department
open access

The effect of spacer ribs on Ledinegg type flow instabilities

Description: An experimental program has been completed which evaluated the effect of a flow obstruction in a heated channel on the onset of flow instability (OBI). The test channel was rectangular (80 {times} 3 mm), heated on one surface, and equipped with view ports. Tests were conducted in a flow controlled mode at heat fluxes of 370 kW/M{sup 2}, and 610 kW/m{sup 2}. Direct comparisons were made between the demand curve minimum for the unobstructed channel and a channel equipped with a 2.07 mm wide rib t… more
Date: September 9, 1993
Creator: Coutts, D. A.
Partner: UNT Libraries Government Documents Department
open access

Analysis of the application of decontamination technologies to radioactive metal waste minimization using expert systems

Description: Radioactive metal waste makes up a significant portion of the waste currently being sent for disposal. Recovery of this metal as a valuable resource is possible through the use of decontamination technologies. Through the development and use of expert systems a comparison can be made of laser decontamination, a technology currently under development at Ames Laboratory, with currently available decontamination technologies for applicability to the types of metal waste being generated and the eff… more
Date: September 30, 1993
Creator: Bayrakal, S.
Partner: UNT Libraries Government Documents Department
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