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The analysis and minimization of oxygen contamination in the powder processing of molybdenum disilicide

Description: Problems with MoSi{sub 2} include low-temperature fracture toughness, high-temperature creep resistance, and ``pest`` phenomena. Oxygen introduced by powder processing may be the cause of some of these problems. This study led to the following conclusions: Supplied powders have significant oxygen present prior to processing (up to 2.5 %), in the form of silica on the surface. This oxygen contamination did not increase by exposure to air at room temperature. An improved powder processing method … more
Date: April 24, 1994
Creator: Shannon, K.
Partner: UNT Libraries Government Documents Department
open access

Characterization of Functionalized Self-Assembled Monolayers and Surface-Attached Interlocking Molecules Using Near-Edge X-ray Absorption Fine Structure Spectroscopy

Description: Quantitative knowledge of the fundamental structure and substrate binding, as well as the direct measurement of conformational changes, are essential to the development of self-assembled monolayers (SAMs) and surface-attached interlocking molecules, catenanes and rotaxanes. These monolayers are vital to development of nano-mechanical, molecular electronic, and biological/chemical sensor applications. This dissertation investigates properties of functionalized SAMs in sulfur-gold based adsorbed … more
Date: March 24, 2004
Creator: Willey, T & Willey, T
Partner: UNT Libraries Government Documents Department
open access

Compton Scattering on Nucleons

Description: From introduction: "The present paper deals with a classical calculation in which some of the meson effects can be included to all orders in the meson-nucleon coupling coupling constant, in particular those having to do with the gyration of the nucleon spin and isotopic spin. Such a treatment leads to results qualitatively different from the weak coupling calculations."
Date: May 24, 1954
Creator: Huddlestone, Richard Harold
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

Diffusion of Slow Electrons in Gases

Description: The properties of electrons in a gas and an external electric field, e.g., agitation velocity, free path, energy lost per collision, and collision cross sections, were determined for electrons of energy less than 2 ev in a large number of gases. The computations were made from previously measured values for Townsend's energy factor or the ratio of electron agitation energy to molecule thermal energy. Results are presented for hydrogen, nitrogen, carbon dioxide, methane, ethylene, cyclopropane, … more
Date: October 24, 1961
Creator: Forester, D. W. & Cochran, L. W.
Partner: UNT Libraries Government Documents Department
open access

Experimental Cross Sections for Reactions of Heavy Ions and 208Pb, 209Bi, 238U, and 248Cm Targets

Description: The study of the reactions between heavy ions and {sup 208}Pb, {sup 209}Bi, {sup 238}U, and {sup 248} Cm targets was performed to look at the differences between the cross sections of hot and cold fusion reactions. Experimental cross sections were compared with predictions from statistical computer codes to evaluate the effectiveness of the computer code in predicting production cross sections. Hot fusion reactions were studied with the MG system, catcher foil techniques and the Berkeley Gas-fi… more
Date: May 24, 2002
Creator: Patin, Joshua B.
Partner: UNT Libraries Government Documents Department
open access

Femtosecond nonlinear spectroscopy at surfaces: Second-harmonic probing of hole burning at the Si(111)7x7 surface and fourier-transform sum-frequency vibrational spectroscopy

Description: The high temporal resolution and broad bandwidth of a femtosecond laser system are exploited in a pair of nonlinear optical studies of surfaces. The dephasing dynamics of resonances associated with the adatom dangling bonds of the Si(111)7 x 7 surface are explored by transient second-harmonic hole burning, a process that can be described as a fourth-order nonlinear optical process. Spectral holes produced by a 100 fs pump pulse at about 800 nm are probed by the second harmonic signal of a 100 f… more
Date: November 24, 2004
Creator: McGuire, John Andrew
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

GAiN: Distributed Array Computation with Python

Description: Scientific computing makes use of very large, multidimensional numerical arrays - typically, gigabytes to terabytes in size - much larger than can fit on even the largest single compute node. Such arrays must be distributed across a "cluster" of nodes. Global Arrays is a cluster-based software system from Battelle Pacific Northwest National Laboratory that enables an efficient, portable, and parallel shared-memory programming interface to manipulate these arrays. Written in and for the C and FO… more
Date: April 24, 2009
Creator: Daily, Jeffrey A.
Partner: UNT Libraries Government Documents Department
open access

Investigations of the ground-state hyperfine atomic structure and beta decay measurement prospects of {sup 21}Na with improved laser trapping techniques

Description: This thesis describes an experiment in which a neutral atom laser trap loaded with radioactive {sup 21}Na was improved and then used for measurements. The sodium isotope (half-life=22 sec) is produced on line at the 88in cyclotron at Lawrence Berkeley National Laboratory. The author developed an effective magnesium oxide target system which is crucial to deliver a substantive beam of {sup 21}Na to the experiment. Efficient manipulation of the {sup 21}Na beam with lasers allowed 30,000 atoms to … more
Date: May 24, 1999
Creator: Rowe, Mary A.
Partner: UNT Libraries Government Documents Department
open access

Ion Acceleration from the Interaction of Ultra-Intense Lasers with Solid Foils

Description: The discovery that ultra-intense laser pulses (I > 10{sup 18} W/cm{sup 2}) can produce short pulse, high energy proton beams has renewed interest in the fundamental mechanisms that govern particle acceleration from laser-solid interactions. Experiments have shown that protons present as hydrocarbon contaminants on laser targets can be accelerated up to energies > 50 MeV. Different theoretical models that explain the observed results have been proposed. One model describes a front-surface … more
Date: November 24, 2004
Creator: Allen, M
Partner: UNT Libraries Government Documents Department
open access

Measurement of Spectral Distribution of Positron Flux in an Infinite Copper Medium Containing Cu$sup 64$

Description: The spectral distribution of the flux of positrons inside a beta radioactive medium was experimentally determined using an anthracene coincidence scintillation spectrometer. Positrons leaving a copper cavity source containing Cu/sup 64/ were absorbed in a thin anthracene crystal. The light pulse from the anthracene was recorded in a 256 channel analyzer if a NaI scintillation spectrometer nearby recorded simultaneously a count under the total absorption peak for annihilation radiation. Thus, di… more
Date: December 24, 1963
Creator: Wilkie, W. H. & Birkhoff, R. D.
Partner: UNT Libraries Government Documents Department
open access

The mechanism of the oligomerization of thiophene-based para-quinodimethanes

Description: For the last decade, the Trahanovsky research group has focused on the study of various reactive molecules such as o-quinodimethanes (o-QDM`s) and p-quinodimethanes (p-QDM`s) derived from benzene, furan, and thiophene. These types of molecules are reactive and dimerize or polymerize at room temperature. One of the group`s interests is to understand the dimerization mechanism of these molecules. Paper 1 describes the preparation and dimerization product analyses of 2-ethylidene-5-methylene-2,5-d… more
Date: April 24, 1994
Creator: Wang, Yili
Partner: UNT Libraries Government Documents Department
open access

Novel materials and methods for solid-phase extraction and liquid chromatography

Description: This report contains a general introduction which discusses solid-phase extraction and solid-phase micro-extraction as sample preparation techniques for high-performance liquid chromatography, which is also evaluated in the study. This report also contains the Conclusions section. Four sections have been removed and processed separately: silicalite as a sorbent for solid-phase extraction; a new, high-capacity carboxylic acid functionalized resin for solid-phase extraction; semi-micro solid-phas… more
Date: June 24, 1997
Creator: Ambrose, D.
Partner: UNT Libraries Government Documents Department
open access

Photoisomerization and photodissociation dynamics of reactive free radicals

Description: The photofragmentation pathways of chemically reactive free radicals have been examined using the technique of fast beam photofragment translational spectroscopy. Measurements of the photodissociation cross-sections, product branching ratios, product state energy distributions, and angular distributions provide insight into the excited state potential energy surfaces and nonadiabatic processes involved in the dissociation mechanisms. Photodissociation spectroscopy and dynamics of the predissoci… more
Date: August 24, 2000
Creator: Bise, Ryan T.
Partner: UNT Libraries Government Documents Department
open access

A Search for Neutrinoless Tau Decays to Three Leptons

Description: Using approximately 350 million {tau}{sup +}{tau}{sup -} pair events recorded with the BaBar detector at the Stanford Linear Accelerator Center between 1999 and 2006, a search has been made for neutrinoless, lepton-flavor violating tau decays to three lighter leptons. All six decay modes consistent with conservation of electric charge and energy have been considered. With signal selection efficiencies of 5-12%, we obtain 90% confidence level upper limits on the branching fraction {Beta}({tau} {… more
Date: September 24, 2008
Creator: Kolb, Jeffrey A. & /SLAC, /Oregon U.
Partner: UNT Libraries Government Documents Department
open access

Selective spectroscopic methods for water analysis

Description: This dissertation explores in large part the development of a few types of spectroscopic methods in the analysis of water. Methods for the determination of some of the most important properties of water like pH, metal ion content, and chemical oxygen demand are investigated in detail. This report contains a general introduction to the subject and the conclusions. Four chapters and an appendix have been processed separately. They are: chromogenic and fluorogenic crown ether compounds for the sel… more
Date: June 24, 1997
Creator: Vaidya, B.
Partner: UNT Libraries Government Documents Department
open access

Support minimized inversion of acoustic and elastic wave scattering

Description: This report discusses the following topics on support minimized inversion of acoustic and elastic wave scattering: Minimum support inversion; forward modelling of elastodynamic wave scattering; minimum support linearized acoustic inversion; support minimized nonlinear acoustic inversion without absolute phase; and support minimized nonlinear elastic inversion.
Date: April 24, 1994
Creator: Safaeinili, A.
Partner: UNT Libraries Government Documents Department
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