44 Matching Results

Search Results

Results: 1 - 24 next
open access

Processing of Mo-Si-B intermetallics by extrusion and oxidation properties of the extruded Tl-MoSi{sub 2}-MoB System

Description: An extrusion process was developed that is able to consistently produce large quantities of Mo-Si-B rods without the presence of defects. Binder removal from the extruded rods was studied in detail and it was determined that heating rates on the order of 0.02{degree}/minute (1.2{degree}/hour) are necessary to remove the binder without the formation of defects. This low heating rate resulted in debinding times in excess of 70 hours (approximately 3 days). Wicking was investigated as a means to d… more
Date: November 8, 1999
Creator: Summers, Eric
Partner: UNT Libraries Government Documents Department
open access

The use of ultraviolet Thomson scattering as a versatile diagnostic for detailed measurements of a collisional laser produced plasma

Description: Collective Thomson scattering from ion-acoustic waves at 266nm is used to obtain spatially resolved, two-dimensional electron density, sound speed, and radial drift profiles of a collisional laser plasma. An ultraviolet diagnostic wavelength minimizes the complicating effects of inverse bremsstrahlung and refractive turning in the coronal region of interest, where the electron densities approach n{sub c}/10. Laser plasmas of this type are important because they model some of the aspects of the … more
Date: January 8, 1993
Creator: Tracy, M. D.
Partner: UNT Libraries Government Documents Department
open access

Application of spectral hole burning to the study of in vitro cellular systems

Description: Chapter 1 of this thesis describes the various stages of tumor development and a multitude of diagnostic techniques used to detect cancer. Chapter 2 gives an overview of the aspects of hole burning spectroscopy important for its application to the study of cellular systems. Chapter 3 gives general descriptions of cellular organelles, structures, and physical properties that can serve as possible markers for the differentiation of normal and cancerous cells. Also described in Chapter 3 are the p… more
Date: November 8, 1999
Creator: Milanovich, Nebojsa
Partner: UNT Libraries Government Documents Department
open access

Laser Intertial Fusion Energy: Neutronic Design Aspects of a Hybrid Fusion-Fission Nuclear Energy System

Description: This study investigates the neutronics design aspects of a hybrid fusion-fission energy system called the Laser Fusion-Fission Hybrid (LFFH). A LFFH combines current Laser Inertial Confinement fusion technology with that of advanced fission reactor technology to produce a system that eliminates many of the negative aspects of pure fusion or pure fission systems. When examining the LFFH energy mission, a significant portion of the United States and world energy production could be supplied by LF… more
Date: April 8, 2010
Creator: Kramer, K
Partner: UNT Libraries Government Documents Department
open access

Improved resins and novel materials and methods for solid phase extraction and high performance liquid chromatography

Description: Solid-phase extraction (SPE) has grown to be one of the most widely used methods for isolation and preconcentration of a vast range of compounds from aqueous solutions. By modifying polymeric SPE resins with chelating functional groups, the selective uptake of metals was accomplished. The resin, along with adsorbed metals, was vaporized in the ICP and detection of the metals was then possible using either mass or emission spectroscopy. Drug analyses in biological fluids have received heightened… more
Date: October 8, 1997
Creator: Freeze, R.
Partner: UNT Libraries Government Documents Department
open access

Soft x-ray generation in gases with an ultrashort pulse laser

Description: An experimental investigation of soft x-ray production resulting from the interaction of intense near infra-red laser radiation with gases is presented in this thesis. Specifically, soft x-ray generation through high order harmonic generation or exploiting intense inverse bremsstrahlung heating is examined. Most of these studies are conducted with femtosecond, terawatt class Cr:LiSrAlF{sub 6} (LiSAF) laser, though results derived from studies with other laser systems are presented as well. The … more
Date: January 8, 1996
Creator: Ditmire, T.R.
Partner: UNT Libraries Government Documents Department
open access

Rhodium Catalysts in the Oxidation of CO by O<sub>2</sub> and NO: Shape, Composition, and Hot Electron Generation

Description: It is well known that the activity, selectivity, and deactivation behavior of heterogeneous catalysts are strongly affected by a wide variety of parameters, including but not limited to nanoparticle size, shape, composition, support, pretreatment conditions, oxidation state, and electronic state. Enormous effort has been expended in an attempt to understand the role of these factors on catalytic behavior, but much still remains to be discovered. In this work, we have focused on deepening the pr… more
Date: March 8, 2010
Creator: Renzas, James R.
Partner: UNT Libraries Government Documents Department
open access

Synthesis and characterization of nickel hydroxide powders for battery application

Description: The primary objective of this research was to investigate the synthesis and characterization of Ni(OH){sub 2} powders by homogeneous precipitation. Previous research of the same method showed conflicting results and complete characterization of the particle morphology was not carried out. This study has produced precipitates having a composition of 2Ni(OH){sub 2}{center_dot}Ni(HCO{sub 3}){sub 1.85}(NO{sub 3}){sub 0.15}. The XRD patterns showed peaks commonly observed for {alpha}-Ni(OH){sub 2}. … more
Date: October 8, 1997
Creator: Widjaja, A.
Partner: UNT Libraries Government Documents Department
open access

High temperature phase equilibria studies in the Bi-Sr-Ca-Cu-O-Ag system

Description: A variety of experimental techniques were utilized to examine the high temperature phase equilibria in the Bi-Sr-Ca-Cu-O-Ag system. Quenching studies were used to determine the liquid solubility of Ag in the Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8} (Bi2212) melt and the details of the peritectic decomposition pathway of Bi2212 as a function on Ag content and oxygen partial pressure (PO{sub 2}). A liquid immiscibility region between oxide and Ag liquids in the 8--98 at% range was found above 900 C.… more
Date: November 8, 1999
Creator: Margulies, Lawrence
Partner: UNT Libraries Government Documents Department
open access

Kinetics and mechanism of the oxidation of alkenes and silanes by hydrogen peroxide catalyzed by methylrhenium trioxide (MTO) and a novel application of electrospray mass spectrometry to study the hydrolysis of MTO

Description: Conjugated dienes were oxidized by hydrogen peroxide with methylrhenium trioxide (MTO) as catalyst. Methylrhenium bis-peroxide was the major reactive catalyst present. Hydroxyalkenes and trisubstituted silane were also tested. Mechanisms for each of these reactions are presented.
Date: November 8, 1999
Creator: Tan, Haisong
Partner: UNT Libraries Government Documents Department
open access

Kinetics and mechanisms of the reactions of alkyl radicals with oxygen and with complexes of Co(III), Ru(III), and Ni(III)

Description: The kinetics of the reactions of C{sub 2}H{sub 5} radical with Co(NH{sub 3}){sub 5}X{sup 2+}, Ru(NH{sub 3}){sub 5}X{sup 2+}, and Co(dmgH){sub 2} (X) (Y) (X = Br, Cl, N{sub 3}, SCN; Y = H{sub 2}O, CH{sub 3}CN) complexes were studied using laser flash photolysis of ethylcobalt complexes. The kinetics were obtained by the kinetic probe method. Some relative rate constants were also determined by a competition method based on ethyl halide product ratios. The kinetics of colligation reactions of a s… more
Date: October 8, 1990
Creator: Kelley, Douglas
Partner: UNT Libraries Government Documents Department
open access

Nonlinear response of superconductors to alternating fields and currents

Description: This report discusses the following topics on superconductivity: nonlinearities in hard superconductors such as surface impedance of a type II superconductimg half space and harmonic generation and intermodulation due to alternating transport currents; and nonlinearities in superconducting weak links such as harmonic generation by a long Josephson Junction in a superconducting slab.
Date: October 8, 1997
Creator: McDonald, J.
Partner: UNT Libraries Government Documents Department
open access

Application of Ultrasonic Guided Waves to the Characterization of Texture in Metal Sheets of Cubic and Hexagonal Crystallites

Description: Ultrasonic techniques have recently been applied to the texture characterization in polycrystalline aggregates of hexagonal crystals. The basis of this application lies in the relations between the elastic constants {bar C}{sub ij} of the aggregates, which can be inferred from ultrasonic wave velocity measurements, and the orientation distribution coefficients. This communication present such relations for aggregates which possess orthotopic material symmetry and hexagonal crystal symmetry for … more
Date: October 8, 1990
Creator: Li, Yan
Partner: UNT Libraries Government Documents Department
open access

The use of Fourier reverse transforms in crystallographic phase refinement

Description: Often a crystallographer obtains an electron density map which shows only part of the structure. In such cases, the phasing of the trial model is poor enough that the electron density map may show peaks in some of the atomic positions, but other atomic positions are not visible. There may also be extraneous peaks present which are not due to atomic positions. A method for determination of crystal structures that have resisted solution through normal crystallographic methods has been developed. … more
Date: October 8, 1997
Creator: Ringrose, S.
Partner: UNT Libraries Government Documents Department
open access

A Parallel Ocean Model With Adaptive Mesh Refinement Capability For Global Ocean Prediction

Description: An ocean model with adaptive mesh refinement (AMR) capability is presented for simulating ocean circulation on decade time scales. The model closely resembles the LLNL ocean general circulation model with some components incorporated from other well known ocean models when appropriate. Spatial components are discretized using finite differences on a staggered grid where tracer and pressure variables are defined at cell centers and velocities at cell vertices (B-grid). Horizontal motion is model… more
Date: September 8, 2005
Creator: Herrnstein, A
Partner: UNT Libraries Government Documents Department
open access

Microstructure-strength relationships of heavily deformed magnesium-lithium composites containing steel fibers

Description: The successful development of deformation-processed metal-metal composites (DMMC) offers the potential for ductile, high-strength structural materials with high-temperature stability. An infiltration casting process was used to permeate steel wool preforms with molten magnesium-lithium (Mg-Li) alloys. The selected matrix alloys were hexagonal close packed (HCP) Mg-4wt%Li or body centered cubic (BCC) Mg-12wt%Li; the low carbon steel wool fibers were predominantly BCC ferrite. These cast HCP/BCC … more
Date: October 8, 1997
Creator: Jensen, J.
Partner: UNT Libraries Government Documents Department
open access

Ligand Rearrangements of Organometallic Complexes inSolution

Description: Many chemical reactions utilize organometallic complexes as catalysts. These complexes find use in reactions as varied as bond activation, polymerization, and isomerization. This thesis outlines the construction of a new ultrafast laser system with an emphasis on the generation of tunable mid-infrared pulses, data collection, and data analysis.
Date: May 8, 2006
Creator: Shanoski, Jennifer E.
Partner: UNT Libraries Government Documents Department
open access

The addition of disilanes to cumulenes

Description: The syntheses of silicon-containing compounds and the studies of their rearrangements have been active research areas in the Barton research group. Previously, the addition of disilanes to acetylenes was studied in the group and an intramolecular 2S + 2A mechanism has been proposed. In this thesis, the work is focused on the addition of disilanes to cumulenes. The syntheses of the precursors are discussed and the possible mechanisms for their thermal, photochemical and catalytic rearrangements … more
Date: October 8, 1997
Creator: Chen, Y.
Partner: UNT Libraries Government Documents Department
open access

Exploration of deeply virtual Compton scattering on the neutron in the Hall A of Jefferson Laboratory

Description: Generalized Parton Distributions (GPDs) are universal functions which provide a comprehensive description of hadron properties in terms of quarks and gluons. Deeply Virtual Compton Scattering (DVCS) is the simplest hard exclusive process involving GPDs. In particular, the DVCS on the neutron is mostly sensitive to E, the less constrained GPD, wich allows to access to the quark angular momentum. The first dedicated DVCS experiment on the neutron ran in the Hall A of Jefferson Lab in fall 2004. T… more
Date: December 8, 2006
Creator: Mazouz, Malek
Partner: UNT Libraries Government Documents Department
open access

Investigation of the relative abundance of heavy versus light nuclei in primary cosmic rays using underground muon bundles

Description: We study multiple muon events (muon bundles) recorded underground at a depth of 2090 mwe. To penetrate to this depth, the muons must have energies above 0.8 TeV at the Earth`s surface; the primary cosmic ray nuclei which give rise to the observed muon bundles have energies at incidence upon the upper atmosphere of 10 to 10{sup 5}TeV. The events are detected using the Soudan 2 experiment`s fine grained tracking calorimeter which is surrounded by a 14 m {times}10 m {times} 31 m proportional tube … more
Date: June 8, 1993
Creator: Sundaralingam, N.
Partner: UNT Libraries Government Documents Department
open access

Anisotropic magnetization and transport properties of RAgSb{sub 2} (R=Y, La-Nd, Sm, Gd-Tm)

Description: This study of the RAgSb{sub 2} series of compounds arose as part of an investigation of rare earth intermetallic compounds containing antimony with the rare earth in a position with tetragonal point symmetry. Materials with the rare earth in a position with tetragonal point symmetry frequently manifest strong anisotropies and rich complexity in the magnetic properties, and yet are simple enough to analyze. Antimony containing intermetallic compounds commonly possess low carrier densities and ha… more
Date: November 8, 1999
Creator: Myers, Kenneth D.
Partner: UNT Libraries Government Documents Department
open access

Amperometric detection and electrochemical oxidation of aliphatic amines and ammonia on silver-lead oxide thin-film electrodes

Description: This thesis comprises three parts: Electrocatalysis of anodic oxygen-transfer reactions: aliphatic amines at mixed Ag-Pb oxide thin-film electrodes; oxidation of ammonia at anodized Ag-Pb eutectic alloy electrodes; and temperature effects on oxidation of ethylamine, alanine, and aquated ammonia.
Date: January 8, 1996
Creator: Ge, Jisheng
Partner: UNT Libraries Government Documents Department
open access

Ultrasonic texture characterization of aluminum, zirconium and titanium alloys

Description: This work attempts to show the feasibility of nondestructive characterization of non-ferrous alloys. Aluminum alloys have a small single crystal anisotropy which requires very precise ultrasonic velocity measurements for derivation of orientation distribution coefficients (ODCs); the precision in the ultrasonic velocity measurement required for aluminum alloys is much greater than is necessary for iron alloys or other alloys with a large single crystal anisotropy. To provide greater precision, … more
Date: October 8, 1997
Creator: Anderson, A. J.
Partner: UNT Libraries Government Documents Department
Back to Top of Screen