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MagRad: A code to optimize the operation of superconducting magnets in a radiation environment

Description: A powerful computational tool, called MagRad, has been developed which optimizes magnet design for operation in radiation fields. Specifically, MagRad has been used for the analysis and design modification of the cable-in-conduit conductors of the TF magnet systems in fusion reactor designs. Since the TF magnets must operate in a radiation environment which damages the material components of the conductor and degrades their performance, the optimization of conductor design must account not only… more
Date: December 31, 1995
Creator: Yeaw, Christopher T.
Partner: UNT Libraries Government Documents Department
open access

I: Low Frequency NMR and NQR Using a dc SQUID. II: Variable-temperature 13C CP/MAS of Organometallics

Description: NMR and NQR at low frequencies are difficult prospects due to small nuclear spin polarization. Furthermore, the sensitivity'of the inductive pickup circuitry of standard spectrometers is reduced as the frequency is lowered. I have used a cw-SQUID (Superconducting QUantum Interference Device) spectrometer, which has no such frequency dependence, to study the local atomic environment of {sup 14}N via the quadrupolar interaction. Because {sup 14}N has spin I = 1 and a 0-6 MHz frequency range, it i… more
Date: November 29, 1995
Creator: Ziegeweid, M.A.
Partner: UNT Libraries Government Documents Department
open access

Graduate student theses supported by DOE`s Environmental Sciences Division

Description: This report provides complete bibliographic citations, abstracts, and keywords for 212 doctoral and master`s theses supported fully or partly by the U.S. Department of Energy`s Environmental Sciences Division (and its predecessors) in the following areas: Atmospheric Sciences; Marine Transport; Terrestrial Transport; Ecosystems Function and Response; Carbon, Climate, and Vegetation; Information; Computer Hardware, Advanced Mathematics, and Model Physics (CHAMMP); Atmospheric Radiation Measureme… more
Date: July 1995
Creator: Cushman, R. M. & Parra, B. M.
Partner: UNT Libraries Government Documents Department
open access

The picosecond dynamics of electron-hole pairs in graded and homogeneous CdS{sub x}Se{sub 1-x} semiconductors

Description: Wavelength and composition dependence of the time-resolved luminescence were examined. Effects of macroscopic composition gradient and microscopic alloy disorder on e{sup {minus}}-h{sup +} pair dynamics were probed. Materials with both increasing and decreasing S content with distance from the surface were examined, where 0{le} {times} {le}1 over the full range. In these graded materials, the band gap energy also varies with position. The graded semiconductor luminescence shows strong wavelengt… more
Date: May 1, 1995
Creator: Hane, J.K.
Partner: UNT Libraries Government Documents Department
open access

Impulse-based methods for fluid flow

Description: A Lagrangian numerical method based on impulse variables is analyzed. A relation between impulse vectors and vortex dipoles with a prescribed dipole moment is presented. This relation is used to adapt the high-accuracy cutoff functions of vortex methods for use in impulse-based methods. A source of error in the long-time implementation of the impulse method is explained and two techniques for avoiding this error are presented. An application of impulse methods to the motion of a fluid surrounde… more
Date: May 1, 1995
Creator: Cortez, R.
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

Statistical methods in physical mapping

Description: One of the great success stories of modern molecular genetics has been the ability of biologists to isolate and characterize the genes responsible for serious inherited diseases like fragile X syndrome, cystic fibrosis and myotonic muscular dystrophy. This dissertation concentrates on constructing high-resolution physical maps. It demonstrates how probabilistic modeling and statistical analysis can aid molecular geneticists in the tasks of planning, execution, and evaluation of physical maps of… more
Date: May 1, 1995
Creator: Nelson, D. O.
Partner: UNT Libraries Government Documents Department
open access

Evaluation of the {sup 4}I{sub 11/2} terminal level lifetime for several neodymium-doped laser crystals and glasses

Description: All models of lasing action require knowledge of the physical parameters involved, of which many can be measured or estimated. The value of the terminal level lifetime is an important parameter in modeling many high power laser systems since the terminal level lifetime can have a substantial impact on the extraction efficiency of the system. However, the values of the terminal level lifetimes for a number of important laser materials such as ND:YAG and ND:YLF are not well known. The terminal le… more
Date: April 25, 1995
Creator: Bibeau, C.
Partner: UNT Libraries Government Documents Department
open access

Ultrafast studies of photodissociation in solution: Dissociation, recombination and relaxation

Description: Photodissociation of M(CO){sub 6} (M=Cr,Mo,W) and the formation of solvated M(CO){sub 5}{center_dot}S complex was studied in cyclohexane; rate-limiting step is vibrational energy relaxation from the new bond to the solvent. For both M=Cr and Mo, the primary relaxation occurs in 18 ps; for Cr, there is an additional vibrational relaxation (150 ps time scale) of a CO group poorly coupled to other modes. Relaxation of M=W occurs in 42 ps; several possible mechanisms for the longer cooling are disc… more
Date: May 1, 1995
Creator: King, J. C.
Partner: UNT Libraries Government Documents Department
open access

Development of radiation detectors based on hydrogenated amorphous silicon and its alloys

Description: Hydrogenated amorphous silicon and related materials have been applied to radiation detectors, utilizing their good radiation resistance and the feasibility of making deposits over a large area at low cost. Effects of deposition parameters on various material properties of a-Si:H have been studied to produce a material satisfying the requirements for specific detection application. Thick(-{approximately}50 {mu}m), device quality a-Si:H p-i-n diodes for direct detection of minimum ionizing parti… more
Date: April 1, 1995
Creator: Hong, Wan-Shick
Partner: UNT Libraries Government Documents Department
open access

The growth of epitaxial iron oxides on platinum (111) as studied by X-ray photoelectron diffraction, scanning tunneling microscopy, and low energy electron diffraction

Description: Three complementary surface structure probes, x-ray photoelectron diffraction (XPD), scanning tunneling microscopy (STM), and low-energy electron diffraction (LEED) have been combined in a single instrument. This experimental system has been utilized to study the structure and growth mechanisms of iron oxide films on Pt(111); these films were formed by first depositing a single overlayer of Fe with a certain coverage in monolayers (ML`s), and then thermally oxidizing it in an oxygen atmosphere.… more
Date: May 1, 1995
Creator: Kim, Y. J.
Partner: UNT Libraries Government Documents Department
open access

Synthesis and characterization of novel lanthanide- and actinide-containing titanates and zircono-titanates; relevance to nuclear waste disposal

Description: Before experiments using actinide elements are performed, synthetic routes are tested using lanthanides of comparable ionic radii as surrogates. Compound and solid solution formation in several lanthanide-containing titanate and zircono-titanate systems have been established using X-ray diffraction (XRD) analysis, which helped to define interesting and novel experiments, some of which have been performed and are discussed, for selected actinide elements. The aqueous solubilities of several lant… more
Date: August 1, 1995
Creator: Shoup, S.L.S.
Partner: UNT Libraries Government Documents Department
open access

Photofragment translational spectroscopy of three body dissociations and free radicals

Description: This dissertation describes several three-body dissociations and the photodissociation of methyl radicals studied using photofragment translational spectroscopy. The first chapter provides an introduction to three body dissociation, examines current experimental methodology, and includes a discussion on the treatment of photofragment translational spectroscopy data arising from three-body fragmentation. The ultraviolet photodissociation of azomethane into two methyl radicals and nitrogen is dis… more
Date: April 1, 1995
Creator: North, S.W.
Partner: UNT Libraries Government Documents Department
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Trivalent metallocene chemistry of some uranium, titanium, and zirconium complexes

Description: Dicyclopentadienyluranium halide dimers have been prepared and their solution behavior examined. These molecules exist as dimers in solution, and the halide ligands undergo rapid site exchange on the NMR timescale above 50 C. Analogous dicyclopentadienyluranium hydroxide dimers have also been prepared; they oxidatively eliminate hydrogen to give the corresponding oxide dimers. Mechanism of this reaction is consistent with {alpha}migration of one of the hydroxide hydrogen atoms to a uranium cent… more
Date: May 1, 1995
Creator: Lukens, W. W., Jr.
Partner: UNT Libraries Government Documents Department
open access

Transport and sorption of volatile organic compounds and water vapor in porous media

Description: To gain insight on the controlling mechanisms for VOC transport in porous media, the relations among sorbent properties, sorption equilibrium and intraparticle diffusion processes were studied at the level of individual sorbent particles and laboratory columns for soil and activated carbon systems. Transport and sorption of VOCs and water vapor were first elucidated within individual dry soil mineral grains. Soil properties, sorption capacity, and sorption rates were measured for 3 test soils; … more
Date: July 1, 1995
Creator: Lin, Tsair-Fuh
Partner: UNT Libraries Government Documents Department
open access

Connection between NMR and electrical conductivity in glassy chalcogenide fast ionic conductors

Description: The work documented in this thesis follows the traditional order. In this chapter a general discussion of ionic conduction and of glassy materials are followed by a brief outline of the experimental techniques for the investigation of fast ionic conduction in glassy materials, including NMR and impedance spectroscopy techniques. A summary of the previous and present studies is presented in the last section of this introductory chapter. The details of the background theory and models are found i… more
Date: November 1, 1995
Creator: Kim, K. H.
Partner: UNT Libraries Government Documents Department
open access

Anisotropic superconducting and normal state magnetic properties of single crystals of RNi*2*B*2*C compounds (R = Y, Gd, Dy, Ho, Er, and Tm)

Description: The interaction of superconductivity with magnetism has been one of the most interesting and important phenomena in solid state physics since the 1950`s when small amounts of magnetic impurities were incorporated in superconductors. The discovery of the magnetic superconductors RNi{sub 2}B{sub 2}C (R = rare earth, Y) offers a new system to study this interaction. The wide ranges of superconducting transition (T{sub c}) and antiferromagnetic (AF) ordering temperatures (T{sub N}) (0 K {le} T{sub … more
Date: November 1, 1995
Creator: Cho, B.
Partner: UNT Libraries Government Documents Department
open access

NMR investigations of surfaces and interfaces using spin-polarized xenon

Description: {sup 129}Xe NMR is potentially useful for the investigation of material surfaces, but has been limited to high surface area samples in which sufficient xenon can be loaded to achieve acceptable signal to noise ratios. In Chapter 2 conventional {sup 129}Xe NMR is used to study a high surface area polymer, a catalyst, and a confined liquid crystal to determine the topology of these systems. Further information about the spatial proximity of different sites of the catalyst and liquid crystal syste… more
Date: July 1, 1995
Creator: Gaede, H.C.
Partner: UNT Libraries Government Documents Department
open access

Development of new VOC exposure metrics and their relationship to ``Sick Building Syndrome`` symptoms

Description: Volatile organic compounds (VOCs) are suspected to contribute significantly to ``Sick Building Syndrome`` (SBS), a complex of subchronic symptoms that occurs during and in general decreases away from occupancy of the building in question. A new approach takes into account individual VOC potencies, as well as the highly correlated nature of the complex VOC mixtures found indoors. The new VOC metrics are statistically significant predictors of symptom outcomes from the California Healthy Building… more
Date: August 1, 1995
Creator: Ten Brinke, J.
Partner: UNT Libraries Government Documents Department
open access

The dynamics of variable-density turbulence

Description: The dynamics of variable-density turbulent fluids are studied by direct numerical simulation. The flow is incompressible so that acoustic waves are decoupled from the problem, and implying that density is not a thermodynamic variable. Changes in density occur due to molecular mixing. The velocity field is, in general, divergent. A pseudo-spectral numerical technique is used to solve the equations of motion. Three-dimensional simulations are performed using a grid size of 128{sup 3} grid points.… more
Date: November 1, 1995
Creator: Sandoval, D.L.
Partner: UNT Libraries Government Documents Department
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Synthesis and study of novel silicon-based unsaturated polymers

Description: Novel unsaturated polymers have been synthesized and studied as precursors to silicon carbide and third order nonlinear optical materials. X ray structures were obtained. Kinetic and mechanistic studies of the unique thermal isomerization of dimethylenedisilacyclobutane to a carbene were conducted.
Date: June 19, 1995
Creator: Lin, J.
Partner: UNT Libraries Government Documents Department
open access

Excited state carrier dynamics in CdS{sub x}Se{sub 1-x} semisconductor alloys as studied by ultrafast fluorescence spectroscopy

Description: This dissertation discusses studies of the electron-hole pair dynamics of CdS{sub x}Se{sub 1-x} semiconductor alloys for the entire compositional range from x = 1 to x = 0 as examined by the ultrafast fluorescence techniques of time correlated single photon counting and fluorescence upconversion. Specifically, samples with x = 1, .75, .5, .25, and 0 were studied each at a spread of wavelengths about its respective emission maximum which varies according to {lambda} = 718nm - 210x nm. The decays… more
Date: August 1, 1995
Creator: Gadd, S. E.
Partner: UNT Libraries Government Documents Department
open access

Oxidation studies on small atom doped TI*5*SI*3*

Description: This report described the oxidation and oxidation resistance of Ti{sub 5}Si{sub 3}, along with a discussion on general material properties. Single crystal studies of Ti{sub 5}Si{sub 3}Z{sub x} are included.
Date: November 1, 1995
Partner: UNT Libraries Government Documents Department
open access

Synthesis, structure, and reactivity of high oxidation state silver fluorides and related compounds

Description: This thesis has been largely concerned with defining the oxidizing power of Ag(III) and Ag(II) in anhydrous hydrogen fluoride (aHF) solution. Emphasis was on cationic species, since in a cation the electronegativity of a given oxidation state is greatest. Cationic Ag(III) solv has a short half life at ordinary temperatures, oxidizing the solvent to elemental fluorine with formation of Ag(II). Salts of such a cation have not yet been preparable, but solutions which must contain such a species ha… more
Date: May 1, 1995
Creator: Lucier, G.M.
Partner: UNT Libraries Government Documents Department
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