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Intermolecula transfer and elimination of molecular hydrogen in thermal reactions of unsaturated organic compounds

Description: Two reactions which are important to coal liquefaction include intermolecular transfer and the elimination of two hydrogen atoms. We have designed several model reactions to probe the viability of several hydrogen transfer and elimination pathways. This report described studies on these reactions using organic model compounds.
Date: February 10, 1995
Creator: Suria, S.
Partner: UNT Libraries Government Documents Department
open access

Crossed molecular beams study of O({sup 1}D) reactions with H{sub 2} molecules

Description: Reaction dynamics of O({sup 1}D) atoms with H{sub 2} molecules was reinvestigated using the crossed molecular beams technique with pulsed beams. The O({sup 1}D) beam was generated by photodissociating O{sub 3} molecules at 248 nm. Time-of-flight spectra and the laboratory angular distribution of the OH products were measured. The derived OH product center-of-mass flux-velocity contour diagram shows more backward scattered intensity with respect to the O({sup 1}D) beam. In contrast to previous s… more
Date: May 1, 1995
Creator: Miau, T.T.
Partner: UNT Libraries Government Documents Department
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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
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Analysis of stray radiation produced by the advanced light source (1.9 GeV synchrotron radiation source) at Lawrence Berkeley Laboratory

Description: The yearly environmental dose equivalent likely to result at the closest site boundary from the Advanced Light Source was determined by generating multiple linear regressions. The independent variables comprised quantified accelerator operating parameters and measurements from synchronized, in-close (outside shielding prior to significant atmospheric scattering), state-of-the-art neutron remmeters and photon G-M tubes. Neutron regression models were more successful than photon models due to low… more
Date: December 31, 1995
Creator: Ajemian, R. C.
Partner: UNT Libraries Government Documents Department
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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
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Organic transformations catalyzed by methylrhenium trioxide

Description: Methylrhenium trioxide (MTO), CH{sub 3}ReO{sub 3}, was first prepared in 1979. MTO forms stable or unstable adducts with electron-rich ligands, such as amines (quinuclidine, 1,4-diazabicyclo-octane, pyridine, aniline, 2,2{prime}-bipyridine), alkynes, olefins, 1,2-diols, catechols, hydrogen peroxide, water, thiophenols, 1,2-dithiols, triphenylphosphine, 2-aminophenols, 2-aminothiophenols, 8-hydroxyquinoline and halides (Cl-, Br-, I-). After coordination, different further reactions will occur fo… more
Date: November 1, 1995
Creator: Zhu, Z.
Partner: UNT Libraries Government Documents Department
open access

Measurement of the polarized forward-backward asymmetry of B quarks using momentum-weighted track charge at SLD

Description: This thesis presents a direct measurement of the parity-violating parameter A{sub b} by analyzing the polarized forward-backward asymmetry of b quarks in e{sup +}e{sup {minus}} {yields} Z{sup 0} {yields} b{bar b}. Data were taken at the Stanford Linear Accelerator Center (SLAC), with the Stanford Large Detector (SLD), which records the products of e{sup +}e{sup {minus}} interactions at a center of mass energy {radical}s = 91.2 GeV/c{sup 2} at the SLAC Linear Collider (SLC). The SLC/SLD experime… more
Date: November 1, 1995
Creator: Junk, T.R.
Partner: UNT Libraries Government Documents Department
open access

Photoelectron holography applied to surface structural determination

Description: Photoemitted electron waves are used as coherent source waves for angstrom-scale holographic imaging of local atomic geometry at surfaces. Electron angular distribution patterns are collected above a sample surface and serve as a record of the interference between source wave and waves scattered from surrounding ion cores. Using a mathematical imaging integral transformation, the three-dimensional structural information is obtained directly from these collected patterns. Patterns measured with … more
Date: May 1, 1995
Creator: Petersen, B.L.
Partner: UNT Libraries Government Documents Department
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Spectral hole burning studies of photosystem II

Description: Low temperature absorption and hole burning spectroscopies were applied to the D1-D2-cyt b{sub 559} and the CP47 and CP43 antenna protein complexes of Photosystem H from higher plants. Low temperature transient and persistent hole-burning data and theoretical calculations on the kinetics and temperature dependence of the P680 hole profile are presented and provide convincing support for the linker model. Implicit in the linker model is that the 684-nm-absorbing Chl a serve to shuttle energy fro… more
Date: November 1, 1995
Creator: Chang, H.C.
Partner: UNT Libraries Government Documents Department
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Expanded studies of linear collider final focus systems at the Final Focus Test Beam

Description: In order to meet their luminosity goals, linear colliders operating in the center-of-mass energy range from 3,50 to 1,500 GeV will need to deliver beams which are as small as a few Manometers tall, with x:y aspect ratios as large as 100. The Final Focus Test Beam (FFTB) is a prototype for the final focus demanded by these colliders: its purpose is to provide demagnification equivalent to those in the future linear collider, which corresponds to a focused spot size in the FFTB of 1.7 microns (ho… more
Date: December 1, 1995
Creator: Tenenbaum, Peter Gregory
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
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Mathematical modeling plasma transport in tokamaks

Description: In this work, the author applied a systematic calibration, validation and application procedure based on the methodology of mathematical modeling to international thermonuclear experimental reactor (ITER) ignition studies. The multi-mode plasma transport model used here includes a linear combination of drift wave branch and ballooning branch instabilities with two a priori uncertain constants to account for anomalous plasma transport in tokamaks. A Bayesian parameter estimation method is used i… more
Date: December 31, 1995
Creator: Quiang, Ji
Partner: UNT Libraries Government Documents Department
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Optimizing parallel reduction operations

Description: A parallel program consists of sets of concurrent and sequential tasks. Often, a reduction (such as array sum) sequentially combines values produced by a parallel computation. Because reductions occur so frequently in otherwise parallel programs, they are good candidates for optimization. Since reductions may introduce dependencies, most languages separate computation and reduction. The Sisal functional language is unique in that reduction is a natural consequence of loop expressions; the paral… more
Date: June 1, 1995
Creator: Denton, S.M.
Partner: UNT Libraries Government Documents Department
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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

Infrared spectroscopy of nonclassical ions and their complexes

Description: This thesis describes an infrared spectroscopic study on the structures and dynamics of the nonclassical ions and their complexes, using ion trap vibrational predissociation spectroscopy. Chapter One provides an introduction to the experimental apparatus used in this work. Chapter Two describes the previous theoretical and experimental works on the carbonium ion CH{sub 5}{sup +} and infrared spectroscopic and theoretical works on CH{sub 5}{sup +}. CH{sub 5}{sup +} was predicted to scramble cons… more
Date: January 1, 1995
Creator: Boo, D.W.
Partner: UNT Libraries Government Documents Department
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NMR and NQR study of the thermodynamically stable quasicrystals

Description: {sup 27}Al and {sup 61,65}Cu NMR measurements are reported for powder samples of stable AlCuFe and AlCuRu icosahedral quasicrystals and their crystalline approximants, and for a AlPdMn single grain quasicrystal. Furthermore, {sup 27}Al NQR spectra at 4.2 K have been observed in the AlCuFe and AlCuRu samples. From the quadrupole perturbed NMR spectra at different magnetic fields, and from the zero field NQR spectra, a wide distribution of local electric field gradient (EFG) tensor components and… more
Date: February 10, 1995
Creator: Shastri, A.
Partner: UNT Libraries Government Documents Department
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Nuclear magnetic resonance: Its role as a microscopic probe of the electronic and magnetic properties of High-{Tc} superconductors and related materials

Description: NMR experiments are reported for Sr{sub 2}CuO{sub 2}Cl{sub 2}, HgBa{sub 2}CuO{sub 4+d}, YNi{sub 2}B{sub 2}C and YBa{sub 2}Cu{sub 3}O{sub 7}. NMR studies typify three different aspects of microscopic properties of HTSC. In non-superconducting antiferromagnetic (AF) prototype Sr{sub 2}CuO{sub 2}Cl{sub 2}, we used NMR to investigate Cu{sup 2+} correlated spin dynamics and AF phase transition in CuO2 layers. In the superconductors, we used NMR both to investigate the electronic properties of the Fe… more
Date: December 27, 1995
Creator: Suh, Byoung Jin
Partner: UNT Libraries Government Documents Department
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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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Inductively coupled plasma spectrometry: Noise characteristics of aerosols, application of generalized standard additions method, and Mach disk as an emission source

Description: This dissertation is focused on three problem areas in the performance of inductively coupled plasma (ICP) source. The noise characteristics of aerosols produced by ICP nebulizers are investigated. A laser beam is scattered by aerosol and detected by a photomultiplier tube and the noise amplitude spectrum of the scattered radiation is measured by a spectrum analyzer. Discrete frequency noise in the aerosol generated by a Meinhard nebulizer or a direct injection nebulizer is primarily caused by … more
Date: October 6, 1995
Creator: Shen, Luan
Partner: UNT Libraries Government Documents Department
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Quantum effects in unimolecular reaction dynamics

Description: This work is primarily concerned with the development of models for the quantum dynamics of unimolecular isomerization and photodissociation reactions. We apply the rigorous quantum methodology of a Discrete Variable Representation (DVR) with Absorbing Boundary Conditions (ABC) to these models in an attempt to explain some very surprising results from a series of experiments on vibrationally excited ketene. Within the framework of these models, we are able to identify the experimental signature… more
Date: December 1, 1995
Creator: Gezelter, J.D.
Partner: UNT Libraries Government Documents Department
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Incorporating uncertainties into risk assessment with an application to the exploratory studies facilities at Yucca Mountain

Description: A methodology that incorporates variability and reducible sources of uncertainty into the probabilistic and consequence components of risk was developed. The method was applied to the north tunnel of the Exploratory Studies Facility at Yucca Mountain in Nevada. In this assessment, variability and reducible sources of uncertainty were characterized and propagated through the risk assessment models using a Monte Carlo based software package. The results were then manipulated into risk curves at t… more
Date: August 1995
Creator: Fathauer, P. M.
Partner: UNT Libraries Government Documents Department
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The role of calcium in the oxygen evolving center of photosystem II

Description: The photosynthetic oxygen evolving complex (OEC) contains a cluster of four manganese atoms and requires both Ca and Cl for activity. Ca can be replaced by Sr with retention of activity. The role of Ca in the OEC has been investigated by performing Mn X-ray absorption experiments on Ca-depleted samples of photosystem II (PS II) and on PS II samples depleted of Ca and reconstituted by either Ca or Sr. Mn X-ray K-edge spectra exhibit no significant differences in oxidation state or symmetry betwe… more
Date: May 1, 1995
Creator: Latimer, M.J.
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
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Studies of the strong and electroweak interactions at the Z{sub 0} pole

Description: This thesis presents studies of the strong and electroweak forces, two of the fundamental interactions that govern the behavior of matter at high energies. The authors have used the hadronic decays of Z{sup 0} bosons produced with the unique experimental apparatus of the e{sup +}e{sup {minus}} Linear Collider at the Stanford Linear Accelerator Center (SLAC) and the SLAC Large Detector (SLD) for these measurements. Employing the precision tracking capabilities of the SLD, they isolated samples o… more
Date: March 1, 1995
Creator: Hildreth, M.D.
Partner: UNT Libraries Government Documents Department
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