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Fundamental surface chemistry of GaAs OMVPE

Description: Organometallic and hydride compounds are widely used as precursors for the epitaxial growth of GaAs and other compound semiconductors. These precursors are most commonly used to perform organometallic vapor phase epitaxy (OMVPE) and also in related deposition techniques such as atomic layer epitaxy (ALE) and metalorganic molecular beam epitaxy (MOMBE). We have investigated the surface chemical properties of these precursors on GaAs(100) using a variety of surface science diagnostics. Results ha… more
Date: May 1, 1995
Creator: Creighton, J.R. & Truong, C.M.
Item Type: Refine your search to only Article
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.
Item Type: Refine your search to only Thesis or Dissertation
Partner: UNT Libraries Government Documents Department
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Mid-year report: IPC liaison and chemistry of thermal reconstitution

Description: A program of investigation into the chemistry of alkaline Hanford Site tank waste is being conducted. The investigations have two main subtasks: liaison with the Institute of Physical Chemistry of the Russian Academy of Sciences and further laboratory testing of the chemistry of thermal reconstitution of Hanford Site tank waste. Progress to date includes: (1) a technical dialogue has been established with the Institute scientists; (2) editing of a technical literature review on the chemistry of… more
Date: May 1, 1995
Creator: Delegard, C.H.
Item Type: Refine your search to only Report
Partner: UNT Libraries Government Documents Department
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Alkaline chemistry of transuranium elements and technetium and the treatment of alkaline radioactive wastes

Description: Goal of this survey is to generalize the known data on fundamental physical-chemical properties of TRUs and Tc, methods for their isolation, and to provide recommendations that will be useful for partitioning them from alkaline high-level wastes.
Date: May 1, 1995
Creator: Delegard, C. H.; Peretrukhin, V. F.; Shilov, V. P. & Pikaev, A. K.
Item Type: Refine your search to only Report
Partner: UNT Libraries Government Documents Department
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Environmental Chamber Studies of Atmospheric Reactivities of Volatile Organic Compounds: Effects of Varying Chamber and Light Source

Description: Photochemical oxidant models are essential tools for assessing effects of emissions changes on ground-level ozone formation. Such models are needed for predicting the ozone impacts of increased alternative fuel use. The gas-phase photochemical mechanism is an important component of these models because ozone is not emitted directly, but is formed from the gas-phase photochemical reactions of the emitted volatile organic compounds (VOCs) and oxides of nitrogen (NO{sub x}) in air. The chemistry o… more
Date: May 1, 1995
Creator: Carter, W.; Luo, D.; Malkina, I. & Pierce, J.
Item Type: Refine your search to only Report
Partner: UNT Libraries Government Documents Department
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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.
Item Type: Refine your search to only Thesis or Dissertation
Partner: UNT Libraries Government Documents Department
open access

I. On the Mechanism of Acid Promoted Rearrangement of PCU-Derived Pinacols II. Synthesis of a Trimethyltrishomocubyl Helical Tubuland Diol

Description: I. Reductive dimerization of pentacyclo[5.4.0.0.^2,6.0^3,10.0^5'9]undecane-8-one-(PCU-8-one, 53) affords a mixture of meso and d,l pinacols (55a and 55b respectively). Acid promoted rearrangement of 55a and 55b conceivably can proceed with migration of C(7)-C(8) and/or C(8)-C(9) to form the corresponding pinacolone(s). In our hands, acid promoted rearrangement of 55a and 55b each proceeds with exclusive migration of C(7)- C(8) bond, thereby affording 58a and 59a respectively. Mechanistic featur… more
Date: May 1995
Creator: Liu, Zenghui
Item Type: Refine your search to only Thesis or Dissertation
Partner: UNT Libraries
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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.
Item Type: Refine your search to only Thesis or Dissertation
Partner: UNT Libraries Government Documents Department
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Sorption and chemical transformation of PAH`s on coal fly ash

Description: The major objective of this work was to characterize the interactions of coal fly ash with polycyclic aromatic hydrocarbons (PAHS) and their derivatives, and to attempt to understand the influence of the surface properties of coal ash (and other atmospheric particles) on the chemical transformations of polycyclic aromatic compounds. Our studies have concentrated on the photochemical behavior of PAHs sorbed form the vapor phase on coal fly ashes, and compositional subfractions obtained therefrom… more
Date: May 9, 1995
Creator: Mamantov, G. & Wehry, E. L.
Item Type: Refine your search to only Report
Partner: UNT Libraries Government Documents Department
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Quantum chemical studies on the stability of tetramethyl ammonium tetraborohydride

Description: Quantum chemical calculations were performed on tetramethyl ammonium tetraborohydride. The material is of interest chemically as it exists as a molecular ionic solid. Calculations show that there exist low energy barrier pathways to decomposition and, hence, that the stability of the material is largely due to crystal forces. Possible sources of this stability are discussed.
Date: May 1, 1995
Creator: Calef, D.F.
Item Type: Refine your search to only Report
Partner: UNT Libraries Government Documents Department
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A diethyl phosphonate containing oxazoline: Synthesis and characterization of monomer and homopolymer

Description: A diethyl phosphonate oxazoline monomer and its polymer have been synthesized. The monomer appears to polymerize via a ring-opening mechanism giving the expected polyethyleneimine backbone with pendant carbonyl groups. Two distinct molecular weights were produced during polymerization suggesting two mechanisms of chain growth. Studies are underway to elucidate the reasons for this. This polymer has potential as a metal-chelating agent.
Date: May 1, 1995
Creator: Hermes, R.E.; Thompson, R.D. & Valdez, L.S.
Item Type: Refine your search to only Article
Partner: UNT Libraries Government Documents Department
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Characterization of microenvironment polarity and solvent accessibility of polysilsesquioxane xerogels by the fluorescent probe technique

Description: Poly (1, 4 bis(triethoxysilyl)benzene) (PTESB), a representative of a new type of organic-inorganic hybrid polysilsesquioxane material, was characterized by fluorescence spectroscopy for both microenvironmental polarity and solvent accessibility. A dansyl fluorescent molecule was incorporated into the bulk as well as onto the surface of both PTESB and silica materials. Information about the microenvironment polarity and accessibility of PTESB to various organic solvents was determined and compa… more
Date: May 1, 1995
Creator: Shea, K. J.; Zhu, H. D. & Loy, D. A.
Item Type: Refine your search to only Article
Partner: UNT Libraries Government Documents Department
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Measurement of viscosity, density, and gas solubility of refrigerant blends in selected synthetic lubricants. Final report

Description: The lubricants tested in this project were chosen based on the results of liquid/liquid miscibility tests. EMKARATE RL32S and Emery 2968A were selected. The Vapor Liquid Equilibrium (VLE) viscosity reduction and gas fractionation of each was measured with three different refrigerant blends: (1) R-404A; (2) R-507; and (3) R-407C. In addition, the four single refrigerants that make up the blends, HFC-32, HFC-125, HFC-134a, and HFC-143a, were also measured. Lubricants found to have the lowest liqu… more
Date: May 15, 1995
Creator: Cavestri, R.C.
Item Type: Refine your search to only Report
Partner: UNT Libraries Government Documents Department
open access

Fullerene-based materials research and development. LDRD final report

Description: The chemistry and physical properties of fullerenes, the third, molecular allotrope of carbon, have been studied using both experimental and computational techniques. Early computational work investigated the stability of fullerene isomers and oxides, which was followed by extensive work on hydrogenated fullerenes. Our work led to the first synthesis of a polymer containing C{sub 60} and the synthesis of the simplest hydrocarbon derivatives of C{sub 60} and C{sub 70}. The excellent agreement be… more
Date: May 1, 1995
Creator: Cahill, P. A.; Henderson, C. C.; Rohlfing, C. M.; Loy, D. A.; Assink, R. A.; Gillen, K. T. et al.
Item Type: Refine your search to only Report
Partner: UNT Libraries Government Documents Department
open access

Recovery of Propylene Glycol From Dilute Aqueous Solutions by Reversible Chemical Complexation With Organoboronates

Description: Extractants consisting of an ion-pair of Aliquat 336 with phenylboronate or 3-nitrophenylboronate were prepared in various diluents (2-ethylhexanol, toluene, o-xylene or diisobutylketone). In batch experiments propyleneglycol (1,2-PD) was effectively extracted even at low concentrations. Heterogeneous complexation constants {beta}{sub 11} calculated at 25 C were 45-120 (mol/1){sup {minus}1} in 2-ethylhexanol, 34.8 (mol/l){sup {minus}1} in toluene, 37.6 (mol/l){sup {minus}1} in o-xylene and 14.4… more
Date: May 1, 1995
Creator: Broekhuis, R. R.; Lynn, S. & King, C. J.
Item Type: Refine your search to only Report
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.
Item Type: Refine your search to only Thesis or Dissertation
Partner: UNT Libraries Government Documents Department
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Capillary electrokinetic separations with optical detection. Technical progress report, February 1, 1994--January 31, 1995

Description: This multifarious research program is dedicated to the development of capillary electrokinetic separation techniques and associated optical methods of detection. Currently, research is directed at three general objectives. First, fundamental studies of pertinent separation and band broadening mechanisms are being conducted, with the emphasis on achieving rapid separations and understanding separation systems that include highly-ordered assemblies as running buffer additives. Second, instrumenta… more
Date: May 1, 1995
Creator: Sepaniak, M. J.
Item Type: Refine your search to only Report
Partner: UNT Libraries Government Documents Department
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Enhanced shortwave cloud radiative forcing due to anthropogenic aerosols

Description: It has been suggested that anthropogenic aerosols in the troposphere can influence the microphysical properties of clouds and in turn their reflectivity, thereby exerting a radiative influence on climate. This article presents the theoretical basis for of this so-called indirect forcing and reviews pertinent observational evidence and climate model calculations of its magnitude and geographical distribution. We restrict consideration to liquid-water clouds.
Date: May 1995
Creator: Schwartz, S. E. & Slingo, A.
Item Type: Refine your search to only Article
Partner: UNT Libraries Government Documents Department
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Analysis on the sequence of formation of Ti{sub 3}SiC{sub 2} and Ti{sub 3}SiC{sub 2}/SiC composites

Description: Ti{sub 3}SiC{sub 2}, a compound in the ternary Ti-Si-C system, is reported to be ductile. This paper reports the sequence of formation of Ti{sub 3}SiC{sub 2} and Ti{sub 3}SiC{sub 2}/SiC composites involving either combustion synthesis or by displacement reaction, respectively. Onset of exothermic reaction temperatures were determined using Differential Thermal Analysis (DTA). Phases present after the exothermic temperatures were analyzed by X-Ray diffraction. Based on these observations, a rout… more
Date: May 1, 1995
Creator: Radhakrishnan, R.; Bhaduri, S.B. & Henager, C.H. Jr.
Item Type: Refine your search to only Article
Partner: UNT Libraries Government Documents Department
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Toward quantitative STM: Scanning tunneling microscopy study of structure and dynamics of adsorbates on transition metal surfaces

Description: STM was applied to chemisorbed S layers on Re(000l) and Mo(100) surfaces. As function of coverage on both these surfaces, S orders into several different overlayer structures, which have been studied by dynamic LEED. STM images of all these structures were obtained. Approximate location of S atoms in the structures was determined by inspecting the images, especially the regions containing defects. Results are in agreement with LEED except for the p(2{times}l) overlayer of sulfur on Mo(100). The… more
Date: May 1, 1995
Creator: Dunphy, J.C.
Item Type: Refine your search to only Thesis or Dissertation
Partner: UNT Libraries Government Documents Department
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Development of high spectral resolution lidar (HSRL) technology. Final report

Description: This report describes progress achieved during two years of DOE funding provided by grant DE-FG02-90ER61058. This grant was titled {open_quotes}Development of High Spectral Resolution Lidar Technology for use in the DOE ARM Program{close_quotes}. Nearly all grant objectives were achieved despite the fact that DOE abruptly canceled funding after only two years of a planned three year effort. The principal investigator learned of the cancellation only after attempting to determine why third year … more
Date: May 8, 1995
Creator: Eloranta, E.W.
Item Type: Refine your search to only Report
Partner: UNT Libraries Government Documents Department
open access

Waste minimization via preparative scale high performance gel permeation chromatography

Description: The procedures developed here allow removal of radioactivity, as judged by removal of {sup 152}Europium (III) from methylene chloride solutions of CLP analytes without significantly reducing recovery of organic compounds. This allows analysis of nonradioactive extracts on instrumentation maintained in a regular nonradioactive laboratory, resulting in a significant savings in cost.
Date: May 1, 1995
Creator: Boparai, A. S.; Parish, K. J.; Kent, S. D.; Tsai, Y. & Joe, D. A.
Item Type: Refine your search to only Article
Partner: UNT Libraries Government Documents Department
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