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Modified transition state theory and negative apparent activation energies of simple metathesis reactions: Application to the reaction CH₃ + HBr + CH₄ + Br

Description: Article on modified transition state theory and negative apparent activation energies of simple metathesis reactions and application to the reaction CH₃ + HBr + CH₄ + Br.
Date: December 18, 2006
Creator: Krasnoperov, Lev N.; Peng, Jingping & Marshall, Paul
Partner: UNT College of Arts and Sciences

Temperature Dependence of the Absolute Third-order Rate Constant for the Reaction between Na + O₂ + N₂ over the Range 571 - 1016 K Studied by Time-resolved Atomic Resonance Absorption Spectroscopy

Description: Article on temperature dependence of the absolute third-order rate constant for the reaction between Na + O₂ + N₂ over the range 571-1016 K studied by time-resolved atomic resonance absorption spectroscopy.
Date: 1985
Creator: Husain, David; Marshall, Paul & Plane, John M. C.
Partner: UNT College of Arts and Sciences

A temperature dependent ENDF/B-VI, release 4: Cross Section Library

Description: The ENDF/B data library has recently been updated and is now available through the National Nuclear Data Center (NNDC), Brookhaven National Laboratory. This most recent library is identified as ENDF/B- VI, Release 4. This release completely supersedes the preceding release, Release 3, distributed in January 1996. As distributed the ENDF/B-VI, Release 4 data includes cross sections represented in the form of a combination of resonance parameters and/or tabulated energy dependent cross sections, nominally at 0 Kelvin temperature. For use in applications this library has been processed into the form of temperature dependent cross sections at eight temperatures between 0 and 2100 Kelvin, in steps of 300 Kelvin. At each temperature the cross sections are tabulated and linearly interpolable in energy. The all results are in the computer independent ENDF/B-VI character format, which allows the data to be easily transported between 2 computers. It is approximately 1 gigabyte in size and is distributed on two CDs.
Date: June 1, 1997
Creator: Cullen, D. E.
Partner: UNT Libraries Government Documents Department

Report on laboratory tests of drying and re-wetting of intact rocks from the drift scale and single heater tests

Description: The primary focus of this report is the measurement of moisture retention curves of tuff as a function of temperature for both drying and re-wetting conditions. The report contains descriptions of experimental designs and procedures, data, observation, preliminary analyses, and future work. Knowledge of unsaturated transport properties is critical for understanding the movement of water through the unsaturated zone. Evaluation of the performance of a potential nuclear waste repository also depends on these properties. Moisture retention data are important input of numerical models of moisture movement in unsaturated porous media. Also important is the effect of sample history on the moisture retention curves, and whether or not there is significant hysteresis between wetting and drying measurements. This report addresses initial observations regarding this aspect of the research.
Date: January 1, 1998
Creator: Roberts, J.J.; Carlberg, E.; Pletcher, R. & Lin, W.
Partner: UNT Libraries Government Documents Department

Observation of the Fulde-Ferrell-Larkin-Ovchinnikov state in {kappa}-(BEDT-TTF){sub 2}Cu(NCS){sub 2}

Description: Magnetic measurements show that the quasi-two-dimensional superconductor {kappa}-(BEDT-TTF){sub 2}Cu(NCS){sub 2} enters a Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) state below {approximately} 5.5 K in exactly in-plane magnetic fields {approximately} 19--24 T.
Date: August 22, 2000
Creator: Symington, J. A.; Singleton, J.; Nam, M.-S.; Ardavan, A.; Kurmoo, M.; Schlueter, J. A. et al.
Partner: UNT Libraries Government Documents Department

Hydrous pyrolysis of pole treating chemicals: (a) initital measurement of hydrous pyrolysis rates for napthalene and pentachlorophenol; (b) solubility of flourene at temperatures up to 150{degrees}C

Description: The temperature dependencies of the hydrous pyrolysis/oxidation (HPO) aqueous phase oxidation reactions of naphthalene and pentachlorophenol have been determined for phosphate buffered systems using Dickson-type reaction vessels. The HPO experimental temperatures ranged from 114{degrees}C to 148{degrees}C for naphthalene and 114{degrees}C to 137{degrees}C for pentachlorophenol. The loss of the organic species was used to determine activation energies of 95.8 kJ/mole for naphthalene oxidation and 84.8 kJ/mole for pentachlorophenol oxidation. Aqueous concentrations of target compounds and reaction intermediates were determined by gas chromatography and compound identification was verified by gas chromatography - mass spectrometry. During the experiments the pollutants were completely mineralized, as indicated by a stoichiometric production of inorganic carbon in the case of naphthalene and inorganic carbon and chloride in the case of pentachlorophenol. HPO of pentachlorophenol produced 2,3,5,6- tetrachlorophenol as an intermediate, whereas no intermediates amenable by GC were observed during the HPO of naphthalene. Measurements of the aqueous solubility of florin in an unbuffered solution have been made covering the temperature range from 20{degrees}C to 150{degrees}C. There is very good agreement between this data set and data previously published covering the lower temperature range (20{degrees}C to 75{degrees}C). Extension of the solubility measurements to higher temperatures covers the in situ temperatures achievable during field application of HPO and demonstrated a nearly exponential rise in aqueous solubility as a function of temperature, with a 10 fold increase in aqueous florin solubility going from 75{degrees}C to 125{degrees}C and a 20 fold increase in going from 75{degrees}C to 150{degrees}C.
Date: November 15, 1997
Creator: Leif, R. N., LLNL
Partner: UNT Libraries Government Documents Department

Characterization of a fused silica capacitance standard

Description: An ovenized 10 pF standard capacitor was constructed by the National Institute of Standards and Technology (NIST). The dielectric material used as Wuprasil II grade fused silica. This report discusses a temperature coefficient analysis of the capacitor performed at the Primary Standards Laboratory (PSL) of Sandia National Laboratories (SNL). The effects of temperature change on dielectric loss will also be discussed.
Date: January 1, 1995
Creator: Daniel, M.G.
Partner: UNT Libraries Government Documents Department

Recent advances in the measurement of high temperature bimolecular rate constants

Description: Recent advances in the measurement of high temperature reaction rate constants are discussed. The studies carried out by shock tube methods are particularly considered because these results are important not only in theoretical chemical kinetics but also in practical applications. The work on 5 chemical reactions are reviewed in detail. These are: D + H{sub 2}, Cl + H{sub 2}, H + O{sub 2}, CH{sub 3} + CH{sub 3}, and H + NO{sub 2}.
Date: July 1, 1995
Creator: Michael, J.V.
Partner: UNT Libraries Government Documents Department

Creep Properties of Pb-Free Solder Joints

Description: Describes the creep behavior of three Sn-rich solders that have become candidates for use in Pb-free solder joints: Sn-3.5Ag, Sn-3Ag-0.5Cu and Sn-0.7Cu. The three solders show the same general behavior when tested in thin joints between Cu and Ni/Au metallized pads at temperatures between 60 and 130 C. Their steady-state creep rates are separated into two regimes with different stress exponents(n). The low-stress exponents range from {approx}3-6, while the high-stress exponents are anomalously high (7-12). Strikingly, the high-stress exponent has a strong temperature dependence near room temperature, increasing significantly as the temperature drops from 95 to 60 C. The anomalous creep behavior of the solders appears to be due to the dominant Sn constituent. Joints of pure Sn have stress exponents, n, that change with stress and temperature almost exactly like those of the Sn-rich solder joints. Research on creep in bulk samples of pure Sn suggests that the anomalous temperature dependence of the stress exponent may show a change in the dominant mechanism of creep. Whatever its source, it has the consequence that conventional constitutive relations for steady-state creep must be used with caution in treating Sn-rich solder joints, and qualification tests that are intended to verify performance should be carefully designed.
Date: April 1, 2002
Creator: Song, H. G.; Morris, J. W., Jr. & Hua, F.
Partner: UNT Libraries Government Documents Department

High Temperature High Pressure Thermodynamic Measurements for Coal Model Compounds

Description: The overall objective of this project is to develop a better thermodynamic model for predicting properties of high-boiling coal derived liquids, especially the phase equilibria of different fractions at elevated temperatures and pressures. The development of such a model requires data on vapor-liquid equilibria (VLE), enthalpy, and heat capacity which would be experimentally determined for binary systems of coal model compounds and compiled into a database. The data will be used to refine existing models such as UNIQUAC and UNIFAC. The flow VLE apparatus designed and built for a previous project was upgraded and recalibrated for data measurements for thk project. The modifications include better and more accurate sampling technique and addition of a digital recorder to monitor temperature, pressure and liquid level inside the VLE cell. VLE data measurements for system benzene-ethylbenzene have been completed. The vapor and liquid samples were analysed using the Perkin-Elmer Autosystem gas chromatography.
Date: November 12, 1998
Creator: Chen, John C. & Kabadi, Vinayak N.
Partner: UNT Libraries Government Documents Department

Assessing Cumulative Thermal Stress in Fish During Chronic Exposure to High Temperature

Description: As environmental laws become increasingly protective, and with possible future changes in global climate, thermal effects on aquatic resources are likely to receive increasing attention. Lethal temperatures for a variety of species have been determined for situations where temperatures rise rapidly resulting in lethal effects. However, less is known about the effects of chronic exposure to high (but not immediately lethal) temperatures and even less about stress accumulation during periods of fluctuating temperatures. In this paper we present a modeling framework for assessing cumulative thermal stress in fish. The model assumes that stress accumulation occurs above a threshold temperature at a rate depending on the degree to which the threshold is exceeded. The model also includes stress recovery (or alleviation) when temperatures drop below the threshold temperature as in systems with large daily variation. In addition to non-specific physiological stress, the model also simulates thermal effects on growth.
Date: November 14, 1999
Creator: Bevelhimer, M.S. & Bennett, W.R.
Partner: UNT Libraries Government Documents Department

Nature of room-temperature photoluminescence in ZnO

Description: The temperature dependence of the photoluminescence (PL) transitions associated with various excitons and their phonon replicas in high-purity bulk ZnO has been studied at temperatures from 12 K to above room temperature (320 K). Several strong PL emission lines associated with LO phonon replicas of free and bound excitons are clearly observed. The room temperature PL spectrum is dominated by the phonon replicas of the free exciton transition with the maximum at the first LO phonon replica. The results explain the discrepancy between the transition energy of free exciton determined by reflection measurement and the peak position obtained by the PL measurement.
Date: November 11, 2004
Creator: Shan, W.; Walukiewicz, W.; Ager III, J.W.; Yu, K.M.; Yuan, H.B.; Xin, H.P. et al.
Partner: UNT Libraries Government Documents Department


Description: Here I review the temperature-dependence of heavy quarkonia correlators in potential models with three different screened potentials, and compare these to the results from lattice QCD. None of the potentials investigated yield results consistent with the lattice data, indicating that screening is likely not the mechanism for heavy quarkonia suppression. I also discuss a simple toy model, not based on temperature-dependent screening, that can reproduce the lattice results.
Date: March 11, 2006
Creator: MOCSY, A.
Partner: UNT Libraries Government Documents Department

The Effect of Temperature on the Breakdown and Repassivation Potentials of Welded Alloy 22 In 5 M CACI2

Description: The study of the electrochemical behavior of wrought and welded Alloy 22 was carried out in 5 M CaCl{sub 2} as a function of temperatures between 45 and 120 C with Multiple Crevice Assembly (MCA) specimens. The susceptibility to corrosion was found to increase with increase in electrolyte temperature in both the wrought (in the mill annealed condition) and the welded forms of the alloy. The weld metal was found to be less susceptible to localized corrosion under the conditions tested.
Date: July 5, 2006
Creator: IIevbare, G.O.
Partner: UNT Libraries Government Documents Department

Superlattice effects on the amorphization of ni-ti multilayers

Description: A phenomenological model is proposed to correlate the onset of solid-state amorphization with the loss of interfacial stability in Ni-Ti multilayers. Additionally, a temperature dependence to the onset of amorphization is attributed to the effect of interfacial coherency that varies with the Ni-Ti layer pair spacing.
Date: February 10, 2000
Creator: Jankowski, A F
Partner: UNT Libraries Government Documents Department