32 Matching Results

Search Results

Advanced search parameters have been applied.

Feasibility and advantages of off-resonance lasers in chemically reacting systems

Description: The problem of understanding the semiclassical description of the time evolution of an ensemble of two state systems under the influence of a coherent radiation field is of considerable importance. Previous attempts to deal with these problems have dealt with either broad pulses or ultrashort pulses which allow the use of the rate equations or finite phase memory to be incorporated into the description. In neither case, however, has the effect of incoherent feeding and off-resonance effects in a coherently driven two-level system been analyzed. A closed form solution that includes the effects of relaxation and spontaneous emission between the two levels has been obtained for the general case when the ensemble is being incoherently fed from a population reservoir, as would be the case, for example, in a chemical laser. In addition to providing a basis for understanding the modifications which occur for such a system, the mathematical formulation predicts that an important effect may be observed. This effect, which is termed ''kinetic coherence,'' is the production of a long-term coherent component that results directly from the kinetic feeding. The magnitude of the component is related to the rate of creating excited states, relaxation pathways and the off-resonance frequency. It is shown how, in principle, it is possible to utilize these off-resonance effects in any inhomogeneously broadened system to significantly overcome the losses from T$sub 2$ relaxation processes and to provide an experimental system capable of controlling the relative ratio of spontaneous and stimulated emission. Finally, the relationships between chemical kinetics, the off-resonance feature and sustained self-regulation in a system exhibiting gain are discussed. (auth)
Date: June 1, 1975
Creator: Harris, C.B.
Partner: UNT Libraries Government Documents Department

POWER-SUPPLY SYSTEM FOR THE BEVATRON AUXILIARY MAGNETS

Description: Some of thc basic considerations in the design of the protective interlocking of the d-c power system for auxiliary magnets used at the Bevatron are described. The required current-regulation tolerarices are given along with a discussion of the various problems associated with certain special applications of the magnets. (auth)
Date: May 1, 1959
Creator: Harris, C.A.
Partner: UNT Libraries Government Documents Department

Digital spall radiograph analysis system: Report on simulated three- dimensional digital spall image reconstruction fidelity

Description: This report describes progress on work to develop a cost effective, rapid response system for measuring momentum and kinetic energy of spall for the Advanced Technology Assessment Center (ATAC) Armor/Anti-Armor (A{sup 3}) program at Los Alamos National Laboratory. The system will exploit data contained in two sets of simultaneous co-planar flash radiographs taken along the center line of anticipated spall motion. Data contained in each set (which is proportional to the mass and z- number of the spall material intersected by the exposing x-ray at each point) is digitized and used to construct a three dimensional model (called the reconstructed spall image) that approximates the original spall cloud. From the model the mass of spall fragments is computed. The two sets of radiographs, separated in time, represent the spall configuration at two instants of time. Spall fragments from the first instant are matched with those from the second instant to determine velocity. Evaluation of the fidelity of candidate reconstruction algorithms is the highest priority task in this development program for the obvious reason that the efficacy of the projected spall analysis system depends upon the fidelity of the reconstruction techniques. The purpose of this document is to report the results of analysis of the fidelity of best reconstruction procedure (for one radiograph set) investigated to date. The reconstruction procedure uses data from four simultaneous radiographs representing two sides and two diagonals of a cube. The procedure makes use of an available space algorithm, two probabilistic devices (a mass placement probability heuristic, and a mass clumping heuristic), and a stochastic procedure for mass that cannot be placed by the algorithm or either of the heuristics. The procedure is fully described in the body of the report.
Date: January 1, 1990
Creator: Harris, C.L.
Partner: UNT Libraries Government Documents Department

Excitonic Superconductivity in Copper Oxides

Description: We discuss the possibility of excitonic superconductivity in high T/sub c/ copper oxides. The Hamiltonians describing CuO/sub 2/ planes supports both antiferromagnetism and low-lying Cu /longleftrightarrow/ O intra- and interband charge fluctuations. One crosses from one regime to another as the number of holes per unit cell increases. The high T/sub c/ superconductivity takes place at hole concentrations most favorable for intraband charge transfer excitations. The dynamic polarizability of the environment surrounding CuO/sub 2/ planes plays an important role in enhancing T/sub c/. 15 refs., 4 figs.
Date: 1988~
Creator: Tesanovic, Z.; Bishop, A. R.; Martin, R. L. & Harris, C.
Partner: UNT Libraries Government Documents Department

Hydroprocessing SRC. Final technical report

Description: Catalyst activity and aging rate were studied in ICRC's process development unit (PDU) and at the Wilsonville Advanced Coal Liquefaction Facility under SRC-I Demonstration Plant hydroprocessing conditions. Similar studies using both high- and low-conversion modes were conducted by The Lummus Company. The studies determined variations in SRC conversion, hydrocarbon gas production, hydrogen consumption, and heteroatom removal. Samples of spent catalyst were analyzed to ascertain the reasons for catalyst deactivation. Finally, the ICRC PDU hydroprocessing results were compared with those generated at Lummus and Wilsonville pilot plants.
Date: September 1, 1983
Creator: Bronfenbrenner, J.C.; Garg, D.; Harris, C.F. & Znaimer, S.
Partner: UNT Libraries Government Documents Department

A Critical Test of Vibrational Dephasing Theories in Solids Using Spontaneous Raman Scattering in Isotopically Mixed Crystals

Description: A series of experiments has been conducted in order to evaluate the relative importance of several recent theories of vibrational dephasing in solids. The theories are discussed briefly, and are used to interpret the temperature dependence of the C-H and C-D stretch bands in the spontaneous Raman spectra of h{sub 14} - and d{sub 14}-1,2,4,5-tetramethyl benzene (durene). The infrared spectra of these same molecules are also reported in the region of the combination bands involving C-H (or C-D) stretches and low-frequency modes. The results support the applicability of the model of Harris, et. al., based on energy exchange in anharmonically coupled low-frequency modes. This theory is then used, in connection with Raman spectra obtained in isotopically mixed samples of durene, to elucidate the vibrational dynamics underlying the dephasing. It is found that the results are consistent with the hypothesis that some low-frequency modes in this molecule are significantly delocalized or 'excitonic' in character, and that this delocalization may be studied by means of a Raman spectroscopy on the low-frequency modes themselves, as well as by exchange analysis of the coupled high-frequency modes. These conclusions represent a generalization and extension of the previously published exchange model.
Date: April 1, 1980
Creator: Marks, S.; Cornelius, P. A. & Harris, C.B.
Partner: UNT Libraries Government Documents Department

Optical Properties of Molecules Chemisorbed on the Ni(111) Surface

Description: The adsorption of a variety of molecules on Ni(111) is studied UV/visible spectroscopic ellipsometry. The spectra were analyzed within a simple dielectric model. The absorption spectra of annealed, thin, condensed layers of pyrazine, pyridine, and naphthalene on the Ni(111) surface resemble bulk crystal spectra, indicating minimal perturbations due to the metal substrate. Chemisorption of molecules on the Ni(111) surface produced enhanced absorption between 2800{Angstrom} and 3100{Angstrom}. The wide range of adsorbate properties and surface chemistry suggest a modification of the optical response of the metal upon chemisorption. This enhanced optical absorption is attributed to nonvertical interband transitions made possible by loss of translational invariance at the surface.
Date: February 1, 1981
Creator: Harris, C. B.; Robota, H. J. & Whitmore, P. M.
Partner: UNT Libraries Government Documents Department

Optical Properties of Molecules Chemisorbed on the Ni(111) Surface

Description: The adsorption of a series of molecules on Ni(111) is studied by UV/visible spectroscopic ellipsometry. The spectra were analyzed within a simple dielectric model. Chemisorption of molecules on the Ni(111) surface produces a peak in the overlayer optical response at 4.2 eV. This absorption peak is attributed to the selective enhancement of bulk interband excitations resulting from perturbations of the metal orbitals upon chemisorption.
Date: August 1, 1981
Creator: Robota, H. J.; Whitmore, P. M. & Harris, C. B.
Partner: UNT Libraries Government Documents Department

LSi-11 Microcomputer-Based Data Acquisition System for an Optical Multichannel Analyzer

Description: A microcornputer based operating system for programming and data acquisition from a two a dimensional target optical multichannel analyzer used for high-speed UV/visible spectroscopy is described. The hardware and software interfacing requirements for such a system to provide dedicated real time data acquisition is considered. It is found that a relatively simple parallel interface to an inexpensive microcomputer can be properly configured to perform adequately for high-speed image processing.
Date: April 1, 1980
Creator: Chao, J. L. & Harris, C. B.
Partner: UNT Libraries Government Documents Department

The systems prioritization method (SPM) CD-ROM demonstration for Waste Management `96

Description: In March 1994, the Department of Energy Carlsbad Area Office (DOE/CAO) implemented a performance-based planning method to assist in prioritization within the Waste Isolation Pilot Plant (WIPP). Probabilistic performance calculations were required for the Systems Prioritization Method (SPM) and roughly 46,700 combinations of activities were analyzed, generating a large volume of information to be documented, analyzed, and communicated. A self-contained information management system consisting of a relational database on a 600-megabyte CD-ROM was built to meet this need. The CD-ROM was used to store performance assessment results, data analysis and visualization tools, information about the activities, electronic copies of 40 ILFR 191 and 40 CFR 268, technical reference papers, and the final SPM report. Copies of the CD-ROM were distributed to interested members of the public, WIPP participants, and the Environmental Protection Agency (EPA).
Date: March 1, 1996
Creator: Harris, C.L.; Boak, D.M.; Prindle, N.H. & Beyeler, W.
Partner: UNT Libraries Government Documents Department

Separation of rapidly and slowly varying intermolecular forces in liquids using the temperature dependence of coherent picosecond Stokes scattering

Description: The temperature dependence of attractive and repulsive force contributions to vibrational line broadening are studied in liquid acetonitrile by using Coherent Picosecond Stokes scattering.
Date: February 1, 1982
Creator: Harris, C.B.; George, S.M.; Harris, A.L. & Berg, M.
Partner: UNT Libraries Government Documents Department

Cascade effects on the polarization of He-like Fe 1s 2l - 1s2 X-ray line emission

Description: We calculate X-ray line polarization degrees for cases with axial symmetry using a collisional-radiative magnetic-sublevel atomic kinetics model and the properties of multipole radiation fields. This approach is well-suited for problems where the alignment is determined by the competition between many atomic processes. We benchmark this method against polarization measurements performed at the Livermore electron beam ion trap, and we study the 3-to-2 cascade effects on the polarization of 2-to-1 lines in He-like Fe.
Date: December 21, 2006
Creator: Hakel, P; Mancini, R; Harris, C; Neill, P; Beiersdorfer, P; Csanak, G et al.
Partner: UNT Libraries Government Documents Department

Ohmic Contacts to n-type GaSb and n-type GaInAsSb

Description: An investigation with the objective of improving n-type ohmic contacts to GaSb-based devices is described. This study involves a series of n-GaInAsSb and n-GaSb samples with varying doping, grown on both n-GaSb and semi-insulating GaAs substrates. These samples were fabricated into mesa-etched TLM structures, and the specific contact resistivity and sheet resistance of these layers as a function of majority electron concentration were measured. Extremely low specific contact resistivities of about 2 x 10{sup -6} {Omega}-cm{sup 2} and sheet resistances of about 4 {Omega}/{open_square} are found for n-type GaInAsSb doped at about 3 x 10{sup 18} cm{sup -3}.
Date: June 16, 2003
Creator: Huang, R.K.; Wang, C.A.; Harris, C.T.; Connors, M.K. & Shiau, D.A.
Partner: UNT Libraries Government Documents Department

Organometallic Vapor Phase Epitaxy of n-GaSb and n-GaInAsSb for Low Resistance Ohmic Contacts

Description: A comparison of n-GaSb and n-GaInAsSb epilayers for ohmic contacts in GaSb-based devices is studied. The epilayers were grown by organometallic vapor phase epitaxy and doped with Te. At similar electron concentrations, the atomic Te concentration, as determined by secondary ion mass spectroscopy, is more than 2 times higher in n-GaSb compared to n-GaInAsSb. In addition, the electron mobility is lower in n-GaSb than n-GaInAsSb at similar electron concentrations. The electron concentration saturates at about 1.3 x 10{sup 18} cm{sup -3} for n-GaSb, but linearly increases for n-GaInAsSb. Pd/Ge/Au/Pt/Au metallization was studied for ohmic contacts. A specific contact resistivity of 1 x 10{sup -5}{Omega}-cm{sup 2} for n-GaSb was measured. The specific contact resistivity can be greatly improved by contacting n-GaInAsSb, and a significantly lower specific contact resistivity of 2 x 10{sup -6} {Omega}-cm{sup 2} for n-GaInAsSb was measured.
Date: July 10, 2003
Creator: Wang, C.A.; Shiau, D.A.; Huang, R.K.; Harris, C.T. & Connors, M.K.
Partner: UNT Libraries Government Documents Department

On the Significance of the Contribution of Multiple-Electron Capture Processes to Cometary X-Ray Emission

Description: We report laboratory studies of the role played by multiple-electron capture (MEC) in solar wind induced cometary X-ray emission. Collisions of Ne{sup 10+} with He, Ne, Ar, CO, and CO{sub 2} have been investigated by means of the traditional singles X-ray spectroscopy in addition to the triple-coincidence measurements of X-rays, scattered projectile, and target recoil ions for the atomic targets. The coincidence measurements enable the reduction of the singles X-ray spectra into partial spectra originating in single-electron capture (SEC) and MEC collisions. The measurements provide unequivocal evidence for a significant role played by MEC, and strongly suggest that models based solely on SEC are bound to yield erroneous conclusions on the solar wind composition and velocities and on cometary atmospheres. The experimental relative importance of MEC collisions is compared with molecular classical-over-the-barrier model (MCBM), classical trajectory Monte Carlo (CTMC), and multi-channel Landau-Zener (MCLZ), calculations which can qualitatively reproduce the experimental trends.
Date: May 12, 2005
Creator: Ali, R; Neill, P A; Beiersdorfer, P; Harris, C L; Rakovi?, M J; Wang, J G et al.
Partner: UNT Libraries Government Documents Department

Spectral Catalogue of Kr Optical Lines for the Development of Diagnostics for Fusion Plasmas

Description: We made an inventory of krypton spectra over the wavelength range 3700-6000 {angstrom} for the development of fusion plasma diagnostics. The measurements were performed using a Steinheil prism spectrometer on the LLNL low energy electron beam ion trap (EBIT II). With the electron energy from 150 eV to 17000 eV, we recorded low ionization stages together with a number of magnetic dipole transitions from higher charge states. In total, we observed over 80 lines, of which about 70% of the lines have not been listed in the literature. This measurement established a baseline for future extension using spectrometers with very high resolution. As an example, we present the Kr spectra from 3770 {angstrom} to 3900 {angstrom} measured with a transmission grating spectrometer that has a resolving power of about 15000. Among the 41 lines observed, only 6 lines have been listed in the databases.
Date: June 14, 2000
Creator: Hui, C.; Beiersdorfer, P.; Harris, C.L.; Utter, S.B. & Wong, K.L.
Partner: UNT Libraries Government Documents Department

Energy dissipation in chemical reactions on ultrafast timescales

Description: A series of picosecond experiments and computer simulations will be presented that test collisional and hydrodynamic models for vibrational relaxation in liquids. The relationships between isolated binary collision models (IBC) and stochastic dynamics will be presented. The appropriateness of IBC theory in describing vibrational relaxation in liquids will also be discussed.
Date: October 1, 1990
Creator: Russell, D. J.; Paige, M. E. & Harris, C. B.
Partner: UNT Libraries Government Documents Department

Development of a coal-fired gas turbine cogeneration system: Status report

Description: The Allison Advanced Coal-Fueled Turbine Program is now in the sixth year of a development effort that has led to a POC engine demonstration test on a Coal-Water-Slurry (CWS) fuel. Earlier forecasts by CWS suppliers that suitable CWS fuels would be commercially available at an economic price have not been realized. A program replan has, therefore, been executed that incorporates the use of readily available dry pulverized coal. To support this program, technology issues relating to combustor performance and emission control, hot gas cleanup, and turbine deposition, erosion and corrosion (DEC) have been addressed. In addition, system assessment studies have been performed to evaluate the commercial prospects for small (<8 MWe) coal-fired industrial cogeneration systems and the application of the rich-quench-lean (RQL) coal-combustion technology to larger (> 100 MWe) utility-sized gas turbines. These results are reported by Wenglarz (1992). Combustor and engine tests on dry coal are now planned in preparation for a commercial demonstration that will follow the completion of this program.
Date: January 1, 1992
Creator: Wilkes, C.; Wenglarz, R.A.; Hart, P.J.; Thomas, W.H.; Rothrock, J.W.; Harris, C.N. et al.
Partner: UNT Libraries Government Documents Department

Development of a coal-fired gas turbine cogeneration system: Status report

Description: The Allison Advanced Coal-Fueled Turbine Program is now in the sixth year of a development effort that has led to a POC engine demonstration test on a Coal-Water-Slurry (CWS) fuel. Earlier forecasts by CWS suppliers that suitable CWS fuels would be commercially available at an economic price have not been realized. A program replan has, therefore, been executed that incorporates the use of readily available dry pulverized coal. To support this program, technology issues relating to combustor performance and emission control, hot gas cleanup, and turbine deposition, erosion and corrosion (DEC) have been addressed. In addition, system assessment studies have been performed to evaluate the commercial prospects for small (<8 MWe) coal-fired industrial cogeneration systems and the application of the rich-quench-lean (RQL) coal-combustion technology to larger (> 100 MWe) utility-sized gas turbines. These results are reported by Wenglarz (1992). Combustor and engine tests on dry coal are now planned in preparation for a commercial demonstration that will follow the completion of this program.
Date: December 1, 1992
Creator: Wilkes, C.; Wenglarz, R. A.; Hart, P. J.; Thomas, W. H.; Rothrock, J. W.; Harris, C. N. et al.
Partner: UNT Libraries Government Documents Department

Two-photon photoemission and the dynamics of electrons at interfaces

Description: A new instrument for angle-resolved two-photon photoemission with exceptional sensitivity and energy resolution has allowed a detailed examination of the interaction of image-state electrons with adsorbates. In addition to measuring the electrostatic properties of molecular-thickness films, the technique serves as a probe of adsorbate growth modes, and provides new opportunities to explore the dynamics of electrons in well-controlled two-dimensional systems.
Date: January 1, 1994
Creator: Padowitz, D. F.; Harris, C. B.; Jordan, R. E.; Lingle, R. L. Jr.; McNeill, J. D. & Merry, W. R.
Partner: UNT Libraries Government Documents Department