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D{O} results on searches for the top quark

Description: We have performed a search for creation of the top quark in p{bar p} collisions at {radical}s = 1.8 GeV at Tevatron, Fermilab. t{bar t} production followed by top decay to W + b quark is assumed. We have searched for the decay channels with both W`s decaying leptonically, and with one W decay to an electron and the other to quarks. A preliminary report on the status of one interesting event is presented. By combining the results from the ee and e{mu} channels a lower top mass limit of 99 GeV on the 95% confidence level is obtained.
Date: September 1, 1993
Creator: Abachi, S.
Partner: UNT Libraries Government Documents Department

Analysis of neon soft x-ray spectra from short-pulse laser-produced plasmas

Description: We report preliminary results from the analysis of streaked soft x-ray neon spectra obtained from the interaction of a picosecond Nd:glass laser with a gas jet target. In these experiments streaked spectra show prompt harmonic emission followed by longer time duration soft x-ray line emission. The majority of the line emission observed was found to originate from Li- and Be-like Ne and the major transitions in the observed spectra have been identified. Li-like emission lines were observed to decay faster in time than Be-like transitions, suggesting that recombination is taking place. Line ratios of n=4-2 and n=3-2 transitions supported the view that these lines were optically thin and thick, respectively. The time history of Li-like Ne 2p-4d and 2p-3d lines is in good agreement with a simple adiabatic expansion model coupled to a time dependent collisional-radiative code. Further x-ray spectroscopic analysis is underway which is aimed at diagnosing plasma conditions and assessing the potential of this recombining neon plasma as a quasi-steady-state recombination x-ray laser medium.
Date: April 1, 1993
Creator: Abare, A. C.; Keane, C. J.; Crane, J. K.; DaSilva, L. B.; Lee, R. W.; Perry, M. D. et al.
Partner: UNT Libraries Government Documents Department

Comparison of a constraint directed search to a genetic algorithm in a scheduling application

Description: Scheduling plutonium containers for blending is a time-intensive operation. Several constraints must be taken into account; including the number of containers in a dissolver run, the size of each dissolver run, and the size and target purity of the blended mixture formed from these runs. Two types of algorithms have been used to solve this problem: a constraint directed search and a genetic algorithm. This paper discusses the implementation of these two different approaches to the problem and the strengths and weaknesses of each algorithm.
Date: April 1, 1993
Creator: Abbott, L.
Partner: UNT Libraries Government Documents Department

Multiphoton physics with x-rays: Two photon K-shell ionization of chlorine

Description: A calculation of the two X-ray K-shell photoionization cross section of chlorine will be presented and the feasibility of an experiment will be discussed.
Date: April 1, 1993
Creator: Abdallah, J.; Collins, L. A.; Csanak, G.; Kyrala, G. A. & Schappert, G. T.
Partner: UNT Libraries Government Documents Department

Multiphoton physics with x-rays: Two photon K-shell ionization of chlorine

Description: A calculation of the two X-ray K-shell photoionization cross section of chlorine will be presented and the feasibility of an experiment will be discussed.
Date: January 1, 1993
Creator: Abdallah, J.; Collins, L. A.; Csanak, G.; Kyrala, G. A. & Schappert, G. T.
Partner: UNT Libraries Government Documents Department

Superconducting magnet design for Fixed-Field Alternating-Gradient (FFAG) accelerator

Description: The FFAG accelerator requires static fields that increase with radius along the accelerator midplane according to B = B{sub 0} (R/R{sub 0}){sup 13.4}. The field is generated by equally spaced magnets around the circumference and varies from a maximum of 4.1 T to a minimum of {minus}1.9 T. The general coil design employs cryostable magnets wound with aluminum stabilized superconductor. Each magnet has resistive pole face windings outside of the cryostat to allow for field fine tuning after construction. A set of iron-free coil windings generate the required field distribution.
Date: November 1, 1993
Creator: Abdelsalam, M. & Kustom, R.
Partner: UNT Libraries Government Documents Department

Results from the SLD barrel CRID detector

Description: We report on operational experience with and experimental performance of the SLD barrel Cherenkov Ring Imaging Detector from the 1992 and 1993 physics runs. The liquid (C{sub 6}F{sub 14}) and gas (C{sub 5}F{sub 12}) radiator recirculation systems have performed well, and the drift gas supply system has operated successfully with TMAE for three years. Cherenkov rings have been observed from both the liquid and gas radiators. The number and angular resolution of Cherenkov photons have been measured, and found to be close to design specifications.
Date: November 1, 1993
Creator: Abe, K.; Antilogus, P. & Aston, D.
Partner: UNT Libraries Government Documents Department

Scintillating glass fiber neutron sensors: 1, Production and optical characterization

Description: The production and optical characterization of cerium-doped lithium silicate scintillating fibers used as thermal neutron detectors are discussed. The bulk glass continuing enriched {sup 6}Li is produced starting from high-purity commercial materials which are further purified at Pacific Northwest Laboratory (PNL). The fibers are drawn at PNL in a hot down-draw process. The fibers are coated with a silicone polymer that serves as both an optical cladding and a physical buffer coat. Optical characterization has included measurements of light output as a function of glass composition, optical attenuation lengths, and fluorescence lifetimes. Fibers have been prepared in our laboratory with as-drawn attenuation lengths (l/e distance) in excess of 2 meters over sub-meter distances.
Date: October 1, 1993
Creator: Abel, K. H.; Arthur, R. J. & Bliss, M.
Partner: UNT Libraries Government Documents Department

Scintillating glass fiber neutron sensors: 2, Light transmission in scintillating fibers

Description: The capture and transmission of light from an event through a scintillating fiber is somewhat different than in conventional optical waveguide applications. A theoretical all-ray model that depends on surface and bulk loss factors is developed for this transmission. The capture fraction can be significantly greater than that predicted on the basis of meridional rays alone and the gross loss is nonexponential for short distances (less than or of the order of one 1/e distance). The latter phenomenon occurs because high-angle and skew rays are more rapidly attenuated than meridional rays.
Date: October 1, 1993
Creator: Abel, K. H.; Arthur, R. J. & Bliss, M.
Partner: UNT Libraries Government Documents Department

Scintillating glass fiber neutron sensors: 3, Photon economy in scintillating fibers

Description: In an optical detector such as those constructed from scintillating glass fibers, the photons represent information. This study of the flow of information in a system of devices using PNL glass fibers was undertaken in order to resolve the conflict between expected and observed peak heights. This work concentrates on the number of photons produced and the fraction of photons trapped. It is found that the number of photons produced in bulk samples of the standard glass is about one-third that expected, based on published values; there is evidence that, in fiberized glass, this may be as small as one-fifth the expected value. Additionally, the fraction of trapped photons is found to be about three-fourths that expected because the glass has a smaller refractive index and the cladding a larger refractive index than published values in the spectral region of importance. These factors, taken together, are sufficient to resolve the conflict between the expected and observed peak heights. This analysis provides guidance for those who would use published materials properties to fabricate detectors in a new geometry where the materials properties may have been changed by the fabrication process.
Date: October 1, 1993
Creator: Abel, K. H.; Arthur, R. J. & Bliss, M.
Partner: UNT Libraries Government Documents Department

Development of an electrochemical hydrogen separator

Description: The EHS is an electrochemical hydrogen separator based on the uniquely reversible nature of hydrogen oxidation-reduction reactions in electrochemical systems. The principle and the hardware concept are shown in Figure 1. Hydrogen from the mixed gas stream is oxidized to H{sup +} ions, transported through a cation transport electrolyte membrane (matrix) under an applied electric field and discharged in a pure hydrogen state on the cathode. The cation transfer electrolyte membrane provides a barrier between the feed and product gases. The EHS design is an offshoot of phosphoric acid fuel cell development. Although any proton transfer electrolyte can be used, the phosphoric acid based system offers a unique advantage because its operating temperature of {approximately}200{degree}C makes it tolerant to trace CO and also closely matches the water-shift reactor exit gas temperature ({approximately}250{degree}C). Hydrogen-containing streams in coal gasification systems have large carbon monoxide contents. For efficient hydrogen recovery, most of the CO must be converted to hydrogen by the low temperature water-shift reaction (Figure 2). Advanced coal gasification and gas separation technologies offer an important pathway to the clean utilization of coal resources.
Date: September 1, 1993
Creator: Abens, S.; Fruchtman, J. & Kush, A.
Partner: UNT Libraries Government Documents Department

Thermal phase behavior of metal surfaces: X-ray scattering studies of Pt(001)

Description: Recent highlights of the results of x-ray scattering studies of the structure and phase behavior of smooth and vicinal Pt(001) surfaces are reviewed.
Date: November 1, 1993
Creator: Abernathy, D. L.; Mochrie, S. G. J.; Yoon, M.; Gibbs, D.; Gruebel, G.; Watson, G. M. et al.
Partner: UNT Libraries Government Documents Department

Non-local transport in a tokamak plasma divertor with recycling

Description: The plasma transport, particle and energy fluxes, near the diverter plate with high recycling has been modeled by using an electron kinetic code (Fokker-Planck International) in conjunction with a two-fluid ambipolar code. We include the effects of ionization and excitation of the hydrogen atoms. The electron energy distribution calculated from the kinetic code shows a large deviation from Maxwellian especially near the plate. This deviation from Maxwellian is due to the non-local transport of the suprathermal electrons from the SOL, and due also to the absorption of the fast electrons by the target plate. The heat flux near the plate is shown to be nonlocal, in that it is not determined uniquely by the local plasma parameters. Therefore the classical transport coefficients in the fluid model must be modified by including a nonlocal effect to produce the kinetic results. The kinetic calculation is compared with those of the fluid code with different values of the electron heat flux limiter factor (f). To reduce the computer load, the initial condition we used corresponds to the equilibrium solution already found with the fluid code with f=0.2. The fluid and Fokker-Planck codes are relaxed until all transients associated with electron dynamics have disappeared. In section 2, we present the kinetic code. The fluid code is presented in section 3. The boundary conditions used in these simulations are given in section 4. Finally the results and conclusion of these simulations are presented in section 5.
Date: October 1, 1993
Creator: Abou-Assaleh, Z.; Petravic, M.; Vesey, R.; Matte, J. P. & Johnston, T. W.
Partner: UNT Libraries Government Documents Department

Thermal and flow considerations for the 80 K shield of the SSC magnet cryostats

Description: The nominal temperatures in the SSC cryostat range between 4.2 K in the superconducting magnet and 300 K on the cryostat outer wall. To minimize the 4 K heat load, a thermal shield cooled by liquid and vapor nitrogen flows at 84 K and one a 20 K cooled by helium flow are incorporated in the cryostat. Tubes attached to the shields serve as conduits for cryogens. The liquid nitrogen tube in the cryostat is used for cryostat refrigeration and also for liquid distribution around the SSC rings. The second nitrogen line is used to return the vapor to the helium refrigerators for further processing. The nominal GN2 flow from a 4.3-km long cryogenic string (4 sections) to the surface is 64 g/s. The total liquid nitrogen consumption of approximately 5000 g/s will be supplied at one, two or more locations on the surface. The total heat load of the 80 K shield is estimated as 3.2 W/m. About 50% is composed of infrared radiation and remaining 50% by heat conduction through supports, vacuum barriers and other thermal connections between the shield and the 300 K outer wall. The required LN2 flow rate depends on the distribution and circulation schemes. The LN2 temperature will in turn vary depending on the flow rate and on the recooling methods used. For example, with a massflow of 400 g/s of LN2 the temperature rises from 82 K to 86 K between two compact recoolers 1 km apart. This temperature is higher thin desired. The temperature can be reduced by increasing the flow rate of the liquid or by using the continuous recooling. This paper discusses some thermal problems caused by certain mechanical designs of the 80 K shielding the possible improvement by using continuous recooling. In the following, we present results of the ...
Date: April 1993
Creator: Abramovich, S.; Yuecel, A.; Demko, J. & Thirumaleshwar, M.
Partner: UNT Libraries Government Documents Department

Multidimensional solitons in fiber arrays

Description: We demonstrate that nonlinear optical fiber arrays can support stable soliton-like pulses with finite energy. The bound state that we have found is localized both in time and in a spatial domain in the direction perpendicular to the pulse propagation. We have proved the boundedness of the Hamiltonian function for the array. Finally, numerical studies support our analytical conclusions.
Date: August 16, 1993
Creator: Aceves, A. B.; De Angelis, C.; Rubenchik, A. M. & Turitsyn, S. K.
Partner: UNT Libraries Government Documents Department

New high-level waste management technology for IFR pyroprocessing wastes

Description: The pyrochemical electrorefining process for recovery of actinides in spent fuel from the Integral Fast Reactor accumulates fission product wastes as chlorides dissolved in molten LiCI-KCI and as metals, some of which are in molten cadmium. Pyrochemical processes are being developed to recover uranium and transuranium elements for return to the reactor, and to separate and immobilize fission products in suitable waste forms. Solvent cadmium is recycled within the process. Electrolyte salt is treated in a series of salt/cadmium extraction steps; it is also returned to the process. Salt-borne fission products are concentrated on a zeolite bed that is converted to a stable, leach-resistant mineral. Rare earth fission products from the salt, noble metal fission products, and cladding hulls are dispersed in a metal matrix.
Date: September 1, 1993
Creator: Ackerman, J. P. & Johnson, T. R.
Partner: UNT Libraries Government Documents Department

Partition of actinides and fission products between metal and molten salt phases: Theory, measurement, and application to IFR pyroprocess development

Description: The chemical basis of Integral Fast Reactor fuel reprocessing (pyroprocessing) is partition of fuel, cladding, and fission product elements between molten LiCl-KCl and either a solid metal phase or a liquid cadmium phase. The partition reactions are described herein, and the thermodynamic basis for predicting distributions of actinides and fission products in the pyroprocess is discussed. The critical role of metal-phase activity coefficients, especially those of rare earth and the transuranic elements, is described. Measured separation factors, which are analogous to equilibrium constants but which involve concentrations rather than activities, are presented. The uses of thermodynamic calculations in process development are described, as are computer codes developed for calculating material flows and phase compositions in pyroprocessing.
Date: October 1, 1993
Creator: Ackerman, J. P. & Johnson, T. R.
Partner: UNT Libraries Government Documents Department

Thermodynamic Properties of Organic Compounds. 3. Sublimation Enthalpy and Heat Capacities of 2,4,6-Trimethylbenzonitrile N-oxide

Description: Article discussing thermodynamic properties of organic compounds and sublimation enthalpy and heat capacities of 2,4,6-trimethylbenzonitrile N-oxide.
Date: January 1993
Creator: Acree, William E. (William Eugene); Sevruk, Viktor M.; Kozyro, Alexander A.; Krasulin, Alexander P.; Kabo, Gennady J. & Frenkel, Michael L.
Partner: UNT College of Arts and Sciences

Spectrochemical Investigations of Preferential Solvation. Fluorescence Emission Behavior of Select Polycyclic Aromatic Hydrocarbon Solute Probes Dissolved in Mixed Solvents

Description: Article discussing spectrochemical investigations of preferential solvation and fluorescence emission behavior of select polycyclic aromatic hydrocarbon solute probes dissolved in mixed solvents.
Date: October 1993
Creator: Acree, William E. (William Eugene); Tucker, Sheryl A. (Sheryl Ann) & Wilkins, Denise C.
Partner: UNT College of Arts and Sciences

The design and construction of a double-sided Silicon Microvertex Detector for the L3 experiment at CERN

Description: A Silicon Microvertex Detector (SMD) has been commissioned for the L3 experiment at the Large Electron-Positron colliding-beam accelerator (LEP) at the European Center for Nuclear Physics, (CERN). The SMD is a 72,672 channel, two layer barrel tracker that is comprised of 96 ac-coupled, double-sided silicon detectors. Details of the design and construction are presented.
Date: December 1, 1993
Creator: Adam, A.; Ahlen, S.; Marin, A.; Zhou, B.; Ambrosi, G.; Babucci, E. et al.
Partner: UNT Libraries Government Documents Department

Orientation Imaging Microscopy: New possibilities for microstructural investigations using automated BKD analysis

Description: A new microscopy, called Orientation Imaging Microscopy, is described. Imaging results from precise measurements of local lattice orientation rapidly obtained by Backscattered Kikuchi Diffraction. The hardware configuration of the microscope is described and a description of image formation presented. Applications to several materials of differing lattice structure are described. Connections of the microscopy with various aspects of modern texture analysis are emphasized.
Date: October 1, 1993
Creator: Adams, Brent L.; Kunze, Karsten; Dingley, David J. & Wright, Stuart I.
Partner: UNT Libraries Government Documents Department