The ternary semiconductor GaAs{sub 1{minus}x}N{sub x} with 0 < x < 0.3 can be grown epitaxially on GaAs and has a very large bowing coefficient. The alloy bandgap can be reduced to about 1.0 eV with about a 3% nitrogen addition. In this work, the authors measured the internal spectral response and recombination lifetime of a number of alloys using the ultra-high frequency photoconductive decay (UHFPCD) method. The data shows that the photoconductive excitation spectra of the GaAs{sub 0.97}N{sub 0.03} alloy shows a gradual increase in response through the absorption edge near E{sub g}. This contrasts with most direct bandgap semiconductors that show a steep onset of photoresponse at E{sub g}. The recombination lifetimes frequently are much longer than expected from radiative recombination and often exceeded 1.0{mu}s. The data were analyzed in terms of a band model that includes large potential fluctuations in the conduction band due to the random distribution of nitrogen atoms in the alloy.

Transversely polarized {Lambda} production in hard scattering processes is discussed in terms of a leading twist T-odd fragmentation function which describes the fragmentation of an unpolarized quark into a transversely polarized {Lambda}. We focus on the properties of this function and its relevance for the RHIC and HERMES experiments.

The following topics related to the treatment of cuttings, cavings and spallings releases to the surface environment in the 1996 performance assessment for the Waste Isolation Pilot Plant (WIPP) are presented: (1) mathematical description of models. (2) uncertainty and sensitivity analysis results arising from subjective (i.e., epistemic) uncertainty for individual releases, (3) construction of complementary cumulative distribution functions (CCDFs) arising from stochastic (i.e., aleatory) uncertainty, and (4) uncertainty and sensitivity analysis results for CCDFs. The presented results indicate that direct releases due to cuttings, cavings and spallings do not constitute a serious threat to the effectiveness of the WIPP as a disposal facility for transuranic waste. Even when the effects of uncertain analysis inputs are taken into account, the CCDFs for cuttings, cavings and spallings releases fall substantially to the left of the boundary line specified in the US Environmental Protection Agency standard for the geologic disposal of radioactive waste (40 CFR 191, 40 CFR 194).

The authors have fabricated high-efficiency thin-film CuIn{sub 1{minus}x}Ga{sub x}Se{sub 2} (CIGS)-based photovoltaic devices from solution-based electroplated (EP) and auto-plated (AP) precursors. As-deposited precursors are Cu-rich CIGS. Compositions were adjusted to CuIn{sub 1{minus}x}Ga{sub x}Se{sub 2} with additional In and Ga by physical vapor deposition (PVD) to the EP and AP precursor films. Auger analysis and grazing incident X-ray diffraction (GIXRD) were performed on devices prepared from EP and AP precursor films. The authors have also analyzed and compared EP, AP, and an PVD CIGS device by deep-level transient spectroscopy (DLTS).

Laser deposits fabricated from two different compositions of 304L stainless steel powder were characterized to determine the nature of the solidification and solid state transformations. One of the goals of this work was to determine to what extent novel microstructure consisting of single-phase austenite could be achieved with the thermal conditions of the LENS [Laser Engineered Net Shape] process. Although ferrite-free deposits were not obtained, structures with very low ferrite content were achieved. It appeared that, with slight changes in alloy composition, this goal could be met via two different solidification and transformation mechanisms.

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The Sustained Spheromak Physics Experiment (SSPX) will examine the confinement properties of spheromak plasmas sustained by DC helicity injection. Understanding the plasma-surface interactions is an important component of the experimental program since the spheromak plasma is in close contact with a stabilizing wall (flux conserver) and is maintained by a high-current discharge in the coaxial injector region. Peak electron temperatures in the range of 400 eV are expected, so the copper plasma facing surfaces in SSPX have been coated with tungsten to minimize sputtering and plasma contamination. Here the authors report on the characterization and conditioning of these surfaces used for the initial studies of spheromak formation in SSPX. The high-pressure plasma-sprayed tungsten facing the SSPX plasma was characterized in-situ using beta-backscattering and ex-situ using laboratory measurements on similarly prepared samples. Measurements indicate that water can be desorbed effectively through baking while hydrocarbon/oxide removal using glow discharge and shot conditioning is slow due to the coating's high porosity.

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At the WRAP facility, there are two identical imaging passive/active neutron (IPAN) assay systems and two identical gamma energy assay (GEA) systems. Currently, only the GEA systems are used to characterize waste, therefore, only the GEA systems are addressed in this document. This document contains the limiting factors relating to the waste drum analysis for shipments destined for WIPP. The TMU document provides the uncertainty basis in the NDA analysis of waste containers at the WRAP facility. The defined limitations for the current analysis scheme are as follows: The WRAP waste stream debris is from the Hanford Plutonium Finishing Plant's process lines, primarily combustible materials. Plutonium analysis range is from the minimum detectable concentration (MDC), Reference 6, to 160 grams (8). The GEA system calibration density ranges from 0.013 g/cc to 1.6 g/cc. PDP Plutonium drum densities were evaluated from 0.065 g/cc to 0.305 gkc. PDP Plutonium source weights ranged from 0.030 g to 3 18 g, in both empty and combustibles matrix drums. The GEA system design density correction macroscopic absorption cross section table (MAC) is Lucite, a material representative of combustible waste. Drums with material not fitting the debris waste criteria are targeted for additional calculations, reviews, and …

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The disordered vortex phases induced by line and point pinning in YBa{sub 2}Cu{sub 3}O{sub x} are explored. At high defect densities there is a single disordered solid separated from the liquid phase by a melting line. At low defect densities the topology of the phase diagram changes dramatically, with a vortex lattice phase adjoining disordered phases at high or low field. Critical points at the termination of first order melting separate the lattice and disordered phases. The line defect disordered phases follow the expected Bose glass behavior, while the point defect disordered phases do not exhibit the expected vortex glass behavior.

Most algorithms used in preconditioned iterative methods are generally applicable to complex valued linear systems, with real valued linear systems simply being a special case. However, most iterative solver packages available today focus exclusively on real valued systems, or deal with complex valued systems as an afterthought. One obvious approach to addressing this problem is to recast the complex problem into one of a several equivalent real forms and then use a real valued solver to solve the related system. However, well-known theoretical results showing unfavorable spectral properties for the equivalent real forms have diminished enthusiasm for this approach. At the same time, experience has shown that there are situations where using an equivalent real form can be very effective. In this paper, the authors explore this approach, giving both theoretical and experimental evidence that an equivalent real form can be useful for a number of practical situations. Furthermore, they show that by making good use of some of the advance features of modem solver packages, they can easily generate equivalent real form preconditioners that are computationally efficient and mathematically identical to their complex counterparts. Using their techniques, they are able to solve very ill-conditioned complex valued linear systems for …

Enormous progress has been made in recent years on a number of photovoltaic (PV) materials and devices in terms of conversion efficiencies. Ultrahigh-efficiency (>30{percent}) PV cells have been fabricated from gallium arsenide (GaAs) and its ternary alloys such as gallium indium phosphide (GaInP{sub 2}). The high-efficiency GaAs-based solar cells are being produced on a commercial scale, particularly for space applications. Efficiencies in the range of 18{percent} to 24{percent} have been achieved in traditional silicon-based devices fabricated from both multicrystalline and single-crystal materials. Major advances in efficiency have also been made on various thin-film solar cells based on amorphous silicon (aSi:H), copper gallium indium diselenide (CIGS), and cadmium telluride materials. This paper gives a brief overview of the recent progress in PV cell efficiencies based on these materials and devices.

The average {sup 235}U neutron total cross sections were obtained in the energy range 2 keV to 330 keV from high-resolution transmission measurements of a 0.033 atom/b sample. The experimental data were corrected for the contribution of isotope impurities and for resonance self-shielding effects in the sample. The results are in very good agreement with the experimental data of Poenitz et al. in the energy range 40 keV to 330 keV and are the only available accurate experimental data in the energy range 2 keV to 40 keV. ENDF/B-VI evaluated data are 1.7% larger. The SAMMY/FITACS code was used for a statistical model analysis of the total cross section, selected fission cross sections and {alpha} data in the energy range 2 keV to 200 keV. SAMMY/FITACS is an extended version of SAMMY which allows consistent analysis of the experimental data in the resolved and unresolved resonance region. The Reich-Moore resonance parameters were obtained from a SAMMY Bayesian fits of high resolution experimental neutron transmission and partial cross section data below 2.25 keV, and the corresponding average parameters and covariance data were used in the present work as input for the statistical model analysis of the high energy range of the …

This section reviews extensions and variations of the direct-semidirect (DSD) model for understanding the high-energy component of gamma spectra resulting from radiative capture of fast nucleons; i.e., the part of the spectrum that is not amenable to standard statistical model (Hauser-Feshbach) treatments. We describe recent results on the extension of the DSD model to unbound final states, including comparison with proton and neutron capture data. The importance of including convective-current magnetic radiation to explain proton capture angular distributions in the 30 MeV region is shown. We conclude with a brief discussion of a model closely related to the DSD, the pure-resonance model.

In this section we review the available data on gamma spectra following radiative capture of neutrons above 10 MeV. A few measurements below that energy are included. An important source for references to this topic is the CINDA compilation maintained by the IAEA in cooperation with three other major data centers. An additional useful source is the review article by Weller and Roberson, which treats capture reactions with neutrons, protons, and alpha particles. The following discussion refers only to data that are easily accessible through readily-available journals, reports, or the EXFOR database. Most of the reported measurements were made for the purpose of determining cross sections for discrete states at the high energy end of the gamma spectra which are resolvable or nearly so. In only a few cases have cross sections been measured over a wide range of gamma energies. These measurements are first reviewed below, followed by a review of more detailed measurements such as angular distributions and analyzing powers. Neutron capture on hydrogen isotopes have not been included with the exception of a fairly recent measurement on deuterium; see CINDA for references to this specialized topic.

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The authors present a new shape measure for tetrahedral elements that is optimal in that it gives the distance of a tetrahedron from the set of inverted elements. This measure is constructed from the condition number of the linear transformation between a unit equilateral tetrahedron and any tetrahedron with positive volume. Using this shape measure, they formulate two optimization objective functions that are differentiated by their goal: the first seeks to improve the average quality of the tetrahedral mesh; the second aims to improve the worst-quality element in the mesh. They review the optimization techniques used with each objective function and presents experimental results that demonstrate the effectiveness of the mesh improvement methods. They show that a combined optimization approach that uses both objective functions obtains the best-quality meshes for several complex geometries.

An imaging detector has been developed for the purpose of providing a non-destructive, real time method of determining tritium concentrations on the surface of internal TFTR vacuum vessel components. The detector employs a green phosphor screen (P31, zinc sulfide: copper) with a wave length peak of 530 nm, a charge-coupled device (CCD) camera linked to a computer, and a detection chamber for inserting components recovered from the vacuum vessel. This detector is capable of determining tritium concentrations on the surfaces. The detector provides a method of imaging tritium deposition on the surfaces in a fairly rapid fashion.

An astonishing variety of inorganic networks templated by organic species have been reported over the last 10 years. A great deal of attention has been paid to the structure-directing role of the organic species, and the structural effect of variously coordinated cations, for example distorted octahedral vanadium and pyramidal tin. Less exploratory work has been carried out on the anionic part of the inorganic network, and most groups reported so far (phosphate, germanate, etc.) invariably adopt tetrahedral coordination. The possibilities of incorporating the pyramidal [HP0{sub 3}]{sup 2{minus}} hydrogen phosphite group into extended structures templated by inorganic, alkaline earth cations was explored a few years ago. In this paper the authors report the synthesis, crystal structure, and some properties of (CN{sub 3}H{sub 6}){sub 4}{center_dot}Zn{sub 3}(SeO{sub 3}){sub 5}, the first organically-templated phase to contain the pyramidal selenite [SeO{sub 3}]{sup 2{minus}} anion.

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A perspective on the contemporary application of Dyson-Schwinger equations, focusing on some recent phenomenological applications: a description and unification of light-meson observable using a one-parameter model of the effective quark-quark interaction, and studies of leptonic and nonleptonic nucleon form factors. The theory and phenomenological application of Dyson-Schwinger equations (DSEs) have seen something of a renaissance. For example, they have been applied simultaneously to phenomena as apparently unconnected as low-energy {pi}{pi} scattering, B {r_arrow} D{sup *} decays and the equation of state for a quark gluon plasma, and there are renewed attempts to understand the origin of the infrared enhancement necessary in the kernel of the quark DSE (QCD gap equation) to generate dynamical chiral symmetry breaking (DCSB). Also significant is the appreciation that in this approach current algebra's anomalies remain a feature of the global aspects of DCSB.

Uncertainty and sensitivity analysis results obtained in the 1996 performance assessment (PA) for the Waste Isolation Pilot Plant (WIPP) are presented for two-phase flow in the vicinity of the repository under disturbed conditions resulting from drilling intrusions. Techniques based on Latin hypercube sampling, examination of scatterplots, stepwise regression analysis, partial correlation analysis and rank transformations are used to investigate brine inflow, gas generation repository pressure, brine saturation and brine and gas outflow. Of the variables under study, repository pressure and brine flow from the repository to the Culebra Dolomite are potentially the most important in PA for the WIPP. Subsequent to a drilling intrusion repository pressure was dominated by borehole permeability and generally below the level (i.e., 8 MPa) that could potentially produce spallings and direct brine releases. Brine flow from the repository to the Culebra Dolomite tended to be small or nonexistent with its occurrence and size also dominated by borehole permeability.