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Hydrogen Storage Properties of the Tetrahydrofuran Treated Magnesium

Description: The electronic structure, crystalline feature and morphology of the tetrahydrofuran (THF) treated magnesium, along with its hydriding and dehydriding properties have been investigated. The THF treated magnesium absorbs 6.3 wt per cent hydrogen at 723K and 3.5 MPa. After hydrogenation, in addition to the expected MgH2, a new less-stable hydride phase appears at 673K, but not at a lower temperature. Desorption produces 5.5 wt per cent hydrogen at 723K against a back pressure of 1.3 Pa after 20 cycles of hydriding-dehydriding. The THF treatment improves the kinetics of hydrogen absorption and desorption significantly. From 723K to 623K, the THF treated Mg demonstrates acceptable reaction rates. XPS studies show that tetrahydrofuran treatment causes the electronic energy state of the magnesium surface atoms to change, but the XRD studies show the crystal structure remains unchanged. Metallographic observation of the bulk hydrides of THF treated magnesium reveal they are poly-crystalline wi th the wide-spreading slip bands and twins within the crystals, indicating the phase transformation upon hydriding causes serious stress and distortion. It appears this microstructural deformation explains the much higher energy requirements (higher pressure and temperature) for magnesium hydrogenation than the simple lattice expansion that accompany hydrogen uptake for LaNi5 and FeTi.
Date: May 25, 2004
Creator: AU, MING
Partner: UNT Libraries Government Documents Department

The CDF Run IIb Silicon Detector

Description: Fermilab plans to deliver 5-15 fb{sup -1} of integrated luminosity to the CDF and D0 experiments. The current inner silicon detectors at CDF (SVXIIa and L00) will not tolerate the radiation dose associated with high luminosity running and will need to be replaced. A new readout chip (SVX4) has been designed in radiation-hard 0.25 {micro}m CMOS technology. Single sided sensors are arranged in a compact structure, called a stave, with integrated readout and cooling systems. This paper describes the general design of the Run IIb system, testing results of prototype electrical components (staves), and prototype silicon sensor performance before and after irradiation.
Date: February 25, 2004
Creator: Aoki, M.; Bacchetta, N. & al., S. Behari et
Partner: UNT Libraries Government Documents Department

Large-Actuator-Number Horizontal Path Correction of Atmospheric Turbulence utilizing an Interferometric Phase Conjugate Engine

Description: An adaptive optical system used to correct horizontal beam propagation paths has been demonstrated. This system utilizes an interferometric wave-front sensor and a large-actuator-number MEMS-based spatial light modulator to correct the aberrations incurred by the beam after propagation along the path. Horizontal path correction presents a severe challenge to adaptive optics systems due to the short atmospheric transverse coherence length and the high degree of scintillation incurred by laser propagation along these paths. Unlike wave-front sensors that detect phase gradients, however, the interferometric wave-front sensor measures the wrapped phase directly. Because the system operates with nearly monochromatic light and uses a segmented spatial light modulator, it does not require that the phase be unwrapped to provide a correction and it also does not require a global reconstruction of the wave-front to determine the phase as required by gradient detecting wave-front sensors. As a result, issues with branch points are eliminated. Because the atmospheric probe beam is mixed with a large amplitude reference beam, it can be made to operate in a photon noise limited regime making its performance relatively unaffected by scintillation. The MEMS-based spatial light modulator in the system contains 1024 pixels and is controlled to speeds in excess of 800 Hz, enabling its use for correction of horizontal path beam propagation. In this article results are shown of both atmospheric characterization with the system and open loop horizontal path correction of a 1.53 micron laser by the system. To date Strehl ratios of greater than 0.5 have been achieved.
Date: August 25, 2004
Creator: Baker, K L; Stappaerts, E A; Gavel, D; Tucker, J; Silva, D A; Wilks, S C et al.
Partner: UNT Libraries Government Documents Department

Synthesis of High Surface Area Alumina Aerogels without the Use of Alkoxide Precursors

Description: Alumina aerogels were prepared through the addition of propylene oxide to aqueous or ethanolic solutions of hydrated aluminum salts, AlCl{sub 3} {center_dot} 6H{sub 2}O or Al(NO{sub 3}){sub 3} {center_dot} 9H{sub 2}O, followed by drying with supercritical CO{sub 2}. This technique affords low-density (60-130 kg/m{sup 3}), high surface area (600-700 m{sup 2}/g) alumina aerogel monoliths without the use of alkoxide precursors. The dried alumina aerogels were characterized using elemental analysis, high-resolution transmission electron microscopy, powder X-ray diffraction, solid state NMR, acoustic measurements and nitrogen adsorption/desorption analysis. Powder X-ray diffraction and TEM analysis indicated that the aerogel prepared from hydrated AlCl{sub 3} in water or ethanol possessed microstructures containing highly reticulated networks of pseudoboehmite fibers, 2-5 nm in diameter and of varying lengths, while the aerogels prepared from hydrated Al(NO{sub 3}){sub 3} in ethanol were amorphous with microstructures comprised of interconnected spherical particles with diameters in the 5-15 nm range. The difference in microstructure resulted in each type of aerogel displaying distinct physical and mechanical properties. In particular, the alumina aerogels with the weblike microstructure were far more mechanically robust than those with the colloidal network, based on acoustic measurements. Both types of alumina aerogels can be transformed to {gamma}-Al{sub 2}O{sub 3} through calcination at 800 C without a significant loss in surface area or monolithicity.
Date: June 25, 2004
Creator: Baumann, T F; Gash, A E; Chinn, S C; Sawvel, A M; Maxwell, R S & Satcher Jr., J H
Partner: UNT Libraries Government Documents Department

Anaerobic, Nitrate-Dependent Oxidation of U(IV) Oxide Minerals by the Chemolithoautotrophic Bacterium Thiobacillus denitrificans

Description: Under anaerobic conditions and at circumneutral pH, cells of the widely-distributed, obligate chemolithoautotrophic bacterium Thiobacillus denitrificans oxidatively dissolved synthetic and biogenic U(IV) oxides (uraninite) in nitrate-dependent fashion: U(IV) oxidation required the presence of nitrate and was strongly correlated to nitrate consumption. This is the first report of anaerobic U(IV) oxidation by an autotrophic bacterium.
Date: June 25, 2004
Creator: Beller, H R
Partner: UNT Libraries Government Documents Department

Bounds and Estimates for Elastic Constants of Random Polycrystals of Laminates

Description: In order to obtain formulas providing estimates for elastic constants of random polycrystals of laminates, some known rigorous bounds of Peselnick, Meister, and Watt are first simplified. Then, some new self-consistent estimates are formulated based on the resulting analytical structure of these bounds. A numerical study is made, assuming first that the internal structure (i.e., the laminated grain structure) is not known, and then that it is known. The purpose of this aspect of the study is to attempt to quantify the differences in the predictions of properties of the same system being modeled when such internal structure of the composite medium and spatial correlation information is and is not available.
Date: August 25, 2004
Creator: Berryman, J G
Partner: UNT Libraries Government Documents Department

Study of Current Profile Evolution in Presence of Tearing Modes in DIII-D Hybrid Discharges

Description: An intermediate regime for tokamak operation has been obtained in DIII-D and in other tokamaks in which the inductive flux consumption is reduced and a broad current profile with the safety factor just above or near the sawtoothing limit is obtained and maintained. The DIII-D tokamak was operated in this regime near the no-wall b limit. High stability and good confinement was achieved at a desired level of q{sub 95} {approx} 3 to 4 for durations as long as 35{tau}{sub E}, three times the current-diffusion time. This regime offers the promise of achieving higher fusion gain and yield and/or longer burn duration for ITER.
Date: June 25, 2004
Creator: Casper, T; Jayakumar, R; Pearlstein, L & Lodestro, L
Partner: UNT Libraries Government Documents Department

Using Very Small-scale Experiments to Investigate Materials: The 21st Century Direction in Basic Pu Research?

Description: Researchers at Lawrence Livermore National Laboratory have developed several techniques to probe the properties of Plutonium using tiny microgram-to-milligram samples. This commentary describes the advantages of this experimental approach, and contains examples of successful experimental setups. One motivation for such experiments is that they couple well to computational simulations of electronic and atomistic properties and processes, and examples of this coupling are discussed.
Date: October 25, 2004
Creator: Chandler, E A
Partner: UNT Libraries Government Documents Department

Prospects for single-particle imaging at XFELs

Description: X-ray free-electron lasers will produce pulses of x-rays that are 10 orders of magnitude brighter than today's undulator sources at synchrotrons. This may enable atomic resolution imaging of single macromolecules.
Date: April 25, 2004
Creator: Chapman, H N; Hau-Riege, S P; London, R A; Marchesini, S; Noy, A; Szoke, A et al.
Partner: UNT Libraries Government Documents Department

Excitation Cross Section Measurement for n=3 to n=2 Line Emission in Fe{sup 20+} to Fe{sup 23+}

Description: Electron impact excitation cross sections have been measured for iron L-shell 3 {yields} 2 lines of FeXXI to FeXXIV at the EBIT-II electron beam ion trap using a crystal spectrometer and a 6 x 6-element array microcalorimeter. The cross sections were determined by direct normalization to the well established cross section of radiative electron capture and a summary of calculated energy dependent radiative recombination cross sections for electron capture into the ground state fine structure levels of Fe{sup 16+} to Fe{sup 23+} ions is given. The measurement results for 17 lines and their comparison with model calculations are presented. While agreement of the model calculations with experiment is good for most measured lines, significant discrepancies were found for a few lines, including the strongest line in Fe XXI.
Date: August 25, 2004
Creator: Chen, H; Beiersdorfer, P; Scofield, J; Brown, G; Boyce, K; Kelley, R L et al.
Partner: UNT Libraries Government Documents Department

Harmonic cascade FEL designs for LUX, a facility for ultrafast x-ray science

Description: LUX is a design study to develop concepts for future ultrafast x-ray facilities. Presently, LUX is based on an electron beam accelerated to {approx}3-GeV energy in a superconducting, recirculating linac. Included in the design are multiple free-electron laser (FEL) beamlines which use the harmonic cascade approach to produce coherent XUV and soft X-ray emission beginning with a strong input seed at {approx}200-nm wavelength obtained from a ''conventional'' laser. Each cascade module generally operates in the low-gain regime and is composed of a radiator together with a modulator section, separated by a magnetic chicane. The chicane temporally delays the electron beam pulse in order that a ''virgin'' pulse region (with undegraded energy spread) be brought into synchronism with the radiation pulse. For a given cascade, the output photon energy can be selected over a wide range by varying the seed laser wavelength and the field strength in the undulators. We present numerical simulation results, as well as those from analytical models, to examine certain aspects of the predicted FEL performance. We also discuss lattice considerations pertinent to harmonic cascade FELs, some sensitivity studies and requirements on the undulator alignment, and temporal pulse evolution initiated by short input radiation seeds.
Date: August 25, 2004
Creator: Corlett, John; Fawley, William; Penn, Gregory; Wan, Weishi; Zholents, A.; Reinsch, M. et al.
Partner: UNT Libraries Government Documents Department

ProteinShop: A tool for interactive protein manipulation and steering

Description: We describe ProteinShop, a new visualization tool that streamlines and simplifies the process of determining optimal protein folds. ProteinShop may be used at different stages of a protein structure prediction process. First, it can create protein configurations containing secondary structures specified by the user. Second, it can interactively manipulate protein fragments to achieve desired folds by adjusting the dihedral angles of selected coil regions using an Inverse Kinematics method. Last, it serves as a visual framework to monitor and steer a protein structure prediction process that may be running on a remote machine. ProteinShop was used to create initial configurations for a protein structure prediction method developed by a team that competed in CASP5. ProteinShop's use accelerated the process of generating initial configurations, reducing the time required from days to hours. This paper describes the structure of ProteinShop and discusses its main features.
Date: May 25, 2004
Creator: Crivelli, Silvia; Kreylos, Oliver; Max, Nelson; Hamann, Bernd & Bethel, Wes
Partner: UNT Libraries Government Documents Department

2004 Atomic and Molecular Interactions Gordon Research Conference

Description: The 2004 Gordon Research Conference on Atomic and Molecular Interactions was held July 11-16 at Colby-Sawyer College, New London, New Hampshire. This latest edition in a long-standing conference series featured invited talks and contributed poster papers on dynamics and intermolecular interactions in a variety of environments, ranging from the gas phase through surfaces and condensed media. A total of 90 conferees participated in the conference.
Date: October 25, 2004
Creator: Dagdigian, Dr. Paul J.
Partner: UNT Libraries Government Documents Department

Interferometric resolution boosting for spectrographs

Description: Externally dispersed interferometry (EDI) is a technique for enhancing the performance of spectrographs for wide bandwidth high resolution spectroscopy and Doppler radial velocimetry. By placing a small angle-independent interferometer near the slit of a spectrograph, periodic fiducials are embedded on the recorded spectrum. The multiplication of the stellar spectrum times the sinusoidal fiducial net creates a moir{acute e} pattern, which manifests high detailed spectral information heterodyned down to detectably low spatial frequencies. The latter can more accurately survive the blurring, distortions and CCD Nyquist limitations of the spectrograph. Hence lower resolution spectrographs can be used to perform high resolution spectroscopy and radial velocimetry. Previous demonstrations of {approx}2.5x resolution boost used an interferometer having a single fixed delay. We report new data indicating {approx}6x Gaussian resolution boost (140,000 from a spectrograph with 25,000 native resolving power), taken by using multiple exposures at widely different interferometer delays.
Date: May 25, 2004
Creator: Erskine, D J & Edelstein, J
Partner: UNT Libraries Government Documents Department

Population genetic variation in gene expression is associated withphenotypic variation in Saccharomyces cerevisiae

Description: The relationship between genetic variation in gene expression and phenotypic variation observable in nature is not well understood. Identifying how many phenotypes are associated with differences in gene expression and how many gene-expression differences are associated with a phenotype is important to understanding the molecular basis and evolution of complex traits. Results: We compared levels of gene expression among nine natural isolates of Saccharomyces cerevisiae grown either in the presence or absence of copper sulfate. Of the nine strains, two show a reduced growth rate and two others are rust colored in the presence of copper sulfate. We identified 633 genes that show significant differences in expression among strains. Of these genes,20 were correlated with resistance to copper sulfate and 24 were correlated with rust coloration. The function of these genes in combination with their expression pattern suggests the presence of both correlative and causative expression differences. But the majority of differentially expressed genes were not correlated with either phenotype and showed the same expression pattern both in the presence and absence of copper sulfate. To determine whether these expression differences may contribute to phenotypic variation under other environmental conditions, we examined one phenotype, freeze tolerance, predicted by the differential expression of the aquaporin gene AQY2. We found freeze tolerance is associated with the expression of AQY2. Conclusions: Gene expression differences provide substantial insight into the molecular basis of naturally occurring traits and can be used to predict environment dependent phenotypic variation.
Date: February 25, 2004
Creator: Fay, Justin C.; McCullough, Heather L.; Sniegowski, Paul D. & Eisen, Michael B.
Partner: UNT Libraries Government Documents Department

A "First Principles" Potential Energy Surface for Liquid Water from VRT Spectroscopy of Water Clusters

Description: We present results of gas phase cluster and liquid water simulations from the recently determined VRT(ASP-W)III water dimer potential energy surface. VRT(ASP-W)III is shown to not only be a model of high ''spectroscopic'' accuracy for the water dimer, but also makes accurate predictions of vibrational ground-state properties for clusters up through the hexamer. Results of ambient liquid water simulations from VRT(ASP-W)III are compared to those from ab initio Molecular Dynamics, other potentials of ''spectroscopic'' accuracy, and to experiment. The results herein represent the first time that a ''spectroscopic'' potential surface is able to correctly model condensed phase properties of water.
Date: May 25, 2004
Creator: Goldman, N.; Leforestier, C. & Saykally, R. J.
Partner: UNT Libraries Government Documents Department

Isentropic Compression Loading of HMX and the Pressure-induced Phase Transition at 27 GPa

Description: The 27 GPa pressure-induced epsilon-phi phase transition in HMX is explored using the Isentropic Compression Experiment (ICE) technique at the Sandia National Laboratories Z-machine facility. Our data indicate that this phase transition is sluggish and if it does occur to any extent under the time scales (200-500 ns) and strain rates (5 x 10{sup 5}) typical of ICE loading conditions, the amount of conversion is small.
Date: February 25, 2004
Creator: Hare, D E; Reisman, D B; Dick, J J & Forbes, J W
Partner: UNT Libraries Government Documents Department

Experiments on the Scaling of Ionization Balance vs. Electron and Radiation Temperature in Non-LTE Gold Plasmas

Description: Understanding and predicting the behavior of high-Z non-LTE plasmas is important for developing indirect-drive inertial confinement fusion. Extending earlier work from the Nova laser, we present results from experiments using the Omega laser to study the ionization balance of gold as a function of electron and radiation temperature. In these experiments, gold samples embedded in Be disks expand under direct laser heating to n{sub e} {approx} 10{sup 21} cm{sup -3}, with T{sub e} varying from 0.8 to 2.5 keV. An additional finite radiation field with effective temperature T{sub r} up to 150 eV is provided by placing the gold-Be disks inside truncated 1.2 mm diameter tungsten-coated cylindrical hohlraums with full laser entrance holes. Densities are measured by imaging of plasma expansion. Electron temperatures are diagnosed with either 2 {omega} or 4 {omega} Thomson scattering, and also K-shell spectroscopy of KCl tracers co-mixed with the gold. Hohlraum flux and effective radiation temperature are measured using an absolutely-calibrated multichannel filtered diode array. Spectroscopic measurements of the M-shell gold emission in the 2.9-4 keV spectral range provide ionization balance and charge state distribution information. The spectra show strong variation with T{sub e}, strong variation with the applied T{sub r} at T{sub e} below 1.6 keV, and relatively little variation with T{sub r} at higher T{sub e} (upwards of 2 keV). We summarize our most recent spectral analyses and discuss emerging and outstanding issues.
Date: June 25, 2004
Creator: Heeter, R F; Hansen, S B; Beiersdorfer, P; Foord, M E; Fournier, K B; Froula, D H et al.
Partner: UNT Libraries Government Documents Department

Fabrication of a Carbon Nanotube-Embedded Silicon Nitride Membrane for Studies of Nanometer-Scale Mass Transport

Description: A membrane consisting of multiwall carbon nanotubes embedded in a silicon nitride matrix was fabricated for fluid mechanics studies on the nanometer scale. Characterization by tracer diffusion and scanning electron microscopy suggests that the membrane is free of large voids. An upper limit to the diffusive flux of D{sub 2}O of 2.4x10-{sup 8} mole/m{sup 2}-s was determined, indicating extremely slow transport. By contrast, hydrodynamic calculations of water flow across a nanotube membrane of similar specifications predict a much higher molar flux of 1.91 mole/m{sup 2}-s, suggesting that the nanotubes produced possess a 'bamboo' morphology. The carbon nanotube membranes were used to make nanoporous silicon nitride membranes, fabricated by sacrificial removal of the carbon. Nitrogen flow measurements on these structures give a membrane permeance of 4.7x10{sup -4} mole/m{sup 2}-s-Pa at a pore density of 4x10{sup 10} cm{sup -2}. Using a Knudsen diffusion model, the average pore size of this membrane is estimated to be 66 nm, which agrees well with TEM observations of the multiwall carbon nanotube outer diameter. These membranes are a robust platform for the study of confined molecular transport, with applications inseparations and chemical sensing.
Date: August 25, 2004
Creator: Holt, J K; Noy, A; Huser, T; Eaglesham, D & Bakajin, O
Partner: UNT Libraries Government Documents Department

Carbon Nanotube-Based Permeable Membranes: A Platform for Studying Nanofluidics

Description: A membrane of multiwalled carbon nanotubes embedded in a silicon nitride matrix was fabricated for use in studying fluid mechanics on the nanometer scale. Characterization by fluorescent tracer diffusion and scanning electron microscopy suggests that the membrane is void-free near the silicon substrate on which it rests, implying that the hollow core of the nanotube is the only conduction path for molecular transport. Nitrogen flow measurements of a nanoporous silicon nitride membrane, fabricated by sacrificial removal of carbon, give a flow rate of 0.086 cc/sec. Calculations of water flow across a nanotube membrane give a rate of 2.1x10{sup -6} cc/sec (0.12 {micro}L/min).
Date: May 25, 2004
Creator: Holt, J K; Park, H G; Noy, A; Huser, T; Eaglesham, D & Bakajin, O
Partner: UNT Libraries Government Documents Department

COPING WITH CONTAMINATED SEDIMENTS AND SOILS IN THE URBAN ENVIRONMENT.

Description: Soils and sediments contaminated with toxic organic and inorganic compounds harmful to the environment and to human health are common in the urban environment. We report here on aspects of a program being carried out in the New York/New Jersey Port region to develop methods for processing dredged material from the Port to make products that are safe for introduction to commercial markets. We discuss some of the results of the program in Computational Environmental Science, Laboratory Environmental Science, and Applied Environmental Science and indicate some possible directions for future work. Overall, the program elements integrate the scientific and engineering aspects with regulatory, commercial, urban planning, local governments, and community group interests. Well-developed connections between these components are critical to the ultimate success of efforts to cope with the problems caused by contaminated urban soils and sediments.
Date: May 25, 2004
Creator: JONES,K. W.; VAN DER LELIE,D.; MCGUIGAN,M. & AL., ET
Partner: UNT Libraries Government Documents Department

Characterization of Vapor Deposited Nano Structured Membranes

Description: The vapor deposition methods of planar magnetron sputtering and electron-beam evaporation are used to synthesize materials with nano structured morphological features that have ultra-high surface areas with continuous open porosity at the nano scale. These nano structured membranes are used in a variety of fuel cells to provide electrode and catalytic functions. Specifically, stand alone and composite nickel electrodes for use in thin film solid-oxide, and molten carbonate fuel cells are formed by sputter deposition and electron bean evaporation, respectively. Also, a potentially high-performance catalyst material for the direct reformation of hydrocarbon fuels at low temperatures is deposited as a nano structure by the reactive sputtering of a copper-zinc alloy using a partial pressure of oxygen at an elevated substrate temperature.
Date: March 25, 2004
Creator: Jankowski, A; Cherepy, N; Ferreira, J & Hayes, J
Partner: UNT Libraries Government Documents Department