Showing papers by "Argonne National Laboratory published in 1991"

Mechanical behavior of nanocrystalline Cu and Pd

Abstract: This report gives results of a study of the bulk mechanical properties of samples of nanocrystalline Cu and Pd consolidated from powders prepared by inert gas condensation. Fourier analysis x-ray diffraction techniques, used to determine average grain size and mean lattice strains of the as-consolidated samples, show grain sizes in the range of 3–50 nm and lattice strains ranging from 0.02–3%. Sample densities range from 97–72% of the density of a coarse-grained standard. Microhardness of the nanocrystalline samples exceeds that of annealed, coarse-grained samples by a factor of 2–5, despite indications that sample porosity reduces hardness values below the ultimate value. Uniaxial tensile strength of the nanocrystalline samples is similarly elevated above the value of the coarse-grained standard samples. Restrictions on dislocation generation and mobility imposed by ultrafine grain size are believed to be the dominant factor in raising strength. Residual stress may also play a role. Room temperature diffusional creep, predicted to be appreciable in nanocrystalline samples, was not found. Instead, samples appear to show logarithmic creep that is much smaller than the predicted Coble creep.

Hard-scattering scaling laws for single-spin production asymmetries

Abstract: The extraction of a scaling law of the form (({ital p}{sub {ital T}}{sup 2}+{mu}{sup 2})/{mu}{ital p}{sub {ital T}}){ital A}{sub {ital N}}{congruent}{ital g}({ital x}{sub {ital T}}) (where {ital x}{sub {ital T}}=2{ital p}{sub {ital T}}/ {radical}{ital s} ) from data on a single-spin production asymmetry such as {ital A}{sub {ital N}d}{sigma}({ital pp}{sub {up arrow}}{r arrow}{pi}{sup 0}{ital X}) at large transverse momentum can be used to argue for an underlying hard-scattering'' mechanism. Data from the upcoming Fermilab polarized beam experiment (E-704) can be used to test the scaling hypothesis.

Trading Off Longer Life for Worsening Health The Expansion of Morbidity Hypothesis

Abstract: This article demonstrates and explains why future declines in mortality will have a diminishing effect on the metric of life expectancy but a large impact on the size of future elderly cohorts. Additionally, the article addresses a hypothesis in which it is argued that morbidity and disability will decline and become compressed into a shorter duration of time before death. Although studies have demonstrated that declining mortality can lead to worsening health, what is missing from the literature is a formal mechanistic hypothesis that describes why this phenomenon takes place. Two primary mechanisms are identified. One is based on arguments in which medical technology is identified to improve the survival of those with disabling conditions; the other is that declining mortality from fatal diseases leads to a shift in the distribution of causes of disability from fatal to nonfatal diseases of aging. Procedures for testing this hypothesis are discussed.

Organic superconductors--new benchmarks.

Abstract: Recent advances in the design and synthesis of organic synthetic metals have yielded materials that have the highest superconducting transition temperatures ( T c ≈ 13 kelvin) reported for these systems These materials have crystal structures consisting of alternating layers of organic donor molecules and inorganic anions Organic superconductors have various electronic and magnetic properties and crystal structures that are similar to those of the inorganic copper oxide superconductors (which have high T c values); these similarities include highly anisotropic conductivities, critical fields, and short coherence lengths The largest number of organic superconductors, including those with the highest T c values, are charge-transfer salts derived from the electron donor molecule BEDT-TTF or ET [bis(ethylenedithio)-tetrathiafulvalene] The synthesis and crystal structures of these salts are discussed; their electrical, magnetic, and band electronic structure properties and their many similarities to the copper oxide superconductors are treated as well

Structure of the membrane-bound protein photosynthetic reaction center from Rhodobacter sphaeroides

Abstract: The structure of the photosynthetic reaction center (RC) from Rhodobacter sphaeroides was determined at 3.1-A resolution by the molecular replacement method, using the Rhodopseudomonas viridis RC as the search structure. Atomic coordinates were refined with the difference Fourier method and restrained least-squares refinement techniques to a current R factor of 22%. The tertiary structure of the RC complex is stabilized by hydrophobic interactions between the L and M chains, by interactions of the pigments with each other and with the L and M chains, by residues from the L and M chains that coordinate to the Fe2+, by salt bridges that are formed between the L and M chains and the H chain, and possibly by electrostatic forces between the ends of helices. The conserved residues at the N-termini of the L and M chains were identified as recognition sites for the H chain.

Srex: a newprocess for the extraction and recovery of strontium from acidic nuclear waste streams

Abstract: A new process for the extraction and recovery of strontium from acidic waste streams is described. In this process, called SREX (for Strontium Extraction), strontium is extracted from acidic ( ≥ 1 M HNO3) solution using a 0.20M solution of di-t-butylcyclohexano-18-crown-6 in 1-octanol. Extracted strontium is readily stripped from the organic phase using either water or dilute (<0.05 M) HNO3. Tests of the process on a synthetic dissolved sludge waste solution show that only strontium, barium, and technetium are appreciably extracted by the crown ether. Prolonged exposure of the process solvent to nitric acid at elevated temperatures or to ≤ 50 Wh/L γ radiation from a 60Co source produces essentially no deterioration in its performance. Benchtop batch countercurrent extraction experiments show that 99.7% of the strontium initially present in a feed solution can be removed in only three extraction stages.

Effect of cu-o layer spacing on the magnetic field induced resistive broadening of high-temperature superconductors

Abstract: For H‖c-axis, the magnetic field induced broadening of the resistive transitions of high-Tc superconductors (HTS) is shown to depend strongly on the Cu-O layer spacing. For the highly anisotropic HTS, we show experimental evidence that flux motion results from a thermally activated crossover from three dimensional (3D) vortex lines to 2D independent pancake-like vortices in the Cu-O layers, which is intrinsic to the material and occurs when kBT exceeds the Josephson coupling energy of these layers. At low temperatures, however, thermally activated conventional depinning (which can be sample dependent) or melting in the uncoupled 2D Cu-O layers is also required for flux motion. For YBa2Cu3O7, this dimensional crossover does not occur belowHc2, presumably because the conducting Cu-O chains short-circuit the Josephson interlayer coupling, leading to better superconducting properties in a magnetic field. These results show that strong interlayer coupling is a key to finding good alternatives.

Intermediate-range order in permanently densified vitreous SiO2 : a neutron-diffraction and molecular-dynamics study

Abstract: The structure of pressure-densified vitreous ${\mathrm{SiO}}_{2}$ has been investigated using neutron-diffraction and molecular-dynamics techniques. After compression to 16 GPa at room temperature, recovered samples have densities 20% higher than normal vitreous ${\mathrm{SiO}}_{2}$ and show substantial changes in the first sharp diffraction peak (FSDP): an indication of modification in the intermediate-range order. The changes in the FSDP are due to increased frustration caused by the decrease in the Si-O-Si bond angle and a shift in the Si-Si and O-O correlations in the range of 4--8 \AA{} toward lower distances.

Materials aspects of GaAs and InP based structures

Abstract: Presents a comprehensive treatment of materials aspects of GaAs, InP and related alloys used in the fabricating of photonic and electronic devices. It includes discussions on point defects and dislocations in III-V compounds. Coverage focuses on state-of-the-art materials growth and characterization; physics and chemistry of point defects; and dislocations and the connection between defects and device reliability.

Table-lookup algorithms for elementary functions and their error analysis

Abstract: Table-lookup algorithms for calculating elementary functions offer superior speed and accuracy when compared with more traditional algorithms. It is shown that, with careful design, it is feasible to implement table-lookup algorithms in hardware. A uniform approach for carrying out a tight error analysis for such implementations is presented. The advantages of table-lookup algorithms over CORDIC and ordinary (without table-lookup) polynomial algorithms are described. >

Comparison of reaction centers from Rhodobacter sphaeroides and Rhodopseudomonas viridis: overall architecture and protein-pigment interactions.

Abstract: Photosynthetic reaction centers (RCs) from the photosynthetic bacteria Rhodobacter sphaeroides and Rhodopseudomonas viridis are protein complexes closely related in both structure and function. The structure of the Rps. viridis RC was used to determine the structure of the RC from Rb. sphaeroides. Small but meaningful differences between the positions of the helices and the cofactors in the two complexes were identified. The distances between helices AL and AM, between BL and BM, and between bacteriopheophytins BPL and BPM are significantly shorter in Rps. viridis than they are in Rb. sphaeroides RCs. There are a number of differences in the amino acid residues that surround the cofactors; some of these residues form hydrogen bonds with the cofactors. Differences in chemical properties and location of these residues account in some manner for the different spectral properties of the two RCs. In several instances, the hydrogen bonds, as well as the apparent distances between the histidine ligands and the Mg atoms of the bacteriochlorophylls, were found to significantly differ from the Rb. sphaeroides RC structure previously described by Yeates et al. [(1988) Proc. Natl. Acad. Sci. U.S.A. 85, 7993-7997] and Allen et al. [(1988) Proc. Natl. Acad. Sci. U.S.A. 85, 8487-8491].

Photoinduced electron transfer in the solid state : rate vs free energy dependence in fixed-distance porphyrin-acceptor molecules

Abstract: The authors recently reported that the ion-pair states in two porphyrin-triptycene-acceptor molecules are destabilized by as much as 0.9 eV in going from a polar liquid to a rigid glass. To obtain a quantitative picture of the dependence of charge-separation rate on free energy of reaction in the rigid glass they present electron transfer rate data on 14 porphyrin-triptycene-acceptor molecules, which possess sufficiently large, negative free energies for charge separation to allow electron transfer to compete with excited singlet state decay in glassy 2-methyltetrahydrofuran (MTHF) at 77 K.

Design and construction of the ZEUS barrel calorimeter

Abstract: We present the mechanical design and construction techniques used in building the barrel calorimeter for the ZEUS detector. The latter is currently under construction for use at the HERA electron-proton colliding beam facility. The calorimeter consists of 32 wedge shaped modules with approximate dimensions of 3×0.5×1.7 m 3 . The modules use alternate layers of depleted uranium and scintillator with one radiation length sampling. The light is collected via wavelength shifter plates placed on the sloping sides of the modules and read out by photomultiplier tubes located at the outer radius. The unit cell dimensions result in a ratio e h = 1 which yields an optimal energy resolution for hadronic jets. The placing of the structural components and the arrangement of the cracks between modules were chosen to maximize the uniformity of the response. Details of the construction and assembly effort needed to realize the total calorimeter are given. We finally describe the procedures used for transporting the completed modules to DESY and to install them on ZEUS.

Magneto-optics of multilayers with arbitrary magnetization directions

Abstract: Equations are derived for determining magneto-optic coefficients in multilayer systems with arbitrary directions of their magnetizations. The equations are cast in a matrix form that is suitable for numerical simulations. This establishes a framework for calculating the Kerr and Faraday effects for a multilayer system in much the same way as has been applied previously to the bulk. Numerical Kerr results are presented for the following systems: bulk Fe, an overlayer of 50 \AA{} of Fe on Au, and for an Fe/Au superlattice for different directions of the magnetization and different angles of incidence.

Anisotropy of oxygen tracer diffusion in single-crystal YBa 2 Cu 3 O 7-δ

Abstract: Oxygen tracer diffusion has been measured in single-crystalline ${\mathrm{YBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{7\mathrm{\ensuremath{-}}\mathrm{\ensuremath{\delta}}}$ from 300 to 650 \ifmmode^\circ\else\textdegree\fi{}C in the c direction, at a few temperatures in the ab plane of twinned crystals, and in the b direction of an untwinned crystal. The diffusion coefficient in the c direction, ${\mathit{D}}_{\mathit{c}}$, is \ensuremath{\approxeq}${10}^{6}$ lower than the diffusion coefficient in polycrystals at 400 \ifmmode^\circ\else\textdegree\fi{}C and diffusion in the b direction is at least 100 times faster than diffusion in the a direction at 300 \ifmmode^\circ\else\textdegree\fi{}C. The oxygen diffusion coefficient in polycrystals is, within an experimental uncertainty of a factor of 2, independent of oxygen partial pressure at 400 \ifmmode^\circ\else\textdegree\fi{}C, in agreement with previous results measured at 600 \ifmmode^\circ\else\textdegree\fi{}C. Some suggestions are presented on the mechanism of diffusion, the relation of diffusion and internal friction in ${\mathrm{YBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{7\mathrm{\ensuremath{-}}\mathrm{\ensuremath{\delta}}}$, and on the meaning of the activation energy.

DNA sequencing by hybridization: 100 bases read by a non-gel-based method.

Abstract: Determination of the sequences of human and other complex genomes requires much faster and less expensive sequencing processes than the methods in use today. Sequencing by hybridization is potentially such a process. In this paper we present hybridization data sufficient to accurately read a known sequence of 100 base pairs. In independent reactions, octamer and nonamer oligonucleotides derived from the sequence hybridized more strongly to this DNA than to controls. The 93 consecutive overlapping probes were derived from a 100-base-pair segment of test DNA and additional probes were generated by incorporation of a noncomplementary base at one of the ends of 12 of the basic probes. These 12 additional probes also had a full-match target in one of the control DNAs. The test and one of five control DNAs spotted on nylon filters were hybridized with 83 octamers and 22 nonamers under low-temperature conditions. A stronger signal in DNA containing a full-match target compared to DNA with only mismatched targets was obtained with all 105 probes. In 3 cases (2.9%), the difference of signals was not significant (less than 2-fold) due to inefficient hybridization and the consequently higher influence of background. The hybridization pattern obtained enabled us to resequence the 100 base pairs by applying an algorithm that tolerates an error rate much higher than was observed in the experiment. With this result, the technological components of large-scale DNA sequencing using the sequencing by hybridization method are in place.

Superfluid-insulator transition in disordered boson systems.

Abstract: We present results of path-integral Monte Carlo simulations of bosons on a two-dimensional square lattice in a random potential of average strength {ital V} and with on-site repulsion {ital U}. We find that the superfluid density {rho}{sub {ital s}} is enhanced by increasing {ital V} and {ital U} in certain regions of parameter space. By combining the results of {rho}{sub {ital s}}, with the behavior of the density-density correlation function on lattices of size up to 10{times}10, we study the superfluid--to--Mott-insulator transition and the transition from a superfluid to a disorder-localized ( Bose glass'') phase.

A tribological investigation of the graphite-to-diamond-like behavior of amorphous carbon films ion beam deposited on ceramic substrates☆

Abstract: A tribological investigation was conducted on the graphite-to-diamond-like behavior of hard carbon films produced on SiC, Si 3 N 4 and ZrO 2 substrates by ion beam deposition. Friction tests were performed on a ball-on-disk machine with pairs of various ceramic balls and disks coated with hard carbon films in dry and humid air, argon and N 2 . The friction coefficients of carbon films sliding against Si 3 N 4 and sapphire balls were in the range 0.02–0.04 in N 2 and argon, but were significantly higher (about 0.15) in humid air. The wear rates of ceramic disks coated with carbon films were unmeasurable, and, depending on the test environment, the wear rates of counterface ceramic balls were reduced by two to four orders of magnitude below those of balls slid against uncoated ceramic disks. Graphite disks were also tested, to obtain friction data that can help us to understand the graphite-to-diamond-like tribological behavior of carbon films. Micro laser Raman spectroscopy and scanning electron microscopy were used to analyze the structure and chemistry of worn surfaces and to elucidate the graphite- and diamond-like tribological behavior of amorphous carbon films.

High-field scaling behavior of thermodynamic and transport quantities of YBa2Cu3O7- delta near the superconducting transition.

Abstract: The superconducting contribution to the magnetization and resistivity of twinned and untwinned YBa 2 Cu 3 O 7-δ crystals which are presented here, as well as to the specific heat (Inderhees et al.) and Ettinghausen coefficient (Palstra et al.), displays scaling behavior in the variable [T-T c (H)]/(TH) 2/3 . This is consistent with Ginzburg-Landau fluctuation theory for a 3D system in a high magnetic field

Raman scattering in diamond up to 1900 K

Abstract: The temperature dependence of the zone-center optical phonon of diamond has been investigated up to 1900 K using Raman scattering. Our frequencies agree well with the first measurements of the temperature dependence of this mode but are found to fall halfway between those obtained in two later determinations up to 1000 K. Up to \ensuremath{\sim}1000 K, there is a noticeable nonlinearity in the frequency changes; above \ensuremath{\sim}1000 K the frequency change is almost linear with temperature. The measured positions and widths are also compared with theoretical calculations.

Strain index, lattice softness and superconductivity of organic donor-molecule salts: Crystal and electronic structures of three isostructural salts k-(BEDT- TTF)2Cu[N(CN)2]X (X=Cl, Br, I)

Abstract: The recently discovered k -phase salts k -(BEDT-TTF) 2 ]Cu[N(CN) 2 ]X (X=Cl,Br, I) are isostructural but differ in their superconducting properties: the Br-salt is an ambient-pressure superconductor with T c =116K, the Cl-salt becomes superconducting ( T c =128K) under a slight applied pressure of 03 kbar, and the I-salt does not exhibit superconductivity under an applied-pressure of up to 5 kbar We examine the structural and electronic properties of these three salts on the basis of their crystal structures determined at 127 K by single crystal X-ray diffraction measurements The band electronic structure of the three salts are virtually the same and do not account for the differences in the conduction properties The differences in the three salts with regard to superconductivity are examined from the viewpoint of lattice softness by calculating strain indices for short intermolecular contacts The random potential arising from ethylene group conformational disorder prevents superconductivity in the iodide salt

Direct observation of intrinsic pinning by layered structure in single-crystal YBa 2 Cu 3 O 7 − δ

Abstract: The intrinsic pinning in twinned and untwinned single-crystal ${\mathrm{YBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{7\mathrm{\ensuremath{-}}\mathrm{\ensuremath{\delta}}}$ is observed using a novel crossed-magnetic-field technique for obtaining angular resolutions of \ensuremath{\Delta}\ensuremath{\theta}0.005\ifmmode^\circ\else\textdegree\fi{}. The pinning occurs for magnetic-field directions within a critical angle ${\mathrm{\ensuremath{\theta}}}^{\mathrm{*}}$1\ifmmode^\circ\else\textdegree\fi{} of the Cu-O planes. The data are discussed in the context of a lock-in transition of vortices in the a-b plane of the crystal.