Showing papers by "Argonne National Laboratory published in 1997"
01 Jun 1997
TL;DR: The Globus system is intended to achieve a vertically integrated treatment of application, middleware, and net work, an integrated set of higher level services that enable applications to adapt to heteroge neous and dynamically changing metacomputing environ ments.
Abstract: The Globus system is intended to achieve a vertically integrated treatment of application, middleware, and net work. A low-level toolkit provides basic mechanisms such as communication, authentication, network information, and data access. These mechanisms are used to con struct various higher level metacomputing services, such as parallel programming tools and schedulers. The long- term goal is to build an adaptive wide area resource environment AWARE, an integrated set of higher level services that enable applications to adapt to heteroge neous and dynamically changing metacomputing environ ments. Preliminary versions of Globus components were deployed successfully as part of the I-WAY networking experiment.
3,450 citations
TL;DR: The Ribosomal Database Project (RDP-II), previously described by Maidak et al. (2000), continued during the past year to add new rRNA sequences to the aligned data and to improve the analysis commands.
Abstract: The Ribosomal Database Project (RDP) is a curated database that offers ribosome-related data, analysis services and associated computer programs. The offerings include phylogenetically ordered alignments of ribosomal RNA (rRNA) sequences, derived phylogenetic trees, rRNA secondary structure diagrams, and various software for handling, analyzing and displaying alignments and trees. The data are available via anonymous FTP (rdp.life.uiuc.edu), electronic mail (server@rdp.life.uiuc.edu), gopher (rdpgopher.life.uiuc.edu) and WWW (http://rdpwww.life.uiuc.edu/ ). The electronic mail and WWW servers provide ribosomal probe checking, approximate phylogenetic placement of user-submitted sequences, screening for possible chimeric rRNA sequences, automated alignment, and a suggested placement of an unknown sequence on an existing phylogenetic tree.
2,106 citations
01 May 1997
TL;DR: The PETSc 2.0 package as discussed by the authors uses object-oriented programming to conceal the details of the message passing, without concealing the parallelism, in a high-quality set of numerical software libraries.
Abstract: Parallel numerical software based on the message passing model is enormously complicated. This paper introduces a set of techniques to manage the complexity, while maintaining high efficiency and ease of use. The PETSc 2.0 package uses object-oriented programming to conceal the details of the message passing, without concealing the parallelism, in a high-quality set of numerical software libraries. In fact, the programming model used by PETSc is also the most appropriate for NUMA shared-memory machines, since they require the same careful attention to memory hierarchies as do distributed-memory machines. Thus, the concepts discussed are appropriate for all scalable computing systems. The PETSc libraries provide many of the data structures and numerical kernels required for the scalable solution of PDEs, offering performance portability.
1,854 citations
TL;DR: The surface modification scheme reported in this paper enables rational design of the surface properties of tailored porous materials and may lead to the synthesis of more sophisticated functionalized composites for environmental and industrial applications.
Abstract: Mesoporous silica materials containing functionalized organic monolayers have been synthesized. Solid-state nuclear magnetic resonance suggests that a cross-linked monolayer of mercaptopropylsilane was covalently bound to mesoporous silica and closely packed on the surface. The relative surface coverage of the monolayers can be systematically varied up to 76 percent. These materials are extremely efficient in removing mercury and other heavy metals from both aqueous and nonaqueous waste streams, with distribution coefficients up to 340,000. The stability of these materials and the potential to regenerate and reuse them have also been demonstrated. The surface modification scheme reported here enables rational design of the surface properties of tailored porous materials and may lead to the synthesis of more sophisticated functionalized composites for environmental and industrial applications.
1,523 citations
TL;DR: The A. fulgidus genome encodes functionally uncharacterized yet conserved proteins, two-thirds of which are shared with M. jannaschii (428 ORFs), indicating substantial archaeal gene diversity.
Abstract: Archaeoglobus fulgidus is the first sulphur-metabolizing organism to have its genome sequence determined. Its genome of 2,178,400 base pairs contains 2,436 open reading frames (ORFs). The information processing systems and the biosynthetic pathways for essential components (nucleotides, amino acids and cofactors) have extensive correlation with their counterparts in the archaeon Methanococcus jannaschii. The genomes of these two Archaea indicate dramatic differences in the way these organisms sense their environment, perform regulatory and transport functions, and gain energy. In contrast to M. jannaschii, A. fulgidus has fewer restriction-modification systems, and none of its genes appears to contain inteins. A quarter (651 ORFs) of the A. fulgidus genome encodes functionally uncharacterized yet conserved proteins, two-thirds of which are shared with M. jannaschii (428 ORFs). Another quarter of the genome encodes new proteins indicating substantial archaeal gene diversity.
1,394 citations
1,332 citations
01 Jan 1997
TL;DR: This chapter summarizes basic ideas of domain decomposition methods and references are furnished to several recent uses ofdomain decomposition.
Abstract: Domain decomposition methods are iterative methods for the solution of linear or nonlinear systems that use explicit information about the geometry, discretization, and/or partial differential equations that underlie the discrete systems. Considerable research in domain decomposition methods for partial differential equations has been carried out in the past dozen years. Recently, these techniques have begun to be applied to “real-world” engineering problems. This chapter summarizes basic ideas of domain decomposition methods. Though no particular applications are discussed, references are furnished to several recent uses of domain decomposition.
955 citations
TL;DR: The elastic and tensile behavior of high-density, high-purity nanocrystalline Cu and Pd was determined in this paper, showing that porosity increases with decreasing porosity, and may be significantly affected by a few large processing flaws.
791 citations
TL;DR: In this paper, a detailed description of the Green's-function Monte Carlo algorithm for systems with state-dependent potentials is given and a number of tests of its convergence and accuracy are performed.
Abstract: We report quantum Monte Carlo calculations of ground and low-lying excited states for nuclei with $Al~7$ using a realistic Hamiltonian containing the Argonne ${v}_{18}$ two-nucleon and Urbana IX three-nucleon potentials. A detailed description of the Green's-function Monte Carlo algorithm for systems with state-dependent potentials is given and a number of tests of its convergence and accuracy are performed. We find that the Hamiltonian being used results in ground states of both ${}^{6}$Li and ${}^{7}$Li that are stable against breakup into subclusters, but somewhat underbound compared to experiment. We also have results for ${}^{6}$He, ${}^{7}$He, and their isobaric analogs. The known excitation spectra of all these nuclei are reproduced reasonably well and we predict a number of excited states in ${}^{6}$He and ${}^{7}$He. We also present spin-polarized one-body and several different two-body density distributions. These are the first microscopic calculations that directly produce nuclear shell structure from realistic interactions that fit $\mathrm{NN}$ scattering data.
777 citations
TL;DR: In this article, the evolution of the structural properties of the metal-insulator transition was determined as a function of temperature, average $A$-site radius and applied pressure for the ''optimal'' doping range $x=0.25,$ 0.30, by using high-resolution neutron powder diffraction.
Abstract: The evolution of the structural properties of ${A}_{1\ensuremath{-}x}{A}_{x}^{\ensuremath{'}}{\mathrm{MnO}}_{3}$ was determined as a function of temperature, average $A$-site radius $〈{r}_{A}〉,$ and applied pressure for the ``optimal'' doping range $x=0.25,$ 0.30, by using high-resolution neutron powder diffraction. The metal-insulator transition, which can be induced both as a function of temperature and of $〈{r}_{A}〉,$ was found to be accompanied by significant structural changes. Both the paramagnetic charge-localized phase, which exists at high temperatures for all values of $〈{r}_{A}〉,$ and the spin-canted ferromagnetic charge-ordered phase, which is found at low temperatures for low values of $〈{r}_{A}〉,$ are characterized by large metric distortions of the ${\mathrm{MnO}}_{6}$ octahedra. These structural distortions are mainly incoherent with respect to the space-group symmetry, with a significant coherent component only at low $〈{r}_{A}〉.$ These distortions decrease abruptly at the transition into the ferromagnetic metal phase. These observations are consistent with the hypothesis that, in the insulating phases, lattice distortions of the Jahn-Teller type, in addition to spin scattering, provide a charge-localization mechanism. The evolution of the average structural parameters indicates that the variation of the electronic bandwidth is the driving force for the evolution of the insulator-to-metal transition at ${T}_{C}$ as a function of ``chemical'' and applied pressure.
733 citations
TL;DR: In this paper, the authors describe a novel class of magnetoresistive compounds, the silver chalcogenides, and show that slightly altering the stoichiometry can lead to a marked increase in the magnetic response.
Abstract: Several materials have been identified over the past few years as promising candidates for the development of new generations of magnetoresistive devices. These range from artificially engineered magnetic multilayers' and granular alloys, in which the magnetic-field response of interfacial spins modulates electron transport to give rise to 'giant' magnetoresistance, to the manganite peravskites, in which metal-insulator transitions driven by a magnetic field give rise to a `colossal' magnetoresistive response (albeit at very high fields). Here we describe a hitherto unexplored class of magnetoresistive compounds, the silver chalcogenides. At high temperatures, the compounds Ag_2S, Ag_2Se and Ag_2Te are superionic conductors; below similar to 400 K, ion migration is effectively frozen and the compounds are non-magnetic semiconductors that exhibit no appreciable magnetoresistance. We show that slightly altering the stoichiometry can lead to a marked increase in the magnetic response. At room temperature and in a magnetic field of similar to 55 kOe, Ag_(2+δ)Se and Ag_(2+δ)Te show resistance increases of up to 200%, which are comparable with the colossal-magnetoresistance materials. Moreover, the resistance of our most responsive samples exhibits an unusual linear dependence on magnetic field, indicating both a potentially useful response down to fields of practical importance and a peculiarly long length scale associated with the underlying mechanism.
TL;DR: In this article, the impact of precision measurements of DIS structure functions and inclusive jet production at the Fermilab Tevatron on the global QCD analysis of parton distribution functions is studied in detail.
Abstract: The impact of recent precision measurements of DIS structure functions and inclusive jet production at the Fermilab Tevatron on the global QCD analysis of parton distribution functions is studied in detail. Particular emphasis is placed on exploring the range of variation of the gluon distribution $G(x,Q)$ allowed by these new data. The strong coupling of $G(x,Q)$ with ${\ensuremath{\alpha}}_{s}$ is fully taken into account. A new generation of CTEQ parton distributions, CTEQ4, is presented. It consists of the three standard sets [modified minimal subtraction $(\overline{\mathrm{MS}})$, deep inelastic scattering (DIS), and leading order (LO)], a series that gives a range of parton distributions with corresponding ${\ensuremath{\alpha}}_{s}$'s, and a set with a low starting value of $Q$. Previously obtained gluon distributions that are consistent with the high ${E}_{t}$ jet cross section are also discussed in the context of this new global analysis.
TL;DR: In this article, the synthesis and metal ion responsive properties of two 2,2‘-bipyridyl-phenylene-vinylene-based polymers are reported.
Abstract: The synthesis and metal ion responsive properties of two 2,2‘-bipyridyl-phenylene-vinylene-based polymers is reported. These polymers are designed to be partially conjugated in their metal-free state and fully conjugated when exposed to metal ions so that the ion-induced conjugation enhancement can be transduced into a measurable signal. It is found that these polymers exhibit highly ionochromic effects with a wide variety of transition and main group metal ions excluding metal ions of the alkali and alkaline earth groups. For instance, both absorption and fluorescence emission bands of the polymers upon exposure to metal ions can be red-shifted up to 120 nm, depending on the metal ions present and the polymers used.
TL;DR: Kinetic analysis suggests that duplex DNA is somewhat more effective than proteins as a medium for electron transfer but that it does not function as a molecular wire.
Abstract: The distance dependence of photoinduced electron transfer in duplex DNA was determined for a family of synthetic DNA hairpins in which a stilbene dicarboxamide forms a bridge connecting two oligonucleotide arms. Investigation of the fluorescence and transient absorption spectra of these hairpins established that no photoinduced electron transfer occurs for a hairpin that has six deoxyadenosine-deoxythymidine base pairs. However, the introduction of a single deoxyguanosine-deoxycytidine base pair resulted in distance-dependent fluorescence quenching and the formation of the stilbene anion radical. Kinetic analysis suggests that duplex DNA is somewhat more effective than proteins as a medium for electron transfer but that it does not function as a molecular wire.
TL;DR: In this paper, the authors derived the explicit relation between the flavor-nonsinglet pseudoscalar-meson Bethe-Salpeter amplitude and the dressed-quark propagator in the chiral limit.
Abstract: Independent of assumptions about the form of the quark-quark scattering kernel $K$, we derive the explicit relation between the flavor-nonsinglet pseudoscalar-meson Bethe-Salpeter amplitude ${\ensuremath{\Gamma}}_{H}$ and the dressed-quark propagator in the chiral limit. In addition to a term proportional to ${\ensuremath{\gamma}}_{5}$, ${\ensuremath{\Gamma}}_{H}$ necessarily contains qualitatively and quantitatively important terms proportional to ${\ensuremath{\gamma}}_{5}\ensuremath{\gamma}\ensuremath{\cdot}P$ and ${\ensuremath{\gamma}}_{5}\ensuremath{\gamma}\ensuremath{\cdot}\mathrm{kk}\ensuremath{\cdot}P$, where $P$ is the total momentum of the bound state. The axial-vector vertex contains a bound state pole described by ${\ensuremath{\Gamma}}_{H},$ whose residue is the leptonic decay constant for the bound state. The pseudoscalar vertex also contains such a bound state pole and, in the chiral limit, the residue of this pole is related to the vacuum quark condensate. The axial-vector Ward-Takahashi identity relates these pole residues, with the Gell-Mann--Oakes--Renner relation a corollary of this identity. The dominant ultraviolet asymptotic behavior of the scalar functions in the meson Bethe-Salpeter amplitude is fully determined by the behavior of the chiral limit quark mass function, and is characteristic of the QCD renormalization group. The rainbow-ladder Ansatz for $K$, with a simple model for the dressed-quark-quark interaction, is used to illustrate and elucidate these general results. The model preserves the one-loop renormalization group structure of QCD. The numerical studies also provide a means of exploring procedures for solving the Bethe-Salpeter equation without a three-dimensional reduction.
TL;DR: In this paper, the fabrication of nanotube field emitters with an onset field as low as 0.8 V/μm is described and the low-field electron emission mechanism is discussed.
Abstract: The fabrication of nanotube field emitters with an onset field as low as 0.8 V/μm is described and the low-field electron emission mechanism is discussed. These emitters are made using nanotube cathode deposit with the addition of epoxy resin. The preferred orientation of nanotubes in nanotube bundles of the deposit is preserved. The nanotube tips are sharpened by exposing the nanotube bundle surface to a microwave oxygen plasma. The local-field enhancement factor is estimated to be 8000 by using the Fowler–Nordheim equation. The low onset field is attributed to the well-distributed, highly orientated sharp tips at the sample surface.
TL;DR: Computational experiments show that swapping is critical to the improvement of general mesh quality and that optimization-based smoothing is highly effective in eliminating very small and very large angles.
Abstract: Automatic mesh generation and adaptive refinement methods for complex three-dimensional domains have proven to be very successful tools for the efficient solution of complex applications problems. These methods can, however, produce poorly shaped elements that cause the numerical solution to be less accurate and more difficult to compute. Fortunately, the shape of the elements can be improved through several mechanisms, including face- and edge-swapping techniques, which change local connectivity, and optimization-based mesh smoothing methods, which adjust mesh point location. We consider several criteria for each of these two methods and compare the quality of several meshes obtained by using different combinations of swapping and smoothing. Computational experiments show that swapping is critical to the improvement of general mesh quality and that optimization-based smoothing is highly effective in eliminating very small and very large angles. High-quality meshes are obtained in a computationally efficient manner by using optimization-based smoothing to improve only the worst elements and a smart variant of Laplacian smoothing on the remaining elements. Based on our experiments, we offer several recommendations for the improvement of tetrahedral meshes. © 1997 John Wiley & Sons, Ltd.
TL;DR: With only the addition of head-end processing steps, the pyroprocess can be applied with equal success to fuel types other than metal, enabling a symbiotic system wherein the IFR can be used to fission the actinide elements in spent nuclear fuel from other types of reactor.
Pacific Northwest National Laboratory1, University of New Mexico2, Arizona State University3, Alfred University4, United States Naval Research Laboratory5, Massachusetts Institute of Technology6, Princeton University7, Argonne National Laboratory8, University College London9, University of Arizona10
TL;DR: In this paper, a comprehensive review of the state-of-the-art in the field of radiation effects in glasses that are to be used for the immobilization of high-level nuclear waste and plutonium disposition is presented.
Abstract: This paper is a comprehensive review of the state-of-knowledge in the field of radiation effects in glasses that are to be used for the immobilization of high-level nuclear waste and plutonium disposition. The current status and issues in the area of radiation damage processes, defect generation, microstructure development, theoretical methods and experimental methods are reviewed. Questions of fundamental and technological interest that offer opportunities for research are identified.
TL;DR: Oligonucleotides complementary to small-subunit rRNA sequences of selected microbial groups, encompassing key genera of nitrifying bacteria, were shown to selectively retain labeled target nucleic acid derived from either DNA or RNA forms of the target sequences.
Abstract: The utility of parallel hybridization of environmental nucleic acids to many oligonucleotides immobilized in a matrix of polyacrylamide gel pads on a glass slide (oligonucleotide microchip) was evaluated. Oligonucleotides complementary to small-subunit rRNA sequences of selected microbial groups, encompassing key genera of nitrifying bacteria, were shown to selectively retain labeled target nucleic acid derived from either DNA or RNA forms of the target sequences. The utility of varying the probe concentration to normalize hybridization signals and the use of multicolor detection for simultaneous quantitation of multiple probe-target populations were demonstrated.
TL;DR: In this paper, a truncation scheme for the Dyson-Schwinger equations of Euclidean QCD in Landau gauge is presented, which implements the Slavnov-Taylor identities for the three gluon and ghost-gluon vertices.
Abstract: A truncation scheme for the Dyson-Schwinger equations of Euclidean QCD in Landau gauge is presented. It implements the Slavnov-Taylor identities for the three-gluon and ghost-gluon vertices, whereas irreducible four-gluon couplings as well as the gluon-ghost and ghost-ghost scattering kernels are neglected. The infrared behavior of gluon and ghost propagators is obtained analytically: The gluon propagator vanishes for small momenta, whereas the ghost propagator diverges strongly. The numerical solutions are compared with recent lattice results. The running coupling approaches a fixed point, ${\ensuremath{\alpha}}_{c}\ensuremath{\simeq}9.5$, in the infrared.
TL;DR: In this paper, the reconstruction of African tropical grassland history during the late Holocene can be carried out using phytolith analysis, where tall or short grass associations are discriminated by their phytochemical index Iph(%) = saddle/(cross + dumbel + saddle), while the density of shrubs and trees is indicated by relative proportions of the dicotyledon phytophylls.
TL;DR: In this paper, the basic phenomena governing the performance of this type of fuel are well known, and have been sufficiently well modeled to specify design parameters that will assure reliable performance, such as fuel swelling, mechanical and chemical interactions with various cladding materials, performance during transients, failure mechanisms, and behavior following both benign and complete failure of fuel pins.
TL;DR: In this paper, a crossover from localized moment magnetism to heavy Fermi liquid behavior was reported for the metallic compound with the fcc normal-spinel structure, and the electronic heat capacity coefficient was reported to be approximately 0.42.
Abstract: A crossover with decreasing temperature $T$ from localized moment magnetism to heavy Fermi liquid behavior is reported for the metallic compound ${\mathrm{LiV}}_{2}{\mathrm{O}}_{4}$ with the fcc normal-spinel structure. At $T\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}1\mathrm{K}$, the electronic heat capacity coefficient $\ensuremath{\gamma}\ensuremath{\approx}0.42\mathrm{J}/\mathrm{mol}{\mathrm{K}}^{2}$ is exceptionally large for a transition metal compound, the Wilson ratio $\ensuremath{\approx}1.7$, and the Korringa ratio $\ensuremath{\approx}0.7$. Our sample with the lowest level of paramagnetic defects showed no static magnetic order above 0.02 K. Superconductivity was not observed above 0.01 K.
TL;DR: In this paper, a rare surface freezing phenomenon is observed in normal alkanes, using x-ray and surface tension measurements, and an ordered monolayer forms on the surface of the liquid alkane at temperatures up to 3 \ifmmode^\circ\else\textdegree\fi{}C above the bulk freezing temperature.
Abstract: A rare surface freezing phenomenon is observed in molten normal alkanes, using x-ray and surface tension measurements. An ordered monolayer forms on the surface of the liquid alkane at temperatures up to 3 \ifmmode^\circ\else\textdegree\fi{}C above the bulk freezing temperature ${\mathrm{T}}_{\mathrm{f}}$. The structure of the monolayer was studied in detail for a wide range of molecular lengths and temperatures. The single layer formed persists down to ${\mathrm{T}}_{\mathrm{f}}$. The rare surface phase exists only for carbon numbers of 16\ensuremath{\leqslant}n\ensuremath{\leqslant}50. The molecules in the layer are hexagonally packed and show three distinct ordered phases: two rotator phases, with molecules oriented vertically (16\ensuremath{\leqslant}n\ensuremath{\leqslant}30) and tilted towards nearest neighbors (3044) and one crystalline phase with molecules tilted towards next-nearest neighbors (n\ensuremath{\geqslant}44). The temperature dependence of the surface tension and the range of existence vs carbon number are satisfactorily accounted for within a simple theory based on surface energy considerations.
TL;DR: A simple procedure for manufacturing microchips containing various gel-immobilized compounds is described and the effect of the lengths of the immobilized oligon nucleotides and the hybridized RNA and DNA on hybridization of the oligonucleotidemicrochips was evaluated.
TL;DR: In situ neutron diffraction experiments show that at pressures above 2 kilobars, cubic zirconium tungstate (ZrW2O8) undergoes a quenchable phase transition to an orthorhombic phase, the structure of which has been solved from powder diffraction data.
Abstract: In situ neutron diffraction experiments show that at pressures above 2 kilobars, cubic zirconium tungstate (ZrW2O8) undergoes a quenchable phase transition to an orthorhombic phase, the structure of which has been solved from powder diffraction data. This phase transition can be reversed by heating at 393 kelvin and 1 atmosphere and involves the migration of oxygen atoms in the lattice. The high-pressure phase shows negative thermal expansion from 20 to 300 kelvin. The relative thermal expansion and compressibilities of the cubic and orthorhombic forms can be explained in terms of the “cross-bracing” between polyhedra that occurs as a result of the phase transition.
TL;DR: In this article, a functional integral formulation, used previously to calculate the BCS-Bose crossover and describe normal state properties of the crossover, is extended to T${\mathrm{T}}_{\mathrm {c}}$.
Abstract: A functional integral formulation, used previously to calculate ${\mathrm{T}}_{\mathrm{c}}$ and describe normal state properties of the BCS-Bose crossover, is extended to T${\mathrm{T}}_{\mathrm{c}}$. The saddle point approximation is shown to be qualitatively correct for T\ensuremath{\ll}${\mathrm{T}}_{\mathrm{c}}$ for all couplings, in contrast to the situation above ${\mathrm{T}}_{\mathrm{c}}$. Several features of the crossover are described. The difference between the T=0 ``pair size'' and the (prefactor of the T dependent) Ginzburg-Landau coherence length is pointed out: the two quantities are the same only in the BCS limit. The evolution of the collective modes from the BCS to the Bose regime is discussed together with the mixing of the amplitude and phase in the absence of a particle-hole symmetry.
TL;DR: This article shows that the three equations known as commutativity, association, and the Robbins equation are a basis for the variety oflean algebras and presents the proof and the search strategies that enabled the program EQP to find the proof.
Abstract: In this article we show that the three equations known as commutativity, associativity, and the Robbins equation are a basis for the variety of Boolean algebras. The problem was posed by Herbert Robbins in the 1930s. The proof was found automatically by EQP, a theorem-proving program for equational logic. We present the proof and the search strategies that enabled the program to find the proof.