Showing papers by "Argonne National Laboratory published in 2000"

Review of Particle Physics

Abstract: This biennial Review summarizes much of particle physics. Using data from previous editions., plus 2778 new measurements from 645 papers, we list, evaluate, and average measured properties of gauge bosons, leptons, quarks, mesons, and baryons. We also summarize searches for hypothetical particles such as Higgs bosons, heavy neutrinos, and supersymmetric particles. All the particle properties and search limits are listed in Summary Tables. We also give numerous tables, figures, formulae, and reviews of topics such as the Standard Model, particle detectors., probability, and statistics. Among the 108 reviews are many that are new or heavily revised including those on CKM quark-mixing matrix, V-ud & V-us, V-cb & V-ub, top quark, muon anomalous magnetic moment, extra dimensions, particle detectors, cosmic background radiation, dark matter, cosmological parameters, and big bang cosmology.

Global QCD analysis of parton structure of the nucleon: CTEQ5 parton distributions

Abstract: An up-to-date global QCD analysis of high energy lepton-hadron and hadron-hadron interactions is performed to better determine the gluon and quark parton distributions in the nucleon. Improved experimental data on inclusive jet production, in conjunction with precise deep inelastic scattering data, place good constraints on the gluon over a wide range of x; while new data on asymmetries in Drell-Yan processes contribute to better determine the d/u ratio. Comparisons with results of other recent global analyses are made, and the differences are described. Open issues and the general problem of determining the uncertainties of parton distributions are discussed.

Alternative dielectrics to silicon dioxide for memory and logic devices

Abstract: The silicon-based microelectronics industry is rapidly approaching a point where device fabrication can no longer be simply scaled to progressively smaller sizes. Technological decisions must now be made that will substantially alter the directions along which silicon devices continue to develop. One such challenge is the need for higher permittivity dielectrics to replace silicon dioxide, the properties of which have hitherto been instrumental to the industry's success. Considerable efforts have already been made to develop replacement dielectrics for dynamic random-access memories. These developments serve to illustrate the magnitude of the now urgent problem of identifying alternatives to silicon dioxide for the gate dielectric in logic devices, such as the ubiquitous field-effect transistor.

PVFS: a parallel file system for linux clusters

Abstract: As Linux clusters have matured as platforms for low-cost, high-performance parallel computing, software packages to provide many key services have emerged, especially in areas such as message passing and networking. One area devoid of support, however, has been parallel file systems, which are critical for high-performance I/O on such clusters. We have developed a parallel file system for Linux clusters, called the Parallel Virtual File System (PVFS). PVFS is intended both as a high-performance parallel file system that anyone can download and use and as a tool for pursuing further research in parallel I/O and parallel file systems for Linux clusters. In this paper, we describe the design and implementation of PVFS and present performance results on the Chiba City cluster at Argonne. We provide performance results for a workload of concurrent reads and writes for various numbers of compute nodes, I/O nodes, and I/O request sizes. We also present performance results for MPI-IO on PVFS, both for a concurrent read/write workload and for the BTIO benchmark. We compare the I/O performance when using a Myrinet network versus a fast-ethernet network for I/O-related communication in PVFS. We obtained read and write bandwidths as high as 700 Mbytes/sec with Myrinet and 225 Mbytes/sec with fast ethernet.

Formation of sphalerite (ZnS) deposits in natural biofilms of sulfate-reducing bacteria.

Abstract: Abundant, micrometer-scale, spherical aggregates of 2- to 5-nanometer-diameter sphalerite (ZnS) particles formed within natural biofilms dominated by relatively aerotolerant sulfate-reducing bacteria of the family Desulfobacteriaceae. The biofilm zinc concentration is about 106 times that of associated groundwater (0.09 to 1.1 parts per million zinc). Sphalerite also concentrates arsenic (0.01 weight %) and selenium (0.004 weight %). The almost monomineralic product results from buffering of sulfide concentrations at low values by sphalerite precipitation. These results show how microbes control metal concentrations in groundwater- and wetland-based remediation systems and suggest biological routes for formation of some low-temperature ZnS deposits.

Mycorrhizal Fungi Influence Soil Structure

Abstract: A series of closely related processes is presented, by which arbuscular mycorrhizal (AM) fungi contribute to the formation of relatively stable aggregate structures. Fibrous roots and AM fungal hyphae can be viewed as a “sticky-string bag” that contributes to the entanglement and enmeshment of soil particles to form macroaggregates, a basic building block of soil structure. Furthermore, AM fungi produce a glycoprotein, glomalin, that is deposited on their outer hyphal walls and on adjacent soil particles. Glomalin appears to be a rather stable hydrophobic glue that might reduce macroaggregate disruption during wetting and drying events by retarding water movement into the pores within the aggregate structure. Examples from various soil types are used to demonstrate the contributions of AM fungi to soil aggregation and its subsequent stabilization. Over a wide range of soil types, these contributions depend largely on broad textural characteristics and whether the soil’s structure is hierarchical in construction, among other factors.

Surface magneto-optic Kerr effect

Abstract: The surface magneto-optic Kerr effect (SMOKE) has significantly impacted research on magnetic thin films. This is due to its sensitivity, local probing nature, and experimental simplicity. The polar and longitudinal Kerr effects are characterized by a complex rotation of the plane of polarization of linearly polarized incident light upon reflection from the surface of a ferromagnetic material. The rotation is directly related to the magnetization of the material within the probing region of the light. Light penetrates into metals >20 nm deep, but the SMOKE technique derives its surface sensitivity from the limited thickness of the deposited magnetic film, which can be as thin as one atomic layer. Basic principles, experimental arrangements, and applications of SMOKE are reviewed in order to acquaint the nonspecialist with the technique and place it into perspective.

Single molecule force spectroscopy in biology using the atomic force microscope

Abstract: The importance of forces in biology has been recognized for quite a while but only in the past decade have we acquired instrumentation and methodology to directly measure interactive forces at the level of single biological macromolecules and/or their complexes. This review focuses on force measurements performed with the atomic force microscope. A general introduction to the principle of action is followed by review of the types of interactions being studied, describing the main results and discussing the biological implications.

A quality of service architecture that combines resource reservation and application adaptation

Abstract: Reservation and adaptation are two well-known and effective techniques for enhancing the end-to-end performance of network applications. However, both techniques also have limitations, particularly when dealing with high-bandwidth, dynamic flows: fixed-capability reservations tend to be wasteful of resources and hinder graceful degradation in the face of congestion, while adaptive techniques fail when congestion becomes excessive. We propose an approach to quality of service (QoS) that overcomes these difficulties by combining features of reservations and adaptation. In this approach, a combination of online control interfaces for resource management, a sensor permitting online monitoring, and decision procedures embedded in resources enable a rich variety of dynamic feedback interactions between applications and resources. We describe a QoS architecture, GARA, that has been extended to support these mechanisms, and use three examples of application-level adaptive strategies to show how this framework can permit applications to adapt both their resource requests and behavior in response to online sensor information.

Supersymmetry breaking through transparent extra dimensions

Abstract: We propose a new framework for mediating supersymmetry breaking through an extra dimension. It predicts positive scalar masses and solves the supersymmetric flavor problem. Supersymmetry breaks on a ``source'' brane that is spatially separated from a parallel brane on which the standard model matter fields and their superpartners live. The gauge and gaugino fields propagate in the bulk, the latter receiving a supersymmetry breaking mass from direct couplings to the source brane. Scalar masses are suppressed at the high scale but are generated via the renormalization group. We briefly discuss the spectrum and collider signals for a range of compactification scales.

High-gain harmonic-generation free-electron laser.

Abstract: A high-gain harmonic-generation free-electron laser is demonstrated. Our approach uses a laser-seeded free-electron laser to produce amplified, longitudinally coherent, Fourier transform-limited output at a harmonic of the seed laser. A seed carbon dioxide laser at a wavelength of 10.6 micrometers produced saturated, amplified free-electron laser output at the second-harmonic wavelength, 5.3 micrometers. The experiment verifies the theoretical foundation for the technique and prepares the way for the application of this technique in the vacuum ultraviolet region of the spectrum, with the ultimate goal of extending the approach to provide an intense, highly coherent source of hard x-rays.

Depositional Facies and Aqueous-Solid Geochemistry of Travertine-Depositing Hot Springs (Angel Terrace, Mammoth Hot Springs, Yellowstone National Park, U.S.A.)

Abstract: Petrographic and geochemical analyses of travertine-depositing hot springs at Angel Terrace, Mammoth Hot Springs, Yellowstone National Park, have been used to define five depositional facies along the spring drainage system. Spring waters are expelled in the vent facies at 71 to 73 degrees C and precipitate mounded travertine composed of aragonite needle botryoids. The apron and channel facies (43-72 degrees C) is floored by hollow tubes composed of aragonite needle botryoids that encrust sulfide-oxidizing Aquificales bacteria. The travertine of the pond facies (30-62 degrees C) varies in composition from aragonite needle shrubs formed at higher temperatures to ridged networks of calcite and aragonite at lower temperatures. Calcite "ice sheets", calcified bubbles, and aggregates of aragonite needles ("fuzzy dumbbells") precipitate at the air-water interface and settle to pond floors. The proximal-slope facies (28-54 degrees C), which forms the margins of terracette pools, is composed of arcuate aragonite needle shrubs that create small microterracettes on the steep slope face. Finally, the distal-slope facies (28-30 degrees C) is composed of calcite spherules and calcite "feather" crystals. Despite the presence of abundant microbial mat communities and their observed role in providing substrates for mineralization, the compositions of spring-water and travertine predominantly reflect abiotic physical and chemical processes. Vigorous CO2 degassing causes a +2 unit increase in spring water pH, as well as Rayleigh-type covariations between the concentration of dissolved inorganic carbon and corresponding delta 13C. Travertine delta 13C and delta 18O are nearly equivalent to aragonite and calcite equilibrium values calculated from spring water in the higher-temperature (approximately 50-73 degrees C) depositional facies. Conversely, travertine precipitating in the lower-temperature (< approximately 50 degrees C) depositional facies exhibits delta 13C and delta 18O values that are as much as 4% less than predicted equilibrium values. This isotopic shift may record microbial respiration as well as downstream transport of travertine crystals. Despite the production of H2S and the abundance of sulfide oxidizing microbes, preliminary delta 34S data do not uniquely define the microbial metabolic pathways present in the spring system. This suggests that the high extent of CO2 degassing and large open-system solute reservoir in these thermal systems overwhelm biological controls on travertine crystal chemistry.

Quantum linear magnetoresistance

Abstract: A description is presented of experimental results, old and new ones, in which a magnetoresistance was discovered, linear in magnetic field. It is explained that there are two theoretical possibilities for such a phenomenon. The first one happens in a polycrystalline metal in a classically large field; it was known since the late 1950s. The other one is the so-called quantum magnetoresistance in semimetals and in some single crystalline metals having small pockets of the Fermi surface with a small effective mass.

A national-scale authentication infrastructure

Abstract: Participants in virtual organizations commonly need to share resources such as data archives, computer cycles, and networks, resources usually available only with restrictions based on the requested resource's nature and the user's identity. Thus, any sharing mechanism must have the ability to authenticate the user's identity and determine whether the user is authorized to request the resource. Virtual organizations tend to be fluid, however, so authentication mechanisms must be flexible and lightweight, allowing administrators to quickly establish and change resource-sharing arrangements. Nevertheless, because virtual organizations complement rather than replace existing institutions, sharing mechanisms cannot change local policies and must allow individual institutions to maintain control over their own resources. Our group has created and deployed an authentication and authorization infrastructure that meets these requirements: the Grid Security Infrastructure (I. Foster et al., 1998). GSI offers secure single sign-ons and preserves site control over access policies and local security. It provides its own versions of common applications, such as FTP and remote login, and a programming interface for creating secure applications. Dozens of supercomputers and storage systems already use GSI, a level of acceptance reached by few other security infrastructures.

Scheduling with advanced reservations

Abstract: Some computational grid applications have very large resource requirements and need simultaneous access to resources from more than one parallel computer. Current scheduling systems do not provide mechanisms to gain such simultaneous access without the help of human administrators of the computer systems. In this work, we propose and evaluate several algorithms for supporting advanced reservation of resources in supercomputing scheduling systems. These advanced reservations allow users to request resources from scheduling systems at specific times. We find that the wait times of applications submitted to the queue increases when reservations are supported and the increase depends on how reservations are supported. Further, we find that the best performance is achieved when we assume that applications can be terminated and restarted, backfilling is performed, and relatively accurate run-time predictions are used.

Quantum Monte Carlo calculations of A = 8 nuclei

Abstract: We report quantum Monte Carlo calculations of ground and low-lying excited states for $A=8$ nuclei using a realistic Hamiltonian containing the Argonne ${v}_{18}$ two-nucleon and Urbana IX three-nucleon potentials The calculations begin with correlated eight-body wave functions that have a filled $\ensuremath{\alpha}$-like core and four p-shell nucleons $\mathrm{LS}$ coupled to the appropriate ${(J}^{\ensuremath{\pi}};T)$ quantum numbers for the state of interest After optimization, these variational wave functions are used as input to a Green's function Monte Carlo calculation made with a new constrained path algorithm We find that the Hamiltonian produces a ${}^{8}\mathrm{Be}$ ground state that is within 2 MeV of the experimental resonance, but the other eight-body energies are progressively worse as the neutron-proton asymmetry increases The ${}^{8}\mathrm{Li}$ ground state is stable against breakup into subclusters, but the ${}^{8}\mathrm{He}$ ground state is not The excited state spectra are in fair agreement with experiment, with both the single-particle behavior of ${}^{8}\mathrm{He}$ and ${}^{8}\mathrm{Li}$ and the collective rotational behavior of ${}^{8}\mathrm{Be}$ being reproduced We also examine energy differences in the $T=1,2$ isomultiplets and isospin-mixing matrix elements in the excited states of ${}^{8}\mathrm{Be}$ Finally, we present densities, momentum distributions, and studies of the intrinsic shapes of these nuclei, with ${}^{8}\mathrm{Be}$ exhibiting a definite $2\ensuremath{\alpha}$ cluster structure

A crystal-chemical approach to lubrication by solid oxides

Abstract: This paper introduces a new approach to the selection, classification, and mechanistic understanding of lubricious oxides that are used to combat friction and wear at elevated temperatures. Specifically, it describes a crystal-chemical model that enables one to predict the shear rheology or lubricity of an oxide or oxide mixture at elevated temperatures. This model can be used to formulate new alloy compositions or composite oxide structures that can provide low friction at high temperatures. In the case of composite oxides, the model allows one to estimate the solubility limits, chemical reactivity, compound forming tendencies, as well as the lowering of the melting point of one oxide when a second oxide is present. From a tribological standpoint, a prior knowledge of these details is important because they are strongly related to the extent of adhesive interactions, shear rheology, and hence to lubricity of oxides. In light of certain crystal-chemical considerations, general guidelines are provided for the selection of those oxides that can provide low friction at high temperatures. The major goal of this paper is to establish model relationships between relevant crystal-chemical and tribological properties of oxides that can be used as lubricants at high temperatures. Such a model may help eliminate guesswork in high-temperature lubrication and provide a new means to address the difficult lubrication problems experienced at high temperatures.