Showing papers by "Argonne National Laboratory published in 1994"

Review of particle properties.

Abstract: This biennial Review summarizes much of Particle Physics. Using data from previous editions, plus 2205 new measurements from 667 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. This edition features expanded coverage of CP violation in B mesons and of neutrino oscillations. For the first time we cover searches for evidence of extra dimensions (both in the particle listings and in a new review). Another new review is on Grand Unified Theories. A booklet is available containing the Summary Tables and abbreviated versions of some of the other sections of this full Review. All tables, listings, and reviews (and errata) are also available on the Particle Data Group website: http://pdg.lbl.gov.

Vortices in high-temperature superconductors

Abstract: With the high-temperature superconductors a qualitatively new regime in the phenomenology of type-II superconductivity can be accessed. The key elements governing the statistical mechanics and the dynamics of the vortex system are (dynamic) thermal and quantum fluctuations and (static) quenched disorder. The importance of these three sources of disorder can be quantified by the Ginzburg number $Gi=\frac{{(\frac{{T}_{c}}{{H}_{c}^{2}}\ensuremath{\varepsilon}{\ensuremath{\xi}}^{3})}^{2}}{2}$, the quantum resistance $Qu=(\frac{{e}^{2}}{\ensuremath{\hbar}})(\frac{{\ensuremath{\rho}}_{n}}{\ensuremath{\varepsilon}\ensuremath{\xi}})$, and the critical current-density ratio $\frac{{j}_{c}}{{j}_{o}}$, with ${j}_{c}$ and ${j}_{o}$ denoting the depinning and depairing current densities, respectively (${\ensuremath{\rho}}_{n}$ is the normal-state resistivity and ${\ensuremath{\varepsilon}}^{2}=\frac{m}{M}l1$ denotes the anisotropy parameter). The material parameters of the oxides conspire to produce a large Ginzburg number $\mathrm{Gi}\ensuremath{\sim}{10}^{\ensuremath{-}2}$ and a large quantum resistance $\mathrm{Qu}\ensuremath{\sim}{10}^{\ensuremath{-}1}$, values which are by orders of magnitude larger than in conventional superconductors, leading to interesting effects such as the melting of the vortex lattice, the creation of new vortex-liquid phases, and the appearance of macroscopic quantum phenomena. Introducing quenched disorder into the system turns the Abrikosov lattice into a vortex glass, whereas the vortex liquid remains a liquid. The terms "glass" and "liquid" are defined in a dynamic sense, with a sublinear response $\ensuremath{\rho}={\frac{\ensuremath{\partial}E}{\ensuremath{\partial}j}|}_{j\ensuremath{\rightarrow}0}$ characterizing the truly superconducting vortex glass and a finite resistivity $\ensuremath{\rho}(j\ensuremath{\rightarrow}0)g0$ being the signature of the liquid phase. The smallness of $\frac{{j}_{c}}{{j}_{o}}$ allows one to discuss the influence of quenched disorder in terms of the weak collective pinning theory. Supplementing the traditional theory of weak collective pinning to take into account thermal and quantum fluctuations, as well as the new scaling concepts for elastic media subject to a random potential, this modern version of the weak collective pinning theory consistently accounts for a large number of novel phenomena, such as the broad resistive transition, thermally assisted flux flow, giant and quantum creep, and the glassiness of the solid state. The strong layering of the oxides introduces additional new features into the thermodynamic phase diagram, such as a layer decoupling transition, and modifies the mechanism of pinning and creep in various ways. The presence of strong (correlated) disorder in the form of twin boundaries or columnar defects not only is technologically relevant but also provides the framework for the physical realization of novel thermodynamic phases such as the Bose glass. On a macroscopic scale the vortex system exhibits self-organized criticality, with both the spatial and the temporal scale accessible to experimental investigations.

Using MPI: Portable Parallel Programming with the Message-Passing Interface

Abstract: This book offers a thoroughly updated guide to the MPI (Message-Passing Interface) standard library for writing programs for parallel computers Since the publication of the previous edition of Using MPI, parallel computing has become mainstream Today, applications run on computers with millions of processors; multiple processors sharing memory and multicore processors with multiple hardware threads per core are common The MPI-3 Forum recently brought the MPI standard up to date with respect to developments in hardware capabilities, core language evolution, the needs of applications, and experience gained over the years by vendors, implementers, and users This third edition of Using MPI reflects these changes in both text and example code The book takes an informal, tutorial approach, introducing each concept through easy-to-understand examples, including actual code in C and Fortran Topics include using MPI in simple programs, virtual topologies, MPI datatypes, parallel libraries, and a comparison of MPI with sockets For the third edition, example code has been brought up to date; applications have been updated; and references reflect the recent attention MPI has received in the literature A companion volume, Using Advanced MPI, covers more advanced topics, including hybrid programming and coping with large data

The crystal structure of the bacterial chaperonin GroEL at 2.8 A.

Abstract: The crystal structure of Escherichia coli GroEL shows a porous cylinder of 14 subunits made of two nearly 7-fold rotationally symmetrical rings stacked back-to-back with dyad symmetry. The subunits consist of three domains: a large equatorial domain that forms the foundation of the assembly at its waist and holds the rings together; a large loosely structured apical domain that forms the ends of the cylinder; and a small slender intermediate domain that connects the two, creating side windows. The three-dimensional structure places most of the mutationally defined functional sites on the channel walls and its outward invaginations, and at the ends of the cylinder.

fastDNAml: a tool for construction of phylogenetic trees of DNA sequences using maximum likelihood

Abstract: We have developed a new tool, called fastDNAml, for constructing phylogenetic trees from DNA sequences. The program can be run on a wide variety of computers ranging from Unix workstations to massively parallel systems, and is available from the Ribosomal Database Project (RDP) by anonymous FTP. Our program uses a maximum likelihood approach and is based on version 3.3 of Felsenstein's dnaml program. Several enhancements, including algorithmic changes, significantly improve performance and reduce memory usage, making it feasible to construct even very large trees. Trees containing 40-100 taxa have been easily generated, and phylogenetic estimates are possible even when hundreds of sequences exist. We are currently using the tool to construct a phylogenetic tree based on 473 small subunit rRNA sequences from prokaryotes.

Line search algorithms with guaranteed sufficient decrease

Abstract: The development of software for minimization problems is often based on a line search method. We consider line search methods that satisfy sufficient decrease and curvature conditions, and formulate the problem of determining a point that satisfies these two conditions in terms of finding a point in a set T(m). We describe a search algorithm for this problem that produces a sequence of iterates that converge to a point in T(m) and that, except for pathological cases, terminates in a finite number of steps. Numerical results for an implementation of the search algorithm on a set of test functions show that the algorithm terminates within a small number of iterations.

The genetic data environment an expandable GUI for multiple sequence analysis.

Abstract: An X-Windows-based graphic user interface is presented which allows the seamless integration of numerous existing biomolecular programs into a single analysis environment. This environment is based on a core multiple sequence editor that is linked to external programs by a user-expandable menu system and is supported on Sun and DEC workstations. There is no limitation to the number of external functions that can be linked to the interface. The length and number of sequences that can be handled are limited only by the size of virtual memory present on the workstation. The sequence data itself is used as the reference point from which analysis is done, and scalable graphic views are supported. It is suggested that future software development utilizing this expandable, user-defined menu system and the I/O linkage of external programs will allow biologists to easily integrate expertise from disparate fields into a single environment.

Geometrical barriers in high-temperature superconductors.

Abstract: A theoretical description of vortex dynamics in thin flat samples is derived and is found to compare favorably with experimental results. In perpendicular applied magnetic field the vortex penetration is delayed significantly due to the presence of a potential barrier of geometrical origin. This novel geometrical barrier effect results in hysteretic magnetization and in the existence of an irreversibility line in the absence of bulk pinning. Among the unique characteristics of the barrier are a vortex concentration in the center of the sample and a zero-field peak in the magnetization loops.

Photophysics of the carotenoids associated with the xanthophyll cycle in photosynthesis

Abstract: Green plants use the xanthophyll cycle to regulate the flow of energy to chlorophylla within photosynthetic proteins. Under conditions of low light intensity violaxanthin, a carotenoid possessing nine conjugated double bonds, functions as an antenna pigment by transferring energy from its lowest excited singlet state to that of chlorophylla within light-harvesting proteins. When the light intensity increases, violaxanthin is biochemically transformed into zeaxanthin, a carotenoid that possesses eleven conjugated double bonds. The results presented here show that extension of the ⧄ conjugation of the polyene lowers the energy of the lowest excited singlet state of the carotenoid below that of chlorophylla. As a consequence zeaxanthin can act as a trap for the excess excitation energy on chlorophylla pigments within the protein, thus regulating the flow of energy within photosynthetic light-harvesting proteins.

Dynamic Melting of the Vortex Lattice.

Abstract: We investigate analytically and numerically the melting of the vortex lattice moving in an inhomogeneous environment under the applied current [ital j]. We predict the existence of a dynamic phase transition at some characteristic current [ital j]=[ital j][sub [ital t]] (crystallization current) from the motion of the amorphous vortex configuration at [ital j][lt][ital j][sub [ital t]] to the motion of the vortex crystal at [ital j][gt][ital j][sub [ital t]]. The crystallization current [ital j][sub [ital t]] exceeds essentially the critical current [ital j][sub [ital c]] for strongly disordered systems and diverges as temperature approaches the melting temperature [ital T][sub [ital m]] of the undisturbed lattice.

Mechanical properties of nanophase metals

Abstract: Nanophase metals have grain-size dependent mechanical properties that are significantly different than those of their coarse-grained counterparts. Pure metals are much stronger and apparently less ductile than conventional ones; intermetallics are also strengthened, but they tend toward increased ductility at the smallest grain sizes. These property changes are primarily related to grain size limitations, but they are also affected by the large percentage of atoms in grain boundaries and other microstructural features. Strengthening appears to result from a limitation of dislocation activity, while increased ductility probably relates to grain boundary sliding. A brief overview of our present understanding of the mechanical properties of nanophase metals is presented.

The Experimental Physics and Industrial Control System architecture: Past, present, and future

Abstract: The Experimental Physics and Industrial Control System (EPICS), has been used at a number of sites for performing data acquisition, supervisory control, closed-loop control, sequential control, and operational optimization. The EPICS architecture was originally developed by a group with diverse backgrounds in physics and industrial control. The current architecture represents one instance of the “standard model”. It provides distributed processing and communication from any local area network (LAN) device to the front end controllers. This paper presents the current architecture, performance envelope, current installations, and planned extensions for requirements not met by the current architecture.

Limitation of the magnetic-circular-dichroism spin sum rule for transition metals and importance of the magnetic dipole term.

Abstract: Magnetic-circular-dichroism (MCD) spectra and the spin magnetic dipole term ([l angle][ital T][sub [ital z]][r angle]) for bulk 3[ital d] transition metals and their surfaces were calculated from full potential linearized augmented plane wave electronic band structure results. The recently proposed MCD spin sum rule is found to result in a much larger error [of up to 50% for the Ni(001) surface] than does its orbital counterpart. In support of recent experiments for bulk, we find that by combining the MCD orbital and spin sum rules the ratio of spin and orbital moments can be determined from the MCD spectra even for low dimension systems with an error of 10% when the [l angle][ital T][sub [ital z]][r angle] contribution is included.

Magnetic phases of ultrathin Fe grown on Cu(100) as epitaxial wedges

Abstract: Magnetic wedges of Fe on Cu(100) are explored magneto-optically. In the region of 6--11 monolayers (ML) of fcc Fe grown at room temperature, in addition to a surface ferromagnetic layer with a Curie temperature \ensuremath{\sim}250 K, the Fe bulk is antiferromagnetic with a N\'eel temperature of \ensuremath{\sim}200 K. This fcc phase is stable only above a growth temperature of order \ensuremath{\sim}200 K, below which the ferromagnetic spin-reorientation transition occurs at \ensuremath{\sim}6 ML. The phase boundaries are delineated by cusps in the coercivity along the wedge.

Monitors, messages, and clusters: the p4 parallel programming system

Abstract: p4 is a portable library of C and Fortran subroutines for programming parallel computers. It is the current version of a system that has been in use since 1984. It includes features for explicit parallel programming of shared-memory machines, distributed-memory machines (including heterogeneous networks of workstations), and clusters, by which we mean shared-memory multiprocessors communicating via message passing. We discuss here the design goals, history, and system architecture of p4 and describe briefly a diverse collection of applications that have demonstrated the utility of p4.

Measurements of the proton elastic form factors for 1 <= Q2 <= 3 (GeV/c)2 at SLAC.

Abstract: We report measurements of the proton form factors [ital G][sub [ital E]][sup [ital p]] and [ital G][sub [ital M]][sup [ital p]] extracted from elastic scattering in the range 1[le][ital Q][sup 2][le]3 (GeV/[ital c])[sup 2] with total uncertainties [lt] 15% in [ital G][sub [ital E]][sup [ital p]] and [lt] 3% in [ital G][sub [ital M]][sup [ital p]]. Comparisons are made to theoretical models, including those based on perturbative QCD, vector-meson dominance, QCD sum rules, and diquark constituents in the proton. The results for [ital G][sub [ital E]][sup [ital p]] are somewhat larger than indicated by most theoretical parametrizations, and the ratios of the Pauli and Dirac form factors [ital Q][sup 2]([ital F][sub 2][sup [ital p]]/[ital F][sub 1][sup [ital p]]) are lower in value and demonstrate a weaker [ital Q][sup 2] dependence than those predictions. A global extraction of the elastic form factors from several experiments in the range 0.1 [lt] [ital Q][sup 2] [lt] 10 (GeV/[ital c])[sup 2] is also presented.

Measurement of total and partial photon proton cross sections at 180 GeV center of mass energy

Abstract: Photon proton cross sections for elastic light vector meson production, σelνp, inelastic diffractive production, σndνp, non-diffractive production, σdνp, as well as the total cross section, σtotνp, have been measured at an average υp center of mass energy of 180 GeV with the ZEUS detector at HERA. The resulting values are σelνp = 18 ± 7 μb, σdνp = 33 ± 8 μb, σndνp = 91 ± 11 μb, and σtotνp 143 ± 17 μb, where the errors include statistical and systematic errors added in quadrature.

C-axis response of yba2cu4o8 : a pseudogap and possibility of josephson coupling of cuo2 planes

Abstract: We report on the temperature dependence of the far-infrared conductivity of YBa[sub 2]Cu[sub 4]O[sub 8] single crystals for [bold E][parallel][ital c]. With decreasing temperature, the conductivity shows a transition from a Drude-like behavior to a pseudogap at 180 cm[sup [minus]1] which grows deeper below 180 K without any abrupt changes at the superconducting transition at [ital T][sub [ital c]]=80 K. In the superconducting state the formation of the superfluid condensate can be seen. We show that in a variety of high-[ital T][sub [ital c]] superconductors the value of the London penetration depth for [bold E][parallel][ital c] correlates with the conductivity along the [ital c] direction. With respect to this correlation we discuss the possibility of Josephson coupling between the CuO[sub 2] layers.

Currents, charges, and canonical structure of pseudodual chiral models.

Abstract: We discuss the pseudodual chiral model to illustrate a class of two-dimensional theories which have an infinite number of conservation laws but allow particle production, at variance with naive expectations. We describe the symmetries of the pseudodual model, both local and nonlocal, as transmutations of the symmetries of the usual chiral model. We refine the conventional algorithm to more efficiently produce the nonlocal symmetries of the model, and we discuss the complete local current algebra for the pseudodual theory. We also exhibit the canonical transformation which connects the usual chiral model to its fully equivalent dual, further distinguishing the pseudodual theory.

The solid-state properties of uranium A historical perspective and review

Abstract: We review our current understanding of the mechanical, electronic and structural properties of the element uranium, with the focus on the low-temperature regime in which the α-phase is stable We start with a historical perspective, as the need for understanding the metallurgy of uranium so that its use as a nuclear fuel in the late 1940s could be optimized led to an increasing number of experiments aimed at exploring the solid-state properties This was further accelerated when single crystals became available in the 1950s and when the superconductivity of the low-temperature α phase became the subject of controversy in the 1960s The late 1960s and 1970s saw a considerable effort towards understanding the nature of the 5f electrons around the uranium nucleus The increasing availability of sophisticated methods in computational physics first showed in the 1970s that the 5f electrons should be treated as itinerant, and the decade ended with the observation (by neutron diffraction) of a subtle pe

Fullerenes in the 1.85-Billion-Year-Old Sudbury Impact Structure

Abstract: Fullerenes (C60 and C70) have been identified by laser desorption, laser desorption post-ionization, and high-resolution electron-impact mass spectrometry in shock-produced breccias (Onaping Formation) of the Sudbury impact structure in Ontario, Canada. The C60 isotope is present at a level of a few parts per million. The fullerenes were likely synthesized within the impact plume from the carbon contained in the bolide. The oxidation of the fullerenes during the 1.85 billion years of exposure was apparently prevented by the presence of sulfur in the form of sulfide-silicate complexes associated with the fullerenes.

Peak effect as a precursor to vortex lattice melting in single crystal YBa2Cu3O7- delta.

Abstract: We present direct evidence of a "peak effect" as a precursor to vortex lattice melting in a single crystal of $\mathrm{Y}{\mathrm{Ba}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{7\ensuremath{-}\ensuremath{\delta}}$ containing only two twin planes. The peak effect occurs just below the vortex liquid to solid phase transition in a narrow field region between 0.3 and 1.5 T for $H\ensuremath{\parallel}\mathbf{c}$ and is clearly observed as a function of both magnetic field and temperature. We demonstrate that the peak effect is due to enhanced vortex pinning by the twin boundaries, indicative of lattice softening prior to melting. In addition, we show evidence for a non-Ohmic behavior in the vortex liquid state due to depinning of the vortices from the two twin boundaries with increasing Lorentz force.

Ultrahigh-Resolution X-ray Tomography.

Abstract: Ultrahigh-resolution three-dimensional images of a microscopic test object were made with soft x-rays collected with a scanning transmission x-ray microscope The test object consisted of two different patterns of gold bars on silicon nitride windows that were separated by ∼5 micrometers Depth resolution comparable to the transverse resolution was achieved by recording nine two-dimensional images of the object at angles between –50 and +55 degrees with respect to the beam axis The projections were then combined tomographically to form a three-dimensional image by means of an algorithm using an algebraic reconstruction technique A transverse resolution of ∼1000 angstroms was observed Artifacts in the reconstruction limited the overall depth resolution to ∼6000 angstroms; however, some features were clearly reconstructed with a depth resolution of ∼1000 angstroms

Surface spin-flop transition in Fe/Cr(211) superlattices: Experiment and theory

Abstract: We report experimental and theoretical studies of the magnetization curves of Fe/Cr(211) superlattices with antiferromagnetic interlayer coupling and uniaxial in-plane anisotropy. There are substantial differences between structures with an even and an odd number of Fe layers, when the magnetic field is applied along the easy axis. For even layered superlattices, the inequivalence of the terminal Fe layers gives rise to a surface spin-flop transition that evolves into a bulk spin-flop arrangement with increasing magnetic field, as originally envisioned by Keffer and Chow [Phys. Rev. Lett. 31, 1061 (1973)].

2-D Fluid Transport Simulations of Gaseous/Radiative Divertors

Abstract: The features of the fully implicit 2-D fluid code UEDGE are described. The utility of the code is demonstrated by showing bifurcations or multiple solutions of the tokamak edge plasma for both deuterium and impurity injection in the divertor.