Physical Sciences and Mathematics Commons^™

Measurements Of Deuteron Threshold Electrodisintegration: A Probe Of Short-Range Meson Exchange, K S. Lee, W Schmitt, H Baghaei, S Churchwell, R S. Hicks, R A. Miskimen, Gerald Alvin Peterson, K Wang

Gerald Alvin Peterson

The threshold electrodisintegration of the deuteron was measured with good energy resolution to a maximum four-momentum transfer squared of 42 fm-2. The data are compared with meson exchange calculations that show sensitivity to the choice of exchange-current form factor, the nucleon electromagnetic form factors, and the nucleon-nucleon potential. While conventional theories can give a reasonable description of the data, comparison of the data with quark cluster calculations shows poor agreement.

Elastic Magnetic Electron Scattering From ' C At Q2= 1 Gev2/C, R A. Miskimen, H Baghaei, M Frodyma, R S. Hicks, K S. Lee, Gerald Alvin Peterson

Gerald Alvin Peterson

Electron scattering from C was measured at a momentum transfer of 5.08 fm . No electron events were observed in the vicinity of the elastic peak, giving an upper limit for the elastic cross section of 1.2 x 10 cm /sr with a confidence level of 90%. At this momentum transfer, the square of the elastic M1 form factor apparently continues to fall exponentially with q. Comparison of the data with shell-model calculations indicates that admixtures of 2hu configurations in the C ground state cannot entirely explain the high-q enhancement of the Ml form factor relative to 1p-shell calculations.

First-Principles Study Of Phase Stability In Cu-Zn Substitutional Alloys, P. E. A. Turchi, M. Sluiter, F. J. Pinski, Duane D. Johnson, D. M. Nicholson, G. M. Stocks, J. B. Staunton

Duane D. Johnson

A parameter-free approach to phase stability in Cu-Zn substitutional alloys is shown to describe order-disorder phenomena and structural transformations with remarkable accuracy. The method is based on a multiple-scattering description of the electronic structure properties of the random alloy. Configurational order is treated within the generalized perturbation method and the concentration-functional theory. Thermodynamical properties of α and β brasses are derived from the cluster variation method. This advanced scheme is of general validity and is expected to yield similarly accurate results for other Hume-Rothery alloys.

Equatorial Thermospheric Wind Changes During The Solar Cycle: Measurements At Arequipa,Peru From 1983 To 1990, M. A. Biondi, J. W. Meriwether, Bela G. Fejer, S. A. Gonzalesz, D. C. Hallenbeck

Bela G. Fejer

Fabry-Perot interferometer measurements of Doppler shifts in the nightglow 630-nm emission line have been used to determine near-equatorial thermospheric wind velocities at Arequipa, Peru, over ∼2/3 of a solar cycle. Monthly-average nocturnal variations in the meridional and zonal wind components were calculated from the nightly data to remove short term (day-to-day) variability, facilitating display of seasonal changes in the wind patterns, as well as any additional changes introduced by the progression of the solar cycle. The measured seasonal variations in the wind patterns are more pronounced than the solar cycle variations and are more readily understandable in terms of the …

Average Vertical And Zonal F-Region Plasma Drifts Over Jicamarca, Bela G. Fejer, E. R. De Paula, S. Gonzalez, R. F. Woodman

Bela G. Fejer

The seasonal averages of the equatorial F region vertical and zonal plasma drifts are determined using extensive incoherent scatter radar observations from Jicamarca during 1968–1988. The late afternoon and nighttime vertical and zonal drifts are strongly dependent on the 10.7-cm solar flux. We show that the evening prereversal enhancement of vertical drifts increases linearly with solar flux during equinox but tends to saturate for large fluxes during southern hemisphere winter. We examine in detail, for the first time, the seasonal variation of the zonal plasma drifts and their dependence on solar flux and magnetic activity. The seasonal effects on the …

Three-Point Correlations In Driven Diffusive Systems With Ising Symmetry, Beate Schmittmann, R. K. P. Zia

Beate Schmittmann

For equilibrium systems with Ising symmetry, the three-point correlation function is always zero above criticality. When a lattice-gas version of this system is driven to a nonequilibrium steady state, this correlation becomes nontrivial. Its dominant large-scale behavior is found to be a consequence of both the manifest breaking of Ising symmetry by the driving force and the more subtle violation of the fluctuation-dissipation theorem.

Interpretation Issues In Force Microscopy, Nancy Burnham, Richard Colton, Hubert Pollock

Nancy A. Burnham

In this paper, we will discuss force microscopy (FM) and its potential for determining mechanical properties of thin films. We will introduce the basic principles of FM, and demonstrate how FM can be used to determine materials properties as well as image surface topography, both with nanonewton or sub‐nanonewton force resolution and sub‐nanometer position resolution. As FM is still a new field, not all of the questions concerning interpretation have been fully answered. We will elucidate four current issues that must be resolved before the full potential of FM can be realized. They are: (1) the role of water vapor …

Finger Formation In A Driven Diffusive System, D. H. Boal, Beate Schmittmann, R. K. P. Zia

Beate Schmittmann

A driven diffusive lattice gas is studied in a rectangular geometry: particles are fed in at one side and extracted at the other, after being swept through the system by a uniform driving field. Being periodic in the transverse direction, the lattice lies on the surface of a cylinder. The resulting nonequilibrium steady state depends strongly on this choice of boundary conditions. Both Monte Carlo and analytic techniques are employed to investigate the structure of typical configurations, the density profile, the steady-state current, and the nearest-neighbor correlations. As the temperature is lowered in a finite system, the simulations indicate a …

Observability Of The Anapole Moment And Neutrino Charge Radius, Mj Musolf, Br Holstein

Barry R Holstein

The properties of the neutrino charge radius (NCR) and anapole moments (AM's) of elementary fermions, nucleons, and nuclei are discussed. The dependence of these off-shell electromagnetic couplings on the weak gauge parameter is explicitly demonstrated by a calculation performed in the Rξ gauge. The gauge dependence of the AM's and NCR implies that they cannot be observed in isolation from other second-order, electroweak effects. It is shown, however, that the AM's of various hadronic systems having an SU(2)L quantum number TL3=0 can be considered ``observables'' in certain formal, though unphysical, limits. It is argued that, apart from these special limits, …

Transport Processes And Traveling Waves In Systems With Local Nonequilibrium, Sergey Sobolev

Sergey Sobolev

No abstract provided.

Origins Of Compositional Order In Nipt Alloys, F. J. Pinski, B. Ginatempo, Duane D. Johnson, J. B. Staunton, G. M. Stocks, B. L. Gyorffy

Duane D. Johnson

We investigate the cause of compositional ordering in fcc Ni0.50Pt0.50 on the basis of a first-principles theory of electronic structure and finite-temperature concentration fluctuations. We treat the size effect, electronegativity, and band filling on an equal footing and find that the first of these dominates, leading to L10 ordering in agreement with experiment. An electronic origin is given for the metallurgical ‘‘rule of thumb’’ that alloys comprised of big atoms and little atoms tend to order into simple stuctures.

The Interaction Between Dislocations And Intergranular Cracks, H. Zhang, Alexander H. King, R. Thomson

Alexander H. King

The elastic interactions of dislocations and intergranular cracks in isotropic materials have been studied. In the first part of the paper, a model based on the Rice–Thomson theory is established under which the conditions for dislocation emission and crack propagation can be described in terms of an emission surface, cleavage surface, and loading line in the local k-space associated with a mixed mode intergranular crack. For a given crack, the local k-field changes with the emission of dislocations from the crack tip, which alters the balance of cleavage and emission. In the second part, we present experimental results of in …

Critical Properties Of A Randomly Driven Diffusive System, Beate Schmittmann, R. K. P. Zia

Beate Schmittmann

We consider a system of interacting particles, diffusing under the influence of both thermal noise and a random, external electric field which acts in a subspace of m dimensions. In the nonequilibrium steady state, the net current is zero. When the interparticle interaction is short ranged and attractive, a second-order phase transition is expected. Analyzing this system in field-theoretic terms, we find the upper critical dimension to be 4-m and its behavior to fall outside the universality classes of the equilibrium Ising model and the usual driven diffusive system. A new fixed point and critical exponents are computed.

Cluster As Solitons On The Nuclear Surface, Andrei Ludu

Andrei Ludu

No abstract provided.

The Slater–Pauling Curve: First Principles Calculations Of The Moments Of Fe1 − C Ni C And V1 − C Fe C, Duane Johnson, F. Pinski, J. Staunton

Duane D. Johnson

We have performed calculations of the electronic structure of the random substitutional alloys Fe1−c Ni c and V1−c Fe c using the spin‐polarized, self‐consistent Korringa–Kohn–Rostoker coherent‐potential approximation (KKR‐CPA) method. This is a first principles method based on spin density functionaltheory and a local spin density approximation for the exchange and correlation functional. For fcc Fe1−c Ni c , a range of volumes were considered for 0.25

Novel Ce Magnetism In Cedipnictide And Di‐Ce Pnictide Structures, Paul C. Canfield, J. D. Thompson, Z. Fisk

Paul C. Canfield

Results of electrical resistance and magnetic susceptibility measurements on Ce2Bi, Ce2Sb, CeScGe, CeScSi and CeSb2 are presented. Ce2Bi and Ce2Sb have antiferromagnetictransitions at low temperatures, while CeSb2, CeScGe and CeScSi have ferromagnetictransitions, CeScGe having a T c = 46 K. The data are analyzed with respect to the similarities of the two crystal structure groups that these materials fall into: CeSb2 having the LaSb2structure and the other materials all having the La2Sb structure.

Magnetism And Heavy Fermion‐Like Behavior In The Rbipt Series, Paul C. Canfield, J. D. Thompson, W. P. Beyermann, A. Lacerda, M. F. Hundley, E. Peterson, Z. Fisk, H. R. Ott

Paul C. Canfield

Members of the RBiPt (R=Ce–Lu with the exceptions of Pm and Eu) series have been grown as single crystals.Magnetic susceptibility and electrical resistance have been measured on all members of the series, and specific heatmeasurements have been performed on representatives. The high temperature resistance uniformly changes from that of a small‐gap semiconductor or semimetal seen in NdBiPt to that of a heavy‐fermion metal seen in YbBiPt, which shows a linear coefficient of specific heat at low temperatures of 8 J/K2 mole. Further, the lighter rare earth members show an unusually sharp increase in their resistance associated with antiferromagnetic ordering at …

Ion Irradiation Effects On Graphite With Scanning Tunneling Microscope, T. -C. Shen, R. T. Brockenbrough, J. R. Tucker, J. W. Lyding

T. -C. Shen

Scanning tunneling microscope is used to create local surface modifications by means of ion impact damage. Graphite has been used as a test case to demonstrate this local surface sputtering. Using 0.1-µs voltage pulse of - 30 to - 140 V applied to the sample in a rough vacuum of 10-2 Torr, a confined area of damage (typically about 100 Å in diameter) is usually obtained. The damaged area consists of several layers of terraces. Defects of the size of a few atoms can also be found. Electronic perturbations caused by defects can form superlattices with a spacing three times …

Longitudinal Nmr Relaxation Of Degenerate 2-D 3he In 4he Films, Robert Hallock, D. T. Sprague, N. Alikacem

Robert Hallock

The NMR spin-lattice relaxation time T1 of a degenerate submonolayer coverage of 3He in a thin adsorbed 4He film has been measured. As a function of 4He coverage, T1 exhibits a maximum and undergoes a change in temperature dependence at a coverage near that of the superfluid transition in the underlying 4He film. Two relaxation mechanisms contribute to the observed T1.

Linear Tc Depression In Mg Doped Yba2cu3o7-X, Robert Hallock, W. M. Tiernan

Robert Hallock

We report resistivity-versus-temperature measurements performed on polycrystalline pellets of YBa2(Cu1-xMgx)3O7-δ made using the polymer-metal-complex precursor method. Tc was found to decrease linearly with increasing Mg doping in the range x=8.6×10-4 to 8.6×10-3 with slope -1400 K/x; the normal-state resistivity and the superconducting transition width showed little or no change. Mg was found to have a maximum solubility in YBa2(Cu1-xMgx)3O7-δ of x~=9×10-3.

Nonequilibrium Processes In Polymers Undergoing Interchange Reactions. Part 2: Reaction-Diffusion Processes, Alejandro Garcia, J. Pojman, D. Kondepudi, C. Van De Broeck

Alejandro Garcia

A reactiodffusion system of polymers undergoing interchange reactions is studied. The equation that describes the dynamics of the system is similar to the Boltzmann equation for a gas of hard spheres. We consider a one-dimensionsl system in which the average length and the concentrations at the boundaries are fixed. The resulting steady states are obtained analytically and with numerical integration of equations obtained by using a local equilibrium approximation. Monte Carlo simulations of experimentally realizable conditions were performed and compared. The results reveal a nonlinear distribution of molecular concentration and mass. The entropy of the polymer distributions is calculated as …

The (First) Three B’S Of The Skyrme Model, Alec Schramm

Alec J Schramm

No abstract provided.

Higgs Boson Production In Peripheral Heavy-Ion Collisions: Coherent Double-Pomeron Exchange, Alec Schramm, Berndt Muller

Alec J Schramm

Higgs boson production by coherent double-pomeron exchange in peripheral nuclear collisions at energies of several TeV per nucleon is calculated. It is shown that a trigger on quasi-elastic nuclear collisions strongly suppresses the cross section. The analogous two-photon process is predicted to dominate for collisions of heavy nuclei.

Digital-Image-Based Study Of Circular Holes In An Elastic Matrix, Anthony Day, K. Snyder, E. Garboczi, M. Thorpe

Anthony Roy Day

No abstract provided.

Solving Ill-Posed Problems With Artificial Neural Networks, Arun D. Kulkarni

Arun Kulkarni

Universal Conductivity Curve For A Plane Containing Random Holes., E. J. Garboczi, M. F. Thorpe, M. S. Devries, Anthony Roy Day

Anthony Roy Day

This paper examines the general percolation problem of cutting randomly centered insulating holes in a two-dimensional conducting sheet, and explores how the electrical conductivity sigma decreases with the remaining area fraction. This problem has been studied in the past for circular, square, and needlelike holes, using both computer simulations and analog experiments. In this paper, we extend these studies by examining cases where the insulating hole is of arbitrary shape, using digital-image-based numerical techniques in conjunction with the Y- [nabla] algorithm. We find that, within computational uncertainty, the scaled percolation threshold, xc=nc=5.9±0.4, is a universal quantity for all the cases …