174 research outputs found
MgB2 superconducting thin films with a transition temperature of 39 Kelvin
We report the growth of high-quality c-axis-oriented epitaxial MgB2 thin
films by using a pulsed laser deposition technique. The thin films grown on
(1`1 0 2) Al2O3 substrates show a Tc of 39 K. The critical current density in
zero field is ~ 6 x 10^6 A/cm2 at 5 K and ~ 3 x 10^5 A/cm^2 at 35 K, suggesting
that this compound has great potential for electronic device applications, such
as microwave devices and superconducting quantum interference devices. For the
films deposited on Al2O3, X-ray diffraction patterns indicate a highly
c-axis-oriented crystal structure perpendicular to the substrate surface.Comment: 3 pages and 3 figure
Optimization of drift gases for accuracy in pressurized drift tubes
Modern detectors such as ATLAS use pressurized drift tubes to minimize diffusion and achieve high coordinate accuracy. However, the coordinate accuracy depends on the exact knowledge of converting measured times into coordinates. Linear space-time relationships are best for reconstruction, but difficult to achieve in the field. Previous mixtures, which contained methane or other organic quenchers, are disfavored because of ageing problems. From our studies of nitrogen and carbon dioxide, two mixtures with only small deviations from linearity were determined and measured. Scaling laws for different pressures and magnetic fields are also given
Keck Adaptive Optics Observations of the Radio Galaxy 3C294: A Merging System at z = 1.786?
We present seeing-limited and adaptive optics (AO) images of the z = 1.786
radio galaxy 3C294 in the H and K' infrared bands obtained at Keck Observatory.
The infrared emission of 3C294 is dominated by two distinct components
separated by ~1" (9 kpc). The eastern knot contains an unresolved core that
contributes ~4% of the K'-band light; we identify this core with the active
nucleus. The western component is about 2.5 times brighter. The most plausible
interpretation of the near-infrared morphology is an ongoing merger event, with
the active nucleus located in the less massive of the two galaxies.Comment: Accepted for Publication in Astrophysical Journa
Numerical Evaluation of P-Multigrid Method for the Solution of Discontinuous Galerkin Discretizations of Diffusive Equations
This paper describes numerical experiments with P-multigrid to corroborate analysis, validate the present implementation, and to examine issues that arise in the implementations of the various combinations of relaxation schemes, discretizations and P-multigrid methods. The two approaches to implement P-multigrid presented here are equivalent for most high-order discretization methods such as spectral element, SUPG, and discontinuous Galerkin applied to advection; however it is discovered that the approach that mimics the common geometric multigrid implementation is less robust, and frequently unstable when applied to discontinuous Galerkin discretizations of di usion. Gauss-Seidel relaxation converges 40% faster than block Jacobi, as predicted by analysis; however, the implementation of Gauss-Seidel is considerably more expensive that one would expect because gradients in most neighboring elements must be updated. A compromise quasi Gauss-Seidel relaxation method that evaluates the gradient in each element twice per iteration converges at rates similar to those predicted for true Gauss-Seidel
Drag Prediction Using Adaptive Discontinuous Finite Elements
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/106502/1/AIAA2013-51.pd
Einstein black holes, free scalars and AdS/CFT correspondence
We investigate AdS/CFT correspondence for two families of Einstein black
holes in d > 3 dimensions, modelling the boundary CFT by a free conformal
scalar field and evaluating the boundary two-point function in the bulk
geodesic approximation. For the d > 3 counterpart of the nonrotating BTZ hole
and for its Z_2 quotient, the boundary state is thermal in the expected sense,
and its stress-energy reflects the properties of the bulk geometry and suggests
a novel definition for the mass of the hole. For the generalised
Schwarzschild-AdS hole with a flat horizon of topology R^{d-2}, the boundary
stress-energy has a thermal form with energy density proportional to the hole
ADM mass, but stress-energy corrections from compactified horizon dimensions
cannot be consistently included at least for d=5.Comment: 32 pages. LaTeX with amsfonts, amsmath, amssymb. (v2: References
added. v3: Geodesic horizon-crossing clarified in section 2; comparison with
quasilocal energy-momentum included in section 4.
String Theory on Lorentzian AdS_3 in Minisuperspace
We investigate string theory on Lorentzian AdS_3 in the minisuperspace
approximation. The minisuperspace model reduces to the worldline theory of a
scalar particle in the Lorentzian AdS_3. The Hilbert space consists of
normalizable wave functions, and we see that the unitarity of the theory (or
the self-adjointness of the Hamiltonian) restricts the possible sets of wave
functions. The restricted wave functions have the property of probability
conservation (or current conservation) across the horizons. Two and three point
functions are also computed. In the Euclidean model functional forms of these
quantities are restricted by the SL(2,R) symmetry almost uniquely, however, in
the Lorentzian model there are several ambiguities left. The ambiguities are
fixed by the direct computation of overlaps of wave functions.Comment: 32 pages, no figures, minor changes, references adde
A Robust Adaptive Solution Strategy for High-Order Implicit CFD Solvers
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/90694/1/AIAA-2011-3696-676.pd
A Matrix Model for the Null-Brane
The null-brane background is a simple smooth 1/2 BPS solution of string
theory. By tuning a parameter, this background develops a big crunch/big bang
type singularity. We construct the DLCQ description of this space-time in terms
of a Yang-Mills theory on a time-dependent space-time. Our dual Matrix
description provides a non-perturbative framework in which the fate of both
(null) time, and the string S-matrix can be studied.Comment: 26 pages, LaTeX; references adde
Scattering of Long Folded Strings and Mixed Correlators in the Two-Matrix Model
We study the interactions of Maldacena's long folded strings in
two-dimensional string theory. We find the amplitude for a state containing two
long folded strings to come and go back to infinity. We calculate this
amplitude both in the worldsheet theory and in the dual matrix model, the
Matrix Quantum Mechanics. The matrix model description allows to evaluate the
amplitudes involving any number of long strings, which are given by the mixed
trace correlators in an effective two-matrix model.Comment: 39 pages, 6 figure
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