5,025 research outputs found
Study of Microstructure and Phase of Plasma Sprayed Cr3C2-NiCr Coating before and after the Sparking Plasma Sintering
AbstractPlasma sprayed chromium carbide coating has poor adhesion strength and wear-resistance, sparking plasma sintering(SPS) process can change the coating microstructure and improve its performance. The microstructure and phase of plasma sprayed Cr3C2-NiCr coating before and after the sparking plasma sintering were studied in this paper. The results show that the microstructure of plasma sprayed Cr3C2-NiCr coating after SPS become more compact and most of the pores and micro-cracks disappear. Some new oxides appear after SPS process. Hard Chromium carbides and oxides phase distribute in the NiCr-based solid solution to improve the wear resistance of the coating. Obvious crack at the interface has disappeared. The coating and the substrate form a good metallurgical bond
Issues and Observations on Applications of the Constrained-Path Monte Carlo Method to Many-Fermion Systems
We report several important observations that underscore the distinctions
between the constrained-path Monte Carlo method and the continuum and lattice
versions of the fixed-node method. The main distinctions stem from the
differences in the state space in which the random walk occurs and in the
manner in which the random walkers are constrained. One consequence is that in
the constrained-path method the so-called mixed estimator for the energy is not
an upper bound to the exact energy, as previously claimed. Several ways of
producing an energy upper bound are given, and relevant methodological aspects
are illustrated with simple examples.Comment: 28 pages, REVTEX, 5 ps figure
Two-flux Colliding Plane Waves in String Theory
We construct the two-flux colliding plane wave solutions in higher
dimensional gravity theory with dilaton, and two complementary fluxes. Two
kinds of solutions has been obtained: Bell-Szekeres(BS) type and homogeneous
type. After imposing the junction condition, we find that only Bell-Szekeres
type solution is physically well-defined. Furthermore, we show that the future
curvature singularity is always developed for our solutions.Comment: 16 pages, Latex; typoes corrected; references added, minor
modification
Topological Charge Fluctuations and Low-Lying Dirac Eigenmodes
We discuss the utility of low-lying Dirac eigenmodes for studying the nature
of topological charge fluctuations in QCD. The implications of previous results
using the local chirality histogram method are discussed, and the new results
using the overlap Dirac operator in Wilson gauge backgrounds at lattice
spacings ranging from a~0.04 fm to a~0.12 fm are reported. While the degree of
local chirality does not change appreciably closer to the continuum limit, we
find that the size and density of local structures responsible for chiral
peaking do change significantly. The resulting values are in disagreement with
the assumptions of the Instanton Liquid Model. We conclude that the
fluctuations of topological charge in the QCD vacuum are not locally quantized.Comment: 3 pages, 4 figures, Lattice2001(confinement
Quantum Computing via The Bethe Ansatz
We recognize quantum circuit model of computation as factorisable scattering
model and propose that a quantum computer is associated with a quantum
many-body system solved by the Bethe ansatz. As an typical example to support
our perspectives on quantum computation, we study quantum computing in
one-dimensional nonrelativistic system with delta-function interaction, where
the two-body scattering matrix satisfies the factorisation equation (the
quantum Yang--Baxter equation) and acts as a parametric two-body quantum gate.
We conclude by comparing quantum computing via the factorisable scattering with
topological quantum computing.Comment: 6 pages. Comments welcom
Towards the Continuum Limit of the Overlap Quark Propagator in Landau Gauge
The properties of the momentum space quark propagator in Landau gauge are
examined for the overlap quark action in quenched lattice QCD. Numerical
calculations were done on two lattices with different lattice spacing and
similar physical volumes to explore the quark propagator in the continuum
limit. We have calculated the nonperturbative wavefunction renormalization
function and the nonperturbative mass function for a variety of
bare quark masses and perform a simple linear extrapolation to the chiral
limit. We find the behaviour of and in the chiral limit are in
good agreement between the two lattices.Comment: 3 pages, 2 figures, talk, Lattice2002(Chiral Fermion
Overlap Fermions on a Lattice
We report results on hadron masses, fitting of the quenched chiral log, and
quark masses from Neuberger's overlap fermion on a quenched lattice with
lattice spacing fm. We used the improved gauge action which is shown
to lower the density of small eigenvalues for as compared to the Wilson
gauge action. This makes the calculation feasible on 64 nodes of CRAY-T3E. Also
presented is the pion mass on a small volume ( with a Wilson
gauge action at ). We find that for configurations that the
topological charge , the pion mass tends to a constant and for
configurations with trivial topology, it approaches zero possibly linearly with
the quark mass.Comment: Lattice 2000 (Chiral Fermion), 4 pages, 4 figure
Topological Charge Correlators, Spectral Bounds, and Contact Terms
The structure of topological charge fluctuations in the QCD vacuum is
strongly restricted by the spectral negativity of the Euclidean 2-point
correlator for and the presence of a positive contact term. Some
examples are considered which illustrate the physical origin of these
properties.Comment: Lattice 2002 Conference Proceeding
Metamaterials proposed as perfect magnetoelectrics
Magnetoelectric susceptibility of a metamaterial built from split ring
resonators have been investigated both experimentally and within an equivalent
circuit model. The absolute values have been shown to exceed by two orders of
magnitude that of classical magnetoelectric materials. The metamaterial
investigated reaches the theoretically predicted value of the magnetoelectric
susceptibility which is equal to the geometric average of the electric and
magnetic susceptibilities.Comment: 5 pages, 3 figure
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