16,157 research outputs found
Elementary transformation analysis for Array-OL
Array-OL is a high-level specification language dedicated to the definition
of intensive signal processing applications. Several tools exist for
implementing an Array-OL specification as a data parallel program. While
Array-OL can be used directly, it is often convenient to be able to deduce part
of the specification from a sequential version of the application. This paper
proposes such an analysis and examines its feasibility and its limits
Center Vortex Model for the Infrared Sector of SU(3) Yang-Mills Theory - Confinement and Deconfinement
The center vortex model for the infrared sector of Yang-Mills theory,
previously studied for the SU(2) gauge group, is extended to SU(3). This model
is based on the assumption that vortex world-surfaces can be viewed as random
surfaces in Euclidean space-time. The confining properties are investigated,
with a particular emphasis on the finite-temperature deconfining phase
transition. The model predicts a very weak first order transition, in agreement
with SU(3) lattice Yang-Mills theory, and also reproduces a consistent behavior
of the spatial string tension in the deconfined phase. The geometrical
structure of the center vortices is studied, including vortex branchings, which
are a new property of the SU(3) case.Comment: 22 pages, 12 figures (30 eps-files), uses LaTeX package "psfrag
The fundamentals of non-singular dislocations in the theory of gradient elasticity: dislocation loops and straight dislocations
The fundamental problem of non-singular dislocations in the framework of the
theory of gradient elasticity is presented in this work. Gradient elasticity of
Helmholtz type and bi-Helmholtz type are used. A general theory of non-singular
dislocations is developed for linearly elastic, infinitely extended,
homogeneous, and isotropic media. Dislocation loops and straight dislocations
are investigated. Using the theory of gradient elasticity, the non-singular
fields which are produced by arbitrary dislocation loops are given. `Modified'
Mura, Peach-Koehler, and Burgers formulae are presented in the framework of
gradient elasticity theory. These formulae are given in terms of an elementary
function, which regularizes the classical expressions, obtained from the Green
tensor of the Helmholtz-Navier equation and bi-Helmholtz-Navier equation. Using
the mathematical method of Green's functions and the Fourier transform, exact,
analytical, and non-singular solutions were found. The obtained dislocation
fields are non-singular due to the regularization of the classical singular
fields.Comment: 29 pages, to appear in: International Journal of Solids and
Structure
Statistical Properties of Strings
We investigate numerically the configurational statistics of strings. The
algorithm models an ensemble of global cosmic strings, or equivalently
vortices in superfluid He. We use a new method which avoids the
specification of boundary conditions on the lattice. We therefore do not have
the artificial distinction between short and long string loops or a `second
phase' in the string network statistics associated with strings winding around
a toroidal lattice. Our lattice is also tetrahedral, which avoids ambiguities
associated with the cubic lattices of previous work. We find that the
percentage of infinite string is somewhat lower than on cubic lattices, 63\%
instead of 80\%. We also investigate the Hagedorn transition, at which infinite
strings percolate, controlling the string density by rendering one of the
equilibrium states more probable. We measure the percolation threshold, the
critical exponent associated with the divergence of a suitably defined
susceptibility of the string loops, and that associated with the divergence of
the correlation length.Comment: 20 pages, 8 figures (uuencoded) appended, DAMTP-94-56, SUSX-TP-94-7
Extended matter coupled to BF theory
Recently, a topological field theory of membrane-matter coupled to BF theory
in arbitrary spacetime dimensions was proposed [1]. In this paper, we discuss
various aspects of the four-dimensional theory. Firstly, we study classical
solutions leading to an interpretation of the theory in terms of strings
propagating on a flat spacetime. We also show that the general classical
solutions of the theory are in one-to-one correspondence with solutions of
Einstein's equations in the presence of distributional matter (cosmic strings).
Secondly, we quantize the theory and present, in particular, a prescription to
regularize the physical inner product of the canonical theory. We show how the
resulting transition amplitudes are dual to evaluations of Feynman diagrams
coupled to three-dimensional quantum gravity. Finally, we remove the regulator
by proving the topological invariance of the transition amplitudes.Comment: 27 pages, 7 figure
Noisy Monte Carlo revisited
We present an exact Monte Carlo algorithm designed to sample theories where
the energy is a sum of many couplings of decreasing strength. Our algorithm,
simplified from that of L. Lin et al. hep-lat/9905033, avoids the computation
of almost all non-leading terms. We illustrate its use by simulating SU(2)
lattice gauge theory with a 5-loop action, and discuss further applications to
full QCD.Comment: latex, 8 page
Pseudo-Cartesian coordinates in a model of Causal Dynamical Triangulations
Causal Dynamical Triangulations is a non-perturbative quantum gravity model,
defined with a lattice cut-off. The model can be viewed as defined with a
proper time but with no reference to any three-dimensional spatial background
geometry. It has four phases, depending on the parameters (the coupling
constants) of the model. The particularly interesting behavior is observed in
the so-called de Sitter phase, where the spatial three-volume distribution as a
function of proper time has a semi-classical behavior which can be obtained
from an effective mini-superspace action. In the case of the three-sphere
spatial topology, it has been difficult to extend the effective semi-classical
description in terms of proper time and spatial three-volume to include genuine
spatial coordinates, partially because of the background independence inherent
in the model. However, if the spatial topology is that of a three-torus, it is
possible to define a number of new observables that might serve as spatial
coordinates as well as new observables related to the winding numbers of the
three-dimensional torus. The present paper outlines how to define the
observables, and how they can be used in numerical simulations of the model.Comment: 26 pages, 15 figure
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