12,447 research outputs found
QCDF90: Lattice QCD with Fortran 90
We have used Fortran 90 to implement lattice QCD. We have designed a set of
machine independent modules that define fields (gauge, fermions, scalars,
etc...) and overloaded operators for all possible operations between fields,
matrices and numbers. With these modules it is very simple to write high-level
efficient programs for QCD simulations. To increase performances our modules
also implements assignments that do not require temporaries, and a machine
independent precision definition. We have also created a useful compression
procedure for storing the lattice configurations, and a parallel implementation
of the random generators. We have widely tested our program and modules on
several parallel and single processor supercomputers obtaining excellent
performances.Comment: LaTeX file, 8 pages, no figures. More information available at:
http://hep.bu.edu/~leviar/qcdf90.htm
Phase Diagram of a Classical Fluid in a Quenched Random Potential
We consider the phase diagram of a classical fluid in the presence of a
random pinning potential of arbitrary strength. Introducing replicas for
averaging over the quenched disorder, we use the hypernetted chain
approximation to calculate the correlations in the replicated liquid. The
freezing transition of the liquid into a nearly crystalline state is studied
using a density functional approach, and the liquid-to-glass transition is
studied using a phenomenological replica symmetry breaking approach introduced
by Mezard and Parisi. The first-order liquid-to-crystal transition is found to
change to a continuous liquid-to-glass transition as the strength of the
disorder is increased above a threshold value.Comment: 7 pages, 4 figures, to appear in EuroPhysics Letter
Spatial persistence and survival probabilities for fluctuating interfaces
We report the results of numerical investigations of the steady-state (SS)
and finite-initial-conditions (FIC) spatial persistence and survival
probabilities for (1+1)--dimensional interfaces with dynamics governed by the
nonlinear Kardar--Parisi--Zhang (KPZ) equation and the linear
Edwards--Wilkinson (EW) equation with both white (uncorrelated) and colored
(spatially correlated) noise. We study the effects of a finite sampling
distance on the measured spatial persistence probability and show that both SS
and FIC persistence probabilities exhibit simple scaling behavior as a function
of the system size and the sampling distance. Analytical expressions for the
exponents associated with the power-law decay of SS and FIC spatial persistence
probabilities of the EW equation with power-law correlated noise are
established and numerically verified.Comment: 11 pages, 5 figure
Entropic Origin of the Growth of Relaxation Times in Simple Glassy Liquids
Transitions between ``glassy'' local minima of a model free-energy functional
for a dense hard-sphere system are studied numerically using a
``microcanonical'' Monte Carlo method that enables us to obtain the transition
probability as a function of the free energy and the Monte Carlo ``time''. The
growth of the height of the effective free energy barrier with density is found
to be consistent with a Vogel-Fulcher law. The dependence of the transition
probability on time indicates that this growth is primarily due to entropic
effects arising from the difficulty of finding low-free-energy saddle points
connecting glassy minima.Comment: Four pages, plus three postscript figure
Third-Generation TB-LMTO
We describe the screened Korringa-Kohn-Rostoker (KKR) method and the
third-generation linear muffin-tin orbital (LMTO) method for solving the
single-particle Schroedinger equation for a MT potential. The simple and
popular formalism which previously resulted from the atomic-spheres
approximation (ASA) now holds in general, that is, it includes downfolding and
the combined correction. Downfolding to few-orbital, possibly short-ranged,
low-energy, and possibly orthonormal Hamiltonians now works exceedingly well,
as is demonstrated for a high-temperature superconductor. First-principles sp3
and sp3d5 TB Hamiltonians for the valence and lowest conduction bands of
silicon are derived. Finally, we prove that the new method treats overlap of
the potential wells correctly to leading order and we demonstrate how this can
be exploited to get rid of the empty spheres in the diamond structure.Comment: latex2e, 32 printed pages, Postscript figs, to be published in:
Tight-Binding Approach to Computational Materials Science, MRS Symposia
Proceedings No. 491 (MRS, Pittsburgh, 1998
Melting and structure of the vortex solid in strongly anisotropic layered superconductors with random columnar pins
We study the melting transition of the low-temperature vortex solid in
strongly anisotropic layered superconductors with a concentration of random
columnar pinning centers small enough so that the areal density of the pins is
much less than that of the vortex lines. Both the external magnetic field and
the columnar pins are assumed to be oriented perpendicular to the layers Our
method, involving numerical minimization of a model free energy functional,
yields not only the free energy values at the local minima of the functional
but also the detailed density distribution of the system at each minimum: this
allows us to study in detail the structure of the different phases. We find
that at these pin concentrations and low temperatures, the thermodynamically
stable state is a topologically ordered Bragg glass. This nearly crystalline
state melts into an interstitial liquid (a liquid in which a small fraction of
vortex lines remain localized at the pinning centers) in two steps, so that the
Bragg glass and the liquid are separated by a narrow phase that we identify
from analysis of its density structure as a polycrystalline Bose glass. Both
the Bragg glass to Bose glass and the Bose glass to interstitial liquid
transitions are first-order. We also find that a local melting temperature
defined using a criterion based on the degree of localization of the vortex
lines exhibits spatial variations similar to those observed in recent
experiments.Comment: 17 page
The Taming of QCD by Fortran 90
We implement lattice QCD using the Fortran 90 language. We have designed
machine independent modules that define fields (gauge, fermions, scalars,
etc...) and have defined overloaded operators for all possible operations
between fields, matrices and numbers. With these modules it is very simple to
write QCD programs. We have also created a useful compression standard for
storing the lattice configurations, a parallel implementation of the random
generators, an assignment that does not require temporaries, and a machine
independent precision definition. We have tested our program on parallel and
single processor supercomputers obtaining excellent performances.Comment: Talk presented at LATTICE96 (algorithms) 3 pages, no figures, LATEX
file with ESPCRC2 style. More information available at:
http://hep.bu.edu/~leviar/qcdf90.htm
Dilaton Brane Cosmology with Second Order String Corrections and the Cosmological Constant
We consider, in five dimensions, the effective action from heterotic string
which includes quantum gravity corrections up to (a')^2. The expansion, in the
string frame, is in terms of |a'R|, where R is the scalar curvature and uses
the third order Euler density, next to the Gauss-Bonnet term. For a positive
tension brane and infinite extra dimension, the logarithmic class of solutions
is less dependent from fine-tuning problems than in previous formulations. More
importantly, the model suggests that in the full non-perturbative formulation,
the string scale can be much lower than the effective Planck mass, without the
string coupling to be vanishingly small. Also a less severe fine-tuning of the
brane tension in needed.Comment: 19 pages, 5 figures LaTeX. Accepted for publication in IJMP
CONSUMER PERCEPTIONS OF TROUT AS A FOOD ITEM
The impacts of socioeconomic/demographic characteristics, experiences and preferences of consumers on trout purchasing decisions were estimated using Probit and Ordered Probit regression techniques. Data from a survey of consumer purchasing behavior and personal attributes were used to deduce factors that led to either a high or low likelihood of purchasing trout products. Analysis of data pertaining to whole trout and value-added products yielded consistently different characteristics of consumers who show a high affinity toward purchasing one or more of such products. Results from these analyses were used to suggest techniques for marketing whole trout and value-added trout products to specific segments of the consumer population.Food Consumption/Nutrition/Food Safety,
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