535 research outputs found
A new comprehensive study of the 3D random-field Ising model via sampling the density of states in dominant energy subspaces
The three-dimensional bimodal random-field Ising model is studied via a new
finite temperature numerical approach. The methods of Wang-Landau sampling and
broad histogram are implemented in a unified algorithm by using the N-fold
version of the Wang-Landau algorithm. The simulations are performed in dominant
energy subspaces, determined by the recently developed critical minimum energy
subspace technique. The random fields are obtained from a bimodal distribution,
that is we consider the discrete case and the model is studied on
cubic lattices with sizes . In order to extract information
for the relevant probability distributions of the specific heat and
susceptibility peaks, large samples of random field realizations are generated.
The general aspects of the model's scaling behavior are discussed and the
process of averaging finite-size anomalies in random systems is re-examined
under the prism of the lack of self-averaging of the specific heat and
susceptibility of the model.Comment: 10 pages, 4 figures, presented at the third NEXT Sigma Phi
International Conference, Kolymbari, Greece (2005
Wetting and interfacial adsorption in the Blume-Capel model on the square lattice
We study the Blume-Capel model on the square lattice. To allow for wetting
and interfacial adsorption, the spins on opposite boundaries are fixed in two
different states, "+1" and "-1", with reduced couplings at one of the
boundaries. Using mainly Monte Carlo techniques, of Metropolis and Wang-Landau
type, phase diagrams showing bulk and wetting transitions are determined. The
role of the non-boundary state, "0", adsorbed preferably at the interface
between "-1" and "+1" rich regions, is elucidated.Comment: 7 pages, 8 figures, minor corrections to previous versio
A study for the static properties of symmetric linear multiblock copolymers under poor solvent conditions
We use a standard bead-spring model and molecular dynamics simulations to
study the static properties of symmetric linear multiblock copolymer chains and
their blocks under poor solvent conditions in a dilute solution from the regime
close to theta conditions, where the chains adopt a coil-like formation, to the
poorer solvent regime where the chains collapse obtaining a globular formation
and phase separation between the blocks occurs. We choose interaction
parameters as is done for a standard model, i.e., the Lennard-Jones fluid and
we consider symmetric chains, i.e., the multiblock copolymer consists of an
even number of alternating chemically different A and B blocks of the same
length . We show how usual static properties of the individual
blocks and the whole multiblock chain can reflect the phase behavior of such
macromolecules. Also, how parameters, such as the number of blocks can
affect properties of the individual blocks, when chains are in a poor solvent
for a certain range of . A detailed discussion of the static properties of
these symmetric multiblock copolymers is also given. Our results in combination
with recent simulation results on the behavior of multiblock copolymer chains
provide a complete picture for the behavior of these macromolecules under poor
solvent conditions, at least for this most symmetrical case. Due to the
standard choice of our parameters, our system can be used as a benchmark for
related models, which aim at capturing the basic aspects of the behavior of
various biological systems.Comment: 13 pages, 11 figure
Geometry effects in the magnetoconductance of normal and Andreev Sinai billiards
We study the transport properties of low-energy (quasi)particles
ballistically traversing normal and Andreev two-dimensional open cavities with
a Sinai-billiard shape. We consider four different geometrical setups and focus
on the dependence of transport on the strength of an applied magnetic field. By
solving the classical equations of motion for each setup we calculate the
magnetoconductance in terms of transmission and reflection coefficients for
both the normal and Andreev versions of the billiard, calculating in the latter
the critical field value above which the outgoing current of holes becomes
zero.Comment: 4 pages, 4 figure
Universality aspects of the d=3 random-bond Blume-Capel model
The effects of bond randomness on the universality aspects of the simple
cubic lattice ferromagnetic Blume-Capel model are discussed. The system is
studied numerically in both its first- and second-order phase transition
regimes by a comprehensive finite-size scaling analysis. We find that our data
for the second-order phase transition, emerging under random bonds from the
second-order regime of the pure model, are compatible with the universality
class of the 3d random Ising model. Furthermore, we find evidence that, the
second-order transition emerging under bond randomness from the first-order
regime of the pure model, belongs to a new and distinctive universality class.
The first finding reinforces the scenario of a single universality class for
the 3d Ising model with the three well-known types of quenched uncorrelated
disorder (bond randomness, site- and bond-dilution). The second, amounts to a
strong violation of universality principle of critical phenomena. For this case
of the ex-first-order 3d Blume-Capel model, we find sharp differences from the
critical behaviors, emerging under randomness, in the cases of the
ex-first-order transitions of the corresponding weak and strong first-order
transitions in the 3d three-state and four-state Potts models.Comment: 12 pages, 12 figure
Analysis of the convergence of the 1/t and Wang-Landau algorithms in the calculation of multidimensional integrals
In this communication, the convergence of the 1/t and Wang - Landau
algorithms in the calculation of multidimensional numerical integrals is
analyzed. Both simulation methods are applied to a wide variety of integrals
without restrictions in one, two and higher dimensions. The errors between the
exact and the calculated values of the integral are obtained and the efficiency
and accuracy of the methods are determined by their dynamical behavior. The
comparison between both methods and the simple sampling Monte Carlo method is
also reported. It is observed that the time dependence of the errors calculated
with 1/t algorithm goes as N^{-1/2} (with N the MC trials) in quantitative
agreement with the simple sampling Monte Carlo method. It is also showed that
the error for the Wang - Landau algorithm saturates in time evidencing the
non-convergence of the methods. The sources for the error are also determined.Comment: 8 pages, 5 figure
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