1,737 research outputs found
Comment on "Dynamic Opinion Model and Invasion Percolation"
In J. Shao et al., PRL 103, 108701 (2009) the authors claim that a model with
majority rule coarsening exhibits in d=2 a percolation transition in the
universality class of invasion percolation with trapping. In the present
comment we give compelling evidence, including high statistics simulations on
much larger lattices, that this is not correct. and that the model is trivially
in the ordinary percolation universality class.Comment: 1 pag
Reply to "Comment on `Performance of different synchronization measures in real data: A case study on electroencephalographic signals'"
We agree with the Comment by Nicolaou and Nasuto about the utility of mutual information (MI) when properly estimated and we also concur with their view that the estimation based on k nearest neighbors gives optimal results. However, we claim that embedding parameters can indeed change MI results, as we show for the electroencephalogram data sets of our original study and for coupled chaotic systems. Furthermore, we show that proper embedding can actually improve the estimation of MI with the k nearest neighbors algorithm
Monte Carlo Protein Folding: Simulations of Met-Enkephalin with Solvent-Accessible Area Parameterizations
Treating realistically the ambient water is one of the main difficulties in
applying Monte Carlo methods to protein folding. The solvent-accessible area
method, a popular method for treating water implicitly, is investigated by
means of Metropolis simulations of the brain peptide Met-Enkephalin. For the
phenomenological energy function ECEPP/2 nine atomic solvation parameter (ASP)
sets are studied that had been proposed by previous authors. The simulations
are compared with each other, with simulations with a distance dependent
electrostatic permittivity , and with vacuum simulations
(). Parallel tempering and a recently proposed biased Metropolis
technique are employed and their performances are evaluated. The measured
observables include energy and dihedral probability densities (pds), integrated
autocorrelation times, and acceptance rates. Two of the ASP sets turn out to be
unsuitable for these simulations. For all other sets, selected configurations
are minimized in search of the global energy minima. Unique minima are found
for the vacuum and the system, but for none of the ASP models.
Other observables show a remarkable dependence on the ASPs. In particular,
autocorrelation times vary dramatically with the ASP parameters. Three ASP sets
have much smaller autocorrelations at 300 K than the vacuum simulations,
opening the possibility that simulations can be speeded up vastly by
judiciously chosing details of the forceComment: 10 pages; published in "NIC Symposium 2004", eds. D. Wolf at el.
(NIC, Juelich, 2004
Epidemic analysis of the second-order transition in the Ziff-Gulari-Barshad surface-reaction model
We study the dynamic behavior of the Ziff-Gulari-Barshad (ZGB) irreversible
surface-reaction model around its kinetic second-order phase transition, using
both epidemic and poisoning-time analyses. We find that the critical point is
given by p_1 = 0.3873682 \pm 0.0000015, which is lower than the previous value.
We also obtain precise values of the dynamical critical exponents z, \delta,
and \eta which provide further numerical evidence that this transition is in
the same universality class as directed percolation.Comment: REVTEX, 4 pages, 5 figures, Submitted to Physical Review
Chaotic synchronizations of spatially extended systems as non-equilibrium phase transitions
Two replicas of spatially extended chaotic systems synchronize to a common
spatio-temporal chaotic state when coupled above a critical strength. As a
prototype of each single spatio-temporal chaotic system a lattice of maps
interacting via power-law coupling is considered. The synchronization
transition is studied as a non-equilibrium phase transition, and its critical
properties are analyzed at varying the spatial interaction range as well as the
nonlinearity of the dynamical units composing each system. In particular,
continuous and discontinuous local maps are considered. In both cases the
transitions are of the second order with critical indexes varying with the
exponent characterizing the interaction range. For discontinuous maps it is
numerically shown that the transition belongs to the {\it anomalous directed
percolation} (ADP) family of universality classes, previously identified for
L{\'e}vy-flight spreading of epidemic processes. For continuous maps, the
critical exponents are different from those characterizing ADP, but apart from
the nearest-neighbor case, the identification of the corresponding universality
classes remains an open problem. Finally, to test the influence of
deterministic correlations for the studied synchronization transitions, the
chaotic dynamical evolutions are substituted by suitable stochastic models. In
this framework and for the discontinuous case, it is possible to derive an
effective Langevin description that corresponds to that proposed for ADP.Comment: 12 pages, 5 figures Comments are welcom
Synchronization of Coupled Systems with Spatiotemporal Chaos
We argue that the synchronization transition of stochastically coupled
cellular automata, discovered recently by L.G. Morelli {\it et al.} (Phys. Rev.
{\bf 58 E}, R8 (1998)), is generically in the directed percolation universality
class. In particular, this holds numerically for the specific example studied
by these authors, in contrast to their claim. For real-valued systems with
spatiotemporal chaos such as coupled map lattices, we claim that the
synchronization transition is generically in the universality class of the
Kardar-Parisi-Zhang equation with a nonlinear growth limiting term.Comment: 4 pages, including 3 figures; submitted to Phys. Rev.
Phase transitions and critical behaviour in one-dimensional non-equilibrium kinetic Ising models with branching annihilating random walk of kinks
One-dimensional non-equilibrium kinetic Ising models evolving under the
competing effect of spin flips at zero temperature and nearest-neighbour spin
exchanges exhibiting directed percolation-like parity conserving(PC) phase
transition on the level of kinks are now further investigated, numerically,
from the point of view of the underlying spin system. Critical exponents
characterising its statics and dynamics are reported. It is found that the
influence of the PC transition on the critical exponents of the spins is strong
and the origin of drastic changes as compared to the Glauber-Ising case can be
traced back to the hyperscaling law stemming from directed percolation(DP).
Effect of an external magnetic field, leading to DP-type critical behaviour on
the level of kinks, is also studied, mainly through the generalised mean field
approximation.Comment: 15 pages, using RevTeX, 13 Postscript figures included, submitted to
J.Phys.A, figures 12 and 13 fixe
The three species monomer-monomer model in the reaction-controlled limit
We study the one dimensional three species monomer-monomer reaction model in
the reaction controlled limit using mean-field theory and dynamic Monte Carlo
simulations. The phase diagram consists of a reactive steady state bordered by
three equivalent adsorbing phases where the surface is saturated with one
monomer species. The transitions from the reactive phase are all continuous,
while the transitions between adsorbing phases are first-order. Bicritical
points occur where the reactive phase simultaneously meets two adsorbing
phases. The transitions from the reactive to an adsorbing phase show directed
percolation critical behaviour, while the universal behaviour at the bicritical
points is in the even branching annihilating random walk class. The results are
contrasted and compared to previous results for the adsorption-controlled limit
of the same model.Comment: 12 pages using RevTeX, plus 4 postscript figures. Uses psfig.sty.
accepted to Journal of Physics
One Dimensional Nonequilibrium Kinetic Ising Models with Branching Annihilating Random Walk
Nonequilibrium kinetic Ising models evolving under the competing effect of
spin flips at zero temperature and nearest neighbour spin exchanges at
are investigated numerically from the point of view of a phase
transition. Branching annihilating random walk of the ferromagnetic domain
boundaries determines the steady state of the system for a range of parameters
of the model. Critical exponents obtained by simulation are found to agree,
within error, with those in Grassberger's cellular automata.Comment: 10 pages, Latex, figures upon request, SZFKI 05/9
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