1,018 research outputs found
Crossovers from parity conserving to directed percolation universality
The crossover behavior of various models exhibiting phase transition to
absorbing phase with parity conserving class has been investigated by numerical
simulations and cluster mean-field method. In case of models exhibiting Z_2
symmetric absorbing phases (the NEKIMCA and Grassberger's A stochastic cellular
automaton) the introduction of an external symmetry breaking field causes a
crossover to kink parity conserving models characterized by dynamical scaling
of the directed percolation (DP) and the crossover exponent: 1/\phi ~ 0.53(2).
In case an even offspringed branching and annihilating random walk model (dual
to NEKIMCA) the introduction of spontaneous particle decay destroys the parity
conservation and results in a crossover to the DP class characterized by the
crossover exponent: 1/\phi\simeq 0.205(5). The two different kinds of crossover
operators can't be mapped onto each other and the resulting models show a
diversity within the DP universality class in one dimension. These
'sub-classes' differ in cluster scaling exponents.Comment: 6 pages, 6 figures, accepted version in PR
A comparative study for the pair-creation contact process using series expansions
A comparative study between two distinct perturbative series expansions for
the pair-creation contact process is presented. In contrast to the ordinary
contact process, whose supercritical series expansions provide accurate
estimates for its critical behavior, the supercritical approach does not work
properly when applied to the pair-creation process. To circumvent this problem
a procedure is introduced in which one-site creation is added to the
pair-creation. An alternative method is the generation of subcritical series
expansions which works even for the case of the pure pair-creation process.
Differently from the supercritical case, the subcritical series yields
estimates that are compatible with numerical simulations
Generalized Manna sandpile model with height restrictions
Sandpile models with conserved number of particles (also called fixed energy
sandpiles) may undergo phase transitions between active and absorbing states.
We generalize the Manna sandpile model with fixed number of particles,
introducing a parameter related to the toppling of
particles from active sites to its first neighbors. In particular, we discuss a
model with height restrictions, allowing for at most two particles on a site.
Sites with double occupancy are active, and their particles may be transfered
to first neighbor sites, if the height restriction do allow the change. For
each one of the two particles is independently assigned to one of
the two first neighbors and the original stochastic sandpile model is
recovered. For exactly one particle will be placed on each first
neighbor and thus a deterministic (BTW) sandpile model is obtained. When
two particles are moved to one of the first neighbors, and this
implies that the density of active sites is conserved in the evolution of the
system, and no phase transition is observed. Through simulations of the
stationary state, we estimate the critical density of particles and the
critical exponents as functions of .Comment: 5 pages, 11 figures, IV BMS
A supercritical series analysis for the generalized contact process with diffusion
We study a model that generalizes the CP with diffusion. An additional
transition is included in the model so that at a particular point of its phase
diagram a crossover from the directed percolation to the compact directed
percolation class will happen. We are particularly interested in the effect of
diffusion on the properties of the crossover between the universality classes.
To address this point, we develop a supercritical series expansion for the
ultimate survival probability and analyse this series using d-log Pad\'e and
partial differential approximants. We also obtain approximate solutions in the
one- and two-site dynamical mean-field approximations. We find evidences that,
at variance to what happens in mean-field approximations, the crossover
exponent remains close to even for quite high diffusion rates, and
therefore the critical line in the neighborhood of the multicritical point
apparently does not reproduce the mean-field result (which leads to )
as the diffusion rate grows without bound
Asymptotic behavior of the entropy of chains placed on stripes
By using the transfer matrix approach, we investigate the asymptotic behavior
of the entropy of flexible chains with monomers each placed on stripes. In
the limit of high density of monomers, we study the behavior of the entropy as
a function of the density of monomers and the width of the stripe, inspired by
recent analytical studies of this problem for the particular case of dimers
(M=2). We obtain the entropy in the asymptotic regime of high densities for
chains with monomers, as well as for the special case of polymers,
where , and find that the results show a regular behavior similar
to the one found analytically for dimers. We also verify that in the
low-density limit the mean-field expression for the entropy is followed by the
results from our transfer matrix calculations
Uso de marcadores RAPD para avaliar a divergência genética em mamoneira.
bitstream/CNPA-2009-09/22283/1/COMTEC360.pd
Crossover from directed percolation to mean field behavior in the diffusive contact process
Recently Dantas, Oliveira and Stilck [J. Stat. Mech. (2007) P08009] studied
how the one-dimensional diffusive contact process crosses over from the
critical behavior of directed percolation to an effective mean field behaviour
when the diffusion rate is sent to infinity. They showed that this crossover
can be described in terms of a crossover exponent , finding the
boundaries 3 <= <= 4 in one spatial dimension. In the present work we
refine and extend this result up to four spatial dimensions by a
field-theoretic calculation and extensive numerical simulations.Comment: 6 pages, 2 figure
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