596 research outputs found
Aging and fluctuation-dissipation ratio in a nonequilibrium -state lattice model
A generalized version of the nonequilibrium linear Glauber model with
states in dimensions is introduced and analyzed. The model is fully
symmetric, its dynamics being invariant under all permutations of the
states. Exact expressions for the two-time autocorrelation and response
functions on a -dimensional lattice are obtained. In the stationary regime,
the fluctuation-dissipation theorem holds, while in the transient the aging is
observed with the fluctuation-dissipation ratio leading to the value predicted
for the linear Glauber model
Self-organized patterns of coexistence out of a predator-prey cellular automaton
We present a stochastic approach to modeling the dynamics of coexistence of
prey and predator populations. It is assumed that the space of coexistence is
explicitly subdivided in a grid of cells. Each cell can be occupied by only one
individual of each species or can be empty. The system evolves in time
according to a probabilistic cellular automaton composed by a set of local
rules which describe interactions between species individuals and mimic the
process of birth, death and predation. By performing computational simulations,
we found that, depending on the values of the parameters of the model, the
following states can be reached: a prey absorbing state and active states of
two types. In one of them both species coexist in a stationary regime with
population densities constant in time. The other kind of active state is
characterized by local coupled time oscillations of prey and predator
populations. We focus on the self-organized structures arising from
spatio-temporal dynamics of the coexistence. We identify distinct spatial
patterns of prey and predators and verify that they are intimally connected to
the time coexistence behavior of the species. The occurrence of a prey
percolating cluster on the spatial patterns of the active states is also
examined.Comment: 19 pages, 11 figure
The fluctuation-dissipation theorem and the linear Glauber model
We obtain exact expressions for the two-time autocorrelation and response
functions of the -dimensional linear Glauber model. Although this linear
model does not obey detailed balance in dimensions , we show that the
usual form of the fluctuation-dissipation ratio still holds in the stationary
regime. In the transient regime, we show the occurence of aging, with a special
limit of the fluctuation-dissipation ratio, , for a quench at
the critical point.Comment: Accepted for publication (Physical Review E
Dynamic critical exponents of the Ising model with multispin interactions
We revisit the short-time dynamics of 2D Ising model with three spin
interactions in one direction and estimate the critical exponents
and . Taking properly into account the symmetry of the
Hamiltonian we obtain results completely different from those obtained by Wang
et al.. For the dynamic exponent our result coincides with that of the
4-state Potts model in two dimensions. In addition, results for the static
exponents and agree with previous estimates obtained from finite
size scaling combined with conformal invariance. Finally, for the new dynamic
exponent we find a negative and close to zero value, a result also
expected for the 4-state Potts model according to Okano et al.Comment: 12 pages, 9 figures, corrected Abstract mistypes, corrected equation
on page 4 (Parameter Q
The Influence of the Interaction between Climate and Competition on the Distributional Limits of European Shrews
It is known that speciesâ distributions are influenced by several ecological factors. Nonetheless,
the geographical scale upon which the influence of these factors is perceived is largely undefined.
We assessed the importance of competition in regulating the distributional limits of species at large
geographical scales. We focus on species with similar diets, the European Soricidae shrews, and how
interspecific competition changes along climatic gradients. We used presence data for the seven most
widespread terrestrial species of Soricidae in Europe, gathered from GBIF, European museums, and
climate data from WorldClim. We made use of two Joint Species Distribution Models to analyse
the correlations between speciesâ presences, aiming to understand the distinct roles of climate and
competition in shaping speciesâ distributions. Our results support three key conclusions: (i) climate
alone does not explain all speciesâ distributions at large scales; (ii) negative interactions, such as competition,
seem to play a strong role in defining speciesâ range limits, even at large scales; and (iii) the
impact of competition on a speciesâ distribution varies along a climatic gradient, becoming stronger
at the climatic extremes. Our conclusions support previous research, highlighting the importance of
considering biotic interactions when studying speciesâ distributions, regardless of geographical scaleinfo:eu-repo/semantics/publishedVersio
Cumulants of the three state Potts model and of nonequilibrium models with C3v symmetry
The critical behavior of two-dimensional stochastic lattice gas models with
C3v symmetry is analyzed. We study the cumulants of the order parameter for the
three state (equilibrium) Potts model and for two irreversible models whose
dynamic rules are invariant under the symmetry operations of the point group
C3v. By means of extensive numerical analysis of the phase transition we show
that irreversibility does not affect the critical behavior of the systems. In
particular we find that the Binder reduced fourth order cumulant takes a
universal value U* which is the same for the three state Potts model and for
the irreversible models. The same universal behavior is observed for the
reduced third-order cumulant.Comment: gzipped tar file containing: 1 latex file + 6 eps figure
Universality and scaling study of the critical behavior of the two-dimensional Blume-Capel model in short-time dynamics
In this paper we study the short-time behavior of the Blume-Capel model at
the tricritical point as well as along the second order critical line. Dynamic
and static exponents are estimated by exploring scaling relations for the
magnetization and its moments at early stage of the dynamic evolution. Our
estimates for the dynamic exponents, at the tricritical point, are and .Comment: 12 pages, 9 figure
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