29,651 research outputs found
Continuous and discontinuous absorbing-state phase transitions on Voronoi-Delaunay random lattices
We study absorbing-state phase transitions in two-dimensional
Voronoi-Delaunay (VD) random lattices with quenched coordination disorder.
Quenched randomness usually changes the criticality and destroys discontinuous
transitions in low-dimensional nonequilibrium systems. We performed extensive
simulations of the Ziff-Gulari-Barshad (ZGB) model, and verified that the VD
disorder does not change the nature of its discontinuous transition. Our
results corroborate recent findings of Barghatti and Vojta [Phys. Rev. Lett.
{\bf 113}, 120602 (2014)] stating the irrelevance of topological disorder in a
class of random lattices that includes VD and raise the interesting possibility
that disorder in nonequilibrium APT may, under certain conditions, be
irrelevant for the phase coexistence. We also verify that the VD disorder is
irrelevant for the critical behavior of models belonging to the directed
percolation and Manna universality classes.Comment: 7 pages, 6 figure
Local vs. long-range infection in unidimensional epidemics
We study the effects of local and distance interactions in the unidimensional
contact process (CP). In the model, each site of a lattice is occupied by an
individual, which can be healthy or infected. As in the standard CP, each
infected individual spreads the disease to one of its first-neighbors with rate
, and with unitary rate, it becomes healthy. However, in our model, an
infected individual can transmit the disease to an individual at a distance
apart. This step mimics a vector-mediated transmission. We observe the
host-host interactions do not alter the critical exponents significantly in
comparison to a process with only L\'evy-type interactions. Our results
confirm, numerically, early field-theoretic predictions.Comment: 8 pages, 6 figures, to appear on Frontiers in Physic
Strategies for Optimize Off-Lattice Aggregate Simulations
We review some computer algorithms for the simulation of off-lattice clusters
grown from a seed, with emphasis on the diffusion-limited aggregation,
ballistic aggregation and Eden models. Only those methods which can be
immediately extended to distinct off-lattice aggregation processes are
discussed. The computer efficiencies of the distinct algorithms are compared.Comment: 6 pages, 7 figures and 3 tables; published at Brazilian Journal of
Physics 38, march, 2008 (http://www.sbfisica.org.br/bjp/files/v38_81.pdf
Simulated Tempering: A New Monte Carlo Scheme
We propose a new global optimization method ({\em Simulated Tempering}) for
simulating effectively a system with a rough free energy landscape (i.e. many
coexisting states) at finite non-zero temperature. This method is related to
simulated annealing, but here the temperature becomes a dynamic variable, and
the system is always kept at equilibrium. We analyze the method on the Random
Field Ising Model, and we find a dramatic improvement over conventional
Metropolis and cluster methods. We analyze and discuss the conditions under
which the method has optimal performances.Comment: 12 pages, very simple LaTeX file, figures are not included, sorr
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