3,881 research outputs found
A general creation-annihilation model with absorbing states
A one dimensional non-equilibrium stochastic model is proposed where each
site of the lattice is occupied by a particle, which may be of type A or B. The
time evolution of the model occurs through three processes: autocatalytic
generation of A and B particles and spontaneous conversion A to B. The
two-parameter phase diagram of the model is obtained in one- and two-site mean
field approximations, as well as through numerical simulations and exact
solution of finite systems extrapolated to the thermodynamic limit. A
continuous line of transitions between an active and an absorbing phase is
found. This critical line starts at a point where the model is equivalent to
the contact process and ends at a point which corresponds to the voter model,
where two absorbing states coexist. Thus, the critical line ends at a point
where the transition is discontinuous. Estimates of critical exponents are
obtained through the simulations and finite-size-scaling extrapolations, and
the crossover between universality classes as the voter model transition is
approached is studied.Comment: 9 pages and 17 figure
Rede de sementes florestais da Caatinga.
Os objetivos da rede são aumentar a oferta de sementes florestais nativas a partir da união de instituições e pessoas que atuam direta ou indiretamente no setor; promover e dinamizar o comércio de sementes e mudas de espécies florestais nativas no semiárido brasileiro A rede também promove a integração entre os diversos segmentos do setor público e privado que atuam no setor florestal a fim de que as ações desenvolvidas pelos diversos setores tenham a maior repercussão possÃvel nos municÃpios do Nordeste brasileiro.Edição dos Anais do 1 Simpósio da Rede de Recursos Genéticos Vegetais do Nordeste, Cruz das Almas, nov. 2013
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
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
The Structure of Graphene on Graphene/C60/Cu Interfaces: A Molecular Dynamics Study
Two experimental studies reported the spontaneous formation of amorphous and
crystalline structures of C60 intercalated between graphene and a substrate.
They observed interesting phenomena ranging from reaction between C60 molecules
under graphene to graphene sagging between the molecules and control of strain
in graphene. Motivated by these works, we performed fully atomistic reactive
molecular dynamics simulations to study the formation and thermal stability of
graphene wrinkles as well as graphene attachment to and detachment from the
substrate when graphene is laid over a previously distributed array of C60
molecules on a copper substrate at different values of temperature. As graphene
compresses the C60 molecules against the substrate, and graphene attachment to
the substrate between C60s ("C60s" stands for plural of C60) depends on the
height of graphene wrinkles, configurations with both frozen and non-frozen
C60s structures were investigated in order to verify the experimental result of
stable sagged graphene when the distance between C60s is about 4 nm and height
of graphene wrinkles is about 0.8 nm. Below the distance of 4 nm between C60s,
graphene becomes locally suspended and less strained. We show that this happens
when C60s are allowed to deform under the compressive action of graphene. If we
keep the C60s frozen, spontaneous "blanketing" of graphene happens only when
the distance between them are equal or above 7 nm. Both above results for the
existence of stable sagged graphene for C60 distances of 4 or 7 nm are shown to
agree with a mechanical model relating the rigidity of graphene to the energy
of graphene-substrate adhesion. In particular, this study might help the
development of 2D confined nanoreactors that are considered in literature to be
the next advanced step on chemical reactions.Comment: 7 pages, 4 figure
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