19,744 research outputs found
Broad histogram relation for the bond number and its applications
We discuss Monte Carlo methods based on the cluster (graph) representation
for spin models. We derive a rigorous broad histogram relation (BHR) for the
bond number; a counterpart for the energy was derived by Oliveira previously. A
Monte Carlo dynamics based on the number of potential moves for the bond number
is proposed. We show the efficiency of the BHR for the bond number in
calculating the density of states and other physical quantities.Comment: 7 pages, 7 figure
Study of the Fully Frustrated Clock Model using the Wang-Landau Algorithm
Monte Carlo simulations using the newly proposed Wang-Landau algorithm
together with the broad histogram relation are performed to study the
antiferromagnetic six-state clock model on the triangular lattice, which is
fully frustrated. We confirm the existence of the magnetic ordering belonging
to the Kosterlitz-Thouless (KT) type phase transition followed by the chiral
ordering which occurs at slightly higher temperature. We also observe the lower
temperature phase transition of KT type due to the discrete symmetry of the
clock model. By using finite-size scaling analysis, the higher KT temperature
and the chiral critical temperature are respectively estimated as
and . The results are in favor of the double
transition scenario. The lower KT temperature is estimated as .
Two decay exponents of KT transitions corresponding to higher and lower
temperatures are respectively estimated as and
, which suggests that the exponents associated with the KT
transitions are universal even for the frustrated model.Comment: 7 pages including 9 eps figures, RevTeX, to appear in J. Phys.
Equilibrium Times for the Multicanonical Method
This work measures the time to equilibrium for the multicanonical method on
the 2D-Ising system by using a new criterion, proposed here, to find the time
to equilibrium, teq, of any sampling procedure based on a Markov process. Our
new procedure gives the same results that the usual one, based on the
magnetization, for the canonical Metropolis sampling on a 2D-Ising model at
several temperatures. For the multicanonical method we found a power-law
relationship with the system size, L, of teq=0.27(15) L^2.80(13), and with the
number of energy levels to explore, kE, of teq=0.7(13) kE^1.40(11), in perfect
agreement with the result just above. In addition, some kind of critical
slowing down was observed around the critical energy. Our new procedure is
completely general, and can be applied to any sampling method based on a Markov
process.Comment: 7 pages, 5 eps figures, to be published in Int. J. Mod. Phys.
The contact process in disordered and periodic binary two-dimensional lattices
The critical behavior of the contact process in disordered and periodic
binary 2d-lattices is investigated numerically by means of Monte Carlo
simulations as well as via an analytical approximation and standard mean field
theory. Phase-separation lines calculated numerically are found to agree well
with analytical predictions around the homogeneous point. For the disordered
case, values of static scaling exponents obtained via quasi-stationary
simulations are found to change with disorder strength. In particular, the
finite-size scaling exponent of the density of infected sites approaches a
value consistent with the existence of an infinite-randomness fixed point as
conjectured before for the 2d disordered CP. At the same time, both dynamical
and static scaling exponents are found to coincide with the values established
for the homogeneous case thus confirming that the contact process in a
heterogeneous environment belongs to the directed percolation universality
class.Comment: submitted to Physical Review
Análise do comportamento geométrico entre imagens RapidEye adotadas no Inventário Florestal Nacional do Brasil (IFN-BR).
Resumo
Which mechanism underlies the water-like anomalies in core-softened potentials?
Using molecular dynamics simulations we investigate the thermodynamic of
particles interacting with a continuous and a discrete versions of a
core-softened (CS) intermolecular potential composed by a repulsive shoulder.
Dynamic and structural properties are also analyzed by the simulations. We show
that in the continuous version of the CS potential the density at constant
pressure has a maximum for a certain temperature. Similarly the diffusion
constant, , at a constant temperature has a maximum at a density
and a minimum at a density
, and structural properties are also
anomalous. For the discrete CS potential none of these anomalies are observed.
The absence of anomalies in the discrete case and its presence in the
continuous CS potential are discussed in the framework of the excess entropy.Comment: 8 page
Indirect organogenesis from leaf explants of Eucalyptus benthamii x Eucalyptus dunnii and shoot multiplication.
Roteiro metodológico para planos de manejo em fazendas experimentais.
bitstream/CNPF-2009-09/44920/1/com_tec205.pd
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