25,554 research outputs found
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
Birds, Ilha Grande, state of Rio de Janeiro, Southeastern Brazil
We provide a list of bird species from our primary surveys and secondary data for an island (Ilha Grande) insoutheastern Brazil. The information derives mainly from primary data collected since 1995, particularly in the oceanicside of the island. The methodologies included capture-mark-recapture studies using mist nets, transects (visual andvocal records) and supplementary observations. Our total species list from primary data is 175 species (127 captured)and 47 species were added from secondary data. This represents 222 species from 58 families. Of this total, 44 areendemic to Atlantic forest and nine are threatened with extinction. Our results are discussed comparing our study areawith another large island included in the Serra do Mar corridor (Ilha de São Sebastião), and also a nearby continentalarea (Paraty). The results indicate the importance of Ilha Grande as a reservoir of bird species of Atlantic forest
Stripe-tetragonal phase transition in the 2D Ising model with dipole interactions: Partition-function zeros approach
We have performed multicanonical simulations to study the critical behavior
of the two-dimensional Ising model with dipole interactions. This study
concerns the thermodynamic phase transitions in the range of the interaction
\delta where the phase characterized by striped configurations of width h=1 is
observed. Controversial results obtained from local update algorithms have been
reported for this region, including the claimed existence of a second-order
phase transition line that becomes first order above a tricritical point
located somewhere between \delta=0.85 and 1. Our analysis relies on the complex
partition function zeros obtained with high statistics from multicanonical
simulations. Finite size scaling relations for the leading partition function
zeros yield critical exponents \nu that are clearly consistent with a single
second-order phase transition line, thus excluding such tricritical point in
that region of the phase diagram. This conclusion is further supported by
analysis of the specific heat and susceptibility of the orientational order
parameter.Comment: to appear in Phys. Rev.
Boletim Agrometeorológico ano 2002 para a sub-região da Nhecolândia, Pantanal, Mato Grosso do Sul, Brasil.
Este boletim tem o intuito de difundir as informações agroclimáticas coletadas no Pantanal da Nhecolândia, visando subsidiar a pesquisa agropecuária da região, além de atender todos àqueles que necessitam de informações dessa natureza.bitstream/CPAP/55971/1/DOC76.pdfFormato Eletrônic
Geometric scaling of purely-elastic flow instabilities
We present a combined experimental, numerical and theoretical investigation
of the geometric scaling of the onset of a purely-elastic flow instability in a
serpentine channel. Good qualitative agreement is obtained between experiments,
using dilute solutions of flexible polymers in microfluidic devices, and
two-dimensional numerical simulations using the UCM model. The results are
confirmed by a simple theoretical analysis, based on the dimensionless
criterion proposed by Pakdel-McKinley for onset of a purely-elastic
instability
Chemical abundances for 11 bulge stars from high-resolution, near-IR spectra
It is debated whether the Milky Way bulge has the characteristics of a
classical bulge sooner than those of a pseudobulge. Detailed abundance studies
of bulge stars is a key to investigate the origin, history, and classification
of the bulge. The aim is to add to the discussion on the origin of the bulge
and to study detailed abundances determined from near-IR spectra for bulge
giants already investigated with optical spectra, the latter also providing the
stellar parameters which are very significant for the results of the present
study. Especially, the important CNO elements are better determined in the
near-IR. High-resolution, near-infrared spectra in the H band are recorded
using the CRIRES spectrometer on the Very Large Telescope. The CNO abundances
can all be determined from the numerous molecular lines in the wavelength range
observed. Abundances of the alpha elements are also determined from the near-IR
spectra. [O/Fe], [Si/Fe] and [S/Fe] are enhanced up to metallicities of at
least [Fe/H]=-0.3, after which they decline. This suggests that the Milky Way
bulge experienced a rapid and early star-formation history like that of a
classical bulge. However, a similarity between the bulge trend and the trend of
the local thick disk seems present. Such a similarity could suggest that the
bulge has a pseudobulge origin. Our [C/Fe] trend does not show any increase
with [Fe/H] which could have been expected if W-R stars have contributed
substantially to the C abundances. No "cosmic scatter" can be traced around our
observed abundance trends; the scatter found is expected, given the
observational uncertainties.Comment: Accepted for publication in A&
The extended gaussian ensemble and metastabilities in the Blume-Capel model
The Blume-Capel model with infinite-range interactions presents analytical
solutions in both canonical and microcanonical ensembles and therefore, its
phase diagram is known in both ensembles. This model exhibits nonequivalent
solutions and the microcanonical thermodynamical features present peculiar
behaviors like nonconcave entropy, negative specific heat, and a jump in the
thermodynamical temperature. Examples of nonequivalent ensembles are in general
related to systems with long-range interactions that undergo canonical
first-order phase transitions. Recently, the extended gaussian ensemble (EGE)
solution was obtained for this model. The gaussian ensemble and its extended
version can be considered as a regularization of the microcanonical ensemble.
They are known to play the role of an interpolating ensemble between the
microcanonical and the canonical ones. Here, we explicitly show how the
microcanonical energy equilibrium states related to the metastable and unstable
canonical solutions for the Blume-Capel model are recovered from EGE, which
presents a concave "extended" entropy as a function of energy.Comment: 6 pages, 5 eps figures. Presented at the XI Latin American Workshop
on Nonlinear Phenomena, October 05-09 (2009), B\'uzios (RJ), Brazil. To
appear in JPC
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