1,436 research outputs found
Mean-field analysis of the majority-vote model broken-ergodicity steady state
We study analytically a variant of the one-dimensional majority-vote model in
which the individual retains its opinion in case there is a tie among the
neighbors' opinions. The individuals are fixed in the sites of a ring of size
and can interact with their nearest neighbors only. The interesting feature
of this model is that it exhibits an infinity of spatially heterogeneous
absorbing configurations for whose statistical properties we
probe analytically using a mean-field framework based on the decomposition of
the -site joint probability distribution into the -contiguous-site joint
distributions, the so-called -site approximation. To describe the
broken-ergodicity steady state of the model we solve analytically the
mean-field dynamic equations for arbitrary time in the cases n=3 and 4. The
asymptotic limit reveals the mapping between the statistical
properties of the random initial configurations and those of the final
absorbing configurations. For the pair approximation () we derive that
mapping using a trick that avoids solving the full dynamics. Most remarkably,
we find that the predictions of the 4-site approximation reduce to those of the
3-site in the case of expectations involving three contiguous sites. In
addition, those expectations fit the Monte Carlo data perfectly and so we
conjecture that they are in fact the exact expectations for the one-dimensional
majority-vote model
Quasi-stationary distributions for the Domany-Kinzel stochastic cellular automaton
We construct the {\it quasi-stationary} (QS) probability distribution for the
Domany-Kinzel stochastic cellular automaton (DKCA), a discrete-time Markov
process with an absorbing state. QS distributions are derived at both the one-
and two-site levels. We characterize the distribuitions by their mean, and
various moment ratios, and analyze the lifetime of the QS state, and the
relaxation time to attain this state. Of particular interest are the scaling
properties of the QS state along the critical line separating the active and
absorbing phases. These exhibit a high degree of similarity to the contact
process and the Malthus-Verhulst process (the closest continuous-time analogs
of the DKCA), which extends to the scaling form of the QS distribution.Comment: 15 pages, 9 figures, submited to PR
Boundary layers in pressure-driven flow in smectic A liquid crystals
This article examines the steady flow of a smectic A liquid crystal sample that is initially aligned in a classical "bookshelf" geometry confined between parallel plates and is then subjected to a lateral pressure gradient which is perpendicular to the initial local smectic layer arrangement. The nonlinear dynamic equations are derived. These equations can be linearized and solved exactly to reveal two characteristic length scales that can be identified in terms of the material parameters and reflect the boundary layer behavior of the velocity and the director and smectic layer normal orientations. The asymptotic properties of the nonlinear equations are then investigated to find that these length scales apparently manifest themselves in various aspects of the solutions to the nonlinear steady state equations, especially in the separation between the orientations of the director and smectic layer normal. Non-Newtonian plug-like flow occurs and the solutions for the director profile and smectic layer normal share features identified elsewhere in static liquid crystal configurations. Comparisons with numerical solutions of the nonlinear equations are also made
IMUNOTERAPIA COM VENENO DE HIMENÓPTEROS: A EXPERIÊNCIA DE UMA CONSULTA
Resumo: Na Europa a prevalência de alergia ao veneno de himenópteros estima-se em 20%. As reacções sistémicas graves são indicação para imunoterapia específica com veneno de himenópteros após confirmação de atopia. Esta é eficaz em 91-100% dos casos de alergia ao veneno de vespa e 77-80% dos casos de alergia ao veneno de abelha. Apresentamos quatro casos clínicos de doentes com reacções sistémicas ao veneno de himenópteros que efectuaram imunoterapia. Três crianças apresentavam alergia ao veneno de abelha e uma ao veneno de vespa. Tinham IgE específica para o veneno de himenópteros, classes IV a VI. A duração da imunoterapia variou entre quatro e sete anos, com diminuição da classe de IgE específica em todos os doentes no final do tratamento. Três crianças tiveram contacto com o alergénio, durante ou após terminarem a imunoterapia, e nenhuma delas desencadeou uma reacção sistémica. A duração da imunoterapia continua a ser controversa. A ausência de reacção após contacto com o alergénio é sugestiva de sucesso do tratamento
O impacto da emigração recente no número de nados-vivos em Portugal
A recente crise económica observada em Portugal não foi exclusiva do país e registou repercussões massivas a
nível internacional. Desde 2008, em Portugal, registaram-se os mais variados cortes no investimento e
despesa pública, resultando num grande aumento da taxa de desemprego. Realizaram-se algumas tentativas
de minoração dos efeitos da crise económica com a institucionalização de medidas de austeridade como o
Programa de Estabilidade e Crescimento (PEC), mas estas não evitaram a intervenção do Fundo Monetário
Internacional (FMI), trazendo a Troika a Portugal (Alves, 2015; Ribeiro et al., 2015). Durante o seu período em
Portugal (2011 – 2014), o país não conseguiu manter a capacidade para atrair novos residentes ou até de fazer
regressar aqueles que tinham há muito saído em busca de melhores condições de vida, voltando a ser um
país com forte emigração à semelhança do já observado no passado. Apesar desta emigração se dividir entre
temporária e permanente, a verdade é que, muito provavelmente, alguns daqueles que pensaram sair do país
apenas temporariamente, poderão passar a emigrantes permanentes
Octatosylaminophthalocyanine: a reusable chromogenic anion chemosensor
Detailed herein is the use of 2,3,9,10,16,17,23,24-octatosylaminophthalocyanine as a chromogenic chemosensor for anions. The host:guest complexes formed during the sensing event can be regenerated by acid treatment without loss of the sensing ability. This allows the phthalocyanine chemosensor to be reused. This system also responds in a colorimetric manner when exposed to the neutral solvent molecules, dimethyl sulfoxide and methanol. A single-crystal X-ray structure of the Pc 1:2 MeOH complex was obtained. It illustrates the main interactions between the host:guest species in the solid state. Fits of the binding curves are consistent with this stoichiometry predominating in the solution state
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
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