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

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 $L$ 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 $L \to \infty$ whose statistical properties we probe analytically using a mean-field framework based on the decomposition of the $L$-site joint probability distribution into the $n$-contiguous-site joint distributions, the so-called $n$-site approximation. To describe the broken-ergodicity steady state of the model we solve analytically the mean-field dynamic equations for arbitrary time $t$ in the cases n=3 and 4. The asymptotic limit $t \to \infty$ reveals the mapping between the statistical properties of the random initial configurations and those of the final absorbing configurations. For the pair approximation ($n=2$) 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

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

Equivalence of stationary state ensembles

We show that the contact process in an ensemble with conserved total particle number, as simulated recently by Tome and de Oliveira [Phys. Rev. Lett. 86 (2001) 5463], is equivalent to the ordinary contact process, in agreement with what the authors assumed and believed. Similar conserved ensembles and equivalence proofs are easily constructed for other models.Comment: 5 pages, no figure

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 $z,$ $\theta,$ $\beta$ and $\nu$. 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 $z$ our result coincides with that of the 4-state Potts model in two dimensions. In addition, results for the static exponents $\nu$ and $\beta$ agree with previous estimates obtained from finite size scaling combined with conformal invariance. Finally, for the new dynamic exponent $\theta$ 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

Surface tension implementation for Gensmac 2D

In the present work we describe a method which allows the incorporation of surface tension into the GENSMAC2D code. This is achieved on two scales. First on the scale of a cell, the surface tension effects are incorporated into the free surface boundary conditions through the computation of the capillary pressure. The required curvature is estimated by fitting a least square circle to the free surface using the tracking particles in the cell and in its close neighbors. On a sub-cell scale, short wavelength perturbations are filtered out using a local 4-point stencil which is mass conservative. An efficient implementation is obtained through a dual representation of the cell data, using both a matrix representation, for ease at identifying neighbouring cells, and also a tree data structure, which permits the representation of specific groups of cells with additional information pertaining to that group. The resulting code is shown to be robust, and to produce accurate results when compared with exact solutions of selected fluid dynamic problems involving surface tension

On Damage Spreading Transitions

We study the damage spreading transition in a generic one-dimensional stochastic cellular automata with two inputs (Domany-Kinzel model) Using an original formalism for the description of the microscopic dynamics of the model, we are able to show analitically that the evolution of the damage between two systems driven by the same noise has the same structure of a directed percolation problem. By means of a mean field approximation, we map the density phase transition into the damage phase transition, obtaining a reliable phase diagram. We extend this analysis to all symmetric cellular automata with two inputs, including the Ising model with heath-bath dynamics.Comment: 12 pages LaTeX, 2 PostScript figures, tar+gzip+u