Connectivity-dependent properties of diluted sytems in a transfer-matrix description

We introduce a new approach to connectivity-dependent properties of diluted systems, which is based on the transfer-matrix formulation of the percolation problem. It simultaneously incorporates the connective properties reflected in non-zero matrix elements and allows one to use standard random-matrix multiplication techniques. Thus it is possible to investigate physical processes on the percolation structure with the high efficiency and precision characteristic of transfer-matrix methods, while avoiding disconnections. The method is illustrated for two-dimensional site percolation by calculating (i) the critical correlation length along the strip, and the finite-size longitudinal DC conductivity: (ii) at the percolation threshold, and (iii) very near the pure-system limit.Comment: 4 pages, no figures, RevTeX, Phys. Rev. E Rapid Communications (to be published

Smoothly-varying hopping rates in driven flow with exclusion

We consider the one-dimensional totally asymmetric simple exclusion process (TASEP) with position-dependent hopping rates. The problem is solved,in a mean field/adiabatic approximation, for a general (smooth) form of spatial rate variation. Numerical simulations of systems with hopping rates varying linearly against position (constant rate gradient), for both periodic and open boundary conditions, provide detailed confirmation of theoretical predictions, concerning steady-state average density profiles and currents, as well as open-system phase boundaries, to excellent numerical accuracy.Comment: RevTeX 4.1, 14 pages, 9 figures (published version

Logarithmic corrections to gap scaling in random-bond Ising strips

Numerical results for the first gap of the Lyapunov spectrum of the self-dual random-bond Ising model on strips are analysed. It is shown that finite-width corrections can be fitted very well by an inverse logarithmic form, predicted to hold when the Hamiltonian contains a marginal operator.Comment: LaTeX code with Institute of Physics macros for 7 pages, plus 2 Postscript figures; to appear in Journal of Physics A (Letter to the Editor

Avaliação zootécnica e ambiental da piscicultura.

A aqüicultura é uma das atividades agropecuárias que cresce em um ritmo superior a 10% ao ano e está associada à produção de uma grande diversidade de espécies aquáticas e sistemas de cultivo. Dependendo das técnicas de manejo utilizadas os sistemas de produção podem ser classificados em extensivos, semi-intensivos e intensivos. Por outro lado, existem poucas metodologias validadas para otimizar os índices zootécnicos e ambientais da piscicultura . Neste trabalho, buscou-se desenvolver um sistema que permita que se façam avaliações zootécnicas e ambientais da aqüicultura de maneira simples, prática e com o objetivo principal de subsidiar os produtores na identificação de Boas Práticas de Manejo (BPMs). A metodologia foi desenvolvida com base em dois estudos realizados, respectivamente, no Alabama, EUA, e em Campinas, SP, sobre a avaliação ambiental da produção de bagre do canal (Ictalurus punctatus), e sobre o uso de indicadores de sustentabilidade para avaliação ambiental em pesque-pagues. A utilização dessas metodologias requer um suporte técnico e laboratorial considerável, o que em muitos casos, dificulta a aplicação e a adoção desses métodos pela maioria dos produtores. A metodologia proposta consiste basicamente de uma matriz sistêmica ponderada que contém questões ordenadas em três colunas, que podem ser respondidas pelo pesquisador e/ou produtor diretamente no próprio local que está sendo avaliado. Uma vez obtidas as respostas, é possível avaliar de forma rápida e objetiva diferentes sistemas de produção de peixes, sem a necessidade de uso de sondas multiparâmetros ou de coletas de amostras de água para posteriores análises laboratoriais. Além disso, a metodologia proposta poderá ser adotada de imediato pelos piscicultores de forma a auxiliá-los na identificação de Boas Práticas de Manejo (BPMs) para otimizar o desempenho zootécnico dos peixes e, concomitantemente, mitigar os possíveis impactos ambientais negativos gerados pela piscicultura

Uso de coletores com substrato artificial para monitoramento biológico de qualidade de água.

bitstream/CNPMA/7463/1/comunicado_39.pd

Surface crossover exponent for branched polymers in two dimensions

Transfer-matrix methods on finite-width strips with free boundary conditions are applied to lattice site animals, which provide a model for randomly branched polymers in a good solvent. By assigning a distinct fugacity to sites along the strip edges, critical properties at the special (adsorption) and ordinary transitions are assessed. The crossover exponent at the adsorption point is estimated as $\phi = 0.505 \pm 0.015$, consistent with recent predictions that $\phi = 1/2$ exactly for all space dimensionalities.Comment: 10 pages, LaTeX with Institute of Physics macros, to appear in Journal of Physics

Boas práticas de manejo (BPMs) para a produção de peixes em tanques-redes.

Aqücultura e meio ambiente; Qualidade de água e BPMs; Manejo alimentar e qualidade de água; Temperatura da água e estratificação; Oxigênio dissolvido e produtividade primária; Qualidade de água e estresse; BPMs nas pisciculturas em tanques-redes; Contrele da erosão e do aporte de sedimentos nos viveiros e reservatórios; Redução da carga orgânica; Conservação dos recursos hídricos.bitstream/item/81186/1/DOC47.pd

Kosterlitz-Thouless transition in three-state mixed Potts ferro-antiferromagnets

We study three-state Potts spins on a square lattice, in which all bonds are ferromagnetic along one of the lattice directions, and antiferromagnetic along the other. Numerical transfer-matrix are used, on infinite strips of width $L$ sites, $4 \leq L \leq 14$. Based on the analysis of the ratio of scaled mass gaps (inverse correlation lengths) and scaled domain-wall free energies, we provide strong evidence that a critical (Kosterlitz-Thouless) phase is present, whose upper limit is, in our best estimate, $T_c=0.29 \pm 0.01$. From analysis of the (extremely anisotropic) nature of excitations below $T_c$, we argue that the critical phase extends all the way down to T=0. While domain walls parallel to the ferromagnetic direction are soft for the whole extent of the critical phase, those along the antiferromagnetic direction seem to undergo a softening transition at a finite temperature. Assuming a bulk correlation length varying, for $T>T_c$, as $\xi (T) =a_\xi \exp [ b_\xi (T-T_c)^{-\sigma}]$, $\sigma \simeq 1/2$, we attempt finite-size scaling plots of our finite-width correlation lengths. Our best results are for $T_c=0.50 \pm 0.01$. We propose a scenario in which such inconsistency is attributed to the extreme narrowness of the critical region.Comment: 11 pages, 6 .eps figures, LaTeX with IoP macros, to be published in J Phys

On locations and properties of the multicritical point of Gaussian and +/-J Ising spin glasses

We use transfer-matrix and finite-size scaling methods to investigate the location and properties of the multicritical point of two-dimensional Ising spin glasses on square, triangular and honeycomb lattices, with both binary and Gaussian disorder distributions. For square and triangular lattices with binary disorder, the estimated position of the multicritical point is in numerical agreement with recent conjectures regarding its exact location. For the remaining four cases, our results indicate disagreement with the respective versions of the conjecture, though by very small amounts, never exceeding 0.2%. Our results for: (i) the correlation-length exponent $\nu$ governing the ferro-paramagnetic transition; (ii) the critical domain-wall energy amplitude $\eta$; (iii) the conformal anomaly $c$; (iv) the finite-size susceptibility exponent $\gamma/\nu$; and (v) the set of multifractal exponents $\{\eta_k \}$ associated to the moments of the probability distribution of spin-spin correlation functions at the multicritical point, are consistent with universality as regards lattice structure and disorder distribution, and in good agreement with existing estimates.Comment: RevTeX 4, 9 pages, 2 .eps figure