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

Correlation decay and conformal anomaly in the two-dimensional random-bond Ising ferromagnet

The two-dimensional random-bond Ising model is numerically studied on long strips by transfer-matrix methods. It is shown that the rate of decay of correlations at criticality, as derived from averages of the two largest Lyapunov exponents plus conformal invariance arguments, differs from that obtained through direct evaluation of correlation functions. The latter is found to be, within error bars, the same as in pure systems. Our results confirm field-theoretical predictions. The conformal anomaly $c$ is calculated from the leading finite-width correction to the averaged free energy on strips. Estimates thus obtained are consistent with $c=1/2$, the same as for the pure Ising model.Comment: RevTeX 3, 11 pages +2 figures, uuencoded, IF/UFF preprin

A new eriophyoid mite species (Acari: Eriophyoidea) damaging Eucalyptus wandoo in Western Australia.

Resumo

On weak vs. strong universality in the two-dimensional random-bond Ising ferromagnet

We address the issue of universality in two-dimensional disordered Ising systems, by considering long, finite-width strips of ferromagnetic Ising spins with randomly distributed couplings. We calculate the free energy and spin-spin correlation functions (from which averaged correlation lengths, $\xi^{ave}$, are computed) by transfer-matrix methods. An {\it ansatz} for the size-dependence of logarithmic corrections to $\xi^{ave}$ is proposed. Data for both random-bond and site-diluted systems show that pure system behaviour (with $\nu=1$) is recovered if these corrections are incorporated, discarding the weak--universality scenario.Comment: RevTeX code, 4 pages plus 2 Postscript figures; to appear in Physical Review B Rapid Communication

Location of the Multicritical Point for the Ising Spin Glass on the Triangular and Hexagonal Lattices

A conjecture is given for the exact location of the multicritical point in the phase diagram of the +/- J Ising model on the triangular lattice. The result p_c=0.8358058 agrees well with a recent numerical estimate. From this value, it is possible to derive a comparable conjecture for the exact location of the multicritical point for the hexagonal lattice, p_c=0.9327041, again in excellent agreement with a numerical study. The method is a variant of duality transformation to relate the triangular lattice directly with its dual triangular lattice without recourse to the hexagonal lattice, in conjunction with the replica method.Comment: 9 pages, 1 figure; Minor corrections in notatio

Dinâmica populacional de Ctenarytaina spatulata (Hemiptera: Psyllidae) em Eucaluptus grandis com novos registros de ocorrência.

Dentre os fatores físicos que exercem influência sobre os insetos, os mais importantes são a temperatura, a umidade, luz e o vento. Quanto à temperatura, os insetos, de um modo geral, desenvolvem-se melhor em temperaturas próximas a 25o C, podendo, no entanto, viver numa larga faixa de temperaturas. Dentro da faixa favorável, os insetos apresentam estreitas faixas de melhor desenvolvimento. De forma análoga à temperatura, as exigências de água pelos insetos variam muito, principalmente devido seus hábitos alimentares. A luz é um dos fatores limitantes aos seres vivos, podendo influenciar na reprodução, dispersão, emergência, alimentação e escolha do hospedeiro (BRENNAN & WEINBAUM 2001d). O vento, além de afetar a temperatura e umidade do ambiente, auxilia os insetos nos processos de dispersão e migração, principalmente quando procuram novo habitat, para alimentação e reprodução (LARA, 1979)

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On surface properties of two-dimensional percolation clusters

The two-dimensional site percolation problem is studied by transfer-matrix methods on finite-width strips with free boundary conditions. The relationship between correlation-length amplitudes and critical indices, predicted by conformal invariance, allows a very precise determination of the surface decay-of-correlations exponent, $\eta_s = 0.6664 \pm 0.0008$, consistent with the analytical value $\eta_s = 2/3$. It is found that a special transition does not occur in the case, corroborating earlier series results. At the ordinary transition, numerical estimates are consistent with the exact value $y_s = -1$ for the irrelevant exponent.Comment: 8 pages, LaTeX with Institute of Physics macros, to appear in Journal of Physics