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

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

Pair of Heavy-Exotic-Quarks at LHC

We study the production and signatures of heavy exotic quarks pairs at LHC in the framework of the vector singlet model (VSM), vector doublet model (VDM) and fermion-mirror-fermion (FMF) model. The pair production cross sections for the electroweak and strong sector are computed.Comment: 7 pages, 6 figures. accept at Int. Jour. of Mod. Phy

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

Domain scaling and marginality breaking in the random field Ising model

A scaling description is obtained for the $d$--dimensional random field Ising model from domains in a bar geometry. Wall roughening removes the marginality of the $d=2$ case, giving the $T=0$ correlation length $\xi \sim \exp\left(A h^{-\gamma}\right)$ in $d=2$, and for $d=2+\epsilon$ power law behaviour with $\nu = 2/\epsilon \gamma$, $h^\star \sim \epsilon^{1/\gamma}$. Here, $\gamma = 2,4/3$ (lattice, continuum) is one of four rough wall exponents provided by the theory. The analysis is substantiated by three different numerical techniques (transfer matrix, Monte Carlo, ground state algorithm). These provide for strips up to width $L=11$ basic ingredients of the theory, namely free energy, domain size, and roughening data and exponents.Comment: ReVTeX v3.0, 19 pages plus 19 figures uuencoded in a separate file. These are self-unpacking via a shell scrip

Efeito da exploração florestal de impacto reduzido sobre a regeneração natural em uma floresta densa de terra firme no município de Paragominas na Amazônia brasileira.

O estudo foi motivado pela escassez de informações sobre a sustentabilidade ecológica da exploração de florestas naturais, em áreas diretamente afetadas pela exploração. O objetivo foi verificar se há diferença florística entre a floresta não-explorada e áreas diretamente afetadas pela exploração, e entre anos pós-exploração, e averiguar a capacidade de recuperação natural da floresta, quanto à estrutura e composição florística anteriores à exploração. Avaliou-se a regeneração natural em três áreas exploradas em diferentes ocasiões (2000, 2003 e 2006), no período de sete anos, na Fazenda Rio Capim, no município de Paragominas, Pará. Os dados foram coletados em clareiras, ramais de arraste primário e secundário, pátio de estocagem e floresta remanescente da exploração, considerando indivíduos entre 2,5 e 10,0 cm de diâmetro. Calculou-se a abundância, índice de diversidade, equitabilidade, similaridade florística. No período de até sete anos após a exploração florestal de impacto reduzido, ocorreram marcantes alterações na composição florística e na abundância de indivíduos com DAP de 2,5-10,0 cm, principalmente nos ramais principais e pátios. Na floresta remanescente, a dinâmica, tanto de espécies quanto de indivíduos, ocorreu mais com espécies tolerantes à sombra, porém nas clareiras, ramais e pátios predominaram as espécies pioneiras. Nos pátios e nos ramais de arraste, o desenvolvimento das plantas foi muito baixo, não permitindo alta abundância de indivíduos com DAP maior que 2,5 cm. A regeneração natural nas áreas abertas pela exploração florestal, embora tenha sofrido influência da floresta remanescente, conta com poucas espécies de alto valor comercial. Portanto, sugere-se que devam ser aplicados tratamentos silviculturais pós-exploratórios para beneficiar mudas de regeneração natural (DAP = 2,5 cm) pré-existentes e sejam realizados enriquecimentos em clareiras para garantir estoque suficiente de espécies comerciais para futuras colheitas

Acceptability and study of shelf life of gluten free cereal bar with popped and extruded sorghum based on a consumer acceptability.

Cereal bars have been an excellent vehicle for delivering functional ingredients to food market. Researches has showed that sorghum is a great source of phenolic compounds. Besides, it is a gluten free cereal, therefore a potential ingredient to celiac diets. Thus, a cereal bar with popped sorghum, sorghum extrudates, cashew fiber and dehydrated banana was formulated. Sensory acceptability of this product was determined by two panels: one panel composed of celiac individuals and another by non-celiac subjects. The product shelf life was estimated by the acceptability limit methodology. After remained stored for 120 days under 25°C, the shelf life was estimated at 163 ± 52 days. The sensorial study has not found significant differences in relation to overall acceptability between celiac and non-celiac individuals. This study suggest that sorghum co-products could be used successfully as a food ingredient to develop new formulations of the gluten free cereal bars

Boundary critical behaviour of two-dimensional random Ising models

Using Monte Carlo techniques and a star-triangle transformation, Ising models with random, 'strong' and 'weak', nearest-neighbour ferromagnetic couplings on a square lattice with a (1,1) surface are studied near the phase transition. Both surface and bulk critical properties are investigated. In particular, the critical exponents of the surface magnetization, 'beta_1', of the correlation length, 'nu', and of the critical surface correlations, 'eta_{\parallel}', are analysed.Comment: 16 pages in ioplppt style, 7 ps figures, submitted to J. Phys.