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

Avaliação de acessos de melancia (Citrullus lanatus) do Banco Ativo de Germoplasma (BAG) de cucurbitáceas da Embrapa Semi-Árido.

Avaliou-se o número de dias para o aparecimento da primeira flor feminina

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

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

Genomic islands of divergence in the Yellow Tang and the Brushtail Tang Surgeonfishes.

The current ease of obtaining thousands of molecular markers challenges the notion that full phylogenetic concordance, as proposed by phylogenetic species concepts, is a requirement for defining species delimitations. Indeed, the presence of genomic islands of divergence, which may be the cause, or in some cases the consequence, of speciation, precludes concordance. Here, we explore this issue using thousands of RAD markers on two sister species of surgeonfishes (Teleostei: Acanthuridae), Zebrasoma flavescens and Z. scopas, and several populations within each species. Species are readily distinguished based on their colors (solid yellow and solid brown, respectively), yet populations and species are neither distinguishable using mitochondrial markers (cytochrome c oxidase 1), nor using 5193 SNPs (pairwise Φst = 0.034). In contrast, when using outlier loci, some of them presumably under selection, species delimitations, and strong population structure follow recognized taxonomic positions (pairwise Φst = 0.326). Species and population delimitation differences based on neutral and selected markers are likely due to local adaptation, thus being consistent with the idea that these genomic islands of divergence arose as a consequence of isolation. These findings, which are not unique, raise the question of a potentially important pathway of divergence based on local adaptation that is only evident when looking at thousands of loci

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

Uso de leitos cultivados no tratamento de efluentes da aquicultura.

In the last fifty years, worldwide aquaculture has increased about 8.8% /year. In Brazil, the tilapia culture, the flagship aquaculture production, represents 39% of the total cultivated fish. The increasing demand for aquatic protein, the demographic increasement and the decline of natural stocks have contributed to the promotion of aquaculture around the world. Nevertheless, concerns about the negative environmental impacts caused by this activity are also increasing. Some of these impacts are: destruction of mangroves, significant inputs of nitrogen, phosphorus and organic matter downstream nurseries, invasion of exotic species in natural aquatic ecosystems. Natural treatment systems such as constructed wetlands are costeffective, do not depend on energy, and the efficiency of removal of the main physico-chemical parameters of water quality are at 70 to 90% on average. By bacteriological metabolism and mechanical filtration, the organic matter is used as food and nutrient for aquatic plants. This study aims to assess the efficiency of constructed wetlands for treatment of effluents from tilapia culture, using a closed cycle of water. At Embrapa Environment (Jaguariúna, SP), a system composed by 54 plastic boxes was constructed to test three kinds of substrates: pebbles, expanded clay and a mixture of both. The plant Vetiver was used as another part of the treatment system. We expect to verify a great reduction in important parameters such as total nitrogen, total phosphorus, biochemical oxygen demand, total suspended solids and others. This system could be very useful at smallholder aquaculture worried with best management practices

Is There a Need for Tailored Graduate Programs for International Students?

International studies often present opportunities for capacity development and mentorship for students to equip them with the knowledge and skills to address the challenges in their home countries. Typically, international graduate students are drawn from diverse educational and cultural backgrounds different from those in their host countries. Adjusting to these changes might be challenging and time-consuming, thus influencing their academic journey. Understanding these challenges might provide international students the opportunity to address them in time and, where possible, seek help. In this paper, we discuss some graduate program-related challenges international students face and provide potential recommendations that might result in tailored programs. It is anticipated that such programs will effectively prepare international graduate students to adapt quickly to new conditions in their host countries and optimize the learning process while acquiring the appropriate tools for their future careers. We conducted a literature search that focused mainly on articles related to international graduate students in the US. Five challenges were explored: Cultural and language barriers, technological literacy and competency, mentorship, career development, and course structure and research priority areas. Graduate programs need to help students identify these challenges while helping them create an ideal environment for excellence. Such programs need to provide adequate support structures, making them known to students at the beginning of their programs. Although it is not feasible to change an entire educational program to accommodate all the needs of international graduate students, pressing concerns need to be identified for action

Impact of Increasing Nitrogen Fertilizer Rates upon an Irrigated Tanzania Grass Pasture. 1. Dry Matter Yield

An experiment was carried out with irrigated Tanzania grass (Panicum maximum, Jacq.) pasture receiving five nitrogen (N) rates of (0, 30, 60, 90 and 120 kg N ha-¹ cut-¹) during the growing season. N application increased dry matter yield and Tanzania growth rate linearly (P \u3c 0.05). Responses to nitrogen applications were higher in the first two cuts of the growing season than in the last two cuts. The N fertilizer conversion into herbage dry matter was also higher in the beginning of the growing season