1,391 research outputs found
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 , consistent with recent
predictions that exactly for all space dimensionalities.Comment: 10 pages, LaTeX with Institute of Physics macros, to appear in
Journal of Physics
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, , consistent with
the analytical value . 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
for the irrelevant exponent.Comment: 8 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
sites, . 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, . From analysis
of the (extremely anisotropic) nature of excitations below , 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 , as , , we attempt finite-size scaling plots of our finite-width
correlation lengths. Our best results are for . 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
Domain scaling and marginality breaking in the random field Ising model
A scaling description is obtained for the --dimensional random field Ising
model from domains in a bar geometry. Wall roughening removes the marginality
of the case, giving the correlation length in , and for power law behaviour with
, . Here, (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 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
Qualidade química e física de dois solos da região produtora de olerícolas em Casa Nova - BA.
A região do Vale do Submédio São Francisco vem sendo alterada de forma intensa nos últimos anos, tendo o desenvolvimento de atividades agrícolas efeito marcante na atual configuração da paisagem. Com isso a preocupação com o processo de degradação principalmente do solo e da água deve ser primordial para garantir a sustentabilidade ambiental. O conhecimento sobre as características físicas e químicas dos solos é a base mais importante para propor práticas de manejo que considerem as condições locais, diminuindo assim a degradação desse recurso. Portanto, o objetivo desse trabalho foi de estudar as características físicas e químicas de duas classes de solos representativas do município de Casa Nova ? BA com a finalidade de avaliar suas potencialidades e limitações para o uso agrícola na produção de olerícolas. Foram realizadas as descrições morfológicas e coletadas as amostras de dois perfis de solos para análises físicas e químicas. Os solos estudados não oferecem impedimentos físicos para o cultivo de oleráceas, no entanto apresentam baixa fertilidade natural, onde se faz necessário o uso adequado de um programa de fertilização para que o uso agrícola dos mesmos seja rentável
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
Correlation functions in the two-dimensional random-field Ising model
Transfer-matrix methods are used to study the probability distributions of
spin-spin correlation functions in the two-dimensional random-field Ising
model, on long strips of width sites, for binary field
distributions at generic distance , temperature and field intensity
. For moderately high , and of the order of magnitude used in
most experiments, the distributions are singly-peaked, though rather
asymmetric. For low temperatures the single-peaked shape deteriorates, crossing
over towards a double- ground-state structure. A connection is obtained
between the probability distribution for correlation functions and the
underlying distribution of accumulated field fluctuations. Analytical
expressions are in good agreement with numerical results for ,
low , not too small, and near G=1. From a finite-size {\it ansatz} at
, , averaged correlation functions are predicted to
scale with , . From numerical data we estimate y=0.875 \pm
0.025WR/L=1W \sim h_0^{\kappa} f(L h_0^u)\kappa \simeq 0.45u \simeq 0.8f(x)x \to \inftyW \sim
h_0^{\kappa}d=2$.Comment: RevTeX code for 8 pages, 7 eps figures, to appear in Physical Review
E (1999
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