Theory of Disordered Itinerant Ferromagnets I: Metallic Phase

A comprehensive theory for electronic transport in itinerant ferromagnets is developed. We first show that the Q-field theory used previously to describe a disordered Fermi liquid also has a saddle-point solution that describes a ferromagnet in a disordered Stoner approximation. We calculate transport coefficients and thermodynamic susceptibilities by expanding about the saddle point to Gaussian order. At this level, the theory generalizes previous RPA-type theories by including quenched disorder. We then study soft-mode effects in the ferromagnetic state in a one-loop approximation. In three-dimensions, we find that the spin waves induce a square-root frequency dependence of the conductivity, but not of the density of states, that is qualitatively the same as the usual weak-localization effect induced by the diffusive soft modes. In contrast to the weak-localization anomaly, this effect persists also at nonzero temperatures. In two-dimensions, however, the spin waves do not lead to a logarithmic frequency dependence. This explains experimental observations in thin ferromagnetic films, and it provides a basis for the construction of a simple effective field theory for the transition from a ferromagnetic metal to a ferromagnetic insulator.Comment: 15pp., REVTeX, 2 eps figs, final version as publishe

How does the beach ecosystem change without tourists during COVID-19 lockdown?

Urban tourist beach ecosystems provide the essential service of recreation. These ecosystems also support critical ecological functions where biodiversity conservation is not usually a priority. The sudden lockdown due to the COVID-19 pandemic created a unique opportunity to evaluate the effects of human absence in these urban-coastal ecosystems. This study examined bioindicators from 29 urban tourist beaches in seven Latin-American countries and assesses their response to lockdown about some relevant anthropogenic stressors such as pollution, noise, human activities, and user density. The presence of animals and plants, as well as the intensity of stressors, were assessed through a standardized protocol during lockdown conditions. Additionally, the environmental conditions of the beaches before and during lockdown were qualitatively compared using multivariate non-parametric statistics. We found notable positive changes in biological components and a clear decrease in human stressors on almost all the beaches. Dune vegetation increased on most sites. Similarly, high burrow densities of ghost crabs were observed on beaches, except those where cleaning activity persisted. Because of the lockdown, there was an exceptionally low frequency of beach users, which in turn reduced litter, noise and unnatural odors. The observed patterns suggest that tourist beaches can be restored to natural settings relatively quickly. We propose several indicators to measure changes in beaches once lockdown is relaxed. Adequate conservation strategies will render the recreational service of tourist beaches more environmental-friendly

Use of whole soy lecithin in diets with energy concentrate from starchy or lipid sources for steers

ABSTRACT Diets with high energy density and additives that enhance energy use are necessary for finishing feedlot cattle. The objective of the present study was to evaluate the performance, ingestive behavior, apparent digestibility of the diet and the carcass traits of feedlot steers fed concentrates from different energy sources, one derived from starchy sources and the other, from lipid sources, combined or not with whole soy lecithin, at a dose of 40 g animal day-1. The experimental design was completely randomized blocks, in a 2 x 2 factorial arrangement. The combination of whole soy lecithin with the lipid energy source concentrate increased the dry matter digestibility and the carcass yield of the animals (76.03% and 57.20%, respectively). The lipid energy source concentrate showed higher ether extract digestibility and animals fed on it had higher carcass yield (84.18% and 56.85%, respectively). Whole soy lecithin promoted a reduction in fecal pH due to a greater fermentation of carbohydrates and fatty acids in the intestinal lumen. Using whole soy lecithin combined with energy concentrate from a lipid source is recommended due to its improvements in the use of the diet and in the carcass yield

A quantum Monte Carlo study of the one-dimensional ionic Hubbard model

Quantum Monte Carlo methods are used to study a quantum phase transition in a 1D Hubbard model with a staggered ionic potential (D). Using recently formulated methods, the electronic polarization and localization are determined directly from the correlated ground state wavefunction and compared to results of previous work using exact diagonalization and Hartree-Fock. We find that the model undergoes a thermodynamic transition from a band insulator (BI) to a broken-symmetry bond ordered (BO) phase as the ratio of U/D is increased. Since it is known that at D = 0 the usual Hubbard model is a Mott insulator (MI) with no long-range order, we have searched for a second transition to this state by (i) increasing U at fixed ionic potential (D) and (ii) decreasing D at fixed U. We find no transition from the BO to MI state, and we propose that the MI state in 1D is unstable to bond ordering under the addition of any finite ionic potential. In real 1D systems the symmetric MI phase is never stable and the transition is from a symmetric BI phase to a dimerized BO phase, with a metallic point at the transition

Dermatophylosis in Santa Inês sheep from Distrito Federal

Relataram-se quatro casos de dermatofilose em ovinos da raça Santa Inês, no período de um ano. Microscopicamente observaram-se filamentos na forma de "trilho de bonde" e zoósporos nos quatro casos. A tentativa do isolamento do microrganismo foi realizada por meio do método de Haalstra e em apenas um caso obteve-se sucesso, observando-se colônias de aparência lisa, formato circular, cor amarelada e hemolítica em ágar sangue. O exame direto com coloração de Gram mostrou-se um método bastante eficiente na confirmação da presença do microrganismo afetando a epiderme em razão da morfologia típica do agente.Four cases of dermatophylosis were reported in Santa Inês sheep in a study period of one year. Microscopically, septate filaments and coccoid forms zoospores were observed. Attempts to isolate the microorganisms were accomplished using Haastra's method and it was successful in only one case. Dermatophilus congolensis samples have grown on blood agar, colonies where hemolytic, small, round and pigmentation vary from yellow to orange. The gram staining method was efficient to confirm the presence of the microorganism affecting the epidermis due to typical morphology of the agent

Perfil hematológico de cabras Saanen e mestiças (1/2 Saanen e 1/2 Anglo-nubiana) criadas em clima tropical do Ceará

Objetivou-se verificar a influência das condições climáticas sobre o perfil hematológico de cabras Saanen e mestiça (1/2 Saanen x 1/2 Anglo-nubiana), bem como determinar valores de referência para esses animais criados no Ceará. Foram utilizadas 30 cabras que tiveram o sangue coletado mensalmente durante a época chuvosa (fevereiro a maio) e seca (agosto a novembro) para realização do eritrograma e leucograma. As médias foram comparadas pelo teste t-Student e Mann Whitney, quando constatada distribuição paramétrica e não paramétrica dos dados, respectivamente, com significância quando p0,05). As hemácias e neutrófilos segmentados apresentaram uma correlação negativa com a temperatura ambiente, porém positiva com a umidade do ar e a temperatura retal (p<0,05). O hematócrito correlacionou-se positivamente com a temperatura ambiente e frequência respiratória (p<0,05). Os leucócitos e linfócitos mostraram uma correlação negativa com a temperatura retal (p<0,05). Conclui-se, portanto, que fêmeas Saanen sofrem mais influência das variações climáticas e a época chuvosa tem maior impacto negativo sobre os parâmetros hematológicos. Os valores obtidos poderão servir como referência para esses genótipos no Ceará