14 research outputs found
Properties of some mean-field-like approximations for the triangular Ising antiferromagnet
Motivated by a recent proposal of a Bethe approximation for the triangular
Ising antiferromagnet [Phys. Rev. B {\bf 56}, 8241 (1997)], which seems to
predict a disordered phase at any temperature in zero field, we analyze in some
detail several mean-field like approximations for this model, namely the Bethe
approximation itself, the cluster variation method and the hard-spin mean-field
theory. We show: (i) that the disordered phase predicted by the Bethe
approximation is unphysical at low enough temperature because of a negative
entropy; (ii) how the results of the cluster variation method (namely, zero
temperature entropy and critical temperature of the spurious transition)
converge to the exact ones for increasing cluster size; (iii) that it is
possible to construct a cluster variation approximation which yields a
disordered phase which is stable down to zero temperature; (iv) a few, so far
unknown, zero temperature results (entropy and internal energy) of the
hard-spin mean-field theory.Comment: 13 REVTeX pages + 9 PostScript figures; deeper analysis of CVM
results has been included; to be published in Phys. Rev.
Internal quality of eggs coated with whey protein concentrate Qualidade interna de ovos de galinha cobertos com concentrado protéico de soro de leite bovino
The functional properties of foods can be preserved when they are coated with edible films, since both the loss of moisture and the transport of O2 and CO2 are reduced. The objectives of this work were: to compare weight loss, Haugh units, and albumen pH between fresh eggs and eggs coated with whey protein concentrate (WPC), under six storage periods (3, 7, 10, 14, 21 and 28 days), at 25°C. During the entire storage period, regardless of whether the eggs were coated or not, the Haugh unit values and the weight loss decreased, and differences between values from the first to the last period were lower for coated eggs. Albumen pH increased. The Haugh unit values for coated eggs were similar to those found in literature references when the same storage period was considered.<br>As vantagens de utilizar filmes e coberturas comestíveis podem ser justificadas pela manutenção das propriedades funcionais dos alimentos, através da diminuição da perda de umidade e da diminuição da troca de gases (O2 e CO2). Aplicação de cobertura em ovos com casca reduz a perda de peso e mantém a qualidade interna do produto. Os objetivos deste trabalho foram comparar a perda de peso, os valores de unidades Haugh e o pH do albume de ovos com e sem cobertura à base de concentrado protéico de soro de leite, armazenados a 25°C, por 3, 7, 10, 14, 21 e 28 dias. Durante todo o período de armazenamento houve decréscimo dos valores de unidades Haugh e perda de peso, tanto para os ovos com cobertura como para os ovos sem cobertura. O pH do albume aumentou para os ovos com e sem cobertura, a variação dos valores nos ovos com cobertura foi menor do que para os ovos sem cobertura. A cobertura de concentrado protéico de soro de leite reduz o transporte de vapor de água e gás (CO2) através dos poros da casca do ovo. Essa cobertura mantém o pH da clara de ovo na faixa de 8, durante quatro semanas de armazenamento e, desse modo, consegue manter as características necessárias para boa conservação do produto