Reentrant valence transition in EuO at high pressures: beyond the bond-valence model

The pressure-dependent relation between Eu valence and lattice structure in model compound EuO is studied with synchrotron-based x-ray spectroscopic and diffraction techniques. Contrary to expectation, a 7% volume collapse at $\approx$ 45 GPa is accompanied by a reentrant Eu valence transition into a \emph{lower} valence state. In addition to highlighting the need for probing both structure and electronic states directly when valence information is sought in mixed-valent systems, the results also show that widely used bond-valence methods fail to quantitatively describe the complex electronic valence behavior of EuO under pressure.Comment: 5 pages, 4 figure

High-Energy Approach for Heavy-Ion Scattering with Excitations of Nuclear Collective States

A phenomenological optical potential is generalized to include the Coulomb and nuclear interactions caused by the dynamical deformation of its surface. In the high-energy approach analytical expressions for elastic and inelastic scattering amplitudes are obtained where all the orders in the deformation parameters are included. The multistep effect of the 2$^+$ rotational state excitation on elastic scattering is analyzed. Calculations of inelastic cross sections for the $^{17}$O ions scattered on different nuclei at about hundred Mev/nucleon are compared with experimental data, and important role of the Coulomb excitation is established.Comment: 9 pages; 3 figures. Submitted to the Physics of Atomic Nucle

Competition between excitonic gap generation and disorder scattering in graphene

We study the disorder effect on the excitonic gap generation caused by strong Coulomb interaction in graphene. By solving the self-consistently coupled equations of dynamical fermion gap $m$ and disorder scattering rate $\Gamma$, we found a critical line on the plane of interaction strength $\lambda$ and disorder strength $g$. The phase diagram is divided into two regions: in the region with large $\lambda$ and small $g$, $m \neq 0$ and $\Gamma = 0$; in the other region, $m = 0$ and $\Gamma \neq 0$ for nonzero $g$. In particular, there is no coexistence of finite fermion gap and finite scattering rate. These results imply a strong competition between excitonic gap generation and disorder scattering. This conclusion does not change when an additional contact four-fermion interaction is included. For sufficiently large $\lambda$, the growing disorder may drive a quantum phase transition from an excitonic insulator to a metal.Comment: 8 pages, 1 figur

Energy gaps at neutrality point in bilayer graphene in a magnetic field

Utilizing the Baym-Kadanoff formalism with the polarization function calculated in the random phase approximation, the dynamics of the $\nu=0$ quantum Hall state in bilayer graphene is analyzed. Two phases with nonzero energy gap, the ferromagnetic and layer asymmetric ones, are found. The phase diagram in the plane $(\tilde{\Delta}_0,B)$, where $\tilde{\Delta}_0$ is a top-bottom gates voltage imbalance, is described. It is shown that the energy gap scales linearly, $\Delta E\sim 14 B[T]K, with magnetic field.Comment: 5 pages, 3 figures, title changed, references added, JETP Letters versio

Caracterização do sistema produtivo da mangabeira no município de Itaporanga D'Ajuda, Sergipe.

bitstream/CPATC-2010/21506/1/bp-48.pd

Características fisico-químicas de frutos de taperebá (Spondia mombin L.) coletados em área de ocorrência de mosca-das-frutas

Este trabalho teve por objetivo avaliar as características físico-químicas de frutos de taperebá a partir de amostras coletadas em dois pontos distintos no município de Mazagão (AP), local reconhecidamente de ocorrência de moscas-das-frutas

Evaluation of operational parameters on the precipitation of endoglucanase and xylanase produced by solid state fermentation of Aspergillus niger

In order to develop cost effective processes for converting biomass into biofuels, it is essential to improve enzyme production yields, stability and specific activity. In this context, the aim of this work was to evaluate the concentration of two enzymes involved in the hydrolysis of biomass, endoglucanase and xylanase, through precipitation. Statistical experimental design was used to evaluate the influence of precipitant agent concentration (ammonium sulfate and ethanol), aging time, and temperature on enzyme activity recovery. Precipitant agent concentration and aging time showed a statistically significant effect at the 95% confidence level, on both enzyme activity recoveries. The recovery of endoglucanase with ammonium sulfate and ethanol reached values up to 65 and 61%, respectively. For xylanase, the recovery rates were lower, 27 and 25% with ammonium sulfate and ethanol, respectively. The results obtained allowed the selection of the variables relevant to improving enzyme activity recovery within operational conditions suitable for industrial applications.1726Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq

Indicadores de viabilidade financeira e econômica do sistema de produção familiar de leite de cabra no Rio Grande do Norte.

Resumo - O trabalho objetivou identificar um modelo e exploração de leite de cabra por agricultores familiares, por meio de indicadores de viabilidade da exploração no Rio Grande Norte, para subsidiar os produtores em suas decisões de gerenciar e/ou investir na atividade. A seleÁ?o do Estado foi feita por ser o maior produtor nordestino de leite de cabra. O modelo adotado de estrutura de custos e receitas e medidas de resultados foi o do Instituto de Economia Agrícola de São Paulo. Utilizaram-se, também, metodologias de análise econômico-financeira para se conhecer a taxa interna de retorno (TIR), o valor presente lÌquido (VPL) e a relação Benefício/Custo sob as óticas financeira e econômica. Os resultados do modelo construído para gerar de três a quatro salários mínimos mensais foram: área de 100 ha, investimentos totais de R$55 mil, 50 matrizes em lactação, 50 litros de leite/dia, custo de produção de um litro de leite: R$ 0,76 e de venda: R$1,03, lucratividade de 24$ 1.276,00, TIR financeira 77% e econômica de 179%. O VPL econômico foi 16% superior ao financeiro e a relação Benefício/Custo foi de 1,57, sob a ótica financeira, e 1,79 na econômica. Os indicadores mostram a viabilidade do negócio, com destaque para a viabilidade econômica, que se traduz na contribução dos caprinocultores para com a sociedade, uma vez que geram um VPL de R$95,4 mil e apropriam-se de apenas R$ 82,3 mil. Abstract - This paper analyses through viability indicator a production of goat milk model used by familiar farmers in Rio Grande do Norte and can be used to subsidize the decision making about management and/or investment on activity. The used model of costs, revenues and results measure was the methodology utilized by Instituto de Economia AgrÌcola of S?o Paulo. Also, were utilized methodologies of analyses economic and financial to know the net present value, internal tax of return and the benefit/cost relation. The model was constructed to generate an average income of three to four minimum wages by month and the results were: area of 100 hectares, total investment of R$55,000.00, fifty does in lactation, fifty liters of milk by day, production cost of R$ 0.76 by liter of milk, selling price of R$1.03, profitability of 24$ 1,276.00, financial internal tax of return of 77% and economic internal tax of return of 179%. The economic net present value was 16% higher than the financial and the benefit/cost relation was 1.57 under the financial vision and 1.79 under the economic vision. The indicators show a viability of the business, emphasizing the economic viability where the producers of goat milk contribute to the society since that they produce a net present value of R$95,400.00 and only take possession of R$ 82,300.00

Dirac fermions in a power-law-correlated random vector potential

We study localization properties of two-dimensional Dirac fermions subject to a power-law-correlated random vector potential describing, e.g., the effect of "ripples" in graphene. By using a variety of techniques (low-order perturbation theory, self-consistent Born approximation, replicas, and supersymmetry) we make a case for a possible complete localization of all the electronic states and compute the density of states.Comment: Latex, 4+ page