Spin-polarized transport in ferromagnetic multilayered semiconductor nanostructures

The occurrence of inhomogeneous spin-density distribution in multilayered ferromagnetic diluted magnetic semiconductor nanostructures leads to strong dependence of the spin-polarized transport properties on these systems. The spin-dependent mobility, conductivity and resistivity in (Ga,Mn)As/GaAs,(Ga,Mn)N/GaN, and (Si,Mn)/Si multilayers are calculated as a function of temperature, scaled by the average magnetization of the diluted magnetic semiconductor layers. An increase of the resistivity near the transition temperature is obtained. We observed that the spin-polarized transport properties changes strongly among the three materials.Comment: 3 pages, 4 figure

A Galaxy Photometric Redshift Catalog for the Sloan Digital Sky Survey Data Release 6

We present and describe a catalog of galaxy photometric redshifts (photo-z's) for the Sloan Digital Sky Survey (SDSS) Data Release 6 (DR6). We use the Artificial Neural Network (ANN) technique to calculate photo-z's and the Nearest Neighbor Error (NNE) method to estimate photo-z errors for ~ 77 million objects classified as galaxies in DR6 with r < 22. The photo-z and photo-z error estimators are trained and validated on a sample of ~ 640,000 galaxies that have SDSS photometry and spectroscopic redshifts measured by SDSS, 2SLAQ, CFRS, CNOC2, TKRS, DEEP, and DEEP2. For the two best ANN methods we have tried, we find that 68% of the galaxies in the validation set have a photo-z error smaller than sigma_{68} =0.021 or $0.024. After presenting our results and quality tests, we provide a short guide for users accessing the public data.Comment: 16 pages, 12 figure

O Planeamento Territorial como um Instrumento de Política para Operacionalização do Desenvolvimento Sustentável

São várias e diversificadas as definições que podemos encontrar na literatura para o conceito de Desenvolvimento Sustentável: … "É o desenvolvimento que vai de encontro às necessidades das gerações presentes sem comprometer a capacidade de desenvolvimento das gerações futuras." (WCED, 1987) … "Não é um estado fixo de harmonia, mas sim um processo de mudança no qual a exploração dos recursos, o direccionamento dos investimentos, as orientações do desenvolvimento tecnológico e as mudanças institucionais são tornadas consistentes tanto com as necessidades futuras como com as necessidades do presente." (WCED, 1987) … "Pode ser visto como o conjunto de programas de desenvolvimento que vão de encontro aos objectivos de satisfação das necessidades humanas sem violar a capacidade de regeneração dos recursos naturais a longo prazo nem os padrões de qualidade ambiental e de equidade social." (Bartelmus, 1994) … "Deve reconhecer os factores sociais e ecológicos, assim como os factores económicos, da base de recursos vivos e não vivos e das vantagens e desvantagens de acções alternativas tanto a longo como a curto prazos." (IUCN, 1980; Gardner, 1989) … "É compreendido como uma forma de mudança social que acrescenta aos tradicionais objectivos de desenvolvimento o objectivo da obtenção da sustentabilidade ecológica." (Lelé, 1991

Measuring the extent of convective cores in low-mass stars using Kepler data: towards a calibration of core overshooting

Our poor understanding of the boundaries of convective cores generates large uncertainties on the extent of these cores and thus on stellar ages. Our aim is to use asteroseismology to consistently measure the extent of convective cores in a sample of main-sequence stars whose masses lie around the mass-limit for having a convective core. We first test and validate a seismic diagnostic that was proposed to probe in a model-dependent way the extent of convective cores using the so-called $r_{010}$ ratios, which are built with $l=0$ and $l=1$ modes. We apply this procedure to 24 low-mass stars chosen among Kepler targets to optimize the efficiency of this diagnostic. For this purpose, we compute grids of stellar models with both the CESAM2k and MESA evolution codes, where the extensions of convective cores are modeled either by an instantaneous mixing or as a diffusion process. Among the selected targets, we are able to unambiguously detect convective cores in eight stars and we obtain seismic measurements of the extent of the mixed core in these targets with a good agreement between the CESAM2k and MESA codes. By performing optimizations using the Levenberg-Marquardt algorithm, we then obtain estimates of the amount of extra-mixing beyond the core that is required in CESAM2k to reproduce seismic observations for these eight stars and we show that this can be used to propose a calibration of this quantity. This calibration depends on the prescription chosen for the extra-mixing, but we find that it should be valid also for the code MESA, provided the same prescription is used. This study constitutes a first step towards the calibration of the extension of convective cores in low-mass stars, which will help reduce the uncertainties on the ages of these stars.Comment: 27 pages, 15 figures, accepted in A&

A Intervenção na Cidade Existente.

A identidade colectiva do grupo, o prestígio das famílias dominantes e o saber técnico foram os pólos de interesse que organizaram a memória colectiva até ao momento em que se tornou possível a celebração de acontecimentos através da sua inscrição em monumentos (elementos materiais resultantes do poder de perpetuação das sociedades históricas). Muitos destes monumentos são involuntários e subsistiram sem que ninguém o tenha deliberado; outros são intencionais, tendo sido edificados propositadamente para recordar um feito ou uma pessoa, ou um grupo, e durante séculos foram os únicos a ser preservados e venerados

Verification of the observer property in discrete event systems

The observer property is an important condition to be satisfied by abstractions of Discrete Event System (DES) models. This technical note presents a new algorithm that tests if an abstraction of a DES obtained through natural projection has the observer property. The procedure, called OP-Verifier, can be applied to (potentially nondeterministic) automata, with no restriction on the existence of cycles of 'non-relevant' events. This procedure has quadratic complexity in the number of states. The performance of the algorithm is illustrated by a set of experiments

Management, Organizations and Contemporary Social Theory

Social theorists speculate about large-scale social questions, asking of any phenomenon, how is it possible? This book addresses how various social theories contribute key insights into the nature of organizations and management