21,112 research outputs found
Disordered two-dimensional superconductors: roles of temperature and interaction strength
We have considered the half-filled disordered attractive Hubbard model on a
square lattice, in which the on-site attraction is switched off on a fraction
of sites, while keeping a finite on the remaining ones. Through Quantum
Monte Carlo (QMC) simulations for several values of and , and for system
sizes ranging from to , we have calculated the
configurational averages of the equal-time pair structure factor , and,
for a more restricted set of variables, the helicity modulus, , as
functions of temperature. Two finite-size scaling {\it ansatze} for have
been used, one for zero-temperature and the other for finite temperatures. We
have found that the system sustains superconductivity in the ground state up to
a critical impurity concentration, , which increases with , at least up
to U=4 (in units of the hopping energy). Also, the normalized zero-temperature
gap as a function of shows a maximum near , for . Analyses of the helicity modulus and of the pair structure factor
led to the determination of the critical temperature as a function of , for
4 and 6: they also show maxima near , with the highest
increasing with in this range. We argue that, overall, the observed
behavior results from both the breakdown of CDW-superconductivity degeneracy
and the fact that free sites tend to "push" electrons towards attractive sites,
the latter effect being more drastic at weak couplings.Comment: 9 two-column pages, 14 figures, RevTe
Siscero - Sistema de clipping da Embrapa Rondônia.
O Siscero, ou Sistema de clipping da Embrapa Rondônia, é uma aplicação desenvolvida em plataforma web para o registro de matérias jornalísticas ou outras inserções na mídia que envolvam a Embrapa Rondônia. As informações são armazenadas em banco de dados relacional e o sistema permite o registro de arquivos digitais, como imagem, PDF, áudio ou vídeo. Uma interface de pesquisa oferece uma série de filtros para busca de registros e gráficos interativos permitem avaliar, comparar e monitorar o desempenho da Empresa na mídia. Este documento contextualiza o clipping no universo corporativo, faz uma retrospectiva das iniciativas passadas e da situação atual do clipping realizado pela Embrapa e apresenta o Siscero como uma ferramenta estratégica. Um manual para utilização do sistema e um guia de instalação também fazem parte do conteúdo.bitstream/item/35944/1/doc137-siscero.pd
Immunization and Aging: a Learning Process in the Immune Network
The immune system can be thought as a complex network of different
interacting elements. A cellular automaton, defined in shape-space, was
recently shown to exhibit self-regulation and complex behavior and is,
therefore, a good candidate to model the immune system. Using this model to
simulate a real immune system we find good agreement with recent experiments on
mice. The model exhibits the experimentally observed refractory behavior of the
immune system under multiple antigen presentations as well as loss of its
plasticity caused by aging.Comment: 4 latex pages, 3 postscript figures attached. To be published in
Physical Review Letters (Tentatively scheduled for 5th Oct. issue
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