Spin-polarized current and shot noise in the presence of spin flip in a quantum dot via nonequilibrium Green's functions

Using non-equilibrium Green functions we calculate the spin-polarized current and shot noise in a ferromagnet--quantum-dot--ferromagnet (FM-QD-FM) system. Both parallel (P) and antiparallel (AP) magnetic configurations are considered. Coulomb interaction and coherent spin-flip (similar to a transverse magnetic field) are taken into account within the dot. We find that the interplay between Coulomb interaction and spin accumulation in the dot can result in a bias-dependent current polarization $\wp$. In particular, $\wp$ can be suppressed in the P alignment and enhanced in the AP case depending on the bias voltage. The coherent spin-flip can also result in a switch of the current polarization from the emitter to the collector lead. Interestingly, for a particular set of parameters it is possible to have a polarized current in the collector and an unpolarized current in the emitter lead. We also found a suppression of the Fano factor to values well below 0.5.Comment: Published version. 13 pages, 7 figure

Optical spectra of a quantum dot in a microcavity in the nonlinear regime

The optical emission spectrum of a quantum dot in strong coupling with the single mode of a microcavity is obtained in the nonlinear regime. We study how exciton-exciton interactions alter the emission spectrum of the system, bringing the linear Rabi doublet into a multiplet structure that is strongly dependent on the cavity-exciton energy detuning. We emphasise how nonlinearity can be used to evidence the genuine quantum nature of the coupling by producing satellites peaks of the Rabi doublet that originate from the quantized energy levels of the interactions.Comment: Low quality figures. To be published in Phys. Rev. B. 78 (2008

Atividade microbiológica em solos sob cultivo de cana de açúcar.

Resumo: O objetivo deste trabalho foi avaliar a atividade microbiológica e enzimática de solos cultivados com cana de açúcar. Os solos, Latossolo Roxo, foram coletados em área de 1 ano de corte A(1), três anos de corte D(3), cinco anos de corte C(5) e 8 anos de corte H(8), nas profundidades de 0-10 cm e 10-20 cm. O solo A(1), ao contrário dos outros, recebe regulares aplicações de vinhaça. Os parâmetros avaliados foram: atividade de hidrólise do diacetato de fluoresceína (HDF), potencial de mineralização de N (PMN) e atividades das enzimas glucosidase e urease. O solo C(5) apresentou os melhores resultados em termos de atividade por unidade de C orgânico do solo. Ressalta-se, porém, que as variabilidades dos dados obtidos foram altas, evidenciando a necessidade de um novo estudo com um número bem maior de amostras, para que os resultados possam ser realmente comprovados. É interessante que as frações de C orgânico dentro de cada solo sejam também avaliadas. Isto nos daria uma idéia da quantidade de C lábil e recalcitrante em cada solo, que poderia ser utilizado pelos micro-organismos. Abstract: The aim of this study was to evaluate the microbiological and enzymatic activity of soils cultivated with sugar cane. The Oxisols were collected in area with one, three, five and eight years after reform of sugar cane plantation, at 0-10 cm and 10-20 cm depth. The soil A(1), unlike the other, receives regular application of vinasse. The parameters evaluated were: fluorescein diacetate hydrolysis activity, nitrogen mineralization potential and glucosidase and urease activities. The C(5) soil showed the best results in terms of activity per unit of soil organic carbon. It should be noted, however, that the data variability obtained were high, suggesting the need for a new study with a much larger number of samples so that results can be truly proven. It is interesting that the organic C fractions within each soil are also evaluated. This would give us an idea of the amount of labile and recalcitrant carbon in each soil that could be used by the microorganisms

Occurrence of subnormal corpus luteum in superovulated Santa Inês sheep using protocols with or without LH administrated at the end of the FSH treatment.

Edição dos Abstracts do II International Symposium on animal Biology or Reproduction, São Paulo, nov. 2008

Variação histológica em dois genótipos de bananeira em diferentes estádios de desenvolvimento.

As bananas são comercializadas em pencas ou buquês, geralmente com quatro ou nove frutos e o despencamento é um dos principais problemas na comercialização, o que diminui a aceitação dos consumidores e o valor de mercado da fruta. O despencamento é uma desordem fisiológica pós-colheita associada com o amadurecimento