Vortex rectification effects in films with periodic asymmetric pinning

We study the transport of vortices excited by an ac current in an Al film with an array of nanoengineered asymmetric antidots. The vortex response to the ac current is investigated by detailed measurements of the voltage output as a function of ac current amplitude, magnetic field and temperature. The measurements revealed pronounced voltage rectification effects which are mainly characterized by the two critical depinning forces of the asymmetric potential. The shape of the net dc voltage as a function of the excitation amplitude indicates that our vortex ratchet behaves in a way very different from standard overdamped models. Rather, as demonstrated by the observed output signal, the repinning force, necessary to stop vortex motion, is considerably smaller than the depinning force, resembling the behavior of the so-called inertia ratchets. Calculations based on an underdamped ratchet model provide a very good fit to the experimental data.Comment: 5 pages, 4 figure

Coleta, introducao e selecao de forrageiras nativas e exoticas.

Este trabalho apresenta resultados da avaliação e seleção de germoplasma forrageiro no semiárido de Sobral, Ceará, especialmente para uso por caprinos e ovinos

de Broglie-Proca and Bopp-Podolsky massive photon gases in cosmology

We investigate the influence of massive photons on the evolution of the expanding universe. Two particular models for generalized electrodynamics are considered, namely de Broglie-Proca and Bopp-Podolsky electrodynamics. We obtain the equation of state (EOS) $P=P(\varepsilon)$ for each case using dispersion relations derived from both theories. The EOS are inputted into the Friedmann equations of a homogeneous and isotropic space-time to determine the cosmic scale factor $a(t)$. It is shown that the photon non-null mass does not significantly alter the result $a\propto t^{1/2}$ valid for a massless photon gas; this is true either in de Broglie-Proca's case (where the photon mass $m$ is extremely small) or in Bopp-Podolsky theory (for which $m$ is extremely large).Comment: 8 pages, 2 figures; v2 matches the published versio

Vacuumless kinks systems from vacuum ones, an example

Some years ago, Cho and Vilenkin, introduced a model which presents topological solutions, despite not having degenerate vacua as is usually expected. Here we present a new model with topological defects, connecting degenerate vacua but which in a certain limit recovers precisely the one proposed originally by Cho and Vilenkin. In other words, we found a kind of parent model for the so called vacuumless model. Then the idea is extended to a model recently introduced by Bazeia et al. Finally, we trace some comments the case of the Liouville model.Comment: 11 pages, 4 figure

Severidade da antracnose do sorgo em misturas de cultivares.

xEdição dos Resumos do XLI Congresso Brasileiro de Fitopatologia, Belo Horizonte, MG, ago. 2008

Caracterização morfológica de acessos de bacurizeiro por meio de descritores florais.

O bacurizeiro é uma espécie frutífera originária da Amazônia, onde são encontradas amplas variações em forma e tamanho de frutos, rendimento e qualidade de polpa, dentre outras características de interesse (CAVALCANTE, 1996). Apesar de apresentar elevado potencial de uso na alimentação humana, ainda há carência de conhecimentos científicos sobre a espécie, com destaque para biologia floral, mecanismos reprodutivos, manejo cultural e estabelecimento de descritores mínimos. O objetivo deste trabalho foi efetuar, com base em descritores florais, a caracterização morfológica de acessos de bacurizeiro da Coleção de Germoplasma da Embrapa Meio-Norte, estabelecidos em Teresina-PI

Maize and grass integrated system fertilized with polyhalite and KCl.

Crop-livestock integrated systems (CLIS) have been used as a strategy of sustainable agricultural intensification which integrates annual crops and livestock activities on the same area and in the same season.Poster number 1143