Collision-Dependent Atom Tunnelling Rate in Bose-Einstein Condensates

We show that the interaction (cross-collision) between atoms trapped in distinct sites of a double-well potential can significantly increase the atom tunneling rate for special trap configurations leading to an effective linear Rabi regime of population oscillation between the trap wells. The inclusion of cross-collisional effects significantly extends the validity of the two-mode model approach allowing it to be alternatively employed to explain the recently observed increase of tunneling rates due to nonlinear interactions.Comment: 4 pages, 2 figures. Replaced with improved versio

On the nature of the spin-polarized hole states in a quasi-two-dimensional GaMnAs ferromagnetic layer

A self-consistent calculation of the density of states and the spectral density function is performed in a two-dimensional spin-polarized hole system based on a multiple-scattering approximation. Using parameters corresponding to GaMnAs thin layers, a wide range of Mn concentrations and hole densities have been explored to understand the nature, localized or extended, of the spin-polarized holes at the Fermi level for several values of the average magnetization of the Mn ystem. We show that, for a certain interval of Mn and hole densities, an increase on the magnetic order of the Mn ions come together with a change of the nature of the states at the Fermi level. This fact provides a delocalization of spin-polarized extended states anti-aligned to the average Mn magnetization, and a higher spin-polarization of the hole gas. These results are consistent with the occurrence of ferromagnetism with relatively high transition temperatures observed in some thin film samples and multilayered structures of this material.Comment: 3 page

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

Magnetic ordering in GaAlAs:Mn double well structure

The magnetic order in the diluted magnetic semiconductor barrier of double AlAs/GaAs: Mn quantum well structures is investigated by Monte Carlo simulations. A confinement adapted RKKY mechanism is implemented for indirect exchange between Mn ions mediated by holes. It is shown that, depending on the barrier width and the hole concentration a ferromagnetic or a spin-glass order can be established.Comment: 3 figure

Estudo dos solos do município de Pelotas.

bitstream/item/41392/1/Pelotas.pdf; bitstream/item/41393/1/mapa-geomorfologia.pdf; bitstream/item/41394/1/mapa-solos.pdf; bitstream/item/41395/1/mapa-uso-das-terras.pd

Estudo comparativo dos testes de termo-resistência rápido, lento e fisiológico em sêmen criopreservado bovino importado.

As avaliações de termo-resistência (TTR) ganharam aceitação por se aproximarem das condições de permanencia do sêmen no trato genital das fêmeas em cio. Porém, muitas variáveis tornam o TTR uma avaliação muito subjetiva. Neste sentido, este estudo foi realizado para comparar a eficiência de três metodologias de TTR. Foram usados 24 touros de 3 centrais de inseminação. Foram comparados o TTR lento (38°C/5h), o TTR fisiológico (36°C/3h) e o TTR rápido (46°C/30 min). As avaliações de motilidade e vigor foram realizadas de modo subjetivo em microscópio de contraste de fase. O TTR lento apresentou resultado médio de motilidade de 29,70 ± 22,95%. Esse resultado foi inferior ao TTR rápido, que apresentou motilidade de 46,45 ± 16,45%, e ao TTR fisiológico que apresentou motilidade de 50,93 ± 14,27%. Esses resultados indicam que o TTR lento compromete os resultados de motilidade e vigor. O TTR deve ser considerado uma avaliação complementar para servir de parâmetro na fiscalização da qualidade do sêmen e deve ser realizado em associação com outros testes de avaliação espermática para predizer a fertilidade de uma amostra de sêmen criopreservado