6,640 research outputs found
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
Relação de longo prazo entre a produtividade do arroz irrigado produzido no Rio Grande do Sul e de Santa Catarina.
O objetivo geral deste trabalho foi analisar a relação entre a produtividade do arroz irrigado no Rio Grande do Sul e de Santa Catarina. A análise de co-integração de Engle e Granger (1987) foi utilizada com forma de corroborar com a ideia de relação de longo prazo entres as produtividades dos arrozais
Margens de comercialização no mercado de arroz em São Paulo, 05/2010 a 04/2013.
O presente trabalho buscou analisar a comercialização do arroz entre 05/2010 e 04/2013 sob a ótica das margens de comercialização nos níveis de produtor, atacado e varejo, em São Paulo. Pretende-se, assim, demonstrar a participação dos diferentes agentes no valor adicionado ao produto arroz
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
Competitividade dos principais produtos agropecuários do Brasil - vantagem comparativa revelada normalizada.
Este trabalho visa analisar a competitividade dos principais produtos agropecuários brasileiros por meio de um índice alternativo, o índice de vantagem comparativa revelada normalizado (VCRN), no período entre 1996 e 2007
A semiquantitative approach to the impurity-band-related transport properties of GaMnAs nanolayers
We investigate the spin-polarized transport of GaMnAs nanolayers in which a
ferromagnetic order exists below a certain transition temperature. Our
calculation for the self-averaged resistivity takes into account the existence
of an impurity band determining the extended ("metallic" transport) or
localized (hopping by thermal excitation) nature of the states at and near the
Fermi level. Magnetic order and resistivity are inter-related due to the
influence of the spin polarization of the impurity band and the effect of the
Zeeman splitting on the mobility edge. We obtain, for a given range of Mn
concentration and carrier density, a "metallic" behavior in which the transport
by extended carriers dominates at low temperature, and is dominated by the
thermally excited localized carriers near and above the transition temperature.
This gives rise to a conspicuous hump of the resistivity which has been
experimentally observed and brings light onto the relationship between
transport and magnetic properties of this material
Generalised verification of the observer property in discrete event systems
The observer property is an important condition to be satisfied by abstractions of Discrete Event Systems (DES) models. This paper presents a generalised version of a previous algorithm which tests if an abstraction of a DES obtained through natural projection has the observer property. The procedure called OP-verifier II overcomes the limitations of the previously proposed verifier while keeping its computational complexity. Results are illustrated by a case study of a transfer line system
Generalised verification of the observer property in discrete event systems
The observer property is an important condition to be satisfied by abstractions of Discrete Event Systems (DES) models. This paper presents a generalised version of a previous algorithm which tests if an abstraction of a DES obtained through natural projection has the observer property. The procedure called OP-verifier II overcomes the limitations of the previously proposed verifier while keeping its computational complexity. Results are illustrated by a case study of a transfer line system
Efetividade e razão ótima de hedge para operações de boi gordo em Goiás.
O objetivo geral deste estudo foi estimar a razão ótima de hedge e a sua efetividade para o mercado de boi gordo em Goiás. Atualmente, o estado ocupa importante posição na pecuária de corte no cenário nacional possuindo o maior número de confinamentos do país. Destaca-se que a rentabilidade dos confinadores pode ser prejudicada pelo risco de reposição da atividade, em que o pecuarista vende o boi gordo e compra o bezerro ou boi magro. Por conseguinte, o mecanismo de proteção de preços no mercado futuro pode minimizar a os riscos de reposição da atividade
Análise da competitividade dos principais produtos agropecuários do Estado de Goiás - vantagem comparativa revelada normalizada.
Este trabalho visa analisar a competitividade dos principais produtos agropecuários do estado de Goiás em relação ao Brasil e ao mundo, por meio do índice de vantagem comparativa revelada normalizado
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