7,510 research outputs found
Melting temperature of screened Wigner crystal on helium films by molecular dynamics
Using molecular dynamics (MD) simulation, we have calculated the melting
temperature of two-dimensional electron systems on \AA-\AA helium
films supported by substrates of dielectric constants
at areal densities varying from cm to cm. Our results are in good agreement with the available
theoretical and experimental results.Comment: 4 pages and 4 figure
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
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
Well-posed problem for a combustion model in a multilayer porous medium
Combustion occurring in porous media has various practical applications, such
as in in-situ combustion processes in oil reservoirs, the combustion of biogas
in sanitary landfills, and many others. A porous medium where combustion takes
place can consist of layers with different physical properties. This study
demonstrates that the initial value problem for a combustion model in a
multi-layer porous medium has a unique solution, which is continuous with
respect to the initial data and parameters in . In
summary, it establishes that the initial value problem is well-posed in
. The model is governed by a one-dimensional
reaction-diffusion-convection system, where the unknowns are the temperatures
in the layers. Previous studies have addressed the same problem in
. However, in this study, we solve the problem in a
less restrictive space, namely . The proof employs
a novel approach to combustion problems in porous media, utilizing an evolution
operator defined from the theory of semigroups in Hilbert space and Kato's
theory for a well-posed associated initial value problem
Zoneamento de riscos climáticos para a cultura de milho no estado do Rio Grande do Sul: períodos favoráveis de semeadura por município, safra 2004-2005.
bitstream/CNPT-2010/40294/1/p-bp21.pd
Uma discussão sobre o conceito de hazards e o caso do furacão/ciclone Catarina.
bitstream/CNPT-2010/40654/1/p-do36.pd
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
Porta-enxertos para laranjeiras-doces (Citrus sinensis (L.) OSB.), em Rio Branco, Acre.
O objetivo deste trabalho foi de avaliar o comportamento de sete cultivares de laranjeiras-doces: 'Baia 101', 'Baianinha IAC 79', 'Monte Parnaso', 'Pêra D6', 'Natal 112', 'Valência 27' e 'Aquiri', sobre diferentes porta-enxertos: limão 'Cravo', tangerinas 'Cleópatra' e 'Sunki' e citrange 'Carrizo', nas condições edafoclimáticas de Rio Branco, Acre. O delineamento experimental foi em parcelas subdivididas, com as cultivares nas parcelas, os porta-enxertos nas subparcelas e os quatro anos de avaliação como repetições. As laranjeiras 'Pêra D6', 'Natal 112' e 'Valência 27' apresentaram tendências de maior produção quando enxertadas sobre o limão 'Cravo', e a laranja 'Aquiri' quando enxertada sobre citrange 'Carrizo'. Em relação aos demais porta-enxertos, o limão 'Cravo' mostrou tendências de induzir maior produção/volume de copa e peso médio do fruto, e menor teor de sólidos solúveis totais e acidez total. As laranjas do grupo Baia ('Baia 101', 'Baianinha IAC 79' e 'Monte Parnaso') produziram frutos com baixa percentagem de suco; não são recomendadas para plantio em Rio Branco, AC. Com base nos resultados obtidos, recomendam-se os porta-enxertos citrange 'Carrizo', tangerina 'Cleópatra' e limão 'Cravo' para a laranja 'Aquiri', e o porta-enxerto limão 'Cravo' para as laranjas 'Pêra D6', 'Natal 112' e 'Valência 27'
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