Determination of the scattering length for Rb-Cs X1Σ+^{1}\Sigma ^{+} ground electronic state using a variational method

We performed the calculation of the scattering length for the elastic collision between the rubidium and cesium atoms. For this we applied a variational procedure based on the R-matrix theory for unbound states employing the finite element method (FEM) for expansion of the wave-function in terms of a finite set of local basis functions. The FEM presents as advantages the possibility of the development of a efficient matrix inversion algorithm which significantly reduces the computation time to calculate the R matrix. We also tested a potential energy curve with spectroscopic accuracy obtained before from a direct adjustment procedure of experimental data of the $X^{1}\Sigma^{+}$ state based on genetic algorithm. The quality of our result was evaluated by comparing them with several ones previously published at literature.Comment: 15 pages, 6 tables and 2 figure

Desenvolvimento regional, efeito de localização e clusters agroindustriais no Brasil.

Objetiva-se, neste artigo, uma breve revisão da literatura acadêmica sobre o desenvolvimento regional e o efeito de localização, buscando-se, para tanto, identificar elementos que possam estar relacionados nas diversas modalidades de organização da produção local, bem como no processo de desenvolvimento recente da agroindústria de determinadas regiões do Brasil. Além de distinguir os conceitos de crescimento econômico e de desenvolvimento, busca-se aqui analisar as relações entre o desenvolvimento regional e o efeito de localização. As principais correntes das chamadas teorias de localização industrial, assim como as principais formas de organização da produção local, com destaque para os clusters e os distritos industriais italianos, são aqui enfocadas. Por fim são sintetizadas algumas análises especializadas sobre clusters agroindustriais no Brasil e seus efeitos sobre o desenvolvimento regional

Graphene-based spin-pumping transistor

We demonstrate with a fully quantum-mechanical approach that graphene can function as gate-controllable transistors for pumped spin currents, i.e., a stream of angular momentum induced by the precession of adjacent magnetizations, which exists in the absence of net charge currents. Furthermore, we propose as a proof of concept how these spin currents can be modulated by an electrostatic gate. Because our proposal involves nano-sized systems that function with very high speeds and in the absence of any applied bias, it is potentially useful for the development of transistors capable of combining large processing speeds, enhanced integration and extremely low power consumption

Graphene as a non-magnetic spin-current lens

In spintronics, the ability to transport magnetic information often depends on the existence of a spin current traveling between two different magnetic objects acting as source and probe. A large fraction of this information never reaches the probe and is lost because the spin current tends to travel omni-directionally. We propose that a curved boundary between a gated and a non-gated region within graphene acts as an ideal lens for spin currents despite being entirely of non-magnetic nature. We show as a proof of concept that such lenses can be utilized to redirect the spin current that travels away from a source onto a focus region where a magnetic probe is located, saving a considerable fraction of the magnetic information that would be otherwise lost.Comment: 9 pages, 3 figure

Steady-state entanglement between distant quantum dots in photonic crystal dimers

We show that two spatially separated semiconductor quantum dots under resonant and continuous-wave excitation can be strongly entangled in the steady-state, thanks to their radiative coupling by mutual interaction through the normal modes of a photonic crystal dimer. We employ a quantum master equation formalism to quantify the steady-state entanglement by calculating the system {\it negativity}. Calculations are specified to consider realistic semiconductor nanostructure parameters for the photonic crystal dimer-quantum dots coupled system, determined by a guided mode expansion solution of Maxwell equations. Negativity values of the order of 0.1 ($20\%$ of the maximum value) are shown for interdot distances that are larger than the resonant wavelength of the system. It is shown that the amount of entanglement is almost independent of the interdot distance, as long as the normal mode splitting of the photonic dimer is larger than their linewidths, which becomes the only requirement to achieve a local and individual qubit addressing. Considering inhomogeneously broadened quantum dots, we find that the steady-state entanglement is preserved as long as the detuning between the two quantum dot resonances is small when compared to their decay rates. The steady-state entanglement is shown to be robust against the effects of pure dephasing of the quantum dot transitions. We finally study the entanglement dynamics for a configuration in which one of the two quantum dots is initially excited and find that the transient negativity can be enhanced by more than a factor of two with respect to the steady-state value. These results are promising for practical applications of entangled states at short time scales.Comment: 10 pages, 7 figure

Dynamic RKKY interaction between magnetic moments in graphene nanoribbons

Graphene has been identified as a promising material with numerous applications, particularly in spintronics. In this paper we investigate the peculiar features of spin excitations of magnetic units deposited on graphene nanoribbons and how they can couple through a dynamical interaction mediated by spin currents. We examine in detail the spin lifetimes and identify a pattern caused by vanishing density of states sites in pristine ribbons with armchair borders. Impurities located on these sites become practically invisible to the interaction, but can be made accessible by a gate voltage or doping. We also demonstrate that the coupling between impurities can be turned on or off using this characteristic, which may be used to control the transfer of information in transistor-like devices.Comment: 10 pages, 10 figure

Influência de sistemas de rotação de culturas nos atributos físicos do solo.

O experimento foi conduzido na Embrapa Arroz e Feijão, em Santo Antônio de Goiás, GO, durante dez anos agrícolas, novembro de 1993 a março de 2003, em Latossolo Vermelho distrófico. Após esse período, foram avaliados os efeitos de sete sistemas de rotação de cultura nos atributos físicos do solo. Foi utilizado o delineamento de blocos ao acaso, com quatro repetições. Os tratamentos consistiram de: cultivo anual contínuo de arroz; arroz em rotações anual, bienal e trienal com soja e milho safrinha; e arroz em rotações anual, bienal e trienal com soja e milheto safrinha. As culturas de arroz e soja foram semeadas em novembro, em solo preparado com arado de aivecas, e as de milho e milheto imediatamente após a colheita da soja, em plantio direto. A rotação anual de arroz com soja e milho ou milheto safrinha propiciou melhor qualidade física do solo em relação às demais rotações, especialmente quando o milho foi usado na safrinha. Esta melhoria foi devida ao maior aporte de matéria orgânica ao solo