Nonmesonic decay of the Lambda hyperon in nuclear matter - implications on the weak Lambda-N interaction

The lifetime of the Lambda hyperon in heavy hypernuclei as measured by the COSY-13 Collaboration in proton - Au, Bi and U collisions has been analysed to yield tau(Lambda) = (145 +- 11) ps. This value for tau(Lambda) is compatible with the lifetime extracted from antiproton annihilation on Bi and U targets, however, much more accurate. We find that the dependence of the lifetime tau(Lambda) on the mass of hypernuclei indicates a violation of the phenomenological Delta I = 1/2 rule known from the weak mesonic decays of strange particles. PACS: {13.30.-a}{Decays of baryons} {13.75.Ev}{Hyperon-nucleon interaction} {21.80}{Hypernuclei} {25.80.Pw}{Hyperon-induced reactions}Comment: 21 pages, 11 PostScript figures, EPJA in prin

Regular networks of Luttinger liquids

We consider arrays of Luttinger liquids, where each node is described by a unitary scattering matrix. In the limit of small electron-electron interaction, we study the evolution of these scattering matrices as the high-energy single particle states are gradually integrated out. Interestingly, we obtain the same renormalization group equations as those derived by Lal, Rao, and Sen, for a system composed of a single node coupled to several semi-infinite 1D wires. The main difference between the single node geometry and a regular lattice is that in the latter case, the single particle spectrum is organized into periodic energy bands, so that the renormalization procedure has to stop when the last totally occupied band has been eliminated. We therefore predict a strongly renormalized Luttinger liquid behavior for generic filling factors, which should exhibit power-law suppression of the conductivity at low temperatures E_{F}/(k_{F}a) > 1. Some fully insulating ground-states are expected only for a discrete set of integer filling factors for the electronic system. A detailed discussion of the scattering matrix flow and its implication for the low energy band structure is given on the example of a square lattice.Comment: 16 pages, 7 figure

Emergence of a confined state in a weakly bent wire

In this paper we use a simple straightforward technique to investigate the emergence of a bound state in a weakly bent wire. We show that the bend behaves like an infinitely shallow potential well, and in the limit of small bending angle and low energy the bend can be presented by a simple 1D delta function potential.Comment: 4 pages, 3 Postscript figures (uses Revtex); added references and rewritte

Bound States and Threshold Resonances in Quantum Wires with Circular Bends

We study the solutions to the wave equation in a two-dimensional tube of unit width comprised of two straight regions connected by a region of constant curvature. We introduce a numerical method which permits high accuracy at high curvature. We determine the bound state energies as well as the transmission and reflection matrices, ${\cal T}$ and ${\cal R}$ and focus on the nature of the resonances which occur in the vicinity of channel thresholds. We explore the dependence of these solutions on the curvature of the tube and angle of the bend and discuss several limiting cases where our numerical results confirm analytic predictions.Comment: 24 pages, revtex file, one style file and 17 PostScript figures include

Conductance distribution between Hall plateaus

Mesoscopic fluctuations of two-port conductance and four-port resistance between Hall plateaus are studied within a realistic model for a two-dimensional electron gas in a perpendicular magnetic field and a smooth disordered potential. The two-port conductance distribution $P(g)$ is concave between $g=0$ and $g=1$ and is nearly flat between $g=0.2$ and $g=0.8$. These characteristics are consistent with recent observations. The distribution is found to be sharply peaked near the end-points $g=0$ and $g=1$. The distribution functions for the three independent resistances in a four-port Hall bar geometry are, on the other hand, characterized by a central peak and a relatively large width.Comment: 11 pages, 5 ps figures, submitted to Phys. Rev.

Uma análise institucionalista do papel do planejamento estratégico na Embrapa.

A Embrapa foi criada em 1973 para aumentar a produtividade da agricultura brasileira, em meio ao esgotamento do Processo de Substituição de Importações. Mas, ao longo do tempo o contexto institucional modificou-se, exigindo diferentes prioridades de pesquisa. Este artigo tem a intenção de analisar a evolução da estrutura de planejamento da Embrapa, seus objetivos e foco de pesquisa. O que foi realizado a partir da leitura de documentos e avaliação dos Planos Diretores, fontes bibliográficas sobre o assunto e sobre Economia Institucional. Verificou-se que a estrutura de planejamento de pesquisa passou de uma visão centrada na reprodução dos objetivos do governo federal na década de 1970 para uma integração maior com a sociedade na década de 1980 e inserindo o planejamento estratégico a partir da década de 1990. Com monitoramento das demandas da sociedade por tais técnicas, passou-se também a diversificar a agenda de pesquisa, porém esta mudança é dependente em sua trajetória

Hall-like effect induced by spin-orbit interaction

The effect of spin-orbit interaction on electron transport properties of a cross-junction structure is studied. It is shown that it results in spin polarization of left and right outgoing electron waves. Consequently, incoming electron wave of a proper polarization induces voltage drop perpendicularly to the direct current flow between source and drain of the considered four-terminal cross-structure. The resulting Hall-like resistance is estimated to be of the order of 10^-3 - 10^-2 h/e^2 for technologically available structures. The effect becomes more pronounced in the vicinity of resonances where Hall-like resistance changes its sign as function of the Fermi energy.Comment: 4 pages (RevTeX), 4 figures, will appear in Phys. Rev. Let

A unified approach for the solution of the Fokker-Planck equation

This paper explores the use of a discrete singular convolution algorithm as a unified approach for numerical integration of the Fokker-Planck equation. The unified features of the discrete singular convolution algorithm are discussed. It is demonstrated that different implementations of the present algorithm, such as global, local, Galerkin, collocation, and finite difference, can be deduced from a single starting point. Three benchmark stochastic systems, the repulsive Wong process, the Black-Scholes equation and a genuine nonlinear model, are employed to illustrate the robustness and to test accuracy of the present approach for the solution of the Fokker-Planck equation via a time-dependent method. An additional example, the incompressible Euler equation, is used to further validate the present approach for more difficult problems. Numerical results indicate that the present unified approach is robust and accurate for solving the Fokker-Planck equation.Comment: 19 page