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Brazilian Journal of Physics, Volume: 28, Número: 2, Publicado: 1998

  • The Partial Revival of the Quadrature Variance Product in the Dynamics of the Squeezed Vacuum Field in the Jaynes-Cummings Model

    Moura, A. P. S. de; Furuya, K.

    Resumo em Inglês:

    We consider the time evolution of a squeezed vacuum cavity field interacting with an initially excited two-level atom via the Jaynes-Cummings model in the Rotating Wave approximation. For large enough initial squeezing, we recognize a new partial revival phenomenon in terms of the quadrature variance product. We show the time evolution of the field quasiprobability Q-function, which provides a quadrature space picture of the partial revival phenomenon. An interpretation of the phenomenon in terms of a certain kind of first momentum of the photon distribution function is given.

  • Design Considerations on a Dispersion Compensating Coaxial Fiber

    Nunes, F. D.; Silva, H. F. da; Zilio, S. C.

    Resumo em Inglês:

    This work reports on the performance of a dispersion compensating coaxial fiber as a function of its geometric parameters. Our analysis is carried out by solving the wave equation under the linearly polarized approximation, which leads to transcendental equations that provide the effective index of refraction. The highest efficiency at a fixed wavelength is achieved for a suitably chosen geometry and this choice constitutes an important factor to determine the general shape of the wavelength-dependent dispersion curve.

  • Remarks on Non-Markov Processes

    van Kampen, N.G.

    Resumo em Inglês:

    It is emphasized that non-Markovian processes, which occur for instance in the case of colored noise, cannot be considered merely as corrections to the class of Markov processes but require special treatment. Many familiar concepts, such as first-passage times, no longer apply and need be reconsidered. Several methods of dealing with non-Markov processes are discussed. As an example a recent application to the transport of ions through a membrane is briefly mentioned.

  • On Entropy Production in Informational Statistical Thermodynamics

    Luzzi, R.; Vasconcellos, A. R.; Ramos, J. G.

    Resumo em Inglês:

    We consider the question of the existence of a generalized H-theorem in the context of the variational method in the information-theoretical approach that generates the nonequilibrium statistical operator formalism. After briefly reviewing how the latter provides mechano-statistical foundations for phenomenological irreversible thermodynamics, the so-called Informational Statistical Thermodynamics, we discuss how dissipative phenomena are accounted for by the procedure. Such effects are related to a generalized H-theorem and a weak criterion of positive entropy production. These results are a consequence of the definition of a coarse-grained statistical entropy, resulting from the projection of the full nonequilibrium distribution on the subspace of the slow relaxing dynamical quantities, that are appropriate for the description of the irreversible evolution of the system from the state of initial preparation.

  • Elastic Cross Sections for Low-Energy e--CH4 Collisions

    Machado, L. E.; Lee, M.-T.; Brescansin, L. M.

    Resumo em Inglês:

    Recently we have extended our codes based on the Schwinger variational iterative method in order to study elastic electron scattering by non-planar molecules with symmetries reducible to the C2v point group and also to include a correlation- polarization contribution to the electron-molecule interaction potential. In this work we report the first application of these newly extended codes to the calculation of cross sections for low-energy elastic scattering of electron by methane. Differential, integral and momentum-transfer cross sections were calculated in the 0.1-50 eV incident energy range. Comparison of our results with the extensive available data, both experimental and theoretical, reveals the reliability of our method. Particularly, the Ramsauer minimum at around 0.4 eV and the resonance structure at around 8 eV are well reproduced in our calculations.

  • Flux Operators of Microdynamical Quantities in a Nonequilibrium Statistical Ensemble Formalism

    Madureira, Justino R.; Vasconcellos, Áurea R.; Luzzi, Roberto

    Resumo em Inglês:

    It is shown how the closure condition for the set of kinetic equations in Zubarev's Nonequilibrium Statistical Operator Method introduces a series of fluxes of a reference set of densities. These fluxes are the average values, over a Gibbs-like nonequilibrium generalized grand-canonical ensemble, of Hermitian operators for fluxes defined at the microscopic-mechanical level. The equations of evolution for these fluxes (or equivalently for their conjugated Lagrange multipliers) are described.

  • Ribeiro, Marcelo B.; Miguelote, Alexandre Y.

    Resumo em Inglês:

    This paper presents a review of the fractal approach for describing the large scale distribution of galaxies. We start by presenting a brief, but general, introduction to fractals, which emphasizes their empirical side and applications rather than their mathematical side. Then we discuss the standard correlation function analysis of galaxy catalogues and many observational facts that brought increasing doubts about the reliability of this method, paying special attention to the standard analysis implicit assumption of an eventual homogeneity of the distribution of galaxies. Some new statistical concepts for analysing this distribution is presented, and without the implicit assumption of homogeneity they bring support to the hypothesis that the distribution of galaxies does form a fractal system. The Pietronero-Wertz's single fractal (hierarchical) model is presented and discussed, together with the implications of this new approach for understanding galaxy clustering.
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