On Ti-18Si-6B and Ti-7.5Si-22.5B powder alloys prepared by high-energy ball milling and sintering

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

CAUSAL PRESCRIPTION FOR THE LIGHT-CONE GAUGE

We present a prescription for light-cone gauge singularities which embeds in it causality and show that it results in simpler and less demanding integrals to be performed.

EVALUATING ONE-LOOP LIGHT-CONE INTEGRALS BY COVARIANTIZING THE GAUGE-DEPENDENT POLE

Making sure that causality be preserved by means of ''covariantizing'' the gauge-dependent singularity in the propagator of the vector potential A(mu)(x), we show that the evaluation of some basic one-loop light-cone integrals reproduce those results obtained through the Mandelstam-Leibbrandt prescription. Moreover, such a covariantization has the advantage of leading to simpler integrals to be performed in the cone variables (the bonus), although, of course, it introduces an additional alpha-parameter integral to be performed (the price to pay).

QED(3) RADIATIVE-CORRECTIONS IN THE HEISENBERG PICTURE

We evaluate the vacuum polarization tensor for three-dimensional quantum electrodynamics (QED3) via Heisenberg equations of motion in order to clarify the problem arising from the use of different regularization prescriptions in the interaction picture. We conclude that the photon does acquire physical mass of topological origin when such contribution is taken into account for the photon propagator.

Obtaining a light-like planar gauge

In the usual and current understanding of planar gauge choices for Abelian and non-Abelian gauge fields, the external defining vector n(mu), can either be space-like (n(2) < 0) or time-like (n(2) > 0) but not light-like (n(2) = 0). In this work we propose a light-like planar gauge that consists of defining a modified gauge-fixing term, L-GF, whose main characteristic is a two-degree violation of Lorentz covariance arising from the fact that four-dimensional space-time spanned entirely by null vectors as basis necessitates two light-like vectors, namely n(mu) and its dual m(mu), with n(2) = m(2) = 0, n . m not equal 0, say, e.g. normalized to n . m = 2.

Causal propagators for algebraic gauges

Applying the principle of analytic extension for generalized functions we derive causal propagators for algebraic non-covariant gauges. The so-generated manifestly causal gluon propagator in the light-cone gauge is used to evaluate two one-loop Feynman integrals which appear in the computation of the three-gluon vertex correction. The result is in agreement with that obtained through the usual prescriptions.

VACUUM POLARIZATION TENSOR IN 3-DIMENSIONAL QUANTUM ELECTRODYNAMICS

We evaluate the one-loop vacuum polarization tensor for three-dimensional quantum electrodynamics (QED), using an analytic regularization technique, implemented in a gauge-invariant way. We show thus that a gauge boson mass is generated at this level of radiative correction to the photon propagator. We also point out in our conclusions that the generalization for the non Abelian case is straightforward.

Low genetic diversities of rabies virus populations within different hosts in Brazil

The low rates of nonsynonymous evolution observed in natural rabies virus (RABV) isolates are suggested to have arisen in association with the structural and functional constraints operating on the virus protein and the infection strategies employed by RABV within infected hosts to avoid strong selection by the immune response. In order to investigate the relationship between the genetic characteristics of RABV populations within hosts and the virus evolution, the present study examined the genetic heterogeneities of RABV populations within naturally infected dogs and foxes in Brazil, as well as those of bat RABV populations that were passaged once in suckling mice. Sequence analyses of complete RABV glycoprotein (G) genes showed that RABV populations within infected hosts were genetically highly homogeneous whether they were infected naturally or experimentally (nucleotide diversities of 0-0.95 x 10(-3)). In addition, amino acid mutations were randomly distributed over the entire region of the G protein, and the nonsynonymous/synonymous rate ratios (d(N)/d(S)) for the G protein gene were less than 1. These findings suggest that the low genetic diversities of RABV populations within hosts reflect the stabilizing selection operating on the virus, the infection strategies of the virus, and eventually, the evolutionary patterns of the virus. (C) 2009 Elsevier B.V. All rights reserved.

SiO2-GeO2 soot preform as a core for Eu2O3 nanocoating: Synthesis and photophysical study

Nowadays solid state chemists have the possibility of work with low temperature strategies to obtain solid state materials with appropriate physical and chemical properties for useful technological applications. Photonic core shell materials having a core and shell domains composed by a variety of compounds have been synthesized by different methods. In this work we used silica-germania soot prepared by vapor-phase axial deposition as a core where a nanoshell of Eu2O3 was deposited. A new sol-gel like method was used to obtain the Eu2O3 nanoshell coating the SiO2-GeO2 particles, which was prepared by the polymeric precursor method. The photophysical properties of Eu3+ were used to obtain information about the rare earth surrounding in the SiO2-GeO2@Eu2O3 material during the sintering process. The sintering process was followed by the luminescence spectra of Eu3+ and all the samples present the characteristic emission related to the D-5(0) -> F-7(J) (J=0, 1, 2, 3 and 4). The ratios of the D-5(0) -> F-7(2)/D-5(0) -> F-7(1) emission intensity for the SiO2-GeO2@Eu2O3 systems were calculated and it was observed an increase in its values, indicating a low symmetry around the Eu3+ as the temperature increases.

Field-theory Two-point Functions via Negative Dimension Integration

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Microstructured chalcogenide optical fibers from As2S3 glass: towards new IR broadband sources

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)