Photo-Induced Dipole Relaxation Current in Natural Amethyst

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Large magnetic dipole moments for neutrinos with arbitrary non-calculable masses

We show that there is a general sort of neutrino effective interactions which allows, under certain conditions, to have relatively large magnetic dipole moments for neutrinos while keeping their masses non-calculable and arbitrarily small. The main ingredient of our mechanism for generating large magnetic moment to the neutrinos is the existence of a neutral scalar which has the only role to give mass to the neutrinos or the existence of flavor changing neutral currents in the neutrino sector. Although our approach is model independent, some models in which those interactions arise are commented.

Teleparallel origin of the Fierz picture for spin-2 particle

A new approach to the description of a spin-2 particle in flat and curved spacetime is developed on the basis of the teleparallel gravity theory. We show that such an approach is in fact a true and natural framework for the Fierz representation proposed recently by Novello and Neves. More specifically, we demonstrate how the teleparallel theory fixes uniquely the structure of the Fierz tensor, discover the transparent origin of the gauge symmetry of the spin-2 model, and derive the linearized Einstein operator from the fundamental identity of the teleparallel gravity. In order to cope with the consistency problem on the curved spacetime, similarly to the usual Riemannian approach, one needs to include the nonminimal (torsion dependent) coupling terms.

A path integral approach to the full Dicke model with dipole-dipole interaction

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

A new proposal for the picture changing operators in the minimal pure spinor formalism

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

Effects of oscillatory behavior of the dipole function on the dissociation dynamics of the classical driven Morse oscillator

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

SEMICLASSICAL ESTIMATE OF THE COULOMB-EXCITATION OF THE GIANT-DIPOLE RESONANCE IN PB-208

A semiclassical approach to study pure Coulomb excitation of Pb-208 giant dipole isovector resonance is examined. We consider medium energy projectiles and assume the target excitation to be described by a simple Goldhaber-Teller model. It is shown that the main features concerning the angular distribution are obtained in the angular range described by the model and an estimate is made of the pure Coulomb dipole contribution to the measured cross sections.

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.

The thermohydrodynamical picture of a charged Brownian particle

We study a charged Brownian gas with a non uniform bath temperature, and present a thermohydrodynamical picture. Expansion on the collision time probes the validity of the local equilibrium approach and the relevant thermodynamical variables. For the linear regime we present several applications (some novel).

Dipole relaxation current in n-type AlxGa1-xAs

We report for the first time the thermally stimulated depolarization current (TSDC) spectrum for a direct band-gap AlGaAs sample, where the presence of DX centers is clearly observed by photoconductivity measurements. A TSDC band is obtained, revealing the presence of dipoles, which could be attributed to DX--d+ pairs as indeed predicted by O'Reilly [Appl. Phys. Lett. 55, 1409 (1989)]. The data are fitted by relaxation time distribution approach yielding an average activation energy of 0.108 eV. This is the most striking feature of our data, since this energy has approximately the same value of the DX center binding energy.

The thermohydrodynamical picture of Brownian motion via a generalized Smoluchowsky equation

Via an operator continued fraction scheme, we expand Kramers equation in the high friction limit. Then all distribution moments are expressed in terms of the first momemt (particle density). The latter satisfies a generalized Smoluchowsky equation. As an application, we present the nonequilibrium thermodynamics and hydrodynamical picture for the one-dimensional Brownian motion. (C) 2000 Elsevier B.V. B.V. All rights reserved.

Dipole moments in Langmuir monolayers from aromatic carboxylic acids

The three-layer capacitor model proposed by Demchak and Fort [J. Colloid Interface Sci. 46 (1974) 191] is employed to relate measured surface potentials of Langmuir monolayers from a series of polyphenyl carboxylic acids to molecular dipole moments calculated using semiempirical quantum methods. The effective dielectric constant at the air/monolayer interface is 3.0 +/- 0.6, very close to that estimated for aliphatic compounds. Good agreement between theory and experiment is obtained by adopting a dielectric constant of 6.4 for the monolayer/water interface and a contribution from the water reorientation of -0.064 +/- 0.006 D, which shows that the parameters in the DF model are essentially the same as for aliphatic amphiphiles, such as esters, acids, alcohols and ethers. (C) 2000 Elsevier B.V. B.V. All rights reserved.