Spin-orbit coupling in the superconducting phase and DDW states of high-T-c cuprates

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

A discrete finite-dimensional phase space approach for the description of Fe8 magnetic clusters: Wigner and Husimi functions

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Filmes de titânio-silício preparados por spin e dip-coating

The conditions for the preparation of luminescent materials, consisting of Eu3+ ions entrapped in a titanium matrix, in the forma of a thin film, using the sol-gel process, are described. The films were obtained from sols prepared with TEOS and TEOT, in the presence of acetylacetone as the hidrolysis-retarding agent, using the dip-coating and spin-coating techniques. The influence of these techniques on the films based on titanium and silicon are presented. The Eu3+ was used as a luminescent probe. The films have been characterized by luminescence, reflection and transmittance. The thickness of the films could be related to the preparation procedure. Transparent thin films have been prepared by dip-coating technique.

The Gerasimov-Drell-Hearn Sum Rule and the Spin Structure of the Proton

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

Spin-1 particle in the light-front approach

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

Characterization of BaTi1-xZrxO3 thin films obtained by a soft chemical spin-coating technique

Single-phase perovskite structure BaZrxTi1-xO3 (BZT) (0.05less than or equal toxless than or equal to0.25) thin films were deposited on Pt-Ti-SiO2-Si substrates by the spin-coating technique. The structural modifications in the thin films were studied using x-ray diffraction and micro-Raman scattering techniques. Lattice parameters calculated from x-ray data indicate an increase in lattice (a axis) with the increasing content of zirconium in these films. Such Zr substitution also result in variations of the phonon mode wave numbers, especially those of lower wave numbers, for BaZrxTi1-xO3 thin films, corroborate to the structural change caused by the zirconium doping. on the other hand, Raman modes persist above structural phase transition, although all optical modes should be Raman inactive in the cubic phase. The origin of these modes must be interpreted as a function of a local breakdown of the cubic symmetry, which could be a result of some kind of disorder. The BZT thin films exhibited a satisfactory dielectric constant close to 181-138, and low dielectric loss tan delta<0.03 at the frequency of 1 kHz. The leakage current density of the BZT thin films was studied at elevated temperatures and the data obey the Schottky emission model. Through this analysis the Schottky barrier height values 0.68, 1.39, and 1.24 eV were estimated to the BZT5, BZT15, and BZT25 thin films, respectively. (C) 2004 American Institute of Physics.

CONTINUED-FRACTION FORMALISM APPLIED TO THE SPIN-1/2 XYZ MODEL

In this paper, we evaluate the correlation functions of the spin-1/2 XYZ model for some particular cases by using the Mori continued-fraction formalism. The results are exactly the same as those well-known ones. This removes any doubt about the convergence of the continued fraction recently raised by some authors.

Two-phase separation observed in thermally treated pellets of ClO4- doped poly(3-methylthiophene) from electron spin resonance measurements

A pressed pellet of CIO (-)(4) poly (3-methylthiophene) (P3MT) was heated for two hours at 85 degrees C and suddenly dropped in liquid nitrogen. A change was observed around 220 K in the Electron Spin Resonance (ESR) spectra when the sample was slowly cooled from room temperature. ESR line asymmetry parameter (A/B) showed two spatially separated phases. One was identified as a small metallic-like phase. The other phase, the larger one, makes a transition to a semiconducting Charge-Density Wave (CDW) state.

Analytical attitude propagation with non-singular variables and gravity gradient torque for spin stabilized satellite

An analytical approach for the spin stabilized satellite attitude propagation is presented using the non-singular canonical variables to describe the rotational motion. Two sets of variables were introduced for Fukushima in 1994 by a canonical transformation and they are useful when the angle between z-satellite axis of a coordinate system fixed in artificial satellite and the rotational angular momentum vector is zero or when the angle between Z-equatorial axis and rotation angular momentum vector is zero. Analytical solutions for rotational motion equations and torque-free motion are discussed in terms of the elliptic functions and by the application of some simplification to get an approximated solution. These solutions are compared with a numerical solution and the results show a good agreement for many rotation periods. When the mean Hamiltonian associated with the gravity gradient torque is included, an analytical solution is obtained by the application of the successive approximations' method for the satellite in an elliptical orbit. These solutions show that the magnitude of the rotation angular moment is not affected by the gravity gradient torque but this torque causes linear and periodic variations in the angular variables, long and short periodic variations in Z-equatorial component of the rotation angular moment and short periodic variations in x-satellite component of the rotation angular moment. The goal of this analysis is to emphasize the geometrical and physical meaning of the non-singular variables and to validate the approximated analytical solution for the rotational motion without elliptic functions for a non-symmetrical satellite. The analysis can be applied for spin stabilized satellite and in this case the general solution and the approximated solution are coincidence. Then the results can be used in analysis of the space mission of the Brazilian Satellites. (C) 2007 COSPAR. Published by Elsevier Ltd. All rights reserved.

INPLANE RESISTIVITY IN GRAPHITE-INTERCALATION COMPOUNDS OBTAINED FROM CONDUCTION-ELECTRON-SPIN-RESONANCE MEASUREMENTS

We developed a procedure to take advantage of the magnetic-field-modulation-frequency effect on the line shape of conduction-electron-spin resonance of graphite intercalation compounds (GIC's) to extract the absolute value of the in-plane resistivity. We calculated the power absorbed in each slice of the sample normal to the wave penetration, multiplied by a factor to account for the magnetic-field-modulation-frequency effect. Room-temperature spectra of stage-I AlCl3-intercalated GIC in both H-0 perpendicular-to c and H-0 parallel-to c configurations were fitted to the theoretical line shapes and the value of in-plane resistivity (and also the value of c-axis resistivity) obtained from the fitting parameters are in reasonable agreement with those from the literature.

Analog Modeling of Human Cognitive Functions with Tripartite Synapses

Searching for an understanding of how the brain supports conscious processes, cognitive scientists have proposed two main classes of theory: Global Workspace and Information Integration theories. These theories seem to be complementary, but both still lack grounding in terms of brain mechanisms responsible for the production of coherent and unitary conscious states. Here we propose following James Robertson's "Astrocentric Hypothesis" - that conscious processing is based on analog computing in astrocytes. The "hardware" for these computations is calcium waves mediated by adenosine triphosphate signaling. Besides presenting our version of this hypothesis, we also review recent findings on astrocyte morphology that lend support to their functioning as Local Hubs (composed of protoplasmic astrocytes) that integrate synaptic activity, and as a Master Hub (composed, in the human brain, by a combination of interlaminar, fibrous, polarized and varicose projection astrocytes) that integrates whole-brain activity.

S-, P-, and D-wave resonances in positronium-lithium-atom scattering

We investigate ortho-positronium-lithium-atom (Ps-Li) scattering using static-exchange and three-Ps-state coupled-channel calculations. The present three-PS-state scheme, while closely agreeing with the resonance and binding energies in the Ps-H system, predicts S-, P-, and D-wave resonances at 4.25 eV, 4.9 eV, and, 5.25 eV. respectively, in the electronic spin-singlet channel of Ps-Li scattering. The present calculation also yields a Ps-Li binding in this attractive singlet channel with an approximate binding energy of 0.218 eV, which is in adherence with the recent findings of a chemically stable PsLi system using stocastic variational and quantum Monte Carlo calculations. We further report elastic, Ps(2s)-, and Ps(2p)-excitation cross sections at low to medium energies (0.068-30 eV).

Relativistic quark spin coupling effects in the nucleon electromagnetic form factors

We investigate the effect of different forms of relativistic spin coupling of constituent quarks in the nucleon electromagnetic form factors. The four-dimensional integrations in the two-loop Feynman diagram are reduced to the null-plane, such that the light-front wave function is introduced in the computation of the form factors. The neutron charge form factor is very sensitive to different choices of spin coupling schemes, once its magnetic moment is fitted to the experimental value. The scalar coupling between two quarks is preferred by the neutron data, when a reasonable fit of the proton magnetic momentum is found. (C) 2000 Elsevier Science B.V.

Mapping Wigner distribution functions into semiclassical distribution functions

A mapping that relates the Wigner phase-space distribution function of a given stationary quantum mechani-cal wave function, a solution of the Schrödinger equation, to a specific solution of the Liouville equation, both subject to the same potential, is studied. By making this mapping, bound states are described by semiclassical distribution functions still depending on Planck's constant, whereas for elastic scattering of a particle by a potential they do not depend on it, the classical limit being reached in this case. Following this method, the mapped distributions of a particle bound in the Pöschl-Teller potential and also in a modified oscillator potential are obtained.

Effect of the Rashba and Dresselhaus spin-splitting terms on the electron g factor in semiconductor quantum wells under applied magnetic fields

We use the Ogg-McCombe Hamiltonian together with the Dresselhaus and Rashba spin-splitting terms to find the g factor of conduction electrons in GaAs-(Ga,Al)As semiconductor quantum wells (QWS) (either symmetric or asymmetric) under a magnetic field applied along the growth direction. The combined effects of non-parabolicity, anisotropy and spin-splitting terms are taken into account. Theoretical results are given as functions of the QW width and compared with available experimental data and previous theoretical works. © 2007 Elsevier B.V. All rights reserved.