Utilização de membranas de borracha natural com nanopartículas de prata como métodos de separação de parasitas de Leishmania braziliensis

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Amorphous ZrF4-a molecular dynamics study

Using an effective two-body interaction potential, a molecular dynamics study of the structural properties of amorphous ZrF4 phase is presented. The effective pair potential includes steric repulsion, Coulomb interaction due to charge transfer, and charge-dipole interaction due to the large electronic polarizability of anions. The results for structural correlations, such as pair distribution functions, coordination numbers, and bond angle distributions are presented. Excellent agreement is obtained by comparing experimental X-ray diffraction and the simulated static X-ray structure factor. © 1993.

New features of the morphotropic phase boundary in the PbZrO 3-PbTiO3 system: A Raman spectroscopy study

In this work we present a Raman study of PbZr1-xTi xO3 ceramics with composition values close to the morphotropic phase boundary region. The analysis of the Raman spectra leads to the determination of the monoclinic phase extension at different temperatures in a very good agreement with those determined by diffraction techniques. Therefore the obtained results show that Raman spectroscopy is a powerful and suitable technique to study structural phase transitions in PbZr 1-xTixO3. © 2002 Taylor & Francis.

Phase transition from a dx2-y2 to a dx2-y2+dxy superconductor

We study the phase transition from a dx2-y2 to a dx2-y2+dxy superconductor using the tight-binding model of two-dimensional cuprates. As the temperature is lowered past the critical temperature Tc, first a dx2-y2 superconducting phase is created. With further reduction of temperature, the dx2-y2+dxy phase is created at temperature T=Tc1. We study the temperature dependencies of the order parameter, specific heat, and spin susceptibility in these mixed-angular-momentum states on a square lattice and on a lattice with orthorhombic distortion. The above-mentioned phase transitions are identified by two jumps in specific heat at Tc and Tc1. ©1999 The American Physical Society.

Phase transition from a d(x(2)-y(2)) to d(x(2)-y(2))+id(xy) superconductor

The temperature dependencies of specific heat and spin susceptibility of a coupled dx2-y2 + idxy superconductor in the presence of a weak dxy component are investigated in the tight-binding model (1) on square lattice and (2) on a lattice with orthorhombic distortion. As the temperature is lowered past the critical temperature Tc, first a less ordered dx2-y2 superconductor is created, which changes to a more ordered dx2-y2 + idxy superconductor at Tcl(< Tc). This manifests in two second order phase transitions identified by two jumps in specific heat at Tc and Tc1. The temperature dependencies of the superconducting observables exhibit a change from power-law to exponential behavior as temperature is lowered below Tc1 and confirm the new phase transition. © 1998 Published by Elsevier Science B.V. All rights reserved.

Effect of vesicles of dimethyldioctadecylammonium chloride and phospholipids on the rate of decarboxylation of 6-nitrobenzisoxazole-3-carboxylate

Sonicated mixtures of dimethyldioctadecylammonium chloride (DODAC), egg phosphatidylcholine (PC), dimyristoyl phosphatidylcholine (DMPC), and dipalmitoyl phosphatidylcholine (DPPC) were used to analyze vesicle effects on the rate of decarboxylation of 6-nitrobenzisoxazol-3-carboxylic acid (Nboc). Electron microscopic images of the vesicles were obtained with trehalose, a know cryoprotector. Phase diagrams and phase transitions temperatures of the vesicle bilayers were determined. Nboc decarboxylation rates increased in the presence of vesicles prepared with both phospholipids and DODAC/phospholipid mixtures. Quantitative analysis of vesicular effects was done using pseudophase models. Phospholipids catalyzed up to 140-fold while the maximum catalysis by DODAC/lipid vesicles reached 800-fold. Acceleration depends on alkyl chain length, fatty acid insaturation of the lipids, and the DODAC/phospholipid molar ratio. Catalysis is not related to the liquid crystalline-gel state of the bilayer and may be related to the relative position of Nboc with respect to the interface.

Influence of Heat Treatment on the Anelastic Properties of MgB(2)

The discovery of the superconductivity of MgB(2) was of great importance, because this material is one of the few known binary compounds and has one of the highest critical temperatures (39 degrees K). As MgB(2) is a granular compound, it is fundamentally important to understand the mechanisms of the interaction of the defects and the crystalline lattice, in addition to the eventual processes involving the grain boundaries that compose the material. In this sense, the mechanical spectroscopy measurements constitute a powerful tool for this study, because through them we can obtain important information about phase transitions, the behavior of interstitial or substitutional elements, dislocations, grain boundaries, diffusion, instabilities, and other imperfections of the lattice. For this paper, the samples were prepared using the PIT method and were characterized by density, X-ray diffraction, scanning electron microscopy, electric resistivity, magnetization, and mechanical spectroscopy. The samples were measured in their as-cast condition and after an ultra-high-vacuum heat treatment. The results showed complex spectra, in which were identified relaxation processes due to dislocation movement, interaction among interstitial elements and dislocations, auto-diffusion, and movement of grain boundaries. Some of these processes disappeared with the heat treatment.

Dielectric response features and oxygen migration on rare earth modified lead titanate ferroelectric ceramics

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

Dynamics of the deconfinement transition of quarks and gluons in a finite volume

We employ finite elements methods for the approximation of solutions of the Ginzburg-Landau equations describing the deconfinement transition in quantum chromodynamics. These methods seem appropriate for situations where the deconfining transition occurs over a finite volume as in relativistic heavy ion collisions. where in addition expansion of the system and flow of matter are important. Simulation results employing finite elements are presented for a Ginzburg-Landau equation based on a model free energy describing the deconfining transition in pure gauge SU(2) theory. Results for finite and infinite system are compared. (C) 2009 Elsevier B.V. All rights reserved.

NOISE and ULTRAVIOLET DIVERGENCES IN SIMULATIONS of GINZBURG-LANDAU-LANGEVIN TYPE of EQUATIONS

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Percolation of Monte Carlo clusters

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

Memory effect and fast spinodal decomposition

We consider the modification of the Cahn-Hilliard equation when a time delay process through a memory function is taken into account. We then study the process of spinodal decomposition in fast phase transitions associated with a conserved order parameter. The introduced memory effect plays an important role to obtain a finite group velocity. Then, we discuss the constraint for the parameters to satisfy causality. The memory effect is seen to affect the dynamics of phase transition at short times and have the effect of delaying, in a significant way, the process of rapid growth of the order parameter that follows a quench into the spinodal region.

Langevin dynamics of the deconfinement transition for pure gauge theory

We investigate the effects of dissipation in the deconfinement transition for pure SU(2) and SU(3) gauge theories. Using an effective theory for the order parameter, we study its Langevin evolution numerically. Noise effects are included for the case of SU(2). We find that both dissipation and noise have dramatic effects on the spinodal decomposition of the order parameter and delay considerably its thermalization. For SU(3) the effects of dissipation are even larger than for SU(2).

Scaling invariance for the escape of particles from a periodically corrugated waveguide

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Quantum entanglement and fixed point Hopf bifurcation

We present the qualitative differences in the phase transitions of the mono-mode Dicke model in its integrable and chaotic versions. These qualitative differences are shown to be connected to the degree of entanglement of the ground state correlations as measured by the linear entropy. We show that a first order phase transition occurs in the integrable case whereas a second order in the chaotic one. This difference is also reflected in the classical limit: for the integrable case the stable fixed point in phase space undergoes a Hopf type whereas the second one a pitchfork type bifurcation. The calculation of the atomic Wigner functions of the ground state follows the same trends. Moreover, strong correlations are evidenced by its negative parts. (c) 2006 Elsevier B.V. All rights reserved.