Structural Evaluation of Mechanically Alloyed (67-x)Ti-xZr-22Si-11B Powders

The present work reports on the structural evaluation of mechanically alloyed Ti-xZr-22Si-11B (x = 5, 7, 10, 15 and 20 at-%) powders. Milled powders and hot-pressed alloys were characterized by X-ray diffraction, electron scanning microscopy, and electron dispersive spectrometry. The Si and B atoms were preferentially dissolved into the Ti and Zr lattices during ball milling of Ti-xZr-22Si-11B (x = 7, 10, 15 and 20 at-%) powders, and extended solid solutions were achieved. The displacement of Ti peaks was more pronounced to the direction of lower diffraction angles with increasing Zr amounts in mechanically alloyed Ti-Zr-Si-B powders, indicating that the Zr atoms were also dissolved into the Ti lattice.

Comparative Study on the Technological Properties of Latex and Natural Rubber from Hancornia speciosa Gomes and Hevea brasiliensis

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

Nonlinear Lattice Within Supersymmetric Quantum Mechanics Formalism

In the last decades, the study of nonlinear one dimensional lattices has attracted much attention of the scientific community. One of these lattices is related to a simplified model for the DNA molecule, allowing to recover experimental results, such as the denaturation of DNA double helix. Inspired by this model we construct a Hamiltonian for a reflectionless potential through the Supersymmetric Quantum Mechanics formalism, SQM. Thermodynamical properties of such one dimensional lattice are evaluated aming possible biological applications.

Localization and delocalization of energy in a Peyrard-Bishop chain

This paper studies energy localization conditions in lattices of the type proposed by Peyrard and Bishop. Homogeneous and inhomogeneous lattices are analyzed and the role of interfaces in the latter is emphasized. Simulations allowed us to identify critical energy values for the existence of localization. After a certain energy value, it is possible to observe the loss of energy localization along the chain.

Dissipative dynamics of matter-wave solitons in a nonlinear optical lattice

Dynamics and stability of solitons in two-dimensional (2D) Bose-Einstein condensates (BEC), with one-dimensional (1D) conservative plus dissipative nonlinear optical lattices, are investigated. In the case of focusing media (with attractive atomic systems), the collapse of the wave packet is arrested by the dissipative periodic nonlinearity. The adiabatic variation of the background scattering length leads to metastable matter-wave solitons. When the atom feeding mechanism is used, a dissipative soliton can exist in focusing 2D media with 1D periodic nonlinearity. In the defocusing media (repulsive BEC case) with harmonic trap in one direction and nonlinear optical lattice in the other direction, the stable soliton can exist. Variational approach simulations are confirmed by full numerical results for the 2D Gross-Pitaevskii equation.

Regge calculus in teleparallel gravity

In the context of the teleparallel equivalent of general relativity, the Weitzenbock manifold is considered as the limit of a suitable sequence of discrete lattices composed of an increasing number of smaller and smaller simplices, where the interior of each simplex (Delaunay lattice) is assumed to be flat. The link lengths l between any pair of vertices serve as independent variables, so that torsion turns out to be localized in the two-dimensional hypersurfaces (dislocation triangle, or hinge) of the lattice. Assuming that a vector undergoes a dislocation in relation to its initial position as it is parallel transported along the perimeter of the dual lattice (Voronoi polygon), we obtain the discrete analogue of the teleparallel action, as well as the corresponding simplicial vacuum field equations.

Cold-atom systems and the scaling limit

With perspective to applications of cold-atom systems, some aspects of few-body physics at very low energies will be reviewed. By exploring the possibilities of varying the two-body interaction via the Feshbach resonance mechanism, some recent results are reported for condensed systems in optical lattices.

Soliton dynamics at an interface between a uniform medium and a nonlinear optical lattice

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

Two-component gap solitons with linear interconversion

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

Ferroelectric fatigue endurance of Bi4-xLaxTi3O12 thin films explained in terms of x-ray photoelectron spectroscopy

The nature of defects in polycrystalline Bi4-xLaxTi3O12 (BLT) thin films with x=0.00, 0.25, 0.50, and 0.75 was evaluated by x-ray photoemission spectroscopy measurements. The influence of oxygen vacancies and substitution of Bi for La atoms were discussed. In the BLT thin films, it was found that the oxygen ions at the metal-oxygen octahedral were much more stable than those at the [Bi2O2] layers. on the other hand, for Bi4Ti3O12 (BIT) thin film, oxygen vacancies could be induced both at the titanium-oxygen octahedral and at the [Bi2O2] layers. The oxygen-vacancy defect pairs determined in BIT and Bi3.75La0.25Ti3O12 (BLT025) can pin the polarization of surrounding lattices leading to fatigue of capacitors. Meanwhile, the concentration of similar defect pairs is relatively low in heavily doped BIT films and then good fatigue resistance is observed.

Dependence of annealing time on structural and morphological properties of Ca(Zr0.05Ti0.95)O-3 thin films

Ca(Zr0.05Ti0.95)O-3 (CZT) thin films were prepared by the polymeric precursor method by spin-coating process. The films were deposited on Pt(1 1 1)/Ti/SiO2/Si(1 0 0) substrates and annealed at 650 degrees C for 2,4, and 6 It in oxygen atmosphere. Structure and morphology of the CZT thin films were characterized by the X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FT-IR), atomic force microscopy (AFM) and field-emission scanning electron microscopy (FEG-SEM). XRD revealed that the film is free of secondary phases and crystallizes in the orthorhombic structure. The annealing time influences the grain size, lattices parameter and in the film thickness. (c) 2006 Elsevier B.V. All rights reserved.

Revisão: efeito dos metais doadores nas propriedades elétricas e microestruturais dos varistores cerâmicos à base de SnO2

O estudo da adição de dopantes trivalentes é uma das principais pesquisas na área de varistores. Vários autores têm buscado entender os efeitos destes dopantes nas propriedades elétricas e microestruturais destas cerâmicas eletrônicas. Tanto metais de transição quanto terras raras são adicionados em cerâmicas à base de SnO2 a fim de verificar o seu comportamento. O que se tem observado é que alguns destes óxidos tais como Cr2O3 e La2O3 melhoram significativamente as propriedades elétricas dos varistores, enquanto que outros como o Bi2O3 e Er2O3, por exemplo, não produzem tal efeito. A evolução do desempenho do comportamento varistor tem sido também atribuída às espécies de oxigênio produzidas pela reação com estes dopantes. Esta revisão apresenta resultados de estudos recentes do comportamento varistor frente a adição de metais doadores.

Monte Carlo renormalization group with evolution in the space of parameters

Using data from a single simulation we obtain Monte Carlo renormalization-group information in a finite region of parameter space by adapting the Ferrenberg-Swendsen histogram method. Several quantities are calculated in the two-dimensional N 2 Ashkin-Teller and Ising models to show the feasibility of the method. We show renormalization-group Hamiltonian flows and critical-point location by matching of correlations by doing just two simulations at a single temperature in lattices of different sizes to partially eliminate finite-size effects.

DYNAMICAL SCALING IN FRAGMENTATION

The dynamics of a fragmentation model is examined from the point of view of numerical simulation and rate equations. The model includes effects of temperature. The number n (s,t) of fragments of size s at time t is obtained and is found to obey the scaling form n(s,t) approximately s(-tau)t(omegasgamma e(-rhot) f(s/t(z)) where f(x) is a crossover function satisfying f(x) congruent-to 1 for x much less than and f(x) much less than 1 for x much greater than 1. The dependence of the critical exponents tau, omega, gamma and z on space dimensionality d is studied from d = 1 to 5. The result of the dynamics on fractal and nonfractal objects as well as on square and triangular lattices is also examined.

Band-edge states of the zero(th)-order gap in quasi-periodic photonic superlattices

The photonic modes of Thue-Morse and Fibonacci lattices with generating layers A and B, of positive and negative indices of refraction, are calculated by the transfer-matrix technique. For Thue-Morse lattices, as well for periodic lattices with AB unit cell, the constructive interference of reflected waves, corresponding to the zero(th)-order gap, takes place when the optical paths in single layers A and B are commensurate. In contrast, for Fibonacci lattices of high order, the same phenomenon occurs when the ratio of those optical paths is close to the golden ratio. In the long wavelength limit, analytical expressions defining the edge frequencies of the zero(th) order gap are obtained for both quasi-periodic lattices. Furthermore, analytical expressions that define the gap edges around the zero(th) order gap are shown to correspond to the = 0 and = 0 conditions.