Maria Carvalho

Bright, dark, and gray spatial soliton states in photorefractive media

A theory based on the Kukhtarev–Vinetskii model is developed that provides the evolution equation of one-dimensional optical spatial solitons in photorefractive media. In the steady-state regime and under appropriate external bias conditions, our analysis indicates that the underlying wave equation can exhibit bright and dark as well as gray spatial soliton states. The characteristics of these self-trapped optical beams are discussed in detail.

Incoherently coupled soliton pairs in biased photorefractive crystals

Summary form only given. Recently it was demonstrated that spatial optical solitons at /spl mu/W power levels can be supported in photorefractive (PR) media. We show that a new type of incoherently coupled soliton pairs is possible under steady-state conditions provided that their carrier beams share the same polarization and wavelength and are mutually incoherent. They can be readily realized in a simple experimental setup where the optical beams co-propagate collinearly in a biased PR crystal in which case they experience equal electrooptic coefficients.

Self-deflection of steady-state bright spatial solitons in biased photorefractive crystals

The self-bending process of steady-state bright spatial solitons in biased photorefractive media is investigated by taking into account diffusion effects. By integrating numerically the nonlinear propagation equation, it is found that the soliton beam evolution is approximately adiabatic. The self-deflection process is further studied using perturbation analysis, which predicts that the center of the optical beam moves on a parabolic trajectory and, moreover, that the central spatial frequency component shifts linearly with the propagation distance. Relevant examples are provided.

Compression, self-bending, and collapse of Gaussian beams in photorefractive crystals

By means of an exact solution, we demonstrate that a Gaussian beam can undergo spatial compression when it traverses a photorefractive medium. This is possible provided that the external bias field exceeds the critical value necessary to establish photorefractive spatial solitons. In this regime and under paraxial assumptions our analysis indicates that a Gaussian beam tends to exhibit self-focusing collapse. Beam self-deflection effects that arise from the pi/2-phase-shifted component of the photorefractive grating are also considered in our study.

Training and Detraining Effects on Functional Fitness after a Multicomponent Training in Older Women

Background: Several studies have been carried out in order to evaluate the potential influence of increased physical activity on the health, biological ageing and functional ability of the elderly. However, only limited information is available on the effects of multicomponent training and detraining on functional performance. Objective: The purpose of the present study was to investigate the effect of 8-month multicomponent training and 3-month detraining on the functional fitness of older women. Methods: Fifty-seven women were randomly assigned to an exercise (n = 32; 68.4 ± 2.93 years) or a control group (n = 25; 69.6 ± 4.20 years). The training program consisted of 2 sessions per week of aerobic, strength, balance and flexibility exercises. The functional fitness test battery was performed to assess the physical parameters associated with independent functioning in older adults. Results: No significant changes were observed in body mass index and cardiovascular endurance as a result of the exercise training. Training induced significant (p < 0.05) improvements in chair stand (27.3%), arm curl (17.4%), chair sit-and-reach (17.4%), up-and-go (11%) and back scratch (14.5%) tests. However, both upper and lower body strength and upper and lower flexibility declined significantly after detraining in the exercise group. Conclusion: The results of this study highlight the negative effects of interrupting exercise on several physical parameters of functional fitness.

Vector photorefractive spatial solitons

We derive vector soliton solutions for photorefractive media in which the refractive-index perturbations must be treated as tensors. The two polarizations of the vector solitons may be coupled through the space-charge field alone and/or through cross terms in the electro-optic tensor, which requires phase matching and specific configurations. We analyze bright planar vector solitons and verify their stability.

Sinai–Ruelle–Bowen measures for N -dimensional derived from Anosov diffeomorphisms

This paper is about the existence of transitive non-hyperbolic attractors with corresponding SRB measures for arcs of diffeomorphisms crossing the boundary of the Axiom A systems, obtained through an elementary generic bifurcation (Hopf, saddle-node or flip) on a transitive Anosov diffeomorphism or an attracting basic set.

Higher-order space charge field effects on the evolution of spatial solitons in biased photorefractive crystals

Summary form only given. Recently, photorefractive (PR) spatial optical solitons have been the focus of considerable attention. Of particular interest are the so-called screening solitons that occur in steady state when an external bias voltage is appropriately applied to a PR crystal. These soliton states are known to occur when the drift term dominates in the expression of the space charge field. In a recent study, the effects arising from first-order diffusion terms have also been investigated. It was found that the PR soliton can experience adiabatically self-deflection that varies linearly with the applied electric field. However, recent experiments suggest that this self-deflection can exceed that predicted by theory, especially in the regime of quite high bias fields. To account for this discrepancy, we investigate the effects of other higher-order electric field terms on the evolution of bright steady-state solitons in PR media.

Modulational instability of quasi-plane-wave optical beams biased in photorefractive crystals

The modulational instability of quasi-plane-wave optical beams in biased photorefractive media is investigated under steady-state conditions. The spatial growth rate of the sideband perturbations is obtained by globally treating the space-charge field. Our analysis indicates that the growth rates depend on the strength of the externally applied electric field and, moreover, on the ratio of the optical beams intensity to that of the dark irradiance. Our results are then compared to previous local treatments of the space-charge field equation. The two approaches are found to be in good agreement in the low spatial-frequency regime provided that the external bias field is sufficiently high. Conversely, in the high spatial-frequency region notable differences may exist. Relevant examples are provided.

Propagation of Airy-related beams

New types of finite energy Airy beams are proposed. We consider two different types of beams, namely, beams that are obtained as blocked and exponentially attenuated versions of Airy functions Ai and Bi, and beams of finite width but having the Airy functions typical phase. All of them show very interesting properties, such as parabolic trajectories for longer propagation distances, profile evolution exhibiting less diffraction, or better definiteness of the main peak, when compared with other finite energy Airy beams studied before.