Biomedical subjects

S R Lopes

Publications and source records attributed to S R Lopes.

5 recordsLinked to original sources

PubMed2004

Multistability and phase-space structure of dissipative nonlinear parametric four-wave interactions.

We investigate the phase-space structure displayed by a system of four waves interacting by means of nonlinear coupling between two wave triplets, which results in a dissipative high-dimensional vector field presenting an invariant manifold, wherein the dynamics is essentially conservative. The focus is on the coexistence of a large number of periodic attractors in the phase space, with an interwoven structure of the basins of attraction, where low-period attractors have predominance. The time behavior of nearly conserved quantities and the properties of the Lyapunov spectra are used to imply the existence of a lower-dimensional invariant manifold where the dynamics is nearly conservative. A three-dimensional map is used to illustrate these findings.

Journal Article↗

PubMed2003

Validity of numerical trajectories in the synchronization transition of complex systems.

We investigate the relationship between the loss of synchronization and the onset of shadowing breakdown via unstable dimension variability in complex systems. In the neighborhood of the critical transition to strongly nonhyperbolic behavior, the system undergoes on-off intermittency with respect to the synchronization state. There are potentially severe consequences of these facts on the validity of the computer-generated trajectories obtained from dynamical systems whose synchronization manifolds share the same nonhyperbolic properties.

Journal Article↗

PubMed2003

Correlation decay and partial coherence in nonlinear wave interactions.

In the present analysis we study the broad-band triplet interaction in regimes of large amplitudes. Linear response theories associated with nonlinear arguments are used to show that even though coherence of high-frequency modes is lost as one first encounters chaotic regimes, it can be restored as field amplitudes grow further. We discuss implications of the feature for fixed-phase interactions.

Journal Article↗

PubMed1999

Nonintegrable dynamics of the triplet-triplet spatiotemporal interaction.

In this paper we examine the coupling of two wave triplets sharing two common modes. The analysis is performed in the solitonic sector of the parameter space where uncoupled solutions departing from linearly unstable homogeneous initial conditions evolve into a collection of regularly interspersed, spatiotemporally localized spikes. The uncoupled system is integrable, but coupling destroys integrability. As coupling grows, energy transfer to smaller spatial scales does appear and becomes faster not only in linearly unstable, but also in linearly stable cases. Chaos in low-dimensional subsystems appears to be responsible for the transfer. We perform a series of numerical tests to verify this idea.

Journal Article↗

PubMed1994

Obstructive sleep apnea treatment with dental appliance.

The case of a 40-year-old male patient with obstructive sleep apnea syndrome (OSAS) is reported, with emphasis on treatment with a dental appliance. This therapeutic approach, which has been focused on recent research, has as its objective, the posturing of the mandibule and, consequently, the tongue more anteriorly, thus in turn leading to an increase in the posterior oropharyngeal airway space (PAS). Cephalometry contributed determining in this case whereby enlargement limits were observed in the PAS with mandibular displacement. Clinical and polysomnographic controls showed subjective reduction of the excessive daytime sleepiness and objective decrease in apneas intensity to normal limits. Eight months follow-up evidenced the steady improvement.

Adult↗