Biomedical subjects

J R Rios Leite

Publications and source records attributed to J R Rios Leite.

4 recordsLinked to original sources

PubMed2004

Experimental deterministic coherence resonance.

We demonstrate coherence resonance in a dynamical system without external noise. The experimental evidence is reported in the low frequency fluctuations of a chaotic diode laser with optical feedback. The phenomenon is also verified numerically using the Lang-Kobayashi equations for a single solitary mode laser, without noise terms. Fast deterministic dynamics plays the role of an effective exciting noise, narrowing the resonance in the autonomous slow power drop cycles of the laser. This new result is the natural extension of deterministic stochastic resonance and noise induced coherence resonance predicted and observed in recent years.

Journal Article↗

PubMed2004

Logarithmic periodicities in the bifurcations of type-I intermittent chaos.

The critical relations for statistical properties on saddle-node bifurcations are shown to display undulating fine structure, in addition to their known smooth dependence on the control parameter. A piecewise linear map with the type-I intermittency is studied and a log-periodic dependence is numerically obtained for the average time between laminar events, the Lyapunov exponent, and attractor moments. The origin of the oscillations is built in the natural probabilistic measure of the map and can be traced back to the existence of logarithmically distributed discrete values of the control parameter giving Markov partition. Reinjection and noise effect dependences are discussed and indications are given on how the oscillations are potentially applicable to complement predictions made with the usual critical exponents, taken from data in critical phenomena.

Journal Article↗

PubMed2003

Intensity coupling and synchronization of chaotic lasers.

The synchronization of chaotic lasers was studied considering the coupling scheme with the intensity of light pulses from one laser saturating the other one. The experimental synchronization of two single mode CO2 lasers with saturable absorber is reviewed. Numerical simulations are presented for diode lasers made chaotic by optical feedback. Optical intensity saturation coupling was introduced in Lang-Kobayashi equations. Parameters were chosen such that both lasers were uncorrelated and chaotic before coupling and partially synchronize after coupling. Correlation functions for the numerical solutions were used to characterize the properties of the synchronism. They show partial in-phase and antiphase synchronism for the pulse intensities, depending on the coupling mechanism. These synchronisms are independent of optical interferometric effects and so, relevant for communication applications.

Lasers↗

PubMed2002

Averages and critical exponents in type-III intermittent chaos.

The natural measure in a map with type-III intermittent chaos is used to define critical exponents for the average of a variable from a dynamical system near bifurcation. Numerical experiments were done with maps and verify the analytical predictions. Physical experiments to test the usefulness of such exponents to characterize the nonlinearity at bifurcations were done in a driven electronic circuit with diode as a nonlinear element. Two critical exponents were determined at the same bifurcation: one from the fitting of the average voltage across the diode and the other one from the average length of the laminar phase events. Both values are consistent with the predictions of a type-III intermittency of cubic nonlinearity. The averages of variables in intermittent chaotic systems is a technique complementary to the measurements of laminar phase histograms, to identify the nonlinear mechanisms. The average exponents may have a broad application in ultrafast chaotic phenomena.

Journal Article↗