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E Allaria

Publications and source records attributed to E Allaria.

17 recordsLinked to original sources
PubMed2005

Attractor selection in chaotic dynamics.

For different settings of a control parameter, a chaotic system can go from a region with two separate stable attractors (generalized bistability) to a crisis where a chaotic attractor expands, colliding with an unstable orbit. In the bistable regime jumps between independent attractors are mediated by external perturbations; above the crisis, the dynamics includes visits to regions formerly belonging to the unstable orbits and this appears as random bursts of amplitude jumps. We introduce a control method which suppresses the jumps in both cases by filtering the specific frequency content of one of the two dynamical objects. The method is tested both in a model and in a real experiment with a CO2 laser.

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PubMed2004

Coupling scheme for complete synchronization of periodically forced chaotic CO2 lasers.

We present a way of coupling two nonautonomous, periodically forced, chaotic C O2 lasers in a master-slave configuration in order to achieve complete synchronization. The method consists of modulating the forcing of the slave laser by means of the difference between the intensities of the two lasers, and lends itself to a simple physical implementation. Experimental evidence of complete synchronization induced by a suitable coupling strength is shown, and a numerical model is used to achieve further insight of the synchronization phenomena. Finally, we describe a possible application of the investigated technique to the design of a digital communication system.

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PubMed2004

Experimental control of coherence of a chaotic oscillator.

We give experimental evidence that a delayed feedback control strategy is able to efficiently enhance the coherence of an experimental self-sustained chaotic oscillator obtained from a CO2 laser with electro-optical feedback. We demonstrate that coherence control is achieved for various choices of the delay time in the feedback control, including values that would lead to the stabilization of an unstable periodic orbit embedded within the chaotic attractor. The relationship between the two processes is discussed.

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PubMed2003

Competition of synchronization domains in arrays of chaotic homoclinic systems.

We investigate the response of an open chain of bidirectionally coupled chaotic homoclinic systems to external periodic stimuli. When one end of the chain is driven by a periodic signal, the system propagates a phase synchronization state in a certain range of coupling strengths and external frequencies. When two simultaneous forcings are applied at different points of the array, a rich phenomenology of stable competitive states is observed, including temporal alternation and spatial coexistence of synchronization domains.

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PubMed2003

Propensity criterion for networking in an array of coupled chaotic systems.

We examine the mutual synchronization of a one-dimensional chain of chaotic identical objects in the presence of a stimulus applied to the first site. We first describe the characteristics of the local elements, and then the process whereby a global nontrivial behavior emerges. A propensity criterion for networking is introduced, consisting in the coexistence within the attractor of a localized chaotic region, which displays high sensitivity to external stimuli, and an island of stability, which provides a reliable coupling signal to the neighbors in the chain. Based on this criterion, we compare homoclinic chaos, recently explored in lasers and conjectured to be typical of a single neuron, with Lorenz chaos.

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PubMed2003

Constructive effects of noise in homoclinic chaotic systems.

Many chaotic oscillators have coherent phase dynamics but strong fluctuations in the amplitudes. At variance with such a behavior, homoclinic chaos is characterized by quite regular spikes but strong fluctuation in their time intervals due to the chaotic recurrence to a saddle point. We study influences of noise on homoclinic chaos. We demonstrate both numerically and experimentally on a CO2 laser various constructive effects of noise, including coherence resonance, noise-induced synchronization in uncoupled systems and noise-enhanced phase synchronization, deterministic resonance with respect to signal frequency, and stochastic resonance versus noise intensity in response to weak signals. The peculiar sensitivity of the system along the weak unstable manifold of the saddle point underlines the unified mechanism of these nontrivial and constructive noise-induced phenomena.

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PubMed2003

Noise-enhanced synchronization of homoclinic chaos in a CO2 laser.

Many chaotic oscillators have rather coherent phase dynamics but strong fluctuation in the amplitudes. Conversely, homoclinic chaos is characterized by quite regular spikes but strong fluctuation in their time intervals. We study the effects of noise on the synchronization of homoclinic chaos to a weak periodic signal and demonstrate numerically and experimentally in a CO2 laser system that noise enhances synchronization of homoclinic chaos. The system exhibits both conventional resonance versus driving frequency and stochastic resonance with respect to noise intensity.

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PubMed2003

Information encoding in homoclinic chaotic systems.

We present a simple method for real-time encoding of information in the interspike intervals of a homoclinic chaotic system. The method has been experimentally tested on a CO2 laser with feedback displaying Sil'nikov chaos and synchronized with an external pulsed signal. Information is encoded by the length of the temporal intervals between consecutive pulses of the external signal. This length is varied each time a new pulse is generated.

Carbon Dioxide↗
PubMed2003

Controlling transient dynamics to communicate with homoclinic chaos.

A control that stabilizes the transient dynamics of a homoclinic chaotic laser is used to encode discrete sources of information. The controlled trajectory is a complex spiking signal that has a constrained interspike interval, and therefore, the ratio of information transmitted is approximately constant. We also show that the controlled signal that encodes the source contains more information than the source. This property is advantageously used to correct possible errors in the transmission, or to increase the ratio of information per transmitted spike.

Carbon Dioxide↗
PubMed2002

Experimental characterization of the transition to phase synchronization of chaotic CO2 laser systems.

We investigate the transition route to phase synchronization in a chaotic laser with external modulation. Such a transition is characterized by the presence of a regime of periodic phase synchronization, in which phase slips occur with maximal coherence in the phase difference between output signal and external modulation. We provide the first experimental evidence of such a regime and demonstrate that it occurs at the crossover point between two different scaling laws of the intermittent-type behavior of phase slips.

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PubMed2002

Delayed self-synchronization in homoclinic chaos.

The chaotic spike train of a homoclinic dynamical system is self-synchronized by applying a time-delayed correction proportional to the laser output intensity. Due to the sensitive nature of the homoclinic chaos to external perturbations, stabilization of very long-periodic orbits is possible. On these orbits, the dynamics appears chaotic over a finite time, but then it repeats with a recurrence time that is slightly longer than the delay time. The effect, called delayed self-synchronization, displays analogies with neurodynamic events that occur in the buildup of long-term memories.

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PubMed2002

Autonomous bursting in a homoclinic system.

The output of a dynamical system in a regime of homoclinic chaos transforms from a continuous train of irregularly spaced spikes to clusters of regularly spaced spikes with quiescent periods in between (bursting), provided a low frequency portion of the output is fed back. We provide experimental evidence of such an autonomous bursting by a CO2 laser with feedback. The phenomena here presented are extremely robust against noise and display qualitative analogies with bursting phenomena in neurons.

Action Potentials↗
PubMed2001

Synchronization of homoclinic chaos.

Homoclinic chaos is characterized by regular geometric orbits occurring at erratic times. Phase synchronization at the average repetition frequency is achieved by a tiny periodic modulation of a control parameter. An experiment has been carried on a CO(2) laser with feedback, set in a parameter range where homoclinic chaos occurs. Any offset of the modulation frequency from the average induces phase slips over long times. Perfect phase synchronization is recovered by slow changes of the modulation frequency based upon the sign and amplitude of the slip rate. Satellite synchronization regimes are also realized, with variable numbers of homoclinic spikes per period of the modulation.

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PubMed1979

3-Methoxy-4-hydroxyphenylglycol and primary depression: clinical and pharmacological considerations.

Pretherapeutic urinary excretion of 3-methoxy-4-hydroxyphenylglycol (MHPG) was studied in 25 primary depressed patients. The results indicate that: (i) There exists a wide variability among primary depressives with respect to MHPG excretion. (ii) Age of onset together with polarity of the disease may account for the nonhomogeneous division of the patients according to MHPG levels. (iii). The other variables considered, with the possible exception of motor activity, do not explain the dichotomy between high or normal and low MHPG levels, even though it is possible that they influence MHPG excretion to some extent, with the consequent possibility of errors in subclassification of the patients at the boundaries between the two groups. (iv) The correlation between motor retardation and low MHPG excretion is positive, but probably due to a frequent association between this motricity state and primary depression of bipolar early onset type. (v) Treatments with chlorimipramine and, to a lesser degree of specificity, with amitriptyline are particularly indicated in patients with normal or high MHPG. Some practical and theoretical implications deriving from these data are briefly discussed.

Adult↗