摘要:

We study the dynamics of active particles advected by 3‐dimensional open incompressible flows. We find that 3D reactive flows have fundamentally novel dynamical features, not found in 2D systems. In particular, we argue that that the reaction’s productivityper reaction stepcan be enhanced, with respect to the 2D case, while the productivityper unit timein some 3D flows goes to zero in the limit of high mixing rates, in contrast to the 2D behavior, in which the productivity goes to a finite constant. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1846472

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

We present experimental results in a mass transfer driven convective experiment. A layer of volatile fluid, is covered by a second one less dense but non volatile immiscible fluid. This configuration results unstable for appropriated depths of the top layer. Under this condition, low “modes” convective patterns are induced in the top layer. Sequence of convective patterns obtained here without heating, is similar to the obtained in small aspect ratio thermocapillary Be´nard‐Marangoni convection. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1846473

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

The different flame spreading regimes over liquid fuels have been experimentally characterized for long channels. A theoretical analysis of the mechanisms that drive flame propagation has been proposed, that correlates well with our experimental data. Within the experimental accuracy, all the fuels tested in our laboratory present common, universal characteristics. The control parameters of flame spreading over liquid fuels (which is a major fire safety problem) have been specified. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1846474

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

We present an analysis of a time series of wind strength measurements recorded at Florence airport in the period October 2002 – March 2003. The data were taken simultaneously by two runway head anemometers, located at a distance of 900 m, at a frequency of 3.3⋅10−3Hz. The data show strong correlations over long time spans of a few tens of hours. We performed an analysis of wind velocity as it is usually done for turbulence laboratory experiments. Wind velocityreturnsand wind velocity differences were considered. The pdfs of these quantities exhibit strong non‐Gaussian fat tails. The distribution of the standard deviations of the fluctuations can be successfully reproduced by a Gamma distribution while the Log‐normal one fails completely. Following Beck and Cohensuperstatisticsapproach, we extract the Tsallis entropic index q from this Gamma distribution. The corresponding q‐exponential curves reproduce with a very good accuracy the pdfs of returns and velocity differences. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1846475

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

Propagating activity waves in disinhibited neocortical slices have been used as an experimental model of epileptic seizure propagation. A mathematical model of a one dimensional network of synaptically‐coupled neurons with threshold dependant excitability has been developed to describe these propagating waves. Solutions of the mathematical model provide relationships between the various parameters of the system that can be tested against the experimental model. Specifically, the mathematical solutions suggest the following: at low threshold values the waves travel quickly through the network, at higher threshold values the waves travel slowly, and at very high values waves fail to propagate. Since applied electric fields have been shown to polarize neurons and thereby control threshold, we hypothesized, and subsequently confirmed experimentally, that such electric fields could be used to increase or decrease the speed of propagation and, at high enough values, block seizure propagation. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1846476

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

We compare the recorded activity of cultured neuronal networks with hybridized model simulations, in which the model neurons are driven by the recorded activity of special neurons. The latter, named ‘spiker’ neurons, that exhibit fast firing with homoclinic chaos like characteristics, are expected to play an important role in the networks’ self regulation. The cultured networks are grown from dissociated mixtures of cortical neurons and glia cells. Despite the artificial manner of their construction, the spontaneous activity of these networks exhibits rich dynamical behavior, marked by the formation of temporal sequences of synchronized bursting events (SBEs), and additional features which seemingly reflect the action of underlying regulating mechanism, rather than arbitrary causes and effects. Our model neurons are composed of soma described by the two Morris‐Lecar dynamical variables (voltage and fraction of open potassium channels), with dynamical synapses described by the Tsodyks‐Markram three variables dynamics. To study the recorded and simulated activities we evaluated the inter‐neuron correlation matrices, and analyzed them utilizing the functional holography approach: the correlations are re‐normalized by the correlation distances — Euclidean distances between the matrix columns. Then, we project theN‐dimensional (forNchannels) space spanned by the matrix of re‐normalized correlations, or correlation affinities, onto a corresponding 3‐Dcausal manifold (3‐DCartesian space constructed by the 3 leading principal vectors of theN‐dimensional space. The neurons are located by their principal eigenvalues and linked by their original (not‐normalized) correlations. This reveals hidden causal motifs: the neuron locations and their links form simple structures. Similar causal motifs are exhibited by the model simulations when feeded by the recorded activity of the spiker neurons. We illustrate that the homoclinic chaotic behavior of the spiker neurons can be generated by glia‐regulated self‐synapses. Since in real networks the glia are regulated back by the networks’ neuronal activity, our findings hint that the structure of the causal manifolds in the affinity space is self‐regulated via collective regulation of the homoclinic behavior of the spiker neurons.We further propose that the existence of such simple causal motifs in the complex activity of stand‐alone cultured networks calls for a new view of the neuro‐glia interactions, where linked neurons and glia cells function as a hybridized fabric by which information is co‐processed. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1846477

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

Spatio‐temporal dynamics of alpha activity during the resting state is characterized by alternation between ordered and disordered states. The ordered state exhibits a variety of phase patterns. We found that the duration distributions of these states and phase patterns obey power laws. These results suggest that the appearance of phase patterns and the alternation between ordered and disordered states are not just due to noise but products of internal dynamics of the brain. We discuss the possibility that these dynamics are manifestation of chaotic itinerancy in the brain dynamics. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1846478

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

Several concepts and analysis techniques originating from Nonlinear Dynamics have been applied to electroencephalography recordings of epilepsy patients to predict seizures. An early prediction of an upcoming seizure would dramatically increase the therapeutic possibilities for this common neurological disease. We suggest standards to assess seizure prediction performance of time series analysis techniques. We present assessment of three methods originating from Nonlinear Dynamics with respect to their ability in predicting epileptic seizures. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1846479

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

Heteroclinic chaos (HC) implies the recurrent return of the dynamical trajectory to a saddle focus (SF) in whose neighborhood the system response to an external perturbation is very high and hence it is very easy to lock to an external stimulus. Thus HC appears as the easiest way to encode information in time by a train of equal spikes occurring at erratic times. Implementing such a dynamics with a single mode CO2 laser with feedback, we have a heteroclinic connection between the SF and a saddle node (SN) whose role it to regularize the phase space orbit away from SF. Due to these two different fixed points, the laser intensity displays identical spikes separated by erratic ISIs (interspike intervals). Such a dynamics is highly prone to spike‐synchronization, either by an external signal or by mutual interaction in a network of identical systems. Applications to communication and noise induced synchronization will be reported. In experimental neuroscience a recent finding is that feature binding ,that is, combination of external stimuli with internal memories into new coherent patterns of meaning, implies the mutual synchronization of axonal spike trains in neurons which can be far away and yet share the same sequence. Several dynamical systems have been proposed to model such a behavior. We introduce a measurable parameter, namely, the synchronization “propensity”. Propensity is the amount of synchronization achieved in a chaotic system by a small sinusoidal perturbation of a control parameter. It is very low for coupled Lorenz or FitzHugh‐Nagumo chains. It displays isolated peaks for the Hindmarsh‐Rose model, showing that this is a convenient description of the bursting behavior typical of neurons in the CPG (central pattern generator) system. Instead, HC shows a high propensity over a wide input frequency range, demonstrating that it is the most convenient model for semantic neurons. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1846480

出版商:AIP    

年代:1904

数据来源: AIP

摘要:

We give experimental evidence of a delayed feedback control method which is able to efficiently enhance the coherence of the self sustained chaotic oscillations in a CO2laser with electro‐optic feedback. We show that coherence control is achieved for various choices of the delay time in the feedback control loop, including values that would lead to the stabilization of a unstable periodic orbit embedded within the chaotic attractor. © 2004 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1846481

出版商:AIP    

年代:1904

数据来源: AIP