Showing papers by "Vito Latora published in 1999"

Kolmogorov-Sinai Entropy Rate versus Physical Entropy

Abstract: We elucidate the connection between the Kolmogorov-Sinai entropy rate {kappa} and the time evolution of the physical or statistical entropy S . For a large family of chaotic conservative dynamical systems including the simplest ones, the evolution of S(t) for far-from-equilibrium processes includes a stage during which S is a simple linear function of time whose slope is {kappa} . We present numerical confirmation of this connection for a number of chaotic symplectic maps, ranging from the simplest two-dimensional ones to a four-dimensional and strongly nonlinear map. {copyright} {ital 1999} {ital The American Physical Society}

Superdiffusion and out-of-equilibrium chaotic dynamics with many degrees of freedoms

Abstract: We study the link between relaxation to the equilibrium and anomalous superdiffusive motion in a classical $N$-body Hamiltonian system with long-range interaction showing a second-order phase transition in the canonical ensemble. Anomalous diffusion is observed only in a transient out-of-equilibrium regime and for a small range of energy, below the critical one. Superdiffusion is due to L\'evy walks of single particles and is checked independently through the second moment of the distribution, power spectra, trapping, and walking time probabilities. Diffusion becomes normal at equilibrium, after a relaxation time which diverges with $N$.

Signals of critical behavior in fragmenting finite systems

Abstract: By studying the disassembly of excited drops within the framework of the classical molecular dynamics (CMD) model, a critical review of observables which can give a signature of a critical behavior is performed. In particular we look at the normalized variance of the mass of the largest fragment (NVM) and to the intermittency signal (IS). It is found the NVM displays a maximum in the critical region for CMD and percolation models, while it is not triggered in ``noncritical'' data like the one resulting from the random partition model. On the other hand, the IS displays a maximum when events with a big fragment are mixed with events composed mainly of small clusters.

The rate of entropy increase at the edge of chaos

Abstract: Under certain conditions, the rate of increase of the statistical entropy of a simple, fully chaotic, conservative system is known to be given by a single number, characteristic of this system, the Kolmogorov-Sinai entropy rate. This connection is here generalized to a simple dissipative system, the logistic map, and especially to the chaos threshold of the latter, the edge of chaos. It is found that, in the edge-of-chaos case, the usual Boltzmann-Gibbs-Shannon entropy is not appropriate. Instead, the non-extensive entropy $S_q\equiv \frac{1-\sum_{i=1}^W p_i^q}{q-1}$, must be used. The latter contains a parameter q, the entropic index which must be given a special value $q^* e 1$ (for q=1 one recovers the usual entropy) characteristic of the edge-of-chaos under consideration. The same q^* enters also in the description of the sensitivity to initial conditions, as well as in that of the multifractal spectrum of the attractor.

Identifying seismicity patterns leading flank eruptions at Mt. Etna Volcano during 1981–1996

Abstract: Seismicity time properties of the Etna Volcano (Italy) are investigated through a systematic pattern recognition analysis. Mean Hypothesis Testing (MHT) has been applied to a long time database of instrumental data recorded from 1981 to 1996 to identify relevant correlation among seismic patterns, main seismogenic volumes and the eight flank eruptions occured in the same period. Time evolution of the test statistic (T-Ratio), calculated on a temporal window starting 75 days prior to a volcanic eruption and extending 25 days after, reveals that there is a pattern of seismic activity prior to the eruptions that can be used as a diagnostic tool as well as a physical modeling support in eruption forecasting.