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Andrea Puglisi

Publications and source records attributed to Andrea Puglisi.

7 recordsLinked to original sources
PubMed2003

Sand stirred by chaotic advection.

We study the spatial structure of a granular material, N particles subject to inelastic mutual collisions, when it is stirred by a bidimensional smooth chaotic flow. A simple dynamical model is introduced where four different time scales are explicitly considered: (i) the Stokes time, accounting for the inertia of the particles, (ii) the mean collision time among the grains, (iii) the typical time scale of the flow, and (iv) the inverse of the Lyapunov exponent of the chaotic flow, which gives a typical time for the separation of two initially close parcels of fluid. Depending on the relative values of these different times, a complex scenario appears for the long-time steady spatial distribution of particles, where clusters of particles may or may not appear.

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PubMed2003

Noise activated granular dynamics.

We study the behavior of two particles moving in a bistable potential, colliding inelastically with each other and driven by a stochastic heat bath. The system has the tendency to clusterize, placing the particles in the same well at low drivings, and to fill all of the available space at high temperatures. We show that the hopping over the potential barrier occurs following the Arrhenius rate, where the heat bath temperature is replaced by the granular temperature. Moreover, within the clusterized "phase" one encounters two different scenarios: For moderate inelasticity, the jumps from one well to the other involve one particle at a time, whereas for strong inelasticity the two particles hop simultaneously.

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PubMed2003

Cardiac resynchronization and implantable cardioverter defibrillator therapy: preliminary results from the InSync Implantable Cardioverter Defibrillator Italian Registry.

The aim of this study was to evaluate ventricular arrhythmias occurring in recipients of the InSync ICD for the primary and secondary prevention of sudden death. The InSync ICD was implanted in 142 patients (128 men; mean age 65 +/- 10 years) with heart failure (mean NYHA functional Class 3.0 +/- 0.7) and wide QRS (mean 159 +/- 33 ms). The underlying etiology was ischemic in 55%, idiopathic in 33%, and valvular or hypertensive cardiomyopathy in 12% of patients. The numbers of arrhythmic episodes/100 patient-months was computed with their 95% CI, assuming a Poisson distribution. Implants were performed in 48 (34%) patients who did not have an ACC/AHA guidelines Class I indication for ICD therapy. A total of 104 patients were compliant for follow-up visits. During a 9-month median (range 0.1-24) follow-up of 104 compliant patients, 19 experienced a total of 94 ventricular arrhythmias, all successfully interrupted or self-terminated, with a median number of two separate episodes, corresponding to a rate of 10 episodes/100 person-month (95% CI 8-12). A rate of 12 episodes/100 person-months (95% CI 10-15) was measured in the subgroup of patients with ACC/AHA class I indications, versus two episodes/100 person-months (95% CI 1-5) in the remainder of the population. Among 12 deaths, 9 were due to heart failure, 1 to a non-cardiovascular cause, and 2 to unknown causes. The implantation of ICD in heart failure patients has been prominently extended to primary prevention. Patients without standard ICD indications experienced life-threatening arrhythmic events. The impact of ICD combined with cardiac resynchronization therapy on arrhythmic profile, mortality, and costs in this subgroup of patients need to be more precisely studied, with a particular focus on the various types of underlying heart disease.

Adult↗
PubMed2002

Driven low density granular mixtures.

We study the steady state properties of a two-dimensional granular mixture in the presence of energy driving by employing simple analytical estimates and direct simulation Monte Carlo. We adopt two different driving mechanisms, (a) a homogeneous heat bath with friction and (b) a vibrating boundary (thermal or harmonic) in the presence of gravity. The main findings are the appearance of two different granular temperatures, one for each species; the existence of overpopulated tails in the velocity distribution functions and of nontrivial spatial correlations indicating the spontaneous formation of cluster aggregates. In the case of a fluid subject to gravity and to a vibrating boundary, both densities and temperatures display nonuniform profiles along the direction normal to the wall, in particular, the temperature profiles are different for the two species while the temperature ratio is almost constant with the height. Finally, we obtained the velocity distributions at different heights and verified the non-Gaussianity of the resulting distributions.

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PubMed2002

Steady-state properties of a mean-field model of driven inelastic mixtures.

We investigate a Maxwell model of inelastic granular mixture under the influence of a stochastic driving and obtain its steady-state properties in the context of classical kinetic theory. The model is studied analytically by computing the moments up to the eighth order and approximating the distributions by means of a Sonine polynomial expansion method. The main findings concern the existence of two different granular temperatures, one for each species, and the characterization of the distribution functions, whose tails are in general more populated than those of an elastic system. These analytical results are tested against Monte Carlo numerical simulations of the model and are in general in good agreement. The simulations, however, reveal the presence of pronounced non-Gaussian tails in the case of an infinite temperature bath, which are not well reproduced by the Sonine method.

Journal Article↗
PubMed2002

Mean-field model of free-cooling inelastic mixtures.

We consider a mean-field model describing the free-cooling process of a two-component granular mixture, a generalization of the so called scalar Maxwell model. The cooling is viewed as an ordering process and the scaling behavior is attributed to the presence of an attractive fixed point at v=0 for the dynamics. By means of asymptotic analysis of the Boltzmann equation and of numerical simulations we get the following results: (1) we establish the existence of two different partial granular temperatures, one for each component, which violates the zeroth law of thermodynamics; (2) we obtain the scaling form of the two distribution functions; (3) we prove the existence of a continuous spectrum of exponents characterizing the inverse-power-law decay of the tails of the velocity, which generalizes the previously reported value of 4 for the pure model; (4) we find that the exponents depend on the composition, masses, and restitution coefficients of the mixture; (5) we also remark that the reported distributions represent a dynamical realization of those predicted by the nonextensive statistical mechanics, in spite of the fact that ours stem from a purely dynamical approach.

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