Massimo Pica Ciamarra

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We study the rheological properties of a granular suspension subject to constant shear stress by constant volume molecular dynamics simulations. We derive the system "flow diagram" in the volume fraction or stress plane (phi, F): at low phi the flow is disordered, with the viscosity obeying a Bagnold-like scaling only at small F and diverging as the jamming(More)
In this paper, we perform simulations of an extended Nagel-Schreckenberg model for one-lane and two-lane roads. We consider the presence of many entry ramps, placed in different locations, and we determine how the flux of cars of each entry ramp must be controlled in order to better exploit the capacity of the road. Our results are of relevance for the(More)
One of the most controversial hypotheses for explaining the heterogeneous dynamics of glasses postulates the temporary coexistence of two phases characterized by a high and by a low diffusivity. In this scenario, two phases with different diffusivities coexist for a time of the order of the relaxation time and mix afterwards. Unfortunately, it is difficult(More)
Dynamical instabilities in fluid mechanics are responsible for a variety of important common phenomena, such as waves on the sea surface or Taylor vortices in Couette flow. In granular media dynamical instabilities have just begun to be discovered. Here we show by means of molecular dynamics simulation the existence of a new dynamical instability of a(More)
We propose a new model of cluster growth according to which the probability that a new unit is placed in a point at a distance r from the city center is a Gaussian with mean equal to the cluster radius and variance proportional to the mean, modulated by the local density ρ(r). The model is analytically solvable in d = 2 dimensions, where the density profile(More)
We investigate the relaxation process and the dynamical heterogeneities of the kinetically constrained Kob-Andersen lattice glass model and show that these are characterized by different time scales. The dynamics is well described within the diffusing defect paradigm, which suggests that we relate the relaxation process to a reverse-percolation transition.(More)
Particles in structural glasses rattle around temporary equilibrium positions, that seldom change through a process which is much faster than the relaxation time, known as particle jump. Since the relaxation of the system is due to the accumulation of many such jumps, it could be possible to connect the single particle short time motion to the macroscopic(More)
We measure the number Omega(phi) of mechanically stable states of volume fraction phi of a granular assembly under gravity. The granular entropy S(phi)=logOmega(phi) vanishes both at high density, at phi approximately equal to phi_rcp, and a low density, at phi approximately equal to phi_rvlp, where phi_rvlp is a new lower bound we call random very loose(More)