We use large-scale molecular dynamics simulations to study freely evolving granular gases with dimensionality d=2,3 . The system dissipates kinetic energy (or cools) due to inelastic collisions between granular particles. The density and velocity fields are approximately homogeneous at early times, and the system is said to be in a homogeneous cooling state (HCS). However, fluctuations in the density and velocity fields grow, and the system evolves into an inhomogeneous cooling state (ICS). We study the nature of velocity distributions in both the HCS and ICS. We also investigate the aging property of the velocity autocorrelation function.

We study freely evolving inelastic granular gases via molecular dynamics simulations in d = 2, 3 dimensions. This system initially loses energy or cools in a homogeneous cooling state (HCS). However, the granular gas is unstable to fluctuations in the velocity and density fields, and its asymptotic state is an inhomogeneous cooling state (ICS). We discuss the nature of velocity distributions in both the HCS and the ICS.

The lattice model of Coulomb Glass in two dimensions with box-type random field distribution is studied at zero temperature for system size upto 96 2 . To obtain the minimum energy state we annealed the system using Monte Carlo simulation followed by further minimization using clusterflipping. The values of the critical exponents are determined using the standard finite size scaling. We found that the correlation length ξ diverges with an exponent ν = 1.0 at the critical disorder Wc = 0.2253 and that χ dis ≈ ξ 4−η withη = 2 for the disconnected susceptibility. The staggered magnetization behaves discontinuously around the transition and the critical exponent of magnetization β = 0. The probability distribution of the staggered magnetization shows a three peak structure which is a characteristic feature for the phase coexistence at first-order phase transition. In addition to this, at the critical disorder we have also studied the properties of the domain for different system sizes. In contradiction with the Imry-Ma arguments, we found pinned and noncompact domains where most of the random field energy was contained in the domain wall. Our results are also inconsistent with Binder's roughening picture.

The free evolution of a two component or binary granular gas (in dimensions d = 2, 3) is studied using large-scale molecular dynamics simulation. To prepare a binary granular gas, we consider half the particles to be of a different mass. The time dependence of temperature of the system as well as the components is studied. The results are compared with the free cooling of a single component granular gas. The results are found to be at variance with Haff's law that single component granular gases obey in the homogeneous cooling state.

No abstract

No abstract

In this paper we study aging of the velocity autocorrelation function of a uniformly heated granular gas using large scale event-driven molecular dynamics simulations in both 2 and 3 dimensional system. The system is heated by adding Gaussian white noise to each velocity component of all the particles. After a few collisions per particle, the system attains steady state. During early stages, the velocity autocorrelation function shows aging as there is explicit dependence of the function on τ w but after steady state is reached, the velocity autocorrelation function become independent of τ w and does not show any aging. Velocity correlations develop even after steady state is reached, these correlations are less pronounced in 3 dimensional system.

No abstract