We carry out numerical simulations to study transport behavior about the jamming transition of a model granular material in two dimensions at zero temperature. Shear viscosity η is computed as a function of particle volume density ρ and applied shear stress σ, for diffusively moving particles with a soft core interaction. We find an excellent scaling collapse of our data as a function of the scaling variable σ/|ρc − ρ| ∆ , where ρc is the critical density at σ = 0 ("point J"), and ∆ is the crossover scaling critical exponent. We define a correlation length ξ from velocity correlations in the driven steady state, and show that it diverges at point J. Our results support the assertion that jamming is a true second order critical phenomenon.PACS numbers: 83.80.Fg Keywords: In granular materials, or other spatially disordered systems such as colloidal glasses, gels, and foams, in which thermal fluctuations are believed to be negligible, a jamming transition has been proposed: upon increasing the volume density (or "packing fraction") of particles ρ above a critical ρ c , the sudden appearance of a finite shear stiffness signals a transition between flowing liquid and rigid (but disordered) solid states [1]. It has further been proposed by Liu and Nagel and co-workers [2,3] that this jamming transition is a special second order critical point ("point J") in a wider phase diagram whose axes are volume density ρ, temperature T , and applied shear stress σ (the latter parameter taking one out of equilibrium to non-equilibrium driven steady states). A surface in this three dimensional parameter space then separates jammed from flowing states, and the intersection of this surface with the equilibrium ρ − T plane at σ = 0 is related to the structural glass transition. Several numerical [3,4,5,6,7,8,9, 10], theoretical [11,12,13,14] and experimental [5,15,16,17,18] works have investigated the jamming transition, mostly by considering behavior as the transition is approached from the jammed side. In this work we consider the flowing state, computing the shear viscosity η under applied uniform shear stress. Previous works have simulated the flowing response to applied shear in glassy systems at finite temperature [19,20,21], and in foams [4] and granular systems [10] at T = 0, ρ > ρ c . Here we consider the ρ − σ plane at T = 0, showing for the first time that, near point J, η −1 (ρ, σ) collapses to a universal scaling function of the variable σ/|ρ c − ρ| ∆ for both ρ < ρ c and ρ > ρ c . We further define a correlation length ξ from steady state velocity correlations, and show that it diverges at point J. Our results support that jamming is a true second order critical phenomenon.Following O'Hern et al.[3], we simulate frictionless soft disks in two dimensions (2D) using a bidisperse mixture with equal numbers of disks of two different radii. The radii ratio is 1.4 and the interaction between the particles is,where r ij is the distance between the centers of two particles i and j, and d ij is the sum of their radii. Part...

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Molecular dynamics simulations show that gold clusters with about 600-3000 atoms crystallize into a Mackay icosahedron upon cooling from the liquid. A detailed surface analysis shows that the facets on the surface of the Mackay icosahedral gold clusters soften but do not premelt below the bulk melting temperature. This softening is found to be due to the increasing mobility of vertex and edge atoms with temperature, which leads to inter-layer and intra-layer diffusion, and a shrinkage of the average facet size, so that the average shape of the cluster is nearly spherical at melting.

We perform numerical simulations to determine the shear stress and pressure of steady-state shear flow in a soft-disk model in two dimensions at zero temperature in the vicinity of the jamming transition φJ . We use critical point scaling analyses to determine the critical behavior at jamming, and we find that it is crucial to include corrections to scaling for a reliable analysis. We find that the relative size of these corrections are much smaller for pressure than for shear stress. We furthermore find a superlinear behavior for pressure and shear stress above φJ , both from the scaling analysis and from a direct analysis of pressure data extrapolated to the limit of vanishing shear rate.