We describe a series of experiments and computer simulations on vibrated granular media in a geometry chosen to eliminate gravitationally induced settling. The system consists of a collection of identical spherical particles on a horizontal plate vibrating vertically, with or without a confining lid. Previously reported results are reviewed, including the observation of homogeneous, disordered liquid-like states, an instability to a 'collapse' of motionless spheres on a perfect hexagonal lattice, and a fluctuating, hexagonally ordered state. In the presence of a confining lid we see a variety of solid phases at high densities and relatively high vibration amplitudes, several of which are reported for the first time in this article. The phase behavior of the system is closely related to that observed in confined hard-sphere colloidal suspensions in equilibrium, but with modifications due to the effects of the forcing and dissipation. We also review measurements of velocity distributions, which range from Maxwellian to strongly non-Maxwellian depending on the experimental parameter values. We describe measurements of spatial velocity correlations that show a clear dependence on the mechanism of energy injection. We also report new measurements of the velocity autocorrelation function in the granular layer and show that increased inelasticity leads to enhanced particle selfdiffusion.

We report the observation of the homogenous nucleation of crystals in a dense layer of steel spheres confined between two horizontal plates vibrated vertically. Above a critical vibration amplitude, two-layer crystals with square symmetry were found to coexist in steady state with a surrounding granular liquid. By analogy to equilibrium hard-sphere systems, the phase behavior may be explained through entropy maximization. However, dramatic nonequilibrium effects are present, including a significant difference in the granular temperatures of the two phases.

The role of forcing on the dynamics of a vertically shaken granular monolayer is investigated. Using a flat plate, surprising negative velocity correlations are measured. A mechanism for this anti-correlation is proposed with support from both experimental results and molecular dynamics simulations. Using a rough plate, velocity correlations are positive, and the velocity distribution evolves from a gaussian at very low densities to a broader distribution at high densities. These results are interpreted as a balance between stochastic forcing, interparticle collisions, and friction with the plate.PACS numbers: 45.70.Mg,05.20.Dd,05.20.Jj,83.10.Rs Granular gases, systems of large numbers of macroscopic grains in rapid motion and interacting through dissipative collisions, appear in a wide range of industrial applications and natural phenomena. Energy must be supplied externally to compensate for the inelastic collisions, so granular gases are necessarily systems out of equilibrium. As a result, they may display dramatic nonequilibrium effects such as non-gaussian velocity distributions [1,2,3,4,5,6] and long-range spatial velocity correlations [7,8,9,10]. Non-gaussian velocity distributions are a direct demonstration of the inapplicability of the Gibbs distribution, and significant velocity correlations indicate the absence of 'molecular chaos', which is a crucial approximation normally used to solve the Boltzmann equation and to calculate other fundamental quantities in kinetic theory. Recent theoretical work has focused on the non-equilibrium steady state obtained when the energy supplied by spatially homogeneous random external forcing is balanced by the dissipation due to the collisions such that the average energy of the system remains constant [4,7,8]. Non-gaussian velocity distributions and algebraically decaying velocity correlations arise as a direct consequence of the energy injection. Non-gaussian velocity distributions and velocity correlations have been observed in a number of experiments [1,2,3,10], but in each case the forcing is sufficiently different from that of the theoretical models that a direct comparison is difficult. In this Letter, we provide a direct demonstration of the determining role that the forcing plays on the spatial velocity correlations in a homogeneously forced granular gas. We will also show how the framework of kinetic theory can provide a coherent description of the origin of the observed velocity distributions and correlations.We have investigated a quasi-2D granular system consisting of a layer of a large number of spherical particles partially covering a vertically driven horizontal plate. Two plates with different surface properties were used in the experiments: a smooth circular plate (20 cm in diameter) made of black anodized aluminum, and a rough hexagonally shaped plate (30 cm between opposite corners). The roughness of the latter is provided by a closepacked lattice of blackened steel balls (1.19 mm diameter) glued to a flat plate. The granular gas is made of uni...

We study the range of orientational order of a single layer of cylindrical block copolymer microdomains annealed on several types of substrates. The orientational persistence length or nematic correlation length (ξ) is evaluated using recently developed imaging and analysis methods to measure the grain size of the block copolymer microdomains. We show that the substrate can lower ξ for block copolymers with a majority component that interacts strongly with the substrate, but this can be mitigated by attaching a buffer layer of polystyrene brushes to the substrate. In addition, we show that, for a block copolymer where the block that strongly interacts with the substrate is the minority component, the microdomain correlation length does not increase when substrates are treated with this buffer layer. We suggest that in this case the brushes do not increase ξ not only because of the lower volume fraction of the strongly interacting component but also because there are block copolymer wetting layers at the free and substrate interfaces that decouple the microdomains from the substrate in a similar manner as the polystyrene brushes.

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