CiteULike: dchens density

Critical packing in granular shear bands

S Fazekas — 2008-06-11T19:37:09-00:00

Physical Review E (Statistical, Nonlinear, and Soft Matter Physics), Vol. 75, No. 1. (2007)

In a realistic three-dimensional setup, we simulate the slow deformation of idealized granular media composed of spheres undergoing an axisymmetric triaxial shear test. We follow the self-organization of the spontaneous strain localization process leading to a shear band and demonstrate the existence of a critical packing density inside this failure zone. The asymptotic criticality arising from the dynamic equilibrium of dilation and compaction is found to be restricted to the shear band, while the density outside of it keeps the memory of the initial packing. The critical density of the shear band depends on friction (and grain geometry) and in the limit of infinite friction it defines a specific packing state, namely the dynamic random loose packing.

Structure of colloidal glasses calculated by the molecular-dynamics method and measured by light scattering

I Snook — 2007-09-28T20:36:00-00:00

Physical Review A, Vol. 43, No. 12. (15 June 1991), 6900.

Static structure factors S ( q ) were measured by laser light scattering for very concentrated systems of spherical; near-monosized; sterically stabilized particles dispersed in nonpolar liquids. A range of systems with particle concentrations beyond that corresponding to the disorder to order transition configurations were found to have amorphous structures. As the particles were stabilized by means of very short chain polymers; these systems were thought to closely approximate the fundamentally important amorphous; hard-sphere system. Subsequent analysis of S ( q ) carried out by means of data generated by the molecular-dynamics method for very concentrated; amorphous states of the hard-sphere system confirmed this interpretation. Thus we were able; by a combination of experiment and simulation; to give an extensive analysis and description of the structure of the amorphous state of a system of hard spheres. This study complements past work on the thermodynamic and transport properties of metastable; amorphous states of a system of hard spheres.

On the theory of concentrated hard-sphere suspensions

Michio Tokuyama — 2007-10-29T15:17:13-00:00

Physica A: Statistical and Theoretical Physics, Vol. 216, No. 1-2. (1 June 1995), pp. 85-119.

A systematic theory for the dynamics of hard-sphere suspensions of interacting Brownian particles with both hydrodynamic and direct interactions is presented. A generalized diffusion equation is derived for concentrated suspensions. The volume fraction ([phi]) dependence of the short- and long-time self-diffusion coefficients are thus explored from a unifying point of view. The long-range hydrodynamic interactions due to the Oseen tensor are shown to play a crucial role in both coefficients, while the short-range hydrodynamic interactions just lead to corrections. The importance of the correlation effects between particles due to the long-range hydrodynamic interactions is also stressed. The nonlocal correlation effect is an important factor, leading to the behavior of the long-time self-diffusion coefficient (DSL) as DSL ~ (1 - [phi]/[phi]0)2 near the volume fraction of [phi]0 = 0.5718. The direct interactions are also found to be drastically reduced by the short-range hydrodynamic interactions.

Nature of the divergence in low shear viscosity of colloidal hard-sphere dispersions

Zhengdong Cheng — 2007-07-11T20:42:14-00:00

Physical Review E, Vol. 65, No. 4. (April 2002), 041405.

Measurements of the low-shear viscosity η o with a Zimm-Crothers viscometer for dispersions of colloidal hard spheres are reported as a function of volume fraction φ up to 0.56. Nonequilibrium theories based on solutions to the two-particle Smoluchoski equation or ideal mode coupling approximations do not capture the divergence. However; the nonhydrodynamic contribution to the relative viscosity Δη o is correlated over a wide range of volume fractions by the Doolittle and Adam-Gibbs equations; indicating an exponential divergence at φ m =0.625±0.015. The data extend the previously proposed master curve; providing a test for improved theories for the many-body thermodynamic and hydrodynamic interactions that determine the viscosity of hard-sphere dispersions.

Density fluctuations in vibrated granular materials

Edmund Nowak — 2007-06-03T19:15:17-00:00

Physical Review E, Vol. 57, No. 2. (February 1998), 1971.

We report systematic measurements of the density of a vibrated granular material as a function of time. Monodisperse spherical beads were confined to a cylindrical container and shaken vertically. Under vibrations; the density of the pile slowly reaches a final steady-state value about which the density fluctuates. We have investigated the frequency dependence and amplitude of these fluctuations as a function of vibration intensity Γ. The spectrum of density fluctuations around the steady state value provides a probe of the internal relaxation dynamics of the system and a link to recent thermodynamic theories for the settling of granular material. In particular; we propose a method to evaluate the compactivity of a powder; first put forth by Edwards and co-workers; that is the analog to temperature for a quasistatic powder. We also propose a stochastic model based on free volume considerations that captures the essential mechanism underlying the slow relaxation. We compare our experimental results with simulations of a one-dimensional model for random adsorption and desorption.

Dynamical density functional theory for glassy behaviour

Kazuhiro Fuchizaki — 2008-03-01T21:07:23-00:00

Journal of Physics: Condensed Matter, Vol. 14, No. 46. (2002), pp. 12203-12222.

Glassy dynamics of fluid particles in a supercooled liquid is discussed on the basis of the time-evolution equation obtained through the dynamical density functional theory (DDFT). The advantage, brought about by the coarse-grained nature of the formalism, in treating such strongly correlated motion over other approaches, such as the mode-coupling theories and direct computer simulations, is emphasized. A direction in which the DDFT should prove its worth on examining the phenomena is suggested.