CiteULike: dchen's durian

Shape and erosion of pebbles

DJ Durian — 2007-03-19T13:52:50-00:00

Physical Review E (Statistical, Nonlinear, and Soft Matter Physics), Vol. 75, No. 2. (2007)

The shapes of flat pebbles may be characterized in terms of the statistical distribution of curvatures measured along their contours. We illustrate this method for clay pebbles eroded in a controlled laboratory apparatus, and also for naturally occurring rip-up clasts formed and eroded in the Mont St.-Michel bay. We find that the curvature distribution allows finer discrimination than traditional measures of aspect ratios. Furthermore, it connects to the microscopic action of erosion processes that are typically faster at protruding regions of high curvature. We discuss in detail how the curvature may be reliably deduced from digital photographs.

Topological persistence and dynamical heterogeneities near jamming

AR Abate — 2008-01-06T13:11:39-00:00

Physical Review E (Statistical, Nonlinear, and Soft Matter Physics), Vol. 76, No. 2. (2007)

We introduce topological methods for quantifying spatially heterogeneous dynamics, and use these tools to analyze particle-tracking data for a quasi-two-dimensional granular system of air-fluidized beads on approach to jamming. In particular, we define two overlap order parameters, which quantify the correlation between particle configurations at different times, based on a Voronoi construction and the persistence in the resulting cells and nearest neighbors. Temporal fluctuations in the decay of the persistent area and bond order parameters define two alternative dynamic four-point susceptibilities A() and B(), well suited for characterizing spatially heterogeneous dynamics. These are analogous to the standard four-point dynamic susceptibility 4(l,), but where the space dependence is fixed uniquely by topology rather than by discretionary choice of cutoff function. While these three susceptibilities yield characteristic time scales that are somewhat different, they give domain sizes for the dynamical heterogeneities that are in good agreement and that diverge on approach to jamming.

Foam Mechanics at the Bubble Scale

DJ Durian — 2007-09-27T03:41:32-00:00

Physical Review Letters, Vol. 75, No. 26. (25 December 1995), 4780.

By focusing on entire bubbles rather than films or vertices; a simple model is proposed for the deformation and flow of foam in which dimensionality; polydispersity; and liquid content can easily be varied. Simulation results are presented for the linear elastic properties as a function of bubble volume fraction; showing a melting transition where the static shear modulus vanishes and the relaxation time scale peaks. Results are also presented for shear stress versus strain rate; showing intermittent flow via avalanchelike topological rearrangements and Bingham-plastic behavior.