Bulletin of the American Physical Society
APS March Meeting 2010
Volume 55, Number 2
Monday–Friday, March 15–19, 2010; Portland, Oregon
Session V13: Focus Session: Jamming I |
Hide Abstracts |
Sponsoring Units: GSNP Chair: Corey O’Hern, Yale University Room: B112 |
Thursday, March 18, 2010 8:00AM - 8:12AM |
V13.00001: Scaling relations in shear flow near the jamming transition Brian Tighe, Erik Woldhuis, Joris Remmers, Martin van Hecke, Wim van Saarloos We present a simple model for the rheology of dense systems of viscous soft repulsive disks, which are themselves an idealized model for foams and other disordered soft matter systems that undergo a jamming transition. The model predicts rational-valued scaling exponents and connects macroscopic stresses and microscopic velocity fluctuations. We predict three scaling regimes in the rheology. Exponents depend non-trivially on the form of the viscous interaction between bubbles, while the width of each regime is set by the distance to the critical packing fraction associated with jamming. The model makes specific predictions for rheology near the jamming transition, which we test with numerical simulations. [Preview Abstract] |
Thursday, March 18, 2010 8:12AM - 8:24AM |
V13.00002: Anisotropic Heterogeneous Dynamics in Confined Colloidal Liquids under Oscillatory Shear Prasad Sarangapani, Andrew Schofield, Yingxi Elaine Zhu We have investigated the dynamics of confined amorphous ``hard-sphere'' colloidal suspensions under oscillatory shear using a home-designed micron-gap rheometer interfaced with a confocal microscope. We have focused on model hard-sphere colloidal suspensions of micron-sized poly-(methyl methacrylate) (PMMA) particles suspended in density and refractive index matched nonpolar solvents at particle volume fractions, $\phi $ = 0.40 and 0.43. We simultaneously visualize the dynamical response of confined PMMA particles between two solid surfaces at narrow gap spacing of 10-28 particle layers to applied shear deformation and measure their viscoelasticity. Above a threshold strain of $\sim $6{\%} where an applied deformation is sufficient to induce plastic behavior, we find that structural rearrangements are highly anisotropic. Non-affine motion, determined by subtracting the globally uniform strain from the bare particle coordinates, reveals that particles move as cooperatively rearranging groups with a preferred orientation along the flow direction. Metrics which probe cooperative dynamics all reveal a strong amplitude, thickness, and directional dependence on the characteristic sizes of the cooperatively rearranging regions. [Preview Abstract] |
Thursday, March 18, 2010 8:24AM - 8:36AM |
V13.00003: The Jamming Transition and Crossover to Clogging for Disks with Quenched Disorder Charles Reichhardt, Cynthia J. Olson Reichhardt, Evan Groopman, Zohar Nussinov In the jamming phase diagram proposed by Liu and Nagel [1], a transition occurs from a flowing liquid-like state to a rigid shear-resisting state as a function of increasing density, decreasing shear, or decreasing temperature. Here we show that quenched disorder in the form of fixed grains serves as a new axis to the jamming phase diagram for a system of bidisperse two- dimensional disks. By analyzing the flow of disks driven with constant force through the system, we find that the jamming density decreases with increasing density of fixed disks, and we also observe the same type of jamming behavior associated with point J. At a sufficiently large density of fixed disks, the jamming behavior is replaced by a clogging behavior characterized by the formation of a giant void that spans the system. At the clogging transition, disks outside of the void region reach the density associated with jamming at point J. [1] A. Liu and S. Nagel, Nature 396, 21 (1998). [Preview Abstract] |
Thursday, March 18, 2010 8:36AM - 9:12AM |
V13.00004: Thermodynamics of Sphere Packings at Small N: Experiments and Theory Invited Speaker: We study the formation and structure of equilibrium colloidal clusters at small particle number ($N \leq 10$) using optical microscopy. Our experimental system consists of an ensemble of isolated groups of colloidal microspheres interacting through a short-ranged depletion attraction. For $N < 6$ we observe only a single configuration at each $N$, but as $N$ increases we observe an increasing number of coexisting configurations. We find that highly symmetric clusters are strongly suppressed by rotational entropy, and many of the clusters with the lowest free energy are subsets of close-packed crystal lattices. We compare our results for the cluster structures to those from a geometrical theory that enumerates all possible finite sphere packings for $N \leq 10$. The geometrical model may give some insights into how phase transitions emerge as $N$ approaches the bulk limit. [Preview Abstract] |
Thursday, March 18, 2010 9:12AM - 9:24AM |
V13.00005: Topology of force chains in dense granular materials Miroslav Kramar, Konstantin Mischaikow, Lou Kondic, Yiguang Yan We will present a novel approach to study force chain structures of dense particulate systems. These structures are very important in understanding static and dynamic features of dense particulate systems. However, so far there is no well defined approach towards understanding them. Our approach deploys algebraic topology techniques which allow us to distinguish between the systems exposed to shear and compression. We use our method to compare experimental and theoretical results in a well defined and precise manner. We will also discuss how the topological measures can be used to understand the dynamic features of the system and correlate these measures to the phenomena such as jamming. [Preview Abstract] |
Thursday, March 18, 2010 9:24AM - 9:36AM |
V13.00006: ABSTRACT WITHDRAWN |
Thursday, March 18, 2010 9:36AM - 9:48AM |
V13.00007: From the local Coulomb rule to a global failure criterion for packings of frictional particles Silke Henkes, Carolina Brito, Olivier Dauchot, Martin van Hecke, Wim van Saarloos Frictional contacts at the Coulomb threshold are unstable to tangential perturbations and thus contribute to failure at the microscopic level. How can they be linked to global failure? Here, we use a simulated bed of frictional disks under the action of gravity undergoing a slow tilt. Based on contact information, we develop a novel criterion to separate the quiet state from the avalanching state. During the quiet state, we find both spatial and temporal correlations between failure and the clusters of particles with fully mobilized contacts. These clusters are strongly fluctuating, and eventually approach system spanning size near the avalanche. We find that the clusters cross the line of marginal stability at the start of the avalanche, while the global system does not. We conclude that to initiate failure, it is only necessary for a correlated subset of the packing to violate the generalized isostaticity stability criterion. [Preview Abstract] |
Thursday, March 18, 2010 9:48AM - 10:00AM |
V13.00008: The Statistical Mechanics of Small Packings S.S. Ashwin, Jerzy Blawzdziewicz, Corey O'Hern, Mark Shattuck We explore the statistical mechanics of mechanically stable (MS) packings composed of six or more monodisperse hard discs confined within a unit box. This system has the advantage that all MS packings can be enumerated, yet it has a topologically nontrivial density landscape in contrast to systems with fewer than six disks. We compare the packing probabilities obtained using discrete particle simulations to those obtained using master equation approaches, which relate entropic bottlenecks to transition probabilities. We determine how the MS packing probabilities vary with the packing protocol, and in particular, the extent to which the Edwards' equal-probability assumption is violated. [Preview Abstract] |
Thursday, March 18, 2010 10:00AM - 10:12AM |
V13.00009: Measuring an Equation of State in an Air-Fluidized Monolayer on Approach to Jamming Lynn J. Daniels, Ning Xu, Douglas J. Durian We examine the pressure in a quasi-two-dimensional monolayer of bidisperse steel beads, fluidized by an upflow of air, and its dependence on packing fraction and temperature on approach to the jamming transition. By tilting the system at an angle $\theta$, we introduce a component of gravity into the plane of our system and measure a depth-dependent pressure, $P = m_{>}(z)g \sin (\theta)/L$ where $m_{>}(z)/L$ is the total mass per unit length above a depth $z$, over three orders of magnitude. By tracking the beads in time, we calculate packing fraction $\phi$, effective temperature $kT$, mean square displacement, and relaxation time, all as functions of depth. This is done for different tilt angles as well as initial filling fractions. The data for $P\sigma^{2}/kT$ vs $\phi$, where $\sigma$ is the small bead radius, constitute an equation of state. The results show excellent collapse and agree well with the results of a simulation of two-dimensional bidisperse disks interacting via hardcore repulsion. [Preview Abstract] |
Thursday, March 18, 2010 10:12AM - 10:24AM |
V13.00010: Power law avalanche distributions in quasistatic shear of disordered systems with inertia Kenneth Salerno, Mark Robbins, Craig Maloney Crackling noise, or avalanche behavior can occur in a wide variety of systems. These avalanches are often characterized by scale-free, power law behavior. Our molecular dynamics simulations subject an amorphous bidisperse solid with Lennard-Jones or repulsive harmonic interactions to quasistatic shear. A variety of two and three dimensional geometries with periodic or confined boundary conditions under pure or simple shear are considered. Deformation occurs through a series of avalanches of plastic activity whose energy, duration and physical size are determined. Similar power law distributions of avalanche energies are found for all geometries as long as the particle dynamics is underdamped. Results for different system sizes can be collapsed using finite-size scaling. This power law scaling is eliminated when particle motion is overdamped, and the probability decays exponentially with energy. [Preview Abstract] |
Thursday, March 18, 2010 10:24AM - 10:36AM |
V13.00011: ABSTRACT WITHDRAWN |
Thursday, March 18, 2010 10:36AM - 10:48AM |
V13.00012: Jamming of Granular Materials in Wedge Hoppers Summer Saraf, Scott Franklin We study the jamming of ordinary and rod-like granular materials in wedge-shaped hoppers and compare the probability distributions for exit mass with those obtained from cylindrical hoppers. While cylindrical hoppers show an exponential probability distribution, we find that the rectangular exit aperture of wedge-shaped hoppers exhibit a power law decay for both spheres and rods. This behavior can be explained with a model of the rectangular exit aperture as composed of a series of round, adjacent apertures each with a statistically independent jamming probability. We speculate that the spatially varying jamming probability results from inhomogeneities in the granular material, with regions of the material more tightly packed than others, and thus more likely to jam. [Preview Abstract] |
Thursday, March 18, 2010 10:48AM - 11:00AM |
V13.00013: Local Packing Fraction Statistics in a Two-Dimensional Granular Media James Puckett, Frederic Lechenault, Karen Daniels We experimentally investigate local packing fraction statistics of a two-dimensional bidisperse granular material supported by a horizontal air table and rearranged under impulses from the boundary. Our apparatus permits investigation of dense liquids close to the jamming transition under either constant pressure (CP) or constant volume (CV) boundary conditions and three different coefficients of friction. We calculate the probability distribution of the local packing fraction $\phi$ using both radical Voronoi tessellations ($\phi_{V}$) and the Central Limit Theorem ($\phi_{CLT}$). The two distributions have the same mean: $\langle \phi_{V}\rangle=\langle \phi_{CLT} \rangle$. For both methods, we observe that the variance strictly decreases as the mean increases; the functional dependence reveals information about the system. The variance of $\phi_{V}$ is larger under CP than CV, as expected since the cell volumes adjust to fluctuations in global volume. Interestingly, this feature is missing from $\phi_{CLT}$. Instead, the variance of $\phi_{CLT}$ is sensitive to the internal friction of the system. [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700