Name: Ning Xu
Affiliation: Yale University
Email: ning.xu@yale.edu
Phone Number: 203-432-8249
Give Talk: no
Poster: yes
Title: Velocity Profiles in Repulsive Athermal and Glassy Systems under Shear
Abstract: We conduct molecular dynamics simulations of repulsive glasses and athermal systems undergoing boundary-driven planar shear flow in two (2D) and three (3D) spatial dimensions. We find that these systems possess nonlinear mean velocity profiles when the velocity $u$ of the shearing wall exceeds a critical value $u_c$. Above $u_c$, we also show that the density and mean-square velocity profiles become spatially-dependent with dilation and enhanced velocity fluctuations near the moving boundary. In athermal systems with overdamped dynamics, $u_c$ is only weakly dependent on packing fraction $\phi$. However, in systems with underdamped dynamics, $u_c$ is set by the speed of sound in the material and tends to zero as $\phi$ approaches $\phi_c$. In the small damping limit, $\phi_c$ approaches values for random close-packing obtained in systems at zero temperature. For underdamped systems with $\phi<\phi_c$, $u_c$ is zero and thus they possess nonlinear velocity profiles at any nonzero boundary velocity.

Name: Corey S. O'Hern
Affiliation: Yale University
Position: Assistant Professor
Email: corey.ohern@yale.edu
Position: Assistant Professor
Phone Number: 203-432-4258
Give Talk: no
Poster: yes
Title: Topological Classification of Jammed States
Abstract: We enumerate and classify jammed configurations that occur at zero temperature in small 2D and 3D periodic systems composed of monodisperse and polydisperse particles that interact via hard-sphere and soft finite-range potentials. Jammed configurations are created using two algorithms: 1) random displacements of individual hard particles followed by particle growth and 2) collective moves of soft particles based on potential energy minimization followed by compression. In algorithm 1, configurations are jammed when a given particle cannot be displaced when all other particles are held fixed. In algorithm 2, configurations are jammed when no group of particles can be displaced simultaneously. We find that jammed states occur in continuous topological families when only single-particle moves (algorithm 1) are allowed. However, when collective moves (algorithm 2) are allowed, jammed states are discrete, i.e. each possesses a distinct network of particle contacts. We decompose the frequency distribution of jammed states into distributions for each topology and then calculate the density of jammed states and their basins of attraction.

Name: Martin Z. Bazant
Affiliation: MIT
Position: Associate Professor
Email: bazant@math.mit.edu
Position: Associate Professor
Phone Number: 617-253-1713
Give Talk: yes
Poster: no
Title: A theory of cooperative diffusion in dense granular flows
Abstract: Although diffusion in fast, dilute granular flows may be described by variations of classical kinetic theory, recent experiments suggest that slow, dense flows require a fundamentally different approach, due to long-lasting, many-body contacts. In the case of slow silo drainage, many continuum models have been proposed for the mean flow, but no microscopic theory of fluctuations is available. Here, we propose describe a statistical theory of dense flows in which particles undergo cooperative random motion in response to diffusing spots'' of free volume. The Spot Model may be either used in Monte Carlo simulations or analyzed in the continuum limit, where some new partial differential equations arise. The theory predicts spatial velocity correlations, athermal diffusion and cage breaking controlled by free volume and geometry-dependent density waves. Particle-tracking experiments in the MIT Dry Fluids Lab provide strong support for the spot hypothesis.

Name: Alexander Lobkovsky
Affiliation: MIT
Position: Postdoc
Email: leapfrog@mit.edu
Position: Postdoc
Phone Number: 617-324-6712
Give Talk: yes
Poster:
Title: Growth of seepage driven channels
Abstract: We analyze an experiment in which water, driven through a pile of sand, emerges on the surface of the pile and incises channels. The channels coarsen and deepen while the heads of the channels migrate up the slope of the sand pile towards the water source. A laser aided technique allows us to obtain time-dependent sand height information with spatial resolution of a few millimeters and time resolution of 30 seconds. We use this information to establish a quantitative test of the microscopic models of erosion. We describe channels in terms of their depth and distance to water source. Simple evolution equations for these two variables explain the convergence of channel trajectories.

Name: Hernan Makse
Affiliation: City College of New York
Position: Assistant Professor
Email: makse@mailaps.org
Position: Assistant Professor
Phone Number: 212-650-6847
Give Talk:
Poster:
Title: Measurements of effective temperatures in jammed granular matter validate the thermodynamic hypothesis.
Abstract: A densely packed granular system, in which all the grains are in contact with their neighbors, is an example of jammed matter. Since there is no thermal energy of consequence within the system, the exploration of the available jammed configurations of the constituent particles for a given system volume must be facilitated by an external energy input, such as tapping or slow shear. Provided that all the jammed configurations are equally probable and bear no memory of their creation, we arrive at the ergodic hypothesis, implying that a statistical mechanics approach is justified. This forms the basic tenet of the thermodynamic formulation for jammed matter, which characterizes the state of the packing by the compactivity' or 'effective temperature' and the entropy. The existence of jammed reversible states has been suggested by compaction experiments employing tapping, oscillatory compression or sound propagation as the external mechanical perturbation. On the other hand, macroscopic variables, such as the effective temperature, have not been previously measured in the laboratory. The measurement of the granular effective temperature is realized in the laboratory by slowly shearing a jammed ensemble of spherical beads in a couette geometry confined by an external pressure. The particle trajectories yield the diffusivity and the mobility from which the effective temperature is deduced. All the particles, independent of their properties, equilibrate at the same effective temperature, which is in turn independent on the slow shear rate, thus satisfying the condition of a true thermodynamic variable for the jammed system. This result suggests that the problem of jammed matter is a generalization of the statistical mechanics introduced by Boltzmann.

Affiliation: Clark University
Position: Associate Professor
Email: akudrolli@clarku.edu
Position: Associate Professor
Phone Number: 508 793 7752
Give Talk: yes
Poster: no
Title: Anisotropic Granular Materials
Abstract: Granular materials come in all shapes and sizes. Idealized spherical particles have been typically used to unravel the fascinating properties displayed by granular materials. However, anisotropic grains are nearly as numerous, and experience with thermal systems teaches us that shape matters. Only a handful of investigations have studied the impact of anisotropy on granular systems, but the ones that have been accomplished point to a rich phenomenology. For example, compaction experiments with granular rods have noted ordered stacks i.e. a smectic phase similar to that found in thermal systems. More recently, self-organization of vortices was observed to occur when a shallow bed of granular rods was vibrated. We will first review what little is known about the impact of anisotropy, and then discuss a series of experiments with dimers and rods excited by vibration. Examples of how shape anisotropy leads to novel dynamics will be discussed. *Work in collaboration with S. Dorbolo, D. Blair, D. Volson, and L. Tsimring

Name: Eric R. Dufresne
Affiliation: Yale University
Position: Faculty
Email: eric.dufresne@yale.edu
Position: Faculty
Phone Number: 203 432 4351
Give Talk: no
Poster: no
Title:
Abstract:

Name: Mark Shattuck
Affiliation: Levich Institute, City College of New York
Position: Assistant Professor
Email: shattuck@ccny.cuny.edu
Position: Assistant Professor
Phone Number: 212-650-8161
Give Talk: no
Poster: no
Title:
Abstract:

Name: Lou Kondic
Affiliation: NJIT
Position: Associate Professor
Email: kondic@njit.edu
Position: Associate Professor
Phone Number: 973 596 2996
Give Talk: no
Poster: no
Title:
Abstract:

Name: Mark Brandon
Affiliation: Yale University
Position: Professor
Email: mark.brandon@yale.edu
Position: Professor
Phone Number: 203-432-3135
Give Talk: no
Poster: no
Title:
Abstract:

Name: Oleh Baran
Affiliation: New Jersey Institute of Technology
Position: Postdoc
Email: oleh.baran@njit.edu
Position: Postdoc
Phone Number: (973) 596-3141
Give Talk: no
Poster: yes
Title: Sheared Granular Systems: Velocity Profiles, Stresses, and Bagnold Scaling
Abstract: We will present the results of three-dimensional hard-sphere molecular dynamics simulations of sheared granular system in Couette geometry. The simulations use realistic boundary conditions that may be expected in physical experiments. For a range of boundary properties we report velocity and volume fraction profiles and stresses on the boundaries and their distributions. In particular, we simulate constant pressure'' boundary condition and we discuss the differences between the results in constant volume and constant pressure settings. A key observation here is different reaction to the increase of shearing velocity in the system with constant pressure boundary condition compared to the systems with constant volume boundary condition. In the first case the shearing velocities are increasing while in the second case they are decreasing. Analysis of the stresses on the boundaries leads to some interesting new results regarding the influence of the details of averaging procedure on the computed force distributions. Movies of the simulations can be found at http://math.njit.edu/~oleh/shear_shake .

Name: Hans Wyss
Affiliation: Harvard University
Position: postdoc
Email: hwyss@fas.harvard.edu
Position: postdoc
Phone Number: 617 384 9506
Give Talk: no
Poster: yes
Title: Jamming of wet granular materials
Abstract:

Name: Samuel G. paikowsky
Affiliation: Geotechnical Eng Research Lab UMASS Lowell
Position: Professor and Lab Director
Email: Samuel_Paikowsky@uml.edu
Position: Professor and Lab Director
Phone Number: 978 934-2277
Give Talk: yes
Poster: no
Title: The Application of Grid-Based Tactile Pressure Technology
Abstract: The behavior of discontinuous (discrete, granular) materials is an important factor in many disciplines. These materials display unique behavior in the form of volume change during shear and arching. The fundamental mechanism of arching relates to the ability of discrete units to transfer loads through interaction in a preferable geometry and thus to bridge between the zone (or point) of load application to the zone (or points) of reaction. These features result in a unique load transformation and stress distribution within discontinuous materials and on the boundary between them and solid surfaces. Accurate measurements of stress distribution are cardinal therefore for the understanding of the physical phenomena as well as the evaluation of design criteria and monitoring performance. The existing methods of evaluating stress distribution in a granular mass rely mostly on the use of buried or surface mounted load cells. These measurements are difficult to perform and are limited in their ability to capture the stress variation. A new technology, which makes use of flexible, grid-based, tactile pressure sensors, allows to measure stresses at a large number of points in proximity to one another, hence providing a realistic normal stress distribution. Their flexibility overcomes the effect of stiffness variation introduced by rigid load cells and thus allows for measurements that better represent the existing stress conditions. The application of the tactile pressure technology to granular materials requires adaptation and calibration due do its innovative principle of operation. The presented research addresses five subjects in soil mechanics: (i) the effect of grain size on stress distribution measurement (internal and along a boundary with a solid surface), (ii) the pressure dip under the sand heap (iii) the contact stresses under a rigid strip footing, (iv) the measurement of the stress distribution behind a model retaining wall, and (v) the pressures developed on the front wall in a pull-out test. 3D Isometric View of Vertical Stress Distribution at the Base of a Sand Pile (experiment #3) Presentations/tactile sensors in geotech lecture abstract.doc

Name: Greg Voth
Affiliation: Wesleyan University
Position: Assistant Professor
Email: gvoth@wesleyan.edu
Position: Assistant Professor
Phone Number: (860) 685-2035
Give Talk: no
Poster: no
Title:
Abstract:

Name: Naomi Goldenson
Affiliation: Wesleyan University
Position: student
Email: ngoldenson@wesleyan.edu
Position: student
Phone Number: 860-961-2710
Give Talk: no
Poster: no
Title:
Abstract:

Name: Thomas C. Halsey
Affiliation: ExxonMobil Research & Engineering
Position: Laboratory Director
Email: thomas.c.halsey@exxonmobil.com
Position: Laboratory Director
Phone Number: 908.730.2138
Give Talk:
Poster: no
Title: Dense Granular Flow
Abstract: This talk will focus on one of the classical problems in the granular field, the behavior of dense granular flows driven by gravity. I will give examples of such flows drawn from geophysics, and then introduce some of the ideas of Ralph Bagnold, who developed the concepts on which the modern study of granular flows are based. A systematic phenomenology of dense granular flows down inclines has recently been developed, based both on numerical work and on experiments. This phenomenology emphasizes the role of inelastic collapse in controlling the rheology of these flows.

Name: Ping Wang
Affiliation: Levich Institute and Physics Department, City College of NY
Position: PH.D student
Email: anyon_wang@yahoo.com
Position: PH.D student
Phone Number: 1-212-650-8871
Give Talk: no
Poster: yes
Title: Granular Dynamics in Compaction and Stress Relaxation
Abstract: The nonlinear elastic and dissipative properties of cohesionless granular assemblies are studied experimentally and numerically, under uniaxial compression. As a prelude to granular dynamics measurements, we investigate the system's exploration of all possible static configurations through a novel compaction procedure at varying confining pressures. Once the system is fully compacted we assume no further changes in volume and study the slow relaxation dynamics purely in terms of grain-grain interactions and possible rearrangements through grains sliding and rolling. Computer simulations resolve the problem of the origin of the long stress-relaxation dynamics found in the system.

Name: Chaoming Song
Affiliation: Levich Institute of CCNY
Position: PHD. student
Email: song@levdec.engr.ccny.cuny.edu
Position: PHD. student
Phone Number: 1-212-650-8871
Give Talk: no
Poster: yes
Title: Does the effective temperature of jammed granular matter have a true thermodynamic meaning? Experiments have the answer
Abstract: A densely packed granular system, in which all the grains are in contact with their neighbors, is an example of jammed matter. Since there is no thermal energy of consequence within the system, the exploration of the available jammed configurations of the constituent particles for a given system volume must be facilitated by an external energy input, such as tapping or slow shear. Provided that all the jammed configurations are equally probable and bear no memory of their creation, we arrive at the ergodic hypothesis, implying that a statistical mechanics approach is justified. This forms the basic tenet of the thermodynamic formulation for jammed matter, which characterizes the state of the packing by the 'compactivity' or 'effective temperature' and the entropy. The existence of jammed reversible states has been suggested by compaction experiments employing tapping, oscillatory compression or sound propagation as the external mechanical perturbation. On the other hand, macroscopic variables, such as the effective temperature, have not been previously system has emerged from theoretical mean field models of glasses and computer simulations of glassy systems and sheared granular matter. This line of research has led to the design of a decisive experiment which we are about to present. The measurement of the granular effective temperature is realized in the laboratory by slowly shearing a jammed ensemble of spherical beads in a geometry confined by an external pressure. The particle trajectories yield the diffusivity and the mobility from which the effective temperature is deduced. All the particles, independent of their properties, equilibrate at the same effective temperature, which is in turn independent on the slow shear rate, thus satisfying the condition of a true thermodynamic variable for the jammed system. This result suggests that the problem of jammed matter is a generalization of the statistical mechanics introduced by Boltzmann.

Name: Guo-Jie Gao
Affiliation: Yale University
Email: guo-jie.gao@yale.edu
Phone Number: 203-624-9238
Give Talk: no
Poster: no
Title:
Abstract:

Name: Saloome Siavoshi
Affiliation: Clark University
Email: ssiavoshi@clarku.edu
Phone Number: 508-793-7338
Give Talk: no
Poster: yes
Title: Gravity driven relaxation of a granular step
Abstract: We study the gravity driven evolution of a step composed of steel beads using high-speed imaging. A motivation for the study is the unusually long runoff observed in large avalanches. The step is initially held together with electromagnets, and released when the current is switched off. The initial failure of the pile occurs at the surface and the depth of the flow first increases and then decreases as the pile relaxes. We compare and contrast the final shape of the surface with that obtained by pouring beads slowly in the rectangular box. The final angle of inclination is lower than the angle of repose of the grains, and the rate of change of the surface inclination reaches a maximum well before angle of repose is reached. We will discuss the relevance of a recent convective-diffusion model in describing our data.

Name: Jonathan Saragos
Affiliation: Levich Institute, City College of CUNY / ENS-Cachan
Position: Intern
Email: saragost@rip.ens-cachan.fr
Position: Intern
Phone Number: 212-650-8012
Give Talk: no
Poster: no
Title:
Abstract:

Name: Braunen Smith
Affiliation: Clark University
Email: braunen@physics.clarku.edu
Phone Number: 508-793-7707
Give Talk: no
Poster: no
Title:
Abstract:

Name: Rohit Ingale
Affiliation: Levich Institute, City College of New York
Email: rohitingale@rediffmail.com
Phone Number: 212-844-9901
Give Talk: no
Poster: no
Title:
Abstract:

Name: Donald Candela
Affiliation: University of Massachusetts
Position: Professor
Email: candela@physics.umass.edu
Position: Professor
Phone Number: (413)545-3666
Give Talk: yes
Poster: no
Title: Probing the gas-fluidized granular bed and vertical channel flow with NMR
Abstract: Recently, our group has used NMR methods to measure the granular temperature profile of a vibrofluidized granular system, for comparison with the predictions of granular hydrodynamics. Here we describe the extension of these methods to two other granular flow systems, the gas-fluidized bed and vertical-channel flow. In these systems we are using NMR to measure spatial profiles of density, average flow velocity, and grain displacement probability distributions over time intervals of 1-100 ms. For the gas-fluidized bed key issues are applicability of granular fluid models and nature and role of gas bubbles. Flow-compensated NMR pulse sequences are used to probe time correlations in grain movements and to distinguish grain-scale diffusion from random advection on larger scales. For vertical channel flow the radial dependences of the velocity and the grain diffusion are expected to differ drastically from those of a simple fluid, possibly reflecting the glassy nature of this dense granular flow.

Name: Chao Huan
Affiliation: University of Massachusetts
Email: huan@physics.umass.edu
Phone Number: (413)545-3666
Give Talk: no
Poster: no
Title:
Abstract:

Name: Kevin Facto
Affiliation: University of Massachusetts
Email: kfacto@physics.umass.edu
Phone Number: (413)545-3666
Give Talk: no
Poster: no
Title:
Abstract:

Name: Nicolas Gland
Affiliation: Levich Institute, City College of CUNY
Position: Post-doctoral fellow
Email: gland@levdec.engr.ccny.cuny.edu
Position: Post-doctoral fellow
Phone Number: 212-650-8012
Give Talk: no
Poster: yes
Title: Numerical Study of the Response Function of Random Two-Dimensional Granular Packings
Abstract: Understanding the structural and mechanical status of static granular assemblies is still an open issue. Except by numerical simulations (for instance Molecular Dynamics), it is difficult to study the Mechanical properties of spheres packings. There's no consensus on how the stress distribution should be expressed and how granular materials respond to applied perturbations. Different models exist: (1) in elasto-plastic modeling, for small deformations, an elastic response is assumed; (2) the Oriented Stress Linearity model (OSL) uses a constitutive law based only on relations between the components of the stress tensor; unlike in the elasticity framework where the stress field can be described by elliptic PDE, it implies hyperbolic (i.e.propagative) PDE; (3) q-model in the continuum limit reduces to the diffusion equation. The importance of resolving which of these models applies under which circumstances is of major interest to reveal the real mechanical status of static granular assemblies. In this work, we'll present MD simulations of the response of 2D packings subjected to a localized force perturbation in order to discriminate between the different theories.

Name: Allison Ferguson
Affiliation: Brandeis University
Email: shamrock@brandeis.edu
Phone Number: 781-236-2896
Give Talk: yes
Poster: no
Title: Large Scale Dynamical Structures in Gravity-Driven Granular Flow
Abstract: Studies have suggested that the force distribution P(f) can be used as a static measure distinguishing between flowing and jammed regimes in both thermal and athermal systems (PRL 86, 111 (2001)). Experimental work on dense gravity-driven granular flows (PRL 89, 045501 (2002)) seems to indicate that the complete picture may be more complex. We have constructed a simulation of the experimental system in which we observe the presence of large-scale linear clusters of �frequently-colliding?particles. The observed changes in the impulse distribution P(I) can be directly related to the existence of these correlated clusters via a simple model (EPL 66, 277 (2004)). Distributions of time between collisions measured in experiment and simulations as well as considerations of conditions for steady state flow reveal an increasing separation of time scales as the system approaches jamming: an average collision time will decrease as flow velocity decreases while the time for a particle to fall through it�s own diameter will rise. This separation cannot be derived by considering a flow of uncorrelated particles. Finally, a microscopic stress tensor can be constructed which relates the frequent collision chains to interesting features in the measured distributions and may provide a promising pathway for constructing coarse-grained theories of this system.

Name: Mathew Wells
Affiliation: Yale University
Position: Associate Research Scientist
Email: mathew.wells@yale.edu
Position: Associate Research Scientist
Phone Number:
Give Talk: no
Poster: no
Title:
Abstract:

Name: Scott Johnson
Affiliation: Massachusetts Institute of Technology
Email: smjohns@mit.edu
Phone Number: 617-258-0846
Give Talk: yes
Poster: yes
Title: Pathologies in Dynamic Soft Sphere Systems
Abstract: Flows of granular material are typically modeled using analytical models or, more recently, molecular dynamics based approaches known as discrete element modeling (DEM) in the literature. For simplicity and efficiency of numerical calculation, it is often desirable to model particle geometry through scaled disc (2D) or sphere (3D) primitives. This short talk will outline some of the micromechanical considerations a modeler must evaluate when deciding on particle geometry to be used, especially when considering fixed radius geometries. It will also detail some pathological phenomena, such as regular packing, excessive rolling, and lack of geometric interlocking, that can arise when using fixed radius geometries.

Name: Klebert Feitosa
Affiliation: University of Massachusetts Amherst
Email: kfeitosa@physics.umass.edu
Phone Number: 413-545-1291
Give Talk:
Poster: yes
Title: Rotation dynamics in a 2D granular gas
Abstract: We perform an experiment to investigate rotational motions in dilute granular media in 2 dimensions. The system is composed of spherical inelastic beads confined to a vertical plane and excited by intense vertical vibrations. We perform full-field tracking of positions and orientations of the beads by fast video imaging. We find that the components of the angular velocity vector are comparable in magnitude and have non-gaussian velocity distributions. However, the rotational and translational degrees of freedom have different �temperatures.?br>

Name: Daniel Blair
Affiliation: Harvard University
Position: postdoc
Email: blair@deas.harvard.edu
Position: postdoc
Phone Number: 617-496-8688
Give Talk: no
Poster: no
Title:
Abstract:

Name: Jerzy Blawzdziewicz
Affiliation: Yale University
Position: Assistant Professor
Email: jerzy.blawzdziewicz@yale.edu
Position: Assistant Professor
Phone Number: 203-432-7754
Give Talk:
Poster:
Title: Dynamics of suspensions in slit-pore geometries
Abstract: The talk will focus on hydrodynamic properties of suspensions confined in thin liquid films and slit pores. We will describe our recently developed Stokesian-dynamics algorithms for evaluating many-particle friction matrix in such systems. One of the algorithms relies on the image representation of the flow reflected from the walls, and the other uses Fourier representation of the reflected flow. Applications of our algorithms to evaluate friction matrix for clusters of particles between two parallel walls and to determine effective diffusion and viscosity coefficients for a suspension-stabilized thin liquid films will be described.

Name: Chris H. Rycroft
Affiliation: Department of Mathematics, MIT
Email: chr@mit.edu
Phone Number: 617-441-0362
Give Talk:
Poster: yes
Title: Toward a Theory of Diffusion in Dense Granular Flows
Abstract: Although diffusion in fast, dilute granular flows may be described by variations of classical kinetic theory, recent experiments suggest that slow, dense flows require a fundamentally different approach, due to long-lasting, many-body contacts. In the case of dense granular drainage, many continuum models have been proposed for the mean flow, but no theory of fluctuations is available. The classical Kinematic Model for the mean flow is based on the concept of diffusing voids, which rise up from an orifice and cause the random downward motion of passive particles. Taking this microscopic picture seriously, we present the first study of single-particle dynamics, including discrete simulations and exact solutions to some new partial differential equations (in the continuum limit). We show that, although the Void Model captures the geometrical dominance of diffusion, it greatly overpredicts the degree of mixing seen in experiments. On the other hand, a new model, based on the concept of diffusing "spots" of free volume causing cooperative diffusion, is consistent with experimental data.

Name: John Wettlaufer
Affiliation: Yale University
Position: Professor
Email: john.wettlaufer@yale.edu
Position: Professor
Phone Number: 432-0892
Give Talk: no
Poster: no
Title:
Abstract:

Name: John A. Perez
Affiliation: Wesleyan University
Email: jperez@wesleyan.edu
Phone Number: 860-685-2035
Give Talk: no
Poster: no
Title:
Abstract:

Name: Dominic Vella
Affiliation: Harvard University
Email: vella@fas.harvard.edu
Phone Number: 617-493-3318
Give Talk: yes
Poster: no
Title: The Elasticity of an Interfacial Particle Raft
Abstract: We study the collective behavior of a close packed monolayer of non-Brownian particles at a fluid-liquid interface. Such a particle raft forms a two-dimensional elastic solid and can support anisotropic stresses and strains, e.g. it buckles in compression and cracks in tension. We characterize the solid in terms of a Young's modulus and Poisson ratio derived from simple theoretical considerations. These predictions are subsequently borne out by measurements of the Young's modulus as inferred from a buckling assay.

Name: Jaehyuk Choi
Affiliation: MIT
Email: jaehyuk@math.mit.edu
Phone Number: 617-869-1397
Give Talk: no
Poster: yes
Title: Diffusion and mixing in gravity-driven dense granular flows
Abstract: We study the transport properties of particles draining from a silo using direct particle tracking. The mean squared displacements of particles only depend on the mean distance fallen, regardless of the flow speed, and show a universal transition from super-diffusion to normal diffusion. The super- diffusive regime is observed before a particle falls its diameter. The displacements have fat-tailed and anisotropic distributions. However, the motion in this regime is always sub-ballistic. In the diffusive regime, we observe mixing and cage breaking occur very slowly with constant P?let numbers of order 100. Overall, our experiments show that diffusion is dominated by geometry, which is consistent with fluctuating contact networks but not thermal collisions, as in normal fluids. Since the rate of mixing is highly over- estimated by the previous microscopic model based on `diffusing voids,'' we also develop a new mathematical model for cooperative diffusion, consistent with all of our data, which predicts spatial velocity correlations also seen in the experiments.

Name: Yevgeny Yurkovetsky
Affiliation: Levich Institute, CCNY
Position: Postdoc
Email: yyurkovetsky@ccny.cuny.edu
Position: Postdoc
Phone Number: 212-650-8219
Give Talk: no
Poster: no
Title:
Abstract:

Name: Ian Morrison
Affiliation: Cabot Corporation
Position: Principal Scientist
Email: ian_morrison@cabot-corp.com
Position: Principal Scientist
Phone Number: 978-670-6950
Give Talk: no
Poster: no
Title:
Abstract:

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Affiliation: test
Position: test
Email: test
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Phone Number: test
Give Talk: no
Poster: no
Title: test
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Name: Greg Voth
Affiliation: Wesleyan
Position: test
Email: em
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Phone Number:
Give Talk: no
Poster: yes
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