Name: Greg Voth
Affiliation: Wesleyan University
Position: Assistant Professor
Email: gvoth@wesleyan.edu
PhoneNumber: 860 685 2035
talk: no
poster: no
Title:
Name: Corey S. O'Hern
Affiliation: Yale University
Position: Professor
Email: corey.ohern@yale.edu
PhoneNumber: 203-432-4258
talk: yes
poster: no
Title: Velocity Profiles in Sheared Athermal Systems
We discuss our recent molecular dynamics simulations of model granular materials undergoing boundary-driven planar shear flow in 2D aimed at obtaining a more complete understanding of velocity profiles in dense granular systems. Thus far, we have focused primarily on simple models that include damping forces but do not include gravity or frictional forces. Even in these simplified systems, we find several interesting and novel results. First, nonlinear velocity profiles quickly form when these systems are sheared, but they slowly evolve into linear profiles on a time scale that increases with shear rate and decreases with increasing damping. Second, nonlinear velocity profiles can be stabilized in these systems if a sufficiently large granular temperature gradient is maintained, for example by vibrating one of the boundaries during the shear flow. Furthermore, if the shear stress of the flowing part of the system is less than the yield stress, highly localized nonlinear velocity profiles will form. These new simulation results will also be compared to recent experimental studies of shear banding in granular materials.
Name: Douglas Durian
Affiliation: University of Pennsylvania
Position: Professor, Dept. of Physics & Astronomy
Email: djdurian@physics.upenn.edu
PhoneNumber: 215-898-8147
talk:
poster:
Title: Impact cratering in loose granular media
In this talk I shall describe the penetration of projectiles into granular media, and how the results vary with the properties of both the projectile and the medium. In contrast to wide assumption, the penetration depth and crater diameter represent two distinct length scales. The diameter scales as the 1/4 power of projectile energy, but curiously the depth is not a simple function of either the projectile energy or momentum at impact. Rather, it scales as the 1/2 power of density, the 2/3 power of projectile diameter, and the 1/3 power of total drop distance. This same result also holds for cylinders with a variety of tips, and so is not an accident of projectile shape. It is crucial to understand the penetration depth because it is directly related to the mechanics of impact, namely the average stopping force acting between projectile and medium. In addition to this discussion, I shall also present new data on the dynamics of impact. All experiments were constructed and carried out at UCLA by undergraduate physics majors: Jun Uehara, Katie Newhall, Chris Santore, and Mike Ambroso.
[1] J. S. Uehara, M. A. Ambroso, R. P. Ojha, and D. J. Durian, "Low-Speed Impact Craters in Loose Granular Media", Physical Review Letters 90, 194301 (2003). [2] K. A. Newhall and D. J. Durian, "Projectile-shape dependence of impact craters in loose granular media", Physical Review E 68, 060301/1-3 (2003). [3] M. A. Ambroso, C. R. Santore, A. R. Abate, and D. J. Durian, "Penetration depth for shallow impact cratering", cond-mat/0411231. [4] M. A. Ambroso and D. J. Durian, "Dynamics of low-speed impact cratering", cond-mat/0503454.
Name: Alexander Lobkovsky
Affiliation: MIT
Position: Post Doc
Email: leapfrog@mit.edu
PhoneNumber: 617-324-6712
talk:
poster:
Title: Wet granular flow in a channel.
Although much progress has been made, a comprehensive framework for understanding granular flow has not yet emerged. Successful specific models have to be constructed to describe specific situations. How the granular material is driven, the boundary conditions, the prior deformation history, precise nature of the contacts all seem to be important. I will briefly review the state of the art in experiments and theory of dry surface granular flow and the launch into our own investigation of surface granular flow driven by water. The main result of our investigation so far is an effective evolution equation for channel transects. It has a form on a Burgers equation with a non-local driving term.
<p> <img align="middle" src="http://segovia.mit.edu/~leapfrog/Images/03oct31a_channel.jpg">
Name: Seth Fraden
Affiliation: Brandeis University
Position: Professor
Email: fraden@brandeis.edu
PhoneNumber: 781-736-2888
talk:
poster:
Title: From Viruses to Vertically Vibrated Rods: The Effect of Shape on
Order.
Onsager, in the 1940's, realized that Tobacco Mosaic Virus was a model experimental system for the study of phase transitions in liquid crystals. We are examining the relevance of concepts such as phases and phase transitions, which make sense in the context of equilibrium statistical mechanics, to rod-like granular materials, which are systems where equilibrium statistical mechanics does not apply. There are, however, two major obstacles to adopting a thermodynamic approach for the description of these systems. First, granular materials dissipate energy through inelastic collisions and energy has to be supplied externally in order to maintain a steady state. Secondly, the external driving forces are non-thermal. Thermal energy is small compared to other energy contributions such as gravitational potential energy or the work done by shearing forces and, therefore these systems live virtually at zero temperature. In spite of the intrinsically non-equilibrium nature of granular systems there recently has been published several experimental studies, as well as several experimental observations of our own, that strongly suggest that something akin to a phase transition is occurring in granular rods. This is in contrast to the case of vertically vibrated granular spheres where ordering is always associated with a coupling between dynamics and dissipation.
Name: Chaoming Song
Affiliation: Levich institute of CCNY
Position: phd
Email: song@levdec.engr.ccny.cuny.edu
PhoneNumber: 212-650-8871
talk: yes
poster: no
Title: Experimental measurement of an effective temperature for jammed
granular materials
A densely packed granular system is an example of an out-of-equilibrium system in the jammed state. It has been a longstanding problem to determine whether this class of systems can be described by concepts arising from equilibrium statistical mechanics, such as an effective temperature and compactivity. The measurement of the effective temperature is realized in the laboratory by slowly shearing a closely packed ensemble of spherical beads confined by an external pressure in a Couette geometry. All of the probe particles considered in this study, independent of their characteristic features, equilibrate at the same temperature, given by the packing density of the system.
Name: Ping Wang
Affiliation: Levich Institute and Physicas Department of City College of
New York
Position: PH.D
Email: anyon_wang@yahoo.com
PhoneNumber: 1-212-650-8871
talk: yes
poster:
Title: The effective temperature of a colloidal glass
A dense colloidal suspension above the glass transition is an example of an out-of-equilibrium system in the jammed state. It has been a longstanding problem to determine whether this class of systems can be described by concepts arising from equilibrium statistical mechanics, such as an effective temperature. Here we study the motion of magnetic tracers in a dense aging colloidal suspension and measure an effective temperature by adding a very gentle magnetic force on the tracers and following their trajectories. At long time scale, both the diffusivity and mobility of the tracers decrease with the waiting time, but give rise to a constant effective temperature which is higher than the bath temperature.
Name: Joshua Bloustine
Affiliation: Brandeis University Physics Department
Position: PhD. Student
Email: bloustine@brandeis.edu
PhoneNumber: 7817362877
talk: yes
poster:
Title: On the coordination of granular rods and granular gelation
A. Philipse (Langmuir (1996)) first noticed that piles of granular rods of sufficiently high aspect ratio form solid-like plugs which we term granular gelation. In this work Philipse also presented a mean field excluded volume method to describe piles of granular rods. We investigate two questions raised by Philipse's work concerning piles of granular rods: 1. Does the random contact model correctly describe the coordination of granular rods in a pile? 2. Why do piles of granular rods of sufficiently high enough aspect ratio gel?
In order to address both these questions we used Bernal & Mason's (Nature 1960) method to measure the number of touching neighbors, or coordination, of rods in a pile as a function of rod aspect ratio and pile density. We also measure the critical aspect ratio for granular gelation. We find no clear signature of gelation in the coordination of rods and so the origin of gelation remains unknown. We find that the average number of neighbors increases as the rod aspect ratio increases and demonstrate the role of the boundary layer on rod coordination. From these coordination experiments we conclude that Philipse's random contact model approximately correctly predicts the relation between the macroscopic density of a pile and the coordination of rods in the pile.
Name: Bulbul Chakraborty
Affiliation: Brandeis University
Position: Professor
Email: bulbul@brandeis.edu
PhoneNumber: 508-259-8560
talk: no
poster: no
Title:
Name: fenistein Denis
Affiliation: levich institute New york
Position: post doc
Email: fenistein@levdec.engr.ccny.cuny.edu
PhoneNumber: 212 650 8219
talk: no
poster: yes
Title: Wide and universal shear zones in granular materials
Denis Fenistein1,2, Martin van Hecke1
1 Kamerlingh Onnes Laboratory Leiden university, The netherlands 2 Present address: Levich institute, New york, USA.
We present experiments in which wide and universal shear zones are created in the bulk of granular material (Fenistein & van Hecke, Nature 425, 256 2003). The modification of a Couette cell whose bottom is split at a given radius allows the observation of bulk shear zones that strongly contrat the usual picture of granular matter flow where narrow particle-dependent shear bands are localized at a boundary. We focuss on the description of the universal Gaussian strain rate profiles. The position and width of the shear zones appear to be uncorrelated and can be tuned by the experimental geometry and the particle properties.
Name: Chris Rycroft
Affiliation: Department of Mathematics, MIT
Position: Graduate Student
Email: chr@mit.edu
PhoneNumber: 6174410362
talk: yes
poster: no
Title: Dynamics of Random Packings in Granular Flow
How do random packings flow? Dilute ``packings'' (gases) flow by the accumulated effect of independent, random collisions. Dense, ordered packings (crystals) flow collectively via the motion of defects, such as vacancies, interstitials, and dislocations. Similarly, existing theories of the dense, disordered packings in granular drainage are based on either gas-like inelastic collisions or crystal-like void diffusion, but experiments show that a fundamentally different approach is needed. Here, we propose that dense random packings flow co-operatively in response to diffusing ``spots'' of free volume. The Spot Model is very simple to simulate and may be analyzed in the continuum limit (via a non-local stochastic differential equation). With only a few fitting parameters, it predicts the mean flow, spatial velocity correlations, cage breaking, diffusion, and packing structure, in good agreement with experiments and molecular dynamics simulations. The results suggest that flowing random packings have universal structural features.
Name: Silke Henkes
Affiliation: Brandeis University
Position: Graduate student
Email: shenkes@brandeis.edu
PhoneNumber:
talk: yes
poster: no
Title: Jamming as a critical phenomenon: a field theory of
zero-temperature grain packings
In a remarkably diverse range of systems, the transition from a flowing, liquid state to a jammed, solid state is heralded by a dramatic slowing down of relaxations. Does an equilibrium critical point underlie this glassy dynamics? Experiments on weakly sheared granular media indicate that at a critical packing fraction there is a transition accompanied by slow dynamics, vanishing of mean stress, increasing stress fluctuations and a change in the distribution of contact forces. Simulations indicate a critical point occurring at zero temperature and a packing fraction close to the random close packing value. At this critical point the grain packing is isostatic, having reached the special coordination where all contact forces are completely determined by the packing geometry. In this talk, I will demonstrate that a statistical field theory of two-dimensional, zero-temperature, frictionless grain packings exhibits a critical point. This point separates a disordered phase from an ordered one characterized by two order parameters: (i) the magnitude of the force per contact, $<\phi>$, and (ii) $<z>$, the deviation of the contact number per grain from its isostatic value. At the critical point, the fluctuations around $<\phi>$, diverge but those around $<z>$ go to zero. An analytic prediction for P (F), the distribution of contact forces, is in excellent agreement with experiments, and the theory makes falsifiable predictions regarding the spatial correlations of the forces.
Name: Francis Starr
Affiliation: Wesleyan University
Position: Professor
Email: fstarr@wesleyan.edu
PhoneNumber: 860-346-6998
talk: yes
poster: no
Title: What can the physics of the glass transition contribute to the
understanding of granular materials?
The glass transition is one of the longest studied problems in condensed matter physics. As a result, a wide range of approaches have been developed to understand the behavior of liquids as they are cooled toward the glass transition. In this talk, I will briefly discuss some of the canonical features of glass-forming liquids and the approaches used to understand those features. I will pay special attention to thermodynamical and energy landscape ideas that have gained recent attention in granular materials.
Name: Ken Kamrin
Affiliation: MIT
Position: PhD student
Email: kenman@mit.edi
PhoneNumber: 9258995775
talk: yes
poster: no
Title: Evaluation and Comparison of Continuum Models for Dense Granular
Flow
Which dense flow model is the best for which problems? Currently, there exist several known models for predicting steady-state velocity distributions in hopper or silo flow. This work offers a detailed comparison of the common dense flow models. Mohr-Coulomb Plasticity, Hourglass Theory, and the Kinematic Model are applied within a narrow wedge hopper geometry, and the predicted flow is closely compared with experimental velocity profiles for glass beads in quasi-two-dimensional flows. Due consideration is also made for the ease-of-use and restrictions of each model. We also evaluate the microscopic physical justifications for each model. This segues into a new approach for quasi-2-D flow, so called Stochastic Plasticity, which reconciles the theoretical differences between Mohr-Coulomb Plasticity and the Kinematic Model by solely mechanical means. It also offers a formula for the Kinematic b parameter which before had only been defined empirically.
Name: Ashish V. Orpe
Affiliation: Clark University
Position: Post-doctoral Research Associate
Email: avorpe@physics.clarku.edu
PhoneNumber: 508-793-7707
talk: yes
poster:
Title: Experiments on shear of thin granular layers
We will discuss a study of the friction encountered by a mass sliding on a granular layer as a function of bed thickness and boundary conditions. Such a situation is important in a variety of contexts such as walking on sand, braking on a pebble strewn road, and jamming of joints in a dusty environment. The measured friction coefficient shows a minimum for a small number of layers before increasing and saturating for deep beds. Higher friction is encountered for geometrically rough boundary conditions. Similar magnitudes of friction and layer dependence are found when the entire system is immersed in a liquid, provided that the shear rates are small. Therefore, we exploit a fluorescent index-matching imaging technique to measure the velocity profiles of the grains inside the bed. We propose that the observed friction behavior depends on the degree of grain confinement relative to the sliding surfaces.
- Ashish V. Orpe, Salome Siavoshi and Arshad Kudrolli
Name: Shubha Tewari
Affiliation: Mount Holyoke College
Position: Visiting Assistant Professor
Email: stewari@mtholyoke.edu
PhoneNumber: 413 538 2816
talk: no
poster: no
Title:
Name: Braunen Smith
Affiliation: Clark University
Position: Graduate Student
Email: braunen@physics.clarku.edu
PhoneNumber:
talk: no
poster: no
Title:
Name: Ning Xu
Affiliation: Yale University
Position: graduate student
Email: ning.xu@yale.edu
PhoneNumber: 203-432-8249
talk: no
poster: yes
Title: Random close packing revisited: Ways to pack frictionless disks
We create collectively jammed (CJ) packings of $50$-$50$ bidisperse mixtures of smooth disks in 2d using an algorithm in which we successively compress or expand soft particles and minimize the total energy at each step until the particles are just at contact. We focus on small systems in 2d and thus are able to find nearly all of the collectively jammed states at each system size. We decompose the probability $P(\phi)$ for obtaining a collectively jammed state at a particular packing fraction $\phi$ into two composite functions: 1) the density of CJ packing fractions $\rho(\phi)$, which only depends on geometry and 2) the frequency distribution $\basinAv(\phi)$, which depends on the particular algorithm used to create them. We find that the function $\rho(\phi)$ is sharply peaked and that $\basinAv(\phi)$ depends exponentially on $\phi$. We predict that in the infinite system-size limit the behavior of $P(\phi)$ in these systems is controlled by the density of CJ packing fractions---not the frequency distribution. These results suggest that the location of the peak in $P(\phi)$ when $N \rightarrow \infty$ can be used as a protocol-independent definition of random close packing.
Name: Rohit Ingale
Affiliation: Levich Institute, CUNY
Position: Research Assistant
Email: rohitingale@rediffmail.com
PhoneNumber: 917-892-2190
talk: no
poster: no
Title:
Name: PALACCI Jeremie
Affiliation: Martin Bazant Math Applied Lab MIT
Position: Undergraduate/Summer internship
Email: jpalacci@ens-lyon.fr
PhoneNumber: 33683871853
talk: no
poster: no
Title:
Name: Guo-Jie Gao
Affiliation: Yale University
Position: Grad student
Email: guo-jie.gao@yale.edu
PhoneNumber: 203-4328249
talk: no
poster: yes
Title: Measuring the frequency distribution of collectively jammed states
We study collectively jammed (CJ) states in 2D systems composed N/2 large and N/2 small frictionless disks with diameter ratio d=1.4. To create collectively jammed states, we repeatedly swell and shrink the disks and then allow the particles to interact via purely repulsive linear spring forces and viscous damping forces until all of the particles are in contact and at rest. We focus on small systems; we are therefore able to generate nearly all of the collectively jammed states and to decompose the probability distribution $P(\phi)$ of finding a CJ state at packing fraction $\phi$ into the density of CJ volume fractions and the frequency with which each CJ volume fraction occurs. We calculate the frequency distribution as a function of the thermal quench rate and comment on how changes in the frequency distribution influence $P(\phi)$ in the large system limit.
Name: Nalini Easwar
Affiliation: Smith College
Position: Professor
Email: neaswar@smith.edu
PhoneNumber: 4135853887
talk:
poster: yes
Title: Crossover from Collisional to Frictional Regime in 3D granular
flow.
Name: Donald Candela
Affiliation: University of Massachusetts, Amherst
Position: Professor
Email: candela@physics.umass.edu
PhoneNumber: 413-545-3666
talk: no
poster: yes
Title: NMR Measurements of Grain Motion in a Gas-Fluidized Granular Bed
The fluctuating motions of grains in a gas-fluidized granular bed were measured using NMR. The granular bed was 10.1 mm in diameter and 16 cm deep and consisted of porous alumina grains of diameter 75-105 micrometers to which a small amount of dodecane was adsorbed to provide NMR sensitivity. The bed was fluidized by nitrogen gas flowing through a porous glass distributor at the bottom. We have systematically varied the gas flow rate, the height in the bed at which NMR data is acquired, and the time interval over which NMR displacements are measured. The bed density as a function of gas flow rate is hysteretic, and over the "uniformly fluidized" flow range for which the density is multivalued the NMR data show that no grain motion occurs. The distribution of vertical grain displacements was measured as a function of height in the bed, for a gas flow rate above the onset of bubbling. The evolution from small bubbles near the bottom of the bed to slugging motion near the top of the bed is clearly visible in the displacement distributions. Finally, the RMS grain displacements were measured as a function of displacement time both with and without velocity compensation. By comparing these two types of data diffusive and convective motions of the granular medium can be distinguished. This work was supported by NSF Grant 0310006.
Name: Chao Huan
Affiliation: University of Massachusetts, Amherst
Position: Graduate Student
Email: huan@physics.umass.edu
PhoneNumber: 413-545-9448
talk: no
poster: no
Title:
Name: Lynn Daniels
Affiliation: Doug Durian - University of Pennsylvania
Position: graduate student
Email: ldaniels@sas.upenn.edu
PhoneNumber: 7243662591
talk: no
poster: no
Title:
Name: Adam Roth
Affiliation: University of Pennsylvania
Position: Undergraduate
Email: aeroth@sas.upenn.edu
PhoneNumber: 215-898-5425
talk: no
poster: no
Title:
Name: Arshad Kudrolli
Affiliation: Clark University
Position: Faculty
Email: akudrolli@clarku.edu
PhoneNumber: 5087937752
talk: no
poster: no
Title:
Name: Klebert Feitosa
Affiliation: University of Pennsylvania
Position: Post-doctoral Research Assistant
Email: klebert@physics.upenn.edu
PhoneNumber: 215-746-2271
talk:
poster: yes
Title: Transport of gas in steady state aqueous foams
An experiment is performed to investigate the transport of gas in a column of aqueous foam. The foam is maintained in steady state by a constant flux of gas at the bottom. The bubble velocity, liquid-fraction and bubble-size profiles are measured vertically in the sample. The results show that in steady state the the bubble velocity is constant, the liquid is held in place by viscous drag, and the coarsening rate depends on the inverse of the square root of liquid fraction. These findings provide a simple description of steady state foams via the drainage and coarsening equations.
Name: Kevin Facto
Affiliation: University of Massachusetts-Amherst
Position: Grad student
Email: kfacto@physics.umass.edu
PhoneNumber: (413) 545-9448
talk: no
poster: no
Title:
Name: HONGQIANG WANG
Affiliation: University of Massachusetts, Amherst
Position: Graduate Student
Email: hqwang@physics.umass.edu
PhoneNumber: 4135450489
talk: no
poster: no
Title:
Name: Xiangdong Gu
Affiliation: University of Massachusetts, Amherst
Position: Graduate Student
Email: xdgu@physics.umass.edu
PhoneNumber: 4135450489
talk: no
poster: no
Title:
Name: Narayanan Menon
Affiliation: University of Massachusetts
Position:
Email: menon@physics.umass.edu
PhoneNumber: 413 545 0852
talk: no
poster: no
Title:
Name: Qing Xu
Affiliation: Clark University
Position: Graduate student
Email: qixu@clarku.edu
PhoneNumber: 508-793-7338
talk: no
poster: yes
Title: Dynamic angle of inclination of wet and cohesive granular matter
We will discuss a study of the surface profile of glass beads mixed with a small amount of liquid using a horizontally rotated drum apparatus. A wide drum is used to minimize boundary effects, and the surface angles are measured by taking and processing digital images. Here, we focus on the influence of the amount and viscosity of the liquid on the dynamic angle of the surface in the continuous flow regime. We will discuss the influence of the amount and viscosity of the liquid on the shape of the surface and the scaling of the surface angle as a function of rotation rate.
Name: Vijay Narayan
Affiliation: Indian Institute of Science
Position: Graduate Student
Email: vj@physics.iisc.ernet.in
PhoneNumber: 413-545-4961
talk: no
poster: yes
Title: Nonequilibrium liquid crystal phases in a vertically vibrated
monolayer of rods
We present experimental results on the nonequilibrium phase diagram and dynamics of a vertically vibrated monolayer of rodlike particles (diameter d from 0.5 to 1 mm) lying horizontally in a quasi-2d cell of height < 2d. With increasing area fraction, rods with aspect ratio ~12 form nematics. Particles with aspect ratio ~5 form striped phases instead. While these results agree with thermal equilibrium simulations [Bates and Frenkel, (2000), Lagomarsino et al. (2003), Khandkar and Barma (unpublished)], some clear nonequilibrium signatures are observed, including global, systematic rotation of the ordered phase in response to weak asymmetries in the sample cell. To find nematics and smectics it was crucial to taper the tips of the rods, without which only tetratic correlations were seen. We will present comparisons with the theory of active nematics [EPL 62 (2003) 196-202], and discuss the possibility of long-ranged nematic and quasi-long-ranged smectic order in these nonequilibrium 2d systems.
Name: Adam Abate
Affiliation: U. Penn Durian Group
Position: Grad Student
Email: aabate@physics.upenn.edu
PhoneNumber: 310.920.2731
talk: yes
poster: no
Title: The partition of energy for air-fluidized grains
The dynamics of one and two identical spheres rolling in a nearly-levitating upflow of air obey the Langevin Equation and the Fluctuation-Dissipation Relation [Ojha et al. Nature 427, 521 (2004) and Phys. Rev. E 71, 01631 (2005)]. To probe the range of validity of this statistical mechanical description, we perturb the original experiments in four ways. First, we break the circular symmetry of the confining potential by using a stadium-shaped trap, and find that the velocity distributions remain circularly symmetric. Second, we fluidize multiple spheres of different density, and find that all have the same effective temperature. Third, we fluidize two spheres of different size, and find that the thermal analogy progressively fails according to the size ratio. Fourth, we fluidize individual grains of aspherical shape, and find that the applicability of statistical mechanics depends on whether or not the grain chatters along its length, in the direction of airflow.
Name: Doug Rubin
Affiliation: Wesleyan University
Position: student
Email: dsrubin@wesleyan.edu
PhoneNumber:
talk: no
poster: no
Title:
Name: Joshua Kalb
Affiliation: Brandeis University
Position: Graduate Student
Email: ringwrld@brandeis.edu
PhoneNumber: 617-497-2598
talk: no
poster: yes
Title: 1-D Inelastic Gas Statistics
Name: John Perez
Affiliation: Wesleyan University
Position: Grad Student
Email: jperez@wesleyan.edu
PhoneNumber: 860-685-2018
talk: no
poster: no
Title:
