CiteULike: dchen's jamming

Shear-induced crystallization in jammed systems

Nathan Duff — 2008-06-11T18:55:11-00:00

Physical Review E (Statistical, Nonlinear, and Soft Matter Physics), Vol. 75, No. 3. (2007)

Simulations are used to address the effects of oscillating shear strain on jammed systems composed of spherical particles. The simulations show that shear oscillations with amplitudes of more than a few percent lead to substantial crystallization of the system. To ensure that the conclusions are independent of the simulation methodology, a range of simulations are carried out that use both molecular dynamics and athermal dynamics methods, soft and hard potentials, potentials with and without attractive forces, and systems with and without surrounding walls. The extent of crystallization is monitored primarily by the Q6 order parameter, but also in some simulations by the potential energy and the radial distribution function, and by direct visual inspection. A mechanism is proposed for shear-induced crystallization of jammed systems, based on fold catastrophes of the free-energy landscape.

Physical age of soft-jammed systems

G Ovarlez — 2008-06-10T23:51:18-00:00

Physical Review E (Statistical, Nonlinear, and Soft Matter Physics), Vol. 76, No. 1. (2007)

We study experimentally the liquid-solid transition in a soft-jammed system and focus on its aging in the solid regime. We investigate the impact of temperature, density, and load changes on the material behavior. We show that all elastic modulus versus time curves fall on a single master curve when rescaled by an appropriate factor function of the density, the temperature, the load, and the time elapsed since preshear. This allows us to distinguish the effect of temperature and density on the mechanical properties and their effect on aging. Since the time evolutions of the elastic modulus under various conditions are similar within a factor, we suggest that the rescaled time reflects the physical age of the material; i.e., it describes the degree of progress of the structural organization relative to a state of reference of the system in the solid regime and constitutes a means for characterizing the effective state of such systems.

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.

Evolving loop structure in gradually tilted two-dimensional granular packings

Ashley Smart — 2008-06-08T23:25:21-00:00

Physical Review E (Statistical, Nonlinear, and Soft Matter Physics), Vol. 77, No. 4. (2008)

Granular packings, especially near the jamming transition, form fragile networks where small perturbations can lead to destabilization and large scale rearrangements. A key stabilizing element in two dimensions is the contact loop, yet surprisingly little is known about contact loop statistics in realistic granular networks. In this paper, we use particle dynamics to study the evolution of contact loop structure in a gradually tilted two-dimensional granular bed. We find that the resulting contact loop distributions (1) are sensitive to material properties, (2) deviate from the expected structure of a randomly wired lattice, and (3) are uniquely dependent on tilting angle. Also, we introduce a quantitative measure of loop stability and show that increased tilting results in a gradual destabilization of individual loops. We briefly discuss the considerations for extending our approach to three dimensions.

Experimental measurement of an effective temperature for jammed granular materials

Chaoming Song — 2008-04-29T00:38:58-00:00

Proceedings of the National Academy of Sciences, Vol. 102, No. 7. (15 February 2005), pp. 2299-2304.

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. 10.1073/pnas.0409911102

Jamming and Fluctuations in Granular Drag

I Albert — 2007-09-27T03:46:04-00:00

Physical Review Letters, Vol. 84, No. 22. (29 May 2000), 5122.

We investigate the dynamic evolution of jamming in granular media through fluctuations in the granular drag force. The successive collapse and formation of jammed states give a stick-slip nature to the fluctuations which is independent of the contact surface between the grains and the dragged object; thus implying that the stress-induced collapse is nucleated in the bulk of the granular sample. We also find that while the fluctuations are periodic at small depths; they become “stepped” at large depths; a transition which we interpret as a consequence of the long-range nature of the force chains.

Jamming of Granular Flow in a Two-Dimensional Hopper

Kiwing To — 2007-09-27T03:12:29-00:00

Physical Review Letters, Vol. 86, No. 1. (1 January 2001), 71.

We study experimentally the jamming phenomenon of granular flow of monodisperse disks of D = 5 mm diameter in a two-dimensional hopper with opening R . The jamming probability J ( d ) is measured where d ≡ R / D . We found that J ( d ) decreases from 1 to zero when d increases from 2 to 5. From observing the disk configurations of the arch in the jamming events; the jamming probability can be explained quantitatively by treating the arch as the trajectory of a restricted random walker.

Granular matter A tale of tails

Martin van Hecke — 2005-06-23T02:21:28-00:00

Nature, Vol. 435, No. 7045. (22 June 2005), pp. 1041-1042.

Structural signature of jamming in granular media

Eric Corwin — 2005-06-23T02:21:24-00:00

Nature, Vol. 435, No. 7045., pp. 1075-1078.

Jamming at zero temperature and zero applied stress: The epitome of disorder

Corey O’hern — 2007-09-21T04:00:05-00:00

Physical Review E, Vol. 68, No. 1. (25 July 2003), 011306.

We have studied how two- and three-dimensional systems made up of particles interacting with finite range; repulsive potentials jam (i.e.; develop a yield stress in a disordered state) at zero temperature and zero applied stress. At low packing fractions φ; the system is not jammed and each particle can move without impediment from its neighbors. For each configuration; there is a unique jamming threshold φ c at which particles can no longer avoid each other; and the bulk and shear moduli simultaneously become nonzero. The distribution of φ c values becomes narrower as the system size increases; so that essentially all configurations jam at the same packing fraction in the thermodynamic limit. This packing fraction corresponds to the previously measured value for random close packing. In fact; our results provide a well-defined meaning for “random close packing” in terms of the fraction of all phase space with inherent structures that jam. The jamming threshold; point J ; occurring at zero temperature and applied stress and at the random-close-packing density; has properties reminiscent of an ordinary critical point. As point J is approached from higher packing fractions; power-law scaling is found for the divergence of the first peak in the pair correlation function and in the vanishing of the pressure; shear modulus; and excess number of overlapping neighbors. Moreover; near point J ; certain quantities no longer self-average; suggesting the existence of a length scale that diverges at J . However; point J also differs from an ordinary critical point: the scaling exponents do not depend on dimension but do depend on the interparticle potential. Finally; as point J is approached from high packing fractions; the density of vibrational states develops a large excess of low-frequency modes. Indeed; at point J ; the density of states is a constant all the way down to zero frequency. All of these results suggest that point J is a point of maximal disorder and may control behavior in its vicinity—perhaps even at the glass transition.

Nonlinear dynamics: Jamming is not just cool any more

Andrea Liu — 2007-05-18T10:34:26-00:00

Nature, Vol. 396, No. 6706. (5 November 1998), pp. 21-22.

Jamming at zero temperature and zero applied stress: the epitome of disorder.

CS O'Hern — 2008-04-26T22:26:44-00:00

Physical review. E, Statistical, nonlinear, and soft matter physics, Vol. 68, No. 1 Pt 1. (July 2003)

We have studied how two- and three-dimensional systems made up of particles interacting with finite range, repulsive potentials jam (i.e., develop a yield stress in a disordered state) at zero temperature and zero applied stress. At low packing fractions phi, the system is not jammed and each particle can move without impediment from its neighbors. For each configuration, there is a unique jamming threshold phi(c) at which particles can no longer avoid each other, and the bulk and shear moduli simultaneously become nonzero. The distribution of phi(c) values becomes narrower as the system size increases, so that essentially all configurations jam at the same packing fraction in the thermodynamic limit. This packing fraction corresponds to the previously measured value for random close packing. In fact, our results provide a well-defined meaning for "random close packing" in terms of the fraction of all phase space with inherent structures that jam. The jamming threshold, point J, occurring at zero temperature and applied stress and at the random-close-packing density, has properties reminiscent of an ordinary critical point. As point J is approached from higher packing fractions, power-law scaling is found for the divergence of the first peak in the pair correlation function and in the vanishing of the pressure, shear modulus, and excess number of overlapping neighbors. Moreover, near point J, certain quantities no longer self-average, suggesting the existence of a length scale that diverges at J. However, point J also differs from an ordinary critical point: the scaling exponents do not depend on dimension but do depend on the interparticle potential. Finally, as point J is approached from high packing fractions, the density of vibrational states develops a large excess of low-frequency modes. Indeed, at point J, the density of states is a constant all the way down to zero frequency. All of these results suggest that point J is a point of maximal disorder and may control behavior in its vicinity-perhaps even at the glass transition.

Jamming, Force Chains, and Fragile Matter

ME Cates — 2008-04-26T21:58:44-00:00

Physical Review Letters, Vol. 81, No. 9. (1998), 1841.

Improving the Density of Jammed Disordered Packings Using Ellipsoids

Aleksandar Donev — 2008-04-24T18:23:40-00:00

Science, Vol. 303, No. 5660. (13 February 2004), pp. 990-993.

Packing problems, such as how densely objects can fill a volume, are among the most ancient and persistent problems in mathematics and science. For equal spheres, it has only recently been proved that the face-centered cubic lattice has the highest possible packing fraction [IMG]f1.gif" BORDER="0">. It is also well known that certain random (amorphous) jammed packings have varphi approx 0.64. Here, we show experimentally and with a new simulation algorithm that ellipsoids can randomly pack more densely--up to varphi= 0.68 to 0.71for spheroids with an aspect ratio close to that of M&M's Candies--and even approach varphi approx 0.74 for ellipsoids with other aspect ratios. We suggest that the higher density is directly related to the higher number of degrees of freedom per particle and thus the larger number of particle contacts required to mechanically stabilize the packing. We measured the number of contacts per particle Z approx 10 for our spheroids, as compared to Z approx 6 for spheres. Our results have implications for a broad range of scientific disciplines, including the properties of granular media and ceramics, glass formation, and discrete geometry. 10.1126/science.1093010

Jamming as a Critical Phenomenon: A Field Theory of Zero-Temperature Grain Packings

Silke Henkes — 2008-03-24T21:59:24-00:00

Physical Review Letters, Vol. 95, No. 19. (2005)

A field theory of frictionless grain packings in two dimensions is shown to exhibit a zero-temperature critical point at a nonzero value of the packing fraction. The zero-temperature constraint of force balance plays a crucial role in determining the nature of the transition. Two order parameters, z, the deviation of the average number of contacts from the isostatic value, and , the average magnitude of the force per contact, characterize the transition from the jammed (high packing fraction) to the unjammed (low packing fraction state). The critical point has a mixed character with the order parameters showing a jump discontinuity but with fluctuations of the contact force diverging. At the critical point, the distribution of shows the characteristic plateau observed in static granular piles. The theory makes falsifiable predictions about the spatial fluctuations of the contact forces.

Effective Temperatures of a Driven System Near Jamming

Ian Ono — 2007-09-22T19:05:42-00:00

Physical Review Letters, Vol. 89, No. 9. (2002), 095703.

Fluctuations in a model of a sheared; zero-temperature foam are studied numerically. Five different quantities that independently reduce to the true temperature in an equilibrium thermal system are calculated. One of the quantities is calculated up to an unknown coefficient. The other four quantities have the same value and all five have the same shear-rate dependence. These results imply that statistical mechanics is useful for the system even though it is far from thermal equilibrium.

Multiscaling at Point J: Jamming is a Critical Phenomenon

JA Drocco — 2007-08-21T21:39:30-00:00

Physical Review Letters, Vol. 95, No. 8. (2005)

We analyze the jamming transition that occurs as a function of increasing packing density in a disordered two-dimensional assembly of disks at zero temperature for “Point J” of the recently proposed jamming phase diagram. We measure the total number of moving disks and the transverse length of the moving region, and find a power law divergence as the packing density increases toward a critical jamming density. This provides evidence that the $T=0$ jamming transition as a function of packing density is a second order phase transition. Additionally, we find evidence for multiscaling, indicating the importance of long tails in the velocity fluctuations.

Vibrations and Diverging Length Scales Near the Unjamming Transition

Leonardo Silbert — 2008-03-24T21:51:42-00:00

Physical Review Letters, Vol. 95, No. 9. (2005)

We numerically study the vibrations of jammed packings of particles interacting with finite-range, repulsive potentials at zero temperature. As the packing fraction is lowered towards the onset of unjamming at c, the density of vibrational states approaches a nonzero value in the limit of zero frequency. For >c, there is a crossover frequency, * below which the density of states drops towards zero. This crossover frequency obeys power-law scaling with -c. Characteristic length scales, determined from the dominant wave vector contributing to the eigenmode at *, diverge as power laws at the unjamming transition.

Force Distributions near Jamming and Glass Transitions

Corey O'Hern — 2007-05-18T10:36:37-00:00

Physical Review Letters, Vol. 86, No. 1. (1 January 2001), 111.

We calculate the distribution of interparticle normal forces P ( F ) near the glass and jamming transitions in model supercooled liquids and foams; respectively. P ( F ) develops a peak that appears near the glass or jamming transitions; whose height increases with decreasing temperature; decreasing shear stress and increasing packing density. A similar shape of P ( F ) was observed in experiments on static granular packings. We propose that the appearance of this peak signals the development of a yield stress. The sensitivity of the peak to temperature; shear stress; and density lends credence to the recently proposed generalized jamming phase diagram.

Jamming Transition in Granular Systems

TS Majmudar — 2007-12-31T21:59:04-00:00

Physical Review Letters, Vol. 98, No. 5. (2007)

Recent simulations have predicted that near jamming for collections of spherical particles, there will be a discontinuous increase in the mean contact number Z at a critical volume fraction c. Above c, Z and the pressure P are predicted to increase as power laws in -c. In experiments using photoelastic disks we corroborate a rapid increase in Z at c and power-law behavior above c for Z and P. Specifically we find a power-law increase as a function of -c for Z-Zc with an exponent around 0.5, and for P with an exponent around 1.1. These exponents are in good agreement with simulations. We also find reasonable agreement with a recent mean-field theory for frictionless particles.

Granular Fingers on Jammed Systems: New Fluidlike Patterns Arising in Grain-Grain Invasion Experiments

SF Pinto — 2008-03-18T21:05:19-00:00

Physical Review Letters, Vol. 99, No. 6. (2007)

In this Letter we report spontaneous pattern formation in dense granular assemblies confined to a Hele-Shaw cell and quasistatic regime. Varied unexpected patterns, ranging from rounded to fingered, are observed due to the displacement of one granular material by another. Computer simulations reproduce the major features observed in these experiments. Two mechanisms are responsible for the pattern formation: crystallization of the injected grains and plastic deformation of the displaced grains. The experiment suggests analogies with viscous fingering and jamming transition experiments.

Critical Scaling of Shear Viscosity at the Jamming Transition

Peter Olsson — 2008-01-06T13:09:05-00:00

Physical Review Letters, Vol. 99, No. 17. (2007)

We carry out numerical simulations to study transport behavior about the jamming transition of a model granular material in two dimensions at zero temperature. Shear viscosity is computed as a function of particle volume density and applied shear stress , for diffusively moving particles with a soft core interaction. We find an excellent scaling collapse of our data as a function of the scaling variable /|c-|, where c is the critical density at =0 (“point J”), and is the crossover scaling critical exponent. We define a correlation length from velocity correlations in the driven steady state and show that it diverges at point J. Our results support the assertion that jamming is a true second-order critical phenomenon.

Jamming Transition and New Percolation Universality Classes in Particulate Systems with Attraction

Gregg Lois — 2008-03-18T01:13:55-00:00

Physical Review Letters, Vol. 100, No. 2. (2008)

We numerically study the jamming transition in particulate systems with attraction by investigating their mechanical response at zero temperature (T=0). We find three regimes of mechanical behavior separated by two critical transitions—connectivity and rigidity percolation. The transitions belong to different universality classes than their lattice counterparts, due to force balance constraints. We also find that these transitions are unchanged at low temperatures and resemble gelation transitions in experiments on colloidal and silica gels.