Bulletin of the American Physical Society
APS March Meeting 2013
Volume 58, Number 1
Monday–Friday, March 18–22, 2013; Baltimore, Maryland
Session W29: Straight-Up Jamming |
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Sponsoring Units: GSNP Chair: Scott Franklin, Rochester Institute of Technology Room: 337 |
Thursday, March 21, 2013 2:30PM - 2:42PM |
W29.00001: Dynamical Heterogeneity in a Granular System Near the Jamming Transition Karina E. Avila, Annette Zippelius, Horacio E. Castillo We investigate dynamical heterogeneity in event driven simulations of a two-dimensional bidisperse granular fluid. We study the dynamic susceptibility $\chi_4(t)$ extracted from two different correlation functions $Q(t)$ and estimate the dynamic correlation length $\xi(t)$ obtained from the four-point structure factor $S_4(q,\tau_4)$, where $\tau_4$ is the time corresponding to the maximum of $\chi_4(t)$. We find that the dynamic correlation length grows as the volume fraction is increased to approach the jamming transition. [Preview Abstract] |
Thursday, March 21, 2013 2:42PM - 2:54PM |
W29.00002: Jamming in Emulsions and Elastic Tomography Rodrigo Guerra, David Weitz Attempting to bridge the gap between the jamming of soft, athermal particles and soft colloids, we measure the elasticity of packings of $\sim 10\mu m$ droplets using light scattering and tomography. Droplets in this size range retain the soft, frictionless contacts of colloidal dispersions, yet are large enough to resist thermal agitation. Nearly buoyant droplets form disordered piles where the compression varies smoothly and slowly with depth. Using light scattered from different sections of the pile we measure the dependence of the shear modulus on pressure using Diffusing Wave Spectroscopy (DWS) microrheology. We find a shear modulus that is proportional to pressure down to loads corresponding to a $\sim 0.1\%$ compression. However, below a critical pressure, the shear modulus drops abruptly and the droplets exhibit what appears like glassy rearrangements: despite loads many orders of magnitude greater than $\frac{K_{B}T}{a^3}$. [Preview Abstract] |
Thursday, March 21, 2013 2:54PM - 3:06PM |
W29.00003: Jamming of 2D foams Alexander Siemens, Martin van Hecke We probe the jamming of 2D wet foams by lateral compression of a bidisperse foam monolayer sandwiched between a glass plate and a fluid surface. Boundaries and residual gravitational effects prevent the foam to be truly unjammed, obstructing the observation of a jammed/unjammed transition. Instead, we find a clear transition from a ``gravity jammed'' to a ``boundary jammed'' state, where the bulk modulus jumps from essentially zero to a finite value, in agreement with theory. In addition, we probe the nonaffine bubble motion, which becomes large near this transition. [Preview Abstract] |
Thursday, March 21, 2013 3:06PM - 3:18PM |
W29.00004: Stress distributions of jammed particle clusters and the maximum entropy principle Yegang Wu, Stephen Teitel Using a simple model of frictionless bidisperse disks in two dimensions, we consider the distribution of stress on finite clusters of particles, within a statically jammed granular system at fixed global stress tensor. We compare our results against recent theories of the stress ensemble [1] and force network model [2] to investigate whether the distribution of stress is well described by a maximum entropy assumption. \\[4pt] [1] B. P. Tighe, A. R. T. van Eerd, and T. J. H. Vlugt, PRL 100, 238001 (2008);\\[0pt] [2] S. Henkes and B. Chakraborty, PRE 79, 061301 (2009) [Preview Abstract] |
Thursday, March 21, 2013 3:18PM - 3:30PM |
W29.00005: The link between the geometric and mechanical phase transitions at jamming Peter Morse, Eric Corwin We have observed a phase transition in the geometrically defined network of nearest neighbors of sphere packings as a function of packing density. By creating packings in a range of spatial dimension, from $d=2$ to $d=9$, we have amassed evidence suggestive of an upper critical dimension for this transition of $d\leq 3$. However, as of yet we do not have a field theory to confirm this fact. It is suggestive that the geometric transition point coincides with the mechanical jamming point in all dimensions, raising the question of how the geometry of nearest-neighbors relates to the formation of contacts necessary for mechanical stability. We present an answer to this question based on the evolution of geometric constraints as mechanical jamming is approached. In addition, we find that many of the requirements for renormalization are met by the order parameters associated with the geometric phase transition. Taking cues from traditional condensed matter systems and networking theory we explore various renormalization group approaches to this phase transition. [Preview Abstract] |
Thursday, March 21, 2013 3:30PM - 3:42PM |
W29.00006: Sedimentary Deposition and the Kinetics of Jamming Ted Brzinski, R. Karunamuni, A. D. A. Maidment, P. E. Arratia, D. J. Durian We observe a dispersion of spheres sedimenting in a fluid until all grains form a packing. In a Newtonian fluid, the dispersion is roughly homogenous in space and time except at two well-defined interfaces: a dispersion-supernatant interface, and a jamming front below which grains form a jammed packing. This system is ideal for the study of jamming kinetics because the jamming front is stationary: it moves upwards with a constant speed and shape. To characterize the concentration profile at the front, we have utilized x-ray absorption to directly measure volume fraction as a function of height and time. To characterize the grain-scale dynamics across the front, we now utilize a light scattering technique, speckle-visibility spectroscopy, to directly measure fluctuations of the grain velocities as a function of height and time. In order to alter the kinetics of jamming in this model system, we perturb the hydrodynamic interactions between grains by using a viscoelastic fluid, and observe how the shape and speed of the jamming front changes. [Preview Abstract] |
Thursday, March 21, 2013 3:42PM - 3:54PM |
W29.00007: How far is the Jamming point street-lamp illuminating the real world? Olivier Dauchot, Corentin Coulais, Robert P. Behringer The jamming of soft spheres at zero temperature has been extensively studied both numerically and theoretically, thus defining a well defined location, where a street lamp has been lit up. However it has been shown [1] that even model experiments on colloids are rather far away from the scaling regime illuminated by this lamp. Is it that the J-point has little to say about real system? We investigate the statics and the dynamics of the contact network of an horizontally shaken bi-disperse packing of photoelastic discs, close to jamming, we observe a remarkable dynamics of the contact network. It exhibits strong dynamical heterogeneities, which are maximum at a packing fraction $\phi^*$, distinct and smaller than the packing fraction $\phi^\dagger$, where the average number of contact per particle starts to increase. We demonstrate that the two cross-overs, one for the maximum dynamical heterogeneity, and the other for structural jamming, converge at point J in the zero mechanical excitation limit. Our grains are frictional and are far from thermal equilibrium. However we succeed in mapping these behaviors onto those observed for thermal soft spheres and demonstrate that some light of the J-point street-lamp reaches our granular universe. [1] Ikeda et al. arXiv.1209.2814(2012) [Preview Abstract] |
Thursday, March 21, 2013 3:54PM - 4:06PM |
W29.00008: Jamming of Cylindrical Grains in Featureless Vertical Channels G. William Baxter, Nicholas Barr, Seth Weible, Nicholas Friedl We study jamming of low aspect-ratio cylindrical Delrin grains falling through a featureless vertical channel. With a grain height less than the grain diameter, these grains resemble aspirin tablets, poker chips, or coins. Unidisperse grains are allowed to fall under the influence of gravity through a uniform channel of square cross-section where the channel width is greater than the grain size and constant along the length of the channel. Channel widths are chosen so that no combination of grain heights and diameters is equal to the channel width. Collections of grains sometimes form jams, stable structures in which the grains are supported by the channel walls and not by grains or walls beneath them. The probability of a jam occurring and the jam's strength are influenced by the grain dimensions and channel width. We will present experimental measurements of the jamming probability and jam strength and discuss the relationship of these results to other experiments and theories. [Preview Abstract] |
Thursday, March 21, 2013 4:06PM - 4:18PM |
W29.00009: Local strain field fluctuations in quasi-two-dimensional colloidal glasses Ye Xu, Tim Still, Kevin Aptowicz, Arjun Yodh We investigate the local strain field fluctuations in a quasi-two-dimensional colloidal glass as a function of packing fraction as the jamming transition is approached. Using standard video microscopy and particle tracking techniques, we derive the best-fit affine strain tensor and the non-affinity for each particle in the sample; this information is obtained by analyzing the variations of local configurations around each particle due to thermal motion. The spatial and temporal distributions of this local deformation permit us to probe the mechanical properties of our colloidal systems. We study how these mechanical properties evolve as the systems approaches the jamming transition. Furthermore, we explore the connection between the mechanical heterogeneity and the onset of irreversible rearrangements. [Preview Abstract] |
Thursday, March 21, 2013 4:18PM - 4:30PM |
W29.00010: Unusual order in squeezed repulsive spheres Wouter G. Ellenbroek The soft spheres that we have been using for years to study jamming into disordered packings can make a range of surprising ordered structures at higher densities. Monodisperse repulsive harmonic disks in two dimensions form, apart form the triangular lattice everyone would expect, a square lattice and various non-bravais lattices that can be described as a triangular lattice with a basis. The latter class includes the honeycomb structure, a chiral structure, and a structure which is best described as a tiling of pentagons and triangles. The appearance of these structures, some of which have not been previously reported, is surprising because the potential between the disks only very weakly violates the condition of complete monotonicity which has been conjectured to guarantee the triangular lattice to be the ground state structure. I will discuss how these structures come about, how they are related to tiny periodic packings of hard spheres and in what ways the resulting structures might be useful. [Preview Abstract] |
Thursday, March 21, 2013 4:30PM - 4:42PM |
W29.00011: The role of curvature in the jamming of hard spheres on the surface of a spheroid Donald W. Blair, Badel Mbanga, Christopher Burke, Timothy J. Atherton Using various packing protocols, we investigate numerically the jamming of spherical particles that are constrained to the surface of a larger, host spheroid. While jamming has been extensively investigated for different particle shapes and containers, the role played by curvature in the frustration that arises when spherical particles are adsorbed to curved interfaces is not yet well understood. Accordingly, we explore the dependence of the critical particle coverage fraction $\Phi$ required for jamming to occur upon the number and polydispersity of the smaller particles as well as the shape and relative size of the host spheroid. Along the way, we evaluate the relative efficiency of the numerical algorithms we employ in terms of their efficiency and their relevance to the physics of recent experiments in microfluidics and colloid deposition on curved surfaces. [Preview Abstract] |
Thursday, March 21, 2013 4:42PM - 4:54PM |
W29.00012: Thinking Inside the Box: The Optimal Filling of Shapes Carolyn Phillips, Joshua Andersaon, Greg Huber, Sharon Glotzer We introduce a new spatial partitioning problem called filling[1,2], which combines aspects of traditional packing and covering problems from mathematical physics. Filling involves the optimal placement of overlapping objects lying entirely inside an arbitrary shape so as to cover the most interior volume. In n-dimensional space, if the objects are polydisperse n-balls, we show that solutions correspond to sets of maximal n-balls. We investigate the mathematical space of filling solutions and provide a heuristic for finding the optimal filling solutions for polygons filled with disks of varying radii. We consider the properties of ideal distributions of N disks as N approaches infinity. We discuss applications of filling to such problems as tumor irradiation, designing wave fronts and wireless networks, minimal information representations of complex shapes, and molecular modeling of nanoparticles and colloids. \\[4pt] [1] Phillips, Anderson, Huber, Glotzer, The Optimal Filling of Shapes, PRL 108, 198304, 2012\\[0pt] [2] Phillips, Anderson, Huber, Glotzer, Optimal Fillings - A new subdivision problem related to packing and covering, arXiv:1208.5752, 2012 [Preview Abstract] |
Thursday, March 21, 2013 4:54PM - 5:06PM |
W29.00013: Jammed frictional tetrahedra are hyperstatic Matthias Schr\"oter, Max Neudecker, Stephan Herminghaus, Stephan Ulrich We prepare packings of frictional tetrahedra with volume fractions $\phi$ ranging from 0.469 to 0.622 using three different experimental protocols under isobaric conditions. Analysis via X-ray micro-tomography reveals that the contact number Z grows with $\phi$, but does depend on the preparation protocol. While there exist four different types of contacts in tetrahedra packings, our analysis shows that the edge-to-face contacts contribute about 50\% of the total increase in Z. The number of constraints per particle C increases also with $\phi$ and even the loosest packings are strongly hyperstatic i.e. mechanically over-determined with C approximately twice the degrees of freedom each particle possesses. [Preview Abstract] |
Thursday, March 21, 2013 5:06PM - 5:18PM |
W29.00014: Packings and assemblies of hard convex polyhedra Daphne Klotsa, Elizabeth Chen, Pablo Damasceno, Michael Engel, Sharon Glotzer Dense packings of hard polyhedra have been studied for centuries due to their mathematical aesthetic and more recently for their applications in fields such as granular matter, amorphous matter, and biology. The spontaneous organization of hard polyhedra under compression has only recently been addressed, demonstrating a plethora of assembled complex structures. The infinite pressure dense packings and the finite pressure, thermodynamically assembled structures for a given shape, however, are often different. In this talk we investigate connections between those two limits for convex polyhedra. We discuss the possibility of predicting one limit from the other, discuss some general rules, and link with previous works. [Preview Abstract] |
Thursday, March 21, 2013 5:18PM - 5:30PM |
W29.00015: Jamming of Ordered Vortex Lattice Domains C. Rastovski, M.R. Eskildsen, C.D. Dewhurst, W.J. Gannon, N.D. Zhigadlo, J. Karpinski Jamming is mostly associated with granular materials, but is applicable in a variety of physical situations. Our results indicate that the vortex lattice (VL) in type-II superconductors can be used as a model system to study jamming. Previous small-angle neutron scattering (SANS) studies of the VL in MgB$_2$ with H $\parallel$ c found a triangular VL which undergoes a field-driven 30$^\circ$ reorientation transition, forming three distinct ground state phases. The low and high field phases have hexagonal VLs aligned with high symmetry directions in the crystal, whereas at intermediate fields the VL is marked by the presence of domains of vortices continuously rotating from one high symmetry direction to another. A high degree of metastability between the VL phases of MgB$_2$ has been observed [P. Das et al., Phys. Rev. Lett. 2012]. Our recent SANS measurements show that this cannot be understood based on the single domain free energy. We applied a transverse AC magnetic field to the sample and found the decrease in the metastable volume fraction depends logarithmically on the number of AC cycles, similar to some jamming scenarios. We propose that the origin for the VL metastability is a jamming of counter-rotated VL domains that prevents rotation to the equilibrium orientation. [Preview Abstract] |
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