Bulletin of the American Physical Society
APS March Meeting 2019
Volume 64, Number 2
Monday–Friday, March 4–8, 2019; Boston, Massachusetts
Session K56: Jamming and Glassy Behavior |
Hide Abstracts |
Sponsoring Units: GSNP Chair: Andrea Liu, University of Pennsylvania Room: BCEC 255 |
Wednesday, March 6, 2019 8:00AM - 8:12AM |
K56.00001: Isostatic jamming of two-dimensional monodisperse system under quenched disorder Wen Zhang, Shiyun Zhang, Ning Xu The existence of amorphous packings in two-dimensional monodisperse system is a classical unsolved problem. By minimizing the enthalpy of packings of frictionless particles, we obtain isostatic jammed packings under quenched disorder at desired pressures. Quenched disorder is introduced by pinning a fraction of particles Nf=nfN. The result shows that there is a unique critical pinning density, nfc, at which packings become completely disorder. The static correlation length ξ6 diverges at the same nfc for different pressure p, which suggests new ways to investigate the jamming transition in two-dimensional monodisperse system. Finally, we confirm the existence of isostatic jammed packings with packing fraction ΦJ∞=0.845, and jamming scaling is still satisfied in two-dimensional monodisperse system. |
Wednesday, March 6, 2019 8:12AM - 8:24AM |
K56.00002: Spatio-temporal correlations of local relaxation rates in glassy systems Rajib Pandit, Elijah Flenner, Horacio Castillo
|
Wednesday, March 6, 2019 8:24AM - 8:36AM |
K56.00003: Machine-learned structure/dynamics relation in sheared jammed packings Sean Ridout, Jason W Rocks, Andrea Liu In disordered systems, using local structure to identify which particles are likely to rearrange under thermal fluctuations or applied load has been a longstanding challenge. Recently, machine learning has been used to construct a local structural variable, "softness", that is highly predictive of rearrangements in several disordered systems. Here we describe modifications made in the analysis that simplify interpretation and raise training accuracy for athermal packings of soft spheres under quasistatic shear. We obtain a "softness" that is highly predictive of the rearrangements at the onset of instabilities. Furthermore, we show that for jammed Hertzian packings, softness can be represented simply in terms of gaps and contacts between neighboring particles. We show how this picture depends on pressure above jamming and spatial dimension. |
Wednesday, March 6, 2019 8:36AM - 8:48AM |
K56.00004: Contact numbers and radial distributions in suspensions of smooth and rough colloids Shravan Pradeep, Lilian Hsiao The contact number distribution for hard sphere suspensions is a measure of nearest neighbor interactions between colloidal particles. Many experimental studies in the literature uses the primary minima of the radial distribution function, g(r), to estimate the contact number distribution. Our experimental data show that this method overestimates the mean contact number, <z>. Instead, we investigate a different method to estimate the contact distance by extrapolating contact values of different volume fractions (f) to jamming point at random close packing (RCP). For a 3D suspension of smooth spheres, fRCP ~ 0.64 with <z> ~ 6. For rough colloids, the added friction is expected to generate a reduced fRCP and <z>. We hypothesize that these values of <z> at RCP could be extrapolated to better understand particle contacts at lower values of f. To test this hypothesis, we synthesized sterically stabilized, fluorescent poly(methyl methacrylate) colloids with smooth and rough surface morphologies. Confocal microscopy imaging and processing shows that the g(r) of the suspensions agree well with the Orstein-Zernicke equation for hard spheres. Depending on the stabilizer length and roughness, we found that the contact distance ranges between 1 to 1.1 times the particle diameter. |
Wednesday, March 6, 2019 8:48AM - 9:00AM |
K56.00005: A real-space renormalization group for jamming Abe Clark Jamming occurs in grains, emulsions, dense suspensions, and other amorphous, particle-based systems. As the packing fraction φ, defined as the ratio of particle volume to system volume, is increased past a critical value φc, a liquid-solid phase transition occurs, and grains are no longer able to rearrange. Previous studies have shown evidence of spatial correlations, corresponding to collective rearrangements, that diverge near φ ≈ φc, but there has been no explicit spatial renormalization group scheme that has captured this transition. Here, I present a candidate for such a scheme, using a simple block-spin-like transformation of a randomly vacated lattice of grains. I define a real-space renormalization transformation that coarse-grains the lattice based on local mechanical stability. This model displays a critical packing fraction φc and estimates of critical exponents in 2D and 3D that are consistent with previous work. |
Wednesday, March 6, 2019 9:00AM - 9:12AM |
K56.00006: Marginality gap in Mari-Kurchan mean-field model for jammed packings Yue Li, Eric Corwin, Andrea Liu A marginal system is one for which there exists an infinitesimal deformation that will lead to instability. Frictionless sphere packings at jamming, as well as infinite packings above jamming, seem to meet this definition. Further, the scaling of the excess contact number with pressure is consistent with the mean-field expectation of marginal stability. However, the prefactor in three-dimensional systems is slightly larger than predicted. This discrepancy in the prefactor, termed the “marginality gap”, is expected to vanish in the mean-field limit. We investigate numerically the Mari-Kurchan model of jammed packings, in which a Gaussian random shift is added to each separation of pairs of particles in the pair potential. By tuning the amplitude of the random shift, we study the range from jammed packings to the mean-field limit to see how the marginality gap evolves. |
Wednesday, March 6, 2019 9:12AM - 9:24AM |
K56.00007: Jamming as a Multicritical Point Danilo Liarte, Xiaoming Mao, Olaf Stenull, Tom Carl Lubensky The discontinuous jump in the bulk modulus B at the jamming transition is a consequence of the formation of a critical contact network of spheres that resists compression. We introduce lattice models with underlying under-coordinated compression-resistant spring lattices to which next-nearest-neighbor springs can be added. In these models, the jamming transition emerges as a kind of multicritical point terminating a line of rigidity-percolation transitions. Tuning the under-coordinated lattice to the jamming critical point yields a faithful description of jamming and its relation to rigidity percolation. |
Wednesday, March 6, 2019 9:24AM - 9:36AM |
K56.00008: Can a large jammed packing be assembled from smaller ones ? Daniel Hexner, Pierfrancesco Urbani, Francesco Zamponi The principle of equivalence of ensembles asserts that, in the thermodynamic limit, a system with periodic boundary conditions behaves identically to a subsystem of the same size, cut out from a larger system. We compare these two ensembles on finite length scales in the case of amorphous jammed packings of soft spheres at zero temperature. Focusing on the statistics of the contact fluctuations, we find that systems with periodic boundary conditions have significantly smaller fluctuations compared to the subsystems. This difference is largest near the jamming transition. Moreover, these two ensembles converge only at a surprisingly large system size. The crossover to the thermodynamic limit defines a length scale for each ensemble. Surprisingly, these diverge, as a function of the distance to the transition, with two different exponents. We argue that this disparity is the result of the system being above the upper critical dimension and that, based on the values of the exponents, the upper critical dimension can be measured. |
Wednesday, March 6, 2019 9:36AM - 9:48AM |
K56.00009: Response to controlled perturbations in frictional granular jamming Mahesh Bandi Jamming in frictional granular media results in metastable configurations due to stability imparted by frictional contacts against sliding. We experimentally study the frictional energy differene (ΔE) between an unperturbed and a perturbed configuration subject to uni-axial compression under identical conditions in a two-dimensional system comprised of a bidispersed set of disks whose friction we tune through contact roughness d. The homogeneous system-wide acoustic perturbations are independently tuned with amplitude A and frequency f. We find the frictional stress σ released from perturbation follows a stretched exponential form σ = σ0 exp[-(ΔE/Teff)β], where σ0 is the unperturbed stress, Teff = (1/2)M (ARMS fRMS)2, M is total mass of disks in the configuration, and ARMS and fRMS are the respective RMS perturbation amplitude and frequency; the stretched exponent β is the only fit parameter. At low Teff, we obtain a best fit around β ~ 1/3. As Teff increases and more frictional stress is relieved, the stretched exponent β transitions smoothly and approaches an asymptotic value of β = 1 with an Activated or Arrhenius-like relaxation behavior. Eventually when ARMS ≥ d, all frictional stresses in the system are relieved and frictionless jamming behavior is recovered. |
Wednesday, March 6, 2019 9:48AM - 10:00AM |
K56.00010: Aging is a (log-)Poisson Process, not a Renewal Process1 Stefan Boettcher, Dominic M Robe, Paolo Sibani Aging is a ubiquitous relaxation dynamic in disordered materials. It ensues after a rapid quench from an equilibrium ``fluid'' state into a non-equilibrium, history-dependent jammed state. We propose a physically motivated description that contrasts sharply with the trap model2 or a continuous-time random walk (CTRW) with broadly distributed trapping times commonly used to fit aging data.3 A renewal process like CTRW proves irreconcilable with the log-Poisson statistic exhibited, for example, by jammed colloids as well as by disordered magnets. A log-Poisson process is characteristic of the intermittent and decelerating dynamics of jammed matter usually activated by record-breaking fluctuations (``quakes''). We show that such a record dynamics (RD) provides a universal model for aging, physically grounded in generic features of free-energy landscapes of disordered systems.4 |
Wednesday, March 6, 2019 10:00AM - 10:12AM |
K56.00011: Direct Measurement of Force Configuration Entropy in Jamming James Sartor, Eric Corwin Thermodynamics connects the microscopic details of a system’s entropy to bulk measurements of the system’s properties. In granular systems, for which the thermal energy scale is so small as to be irrelevant, this has been proposed using temperature analogues such as compactivity and angoricity. We present a method of linking the measurements of such quantities to the entropy of the force network by measuring the multiplicity directly. For systems at the critical jamming point there is only one mechanically equilibrium force network compatible with the spring network representation of the system, so the force configurational entropy of a jammed system is zero. For each new contact formed, the dimensionality of the space of allowed force configurations increases by one. Within this space lies a subspace of positive-definite forces, which is compatible with a granular packing. We propose that the volume of this subspace is proportional to the multiplicity of the packing’s force network configuration. To determine the constant of proportionality, we measure the angoricity over 6 decades of pressure using the method of overlapping histograms. |
Wednesday, March 6, 2019 10:12AM - 10:24AM |
K56.00012: Void Percolation Threshold and Critical Proporties of the Random Lorentz Gas Patrick Charbonneau, Eric Corwin, Yi Hu Percolation and glass formation share interesting dynamical features, in which they both exhibit caging of tracers/particles. Although first noticed long ago, this analogy has grown in physical relevance since a simplified model of structural glasses (Mari-Kurchan) was found to display corrections to caging that are analogous to those observed in percolating systems. Interestingly, our recent study has shown that the glass-like caging transition is absent in lattice percolation for all dimensions. In order to better understand the origin of caging, we consider transport in an off-lattice percolation model. Specifically, we study the caging and critical scaling of transport in the random Lorentz gas, which can be mapped onto the Mari-Kurchan model and to void percolation. We first develop numerical strategies to determine precisely the void percolation threshold in high dimensions, and then study dynamical criticality around that threshold. Our results provide key insights into the dynamics of glass formers and transport in heterogenous media, more generally. |
Wednesday, March 6, 2019 10:24AM - 10:36AM |
K56.00013: Fluctuation Distributions of Energy Minima in Complex Landscapes Horst-Holger Boltz, Andrea Liu, Jorge Kurchan We discuss the properties of the distributions of energies of minima obtained by gradient descent in complex energy landscapes.Specifically, we study the distribution of energies of minima in the spherical p-spin model and the distribution of jamming threshold packing fractions in jammed particle configurations as archetypal manifestations of disorder-induced complexity. We numerically find universal distributions that resemble the Tracy-Widom distributions often found in problems of random correlated variables, and non-trivial finite-size scaling. Deeper insight into this problem is achieved by realizing the importance of a first-passage process in the eigenvalues of the Hessian to the termination of the steepest descent process, which also manifests the link to problems where the Tracy-Widom distribution is established. This first-passage view of steepest descent dynamics is generic and therefore we expect similar phenomenology in many problems. |
Wednesday, March 6, 2019 10:36AM - 10:48AM |
K56.00014: Shear response of jammed disk and sphere packings Kyle VanderWerf, Mark Shattuck, Corey Shane O'Hern The response of purely repulsive disk and sphere packings to athermal, quasistatic simple shear near jamming onset is highly nonlinear. Previous studies have shown that the ensemble-averaged static shear modulus G is nearly constant at small pressure p, and at a characteristic pressure p*, G begins to increase as a power-law: G ~ pα, where α=0.5. Also, p* decreases with increasing system size N, such that p* ~ N-β, where β=1. Although scaling arguments have rationalized the scaling behavior of p* and G, there is currently no quantitative theoretical framework that can predict the values of α and β. Here, we carry out numerical simulations of 2D bidisperse disk packings near jamming onset undergoing athermal, quasistatic simple shear at fixed pressure to explain these exponents. We show that α and β can be understood by examining the "geometrical families" of jammed packings, which are intervals of shear or pressure where the packings maintain the same network of interparticle contacts without rearrangements. We present a statistical model based on random switching of the packings from one geometrical family to another to predict the values of the exponents α and β. |
Wednesday, March 6, 2019 10:48AM - 11:00AM |
K56.00015: Densest vs. jammed packings of 2D bent-core trimers Austin Griffith, Robert Hoy We identify the maximally dense lattice packings of tangent-disk trimers with fixed bond angles (θ = θ0) and contrast them to both their nonmaximally-dense-but-strictly-jammed lattice packings as well as the disordered jammed states they form for a range of compression protocols. While only θ0 = 0, 60°, and 120° trimers can form the triangular lattice, maximally-dense maximally-symmetric packings for all θ0 fall into just two categories distinguished by their bond topologies: half-elongated-triangular for 0 < θ0 < 60° and elongated-snub-square for 60° < θ0 < 120°. The presence of degenerate, lower-symmetry versions of these densest packings combined with several incommensurable families of less-dense-but-strictly-jammed lattice packings act in concert to promote jamming. Systems jam via a two-stage, two-length-scale process. First, randomly-oriented crystalline grains form and grow to a size that increases with decreasing compression rate and depends strongly on θ0. Since these grains cannot be compressed further, they effectively behave as single nearly-rigid particles as compression continues. Jamming occurs when they can no longer rotate/translate away from one another upon colliding. |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700