Bulletin of the American Physical Society
APS March Meeting 2023
Volume 68, Number 3
Las Vegas, Nevada (March 5-10)
Virtual (March 20-22); Time Zone: Pacific Time
Session B02: Jamming and Glassy BehaviorFocus
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Sponsoring Units: GSNP Chair: Timothy Atherton, Tufts University Room: Room 125 |
Monday, March 6, 2023 11:30AM - 12:06PM |
B02.00001: The Clogging Transition in a 2D Granular Silo Invited Speaker: Kerstin Nordstrom The flow of granular material through a silo or hopper has been studied for many years. In addition to its great practical importance in many industrial processing situations, it is also thought to be a model system for other bottleneck flows such as blood flow, crowd egress, and traffic merges. In recent times, advances in computing and high-speed imaging have allowed detailed study of these flows. We present results from a high-speed imaging study of silo flow. Specifically, we report on how metrics such as velocity fluctuations, non-affine motion, and dynamical heterogeneities change on approach to the clogging point. We do find systematic changes in these metrics on approach to the clogging point. We compare and contrast the clogging transition to the jamming transition in light of these results. We will also summarize some extensions to this work involving obstacles and soft particles. |
Monday, March 6, 2023 12:06PM - 12:18PM |
B02.00002: Searching for the Jamming Transition in the Energy Landscape Using a Transect Method Eduardo Bautista, Eric I Corwin
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Monday, March 6, 2023 12:18PM - 12:30PM |
B02.00003: Free energy landscapes for a small number of hard disks Cordell J Donofrio, Eric R Weeks We present our analysis on the free energy landscapes of a small number of simulated particles undergoing a 2D random walk inside of a circular corral. This follows up on previous work by members of our research group who simulated both 3 and 4 particles under similar conditions. Those studies showed that parameters could be defined such that 1 or 2 dimensional free energy landscapes could be constructed in order to help understand the barriers to re-arrangement and the timescales on which they happen. In particular, we are interested in how these barriers change as the particles become more confined by reducing the size of the corral. Our simulations increase the number of particles simulated to 5 and higher with the goal of generalizing the processes for defining parameters that give rise to low dimensional energy landscapes. The ultimate goal of this research is to understand configurational changes on a small scale in order to give insight into glassy dynamics for much larger systems. |
Monday, March 6, 2023 12:30PM - 12:42PM |
B02.00004: Collective Motion in a Dusty Plasma Md. Rakib Hassan, Francis W Starr Dusty plasmas containing micron-sized particles occur naturally in solar nebulae, planetary rings, and comet tails, and can be studied in controlled laboratory experiments in 2D or 3D. The organization of dust in the plasma can be amorphous or crystalline, and 2D dusty plasmas offer the opportunity to directly image the rearrangement of dust grains; these rearrangements are complex in the crystal state, and similar to the collective motion that occurs in glass forming or jamming materials. Here we take advantage of the fact that dust interactions can be quantitatively modelled using a simple Yukawa potential to simulate the dynamics of a 2D dusty plasma in amorphous and crystalline states. In the crystal, we find that dust grains diffuse through highly collective rearrangements that are similar to the string-like rearrangements occurring in glass-forming materials. By mapping the trajectory of dust grains to their corresponding energy-minimized states, we remove thermal noise which makes it possible to identify collectively rearranging dust grains without needing to employ any ad hoc criteria, eliminating the selection ambiguity that is challenging in many condensed phased materials. In doing so, we explore the interplay between structural defects and collective motion and also show that the number of defects characterizes distinct energy levels of the crystal. |
Monday, March 6, 2023 12:42PM - 12:54PM |
B02.00005: Jammed disks of two sizes and weights in a narrow channel Dan Liu, Gerhard Müller Jammed disk models are often studied for the properties of granular materials. Here we introduce our approach to the models of jammed disks of two sizes and weights in a long narrow channel. The channel is closed off by pistons that freeze jammed microstates out of loose disk configurations subject to moderate pressure, gravity, and random agitations. Disk sizes and channel width are such that underjamming no disk remains loose and all disks touch one wall. Based on a generalized Pauli Principle and configuration statistics, we calculate the models where the two types of disks are in alternating and random sequences. The exact results for the characterization of jammed macrostates including volume and entropy are presented. |
Monday, March 6, 2023 12:54PM - 1:06PM |
B02.00006: The Ising Spin Glass on Random Graphs at zero temperature: Not all Spins are Glassy in the Glassy Phase Gianmarco Perrupato, Maria Chiara Angelini, Giorgio Parisi, Federico Ricci-Tersenghi, Tomaso Rizzo We investigate the replica symmetry broken (RSB) phase of spin glass (SG) models in a random field defined on Bethe lattices at zero temperature. From the properties of the RSB solution, we deduce a closed equation for the extreme values of the cavity fields. This equation turns out not to depend on the parameters defining the RSB, and it predicts that the spontaneous RSB does not take place homogeneously on the whole system. Indeed, there exist spins having the same effective local field in all local ground states, exactly as in the replica symmetric (RS) phase, while the spontaneous RSB manifests only on the remaining spins, whose fraction vanishes at criticality. The characterization in terms of spins having fixed or fluctuating local fields can be extended also to the random field Ising model (RFIM), in which case the fluctuating spins are the only ones responsible for the spontaneous magnetization in the ferromagnetic phase. Close to criticality we are able to connect the statistics of the local fields acting on the spins in the RSB phase with the correlation functions measured in the paramagnetic phase. Identifying the two types of spins on given instances of SG and RFIM, we show that they participate very differently to avalanches produced by flipping a single spin. From the scaling of the number of spins inducing RSB effects close to the critical point and using the M-layer expansion, we estimate the upper critical dimension equal to eight for the SG. |
Monday, March 6, 2023 1:06PM - 1:18PM |
B02.00007: Structure of jammed ellipse packings over a wide range of aspect ratios Sebastian Rocks, Robert S Hoy Motivated by the recent observation of liquid glass in suspensions of ellipsoidal colloids [J. Roller et al., Proc. Nat. Acad. Sci. 118, e2018072118 (2021)], we examine the structure of jammed ellipse packings over a much wider range of aspect ratios α than has been previously examined. We determine φJ(α) to high precision, and find an empirical analytic formula that predicts φJ(α) to within less than 0.1% for all α ≤ 10. Then we explore how these packings’ positional-orientational order varies with α. Local nematic order and structures comparable to the precursor domains observed in experiments gradually emerge as α increases beyond 3. For α ≥ 5, single-layer lamellae become more prominent, and long-wavelength density fluctuations increase with α as packings gradually approach the rod-like limit. We compare these jammed packings to saturated RSA ellipse packings, with the aim of understanding why both the density maximum and the transition from tip/side- to side/side-contact-dominated structure occur at different α. |
Monday, March 6, 2023 1:18PM - 1:30PM |
B02.00008: Universal Fragility in the Response of Spin Glass Ground States to Single Bond Changes Mutian o Shen, Zohar Nussinov, Martin Weigel, Gerardo Ortiz, Yang-Yu Liu We examine the effects of changing a single bond (local interaction) on the ground states of two- and three-dimensional Edwards-Anderson Ising spin glasses with a Gaussian distribution of coupling strengths. We find those ground states to be exceedingly fragile - altering the strength of only a single bond beyond a threshold value leads to a new ground state that differs from the original one by a cluster of flipped spins whose surface (contour) diverges with the volume of the system. These single contours provide the minimal-energy excitations of these spin glasses. Within our numerical accuracy, we find that the geometrical size of these excitations is governed by a nearly universal power-law distribution with exponents that depend only on the spatial dimension of the system. Further interesting properties of these excitations will also be discussed. |
Monday, March 6, 2023 1:30PM - 1:42PM |
B02.00009: Elasticity of soft matter stabilized by non-spring-like forces Brian P Tighe The mechanics of many soft matter systems are closely related to spring networks. If elements interact exclusively via pairwise, central, finite-ranged forces – as in a spring network – then the system is floppy/fluid-like below a critical coordination known as the isostatic point. However, many soft materials possess additional interactions that rigidify/jam the system below the isostatic point. These “non-spring-like forces” have various and unrelated physical origins – here I consider pre-tensioning, fiber bending in biopolymer networks, static friction in jammed granular matter, and an elastic matrix in particle-filled composites. Using these four model systems, I will show that the elasticity of soft matter stabilized by non-spring-like forces has universal features, independent of the forces’ origin. These features manifest as scaling relations in the shear modulus, which can be explained by relating them to floppy modes that appear in the limit where non-central forces are "turned off." |
Monday, March 6, 2023 1:42PM - 1:54PM |
B02.00010: Droplet rearrangements during slow compression of a jammed 2D emulsion Eric R Weeks, Xin Du We experimentally study droplet rearrangements within an evaporating quasi-two-dimensional emulsion system. Our samples are oil-in-water emulsions confined between two close-spaced parallel plates, so that the oil droplets are deformed into pancake shapes. In this system, water slowly evaporates from an open edge of the chamber and, as a consequence, the volume fraction of oil droplets gradually increases. By means of microscopy, we analyzed the packing structure of the droplets and their rearrangement motions. Following the methods of [Rieser et al., PRL 116, 088001 (2016)], at each time we construct the radial Voronoi tesselation. We then calculate the Voronoi cell anisotropy vectors which point from the center of each droplet to the corresponding Voronoi cell centroid. This identifies void spaces where droplets, which bias droplet rearrangement motions. In particular, T1 rearrangement events are oriented to induce droplet motion that fills in the voids. |
Monday, March 6, 2023 1:54PM - 2:06PM |
B02.00011: Constructing Ideal Amorphous Packings in Two Dimensions Viola M Bolton-Lum, Varda F Hagh, Eric I Corwin We propose that an ideal amorphous packing is one that is free of any crystalline order, stable, fully coordinated, and as densely packed as possible for a given pressure. We initially produce nearly ideal, polydisperse, amorphous packings of soft spheres by performing an energy minimization with respect to both particle radii and positions as degrees of freedom, while fixing several of the moments of the radius distribution. Radii are chosen from a log normal distribution, with a packing fraction selected to ensure overjamming. Such a method produces systems that are nearly triangulated. The fully triangulated network of contacts and nearest neighbors is fed into the CirclePack[1] circle packing algorithm, which produces packings that are stable and defect free at critical jamming while nearly preserving the distribution of radii. Surprisingly, shear and bulk moduli are of the same order, even at vanishing pressure, and the jamming density is greater than that of size-segregated crystals, independent of system size and initial conditions. We argue that these constitute ideal amorphous packings, and that given their mechanical properties ‘amorphous crystal’ is an appropriate appellation. |
Monday, March 6, 2023 2:06PM - 2:18PM |
B02.00012: Multi species asymmetric simple exclusion process with impurity activated flips Amit K Chatterjee The asymmetric simple exclusion process (ASEP) is broadly regarded as a paradigmatic model for non-equilibrium transport processes. Motivated by a simplistic description of multi lane traffic flow, we present a multi species generalization of ASEP along with impurities. The impurities can activate flips between species, imitating the lane change dynamics in multi lane traffic flow. This model, being disordered and non-ergodic, is of intrinsic interest. The exact nonequilibrium steady state probability distribution is obtained using the technique of matrix product ansatz. For special choices of the microscopic dynamics, the model exhibits (i) negative differential mobility where current can decrease with increasing bias, (ii) cluster formation as a result of counter-flow of different species. |
Monday, March 6, 2023 2:18PM - 2:30PM |
B02.00013: Phase transition prediction and entropy estimation with restricted Boltzmann machines Jing Gu, Kai Zhang The restricted Boltzmann machine (RBM) is an energy-based model consisting of a visible and a hidden layer. Previous studies applying the RBM to the Ising model demonstrated its ability of learning the Boltzmann distribution and reconstructing thermal quantities. However, how the RBM extracts physical information and captures the phase transition without extra human knowledge are not fully explored. We train RBMs on 2d and 3d Ising model with a system size much larger than those used before and carefully examine the mechanism of RBM learning. By analyzing machine learning parameters and functions, such weight matrix, hidden layer embedding, visible energy, and pseudo-likelihood, we find several characteristics for the phase transition. We verify that the hidden layer contains an approximately equal number of positive and negative units without special spatial correlation. We also prove that the pseudo-likelihood can be used to estimate the (physical) entropy. |
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