Bulletin of the American Physical Society
APS March Meeting 2016
Volume 61, Number 2
Monday–Friday, March 14–18, 2016; Baltimore, Maryland
Session F43: Jamming and the Glass Transition II |
Hide Abstracts |
Sponsoring Units: GSNP GSOFT Chair: Paolo Sibani Room: 346 |
Tuesday, March 15, 2016 11:15AM - 11:27AM |
F43.00001: Jamming vs Caging in Three Dimensional Jamming Percolation Yair Shokef, Nimrod Segall, Eial Teomy We study a three-dimensional kinetically-constrained lattice-gas model [1], in which the ability of a particle to move depends on the occupation of neighboring sites in an orientational manner. The kinetic rules are constructed such that chains of permanently-frozen particles reach an infinite length at the critical density of directed percolation. Thus at this critical density the system undergoes a jamming transition, above which there is a finite fraction of jammed particles. We demonstrate that the three-dimensional mesh-like structure of the one-dimensional jammed chains enables the free particles to propagate through the holes in this mesh. This diffusive motion is terminated at a second critical density above which all particles are caged. The largest and second largest clusters of dynamically-connected sites exhibit singularities at both densities. Thus our model assists in separating between the two distinct phenomena of jamming and caging. [1] A. Ghosh, E. Teomy and Y. Shokef, Europhys. Lett. 106, 16003 (2014). [Preview Abstract] |
Tuesday, March 15, 2016 11:27AM - 11:39AM |
F43.00002: Relation between structure of blocked clusters and relaxation dynamics in kinetically constrained models Eial Teomy, Yair Shokef In a liquid all the particles are mobile, while in a glass only some of them are mobile at any given time. Although overall the structure is amorphous in both cases, the difference is that in glasses there are local structures that inhibit the movement of particles inside them. We investigate the size of these structures by considering the minimum number of particles that need to move before a specific particle can move. In kinetically-constrained models this structural property, the mean culling time, is easy to find by iteratively culling mobile particles from a snapshot of the system. We use the Kob-Andersen, Fredrickson-Andersen, and the spiral models, which are either lattice gases in which a particle may hop to a nearby site if its local environment satisfies some constraint, or Ising-like models in which a spin, representing regions of high and low mobility, can flip if its environment satisfies some constraint. We compare these structural properties to the dynamics in these models by measuring the persistence time, which is the average time it takes a particle to move for the first time. We find an algebraic relation between the mean culling time and the persistence time, with a model-dependent exponent. [Preview Abstract] |
Tuesday, March 15, 2016 11:39AM - 11:51AM |
F43.00003: Growing Hyperuniformity of Bidisperse Soft Discs on Approach to Jamming Anthony Chieco, Carl Goodrich, Andrea Liu, Douglas Durian We study the development of hyperuniformity in simulated systems of bidisperse soft discs as the packing fraction $\phi$ is increased from below to above jamming, using the real-space spectrum of hyperuniformity disorder lengths, $h(L)$. For a set of randomly placed $L\times L$ measuring windows, $h(L)$ specifies the distance from the window boundaries over which fluctuations are important; for liquid-like systems, $h(L)$ scales like $L$; but for strongly hyperuniform systems, $h(L)=h_e$ is constant. We use two preparation protocols, one rapidly-quenches a system by immediately minimizing particle overlap and the other allows particles to move under low temperature thermal driving. Above jamming, both systems become strongly hyperuniform as signified by $h(L) \rightarrow R_{small}/5$ at large $L$. Below jamming, but near the transition, the behavior of $h(L)$ at small $L$ is just like above jamming. But for larger $L$, $h(L)$ breaks away and grows in a protocol-dependent fashion. In general, thermal systems are more uniform than quenched systems, as signified by smaller hyperuniformity disorder lengths. And the development of hyperuniformity happens simultaneously with the onset of jamming. [Preview Abstract] |
Tuesday, March 15, 2016 11:51AM - 12:03PM |
F43.00004: Crossover from facilitation to hopping in a colloidal glass-former Shreyas Gokhale, Rajesh Ganapathy, K Hima Nagamanasa, A K Sood Despite extensive research, it remains to be established whether glass formation is a fundamentally thermodynamic or dynamic phenomenon. In particular, it is not yet clear whether structural relaxation is dominated by the correlated motion of localized excitations, as postulated by the dynamical facilitation (DF) theory, or by the collective hopping of groups of particles, as envisioned by various thermodynamic approaches. Here, by analyzing data from experiments on dense colloidal suspensions, we critically compare the role of facilitation and hopping in governing structural relaxation in glass-forming liquids. In particular, we investigate the spatial organization of localized excitations within clusters of most mobile particles as well as their partitioning into shell-like and core-like regions. Our study reveals the existence of a dynamical crossover from a facilitation dominated regime at low area fractions to one dominated by collective hopping close to the glass transition. Our findings strongly suggest that glass formation is thermodynamic in origin. [Preview Abstract] |
Tuesday, March 15, 2016 12:03PM - 12:15PM |
F43.00005: Measuring Temperaturelike State Variables in History-Dependent Jammed Granular Systems Ephraim Bililign, Karen Daniels Granular systems are athermal, thus a complete statistical mechanics framework must be based on a set of macroscopic state variables which excludes temperature. One leading theory incorporates a stress-based ensemble, and predicts a Boltzmann-like distribution of the force-moment tensor with respect to the conjugate, temperature-like variable, angoricity. We experimentally test this theory on a static, bidisperse, two-dimensional packing of discs. Basal friction is eliminated by floating the discs on a sub-fluidizing upflow of air, and the packings are subjected to either uniaxial compression or simple shear. We simultaneously measure the contact forces acting on each disc using photoelasticity. These measurements are repeated over many configurations of discs by dilating and rearranging the system, and the angoricity is computed as a function of the confining pressure. In particular, we test the predicted linear relationship between angoricity and pressure. Comparison to prior results and numerical simulations also suggests a history-dependent angoricity, an undesirable feature in the proposed state variable. [Preview Abstract] |
Tuesday, March 15, 2016 12:15PM - 12:27PM |
F43.00006: Universal, non-Debye scaling in the density of states for jammed amorphous systems Eric Corwin, Alexis Poncet The presence of anomalous modes in amorphous packings close to jamming is well known: the density of states of packings close to jamming goes to a constant at low frequency. But the scaling at higher densities is still unclear. Naively, one might expect to find simple Debye scaling. However, newly available theories for systems thought to belong to the same universality class as jamming predict anomolous, non-Debye scaling, but are only strictly applicable to the infinite dimensional case. Do these (mean-field) predictions bring some information about finite-dimensional systems? Here we study packings of soft spheres in dimensions 3 through 7 and show that indeed, far from jamming, we find a universal non-Debye scaling in the density of states, consistent with the mean-field predictions. [Preview Abstract] |
Tuesday, March 15, 2016 12:27PM - 12:39PM |
F43.00007: Nonconvex optimization and jamming Yoav Kallus Recent work on the jamming transition of particles with short-range interactions has drawn connections with models based on minimization problems with linear inequality constraints and a concave objective. These properties reduce the continuous optimization problem to a discrete search among the corners of the feasible polytope. I will discuss results from simulations of models with and without quenched disorder, exhibiting critical power laws, scaling collapse, and protocol dependence. These models are also well-suited for study using tools of algebraic topology, which I will discuss briefly. [Preview Abstract] |
Tuesday, March 15, 2016 12:39PM - 12:51PM |
F43.00008: Configurational entropy of glass-forming systems from graph isomorphism Yuxing Zhou, Scott Milner The configurational entropy plays a central role in the thermodynamic scenarios of glass transition, such as Adam-Gibbs theory and random first-order transition theory. By definition, the configurational entropy $S_\text{c}$ is the difference between the entropy of liquid and the vibrational entropy with structural rearrangement restricted, both of which can be obtained by means of thermodynamic integration. On the other hand, $S_\text{c}$ is essentially a measure of the number of basins in the energy landscape, and therefore it can also be estimated by explicitly enumerating inherent structures. To this end, we first coarse-grain the vibrational motions by mapping configurations to Voronoi diagrams and then categorize them using canonical labelling. The Voronoi graph entropy is calculated as $S_\text{G}/k_\text{B}= -\sum p_i \log (p_i)$, where $p_i$ is the probability of finding distinct graph $i$. We find for an $n$-particle subsystem of glass-forming hard-disk/sphere fluids, $S_\text{G}(n)$ scales linearly with $n$, and $S_\text{c}$ can be estimated from the slope. [Preview Abstract] |
Tuesday, March 15, 2016 12:51PM - 1:03PM |
F43.00009: Suppression of the threshold of a granular solid by mechanical fluctuations Axelle Amon, Adeline Pons, Thierry Darnige, J\'er\^ ome Crassous, Eric Cl\'ement For a granular material, when the ratio between the shear stress and the confining pressure is smaller than the Mohr-Coulomb threshold, the system can be considered as a solid. Nevertheless, a long-term creep is observed in this solid phase in stress imposed experiments. We present recent experimental and theoretical results demonstrating that the superposition of tiny modulations to the imposed stress are sufficient to change the response of the system from a logarithmic creep to a linear one even deep in the jammed phase. We give a theoretical interpretation of this fluidization without invoking an effective temperature due to a mechanical noise. We interpret our observations as a secular effect, i.e. a ratcheting process which is revealed only on very long times. We show that a local fluidity model is sufficient to interpret fully our experimental observations. [Preview Abstract] |
Tuesday, March 15, 2016 1:03PM - 1:15PM |
F43.00010: Fast magnetic resonance imaging of the internal impact response of dense granular suspensions Christoph Müller, Alexander Penn, Klaas P. Pruessmann Dense granular suspensions exhibit a number of intriguing properties such as discontinuous shear-thickening and the formation of dynamic jamming fronts when impacted by a solid. Probing non-intrusively these phenomena experimentally in full three-dimensional systems is, however, highly challenging as suspensions are commonly opaque and thus, not accessible optically. Here we report the development and implementation of a fast magnetic resonance imaging (MRI) methodology allowing us to image the internal dynamics of dense granular suspensions at high temporal resolutions. An important facet of this work is the implementation of parallel MRI using tailored multi-channel receive hardware and the optimization of magnetic properties (susceptibility and NMR relaxivity) of the liquid phase. These two improvements enable us to utilize fast single-shot pulse sequences while yielding sufficient signal intensity at temporal resolutions of less than 50 ms. Furthermore, using motion-sensitive MR pulse sequences we are able to image bulk motion within the system and the response of dense granular suspensions to fast impacts. [Preview Abstract] |
Tuesday, March 15, 2016 1:15PM - 1:27PM |
F43.00011: Local fluctuations in the relaxation rate in a glassy system Rajib Pandit, Elijah Flenner, Horacio E. Castillo We numerically study the equilibrium dynamics of a glass-forming binary hard-sphere mixture, for different packing fractions. We extract a correlator that probes the integrated fluctuations in the local relaxation rate in the system. We find that the strength of this correlator at $t=\tau_{\alpha}$ (the $\alpha$-relaxation time) grows with packing fraction approximately as a power of $\tau_{\alpha}$. We also find that for a fixed packing fraction, the correlator grows as a power of time, for very long times, with an exponent that depends on the packing fraction. This exponent probes the time correlations of the relaxation rate fluctuations. We find that the exponent is around 3 for very low packing fractions, and gradually decreases to a value below 2 as the glass transition is approached. We conclude that a description of fluctuations in terms of local relaxation rates is only applicable at long times and for packing fractions close to the glass transition. [Preview Abstract] |
Tuesday, March 15, 2016 1:27PM - 1:39PM |
F43.00012: Finite temperature mechanical instability in disordered lattices Leyou Zhang, Xiaoming Mao Mechanical instability takes different forms in various ordered and disordered systems, and little is known about how thermal fluctuations affect different classes of mechanical instabilities. We develop an analytic theory involving renormalization of rigidity and coherent potential approximation that can be used to understand finite-temperature mechanical stabilities in various disordered systems. We used this theory to study two disordered lattices: randomly diluted triangular lattice and randomly braced square lattice. These two lattices belong to two different universality classes as they approach mechanical instability at $T=0$. We show that thermal fluctuations stabilize both lattices. In particular, the triangular lattice displays a critical regime in which the shear modulus scales as $G \sim T^{1/2}$, whereas the square lattice shows $G \sim T^{2/3}$. We discuss generic scaling laws for finite $T$ mechanical instabilities and relate to experimental systems including jamming and glass transitions. [Preview Abstract] |
Tuesday, March 15, 2016 1:39PM - 1:51PM |
F43.00013: Scaling theory for the jamming transition Carl Goodrich, Andrea Liu, James Sethna We propose a scaling ansatz for the elastic energy of a system near the critical jamming transition in terms of three relevant fields: the compressive strain $\Delta \phi$ relative to the critical jammed state, the shear strain $\epsilon$, and the inverse system size $1/N$. We also use $\Delta Z$, the number of contacts relative to the minimum required at jamming, as an underlying control parameter. Our scaling theory predicts new exponents, exponent equalities and scaling collapses for energy, pressure and shear stress that we verify with numerical simulations of jammed packings of soft spheres. It also yields new insight into why the shear and bulk moduli exhibit different scalings; the difference arises because the shear stress vanishes as $1/\sqrt{N}$ while the pressure approaches a constant in the thermodynamic limit. The success of the scaling ansatz implies that the jamming transition exhibits an emergent scale invariance, and that it should be possible to develop a renormalization-group theory for jamming. [Preview Abstract] |
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