Bulletin of the American Physical Society
APS March Meeting 2014
Volume 59, Number 1
Monday–Friday, March 3–7, 2014; Denver, Colorado
Session D17: Granular Materials & GSNP Student Speaker Session |
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Sponsoring Units: GSNP Room: 402 |
Monday, March 3, 2014 2:30PM - 2:42PM |
D17.00001: Thermodynamics of cellular statistical inference Alex Lang, Charles Fisher, Pankaj Mehta Successful organisms must be capable of accurately sensing the surrounding environment in order to locate nutrients and evade toxins or predators. However, single cell organisms face a multitude of limitations on their accuracy of sensing. Berg and Purcell first examined the canonical example of statistical limitations to cellular learning of a diffusing chemical and established a fundamental limit to statistical accuracy. Recent work has shown that the Berg and Purcell learning limit can be exceeded using Maximum Likelihood Estimation. Here, we recast the cellular sensing problem as a statistical inference problem and discuss the relationship between the efficiency of an estimator and its thermodynamic properties. We explicitly model a single non-equilibrium receptor and examine the constraints on statistical inference imposed by noisy biochemical networks. Our work shows that cells must balance sample number, specificity, and energy consumption when performing statistical inference. These tradeoffs place significant constraints on the practical implementation of statistical estimators in a cell. [Preview Abstract] |
Monday, March 3, 2014 2:42PM - 2:54PM |
D17.00002: Macroscopic consequences of contact breaking in the vibrational response of jammed packings W. Wendell Smith, Mark D. Shattuck, Corey S. O'Hern Computational studies of the linear vibrational response regime of packings of frictionless spherical particles have yielded many insights into our understanding of the mechanical properties of amorphous solids. However, many jammed systems such as granular media display strongly nonlinear vibrational response. Even the model systems of spherical particles that interact via purely repulsive linear springs and are typically used in computational studies of jamming display nonlinear vibrational response due to the breaking and forming interparticle contacts.\\ In this work, we perform molecular dynamics simulations of spherical particles with purely repulsive contact interactions and study their vibrational response as a function of the energy and frequency content of the initial perturbation. In particular, we explore the consequences of contact breaking on macroscopic quantities such as the specific heat, momentum current, and energy flux. [Preview Abstract] |
Monday, March 3, 2014 2:54PM - 3:06PM |
D17.00003: Electrical charging of granular media in a shaking experiment Freja Nordsiek, Allison Bradford, Tyler Holland-Ashford, Julia Salevan, Eric Spieglan, Daniel Lathrop We present preliminary results on the electrical charging of granular media (particle size $\sim 100$ $\mu$m to $\sim 1$ mm) shaken between two conducting plates. Voltage measurements were done between the plates for both monodisperse and bidisperse sets of particles. Particle charging and electrical discharges to the plates ($\sim 1$ kV) were observed. We discuss the potential relevance to natural charging phenomena seen in sand storms, volcanic ash clouds, thunderstorms, and thundersnow. Several types of theoretical models seem plausible. [Preview Abstract] |
Monday, March 3, 2014 3:06PM - 3:18PM |
D17.00004: In Granular Charging, Does Size Really Matter? Theodore Siu, Gregory Mattson, Troy Shinbrot Spontaneous charging in systems of particles, causing particle separation and electrical discharges, is commonly observed in pharmaceutical powder beds, sandstorms and natural dust plumes. Previous studies have attributed size difference or external factors such as wind or an outside electric field as the primary driving force behind such large scale charging. In this talk we discuss experimental results showing that systems of uniformly sized particles with no external field still exhibit net polarization and charging buildup. We also present computational results modeled from a variation of Dyson's Ising model, which validates this behavior and predicts new types of phenomena. [Preview Abstract] |
Monday, March 3, 2014 3:18PM - 3:30PM |
D17.00005: Contact Network Statistics During Vibration of Disk Packings Mark R. Kanner, Carl Schreck, Corey O'Hern, Mark D. Shattuck We use simulations of bidisperse disks that interact via purely repulsive linear springs to determine properties of contact networks during vibration at various energies and pressures. From a set of initially existing contacts in a mechanically stable reference state the contact probability during vibration can be predicted by measuring the inter-particle potential before vibration. ~We explore the energy regions below particle rearrangement where our prediction is valid and discuss a physical mechanism for this behavior based on the exchange of potential and kinetic energy between particles. [Preview Abstract] |
Monday, March 3, 2014 3:30PM - 3:42PM |
D17.00006: Mechanical Friction: Tuning the Janssen Pressure by Varying Particle and Wall Geometry Yasin Karim, Eric Corwin Friction provides a way for granular materials to interact with other particles and the system boundaries. Friction mediated interactions can give rise to interesting properties like the Janssen effect, that are unique to granular materials. Using a conveyor belt we study friction-compacted 2D granular systems to explore the effects of changing particle geometries on the underlying physics of the system. As we have previously shown stick-slip motion due to sliding friction forces can relax away particle-wall friction. These tangential forces can be recovered by suitably changing the shape of the side-walls. We report on 2D gears as a model for high-friction granular particles for which tangential forces cannot be relaxed away by vibration. We use such particles to study the Janssen effect in systems with very high inter-particle friction. [Preview Abstract] |
Monday, March 3, 2014 3:42PM - 3:54PM |
D17.00007: Solitary Wave Propagation through 2D Tree-like structures William Falls, Surajit Sen It is well known that a velocity perturbation can travel through a mass spring chain with quadratic and quartic interactions as a solitary and antisolitary wave pair. In this talk we first consider the propagation of such a velocity perturbation for cases where the system has a 2D ``Y'' shaped structure. Where each of the three pieces that make up the ``Y'' are made of a small mass spring chain. From there we consider the case where multiple ``Y'' shaped structures are used to generate a ``tree'' shaped network. We examine the energy transmission properties on these ``tree'' shaped structures and our findings suggest the following broad observations: (i) for strongly nonlinear interactions, mechanical energy propagation resembles pulse propagation with the energy propagation being dispersive in the linear case, (ii) for strongly nonlinear interactions, the ``tree'' like structure acts as an energy gate showing a directional dependence of the perturbation made to the system while the behavior of the linear case shows no such preference, thereby suggesting that such nonlinear structures can act as switches for mechanical energy. [Preview Abstract] |
Monday, March 3, 2014 3:54PM - 4:06PM |
D17.00008: Breaking Size-Segregation Waves in Granular Avalanches Kasper van der Vaart, C.G. Johnson, P. Gajjar, J.M.N.T. Gray, C. Ancey We experimentally prove the existence of the theoretically predicted breaking size-segregation wave within a binary granular avalanche. This complex structure involves the recirculation of particles through a pattern of shocks and rarefaction waves, and causes large particles to accumulate at the avalanche front and small particles in the tail. Using the non-intrusive imaging technique of refractive-index matching we study particle-size segregation inside the flow---far from the sidewall---on an inclined moving-bed channel. In this configuration the bottom layers of the flow are dragged upslope while upper layers are avalanching downslope due to gravity; effectively, the flow remains stationary in the reference frame of the observer. This allows us to time-average discrete particle positions in the steady-state flow and arrive at a continuous particle concentration. The measured particle concentration and particle trajectories match qualitatively with the theoretical predictions. [Preview Abstract] |
Monday, March 3, 2014 4:06PM - 4:18PM |
D17.00009: Acoustic measurements in sheared granular materials Theodore Brzinski, Karen Daniels Acoustic measurements in static, jammed granular materials have revealed an excess of low-frequency vibrational modes which decreases as the confining pressure is increased. This behavior may be analogous to the excess in low-frequency modes associated with the loss of rigidity in molecular and colloidal glasses. To test this analogy, we measure the acoustic emissions from jammed, quasi-2D granular packings under shear. In contrast to static experiments, shear enables direct comparison of acoustic properties as a packing approaches failure. We use a split-bottom geometry with flexible boundaries held under controlled tension, allowing experiments to be conducted at a set confining pressure. [Preview Abstract] |
Monday, March 3, 2014 4:18PM - 4:30PM |
D17.00010: The role of crystal contacts in protein crystallization: soft matter characterization of two protein families Diana Fusco, Jeffrey Headd, Alfonso De Simone, Jun Wang, Patrick Charbonneau Crystallizing proteins is the bottleneck to systematically determining their structures, which are key to understanding certain biological processes and engineering bio-inspired materials. Identifying the conditions under which proteins crystallize should be equivalent to determining their phase diagram, but one typically resorts to combinatorial rather than physics-based sampling of solution conditions to tackle this difficult problem. Although several soft matter ``patchy particle'' models have been suggested to rationalize the phase behavior of proteins, the interactions that drive crystallization are insufficiently characterized for them to be of much use. We use atomistic simulations of solvated proteins of the rubredoxin family to parameterize patchy models. Their phase diagram is then compared with experimental crystallization conditions. The agreement between model and experiment supports the suitability of patchy models to describe globular proteins crystallization and provides physical guidelines to systematically improve protein crystallization experiments. An analogous analysis of ubiquitin, which crystallizes in multiple crystal forms, further clarifies the role of competing patches in controlling crystal assembly. [Preview Abstract] |
Monday, March 3, 2014 4:30PM - 4:42PM |
D17.00011: Coiling rods onto moving substrates Mohammad Jawed, Fang Da, Eitan Grinspun, Pedro Reis We present results on the nonlinear patterns obtained when a thin elastic rod is deployed onto a moving substrate. Our experiments comprise an injector that deposits an elastomeric rod onto a conveyor belt, where it coils in a variety of nonlinear patterns, depending on the control parameters. The portion of the rod that is suspended between the injector and the point of contact with the belt can exhibit strong geometric nonlinearities that are a challenge for traditional analytical and numerical methods. We tackle this challenge by coupling our precision model experiments with cutting-edge simulation tools ported from the computer graphics community. By systematically exploring parameter space, we map out the basins of stability of the various nonlinear coiling patterns, which are then rationalized using a detailed energy balance. We give particular emphasis to the sinusoidal patterns that emerge from a straight-to-meandering instability that we find to be consistent with a Hopf bifurcation. Closed-form solutions are derived to describe the amplitude and wavelength of the meandering patterns. The excellent agreement between experiments, simulations and theory conveys the predictive ability of our tools to be used, upon scaling, in the original engineering applications that motivated this study: serpentines created from the coiling of carbon nanotubes (at the micron-scale) and the laying down of transoceanic undersea cables (at the kilometer-scale). [Preview Abstract] |
Monday, March 3, 2014 4:42PM - 4:54PM |
D17.00012: Origin of Rigidity in Dry Granular Solids Sumantra Sarkar, Bulbul Chakraborty In traditional solids, the resistance to shear is associated with broken translational symmetry as exhibited by a nonuniform density pattern. In this talk, we show that the emergence of shear rigidity in granular solids is a collective process, which is controlled solely by boundary forces, the constraints of force and torque balance, and the positivity of the contact forces, and not energetic or entropic considerations. We present a theoretical framework that connects rigidity to broken translational symmetry in a reciprocal space representing contact forces. We apply our theory to experimentally generated shear-jammed states and show that these states are indeed characterized by a persistent, non-uniform density modulation in force space, which emerges at the shear-jamming transition\footnote{Sumantra Sarkar et al, Phys. Rev. Lett. 111, 068301}. Crucial to these analyses was an algorithm that was developed to obtain the reciprocal space structures for any real space configuration under mechanical equilibrium. Also, this algorithm help us identify the source of plastic failure which leads to avalanches in these systems. We argue that continuum theories of granular solidification and response should be based on the reciprocal space picture. [Preview Abstract] |
Monday, March 3, 2014 4:54PM - 5:06PM |
D17.00013: Mechanics of Miura-ori Origami Lattice Defects Jesse Silverberg, Lauren McLeod, Arthur Evans, Jessica Ginepro, Christian Santangelo, Thomas Hull, Itai Cohen The mechanical properties of origami-inspired materials show remarkable potential for responsive, tunable next-generation materials. For example, the Miura-ori fold is predicted to have negative Poisson ratio and anisotropic compressive properties. Using a custom mechanical testing device and 3D laser profilometry, we investigate the moduli and the role of curvature in setting these material properties. Because defects are known to dramatically alter the bulk properties in other periodic materials, we introduce defects into the folding pattern to investigate their effects on the macroscopic mechanical properties. Interestingly, we find that a single defect increases the overall material stiffness, but the introduction of a second defect in the opposite direction can cancel out the first, tending to restore the original material properties. Moreover, these defect pairs can be arranged to form edge dislocations, grain boundaries, and many other topological configurations familiar from the study of crystallographic lattice defects. [Preview Abstract] |
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