Bulletin of the American Physical Society
2009 APS March Meeting
Volume 54, Number 1
Monday–Friday, March 16–20, 2009; Pittsburgh, Pennsylvania
Session W9: Systems Far from Equilibrium III |
Hide Abstracts |
Sponsoring Units: GSNP Chair: Narayanan Menon, University of Massachusetts Room: 303 |
Thursday, March 19, 2009 11:15AM - 11:27AM |
W9.00001: Depinning transition in failure of disordered materials Laurent Ponson Crack propagation is the fundamental process leading to
material failure. However, its dynamics is far from being fully
understood. In this work, we investigate both experimentally
and theoretically the far-from-equilibrium propagation of a
crack within a disordered brittle material. The variations of
its growth velocity $v$ with respect to the external driving
force $G$ are carefully measured on a brittle rock of average
fracture energy $\langle \Gamma \rangle$. The crack dynamics is
shown to display two regimes, well described by a sub-critical
creep law $v \sim e^{-\frac{c}{(G- \langle \Gamma \rangle)^
{\mu}}}$ with $\mu \simeq 1$ for $G |
Thursday, March 19, 2009 11:27AM - 11:39AM |
W9.00002: Random Organization and Irreversibility at Plastic Depinning Charles Reichhardt, Cynthia Reichhardt We provide evidence that plastic depinning falls into the same class of phenomena as the random organization which was recently studied for periodically driven particle systems by L.~Corte {\it et al.} [Nature Phys. {\bf 4}, 420 (2008)]. In the plastic flow system that we consider, the pinned regime corresponds to a quiescent state while the moving regime corresponds to a fluctuating state. Upon the sudden application of an external force, the system organizes into one of these two states and the time scale required to reach the final state diverges as a power law when approaching a nonequilibrium transition. We propose a simple experiment to test for this transition in colloidal systems with random disorder and in superconducting vortex systems. [Preview Abstract] |
Thursday, March 19, 2009 11:39AM - 11:51AM |
W9.00003: Static Avalanches in a Random Landscape A. Alan Middleton, Pierre Le Doussal, Kay J. Wiese We study jumps or avalanches in a model of a $d$-dimensional elastic interface that is pinned by disorder and tied to a harmonic spring. The interface configuration is the most stable one, given the disorder and spring position: as the spring is moved, this most stable configuration undergoes discrete jumps or shocks. We carry out numerical simulations to study these shocks and find: (1) detailed qualitative and quantitative verification of the validity of the functional renormalization group analysis of such interfaces and (2) that the distribution of avalanche sizes is numerically consistent with our new calculation of the exact shape of the avalanche distribution, computed in an $\epsilon=4-d$ expansion. The results are quite similar to those seen for dynamic avalanches, where the drive pushes interface configurations between metastable (not globally stable) states. [Preview Abstract] |
Thursday, March 19, 2009 11:51AM - 12:03PM |
W9.00004: A simple model for deformation in solids with universal predictions for stress-strain curves and slip avalanches Karin Dahmen, Yehuda Ben-Zion, Jonathan Uhl A basic model for deformation of solids with only one tuning parameter (weakening epsilon) is introduced. The model can reproduce observed stress-strain curves, acoustic emissions and related power spectra, event statistics, and geometrical properties of slip, with a continuous phase transition from brittle to ductile behavior. Exact universal predictions are extracted using mean field theory and renormalization group tools. The results agree with recent experimental observations and simulations of related models for dislocation dynamics, material damage, and earthquake statistics. [Preview Abstract] |
Thursday, March 19, 2009 12:03PM - 12:15PM |
W9.00005: Hysteresis loop area of the kinetic Ising model with next-nearest neighbor interaction William Baez, Trinanjan Datta, Christian Poppeliers We investigate the effects of the next-nearest neighbor interaction on the hysteresis loop area of the two-dimensional kinetic Ising model subject to a time dependent magnetic field. For the nearest neighbor model it is known that the loop area, $A(H_{o},f)$, has a dispersion relationship given by $A(H_ {o},f) \propto H^{2/3}_{o}f^{1/3}$ in the low frequency limit, $f \rightarrow 0$, where $H_{o}$ is the external magnetic field amplitude. Using the Metropolis algorithm we explore the hysteresis dispersion in the low frequency limit for various external magnetic fields. We find that the hysteresis relationship changes, as compared to the nearest neighbor model, in the presence of next-nearest neighbor interaction. [Preview Abstract] |
Thursday, March 19, 2009 12:15PM - 12:27PM |
W9.00006: Decay of metastable states in the N-neighbor Ising model Ranjit Chacko, Harvey Gould, W. Klein We study the decay of metastable states in the N-neighbor Ising model in which each spin equally interacts with all other spins. Previous work has shown that near the pseudospinodal in an Ising model with long-range interactions nucleation occurs when many clusters which span a correlation volume coalesce to form the nucleating droplet. By observing the decay of a metastable state in the N-neighbor Ising model we can study the effect of the pseudospinodal on nucleation in a model which does not possess a length scale. This study has implications for spin-crossover materials. [Preview Abstract] |
Thursday, March 19, 2009 12:27PM - 12:39PM |
W9.00007: Physical criteria for comparing length and time scales of coarsening models Benjamin Vollmayr-Lee A variety of models have been introduced to study the dynamics of phase separation, ranging from sub-critical kinetic Ising models to phase-field models to Oono and Puri's cell dynamical systems (CDS). These models have in common that at asymptotic late times the dynamics reduces to that of sharp interfaces driven by a surface tension. In practical terms, one is typically interested in simulating these models into the asymptotic late-time regime, but it is not clear how to compare the rates of approach to asymptotia. Additionally, while the sharp interface dynamics have a high degree of universality, it is not clear to what degree this applies to the sub-asymptotic dynamics. A scheme is presented to address these questions. Essentially, one first identifies the relevant parameters that determine the asymptotic dynamics and leading sub-asymptotic dynamics. From these, the appropriate dimensionless measures of effective convergence can be obtained. The technique will be illustrated by a comparison of CDH to the Cahn-Hilliard phase field model. [Preview Abstract] |
Thursday, March 19, 2009 12:39PM - 12:51PM |
W9.00008: Dynamics of Nucleation in the Ising model Seunghwa Ryu, Wei Cai While several theories have been developed to describe the kinetics of first order phase transitions, the range of applicability of each theory is not fully understood due to uncertainties in experiments and numerical difficulties in rare event simulations. In this study, we compute the decay rate of meta-stable states of the Ising model to test the validity of several existing nucleation theories. We employ advanced sampling methods to compute the nucleation rate, which spans a range over ten orders of magnitude, as a function of temperature and external field. Investigation of the critical nuclei and the pre-exponential factor reveals that nucleation in the 2d Ising model is well described by the field-theoretic model of Langer (1969). However, discrepancies between theory and numerical results are observed in the 3d Ising model. This discrepancy points to the importance of the shape of the critical nuclei to the nucleation kinetics. [Preview Abstract] |
Thursday, March 19, 2009 12:51PM - 1:03PM |
W9.00009: Scaling of the Island Density, Size Distribution and Capture Numbers in 3D Nucleation and Growth John Royston, Jacques Amar The results of kinetic Monte Carlo (KMC) simulations of a model of the irreversible nucleation and growth of fractal islands in 3D are presented along with a comparison with rate-equation (RE) results and mean-field (MF) theory. In previous work for point-islands in 3D it was found that both the scaled island-size distribution (ISD) and capture-number distribution (CND) approach the MF prediction of a diverging ISD and size-independent CND in the limit of large $D/F$ (where $D$ is the monomer diffusion rate and $F$ is the deposition rate). In contrast, here we find that the divergence of the ISD with increasing $D/F$ is much weaker for the case of fractal islands while the scaled CND $C(s/S)$ (where $S$ is the average island size) is not constant but increases linearly with island size $s$. We also find that the exponent $\chi$ describing the dependence of the peak island-density on $D/F$ (e.g. $N_{pk} \sim (D/F)^{-\chi}$) deviates significantly from the standard prediction $\chi = 1/3$. Self-consistent RE results for the average island and monomer densities which give good agreement with simulations are also presented, along with an analytical expression for the exponent $\chi$. [Preview Abstract] |
Thursday, March 19, 2009 1:03PM - 1:15PM |
W9.00010: The effects of spatial symmetry breaking on unstable state evolution Rachele Dominguez, Kipton Barros, W. Klein We develop a theory that predicts two distinct stages for the early unstable kinetics of systems with spatial symmetry breaking transitions. In the first stage the kinetics is dominated by symmetry preserving dynamics which acts on a short time scale. In the second stage, which shares some characteristics with the Cahn-Hilliard-Cook theory, noise driven fluctuations break the symmetry of the initial phase on a time scale that is large compared to the first stage for systems with an effective long-range interaction. Our simulations of the initial evolution of a long-range antiferromagnetic Ising model quenched into an unstable region are consistent with our predictions. [Preview Abstract] |
Thursday, March 19, 2009 1:15PM - 1:27PM |
W9.00011: Liquid to solid nucleation through onion-structure droplets Kipton Barros, William Klein We start from a Landau-Ginzburg free energy and develop a theory of crystal nucleation for metastable liquids. Saddle points of the free energy represent nucleating droplets and are obtained analytically and numerically. We find nucleating droplets with hexagonal symmetry in two dimensions and bcc and icosahedral symmetries in three dimensions. Surprisingly, we also find nucleating droplets in three dimensions with a spherically symmetric structure resembling the layers of an onion. These onion-structure objects are the preferred nucleating droplets near the spinodal. We discuss recent experiments and simulations which are consistent with our predictions. [Preview Abstract] |
Thursday, March 19, 2009 1:27PM - 1:39PM |
W9.00012: Dynamical non-ergodic scaling in continuous finite-order quantum phase transitions Shusa Deng, Gerardo Ortiz, Lorenza Viola We investigate the emergence of universal dynamical scaling in quantum critical spin systems adiabatically driven out of equilibrium, with emphasis on quench dynamics which involves non-isolated critical points ( i.e., critical regions) and cannot be a priori described through standard scaling arguments nor time-dependent perturbative approaches. Comparing to the case of an isolated quantum critical point, we find that non-equilibrium scaling behavior of a large class of physical observables may still be explained in terms of equilibrium critical exponents. However, the latter are in general non-trivially path-dependent, and detailed knowledge about the time-dependent excitation process becomes essential. In particular, we show how multiple level crossings within a gapless phase may completely suppress excitation depending on the control path. Our results typify non-ergodic scaling in continuous finite-order quantum phase transitions. [Preview Abstract] |
Thursday, March 19, 2009 1:39PM - 1:51PM |
W9.00013: A deposition model with temperature dependent diffusion Yen-Liang Chou, Michel Pleimling We study a deposition process where the deposed particles are allowed to hope to their neighboring sites with a probability that depends both on the temperature and on the height difference. Changing the temperature, the model evolves from the random deposition model with surface relaxation at zero temperature to the random deposition model at infinite temperature. A generalized dynamic scaling of the surface width as a function of the lattice size, the deposition time, and the temperature is given. The response to a sudden change in temperature is studied. Two types of quenching behavior are observed: a power law decay within the Edwards-Wilkinson regime and an exponential decay in the saturation regime. [Preview Abstract] |
Thursday, March 19, 2009 1:51PM - 2:03PM |
W9.00014: Hydrodynamic limit of a model of unstable diffusive interface growth Matteo Nicoli, Mario Castro, Rodolfo Cuerno Recently we have proposed a stochastic moving boundary model to describe the morphological evolution of a large class of diffusive growth systems, with thin film production by Chemical Vapor Deposition and Electrochemical Deposition (ECD) as relevant physical examples. The model has a direct connection with measurable experimental parameters. In order to study the hydrodynamic limit of this model we have performed a small slopes expansion (SSE) that leads to an effective interfacial stochastic equation (ISE). In case of attachment kinetics much larger than the mean growth velocity the kinetic roughening exponents of this ISE are completely different from those of standard universality classes. This equation is a particular instance of a new class of nonlocal interface equations whose novel properties we have studied by numerical and RG techniques. In order to study the model beyond the SSE we have mapped it into an equivalent phase-field model. Numerical simulations of the latter show a remarkable quantitative agreement with ECD experiments. [Preview Abstract] |
Thursday, March 19, 2009 2:03PM - 2:15PM |
W9.00015: The Isothermal Dendritic Growth Experiment Archive Matthew Koss The growth of dendrites is governed by the interplay between two simple and familiar processes---the irreversible diffusion of energy, and the reversible work done in the formation of new surface area. To advance our understanding of these processes, NASA sponsored a project that flew on the Space Shuttle Columbia is 1994, 1996, and 1997 to record and analyze benchmark data in an apparent-microgravity ``laboratory.'' In this laboratory, energy transfer by gravity driven convection was essentially eliminated and one could test independently, for the first time, both components of dendritic growth theory. The analysis of this data shows that although the diffusion of energy can be properly accounted for, the results from interfacial physics appear to be in disagreement and alternate models should receive increased attention. Unfortunately, currently and for the foreseeable future, there is no access or financial support to develop and conduct additional experiments of this type. However, the benchmark data of 35mm photonegatives, video, and all supporting instrument data are now available at the IDGE Archive at the College of the Holy Cross. This data may still have considerable relevance to researchers working specifically with dendritic growth, and more generally those working in the synthesis, growth {\&} processing of materials, multiscale computational modeling, pattern formation, and systems far from equilibrium. [Preview Abstract] |
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