Bulletin of the American Physical Society
2008 APS March Meeting
Volume 53, Number 2
Monday–Friday, March 10–14, 2008; New Orleans, Louisiana
Session Q39: Focus Session: Models and Materials Far from Equilibrium |
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Sponsoring Units: GSNP Chair: Michel Pleimling, Virginia Polytechnic Institute and State University Room: Morial Convention Center 231 |
Wednesday, March 12, 2008 11:15AM - 11:27AM |
Q39.00001: Self-Organized Porous Nanostructures in Anodized Metal Oxide Liam Stanton, Alexander Golovin We consider the self-organization of porous nanostructures in anodized metal oxide. We have developed a mathematical model which incorporates the electro-chemical transport of oxygen anions within the oxide layer and the chemical reactions at the metal-oxide and oxide-electrolyte interfaces. It is shown through linear stability analysis, that a short-wave instability exists in certain parameter regimes which leads to the formation of hexagonally ordered pores observed in anodized aluminum oxide. Numerical simulations validate these results. [Preview Abstract] |
Wednesday, March 12, 2008 11:27AM - 11:39AM |
Q39.00002: Intercalation of Li Ions into a Graphite Anode Material: Molecular Dynamics Simulations Ibrahim Abou Hamad, Mark Novotny Large-scale molecular dynamics simulations of the anode half-cell of a lithium-ion battery are presented. The model system is composed of an anode represented by a stack of graphite sheets, an electrolyte of ethylene carbonate and propylene carbonate molecules, and lithium and hexafluorophosphate ions. The simulations are done in the NVT ensemble and at room temperature. One charging scheme explored is normal charging in which intercalation is enhanced by electric charges on the graphitic sheets. The second charging mechanism has an external applied oscillatory electric field of amplitude A and frequency f. The simulations were performed on 2.6 GHz Opteron processors, using 160 processors at a time. Our simulation results show an improvement in the intercalation time of the lithium ions for the second charging mechanism. The dependence of the intercalation time on A and f will be discussed. [Preview Abstract] |
Wednesday, March 12, 2008 11:39AM - 11:51AM |
Q39.00003: Aging processes in reversible diffusion-limited reactions Vlad Elgart, Michel Pleimling Reversible diffusion-limited reactions display anomalous (i.e. slow) dynamics characterized by a power-law relaxation toward stationarity. In contrast to previous studies that focused on the time-dependence of this relaxation, we study here the nonequilibrium behavior of various simple reversible reaction-diffusion models in the aging regime. Starting from the exact Langevin equations describing these models, we derive expressions for two-time autocorrelation and autoresponse functions and obtain a simple aging behavior for these quantities. The autoresponse function is thereby found to depend on the specific nature of the chosen perturbation of the system. [Preview Abstract] |
Wednesday, March 12, 2008 11:51AM - 12:03PM |
Q39.00004: Lyapunov modes in coupled map lattices Guenter Radons, Hongliu Yang Hydrodynamic Lyapunov modes, which have recently been observed in many extended systems with translational symmetry, such as hard sphere systems, dynamic XY-models, or Lennard-Jones fluids, are nowadays regarded as fundamental objects connecting Nonlinear Dynamics and Statistical Physics. A solution to one of the puzzles, the appearance of good and of ``vague'' modes, is presented here for the model system of coupled map lattices: The structural properties of these modes are related to the phase space geometry, especially the angles between Oseledec subspaces, and to fluctuations of local Lyapunov exponents. The numerical calculation of these quantities is achieved with the new algorithm proposed in [1]. In this context we report also on the possible appearance of branches in the Lyapunov spectra of inhomogeneous systems [2], similar to acoustic and optical branches for phonons. \newline [1] F. Ginelli et al., PRL 99, 130601 (2007) \newline [2] H. Yang and G. Radons, PRL 99, 164101 (2007) [Preview Abstract] |
Wednesday, March 12, 2008 12:03PM - 12:15PM |
Q39.00005: Simulation of nonlinear pattern formation dynamics in photoinduced structure change Kunio Ishida, Keiichiro Nasu We study the nonlinear dynamics of pattern formation triggered by injection of photoexcited states. In order to describe the nonadiabatic transition during the relaxation process, we employ a model of localized electrons coupled with a fully quantized phonon mode, and the time-dependent Schr\"odinger equation for the model is numerically solved. We found that the photoinduced nucleation process is switched on only when certain amount of excitation energy is supplied in a narrow part of the system, i.e., there exists a smallest cluster of excited molecules which makes the nucleation possible. As a result, the portion of the cooperatively converted molecules is nonlinearly dependent on the photoexcitation strength, which has been observed in various materials. [Preview Abstract] |
Wednesday, March 12, 2008 12:15PM - 12:27PM |
Q39.00006: A study of some non-equilibrium driven models and their contribution to the understanding of molecular motors Irina Mazilu, Joshua Gonzalez From the point of view of a physicist, a bio-molecular motor represents an interesting non-equilibrium system and it is directly amenable to an analysis using standard methods of non-equilibrium statistical physics. We conduct a rigorous Monte Carlo study of three different driven lattice gas models that retain the basic behavior of three types of cytoskeletal molecular motors. Our models incorporate novel features such as realistic dynamics rules and complex motor-motor interactions. We are interested to have a deeper understanding of how various parameters influence the macroscopic behavior of these systems, what is the density profile and if the system undergoes a phase transition. On the analytical front, we computed the steady-state probability distributions exactly for the one of the models using the matrix method that was established in 1993 by B. Derrida et al. We also explored the possibilities offered by the ``Bethe ansatz'' method by mapping some well studied spin models into asymmetric simple exclusion models (already analyzed using computer simulations), and to use the results obtained for the spin models in finding an exact solution for our problem. We have exhaustive computational studies of the kinesin and dynein molecular motor models that prove to be very useful in checking our analytical work. [Preview Abstract] |
Wednesday, March 12, 2008 12:27PM - 12:39PM |
Q39.00007: Controlling surface morphologies by time-delayed feedback Beate Schmittmann, Michael Block, Eckehard Schoell We propose a new method to control the roughness of a growing surface, via a time-delayed feedback scheme. The method is very general and can be applied to a wide range of non-equilibrium growth phenomena, from solid-state epitaxy to tumor growth. Possible experimental realizations are suggested. As an illustration, we consider the Kardar-Parisi-Zhang equation in 1+1 dimensions and show that the effective growth exponent of the surface width can be stabilized at any desired value in the interval [0.25,0.33], for a significant length of time. [Preview Abstract] |
Wednesday, March 12, 2008 12:39PM - 12:51PM |
Q39.00008: Schwinger-Keldysh Formalism for Non-Hermitian Quantum Problems: A Case Study on Non-Equilibrium Steady State Transport Paata Kakashvili, C.J. Bolech Non-unitary quantum mechanics has been used in the past to study irreversibility, dissipation and decay in a variety of physical systems. In this presentation, we propose a general scheme to deal with systems governed by non-Hermitian Hamiltonians. We argue that the Schwinger-Keldysh formalism gives a natural description for those problems. To be concrete, we study a simple model inspired by mesoscopic physics --an asymmetric junction (relevant to spin-valve devices). The system is governed by a non-Hermitian Hamiltonian which captures essential aspects of irreversibility. Calculated steady state transport properties show behavior which is anticipated on physical grounds. [Preview Abstract] |
Wednesday, March 12, 2008 12:51PM - 1:03PM |
Q39.00009: ABSTRACT WITHDRAWN |
Wednesday, March 12, 2008 1:03PM - 1:15PM |
Q39.00010: Caliber approach for non-equilibrium systems with a small number of states Jeremy Schmit, Kingshuk Ghosh, Ken Dill We present a theory for the dynamics of systems with a small number of states based on E.T. Jaynes' principle of Maximum Caliber. We construct the full dynamical partition function using a transfer matrix formalism with the transition rates as input parameters. Using this partition function, we are able to calculate all moments of dynamical quantities, and thus are able to predict fluctuations around the average behavior. We compare our results to single molecule and microfluidics experiments and contrast our results to the predictions of Minimum Entropy Production. [Preview Abstract] |
Wednesday, March 12, 2008 1:15PM - 1:27PM |
Q39.00011: Transition rates for a Blume-Capel model coupled to a phonon bath Kyungwha Park In nanoscale systems ranging from semiconductor quantum dots to arrays of magnetic nanoparticles or nanoscale magnetic molecules, dynamic properties play a crucial role in understanding the underlying physics and in designing systems of interest for applications. Dynamic properties are highly sensitive to transition rates used, so it is crucial to use a physically correct stochastic dynamic to examine dynamic properties. However, spin Hamiltonians do not provide generic dynamics, so a dynamic should be determined from microscopic Hamiltonians. As the first step towards deriving a realistic spin dynamic of nanoscale systems, we consider the ferromagnetic S=1 Blume-Capel model on a square lattice in which each spin is weakly coupled to a d-dimensional phonon bath, and derive transition rates from a spin-phonon coupling Hamiltonian. Based on the derived transition rates, dynamical properties such as metastability and nucleation are studied in the low-temperature limit using kinetic Monte Carlo simulations. The properties obtained from the phonon-assisted transition rates are compared with those from the Glauber transition rate. [Preview Abstract] |
Wednesday, March 12, 2008 1:27PM - 1:39PM |
Q39.00012: Statistical mechanics far from equilibrium: prediction and test for a sheared system A. Baule, R. M. L. Evans, R. A. Simha, P. D. Olmsted Beginning from a description of the forces of interaction between microscopic particles in motion, equilibrium statistical mechanics can predict both the statistical properties of their resulting configurations and the properties of the fluid (or other material) that they constitute. Despite the existence of statistical steady states of complex fluids under continuous shear flow, with intriguing similarities to equilibrium phase behaviour, a similarly complete statistical solution has hitherto been unobtainable away from thermodynamic equilibrium. Instead, theorists have had to resort to artificial models with simple dynamics (e.g. some invented set of microscopic transition rates) or, alternatively, to use near-equilibrium approximations. We report the first complete statistical treatment of a collection of particles interacting via Newtonian forces in the presence of continuous boundary-driven flow, arbitrarily far from equilibrium [1]. Our investigation is based on a non-equilibrium counterpart to detailed balance [2] which leads to a set of simple constraints for the driven transition rates in our model system. We have tested the predictions in simulations, by numerically solving and time-stepping the force-balance equations. [1] R. M. L. Evans, R. A. Simha, A. Baule and P. D. Olmsted, to be submitted. [2] R. M.L. Evans, Phys. Rev. Lett. 92, 150601 (2004). [Preview Abstract] |
Wednesday, March 12, 2008 1:39PM - 2:15PM |
Q39.00013: Dynamic phase transitions in model glass formers Invited Speaker: Glassy dynamics is identified through a series of signatures, such as aging, slow relaxation and the presence of dynamical heterogeneities. Basing our considerations on kinetically constrained glass formers, we argue that these phenomena are the byproduct of an intrinsically dynamic phase transition. The latter can be unravelled by performing, in the spirit of Ruelle, a Gibbs-like statistical mechanics over the set of time realizations of the systems' evolution, rather than over the conventional set of phase space configurations. [Preview Abstract] |
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