Pattern Formation in Nonequilibrium Systems
Satellite Meeting to STATPHYS-22

List of Participants/ Posters

1. S.R. Ahmad: catchrashid@yahoo.com

2. Varsha Banerjee: varsha@physics.iitd.ernet.in

3. Abhik Basu: basu@hmi.de
   Title: Novel universality classes of coupled driven diffusive systems
   Authors: Abhik Basu (Poornaprajna Institute of Scientific Research, Bangalore, India, and Abteilung Theorie, Hahn-Meitner-Institut, Berlin, Germany); and Erwin Frey (Abteilung Theorie, Hahn-Meitner-Institut, Berlin, Germany)
   Abstract: Motivated by the phenomenologies of dynamic roughening of strings in random media and magnetohydrodynamics, we examine the universal properties of a driven diffusive system with coupled fields. We demonstrate that cross-correlations between the fields lead to amplitude-ratios and scaling exponents varying continuously with the strength of these cross-correlations. The implications of these results for experimentally relevant systems are discussed.

4. Sakuntala Chatterjee: sakuntala@theory.tifr.res.in
   Title: Strong System Size Effect on the Dynamics of Coarse-grained Interface Fluctuations
   Authors: Sakuntala Chatterjee and Mustansir Barma, Dept. of Theoretical Physics, Tata Institute of Fundamental Research, Mumbai.
   Abstract: To understand several types of physical processes taking place on fluctuating interfaces, it is useful to study the dynamics of hills and valleys, i.e. those portions of the interface, respectively above and below a reference level. To this end we define a coarse grained variable $\sigma(x,t)= sgn\left [ h(x,t)-\langle h(t)\rangle \right ]$ and study the auto-correlation function $A(t)=\frac{1}{L}\int_{0}^{L}dx\langle \sigma (x,t)\sigma (x,0)\rangle$ . For $t \geq 1$ , our numerical simulations of $1-d$ interface suggests the scaling form $A(t) \sim 1-b \left ( \frac{t}{L^{z}} \right ) ^{\beta}$ , where $z$ is the dynamical exponent and $\beta$ describes the temporal growth of height correlation. The unusual point is that the system size $L$ enters strongly in the decay of $A(t)$ even at small times $(t \geq 1)$ , in contrast to the height-height correlation function. Using the Gaussian character of the Edwards-Wilkinson interface, we are able to calculate $A(t)$ analytically. We verify that the scaling form for $A(t)$ is valid with $\beta = \frac{1}{4}$ , $z=2$ and $b=2/\pi ^{\frac{1}{4}}$ . For the Kardar-Parisi-Zhang interface we have carried out numerical simulations and find that the scaling form holds with $\beta = \frac{1}{3}$ , $z=\frac{3}{2}$ .

5. Apratim Chatterji: apratim@uni-mainz.de
   Title: Simulation Study of Transport Phenomena in (Charged) Colloidal Systems: A New Hybrid MD-LB Method with Hydrodynamic Interactions
   Authors: Apratim Chatterji and Jürgen Horbach
   Abstract: We present a hybrid computational scheme in which we couple Molecular Dynamics (MD) and Lattice Boltzmann (LB) simulation techniques in order to study the dynamics of (charged) colloidal dispersions. We consider explicitly a system of spherical macroions, counterions and coions in the framework of the primitive model. In the LB technique used, a simple kinetic equation is solved on a lattice such that the linearised Navier-Stokes equations are recovered. In our new simulation scheme, we couple the colloidal particles to the LB fluid in order to describe the hydrodynamic interactions, i.e., long-range interactions between the colloids that stem from momentum transport by the fluid. The coupling of the LB fluid with the ionic particles is achieved by exchanging momentum by local viscous forces between the points on the surface of the colloidal particles and the nearest lattice nodes of the LB fluid, keeping the momentum conserved. This is similar to the method used by P. Ahlrichs and B. Dünweg for study of polymeric systems [JCP, 111, 8225, (1999)]. The phase space coordinates of the ionic particles are updated by MD where the forces from the fluid are taken into account. We reproduce the long time tails for the velocity $\vec{v}$ and angular velocity $\vec{\Omega}$ relaxation of a colloidal particle in the fluid, $\vec{v}$ and $\vec{\Omega}$ relax as $t^{-3/2}$ and $t^{-5/2}$ , respectively. We calculate the effective friction coefficient $\xi_{eff}$ of a colloidal particle moving with a constant velocity in a fluid, account for finite size effects, and see that the value of $\xi_{eff}$ is consistent with the stick boundary conditions. Thermal fluctuations applied in our model are in accordance with the fluctuation dissipation theorem. Using this scheme, we measure the translational and rotational diffusion constants as a function of the colloid packing fraction for neutral and charged colloidal systems. We also present results of the investigation of electrokinetic effects by studying the motion of a single macroion, surrounded by counterions and coions, in a flow field.

6. Federico Corberi: corberi@sa.infn.it
   Title: The fluctuation dissipation relation in coarsening systems
   Abstract: The integrated response function in phase-ordering systems with scalar, vector, conserved and nonconserved order parameter is studied at various space dimensionalities. Assuming scaling of the aging contribution $\chi_{ag} (t,t_w)= t_w ^{-a_\chi} \widehat \chi (t/t_w)$ we obtain, by numerical simulations and analytical arguments, the phenomenological formula describing the dimensionality dependence of $a_\chi$ in all cases considered. The primary result is that $a_\chi$ vanishes continuously as $d$ approaches the lower critical dimensionality $d_L$ . This implies that i) the existence of a non trivial fluctuation dissipation relation and ii) the failure of the connection between statics and dynamics are generic features of phase ordering at $d_L$ .

7. Subir Das: subird1@hotmail.com

8. Subhrajit Dutta: subhro@juphys.ernet.in

9. Ebrahim Fouladvand: foolad@mail.znu.ac.ir
   Title: Characteristics of Vehicular Traffic Flow at Roundabout

10. Shamik Gupta: shamikg@godot.theory.tifr.res.in 
    No presentation.

11. Atsunari Katsuki: katsuki@cp.cmc.osakau.ac.jp
    Abstract: Collision processes of two crescentic shaped dunes called barchans are systematically studied using a simple computer simulation model. Two types of collision processes, coalescence and reorganization, are observed, both of which are observed in recent water tank experiments. The realized types of collision depend both on the mass ratio and on the lateral distance between barchans in initial conditions. Besides, a simple set of differential equations to describe the collision of one-dimensional (1D) dunes is introduced. The calculation of the equation indicates that the main features of collision can be reproduced without taking lateral sand flux into account.

12. So Kitsunezaki: kitsune@ki-rin.phys.nara-wu.ac.jp

13. Niraj Kumar: niraj@iopb.res.in
    Title: Front propagation in the restricted bosonic lattice model
    Abstract: We study front propagation in the reaction-diffusion process A+A* )A on the one-dimensional lattice, where maximum of N particles can occupy per lattice site. We observe that velocity and diffusion-coeffcient of the front differ drastically from the mean-field behavior,which is given by Fisher equation. This reflects how the internal fluctuations play an important role in the case of lower values of N. We also discuss some exact results as well as the results based on some approximations for N=2.

14. Akihiko Minami: minami_a@scphys.kyoto-u.ac.jp
    Title: Dislocation Formation in Phase-Separating Alloys
    Abstract: Proliferation of edge dislocations occurs around two-phase boundaries in deeply quenched binary alloys. The dynamics is studied numerically using a nonlinear strain theory in which the elastic energy is a periodic function of the shear and tetragonal strains (a 2D or 3D generalization of the Frenkel-Kontrova model). We find that the dislocations appear near the interface and preferentially glide into the softer regions with smaller shear moduli. The multiple slips thus created result in coherency loss. These effects are important in technology, but have rarely been studied theoretically.

15. Anupam Mukherjee

16. Srutarshi Pradhan: pradhan.srutarshi@phys.ntnu.no
    Title: Failure properties of over-loaded fiber bundles
    Authors: Srutarshi Pradhan, NTNU, Norway
    Abstract: We study the failure properties of fiber bundles at an applied stress (load per fiber) greater than the critical strength ($\sigma_c$ ) of the bundles. These over-loaded bundles finally fails through several stress redistributions. The failure time at different values of applied stress ( $\sigma > \sigma_c$ ) follows a power law decay which helps to determine the exact value of critical strength ($\sigma_c$ ). Also the avalanches of intermediate failures show distinct features. We hope this study should illuminate the nature of breakdown in real materials.

17. Tridib Sadhu: tridib@iitk.ac.in
    No presentation.

18. Prasant Kumar Samantaray: P.K.Samantaray@tnw.tudelft.nl
    Title: Pattern formation in Pulsed Fluidized bed

19. Tania Tome (BRAZIL): ttome@if.usp.br
    Title: Dynamic patterns in cellular automata for Lotka-Volterra models
    Abstract: We study the dynamic patterns exhibited by two probabilistic cellular automata which describe a two-species competing biological system. The birth and death of individuals are described by sthocastic local rules similar to the ones of the contact process. They try to mimic the Lotka-Volterra mechanisms of interactions between competitive species. In one of the models it was exploited the effect of spatial anisotropic rules in the stability of the temporally periodic oscillations. We performed dynamical mean-field approximations and Monte Carlo simulations and verified that oscillations occurs at a local level. We also investigated the nonequilibrium phase transitions between the two possible steady states: an absorbing state and an active state. The latter can or cannot present oscillations, depending on the value of the external parameters.

20. Doris Vollmer (GERMANY): vollmerd@mpip-mainz.mpg.de
    Title: Phase separation in binary mixtures: Oscillatory instabilities under continuously ramping the temperature
    Abstract: The kinetics of phase separation of binary mixtures under slowly ramping the temperature is discussed for systems varying significantly in their microscopic structure. For a broad range of compositions and heating rates pronounced oscillations in the turbidity are reported. It hardly matters if phase separation is induced by cooling or heating, and whether the liquids are of low molecular weight or if polymer solutions are investigated. The origin of the oscillations is discussed on the non-linear advection diffusion equation for the transport of the microscopic constituents. They are caused by repeated cycles of nucleation and coarsening. Finally, the relation of these oscillations to oscillations in chemical systems and their relevance to rain-formation will be addressed.