POSTER SESSION
"MOLECULAR MOTORS AND COLLECTIVE MOTIONS IN BIOLOGY"

JIANG Rui
School of Engineering Science, University of Science and technology of China, Hefei , China
Numerical investigations on coupling of asymmetric exclusion process with zero range process
Rui Jiang, Bin Jia, Mao-Bin Hu, Ruili Wang, and Qing-Song Wu
In recent years, the driven diffusive system has attracted the interests of physicists because it shows a variety of nonequilibrium effects. Some prominent examples are asymmetric simple exclusion processes (ASEPs), and zero-range process (ZRP).
The coupling of ASEPs with other processes has led to many unusual and unexpected phenomena. See, e.g., the investigations on the interplay of ASEP with the creation and annihilation of particles, and the coupling of ASEPs with symmetric diffusive process.
Inspired by the previous works, we study the coupling of ASEPs with ZRP in this paper. Our model is defined in a closed ring system consisting of two equally sized compartments. For the lower compartment, the dynamics is governed by TASEP; for the upper compartment, the dynamics is governed by ZRP. Moreover, particle exchange happens between the two compartments in both ends and in the bulk. We employ Monte Carlo (MC) simulations to characterize the emerging nonequilibrium steady states, and various interesting nonlinear effects are revealed.
In our simulations, the density profiles in both compartments are investigated. Four thresholds for $\omega_{out}$ are identified. In the upper compartment, the density in the left bulk is high and the density in the right bulk is very small when $\omega_{out}=0$. The different densities are separated by a domain wall. With the increase of $\omega_{out}$, the density increases in the right bulk and the domain wall moves left. At the first threshold $\omega_{out}=\omega_{out,1}$, the domain wall reaches the left boundary. For $\omega_{out} > \omega_{out,1}$, a very small density appears in the left bulk. With the increase of $\omega_{out}$, the domain wall moves right and the density in the right bulk continues to increase. When $\omega_{out}$ is larger than a second threshold $\omega_{out,2}$, a zero density will appear in the left bulk and the density in the right bulk reaches one. The state remains if $\omega_{out}$ is smaller than a third threshold $\omega_{out,3}$. When $\omega_{out} > \omega_{out,3}$, the density begins to increase with $\omega_{out}$ in the left bulk and the domain wall moves right. The density in the right bulk is still one. At the fourth threshold $\omega_{out,4}$, the domain wall reaches the right boundary. When $\omega_{out} > \omega_{out,4}$, a zero density appears in the right bulk. The domain wall moves left and the density in the left bulk still increases with the increase of $\omega_{out}$ until $\omega_{out}=1$.
In the lower compartment, the density is very high when $\omega_{out} < \omega_{out,1}$, despite a small density jump exists in the bulk. When $\omega_{out,1} < \omega_{out} < \omega_{out,2}$, the density is monotonically increasing with $x$ in the left bulk and it is high in the right bulk. When $\omega_{out,2} < \omega_{out} < \omega_{out,3}$, a zero density is reached in the left bulk and density one is reached in the right bulk as in the upper compartment. Then similar results as in upper compartment is observed with the increase of $\omega_{out}$.

MULLER Melanie
Max Planck Institute of Colloids and Interfaces, Potsdam, Germany
Bidirectional cargo transport by two species of molecular motors
Melanie J.I. Muller, Stefan Klumpp and Reinhard Lipowsky
Long-range intracellular transport is based on molecular motors that pull cargos along cytoskeletal filaments. One type of motor always moves in one direction, e.~g. conventional kinesin moves to the microtubule plus end, while cytoplasmic dynein moves to the microtubule minus end. However, many cellular cargos are observed to move bidirectionally, involving both plus-end and minus-end directed motors. We present a stochastic 'tug-of-war' model for this scenario, in which motors work independently and are coupled only via the mechanical interaction with their common cargo. Depending on the motor parameters (such as microtubule affinity or stall force), the cargo displays stochastic switching between fast plus end motion,fast minus end motion and / or no significant motion. In the parameter range which leads to switches between fast plus and minus end motion, the motors appear to act in a cooperative way despite the underlying tug-of-war.

SCHADSCHNEIDER Andreas
University of Cologne, Germany
Traffic flow on ant trails: Empirical results
A. John, A. Schadschneider, D. Chowdhury, K. Nishinari
We report results of an empirical study of traffic flow on ant trails. In analogy to vehicular traffic "single-vehicle data" like individual velocities, time-headways etc. have been measured for uni-directional and bi-directional trails. Apart from velocity and headway distributions also fundamental diagrams have been calculated. In contrast to highway traffic no jammed regime is observed and the average velocity is constant over a large density regime. We discuss our findings in terms of the spatio-temporal organisation of the ants on their trails and compare with theoretical predictions of a simple cellular automaton approach.

YANG Xian-qing
College of Science, China University of Mining and Technology, Xuzhou, China
Effects of Detachment and size of particles in Totally Asymmetric Simple Exclusion Processes
Xian-qing Yang, Kang Qiu,Lin Ren, Wen-tao Xu
In this article, the effects of irreversible detachments of particles in totally asymmetric simple exclusion processes (TASEPs) with extended particles which occupy more than one lattice site, are investigated. First, an approximate mean-field theory is used to calculate phase diagrams and density profiles. The results show that the detachment and the size of the particles have distinct effects on the stationary phases in the two sublattices divided by the detachment, especially in the mc/hd and the hd/hd phase. Here, symbols ''mc'', ''hd'', and ''ld'' are initials of maximal current, high density, and low density, respectively, and ''mc/hd'' represents the stationary state that the left sublattice is in the maximum current (mc) phase while the right sublattice is in the high density (hd) phase. When the detachment rate is very large, there are four stationary phases, including ld/ld, ld/hd, mc/ld, and mc/hd phases. When the value of the detachment rate is in the middle range, the hd/hd phase occurs, and hence there exist five stationary phases. When the rate is very small, the mc/hd phase disappears, and there are only four phases again. These theoretical results qualitatively and quantitatively agree with computer Monte Carlo simulations especially in the case of large value of the detachment rate.