arXiv subjects

Akinori Awazu

Publications and source records attributed to Akinori Awazu.

31 records · Page 2Linked to original sources

arXiv2010

3D Dune Skeleton Model as a Coupled Dynamical System of 2D Cross-Sections

To analyze theoretically the stability of the shape and the migration process of transverse dunes and barchans, we propose a {\it skeleton model} of 3D dunes described with coupled dynamics of 2D cross-sections. First, 2D cross-sections of a 3D dune parallel to the wind direction are extracted as elements of a skeleton of the 3D dune, hence, the dynamics of each and interaction between them is considered. This model simply describes the essential dynamics of 3D dunes as a system of coupled ordinary differential equations. Using the model we study the stability of the shape of 3D transversal dunes and their deformation to barchans depending on the amount of available sand in the dune field, sand flow in parallel and perpendicular to wind direction.

nlin.PS↗

arXiv2010

Discreteness-Induced Slow Relaxation in Reversible Catalytic Reaction Networks

Slowing down of the relaxation of the fluctuations around equilibrium is investigated both by stochastic simulations and by analysis of Master equation of reversible reaction networks consisting of resources and the corresponding products that work as catalysts. As the number of molecules $N$ is decreased, the relaxation time to equilibrium is prolonged due to the deficiency of catalysts, as demonstrated by the amplification compared to that by the continuum limit. This amplification ratio of the relaxation time is represented by a scaling function as $h = N \exp(-βV)$, and it becomes prominent as $N$ becomes less than a critical value $h \sim 1$, where $β$ is the inverse temperature and $V$ is the energy gap between a product and a resource.

cond-mat.stat-mech↗

arXiv2010

Counter Chemotactic Flow in Quasi-One-Dimensional Path

Quasi-one-dimensional bidirectional particle flow including the effect of chemotaxis is investigated through a modification of the John-Schadschneider-Chowdhury-Nishinari model. Specifically, we permit multiple lanes to be shared by both directionally traveling particles. The relation between particle density and flux is studied for several evaporation rates of pheromone, and the following results are obtained: i) in the low-particle-density range, the flux is enlarged by pheromone if the pheromone evaporation rate is sufficiently low, ii) in the high particle-density range, the flux is largest at a reasonably high evaporation rate and, iii) if the evaporation rate is at the level intermediate between the above two cases, the flux is kept small in the entire range of particle densities. The mechanism of these behaviors is investigated by observing the spatial-temporal evolution of particles and the average cluster size in the system.

nlin.PS↗

arXiv2009

Discreteness-Induced Criticality in Random Catalytic Reaction Networks

Universal intermittent dynamics in a random catalytic reaction network, induced by smallness in the molecule number is reported. Stochastic simulations for a random catalytic reaction network subject to a flow of chemicals show that the system undergoes a transition from a stationary to an intermittent reaction phase when the flow rate is decreased. In the intermittent reaction phase, two temporal regimes with active and halted reactions alternate. The number frequency of reaction events at each active regime and its duration time are shown to obey a universal power laws with the exponents 4/3 and 3/2, respectively. These power laws are explained by a one-dimensional random walk representation of the number of catalytically active chemicals. Possible relevance of the result to intra-cellular reaction dynamics is also discussed.

cond-mat.stat-mech↗

arXiv2008

"Glassy" Relaxation in Catalytic Reaction Networks

Relaxation dynamics in reversible catalytic reaction networks is studied, revealing two salient behaviors that are reminiscent of glassy behavior: slow relaxation with log(time) dependence of the correlation function, and emergence of a few plateaus in the relaxation. The former is explained by the eigenvalue distribution of a Jacobian matrix around the equilibrium state that follows the distribution of kinetic coefficients of reactions. The latter is associated with kinetic constraints, rather than metastable states, and is due to the deficiency of catalysts for chemicals in excess and negative correlation between the two chemical species. Examples are given, and generality is discussed.

cond-mat.dis-nn↗

arXiv2007

Discreteness-induced Transition in Catalytic Reaction Networks

Drastic change in dynamics and statistics in a chemical reaction system, induced by smallness in the molecule number, is reported. Through stochastic simulations for random catalytic reaction networks, transition to a novel state is observed with the decrease in the total molecule number N, characterized by: i) large fluctuations in chemical concentrations as a result of intermittent switching over several states with extinction of some molecule species and ii) strong deviation of time averaged distribution of chemical concentrations from that expected in the continuum limit, i.e., $N \to \infty$. The origin of transition is explained by the deficiency of molecule leading to termination of some reactions. The critical number of molecules for the transition is obtained as a function of the number of molecules species M and that of reaction paths K, while total reaction rates, scaled properly, are shown to follow a universal form as a function of NK/M.

nlin.AO↗

arXiv2006

Complex Transport Phenomena in a Simple Lattice Gas System

The transport phenomena of a nonequilibrium lattice gas system are investigated. We consider a simple system that consists of two particles interacting repulsively and the potential forces acting on these particles. Under an external driving field applied to only one particle, we found the following relation between the mean velocity of the driven particle and the coefficient of effective drag of this particle under certain conditions; With the increase in the mean velocity, the coefficient of effective drag varies in the form, increase $\to$ decrease $\to$ increase $\to$ decrease. Moreover, under other conditions, we found the following relations between these values which show changes similar to those between shear rate and shear viscosity observed in the shear-thickening polymer or colloidal suspensions; With the increase in the mean velocity, the coefficient of effective drag varies in the form, increase $\to$ decrease or decrease $\to$ increase $\to$ decrease. We explain the mechanisms of such phenomena by considering the transition diagrams.

cond-mat.soft↗

arXiv2005

Transmission and Conversion of Energy by Coupled Soft Gears

Dynamical aspects of coupled deformable gears are investigated to clarify the differences of mechanical properties between the machines consist of hard materials and those of soft materials. In particular, the performances of two functions, the transmission and the conversion of the energy, are compared between the hard and soft gears systems. First, the responses of the coupled gears against a constant torque working on one of gears are focused for two types of couplings; P) a pair gears are coupled, and T) three gears are coupled with forming a regular triangle. In systems with the coupling P), we obtain trivial results that the rotational energy can be transmitted to other gear only if these gears are hard enough. On the other hand, in systems with the coupling T), the transmission of the rotational energy to one of the other gears appears only if these gears are soft enough. Second, we show the responses of this system in which one of gears have contact with a high temperature heat bath and the other gears have contact with a 0 temperature heat bath. With the coupling T), the directional rotations appear in two gears having contact with 0 temperature heat bath. Here, the direction of these rotations change depending on the noise strength.

cond-mat.soft↗

arXiv2003

Is relaxation to equilibrium hindered by transient dissipative structures in closed systems?

Dissipative structures are generally observed when a system relaxes from a far from equilibrium state. To address the reverse question given by the title, we investigate the relaxation process in a closed chemical reaction-diffusion system which can potentially form Turing-like patterns during the transient. We find that when certain conditions are fulfilled the relaxation process is indeed drastically hindered, once the pattern is formed. This slowing-down is shown to be due to stepwise relaxation, where each plateau in the relaxation process corresponds to residence at a certain spatial pattern. Universality of the phenomena as well as their biological relevance is briefly discussed.

nlin.PS↗

arXiv2003

Segregation and Phase Inversion in a Simple Granular System

The segregation and the phase inversion are investigated through a simple granular system which consists of only two inelastic hard spheres in a square box with an energy source. With the variation of the coefficient of restitution, the mass ratio between two spheres or the box size, we show that two types of segregated states and crossover between them are realized in such a small simple system.

cond-mat.soft↗

arXiv2000

Effective Dimension Transition of the Dynamics of Granular Materials in the Pipe

Phase transition of strongly excited granular materials in 2D pipe is investigated numerically. By changing the ratio between width of the pipe and the height of the granular bed, we observe the transition between the 1 dimensional like state and the actual 2 dimensional state. Moreover, it is found that the character of the transition changes when the magnitude of dissipation passes through a critical value.

cond-mat↗

arXiv2000

Liquid-Solid Phase Transition of the System with Two particles in a Rectangular Box

We study the statistical properties of two hard spheres in a two dimensional rectangular box. In this system, the relation like Van der Waals equation loop is obtained between the width of the box and the pressure working on side walls. The auto-correlation function of each particle's position is calculated numerically. By this calculation near the critical width, the time at which the correlation become zero gets longer according to the increase of the height of the box. Moreover, fast and slow relaxation processes like $α$ and $β$ relaxations observed in supper cooled liquid are observed when the height of the box is sufficiently large. These relaxation processes are discussed with the probability distribution of relative position of two particles.

cond-mat↗

arXiv1999

Size Segregation and Convection of Granular Mixtures Almost Completely Packed in the Rotating Thin Box

Size segregation of granular mixtures which are almost completely packed in a rotating drum is discussed with an effective simulation and a brief analysis. Instead of a 3D drum, we simulate 2D rotating thin box which is almost completely packed with granular mixtures. The phase inversion of radially segregated pattern which was found in a 3D experiment are qualitatively reproduced with this simulation, and a brief analysis is followed. Moreover in our simulation, a global convection appears after radial segregation pattern is formed, and this convection induces axially segregated pattern.

cond-mat.stat-mech↗