Fumiko Ogushi

Asymmetric Structure of Gas–Liquid Interface

The density profiles of the gas–liquid interface of the three-dimensional Lennard-Jones (12-6) particle system are studied by nonequilibrium molecular dynamics simulation. The system is a rectangular parallelepiped box of the size of L x ≫ L y × L z . Two Nose–Hoover heat baths with different temperature are attached to the regions near both ends in the x -direction. Heat flows in the system in the x -direction and it maintains the system in a gas–liquid coexisting state. A gas–liquid interface exists steadily in the system box and an asymmetric density profile is observed. We consider the characteristic lengths ξ g and ξ l in the gas and liquid phase sides defined using density in each phase ρ g,l = a ξ g,l -3 , respectively. The sum of the characteristic lengths ξ=ξ g +ξ l corresponds to the thickness of the interface. Using ξ g,l , the density profile in the interface is well described by the tanh form in each phase side ρ g,l ( x )=ρ g,l +β g,l tanh |( x - x 0 )/ξ g,l |. The critical behavior of this ...

Nonequilibrium Microscopic Distribution of Thermal Current in Particle Systems

A nonequilibrium distribution function of microscopic thermal current is studied by a direct numerical simulation in a thermal conducting steady state of particle systems. Two characteristic temperatures of the thermal current are investigated on the basis of the distribution. It is confirmed that the temperature depends on the current direction; Parallel temperature to the heat-flux is higher than antiparallel one. The difference between the parallel temperature and the antiparallel one is proportional to a macroscopic temperature gradient.

A mean-field analysis of the simple model of evolving open systems

A recently reported mechanism of letting evolving systems grow only if the interactions in it is moderately sparse is reviewed and examined. It is shown that the mean field analysis, which is known to give a good simple understanding for this transition from growing to non-growing phase but with about 30% difference in its position, is well improved by taking only mean field type information from the simulation of the original model. This supports the validity of the understanding for the mechanism of the transition, obtained from the mean field analysis. The transition stems from an essential balance of two effects: although having more interactions makes each node robust, it also increases the impact of the loss of a node.

Distribution of microscopic energy flux in equilibrium state

The distribution function P(j) of the microscopic energy flux, j, in equilibrium state is studied. It is observed that P(j) has a broad peak in small j regime and a stretched-exponential decay for large j. The peak structure originates in a potential advection term and energy transfer term between the particles. The stretched exponential tail comes from the momentum energy advection term.

DYNAMICS AND STRUCTURE OF GAS-LIQUID INTERFACE

The structure and the dynamics of the gas-liquid phase interface of the three-dimensional Lennard-Jones (12-6) particle system are studied using nonequilibrium molecular dynamics simulation. Heat flux maintains the system into a gas-liquid coexisting state with a steady interface. In the steady state, the interface shows an asymmetric structure and this is well described by a free energy density model with an asymmetric double-well form. When the system approaches to the steady state, a gas of the temperature profile appears between each phase and the gap value is relaxed to that in the steady state following for large t. It is observed that heat resistance exists in gas-liquid interface in this scale.

Nonequilibrium Distribution of the Microscopic Thermal Current in Steady Thermal Transport Systems

Nonequilibrium distribution of the microscopic thermal current is investigated by direct molecular dynamics simulations. The microscopic thermal current in this study is defined by a flow of kinetic energy carried by a single particle. Asymptotic parallel and antiparallel tails of the nonequilibrium distribution to an average thermal current are identical to ones of equilibrium distribution with different temperatures. These temperatures characterizing the tails are dependent on a characteristic length in which a memory of dynamics is completely erased by several particle collisions. This property of the tails of nonequilibrium distribution is confirmed in other thermal transport systems. In addition, statistical properties of a particle trapped by a harmonic potential in a steady thermal conducting state are also studied. This particle feels a finite force parallel to the average thermal current as a consequence of the skewness of the distribution of the current. This force is interpreted as the microscopic origin of thermophoresis.

Microscopic Energy Flux in Particle Systems and Nonlinear Lattices

We study the distribution of the microscopic energy flux j which is carried by a single particle. It is observed in Lennard-Jones particle system that the distribution of the norm of the energy flux Pn(j) has a broad peak in small j regime and a stretched-exponential decay for large j. The broad peak originates in the potential advection and energy transfer between particles. The stretched exponential tail is from the momentum energy advection.In nonlinear-lattice systems, all the flux components jK , jU , and jF show stretched exponential decay.

Simulation Study of Gas-Liquid Interface

Heat conduction of three-dimensional Lennard-Jones particle system are studied using nonequilibrium moleculer dynamics simulation. Geometry of the system is a rectanguler parallelepiped box of the size of L x ≫ L y × L z. Two Nose-Hoover heat bathes with different temperature T H,L (T H ≥ T L) are attatched on the regions near both ends of x-direction. The density and T H,L are set to be in supercritical fluid, liquid and solid phase. In a single phase system, the heat conductivity shows the system size dependence 1/√L x where L x is the system size. Heat flux keeps the system in a gas-liquid coexisting state and an interface exists steadily. Its interface is thicker in gas-side than in liquid-side. Using a characteristic length X g,l that is desided by the constant density in each phase, we construct a minimul model of an asymmetric interface with tanh form. This model has one parameter L that is the thickness of the interface and this shows good agreement with the simulation results.