Yafeng He

Self-Organized Gas-Discharge Patterns in a Dielectric-Barrier Discharge System

A rich variety of gas-discharge patterns have been observed in a specially designed dielectric-barrier discharge system with two liquid electrodes. The patterns presented here include square-lattice pattern, square-texture pattern, square-superlattice pattern, hexagonal superlattice state, multiarmed-spiral pattern, hollow-hexagonal pattern, and rotating-wheels pattern.

Rectification and diffusion of self-propelled particles in a two-dimensional corrugated channel.

Rectification and diffusion of noninteracting self-propelled particles is numerically investigated in a two-dimensional corrugated channel. From numerical simulations, we obtain the average velocity and the effective diffusion coefficient. It is found that the self-propelled particles can be rectified by the self-propelled velocity. There exist optimal values of the parameters (the self-propelled velocity, the translational diffusion constant, and the height of the potential) at which the average velocity takes its maximal value. There exists an optimal translational diffusion at which the effective diffusion constant is maximal. The self-propelled velocity can strongly increase the effective diffusion, while the large rotational diffusion rate can strongly suppress the effective diffusion.

Concentric-roll pattern in a dielectric barrier discharge in air

Concentric-roll pattern in a dielectric barrier discharge in air at pd value 29.3 hPa cm is observed in the presence of circular boundary and studied by an optical method for the first time. The weak correlation between microdischarges in concentric-roll patterns indicates that the concentric roll is a spatiotemporal chaos although the space integral of microdischarges is quasiperiodic in time. Spatiotemporal measurements of microdischarges suggest that the effective electric field near the boundary is weaker than that in the interior region. The bifurcation of concentric-roll patterns with the increase of voltage and selection of characteristic wavelength are also studied.

Formation of white-eye patterns with microdischarge in an air dielectric-barrier-discharge system.

We report on the observation of a white-eye pattern in an air dielectric barrier discharge. The patterned discharges undergo a development as follows: random spots-quasihexagonal pattern-hexagonal pattern (type I)-hexagonal pattern (type II)-white-eye pattern-chaos, as the voltage is increased. The spatiotemporal characteristics of the patterned discharges are investigated by using an optical method. Results show that the two discharge modes, uniform mode and filamentary mode, are actually two different spatial presentations of the same origin: the microdischarge. From the viewpoint of pattern dynamics, the white-eye pattern results from a three-wave resonance interaction.

Simulation of stationary glow patterns in dielectric barrier discharges at atmospheric pressure

Self-organized stationary patterns in dielectric barrier discharges operating in glow regime at atmospheric pressure are investigated by a self-consistent two-dimensional fluid model. The simulation results show that two different modes, namely, the diffuse mode and the static patterned mode, can be formed in different ranges of the driving frequency. The discharge operates in Townsend regime in the diffuse mode, while it operates in a glow regime inside the filaments and in a Townsend regime outside the filaments in the stable pattered mode. The forming process of the stationary filaments can be divided into three stages, namely, destabilizing stage, self-assembling stage, and stable stage. The space charge associated with residual electron density and surface charge is responsible for the formation of these stationary glow patterns.

Entropic Ratchet transport of interacting active Brownian particles

Directed transport of interacting active (self-propelled) Brownian particles is numerically investigated in confined geometries (entropic barriers). The self-propelled velocity can break thermodynamical equilibrium and induce the directed transport. It is found that the interaction between active particles can greatly affect the ratchet transport. For attractive particles, on increasing the interaction strength, the average velocity first decreases to its minima, then increases, and finally decreases to zero. For repulsive particles, when the interaction is very weak, there exists a critical interaction at which the average velocity is minimal, nearly tends to zero, however, for the strong interaction, the average velocity is independent of the interaction.

Transport in periodic potentials induced by fractional Gaussian noise.

Directed transport of overdamped Brownian particles driven by fractional Gaussian noises is investigated in asymmetrically periodic potentials. By using Langevin dynamics simulations, we find that rectified currents occur in the absence of any external driving forces. Unlike white Gaussian noises, fractional Gaussian noises can break thermodynamical equilibrium and induce directed transport. Remarkably, the average velocity for persistent fractional noise is opposite to that for antipersistent fractional noise. The velocity increases monotonically with Hurst exponent for the persistent case, whereas there exists an optimal value of Hurst exponent at which the velocity takes its maximal value for the antipersistent case.

Generation of tunable plasma photonic crystals in meshed dielectric barrier discharge

Tunable superlattice plasma photonic crystals are obtained in a meshed dielectric barrier discharge. These plasma photonic crystals are composed of thin artificial lattices and thick self-organized lattices, and can be tuned easily by adjusting the applied voltage. A plasma photonic crystal with self-organized hexagonal lattice coupled to artificial square lattice is first realized. The dispersion relations of the square sublattices with different radii, which are recorded by an intensified charge-coupled device camera, are calculated. The results show that the thick square sublattice has the higher band edge frequencies and wider band widths. Band gaps of superlattice plasma photonic crystals are actually temporal integrations of those of transient sublattices.

Core dynamics of a multi-armed spiral pattern in a dielectric barrier discharge

Stable multi-armed spiral patterns have been observed in a gas discharge by using water electrodes. It is found that the multi-armed spirals in our experiments generally result from the interaction between a single-armed spiral pattern and dislocations. The number of spiral arms can be increased or decreased depending on the topological charge of the dislocation when it glides into the spiral core. The complex spatiotemporal dynamics of the multi-armed spiral tips has also been investigated. The spiral tips rotate about a common circle for a two-armed spiral pattern. The core dynamics of a three-armed spiral pattern involves intermittent pairwise collision of tips at or near their tips, and it is more complex for a four-armed spiral pattern.

Enhancement of the longitudinal transport by a weakly transversal drive.

Transport of Brownian particles in a two-dimensional asymmetric tube is investigated by applying a polarized field. From the Brownian dynamics simulations, we find that the longitudinal current can be enhanced remarkably by applying a weakly transversal drive. Multiple current reversals can be realized by altering the driving frequency of the polarized field. By coupling the longitudinal and transversal forces together, one can control the particle transport flexibly.