Bénard-von Kármán vortex street in a spin-orbit-coupled Bose-Einstein condensate.

The dynamics of pseudo-spin-1/2 Bose-Einstein condensates with weak spin-orbit coupling through a moving obstacle potential are studied numerically. Four types of wakes are observed and the phase diagrams are determined for different spin-orbit coupling strengths. The conditions to form Bénard-von Kármán vortex street are rather rigorous, and we investigate in detail the dynamical characteristics of the vortex streets. The two point vortices in a pair rotate around their center, and the angular velocity and their distance oscillate periodically. The oscillation intensifies with increasing spin-orbit coupling strengths, and it makes part of the vortex pairs dissociate into separate vortices or combine into single ones and destroys the vortex street in the end. The width b of the street and the distance l between two consecutive vortex pairs of the same circulation are determined by the potential radius and its moving velocity, respectively. The b/l ratios are independent of the spin-orbit coupling strength and fall in the range 0.19-0.27, which is a little smaller than the stability criterion 0.28 for classical fluids. Proper b/l ratios are necessary to form Bénard-von Kármán vortex street, but the spin-orbit coupling strength affects the stability of the street patterns. Finally, we propose a protocol to experimentally realize the vortex street in ^{87}Rb spin-orbit-coupling Bose-Einstein condensates.

Shock wave due to the short-period impact in one-dimensional plasticity bead chain.

The waves in a one-dimensional (1-D) bead chain produced by a constant velocity impact in a short period are studied numerically in the present paper. It seems that in some cases, the waves look like a shock wave, while in other cases they may be composed of several solitary waves or some oscillations. These characteristics depend on both the bead parameters and the impact parameters, such as the plasticity of the bead material, the piston velocity and the impact duration. It is found that the shock structure appears if the duration of the impact is longer, while it will evolve into several solitary waves if the duration of the impact is small enough. This indicates that the bead velocity attenuates with power function. The strength of the attenuation depends on the plasticity, the piston velocity and the bead radius.

Existence and damping of dust acoustic solitary waves in a bounded geometry.

The propagation of the solitary wave in a dusty plasma bounded in finite geometry has been investigated. By employing the reductive perturbation method, we obtain a quasi Korteweg-de Vries-type equation. It is noted that the larger the value of viscosity coefficient µ(0), the stronger the damping of the solitary wave. On the other hand, the larger the value of the radius of bounded geometry R, the weaker the damping of the solitary wave. It is also found that the quasisolitary wave exists. However, the solitary wave is a damping one, and it will disappear in the limited case of R→0 or µ(0)→+∞.