Self-Trapping of Bose-Einstein Condensates in an Optical Lattice: the Effect of the System Dimension

In the present paper, we investigate the dynamics of a Bose-Einstein condensates (BEC) loaded into an deep optical lattice of 1D, 2D and 3D, both analytically and numerically. We focus on the self-trapping state and the effect of the system dimension. Under the tight-binding approximation we obtain an analytical criterion for the self-trapping state of BEC using time-dependent variational method. The phase diagram for self-trapping, soliton, breather, or diffusion of the BEC cloud is obtained accordingly and verified by directly solving the discrete Gross-Pitaevskii equation (GPE) numerically. In particular, we find that the criterion and the phase diagrams are modified dramatically by the dimension of the lattices.Comment: 8pages, 9 figure

Numerical simulation on the aerodynamic force of the iced conductor for different angles of attack

According to the galloping mechanism of iced conductors, the aerodynamic simulations were performed based on actual wind tunnel tests. Aeroelastic models of single and bundled conductors with a typical ice-coating section forms (crescent section) were set up. The simulation results were in good agreements with wind tunnel tests, and it showed that numerical simulation method can be used instead of wind tunnel tests. The wind attack angles have seriously affected the aerodynamic force of the iced conductor. The wake of vortex shedding for the iced single conductor was analyzed. As for the iced bundled conductors, sub-conductors at the downstream were seriously influenced by the ones at the upstream locations and the aerodynamic force of the sub-conductors at the downstream was lower than of those at the upstream. The negative slope of Nigol coefficient to the bundled conductors was larger than that of the single wire, but the absolute value of the amplitude was less than that of the single conductor, and the bundled conductors were more likely to gallop than the single ones. The Den. Hartog and O.Nigol mechanism were used to predict galloping of iced conductors, which can be convenient for analyzing vibration of iced conductors

Disturbance-Estimated Adaptive Backstepping Sliding Mode Control of a Pneumatic Muscles-Driven Ankle Rehabilitation Robot.

A rehabilitation robot plays an important role in relieving the therapists' burden and helping patients with ankle injuries to perform more accurate and effective rehabilitation training. However, a majority of current ankle rehabilitation robots are rigid and have drawbacks in terms of complex structure, poor flexibility and lack of safety. Taking advantages of pneumatic muscles' good flexibility and light weight, we developed a novel two degrees of freedom (2-DOF) parallel compliant ankle rehabilitation robot actuated by pneumatic muscles (PMs). To solve the PM's nonlinear characteristics during operation and to tackle the human-robot uncertainties in rehabilitation, an adaptive backstepping sliding mode control (ABS-SMC) method is proposed in this paper. The human-robot external disturbance can be estimated by an observer, who is then used to adjust the robot output to accommodate external changes. The system stability is guaranteed by the Lyapunov stability theorem. Experimental results on the compliant ankle rehabilitation robot show that the proposed ABS-SMC is able to estimate the external disturbance online and adjust the control output in real time during operation, resulting in a higher trajectory tracking accuracy and better response performance especially in dynamic conditions