We investigate thermal relaxation of superfluid turbulence in a highly oblate Bose-Einstein condensate. We generate turbulent flow in the condensate by sweeping the center region of the condensate with a repulsive optical potential. The turbulent condensate shows a spatially disordered distribution of quantized vortices and the vortex number of the condensate exhibits nonexponential decay behavior which we attribute to the vortex pair annihilation. The vortex-antivortex collisions in the condensate are identified with crescent-shaped, coalesced vortex cores. We observe that the nonexponential decay of the vortex number is quantitatively well described by a rate equation consisting of one-body and two-body decay terms. In our measurement, we find that the local two-body decay rate is closely proportional to T 2 /µ, where T is the temperature and µ is the chemical potential.

This article presents the reconfigurable flight controller using an adaptive sliding mode control scheme for actuator fault case. Sliding mode controller, which has good performance for the systems with various uncertainties, is used to deal with the actuator faults. Actuator fault can be considered as a disturbance or an unexpected parameter change, which degrades the system performance and may destabilize the system. In this study, the adaptive sliding mode control technique is adopted to compensate the effects of the disturbance generated by actuator faults. Lyapunov stability theory is used to derive the adaptive rule, and the closed-loop system stability analysis is performed. To demonstrate the effectiveness of the proposed controller, numerical simulation is performed for aircraft having redundant control surfaces.

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We investigate the dissipative dynamics of a corotating vortex pair in a highly oblate axisymmetric Bose-Einstein condensate trapped in a harmonic potential. The initial vortex state is prepared by creating a doubly charged vortex at the center of the condensate and letting it dissociate into two singly charged vortices. The separation of the vortex pair gradually increases over time and its increasing rate becomes higher with increasing the sample temperature $T$. The evolution of the vortex state is well described with a dissipative point vortex model including longitudinal friction on the vortex motion. For condensates of sodium atoms having a chemical potential of $\mu\approx k_B\times 120$ nK, we find that the dimensionless friction coefficient $\alpha$ increases from 0.01 to 0.03 over the temperature range of 200 nK $

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