This paper addresses the drag force and formation of vortices in the boundary layer of a Bose-Einstein condensate stirred by a laser beam following the experiments of Phys. Rev. Lett. 83, 2502 (1999)]. We make our analysis in the frame moving at constant speed where the beam is fixed. We find that there is always a drag around the laser beam. We also analyze the mechanism of vortex nucleation. ...

The 1D flow of a continuous beam of Bose-Einstein condensed atoms in the presence of an obstacle is studied as a function of the beam velocity and of the type of perturbing potential (representing the interaction of the obstacle with the atoms of the beam). We identify the relevant regimes: stationary/time-dependent and superfluid/dissipative; the absence of drag is used as a criterion for supe...

Subjects observed a random dot pattern that moved horizontally with modulated velocity within an invisible aperture. The velocity contrast, (V2-V1)/V1, was 2/3. Two different percepts occurred while observing this stimulus. At lower modulation frequencies, between 2 and 12 Hz, velocity changes were clearly seen; this percept is called "motion irregularity". At frequencies higher than 20 Hz velo...

The direciional backprojection i s one of the primary tools used b y fine-motion planning systems. Informally, a directional backprojection i s the set of configurations f rom which a commanded motion i s guaranteed to reach a goal configuration. It has been shown that, for force controlled motions, the topology of the directional backprojection only changes at a finite set of critical velocity...

We study numerically thermal effects at the depinning transition of an elastic string driven in a two-dimensional uncorrelated disorder potential. The velocity of the string exactly at the sample critical force is shown to behave as V~T(ψ), with ψ the thermal rounding exponent. We show that the computed value of the thermal rounding exponent, ψ=0.15, is robust and accounts for the different sca...

BACKGROUND This study was designed to determine the minimal mean flow velocity and pressure-flow relation necessary to preserve human consciousness. METHODS Passive upright tilt provocation was used in conjunction with transcranial Doppler in 80 patients with a history of syncope of unknown etiology. Cerebral blood flow velocity, blood pressure, and heart rate were monitored noninvasively. ...

abstract study of turbidity current hydrodynamics plays an important role in increasing the economical life of dams though reduction in sediment accumulation. in the present experimental study, the effect of entrance densimetric froude number of turbidity current in sub and super critical conditions (fr =0.6-3.5) have been tested through effect of channel slope and change related to opening hei...

The flashback or propagation of premixed flames along the near-wall low-velocity region at the base of a laminar boundary layer of a reactive mixture has been studied numerically. The analysis, carried out using the constant density approximation for an Arrhenius overall reaction, accounts for the effects of the Lewis number of the fuel. The flow field, as seen by an observer moving with the fr...

The aim of this study was to investigate the influence of interpersonal interactions between players on the regulation of ball passing velocity in the team sport of futsal. For this purpose 28 sequences of play, in which passes were performed between outfield players, were selected from an elite futsal competition and analyzed using TACTO software. Relative angles between attackers and defender...