Sub-threshold stimuli cannot initiate excitations in active media, but surprisingly as we show in this paper, they can alter the time-evolution of spatially heterogeneous activity by modifying the recovery dynamics. This results in significant reduction of waveback velocity which may lead to spatial coherence, terminating all activity in the medium including spatiotemporal chaos. We analyticall...

An intense cold-atom beam source based on a modified pyramidal magneto-optical trap has been developed and characterized. We have produced a slow beam of cold cesium atoms with a continuous flux of 2.2 3 109 atoms/s at a mean velocity of 15 m/s and with a divergence of 15 mrad. The corresponding radiant intensity is 1.2 3 1013 atom s21 sr21. We have characterized the performance of our beam sou...

Thresholds for the detection of rotation and divergence in the presence of a translational component in sparse random dot patterns are determined for human observers and two computer algorithms. The algorithms only make use of local velocity directions and not of local velocity magnitude (speed). The results show that psychophysical performance in this task can be well described without the nee...

We introduce a hybridizable discontinuous Galerkin method for the incompressible Navier–Stokes equations for which the approximate velocity field is pointwise divergence-free. The method proposed here builds on the method presented by Labeur and Wells [SIAM J. Sci. Comput., vol. 34 (2012), pp. A889–A913]. We show that with simple modifications of the function spaces in the method of Labeur and ...

Developing suitable interpolation methods to simulate dynamic motions of continuous materials such as fluids is an important problem. In this paper, we propose a novel method to enforce the divergence condition to the interpolated velocity field by moving least squares, by means of the diffusive derivatives and moving divergence constraints that allow the practical use and easy implementation. ...

Velocity data from an array of acoustic Doppler current profilers moored about 0 , 140 W from May 1990 through June 1991 during the Tropical Instability Wave Experiment are used in conjunction with Tropical Atmosphere-Ocean array data and a blended sea surface temperature (SST) product to study the processes that control SST variations. The horizontal velocity data allow us to calculate the ver...

Introduction Phase-contrast magnetic resonance imaging (PC-MRI) provides time-resolved 3D information of velocity fields of flowing blood in vessels. It has however been noted that system imperfections including eddy current related phase offsets, sample noise, displacement and partial volume effects can compromise the accuracy of velocity data derived from phase-contrast measurements [1]. If o...

We consider a finite element method of higher order on a quadrilateral or triangular, hexahedral or tetrahedral mesh for solving the Stokes or Navier–Stokes problem by means of discontinuous elements for the pressure and suitable conforming elements for the velocity such that the global and the local inf-sup condition are satisfied. Our goal is the construction of a multigrid solver for the cor...

It is shown that the conforming Q2,1;1,2-Q ′ 1 mixed element is stable, and provides optimal order of approximation for the Stokes equations on rectangular grids. Here Q2,1;1,2 = Q2,1 ×Q1,2 and Q2,1 denotes the space of continuous piecewise-polynomials of degree 2 or less in the x direction but of degree 1 in the y direction. Q′1 is the space of discontinuous bilinear polynomials, with spurious...