Annular electroconvection with shear

We report experiments on convection driven by a radial electrical force in suspended annular smectic-A liquid crystal films. In the absence of an externally imposed azimuthal shear, a stationary 1D pattern consisting of symmetric vortex pairs is formed via a supercritical transition at the onset of convection. Shearing reduces the symmetries of the base state and produces a traveling 1D pattern whose basic periodic unit is a pair of asymmetric vortices. For a sufficiently large shear, the primary bifurcation changes from supercritical to subcritical. We describe measurements of the resulting hysteresis as a function of the shear at radius ratio eta similar to 0.8. [S0031-9007(97)05181-8].