Invited Lecture. New results on the electrohydrodynamic instability in nematics

We present theoretical results on the threshold and near-threshold behaviour of electrohydrodynamic convection of planarly aligned nematics under D.C. and A.C. driving. We use the general three dimensional description and include the flexoelectric effect. The experimentally established threshold behaviour is captured in many cases quantitatively, an exception being the extended travelling patterns. Slightly above threshold the observed undulated rolls pose some problems. Defectmediated turbulence can presumably be explained by mean-flow effects.