Observation of stable phase jump lines in convection of a twisted   nematic
  We report observations of stable, localized, line-like structures in the spatially periodic pattern formed by nematic electroconvection, along which the phase of the pattern jumps by $\pi$. With increasing electric voltage, these lines form a grid-like structure that goes over into a structure indistinguishable from the well known grid pattern. We present theoretical arguments that suggest that the twisted cell geometry we are using is indirectly stabilizing the phase jump lines, and that the PJL lattice is caused by an interaction of phase jump lines and a zig-zag instability of the surrounding pattern. 
Soichi Tatsumi, A. G. Rossberg and Masaki Sano