Discontinuity walls terminated by twist disclinations in smectic a liquid crystals

A discontinuity wall in smectic A liquid crystals was discussed in M. Klema n: Points, Lines and Walls in Liquid Crystals, Magnetic Systems and Various Ordered Media (J. Wiley, Chichester, 1983). Possible solutions describing a singularity - twist disclination which terminates the discontinuity wall in an infinite model smectic A liquid crystal are discussed. One of solutio ns proposed can be used to describe the so-called zigzag defect line in chi ral smectic C liquid crystals on which opposite oriented chevrons are termi nated.