Abstract
Domains meet on walls where the order parameter changes in a continuous or discontinuous way. For aperiodic crystals domain walls may be ordered (discommensurations) or disordered. The dynamics of these domain walls depends strongly on the character (continuous or discontinuous) of the order parameter change. The situation is still more complicated when coupled order parameters are present. A discussion is given of the dynamics in the different cases.
Acknowledgments
The author wants to express his gratitude for the many discussions and for stimulating cooperation with Professor Yoshihiro Ishibashi. He also appreciates the enthusiasm and the practical approach to physical problems of the latter.