Aperiodic and incommensurate structures

This minisymposium concerned with symmetry and theory included a discussion of random tiling theory treating diffuse scattering from phason fluctuations in a hydrodynamic approach (M. Widom); colour symmetry of aperiodic structures (R. Lifshitz); a reversible phase transition from a quasiperiodic to a periodic structure with tetrahedral symmetry (M. de Boissieu); and generalization of the symmetry concept to include general point sets, such as model and Meyer sets (D. Joseph). The most mathematical contribution came from J.-L. Verger-Gaugry, who showed calculation of the intensity of systems even in the case of a singular continuous spectrum, and the power laws with which the intensity scales as a function of sample size.