1. University of Patras, Department of Physics, GR 26 500, Patras, Greece, FORTH, P.O. Box 1527, GR 711 10, Heraklion, Crete, Greece, LANSCE, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, and CSIRO, Division of Chemicals and polymers, Private Bag 1D, Rosebank MDC, Clayton, Victoria 3169, Australia