1. Physical Chemistry 1, Center for Chemistry and Chemical Engineering, University of Lund, P. O. Box 124, S-221 00 Lund, Sweden
2. Laboratoire de Physico-Chimie Macromoléculaire, Université P. et M. Curie, CNRS URA-278, ESPCI, 10 rue Vauquelin, F-75231 Paris cedex 05, France
3. Physics Department, Risø National Laboratory, DK-4000 Roskilde, Denmark