1. Laboratoire de Physicochimie des Polymères, Université de Mons-Hainaut, Place du Parc, 20, B-7000 Mons, Belgium; Department of Systems Engineering, Nagoya Institute of Technology, Gokiso-cho, Showa-ku, Nagoya 466-8555, Japan; and European Molecular Biology Laboratory, Hamburg Outstation, EMBL c/o DESY, Notkestrasse 85, D-22603 Hamburg, Germany