1. Helsinki Biophysics and Biomembrane Group, Institute of Biomedicine/Biochemistry, P.O. Box 63, University of Helsinki, 00014 Helsinki, Finland, MEMPHYS, Center for Biomembrane Physics, Physics Department, University of Southern Denmark, Campusvej 55, DK-5230 Odense M, Denmark, Crime Laboratory, National Bureau of Investigations, P.O. Box 285, 01301 Vantaa, Finland, and Free University of Brussels, Campus Plaine CP 206/2, Boulevard du Triomphe, 1050 Brussels, Belgium