1. Technische Universität München, Physik-Department, Physik weicher Materie; James-Franck-Str. 1 85748 Garching Germany
2. IMFUFA, Department of Science, Systems and Models; Roskilde University; P.O. Box 260, 4000 Roskilde Denmark
3. Deutsches Elektronen-Synchrotron (DESY); Notkestr. 85 Hamburg Germany
4. Cornell High Energy Synchrotron Source (CHESS), Wilson Laboratory,; Cornell University; Ithaca, New York 14853 USA