1. General Energy Research Department, Paul-Scherrer-Institut, CH-5232 Villigen, Switzerland, Lehrstuhl für Makromolekulare Stoffe, Technische Universität München, Lichtenbergstrasse 4, D-85747 Garching, Germany, Hahn-Meitner-Institut Berlin GmbH, Glienicker Strasse 100, D-14109 Berlin, Germany, and Condensed Matter Research with Neutrons and Muons, Paul-Scherrer-Institut, CH-5232 Villigen, Switzerland