1. DWI an der RWTH Aachen, Pauwelsstrasse 8, D-52056 Aachen, Germany, Institut für Technische und Makromolekulare Chemie, RWTH Aachen University, Worringer Weg 1, D-52074 Aachen, Germany, Technical University Cluj-Napoca, Department of Physics, RO-400020 Cluj-Napoca, Romania, and University “Aurel Vlaicu” Arad, Bd. Revolutiei 77, RO-310130 Arad, Romania