1. Fakultät für Mathematik und Naturwissenschaften; Bergische Universität Wuppertal, Arbeitsgruppe Funktionalanalysis; Wuppertal Germany
2. Faculty of Electrical Engineering, Mathematics and Computer Science, Department of Applied Mathematics; University of Twente; Enschede The Netherlands
3. Department of Mechanical Engineering; Eindhoven University of Technology; Eindhoven The Netherlands