Affiliation: | a Department of Metal Physics, Charles University Prague, Ke Karlovu 5, 121 16, Prague 2, Czech Republic;b Department of Applied Mathematics, VSB-Technical University Ostrava, 17. listopadu 15, 708 33, Ostrava 8, Czech Republic;c Department for Mathematics, University of Graz, Heinrichstrasse 36, A-8010, Graz, Austria |