1. Institute
for Applied Physics, Justus-Liebig-Universität, 35392 Gießen, Germany
2. CCMS,
Institute of Physics, Slovak Academy of Sciences, 845 11 Bratislava, Slovakia
3. Institute
of Informatics, Slovak Academy of Sciences, 845 07 Bratislava, Slovakia
4. Department
of Natural Sciences, University of Ss. Cyril and Methodius, 917 01 Trnava, Slovakia