1. Polymer Laboratory, Latvian State Institute of Wood Chemistry, 27 Dzerbenes Street, LV-1006 Riga, Latvia
2. Polymer Institute, Slovak Academy of Sciences, 845 41 Bratislava, Slovakia
3. Department of Nuclear Chemistry, Comenius University in Bratislava, 842 15 Bratislava, Slovakia
4. Institute of Physics, Slovak Academy of Sciences, 845 11 Bratislava, Slovakia
5. Institute for Mechanics of Materials, University of Latvia, 3 Jelgavas Street, LV-1004 Riga, Latvia