1. a Physico-Chemistry Department , Tver' State University , Tver', 170002, Russia
2. b Institute of Synthetic Fiber , Tver', 170032, Russia
3. c Physics Department , University Osnabrueck , Barbara str. 7, Osnabrueck, D-49069, Germany
4. d St. Petersburg State University of Technology and Design , B. Morskaya 18, St. Petersburg, 191185, Russia
5. e Ioffe Physico-Technical Institute , Russian Academy of Sciences , St. Petersburg, 194021, Russia