Affiliation: | (1) Department of Mathematics, Lund Institute of Technology, Box 118, 22100 Lund, Sweden;(2) Institute for Physics, St. Petersburg University, 198904 St. Petersburg, Russia;(3) A. Friedmann Laboratory for Theoretical Physics, 30/32 Griboedov can., St. Petersburg, 191023, Russia;(4) Institute of Mechanical Engineering, Russian Academy of Sciences, 61 Bolshoy, V.O., St. Petersburg, 199178, Russia |