1. Research Laboratory for Mechanics of New Nanomaterials, St Petersburg State Polytechnical University, St Petersburg 195251, Russia
2. Institute of Problems of Mechanical Engineering, Russian Academy of Sciences, Bolshoj 61, Vasil. Ostrov, St Petersburg 199178, Russia
3. Department of Mathematics and Mechanics, St Petersburg State University, Universitetskii pr. 28, Staryi Petergof, St Petersburg 198504, Russia