1. Department of Mathematics, Linköping University, Linköping, Sweden.
2. St. Petersburg State University, St. Petersburg, Russia.
3. St. Petersburg State Polytechnical University, St. Petersburg, Russia.
4. Institute of Problems of Mechanical Engineering RAS Laboratory “Mathematical Methods in Mechanics of Materials”, St. Petersburg, Russia.
5. St. Petersburg Department of the Steklov Mathematical Institute, St. Petersburg, Russia.