[1] Voronezh State Univ, Math Phys & Informat Technol Dept, Voronezh 394018, Russia
[2] Russian Acad Sci, Prokhorov Gen Phys Inst, Moscow 119991, Russia
[3] Univ Wuppertal, Appl & Computat Math, Gaussstr 20, D-42119 Wuppertal, Germany
[4] Russian Acad Sci, Inst Marine Technol Problems, Far East Branch, Vladivostok 690091, Russia