Tkachenko, Viktor I., National Science Center «Kharkov Institute Of Physics And Technology» The National Academy of Science of Ukraine 61108, Kharkov, Akademicheskaya str., 1, phone/fax 8-057-335-08-47V.N. Karazin Kharkov National University61022, Kharkov, Svoboda square, 4, phone/fax 8-057-705-14-05, Ukraine