Fatkhulla Abdullaev Theor. Div. of Phys.-Techn. Inst. Uzbek Academy of Sciences Gani Mavlyanova str. 2-b 700084 Taschkent-84 Uzbekistan E-mail: fatkh@pti.tashkent.su Phone work: (+7) 3712 354338 Phone home: (+7) 3712 444769 Fax: (+7) 3712 354311