1. International Tomography Center, Institutskaya 3a, 630090 Novosibirsk-90, Russia, Institute of Experimental Physics, Free University of Berlin, Arnimallee 14, D-14195, Germany, Novosibirsk State University, Novosibirsk 630090, Russia, and Center of Magnetic Tomography and Spectroscopy, Moscow State University, Leninskie Gory 1-73, 119992 Moscow, Russia