Affiliation: | (1) Faculty of Mathematics and Physics, Charles University, Ke Karlovu 3, 121 16 Praha 2, Czechoslovakia;(2) Faculty of Physics and Mathematics, Vilnius State University, Knyvos 4s, Vilnius, U.S.S.R;(3) Research Institute of Electrotechnical Ceramics, Pospíilova 281, 500 64 Hradec Králové, Czechoslovakia |