Affiliation: | (1) Institute of Solid State Physics, Czechosl. Acad. Sci., Prague, Cukrovarnická 10, Prague 6, Czechoslovakia;(2) Institute of Radioengineering and Electronics, Czechosl. Acad. Sci., Prague, Lumumbova 1, Prague 8, Czechoslovakia;(3) College of Transport Engineering, ilina, Marxe-Engelse 25, ilina, Czechoslovakia |