1. Institute of Physiology of the Czech Academy of Sciences; Videnska 1083 142 20 Prague 4 Czech Republic
2. Institute of Physics of the Czech Academy of Sciences; Cukrovarnicka 10 162 00 Prague 6 Czech Republic
3. Faculty of Electrical Engineering, Czech Technical University; Technicka 2 166 27 Prague 6 Czech Republic
4. Department of Solid State Engineering; University of Chemistry and Technology; Technicka 6 166 28 Prague 6 Czech Republic