1. J. Heyrovský Institute of Physical Chemistry, Academy of Sciences of the Czech Republic, v.v.i., Dolejškova 3, 18223 Prague 8, Czech Republic
2. Faculty of Mathematics and Physics, Charles University, 121 16 Prague, Czech Republic
3. Institute of Physics, Lodz University of Technology, ul. Wolczanska 217/221, 93-005 Lodz, Poland
4. Algorithmiq Limited, Kanavakatu 3C, FI-00160 Helsinki, Finland