1. Institute of Molecular Physics, Polish Academy of Sciences, M. Smoluchowskiego 17, 60-179 Poznań, Poland
2. Groupe de Physique Statistique et Moléculaire, MEPS, Université de Perpignan, 52 Avenue Paul Alduy, 66860 Perpignan Cedex, France
3. Faculty of Electrical Engineering, University of Saints Cyril and Methodius, P. O. Box 574, 91000 Skopje, Macedonia