1. Faculty of Humanities and Natural Sciences University of Prešov 17. novembra 1 Prešov Slovakia
2. Department of Chemistry University of Genova Via Dodecaneso 31 Genova Italy
3. Institute of Experimental Physics Slovak Academy of Science Watsonova 47 Košice Slovakia
4. Department of Physics CAB-CNEA CONICET IB-UNCuyo 8400 S. C. de Bariloche Argentina