1. a Institute of Physics , Kazimierz Wielki University , Plac Weyssenhoffa 11, PL-85072 , Bydgoszcz , Poland
2. b Institute of Mathematics , Kazimierz Wielki University , Plac Weyssenhoffa 11, PL-85072 , Bydgoszcz , Poland
3. c Consiglio Nazionale delle Ricerche , Istituto per i Processi Chimico-Fisici (IPCF-CNR) , Pisa , Italy