Ildiko Csajbok-Twerefou, University of Ghana, P.O. Box LG 207, Legon, Accra, Ghana
Liu Youren , Lomonosov Moscow State University, 27/4, Lomonosovsky av., Moscow, 119991, Russia
Yuriy I. Dzyadyk , University of Ghana, P.O. Box LG 207, Legon, Accra, Ghana