1. Politehnica University Bucharest , Department of Chemical and Biochemical Engineering , Polizu 1 , Bucharest 011061 , Romania
2. Ovidius University of Constanta , Faculty of Mathematics and Informatics , Blvd. Mamaia 124, 900527 , Constanta , Romania ; anicola@univ-ovidius.ro
3. Research Center for Navy , Str. Stefanita Voda, nr. 4 , Constanta 900402 , Romania