1. Faculty of Technical Sciences , University of Novi Sad , “Trg D. Obradovića”, 6 Novi Sad – 21000 , Serbia
2. Department of Mathematics and Informatics Faculty of Sciences , University of Novi Sad , “Trg D. Obradovića”, 4 Novi Sad – 21000 , Serbia
3. Mathematical Institute , Serbian Academy of Arts and Sciences , “Kneza Mihaila”, 36 Beograd – 11000 , Serbia
4. Department of Physics, Faculty of Sciences , University of Novi Sad “Trg D. Obradovića”, 4 Novi Sad – 21000 , Serbia