1. Division of Arts & Sciences, Texas A&M, Education City, Doha, Qatar.
2. Department of Mathematics and Informatics, Faculty of Sciences, University of Novi Sad, Trg Dositeja Obradovića 4, 21000, Novi Sad, Serbia and Applied and Computational Mathematics, RWTH Aachen University, Schinkelstrasse 2, 52062, Aachen, Germany.