1. Department of Mathematics, “1 Decembrie 1918” University of Alba Iulia, 510009 Alba Iulia, Romania
2. Department of Mathematics, Technical University of Cluj-Napoca, Cluj-Napoca, Romania
3. Department of Mathematics and Statistics, College of Natural and Health Sciences, Zayed University, Abu Dhabi, UAE
4. Department of Applied Mathematics and Science, National University of Science & Technology, Muscat, P.O. Box 620, Oman