1. Department of Mathematics and Statistics, University of Cyprus, Nicosia, Cyprus.
2. Department of Mathematics, King Saud University, Riyadh, Saudi Arabia.
3. Department of Applied Mathematics, University of Leeds, Leeds, UK.
4. Faculty of Mathematics and Computer Science, Department of Mathematics, University of Bucharest, Bucharest, Romania.
5. Institute of Solid Mechanics, Romanian Academy, Bucharest, Romania.