1. Department of Mathematics, University of the Punjab, Lahore 54590, Pakistan
2. Department of Mathematical Sciences, College of Science, Princess Nourah bint Abdulrahman University, P.O. Box 84428, Riyadh 11671, Saudi Arabia
3. Faculty of Mechanical Engineering, University of Nis, 18000 Nis, Serbia
4. Department of Structural Analysis, Technical University of Berlin, 10623 Berlin, Germany