Affiliation: | 1. Department of Mathematics and Statistics, King Fahd University of Petroleum and Minerals, Dhahran 31261, Saudi Arabiamyousuf@kfupm.edu.sa;3. Department of Mathematical Sciences, Middle Tennessee State University, Murfreesboro, TN 37132-0001, USA;4. Department of Mathematics, University of Dayton, 300 College Park, Dayton, OH 45469-2316, USA |