1. Department of Applied Mathematics, The University of Western Ontario, London, ON N6A 5B7, Canada; Department of Space Science, Institute of Space Technology, Islamabad 44000, Pakistan.
2. Department of Applied Mathematics, The University of Western Ontario, London, ON N6A 5B7, Canada; Department of Mathematics and Computer Science, Algoma University, Sault St.Marie, ON P6A 2G4, Canada.