Kumam, Poom, Department of Mathematics & Theoretical and Computational Science (TaCS) Center, Science Laboratory Building, Faculty of Science, King Mongkut's University of Technology Thonburi (KMUTT), 126 Pracha Uthit Rd., Bang Mod, Thung Khru, Bangkok 10140, Thailand; Department of Medical Research, China Medical University Hospital, China Medical University, Taichung 40402, Taiwan