1. Faculty of Industrial Sciences and Technology, Universiti Malaysia Pahang, Gambang, Kuantan 26300, Pahang, Malaysia e-mail:
2. School of Mathematical Sciences, Faculty of Science and Technology, Universiti Kebangsaan Malaysia, UKM Bangi, Selangor 43600, Malaysia e-mail:
3. Department of Mathematics, Babes-Bolyai University, Cluj-Napoca R-400084, Romania e-mail: