1. Department of Mathematical Sciences, Faculty of Science and Technology, Universiti Kebangsaan Malaysia, Bangi, Selangor, Malaysia
2. School of Distance Learning, Universiti Sains Malaysia, Pulau Pinang, Malaysia
3. Institut National de la Recherche Scientifique, Énergie Matériaux Télécommunications Research Centre, Montréal, Québec, Canada
4. School of Quantitative Sciences, College of Arts and Sciences, Universiti Utara Malaysia, Sintok Kedah, Malaysia