1. Department of Mathematics; Bharathiar University; Coimbatore 641046 India
2. Department of Mathematics; Sungkyunkwan University; Suwon 440-746 South Korea
3. Department of Mechanical Engineering; Politecnico di Milano; 20156 Milan Italy
4. Department of Mathematics; Anna University Regional- Campus; Coimbatore 641046 India
5. Department of Mathematics; Anhui Normal University; Wuhu 241000 China