1. Department of Mathematics and Computing, Indian Institute of Technology (Indian School of Mines), Dhanbad 826004, India
2. School of Engineering, Amrita Vishwa Vidyapeetham, Amritapuri, Kollam 690525, India
3. Department of Mathematical Sciences, University of Essex, Wivenhoe Park, UK
4. Department of Physics, Lanzhou University of Technology, Lanzhou 730050, P. R. China