1. Department of Mathematics, Indian Institute of Technology Guwahati 1 , Guwahati, India
2. Mathematical and Computational Sciences (Physical Sciences Division), Institute of Advanced Study in Science and Technology 2 , Guwahati, India
3. School of Information and Physical Sciences, The University of Newcastle 3 , Newcastle, Australia
4. Centre for Clean Environment, Vellore Institute of Technology 4 , Vellore 632014, India
5. Department of Mathematics, School of Advanced Sciences, Vellore Institute of Technology 5 , Vellore 632014, India
6. School of Engineering, Computing and Mathematics, University of Plymouth 6 , Plymouth, United Kingdom