[1] RUB, Coll Sci & Technol, Dept Sci & Humanities, Thimphu, Bhutan
[2] RG Baruah Coll, Dept Math, Gauhati 781025, Assam, India
[3] Ctr Plasma Phys, Kamrup, Assam, India
[4] Visva Bharati Univ, Dept Math, Siksha Bhavana, Santini Ketan 731235, W Bengal, India
[5] Inst Adv Study Sci & Technol, Div Phys Sci, Gauhati 781035, Assam, India