[1] Univ Nizwa, Coll Arts & Sci, Dept Math & Phys Sci, Nizwa, Oman
[2] GLA Univ, Inst Appl Sci & Humanities, Dept Math, Mathura 281406, Uttar Pradesh, India
[3] Univ KwaZulu Natal, Astrophys & Cosmol Res Unit, Private Bag X54001, ZA-4000 Durban, South Africa
[4] Univ Antofagasta, Fac Ciencias Basicas, Dept Fis, Casilla 170, Antofagasta, Chile