1. Theoretical Plasma Physics Group, Quaid-i-Azam University, Islamabad 44000, Pakistan
2. Department of Physics, COMSATS University, Park Road, Chak Shahzad, Islamabad 44000, Pakistan
3. National Center for Physics, Islamabad 44000, Pakistan
4. The Abdus Salam International Centre for Theoretical Physics, Strada Costiera 11, 34151 Trieste, Italy