1. Department of Mathematics, National Institute of Technology Rourkela, Odisha, India. sne_chak@yahoo.com
2. Department of Applied Mathematics, Faculty of Mathematics and Physics, Charles University, Malostranské nám. 25, 11800 Prague, Czech Republic. milan.hladik@matfyz.cz, hladik@kam.mff.cuni.cz
3. Department of Mathematics, National Institute of Technology Rourkela, Odisha, India. nisha.mahato1@gmail.com