Nonlinear ion acoustic solitary wave in collisional pair ion plasma with trapped electrons B. Boro, A. N. Dev, B. K. Saikia and N. C. Adhikary Eur. Phys. J. Plus, 136 8 (2021) 831 Published online: 12 August 2021 DOI: 10.1140/epjp/s13360-021-01820-2