Using nonlocal operators for measuring dimensions of defects in radiograph of welded objects Amir Movafeghi, Mahdi Mirzapour and Effat Yahaghi Eur. Phys. J. Plus, 136 6 (2021) 655 Published online: 14 June 2021 DOI: 10.1140/epjp/s13360-021-01652-0