Nikoufar, I., and J. M. Rassias. “θ-Centralizers on Semiprime Banach *-Algebras”. Ukrains’kyi Matematychnyi Zhurnal, Vol. 66, no. 2, Feb. 2014, pp. 269–278, https://umj.imath.kiev.ua/index.php/umj/article/view/2129.