Makhmudova, M. G., and A. K. Khanmamedov. “On the Spectral Properties of the One-dimensional Stark Operator on the Half-Line”. Ukrains’kyi Matematychnyi Zhurnal, Vol. 71, no. 11, Nov. 2019, pp. 1579-84, http://umj.imath.kiev.ua/index.php/umj/article/view/1537.