S.A. Kashchenko, "Asymptotic Expansions of Eigenvalues of Periodic and Antiperiodic Boundary Value Problems for Singularly Perturbed Second-Order Differential Equation with Turning Points", Automatic Control and Computer Sciences, 52:7, 728--744 (2018).

S.A. Kashchenko, Asymptotic Expansions of Eigenvalues of Periodic and Antiperiodic Boundary Value Problems for Singularly Perturbed Second-Order Differential Equation with Turning Points, Automatic Control and Computer Sciences, 52:7, 728--744 (2018).