In this paper, we investigate the boundary value problem for fourth order differential operator equations with unbounded operator coefficients and one $\lambda $-dependent boundary condition. We obtain an asymptotic formula for eigenvalues and a trace formula for the corresponding self-adjoint operator.
"Eigenvalue problem associated with the fourth order differential-operator equation." Rocky Mountain J. Math. 48 (6) 1763 - 1779, 2018. https://doi.org/10.1216/RMJ-2018-48-6-1763