S. A. Nazarov, J. Taskinen, “Asymptotics of the spectrum of the mixed boundary value problem for the Laplace operator in a thin spindle-shaped domain”, St. Petersburg Math. J., 33:2 (2022), 283–325
S. A. Nazarov, “Estimates for second order derivatives of eigenvectors in thin anisotropic plates with variable thickness”, J. Math. Sci. (N. Y.), 132:1 (2006), 91–102