SUN, He-Jun. Estimates for weighted eigenvalues of fourth-order elliptic operator with variable coefficients. Ukrains’kyi Matematychnyi Zhurnal, [S. l.], v. 63, n. 7, p. 999–1008, 2011. Disponível em: https://umj.imath.kiev.ua/index.php/umj/article/view/2780. Acesso em: 14 apr. 2025.