2 citations to https://www.mathnet.ru/eng/dan4473

1. S. A. Nazarov, “Asymptotics of negative eigenvalues of the Dirichlet problem with the density changing sign”, J. Math. Sci. (N. Y.), 163:2 (2009), 151–175          
2. T. A. Mel'nik, P. S. Vashchuk, “Homogenization of the Neumann–Fourier problem in a thick two-level junction of type 3:2:1”, Zhurn. matem. fiz., anal., geom., 2:3 (2006), 318–337