We investigate the eigenvalues and eigenfunctions of the Schur complement operator of the first kind of Stokes problem posed on a plane domain and give results on the number, multiplicity and stability of these eigenvalues in dependence on the problem domain.
"On the Spectrum of the Schur Complement of the Stokes Operator via Conformal Mapping." Methods Appl. Anal. 11 (1) 133 - 154, March 2004.