On the spectral gap for fixed membranes
The author studies the Dirichlet Laplacian in a convex planer domain \(D\) symmetric about both the \(x\) and \(y\) axes. It is shown that the gap (the distance between the second and first eigenvalues) of \(D\) is no smaller that the gap of the smallest oriented rectangle containing \(D.\)
scientific article; zbMATH DE number 1928896