Payne-Weinberger showed that 'among the class of membranes with given area A, free along the interior boundaries and fixed along the outer boundary of given length L 0 , the annulus Ω # has the highest fundamental frequency,' where Ω # is a concentric annulus with the same area as Ω and the same outer boundary length as L 0 .We extend this result for the higher dimensional domains and p-Laplacian with p ∈ (1, ∞), under the additional assumption that the outer boundary is a sphere. As an application, we prove that the nodal set of the second eigenfunctions of p-Laplacian (with mixed boundary conditions) on a ball and a concentric annulus cannot be a concentric sphere.Keywords Reverse Faber-Krahn inequality · Interior parallels · Isoperimetric inequality · Nagy's inequalities · First eigenvalue of p-Laplacian · Mixed boundary value problems · Elasticity problems · Non-radiality
IntroductionLet us first recall the famous conjecture by Lord Rayleigh from his book 'The theory of sound' [23] published in 1877. He conjectured that 'among all planar domains Ω of fixed area, the disk is the domain that minimises the first Dirichlet eigenvalue λ 1 (Ω) of the Laplacian.' This conjecture was open for a very long time. The first proof of this conjecture was published in 1923 by Faber [8]. In 1925, Krahn [14] gave an independent proof for this conjecture, and later he extended the same to the higher dimension. Now this result is collectively known as the Faber-Krahn inequality, and it states that:with the equality if and only if Ω is a ball (up to a measure zero set), where Ω * is a ball of the same measure as Ω.For more on Faber-Krahn inequality and related results, we refer to [18] and [21].