Existence and multiplicity of nodal solutions for Dirichlet problems in upper half strip with holes

In this paper, we consider the existence and multiplicity of nodal solutions of semilinear elliptic equations. We prove that a semilinear elliptic equation in large domains does not admit any least energy nodal (sign-changing) solution and in an upper half strip with mm-holes has at least m2m2 2-nodal solutions.