Nodal ground state solution to a biharmonic equation via dual method

Using the dual method we establish the existence of a nodal ground state solution for the following class of problems{Δ2u=f(u),inΩ,u=Bu=0,on∂Ω, where Ω⊂RN(N≥1)Ω⊂RN(N≥1) is a smooth bounded domain, Δ2Δ2 is the biharmonic operator, B=ΔB=Δ or B=∂∂ν and f   is a C1C1-function having subcritical growth.