On Positive Periodic Solutions to Nonlinear Fifth-Order Differential Equations with Six Parameters

We study the existence and multiplicity of positive periodic solutions to the nonlinear differential equation: u5(t)+ku4(t)-βu3-ξu″(t)+αu'(t)+ωu(t)=λh(t)f(u), in 0≤t≤1, ui(0)=ui(1), i=0,1,2,3,4, where k,α,ω,λ>0, β,ξ∈R, h∈C(R,R) is a 1-periodic function. The proof is based on the Krasnoselskii fixed point theorem