On mode interactions for a weakly nonlinear beam equation / G.J. Boertjens and W.T. van HorssenAn asymptotic theory for a weakly nonlinear beam equation with a quadratic perturbation / G.J. Boertjens and W.T. van HorssenOn interactions of oscillation modes for a weakly nonlinear elastic beam with an external force / G.J. Boertjens, W.T. van HorssenWeakly nonlinear beam equations: an asymptotic analysis / Gerdineke Judith Boertjens