Validity of the linear marginal stability principle for monotonic fronts of the extended Fisher-Kolmogorov equation

The extended Fisher Kolmogorov equation ut = uxx i∞uxxxx +f(u) with arbitrary positive f(u), satisfying f(0) = f(1) = 0, has monotonic traveling fronts for ∞ < 1=12. We flnd a simple lower bound on the speed of the fronts which allows to assess the validity of linear marginal stability.