Euler equation and burger equation โ{128}{148} Relation with turbulence -- Asymptotic behavior of a model in population genetics -- A minimax principle and applications to elliptic partial differential equations -- The existence of periodic water waves -- An application of the Nash-moser theorem to a free boundary problem -- Singularities in non-linear waves of Klein-Gordon type -- Bifurcations of dynamical systems and nonlinear oscillations in engineering systems