Pseudo-orthogonal groups and integrable dynamical systems in two   dimensions
  Integrable systems in low dimensions, constructed through the symmetry reduction method, are studied using phase portrait and variable separation techniques. In particular, invariant quantities and explicit periodic solutions are determined. Widely applied models in Physics are shown to appear as particular cases of the method. 
J.A. Calzada, M.A. del Olmo, M.A. Rodriguez