1. Perturbation Methods;Nayfeh,1973
2. Oscillations in Planar Dynamics Systems;Mickens,1996
3. Nonlinear Ordinary Differential Equations;Jordan,1987
4. Nonlinear Oscillations;Hagedorn,1981
5. Self-excited systems: analytical determination of limit cycles;D’Acunto;Chaos Solitons & Fractals,2006