1. Theory of Oscillators;Andronov,1966
2. Traité de mécanique rationelle, v.4;Appel,1932
3. Nonlinear dynamic behavior of shallow spherical shells;Archer;AIAA J.,1965
4. Bifurcations and singularities in mathematics and mechanics;Arnold,1988
5. Stability of nonlinear deformed systems;Ashkenazi,1994