1. G.M. Mahmoud, A. Rauh, A.A. Mohamed, On modulated complex non-linear dynamical systems, IL Nuovo Cimento 114 (B.1) (1999) 31–47.
2. G.M. Mahmoud, S.A. Aly, On periodic solutions of parametrically excited complex nonlinear dynamical systems, 4th Int. Conf. on Difference Equations and Applications, August 27–31, Poznan, Poland, 1998, accepted for presentation.
3. R.H. Helleman, Self-generated chaotic behavior in nonlinear mechanics, in: G.D. Cohen (Ed.), Fundamental Problems in Statistical Mechanics, Vol. 5, North-Holland, Amsterdam, 1980, pp. 165–233.
4. Whirl and whip-rotor bearing stability problems;Muszynska;J. Sound Vib.,1986