Three dimensional nilpotent singularity and Sil'nikov bifurcation

In this paper, by using the normal form, blow-up theory and the technique of global bifurcations, we study the singularity at the origin with threefold zero eigenvalue for nonsymmetric vector fields with nilpotent linear part and 4-jet C∞-equivalent toy∂∂x+z∂∂y+ax3y∂∂z,with a ≠ 0, and analytically prove the existence of Sil'nikov bifurcation, and then of the strange attractor for certain subfamilies of the nonsymmetric versal unfoldings of this singularity under some conditions.