Limit cycles for a class of polynomial systems and applications. Feng, Hanying, Xu, Rui, Liu, Qiming, Yang, Pinghua (2003) Electronic Journal of Differential Equations (EJDE) [electronic only]
Limit cycles of a class of Hilbert's sixteenth problem presented by fractional differential equations. Erjaee, G.H., Zangeneh, H.R.Z., Nyamoradi, N. (2010) Advances in Difference Equations [electronic only]