Bifurcation and Distribution of Limit Cycles for Quadratic Differential Systems of Type II

In this paper, we first solve an open problem of quadratic differential systems of type II.ls0 in the Chinese classification. Then by making use of the theory of rotated vector fields we investigate the bifurcation phenomena and all the possible distributions of the limit cycles for quadratic systems of type II. Moreover, under a conjecture of Ye Yanqian we prove that the 2, 2. limit cycle distribution is impossible.