THE MULTIPLICITY OF ZERO AND LIMIT CYCLES FOR ABEL EQUATIONS

In this paper we will investigate the multiplicity of zero solution for a class of Abel equation, and obtain better estimation on multiplicity than that given by Alwash and Lloyd for the equation of a certain form, and solve a conjecture posed by Ye Yanqian for the equation of another form. As a by-product, the considered equation may have at least four small amplitude limit cycles. The method of this paper is useful for computing the focal value of a critical point of focus type for polynomial system that can be transformed into Abel equation or Abel form.

一类平面五次系统的定性分析

本文研究平面五次系统（１．１），应用［４，５］的最新结果，给出了奇点Ｏ（０，０）为中心的充要条件和焦点量公式，以及（１．１）至多有一个，二个极限环的充分条件．

具有等时中心的二次微分系统的极限环分支

对于扰动等时微分系统x=√2/2 xy+εf(x,y),y=√2/2(2-2x+y^(2))+εg(x,y),其中0<ε<<1,f(x,y)和g(x,y)是关于x和y的n次多项式,应用Picard-Fuchs方程给出其Abel积分零点个数的上界,进而得到该系统极限环个数的上界.

一类2n-1次系统的极限环

本文研究了一类 2n - 1次系统 ,通过将其化为Abel方程 ,给出了极限环唯一性的充分条件 ,得到的结论推广了文献 [1 ]的主要结果 。

Darboux integrability and algebraic limit cycles for a class of polynomial differential systems

This paper deals with the existence of Darboux first integrals for the planar polynomial differential systems x=x-y+P n+1(x,y)+xF2n(x,y),y=x+y+Q n+1(x,y)+yF2n(x,y),where P i(x,y),Q i(x,y)and F i(x,y)are homogeneous polynomials of degree i.Within this class,we identify some new Darboux integrable systems having either a focus or a center at the origin.For such Darboux integrable systems having degrees 5and 9 we give the explicit expressions of their algebraic limit cycles.For the systems having degrees 3,5,7 and 9and restricted to a certain subclass we present necessary and sufficient conditions for being Darboux integrable.

Abel方程闭解的个数问题及应用

讨论Abel方程闭解的存在性、个数和稳定性,改进了以前文献的结果,并利用关于Abel方程的这些结果得到了一类n次多项式系统在一定条件下极限环的个数和稳定性．

一类阿贝尔方程极限环的几个判定准则

当ｎ次微分系统ｘ′＝λｘ－ｙ＋Ｐｎ（ｘ，ｙ），ｙ′＝ｘ＋λｙ＋Ｑｎ（ｘ，ｙ）（ｎ≥２）化为Ａｂｅｌ方程ｄｚ／ｄθ＝Ａ（θ）ｚ３＋Ｂ（θ）ｚ２＋Ｃ（θ）ｚ后，利用λＡ（θ）的符号给出了判定Ａｂｅｌ方程极限环的几个准则：（１）当λＡ（θ）≥０且ｎ为偶数时方程无极限环；（２）若λＡ（θ）≤０时，则方程存在唯一极限环；（３）若λＡ（θ）≥０且ｎ为奇数，则方程最多只有两个极限环．