方程=Φ(y)-F(x),=-g(x)的中心焦点判定

众所周知,已有很多文章研究过平面系统的奇点的中心焦点判定方法和判定量的计算.但实际使用起来,都感到很麻烦.本文研究平面广义Lienard方程     

广义Liénard系统周期解的不存在性

本文建立了广义Lienard系统不存在周期解的若干充分条件．     

Lienard方程的新双周期解及其应用

给出了六种情形下Lienard方程的Jacobi椭圆函数形式新双周期解.通过适当的变换,将含有三次方和五次方非线性项的广义Pochhammer-Chree(PC)方程、Kundu方程和广义长波-短波共振方程转换为Lienard方程,从而系统地构造出了它们的若干双周期解.     

一类时滞广义Lienard系统的概周期解的存在唯一性

运用二分性理论及不动点方法,研究一类时滞广义Lienard系统x″+[x~m(t-τ)+h(t)]x′+q(t)x+g(t,x(t-τ))=p(t).的概周期解的存在性和稳定性,得到广义Lienard系统的概周期解存在唯一性和稳定性的充分性定理.     

以滞量为参数的广义Liénard方程的Hopf分支

本文讨论广义Lienard方程的Hopf分支问题首先指出文［3］的错误，并分析了时滞对周期的影响，估计出k＝－f（O）可取多少个不同的值使广义Lienard方程有周期解．然后考虑以时滞r为参数的Hopf分支问题，得到了Hopf分支值及分支方向，并估计出时滞r可取多少个不同的值使方程有周期解，再运用Hassard“规范形”方法，给出了计算以滞量为参数的Lienard方程的Hopf分支公式，利用该公式，能判断周期解的稳定性井得到周期解的近似表达式．     

平面上全局半稳定的广义Liénard系统

该文研究了广义Lienard系统的全局半稳定,获得了系统（E）为全局半稳定系统的充要条件．     

Lienard系统的某些性质

给出了广义Lienard系统有与垂直等倾线不交的正、负半轨的精细条件,并对多项式系统给出了应用例子.     

广义Liénard方程极限环的惟一性问题

本文证明了广义Lienard方程极限环的一个惟一性定理,并用它证明了具有 稀疏效应的捕食-食饵系统在其正奇点外围至多有一个极限环.     

广义Liénard系统的同宿轨族的存在性

本文研究广义Lienard系统解的一些定性性质,证明了（E）至多存在一个最大椭圆扇形,并获得系统（E）的轨线趋于原点及存在同宿轨族的充要条件．     

关于广义Lienard系统解振动的充要条件

本文给出了广义Lienard系统Dx＝h(h)-F(x),Dy=-g(x)解振动的充要条件,所得结果推广和改进了文献[1-6]的主要结果。     

Classification of the centers and isochronicity for a class of quartic polynomial differential systems

In this paper, the conditions of center and isochronous center at the origin for a class of planar quartic differential systems are studied. At first, a constructive theorem of singular point quantities is presented, which plays an important role in simplifying periodic constants. The sufficient and necessary conditions for the origin of the systems being a center are obtained. Then a complete classification of the sufficient and necessary conditions are given for the origin of the systems being an isochronous center.     

Stochastic center of systems of stochastic differential equations on the plane

We study a stochastic analogy of the famous center problem of Dulac for quadratic differential equations in the plane. We introduce the concept of center for systems of stochastic differential equations of It\^o''s type on the plane, called stochastic center. We derive a criterion for the existence of such a center. We apply it to obtain necessary and sufficient conditions for quadratic stochastic differential equations in dimension 2.     

中心条件推导的间接方法

对于一类多项式系统,给出两类对称条件的推导算法,具体讨论了一类三次系统的中心条件;对于Poincare型系统,给出一类等时中心的充分条件．     

Isochronicity of centers in a switching Bautin system

In this paper isochronicity of centers is discussed for a class of discontinuous differential system, simply called switching system. We give some sufficient conditions for the system to have a regular isochronous center at the origin and, on the other hand, construct a switching system with an irregular isochronous center at the origin. We give a computation method for periods of periodic orbits near the center and use the method to discuss a switching Bautin system for center conditions and isochronous center conditions. We further find all of those systems which have an irregular isochronous center.     

Sufficient conditions for existence and uniqueness of a Chebyshev center of a nonempty bounded set in a geodesic space

We obtain sufficient conditions for existence and uniqueness of a Chebyshev center of a nonempty bounded set in a geodesic space. We also establish conditions under which the unique Chebyshev center of a nonempty bounded set in a geodesic space belongs to the closure of the convex hull of this set.     

The generalized center problem of degenerate resonant singular point

In this paper, generalized center condition and integrability of degenerate resonant singular point for a class of complex polynomial differential system were studied. The method was based on a homeomorphic transformation of the degenerate singular point into elementary singular point, which allows us to compute the generalized singular point quantities and determine the generalized center condition for the origin. In the end, we obtained the necessary and sufficient conditions of generalized complex center of degenerate resonant singular point.     

Research on the composition center of a class of rigid differential systems

In this paper, we answer the question: under what conditions a class of rigid differential systems have a composition center. We give the sufficient and necessary conditions for these systems to have a center at origin point. At the same time, we give the formula of focal values and the highest order of fine focus.     

On the Congruences in Right Loops

In case the stability relation is a congruence, a necessary and also a sufficient condition for its equality with the center congruence is given.     

关于系统(x)=h(y)-F(x),(y)=-g(x) 的中心

本文给出了广义Ｌｉｅｎａｒｄ系统的原点为局部中心和全局中心的几个充分条件及原点为全局中心的充要条件,所得结果推广和改进了文献［１－６］的结果．     

Generalized isochronous centers for complex systems

In this paper, the definition of generalized isochronous center is given in order to study unitedly real isochronous center and linearizability of polynomial differential systems. An algorithm to compute generalized period constants is obtained, which is a good method to find the necessary conditions of generalized isochronous center for any rational resonance ratio. Its two linear recursive formulas are symbolic and easy to realize with computer algebraic system. The function of time-angle difference is introduced to prove the sufficient conditions. As the application, a class of real cubic Kolmogorov system is investigated and the generalized isochronous center conditions of the origin are obtained.