论广义Liénard系统的全局中心

本文讨论了广义Liénard系统的局部和全局中心,给出了两个定理,它们推广和改进了文[1—3]的结果.文中引理对研究广义Liénard系统解的震荡性,稳定性和极限环的存在性也是有用的.     

Liénard系统的比较定理

研究了Liénard方程的一类新的等价系统解的有界性与周期解的存在性.证明了几个比较定理,使传统Liénard方程等价系统解的有界性和周期解的存在性可用于判定新等价系统解的有界性与周期解的存在性.     

具多个奇点的广义Liénard系统解的有界性

本文讨论具有有限多个奇点的广义Liénard系统解的有界性,得到一组保证系统的解正向有界的充分条件,进而得到存在极限环的条件。     

一类广义Liénard系统解的有界性

获得了广义 Liénard系统dxdt=p(y) -F(x) ,　 dydt=-g(x) q(y)所有正半轨线有界的若干充分条件 ,推广改进了已有文献 [1— 1 2 ]中的相应结果 .     

全局半稳定的Liénrd系统的充要条件

本文研究了 Liénard系统的全局半稳定问题 ,获得了系统为全局半稳定的充要条件 ,且推广和改进了 [5]的结果     

一类广义Liénard系统解的有界性

研究了一类广义 Liénard系统dxdt=p(y) -F(x) ,　 dydt=-g(x) (E)解的有界性 .首先获得了系统 (E)存在无界解的两个新的充分条件 ,然后获得系统 (E)所有解正向有界的若干充分条件和充要条件 ,所获结果改进和扩展了文 [1 -2 ]中的相应结果 .     

关于Filippov变换的一个注记

本文利用 Filippov变换导出来一个研究 Liénard方程极限环不存在性的判据 ,它为证明某些Liénard方程不存在极限环提供了一个简捷有效的思想方法 .     

一类广义Liénard型系统解振荡的充要条件

给出了一类广义Liénard型系统(x)=p(y)k(x),(y)=-f(x,y)p(y)q(y)-g(x)h(y).解振荡的充要条件,文中的引理也有助于研究这类系统周期解的存在性.     

关于广义Liénard系统解的有界性及整体渐近性态

本文研究非自治的广义 Liénard系统 :x=h(y) -F (x)y=-g(x) +e(t)解的有界性及整体渐近性态 ,获得了方程每个解是有界及收敛于原点的充分必要条件 ,推广与改进了文 [1～1 0 ]是于同样问题的一些重要结果     

一类广义Liénard型系统周期解的存在性和不存在性

讨论了一类广义Liénard型系统.x=p(y)k(x),.y=-f(x,y)p(y)q(y)-g(x)h(y)非零周期解的存在性和不存在性,给出了非零周期解的存在和不存在的一类充分条件.     

具偏差变元的Liénard型方程的周期解

在本文中，Ｌｉéｎａｒｄ型方程周期解存在性的结果被推广到具偏差变元的Ｌｉéｎａｒｄ型方程     

Proof of Artés–Llibre–Valls's conjectures for the Higgins–Selkov and the Selkov systems

The aim of this paper is to prove Artés–Llibre–Valls's conjectures on the uniqueness of limit cycles for the Higgins–Selkov system and the Selkov system. In order to apply the limit cycle theory for Liénard systems, we change the Higgins–Selkov and the Selkov systems into Liénard systems first. Then, we present two theorems on the nonexistence of limit cycles of Liénard systems. At last, the conjectures can be proven by these theorems and some techniques applied for Liénard systems.     

关于一类高阶Liénard型方程周期解的注记

本文研究一类具偏差变元的高阶 Liénard型方程的周期解存在性 ,给出了这类方程周期解存在性的若干充分条件 .     

具有多个奇点的广义的Liénard系统不存在任何闭轨的条件

本文不同于一般的方法，利用辅助函数建立了具有多个奇点的广义的Ｌｉéｎａｒｄ系统（Ｅ）不存在任何闭轨的若干判别条件，关于（Ｅ）的经典的Ｂｅｎｄｉｘｓｏｎ判别法则和Ｐｏｉｎｃａｒé地形系法则是其特例．此外，给出了包括三次振动系统在内的例子．     

On the criteria for integrability of the Liénard equation

The Liénard equation is of a high importance from both mathematical and physical points of view. However a question about integrability of this equation has not been completely answered yet. Here we provide a new criterion for integrability of the Liénard equation using an approach based on nonlocal transformations. We also obtain some of the previously known criteria for integrability of the Liénard equation as a straightforward consequence of our approach’s application. We illustrate our results by several new examples of integrable Liénard equations.     

Small-amplitude limit cycles of some Liénard-type systems

As we know, the Liénard system and its generalized forms are classical and important models of nonlinear oscillators, and have been widely studied by mathematicians and scientists. The main problem considered by most people is the number of limit cycles. In this paper, we investigate two kinds of Liénard systems and obtain the maximal number (i.e. the least upper bound) of limit cycles appearing in Hopf bifurcations by applying some known bifurcation theorems with technical analysis.     

Integrability and solvability of polynomial Liénard differential systems

We provide the necessary and sufficient conditions of Liouvillian integrability for Liénard differential systems describing nonlinear oscillators with a polynomial damping and a polynomial restoring force. We prove that Liénard differential systems are not Darboux integrable excluding subfamilies with certain restrictions on the degrees of the polynomials arising in the systems. We demonstrate that if the degree of a polynomial responsible for the restoring force is greater than the degree of a polynomial producing the damping, then a generic Liénard differential system is not Liouvillian integrable with the exception of linear Liénard systems. However, for any fixed degrees of the polynomials describing the damping and the restoring force we present subfamilies possessing Liouvillian first integrals. As a by-product of our results, we find a number of novel Liouvillian integrable subfamilies. In addition, we study the existence of nonautonomous Darboux first integrals and nonautonomous Jacobi last multipliers with a time-dependent exponential factor.     

Qualitative analysis of Holling type II predator–prey systems with prey refuges and predator restricts

This paper is devoted to investigation of Holling type II predator–prey systems with prey refuges and predator restricts. Using a transformation technique, we change the system into a generalized Liénard system and give sufficient conditions to ensure the global stability of the positive equilibrium and existence and uniqueness of a stable limit cycle. We also find the property of alternation for phase structure of the system.