The uniqueness of limit cycles for Liénard system

In monographs [Theory of Limit Cycles, 1984] and [Qualitative Theory of Differential Equations, 1985], eleven propositions by several mathematicians are listed on the uniqueness of limit cycles for equations of type (I), (II), and (III) of the quadratic ordinary differential systems. In this paper, we first point out that all these propositions were not completely proved since the equations under consideration do not satisfy the conditions of the theorems used to guarantee the uniqueness of limit cycles. Then we give a new set of theorems that guarantee the uniqueness of limit cycles for the Liénard systems, which not only can be applied to complete the proof of the propositions mentioned above but generalize many other uniqueness theorems as well. The conditions in these uniqueness theorems, which are independent and were obtained by different methods, can be combined into one improved general theorem that is easy to apply. Thus many of the most frequently used theorems on the uniqueness of limit cycles are corollaries of the results in this paper.     

Oscillations in some nonlinear economic relationships

In this paper we consider a simple family of nonlinear dynamical systems generated by smooth functions. Some theorems for the existence and the uniqueness of the limit cycles of the systems are presented. If f and g are generating functions with unique limit cycles and xf(x) < xg(x), for all x ≠ 0, then according to the ‘bounding theorem’ proved in the paper, the limit cycle of the system generated by f is bounded by the limit cycle of the system generated by g. This gives us a method to estimate the amplitude of the oscillations also for systems for which we do not know the generating function exactly. As an application we extend the nonlinear business cycle model proposed by Tönu Puu (1989).     

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.     

QUALITATIVE ANALYSIS OF A MULTIMOLECULEBIOCHEMICAL SYSTEM

ＱＵＡＬＩＴＡＴＩＶＥＡＮＡＬＹＳＩＳＯＦＡＭＵＬＴＩＭＯＬＥＣＵＬＥＢＩＯＣＨＥＭＩＣＡＬＳＹＳＴＥＭＧｕＤａｏｘｉｕ（ＨｕｎａｎＥｄｕｃａｔｉｏｎａｌｉｎｓｔｉｔｕｔｅ）Ａｂｓｔｒａｃｔ：Ｉｎｔｈｉｓｐａｐｅｒｔｈｅａｕｔｈｏｒｐｒｏｖｅｓｓｏｍ...     

THE POINCAR BIFURCATION OF QUADRATIC SYSTEMS HAVING A REGION CONSISTING OF PERIODIC CYCLES BOUNDED BY A HYPERBOLA AND AN ARC OF EQUATOR

The usual bifureation problems oeeurred in the study of the Planar differential systems having a region eonsisting of Periodie eycles are as follows:15 there any closed orbit whieh generates limit eyeles after a small perturbation?How many limit eyel     

THE POINCARE BIFURCATION OF QUADRATIC SYSTEMS HAVING A REGION CONSISTING OF PERIODIC CYCLES BOUNDED BY A HYPERBOLA AND AN ARC OF EQUATOR

In this paper, we discuss the Poincar&#233; bifurcation for a class of quadratic systems having a region consisting of periodic cycles bounded by a hyperbola and an arc of equator. We prove that the system can at most generate two limit cycles after a small perturbation.     

Relationships between limit cycles and algebraic invariant curves for quadratic systems

Algebraic limit cycles for quadratic systems started to be studied in 1958. Up to now we know 7 families of quadratic systems having algebraic limit cycles of degree 2, 4, 5 and 6. Here we present some new results on the limit cycles and algebraic limit cycles of quadratic systems. These results provide sometimes necessary conditions and other times sufficient conditions on the cofactor of the invariant algebraic curve for the existence or nonexistence of limit cycles or algebraic limit cycles. In particular, it follows from them that for all known examples of algebraic limit cycles for quadratic systems those cycles are unique limit cycles of the system.     

关于方程 +φ(y)+Ψ(y)η(y)=0的极限环问题

本文研究了(1)的极限环问题,给出了判定其有无闭轨及极限环唯一的若干准则。推广和改进了[1]的结果。     

一类不连续平面二次微分系统的极限环

本文考虑了一类不连续平面二次可积非Hamilton微分系统在二次扰动下的极限环个数问题.利用一阶平均法,我们得到了从该系统中心的周期环域至少可以分支出5个极限环的结论.该结果表明不连续二次微分系统比其相应光滑微分系统至少可以多分支出2个极限环.     

关于一类平面n+2次系统极限环唯一性的一个注记

本文继续完善文[1]和[2]的工作,利用广义Lienard方程和张芷芬唯一性定 理证明了,当n≥3时一类n+2次生化反应系统极限环的唯一性.至此,该系统极 限环唯一性问题得到完整解决.     

STUDY ON THE UNIQUENESS OF LIMIT CYCLE OF THE QUADRATIC SYSTEM BY USING THE QUADRATIC CURVE WITHOUT CONTACT(CONTINUED 1)

１ＩｎｔｒｏｄｕｃｔｉｏｎａｎｄＲｅｓｕｌｔｓＣｏｎｓｉｄｅｒｔｈｅｑｕａｄｒａｔｉｃｓｙｓｔｅｍ［１］ｄｘｄｔ＝－ｙ＋δｘ＋ｌｘ２＋ｍｘｙ＋ｎｙ２＝Ｐ２（ｘ，ｙ），ｄｙｄｔ＝ｘ（１＋ａｘ＋ｂｙ）＝Ｑ２（ｘ，ｙ），（ｎ≥０，ａｂ≠０）Ｅ２ｗｉｔｈｏｕ...     

Liénard方程的推广及其应用

本文推广了Ｌｉéｎａｒｄ方程的类型，并用其研究了一个二次微分系统极限环的唯一性问题．     

Ten limit cycles around a center-type singular point in a 3-d quadratic system with quadratic perturbation

In this paper, we show that perturbing a simple 3-d quadratic system with a center-type singular point can yield at least 10 small-amplitude limit cycles around a singular point. This result improves the 7 limit cycles obtained recently in a simple 3-d quadratic system around a Hopf singular point. Compared with Bautin’s result for quadratic planar vector fields, which can only have 3 small-amplitude limit cycles around an elementary center or focus, this result of 10 limit cycles is surprisingly high. The theory and methodology developed in this paper can be used to consider bifurcation of limit cycles in higher-dimensional systems.     

Local Existence And Uniqueness of Solutions of Degenerate Parabolic Equations

We consider a class of degenerate parabolic equaitons on a bounded domain with mixed boundary conditions. These problems arise, for example, in the study of flow through porous media. Under appropriate hypotheses, we establish the existence of a nonegative solution which is obtainable as a monotone limit of solutions of quasilinear parabolic equations. This construction is used establish uniqueness, cinparison, and L¹ continuous dependence theorems, as well some results on blow up of solutions in finite time     

QUADRATIC SYSTEMS WITH A 3RD-ORDER (OR 2ND-ORDER) WEAK FOCUS

1 IntroductionSince a quadratic system has no limit cycle around a 3rd-order weak focu,[1]and has at most one limit cycle surrounding a 2nd-order weak fOcus['], study-ing the number of limit cycles of a p1anar quadratic system with a 3rd-order(or 2nd-order) weak focus we only need to study the number of limit cyclessurrounding the strong focus for the system. Without loss of generality thequadratic system with a 3rd--order (or 2nd--order) weak foclls and a strong focuscan be written in the fo.…     

Some criteria for the existence of limit cycles for quadratic vector fields

In this paper we consider real quadratic systems. We present new criteria for the existence and uniqueness of limit cycles for such systems by using Darbouxian particular solutions. Some results are based on the study of such systems in . We also generalize the well-know result of Bautin on the nonexistence of limit cycles for quadratic Lotka-Volterra systems.     

一类异宿环分支问题中极限环的唯一性

在具余维２奇点的四维系统的两参数开折的研究中出现一类三点异宿环的扰动分支,对此异宿环产生极限环的唯一性一直未得到完整的解决,本文圆满地解决了这一问题,并获得了全局分支中极限环的唯一性。     

Z~2上相依渗流开簇的极限定理(英文)

中心极限定理, 大偏差定理和大数定律等极限定理在概率论中起着很重要的角色. 本文我们研究Z2上一类相依渗流模型. 对此模型, 我们不仅证明了其无穷开簇的存在唯一性, 而且得到了关于格点盒子类极大开簇的中心极限定理.     

Der induktive Limes von abzählbar vielen FH-Räumen. Vereinigungsverfahren

The paper deals with the inductive limit of a countable set of FH-spaces (IFH-spaces). In contrast to completeness or metrizability there are properties such as the uniqueness of the topology of IFH-spaces which are preserved by the change from FH-spaces to IFH-spaces. In the special case of IFK-spaces the set of bounded sequences with weakly sectional convergence is considered. In particular, the convergence domain of the union of matrix transformations is an IFK-space. Analogous to the case of matrix transformations it is possible to prove theorems of the Mazur-Orlicz-type and theorems on perfectness and consistency.     

联合最佳逼近

本文研究了二元函数用紧Hausdorff空间上的连续函数集的联合逼近问题,建立了包括特征定理、唯一性定理、强唯一性定理和dela Vallée Poussin定理在内的Chebyshev逼近理论。给出了求解最佳逼近元的Remes型第一算法和两种一般的简化方法。