LIMIT CYCLE PROBLEM OF QUADRATIC SYSTEM OF TYPE （ Ⅲ ）m=0, （ Ⅲ ）

To continue the discussion in （Ⅰ ） and （ Ⅱ ）,and finish the study of the limit cycle problem for quadratic system （ Ⅲ ）m=0 in this paper. Since there is at most one limit cycle that may be created from critical point O by Hopf bifurcation,the number of limit cycles depends on the different situations of separatrix cycle to be formed around O. If it is a homoclinic cycle passing through saddle S1 on 1 ＋ax-y = 0,which has the same stability with the limit cycle created by Hopf bifurcation,then the uniqueness of limit cycles in such cases can be proved. If it is a homoclinic cycle passing through saddle N on x= 0,which has the different stability from the limit cycle created by Hopf bifurcation,then it will be a case of two limit cycles. For the case when the separatrix cycle is a heteroclinic cycle passing through two saddles at infinity,the discussion of the paper shows that the number of limit cycles will change from one to two depending on the different values of parameters of system.     

THE PROBLEM OF LIMIT CYCLES FOR A LIENARD TYPE CUBIC SYSTEM

The purpose of this paper is to study a general Lienard type cubic system with one antisaddle and two saddles. We give some results of the existence and uniqueness of limit cycles as well as the evolution of limit cycles around the antisaddle for system (2) in the following when parameter a1 changes.     

On the Number of Limit Cycles in Small Perturbations of a Piecewise Linear Hamiltonian System with a Heteroclinic Loop

In this paper, the authors consider limit cycle bifurcations for a kind of nonsmooth polynomial differential systems by perturbing a piecewise linear Hamiltonian system with a center at the origin and a heteroclinic loop around the origin. When the degree of perturbing polynomial terms is n(n ≥ 1), it is obtained that n limit cycles can appear near the origin and the heteroclinic loop respectively by using the first Melnikov function of piecewise near-Hamiltonian systems, and that there are at most n + [(n+1)/2] limit cycles bifurcating from the periodic annulus between the center and the heteroclinic loop up to the first order in ε. Especially, for n = 1, 2, 3 and 4, a precise result on the maximal number of zeros of the first Melnikov function is derived.     

Linear estimation and distribution of the limit cycles bifurcated from a kind of degenerate polycycles

In this paper, we investigate the number and the distribution of the limit cycles bifurcated from a kind of degenerate planar polycycles through three singular points: a saddle-node P0, a fine saddle P1 with finite order m∈N, a contractive (attracting) saddle P2 with the hyperbolicity ratio q2(0)■Q. The connection between P0 and P1 is of hh-type and the connection between P0 and P2 is of hp-type. It is assumed that the connections between P0 to P2 and P0 to P1 keep unbroken. We obtain that the cyclicity of this polycycle is not more than 3m 1, which is linearly dependent on the order of the resonant saddle P1 We also show that the cyclicity is not more than m 3 if q2(0)>m, and that the nearer q2(0)is close to 1, the more the limit cycles are bifurcated.     

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.…     

Quadratic systems with a weak focus and a strong focus

It is proved that the quadratic system with a weak focus and a strong focus has a unique limit cycle around one of the two foci, if there exists simultaneously limit cycles around each of the two foci for the system.     

Number and Location of Limit Cycles in a Class of Perturbed Polynomial Systems

In this paper,we investigate the number,location and stability of limit cycles in a class of perturbedpolynomial systems with (2n 1) or (2n 2)-degree by constructing detection function and using qualitativeanalysis.We show that there are at most n limit cycles in the perturbed polynomial system,which is similar tothe result of Perko in [8] by using Melnikov method.For n=2,we establish the general conditions dependingon polynomial's coefficients for the bifurcation,location and stability of limit cycles.The bifurcation parametervalue of limit cycles in [5] is also improved by us.When n=3 the sufficient and necessary conditions for theappearance of 3 limit cycles are given.Two numerical examples for the location and stability of limit cycles areused to demonstrate our theoretical results.     

BIFURCATION 0F LIMIT CYCLES FROM A CENTER IN TWO-PARAMETER SYSTEM

In this paper we consider a two-parameter perturbated system which takes the systems discussedin [1], [2], [3] as its special case. The bifurcation region of the limit cycles is given on theparameter plane. The author also studies the stability of the limit cycles. At the end of this paperthe author discusses the difference of the bifurcation of the limit cycles from a center between thecase of two-parameter and the case of one-parameter.     

ON THE RELATIVE POSITION OF LIMIT CYCLES FOR THE EQUATION OF TYPE(Ⅱ)τ=0

In this paper,we consider the relative position of limit cycles for the system(dx)/(dt)=δx-y mxy-y~2,(dy)/(dt)=x-ax~2, (1)under the conditiona<0,0<δ≤m,m≤1/a-a.(2)The main result is as follows:(i)Under Condition(2),if δ=m/2 m~2/(4a)≡δ_0,then system(1)_(δ_0)has no limit cycles andon singular closed trajectory through a saddle point in the whole plane.(ii)Under condition(2),the foci O and R'cannot be surrounded by the limit cyclesof system(1)simultaneously.     

NECESSARY AND SUFFICIENT CONDITIONS OF EXISTENCE AND UNIQUENESS OF LIMIT CYCLES FOR A CLASS OF POLYNOMIAL SYSTEM

In this paper, we discuss the limit cycles of the systemdx/dt=y·[1+(A(x)]oy/dt=(-x+δy+α_1x~2+α_2xy+α_5x~2y)[1+B(x)] (1)where A(x)=sum form i=1 to n(a_ix~), B(x)=sum form j=1 to m(β_jx~j) and 1+B(x)>0. We prove that (1) possesses at most one limit cycle and give out the necessary and sufficient conditions of existence and uniqueness of limit cycles.     

Recognition of Finite Simple Groups S 4(q) by Their Element Orders

It is proved that among simple groups $S_4(q)$ in the class of finite groups, only the groups $S_4(3^n)$, where $n$ is an odd number greater than unity, are recognizable by a set of their element orders. It is also shown that simple groups $U_3(9)$, ${^3D}_4(2)$, $G_2(4)$, $S_6(3)$, $F_4(2)$, and ${^2E}_6(2)$ are recognizable, but $L_3(3)$ is not.     

三维Minkowski空间中的一类直线汇

研究了由三维Minkowski空间$E^3_1$中一个类空曲面$S_1$上一个单参数测地曲线族的切线所构成的直线汇$T$,它以$S_1$为一个焦曲面.证明了$T$的两个可展曲面族沿着第二个焦曲面$S_2$的正交曲线网相交的充要条件是$S_1$是可展曲面.对于$T$的两个焦曲面$S_1$和$S_2$之间沿着同一光线的对应,还证明了其保持渐近曲线网的充要条件.最后,研究了$T$的正交曲面$S$,并且证明了如果$S$是$E^3_1$中的一个极大曲面,那么,$T$的焦曲面$S_1$和$S_2$之间沿着同一光线的对     

Homogenization of Elasticity Problems with Boundary Conditions of Signorini type

In a perforated domain $\Omega ^\varepsilon = \Omega \cap \varepsilon \omega $ formed of a fixed domain Ω and an ε-compression of a 1-periodic domain ω, we consider problems of elasticity for variational inequalities with boundary conditions of Signorini type on a part of the surface $S_0^\varepsilon $ of perforation. We study the asymptotic behavior of solutions as ε → 0 depending on the structure of the set $S_0^\varepsilon $ . In the general case, the limit (homogenized) problem has the two distinguishing properties: (i) the limit set of admissible displacements is determined by nonlinear restrictions almost everywhere in the domain Ω, i.e., in the limit, the Signorini conditions on the surface $S_0^\varepsilon $ can turn into conditions posed at interior points of Ω (ii) the limit problem is stated for an homogenized Lagrangian which need not coincide with the quadratic form usually determining the homogenized elasticity tensor. Theorems concerning the homogenization of such problems were obtained by the two-scale convergence method. We describe how the limit set of admissible displacements and the homogenized Lagrangian depend on the geometry of the set $S_0^\varepsilon $ on which the Signorini conditions are posed.     

二维严格凸赋范空间单位球面间等距映射的线性延拓

主要研究二维严格凸实赋范空间E和F的单位球面S_1(E)和S_1(F)之间的等距映射的线性延拓问题.利用二维严格凸赋范空间单位球面的性质得到:若等距映射V_0:S_1(E)→S_1(F)满足一定条件,则V_0可延拓为全空间E上的线性等距映射V:E→F.     

A kind of bifurcation of limit cycle from a nilpotent critical point

In this paper, an interesting and new bifurcation phenomenon that limit cycles could be bifurcated from nilpotent node (focus) by changing its stability is investigated. It is different from lowing its multiplicity in order to get limit cycles. We prove that $n^2+n-1$ limit cycles could be bifurcated by this way for $2n+1$ degree systems. Moreover, this upper bound could be reached. At last, we give two examples to show that $N(3)=1$ and $N(5)=5$ respectively. Here, $N(n)$ denotes the number of small-amplitude limit cycles around a nilpotent node (focus) with $n$ being the degree of polynomials in the vector field.     

一类Sierpinski垫的Hausdorff测度

设S_λ为压缩比为λ(λ≤1/3)的一类Sierpinski垫,s=-log_λ3为S_λ的Hausdorff维数,N为产生S_λ的所有基本三角形的集合.本文使用网测度方法,获得了S_λ的s-维Hausdorff测度的精确值H~s(S_λ)=1,同时证明了H~s(S_λ)可由S_λ关于网N的s-维Hausdorff测度H_N~s(S_λ)确定,获得了S_λ的非平凡的最佳覆盖.     

Boundedness of Area Functions Related to Schrödinger Operators and Their Commutators in Weighted Hardy Spaces

In this paper, we consider the area function $S_Q$ related to the Schrödinger operator $\mathcal{L}$ and its commutator $S_{Q,b}$, establish the boundedness of $S_Q$ from $H^p_\rho(w)$ to $L^p(w)$ or $WL^p(w),$ as well as the boundedness of $S_{Q,b}$ from $H^1_\rho(w)$ to $WL^1(w).$     

On Factorisations and Generators in Transformation Semigroups

It is shown that the classical decomposition of permutations into disjoint cycles can be extended to more general mappings by means of path-cycles, and an algorithm is given to obtain the decomposition. The device is used to obtain information about generating sets for the semigroup of all singular selfmaps of $X_{n} = \{1, 2, \dots, n\}$. Let $T_{n,r} = S_{n}\cup K_{n,r}$, where $S_{n}$ is the symmetric group and $K_{n,r}$ is the set of maps $\alpha\,:\, X_{n} \to X_{n}$ such that $|im(\alpha)| \le r$. The smallest number of elements of $K_{n,r}$ which, together with $S_{n}$, generate $T_{n,r}$ is $p_{r}(n)$, the number of partitions of $n$ with $r$ terms.     

矩阵空间之间的保幂线性映射

在本文中,设C是复数域,n和m是正整数,k为固定的自然数,且k≥2．设Mm(C)为C上m阶全矩阵空间,Sn(C)为C上n阶对称矩阵空间．本文分别刻画了从Sn(C)到Mm(C)和Sn(C)到Sm(C)上的保矩阵k次幂的线性映射．     

Asymptotics of Analytic Semigroups,II

Let $T(\cdot)$ be an analytic $C_0$-semigroup of operators in a sector $S_{\theta}$, such that $||T(\cdot)||$ is bounded in each proper subsector $S_{\theta_0}$. Let $A$ be its generator, and let $D^{\infty}(A)$ be its set of $C^{\infty}$-vectors. It is observed that the (general) Cauchy integral formula implies the following extension of Theorem 5.3 in [1] and Theorem 1 in [4]: for each proper subsector $S_{\theta_0}$, there exist positive constants $M,\,\delta$ depending only on $\theta_0$, such that $(\delta^n/n!)||z^nA^nT(z)x||\leq M\,||x||$ for all $n\in\Bbb N,\, z\in S_{\theta_0}$, and $x\in D^{\infty}(A)$. It follows in particular that the vectors $T(z)x$ (with $z\in S_{\theta}$ and $x\in D^{\infty}(A)$) are analytic vectors for $A$ (hence $A$ has a dense set of analytic vectors).