周期扰动的非保守系统的周期解的存在性与唯一性

考虑具有周期扰动的Lienard型非保守系统x+Cx+gradG(x)=p(t),其中C是n×n的实对称方阵,x=(x1,x2,…,xn)T∈Rn,G∈C2(Rn,R),p∈C(R,Rn)且p(t+ω)≡p(t),ω＞0是常数,利用重合度理论讨论周期解的存在性与唯一性,得到了若干简便的判别条件.     

关于Liénard方程周期解的存在性与唯一性

考虑微分方程x+f(x)+g(x)=p(t),其中g(x)∈C(R),p(t)∈C2π,f∈C(R),在g(x)满足(g(x)-g(y))/(x-y)＜a＜1时,给出周期解的存在性,并对f(x)=cx的特殊情形,g(x)严格递减的条件下,给出周期解存在唯一的充要条件.     

Liénard方程周期解的存在唯一与唯二性问题

本文考虑微分方程 x+f(x)x+g(x)=p(t),其中g∈C~1(R)为严格递减,f ∈ C(R),p(t)为2π周期的连续函数,给出周期解的存在唯一的充要条件;在f(x)=c,g(x)严格凸函数且跨越第一共振点零时,给出唯二性定理。     

三角函数周期的探讨

有高中“三角函数”这一章中,我们知道y =Asin(ωx + φ) (x∈R ,Aω≠0 ,A ,ω,φ为常数)与y =Acos(ωx + φ) (x∈R ,Aω≠0 ,A ,ω,φ为常数)及y =Asin2 (ωx + φ) (x∈R ,Aω≠0 ,A ,ω,φ为常数)与y =Acos2 (ωx +φ) (x∈R ,A·ω≠0 ,A ,ω,φ为常数)这些三角函数的周期.那么,三角函数y =Asinn(ωx+ φ)与y =Acosn(ωx + φ) (A·ω≠0 ,A ,ω,φ为常数x∈R)的周期又是怎样的呢?定理1　1 )函数y =sinnx (x∈R) .当n为偶数时的周期为kπ,(k∈Z ,k≠0 ) ,最小正周期为π;当n为奇数时,周期为2kπ(k∈Z ,k≠0 ) ,最小正周期为…     

关于Liénard方程周期解的存在性与唯一性

考虑微分方程x f(x) g(x)=p(t)其中g（x）∈C（R),p（t)∈πC2,f∈C(R),在g（x)满足（g（x）-g（y))／（x-y）＜ａ＜1时,给出周期解的存在性,并对f(x)=cx的特殊情形,ｇ（x）严格递减的条件下,给出周期解存在唯一的充要条件．     

具有时滞的保守系统的2π周期解

对于如下的保守系统■ gradG(x)=P(t)=P(t 2π) (1)的2π周期解的存在性与唯一性,很早以来就受到重视,1974年 R.Kannan 证明了定理 A.设 P(t)∈C(R,P~n)是 2π周期的,G∈C~2(R~n,R),如果存在非负整数 M 及正数 p,q 满足     

概周期摆型方程无界解的存在性

对摆型方程x+Gx(x,t)=p(t),其中G(x,t)∈C1(R2)关于变量x是1周期的,并且sup(x,t)∈R2|Gx(x,t)|<+∞,limsupt→∞{supx∈R}=0,p(t)是平均值非零的概周期函数,证明了在柱面S1×R上方程具有无穷多的无界解.     

向量Lienard型方程的多个调和解

存在多个(无穷多个)调和解的条件,其中x∈R~n,F∈C~2(R~n,R),G∈C~2(R~n,R),p∈C~0(R,R~n),且p(t+T)≡p(t),integral from n=1 to p(t)dt=0。 对高维非线性非自治系统调和解的讨论,通常都要给出条件,保证周期解只在一个有界集内存在,然后对包含上述有界集的有界凸域利用不动点原理证明调和解的存在性。这样的处理方法很难对调和解的个数问题作深入讨论。本文采用广义Lienard变换首     

关于Liénard方程周期解的存在性与唯一性

考虑微分方程 x+f(x)+g(x)=p(t),其中g(x)∈C(R),p(t)∈C2π,f∈C(R),在g(x)满足(g(x)-g(y))/(x-y)＜a＜1时,给出周期解的存在性,并对f(x)=cx的特殊情形,g(x)严格递减的条件下,给出周期解存在唯一的充要条件.     

ON THE EXISTENCE OF PERIODIC SOLUTIONS FOR LIENARD SYSTEMS

<正> In this paper we study the existence of periodic solutions for n-dimensional Liénard syste-ms of the formx″+((?)~2F(x))/((?)x~2)x′+grad G(x)=e(t), (1.1)where F∈C~2(R~n,R),G∈C~1(R~n,R),e∈C(R,R~n)and e(t)≡e(t+T)for some con-stant T>0.By((?)~2F(x))/((?)x~2),we denote the Hessian Matrix of F at x.     

RECENT PROGRESS ON SPHERICAL HARMONIC APPROXIMATION MADE BY BNU RESEARCH GROUP ——In memory of Professor Sun Yongsheng

As early as in 1990, Professor Sun Yongsheng, suggested his students at Beijing Normal University to consider research problems on the unit sphere. Under his guidance and encouragement his students started the research on spherical harmonic analysis and approximation. In this paper, we incompletely introduce the main achievements in this area obtained by our group and relative researchers during recent 5 years （2001-2005）. The main topics are： convergence of Cesaro summability, a.e. and strong summability of Fourier-Laplace series; smoothness and K-functionals; Kolmogorov and linear widths.     

A unified approach to certain problems of best local approximation

In this paper we study best local quasi-rational approximation and best local approximation from finite dimensional subspaces of vectorial functions of several variables. Our approach extends and unifies several problems concerning best local multi-point approximation in different norms.     

Boundedness for commutators of multipliers on Hardy type spaces

In this paper, we study the commutators generalized by multipliers and a BMO function. Under some assumptions, we establish its boundedness properties from certain atomic Hardy space Hb^p（R^n） into the Lebesgue space L^p with p 〈 1.     

THE 8~(th) INTERNATIONAL CONGRESS ON INDUSTRIAL AND APPLIED MATHEMATICS

<正>August 10-14,2015Beijing,ChinaThe International Congress on Industrial and Applied Mathematics(ICIAM)is the premier international congress in the field of applied mathematics held every four years under the auspices of the International Council for Industrial and Applied Mathematics.From August 10 to 14,2015,mathematicians,scientists     

Towards Excellence in Science Chinese Academy of Sciences

<正>May 26,2014,Beijing Science is a human enterprise in the pursuit of knowledge.The scientific revolution that occurred in the 17th Century initiated the advances of modern science.The scientific knowledge system created by     

Bounds for the zeros of polynomials

Let P(z)=∑↓j=0↑n ajx^j be a polynomial of degree n. In this paper we prove a more general result which interalia improves upon the bounds of a class of polynomials. We also prove a result which includes some extensions and generalizations of Enestrǒm-Kakeya theorem.     

Boundedness of commutators related to Marcinkiewicz integrals on hardy type spaces

In this paper, the authors study the boundedness of the operator [μΩ, b], the commutator generated by a function b ∈ Lipβ(Rn)(0 ＜β≤ 1) and the Marcinkiewicz integrals μΩ, on the classical Hardy spaces and the Herz-type Hardy spaces in the case Ω∈ Lipα(Sn-1)(0 ＜α≤ 1).     

Jacobi polynomials used to invert the laplace transform

Given the Laplace transform F(s) of a function f(t), we develop a new algorithm to find an approximation to f(t) by the use of the classical Jacobi polynomials. The main contribution of our work is the development of a new and very effective method to determine the coefficients in the finite series expansion that approximation f(t) in terms of Jacobi polynomials. Some numerical examples are illustrated.     

Generalization of the interaction between Haar approximation and polynomial operators to higher order methods

In applications it is useful to compute the local average empirical statistics on u. A very simple relation exists when of a function f（u） of an input u from the local averages are given by a Haar approximation. The question is to know if it holds for higher order approximation methods. To do so, it is necessary to use approximate product operators defined over linear approximation spaces. These products are characterized by a Strang and Fix like condition. An explicit construction of these product operators is exhibited for piecewise polynomial functions, using Hermite interpolation. The averaging relation which holds for the Haar approximation is then recovered when the product is defined by a two point Hermite interpolation.