关于一个平面二次系统极限环的唯一性

<正> 我们这里研究平面二次系统容易知道方程（1）当δ=0时不存在闭轨与奇闭轨线，事实上只要引进变数变换d而且1+by=0是无切直线,因此当δ=0时(1)无闭轨与奇闭轨.因为(1)对于参数δ构成旋转向量场,因而我们知道(1)当δa(b+2l)≤0时在原点附近不存在极限环,而当δa(b+2l)>0且|δ|《1时在原点附近存在极限环,本文证明了(1)的极限环是唯一的.     

一类具有二虚不变直线的三次系统的极限环

研究一类具有二虚不变直线的三次系统:X′=y(1+X2),y′=-x+δy+nx2+mxy+ly2+bxy2,分析奇点的性态并求出奇点O的焦点量w0=δ,w1=m(n+l),w2=-mn(b-1).证明了w0=w1=w2=0时O为中心,并证明了w0=0,w1w2≥0时系统无极限环;w0=0,w1w2<0时系统至多有一个极限环.     

具不变集的平面多项式系统

本文证明了以y＝xm为不变集的平面n次多项式系统（m＞n）不会有极限环，但可以存在奇闭轨．     

一类三次系统极限环的存在唯一性

本文研究三次系统 (?)=-y δx a_1y~2 a~2xy a~5xy~2,(?)=x的极限环的存在唯一性。证明了:当δ<0,|δ|《1时至少有一个极限环;当-(a_1a_2 a_5)a_1~(-2)<δ<0时至多有一个极限环;当δ≥0或δ≤-(a_1a_2 a_5)a_1~(-2)时没有极限环。当a_1=0,δ<0时存在唯一的极限环。此外还证明了,当-(a_1a_2 a_5)a_1~(-2)≤δ<0时存在鞍点分界线环。     

一类“数学问题”的统一证法

文[1]给出了不等式:已知x,y,z∈R+,m∈N+.求证:x/mx+y+z+y/x+my+z+z/x+y+mz≤3/m+2. 文[2]给出了不等式:已知xi＞0(i=1,2,…n),k＜1,求证: n∑i=1 xi/x1+x2+…+xi-1+kxi+xi+1+…+xn≥n/n+k-1. 文[3]给出了不等式:设ai＞0(i=1,2,3,…,n),p∈R,q＞0,且n∑i=1ai=A,Si=pai+q(A一ai)＞0(i=1,2,…,n),求证:     

赫尔德不等式的推论变形与运用

一、引式:赫尔德不等式 设aij＞0(1≤i≤j≤n,1≤j≤m),若aj(1≤j≤m),且α1+α2+…+αm=1,则mП(n∑aij)aj≥n∑aijaj. 显然,当这个不等式只有两项,即当1/p+1/q=1时,(xp0+xp1+…+xpn)1/p(yq0+yq1+…+yqn)1/a≥x0y0+x1y1+…+xnyn,当α1=α2时即为(Cauchy)不等式,从中可以看到Cauchy不等式是Holder不等式的特殊情况.     

系统x=-y d·x x~2 d·xy-(a 1)y~2-a·y~3 y=x·(1 ax y)(0≤a≤1)的极限环讨论

本文讨论了系统x=-y dx x~2 dxy-(a 1)y~2-ay~3(1)y=x(1 ax y)(0≤a≤1)的极根环,证明了: 1)ad≤0时,(1)在全平面上无极限环。 2)ad≥3时,(1)不存在围绕原点的极限环。 3)3>ad>0,|d|1时,(1)存在包围原点的极限环。 4)3>ad>0时,(1)至多有一个围绕原点的极限环。 本文包含了文[1]的全部结论。     

一类系统的极限环讨论

文[1]研究了二次系统 dx/dt=-y+dx+x~2+dxy-y~2 dy/dt=x·(1+ax+y)证明了ad≤0或ad≥3时,(E_2)无围绕原点的极限环,0相似文献   

二维渗流最低水平开穿透的宽度

在二维渗流中,设rn是矩形[O,n]2的最低水平开穿透,令ξn=max｛y：（xy）∈rn｝．本文证明了在临界状态p＝pc时,存在常数0＜C1＜C2＜1,当n充分大时有存在,而在上临界状态p＞pc时,有存在］＝0.     

一类三次系统极限环的惟一性

讨论三次系统x=x(A0+A1x+A2y+A3xy-A4y2)y=y(x-1)的极限环问题.得到了该系统不存在极限环和存在惟一极限环的条件.     

Estimates of stability of characterization of additive types of distributions

An estimate of stability of characterization of distribution types is obtained for the case of additive types. Under some conditions, the estimate has the order ε^1/3L(ε), where L(ε) is a slowly varying function. Proceedings of the Seminar on Stability Problems for Stochastic Models, Moscow, Russia, 1996, Part I.     

一类完全正则半群簇子簇格的性质

本文研究了完全正则半群簇的子簇格［Ｖ＋∩ＰＶ，Ｖ＋∩ＰＶ］的某些格运算性质，我们证明了簇Ｖ＋∩ＰＶ可分解为Ｖ与Ｖ＋∩ＰＶ的并；对任意完全正则半群簇Ｗ，有Ｗ∩（Ｖ∨Ｖ＋∩ＰＶ）＝（Ｗ∩Ｖ）∨（Ｗ∩Ｖ＋∩ＰＶ）．特别地，我们得到了等式Ｖ＋∩ＰＶ＝Ｖ成立的若干条件．     

Study of the blow-up of solutions of systems of equations of hydrodynamic type

Mathematical Notes - We study the initial boundary-value problem for three-dimensional systems of equations of pseudoparabolic type. The system is similar to the Oskolkov system, but differs from...     

Characterization of types of asymptotic discernibility of families of hypotheses

We give a characterization of the types of asymptotic discernibility of families of hypotheses in the case of hypothetical measures that are not, in general, mutually absolutely continuous. The case when the logarithm of the likelihood ratio admits an asymptotic expansion of the type of an expansion with local asymptotic normality is examined in detail. Examples are studied.Translated fromTeoriya Sluchainykh Protsessov, Vol. 15, pp. 64–71, 1987.     

Distribution of types of symmetry of tensors of high degree

The asymptotic distribution of tensors of degree N in symmetry types is studied in this paper.Translated from Zapiski Nauchnykh Seminarov Leningradskogo Otdeleniya Matematicheskogo Instituta im. V. A. Steklova AN SSSR, Vol. 155, pp. 181–186, 1986.     

Preservation of equivalence of derivations under reduction of depth of formulas

In this paper we consider derivations in the (&, )-fragment of the intuitionistic propositional calculus. As is known, replacement of any occurrence of a formula [F] in a sequent S by an occurrence of the formula [p], where p is a new propositional variable, with the simultaneous addition to the antecedent of the formula F p or p F depending on the sign of the occurrence of F in S, leaves the derivability unchanged. We give a proof of the fact that the natural extension of this transformation to derivations preserves the relation of equivalence of derivations, i.e., transformed derivations are equivalent if and only if the originals are equivalent. (Derivations are considered equivalent if certain of their normal forms coincide, or, what is the same, if their deductive terms coincide.) It is proved that by the iteration of this transformation, each derivation of an arbitrary sequent S can be transformed into a derivation of a sequent S, depending only on S, whose succedent is a variable, and in the antecedent there occur only formulas of the form a,a & b, a b,,(a b) c, a & b c, a (b & c), wherea, b, c are variables. Here if S is balanced, then S is also balanced. (A sequent is called balanced if each variable occurs in it no more than twice.) The familiar correspondence between certain concepts of the theory of categories and concepts of the theory of proofs allows one to assert that there has been constructed a univalent functor, mapping a free Cartesian closed category into itself.Translated from Zapiski Nauchnykh Seminarov Leningradskogo Otdeleniya Matematicheskogo Instituta im. V. A. Steklova AN SSSR, Vol. 88, pp. 197–207, 1979.     

Estimate of growth of Lebesgue functions of linear methods of summation

Sufficient conditions are obtained in terms of matrix elements for the boundedness of Lebesgue functions of linear methods of summation of expansions in orthogonal systems of polynomial type.Translated from Matematicheskie Zametki, Vol. 6, No. 3, pp. 277–286, September, 1969.