证明优选法的最优性

<正> 令f为[0,1]内的单值函数,D为f的全体.n+1次试验后,优选法(取分点a=剩余区间长度为L_n=a~n.任一选法P,相对于某f∈D,n+1次试验后剩余区间长度为L_(p_n)(f).     

关于四元数矩阵乘积迹的不等式

设 H~(m×n)为 m×n 四元数矩阵的集合,σ_1(A)≥…≥σ_n(A)为 A∈H~(mxn)的奇异值。本文证明了:1)设 A∈H~(mxm),B∈H~(mxm),r=min(m,m),则|tr(4B)|≤c r σ_i(A)σ_i(B).2)设 A_i∈H~(mxm),i=1,2,…,n,(A_1A_2…A_n)k为 A_1A_2…A_n 的任一个 k 阶主子阵,则|tr(A_1.A_2…A_n)_k|≤sun form i=1 to k σ_i(A_1)…σ_i(A_n).我们还得到四元数矩阵迹的其它一些不等式。这些结果推广和改进了文[1],[2]中的结果,进一步解决了 Bellman 猜想。     

可换格群的拓扑完备化

<正> Redfield在[1]中证明了任意一个附有局部凸拓扑τ的可换tl-群G有一个完备化(G,τ).但[1]中的证明冗长,本文将给出一个简短的直接证明.有关概念及术语符号见[2]、[3]. 设(G,τ)是一个可换tl-群,为G上由τ导出的一致结构,即     

一类传染病中立型积分方程模型的多个正解的存在性

§ 1 .　IntroductionThispaperconsidersthefollowingneutralnonlinearintegraleuqation :x(t) =γx(t-τ) +( 1-γ) ∫tt-τf(s,x(s) )ds,( 1.1)0≤γ<1.Ifγ=0theequation ( 1.1) yieldsx(t) =∫tt-τf(s,x(s) )ds. ( 1.2 )SimilarequationwereconideredbyAIDDADS [1],GUODa jun [2 ],LEGGETT [3]andWILLIAMS [4 ].Nowwebrieflydescirbethemeaningoftheequationinthecontextofepidemics.Thenumberτcanbeinterpretedasthedurationofinfectivity .Insuchamodelitisassumedthatthetotalpoputationisconstant,x(t)isthepoputa…     

等距节点三角插值的Lebesgue常数的渐近展开

设 f(x)是以2π为周期的一个周期函数,我们知道对于[0,2π]上的2n 1个节点 θ_k=k(2π/(2n 1)),k=0,1,2,…,2n,(1)存在唯一的n次三角多项式L_n(f,θ),满足L_n(f,θ_k)=f(θ_k),k=0,1,2,…,2n。这里     

对“论广义的Канторович,Л.В.多项式及其渐近行为”一文的几点注记

在[1]中,曹家鼎讨论了用线性正算子逼近连续函数,给出一些函数类逼近上界的估计,该文中主要结果是 定理A 设A_n是一列C[a,b]C[a,b]的线性正算子,A_n(1,x)=1,则当x∈[a,b]时。 _n(w~2,x)=1/2A((t-x)~2,x), (1) 其中 如果再设A_n(t,x)=x,则     

von Neumann代数上的局部可乘Lie n-导子

A_1,…,A_n的(n-1)-换位子记为p_n(A_1,…,A_n).令M是von Neumann代数,n≥2是任意正整数,L:M→M是一个映射.本文证明了,若M不含I_1型中心直和项,且L满足L(p_n(A_1,…,A_n))=∑_(k=1)~np_n(A_1,…,A_(k-1),L(A_k),A_(k+1),…,A_n)对所有满足条件A_1A_2=0的A_1,A_2,…,A_n∈M成立,则L(A)=φ(A)+f(A)对所有A∈M成立,其中φ:M→M和f:M→E(M)(M的中心)是两个映射,且满足φ在P_iMP_j上是可加导子,f(p_n(A_1,A_2,…,A_n))=0对所有满足A_2A_2=0的A_1,A_2,…,A_n,∈P_iMP_j成立(1≤i,j≤2),P_1∈M是core-free投影,P_2=I-P_1;若M还是因子且n≥3,则L满足条件L(p_n(A_1,A_2,…,A_n))=∑_(k=1)~n=p_n(A_1,…,A_(k-1),L(A_k),A_(k+1),…,A_n)对所有满足A_1A_2A_1=0的A_1,A_2,…,A_n∈M成立当且仅当L(A)=Φ(A)+h(A)I对所有A∈M成立,其中Φ是M上的可加导子,h是M上的泛函且满足h(p_n(A_1,A_2,…,A_n))=0对所有满足条件A_1A_2A_1=0的A_1,A_2,…,A_n∈M成立.     

一类二阶递推数列含有平方数的充要条件

设a,b是适合a~2>b,(a,b)=1的非零整数;数列{L_n}_(n-1)~∞满足L_o=1,L=a,L_(n 1)=2aL_n-bL_(n-1)(n>0).本文证明了:当b≡1(mod4)时。{L_n}_(n-1)~∞中含有平方数的充要条件是某-L_m是平方数,这里m∈{1,2,4,8}.     

试题研讨(21)

题目　( 2 0 0 3年南昌市高三第二次调研测试题)设函数f ( x)是定义在[- 1 ,0 )∪( 0 ,1 ]上的奇函数,当x∈[- 1 ,0 )时,f ( x) =2 ax 1x2 　( a为实数) .1求当x∈( 0 ,1 ]时,f ( x)的解析式;2若f ( x)在区间( 0 ,1 ]上为增函数,求a的取值范围;3求f( x)在x∈( 0 ,1 ]上的最大值.命题溯源　本题研究了函数y =2 ax -1x2 的单调性及最值,2 0 0 2年天津市高中质量调查理科第1 9题与2 0 0 3年合肥市高三抽样测试第2 2题都涉及此类问题.原解思路　1设x∈( 0 ,1 ],则- x∈[- 1 ,0 ) .又f ( x)为奇函数,则f ( x) =- f ( - x) =- [2 a( - x) 1( -…     

加权幂——算术(几何)平均值不等式的加强

设a_i>0,p_i>O,(i=1,2,…,n),p_n=m∈R,M_n(a,p)=1/m,A_n(a,p)=那么 A_n(a,P)≥G_n(a,p) (1) M_n(a,p)≥G_n(a,p)(m>0) (2) M_n(a,p)≥A_n(a,p)(m>1) (3) 作者在文[1]将(1)加强为: P_n[A_n(a,p)-G_n(a,p)]≥p_n-1[A_(n1)(a,p)-G_(n-1)(a,p)], (4)或[A_n(a,p)/G_n(a,p)]~(p_n)≥[A_(n-1)(a,p)/G_(n-1)(a,p)]~(p_n-1) (5) 本文给出(2),(3)的加强定理1 a_i,p_i,P_n,M_n(a,p),G_n(a,p)意义同(2),λ>0,m>0,n∈N且n≥2,则P_n{[M_n(a,p)]~mλ~(1/p_n)[G_n(a,p)]~m}     

带有时间延迟的优选问题

<正> §1 目前在国内进行普及的单因素优选法,主要解决在一维区间内安排序贯实验(在本文中指每相隔单位时间安排一次,每次只做一个的实验),如何最优地确定在区间上的单峰函数的峰值点的位置问题.现有的方法要求下一个实验的安排须视上一个实验的结果如何而定,因而这种方法对那种实验周期(指从做实验到取得实验结果需要的时间)比较长,     

Super-high-frequency oscillations in a discontinuous dynamic system with time delay

We study oscillations in the discontinuous dynamic system with time delay . This is a typical model of relay feedback with delay. It is known that stable modes in this system have a bounded oscillation frequency. Here we consider transient processes and obtain the following result: under some restrictions ofF, the average oscillation frequency of any solution becomes finite after a period of time, i.e. super-high-frequency oscillations (with infinite frequency) exist only in a finite time interval. Moreover, we give an effective upper bound on the length of this interval.     

Posets with interval upper bound graphs

Competition graphs of transitive acyclic digraphs are strict upper bound graphs. This paper characterizes those posets, which can be considered transitive acyclic digraphs, which have upper bound graphs that are interval graphs. The results proved here may shed some light on the open question of those digraphs which have interval competition graphs.This material is taken from Chapter 3 of my (maiden name Diny) PhD Dissertation.     

Optimal policies for a delay time model with postponed replacement

We develop a delay time model (DTM) to determine the optimal maintenance policy under a novel assumption: postponed replacement. Delay time is defined as the time lapse from the occurrence of a defect up until failure. Inspections can be performed to monitor the system state at non-negligible cost. Most works in the literature assume that instantaneous replacement is enforced as soon as a defect is detected at an inspection. In contrast, we relax this assumption and allow replacement to be postponed for an additional time period. The key motivation is to achieve better utilization of the system’s useful life, and reduce replacement costs by providing a sufficient time window to prepare maintenance resources. We model the preventive replacement cost as a non-increasing function of the postponement interval. We then derive the optimal policy under the modified assumption for a system with exponentially distributed defect arrival time, both for a deterministic delay time and for a more general random delay time. For the settings with a deterministic delay time, we also establish an upper bound on the cost savings that can be attained. A numerical case study is presented to benchmark the benefits of our modified assumption against conventional instantaneous replacement discussed in the literature.     

Decentralized stability for switched nonlinear large-scale systems with interval time-varying delays in interconnections

In this paper, the problem of decentralized stability of switched nonlinear large-scale systems with time-varying delays in interconnections is studied. The time delays are assumed to be any continuous functions belonging to a given interval. By constructing a set of new Lyapunov–Krasovskii functionals, which are mainly based on the information of the lower and upper delay bounds, a new delay-dependent sufficient condition for designing switching law of exponential stability is established in terms of linear matrix inequalities (LMIs). The developed method using new inequalities for lower bounding cross terms eliminate the need for overbounding and provide larger values of the admissible delay bound. Numerical examples are given to illustrate the effectiveness of the new theory.     

Robust stability criteria for systems with interval time-varying delay and nonlinear perturbations

This paper considers the robust stability for a class of linear systems with interval time-varying delay and nonlinear perturbations. A Lyapunov-Krasovskii functional, which takes the range information of the time-varying delay into account, is proposed to analyze the stability. A new approach is introduced for estimating the upper bound on the time derivative of the Lyapunov-Krasovskii functional. On the basis of the estimation and by utilizing free-weighting matrices, new delay-range-dependent stability criteria are established in terms of linear matrix inequalities (LMIs). Numerical examples are given to show the effectiveness of the proposed approach.     

ASYMPTOTIC BEHAVIOR OF THE DRIFT-DIFFUSION SEMICONDUCTOR EQUATIONS

This paper is devoted to the long time behavior for the Drift-diffusion semi-conductor equations. It is proved that the dynamical system has a compact, connected and maximal attractor when the mobilities are constants and generation-recombination term is the Auger model; as well as the semigroup S(t) defined by the solutions map is differential. Moreover the upper bound of Hausdorff dimension for the attractor is given.     

On exponential stability analysis for neural networks with time-varying delays and general activation functions

This paper is concerned with the exponential stability analysis for a class of cellular neural networks with both interval time-varying delays and general activation functions. The boundedness assumption of the activation function is not required. The limitation on the derivative of time delay being less than one is relaxed and the lower bound of time-varying delay is not restricted to be zero. A new Lyapunov-Krasovskii functional involving more information on the state variables is established to derive a novel exponential stability criterion. The obtained condition shows potential advantages over the existing ones since no useful item is ignored throughout the estimate of upper bound of the derivative of Lyapunov functional. Finally, three numerical examples are included to illustrate the proposed design procedures and applications.     

Impulsive control for differential systems with delay

This paper deals with the impulsive control for a class of differential systems with delay. Using Lyapunov functions and the comparison principle, we present some sufficient conditions for the asymptotic stability and exponential stability of impulsive control systems with delay. Moreover, we give an estimate of the upper bound of impulse interval. The results in this paper extend and improve the earlier publications. Copyright © 2012 John Wiley & Sons, Ltd.     

A tight asymptotic bound on the size of constant-weight conflict-avoiding codes

In the study of multiple-access in the collision channel, conflict-avoiding code is used to guarantee that each transmitting user can send at least one packet successfully in the worst case within a fixed period of time, provided that at most k users out of M potential users are active simultaneously. The number of codewords in a conflict-avoiding code determines the number of potential users that can be supported in a system. Previously, upper bound on the size of conflict-avoiding code is known only for Hamming weights three, four and five. The asymptotic upper in this paper extends the known results to all Hamming weights, and is proved to be tight by exhibiting infinite sequences of conflict-avoiding codes which meet this bound asymptotically for all Hamming weights.