现代信息技术中的快速收敛取样定理

在现代信息技术中,取样定理是模拟信号的量化以及复原为模拟信号的基础.模拟信号一般是频谱有限函数,彭瑞仁教授虽然得到了收敛速度比Shannon取样定理快得多的取样定理,然而,本文给出了收敛速度更快的负2N 1次幂取样定理(N为任意自然数),其结果比彭教授的结果更加优越.     

高阶取样定理*

Shannon取样定理是通讯理论中根据离散取样值重建信号的一个最基本定理。彭瑞仁先生在对取样间隔作微小牺牲的前提下,得出了收敛速度比Shannon取样公式快得多的三阶、四阶和五阶的取样公式[1].本文在彭先生工作的基础上,给出了构造高阶取样公式的一般方法以及一种N阶取样公式的简单形式。     

主平移不变子空间的平移整采样

给出主平移不变子空间的一个平移整采样定理,其采样公式不仅在L2(R)收敛意义下成立,而且在适当的1周期集上一致收敛的意义下成立.此采样定理包含了经典的Shannon采样公式,Walter在1992年的采样定理以及由紧支函数生成的主平移不变子空间的采样.最后给出了大量例子说明定理应用的广泛性.     

单调集函数的连续性与可测函数序列的收敛

引了单调集函数的几种连续性并且讨论了它们与可测函数依测度收敛之间的关系，给出可加测度论中的Lesbegue定理在单调测度空间上的4种推广形式。讨论单调集函数的连续性和模糊积分与Choquet积分的单调收敛定理之间的等价性。证明Choquet积分的控制收敛定理。     

模糊数值函数Henstock积分的收敛定理

给出模糊数值函数Henstock积分的收敛定理,特别给出了Kaleva积分的收敛定理,该结果推广了Kaleva积分以前若干个收敛定理。     

有界闭区间上连续函数列一致收敛的充要条件

判别函数列一致收敛的方法有函数列一致收敛定义、Cauchy一致收敛准则、limn→∞supx∈D|fn(x)-f(x)|=0及Dini定理,本文由函数列的等度连续性,可得出几个有界闭区间上连续函数列一致收敛的充要条件,推广了Dini定理.     

单调增函数幂次积分序列的一个猜想

本利用函数项级数的一致收敛定理和Lebesgue控制收敛定理证明了单调增函数幂次积分序列的一个猜想，结果如下：     

不动点迭代法的一点注记

对于迭代函数不满足收敛定理假定条件的情况 ,提出了一种简单方法 .此方法对于迭代函数满足收敛定理假定条件的情况 ,可以加速序列收敛 .最后给出了实例和程序 .     

黎曼可积函数列的极限理论及应用

对黎曼可积函数列的极限函数的可积性进行讨论．运用黎曼积分自身的理论依次证明了：一致收敛函数列的极限函数的黎曼可积性,黎曼积分下的控制收敛定理和广义积分下的控制收敛定理。并给出了一些应用例子．     

可测函数序列关于弱收敛概率测度序列积分的极限定理

研究了可测函数序列关于弱收敛概率测度序列积分的极限定理及其控制收敛定理,并给出了概率测度弱收敛的若干新的等价条件.     

Behavior of Shannon’s Sampling Series for Hardy Spaces

In this paper the convergence behavior of the Shannon sampling series is analyzed for Hardy spaces. It is well known that the Shannon sampling series is locally uniformly convergent. However, for practical applications the global uniform convergence is important. It is shown that there are functions in the Hardy space such that the Shannon sampling series is not uniformly convergent on the whole real axis. In fact, there exists a function in this space such that the peak value of the Shannon sampling series diverges unboundedly. The proof uses Fefferman’s theorem, which states that the dual space of the Hardy space is the space of functions of bounded mean oscillation. This work was partly supported by the German Research Foundation (DFG) under grant BO 1734/9-1.     

Pointwise convergence of wavelets of generalized Shannon type

In this paper, a new result on pointwise convergence of wavelets of generalized Shannon type is proved, which improves a theorem established by Zayed.     

Sampling for the fourth-order Sturm-Liouville differential operator

We extend the sampling method to compute the eigenvalues of a fourth-order differential operator. We show that the Shannon sampling theorem is not applicable due to the growth of the solutions on the real line. The inverse spectral theory, as developed by McLaughlin, and Kramer's theorem allow us to express the characteristic function explicitly by a new sampling formula.     

Wavelet subspaces with an oversampling property

In the classical Shannon sampling theorem, the same sequence of functions is both orthonormal and a sampling sequence. This is not true for most wavelet subspaces in which the sampling functions and the orthonormal bases are different. However by oversampling at double the rate the property of the Shannon wavelets is extended to a much larger class which includes the Meyer wavelets. In fact together with another condition, it characterizez them.     

Variable length path coupling

We present a new technique for constructing and analyzing couplings to bound the convergence rate of finite Markov chains. Our main theorem is a generalization of the path coupling theorem of Bubley and Dyer, allowing the defining partial couplings to have length determined by a random stopping time. Unlike the original path coupling theorem, our version can produce multistep (non‐Markovian) couplings. Using our variable length path coupling theorem, we improve the upper bound on the mixing time of the Glauber dynamics for randomly sampling colorings. © 2007 Wiley Periodicals, Inc. Random Struct. Alg., 2007     

Theoretical investigation on error analysis of Sinc approximation for mixed Volterra-Fredholm integral equation

In this study, we propose one of the new techniques used in solving numerical problems involving integral equations known as the Sinc-collocation method. This method has been shown to be a powerful numerical tool for finding fast and accurate solutions. So, in this article, a mixed Volterra-Fredholm integral equation which has been appeared in many science an engineering phenomena is discredited by using some properties of the Sinc-collocation method and Sinc quadrature rule to reduce integral equation to some algebraic equations. Then exponential convergence rate of this numerical technique is discussed by preparing a theorem. Finally, some numerical examples are included to demonstrate the validity and applicability of the convergence theorem and numerical scheme.     

Slow convergence of sequences of linear operators II: Arbitrarily slow convergence

We study the rate of convergence of a sequence of linear operators that converges pointwise to a linear operator. Our main interest is in characterizing the slowest type of pointwise convergence possible. This is a continuation of the paper Deutsch and Hundal (2010) [14]. The main result is a “lethargy” theorem (Theorem 3.3) which gives useful conditions that guarantee arbitrarily slow convergence. In the particular case when the sequence of linear operators is generated by the powers of a single linear operator, we obtain a “dichotomy” theorem, which states the surprising result that either there is linear (fast) convergence or arbitrarily slow convergence; no other type of convergence is possible. The dichotomy theorem is applied to generalize and sharpen: (1) the von Neumann–Halperin cyclic projections theorem, (2) the rate of convergence for intermittently (i.e., “almost” randomly) ordered projections, and (3) a theorem of Xu and Zikatanov.