Cumulants are universal homomorphisms into Hausdorff groups

This is a contribution to the theory of sums of independent random variables at an algebraico-analytical level: Let Prob denote the convolution semigroup of all probability measures on with all moments finite, topologized by polynomially weighted total variation. We prove that the cumulant sequence regarded as a function from Prob into the additive topological group ofall real sequences, is universal among continuous homomorphisms from Prob into Hausdorff topological groups, in the usual sense that every other such homomorphism factorizes uniquely through . An analogous result, referring to just the first cumulants,holds for the semigroup of all probability measures with existing rth moments. In particular, there is no nontrivial continuous homomorphism from the convolution semigroup of all probability measures, topologized by the total variation metric, into any Hausdorff topological group.Mathematics Subject Classification (2000): 60B15, 60E10, 60G50     

走近"2001宽带年"

中国互联网发展的带宽不足、上网速度慢,是长期制约我国电信网络发展的瓶颈.随着"2001宽带年"宽带网建设的启动,将为我们早日铺就信息高速公路.     

A localization argument for characters of reductive Lie groups

This article provides a geometric bridge between two entirely different character formulas for reductive Lie groups and answers the question posed by Schmid (in: Deformation Theory and Symplectic Geometry, Mathematical Physics Studies, Vol. 20, Kluwer Academic Publishers, Dordrecht, 1997, pp. 259-270).A corresponding problem in the compact group setting was solved by Berline et al. (Heat Kernels and Dirac Operators, Springer, Berlin, 1992) by an application of the theory of equivariant forms and particularly the fixed point integral localization formula. This article (besides its representation-theoretical significance) provides a whole family of examples where it is possible to localize integrals to fixed points with respect to an action of a noncompact group. Moreover, a localization argument given here is not specific to the particular setting considered in this article and can be extended to a more general situation.There is a broadly accessible article (Libine, A Localization Argument for Characters of Reductive Lie Groups: An Introduction and Examples, 2002, math.RT/0208024) which explains how the argument works in the case, where the key ideas are not obstructed by technical details and where it becomes clear how it extends to the general case.     

Classification of Hardy Submodules and Characteristic Space Theory（A Brief and Selective Survey）

This paper is a brief and selective survey on classification of Hardy Submodules over the polydisk. The survey reports some progress in classification of Hardy submodules.     

The effect of doping by IV-family elements on the electronic structure and electrical characteristics of Sb2O5

The electronic structures of doped Sb₂O₅ by IV-family elements (Si, Ge and Sn) were examined using the density function theory (DFT). Density of states (DOSs) results showed that the substituted IV-family elements act as acceptors in Sb₂O₅. Partial DOSs indicates that by substituting Ge(Ge _Sb ) or Sn(Sn _Sb ), there may be a larger contribution to the total DOSs near E _F than by substituting Si, which suggests that doping Ge or Sn in Sb₂O₅ produces better ptype doping compared to doping Si. Formation energy results show that IV-family elements are more likely to exist in the substituted position rather than in the interstitial position in Sb₂O₅, decreasing any self-compensation effect and making it easier for IV-family elements to realize ptype doping in Sb₂O₅. Ionization energy results show that Ge _Sb or SnSb, two among the three impurities considered, act as shallow acceptors in Sb₂O₅, thus producing a higher concentration of holes.      

一种高性能电流调节器的设计

基于0.5μm CMOS工艺,设计了一种能够在较大范围内工作的电流调节器。该电路通过适当地利用NMOS和PMOS差分输入对的各自特性,以及改进的差分结构,实现了工作范围的扩展和共阴极LED的驱动。该电流调节器采用的运算放大器都是一级的自补偿结构,从而简化了电路的稳定性设计,提高了物理实现的成功率。仿真结果表明,该电流调节器在整个工作范围内的精度可以达到80%以上。     

工业变频器研发中的特性检测与试验方法

品质是一个产品乃至一个企业的生命，变频器是一种科技含量较高的产品，对质量的要求也就较高。评价试验是保证变频器质量的必要手段，贯穿于整个研发过程。三垦变频器作为进入中国最早的变频器品牌，已经建立了一套完整的试验评价体系。本文旨在介绍研发过程中的特性检测与试验方法，以供参考。     

A versatile signal flow graph realization of a general transfer function by using CDBA

A general synthesis procedure is given for a versatile signal flow graph realization of a general transfer function by using current differencing buffered amplifier (CDBA). The proposed configuration uses n+1 CDBAs, n capacitors and at most 2n+4 resistors. This number of resistors can be reduced to n+1 for special cases. The circuit is eligible to obtain a variety of transfer characteristics with the same common denominator polynomial, and it is easily converted to different modes of operations. It is straightforward to find the values of the passive elements from the coefficients of the transfer function to be realized. Simulations results are obtained by using commercially available active component AD844 and CMOS technology as well. All of these make the proposed circuit attractive.     

Rod-pinch 二极管理论及数值模拟

 介绍了Rod-pinch二极管的基本结构和工作原理，采用Laminar模型分析了Rod-pinch二极管中的粒子运动过程及其阻抗特性。考虑背景空间离子电荷的影响，用1维Laminar方程分析Rod-pinch二极管中电子的自箍缩过程，并且利用Magic程序对其中的粒子运动进行数值模拟，求解二极管中的电压和电流，最终得出二极管的阻抗特性，在较低电压下，负极性RPD的性能明显不如正极性RPD。根据临界电流经验公式，初步验证Laminar理论模型的可行性。     

猝发双脉冲直线感应加速器组元研究

在原单脉冲直线感应加速器（LIA）组元的基础上，利用电缆延时和电缆反射两种方式获得了间隔500～1 000 ns的猝发双脉冲输出。在感应加速腔上进行了双脉冲实验，获得了幅度大于200 kV、前沿小于35 ns、平顶大于60 ns的双脉冲加速电压波形。两种方式中第一个脉冲的前沿和幅度都达到了原单脉冲组元的水平，表明加速腔负载的变化对波形没有明显影响，但由于电缆对波形的损耗，第二个脉冲的幅度和前沿比第一个脉冲略差。可以利用水介质传输线来代替长电缆，减小传输线的长度及其对波形的损耗。两个脉冲间的幅度差异可以通过改变长电缆的阻抗来调节。实验表明，通过这两种猝发双脉冲的产生方式并结合加速腔磁芯的改进，可简单高效地完成原单脉冲LIA的双脉冲改造。