Local chain‐configuration dependence of the mechanisms of the chemical reaction of poly(vinyl chloride). IX. Novel results on stereoselectivity of chlorination reaction

A poly(vinyl chloride) (PVC) sample was chlorinated in solution in the presence of 2,2′‐azobisisobutyronitrile and by the fluid‐bed method. The aim was to evaluate the scope of the stereoselectivity of the chlorination reaction. The quantitative microstructural analysis of the residual PVC with a degree of chlorination was followed by ¹³C NMR spectroscopy. From the evolution of the content of isotactic (mm), heterotactic (mr), and syndiotactic (rr) triads and of mmmm, mmmr, and rmmr isotactic pentads in the unchlorinated parts of the polymer, it was unambiguously inferred that the chlorination reaction proceeds by a stereoselective mechanism in that the mr heterotactic triads are the most reactive structures followed by the isotactic triad at mmmr and rmmr pentads. This conclusion was confirmed on the basis of the Fourier transform infrared results. The results provide valuable information regarding the effect of tacticity and related local conformations in the chemical reactions of PVC. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 508–519, 2003     

Four‐dimensional couplings among BF and matter theories from BRST cohomology

The local and manifestly covariant Lagrangian interactions in four spacetime dimensions that can be added to a “free” model that describes a generic matter theory and an abelian BF theory are constructed by means of deforming the solution to the master equation on behalf of specific cohomological techniques.     

《科技文献检索与利用》课教学的"三原则"和"五结合"

结合教学实践,总结了文献检索课教学中应掌握的原则以及教学中应注意的问题。     

二维正态分布矩形区域概率质量的局部单调性

研究了二维正态分布矩形区域概率质量当矩形区域中心沿某特定方向平移时的局部单调性。同时给出了一簇矩形区域,其中任一矩形区域的概率质量对正态分布相关系数的绝对值具有局部单调性。     

布尔矩阵维数的缺断区间(英)

本文证明了n维布尔矩阵维数的一个新的缺断区间为这一结果扩充了一些已知的结论．     

ContributionsSign-balanced covering matrices

A q × n array with entries from 0, 1,…,q − 1 is said to form a difference matrix if the vector difference (modulo q) of each pair of columns consists of a permutation of [0, 1,… q − 1]; this definition is inverted from the more standard one to be found, e.g., in Colbourn and de Launey (1996). The following idea generalizes this notion: Given an appropriate δ (-[−1, 1]^t, a λq × n array will be said to form a (t, q, λ, Δ) sign-balanced matrix if for each choice C₁, C₂,…, C_t of t columns and for each choice = (₁,…,_t) Δ of signs, the linear combination ∑_j=1^t _jC_j contains (mod q) each entry of [0, 1,…, q − 1] exactly λ times. We consider the following extremal problem in this paper: How large does the number k = k(n, t, q, λ, δ) of rows have to be so that for each choice of t columns and for each choice (₁, …, _t) of signs in δ, the linear combination ∑_j=1^t _jC_j contains each entry of [0, 1,…, q t- 1] at least λ times? We use probabilistic methods, in particular the Lovász local lemma and the Stein-Chen method of Poisson approximation to obtain general (logarithmic) upper bounds on the numbers k(n, t, q, λ, δ), and to provide Poisson approximations for the probability distribution of the number W of deficient sets of t columns, given a random array. It is proved, in addition, that arithmetic modulo q yields the smallest array - in a sense to be described.     

The Experimental and Theoretical Research of “Local Resonance“ in Ultrasonic Honing System

In 1982, Professor Fang Guoliang found the “Non full resonance“ phenomenon in a tool system while he use the thin-long tool ultrasonically machining deep-small hole. He called it as “local resonance“. Also this “Non full resonance“ phenomenon was discovered in the ultrasonic drilling and the ultrasonic honing system later. To its mechanism, professor Fang thought that the coupling of long-thin tool bar and driving system is weak, so the tool bar can vibrate independently, but the quantitative relation betwe...     

On the Decomposition of Hopf Module Coalgebra

In1969,Sweedler[1]giventhedecompositiontheoreyofcoalgebraswhicharecocommu-tative.In1975,Kaplansky[2]showedthatanycoalgebracanbeuniquelydecomposedintoadirectsumofitsindecomposablesubcoalgebras.From1978to1992,Shudo[3]andXu[4]consructuredtheindecomposabledirectsumcomponentsofacoalggebra,viadefineequivalenceralationforthesetofsimplesubcoalgebras.Asweknow,themodolecoalgebraisthennaturalgeneralizationofcoalgebra.AndittakesplayanimportentroleintheDrinfelddouble.Inthispaper,wediscussthedecompositio…     

银行系统网络运行现存的若干问题和解决建议

通过对银行系统网络现状的分析，从广域网和局域网两个不同的角度指出了银行现有的网络结构、体系存在的问题及其原因，并提出了较为可行的解决方法，对现在的大型网络系统有普遍的意义。     

活动课与地方课程资源的开发和利用

历史课程标准特别强调要培养学生的实践活动能力，全国各地出版的九年义务教育历史课本，每一种版本都安排了“活动课”，并将作为必修课内容。“活动课”就其教学内容而言，具有极大的开放性，不仅涉及历史课本上的内容，而且涉及到课本以外的教学内容，涉及整个社会现实和学生的生活实践，所以活动课与地方历史课程紧密相关。因此，教师在教学过程中，要充分开发和利用地方历史课程资源，把地方历史课程资源作为“活动课”的教学资源，使“活动课”教学更加丰富多彩，更加贴近学生的生活，充分展示“活动课”的教学功能。