Subgroups of Free Groups: a Contribution to the Hanna Neumann Conjecture

We prove that the strengthened Hanna Neumann conjecture, on the rank of the inter-section of finitely generated subgroups of a free group, holds for a large class of groups characterized by geometric properties. One particular case of our result implies that the conjecture holds for all positively finitely generated subgroups of the free group F(A) (over the basis A), that is, for subgroups which admit a finite set of generators taken in the free monoid over A.     

Basic zeolite and zeolite-type catalysts for the oxidative methylation of toluene with methane

The oxidative methylation of toluene with methane is used as a test reaction for determining the activity, selectivity and yield of C₈ hydrocarbons (ethylbenzene and styrene) over different zeolite and zeolite-type catalysts, viz., X, Y, mordenite, ZSM-5, silicalite and AlPO₄-5. Selectivity and basicity increase with decreasing Si/Al atomic ratio within the series of the same structural type. The basicity, surface structure and structural integrity are characterized by TPD of CO₂, XPS and IRS, respectively. This revised version was published online in June 2006 with corrections to the Cover Date.     

一种推广的周期Riemann边值问题及其基本解组

在±∞i处提出一种条件推广的周期Riemann边值问题并给出解及可解条件.通过引入基本解组和广义相联周期边值问题的概念使这类边值问题的可解条件有明确的几何意义(正交化条件),而其特例推广了已有的工作.     

An Unusual N-Boc Deprotection of Benzamides under Basic Conditions

For the first time, an unusal cleavage of N‐tert‐butyloxycarbonyl (N‐Boc) protection from N‐Boc‐protected benzamide under basic conditions in excellent yields is reported. The deprotection involves the N‐Boc emigration from the benzamide to form 2‐O‐Boc group followed by O‐Boc deprotection on the phenyl ring.     

Preparation and characterization of novel basic polysulfone polymers

Two synthesis routes for the preparation of novel base‐modified polysulfones (PSUs; Udel®) were investigated: (1) the addition of the basic aromatic ketones 2,2′‐dipyridylketone and 4,4′‐bis‐(diethylamino)benzophenone and the basic aromatic aldehydes N,N‐dimethylamino‐benzaldehyde, pyridine‐2‐aldehyde, pyridine‐3‐aldehyde, and pyridine‐4‐aldehyde to lithiated PSU and (2) the reaction of lithiated PSU with basic aromatic carboxylic acid esters such as 4‐N,N‐dimethylaminobenzoic acid ethylester, pyridine‐2‐carboxylic acid ethylester, pyridine‐3‐carboxylic acid ethylester, and pyridine‐4‐carboxylic acid ethylester. Both synthesis routes lead to a high degree of conversion, without the occurrence of crosslinking. This is remarkable, especially for the reaction of lithiated PSU with the ester compounds, because the ? (C?O)? Ar groups formed by the reaction of the ester with PSU–Li are not further converted with the remaining PSU–Li sites to (crosslinked) PSU? C(? OLi)? Ar? PSU alcoholates, as normally observed when esters are reacted with Li‐organic compounds. Starting with dilithiated PSU, we obtained degrees of substitution of 0.8–2 groups per PSU repeating unit. The structures and compositions of the modified PSU polymers were confirmed with NMR spectroscopy and elemental analysis. The modified polymers were also characterized via thermogravimetric analysis (thermal stability). Interestingly, the product of the reaction of lithiated PSU with 4,4′‐bis‐(diethylamino)benzophenone could be oxidized to a deep blue polymeric dye that showed proton self‐conductivity. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 2874–2888, 2001     

广义不确定性系统理论的特性分析

广义不确定性系统涵盖了目前人们在科学研究中所涉及的一切系统(确定性系统与不确定性系统)，是内涵最深外延最广的系统理论体系。本文讨论了其理论的发展概况，对其概念、特性、体系进行了剖析、探讨，给出了广义不确定性系统理论的基本框架。     

碱性品红分子在纳米磷化镓粒子表面的吸附取向(英文)

利用表面增强拉曼光谱,初步确定了吸附于纳米磷化镓(GaP)粉体表面的碱性品红分子的取向。在295K时,将50 mg GaP粉体分别置于50 ml,4.7×10-3M和50 ml,4.74×10-6M碱性品红水溶液中。对由较高浓度溶液形成的吸附系统持续搅拌24小时;而对极稀溶液吸附系统则连续搅拌处理7天。在经过过滤、干燥处理后,吸附有染料分子的GaP粉体被直接用于碱性品红的表面拉曼光谱测试。通过对染料分子中央碳原子呼吸振动和氮-苯环伸缩振动模式的相对强度进行分析可知:在较高浓度的溶液中,染料分子主要以一种混合取向方式吸附于GaP粉体表面上,即“端基接触”和“平躺”两种方式;而在极稀溶液中,染料分子则仅以“端基接触”方式吸附于GaP粉体表面上。     

中医基本概念和治疗方法原理

为使读者对古中医学有更深的了解、介绍了中医学的基础知识，论述了中医防病与治疗原则、中医治疗方法和中药基本知识及其基本特点。     

直锥形光纤传输性质的研究

光纤通信的发展日新月异,光纤在信息的传输方面起着越来越重要的作用.通过把传输光纤的一端拉制成锥形,研究了光信号在锥形光纤中的传播行为.根据标量波动方程,运用高斯近似法,从理论上说明了光信号在锥形光纤中的传输特性和能量损耗,分析了光功率在光纤中的分布、光纤中基模场的模半径与光纤芯径的关系、光纤中光的传输模式与光纤芯径的关系、锥形光纤的传输效率与锥形光纤尖端直径的关系等.在实验上,用剪断法测量了锥形光纤的传输效率随锥形光纤圆锥角的变化关系.通过选取一系列锥角的大小,测出相应的传输效率,作出?湫是?并用具体数据进行半定量计算,得出锥形光纤顶端锥体的角度及其变化愈大愈光滑,锥形过渡区越短,传输效率就越高的结论.     

电路计算机辅助设计与计算——线性电路频域的图论分析法

应用面对对象的编语言Visual Basic6.0来进行电路的计算机辅助设计，应用更加友好的用户界面，通过结点电压法的矩阵形式完成线性电路频域的分析与计算，并给出一算例及计算结果。