A new class of flavonoids bearing macrocyclic polyethers by stereoselective photochemical cycloaddition reaction

A new class of flavonoids bearing cyclic polyethers involving a phenyl ring was conveniently provided by the intramolecular photochemical dimerization of 2-chromonecarboxylic esters. Irradiation of 2-chromonecarboxylate with a polyether tethered at both ends promoted intramolecular [2 + 2] cyclobutane formation leading to 14- to 27-membered cyclic polyethers. The efficiency depended on the substituted position of the phenyl ring, with ortho- and meta-substituted derivatives giving cycloadducts in good chemical yields and quantum efficiencies, whereas the para-derivatives were inert toward photolysis. X-ray crystallographic analysis revealed that the stereochemistry of the macrocyclic cycloadducts exhibited C₂-symmetry.     

分布式CA下空间网络认证密钥安全度量方法

基于分布式CA的密钥管理策略解决了空间网络中不易实施集中式密钥管理的难题,但也给认证密钥的安全带来了新的威胁。该文在描述和分析空间网络中认证密钥的安全威胁的基础上,提出了一种度量认证密钥安全强度的方法。该方法可根据系统门限值、密钥更新周期等参数的设置情况,定量度量认证密钥的安全强度。通过分析系统门限值和密钥分量更新周期对安全强度的影响,给出了合理设置这两个网络安全参数的方法。     

后发优势与日本新型大学电类教育--日本文化核心思想透视

日本从“求知识于世界”、增强生活力的文化核心思想出发，充分利用再生产科学的后发优势规律，在电类高等教育方面以新型大学为中心同时形成多样化和大众化体系，由赶超型走向成熟型，创造了文化的奇迹。本文从日本文化的奇特阐述了日本以教育促科技，以科技促经济，其多样化的电类高等教育及利用后发优势的思路带给我们很多重要的启迪。     

Determination of submicrogram amounts of selenium(IV) by means of the catalytic reduction of 1,4,6,ii-tetraaza- naphthacene

In the presence of glyoxal and hypophosphorous acid 1,4,6II-tetraazanaph-thacene is reduced to I,6-dihydro-I,4,6,II-tetraazanaphthacene. The reaction is catalyzed by selenium(IV). By means of this catalytic reaction, submicrogram amounts of selenium(IV) can easily be determined. The method is simple and sensitive, and there are few interferences.     

Hexahalogenotin(IV) complexes in aqueous mixed hydrogen halide solutions in the glassy state

The configurations of hexahalogenotin(IV) complex ions in glassy aqueous mixed hydrogen halide solutions were determined by Mössbauer and Raman spectroscopies. Trans-(SnF₄Cl₂)^2-, (SnCl₅Br)^2- and (SnCl₅Br)^2- and trans-(SnF₄Br₂)^2- ions are the main tin complex ions in the aqueous Sn(IV)-HF-HCl, Sn(IV)-HCl-HBr and Sn(IV)-HF-HBr solutions in the glassy state, respectively.     

Reconstruction of glycan chains of glycoprotein : Branching mannopentaoside and mannohexaoside

Synthetic routes to the branching mannopentaoside 4 and mannohexaoside 5 are described employing properly protected mannobioside 13 as a key intermediate.     

Ouput characteristics of a passively mode-locked ruby laser

Characteristics of the pulse train from a ruby laser have been studied at different output intensity levels. At a low output level, broadening of the spectrum of the pulses is followed by a gradual increase of temporal width in the train. At a high output level, rapid deformation arises closer to the peak of the train, resulting in splitting of the pulses into several fragments. The width of a transform-limited pulse obtained at the beginning of the train was 28±2 picoseconds.     

Preparation of extremely fine particles by vacuum evaporation onto a running oil substrate

A large amount of extremely fine particles of Ag were prepared by vacuum evaporation onto a running oil substrate. The size distribution of Ag particles thus prepared was studied by electron microscopy. It was found that the mean diameter of the particles strongly depends upon the deposition rate, and kind and viscosity of the oil. Particles of mean dimater from 30 to 80 Å can be produced. The sticking coefficient on the oil surface for arriving atoms is, in general, smaller than that on a glass surface. The coefficient increases with increasing viscosity for the same kind of oil. Coalescence growth of particles is also detected by heating the oil containing the particles. The heat treatment also enables us to control the practicle size between 30 to 80 Å.     

VI＆P—21世纪日本电信发展的主要方向

本文讨论了日本未来社会的需求,介绍了在日本电信领域起主导作用的NTT公司推出的21世纪初期的电信业务发展目标——VI&P,并对与VI&P相关的技术和市场作了预测。     

中日美移动电子邮件业务比较分析

美国的移动邮件业务是实用主义的商务产品，介绍其双向寻呼移动邮件“黑莓（Blackberry）”。日本的移动邮件是娱乐先锋的载体，它以娱乐为先兼顾商用，介绍了写真邮件（Sha-mail）成功的原因。中国的移动邮件是“彩信”及“彩e ”分别介绍了这两种产品的区别。最后分析了移动邮件的产品定位。