Observation of conformation-specific pathways in the photodissociation of 1-iodopropane ions.

Many molecules can rotate freely around single bonds and thereby interconvert between different conformations, such as gauche and anti 1,2-disubstituted ethane, a classic example of conformational isomerism. Even though rotation occurs rapidly at room temperature, the product selectivity seen in some reactions has been explained by conformation-dependent reaction mechanisms: if reactant molecules differing only in their conformation are located at different positions on the reaction path, they may undergo different reactions. But a direct verification of this effect is difficult, because the energy barrier separating conformational isomers is so low that under ambient conditions reactants with more than one conformation will be present. But by using temperatures low enough to suppress the interconversion between different conformations, gauche-1-iodopropane ions and anti-1-iodopropane ions have been selectively generated. Here we show that the kinetic energy released during the photodissociation of 1-iodopropane ions depends strongly on the conformation of the ions. Thermodynamic arguments and ab initio calculations indicate that this difference in kinetic energy release results from differences in the reaction mechanism, with gauche-1-iodopropane ions forming 2-propyl ions and anti-1-iodopropane ions forming protonated cyclopropane ions. These findings suggest that the well-known concept of conformation selection forms the basis of a simple scheme for reaction control, thus providing in some cases an attractive alternative for more involved schemes that utilize the phase and pulse shape of laser beams to control chemical reactions.     

在线WOM内容和效果的关系:产品知识和相关的影响

以证明在线口传内容对口传效果的影响及收信者的特性的作用为目的。通过已有的研究,把口传内容划分为商品信息和个人经验,把口传效果划分为口传受用和口传行为。以大学生为对象,对MP3购买活动和相关在线口传活动进行了268个问卷调查,并用SPSS 10.0统计法进行了分析。研究结果表明:第一,口传信息的受用度使商品资讯更高,口传行为使个人体验资讯更为受用。第二,商品资讯和个人体验对口传内容的效果(口传受用,口传行为)决定于收信者的产品知识,即对在线的口传内容和口传信息受用的关系有调节作用,而且,对口传行为的影响也有调节效果。最后,关联度变数如先前所设的口传内容和口传效果的关系,对它们的关系有调节作用。     

Applying Petri-Net-Based Reduction Approach for Verifying the Correctness of Workflow Models

0 IntroductionTobadaseyd’s o nintfhoer mflaotiwonof s ywsotrekmss t hhraovueg hbe tehne doervgealnoipzead-tion rather than based ontasks .Duetothistrend,work-flowand business process technology has been applied tovarious applications such as ERP, groupwares , E-mar-ketplaces , E-business etc . When business processes areapplied to these applications ,business processes are de-fined by process designers and business process instancesare executed by workflowengines or workflow manage-ment sys…     

从科学史观点试谈奇门遁甲（续完）：1997—10—03在西北大学的讲演

就最早出现在东晋葛洪的《抱朴子内篇》的遁甲和８世纪最早的有关奇门遁甲的文献记载进行讨论。述及北宋司天台采用奇门遁甲,下至有明一代奇门遁甲成为官方采用三式中的一种秘传术数的过程。示范奇门遁甲的布局方法,并举例解释它在气象学、军事和人事各方面的应用。认为传统中国从来没有科学这个名词,欧洲在文艺复兴时代以前也没有这个名词,可是认识和克服大自然这个理念应该早已存在,这就是所谓科学的前身。又认为奇门遁甲是传统中国理念中的科学,后来在欧洲科学与巫术、哲学、宗教等分手,可是奇门遁甲没有脱离它和人事、巫术等的关系。     

Effect of 723-1723-1723-1on ethanol withdrawal in mice

Summary ⁹ (10 mg/kg, i.p.) administered to mice immediately after withdrawal from a 3-day exposure to ethanol vapor was found to intensify withdrawal reactions. No effect was seen when ⁹ was administered chronically during the exposure to ethanol.     

线性搜索方法的改进

线性搜索是最优化计算中最普遍应用的方法，文中对Ｆｌｅｔｃｈｅｒ线性搜索方法作了改进，它具有减少梯度值计算次数的特点，并用数值结果表明了方法的有效性。     

Analysis of carbon isotopes in airborne carbonate and implications for aeolian sources

Methods were developed to determine the mass ratios of carbon isotopes in trace amounts of aerosol carbonate. A Finnigan MAT 252 mass spectrometer fitted with an on-line Kiel device was to determine the ^13C/^12C ratio in CO2 produced from the carbonate. A study using these methods was conducted to characterize the carbonate carbon isotopes in aerosol samples collected in Xi‘an on dusty and normal days during March and April 2002. Results of the study demonstrate that insights into the origin of the dust can be deduced from its isotopic composition. That is, the δ^13C ofcarbonate for dust storm samples ranged from -1.4‰ to -4.2‰, and this is consistent with sandy materials in dust source regions upwind. In contrast, for non-dusty days δ^13C ranged from -7.5% to -9.3‰, which is more similar to fine particles emitted from local surface soils. Comparisons of dust storm aerosols with surface soils from source regions and with aerosol samples collected downwind indicate that the δ^13C values did not change appreciably during longrange transport. Therefore, carbon isotopes have the potential for distinguishing among source materials, and this approach provides a powerful new tool for identifying dust provenance.     

THE EFFECT OF ALUM AND METALS ON PAPER AGING

Books and archives experience aging which is affected by a variety of factors, such as microorganism, humidity, light and components of paper [1]. Thus, the studies concerning impacts of those factors on paper aging are required. In this paper, an accelerated paper aging was carried out to investigate the effects of acid and metals such as alum, copper ( Ⅱ ) sulfate, copper ( Ⅱ ) chloride, and iron (Ⅲ) chloride on paper aging. It was found that both acid and metals had impacts on paper aging. In particular, paper aging was far more accelerated in case that acid and metals were present in paper at the same time.     

Minimum information about a microarray experiment (MIAME)-toward standards for microarray data.

Microarray analysis has become a widely used tool for the generation of gene expression data on a genomic scale. Although many significant results have been derived from microarray studies, one limitation has been the lack of standards for presenting and exchanging such data. Here we present a proposal, the Minimum Information About a Microarray Experiment (MIAME), that describes the minimum information required to ensure that microarray data can be easily interpreted and that results derived from its analysis can be independently verified. The ultimate goal of this work is to establish a standard for recording and reporting microarray-based gene expression data, which will in turn facilitate the establishment of databases and public repositories and enable the development of data analysis tools. With respect to MIAME, we concentrate on defining the content and structure of the necessary information rather than the technical format for capturing it.