化学领域重要研究方向发展态势分析：酶催化

19世纪，科学家更多地从原子层次上认识和研究化学。20世纪科学家则更多地从分子层次上认识和研究化学。进入21世纪，化学会在哪些方面取得重大突破？会遇到哪些挑战和难题？什么是未来化学的新生长点？化学在整个科学体系中占有什么地位？这些部是对化学有全局性、战略性指导意义的问题。中国科学院院士徐光宪先生曾说过这样一段耐人寻味的话。     

Classification of Asymmetric Proximity Data

When clustering asymmetric proximity data, only the average amounts are often considered by assuming that the asymmetry is due to noise. But when the asymmetry is structural, as typically may happen for exchange flows, migration data or confusion data, this may strongly affect the search for the groups because the directions of the exchanges are ignored and not integrated in the clustering process. The clustering model proposed here relies on the decomposition of the asymmetric dissimilarity matrix into symmetric and skew-symmetric effects both decomposed in within and between cluster effects. The classification structures used here are generally based on two different partitions of the objects fitted to the symmetric and the skew-symmetric part of the data, respectively; the restricted case is also presented where the partition fits jointly both of them allowing for clusters of objects similar with respect to the average amounts and directions of the data. Parsimonious models are presented which allow for effective and simple graphical representations of the results.     

Asymmetric multidimensional scaling of two-mode three-way proximities

An asymmetric multidimensional scaling model and an associated nonmetric algorithm to analyze two-mode three-way proximities (object × object × source) are introduced. The model consists of a common object configuration and two kinds of weights, i.e., for both symmetry and asymmetry. In the common object configuration, each object is represented by a point and a circle (sphere, hypersphere) in a Euclidean space. The common object configuration represents pairwise proximity relationships between pairs of objects for the ‘group’ of all sources. Each source has its own symmetry weight and a set of asymmetry weights. Symmetry weights represent individual differences among sources of data in symmetric proximity relationships, and asymmetry weights represent individual differences among sources in asymmetric proximity relationships. The associated nonmetric algorithm, based on Kruskal’s (1964b) nonmetric multidimensional scaling algorithm, is an extension of the algorithm for the asymmetric multidimensional scaling of one mode two-way proximities developed earlier (Okada and Imaizumi 1987). As an illustrative example, we analyze intergenerational occupational mobility from 1955 to 1985 in Japan among eight occupational categories.     

Asymmetric Agglomerative Hierarchical Clustering Algorithms and Their Evaluations

This paper presents asymmetric agglomerative hierarchical clustering algorithms in an extensive view point. First, we develop a new updating formula for these algorithms, proposing a general framework to incorporate many algorithms. Next we propose measures to evaluate the fit of asymmetric clustering results to data. Then we demonstrate numerical examples with real data, using the new updating formula and the indices of fit. Discussing empirical findings, through the demonstrative examples, we show new insights into the asymmetric clustering.     

手性离子液:新型高效的手性有机小分子催化剂

由于生命物质的手性均一性,人们越来越认识到手性药物、农药、香料等的手征性对其生理作用的重要影响,科学地使用手性物质将提高人们的生活质量和改善生存环境。光学纯手性物质的获得,除了来自天然以外,人工合成是主要的途径。外消旋体拆分、底物诱导的不对称合成和催化不对称合成是获得光学纯手性物质的3种手段,其中催化不对称合成是最有效的方法,因为它很容易实现手性增殖。一个高效的催化剂可以产生成百上千乃至上百万个光学活性产物分子,同时最大限度地消除了无用异构体的生成。因此,催化不对称反应不但可以提供光学纯手性物质制备的关…     

非对称交配互作驱动B型烟粉虱的广泛入侵及对土著烟粉虱的取代

在21世纪经济全球化的新形势下，国际贸易、旅游业和交通业飞速发展，给外来生物入侵提供了大量机遇。近一二十年来生物入侵的迅速加剧，已造成大量的经济损失和生态灾难。毫无疑问，生物入侵在今后较长时期内将有增无减，对经济发展、生态安全和人体健康的危害将是巨大的、长远的，是人类生存必须有效应对的巨大挑战。虽然对生物入侵机制研究的理论和实践意义多有共识，     

液体-固体-溶液界面相转移和相分离——一种通用的纳米晶体合成策略

如何在纳米介观尺度范围内实现对材料结构与性能的调控,是纳米材料功能化及其应用的关键。单分散纳米晶指尺寸及形状均一、且在特定介质中具有良好分散能力的纳米材料。基于纳米粒子自身的尺寸效应、表面效应、量子效应,载流子在纳米粒子限制维度空间内的传输具有不同于其它维度材料的特性,展现出许多独特的光学、电学等物理化学性质。同时形状及尺寸严格均一的单分散纳米晶可以通过各种物理化学相互作用进行组装,在纳米器件、量子点激光器、非线性光学、磁介质、催化、功能材料及纳米生物技术等方面具有极为广阔的应用前景。然而由于不同化…     

三元硼碳氮化合物单壁纳米管的直接合成

本文研究以Fe-Mo/MgO作为催化剂,甲烷、硼烷、乙二胺为反应源气体,采用偏压辅助热丝化学气相沉积(HFCVD)方法直接合成了三元硼碳氮化合物单壁纳米管(BCN-SWNTs)。合成的BCN-SWNTs的结构类似于单壁碳纳米管,B和N原子取代了部分C原子的位置,从而3种原子形成了三元共价化合物纳米管,其中N含量在3—8atom%之间,B含量在2—4atom%之间。并通过透射电镜能量过滤元素成像等手段,证明B、C、N三种元素均匀地分布在单壁纳米管中。不同于碳纳米管由于复杂的手性问题导致的性质不可控性,硼碳氮纳米管的电子结构主要依赖于它的化学组分,与其几何手性无关,而且预测其能隙可以在石墨和氮化硼(0.0—5.5eV)之间调节。这些特有的性质为实现纳米管在电子和光电子等领域的应用开辟了新的途径,有望实现从性质不可控的碳纳米管电子器件到性质基本可控的硼碳氮纳米管电子器件的突破。     

论奎因对分析-综合的批判

奎因对逻辑实证主义的分析命题与综合命题的区分进行了最实质的批判,引发了一场激烈的争论并导致了逻辑实证主义转向逻辑实用主义.奎因的批判引发的哲学界的反思直到现在仍有深远的意义.     

一个超锕系新核素259Db的合成与鉴别

本文简要介绍了超重元素研究的意义及历史背景和国际现状,并叙述了中科院近物所首次合成和鉴别了一个超重新核素259Db.实验是利用兰州国家重离子实验室的SFC加速器提供的22Ne束轰击241Am靶产生了259Db.利用转轮收集系统和精心设计安排的探测器系统测量了产物的α衰变谱,根据母-子核的衰变遗传关系明确无误地鉴别了259Db,并测得它的α能量为9.47 MeV,半衰期为0.5 1秒.该项成果使我们跨入了超重核区的大门,为向"超重岛"迈进打下了良好基础.