用阳离子置换法制备汞系高温超导薄膜

介绍了最近发明的一种制备汞系高温超导薄膜的新方法—阳离子置换法．采用Ｔ１ 系外延超导薄膜作为先驱薄膜,将Ｔ１ 系超导薄膜在Ｈｇ 气氛下进行热处理,用Ｈｇ 置换先驱薄膜中的Ｔ１,进而生成Ｈｇ 系外延超导薄膜．用此方法,成功地在ＬａＡｌＯ３ （００１）衬底上制做出了高质量的ＨｇＢａ２ＣａＣｕ２Ｏｘ 超导薄膜．Ｘ－光衍射θ－２θ扫描和极图测试表明,薄膜具有很纯的超导相和很好的外延结构．超导临界温度可达１２２Ｋ．在７７Ｋ温度下,临界电流密度达到３．４×１０６ Ａ／ｃｍ ２,在１１０Ｋ 温度下,临界电流密度仍可保持在０．７×１０６Ａ／ｃｍ ２ ．     

The C. elegans genome sequencing project: a beginning.

The long-term goal of this project is the elucidation of the complete sequence of the Caenorhabditis elegans genome. During the first year methods have been developed and a strategy implemented that is amenable to large-scale sequencing. The three cosmids sequenced in this initial phase are surprisingly rich in genes, many of which have mammalian homologues.     

句法视角下城市道路交通的预测研究——以广州市人民路高架桥拆除问题为例

基于空间句法理论中较前沿的NAchoice算法,着眼于我国第一座城市高架桥广州市人民路高架桥拆除问题进行案例分析,为空间句法在中国城市交通预测中的应用提供实证,探寻一种较好拟合实际交通流的预测模型,为路网优化提供参考依据. 论证分析从广州人民南路段交通堵塞原因、拆桥与否对桥下路段车流的影响、人民路段周边主干道交通疏导能力评估等3个方面展开,研究发现：（1）车流量偏大是人民南路段交通堵塞问题频发的原因之一;（2）高架桥的拆除会小幅增加桥底路段车流,但不一定会造成车流量的叠加式剧增;（3）人民路段及其周围主干道分流能力受到质疑,建议等到有较强疏导能力路段建成后,再拆除人民路高架桥;（4）空间句法NAchoice模型与广州市交通流数据具有较好拟合程度,运用该模型进行城市道路交通预测具有可行性.     

Structural basis for synthesis of inflammatory mediators by human leukotriene C4 synthase

Cysteinyl leukotrienes are key mediators in inflammation and have an important role in acute and chronic inflammatory diseases of the cardiovascular and respiratory systems, in particular bronchial asthma. In the biosynthesis of cysteinyl leukotrienes, conversion of arachidonic acid forms the unstable epoxide leukotriene A4 (LTA4). This intermediate is conjugated with glutathione (GSH) to produce leukotriene C4 (LTC4) in a reaction catalysed by LTC4 synthase: this reaction is the key step in cysteinyl leukotriene formation. Here we present the crystal structure of the human LTC4 synthase in its apo and GSH-complexed forms to 2.00 and 2.15 A resolution, respectively. The structure reveals a homotrimer, where each monomer is composed of four transmembrane segments. The structure of the enzyme in complex with substrate reveals that the active site enforces a horseshoe-shaped conformation on GSH, and effectively positions the thiol group for activation by a nearby arginine at the membrane-enzyme interface. In addition, the structure provides a model for how the omega-end of the lipophilic co-substrate is pinned at one end of a hydrophobic cleft, providing a molecular 'ruler' to align the reactive epoxide at the thiol of glutathione. This provides new structural insights into the mechanism of LTC4 formation, and also suggests that the observed binding and activation of GSH might be common for a family of homologous proteins important for inflammatory and detoxification responses.     

高校图书馆知识管理浅谈

知识管理是知识经济时代的一种全新的管理思想。阐述了高校图书馆在对自身实施知识管理时应注意的环节、存在的问题以及所要避免陷入的几个误区,并对未来的知识管理进行了展望。