Structure of the cell-puncturing device of bacteriophage T4

Bacteriophage T4 has a very efficient mechanism for infecting cells. The key component of this process is the baseplate, located at the end of the phage tail, which regulates the interaction of the tail fibres and the DNA ejection machine. A complex of gene product (gp) 5 (63K) and gp27 (44K), the central part of the baseplate, is required to penetrate the outer cell membrane of Escherichia coli and to disrupt the intermembrane peptidoglycan layer, promoting subsequent entry of phage DNA into the host. We present here a crystal structure of the (gp5-gp27)3 321K complex, determined to 2.9 A resolution and fitted into a cryo-electron microscopy map at 17 A resolution of the baseplate-tail tube assembly. The carboxy-terminal domain of gp5 is a triple-stranded beta-helix that forms an equilateral triangular prism, which acts as a membrane-puncturing needle. The middle lysozyme domain of gp5, situated on the periphery of the prism, serves to digest the peptidoglycan layer. The amino-terminal, antiparallel beta-barrel domain of gp5 is inserted into a cylinder formed by three gp27 monomers, which may serve as a channel for DNA ejection.     

含二苯基吡啶基膦配体的Fe－Rh配合物的合成、测试及催化性能

二苯基吡啶基膦是个优良的双齿配体。用它制得了铁配合物和含铁－铑的双核配合物。铁－铑双核配合物作为甲醇羰基化制乙酸和乙酸甲酯的催化剂，转化率达１００％，选择性为９９％。对铁配合物和铁－铑双核配合物进行了红外、核磁和穆斯堡尔谱测定。     

Genomic revelations of a mutualism: the pea aphid and its obligate bacterial symbiont

The symbiosis of the pea aphid Acyrthosphion pisum with the bacterium Buchnera aphidicola APS represents the best-studied insect obligate symbiosis. Here we present a refined picture of this symbiosis by linking pre-genomic observations to new genomic data that includes the complete genomes of the eukaryotic and prokaryotic symbiotic partners. In doing so, we address four issues central to understanding the patterns and processes operating at the A. pisum/Buchnera APS interface. These four issues include: (1) lateral gene transfer, (2) host immunity, (3) symbiotic metabolism, and (4) regulation.     

综合赋权法在灌区节水改造评价中的应用

为了对大型灌区节水改造项目进行科学合理的评价;应用综合集成赋权法对灌区评价指标权重进行计算,计算结果表明,与单纯的主观赋权法和客观赋权法相比,综合集成赋权法能够兼顾主客观影响因素,得出更为科学合理的权重计算结果;将该方法应用于陕西省关中大型灌区节水改造项目效益评价中,得出了令人满意的评价结果.说明在灌区评价指标权重确定时综合集成赋权法比单纯的主、客观赋权方法优越,得出的结果更合理,有更好的适用性.     

贵州草海地区赵家院子泥炭层剖面孢粉研究

本文系威宁草海赵家院子附近的一个泥炭层剖面孢粉研究。根据孢粉组合及~(14)C年龄,初步获悉该剖面为距今4.1万～1.6万年左右的沉积物。其古植被、古气候可分为七个阶段。     

异核双金属配合物的合成及催化性能的研究

本文合成了一种新型的金属有机双齿配体，并借助于金属配体中桥配体的桥联作用，合成了与Ｃｄ（Ⅱ）和Ｈｇ（Ⅱ）卤化物所形成的双金属配合物，对其结构进行了表征，研究了此类化合物对于ＣＯ２与环氧乙烷反应制备碳酸乙烯酯反应的催化性能，讨论了反应条件的影响．实验结果表明：（１）在相同的反应条件下，就配合物的催化活性而言：Ｆｅ（ＣＯ）３Ｌ２－（ＨｇＩ２）２＞ＨｇＩ２＞Ｆｅ（ＣＯ）３Ｌ２－（ＨｇＣｌ２）２＞Ｆｇ（ＣＯ）３Ｌ２＞Ｆｇ（ＣＯ）３Ｌ２－ＣｄＣｌ２（Ｌ＝ＰｈＭｅＰｐｙ）．（２）对于同一种化合物，反应条件的影响规律是：高温高压有利于催化反应．     

多旋翼对舰船甲板流场影响数值研究

为了研究多架直升机同时悬停时对舰船甲板流场特性的影响,采用Fluent软件对直升机多旋翼结构和舰船耦合流场进行数值模拟,分析了不同风向工况下的流场结构、螺旋度分布以及湍动能.结果表明:各旋翼周围的流场参数相互耦合、相互影响;侧风的加入使得流场结构更加紊乱,形成来流、多旋翼与上层建筑之间的混合流场;湍动能超限区域覆盖了整个甲板流场,这对于直升机的起降是非常不利的.     

生物电阻抗成像的数值模拟

生物电阻抗成像(EIT)是一种新型无创成像技术.本文在给出EIT的数学物理模型的基础上,利用 计算机的数值模拟得出自适应电流模式下的阻抗成像图.该结果说明这种电流模式和算法的设计能够较清晰的 对目标定位成像.