Rational design of glycerol dehydratase： Swapping the genes encoding the subunits of glycerol dehydratase to improve enzymatic properties

1,3-propanediol (1,3-PD) is an important material for chemical industry,and there has been always much interest in the production of 1,3-PD using all possible routes. The genes encoding glyc-erol dehydratase (GDHt) from Citrobacter freundii,Klebsiella pneumoniae and metagenome were cloned and expressed in E. coli. All glycerol dehy-dratases but the one from metagenome could be detected to show enzyme activities. In order to im-prove the enzymatic properties of GDHts,the genes encoding α and β-γ subunits were cloned,and the enzyme characteristics were evolved by rational de-sign based on their 3D structures which were con-structed by homology modeling. Six heteroenzymes were obtained by swapping the α subunit genes of these three different-source-derived GDHts. The pH,thermal stability and Vmax of some heteroenzymes were dramatically improved by 2―5 times compared with the wild one (GDHtKP). The GDHt cloned from metagenome,originally proved to be with no enzyme activity,was converted into active enzyme by swap-ping its subunits with other different GDHts. In addi-tion,the effect of subtle 3D structural changes on the properties of the enzyme was also observed.     

A Fault Detection Mechanism in Erasure-Code Byzantine Fault-Tolerance Quorum

Fault-tolerance is increasingly significant for large-scale storage systems in which Byzantine failure of storage nodes may happen. Traditional Byzantine Quorum systems that tolerate Byzantine failures by using replication have two main limitations： low space-efficiency and static quorum variables. We propose an Erasure-code Byzantine Fault-tolerance Quorum that can provide high reliability with far lower storage overhead than replication by adopting erasure code as redundancy scheme. Through read/write operations of clients and diagnose operation of supervisor, our Quorum system can detect Byzantine nodes, and dynamically adjust system size and fault threshold. Simulation results show that our method improves performance for the Quorum with relatively small quorums.     

Password-Based Group Key Agreement Protocol for Client-Server Application

0 IntroductionWith the rapid advances of computer networks , moreand more users are connecting together to exchangelarge amounts of information and share useful resources .However ,the security issue is still a major gating factor fortheir full adoption; mainly due to many malicious adversariesresidingin networked environments will eavesdrop,interceptand modify the transmittedinformation.The client-server model , over past years , has enjoyedsignificant and continually increasing popularity in…     

知识型企业知识状态系统演变的PSO机理及其优化模型分析

在知识工作者个人知识挖掘与整个知识型企业知识目标的协同的基础上,知识型企业与知识工作者之间挖掘知识集,不断进行协调从而推动知识状态系统演变的过程与鸟群或鱼群捕食过程的社会行为相似。利用PSO信息处理及优化机理,分析知识型企业知识状态系统演变的知识挖掘、传递以及决策特征,研究知识型企业知识状态系统的PSO模式,为进一步研究知识型企业知识状态系统演变特点的管理理论奠定基础。     

一类反向混合单调算子解的存在唯一性

运用锥与半序理论和非对称迭代方法,讨论半序Banach空间一类反向混合单调算子方程解的存在唯一性,并给出了迭代序列收敛于解的误差估计,作为其应用着重讨论了非反向混合单调算子方程解的存在唯一性,所得结果改进和推广了混合单调算子方程某些已知相应结果.     

外语院校人才培养模式改革刍议

所谓人才培养模式,是指高等学校根据人才培养的目标和质量标准,为大学生设计的知识、能力和素质结构以及怎样实现这种结构的方式。社会对高等学校人才培养模式的评估,主要是以其外显质量特征即高等学校毕业生的质量作为依据来评价毕业生群体能否很好地适应国家、社会和市场的需要,从而提高人才培养对社会的适应程度,提高人才培养与培养目标的符合程度。本文将以外语院校的教育教学模式为基准,对如何有效评估、建立一套与之相适应的人才培养模式尝试进行一番剖析与论证,以供探讨。     

金属电磁带隙波导特性分析

利用有限差分(FDTD)法分析了两维金属电磁带隙(EBG)波导带隙、耦合频率和模场分布,确定了EBG结构参数和对应的频率范围;利用HFSS建立了金属电磁带隙结构分析模型,设计了带有矩形波导转换的EBG波导.基于HFSS分析该波导,得到了这两种结构的传输谱线,对比说明矩形波导接口适用于窄带应用,而圆形波导接口适用于宽带应用.实验测试结果与数值分析符合较好.     

铌酸锂波长转换器中参量过程的研究

考虑到抽运损耗、走离和非线性等效应,对周期性极化LiNbO3光波导的级联二阶非线性效应波长转换中的参量过程进行了理论研究及数值分析,结果表明:抽运光、信号光和差频光之间会发生周期性能量振荡,最优波导长度随抽运光和信号光的注入功率的增大而减小;脉冲抽运时因走离效应的影响,能量振荡相对较弱.利用这种能量振荡特性,通过调整注入控制光功率大小在实现信号波长转换的同时可以实现脉冲整形.     

微细电解加工实验研究

针对微细电解加工中脉冲电源技术,电解液成分配比,以及加工间隙检测、控制等问题开展了微细电解加工技术的试验研究工作.首先讨论了微细电解加工的工艺特点和主要技术步骤,然后利用高频窄脉冲电源进行了加工实验.通过实验现象和实验结果的研究分析,提出了改进加工实验的方案,通过实验证明了本方案和技术路线的可行性,并获得了很好的微结构加工试验结果.通过微细电解加工实验的研究,为微细电解加工的生产应用提供了依据,显示出微细电解加工方法在金属零件微制造方面有着广阔的应用前景.     

PDMS表面形貌调控Au/PDMS褶皱图案的实验

采用超精密车削技术来调控Au/PDMS双层结构形成规则有序的锯齿状褶皱图案.以超精密车削技术在铝合金样品表面上加工的条纹图形,经复制模铸得到了聚二甲基硅氧烷(PDMS)基底表面上的反相结构.用离子溅射方法在PDMS基底表面沉积一层20-50 nm厚的Au膜,在冷却过程中Au/PDMS褶皱图案与基底形貌相互作用,从而成功地调控出规则有序、波长可控的锯齿状褶皱图案.经实验分析,PDMS基底形貌与褶皱图案之间的耦合作用是形成锯齿状褶皱的主要原因.