Archaeal genome organization and stress responses: implications for the origin and evolution of cellular life

For DNA to be used as an informational molecule it must exist in the cell on the edge of stability because all genomic processes require local controlled melting. This presents mechanistic opportunities and problems for genomic DNA from hyperthermophilic organisms, whose unpackaged DNA could melt at optimal temperatures for growth. Hyperthermophiles are suggested to employ the novel positively supercoiling topoisomerase enzyme reverse gyrase (RG) to form positively supercoiled DNA that is intrinsically resistant to thermal denaturation. RG is presently the only archaeal gene that is uniquely found in hyperthermophiles and therefore is central to hypotheses suggesting a hypothermophilic origin of life. However, the suggestion that RG has evolved by the fusion of two pre-existing enzymes has led to hypotheses for a lower temperature for the origin of life. In addition to the action of topoisomerases, DNA packaging and the intracellular ionic environment can also manipulate DNA topology significantly. In the Euryarchaeota, nucleosomes containing minimal histones can adopt two alternate DNA topologies in a salt-dependent manner. From this we hypothesize that since internal salt concentrations are increased following an increase in temperature, the genomic effects of temperature fluctuations could also be accommodated by changes in nucleosome organization. In addition, stress-induced changes in the nucleoid proteins could also play a role in maintaining the genome in the optimal topological state in changing environments. The function of these systems could therefore be central to temperature adaptation and thus be implicated in origin of life scenarios involving hyperthermophiles.     

基于相似反对称结构的大角度机动姿态控制器设计

针对航天器在大角度机动模式下的姿态控制问题.提出两种以相似反对称非线性结构作为期望闭环系统结构的姿态控制器设计方法.第一种方法是一种直接构造方法,其关键思想是利用运动学子系统的零输入稳定性,使设计一步完成,而且得到的控制器具有简单的结构.在第二种方法中,姿态误差的积分变量被引入姿态运动模型中,然后进行面向系统结构的逆推设计,得到含有积分作用的姿态控制器,与常规逆推设计的姿态控制器相比,设计过程较简单.仿真结果表明了设计方法的有效性.     

GLOBAL测量机为航空航天部件生产提供速度和精度

测量机采集的尺寸数据在必要的情况下被用来调整加工设备参数.检验人员向机床操作人员展示某个被测特征的超差位置,机床操作人员可以根据得到的图形指示判断加工过程中何处会超出公差要求.     

函数型数据部分线性模型的估计的r阶收敛性

论文利用一种特殊的加权方法和简单的最小二重法，对稀疏和稠密的函数型数据的半参数部分线性模型提出了一种统一的估计方法，并探讨了估计的r阶收敛性。在提出的方法中，不需要区分对数据的观测是稀疏的还是稠密的。     

Selective laser melting of Al–8.5Fe–1.3V–1.7Si alloy: Investigation on the resultant microstructure and hardness

This article presents the microstructure and hardness variation of an Al–8.5Fe–1.3V–1.7Si(wt%, FVS0812) alloy after selective laser melting(SLM) modification. Three zones were distinguished across the melting pool of the SLM-processed FVS0812 alloy: the laser melted zone(LMZ), the melting pool border, and the heat affected zone(HAZ) in the previously deposited area around the melting pool. Inside the LMZ, either an extremely fine cellular-dendritic structure or a mixture zone of the a-Al matrix and nanoscale Al_(12)(Fe,V)_3Si particles appeared. With a decreased laser beam scanning speed, the cellular-dendritic structure zone within the LMZ shrank significantly while the mixture zone expanded. The a-Al and Al_(12)(Fe,V)_3Si mixture zone was also observed in the HAZ, but another phase, submicron h-Al_(13)Fe_4 particles with rectangular or hexagonal shapes,formed along the melting pool border. Microhardness tests indicated that the hardness of the SLM-processed FVS0812 samples far exceeded that of the as-cast FVS0812 alloy.     

Numerical study on flow fields and aerodynamics of tilt rotor aircraft in conversion mode based on embedded grid and actuator model

A method combining rotor actuator disk model and embedded grid technique is presented in this paper, aimed at predicting the flow fields and aerodynamic characteristics of tilt rotor aircraft in conversion mode more efficiently and effectively. In this method, rotor's influence is considered in terms of the momentum it impacts to the fluid around it; transformation matrixes among different coordinate systems are deduced to extend actuator method's utility to conversion mode flow fields' calculation. Meanwhile, an embedded grid system is designed, in which grids generated around fuselage and actuator disk are regarded as background grid and minor grid respectively, and a new method is presented for ‘donor searching' and ‘hole cutting' during grid assembling. Based on the above methods, flow fields of tilt rotor aircraft in conversion mode are simulated, with threedimensional Navier–Stokes equations discretized by a second-order upwind finite-volume scheme and an implicit lower–upper symmetric Gauss–Seidel(LU-SGS) time-stepping scheme. Numerical results demonstrate that the proposed CFD method is very effective in simulating the conversion mode flow fields of tilt rotor aircraft.     

Enhancing buckling capacity of a rectangular plate under uniaxial compression by utilizing an auxetic material

Auxetic materials have previously been shown to enhance various performances due to its unusual property of becoming fatter when uniaxially stretched and thinner when uniaxially com-pressed (i.e., the materials exhibit a negative Poisson’s ratio). The current study focuses on assessing the potential of an auxetic material to enhance the buckling capacity of a rectangular plate under uniaxial compression. The in-plane translational restraint along the unloaded edges that was often neglected in open literature is taken into consideration in our buckling model proposed in this study. The closed-form expressions for the critical buckling coefficient of the rectangle are provided and the predicted results agree well with those determined by the finite element method. Further-more, the results indicate that the buckling performance of a rectangular plate under uniaxial com-pression can be significantly improved by replacing the traditional material that has a positive Poisson’s ratio with an auxetic material when there is in-plane translation restraint along the unloaded edges.     

更 正

对《强度与环境》1999(4)“基于 Petri网的故障分析方法”中的错误进行更正 :1.割集的表示不正确 ,原文用〔〕应改为 { } ,如 :最小割集为〔1〕,〔2 ,5〕,〔2 ,6〕,〔3,5 ,6〕和〔4,6 ,7〕应改为 :最小割集为 { 1} ,{ 2 ,5 } ,{ 2 ,6 } ,{ 3,5 ,6 }和 { 4 ,6 ,7}。2 .图 5中右边方框上方 :最小割集应改为最小路集。本刊编辑部 2 0 0 0年 1月更正     

马克思关于人的全面发展理论的解读

人的全面发展是马克思主义的最高价值追求,当前,我们处在社会主义初级阶段,不具备实现人的全面发展的现实条件,从现实的角度来看,人的和谐发展是马克思关于人的全面发展理论的时代内涵.