舰载雷达的发展趋势

目前进行的两大多国海军防空计划——北约反空袭系统(NAAWS)和防空导弹系统系列(FAMS)的目的是为了满足对未来舰载雷达的迫切需求.     

A DEVELOPMENT OF COMPUTER SUPPORT SYSTEM FOR WING DESIGN

Since it takes a long time to design an aircraft, the succession to or the acquirement of knowledges and technologies is a key to provide to aircraft design high quality and productivity. This paper describes a computer support system for wing design using a new tool based on an object-oriented approach. The system is programmed in a module of objects which represent design tasks or design knowledges. The modulated program gives advantages to maintain and extend the system easily. The system provides to users a flexible support with excellent user interface which consists of mouse, menu-driven system, and window system.     

晶体滤波器的目前趋势

本文评述了晶体滤波器最近的和预定的研制情况。主要发展方面是:甚高频(VHF)和超高频(UHF)滤波器、数据传输滤波器、线性度、封装以及降低成本。     

超导腔稳频红宝石激射器振荡器

本文介绍一种新型全致冷频率源——超导腔稳频激射器振荡器(SCSMD)的稳定度分析、性能及设计。文中还将介绍该振荡器的各个部件的实验研究结果。它将充分证明采用这一技术方案有可能使频率稳定度达到优于△f/f=10~(-17)的水平。以前设计超导腔稳频振荡器,采用低温下的铌腔与室温下的微波电子器件相结合的方案。但据报道这种方案所能达到的最佳频率稳定度仅为△f/f=3×10~(-16)。这主要是因电子系统与腔体互连的部分不稳定影响了长期性能。但全致冷的方案却不存在这一问题,因为热膨胀系数被冻结(freezing-out)以及完全没有热梯度。红宝石激射器在目前所有微波放大器中噪声温度最低(1.5k),看来它是用于全致冷振荡器的较理想的器件。它的有效输出功率(～10~(-7)W/cm~3在4.2k)足以用来进行时间长于一秒的测量。另外,它具有相当高的增益(Q_m=-100)使得仅需振荡器与稳定腔之间保持很弱的耦合即可。此外,它本身的功耗也很小,即使在低至1k时也能与腔体工作在同一温度环境条件下。但激射器的工作和调谐却需外加磁场,这就产生了一个很重要的技术问题,即需要对超导腔加以磁屏蔽,同时磁场的变化还将产生频率的牵引。为此,文中介绍了采用多腔方案来解决这一问题。该方案将红宝石部件与超导腔隔开一段距离。我们还将谈到具有较大频率牵引效应的低Q腔稳定的激射器振荡器的频率稳定度。最后,本文将介绍有关研制结构最坚固的超导腔的结果。兰宝石的热膨胀系数仅为铌的百分之一,其微波损耗在1.5k时,目前已达的最低值为7×10~(-10)。在兰宝石上镀超导体的谐振腔可达(按设计要求值)Q=10~8。     

结构可靠性设计中的判定理论

在宇航结构可靠性分析方法的基础上,本文引入了试验方案选择概念,并根据统计判定理论推出了一套判定法。应用这个方法对给定结构部件可决定最佳成本效应设计的因子和试验方案。最后以土星V和航天机的几个结构组件为例,算出了结果。由此结果可以看出:设计费用与重量对最优判据有显著影响。     

Effect of temperature on the adsorption of adenine

Equilibrium adsorption isotherms for the purine base adenine on the surface of graphite crystals have been obtained at 30, 40, 50, and 60 degrees C by frontal analysis using water as a mobile phase. These data were fitted to the Langmuir isotherm model and interpreted in terms of the well-characterized adsorbate monolayer structure. A van't Hoff plot was used to estimate the adsorption enthalpy, -delta H degree which we determined to be 20 kJ mol-1. The susceptibility of nucleic acid bases to aqueous-phase hydrolysis may have been a limiting feature for their inclusion in the primordial genetic architecture; our results suggest that the effects of temperature and the presence of inorganic solids must also be included when assessing the prebiotic availability of adenine.     

跨声速流自发凝结水滴的测量

应用基于多波长消光法原理发展的光学探针,测量了跨声速风洞中不同马赫数湿空气流自发凝结形成的水滴尺雨及浓度,并给出了实验结果。     

无剪切湍流混合层中被动标量扩散的实验研究

研究被动标量在无剪切湍流混合层中的扩散。实验在风洞中进行,用大小网格尺度比为2∶1的网格实现无剪切湍流混合层,用烟粒子作为测量用的示踪粒子同时作为被动标量形成浓度场,用PIV测量得到速度场同时用Mie散射测量得到高施密特数的浓度场,由此可以计算得到速度和浓度相关,并用实验数据直接检验大涡模拟中亚格子应力Smagorinsky模式和亚格子质量通量梯度模式。     

Comparison of the roles of nucleotide synthesis, polymerization, and recombination in the origin of autocatalytic sets of RNAs

Ribozymes that act as polymerases and nucleotide synthases are known experimentally, even though no fully self-replicating system has yet been found. If the RNA World hypothesis is true, ribozymes must have arisen initially from within a random abiotic polymerization system. To investigate the origin of the RNA world, we studied a mathematical model of a chemical reaction system describing RNA polymerization. It is supposed that, in absence of ribozymes, polymerization occurs at a small spontaneous rate, and that in the presence of polymerase ribozymes, polymerization occurs at a faster rate that is proportional to the ribozyme concentration. Chains must be longer than a minimum threshold length in order to have the possibility of acting as ribozymes. The reaction system has two stable states that we term dead and living. The dead state is controlled by the small spontaneous rate and has negligible concentration of ribozymes. The living state has high concentration of ribozymes, and the reaction rates are determined by the ribozymes; thus, the system is autocatalytic. Concentration fluctuations in a finite volume can cause a transition to occur from the dead to the living state, that is, an origin of life occurs within this model. We also consider ribozymes that catalyze nucleotide synthesis. We show that living and dead states arise in the presence of synthase ribozymes in the same way as for polymerases. It has been proposed that recombination reactions are a way of generating long RNA chains in the early stages of life. We show that if the possibility of random reversible recombination reactions is added to our model, this does not lead to an increase in long polymer concentration. Thus, if recombination is fully reversible, there is no autocatalytic state controlled by recombination. Nevertheless, recombination can play an important role in ribozyme synthesis if there is an additional process that keeps the recombination reactions out of equilibrium. We modeled a case studied experimentally in which building block strands of moderate length associate due to RNA secondary structure formation. A recombination reaction then occurs between these strands to form a longer sequence that catalyzes its own formation via the recombination reaction. This system has an autocatalytic state, and it is possible for it to arise within our random polymerization system. If complexes formed by associations of shorter strands can act as catalysts without the requirement that the strands be covalently linked, this would alleviate the need for synthesis of very long strands; hence, it makes the emergence of an autocatalytic system from an abiotic random polymerization system much more likely.