波音737飞机电源系统故障分析

本文以波音737飞机为例,结合相关技术资料和排故实例,分析总结飞机电源系统及常见故障件的工作状态,并提出了处理措施。一、故障概述B-2612飞机为国航重庆维修基地737-700型飞机,该机自2010年5月29日     

中兴通讯模式对国有企业改革的启示

论文简要介绍了中兴通讯股份有限公司的发展历程，分析了“中兴模式”的特点和优势，并据此提出了几条对国有企业改革的有益启示。     

用纤维复合板增强砼梁

桥梁钢筋砼梁经长期使用，由于钢筋的锈蚀和砼的剥落，造成强度降低，乐能满足日益发展的交通的要求，必须更新或增强，增强比更新更合算。增强的方法有梁的外部后张拉及在受拉边增设环氧树脂粘结钢板，都存在着实际困难，特别是粘结法有腐蚀的危险。     

利用GPS进行精密轨道确定

全球定位系统完全布满卫星后，将成为近的地卫星的精密轨道确定强有力的工具。该系统具有连续跟踪覆盖能力，不仅可实现传统的动力学精密轨道确定方法，而且还可进行运动学轨道确定。     

“赫尔墨斯”推进系统设计

“赫尔墨斯”航天飞机是一种载人的、可重复使用的飞行器.它要用新的“阿里安”5发射到低地球圆形轨道和极轨道.当“赫尔墨斯”脱离“阿里安”5后,即机动飞行到其所要求的工作轨道上.讨论了两种入轨的推进概念:组合式可重复使用系统和分离式一次性使用系统.重点研究组合式系统.但也分析了一次性使用系统对本研究结果的影响.讨论了推进系统的基本流程图的设计步骤,并提出几种导致选择基本推进系统流程图的比较方案.示出了改变外形的最新“赫尔墨斯”对流程图的影响.     

基于FPGA的动态可重配置方法研究

对FPGA应用的研究发现,随着FPGA门电路总数的增加,其内部布线的数目和复杂度随之增加,但是随着系统规模的增大,单芯片资源的利用率反而下降。在这种背景下,人们开始把注意力转移到FPGA逻辑资源的时分复用上来,对FPGA的逻辑资源进行动态重配置,以提高FPGA芯片的利用率。在对重配置技术的基本概念以及特征分类进行概要介绍的基础上,较为详细地介绍了四种基于FPGA的动态重配置方法,并针对重配置关键技术和发展趋势进行了探讨。     

The PROCESS experiment: exposure of amino acids in the EXPOSE-E experiment on the international space station and in laboratory simulations

To understand the chemical behavior of organic molecules in the space environment, amino acids and a dipeptide in pure form and embedded in meteorite powder were exposed in the PROCESS experiment in the EXPOSE-E facility mounted on the European Technology Exposure Facility (EuTEF) platform on board the International Space Station (ISS). After exposure to space conditions for 18 months, the samples were returned to Earth and analyzed in the laboratory for reactions caused by solar UV and cosmic radiation. Chemical degradation and possible racemization and oligomerization, the main reactions caused by photochemistry in the vacuum ultraviolet domain (VUV, wavelength range 100-200?nm for photon energy from 6.2 to 12.4?eV) were examined in particular. The molecules were extracted and derivatized by silylation and analyzed by gas chromatograph coupled to a mass spectrometer (GC-MS) to quantify the rate of the degradation of the compounds. Laboratory exposure in several wavelength ranges from UV to VUV was carried out in parallel in the Cologne Deutsches Zentrum für Luft- und Raumfahrt (DLR) Center and Centre de biophysique moléculaire (CBM) laboratories. The results show that resistance to irradiation is a function of the chemical nature of the exposed molecules and the wavelengths of the UV light. The most altered compounds were the dipeptide, aspartic acid, and aminobutyric acid. The most resistant were alanine, valine, glycine, and aminoisobutyric acid. Our results also demonstrate the protective effect of meteorite powder, which reemphasizes the importance of exogenic contribution to the inventory of prebiotic organics on early Earth.     

The PROCESS experiment: amino and carboxylic acids under Mars-like surface UV radiation conditions in low-earth orbit

The search for organic molecules at the surface of Mars is a top priority of the next Mars exploration space missions: Mars Science Laboratory (NASA) and ExoMars (ESA). The detection of organic matter could provide information about the presence of a prebiotic chemistry or even biological activity on this planet. Therefore, a key step in interpretation of future data collected by these missions is to understand the preservation of organic matter in the martian environment. Several laboratory experiments have been devoted to quantifying and qualifying the evolution of organic molecules under simulated environmental conditions of Mars. However, these laboratory simulations are limited, and one major constraint is the reproduction of the UV spectrum that reaches the surface of Mars. As part of the PROCESS experiment of the European EXPOSE-E mission on board the International Space Station, a study was performed on the photodegradation of organics under filtered extraterrestrial solar electromagnetic radiation that mimics Mars-like surface UV radiation conditions. Glycine, serine, phthalic acid, phthalic acid in the presence of a mineral phase, and mellitic acid were exposed to these conditions for 1.5 years, and their evolution was determined by Fourier transform infrared spectroscopy after their retrieval. The results were compared with data from laboratory experiments. A 1.5-year exposure to Mars-like surface UV radiation conditions in space resulted in complete degradation of the organic compounds. Half-lives between 50 and 150?h for martian surface conditions were calculated from both laboratory and low-Earth orbit experiments. The results highlight that none of those organics are stable under low-Earth orbit solar UV radiation conditions.     

Formation of replicating saponite from a gel in the presence of oxalate: implications for the formation of clay minerals in carbonaceous chondrites and the origin of life

The potential role of clay minerals in the abiotic origin of life has been the subject of ongoing debate for the past several decades. At issue are the clay minerals found in a class of meteorites known as carbonaceous chondrites. These clay minerals are the product of aqueous alteration of anhydrous mineral phases, such as olivine and orthopyroxene, that are often present in the chondrules. Moreover, there is a strong correlation in the occurrence of clay minerals and the presence of polar organic molecules. It has been shown in laboratory experiments at low temperature and ambient pressure that polar organic molecules, such as the oxalate found in meteorites, can catalyze the crystallization of clay minerals. In this study, we show that oxalate is a robust catalyst in the crystallization of saponite, an Al- and Mg-rich, trioctahedral 2:1 layer silicate, from a silicate gel at 60°C and ambient pressure. High-resolution transmission electron microscopy analysis of the saponite treated with octadecylammonium (n(C)=18) cations revealed the presence of 2:1 layer structures that have variable interlayer charge. The crystallization of these differently charged 2:1 layer silicates most likely occurred independently. The fact that 2:1 layer silicates with variable charge formed in the same gel has implications for our understanding of the origin of life, as these 2:1 clay minerals most likely replicate by a mechanism of template-catalyzed polymerization and transmit the charge distribution from layer to layer. If polar organic molecules like oxalate can catalyze the formation of clay-mineral crystals, which in turn promote clay microenvironments and provide abundant adsorption sites for other organic molecules present in solution, the interaction among these adsorbed molecules could lead to the polymerization of more complex organic molecules like RNA from nucleotides on early Earth.