Adenine synthesis in interstellar space: mechanisms of prebiotic pyrimidine-ring formation of monocyclic HCN-pentamers

The question whether the nucleobases can be synthesized in interstellar space is of fundamental significance in considerations of the origin of life. Adenine is formally the HCN pentamer, and experiments have demonstrated that adenine is formed under certain conditions by HCN pentamerization in gas, liquid, and condensed phases. Most mechanistic proposals invoke the intermediacy of the HCN tetramer AICN (4), and it is thought that adenine synthesis is completed by addition of the 5(th) HCN to 4 to form amidine 5 and subsequent pyrimidine cyclization. In this context, we have been studying the mechanism for prebiotic pyrimidine-ring formation of monocyclic HCN-pentamers with ab initio electronic structure theory. The calculations model gas phase chemistry, and the results primarily inform discussions of adenine synthesis in interstellar space. Purine formation requires tautomerization of 5 to the conjugated amidine 6 (via hydrogen-tunneling, thermally with H(+) -catalysis, or by photolysis) or to keteneimine 7 (by photolysis). It was found that 5-(N'-formamidinyl)-1H-imidazole-4-carbonitrile (6) can serve as a substrate for proton-catalyzed purine formation under photolytic conditions and N-(4-(iminomethylene)-1H-imidazol-5(4H)-ylidene)formamidine (7) can serve as a substrate for uncatalyzed purine formation under photolytic conditions. The absence of any sizeable activation barrier for the cyclization of 7 to the (Z)-imino form of 9H-adenine (Z)-2 is quite remarkable, and it is this feature that allows for the formation of the purine skeleton from 7 without any further activation.     

利用GPS进行精密轨道确定

全球定位系统(GPS)完全布满卫星后,将成为近地卫星的精密轨道确定(POD)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。来自至少四个GPS卫星的伪距测量值,通过载波相位测量值的平滑,可测定天线相位中心的地心位置和用户卫星的时钟修正值,因而后一技术不需要用户卫星受力的动力学模型。运动学法对测量模型的影响非常敏感,如GPS星历误差(给定的或求解的)、信号的多径、接收机噪声等等;然而,动力学方法又受参数误差和/或力模型不完善的影响。为此研究出一种利用过程噪声补偿对运动学和动力学算法进行加权的混合方案。本课题的中心点是利用仿真辅以协方差分析,研究这几种定轨方法。建立了几种动力学和测量误差模型,这些模型造成的轨道不确定性与处理实际GPS数据而估计的星历误差大致相当。协方差分析经调整能反映这些误差,能看出各种滤波技术的特性。     

埃里克森公司计划改进JAS39的航空电子设备

在第11架JAS39“鹰狮”战斗机正在交付的时候,埃里克森公司已计划好第一轮的修改与更新,这些修改可能是针对第二批生产的新飞机提出的.在这些改进中,该公司正在考虑采用彩色显示器、头盔瞄准具、射频(RF)干扰机和固态数字式视频记录器.担负JAS39主要制造工作的有萨伯、伏尔伏、FF及位于肯斯塔和蒙德尔两地的埃里克森等公司.在首批30架正在生产的     

用于助推段目标自动捕获跟踪和助推结束定位的小型地基红外传感等

本文介绍一种叫作ＧＢＡＴＳ的小型，地基红外角度跟踪系统。ＧＢＡＴＳ设计来被动地对感兴趣的助推目标进行二维角度跟踪。     

用声表面波传感器进行压力和温度测量

本文介绍两种不同的声表面波传感器,即弱压压力传感器和声表面波温度传感器。压力传感器制作在一薄的石英晶片上,使两束表面弹性波在同一方向但在两个不同的侧向位置上传播。加在下表面上的压力的变化引起强烈的弯曲,从而改变两波的波速。采用差动检测法能够测出波速的变化(或者相应振荡器的频率偏移),同时也能够人大地消除因温度波动所引起的假速度(或频率)的变化。通过计算应变分布和相应频率漂移来得出石英薄片上声表面波延迟线具有最大压力灵敏度,而温度影响最小的两位置。把Y切割的理论结果与在105MHz取得的测帚结果进行了比较, 用具有LST和JCL晶向的石英片制作的温度传感器已在灵敏度(28ppm/K)、线性、响应时间(0.1S)和分辨力(50μK)方面进行了测试。将用表面波温度传感器取得的温度测量结果与用体波温度传感器(LC切)所测得的结果进行比较,提出一种采用声表面波温度探头的新型石英温度计。     

The Aouda.X space suit simulator and its applications to astrobiology

We have developed the space suit simulator Aouda.X, which is capable of reproducing the physical and sensory limitations a flight-worthy suit would have on Mars. Based upon a Hard-Upper-Torso design, it has an advanced human-machine interface and a sensory network connected to an On-Board Data Handling system to increase the situational awareness in the field. Although the suit simulator is not pressurized, the physical forces that lead to a reduced working envelope and physical performance are reproduced with a calibrated exoskeleton. This allows us to simulate various pressure regimes from 0.3-1 bar. Aouda.X has been tested in several laboratory and field settings, including sterile sampling at 2800 m altitude inside a glacial ice cave and a cryochamber at -110°C, and subsurface tests in connection with geophysical instrumentation relevant to astrobiology, including ground-penetrating radar, geoacoustics, and drilling. The communication subsystem allows for a direct interaction with remote science teams via telemetry from a mission control center. Aouda.X as such is a versatile experimental platform for studying Mars exploration activities in a high-fidelity Mars analog environment with a focus on astrobiology and operations research that has been optimized to reduce the amount of biological cross contamination. We report on the performance envelope of the Aouda.X system and its operational limitations.     

美国航宇局地面跟踪网的联合及发展计划

1979年秋美国航宇局(NASA)制定了统一跟踪网计划,准备将NASA两个地面跟踪网合并成一个统一网。合并两个跟踪网的建议是NASA总网规划组提出的并于同年10月提交给NASA最高管理当局。到1986年,合并后的跟踪网将使用哥达德地面航天跟踪和数据网以及喷气推进试验室滐空网的现有设备。通过组合和改进,这个统一跟踪网将有可能为当时的星际和高地球轨道任务提供支援。推动两网合并的动力来自技术和经济两方面。合并后的跟踪网应该有较高的灵敏度,应能为1936和1989年旅行者2号(Voyager2)飞行器与天王星和海王星相遇提供支援;还应能以大于现有滐空网10倍的数据率为高地球轨道和靠近行星的飞行器提供支援。合并后跟踪网的维护和操作费用应大大低于八十年代末期两个单独网所花费用的总和。文中回顾了决定合并NASA地面跟踪和数据网的起因,简要介绍了从1975年决定合并到八十年代中期NASA两个地面跟踪网计划的进展情况。本文是1981年6月提交给AIAA/NASA空间跟踪和数据系统会议报告的修改稿。