A hydrothermal system associated with the Siljan impact structure, Sweden--implications for the search for fossil life on Mars

The Siljan ring structure (368 +/- 1.1 Ma) is the largest known impact structure in Europe. It isa 65-km-wide, eroded, complex impact structure, displaying several structural units, including a central uplifted region surrounded by a ring-shaped depression. Associated with the impact crater are traces of a post-impact hydrothermal system indicated by precipitated and altered hydrothermal mineral assemblages. Precipitated hydrothermal minerals include quartz veins and breccia fillings associated with granitic rocks at the outer margin of the central uplift, and calcite, fluorite, galena, and sphalerite veins associated with Paleozoic carbonate rocks located outside the central uplift. Two-phase water/gas and oil/gas inclusions in calcite and fluorite display homogenization temperatures between 75 degrees C and 137 degrees C. With an estimated erosional unloading of approximately 1 km, the formation temperatures were probably not more than 10-15 degrees C higher. Fluid inclusion ice-melting temperatures indicate a very low salt content, reducing the probability that the mineralization was precipitated during the Caledonian Orogeny. Our findings suggest that large impacts induce low-temperature hydrothermal systems that may be habitats for thermophilic organisms. Large impact structures on Mars may therefore be suitable targets in the search for fossil thermophilic organisms.     

Fluid inclusion studies of chemosynthetic carbonates: strategy for seeking life on Mars

Fluid inclusions in minerals hold the potential to provide important data on the chemistry of the ambient fluids during mineral precipitation. Especially interesting to astrobiologists are inclusions in low-temperature minerals that may have been precipitated in the presence of microorganisms. We demonstrate that it is possible to obtain data from inclusions in chemosynthetic carbonates that precipitated by the oxidation of organic carbon around methane-bearing seepages. Chemosynthetic carbonates have been identified as a target rock for astrobiological exploration. Other surficial rock types identified as targets for astrobiological exploration include hydrothermal deposits, speleothems, stromatolites, tufas, and evaporites, each of which can contain fluid inclusions. Fracture systems below impact craters would also contain precipitates of minerals with fluid inclusions. As fluid inclusions are sealed microchambers, they preserve fluids in regions where water is now absent, such as regions of the martian surface. Although most inclusions are < 5 microns, the possibility to obtain data from the fluids, including biosignatures and physical remains of life, underscores the advantages of technological advances in the study of fluid inclusions. The crushing of bulk samples could release inclusion waters for analysis, which could be undertaken in situ on Mars.     

Arm end-point trajectories under normal and micro-gravity environments

The purpose of the present experiment was to study the way in which the CNS represents gravitational force during vertical arm pointing movements. Movements in upward and downward directions were executed by two cosmonauts in normal-gravity and weightlessness. Analyses focused upon finger kinematics in the sagittal plane. In normal-gravity, downward direction movements showed smaller curvatures and greater relative times to peak velocity (AT/MT) when compared with upward direction movements. Data from the weightlessness experiments showed that whilst downward movements decreased their curvature during space flight, curvatures of upward movements changed slightly. Furthermore, AT/MT was modified during the first days in micro-gravity for both directions, recovering, however, to pre-flight values after 18 days in space. Results from the present study, provide evidence that gravitational force is centrally treated constituting an important component of the motor plan for vertical arm movements.     

KINETICS OF δ PHASE PRECIPITATION IN COLD ROLLED INCONEL 718 ALLOY

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计划概述

1975年3月18、19、20日,在海军海面武器中心白橡树实验所举行了汇报海军再入技术计划的会议。海军再入技术计划是海军海上系统司令部(SEA-035)主持的一项探索性发展计划。该计划的目的是为今后的先进战略武器系统的再入体开展航空弹道学、材料和结构技术的研究。在整个再入技     

超声自动检测系统的应用

介绍了基于无损探伤技术的C扫描自动检测系统的工作原理和软硬件设计思路,并提供了测试方法.     

随机子阵阵列的旁瓣电平和宽带特征

本文扩展了随机天线阵列的概念。介绍了三种新型的阵列几何图形，它们既具有随机阵列的宽带宽性能，几何图形也更简单，因而更适宜于低成本应用。对随机子阵的周期阵列、周期旋转随机子阵阵列和随机旋转随机子阵阵列的性能都进行了统计性的表征。结果表明子阵旋转能够降低天线阵排列因子的旁瓣电平。文中给出了一个设计过程的例子来说明天线阵排列因子的计算。     

经纬仪测点工艺技术研究

经纬仪定标测点是通过两台经纬仪进行互瞄,并对一根标尺标定组成测量系统,再由该系统进行点坐标测量.该技术是目前卫星部件制造和总装中的一项关键工序.文章阐述了经纬仪定标测点的原理,对测量过程中的定标和测点两个环节进行了精度分析,对标尺的不同摆放方案进行了比较,给出了最佳布局方法和被测点在不同位置时的误差分布曲线.     

异构数据库集成的研究与实现

对异构数据库集成做了详细的研究并提出了具体的实现方法。通过分析比较了目前已有的集成方案,本文提出集成异构数据库可以有四个步骤,分别是用控制表变化法提取有效数据、用XML定义传输数据格式、用JMS传输数据、用全局数据模式集成数据来实现。     

位移约束下火箭橇结构拓扑优化方法研究

兼顾安全性与经济性的高性能结构优化设计是结构设计领域的重要需求,面向火箭橇结构的拓扑优化设计对火箭橇试验具有重要意义.本文在火箭橇结构动力学仿真分析的基础上,基于变密度法建立了火箭橇结构的拓扑优化模型,利用伴随矢量求解了目标函数与约束函数关于设计变量的灵敏度,通过移动渐近线算法驱动了设计变量的更新迭代,最后对拓扑优化设...