The simulated silicification of bacteria--new clues to the modes and timing of bacterial preservation and implications for the search for extraterrestrial microfossils

Evidence of microbial life on Earth has been found in siliceous rock formations throughout the geological and fossil record. To understand the mechanisms of silicification and thus improve our search patterns for evidence of fossil microbial life in rocks, a series of controlled laboratory experiments were designed to simulate the silicification of microorganisms. The bacterial strains Pseudomonas fluorescens and Desulphovibrio indonensis were exposed to silicifying media. The experiments were designed to determine how exposure time to silicifying solutions and to silicifying solutions of different Si concentration affect the fossilization of microbial biofilms. The silicified biofilms were analyzed using transmission electron microscopy (TEM) in combination with energy-dispersive spectroscopy. Both bacterial species showed evidence of silicification after 24 h in 1,000 ppm silica solution, although D. indonensis was less prone to silicification. The degree of silicification of individual cells of the same sample varied, though such variations decreased with increasing exposure time. High Si concentration resulted in better preservation of cellular detail; the Si concentration was more important than the duration in Si solution. Even though no evidence of amorphous silica precipitation was observed, bacterial cells became permineralized. High-resolution TEM analysis revealed nanometer-sized crystallites characterized by lattice fringe-spacings that match the (10-11) d-spacing of quartz formed within bacterial cell walls after 1 week in 5,000 ppm silica solution. The mechanisms of silicification under controlled laboratory conditions and the implication for silicification in natural environments are discussed, along with the relevance of our findings in the search for early life on Earth and extraterrestrial life.     

下一代航天器的多用途贮箱

单组元和双组元推进系统已确定用于下一代航天器的轨道转换与姿态控制上,包括应用于通讯卫星、地球资源卫星、维修及补给卫星、气象卫星和防御卫星。基于上述应用的多用途貯箱是一种改型维金轨道器(VO-75)的圆筒形容器,直径为91厘米并有半球形封头,它92能用于航天飞机又能用于一次使用的助推火箭。本聍箱备有各种被动式全金属推进剂管理装置,以满足各种不同任务对加速度、流量、压力值、增压形式和轨道飞行中的晃动控制所提出的各种各样的要求。对各种装置的工作情况均结合其通用性和局限性来予以说明。对容积、重量、排空效率、容积效率等貯箱系统参数和相对成本,本文亦作了简介。     

Microwave Brightness Temperature and Lunar Soil Dielectric Property Retrieve

Among many scientific objectives of lunar exploration, investigations on lunar soil become more and more attractive to the scientists duo to the existence of abundant 3He and ilmenite in the lunar soil and their possible utilization. Although the soil composition determination on the lunar surface is available by visible light spectrometer,γ/X-ray spectrometer etc, the evaluations on the total reserves of 3He and ilmenite in the lunar deep and on the thickness of the lunar soil are still impossible so far. In this paper, the authors first give a rough analysis of the microwave brightness temperature images of the lunar disc observed using the NRAO 12 Meter Telescope and Siberian Solar Radio Telescope; then introduce our researches on the microwave dielectric properties of lunar soil simulators; finally, discuss some basic relations between the microwave brightness temperature and lunar soil properties.     

PILOT:一个智能化的分布式系统管理器

NASA约翰逊航天中心正在作一系列研究,探索提高当前和未来载人指控中心工作效率和实用性的途径。实时数据系统(RTDS)工程已研究了几种技术并用于指控中心环境。该环境是以工程工作站构成的多机种网络,该网中仿真的和实际的航天飞机任务现场数据作实时分配。该系统由一组复杂的交互进程组成,必须以最少的停顿时间提供多种服务。本文介绍一些能保证系统各功能高度可靠和高度可用的方法。包括一个进程可见性工具,一个本地工作站环境监视器,一个网络级通信工具和一个采用人工智能技术的全局进程。     

实时OTF动态GPS系统定位结果

1988年,美国陆军工程部正式开始研究利用GPS载波相位的实时定位系统。该项研究的最终目标是在1993年做成一台实用样机,能实时获得厘米级的三维定位精度。这一目标实现了,1993年3月开始对样机进行测试。1993年8月进行了首次演示,10月进行了首次公开演示。该设备一般能在“动中”(OTF)15秒时间内分辨模糊整周数,不需要作静态初始化。任一相距20km左右的移动平台可利用该设备进行可靠而稳健的精密定位。在各种工作条件下作了试验,以评价动平台精密定位OTF解模糊的极限。本文总结了这些试验的结果。早期所作的实时试验证明三维方向的定位精度可达1—3cm。本文还介绍了最终实时系统的设计方案以及与水文监测平台的结合问题。     

得到市场推动的庞巴迪CRJ-700

庞巴迪宇航集团新近启动的加拿大飞机公司研制的“地区喷气”(CRJ)700系列客机,已获得首家客户法国不列特航空公司的4架确定订货。首架订货计划于2000年第四季度交付。 新的70座CRJ-700为50座的CRJ的加长型。除不列特公司的订货外,它还吸引了来自另外7家航空公司的63架有条件订货、意向订货和备忘录协议订货(全部付有保证金)。尽管这些客户大都未被公布名称,但据说是目前CRJ的用户和初次考虑采用支线喷气机的客户。     

选用陀螺仪—动调陀螺,激光陀螺,光纤陀螺的比较

本文对现有陀螺仪技术：动调陀螺，激光陀螺和光纤陀螺作了综述。作者以一位系统工程师的观点对这些技术作了比较并列出了不同种类陀螺仪的优、缺点。     

用于飞行器动态控制系统的偏航速率传感器

自１９９５年初以来，ＲｏｂｅｒｔＢｏｓｃｈ开始了飞行器动态控制系统的生产。本文将介绍这一系统的关键部件－偏航速率传感器。     

支援干扰发展趋向探讨

战术支援干扰只有与日趋复杂的威胁系统和战术同步发展,才能保持其威力。一、干扰系统要求大功率机载干扰系统,用干扰敌方防空系统及其有关的指挥、控制与通信(C~3)网络来保护我方飞机。实施战术支援干扰决非易事,干扰系统必须处理许多问题,诸如自卫干扰机、威胁告警接收机以及其它复杂问题。支援干扰的主要任务是,通过远处干扰来保护沿不同飞行途径飞行的各种飞机。故要求它具有以下独特功能:1)特大的功率,至少要比常规自卫干扰机的功率大一千倍。这样,支援干扰机才能通过