基于光纤的雷达目标模拟器设计

光纤延迟线是用微波信号调制激光源而输出光信号 ,光源是激光二极管 ,其光输出能对微波频率进行调制。由于它是将雷达发射脉冲信号直接调制到光载波上 ,通过光纤延迟后再解调为雷达目标回波信号 ,故这种方法是完全相干的 ,且不引入系统的相位噪声。提出了一种用光纤延迟线实现雷达目标相干模拟的设计方法     

改进（DSP）模型运用于货运中心信息系统规划

货运中心信息系统规划,是围绕着公路货物运输网络的信息系统布局,对货运中心适站量的信息输送方式,信息作业规模、以及信息系统的建设水平进行规划。在货物运输过程中,该信息系统需要处理有关物品运输、中转换装、车辆调度、运输代理等多方面的信息流,使之密切配合物流系统的管理,提高货物运输服务水平、工作效率及经济效益。该信息系统群的作业过程,是由一组与物流组织相关的成对信息系统,对每对O—D流进行作业。在满足运输网络流需求的条件下,信息系统的布局应要求以最低的系统费用或最好的效益来安排建设序列。DSP模型是送货系统问题规划模型,本文对该模型进行了适当的改造,首次将之运用到货运中心信息系统规划问题中。主要变化是:(1)一个货运中心为一个节点,所覆盖的运输区内的用户端点都合并到该节点中;(2)成本系数为决策变量的直接相关的函数。本方法已成功地应用于甘肃省货运中心运输网络规划,取得了满意的结果。     

Impact disruption and recovery of the deep subsurface biosphere

Although a large fraction of the world's biomass resides in the subsurface, there has been no study of the effects of catastrophic disturbance on the deep biosphere and the rate of its subsequent recovery. We carried out an investigation of the microbiology of a 1.76 km drill core obtained from the ～35 million-year-old Chesapeake Bay impact structure, USA, with robust contamination control. Microbial enumerations displayed a logarithmic downward decline, but the different gradient, when compared to previously studied sites, and the scatter of the data are consistent with a microbiota influenced by the geological disturbances caused by the impact. Microbial abundance is low in buried crater-fill, ocean-resurge, and avalanche deposits despite the presence of redox couples for growth. Coupled with the low hydraulic conductivity, the data suggest the microbial community has not yet recovered from the impact ～35 million years ago. Microbial enumerations, molecular analysis of microbial enrichment cultures, and geochemical analysis showed recolonization of a deep region of impact-fractured rock that was heated to above the upper temperature limit for life at the time of impact. These results show how, by fracturing subsurface rocks, impacts can extend the depth of the biosphere. This phenomenon would have provided deep refugia for life on the more heavily bombarded early Earth, and it shows that the deeply fractured regions of impact craters are promising targets to study the past and present habitability of Mars.     

Gypsum-permineralized microfossils and their relevance to the search for life on Mars

Abstract Orbital and in situ analyses establish that aerially extensive deposits of evaporitic sulfates, including gypsum, are present on the surface of Mars. Although comparable gypsiferous sediments on Earth have been largely ignored by paleontologists, we here report the finding of diverse fossil microscopic organisms permineralized in bottom-nucleated gypsums of seven deposits: two from the Permian (～260?Ma) of New Mexico, USA; one from the Miocene (～6?Ma) of Italy; and four from Recent lacustrine and saltern deposits of Australia, Mexico, and Peru. In addition to presenting the first report of the widespread occurrence of microscopic fossils in bottom-nucleated primary gypsum, we show the striking morphological similarity of the majority of the benthic filamentous fossils of these units to the microorganisms of a modern sulfuretum biocoenose. Based on such similarity, in morphology as well as habitat, these findings suggest that anaerobic sulfur-metabolizing microbial assemblages have changed relatively little over hundreds of millions of years. Their discovery as fossilized components of the seven gypsiferous units reported suggests that primary bottom-nucleated gypsum represents a promising target in the search for evidence of past life on Mars. Key Words: Confocal laser scanning microscopy-Gypsum fossils-Mars sample return missions-Raman spectroscopy-Sample Analysis at Mars (SAM) instrument-Sulfuretum. Astrobiology 12, 619-633.     

Key science questions from the second conference on early Mars: geologic, hydrologic, and climatic evolution and the implications for life

In October 2004, more than 130 terrestrial and planetary scientists met in Jackson Hole, WY, to discuss early Mars. The first billion years of martian geologic history is of particular interest because it is a period during which the planet was most active, after which a less dynamic period ensued that extends to the present day. The early activity left a fascinating geological record, which we are only beginning to unravel through direct observation and modeling. In considering this time period, questions outnumber answers, and one of the purposes of the meeting was to gather some of the best experts in the field to consider the current state of knowledge, ascertain which questions remain to be addressed, and identify the most promising approaches to addressing those questions. The purpose of this report is to document that discussion. Throughout the planet's first billion years, planetary-scale processes-including differentiation, hydrodynamic escape, volcanism, large impacts, erosion, and sedimentation-rapidly modified the atmosphere and crust. How did these processes operate, and what were their rates and interdependencies? The early environment was also characterized by both abundant liquid water and plentiful sources of energy, two of the most important conditions considered necessary for the origin of life. Where and when did the most habitable environments occur? Did life actually occupy them, and if so, has life persisted on Mars to the present? Our understanding of early Mars is critical to understanding how the planet we see today came to be.     

镁铝复合板制备及成形技术研究进展

镁铝复合板是在镁合金外表上面覆盖一层铝而形成的铝–镁–铝三明治复合板,与镁合金相比,复合板的耐蚀性能得到有效改善,成形能力得到显著提高。对镁铝复合板制备方法及成形工艺进行了综述,介绍了镁铝复合板不同制备方法的研究进展,并对比分析了不同制备方法的优缺点,分析了现有镁铝复合板结构成形方法的不足之处,并提出了相应的解决途径,为镁铝复合板结构在航空航天领域的应用提供参考。     

西安临空经济示范区发展思路探析

2018年4月,西安临空经济示范区获批,开启了西部内陆地区临空经济发展的新征程。为了捋清西安临空经济示范区的发展思路,本文在分析示范区发展现状的基础上,指出示范区尚存政策支持散而弱、管理体制不合理、产业优势待发挥、协同发展力不足等问题,提出示范区应紧抓临空经济发展窗口期机遇,通过构建扶持政策体系,理顺管理体制,遵循临空经济规律,发挥"自贸+临空经济"叠加优势,实施差异化产业策略,编织联运交通网络等加快临空经济发展。     

民机大系统可靠性─费用综合分析

建立了民机营运阶段可靠性－费用蒙特－卡罗仿真模型,该模型既可用于综合评估民机营运的可靠性和费用,也可用以分析民机大系统众多因素对其可靠性和费用的影响。为实现模型功能开发了应用软件。最后以某国产飞机为例给出其部分分析结果。