《国际雷达指南》光盘中的世界现役机载雷达

《国际雷达指南》(IRD)光盘是作者经过二十年的努力收集世界各地公开雷达信息的成果。这项努力辨认了9800种雷达，然而，它们中的大多数已不再使用。IRD包括了674种现役雷达的技术信息。雷达功能(应用)约有50种。这篇文章对世界现役机载雷达作了评述并说明了怎样使用IRD。     

A combinatorial approach to biochemical space: description and application to the redox distribution of metabolism

Redox chemistry is central to life on Earth. It is well known that life uses redox chemistry to capture energy from environmental chemical energy gradients. Here, we propose that a second use of redox chemistry, related to building biomass from environmental carbon, is equally important to life. We apply a method based on chemical structure to evaluate the redox range of different groups of terrestrial biochemicals, and find that they are consistently of intermediate redox range. We hypothesize the common intermediate range is related to the chemical space required for the selection of a consistent set of metabolites. We apply a computational method to show that the redox range of the chemical space shows the same restricted redox range as the biochemicals that are selected from that space. By contrast, the carbon from which life is composed is available in the environment only as fully oxidized or reduced species. We therefore argue that redox chemistry is essential to life for assembling biochemicals for biomass building. This biomass-building reason for life to require redox chemistry is in addition (and in contrast) to life's use of redox chemistry to capture energy. Life's use of redox chemistry for biomass capture will generate chemical by-products-that is, biosignature gases-that are not in redox equilibrium with life's environment. These potential biosignature gases may differ from energy-capture redox biosignatures.     

An astrophysical view of Earth-based metabolic biosignature gases

Microbial life on Earth uses a wide range of chemical and energetic resources from diverse habitats. An outcome of this microbial diversity is an extensive and varied list of metabolic byproducts. We review key points of Earth-based microbial metabolism that are useful to the astrophysical search for biosignature gases on exoplanets, including a list of primary and secondary metabolism gas byproducts. Beyond the canonical, unique-to-life biosignature gases on Earth (O(2), O(3), and N(2)O), the list of metabolic byproducts includes gases that might be associated with biosignature gases in appropriate exoplanetary environments. This review aims to serve as a starting point for future astrophysical biosignature gas research.     

双基火箭推进剂的物理老化

在-40℃～+60℃温度范围内研究了老化对三种双基推进剂力学性能的影响。在60℃左右,主要是化学现象改变了硝化棉的性质。在-40～+20℃主要是类似于无定形聚合物的物理老化观象。把推进剂简单加热到60℃,物理老化的影响就大部分消除。从60℃骤冷,18小时内,双基推进剂在20℃的硬度等温地增加约30％。推进剂老化速率会因机械加载显著地增加。双基推进剂物理老化现象的深入研究可能导出一种使推进剂力学性能复原的方法。     

新世纪技术验证计划的小卫星通信

NASA下一世纪科学探索方式将基于廉价频繁的卫星发射,这些卫星将是轻型、低成本、高度自主的小卫星。通过“新世纪计划”(NMP),NASA准备创建一种新的高度综合的方法,对实现这些卫星目标的一系列技术进行开发和空间验证。要满足这些想象的任务要求,并突出降低寿命期成本的目标,对卫星设计、制造和操作各方面将提出挑战。本文集中讨论先进通信系统的体系结构和技术,这些都是NMP已明确的关键性能需求,也是空间验证计划当前选定的内容。这些系统主要分三大类:小型深空通信,极高码速率近地通信和短程通信。其应用包括:空—地链路,行星间飞行器及其着陆器和漫游年之间数据中继的航天器间链路,以及通过星间交叉链路和数据中继卫星的近地卫星通信。本文将从用途和关键性能参数(如质量、体积、效率和成本)来讨论射频(400MHz-32GHz)和光通信技术。     

Discrimination of aqueous and aeolian paleoenvironments by atomic force microscopy-- a database for the characterization of martian sediments

In the search for aqueous habitats on Mars direct proof of (ancient) flowing water is still lacking, although remote sensing has provided indications of young fluvial systems. To demonstrate that such proof can be given, we examined surface marks on recent terrestrial sand grains by atomic force microscopy (AFM) and applied a quantitative three-dimensional analysis that can numerically distinguish between aeolian and aquatic transport mechanisms in sedimentary deposits on Earth. The surfaces of natural quartz grains as well as olivine, feldspar pyroxene, and monazite sands of known origin were imaged, each image yielding a three-dimensional map of the mineral surface. A fully automated analysis of distribution patterns of the structural elements that constitute the grain surfaces shows that wind-transported quartz grains have short linear elements irregularly distributed on the surface. Linear elements on water-transported grains, however, are longer with orientations that reflect the mineral symmetry. Because the surface patterns found on aqueous grains are due to preferential etching, they can be used as diagnostic fingerprints for the existence of past or present aqueous transport systems. We used a cluster analysis of the cross-correlation distance of distribution patterns in the structures of aeolian and aquatic sand grains to build a phenogram that provides a map for the relationship of the various sediments found on earth. The analysis shows that the method is highly significant and that water and wind transport can clearly be differentiated. In particular, feldspar and olivine sands contributed even more to the discrimination than quartz grains, which indicated that the method is promising for its application on future missions to Mars. Assuming that martian aqueous sand grains exhibit similar erosional patterns to mineral grains on Earth, simple AFM experiments on a Mars lander would be capable of proving the activity of flowing water in modern runoff systems and of analyzing the paleoenvironments of Mars.     

计算机分析加快了波纹喇叭设计

当波纹喇叭天线的张角、轴长和直径给出后,利用写成BASIC语言的计算机程序可以很快地预知天线辐射方向图。