现代雷达的表声波脉压系统：第一部分 表皮波匹配滤波器

相参雷达系统能提供普通脉冲雷达不可能检测到的目标信息，然而普通雷达用的磁控管却不适宜这些相参系统。幸好有行波管或固态放大器可供选用，但这类放大器峰值输出功率有限。采用较宽的脉冲来增大脉冲能量，然后再用表声波（ＳＡＷ）匹配滤波器将脉冲压缩，就能解决这个问题。文章分两部分刊载，第一部分评述了脉压雷达的需要并介绍了ＳＡＷ的基本技术。     

导弹制导综述

在过去的20年里,导弹制导设计方案迅速发展,以至于现代导弹可以采用复杂程度不同的制导系统.其中一些导弹,尤其是面空导弹可在同一枚导弹内装上多种制导系统.下面简要地叙述一下目前正在使用的几种主要的导弹制导系统类型.自动驾驶仪 现代化的自动驾驶仪制导系统通常是和其它制导系统例如雷达、指令或红外系统等一起配合使用的.各种自动驾驶仪的复杂程度各不相同,某些自动驾驶仪仅能保证导弹平直飞行,另外一些则还能提供方位制导.一种仅由自动驾驶仪制导的早期飞航式导弹是V-1导弹,它是由德国人在     

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.     

Three-dimensional confocal optical imagery of precambrian microscopic organisms

A major difficulty that has long hindered studies of organic-walled Precambrian microbes in petrographic thin sections is the accurate documentation of their three-dimensional morphology. To address this need, we here demonstrate the use of confocal laser scanning microscopy. This technique, both non-intrusive and non-destructive, can provide data by which to objectively characterize, in situ and at submicron-scale resolution, the cellular and organismal morphology of permineralized (petrified) microorganisms. Application of this technique can provide information in three dimensions about the morphology, taphonomy, and fidelity of preservation of such fossils at a spatial resolution unavailable by any other means.     

Refuse-to-crash: NASA tackles loss of control

The article reviews technologies under study at NASA that will alert pilots of loss of control in time to take action or be able to take necessary action to avoid crashing. Topics discussed include efforts to understand factors behind loss of control, how flight simulator data has been reviewed to develop a new understanding of aircraft aerodynamics, use of models to simulate accidents, and design changes resulting from the data collected.