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.     

Spatially resolved genomic, stable isotopic, and lipid analyses of a modern freshwater microbialite from cuatro ciénegas, Mexico

Abstract Microbialites are biologically mediated carbonate deposits found in diverse environments worldwide. To explore the organisms and processes involved in microbialite formation, this study integrated genomic, lipid, and both organic and inorganic stable isotopic analyses to examine five discrete depth horizons spanning the surface 25?mm of a modern freshwater microbialite from Cuatro Ciénegas, Mexico. Distinct bacterial communities and geochemical signatures were observed in each microbialite layer. Photoautotrophic organisms accounted for approximately 65% of the sequences in the surface community and produced biomass with distinctive lipid biomarker and isotopic (δ(13)C) signatures. This photoautotrophic biomass was efficiently degraded in the deeper layers by heterotrophic organisms, primarily sulfate-reducing proteobacteria. Two spatially distinct zones of carbonate precipitation were observed within the microbialite, with the first zone corresponding to the phototroph-dominated portion of the microbialite and the second zone associated with the presence of sulfate-reducing heterotrophs. The coupling of photoautotrophic production, heterotrophic decomposition, and remineralization of organic matter led to the incorporation of a characteristic biogenic signature into the inorganic CaCO(3) matrix. Overall, spatially resolved multidisciplinary analyses of the microbialite enabled correlations to be made between the distribution of specific organisms, precipitation of carbonate, and preservation of unique lipid and isotopic geochemical signatures. These findings are critical for understanding the formation of modern microbialites and have implications for the interpretation of ancient microbialite records. Key Words: Microbial ecology-Microbe-mineral interactions-Microbial mats-Stromatolites-Genomics. Astrobiology 12, 685-698.     

Comparative metagenomics of two microbial mats at cuatro ciénegas basin I: ancient lessons on how to cope with an environment under severe nutrient stress

Abstract The Cuatro Ciénegas Basin (CCB) is an oasis in the desert of Mexico characterized by low phosphorus availability and by its great diversity of microbial mats. We compared the metagenomes of two aquatic microbial mats from the CCB with different nutrient limitations. We observed that the red mat was P-limited and dominated by Pseudomonas, while the green mat was N-limited and had higher species richness, with Proteobacteria and Cyanobacteria as the most abundant phyla. From their gene content, we deduced that both mats were very metabolically diverse despite their use of different strategies to cope with their respective environments. The red mat was found to be mostly heterotrophic, while the green mat was more autotrophic. The red mat had a higher number of transporters in general, including transporters of cellobiose and osmoprotectants. We suggest that generalists with plastic genomes dominate the red mat, while specialists with minimal genomes dominate the green mat. Nutrient limitation was a common scenario on the early planet; despite this, biogeochemical cycles were performed, and as a result the planet changed. The metagenomes of microbial mats from the CCB show the different strategies a community can use to cope with oligotrophy and persist. Key Words: Microbial mats-Metagenomics-Metabolism. Astrobiology 12, 648-658.     

典型的—天

在一个与世隔绝的世界里待上105天,生活会是什么样子呢？常人难以想象。而通过“Mars-500”前期试验的志愿者的日志,却能获知他们在试验过程中每天都做些什么？试验之余又如何寻找生活的乐趣？因此．本刊特选载志愿者西里尔·富尼耶于2009年6月23日在封闭模拟舱内写的一篇日志,以帮助大家了解志愿者在模拟舱内的真实生活。     

剪切同轴式喷嘴中心管壁厚对火焰的影响

为了研究剪切同轴式喷嘴中心管壁厚度对火焰的影响,针对LOX/CH4火焰,采用数值方法计算了三种不同喷嘴中心管壁厚的长方体形燃烧室内的燃烧过程,计算表明,对于较大的管壁厚度,在紧贴管壁下游的区域将形成较大的回流区,有利于火焰稳定在喷嘴出口处,还给出了采用相同几何结构燃烧室的LOX/CH4燃烧试验结果,试验也得出了同样的趋势,随着中心管壁厚度的增加,火焰中心明显前移。     

军机维修市场预测

据航空战略咨询公司预测,西方国家的军用飞机的维护、修理和大修(MRO)开支今年将达到607亿美元,而2007年的开支为599亿美元.其中,美国军用飞机MRO的开支超过50%,为310亿美元.日本、法国、以色列、英国和韩国紧随其后,但其总数仅为美国军机MRO开支的三分之一.     

W波段机载断续频率调制连续波成像雷达

按照断续调频连续波（FMICW）原理,已经研制出一台具有用于稳定和扫描的转向支架的94GHz成像雷达,它作为机载测试台用以评估雷达辅助导航和引导算法。直升机机载飞行试验的初步结果给出了所选择的特征（包括跑道）和其周围环境之间用计算机和飞行员人工引导两种情况下的充分比较。特征提取和匹配算法已经证实了该系统比GPS更准确。     

Space-to-space Radio Interferometry System from Medium Earth Orbits

This paper presents a new concept to perform space-to-space Very Long Baseline Interferometry which enables the imaging of cosmic sources at high-resolution and high-sensitivity with small antennas. Several individual apertures are embarked on separate identical satellites staggered in height into Polar or Equatorial Circular Medium Earth Orbits (PECMEO orbits). These orbits are stable and allow GNSS-based on-the-fly centimeter-level relative positioning. Coherent operation is possible by exchanging local oscillator components and measured signals through Inter-Satellite Links (ISL). On-board cross correlation is performed at each satellite over a delay window compatible with the accuracy of the on-the-fly relative positioning and the result sent to the ground. Image reconstruction is completed on the ground thanks to sub-millimeter baseline retrieval from accurate GNSS orbits, ISL ranging and spacecraft attitude information. The application of this concept to image the Super Massive Black Hole Sgr A* is hinted.      

新时期航空航天工业的标准战略

本文是荣获美国庆祝2004年世界标准日论文竞赛头奖的作品,中心内容是在新世纪航空航天工业如何在广泛国际合作,信息技术迅猛发展的环境下结合本行业的实际,制定并适时调整其标准战略。文中分析问题的方法,解决问题的思路具有某种普遍意义,现将该文详细摘译刊登于下,供参考。