Chemical mapping of proterozoic organic matter at submicron spatial resolution

A NanoSIMS ion microprobe was used to map the submicron-scale distributions of carbon, nitrogen, sulfur, silicon, and oxygen in organic microfossils and laminae in a thin section of the approximately 0.85 billion year old Bitter Springs Formation of Australia. The data provide clues about the original chemistry of the microfossils, the silicification process, and the biosignatures of specific microorganisms and microbial communities. Chemical maps of fossil unicells and filaments revealed distinct wall- and sheath-like structures enriched in C, N, and S, consistent with their accepted biological origin. Surprisingly, organic laminae, previously considered to be amorphous, also exhibited filamentous and apparently compressed spheroidal structures defined by strong enrichments in C, N, and S. By analogy to NanoSIMS data from the well-preserved microfossils, these structures were interpreted as being of biological origin, most likely representing densely packed remnants of microbial mats. Given that the preponderance of organic matter in Precambrian sediments is similarly "amorphous," our findings indicate that a re-evaluation of ancient specimens via in situ structural, chemical, and isotopic study is warranted. Our analyses have led us to propose new criteria for assessing the biogenicity of problematic kerogenous materials, and, thus, these criteria can be applied to assessments of poorly preserved or fragmentary organic residues in early Archean sediments and any that might occur in meteorites or other extraterrestrial samples.     

空间目标小型相控阵雷达探测技术

地基探测系统受站点布局限制,难以实现全轨道空间的目标探测与跟踪.为对高价值航天器邻域空间目标进行全时探测与跟踪,提出基于伴随微纳卫星的小型化相控阵雷达技术.通过分析不同波段雷达对大范围空间目标搜索与精细跟踪的性能,并综合考虑系统复杂度与功耗等因素,最终选择C波段作为雷达工作频段.详细阐述小型化相控阵雷达的系统设计、目标...     

球形弹丸超高速斜撞击薄板的碎片云和侵彻特征仿真分析

低地球轨道航天器易受到微流星体及空间碎片的超高速撞击。相较于正撞击,斜撞击现象更加普遍、更具研究价值。文章采用Autodyn-3D数值模拟软件,利用光滑粒子流体动力学（smooth particle hydrodynamics, SPH）方法,模拟Al2017-T4球形弹丸超高速斜撞击Al2A12薄板的过程,开展弹丸撞击速度为3～6 km/s、撞击角度为0°～60°时的撞击特征仿真分析。结果表明:撞击角度对碎片云形貌与几何尺寸,以及穿孔大小和形状特征有显著影响;当撞击角度为30°～45°时会发生滑弹反溅现象,造成弹丸侵彻能力下降。研究结果可为超高速撞击防护结构的设计和改进提供支持。     

"Hairy blobs:" microbial suspects preserved in modern and ancient extremely acid lake evaporites

"Hairy blobs" are unusual clumps of organic bodies and sulfate crystals that have been found in evaporite minerals grown in acid saline lakes. Here, we document modern hairy blobs in halite and gypsum from 5 modern acid saline lakes in southern Western Australia, and Permian hairy blobs trapped in halite from the mid-Permian Opeche Shale in the subsurface of North Dakota. These are among the first microbial remains described from acid saline lake environments. They give clues about the role of microorganisms in the acidity, geochemistry, and mineralogy of these extreme environments. This study also may add to the inventory of life in extreme environments and help predict possible martian life-forms and the method of preservation.     

姿态对地指向不断变化成像时的偏流角分析

 针对敏捷卫星在三轴姿态机动过程中同时进行推扫成像的偏流角问题,基于线阵TDICCD推扫成像原理,分析了动态成像过程中的偏流原理,通过速度矢量法推导出动态成像方式下的偏流角数学解析表达式。数值仿真分析表明：当相机推扫速度方向与星下点速度方向的夹角η为0°（沿航迹方向推扫成像）或180°（沿航迹反方向推扫成像）,偏流是由地球自转产生的,数值较小;当夹角为0°＜η＜180°时,偏流是地球自转和轨道运动共同产生的,偏流角数值较大;当夹角η=90°（垂直于航迹方向推扫成像）时,偏流角随地理纬度的增大而增大。基于以上结论,采用姿态偏航控制对偏流角进行调整,可以实现在三轴姿态机动过程中开启光学有效载荷进行推扫成像的动态成像技术。     

Potential fossil endoliths in vesicular pillow basalt, Coral Patch Seamount, eastern North Atlantic Ocean

The chilled rinds of pillow basalt from the Ampère-Coral Patch Seamounts in the eastern North Atlantic were studied as a potential habitat of microbial life. A variety of putative biogenic structures, which include filamentous and spherical microfossil-like structures, were detected in K-phillipsite-filled amygdules within the chilled rinds. The filamentous structures (～2.5 μm in diameter) occur as K-phillipsite tubules surrounded by an Fe-oxyhydroxide (lepidocrocite) rich membranous structure, whereas the spherical structures (from 4 to 2 μm in diameter) are associated with Ti oxide (anatase) and carbonaceous matter. Several lines of evidence indicate that the microfossil-like structures in the pillow basalt are the fossilized remains of microorganisms. Possible biosignatures include the carbonaceous nature of the spherical structures, their size distributions and morphology, the presence and distribution of native fluorescence, mineralogical and chemical composition, and environmental context. When taken together, the suite of possible biosignatures supports the hypothesis that the fossil-like structures are of biological origin. The vesicular microhabitat of the rock matrix is likely to have hosted a cryptoendolithic microbial community. This study documents a variety of evidence for past microbial life in a hitherto poorly investigated and underestimated microenvironment, as represented by the amygdules in the chilled pillow basalt rinds. This kind of endolithic volcanic habitat would have been common on the early rocky planets in our Solar System, such as Earth and Mars. This study provides a framework for evaluating traces of past life in vesicular pillow basalts, regardless of whether they occur on early Earth or Mars.     

高超声速乘波飞行器气动特性研究

用计算流体力学和风洞试验的方法对以锥导乘波体为基础生成的高超声速乘波飞行器的气动性能进行了研究。结果表明，以马赫数6，攻角4度为设计状态的乘波体，在马赫数5～7，攻角4～6度的范围内，都具有良好的气动特性，升阻比接近4。最后，提出了一个简单的以参考温度方法为基础的粘性阻力分析方法。该方法配合使用风洞试验和计算流体的结果，可以用来验证计算流体中难以计算准确的粘性阻力，也可以用来分析在风洞试验难以直接得到的粘性阻力。对于工程上的粘性阻力分析是一个有用的办法。     

Determination of lethality rate constants and D-values for heat-resistant Bacillus spores ATCC 29669 exposed to dry heat from 125°C to 200°C

Exposing flight hardware to dry heat is a NASA-approved sterilization method for reducing microbial bioburden on spacecraft. The existing NASA specification only allows heating the flight hardware between 104°C and 125°C to reduce the number of viable microbes and bacterial spores. Also, the NASA specifications only allow a four log reduction by dry heat microbial reduction because very heat-resistant spores are presumed to exist in a diverse population (0.1%). The goal of this research was to obtain data at higher temperatures than 125°C for one of the most heat-resistant microorganisms discovered in a spacecraft assembly area. These data support expanding the NASA specifications to temperatures higher than 125°C and relaxing the four log reduction specification. Small stainless steel vessels with spores of the Bacillus strain ATCC 29669 were exposed to constant temperatures between 125°C and 200°C under both dry and ambient room humidity for set time durations. After exposures, the thermal spore exposure vessels were cooled and the remaining spores recovered and plated out. Survivor ratios, lethality rate constants, and D-values were determined at each temperature. The D-values for the spores exposed under dry humidity conditions were always found to be shorter than those under ambient humidity. The temperature dependence of the lethality rate constants was obtained by assuming that they obeyed Arrhenius behavior. The results are compared to those of B. atrophaeus ATCC 9372. In all cases, the D-values of ATCC 29669 are between 20 and 50 times longer than those of B. atrophaeus ATCC 9372.     

The cuatro ciénegas basin in coahuila, Mexico: an astrobiological precambrian park

Abstract The Cuatro Ciénegas Basin (CCB) is a rare oasis in the Chihuahuan Desert in the state of Coahuila, Mexico. It has a biological endemism similar to that of the Galapagos Islands, and its spring-fed ecosystems have very low nutrient content (nitrogen or phosphorous) and are dominated by diverse microbialites. Thus, it has proven to be a distinctive opportunity for the field of astrobiology, as the CCB can be seen as a proxy for an earlier time in Earth's history, in particular the late Precambrian, the biological frontier when prokaryotic life yielded at least partial dominance to eukaryotes and multicellular life. It is a kind of ecological time machine that provides abundant opportunities for collaborative investigations by geochemists, geologists, ecologists, and population biologists in the study of the evolutionary processes that structured Earth-based life, especially in the microbial realm. The CCB is an object of investigation for the identification of biosignatures of past and present biota that can be used in our search for extraterrestrial life. In this review, we summarize CCB research efforts that began with microbial ecology and population biology projects and have since been expanded into broader efforts that involve biogeochemistry, comparative genomics, and assessments of biosignatures. We also propose that, in the future, the CCB is sanctioned as a "Precambrian Park" for astrobiology. Key Words: Microbial mats-Stromatolites-Early Earth-Extremophilic microorganisms-Microbial ecology. Astrobiology 12, 641-647.     

Fluid inclusion studies of chemosynthetic carbonates: strategy for seeking life on Mars

Fluid inclusions in minerals hold the potential to provide important data on the chemistry of the ambient fluids during mineral precipitation. Especially interesting to astrobiologists are inclusions in low-temperature minerals that may have been precipitated in the presence of microorganisms. We demonstrate that it is possible to obtain data from inclusions in chemosynthetic carbonates that precipitated by the oxidation of organic carbon around methane-bearing seepages. Chemosynthetic carbonates have been identified as a target rock for astrobiological exploration. Other surficial rock types identified as targets for astrobiological exploration include hydrothermal deposits, speleothems, stromatolites, tufas, and evaporites, each of which can contain fluid inclusions. Fracture systems below impact craters would also contain precipitates of minerals with fluid inclusions. As fluid inclusions are sealed microchambers, they preserve fluids in regions where water is now absent, such as regions of the martian surface. Although most inclusions are < 5 microns, the possibility to obtain data from the fluids, including biosignatures and physical remains of life, underscores the advantages of technological advances in the study of fluid inclusions. The crushing of bulk samples could release inclusion waters for analysis, which could be undertaken in situ on Mars.     

基于区域网格化的空间目标光学特性计算方法

为了精确计算空间目标光学特性,基于区域分解和网格划分的方法建立了空间目标光学特性计算模型。首先把目标表面分解为若干材料属性单一且易于数学描述的区域;对划分后的区域进行网格划分;对划分后的网格面元进行遮挡与掩蔽分析,给出有效面元的判断准则;最后结合表面材料的双向反射分布函数建立了目标的光学特性计算模型。为了验证计算模型的精确性,搭建了空间目标缩比模型测量平台。当入射天顶角为10°、20°和30°时,缩比模型理论计算结果与实验测量数据的相对均方根误差分别为8.89%、9.39%和8.00%,均小于10%,验证了所建目标光学特性计算模型的准确性。     

星载大型高精度馈源阵抗热变形优化设计

为保证多波束天线在温度大范围变化条件下的指向性能,提出一种高热匹配性大型馈源阵设计方法.首先采用辐射状条形接口实现馈源相位中心自适应拟合,解决了以往热匹配设计时相位中心无法固定的问题;然后通过预设力弹簧来解决游离间隙配合引起的力学环境微损伤和指向变化问题;最后采用遗传算法对各条形接口的分布位置进行优化.利用该方法对某多...     

弹性自驱动卷筒式伸杆机构展开刚度分析及校验

针对弹性自驱动卷筒式伸杆机构(STACER) 的展开刚度问题，分析了卷筒式伸杆机构的工作原理，基于等效连续体模型推导了卷筒式伸杆机构弹性卷筒的构型参数与刚度的关系式，分析了弹性卷筒末端螺旋角、末端半径、带厚、带宽对展开刚度的影响。分析结果表明：(1)末端半径的增大能同时提高弹性卷筒的一阶频率和比刚度，而带宽的增大将导致弹性卷筒的一阶频率和比刚度均降低;(2)弹性卷筒的一阶频率随带厚的增加近似线性增大，但比刚度随带厚的增大而近似按双曲线规律下;(3)弹性卷筒末端螺旋角在62°~75°时，弹性卷筒的比刚度可获得最优值。卷筒式伸杆机构的刚度测试结果与理论分析结果基本一致，校验了理论分析方法的有效性。     

受控液扇撞击的混合特性研究

对溅板式层板喷注单元撞击后产生的两个相同受控液扇的混合特性进行研究,探讨液扇扩张角β对混合效率因子Em的影响。研究过程中对圆柱射流流强分布数学模型进行分析并改进,建立了适用于两个相同受控液扇撞击后的流强分布的数学模型。模拟计算Em值与试验值的偏差在-0.86%~12.9%之间。研究结果表明：当β〈60°时,Em随β的增...     

Infrared spectroscopic characterization of organic matter associated with microbial bioalteration textures in basaltic glass

Microorganisms have been found to etch volcanic glass within volcaniclastic deposits from the Ontong Java Plateau, creating micron-sized tunnels and pits. The fossil record of such bioalteration textures is interpreted to extend back ～3.5 billion years to include meta-volcanic glass from ophiolites and Precambrian greenstone belts. Bioalteration features within glass clasts from Leg 192 of the Ocean Drilling Program were investigated through optical microscopy and Fourier transform infrared (FTIR) spectroscopy of petrographic thin sections. Extended depth of focus optical microscopic imaging was used to identify bioalteration tubules within the samples and later combined with FTIR spectroscopy to study the organic molecules present within tubule clusters. The tubule-rich areas are characterized by absorption bands indicative of aliphatic hydrocarbons, amides, esters, and carboxylic groups. FTIR analysis of the tubule-free areas in the cores of glass clasts indicated that they were free of organics. This study further constrains the nature of the carbon compounds preserved within the tubules and supports previous studies that suggest the tubules formed through microbial activity.     

相机摆放方式对推扫成像试验的影响分析

为了减小空间TDI CCD相机外场成像过程中相机摆放方式引入的误差,更准确地评价相机成像性能,提出了一种相机最佳水平摆放角、半径以及成像仰角的计算方法。建立了推扫成像的像移矢量数学模型,定义了像移矢量与水平摆放角、半径之间的函数关系,对工程近似进行了误差分析。建立了相机仰角与像移失配率之间的函数关系,提出了最佳仰角的计算方法。分析结果表明：在常规大气条件下,水平摆放角为0°,摆放半径为0, 仰角为7°时,相机摆放方式对成像影响最小,成像结果最能客观反映相机性能。     

喷管尺寸对超声速喷流噪声影响研究

为研究喷管尺寸对超声速喷流噪声特性的影响及其声场分布规律而设计了冷流实验系统,选用3种不同尺寸的喷管,采用LMS数据采集系统及噪声处理软件,对不同喷管尺寸、不同来流压强下的喷流噪声进行了采集和处理.实验结果表明,超声速喷流噪声具有较强的指向性,随着测点偏离喷流中心轴线角度从30°增加到180°,其声压级峰值逐渐减小,峰...     

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.     

Formation of replicating saponite from a gel in the presence of oxalate: implications for the formation of clay minerals in carbonaceous chondrites and the origin of life

The potential role of clay minerals in the abiotic origin of life has been the subject of ongoing debate for the past several decades. At issue are the clay minerals found in a class of meteorites known as carbonaceous chondrites. These clay minerals are the product of aqueous alteration of anhydrous mineral phases, such as olivine and orthopyroxene, that are often present in the chondrules. Moreover, there is a strong correlation in the occurrence of clay minerals and the presence of polar organic molecules. It has been shown in laboratory experiments at low temperature and ambient pressure that polar organic molecules, such as the oxalate found in meteorites, can catalyze the crystallization of clay minerals. In this study, we show that oxalate is a robust catalyst in the crystallization of saponite, an Al- and Mg-rich, trioctahedral 2:1 layer silicate, from a silicate gel at 60°C and ambient pressure. High-resolution transmission electron microscopy analysis of the saponite treated with octadecylammonium (n(C)=18) cations revealed the presence of 2:1 layer structures that have variable interlayer charge. The crystallization of these differently charged 2:1 layer silicates most likely occurred independently. The fact that 2:1 layer silicates with variable charge formed in the same gel has implications for our understanding of the origin of life, as these 2:1 clay minerals most likely replicate by a mechanism of template-catalyzed polymerization and transmit the charge distribution from layer to layer. If polar organic molecules like oxalate can catalyze the formation of clay-mineral crystals, which in turn promote clay microenvironments and provide abundant adsorption sites for other organic molecules present in solution, the interaction among these adsorbed molecules could lead to the polymerization of more complex organic molecules like RNA from nucleotides on early Earth.     

Olivine-respiring bacteria isolated from the rock-ice interface in a lava-tube cave, a Mars analog environment

The boundary between ice and basalt on Earth is an analogue for some near-surface environments of Mars. We investigated neutrophilic iron-oxidizing microorganisms from the basalt-ice interface in a lava tube from the Oregon Cascades with perennial ice. One of the isolates (Pseudomonas sp. HerB) can use ferrous iron Fe(II) from the igneous mineral olivine as an electron donor and O(2) as an electron acceptor. The optimum growth temperature is ～12-14°C, but growth also occurs at 5°C. Bicarbonate is a facultative source of carbon. Growth of Pseudomonas sp. HerB as a chemolithotrophic iron oxidizer with olivine as the source of energy is favored in low O(2) conditions (e.g., 1.6% O(2)). Most likely, microbial oxidation of olivine near pH 7 requires low O(2) to offset the abiotic oxidation of iron. The metabolic capabilities of this bacterium would allow it to live in near-surface, icy, volcanic environments of Mars in the present or recent geological past and make this type of physiology a prime candidate in the search for life on Mars.