Nitrogen fixation on early Mars and other terrestrial planets: experimental demonstration of abiotic fixation reactions to nitrite and nitrate

Understanding the abiotic fixation of nitrogen is critical to understanding planetary evolution and the potential origin of life on terrestrial planets. Nitrogen, an essential biochemical element, is certainly necessary for life as we know it to arise. The loss of atmospheric nitrogen can result in an incapacity to sustain liquid water and impact planetary habitability and hydrological processes that shape the surface. However, our current understanding of how such fixation may occur is almost entirely theoretical. This work experimentally examines the chemistry, in both gas and aqueous phases, that would occur from the formation of NO and CO by the shock heating of a model carbon dioxide/nitrogen atmosphere such as is currently thought to exist on early terrestrial planets. The results show that two pathways exist for the abiotic fixation of nitrogen from the atmosphere into the crust: one via HNO and another via NO(2). Fixation via HNO, which requires liquid water, could represent fixation on a planet with liquid water (and hence would also be a source of nitrogen for the origin of life). The pathway via NO(2) does not require liquid water and shows that fixation could occur even when liquid water has been lost from a planet's surface (for example, continuing to remove nitrogen through NO(2) reaction with ice, adsorbed water, etc.).     

Ultrastructural study of iron oxide precipitates: implications for the search for biosignatures in the Meridiani hematite concretions, Mars

Two terrestrial environments that have been proposed as analogs for the iron oxide precipitation in the Meridiani Planum region of Mars include the Rio Tinto precipitates and southern Utah marble concretions. Samples of two typical Utah iron oxide concretions and iron oxide precipitates in contact with biofilms from Rio Tinto have been studied to determine whether evidence could be found for biomediation in the precipitation process and to identify likely locations for fossil microorganisms. Scanning electron microscopy, energy dispersive X-ray, and gas chromatography-mass spectrometry (GC-MS) were used to search for biosignatures in the Utah marbles. The precipitation of iron oxides resembles known biosignatures, though organic compounds could not be confirmed with GC-MS analysis. In contrast, textural variations induced by biological activity are abundant in the modern Rio Tinto samples. Although no compelling evidence of direct or indirect biomediation was found in the Utah marbles, the ultrastructure of the iron oxide cement in the concretion suggests an inward growth during concretion precipitation from an initially spherical redox front. No indication for growth from a physical nucleus was found.     

With a grain of salt: what halite has to offer to discussions on the origin of life

This experimental study investigated how the dynamics of the crystallization of the evaporite mineral halite could affect the accumulation and preservation of organic macromolecules present in the crystallizing solution. Halite was grown under controlled conditions in the presence of polymer nanoparticles that acted as an analog to protocellular material. Optical microscopy, atomic force microscopy, and laser scanning confocal fluorescence microscopy were used to trace the localization of the nanoparticles during and after growth of halite crystals. The present study revealed that the organic nanoparticles were not regularly incorporated within the halite, but were very concentrated on its surfaces. Their distribution was controlled dominantly by the morphologic surface features of the mineral rather than by specific molecular interactions with an atomic plane of the mineral. This means that the distribution of organic molecules was controlled by surfaces like those of halite's evaporitic growth forms. The experiments with halite also demonstrated that a mineral need not continuously incorporate organic molecules during its crystallization to preserve those molecules: After rejection by (non-incorporation into) the crystallizing halite, the organic nanoparticles increased in concentration in the evaporating brine. They ultimately either adsorbed in rectilinear patterns onto the hopper-enhanced surfaces and along discontinuities within the crystals, or they were encapsulated within fluid inclusions. Of additional importance in origin-of-life considerations is the fact that halite in the natural environment rapidly can change its role from that of a protective repository (in the absence of water) to that of a source of organic particles (as soon as water is present) when the mineral dissolves.     

Microbial survival rates of Escherichia coli and Deinococcus radiodurans under low temperature, low pressure, and UV-Irradiation conditions, and their relevance to possible Martian life

Viability rates were determined for microbial populations of Escherichia coli and Deinococcus radiodurans under the environmental stresses of low temperature (-35 degrees C), low-pressure conditions (83.3 kPa), and ultraviolet (UV) irradiation (37 W/m(2)). During the stress tests the organisms were suspended in saltwater soil and freshwater soil media, at variable burial depths, and in seawater. Microbial populations of both organisms were most susceptible to dehydration stress associated with low-pressure conditions, and to UV irradiation. However, suspension in a liquid water medium and burial at larger depths (5 cm) improved survival rates markedly. Our results indicate that planetary surfaces that possess little to no atmosphere and have low water availability do not constitute a favorable environment for terrestrial microorganisms.     

Study of the Enhancement Events of Relativistic Electron at the Geosynchronous Orbit

The high flux of energetic electron on geostationary orbit can induce many kinds of malfunction of the satellite there, within which the bulk-charging is the most significant that several broadcast satellite failures were confirmed to be due to this effect. The electron flux on geostationary orbit varies in a large range even up to three orders accompanied the passage of interplanetary magnetic cloud and the following geomagnetic disturbances. Upon the investigation of electron flux enhancement events, two types of events were partitioned as recurrent events and random ones. Both of the two kinds of events relate to the interplanetary conditions such as solar wind parameters, IMF etc and their evolution characters as well. As for the recurrent events, we found that, (1) all of the events exhibits periodic recurrence about 27 days, (2) significant increase of electron flux relates to interplanetary index and characters of their distribution, (3) the electron flux also has relation to solar activity index. An artificial neural network was constructed to estimate the flux I day ahead. The random electron flux enhancement events are rare and present different distribution figures to the recurrent ones. The figure of the random events and the conditions of their occurrence is also discussed in this paper.      

战斗机敏捷性评估方案及其对未来敏捷性战斗机设计的影响

本文的目的是介绍新型战斗机敏捷性评估方案并讨论评估方案对战斗机设计产生的影响,未来空战中要获胜就要求将飞机的机头,武器首先指出敌机,首先指向敌机就意味着具备了先敌发射的机会,全向攻击导弹（如AIM－9L）出现后,就对战斗机提出了指向－发射能力要求,指向敌机后全向攻击导弹可以从任意方向发射,其中包括飞机迎面遭遇情况,飞机速度较低时,未来战斗机可以利用它在较大过失速迎角（可达90°）下飞行的能力来提高其机头指向能力,未来过失速技术（PST）战斗机的操纵需要推力矢量动力装置和相应的操纵技术,它们使飞机具有了过失速机动能力,文章分析了战斗机的敏感性,并在大于和小于失速迎角这两个范围内评估了它对设计的影响,介绍了一些战斗机敏感性评估方案,在小于失速迎角范围内,用于表征俯仰敏捷性的参数有指向裕度（PM）,相对能态（V／Vc)和作战循环时间（CCT）,用于表征滚转敏捷性的参数有后向间隔距离（RSD）,在大于失速迎角范围内,确定出的关键性能参数为迎角变化率能力,以较大的迎角变化率进入的过失速机动在发射位置具有更长的时间－这是一个性能优势,形成俯仰和偏航矢量控制功率需求设计曲线的假设前提是仅使用推力矢量就有可能实现过失速迎角下飞机的操纵,讨论了应用敏捷性（一般情况下和过失速情况下）方案对未来战斗机设计的影响。     

含激波的湍流流动高精度大涡数值模拟方法

针对采用亚格子模型进行含激波的湍流流动模拟时会面临激波附近的精度损失问题,考虑从通过亚格子模型以及数值模拟方法两方面的改进来实现湍流流动大涡模拟的精度提高.大涡模拟采用了Yee及Sj(o)green (2009)提出的高阶低耗散方法.该方法采用自适应的流场探测器以控制计算中所需区域的数值耗散,并考虑对动力学模型采用在激波位置使用Sagaut和Germano(2005)提出的单边亚格子过滤器和(或)直接禁用亚格子项等方法加以改进.对于标准的马赫数1.5和3条件下的激波-湍流干扰问题,上述新方法相较于全区域采用亚格子模型的方法均表现出了相似的精度提升.同时实现的数值精度改进方案采用了Harten的亚单元分辨过程来定位和锐化激波,并在精确激波位置附近的网格点处采用了单边测试滤波.     

曲面和任意取向表面表面摩阻油膜测量法的进展

本文叙述曲面和任意取向表面表面摩阻测量方法的进一步的发展。介绍用漫射照明获取薄油膜等厚度干涉条纹谱的理论根据和实验结果。讨论了通过油流显示图像的分析,自动探测表面流线方位的可能性。所得结论表明油膜法也能应用于复杂的三维流动。     

弹道靶中超高速发射弹的流场及空气动力特性研究(英)

本文描述的是研究爆炸成型发射弹（ＥＦＰ）模型的流场及超高速空气动力特性所用的弹道试验设备;简要报导了记录全尺寸干涉图形的技术;对径向密度分布再现的方法进行了讨论;在零攻角实验时不同模型的空气动力阻力是采用简化方法来计算的;对各种不同ＥＦＰ型式的气动稳定性提出了定性估计的方法;并阐述了用于组合体超高速飞行特性研究的数值计算技术的基本原理     

MMS星座对磁层顶磁通量绳内离子惯性尺度结构的观测

利用MMS观测数据,对磁层顶通量绳内离子惯性尺度（d_i）的结构进行分析研究.结果发现,许多不同尺度（约1d_i至数十d_i）的通量绳内都存在具有d_i尺度的电流 j _m,其方向在磁层顶局地坐标系的-M方向,即与磁层顶查普曼-费拉罗电流同向,由电子在+M方向的运动（ v _em）携带.这些电流结构具有以下特征:磁鞘与磁层成分混合,磁场为开放形态;离子去磁化,电子与磁场冻结;N方向（即垂直于磁层顶电流片方向）的电场 E _n显著增大,幅度达到约20mV·m-1,并伴有明显的尖峰状起伏,该增强和尖峰状起伏的电场对应于霍尔电场.分析表明,电流、电子与离子运动的偏离以及霍尔电场之间遵从广义欧姆定律,三者密切关联.进一步对磁层顶磁重联的探测数据进行分析发现,在很多重联区内也存在与通量绳内相似的结构,其尺度约为d_i量级,其中霍尔电场 E _N、电流 j _M和电子速度 v _eM均与通量绳内对应物理量的方向相同且幅度相近.基于上述观测事实,采用经典FTE通量绳模型,对通量绳内电流、电子运动和霍尔电场的起源进行了初步探讨,认为其来源于磁层顶无碰撞磁重联区内的相应结构,并且后者在离子尺度通量绳的形成过程中起到重要作用.