Evaluation of early Archean volcaniclastic and volcanic flow rocks as possible sites for carbonaceous fossil microbes

Sedimentary rocks have traditionally been the focus of the search for Archean microfossils; the Earth's oldest fossil bacteria are associated with carbonaceous matter in sedimentary cherts in greenstone belts in the eastern Pilbara block of Western Australia and Barberton greenstone belt of South Africa. Reports of possible fossils in a martian meteorite composed of igneous rock and the discovery of modern bacteria associated with basalts have stimulated a new look at Archean volcanic rocks as possible sites for fossil microbes. This study examines silicified volcaniclastic rocks, near-surface altered volcanic flow rocks, and associated stromatolite- like structures from the Archean Barberton greenstone belt to evaluate their potential for the preservation of carbonaceous fossils. Detrital carbonaceous particles are widely admixed with current-deposited debris. Carbonaceous matter is also present in altered volcanic flow rocks as sparse particles in silica veins that appear to be fed by overlying carbonaceous chert layers. Neither microfossils nor mat-like material was identified in the altered volcanic rocks or adjacent stromatolite-like structures. Ancient volcanic flow and volcaniclastic rocks are not promising sites for carbonaceous fossil preservation.     

A transmission electron microscopy study of silica and kerogen biosignatures in approximately 1.9 Ga gunflint microfossils

Microfossils preserved in chert from the;1.9 Ga Gunflint Formation (Schreiber Beach, Ontario, Canada) were studied with transmission electron microscopy (TEM) and analytical TEM (ATEM). Our goals were to uncover the style of silicification relative to the distribution of organic matter, and to evaluate the distribution and evolution of organic matter, at submicroscopic spatial scales. Petrographically the microfossils typically display filamentous or coccoidal morphologies, and consist of quartz crystals surrounded by kerogen along grain boundaries. ATEM analysis revealed that quartz associated with kerogen consists of 200-500nm-sized, round crystallites, whereas the chert matrix is comprised of randomly oriented, polygonal microquartz (5-10 microm). Silica spheroids found within some fossils consist of quartz subgrains in an amorphous to poorly crystalline matrix, suggesting that precipitation of opaline silica on organic matter occurred with subsequent but incomplete transformation to quartz. Some coccoidal microfossils surround large euhedral quartz crystals (up to 5 microm in diameter) that appeared to have influenced the distribution of kerogen during crystal growth. These euhedral quartz crystals commonly contain elongated (50-100 nm) iron-rich crystallites. Energy-loss, near-edge structure analysis of kerogen associated with a coccoidal microfossil showed that it is composed of amorphous carbon with no evidence of graphitization. TEM results revealed significant differences in the style of silicification between microbe-shaped microfossils and their surrounding chert matrix, as well as the presence of amorphous kerogen.     

Carbonaceous cherts in the Barberton greenstone belt and their significance for the study of early life in the Archean record

The 3.5-3.2 Ga old volcano-sedimentary succession of the Barberton greenstone belt (South Africa) is characterized by lithological units that are repeated in a regular manner. Komatiitic, basaltic, and dacitic volcanic and volcaniclastic sequences are capped by zones of silica enrichment, followed by bedded carbonaceous cherts. Stratiform and crosscutting carbonaceous chert veins are common in silica alteration zones and bedded cherts. A detailed field study of several chert horizons and chert veins that range in age from 3.47 to 3.30 Ga revealed the importance of syndepositional hydrothermal activity for their origin. Bedded cherts consist of silicified detrital and tuffaceous sediments that were deposited on the seafloor. Silicification took place at the sediment-water interface as a result of diffuse upflow of low-temperature hydrothermal fluids, which gave rise to the formation of impermeable chert caps. Fluid overpressure resulted in the breaching of the cap rocks at times. Chert veins contain angular host rock fragments, replace wall rocks, and show evidence of multiple vein fillings and in situ brecciation of earlier generations of vein fillings. They represent hydraulic fractures that were initiated by overpressuring of the hydrothermal system. The vein networks were infilled, partly by hydrothermal chert precipitates, and partly by still unconsolidated (not yet silicified) sedimentary material derived from overlying sedimentary horizons. Field, petrographic, isotopic, and trace element evidence indicate that most carbonaceous matter represents sedimentary material that originated by biogenic processes in the Archean oceans and not by hydrothermal processes in the subsurface.     

Earth's earliest biosphere-a proposal to develop a collection of curated archean geologic reference materials

The discovery of evidence indicative of life in a Martian meteorite has led to an increase in interest in astrobiology. As a result of this discovery, and the ensuing controversy, it has become apparent that our knowledge of the early development of life on Earth is limited. Archean stratigraphic successions containing evidence of Earth's early biosphere are well preserved in the Pilbara Craton of Western Australia. The craton includes part of a protocontinent consisting of granitoid complexes that were emplaced into, and overlain by, a 3.51-2.94 Ga volcanigenic carapace - the Pilbara Supergroup. The craton is overlain by younger supracrustal basins that form a time series recording Earth history from approximately 2.8 Ga to approximately 1.9 Ga. It is proposed that a well-documented suite of these ancient rocks be collected as reference material for Archean and astrobiological research. All samples would be collected in a well-defined geological context in order to build a framework to test models for the early evolution of life on Earth and to develop protocols for the search for life on other planets.     

Spherule beds 3.47-3.24 billion years old in the Barberton Greenstone Belt,South Africa: a record of large meteorite impacts and their influence on early crustal and biological evolution

Four layers, S1-S4, containing sand-sized spherical particles formed as a result of large meteorite impacts, occur in 3.47-3.24 Ga rocks of the Barberton Greenstone Belt, South Africa. Ir levels in S3 and S4 locally equal or exceed chondritic values but in other sections are at or only slightly above background. Most spherules are inferred to have formed by condensation of impact-produced rock vapor clouds, although some may represent ballistically ejected liquid droplets. Extreme Ir abundances and heterogeneity may reflect element fractionation during spherule formation, hydraulic fractionation during deposition, and/or diagenetic and metasomatic processes. Deposition of S1, S2, and S3 was widely influenced by waves and/or currents interpreted to represent impact-generated tsunamis, and S1 and S2 show multiple graded layers indicating the passage of two or more wave trains. These tsunamis may have promoted mixing within a globally stratified ocean, enriching surface waters in nutrients for biological communities. S2 and S3 mark the transition from the 300-million-year-long Onverwacht stage of predominantly basaltic and komatiitic volcanism to the late orogenic stage of greenstone belt evolution, suggesting that regional and possibly global tectonic reorganization resulted from these large impacts. These beds provide the oldest known direct record of terrestrial impacts and an opportunity to explore their influence on early life, crust, ocean, and atmosphere. The apparent presence of impact clusters at 3.26-3.24 Ga and approximately 2.65-2.5 Ga suggests either spikes in impact rates during the Archean or that the entire Archean was characterized by terrestrial impact rates above those currently estimated from the lunar cratering record.     

Enhancement of primary education using EDUSAT: Rajiv Gandhi project for EDUSAT supported elementary education network (RGPEEE) overview

Providing education access to the children in the age group 6–14 years is a constitutional obligation and challenge for the union as well state governments, as the development of elementary education is a key factor for a nation's development. Due to the non-availability of required number of trained and expert teachers’ knowledge-divide exists between students population of urban and rural/remote areas. To bridge this gap Distance Learning or Tele-education is the best option. A dedicated satellite for the purpose (EDUSAT) was launched on 20th September 2004 to serve the nation in all the education activities. It was decided to provide a Tele-education network in and around the Sidhi district of Madhya Pradesh, with uplink and studio facility (Hub) at Jabalpur (MP) and around 700 receive only terminals (ROTs) in various schools. Since the medium of teaching used in this network is Hindi, it was later decided to extend the coverage to connect around 50 primary schools with ROTs in six surrounding states viz. Jharkhand, Bihar, Chhatisgarh, Uttar Pradesh, Rajasthan and Uttaranchal. The network is configured as a DTH network using state-of-art digital technology, in Ku-band with 3.8 m antenna and 16 W power amplifier at Hub. The ROTs are designed to operate on solar power for 2.5 h continuously, taking into consideration the non-availability of primary power in the rural areas. The teachers of the schools are trained for the proper operations of the ROTs. The teachers of these rural schools also contribute to the content generation, with local relevance, in coordination with Indira Gandhi National Open University (IGNOU). At present the network with around 1000 ROTs is being utilized for 2 h per day. The RGPEEE network is in the process of being augmented with 32 satellite interactive terminals (SITs), to be used for teachers training. The project is being managed by two tier management system. In order to oversee the project implementation and monitoring an Apex Core Group, consisting of Apex Committee and Standing Committee, has been constituted. The Apex Committee takes care of policy decisions where as, the Standing Committee takes care of day to day affair.     

一种聚束SAR回波数据压缩成像方法

针对聚束合成孔径雷达(SAR)成像中的海量数据问题,提出了一种基于压缩感知的聚束SAR回波数据压缩成像方法。首先对回波信号进行分析,利用波前匹配字典构造方法得到回波观测矩阵,其次通过构造二维离散余弦变换(2D\|DCT)等效矩阵得到回波信号的稀疏变换矩阵,然后利用平滑L0算法重构得到观测场景的二维像。本文方法可以在采集远小于传统聚束SAR成像方法所需回波数据量的基础上实现准确成像,最后的仿真结果表明了方法的可行性和有效性。     

Discovery of a new chert-permineralized microbiota in the Proterozoic Buxa Formation of the Ranjit window, Sikkim, northeast India, and its astrobiological implications

For the foreseeable future, the search for evidence of past life in rocks acquired from other planets will be constrained by the amount of sample available and by the fidelity of preservation of any fossils present. What amount of rock is needed to establish the existence of past life? To address this question, we studied a minute amount of rock collected from cherty dolomites of the Proterozoic Buxa Formation in the metamorphically altered tectonically active northeastern Himalaya. In particular, we investigated 2 small petrographic thin sections-one from each of 2 bedded chert horizons exposed in the Ranjit River stratigraphic section northwest of Rishi, Sikkim, India-that together comprise an area of approximately 5 cm(2) (about the size of a US postage stamp) and have a total rock weight of approximately 0.1 g. Optical microscopy, confocal laser scanning microscopy, and Raman spectroscopy and imagery demonstrate that each of the thin sections contains a rich assemblage of 3-dimensionally permineralized organic-walled microfossils. This study, the first report of Proterozoic microfossils in units of the Ranjit tectonic window, demonstrates that firm evidence of early life can be adduced from even a minuscule amount of fossil-bearing ancient rock.     

Was there a late Archean biospheric explosion?

There is a growing body of evidence which suggests that the evolution of the planet drives the evolution of the biosphere. There have been 2 significant stages in Earth history when atmospheric oxygen levels rose rapidly, and both appear to be associated with supercontinent cycles. The earlier biospheric event, which extends across the Archean-Proterozoic boundary (ca. 3.0-2.2 Ga), has received little attention and is the focus of this study. Recent work on the Pilbara Craton of Western Australia has shown that concretion formed by microbial activity during the diagenesis of these sediments are absent from early Archean sediments but abundant in late Archean and early Paleoproterozoic successions of the Hamersley Basin, appearing abruptly in sedimentary rocks younger than 2.7 Ga. This study suggests that their internal architecture may have been defined by the diffusion of humic acids and the formation of polymer gels during diagenesis. The data imply that the biosphere expanded suddenly shortly after 3.0 Ga and may have begun to raise the oxygen levels of the oceanic water column earlier than thought-possibly as much as 300 my earlier.     

Does the centre of mass remain stable during complex human postural equilibrium tasks in weightlessness?

In normal gravity conditions the execution of voluntary movement involves the displacement of body segments as well as the maintenance of a stable reference value for equilibrium control. It has been suggested that centre of mass (CM) projection within the supporting base (BS) is the stabilised reference for voluntary action, and is conserved in weightlessness. The purpose of this study was to determine if the CM is stabilised during whole body reaching movements executed in weightlessness. The reaching task was conducted by two cosmonauts aboard the Russian orbital station MIR, during the Franco-Russian mission ALTAIR, 1993. Movements of reflective markers were recorded using a videocamera, successive images being reconstructed by computer every 40ms. The position of the CM, ankle joint torques and shank and thigh angles were computed for each subject pre- in- and post-flight using a 7-link mathematical model. Results showed that both cosmonauts adopted a backward leaning posture prior to reaching movements. Inflight, the CM was displaced throughout values in the horizontal axis three times those of pre-flight measures. In addition, ankle dorsi flexor torques inflight increased to values double those of pre- and post-flight tests. This study concluded that CM displacements do not remain stable during complex postural equilibrium tasks executed in weightlessness. Furthermore, in the absence of gravity, subjects changed their strategy for producing ankle torque during spaceflight from a forward to a backward leaning posture.     

基于卷积神经网络技术的直升机旋翼谱识别方法

针对直升机雷达回波在时频二维分布图上的分布特性,提出一种基于卷积神经网络技术的直升机旋翼谱识别方法,实现了直升机旋翼谱与其他类型目标的区分,从而有效识别直升机。当雷达工作在低重复频率(LPRF)时,直升机旋翼回波在时频分布图上呈现明显的扩展特征。通过仿真与实测数据分析,表明该特征与其他目标回波在频率维分布特性存在较大差异。利用卷积神经网络中的卷积核技术,将实测数据与卷积核矩阵进行二维卷积运算,依据输出矩阵实现了直升机旋翼谱的识别。利用实际采集的直升机回波数据进行验证,证明该方法是有效的,可应用于各种采用脉冲多普勒工作体制的雷达系统。     

深空自主导航系统的可观性分析

研究了深空自主导航系统的可观性分析。建立了自主导航系统的观测模型，并提出了一种基于位置确定分析和可观性秩条件的导航系统可观性分析方法；该方法克服了直接利用多个导航目标的视线方向、视线角、夹角和图像信息等非线性观测量进行导航系统可观性分析的困难。针对观测矩阵的秩无法通过表达式直接确定的问题。给出了基于观测矩阵奇异值分解的导航系统可观性分析方法，并用来分析了几种观测模式对应的导航系统的可观性和轨道参数可观度。可以为在不同轨道段组合不同的敏感器提高轨道的估计精度提供参考。     

Biogenicity of morphologically diverse carbonaceous microstructures from the ca. 3400 Ma Strelley pool formation, in the Pilbara Craton, Western Australia

Morphologically diverse structures that may constitute organic microfossils are reported from three remote and widely separated localities assigned to the ca. 3400?Ma Strelley Pool Formation in the Pilbara Craton, Western Australia. These localities include the Panorama, Warralong, and Goldsworthy greenstone belts. From the Panorama greenstone belt, large (> 40?μm) lenticular to spindle-like structures, spheroidal structures, and mat-forming thread-like structures are found. Similar assemblages of carbonaceous structures have been identified from the Warralong and Goldsworthy greenstone belts, though these assemblages lack the thread-like structures but contain film-like structures. All structures are syngenetic with their host sedimentary black chert, which is associated with stromatolites and evaporites. The host chert is considered to have been deposited in a shallow water environment. Rigorous assessment of biogenicity (considering composition, size range, abundance, taphonomic features, and spatial distributions) suggests that cluster-forming small (<15 μm) spheroids, lenticular to spindle-like structures, and film-like structures with small spheroids are probable microfossils. Thread-like structures are more likely fossilized fibrils of biofilm, rather than microfossils. The biogenicity of solitary large (>15?μm) spheroids and simple film-like structures is less certain. Although further investigations are required to confirm the biogenicity of carbonaceous structures from the Strelley Pool Formation, this study presents evidence for the existence of morphologically complex and large microfossils at 3400?Ma in the Pilbara Craton, which can be correlated to the contemporaneous, possible microfossils reported from South Africa. Although there is still much to be learned, they should provide us with new insights into the early evolution of life and shallow water ecosystems.     

Mass-independent fractionation of sulfur isotopes in Archean sediments: strong evidence for an anoxic Archean atmosphere

Mass-independent fractionation (MIF) of sulfur isotopes has been reported in sediments of Archean and Early Proterozoic Age (> 2.3 Ga) but not in younger rocks. The only fractionation mechanism that is consistent with the data on all four sulfur isotopes involves atmospheric photochemical reactions such as SO2 photolysis. We have used a one-dimensional photochemical model to investigate how the isotopic fractionation produced during SO2 photolysis would have been transferred to other gaseous and particulate sulfur-bearing species in both low-O2 and high-O2 atmospheres. We show that in atmospheres with O2 concentrations < 10(-5) times the present atmospheric level (PAL), sulfur would have been removed from the atmosphere in a variety of different oxidation states, each of which would have had its own distinct isotopic signature. By contrast, in atmospheres with O2 concentrations > or = 10(-5) PAL, all sulfur-bearing species would have passed through the oceanic sulfate reservoir before being incorporated into sediments, so any signature of MIF would have been lost. We conclude that the atmospheric O2 concentration must have been < 10(-5) PAL prior to 2.3 Ga.     

同步与数据缓冲系统的同步定时器

同步定时器是ＣＤＡＳＳ／ＤＢ系统的重要部件。它用高精度数字锁相环，精确地恢复地球同步气象卫星采集的原始云图数据的同步基准信息。数字锁相环由用高速器件组成的相位比较器和用计算机软件实现的滤波器构成，采用标准频率计数方式，完成对模拟太阳（ＳＰ）和数字太阳（ＳＳＤ）的锁相及卫星上时钟频率测量等任务。     

Body orientation and center of mass control in microgravity

The control of the body orientation and the center of mass position with respect to the feet was investigated under normo- and microgravity (space flight Altair), during erect posture and at the end of a forward or backward upper trunk movement.

It was observed that during erect posture, the trunk orientation with respect to the vertical was inclined some 6 ° forward in both subjects under microgravity, whereas it was vertical or slightly backward oriented under normogravity. Under microgravity, on the contrary, the initial position CM changed either backwards or forwards. This result suggests that the inclined trunk posture might be due to misevaluating the vertically under microgravity and that different control mechanisms are involved in orienting the trunk and placing the CM.

It was also noted that the final position of the CM at the end of the movement did not differ markedly between microgravity and normogravity. This result suggests that the kinematic synergies which stabilize the CM during uppertrunk movements may result from an automatic central control which is independent from the gravity constraints.     

Mission design and analysis of European astrophysics missions orbiting libration points

The main characteristics of the trajectory design of space observatory missions in the Earth–Sun libration point region is highlighted, based on experiences gained in work performed by the authors on ESA missions. Free transfers always lead to large-amplitude orbits around L₂, their properties (amplitudes, phases, non-linear behaviour) are related to the conditions at perigee. Launch scenarios with different degrees of freedom in the perigee geometry and different strategies of sharing the apogee raising between launcher and spacecraft propulsion for Soyuz (with circular parking orbit or direct injection) and Ariane 5 launches from French Guiana will be discussed. Besides the orbit selection and transfer analysis, an important aspect of libration missions is the maintenance of the operational orbit. For some missions it is required to maximise the time between maintenance manoeuvres, and for some the thrust authority is limited. In both cases the exponential nature of the state transition matrix has to be considered. If the equivalent velocity error in the unstable direction becomes too large, the orbit can become unrecoverable, leading to a departure from the environment of the Lagrange point within a few months.     

分离式垂直方向充退磁线圈数值仿真研究

针对航天器充退磁试验对简便快捷的垂直方向充退磁设备的需求,文章提出一种分离式垂直方向充退磁线圈结构,避免了安装过程中复杂的接插工序,可有效缩短试验时间。通过理论计算说明了分离式充退磁线圈结构与现有设备的等效性,利用磁仿真平台建立了线圈结构模型,并对其充退磁特性以及由于结构改变带来的磁场均匀性误差进行了仿真分析,充分验证了理论计算的正确性。     

巡航导弹突防中的脉冲多普勒引信干扰技术研究

空空导弹拦截是巡航导弹突防中面临的较大威胁,将空空导弹引信干扰技术应用于巡航导弹的突防。分析了空空导弹脉冲多普勒引信的工作原理,将引信干扰技术分为干扰引信＂早炸＂和干扰引信＂瞎火＂。根据脉冲多普勒引信干扰技术的特点,经比较,选用了干扰引信＂瞎火＂方式。     

Challenges for coring deep permafrost on Earth and Mars

A scientific drilling expedition to the High Lake region of Nunavut, Canada, was recently completed with the goals of collecting samples and delineating gradients in salinity, gas composition, pH, pe, and microbial abundance in a 400 m thick permafrost zone and accessing the underlying pristine subpermafrost brine. With a triple-barrel wireline tool and the use of stringent quality assurance and quality control (QA/QC) protocols, 200 m of frozen, Archean, mafic volcanic rock was collected from the lower boundary that separates the permafrost layer and subpermafrost saline water. Hot water was used to remove cuttings and prevent the drill rods from freezing in place. No cryopegs were detected during penetration through the permafrost. Coring stopped at the 535 m depth, and the drill water was bailed from the hole while saline water replaced it. Within 24 hours, the borehole iced closed at 125 m depth due to vapor condensation from atmospheric moisture and, initially, warm water leaking through the casing, which blocked further access. Preliminary data suggest that the recovered cores contain viable anaerobic microorganisms that are not contaminants even though isotopic analyses of the saline borehole water suggests that it is a residue of the drilling brine used to remove the ice from the upper, older portion of the borehole. Any proposed coring mission to Mars that seeks to access subpermafrost brine will not only require borehole stability but also a means by which to generate substantial heating along the borehole string to prevent closure of the borehole from condensation of water vapor generated by drilling.