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501.
Understanding the abiotic fixation of nitrogen and how such fixation can be a supply of prebiotic nitrogen is critical for understanding both the planetary evolution of, and the potential origin of life on, terrestrial planets. As nitrogen is a biochemically essential element, sources of biochemically accessible nitrogen, especially reduced nitrogen, are critical to prebiotic chemistry and the origin of life. Loss of atmospheric nitrogen can result in loss of the ability to sustain liquid water on a planetary surface, which would impact planetary habitability and hydrological processes that shape the surface. It is known that NO can be photochemically converted through a chain of reactions to form nitrate and nitrite, which can be subsequently reduced to ammonia. Here, we show that NO can also be directly reduced, by FeS, to ammonia. In addition to removing nitrogen from the atmosphere, this reaction is particularly important as a source of reduced nitrogen on an early terrestrial planet. By converting NO directly to ammonia in a single step, ammonia is formed with a higher product yield (~50%) than would be possible through the formation of nitrate/nitrite and subsequent conversion to ammonia. In conjunction with the reduction of NO, there is also a catalytic disproportionation at the mineral surface that converts NO to NO? and N?O. The NO? is then converted to ammonia, while the N?O is released back in the gas phase, which provides an abiotic source of nitrous oxide. 相似文献
502.
Microbially induced iron precipitation associated with a neutrophilic spring at Borra Caves, Vishakhapatnam, India 总被引:1,自引:0,他引:1
The present investigation uncovers various pieces of evidence for the possible biologically induced mineralization in iron mats associated with a pH-neutral spring in the Borra caves, Vishakhapatnam, India. Electron microscopy [scanning electron microscopy (SEM) and transmission electron microscopy (TEM)] demonstrated large numbers of (i) hollow tubes (diameter ~1?μm) resembling sheaths of the iron-oxidizing bacteria Leptothrix, (ii) thin (diameter <1?μm) solid fibers of uncertain origin, (iii) nanoscale subspherical to irregularly shaped particles encrusting tubes and fibers, and (iv) aggregates of broken and partially disintegrated sheaths, fibers, and particles embedded in extracellular polymeric substances (EPS) occasionally including microbial cells. X-ray microanalyses by energy dispersive spectroscopy (EDS) revealed that the mat accumulated largely Fe but also smaller amounts of Si and traces of P and Ca. Particles rich in Si and Al (possibly kaolinite) and Ca (carbonate) were also observed. High-resolution TEM/EDS of unstained ultrathin sections suggests that microbial sheaths were highly mineralized by amorphous to cryptocrystalline Fe-rich phases and less frequently by other fine-grained and fibrous authigenic claylike minerals. Total number of microorganisms in the iron mats was 5.8×10(5) cells, g sed(-1) (wet weight). Analysis of the 16S rRNA gene diversity revealed microorganisms assigned to eight different phyla [Proteobacteria (62%), Chloroflexi (8%), Bacteroidetes (7%), Planctomycetes (1%), Actinobacteria (5%), Acidobacteria (6%), Nitrospira (1%), Firmicutes (5%)]. Within the Proteobacteria, Betaproteobacteria was the predominant class, which accounted for 28% of the sequences. Within this class some obvious similarities between the obtained sequences and sequences from other cave systems could be seen, especially sequences affiliated with Leptothrix, Siderooxidans, Crenothrix, Comamonadaceae, Dechloromonas, and many uncultured Betaproteobacteria. Four (4%) of the sequences could not be assigned to phylum level but were affiliating with the candidate division TM7 (2%), candidate division OP11 (1%), and candidate division WWE3 (1%). The results allow us to infer a possible relationship of microbial sheaths, EPS, and the iron precipitates to microbial community diversity in the Borra cave springs. Understanding biogenic iron oxides in caves has important astrobiological applications as it provides a potential tool for the detection of extraterrestrial life. 相似文献
503.
S. Shimada J. Matsumoto A. Sekiyama B. Aosier M. Yokohana 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2012
The objectives of the present study were to develop a new index based on remotely-sensed data for detecting the abundance of grasses in the family Poaceae, which has a high palatability for livestock in Mongolia, and to map the distribution of these grasses in the semi-arid Mongolian steppes. We measured ground-based spectral reflectance of pure plant leaves – including Poaceae grasses – and soils, as well as in-situ in the Mongolian grasslands. The hyper-spectral data, taken by a spectroradiometer, were converted into four multi-spectral bands (i.e., blue, green, red, and NIR) to simulate satellite-based imagery data. In order to magnify the characteristics of the spectral signal of Poaceae, NGBDI (Normalized Green-Blue Difference Index), NGRDI (Normalized Green-Red Difference Index), NDVI (Normalized Difference Vegetation Index), NNBDI (Normalized NIR-Blue Difference Index) were calculated from the four multi-spectral reflectance values. Poaceae Abundance Index (PAI) was derived by combining these four normalized difference indices. PAI was found out to be a good indicator to discriminate Poaceae grass from the other plant spectral data. 相似文献
504.
Removing orbital debris with lasers 总被引:2,自引:0,他引:2
Claude R. Phipps Kevin L. Baker Stephen B. Libby Duane A. Liedahl Scot S. Olivier Lyn D. Pleasance Alexander Rubenchik James E. Trebes E. Victor George Bogdan Marcovici James P. Reilly Michael T. Valley 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2012
Orbital debris in low Earth orbit (LEO) are now sufficiently dense that the use of LEO space is threatened by runaway collision cascading. A problem predicted more than thirty years ago, the threat from debris larger than about 1 cm demands serious attention. A promising proposed solution uses a high power pulsed laser system on the Earth to make plasma jets on the objects, slowing them slightly, and causing them to re-enter and burn up in the atmosphere. In this paper, we reassess this approach in light of recent advances in low-cost, light-weight modular design for large mirrors, calculations of laser-induced orbit changes and in design of repetitive, multi-kilojoules lasers, that build on inertial fusion research. These advances now suggest that laser orbital debris removal (LODR) is the most cost-effective way to mitigate the debris problem. No other solutions have been proposed that address the whole problem of large and small debris. A LODR system will have multiple uses beyond debris removal. International cooperation will be essential for building and operating such a system. 相似文献
505.
We present the results of a cross-correlation analysis made on the basis of Spearman’s rank correlation method. The quantities
to correlate are daily values of the fluence of energetic electrons at a geosynchronous orbit, intensities of ground and interplanetary
ultra-low-frequency (ULF) oscillations in the Pc5 range, and parameters of the solar wind. The period under analysis is the
23rd cycle of solar activity, 1996–2006. Daily (from 6 h to 18 h of LT) magnetic data at two diametrically opposite observatories
of the Intermagnet network are taken as ground-based measurements. The fluxes of electrons with energies higher than 2 MeV
were measured by the geosynchronous GOES satellites. The data of magnetometers and plasma instruments installed on ACE and WIND spacecraft were used for analysis of the solar wind parameters and of the oscillations of the interplanetary magnetic field
(IMF). Some results elucidating the role played by interplanetary ULF waves in the processes of generation of magneospheric
oscillations and acceleration of energetic electrons are obtained. Among them are (i) high and stable correlation of ground
ULF oscillations with waves in the solar wind; (ii) closer link of mean daily amplitudes of both interplanetary and ground
oscillations with ‘tomorrow’ values of the solar wind velocity than with current values; and (iii) correlation of the intensity
of ULF waves in the solar wind, normalized to the IMF magnitude, with fluxes of relativistic electrons in the magnetosphere. 相似文献
506.
With the growing need for monitoring and awareness of all the objects in space (including debris) now recognized, the types of effort required towards this end are discussed, with the emphasis on European activities. A number of European documents acknowledging the problem are cited and initiatives to promote space situational awareness (SSA) are examined. While there is currently no provision in the EU budget beyond 2013 for protecting ground and space assets from space environmental threats, an encouraging degree of bilateral cooperation between member states suggests that an SSA capability is emerging in Europe. 相似文献
507.
B. Bidaine R. Warnant 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2010
The modelling of the total electron content (TEC) plays an important role in global navigation satellite systems (GNSS) accuracy, especially for single-frequency receivers, the most common ones constituting the mass market. For the latter and in the framework of Galileo, the NeQuick model has been chosen for correcting the ionospheric error contribution and will be integrated into a global algorithm providing the users with daily updated information. 相似文献
508.
S.V. Veretenenko V.A. DergachevP.B. Dmitriyev 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2010
Long-term changes of the Arctic frontal zone characteristics near the south-eastern coasts of Greenland were considered, the NCEP/NCAR reanalysis data being used. It was found that in the cold half of the year the temperature gradients in the layer 1000–500 hPa in the region under study reveal strong ∼10-yr and ∼22-yr periodicities that seem to be related to solar activity cycles. The results obtained suggest the influence of solar activity and cosmic ray variations on the structure of the temperature field of the troposphere resulting in the changes of the temperature contrasts in the Arctic frontal zone that, in turn, may affect the intensity of cyclogenesis at middle latitudes. The detected effects seem to indicate an important part of frontal zones in the mechanism of solar activity and cosmic ray variation influence on the development of extratropical baric systems. It is suggested that the variations of the temperature gradients revealed in the Arctic frontal zone are due to the radiative forcing of cloudiness changes which may be associated with geomagnetic activity and cosmic ray variations. 相似文献
509.
Michalski JR Jean-PierreBibring Poulet F Loizeau D Mangold N Dobrea EN Bishop JL Wray JJ McKeown NK Parente M Hauber E Altieri F Carrozzo FG Niles PB 《Astrobiology》2010,10(7):687-703
The primary objective of NASA's Mars Science Laboratory (MSL) mission, which will launch in 2011, is to characterize the habitability of a site on Mars through detailed analyses of the composition and geological context of surface materials. Within the framework of established mission goals, we have evaluated the value of a possible landing site in the Mawrth Vallis region of Mars that is targeted directly on some of the most geologically and astrobiologically enticing materials in the Solar System. The area around Mawrth Vallis contains a vast (>1?×?10? km2) deposit of phyllosilicate-rich, ancient, layered rocks. A thick (>150?m) stratigraphic section that exhibits spectral evidence for nontronite, montmorillonite, amorphous silica, kaolinite, saponite, other smectite clay minerals, ferrous mica, and sulfate minerals indicates a rich geological history that may have included multiple aqueous environments. Because phyllosilicates are strong indicators of ancient aqueous activity, and the preservation potential of biosignatures within sedimentary clay deposits is high, martian phyllosilicate deposits are desirable astrobiological targets. The proposed MSL landing site at Mawrth Vallis is located directly on the largest and most phyllosilicate-rich deposit on Mars and is therefore an excellent place to explore for evidence of life or habitability. 相似文献
510.
Hasan Yildiz Ole B. Andersen Mehmet Simav Bahadir Aktug Soner Ozdemir 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2013
The differences between coastal altimetry and sea level time series of tide gauges in between March 1993 and December 2009 are used to estimate the rates of vertical land motion at three tide gauge locations along the southwestern coasts of Turkey. The CTOH/LEGOS along-track coastal altimetry retrieves altimetric sea level anomalies closer to the coast than the standard along-track altimetry products. However, the use of altimetry very close to the coast is not found to improve the results. On the contrary, the gridded and interpolated AVISO merged product exhibits the best agreement with tide gauge data as it provides the smoothest variability both in space and time compared with along track altimetry data. The Antalya gauge to the south (in the Mediterranean Sea) and the Mentes/Izmir gauge to the west (in the Aegean Sea) both show subsidence while the Bodrum tide gauge to the south (in the Aegean Sea) shows no significant vertical land motion. The results are compared and assessed with three independent geophysical vertical land motion estimates like from GPS. The GIA effect in the region is negligible. The VLM estimates from altimetry and tide gauge data are in good agreement both with GPS derived vertical velocity estimates and those inferred from geological and archaeological investigations. 相似文献