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41.
Kevin D. Grossman Tamil S. Sakthivel Laurent Sibille James G. Mantovani Sudipta Seal 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2019,63(7):2212-2219
Ferrosilicon is a primary metallic alloy produced during the reduction of metal oxides contained in lunar and Martian regolith by a variety of techniques. This study examines the usefulness of ferrosilicon as a candidate feedstock material for wire-based 3D printers designed for in-space manufacturing. Alloys of composition ranging from pure iron to 12?wt% Si were synthesized and their electrical and mechanical properties characterized. The melts were cast into rods for mechanical testing to determine ultimate strength and ductility. It was determined that the samples above 3?wt% Si were too brittle to be pulled into wire and ruptured at low strain values. The 3?wt% Si sample and iron had comparable mechanical properties relative to samples of higher silicon content but with differences in ductility and ultimate strength. Microstructure and compositional studies revealed the differences between the ductile and brittle samples as being the complete ferrite phase presence on the iron and low-Si content samples. This study establishes an upper limit on the Si content at 3?wt% in ferrosilicon materials to be used in wire feedstock in additive manufacturing for in-space applications. 相似文献
42.
Ralph D. Lorenz Damhnait Gleeson Olga Prieto-Ballesteros Felipe Gomez Kevin Hand Sergey Bulat 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2011
This paper reviews the utility of analog environments in preparations for a Europa lander mission. Such analogs are useful in the demonstration and rehearsal of engineering functions such as sample acquisition from an icy surface, as well as in the exercise of the scientific protocols needed to identify organic, inorganic and possible biological impurities in ice. Particular attention is drawn to Antarctic and Arctic analog sites where progress in these latter areas has been significant in recent years. 相似文献
43.
Biogenic stromatolites are sources of significant information on the evolution of microbial life. Despite their evolutionary significance, little is known about the mechanisms of osmoadaptation by microorganisms that comprise living stromatolites thriving in hypersaline environments. Osmoadaptive strategies for Halococcus hamelinensis, a novel halophilic archaeon recently isolated from living stromatolites in the hypersaline reaches of Shark Bay, were thus a particular interest in this study. To investigate the possibility of "salt-in-cytoplasm"-associated osmoadaptation for this archaeon, flame photometry studies were performed. From the results, it was evident that this halophilic archaeon did not accumulate intracellular K(+) ions when cells were exposed to either osmotic shock or conditions with gradual increments in salinity. These results were further supported by polymerase chain reaction (PCR) analyses where there was no evidence for the existence of homologous genes to an ATP-driven, high-affinity potassium uptake system in Halococcus hamelinensis. To identify an alternative salt adaptation mechanism associated with accumulation of compatible solutes for this archaeon, (1)H nuclear magnetic resonance (NMR) spectroscopy experiments were carried out. Results indicate that glycine betaine, trehalose, and glutamate are solutes likely to be involved in osmoregulation in this archeaon. Subsequent (1)H NMR analysis of cell extracts from this microorganism grown under various NaCl concentrations revealed that intracellular levels of glycine betaine increased with increasing concentrations of NaCl. This behavior of increasing glycine betaine concentration with increasing external NaCl is consistent with its identity as an osmolyte. In contrast, intracellular levels of trehalose were decreased in high concentrations of NaCl. This provides evidence that compatible solute accumulation appears to be the preferential salt regulation mechanism for this haloarchaeon, in contrast to the salt-in-cytoplasm strategy employed by many other halophilic archaea. 相似文献
44.
Reed I.S. Gau Y.L. Truong T.K. 《IEEE transactions on aerospace and electronic systems》1998,34(3):722-735
The algorithm presented here provides both a constant false-alarm rate (CFAR) detection and a maximum likelihood (ML) Doppler-bearing estimator of a target in a background of unknown Gaussian noise. A target is detected, and its parameters estimated within each range gate by evaluating a statistical test for each Doppler-angle cell and by selecting the cell with maximum output and finally comparing it with a threshold. Its CFAR performance is analyzed by the use of the sample matrix inversion (SMI) method and is evaluated in the cases of a fully adaptive space-time adaptive processing (STAP) and two partially adaptive STAPs. The performances of these criteria show that the probability of detection is a function only of the sample size K used to estimate the covariance matrix and a generalized signal-to-noise ratio. The choice of the number K is a tradeoff between performance and computational complexity. The performance curves demonstrate that the finer the resolution is, the poorer the detection capability. That means that one can trade off the accuracy of ML estimation with the performance of the CFAR detection criterion 相似文献
45.
Euan Nisbet Kevin Zahnle M. V. Gerasimov Jörn Helbert Ralf Jaumann Beda A. Hofmann Karim Benzerara Frances Westall 《Space Science Reviews》2007,129(1-3):79-121
The factors that create a habitable planet are considered at all scales, from planetary inventories to micro-habitats in soft
sediments and intangibles such as habitat linkage. The possibility of habitability first comes about during accretion, as
a product of the processes of impact and volatile inventory history. To create habitability water is essential, not only for
life but to aid the continual tectonic reworking and erosion that supply key redox contrasts and biochemical substrates to
sustain habitability. Mud or soft sediment may be a biochemical prerequisite, to provide accessible substrate and protection.
Once life begins, the habitat is widened by the activity of life, both by its management of the greenhouse and by partitioning
reductants (e.g. dead organic matter) and oxidants (including waste products). Potential Martian habitats are discussed: by
comparison with Earth there are many potential environmental settings on Mars in which life may once have occurred, or may
even continue to exist. The long-term evolution of habitability in the Solar System is considered. 相似文献
46.
T Sornchamni G N Jovanovic B P Reed J E Atwater J R Akse R R Wheeler 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2004,34(7):1494-1498
The conversion of solid waste into useful resources in support of long duration manned missions in space presents serious technological challenges. Several technologies, including supercritical water oxidation, microwave powered combustion and fluidized bed incineration, have been tested for the conversion of solid waste. However, none of these technologies are compatible with microgravity or hypogravity operating conditions. In this paper, we present the gradient magnetically assisted fluidized bed (G-MAFB) as a promising operating platform for fluidized bed operations in the space environment. Our experimental and theoretical work has resulted in both the development of a theoretical model based on fundamental principles for the design of the G-MAFB, and also the practical implementation of the G-MAFB in the filtration and destruction of solid biomass waste particles from liquid streams. 相似文献
47.
Kevin Hurley 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2004,34(12):2734-2738
Swift is a first-of-its-kind multiwavelength transient observatory for γ-ray burst astronomy. It has the optimum capabilities for the next breakthroughs in determining the origin of γ-ray bursts and their afterglows, as well as for using bursts to probe the early Universe. Swift will also monitor the soft gamma repeaters and perform the first sensitive hard X-ray survey of the sky. The mission is being developed by an international collaboration and consists of three instruments, the Burst Alert Telescope (BAT), the X-ray Telescope (XRT), and the Ultraviolet and Optical Telescope (UVOT). The BAT, a wide-field γ-ray detector, will detect >100 γ-ray bursts per year with a sensitivity 5× that of BATSE. The sensitive narrow-field XRT and UVOT will be autonomously slewed to the burst location within 20–70 s to determine 0.3–5.0″ positions and perform optical, UV, and X-ray spectrophotometry. Strong education/public outreach and follow-up programs will help to engage the public and the astronomical community. Swift launch is planned for late 2004. 相似文献
48.
Changed political objectives, straitened economic circumstances and an altered balance of capability and expertise in space endeavours have together produced more discussion of the need for international cooperation than ever before, but the meaning of the term has subtly shifted. Insisting on US ‘leadership’ is self-defeating; what is instead firmly desired by the USA's potential partners is a balanced relationship in which each nation makes an identifiable contribution and takes the lead in at least one of a package of projects. If this is going to happen, there must be an international forum or framework in which projects can be discussed and agreed. This in turn requires initiative at governmental level. 相似文献
49.
Clouds and Hazes of Venus 总被引:1,自引:0,他引:1
Dmitrij V. Titov Nikolay I. Ignatiev Kevin McGouldrick Valérie Wilquet Colin F. Wilson 《Space Science Reviews》2018,214(8):126
More than three decades have passed since the publication of the last review of the Venus clouds and hazes. The paper published in 1983 in the Venus book summarized the discoveries and findings of the US Pioneer Venus and a series of Soviet Venera spacecraft (Esposito et al. in Venus, p. 484, 1983). Due to the emphasis on in-situ investigations from descent probes, those missions established the basic features of the Venus cloud system, its vertical structure, composition and microphysical properties. Since then, significant progress in understanding of the Venus clouds has been achieved due to exploitation of new observation techniques onboard Galileo and Messenger flyby spacecraft and Venus Express and Akatsuki orbiters. They included detailed investigation of the mesospheric hazes in solar and stellar occultation geometry applied in the broad spectral range from UV to thermal IR. Imaging spectroscopy in the near-IR transparency “windows” on the night side opened a new and very effective way of sounding the deep atmosphere. This technique together with near-simultaneous UV imaging enabled comprehensive study of the cloud morphology from the cloud top to its deep layers. Venus Express operated from April 2006 until December 2014 and provided a continuous data set characterizing Venus clouds and hazes over a time span of almost 14 Venus years thus enabling a detailed study of temporal and spatial variability. The polar orbit of Venus Express allowed complete latitudinal coverage. These studies are being complemented by JAXA Akatsuki orbiter that began observations in May 2016. This paper reviews the current status of our knowledge of the Venus cloud system focusing mainly on the results acquired after the Venera, Pioneer Venus and Vega missions. 相似文献
50.
Edwards Christopher S. Christensen Philip R. Mehall Greg L. Anwar Saadat Tunaiji Eman Al Badri Khalid Bowles Heather Chase Stillman Farkas Zoltan Fisher Tara Janiczek John Kubik Ian Harris-Laurila Kelly Holmes Andrew Lazbin Igor Madril Edgar McAdam Mark Miner Mark O’Donnell William Ortiz Carlos Pelham Daniel Patel Mehul Powell Kathryn Shamordola Ken Tourville Tom Smith Michael D. Smith Nathan Woodward Rob Weintraub Aaron Reed Heather Pilinski Emily B. 《Space Science Reviews》2021,217(7):1-37
Space Science Reviews - Modern observatories have revealed the ubiquitous presence of magnetohydrodynamic waves in the solar corona. The propagating waves (in contrast to the standing waves) are... 相似文献