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21.
22.
R. H. D. Corbet A. P. Smale J. W. Menzies G. Branduardi-Raymont P. A. Charles K. O. Mason 《Space Science Reviews》1985,40(3-4):415-419
We present optical spectroscopy and photometry of 4U 1258-61 obtained over the course of six years. Evidence for the evolution of a circumstellar envelope throughout the course of the observations is presented. 相似文献
23.
ABSTRACTShadows have long been a challenging topic for computer vision. This challenge is made even harder when we assume that the camera is moving, as many existing shadow detection techniques require the creation and maintenance of a background model. This article explores the problem of shadow modelling from a moving viewpoint (assumed to be a robotic platform) through comparing shadow-variant and shadow-invariant image features — primarily color, texture and edge-based features. These features are then embedded in a segmentation pipeline that provides predictions on shadow status, using minimal temporal context. We also release a public dataset of shadow-related image sequences, to help other researchers further develop shadow detection methods and to enable benchmarking of techniques. 相似文献
24.
The technological advances of the Space Age have enabled us to project our senses through complex instruments to the edge of the Solar System and beyond. The link back to Earth by the communication channel has provided us with a wealth of information. The vast improvement in communication capability, by a factor of 1018, from the launching of the first earth satellites to the capacity of the Voyager telecommunications link across the Solar System, is symbolic of both our technical prowess and our cultural development. The combination of data rate and extreme distance at the Voyager 2 encounters with Uranus and Neptune in 1986 and 1989 will require the ground network to perform an engineering feat of unequalled magnitude. This paper describes the engineering challenge of communicating with spacecraft at the limits of the Solar System and the engineering responses to that challenge. 相似文献
25.
Removal of the mechanical pressure gradient on the soles leads to physiological adaptations that ultimately result in neuromotor degradation during spaceflight. We propose that mechanical stimulation of the soles serves to partially restore the afference associated with bipedal loading and assists in attenuating the negative neuromotor consequences of spaceflight. A dynamic foot stimulus device was used to stimulate the soles in a variety of conditions with different stimulation locations, stimulation patterns and muscle spindle input. Surface electromyography revealed the lateral side of the sole elicited the greatest neuromuscular response in ankle musculature, followed by the medial side, then the heel. These responses were modified by preceding stimulation. Neuromuscular responses were also influenced by the level of muscle spindle input. These results provide important information that can be used to guide the development of a “passive” countermeasure that relies on sole stimulation and can supplement existing exercise protocols during spaceflight. 相似文献
26.
H K Charles T J Beck H S Feldmesser T C Magee T S Spisz V L Pisacane 《Acta Astronautica》2001,49(3-10):447-450
An advanced, multiple projection, dual energy x-ray absorptiometry (AMPDXA) scanner system is under development. The AMPDXA is designed to make precision bone and muscle loss measurements necessary to determine the deleterious effects of microgravity on astronauts as well as develop countermeasures to stem their bone and muscle loss. To date, a full size test system has been developed to verify principles and the results of computer simulations. Results indicate that accurate predictions of bone mechanical properties can be determined from as few as three projections, while more projections are needed for a complete, three-dimensional reconstruction. 相似文献
27.
Physiologic and metabolic responses of wheat seedlings to elevated and super-elevated carbon dioxide
Lanfang H. Levine Hirokazu Kasahara Joachim Kopka Alexander Erban Ines Fehrl Fatma Kaplan Wei Zhao Ramon C. Littell Charles Guy Raymond Wheeler John Sager Aaron Mills Howard G. Levine 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2008
The metabolic consequence of suboptimal (400 μmol mol−1 or ppm), near-optimal (1500 ppm) and supra-optimal (10,000 ppm) atmospheric carbon dioxide concentrations [CO2] was investigated in an attempt to reveal plausible underlying mechanisms for the differential physiological and developmental responses to increasing [CO2]. Both non-targeted and targeted metabolite profiling by GC–MS and LC–MS were employed to examine primary and secondary metabolites in wheat (Triticum aestivum, cv Yocoro rojo) continuously exposed to these [CO2] levels for 14, 21 and 28 days. Metabolite profile was altered by both [CO2] and physiological age. In general, plants grown under high [CO2] exhibited a metabolite profile characteristic of older plants under ambient CO2. Elevated [CO2] resulted in higher levels of phosphorylated sugar intermediates, though no clear trend in the content of reducing sugars was observed. Transient starch content was enhanced by increasing [CO2] to a much greater extent at 10,000 ppm CO2 than at 1500 ppm CO2. The percentage increase of starch content resulting from CO2 enrichment declined as plants develope. In contrast, elevated [CO2] promoted the accumulation of secondary metabolites (flavonoids) progressively to a greater extent as plants became mature. Elevated [CO2] to 1500 ppm induced a higher initial growth rate, while super-elevated [CO2] appeared to negate such initial growth promotion. However, after 4 weeks, there was no difference in vegetative growth between 1500 and 10,000 ppm CO2-grown plants, both elevated CO2 levels resulted in an overall 25% increase in biomass over the control plants. More interestingly, elevated atmospheric [CO2] reduced evapotranspiration rate (ET), but further increase to the supra-optimal level resulted in increased ET (a reversed trend), i.e. ET at 1500 ppm < ET at 10,000 ppm < ET at 400 ppm. The differential effect of elevated and super-elevated CO2 on plants was further reflected in the nitrogen dynamics. These results provide the potential metabolic basis for the differential productivity and stomatal function of plants grown under elevated and super-elevated CO2 levels. 相似文献
28.
Over 200 school children in eight schools in the east of England were surveyed to determine their interest in space exploration and awareness of current space activities. Of those surveyed, 33% were interested in space to ‘discover a new planet’, and 24% to find life on another planet. When asked to list space exploration organisations 77% listed NASA. Six of those surveyed listed ESA (<0.5%). The data bring starkly to light, despite the Huygens landing on Titan and Mars Express, the lack of awareness of the existence of ESA among a new generation of European school children. These data suggest that further surveys are merited to determine the factors that influence interest in space sciences and related disciplines among school children, and the source of their information. 相似文献
29.
Sounding rocket experiment of bare electrodynamic tether system 总被引:1,自引:0,他引:1
Hironori A. Fujii Takeo Watanabe Hirohisa Kojima Koh-Ichiro Oyama Tairo Kusagaya Yoshiki Yamagiwa Hirotaka Ohtsu Mengu Cho Susumu Sasaki Koji Tanaka John Williams Binyamin Rubin Charles Les Johnson George Khazanov Juan R. Sanmartin Jean-Pierre Lebreton Erick J. van der Heide Michiel Kruijff Fabio De Pascal Pavel M. Trivailo 《Acta Astronautica》2009,64(2-3):313-324
An overview of a sounding rocket, S-520-25th, project on space tether technology experiment is presented. The project is prepared by an international research group consisting of Japanese, European, American, and Australian researchers. The sounding rocket will be assembled by the ISAS/JAXA and will be launched in the summer of 2009. The sounding rocket mission includes two engineering experiments and two scientific experiments. These experiments consist of the deployment of bare electrodynamic tape tether in space, a quick ignition test of hollow cathode system in space, the demonstration of bare electrodynamic tether system in space, and the test of the OML (orbital-motion-limit) current collection theory. 相似文献
30.
Icelandic streams with mean annual temperatures of less than 5 °C, which receive the cationic products of basaltic rock weathering, were found to host mats of iron-cycling microorganisms. We investigated two representative sites. Iron-oxidizing Gallionella and iron-reducing Geobacter species were present. The mats host a high bacterial diversity as determined by culture-independent methods. β-Proteobacteria, Actinobacteria, α-Proteobacteria, and Bacteroidetes were abundant microbial taxa. The mat contained a high number of phototroph sequences. The carbon compounds in the mat displayed broad G and D bands with Raman spectroscopy. This signature becomes incorporated into the weathered oxidized surface layer of the basaltic rocks and was observed on rocks that no longer host mats. The presence of iron-oxidizing taxa in the stream microbial mats, and the lack of them in previously studied volcanic rocks in Iceland that have intermittently been exposed to surface water flows, can be explained by the kinetic limitations to the extraction of reduced iron from rocks. This type of ecosystem illustrates key factors that control the distribution of chemolithotrophs in cold volcanic environments. The data show that one promising sample type for which the hypothesis of the existence of past life on Mars can be tested is the surface of volcanic rocks that, previously, were situated within channels carved by flowing water. Our results also show that the carbonaceous signatures of life, if life had occurred, could be found in or on these rocks. 相似文献