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601.
The SOHO Solar EUV Monitor has been in operation since December 1995 onboard the SOHO spacecraft. This instrument is a highly stable transmission grating solar extreme ultraviolet spectrometer. It has made nearly continuous full disk solar irradiance measurements both within an 8 nm bandpass centered at 30.4 nm and throughout the 0.1 to 50 nm solar flux region since launch. The 30.4 nm flux, the 0.1 to 50 nm flux and the extracted soft X-ray (0.1 to 5 nm) flux are presented and compared with the behavior of solar proxies.  相似文献   
602.
    
Currently fielded embedded information systems face readiness challenges imposed by evolving missions and extended service lifespans. The ability to overcome these challenges is constrained by such factors as shrinking budgets, limited computational capacity and diminished manufacturing sources effects that impact both hardware and software options. Wholesale redevelopment is often cost prohibitive, particularly since large portions of embedded applications continue to fulfil mission requirements. Solutions must preserve prior investments while providing efficient pathways for continued technology refresh. A technology solution for affordable modernization of legacy system software is being development. The Embedded Information System Re-engineering (EISR) project is developing an automation-assisted JOVIAL-to-C re-engineering capability that permits simultaneous modernization of both the structure and source language of legacy embedded applications. Engineers will be able to apply the proven labor-saving visualization and analysis features of modern CASE tools to legacy JOVIAL applications. EISR will thus allow the DoD to recapture previous investments in proven legacy algorithms and mission capabilities while permitting the full exploitation of COTS economies of scale. This paper describes in brief the goals and objectives of the EISR project, and provides the current status of the EISR capability.  相似文献   
603.
Ionospheric effects of meteorological origin observed by the continuous HF Doppler sounder over the Czech Republic are reported in this paper. We focused on detection of waves of periods 1–10 min. We discuss the influence of dynamics and intensity of active weather systems on the occurrence of short period waves and dependence of the observed ionospheric effects on the height of reflection of the sounding radio wave. We observed 3–5 min waves during a severe weather event in summer and 2.5–4 min waves during a severe weather event in winter. We excluded possible geomagnetic origin of these oscillations by the analysis of fluctuations of the local geomagnetic field. In eight cases of 10, wave activity in the analysed period range was not significantly increased comparing to quiet days. The intensity of weather systems as well as the location of potential sources of waves towards the points of HF Doppler shift observation influence significantly the occurrence of infrasonic waves in the ionosphere. The results in Central Europe differ considerably from those previously obtained in North America. As a possible reason, we discuss different intensity and dynamics of weather systems in both regions.  相似文献   
604.
605.
Abstract Life Investigation For Enceladus (LIFE) presents a low-cost sample return mission to Enceladus, a body with high astrobiological potential. There is ample evidence that liquid water exists under ice coverage in the form of active geysers in the "tiger stripes" area of the southern Enceladus hemisphere. This active plume consists of gas and ice particles and enables the sampling of fresh materials from the interior that may originate from a liquid water source. The particles consist mostly of water ice and are 1-10?μ in diameter. The plume composition shows H(2)O, CO(2), CH(4), NH(3), Ar, and evidence that more complex organic species might be present. Since life on Earth exists whenever liquid water, organics, and energy coexist, understanding the chemical components of the emanating ice particles could indicate whether life is potentially present on Enceladus. The icy worlds of the outer planets are testing grounds for some of the theories for the origin of life on Earth. The LIFE mission concept is envisioned in two parts: first, to orbit Saturn (in order to achieve lower sampling speeds, approaching 2 km/s, and thus enable a softer sample collection impact than Stardust, and to make possible multiple flybys of Enceladus); second, to sample Enceladus' plume, the E ring of Saturn, and the Titan upper atmosphere. With new findings from these samples, NASA could provide detailed chemical and isotopic and, potentially, biological compositional context of the plume. Since the duration of the Enceladus plume is unpredictable, it is imperative that these samples are captured at the earliest flight opportunity. If LIFE is launched before 2019, it could take advantage of a Jupiter gravity assist, which would thus reduce mission lifetimes and launch vehicle costs. The LIFE concept offers science returns comparable to those of a Flagship mission but at the measurably lower sample return costs of a Discovery-class mission. Key Words: Astrobiology-Habitability-Enceladus-Biosignatures. Astrobiology 12, 730-742.  相似文献   
606.
The rates of the most important ionization processes acting in interplanetary space on interstellar H, He, C, O, Ne and Ar atoms are critically reviewed in the paper. Their long-term modulations in the period 1974 – 1994 are reexamined using updated information on relevant cross-sections as well as direct or indirect data on variations of the solar wind/solar EUV fluxes based on IMP 8 measurements and monitoring of the solar 10.7 cm radio emission. It is shown that solar cycle related variations are pronounced (factor of 3 between maximum and minimum) especially for species such as He, Ne, C for which photoionization is the dominant loss process. Species sensitive primarily to the charge-exchange (as H) show only moderate fluctuations 20% around average. It is also demonstrated that new techniques that make use of simultaneous observations of neutral He atoms on direct and indirect orbits, or simultaneous measurements of He+ and He++ pickup ions and solar wind particles can be useful tools for narrowing the uncertainties of the He photoionization rate caused by insufficient knowledge of the solar EUV flux and its variations.  相似文献   
607.
The profiles of H observed during the 1970–1992 period in the binary hypergiant HR 8752 (G0 Ia) are presented. We distinguish five typical H profiles designated as A, B, C, D and E types according to the number of emission and absorption features. The profiles of H are complex and contain several emission and absorption components, with: –130 km/s in emission or absorption, –84 km/s in absorption, –49 km/s in emission and about +6 km/s in emission. All of them are rather stable in radial velocities except of the main absorption component in the P Cygni profile with –84 km/s. The frequency of appearance and the periods of duration of the occurrence of the components is discussed. The duration times range between about 3 to 10 months for various components. The red emission component E2 is particularly interesting. Possible explanations of its origin are discussed.A long-term acceleration of the absorption component in the P Cygni profile is found; it can be interpreted as monotonous acceleration of the stellar wind.  相似文献   
608.
    
Reverse-bias safe operating area (RBSOA) of high-power Darlington transistors is characterized using a 120 A/1000 V nondestructive reverse-bias second breakdown tester designed and fabricated at Virginia Polytechnic Institute and State University. Elaborate RBSOA characteristics are generated with different forward/reverse base drives and collector current levels. The effects of elevated case temperature and second-base drive on RBSOA of four-terminal Darlington devices are also discussed.  相似文献   
609.
    
It has been suggested that a daily intake of fluid and salt supplements may be used to prevent bone demineralization in human subjects after prolonged exposure to hypokinesia (diminished muscular activity). Thus, the objective of this investigation was to evaluate the effect of fluid and salt supplementation in the prevention of development of osteoporosis in 64 Wistar rats with an initial body weight of 339-345 g, after exposure to 90 days of hypokinesia. They divided into 4 equal groups: the first group of rats placed under ordinary vivarium conditions and served as vivarium control; the second group were also placed under ordinary vivarium conditions but received daily fluid and salt supplements; the third group were subjected to pure hypokinesia, i.e. without the use of any preventive measures; and the fourth group were submitted to hypokinesia and received daily fluid and salt supplements. For the simulation of the hypokinetic effect the experimental group of rats were kept in small, individual, wooden cages. Through the experimental period the second and fourth group of rats received 8 ml/100 g body wt water and 5 ml 100 g body wt NaCl daily. By the end of the experimental period the animals were decapitated and the spongy matter of tibia and vertebrae of the rats were examined for changes referable to osteoporosis. It was found that the daily intake of fluid and salt supplements caused an increase in the volume density of primary spongiosa of bones. It was concluded that a daily intake of fluid and salt supplements may be used to prevent the development of osteoporosis in rats subjected to prolonged motor activity restriction.  相似文献   
610.
    
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