排序方式: 共有54条查询结果,搜索用时 15 毫秒
41.
Serge Habraken Jean-Marc Defise Jean-Paul Collette Pierre Rochus Pierre-Alexis D'Odemont Michel Hogge 《Acta Astronautica》2001,48(5-12)
This paper presents some research activities conducted at the Centre Spatial de Liege (CSL) in the field of space solar arrays and concentration.With the new generation of high efficiency solar cells, solar concentration brings new insights for future high power spacecrafts. A trade-off study is presented in this paper. Two different trough concentrators, and a linear Fresnel lens concentrator are compared to rigid arrays. Thermal and optical behaviors are included in the analysis.Several technical aspects are discussed:
- • Off-pointing with concentrators induces collection loss and illumination non uniformity, reducing the PV efficiency.
- • Concentrator deployment increases the mission risk.
- • Reflective trough concentrators are attractive and already proven. Coating is made of VDA (Aluminum). A comprehensive analysis of PV conversion increase with protected silver is presented.
- • Solar concentration increases the heat load on solar cells, while the conversion efficiency is significantly decreasing at warm temperatures.
42.
QIAO Wei-yang 《中国航空学报》2000,13(3):146-151
After the significant progress that has beenachieved in engine noise reduction in the last twodecades,the airframe noise of civil transportshas now become a major concern for noise certi-fication and environmental considerations.Con-sequently,aircraft manufacturers and researchcenters have been working on airframe noisewith the objectives of developing reliable noiseprediction schemes and reducing aerodynamicnoise generation at the source in recentyears[1~ 2 ] . Of all the airframe noise … 相似文献
43.
Issautier Karine Hoang Sang Moncuquet Michel Meyer-Vernet Nicole 《Space Science Reviews》2001,97(1-4):105-108
The Ulysses spacecraft is reaching high heliolatitudes during the approach to solar maximum. We show preliminary in situ electron observations
from the URAP experiment, using thermal noise spectroscopy. This method is especially suited to measure accurately the electron
density and thermal temperature. The data acquired in the period June–September 2000 are compared to those obtained at similar
heliolatitudes near solar activity minimum and in the ecliptic plane near both solar maximum and minimum.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
44.
François Raulin Kevin P. Hand Christopher P. McKay Michel Viso 《Space Science Reviews》2010,153(1-4):511-535
The outer solar system is an important area of investigation for exobiology, the study of life in the universe. Several moons of the outer planets involve processes and structures comparable to those thought to have played an important role in the emergence of life on Earth, such as the formation and exchange of organic materials between different reservoirs. The study of these prebiotic processes on, and in, outer solar system moons is a key goal for exobiology, together with the question of habitability and the search for evidence of past or even present life. This chapter reviews the aspects of prebiotic chemistry and potential presence of life on Europa, Enceladus and Titan, based on the most recent data obtained from space missions as well as theoretical and experimental laboratory models. The habitability of these extraterrestrial environments, which are likely to include large reservoirs of liquid water in their internal structure, is discussed as well as the particular case of Titan’s hydrocarbon lakes. The question of planetary protection, especially in the case of Europa, is also presented. 相似文献
45.
46.
Nicole Cornilleau-Wehrlin Roger Gendrin Francois Lefeuvre Michel Parrot Rejean Grard Dyfrig Jones Axel Bahnsen Eigil Ungstrup Warwick Gibbons 《Space Science Reviews》1978,22(4):371-382
This paper is concerned mainly with the information which can be extracted from frequency-time spectra in the VLF range. The instrument used is the correlator which has a good frequency resolution (50 Hz) and time resolution (30 ms) in one magnetic and one electric component simultaneously. By suitable computer analysis, it is possible for instance to distinguish between the two dominant electromagnetic emissions, hiss and chorus, as well as to display the complete spectra. This treatment is applied to the Survey periods, which are a fixed sequence of modes, repeated every hour on the hour in order to have reference data from GEOS analogous to many ground-based observatories. One result of this treatment obtained already is that hiss and chorus normally appear together, although one or the other may be dominating in intensity. The occurrence rate of these emissions in local time is also given.For continuous surveillance the filterbank data are used. There are 16 frequency filters supplying magnetic and electric amplitude at few different frequencies. Using these data, a storm sudden commencement can be followed with good time resolution (1 s), and an interesting correlation has been found in a few cases between the VLF signal amplitude and the cold plasma density (as measured by the active part of the S-300 experiment). 相似文献
47.
Transatlantic cooperation has played a key part in developing Europe's capabilities in space, but this has been despite serious drawbacks in the legal status of the agreements concerned. This article traces the history of transatlantic space relations and highlights the misunderstandings that have arisen. These stem from the precedence given in the USA to domestic laws and financial interests over all international agreements except formal treaties, which are generally not considered suitable for scientific and technical agreements. The article concludes with a discussion of how more stable and equitable relationships could be achieved. 相似文献
48.
C.W. Carlson D.W. Curtis G. Paschmann W. Michel 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1982,2(7):67-70
A new instrument which can rapidly measure plasma particle distribution functions has been developed based upon recent innovations in electrostatic analyzer design and position sensitive particle detection. The new analyzer uses a quadrispherical geometry, but has a completely uniform 360° fan-shaped field of view. The polar angular distribution of entering particles is spatially imaged onto a position sensitive detector at the annular exit aperture after a deflection through 90°. Several methods of position sensitive detection have been successfully used in conjunction with this analyzer. The simplest is individual channel multipliers spaced around the annular exit. Microchannel plate electron multipliers permit greater position resolution to be obtained, and a detector using microchannel plates followed by a resistive anode image converter obtains angular resolution of about one degree -- , 360 individual angle pixels. Instruments of this type were flown on a sounding rocket in early 1982 and will be included on the Giotto comet mission and the AMPTE ion release module (IRM). 相似文献
49.
Michel Denis Célia Mores Doriane Gras Valérie Gyselinck Marie-Paule Daniel 《Spatial Cognition & Computation》2014,14(4):284-305
We tested the hypothesis that a route's memorability is dependent on the frequency with which people are exposed to visual landmarks. Undergraduates learned either a route through an urban area lacking visually salient features, or a route in a neighborhood with many shops and urban objects. They were then asked to recall the learned route in the form of route directions and sketch maps. The results showed higher recall performance for the richer environment. When presented with photographs depicting scenes along the route, participants exposed to the richer environment had higher recognition scores and shorter response times than the others. The data confirm the functional role of landmarks in route memory and wayfinding. 相似文献
50.
Jean-Luc Widlowski Thomas Lavergne Bernard Pinty Nadine Gobron Michel M. Verstraete 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2008,41(11):1724-1732
The divergence of horizontal radiation in vegetation canopies is generally considered to be of negligible consequence in algorithms designed for the physically-based interpretation of space borne observations. However, non-zero horizontal radiation balances are likely to occur if the internal variability of a vegetation target and the typical distances that photons may travel horizontally within such three-dimensional (3-D) media extend to spatial scales that are similar to or larger than those of the nominal footprint of the measuring sensor. Detailed radiative transfer simulations in 3-D coniferous forest environments are presented to document the typical distances that photons may travel in such media, and to quantify the impact that the resulting net horizontal fluxes may have with respect to the local and domain-averaged canopy reflectance. Based on these simulations it is possible to identify a fine spatial resolution limit beyond which pixel-based interpretations of remote sensing data over tall forested areas should be avoided because the horizontal radiation transport at the surface may contribute to 10% or more of the measured reflectance signature of the target pixel. 相似文献