排序方式: 共有37条查询结果,搜索用时 15 毫秒
21.
Klaus Wilhelm Eckart Marsch Bhola N. Dwivedi Uri Feldman 《Space Science Reviews》2007,133(1-4):103-179
In Part I of this review, the concepts of solar vacuum-ultraviolet (VUV) observations were outlined together with a discussion
of the space instrumentation used for the investigations. A section on spectroradiometry provided some quantitative results
on the solar VUV radiation without considering any details of the solar phenomena leading to the radiation. Here, in Part
II, we present solar VUV observations over the last decades and their interpretations in terms of the plasma processes and
the parameters of the solar atmosphere, with emphasis on the spatial and thermal structures of the chromosphere, transition
region and corona of the quiet Sun. In addition, observations of active regions, solar flares and prominences are included
as well as of small-scale events. Special sections are devoted to the elemental composition of the solar atmosphere and theoretical
considerations on the heating of the corona and the generation of the solar wind. 相似文献
22.
Geochemical investigation of Martian meteorites (SNC meteorites) yields important constraints on the chemical and geodynamical evolution of Mars. These samples may not be representative of the whole of Mars; however, they provide constraints on the early differentiation processes on Mars. The bulk composition of Martian samples implies the presence of a metallic core that formed concurrently as the planet accreted. The strong depletion of highly siderophile elements in the Martian mantle is only possible if Mars had a large scale magma ocean early in its history allowing efficient separation of a metallic melt from molten silicate. The solidification of the magma ocean created chemical heterogeneities whose ancient origin is manifested in the heterogeneous 142Nd and 182W abundances observed in different meteorite groups derived from Mars. The isotope anomalies measured in SNC meteorites imply major chemical fractionation within the Martian mantle during the life time of the short-lived isotopes 146Sm and 182Hf. The Hf-W data are consistent with very rapid accretion of Mars within a few million years or, alternatively, a more protracted accretion history involving several large impacts and incomplete metal-silicate equilibration during core formation. In contrast to Earth early-formed chemical heterogeneities are still preserved on Mars, albeit slightly modified by mixing processes. The preservation of such ancient chemical differences is only possible if Mars did not undergo efficient whole mantle convection or vigorous plate tectonic style processes after the first few tens of millions of years of its history. 相似文献
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Miniaturization techniques enable the realization of very small satellites with interesting capabilities in space science. The University of Würzburg contributed in the scope of the cubesat program with its own pico satellite UWE-1, which is in orbit since October 2005. Despite reliable and stable operation of the on-board data handling (OBDH) system during the UWE-1 mission, the successor UWE-2 will be equipped with a more sophisticated, modular and extensible OBDH system, which was designed to facilitate the further development of the UWE satellite platform. The OBDH system was designed for high reliability and stability, but with an easier extension capability. The modular structure of the new system thus supports potential transfer to other satellite platforms. 相似文献
25.
D M Klaus P Todd A Schatz 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1998,21(8-9):1315-1318
A clinostat is a device often used in gravitational biology studies. Selecting an appropriate speed of rotation, however, is a frequently debated topic, particularly for suspended cells. In an attempt to define the necessary criteria for determining an acceptable revolution speed, the primary forces governing particle behavior during clinorotation--gravity, diffusion and centrifugation--were mathematically assessed. In support of the theoretical exercise, bacterial growth experiments indicated that results obtained using a clinostat followed trends resembling previous space flight results. It is suspected that this is due, in part at least, to similarly altered external transport processes in each environment. 相似文献
26.
Groemer GE Hauth S Luger U Bickert K Sattler B Hauth E Föger D Schildhammer D Agerer C Ragonig C Sams S Kaineder F Knoflach M 《Astrobiology》2012,12(2):125-134
We have developed the space suit simulator Aouda.X, which is capable of reproducing the physical and sensory limitations a flight-worthy suit would have on Mars. Based upon a Hard-Upper-Torso design, it has an advanced human-machine interface and a sensory network connected to an On-Board Data Handling system to increase the situational awareness in the field. Although the suit simulator is not pressurized, the physical forces that lead to a reduced working envelope and physical performance are reproduced with a calibrated exoskeleton. This allows us to simulate various pressure regimes from 0.3-1 bar. Aouda.X has been tested in several laboratory and field settings, including sterile sampling at 2800 m altitude inside a glacial ice cave and a cryochamber at -110°C, and subsurface tests in connection with geophysical instrumentation relevant to astrobiology, including ground-penetrating radar, geoacoustics, and drilling. The communication subsystem allows for a direct interaction with remote science teams via telemetry from a mission control center. Aouda.X as such is a versatile experimental platform for studying Mars exploration activities in a high-fidelity Mars analog environment with a focus on astrobiology and operations research that has been optimized to reduce the amount of biological cross contamination. We report on the performance envelope of the Aouda.X system and its operational limitations. 相似文献
27.
M.N.S. Qureshi Jiankui Shi Klaus Torkar Zhenxing Liu 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2010
The bipolar electric field solitary (EFS) structures have been frequently observed in the near Earth plasma regions, such as auroral zone, magnetopause, cusp regions, and magneto-tail. Sometimes these structures are observed as offset bipolar structures. In this paper, the properties of the offset bipolar EFS structures parallel to the magnetic field are studied with an ion fluid model in a cylindrical symmetry by considering electrostatic condition. The model results show that the offset bipolar EFS structures can develop from both ion-acoustic waves and ion cyclotron waves, and propagate along the magnetic field line in the space plasmas if plasma satisfies some conditions. The offset bipolar EFS structures can have both polarities. It will be first negative pulse and then positive pulse if the initial electric field E0 < 0 or reverse in order if E0 > 0. The amplitude of the offset bipolar EFS structures first decreases and then increases with the wave propagation velocity. Some results from our model are consistent with the observations. 相似文献
28.
由于大型商用飞机机身结构的复杂性,其碳纤维复合材料部件的设计、制造和取证都不能借用现有的制造维修基本经验.碳纤维复合材料机身壁板超越了现代化金属技术,对应力应变的保守限制要求必须保证将具有损伤容限的机身结构交付到航空公司.这样,碳纤维复合材料壁板技术的应用至少限制了新飞机家族第一代成员的重量. 相似文献
29.
Starting with an introduction into the field of hypervelocity impacts, an overview over current research in the area of protection against space debris is given. Trends and strategies to further develop know-how in protection technology are then discussed. One purpose is to demonstrate that improvements in shield efficiency can be expected. To achieve this aim, a strategy is outlined which tries to avoid the adjustment of numerical and material parameters by fits to penetration experiments. Instead, it is suggested to determine material parameters from carefully selected laboratory tests, covering a broad range of strains, strain rates and stress states. Knowledge of the dynamic material behaviour can then be used for the development of new shield concepts by means of numerical simulation. 相似文献
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