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81.
“嫦娥4号”预计在月球背面的冯·卡门(Von Kármán)撞击坑着陆,为近距离研究月球最大和最古老的南极—艾肯(South Pole-Aitken)盆地的形成和演化提供了机会。综合利用多种光谱数据,本研究分析了冯·卡门撞击坑及其周边地区TiO2和FeO的含量变化,以及铁镁质矿物的分布情况,并推断了其主要的岩石类型。研究结果表明:冯·卡门撞击坑内部贫TiO2(约1.5~2.5 wt%)富FeO(约12~16 wt%),主要岩石类型为低钛玄武岩。撞击坑以外的地层则以苏长岩质物质(低钙辉石)为主,并含有约1 wt%的TiO2和10 wt%的FeO。此外,冯·卡门撞击坑外的南部局fFf), and infilled by low-Ti basalts. The materials outside the crater are dominated by noritic materials (Low-Ca pyroxene) with abundance of TiO2(~1 wt%)and FeO(~10 wt%). In addition, some plagioclase-rich layers are also exposed on the southern region outside the Von Kármán crater. 相似文献
82.
83.
马明臻%曾松岩%张二林%周彼德 《宇航材料工艺》2000,30(1):59-63
采用真空热爆加压法(简称VTEP)工艺制备了高粒子含量TiCp/2024复合材料。通过数据采集器记录了不同铝含量时热爆反应的时间--温度曲线;通过XRD分析了TiCp/2024复合材料的相组成;用SEM和TEM观察了TiCp/2024复合材料的显微组织、微观结构和断口形貌。结果表明:VTEP工艺可以获得颗粒细小圆整、分布均匀、致密的高颗粒含量TiCp/2024复合材料。 相似文献
84.
为在氩弧焊加工过程中提升效率的同时降低能耗,研究了一种氩弧焊高效节能工艺参数的多目标优化模型及算法。首先确定了以焊接速度及焊接电流为优化变量,在综合考虑焊接设备、工件特性、操作方法及焊接质量等约束的前提下,建立了以最小电能消耗以及最短加工时长为优化目标的多目标工艺参数优化模型;提出一种基于云模型的蚁群算法(CBACO)以对所构建的优化模型进行求解,其中包含一种适当的编码方式、一种局部与全局相结合的探索策略、一种基于云模型的变异因子、传统的单点交叉因子、单形交叉因子以及适当的选择策略;通过一个针对某航空器油箱的焊接实例,对所提出的优化模型及算法的实用性进行了验证,结果表明优化参数可在保证加工质量的前提下有效地节省时间60.41%~69.05%,节省电能34.88%~46.30%。 相似文献
85.
周守维 《沈阳航空工业学院学报》2003,20(3):65-68
立体构成学习不再是简单的技能培训,也不是模仿性的学习,重点在于创造意识、创造能力的培养。本文阐述了立体构成中能力的培育、创造力的育成的新观点、新认识。 相似文献
86.
The ionic charge distributions of solar energetic particles (SEP) as observed in interplanetary space provide fundamental
information about the origin of these particles, and the acceleration and propagation processes at the Sun and in interplanetary
space. In this paper we review the measurements of ionic charge states of energetic particles in interplanetary space and
discuss their implication for our understanding of SEP sources, and acceleration and propagation processes. 相似文献
87.
Robert J. Rutten 《Space Science Reviews》1998,85(1-2):269-280
This “rapporteur” report discusses the solar photosphere and low chromosphere in the context of chemical composition studies.
The highly dynamical nature of the photosphere does not seem to jeopardize precise determination of solar abundances in classical
fashion. It is still an open question how the highly dynamical nature of the low chromosphere contributes to first ionization
potential (FIP) fractionation.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
88.
The volatile species released in the coma are an important clue to the composition of the cometary nucleus ices. Their identification
and the measurement of their abundances is possible by remote sensing. Considerable progress has been made recently using
radio and infrared spectroscopy, especially with the observations of the two exceptional comets C/1996 B2 (Hyakutake) and
C/1995 O1 (Hale-Bopp).) 24 molecules likely to be parent molecules outgassed from the nucleus have now been identified. Significant
upper limits exist for many other species, and the presence of unidentified lines suggests that further species are to be
identified. In addition, isotopic varieties have been observed for hydrogen, carbon, nitrogen and sulphur. We will review
these results with a special emphasis on the reliability of the identifications and of the molecular production rate determinations.
A critical point is to assess whether a given species is a genuine parent molecule outgassed from nuclear ices, or is a secondary
product coming from grains or from gas-phase photochemistry. Ground-based spectral imaging, such as radio interferometry,
may help resolving this problem.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
89.
A.A. Leonov A.M. Galper S.V. Koldashov V.V. Mikhailov M. Casolino P. Picozza R. Sparvoli 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2008,41(1):86-91
Nuclear interactions between inner zone protons and atoms in the upper atmosphere provide the main source of energetic H and He isotopes nuclei in the radiation belt. This paper reports on the specified calculations of these isotope intensities using various inner zone proton intensity models (AP-8 and SAMPEX/PET PSB97), the atmosphere drift-averaged composition and density model MSIS-90, and cross-sections of the interaction processes from the GNASH nuclear model code. To calculate drift-averaged densities and energy losses of secondaries, the particles were tracked in the geomagnetic field (modelled through IGRF-95) by integrating numerically the equation of the motion. The calculations take into account the kinematics of nuclear interactions along the whole trajectory of trapped proton. The comparison with new data obtained from the experiments on board RESURS-04 and MITA satellites and with data from SAMPEX and CRRES satellites taken during different phases of solar activity shows that the upper atmosphere is a sufficient source for inner zone helium and heavy hydrogen isotopes. The calculation results are energy spectra and angular distributions of light nuclear isotopes in the inner radiation belt that may be used to develop helium inner radiation belt model and to evaluate their contribution to SEU (single event upset) rates. 相似文献
90.
Rosemary Killen Gabrielle Cremonese Helmut Lammer Stefano Orsini Andrew E. Potter Ann L. Sprague Peter Wurz Maxim L. Khodachenko Herbert I. M. Lichtenegger Anna Milillo Alessandro Mura 《Space Science Reviews》2007,132(2-4):433-509
It has been speculated that the composition of the exosphere is related to the composition of Mercury’s crustal materials.
If this relationship is true, then inferences regarding the bulk chemistry of the planet might be made from a thorough exospheric
study. The most vexing of all unsolved problems is the uncertainty in the source of each component. Historically, it has been
believed that H and He come primarily from the solar wind (Goldstein, B.E., et al. in J. Geophys. Res. 86:5485–5499, 1981), Na and K come from volatilized materials partitioned between Mercury’s crust and meteoritic impactors (Hunten, D.M., et
al. in Mercury, pp. 562–612, 1988; Morgan, T.H., et al. in Icarus 74:156–170, 1988; Killen, R.M., et al. in Icarus 171:1–19, 2004b). The processes that eject atoms and molecules into the exosphere of Mercury are generally considered to be thermal vaporization,
photon-stimulated desorption (PSD), impact vaporization, and ion sputtering. Each of these processes has its own temporal
and spatial dependence. The exosphere is strongly influenced by Mercury’s highly elliptical orbit and rapid orbital speed.
As a consequence the surface undergoes large fluctuations in temperature and experiences differences of insolation with longitude.
Because there is no inclination of the orbital axis, there are regions at extreme northern and southern latitudes that are
never exposed to direct sunlight. These cold regions may serve as traps for exospheric constituents or for material that is
brought in by exogenic sources such as comets, interplanetary dust, or solar wind, etc. The source rates are dependent not
only on temperature and composition of the surface, but also on such factors as porosity, mineralogy, and space weathering.
They are not independent of each other. For instance, ion impact may create crystal defects which enhance diffusion of atoms
through the grain, and in turn enhance the efficiency of PSD. The impact flux and the size distribution of impactors affects
regolith turnover rates (gardening) and the depth dependence of vaporization rates. Gardening serves both as a sink for material
and as a source for fresh material. This is extremely important in bounding the rates of the other processes. Space weathering
effects, such as the creation of needle-like structures in the regolith, will limit the ejection of atoms by such processes
as PSD and ion-sputtering. Therefore, the use of laboratory rates in estimates of exospheric source rates can be helpful but
also are often inaccurate if not modified appropriately. Porosity effects may reduce yields by a factor of three (Cassidy,
T.A., and Johnson, R.E. in Icarus 176:499–507, 2005). The loss of all atomic species from Mercury’s exosphere other than H and He must be by non-thermal escape. The relative
rates of photo-ionization, loss of photo-ions to the solar wind, entrainment of ions in the magnetosphere and direct impact
of photo-ions to the surface are an area of active research. These source and loss processes will be discussed in this chapter. 相似文献