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901.
D. Vaniman M. D. Dyar R. Wiens A. Ollila N. Lanza J. Lasue J. M. Rhodes S. Clegg H. Newsom 《Space Science Reviews》2012,170(1-4):229-255
The ChemCam instrument on the Mars Science Laboratory rover Curiosity will use laser-induced breakdown spectroscopy (LIBS) to analyze major and minor element chemistry from sub-millimeter spot sizes, at ranges of ~1.5–7?m. To interpret the emission spectra obtained, ten calibration standards will be carried on the rover deck. Graphite, Ti?metal, and four glasses of igneous composition provide primary, homogeneous calibration targets for the laser. Four granular ceramic targets have been added to provide compositions closer to soils and sedimentary materials like those expected at the Gale Crater field site on Mars. Components used in making these ceramics include basalt, evaporite, and phyllosilicate materials that approximate the chemical compositions of detrital and authigenic constituents of clastic and evaporite sediments, including the elevated sulfate contents present in many Mars sediments and soils. Powdered components were sintered at low temperature (800?°C) with a small amount (9?wt.%) of lithium tetraborate flux to produce ceramics that retain volatile sulfur yet are durable enough for the mission. The ceramic targets are more heterogeneous than the pure element and homogenous glass standards but they provide standards with compositions more similar to the sedimentary rocks that will be Curiosity’s prime targets at Gale Crater. 相似文献
902.
This chapter mainly deals with magnetic reconnection and particle acceleration in relativistic astrophysical plasmas, where the temperature of the current sheet exceeds the rest mass energy and the Alfvén velocity is close to the speed of light. Magnetic reconnection now receives a great deal of interest for its role in many astrophysical systems such as pulsars, magnetars, galaxy clusters, and active galactic nucleus jets. We review recent advances that emphasize the roles of reconnection in high-energy astrophysical phenomena. 相似文献
903.
为了准确预示固体火箭发动机碳基材料喷管的烧蚀率,依据热化学烧蚀理论,建立了喷管传热烧蚀的二维轴对称气-固-热耦合计算模型,计算通过FLUENT壁面化学反应模型完成,无需事先假设烧蚀控制机制。针对70-lb BATES发动机喷管进行了烧蚀计算,研究了推进剂配方、氧化性组分、燃烧室压强对喷管烧蚀的影响。结果表明:烧蚀率计算值与试验测试值吻合较好;烧蚀率分布遵循喷管内壁热流密度分布规律,在喉部上游入口处达到峰值;烧蚀率随推进剂Al含量增加而降低,随燃烧室压强升高而近似正比例增大;H2O是决定烧蚀的主要氧化性组分。 相似文献
904.
John C. Raymond Raid Suleiman John L. Kohl Giancarlo Noci 《Space Science Reviews》1998,85(1-2):283-289
A great deal of evidence for elemental abundance variations among different structures in the solar corona has accumulated
over the years. Many of the observations show changes in the relative abundances of high- and low-First Ionization Potential
elements, but relatively few show the absolute elemental abundances. Recent observations from the SOHO satellite give absolute
abundances in coronal streamers. Along the streamer edges, and at low heights in the streamer, they show roughly photospheric
abundances for the low-FIP elements, and a factor of 3 depletion of high-FIP elements. In the streamer core at 1.5 R·, both
high- and low-FIP elements are depleted by an additional factor of 3, which appears to result from gravitational settling.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
905.
906.
黄山皖南机床有限公司 《航空制造技术》2011,(4)
黄山皖南机床生产的数控龙门铣床主要用于各种模具制造、各种基础大件、壳体件等多品种零件的加工,工件一次装夹后可自动高效、高精度地连续完成铣、镗、铰、攻丝等多种工序的加工.适用于汽车模具、重型机械、机车、造船、发电、机床、印刷、轻纺、航空航天等制造行业,配备多功能铣头后,可对工作进行五面体加工,以及对各种复杂型面进行三坐标加工.该机床主要有以下特点. 相似文献
907.
The composition of Galactic Cosmic Ray Sources (GCRS) shows the following features: (i) an enhancement of the refractory elements
relative to the volatile ones, and (ii) an enhancement of the heavier volatile elements relative to the lighter ones; this
mass dependence should reflect a mass-to-charge (A/Q) dependence of the acceleration efficiency; among the refractory elements,
there is only a very weak enhancement of heavier species, or none at all. We consider it fortuitous that the GCRS composition
resembles that of the solar corona, which is biased according to first ionization potential. In a companion paper by Ellison
et al. (1998, this issue), this GCRS composition is interpreted in terms of a supernova shock wave acceleration of interstellar
and/or circumstellar (e.g., 22Ne-rich Wolf-Rayet wind) gas phase and especially dust grain material. These two papers summarize
and complement the content of two papers that recently appeared in Astrophys. J. (Meyer et al., 1997; Ellison et al., 1997).
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
908.
Mahaffy P.R. Donahue T.M. Atreya S.K. Owen T.C. Niemann H.B. 《Space Science Reviews》1998,84(1-2):251-263
The Galileo Probe Mass Spectrometer measurements in the atmosphere of Jupiter give D/H = (2.6 ± 0.7) × 10-5 3He/4He = (1.66 ± 0.05) × 10-4These ratios supercede earlier results by Niemann et al. (1996) and are based on a reevaluation of the instrument response at high count rates and a more detailed study of the contributions of different species to the mass peak at 3 amu. The D/H ratio is consistent with Voyager and ground based data and recent spectroscopic and solar wind (SW) values obtained from the Infrared Spectroscopic Observatory (ISO) and Ulysses. The 3He/4He ratio is higher than that found in meteoritic gases (1.5 ± 0.3) × 10-4. The Galileo result for D/H when compared with that for hydrogen in the local interstellar medium (1.6 ± 0.12) × 10-5 implies a small decrease in D/H in this part of the universe during the past 4.55 billion years. Thus, it tends to support small values of primordial D/H - in the range of several times 10-5 rather than several times 10-4. These results are also quite consistent with no change in (D+3He)/H during the past 4.55 billion years in this part of our galaxy. 相似文献
909.
Almost all theoretical and numerical models for the modulation of cosmic ray in the heliosphere are based on Parker's transport equation which contains all the important basic physical processes. The relative importance of the various mechanisms is however not established and may vary significantly over 22 years. The simultaneous measurements of solar wind parameters, heliospheric magnetic field properties and cosmic rays over a wide range of energies and positions in the heliosphere have brought the realization that modulation is much more complicated than what the original drift models predicted. In the process the sophistication of models based on solving Parker's equation has increased by orders of magnitude. A short review of the global modulation of cosmic rays is given from a theoretical and modelling point of view. 相似文献
910.