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91.
武高辉%修子扬%张强%宋美慧 《宇航材料工艺》2007,37(2):26-29
采用挤压铸造方法,制备了高体积分数的Si_p/4032Al复合材料。显微组织观察表明,复合材料组织致密,颗粒分布均匀,材料中没观察到孔洞和缺陷;复合材料的线膨胀系数介于(8.1~12)×10~(-6)/K之间可调,并且随着增强体含量的增加而降低,退火后线膨胀系数略有降低,Kerner模型能够较好的预测复合材料的线膨胀系数;复合材料的热导率可达103 W/(m·K),随着增强体含量的增加略有下降,退火处理后热导率略有升高,热导率计算结果均大于测试值。 相似文献
92.
G. Efstathiou R.I. Jedrzejewski 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1984,3(10-12)
Application of the cosmic virial theorem to galaxy redshift surveys suggests an open universe - if the dark material is distributed in the same way as galaxies. Here we investigate four redshift surveys. We present new results on the amplitudes of the two- and three-point galaxy correlation functions and we estimate the relative peculiar velocities in the deep redshift survey of Kirshner and co-workers (1983). Next, we review evidence which suggests that dark material is clustered on scales comparable to the optical radii of galaxies. In particular, we use spectroscopic and photometric observations to set constraints on the mass distribution in elliptical galaxies. 相似文献
93.
以无水乙醇为隔离剂,通过湿法球磨制备了片型羰基铁粉,研究了球料比对片型化过程、电磁性能的影响。结果表明:增加球料比,羰基铁粉片型化更充分,晶粒尺寸减小;粒子的各向异性提高了片型羰基铁粉的微波电磁性能。以环氧树脂为基体树脂,填充体积分数30%的吸波剂制备了1.0mm 单层吸波涂层,在 X-Ku 波段反射率小于-7.5dB 的带宽大于10GHz,涂层最小面密度为2.96kg /m2。 相似文献
94.
Bernard M. Rabin Kirsty L. Carrihill-Knoll Barbara Shukitt-Hale 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2011
On exploratory class missions astronauts will be exposed to a variety of heavy particles (HZE particles) which differ in terms of particle energy and particle linear energy transfer. The present experiments were designed to evaluate how these physical characteristics of different particles affect cognitive performance, specifically operant responding. Following exposure to 28Si, 48Ti, 12C and 16O particles at the NASA Space Radiation Laboratory rats were tested for their ability to respond appropriately to changes in reinforcement schedules using an operant task. The results showed that the effectiveness of different particles in disrupting cognitive performance, defined as the lowest dose that produced a performance decrement, varied as a function of the energy of the specific particle: for comparisons between different energies of the same particle (e.g., 56Fe) the effectiveness of the particle was directly proportional to particle linear energy transfer, whereas for comparisons between different particles (e.g., 56Fe and 16O) effectiveness was inversely proportional to particle linear energy transfer. The results are discussed in terms of the mechanisms that influence the effectiveness of different particles and energies and in terms of their implications for analyzing the possible risks to astronauts of decrements in cognitive performance following exposure to HZE particles on long-duration exploratory class missions. 相似文献
95.
Kyle Copeland Herbert H. Sauer Frances E. Duke Wallace Friedberg 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2008
From 1 January 1986 through 1 January 2008, GOES satellites recorded 170 solar proton events. For 169 of these events, we estimated effective and equivalent dose rates and doses of galactic cosmic radiation (GCR) and solar cosmic radiation (SCR), received by aircraft occupants on simulated high-latitude flights. Dose rate and dose estimates that follow are for altitudes 30, 40, 50, and 60 kft, in that order. 相似文献
96.
S. Benck M. Cyamukungu J. Cabrera 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2008,42(9):1538-1549
The topic of relativistic electron dynamics in the outer radiation belt has received considerable attention for many years. Nevertheless, the problem of understanding the physical phenomenon involved is far from being resolved. In this paper, we use DEMETER observations to examine the variations of the energetic electron fluxes and ELF/VLF wave intensities in the inner magnetosphere during the intense 8 November 2004 magnetic storm. Electron flux spectra and associated wave intensity spectra are analysed throughout the magnetic storm and common characteristics or differences to other storm events are retained. The overall objective of this study is to identify and derive parameters that are relevant for particle flux modelling; the time constant characterizing the persistent decay after particle enhancement was found to be one of these important model parameters.The analysis of the 8 November 2004 event reveals that for L-shell parameter higher than 4, an electron flux dropout is observed during the storm’s main phase for electrons in the energy range 0.1–1 MeV, as has been reported from other measurements. Characteristic wave spectra accompanying this phase are analysed. They show a typical enhancement in the frequency range 0.3–10 kHz at onset for all L-shell values under consideration (2 < L < 5). During the first stage of the recovery phase, the electron fluxes are increased to a level higher than the pre-storm level, whereas the level of wave intensity in the frequency range observed below 300 Hz is at its highest. In the second stage, the particle flux decrease goes hand in hand with a global wave activity decline, the relaxation time of the latter being smaller than the former’s one. In some other cases, long-lasting electron enhancement associated with constant wave activity has been observed during this latter stage. For the above mentioned storm, while at low L values the decay time constants are higher for low energy electrons than for high energy electrons, this order is reversed at high L values. At about L = 3.6 the time constant is independent of electron energy. 相似文献
97.
带电粒子在材料中的剂量深度分布计算 总被引:4,自引:3,他引:1
航天器在轨道运行期间,会受到各种带电粒子的作用,其能量沉积在表面材料中,对表面材料的性能有较大的损伤。文章介绍了剂量深度计算程序,利用SRIM及ITS软件的计算结果,计算出了带电粒子在材料中的剂量深度分布,并对空间轨道实际环境下材料中的剂量深度分布进行了计算。利用这一程序,在“东四”热控涂层试验中进行了剂量深度分布拟合,计算了多种能量电子拟合试验下荆量深度分布与空间实际环境的比较,得出了相关的试验参数。 相似文献
98.
TiC和ZrC颗粒增强钨基复合材料的烧蚀研究 总被引:6,自引:3,他引:6
用氧乙炔焰喷吹法对 Ti C和 Zr C增强钨基复合材料 ( Ti Cp/W和 Zr Cp/W两系列 )烧蚀性能进行了研究。结果表明 ,复合材料的质量烧蚀率和线烧蚀率由高到低的排列顺序为 :W>30 Ti Cp/W>4 0 Ti Cp/W>30 Zr Cp/W>4 0 Zr Cp/W( 30 Ti Cp/W表示含 Ti Cp 的体积分数为 30 % ,下同 )。对复合材料在烧蚀初期剧烈的升温过程进行了在线监测。 30 Ti Cp/W和 4 0 Ti Cp/W在烧蚀初期剧烈的升温过程中未能经受住约 2 0 0 0℃ /s升温热震而开裂 ,而 30 Zr Cp/W和 4 0 Zr Cp 能经受约 2 0 0 0℃ /s升温热震。在钨中加入 Ti C和 Zr C颗粒能明显提高钨的抗烧蚀性能 ,而且 Zr C颗粒比 Ti C颗粒更能提高 W的抗烧蚀性能。碳化物含量越高 ,材料的抗烧蚀性能越好。复合材料烧蚀机理是 W、Ti C和 Zr C的氧化烧蚀 相似文献
99.
100.
Bernardo Vargas Cárdenas José F. Valdés-Galicia 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2012
We performed a search for ground level solar cosmic ray enhancements on the full five minute database of the Mexico City neutron monitor using wavelet filters and two different statistical tests. We present a detailed analysis of the time series of November 2, 1992, where we found a previously unreported increment matching the onset time of the impulsive phase of GLE 54, thus providing evidence of an effective detection of high energy solar cosmic rays. 相似文献