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81.
A.A. de Almeida D. Trevisan Sanzovo G.C. Sanzovo R. Boczko R. Miguel Torres 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2009,43(12):1993-2000
In an attempt to evaluate correlations between several properties of comets we report the results of a cometary research involving a criterious analysis of gas and dust mass production rates in Comets 67P/Churyumov-Gerasimenko (main target of Rosetta Mission), 1P/Halley, Hyakutake (C/1996 B2), and 46P/Wirtanen and make a comparison between them. 相似文献
82.
针对飞行器进入火星大气时气体辐射加热对防热设计带来不确定性,在简述火星探测和气体辐射研究的发展历程的基础上,对火星进入气体辐射加热研究的进展进行综述。首先,针对火星大气环境描述了气体辐射加热的概念和问题由来。其次,重点综述了近年来火星进入气体辐射加热基础模型的数值和试验研究进展,其中包括:热化学非平衡气体动力学、气体辐射特性和辐射传输的计算模型与方法等数值研究;地面测试设备、试验技术和模拟火星大气环境的气体辐射测量与验证等试验研究。再次,综述了流动辐射耦合和后体气体辐射加热等火星进入器设计方面开展的研究。最后,对未来火星进入气体辐射加热研究进行了展望,提出了研究建议。 相似文献
83.
Kangkang Liu Guozhu Li Baiqi Ning 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2019,63(11):3612-3620
The small-scale wave-like structure (SSWS) of F region bottomside plasma density was proposed to be an important seeding for equatorial plasma bubble (EPB) generation, and employed in theoretical simulations of EPBs in recent years. The seeding role of SSWS, however, is waiting to be demonstrated by observation. Here we present two cases of SSWS and EPB observed by the Fuke all-sky airglow imager (19.3°N, 109.1°E; dip latitude 14.3°N). For each case, the results show that two large-scale wave-like structures (LSWSs) initially appeared around sunset in the longitude regions separated by 3–4°, but EPB irregularities were only generated in one of the LSWSs where SSWSs were seen riding on LSWS. For the other LSWS, no SSWS and EPB irregularities were seen. Considering that the two LSWSs were situated closely in longitude where the amplitude of pre-reversal enhancement of background eastward electric field should be similar, the observation that EPB was only generated in the longitude with simultaneous LSWS and SSWS could provide supporting evidence for SSWS seeding of EPB. 相似文献
84.
Willy Benz 《Space Science Reviews》2000,92(1-2):279-294
The physics of low velocity collisions (5 m/s to 40 m/s) between basalt bodies ranging in size from 1 m to 10 km is studied
in an effort to investigate the early phases of planetesimal accretions. To assess the importance of the internal structure
of planetesimals on the outcome of the collisions, we model them either as solid spheres or as rubble piles with a filling
factor of 0.5.
The collisions are simulated using a three dimensional Smooth Particle Hydrodynamics (SPH) code that incorporates the combined
effects of material strength and a brittle fragmentation model. This approach allows the determination not only of the mass
of the largest fragments surviving the collisions but also their dynamical characteristics.
We find that low velocity collisions are for equal incoming kinetic energy per gram of target material considerably more efficient
in destroying and dispersing bodies than their high velocity counterparts. Furthermore, planetesimals modeled as rubble piles
are found to be characterized by a disruption threshold about 5 times smaller than solid bodies. Both results are a consequence
of a more efficient momentum transfer between projectile and fragments in collisions involving bodies of comparable sizes.
Size and shape dependent gas drag is shown to provide relative collision velocities between similar meter-sized objects well
in excess of the critical disruption threshold of either rubble piles or solid bodies. Unless accretion can proceed avoiding
collisions between bodies of similar masses, the relative weakness of bodies in this size range creates a serious bottleneck
for planetesimal growth.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
85.
Fuel tank inerting technologies are able to reduce the fire risk by injection of inert gas into the ullage or fuel, the former called ullage washing and the latter fuel scrubbing. The Green On-Board Inert Gas Generation System (GOBIGGS) is a novel technology based on flameless catalytic combustion, and owning to its simple structure and high inerting efficiency, it has received a lot of attentions. The inert gas in the GOBIGGS is mainly comprised of CO2, N2, and O2 (hereinafter, Mixed Inert Gas (MIG)), while that in the On-Board Inert Gas Generation System (OBIGGS), which is one of the most widely used fuel tank inerting technologies, is Nitrogen-Enriched Air (NEA). The solubility of CO2 is nearly 20 times higher than that of N2 in jet fuels, so the inerting capability and performance are definitely disparate if the inert gas is selected as NEA or MIG. An inerting test bench was constructed to compare the inerting capabilities between NEA and MIG. Experimental results reveal that, if ullage washing is adopted, the variations of oxygen concentrations on the ullage and in the fuel are nearly identical no matter the inert gas is NEA or MIG. However, the ullage and dissolved oxygen concentrations of MIG scrubbing are always higher than those of NEA scrubbing. 相似文献
86.
为了解管路注气对补燃循环液氧煤油发动机预燃室煤油离心喷嘴喷注过程稳定性的影响,在大气环境下开展了敞口型离心喷嘴注气时喷注过程稳定性试验。使用注气装置在离心喷嘴的上游供应管路中注入空气,通过高速相机记录管路内的两相流特征和喷嘴喷注过程的振荡特征,采用图像区域亮度分析方法定量评估喷注过程的振荡强度。研究发现:注气能显著改变敞口型离心喷嘴的喷注雾化过程及稳定性特征;注气后雾化液膜破碎距离缩短且喷雾角减小,喷注过程出现明显的振荡并伴随Klystron效应;管路内两相流的气泡尺度较大且切向孔较小时,喷注过程的振荡幅值较大;随着注气量增加,喷注过程的振荡频率降低;气泡尺度及两相流型对离心喷嘴喷注振荡过程的影响与普通气泡雾化喷嘴的显著不同,柱状流型时离心喷嘴喷注过程出现1~3 Hz流量振荡且可能间歇性断流。气泡对切向孔的间歇性堵塞作用可能是喷注过程振荡及Klystron效应的原因。 相似文献
87.
Deuterium fractionations in cometary ices provide important clues to the origin and evolution of comets. Mass spectrometers
aboard spaceprobe Giotto revealed the first accurate D/H ratios in the water of Comet 1P/Halley. Ground-based observations
of HDO in Comets C/1996 B2 (Hyakutake) and C/1995 O1 (Hale-Bopp), the detection of DCN in Comet Hale-Bopp, and upper limits
for several other D-bearing molecules complement our limited sample of D/H measurements. On the basis of this data set all
Oort cloud comets seem to exhibit a similar
ratio in H2O, enriched by about a factor of two relative to terrestrial water and approximately one order of magnitude relative to the
protosolar value. Oort cloud comets, and by inference also classical short-period comets derived from the Kuiper Belt cannot
be the only source for the Earth's oceans. The cometary O/C ratio and dynamical reasons make it difficult to defend an early
influx of icy planetesimals from the Jupiter zone to the early Earth. D/H measurements of OH groups in phyllosilicate rich
meteorites suggest a mixture of cometary water and water adsorbed from the nebula by the rocky grains that formed the bulk
of the Earth may be responsible for the terrestrial D/H. The D/H ratio in cometary HCN is 7 times higher than the value in
cometary H2O. Species-dependent D-fractionations occur at low temperatures and low gas densities via ion-molecule or grain-surface reactions and cannot be explained by a pure solar nebula chemistry. It is plausible that cometary
volatiles preserved the interstellar D fractionation. The observed D abundances set a lower limit to the formation temperature
of (30 ± 10) K. Similar numbers can be derived from the ortho-to-para ratio in cometary water, from the absence of neon in
cometary ices and the presence of S2. Noble gases on Earth and Mars, and the relative abundance of cometary hydrocarbons place the comet formation temperature
near 50 K. So far all cometary D/H measurements refer to bulk compositions, and it is conceivable that significant departures
from the mean value could occur at the grain-size level. Strong isotope effects as a result of coma chemistry can be excluded
for molecules H2O and HCN. A comparison of the cometary
ratio with values found in the atmospheres of the outer planets is consistent with the long-held idea that the gas planets
formed around icy cores with a high cometary D/H ratio and subsequently accumulated significant amounts of H2 from the solar nebula with a low protosolar D/H.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
88.
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