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151.
152.
Accurate Mars Express orbits to improve the determination of the mass and ephemeris of the Martian moons 总被引:1,自引:0,他引:1
P. Rosenblatt V. Lainey S. Le Maistre J.C. Marty V. Dehant M. Ptzold T. Van Hoolst B. Husler 《Planetary and Space Science》2008,56(7):1043-1053
The determination of the ephemeris of the Martian moons has benefited from observations of their plane-of-sky positions derived from images taken by cameras onboard spacecraft orbiting Mars. Images obtained by the Super Resolution Camera (SRC) onboard Mars Express (MEX) have been used to derive moon positions relative to Mars on the basis of a fit of a complete dynamical model of their motion around Mars. Since, these positions are computed from the relative position of the spacecraft when the images are taken, those positions need to be known as accurately as possible. An accurate MEX orbit is obtained by fitting two years of tracking data of the Mars Express Radio Science (MaRS) experiment onboard MEX. The average accuracy of the orbits has been estimated to be around 20–25 m. From these orbits, we have re-derived the positions of Phobos and Deimos at the epoch of the SRC observations and compared them with the positions derived by using the MEX orbits provided by the ESOC navigation team. After fit of the orbital model of Phobos and Deimos, the gain in precision in the Phobos position is roughly 30 m, corresponding to the estimated gain of accuracy of the MEX orbits. A new solution of the GM of the Martian moons has also been obtained from the accurate MEX orbits, which is consistent with previous solutions and, for Phobos, is more precise than the solution from the Mars Global Surveyor (MGS) and Mars Odyssey (ODY) tracking data. It will be further improved with data from MEX-Phobos closer encounters (at a distance less than 300 km). This study also demonstrates the advantage of combining observations of the moon positions from a spacecraft and from the Earth to assess the real accuracy of the spacecraft orbit. In turn, the natural satellite ephemerides can be improved and participate to a better knowledge of the origin and evolution of the Martian moons. 相似文献
153.
Neutral gas composition and ionospheric measurements taken by the Dynamic Explorer 2 satellite at F2-region heights (280–300 km) during an intense geomagnetic storm (peak Dst=−187 nT) were used to analyze the role of some possible physical mechanisms responsible for the changes of electron density at high and middle latitudes. The storm considered in this study occurred on 26 September 1982. The main features observed were increases of electron density during the initial stages of the storm at middle latitudes; followed by decreases of electron density at high and mid-high latitudes during the main phase of the storm and the first phase of the recovery. Delayed increases of electron density during the recovery phase have also been observed at mid-high latitudes (50–60°). Several mechanisms were discussed in explaining the features observed for the electron density variations. 相似文献
154.
目前电离层掩星数据反演是基于电离层电子密度分布局部球对称近似的Abel反演方法,实际电离层的非球对称性会给电子密度反演结果带来误差.本文研究利用三维电离层模式来提供电子密度水平变化的先验信息约束电离层掩星反演的方法,即三维模式约束法;并将该方法应用于模拟掩星观测数据和实测掩星数据的反演.模拟观测数据的反演结果表明,与Abel反演方法相比,三维模式约束法能够减小反演误差.采用IRI2001模式作为约束,对COSMIC电离层掩星实测数据反演,将反演结果与全球的垂测仪数据进行比较,结果表明,三维模式约束法和Abel反演方法都能很好地反演电离层掩星. 相似文献
155.
绿色杜氏藻被膜泡囊的超微结构研究 总被引:3,自引:0,他引:3
于1990年5月-1991年5月,运用透射电镜观察绿色杜氏藻,对该氏藻被膜泡囊的形态结构及其在细胞内的分布和形成过程进行研究。观察表明,绿色杜氏藻细胞的高尔基体和细胞膜有许多大小不等的被膜泡囊;这些被膜泡囊由泡囊及其表面的网状结构构成,其直径在45-120nm之间;在细胞膜附近的被膜泡囊直径较大;在高尔基体和细胞膜上还观察到被膜泡囊的形成过程。 相似文献
156.
国内外寻找隐伏矿化探新方法研究进展 总被引:15,自引:2,他引:13
简要总结了根据超显微镜物质的迁移吸附机制和矿物结构与成矿物关系寻找隐伏矿的化探新方法的原理,技术及试验应用效果,预计这些方法技术近期内在寻找隐伏矿及解决环境,地震预报,地热工发等研究领域发挥重要作用。 相似文献
157.
158.
当利用无线电电磁波进行远程通信、卫星导航时,传递信号要受到电离层的影响,因此,对电离层中电子含量的研究显得特别重要.虽然国际上有几种电离层的电子含量预报模型,但其预报只能精确到电子含量的50%~60%.本文提出了一种新的电离层电子含量预报方法:即用球谐函数对IGS(国际GPS服务)所给出的离地面450 km高的球面上的每一网点的电离层电子含量进行拟合,对不同的时间所得到的拟合系数所形成的时间序列用时间序列分析理论中的ARMA(p,q)模型进行预报,从而实现全球的电离层电子含量预报.利用本方法对2004年和2005年IGS所给电离层电子含量资料在地理框架中做了分析预报,5天内电子含量预报相对精度在90%左右. 相似文献
159.
We investigate the temporal correlation function and the mean intensity of monochromatic radio emission in the neighborhood
of a regular caustic produced by radio sounding of near-solar plasma. Using asymptotic analysis and numerical simulation,
we determine conditions under which the temporal correlation function is related to the temporal structure function by a relation
similar to that used for the solar wind diagnostics (Coles and Harmon, Astrophys. J.
337, 1023, 1989) in the case of weak refraction of radio waves. Information on the correlation function and on the mean intensity in the
caustic shadow region can be used to determine the parameters of the electron density fluctuation spectrum at small heliocentric
distances. 相似文献
160.
C. A. McCammon 《Physics and Chemistry of Minerals》1998,25(4):292-300
Mössbauer spectra were recorded at multiple temperatures between 80 and 293 K to study the nature of Fe3+ in Fe0.05Mg0.95SiO3 perovskite that had been synthesised in a multianvil press at 1650 °C and 25 GPa at its mimimum stability limit. The Mössbauer data were fitted to a model with quadrupole splitting distributions (Fe2+) and Lorentzian lineshapes (Fe3+ and Fen+). The centre shift data were fitted to a Debye model with the following results: ΘM (Fe2+)=365±52 K and ΘM (Fe3+)=476±96 K. Hyperfine parameter data for Fe3+ suggest occupation of the octahedral site only. The average valence seen by the Mössbauer effect in rapid electron exchange that occurs between Fe2+ and Fe3+ is calculated from the hyperfine parameters to be 2.50±0.07. Correction of area fractions for site-dependent recoil-free fractions gives a value for Fe3+/∑Fe of 9.4±1.4%, which is independent of temperature. A perovskite phase of similar composition synthesised in the multianvil press at higher oxygen fugacity gives a value for Fe3+/∑Fe of 16±3%, where Fe3+ appears to occupy both sites in the perovskite structure. 相似文献