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991.
Smirnova N. V. Lyakhov A. N. Setzer Yu. I. Osepian A. P. Meng C.-I. Smith R. Stenbaek-Nielsen H. C. 《Cosmic Research》2004,42(3):210-218
Spatial distributions of the electron density in the latitude range 60°–90° N were calculated on the basis of a physical model of the E and lower Fregions of the high-latitude ionosphere using statistical models of auroral proton and electron precipitation. It is shown that precipitating protons can play the key role in the ionization of the Eregion in the dusk and midnight sectors of the auroral oval. However, quantitative estimates of the contribution of protons to the ionization depend on the used statistical models of electron precipitation. Comparison of the electron density profiles calculated for two incoherent scatter radars, EISCAT (Tromsö) and ESR (Svalbard), for simultaneous precipitation of electrons and protons and for electron precipitation only show that the influence of protons is the most significant in the dusk sector over the EISCAT radar and in the midnight sector over the ESR radar. The results presented indicate the need to take protons into account when radar data are used to derive precipitating electron spectra. 相似文献
992.
F. G. von der Dunk E. Back-Impallomeni S. Hobe R. M. Ramirez de Arellano 《Space Policy》2004,20(3):149-156
At a time when scientific and commercial interest in the Moon is being reinvigorated it is becoming fashionable for ordinary individuals to ‘buy’ plots on the lunar surface, with the ‘vendors’ arguing that an absence of specific prohibition of individual private activity in space makes such action legal. It is therefore time for the legal community to address this situation by investigating just how legal such activity is—and bringing their findings to the attention of governments. This can be done through an examination of the relationship between national law and international space law, of the provisions of international space law—especially Article 2 of the Outer Space Treaty—and by answering any claims to private ownership of immovable property. Aside from the fact that individuals appear to be being duped, the pursuit of property claims on the Moon could impede future activities aimed at benefiting society. 相似文献
993.
V. A. Kosmodemyanskii 《Cosmic Research》2004,42(1):84-91
The problem of optimum partitioning of a staged vehicle (SV) and determination of the minimal number of stages to provide for a maximum velocity in the vertical SV motion in a homogeneous gravity field is considered at a given value of payload mass. 相似文献
994.
The motion of a variable-mass spacecraft is considered in the powered section of a descending trajectory. Approximate analytical solutions are obtained for the angles of spatial orientation of the spacecraft, which allows one to analyze the nutation motion and to develop recommendations on the spacecraft’s mass configuration, providing the smallest possible deviations of the longitudinal axis and thrust vector from specified directions. The errors of stabilization of the spacecraft’s longitudinal axis are calculated by means of numerical integration of complete models and using the obtained analytical solutions, the results being in good agreement. 相似文献
995.
A new procedure for restoration of the plasma inhomogeneities with improved resolution is suggested. The procedure deals with the double weighted Fourier transform (DWFT) of the observed wavefield in coordinates of both receivers = (x, y) and sources
0 = (x
0, y
0) [1]. Phase increments between the sources and receivers, being found from DWFT representation, can be used for extracting information on small perturbations of the dielectric constant ~(, z) in a way similar to traditional radio tomography. The resulting resolution of the method is close to the diffraction limit = h/D in the horizontal direction and z = (h/D)2 in the vertical direction, where h is the height of inhomogeneities and D is the length of the ground-based receiving system. 相似文献
996.
997.
Abrashkin V. I. Volkov M. V. Egorov A. V. Zaitsev A. S. Kazakova A. E. Sazonov V. V. 《Cosmic Research》2003,41(6):593-612
We compare the results of two methods used to determine the angular velocity of the Foton-12 satellite and the low-frequency component of microaccelerations onboard it. The first method is based on reconstruction of the satellite's rotational motion using the data of onboard measurements of the strength of the Earth's magnetic field. The motion (time dependence of the orientation parameters and angular velocity) was found from the condition of best approximation of the measurement data by the functions calculated along the solutions to equations of attitude motion of the satellite. The solutions found were used to calculate the quasistatic component of microaccelerations at certain points of the satellite, in particular, at the point of location of an accelerometer of the QSAM system. Filtration of the low-frequency component of the angular velocity and microacceleration from the data of measurements by a sensor of angular velocity and by the accelerometer of this system served as a second method. The filtration was made using the discrete Fourier series. A spectral analysis of the functions representing the results of determining the angular velocity and microacceleration by both methods is performed. Comparing the frequencies and amplitudes of the harmonic component of these functions allowed us to estimate the accuracy of measurements made by the QSAM system in the low-frequency range. 相似文献
998.
999.
化学气相反应法在C/C复合材料抗氧化处理中的应用 总被引:3,自引:0,他引:3
通过把硅蒸气渗入预制体孔隙与碳直接反应生成SiC的化学气相反应(CVR)方法,提高初始密度和预制体结构均不同的C/C复合材料的抗氧化能力,研究了C/C复合材料的密度变化与微观结构,并对其进行了氧化试验。结果表明,因CVR温度、C/C复合材料初始密度不同,抗氧化处理后的密度增加量有显著不同。针刺炭布C/C/SiC复合材料在马福炉中于1160℃经65min氧化后,其失重率仅2.6%,而密度为1.95g/cm^3的同结构C/C复合材料相在同条件下失重率高达32%。 相似文献
1000.
As the USA, Europe and other nations embark on a new voyage of exploration to the Moon, Mars and beyond, they should lay the foundations and establish precedents that invite a host of participants and followers. We argue that international cooperation, driven by foreign-policy and cost-sharing considerations, has taken a prominent role but must be pragmatically and flexibly balanced with economic and strategic self-interest. Since exploration visions are likely to differ, the steps each country will pursue, the funding provided, and schedules followed will also differ. To support an enduring exploration vision, it will be important to remain flexible to changing priorities and amenable to the inclusion of new, non-traditional participants. Open-systems principles and metaprinciples should be employed at all levels—hardware, software, programmatic, political and cultural. Equally important, national leadership and decision makers should be mindful of the potential pitfalls that might undermine the venture. While the new vision inspires us all, it will take creativity, resourcefulness, hard work and cooperation to succeed. 相似文献