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991.
J.-P. Bibring F. Rocard 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1984,4(12):103-106
The irradiation of grains and/or ices by particles from solar or stellar winds, as well as cosmic rays, induces the synthesis of molecular species. We have shown by in-situ infrared spectroscopy of irradiated samples that this chemistry may be responsible for the presence of organic compounds in a large variety of astrophysical sites such as: lunar and asteroidal regoliths, cometary nucleus, rings and satellites of outer planets, circumstellar shells, interstellar clouds. We present our experimental results concerning the nature and efficiency of C and N irradiation chemistries, and give plausible astrophysical implications. 相似文献
992.
The attitude stability of a dual-spin satellite containing energy disipators on both bodies is investigated. Following Mingori, a symmetrical configuration of the satellite with a mass-spring-dashpot damper on each part is considered, and some new stability results are derived by the application of the Routh-Hurwitz criterion. lt is indicated that the Routh-Hurwitz criterion gives only sufficient conditions of stability for the dual-spin satellite considered. A criterion which is believed to represent both the necessary and sufficient condition of stability is presented here and this is used to check the stability of two specific designs of the dual-spin satellite. 相似文献
993.
Hespanha J.M. Yakimenko O.A. Kaminer I.I. Pascoal A.M. 《IEEE transactions on aerospace and electronic systems》2004,40(3):889-902
This paper addresses the problem of nonlinear filter design to estimate the relative position and velocity of an unmanned air vehicle (UAV) with respect to a point on a ship using infrared (IR) vision, inertial, and air data sensors. Sufficient conditions are derived for the existence of a particular type of complementary filters with guaranteed stability and performance in the presence of so-called out-of-frame events that arise when the vision system loses its target temporarily. The results obtained build upon new developments in the theory of linear parametrically varying systems (LPVs) with brief instabilities - also reported in the paper - and provide the proper framework to deal with out-of-frame events. Field tests with a prototype UAV illustrate the performance of the filter and the scope of applications of the new theory developed. 相似文献
994.
The influence of geometry and operating conditions of the centrifugal compressor stage on the radial gas force is determined on the basis of the theoretical method and calculation program using experimental boundary conditions. 相似文献
995.
A two-element adaptively phased array withelement gains of 18 dB was assembled andevaluated at 136 MHz. The gain improvementof the system over that of a single element wasmeasured while tracking ATS-C. The measuredgain improvement fell within 0.5 dB ofthe theoretical maximum 90 percent of thetime, corresponding to a normalized improvementof 2.5 dB for the two-element array. Athorough analysis of the AGC weighting processused in the system was made with particularemphasis placed on the effects of gainand noise figure variations between arraychannels. 相似文献
996.
The analysis of a second-order tracking loop operating in the frequency-search mode is carried out by the quasi-stationary approach. An arbitrary phase detector characteristic is assumed and perfect or imperfect integrating filters are considered. The theory leads to a closed-form expression of the acquisition time versus the relevant system parameters, the initial detuning, and the search rate. The limitations of this analysis concern the absence of noise and the hypothesis of large initial detuning. 相似文献
997.
The scheme variants of implementing the thermal protection against heat flows being generated by the body of a high-temperature stationary gas turbine engine (GTE) are presented. The scheme of the experimental bench with a working section is given. Methodical approaches to the heat transfer calculation at different variants of forced and natural convection organization and under various operating conditions are described. The generalized results of the experiments carried out using a heat curtain being generated by porous injection are presented. 相似文献
998.
999.
In this paper the problem of uplink array calibration for deep-space communication is considered. A phased array of many modest-size reflectors antennas is used to drastically improve the uplink effective isotropic radiated power of a ground station. A radar calibration procedure for the array phase distribution is presented using a number of in-orbit targets. Design of optimal orbit and the number of calibration targets is investigated for providing frequent calibration opportunities needed for compensating array elements phase center movements as the array tracks a spacecraft. Array far-field focusing based on the near-filed in-orbit (low Earth orbit (LEO)) calibration targets is also presented and array gain degradation analysis based on the position error of the array elements and in-orbit targets has been carried out. It is shown that errors in the in-orbit targets positions significantly degrade the far-field array gain while the errors in array elements positions are not very important. Analysis of phase errors caused by thermal noise, system instability, and atmospheric effects show insignificant array gain degradation by these factors 相似文献
1000.