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定向凝固参数对二元铝锂合金共晶生长及组织结构的影响 总被引:2,自引:0,他引:2
本文研究了定向凝固参数对二元铝锂合金共晶生长及组织结构的影响。实验发现,Li少于7wt%的合金中,晶体不能以共晶方式生长。Li多于7wt%的合金中,可以获得平面生长的共晶组织,凝固参数对晶体生长方式及组织形貌有显著的影响 相似文献
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Mehmet B. Guldogan Orhan Arıkan Feza Arıkan 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2009
A novel array signal processing technique is proposed to estimate HF channel parameters including number of paths, their respective direction of arrivals (DOA), delays, Doppler shifts and amplitudes. The proposed technique utilizes the Cross Ambiguity Function (CAF), hence, called as the CAF-DF technique. The CAF-DF technique iteratively processes the array output data and provides reliable estimates for DOA, delay, Doppler shift and amplitude corresponding to each impinging HF propagated wave onto an antenna array. Obtained results for both real and simulated data at different signal to noise ratio (SNR) values indicate the superior performance of the proposed technique over the well known MUltiple SIgnal Classification (MUSIC) technique. 相似文献
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主星带辅星群干涉SAR编队设计的约束条件 总被引:2,自引:0,他引:2
针对主星带辅星群干涉SAR的星载双站、斜视、空间基线等特点,从系统工作过程和测高性能分析角度出发,分别对主星带辅星编队干涉SAR编队设计的几个变量(主星与辅星群的距离、基线的长度和指向角)提出设计约束条件。对辅星回波时序、信噪比进行分析,得到主、辅星间距离设计的约束条件;对干涉测高精度进行分析,重点考虑空间基线去相关对干涉相位误差进而对测高精度的影响,给出基线长度和指向角与干涉测高精度的关系,得到基线长度和指向角设计的约束条件。仿真分析表明,由于干涉车轮和干涉钟摆编队是基于正侧视干涉几何提出的,它们的测高性能不是最优的。 相似文献
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In order to determine an appropriate attitude of three-axis stabilized communication satellites, this paper describes a novel attitude determination method using direction of arrival (DOA) estimation of a ground signal source. It differs from optical measurement, magnetic field measurement, inertial measurement, and global positioning system (GPS) attitude determination. The proposed method is characterized by taking the ground signal source as the attitude reference and acquiring attitude information from DOA estimation. Firstly, an attitude measurement equation with DOA estimation is derived in detail. Then, the error of the measurement equation is analyzed. Finally, an attitude determination algorithm is presented using a dynamic model, the attitude measurement equation, and measurement errors. A developing low Earth orbit (LEO) satellite which tests mobile communication technology with smart antennas can be stabilized in three axes by corporately using a magnetometer, reaction wheels, and three-axis magnetorquer rods. Based on the communication satellite, simulation results demonstrate the effectiveness of the method. The method could be a backup of attitude determination to prevent a system failure on the satellite. Its precision depends on the number of snapshots and the input signal-to-noise ratio (SNR) with DOA estimation. 相似文献