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41.
利用外辐射源(如调频广播、电视、GPS等的发射信号)的无源雷达探测技术一直是国内外研究的热点。在目标检测上,直达波信号的干扰不但对通道的动态范围提出了极高的要求,同时对微弱目标回波的检测构成了限制。文中利用二元阵的方法对直达波的干扰进行抑制,并对其对消性能进行了仿真分析和研究。 相似文献
42.
As a promising numerical tool of structural dynamics in mid-and high frequencies, the wave and finite element method (WFEM) is receiving increasingly attention and applications. In this paper, an enhanced WFEM has been developed with a reduced model and a new eigenvalue scheme. The reduced model is applicable for structures with piezoelectric shunts or local dampers;the new eigenvalue scheme can mitigate the ill-conditioning when the wave basis is calculated. The enhanced WFEM is applied to a thin-wall structure with periodically distributed piezoelectric mate-rials (PZT). Both free wave characteristics and forced response are analyzed and the influences of the suggested enhancements are presented. It is shown that if the control factors are properly cho-sen, these enhancements can improve the accuracy while accelerating the calculation. Resulting from the complexity of the application, these enhancements are not optional but imperative. 相似文献
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44.
A. Taori V. Kamalakar A. Jayaraman 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2012
We summarize two years of Mesosphere Lower Thermosphere Photometer (MLTP) operation of mesospheric OH and O2 emission monitoring. The deduced mesospheric OH and O2 temperatures show large variability. Nightly temperature variations over Gadanki (13.5°N, 79.2°E) are dominated by the short period wave features, while tidal amplitudes are relatively small. Our measurements are the first to report a long period seasonal variation at two upper mesospheric altitudes simultaneously over the Indian sector. Our observations reveal the presence of a dominant semi-annual oscillation (∼6 months periodicity) together with a shorter period (∼2.5 months periodicity) oscillation in both OH and O2 data. 相似文献
45.
Tai-Yin Huang Michael Hickey 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2008,41(9):1478-1487
Secular variations of OH airglow (8,3) band and of the intensity-weighted temperature induced by a gravity wave packet at three latitudes in the northern hemisphere in the Mesosphere/Lower Thermosphere region are investigated using a 2-D, time-dependent, fully nonlinear OH chemistry–dynamics model. A net-cycled average survives due to wave transience and dissipation. The integrated OH (8,3) volume emission rates show a 20 percent increase induced by the wave packet. The corresponding intensity-weighted temperature shows an initial increase up to 2 percent then a gradual decrease for the remainder of the simulation time by the same wave packet. These secular variations could be mistaken as long-period or short-period waves in the airglow observations. Therefore, care must be taken when analyzing the data from observations. 相似文献
46.
Fedir Dudkin Valery Korepanov Georgiy Lizunov 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2009,43(12):1904-1909
The international experiment VARIANT was carried out onboard Ukrainian remote sensing satellite SICH-1M launched 2004, December 24. In spite of other than planned satellite orbit and onboard systems failure about 11 telemetric files from VARIANT payload were obtained. Due to episodic and random payload switching the main goal of VARIANT experiment - study of field aligned currents and monitoring of electromagnetic state of the ionosphere – was not possible to realize. However the data analysis from VARIANT instrumentation allowed us to obtain for the first time a reliable confirmation of proper operation in ionospheric plasma of a new device developed for wave activity study – Wave Probe, which consists of compact combination of Split Langmuir Probe working at floating potential and search-coil magnetic field sensor. Such a probe can simultaneously measure variations of one component of spatial current density and a perpendicular component of magnetic field with a spectral sensitivity threshold up to 0.1 pA/(cm2 Hz1/2) and 0.03 pT/Hz1/2, respectively. 相似文献
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48.
探针特性曲线的初级电子修正及用离子声波速度测电子温度的研究 总被引:1,自引:0,他引:1
在Te》Ti,且存在两种电子能量的等离子体中,讨论了正确进行朗缪尔探针特性曲线修正——初级电子修正方法;用朗缪尔探针方法得到的等离子体电子温度与离子声波速度测量得到的电子温度分布实验结果比较证明,提出的初级电子修正方法是正确的.实验结果还表明,用离子声波速度测量得到的电子温度误差较小,平均测量误差△Te大约只有0.1eV,有望成为一种可行的电子温度测量方法. 相似文献
49.
一种单片机控制超低频任意信号波形发生器 总被引:2,自引:0,他引:2
陈琼 《南昌航空工业学院学报》2004,18(3):72-74
本文介绍一种以AT89C52单片机为控制核心,采用直接数字波形合成技术产生方波、三角波、锯齿波、正弦波和其他周期信号波形的方法。其频率范围在0.001Hz~999.9Hz之间。幅度在0~20V无级连续可调,波形失真度:〈0.5%。具有稳定性好、性能优越、功能强大、操作方便等特点,使用价值高。 相似文献
50.
Research of low boom and low drag supersonic aircraft design 总被引:1,自引:1,他引:1
Sonic boom reduction will be an issue of utmost importance in future supersonic transport, due to strong regulations on acoustic nuisance. The paper describes a new multi-objective optimization method for supersonic aircraft design. The method is developed by coupling Seebass–George–Darden(SGD) inverse design method and multi-objective genetic algorithm.Based on the method, different codes are developed. Using a computational architecture, a conceptual supersonic aircraft design environment(CSADE) is constructed. The architecture of CSADE includes inner optimization level and out optimization level. The low boom configuration is generated in inner optimization level by matching the target equivalent area distribution and actual equivalent area distribution. And low boom/low drag configuration is generated in outer optimization level by using NSGA-II multi-objective genetic algorithm to optimize the control parameters of SGD method and aircraft shape. Two objective functions, low sonic boom and low wave drag, are considered in CSADE. Physically reasonable Pareto solutions are obtained from the present optimization. Some supersonic aircraft configurations are selected from Pareto front and the optimization results indicate that the swept forward wing configuration has benefits in both sonic boom reduction and wave drag reduction. The results are validated by using computational fluid dynamics(CFD) analysis. 相似文献