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211.
近场散射数据的远场变换研究是具有发展前景的由近场测量目标,获取目标远场雷达截面的方法之一。根据近场获得的散射数据,外推获取远场的目标散射特性。主要是利用平面波谱展开,推导了近远场转换公式;以导体圆柱、平板等简单物体作为散射体仿真了近场散射数据的远场变换,证明了方法的可行性和正确性。 相似文献
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213.
时分多址(TDMA)扩频通信系统的同步捕获是一个很重要的问题,如何实现快速同步则更重要。采用声表面波器件,时间延时门和一致检测窗能十分满意地解决同步的快速捕获,精度达正负半个码元。本文还讨论了两种基本的快速同步捕获的方法,並给出了试验结果。 相似文献
214.
本文采用移动式SOUSYVHF雷达1987年6月在挪威Andφya(69°N,10°E)的观测数据,研究中层惯性重力波在临界层的传播特征.数据分析结果表明,在临界层附近波动会突然衰减,波能量被背景风所吸收,惯性重力波的水平传播方向和垂直传播方向在通过临界层后会迅速发生改变,说明临界层附近会产生向下传播的能量源.并且在临界层,回波强度达到峰值,表明临界层对产生雷达回波起着重要作用. 相似文献
215.
E.L. Afraimovich I.K. Edemskiy S.V. Voeykov Yu.V. Yasyukevich I.V. Zhivetiev 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2009,44(7):824-835
Using long-term (1998--2009) total electron content (TEC) measurements from the GPS global network including dense network of GPS sites in USA and Japan, we have obtained the first data regarding the spatio-temporal structure and the statistics of medium-scale traveling wave packets (MS TWPs) excited by the solar terminator (ST). Total amount of the detected TWPs exceeds 565,000. There is no correlation between TWPs occurrence and geomagnetic and solar activity. We found that the diurnal, seasonal and spectral MS TWPs characteristics are specified by the solar terminator (ST) dynamics. MS TWPs are the chains of narrow-band TEC oscillations with single packet’s duration of about 1–2 h and oscillation periods of 10–20 min. The total duration of chain is about 4–6 h. The MS TWPs spatial structure is characterized by a high degree of anisotropy and coherence at the distance of more than 10 wavelengths. Occurrence rate of daytime MS TWPs is high in winter and during equinoxes. Occurrence rate of nighttime MS TWPs has its peak in summer. These features are consistent with previous MS travelling ionosphere disturbance (TID) statistics obtained from 630-nm airglow imaging observations in Japan. In winter, MS TWPs in the northern hemisphere are observed 3–4 h after the morning ST passage. In summer, MS TWPs are detected 1.5–2 h before the evening ST appearance at the point of observations, but at the moment of the evening ST passage in the magneto-conjugate point. The obtained results are the first experimental evidence for the hypothesis of the ST-generated ion sound waves. 相似文献
216.
Aeroelastic stability analysis of heated flexible panel subjected to an oblique shock 总被引:1,自引:1,他引:1
The critical conditions for aeroelastic stability and the stability boundaries of a flexible two-dimensional heated panel subjected to an impinging oblique shock are considered using theoretical analysis and numerical computations, respectively. The von-Karman large deflection theory of isotropic flat plates is used to account for the geometrical nonlinearity of the heated panel, and local first-order piston theory is employed in the region before and after shock waves to estimate the aerodynamic pressure. The coupled partial differential governing equations, according to the Hamilton principle, are established with thermal effect based on quasi-steady thermal stress theory. The Galerkin discrete method is employed to truncate the partial differential equations into a set of ordinary differential equations, which are then solved by the fourth-order Runge-Kutta numerical integration method. Lyapunov indirect method is applied to evaluate the stability of the heated panel. The results show that a new aeroelastic instability (distinct from regular panel flutter) arises from the complex interaction of the incident and reflected wave system with the panel flexural modes and thermal loads. What’s more, stability of the panel is reduced in the presence of the oblique shock. In other words, the heated panel becomes aeroelastically unstable at relatively small flight aerodynamic pressure. 相似文献
217.
Dipak Debnath Sandip K. Chakrabarti Anuj Nandi 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2013
The Galactic black hole candidate H 1743-322 exhibited two X-ray outbursts in rapid succession: one in August 2010 and the other in April 2011. We analyze archival data of this object from the PCA instrument on board RXTE (2–25 keV energy band) to study the evolution of its temporal and spectral characteristics during both the outbursts, and hence to understand the behavioral change of the accretion flow dynamics associated with the evolution of the various X-ray features. We study the evolution of QPO frequencies during the rising and the declining phases of both the outbursts. We successfully fit the variation of QPO frequency using the Propagating Oscillatory Shock (POS) model in each of the outbursts and obtain the accretion flow parameters such as the instantaneous shock locations, the shock velocity and the shock strength. Based on the degree of importance of the thermal (disk black body) and the non-thermal (power-law) components of the spectral fit and properties of the QPO (if present), the entire profiles of the 2010 and 2011 outbursts are subdivided into four different spectral states: hard, hard-intermediate, soft-intermediate and soft. We attempt to explain the nature of the outburst profile (i.e., hardness-intensity diagram) with two different types of mass accretion flow. 相似文献
218.
倾斜分层非均匀介质中磁偶极子场的数值分析 总被引:5,自引:0,他引:5
研究倾斜分层非均匀介质条件下磁偶极子源在介质空间的电磁响应,给出了场表达式和数值递推算法,提出了在大倾角条件下利用电阻率曲线划分界面和进行前向预测的方法,数值模拟和应用实践证明该方法是有效的,结论具有一定的应用价值. 相似文献
219.
220.
E.V. Moskaleva N.Y. Zaalov 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2014
The simulation of the multi-beam ionograms in the polar cap region, assessing absorption effect is performed. It is reasonable to distinguish among four different mechanisms responsible for absorption: regular absorption due to solar UV illumination, absorption associated with energetic particles precipitation, absorption connected with X-rays flare and additional absorption in Auroral oval area. In this paper the absorption attributed to proton precipitations is envisaged. The computational model of the high-latitude ionosphere with irregularities oriented to application for the high frequency wave propagation problem was elaborated (Zaalov et al., 2005). A number of the quasi-vertical ionograms in the polar cap region were simulated on the basis of this model. A well-known algorithm (Sauer and Wilkinson, 2008) is applied for the absorption effects calculation. The simulated high-latitude ionograms with the absorption effect and the measured ionograms exhibit quite a good resemblance. This paper illustrates the importance of the understanding and taking into account the absorption effect in the presence of the various structural features in the polar ionosphere (in particular, patches of enhanced electron density) in interpreting ionosonde data. 相似文献