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161.
当测量参数(或称测量元素)具有强相关性时,运用测量求差法解算测量结果,能消除相关性误差因素的影响,获得高精度测量结果,如电影望远镜同帧画幅测量脱靶量.基于此,运用测量方法和数学手段构建一个虚拟的元素相关测量系统,以消除相关性误差因素的影响,同样能获得理想结果.用多台测速雷达组成的系统,可使火炮弹丸空间坐标的测量精度达到毫米量级,从而满足多种火炮立靶密集度的测量精度要求. 相似文献
162.
Ola A. Abuelezz Ayman M. Mahrous Pierre J. Cilliers Rolland Fleury Mohamed Youssef Mohamed Nedal Ahmed M. Yassen 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2021,67(4):1191-1209
This study presents the first prediction results of a neural network model for the vertical total electron content of the topside ionosphere based on Swarm-A measurements. The model was trained on 5 years of Swarm-A data over the Euro-African sector spanning the period 1 January 2014 to 31 December 2018. The Swarm-A data was combined with solar and geomagnetic indices to train the NN model. The Swarm-A data of 1 January to 30 September 2019 was used to test the performance of the neural network. The data was divided into two main categories: most quiet and most disturbed days of each month. Each category was subdivided into two sub-categories according to the Swarm-A trajectory i.e. whether it was ascending or descending in order to accommodate the change in local time when the satellite traverses the poles. Four pairs of neural network models were implemented, the first of each pair having one hidden layer, and the second of each pair having two hidden layers, for the following cases: 1) quiet day-ascending, 2) quiet day-descending, 3) disturbed day-ascending, and 4) disturbed day-descending. The topside vertical total electron content predicted by the neural network models compared well with the measurements by Swarm-A. The model that performed best was the one hidden layer model in the case of quiet days for descending trajectories, with RMSE = 1.20 TECU, R = 0.76. The worst performance occurred during the disturbed descending trajectories where the one hidden layer model had the worst RMSE = 2.12 TECU, (R = 0.54), and the two hidden layer model had the worst correlation coefficient R = 0.47 (RMSE = 1.57).In all cases, the neural network models performed better than the IRI2016 model in predicting the topside total electron content. The NN models presented here is the first such attempt at comparing NN models for the topside VTEC based on Swarm-A measurements. 相似文献
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An efficient LDPC-coded multi-relay cooperation architecture is proposed based on virtual vertical Bell Labs layered space-time (V-BLAST) processing for uplink communication, where minimum-mean-square-error (MMSE) and BP-based joint iterative decoding based on the introduced muhi-layer Tanner graph are effectively de- signed to detect and decode the corrupted received sequence at the destination. By introducing V-BLAST transmis- sion to the coded multi-relay cooperation, relays send their streams of symbols simultaneously, which increases the data rate and significantly reduces the transmission delay. The theoretical analysis and numerical results show that the new LDPC coded cooperation scheme outperforms the coded non-cooperation under the same code rate, and it also achieves a good trade-off among the performance, signal delay, and the encoding complexity associated with the number of relays. The performance gain can be credited to the proposed V-BLAST processing architecture and BP-based joint iterative decoding by the introduced multi-layer Tanner graph at a receiver-side. 相似文献
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旋翼固定翼复合式垂直起降飞行器概念设计研究 总被引:2,自引:1,他引:2
近些年来垂直起降(VTOL)飞行器发展迅速,并获得了一些突破性进展,但仍有许多尚未解决的问题。结合旋翼机和固定翼飞机的优点,提出一种旋翼固定翼复合式飞行器布局方案,兼具优异的垂直起降性能及高速飞行能力,具有转换过渡稳定平滑、可控性强的特点。在该旋翼固定翼复合式布局中,特型旋翼可旋转以提供垂直升力,也可停转、锁定与固定式机翼保持平行,最终转换为固定翼面使得飞机转换为固定翼布局,并在机翼上布置矢量推力装置,实现高速飞行。概念设计研究围绕设计方法、特型旋翼、矢量推力系统等关键技术展开,并开展了平飞模式飞行特性、垂直起降模式飞行特性、航程、航时以及飞行操纵等性能的分析。通过试制小型原理验证机,并对各飞行状态及转换过渡飞行进行飞行试验,验证了该布局的可行性。结合实际算例展开分析计算,验证了该方案设计方法的准确性和实用性。 相似文献
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引入了一种新型垂直轴传动机构,该机构首次被应用于民用飞机舱门设计中,具有一定的先进性。介绍了其基本构型、传动原理及在舱门上的典型应用。深入分析了其机构特性,并依据解析几何的方法推导出该机构输入输出角度计算公式,从而得出了该机构的参数化设计方法。 相似文献