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841.
Le Cadre J.-P. Jaetffret C. 《IEEE transactions on aerospace and electronic systems》1999,35(3):801-818
This paper deals with the analysis of the convergence of iterative methods for bearings only tracking (BOT). A geometric and unified framework is developed. Explicit sufficient conditions ensuring convergence of iterative methods for maximization of the likelihood functional are then derived 相似文献
842.
随着航空机载系统市场竞争的愈发激烈,航空机载技术的先进性愈发受到重视,您认为航空机载技术的发展趋势是怎样的?滕霖:随着新一代飞行器的发展,航空机载系统正朝着综合化、精密微型化、结构轻量化 相似文献
843.
提出了一种基于单目相机的小型多旋翼无人机的连续避障策略。所提出的方法包括深度估计和导航决策两个模块。其中,在深度估计模块采用条件对抗网络对无人机采集得到的RGB图片进行训练预处理,在导航决策模块采用深度确定性策略梯度(DDPG)算法实现无人机的连续避障。在此基础上,对DDPG中的Actor网络进行改进,通过使用多模态网络代替原有策略网络,从而抑制无人机飞行震动,提高避障能力。最后,在Airsim仿真环境中进行测试,实验表明所提算法模型经过训练能够使无人机成功躲避障碍物并到达指定目标点,与原有算法相比避障轨迹得到明显改善。 相似文献
844.
G. Schubert C. C. Counselman III J. Hansen S. S. Limaye G. Pettengill A. Seiff I. I. Shapiro V. E. Suomi F. Taylor L. Travis R. Woo R. E. Young 《Space Science Reviews》1977,20(4):357-387
With the possible exception of the lowest one or two scale heights, the dominant mode of circulation of Venus' atmosphere is a rapid, zonal, retrograde motion. Global albedo variations in the ultraviolet may reflect planetary scale waves propagating relative to the zonal winds. Other special phenomena such as cellular convection in the subsolar region and internal gravity waves generated in the interaction of the zonal circulation with the subsolar disturbance may also be revealed in ultraviolet imagery of the atmosphere. We discuss the contributions of experiments on the Orbiter and Entry Probes of Pioneer Venus toward unravelling the mystery of the planet's global circulation and the role played by waves, instabilities and convection therein. 相似文献
845.
846.
Theoretical pressure balance arguments have implied that steady convection is hardly possible in the terrestrial magnetotail and that steady energy input necessarily generates a cyclic loading-unloading sequence, i.e., repetitive substorms. However, observations have revealed that enhanced solar wind energy input to the magnetospheric system may either lead to substorm activity or enhanced but steady convection. This topic is reviewed with emphasis on several recent case studies of the Steady Magnetospheric Convection (SMC) events. In these cases extensive data sets from both satellite and ground-based instruments from various magnetospheric and ionospheric regions were available.Accurate distinction of the spatial and temporal scales of the magnetospheric processes is vital for correct interpretation of the observations during SMC periods. We show that on the large scale, the magnetospheric configuration and plasma convection are stable during SMC events, but that both reveal considerable differences from their quiet-time assemblies. On a shorter time scale, there are numerous transient activations which are similar to those found during substorms, but which presumably originate from a more distant tail reconnection process, and map to the poleward boundary of the auroral oval. The available observations and the unresolved questions are summarized here.The tail magnetic field during SMC events resembles both substorm growth and recovery phases in the neartail and midtail, respectively, but this configuration may remain stable for up to ten hours. Based on observations and model results we discuss how the magnetospheric system avoids pressure balance problems when the plasma convects earthward.Finally, the importance of further coordinated studies of SMC events is emphasized. Such studies may shed more light on the substorm dynamics and help to verify quantitatively the theoretical models of the convecting magnetosphere. 相似文献
847.
Sarles F.W. Stanley A.G. Roberge J.K. Godfrey B.W. 《IEEE transactions on aerospace and electronic systems》1973,(6):921-924
For direct measurement of the integrated radiation dose experienced in Earth synchronous orbit, p-i-n diodes were flown as radiation dosimeters on LES-6. The diode, which has a lifetime of 10-4 seconds in the intrinsic region, was originally developed as a neutron dosimeter, but can detect 1-MeV electron fluences as low as 1013 e·cm-2. Observations over three years in orbit are presented. 相似文献
848.
849.
Investigations of Mir, Space Shuttle, Skylab and Apollo missions report extensive colonisation of the spacecraft by bacteria and fungi, which can lead to degradative effects on spacecraft equipment and devastating effects on space-grown crops. More than 80% of terrestrial greenhouse epidemics are due to the fungal genera Phytophthora, Pythium and Fusarium, which have been found in life support system test-beds. The advent of recombinant antibody technologies, including ribosome display and phage display, has made it possible to develop antibodies against virtually any toxin or organism and allows for maturation of antibodies by in vitro molecular evolution. These antibodies may play an important role in an integrated pest management regime for life support systems. Efficacy of existing fungal countermeasures could be increased by chemical linkage to antibodies, which target the site of action of the biocide or trap the pathogen in a biofilter. Novel recombinant antibody-biocide fusions can be expressed in situ by plants or symbiotic microbes to create direct disease resistance. 相似文献
850.
The Sun–Earth connection is studied using long-term measurements from the Sun and from the Earth. The auroral activity is shown to correlate to high accuracy with the smoothed sunspot numbers. Similarly, both geomagnetic activity and global surface temperature anomaly can be linked to cyclic changes in the solar activity. The interlinked variations in the solar magnetic activity and in the solar irradiance cause effects that can be observed both in the Earth's biosphere and in the electromagnetic environment. The long-term data sets suggest that the increase in geomagnetic activity and surface temperatures are related (at least partially) to longer-term solar variations, which probably include an increasing trend superposed with a cyclic behavior with a period of about 90 years. 相似文献