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491.
492.
U. Villante M. De Lauretis P. Francia M. Vellante A. Piancatelli 《Space Science Reviews》2006,122(1-4):107-117
We review the results obtained in the frequency range of Pc3 (22-100 mHz) and Pc4 (7-22 mHz) pulsations at Italian Antarctic
stations in the southern polar cap (“Mario Zucchelli”, at Terra Nova Bay, TNB, 80˚.S; “Concordia”, the Italian/French base at Dome C, DMC, 89˚.S). The absence of a midnight enhancement in the pulsation power suggests a negligible substorm influence at extreme latitudes,
while the sharp noon enhancement, which appears only at TNB, is determined by the closer proximity of the station to cusp
related phenomena. The relationship between the frequency of the band-limited signals and the interplanetary magnetic field
strength, the cone angle influence, and the higher correlation of the Pc3 power with the solar wind speed in the morning hours
suggest a global scenario in which upstream waves would be mainly responsible for the mid-frequency activity in the polar
cap. However, the polarization pattern is odd with respect to the predictions for tailward propagating modes. 相似文献
493.
Robust space-time adaptive processing for airborne radar in nonhomogeneous clutter environments 总被引:1,自引:0,他引:1
Yong-Liang Wang Jian-Wen Chen Zheng Bao Ying-Ning Peng 《IEEE transactions on aerospace and electronic systems》2003,39(1):70-81
Space-time adaptive processing (STAP) holds tremendous potential for the new generation airborne surveillance radar, in which the phased array antennas and pulse Doppler processing mode are adopted. A new STAP approach using the multiple-beam and multiple Doppler channels is presented here for airborne phased array radar. The approach with space-time multiple-beam (STMB) architecture is robust to array errors and has very low system degrees of freedom (DOFs). Hence, it has low sample support requirement and it is very suitable for the practical planar phased array radar under nonhomogeneous clutter environments. Meanwhile, a new nonhomogeneous detector (NHD) based on the correlation dimension (CD) is also proposed here, which is used as an effective method to screen tracing data prior to detection processing. It can further improve the performance of the STAP approach in the severely nonhomogeneous clutter environments. Therefore, a scheme that incorporates the correlation dimension nonhomogeneity detector (CD-NHD) with the STMB is recommended, which we term CD-NHD-STMB. The experimental simulation results indicate that: 1) the STMB processor is robust to array element error and has high performance under nonhomogeneous clutter environments; 2) the CD-NHD is also effective on the nonhomogeneous clutter. As a result, the CD-NHD-STMB scheme is robust to array element error and nonhomogeneous clutter, and therefore available for airborne phased array radar applications. 相似文献
494.
495.
The radar designer must optimize parameters for performance in electronic countermeasures (ECM) and avoid any constraints which could be exploited by ECM. ECM/electronic counter-counter measures (ECCM) strategy must take into account electromagnetic compatibility (EMC) including enemy EMC. Electronic scanning improves search performance, but also reduces ECCM performance in other ways. While electronic scanning avoids some constraints, it imposes others, particularly in the frequency domain. It is argued that simple radars of good performance may be as cost effective in ECM as more complex systems. Some examples of recent developments are given. 相似文献
496.
绿色制造中的干切削技术 总被引:3,自引:0,他引:3
冷却润滑液的存储、使用以及废弃处理需要专门的物流系统,因而费用很高;冷却润滑液处理不当会对人的健康以及环境造成危害;工件经过湿加工后必须进行清洁处理,这都费时费力,同时增加了对系统的要求.基于上述原因,近年来干切削技术受到广泛关注. 相似文献
497.
Andrew P. Ingersoll 《Space Science Reviews》1976,18(5-6):603-639
Current information on the neutral atmosphere of Jupiter is reviewed, with approximately equal emphasis on composition and thermal structure on the one hand, and markings and dynamics on the other. Studies based on Pioneer 10 and 11 data are used to refine the atmospheric model. Data on the interior are reviewed for the information they provide on the deep atmosphere. The markings and dynamics are discussed with emphasis on qualitative relationships and analogies with phenomena in the Earth's atmosphere.Contribution No. 2652 of the Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, Calif. 91125, U.S.A. 相似文献
498.
国内民用航空制造业如今正在加速发展,而相应的备件工程与波音、空客都还是有一定的差距。结合ARJ21飞机项目研究了民用飞机初始备件计划模型,并在此基础上开发了备件计划软件系统,完成了初始备件计划工作的计算机化。 相似文献
499.
Els Peeters Nieves Leticia Martín-HernáNdez Nemesio J. RodríGuez-FernáNdez Xander Tielens 《Space Science Reviews》2005,119(1-4):273-292
An overview is given of ISO results on regions of high excitation ISM and gas, i.e. HII regions, the Galactic Centre and Supernova Remnants. IR emission due to fine-structure lines, molecular hydrogen, silicates,
polycyclic aromatic hydrocarbons and dust are summarised, their diagnostic capabilities illustrated and their implications
highlighted.
Based on observations with ISO, an ESA project with instruments funded by ESA Member States (especially the PI countries:
France, Germany, The Netherlands, and the United Kingdom), and with the participation of ISAS and NASA. 相似文献
500.