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451.
452.
The determination of the range of radar is carried out according to statistical methods which are not always immediate. For this reason, a parametrical method is proposed which condenses the elements necessary for this calculation in the form of three abaci. Furthermore, a general formula condenses this result, and the formula is extended to the other transmission systems. 相似文献
453.
An expression is derived for the cost resultingfrom the stabilization of a satellite using aspecific optimal control (SOC). An exampleis given in which the optimal and SOC yieldvirtually identical costs. 相似文献
454.
455.
456.
为了获得涡流阀参数对发动机推力调节性能的影响规律,针对涡流阀的加注方式以及几何结构,利用建立的基于涡流阀方案的固体火箭发动机推力可调实验系统开展了实验研究。通过实验结果的分析,得到了加注环孔径、涡流室高度和直径以及中心进气面积的不同对涡流阀调节性能的影响规律。结果表明:适当降低涡流室的高度、较大的中心进气面积、较大的涡流室直径有利于提高涡流阀的调节性能。因此,可以通过对涡流阀结构的优化设计来提高发动机的推力调节性能。 相似文献
457.
458.
R. J. Murphy 《Space Science Reviews》2007,130(1-4):127-138
Interactions of ions accelerated in solar flares produce gamma-ray lines and continuum and neutrons. These emissions contain
a rich set of observables that provides information about both the accelerated ions and the environment where the ions are
transported and interact. Ion interactions with the various nuclei present in the ambient medium produce gamma-ray lines at
unique energies. How abundance information is extracted from the measurements is discussed and results from analyses of a
number of solar flares are presented. The analyses indicate that the composition of the ambient gas where the ions interact
(typically at chromospheric densities) is different from that of the photosphere and more like the composition of the corona,
exhibiting low-FIP elemental enhancements that may vary from flare to flare. Evidence for increased Ne/O and the photospheric
3He abundance is also discussed. 相似文献
459.
P. C. Frisch 《Space Science Reviews》2007,130(1-4):355-365
The properties of interstellar matter at the Sun are regulated by our location with respect to a void in the local matter
distribution, known as the Local Bubble. The Local Bubble (LB) is bounded by associations of massive stars and fossil supernovae
that have disrupted dense interstellar matter (ISM), driving low density intermediate velocity ISM into the void. The Sun
appears to be located in one of these flows of low density material. This nearby interstellar matter, dubbed the Local Fluff,
has a bulk velocity of ∼19 km s−1 in the local standard of rest. The flow is coming from the direction of the gas and dust ring formed where the Loop I supernova
remnant merges into the LB. Optical polarization data suggest that the local interstellar magnetic field lines are draped
over the heliosphere. A longstanding discrepancy between the high thermal pressure of plasma filling the LB and low thermal
pressures in the embedded Local Fluff cloudlets is partially mitigated when the ram pressure component parallel to the cloudlet
flow direction is included. 相似文献
460.
Vanjari S.V. Krogmeier J.V. Bell M.R. 《IEEE transactions on aerospace and electronic systems》2007,43(4):1426-1440
In sensor networks distributed over large areas, communication by means of active transmitters on sensor nodes is inherently energy expensive and poses a significant bottleneck to achieve a long battery life. We propose modulated reradiation of radar illumination as a means to transmit information from a group of sensors to an airborne radar. This puts the communications energy burden on the radar transmitter rather than on the sensor nodes, thus increasing their battery lifetimes. To distinguish the sensor return from the clutter return, the modulation on the sensors is done by switching a nonlinear load on the sensor antenna and processing the harmonic reradiation. We present techniques to transmit information from the sensors, which use stripmap mode synthetic aperture radar (SAR) ideas to decode the information and to simultaneously obtain a geographic map of the sensor locations. 相似文献