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61.
We review observations and theories of radio wave emissions from the outer planets. These include radio emissions from the
auroral regions and from the radiation belts, low-frequency electromagnetic emissions, and atmospheric lightning. For each
of these emissions, we present in more details our knowledge of the Saturn counterpart, as well as expectations for Cassini.
We summarize the capabilities of the radio instrument onboard Cassini, observations performed during the Jupiter flyby, and
first (remote) observations of Saturn. Open questions are listed along with the specific observations that may bring responses
to them. The coordinated observations (from the ground and from space) that would be valuable to perform in parallel to Cassini
measurements are briefly discussed. Finally, we outline future missions and perspectives. 相似文献
62.
翼身融合布局飞机具有大升阻比、低阻力、低噪声等优点,是未来民机最具潜力的发展方向之一;但由于特殊布局所采用的非圆截面增压机身,给翼身融合布局民机结构设计带来了巨大挑战。为了降低非圆截面机身承受增压载荷时产生的高弯曲应力、提高机身结构稳定性及承载效率,翼身融合民机机身结构设计先后经历了圆柱组合式多舱室机身、双蒙皮多舱室机身、带加强支撑的盒式机身、基于拉挤杆缝合高效一体化结构(Pultruded Rod Stitched Efficient Unitized Structure,PRSEUS)的盒式中央机体等发展阶段,其中最具承载优势和可实现性的是由美国国家航空航天局NASA和波音公司共同提出的基于PRSEUS盒式中央机体结构设计方案。PRSEUS结构不仅充分利用了复合材料一体化缝合、整体共固化、低成本等制造优势,而且具有抗拉伸/压缩、多路径止损/止裂、刚度和稳定性裕度大、承载效率高、易金属修补等优异的力学特性,已被拓展应用到了翼身融合民机机翼等结构设计中。本文以非圆截面机身结构设计为重点,回顾了翼身融合民机结构设计发展历程;从整机身结构、关键部件结构、整机优化设计等方面详细阐述了翼身融合民机结构设计的研究进展与发展现状,基于国外相关技术研究发展趋势,提出了中国翼身融合民机机身结构设计研究未来需要重点关注的方向。 相似文献
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67.
摇臂式起落架作为起落架的重要形式,对其进行着陆响应分析可为起落架缓冲性能评估提供理论依据和参考。应用粘弹性杆建立摇臂式起落架结构动力学简化模型,并采用MATLAB程序建立线性与非线性摇臂式起落架数值求解模型;应用ANSYS/LS-DYNA显式动力学求解技术进行起落架着陆响应分析;对比研究起落架上端节点的载荷历程曲线、位移历程曲线及输出功量曲线。结果表明:着陆过程中载荷曲线和位移曲线收敛过程较短,曲线较为平滑,说明着陆过程较为平缓;从功量曲线的吸能面积比率可知缓冲器的吸能效率较高。研究结果对起落架系统缓冲性能的初步分析以及机身连接处接头细节设计的载荷输入具有积极的参考价值。 相似文献
68.
All four giant planets in the solar system possess irregular satellites, characterized by large, highly eccentric and/or highly
inclined orbits. These bodies were likely captured from heliocentric orbit, probably in association with planet formation
itself. Enabled by the use of large-format digital imagers on ground-based telescopes, new observational work has dramatically
increased the known populations of irregular satellites, with 74 discoveries in the last few years. A new perspective on the
irregular satellite systems is beginning to emerge.We find that the number of irregular satellites measured to a given diameter
is approximately constant from planet to planet. This is surprising, given the radically different formation scenarios envisioned
for the gas giants Jupiter and Saturn compared to the (much less massive and compositionally distinct) ice giants Uranus and
Neptune. We discuss the new results on the irregular satellites and show how these objects might be used to discriminate amongst
models of giant planet formation. 相似文献
69.
Planetary upper atmospheres-coexisting thermospheres and ionospheres-form an important boundary between the planet itself
and interplanetary space. The solar wind and radiation from the Sun may react with the upper atmosphere directly, as in the
case of Venus. If the planet has a magnetic field, however, such interactions are mediated by the magnetosphere, as in the
case of the Earth. All of the Solar System’s giant planets have magnetic fields of various strengths, and interactions with
their space environments are thus mediated by their respective magnetospheres. This article concentrates on the consequences
of magnetosphere-atmosphere interactions for the physical conditions of the thermosphere and ionosphere. In particular, we
wish to highlight important new considerations concerning the energy balance in the upper atmosphere of Jupiter and Saturn,
and the role that coupling between the ionosphere and thermosphere may play in establishing and regulating energy flows and
temperatures there. This article also compares the auroral activity of Earth, Jupiter, Saturn and Uranus. The Earth’s behaviour
is controlled, externally, by the solar wind. But Jupiter’s is determined by the co-rotation or otherwise of the equatorial
plasmasheet, which is internal to the planet’s magnetosphere. Despite being rapid rotators, like Jupiter, Saturn and Uranus
appear to have auroral emissions that are mainly under solar (wind) control. For Jupiter and Saturn, it is shown that Joule
heating and “frictional” effects, due to ion-neutral coupling can produce large amounts of energy that may account for their
high exospheric temperatures. 相似文献
70.