共查询到20条相似文献,搜索用时 49 毫秒
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直齿渐开线齿轮齿面磨损模拟计算 总被引:1,自引:0,他引:1
在初步研究直齿轮齿面磨损的基础上,对磨损机理做了进一步的分析研究,综合考虑了摩擦系数、载荷、齿面曲率及滑动系数等影响磨损量的主要因素,提出了齿面磨损量的计算公式,并运用齿面离散化方法进行齿廓磨损的数值计算。 相似文献
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Magnetohydrodynamic (MHD) theory has been used in space physics for more than forty years, yet many important questions about space plasmas remain unanswered. We still do not understand how the solar wind is accelerated, how mass, momentum and energy are transported into the magnetosphere and what mechanisms initiate substorms. Questions have been raised from the beginning of the space era whether MHD theory can describe correctly space plasmas that are collisionless and rarely in thermal equilibrium. Ideal MHD fluids do not induce electromotive force, hence they lose the capability to interact electromagnetically. No currents and magnetic fields are generated, rendering ideal MHD theory not very useful for space plasmas. Observations from the plasma sheet are used as examples to show how collisionless plasmas behave. Interpreting these observations using MHD and ideal MHD concepts can lead to misleading conclusions. Notably, the bursty bulk flows (BBF) with large mean velocities left(〈 v 〉≥400 km s right) that have been interpreted previously as E×B flows are shown to involve much more complicated physics. The sources of these nonvanishing 〈 v 〉 events, while still not known, are intimately related to mechanisms that create large phase space gradients that include beams and acceleration of ions to MeV energies. The distributions of these nonvanishing 〈 v 〉 events are associated with large amplitude variations of the magnetic field at frequencies up to and exceeding the local Larmor frequency where MHD theory is not valid. Understanding collisionless plasma dynamics such as substorms in the plasma sheet requires the self-consistency that only kinetic theory can provide. Kinetic modeling is still undergoing continual development with many studies limited to one and two dimensions, but there is urgent need to improve these models as more and more data show kinetic physics is fundamentally important. Only then will we be able to make progress and obtain a correct picture of how collisionless plasmas work in space. 相似文献
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改革开放以来,我国民航事业取得长足发展。民航机场网络渐具规模,机场密度逐步加大,机场保障能力和服务水平不断提高,航线网络加快扩展,形成了以北京、上海、广州等机场为中心,成都、昆明、西安、乌鲁木齐、沈阳、大连、武汉、深圳、重庆、杭州、南京等机场为骨干,众多支线机场相配合的基本格局。 相似文献
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针对当前我国飞行员流动产生的种种问题,作者在广泛访谈调研的基础上,建议可尝试通过市场手段,建立飞行员有序流动机制。 相似文献
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美国空军、海军正在要求武器发展中心和制造商集中精力升级“联合直接攻击弹”(JDAM)和小直径炸弹(SDB)等精确制导武器的性能,除了进一步增加武器的射程和精确度以外,重点要提高耷城区作战和攻击地面移动目标的能力。 相似文献
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在首都机场3号航站楼国际转国内(简称“I-D”)流程需要入境旅客提取托运行李,经过海关查验后?再进行下一国内航段的值机,为了推进首都机场枢纽建设工作,首都机场推出国际转国内旅客免提行李流程,提高旅客中转效率,经不断摸索试行,总结经验,此项目实施3年来,运行情况良好。 相似文献
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加快中部地区对外开放的思考 总被引:3,自引:0,他引:3
对外开放是促进中部崛起的引擎.20世纪90年代以来,中部地区对外贸易快速增长,利用外资水平不断提高,对外经贸工作进展明显,投资环境得到改善,但还存在着开放度低、利用外资规模较小等问题.在对当前面临的开放环境与条件分析的基础上,提出了加快中部地区对外开放的对策建议. 相似文献
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《Air & Space Europe》2001,3(1-2):113
The Aeronautics Days 2001 were welcomed by SMEs (Small and Medium-sized Enterprises) as the conference offered an opportunity for them to meet major European aerospace companies, gather information about European research programmes and to network with other European SMEs.The AeroSME Project coordinated several of the conference activities, aimed at supporting SMEs which, over recent years, have faced strong challenges in a rapidly changing supply chain. 相似文献