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231.
L. S. Anderson-Huang 《Space Science Reviews》1998,85(1-2):203-213
The chromosphere-corona transition region of the Sun enjoys both simplicities of character and complexities of character which
result from its very thin geometrical extent. The simplicities derive from the reasonably clear view of the energy balance
(both observationally and theoretically), while the complexities derive from both the proximity of the not-so-clearly viewed
regions below and above, and the almost certain convolutions and perhaps discontinuities in the three dimensional geometry
of the transition sheet. While observational resolution and spectral information has improved greatly in recent years, the
problems associated with a single vantage point, the Earth and its environs, have not gone away. To understand the transition
region we must resolve structures radially and temporally as well as in the plane of the sky.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
232.
233.
C.M. Denardini H.C. Aveiro J.H.A. Sobral J.V. Bageston L.M. Guizelli L.C.A. Resende J. Moro 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2013
Zonal and vertical electric fields were estimated at E region heights in the Brazilian sector. Zonal electric fields are obtained from the vertical electric fields based on their relation through the Hall-to-Pedersen ionospheric conductivities ratio. The technique for obtaining the vertical electric field is based on its proportionality to the Doppler velocities of type 2 irregularities as detected by coherent radars. The 50 MHz backscatter coherent (RESCO) radar was used to estimate the Doppler velocities of the type 2 irregularities embedded in the equatorial electrojet. A magnetic field-line integrated conductivity model was developed to provide the conductivities. It considers a multi-species ionosphere and a multi-species neutral atmosphere, and uses the IRI 2007, the MISIS 2000 and the IGRF 10 models as input parameters for ionosphere, neutral atmosphere and Earth’s magnetic field, respectively. The ion-neutral collision frequencies of all the species are combined through the momentum transfer collision frequency equation, and different percentages of electron-neutral collisions were artificially included for studying the implication of such increase in the zonal electric field, which resulted ranging from 0.13 to 0.49 mV/m between the 8 and 18 h (LT), under quiet magnetic conditions. 相似文献
234.
Wind tunnel evaluation of the aerodynamic interaction effects between plume and the external flow past the missile body including the wake boundary (“slipstream”) over powered flight envelopes of rocket propelled vehicles can be greatly facilitated — or even made possible — by a methodology replacing the hot propellant by cold, inert gases. Model nozzle design is based on the second order matching of plume geometry and first order modeling of plume stiffness. Since modeled nozzles will have larger throat radii than the prototypes, one can use sting-supported, sting-fed model installations thus eliminating aerodynamic interference effects due to struts. The concepts of simulated altitude and simulated full-scale Reynolds Number greatly reduce wind tunnel occupancy time. Computer programs, covering all steps of evaluating prototype nozzle performance, model sting nozzle design, model test evaluation and interpretation have been developed. The modeling methodology is supported by experimental results obtained in an induction wind tunnel at the FFA, Bromma, Sweden and in the 16 T and VKF-A altitude tunnels at AEDC, Tullahoma, Tenn. 相似文献
235.
236.
Anpredictionsystemforthein-ductsoundfieldinaeroenginecanprovidethetheoreticalfoundationforthepracticalengineeringsup-pressing... 相似文献
237.
叶片弯掠组合设计对风扇气动噪声的被动控制 总被引:1,自引:2,他引:1
转子尾迹与静子叶片干涉是产生风扇离散噪声的主要噪声源之一。环形叶栅几何对于声源项的求解以及管道内的声传播都有重要影响,因此在讨论叶片弯掠组合设计对于风扇噪声的被动控制作用时需要重点强调三维效应的影响。本文利用三维升力面理论,建立了可以考虑叶片弯掠组合影响的气动声学模型。相比数值计算方法,三维升力面理论不存在频散耗散影响,求解快速高效,更加有利于初始阶段的优化设计,以及为数值计算模型提供验证。通过与已有结果的对比,进一步阐述了叶片后掠和周向倾斜对于风扇离散噪声的影响机制。而弯掠组合设计算例的计算结果表明,在某些条件下,选取合适的叶片弯掠造型能够获得很好的降噪效果。由于轴向传播波数的影响,前传声场和后传声场对于弯掠组合的变化趋势存在一定的差异性。 相似文献
238.
具有后挡板的喷流流场的数值研究 总被引:1,自引:0,他引:1
本文对发射台底面与后挡板之间的喷流流场进行了数值研究。采用迎风的Petrov-Galerkin有限元方法求解欧拉方程。描述了喷流出口处及挡板附近的流场细节。计算结果已成功地应用于导弹发射台的设计。 相似文献
239.
Y. J. Kaufman 《Space Science Reviews》2006,125(1-4):139-147
Anthropogenic aerosols affect the climate system and the hydrological cycle. The net effect of aerosols is to cool the climate
system, directly by reflecting sunlight to space, and indirectly by increasing the brightness and cover of clouds that in
turn also reflect more sunlight to space. The uncertainty in the aerosol effect on climate is 5 times greater than that of
the greenhouse gases. The reason for this is the short aerosol lifetime and chemical complexity, that makes it difficult to
represent the global aerosol budget from surface or aircraft measurements. Satellites provide daily global information about
the aerosol content, generating large statistics with excellent regional and global representation of the aerosol column concentration,
and differentiating fine from coarse aerosol. Here we use observations performed with the MODIS instrument onboard the Terra
and Aqua satellites to differentiate natural from anthropogenic aerosols, and to measure the aerosol effect on cloud properties
and on the reflectivity of sunlight. 相似文献
240.
刘强 《郑州航空工业管理学院学报(管理科学版)》2007,25(2):1-5
印度针对软件产业发展的国际趋势与本国的人才、成本优势,通过制定国家战略以及在人才、产业园区、产业国际化、行业组织、知识产权保护、风险投资与企业上市等方面的政策与措施,在软件外包产业方面获得了巨大的发展。印度软件外包产业的发展对于我国中部地区实现崛起在战略的选择、制定与实施方面具有启示意义,具体包括:聚焦战略是中部地区产业发展的可行选择,应根据内外部条件选择适合的产业集中发展;高度重视“趋同空间”在区域崛起中的作用,通过利益相关者达成共识的过程保证战略方向与政策的正确性和有效性;制定产业扶植政策应有系统性、针对性与突破性;应为战略产业构建一个具有异质性的区域支持空间;全力培植与凝聚促进产业爆发式增长的“关键大多数”人才。 相似文献