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91.
刘荣林 《中国民航学院学报》2004,22(3):18-20,36
分析了航空同步电机的磁路结构特点,建立了电机的等效磁路模型,由等效磁路的拓扑结构导出其磁位非线性方程,再由磁路欧姆定律及铁磁材料的磁化曲线求出其数值解,计算了电机的空载特性和零功率因数负载特性,与实测结果非常接近。 相似文献
92.
张乐慧 《西安航空技术高等专科学校学报》2002,20(2):60-61,63
本文介绍了图式理论在阅读理解中的作用。实践表明,图式或背景知识在阅读理解中起着极大的作用。因此,在英语阅读中,教师应该把扩展学生的背景知识放在首位,从而可调动学生的阅读积极性,最终提高学生的阅读理解能力。 相似文献
93.
基础横向振动对电磁轴承转子系统动力特性影响的实验研究 总被引:3,自引:1,他引:3
从实验上研究了电磁轴承基础的横向振动对电磁轴承转子系统动力特性的影响。结果表明电磁轴承的控制器对电磁轴承基础横向振动的抑制能力是非常有限的,在控制器的设计过程中必须考虑基础振动的影响,否则较大的基础振动会使电磁轴承系统不能稳定地工作,甚至失去支撑转子的能力。 相似文献
94.
95.
D. B. Reisenfeld D. S. Burnett R. H. Becker A. G. Grimberg V. S. Heber C. M. Hohenberg A. J. G. Jurewicz A. Meshik R. O. Pepin J. M. Raines D. J. Schlutter R. Wieler R. C. Wiens T. H. Zurbuchen 《Space Science Reviews》2007,130(1-4):79-86
Analysis of the Genesis samples is underway. Preliminary elemental abundances based on Genesis sample analyses are in good
agreement with in situ-measured elemental abundances made by ACE/SWICS during the Genesis collection period. Comparison of
these abundances with those of earlier solar cycles indicates that the solar wind composition is relatively stable between
cycles for a given type of flow. ACE/SWICS measurements for the Genesis collection period also show a continuum in compositional
variation as a function of velocity for the quasi-stationary flow that defies the simple binning of samples into their sources
of coronal hole (CH) and interstream (IS). 相似文献
96.
J. L. Linsky 《Space Science Reviews》2007,130(1-4):367-375
Analysis of UV spectra obtained with the HST, FUSE and other satellites provides a new understanding of the deuterium abundance
in the local region of the galactic disk. The wide range of gas-phase D/H measurements obtained outside of the Local Bubble
can now be explained as due to different amounts of deuterium depletion on carbonaceous grains. The total D/H ratio including
deuterium in the gas and dust phases is at least 23 parts per million of hydrogen, which is providing a challenge to models
of galactic chemical evolution. Analysis of HST and ground-based spectra of many lines of sight to stars within the Local
Bubble have identified interstellar velocity components that are consistent with more than 15 velocity vectors. We have identified
the structures of 15 nearby warm interstellar clouds on the basis of these velocity vectors and common temperatures and depletions.
We estimate the distances and masses of these clouds and compare their locations with cold interstellar clouds. 相似文献
97.
It is widely accepted that diffusive shock acceleration is an important process in the heliosphere, in particular in producing
the energetic particles associated with interplanetary shocks driven by coronal mass ejections. In its simplest formulation
shock acceleration is expected to accelerate ions with higher mass to charge ratios less efficiently than those with lower
mass to charge. Thus it is anticipated that the Fe/O ratio in shock-accelerated ion populations will decrease with increasing
energy above some energy. We examine the circumstances of five interplanetary shocks that have been reported to have associated
populations in which Fe/O increases with increasing energy. In each event, the situation is complex, with particle contributions
from other sources in addition to the shock. Furthermore, we show that the Fe/O ratio in shock-accelerated ions can decrease
even when the shock is traveling through an Fe-rich ambient ion population. Thus, although shock acceleration of an Fe-rich
suprathermal population has been proposed to explain large Fe-rich solar particle events, we find no support for this proposal
in these observations. 相似文献
98.
H. J. Völk 《Space Science Reviews》2007,130(1-4):431-438
The dynamical and chemical effects of the Galactic Wind are discussed. This wind is primarily driven by the pressure gradient
of the Cosmic Rays. Assuming the latter to be accelerated in the Supernova Remnants of the disk which at the same time produce
the Hot Interstellar Medium, it is argued that the gas removed by the wind is enriched in the nucleosynthesis products of
Supernova explosions. Therefore the moderate mass loss through this wind should still be able to remove a substantial amount
of metals, opening the way for stars to produce more metals than observed in the disk, by e.g. assuming a Salpeter-type stellar
initial mass function beyond a few Solar masses. The wind also allows a global, physically appealing interpretation of Cosmic
Ray propagation and escape from the Galaxy. In addition the spiral structure of the disk induces periodic pressure waves in
the expanding wind that become a sawtooth shock wave train at large distances which can re-accelerate “knee” particles coming
from the disk sources. This new Galactic Cosmic Ray component can reach energies of a few×1018 eV and may contribute to the juncture between the particles of Galactic and extragalactic origin in the observed overall
Cosmic Ray spectrum. 相似文献
99.
R. C. Wiens D. S. Burnett C. M. Hohenberg A. Meshik V. Heber A. Grimberg R. Wieler D. B. Reisenfeld 《Space Science Reviews》2007,130(1-4):161-171
The Genesis mission returned samples of solar wind to Earth in September 2004 for ground-based analyses of solar-wind composition,
particularly for isotope ratios. Substrates, consisting mostly of high-purity semiconductor materials, were exposed to the
solar wind at L1 from December 2001 to April 2004. In addition to a bulk sample of the solar wind, separate samples of coronal
hole (CH), interstream (IS), and coronal mass ejection material were obtained. Although many substrates were broken upon landing
due to the failure to deploy the parachute, a number of results have been obtained, and most of the primary science objectives
will likely be met. These objectives include He, Ne, Ar, Kr, and Xe isotope ratios in the bulk solar wind and in different
solar-wind regimes, and 15N/14N and 18O/17O/16O to high precision. The greatest successes to date have been with the noble gases. Light noble gases from bulk solar wind
and separate solar-wind regime samples have now been analyzed. Helium results show clear evidence of isotopic fractionation
between CH and IS samples, consistent with simplistic Coulomb drag theory predictions of fractionation between the photosphere
and different solar-wind regimes, though fractionation by wave heating is also a possible explanation. Neon results from closed
system stepped etching of bulk metallic glass have revealed the nature of isotopic fractionation as a function of depth, which
in lunar samples have for years deceptively suggested the presence of an additional, energetic component in solar wind trapped
in lunar grains and meteorites. Isotope ratios of the heavy noble gases, nitrogen, and oxygen are in the process of being
measured. 相似文献
100.
J. Wicht M. Mandea F. Takahashi U. R. Christensen M. Matsushima B. Langlais 《Space Science Reviews》2007,132(2-4):261-290
Mariner 10 measurements proved the existence of a large-scale internal magnetic field on Mercury. The observed field amplitude,
however, is too weak to be compatible with typical convective planetary dynamos. The Lorentz force based on an extrapolation
of Mariner 10 data to the dynamo region is 10−4 times smaller than the Coriolis force. This is at odds with the idea that planetary dynamos are thought to work in the so-called
magnetostrophic regime, where Coriolis force and Lorentz force should be of comparable magnitude. Recent convective dynamo
simulations reviewed here seem to resolve this caveat. We show that the available convective power indeed suffices to drive
a magnetostrophic dynamo even when the heat flow though Mercury’s core–mantle boundary is subadiabatic, as suggested by thermal
evolution models. Two possible causes are analyzed that could explain why the observations do not reflect a stronger internal
field. First, toroidal magnetic fields can be strong but are confined to the conductive core, and second, the observations
do not resolve potentially strong small-scale contributions. We review different dynamo simulations that promote either or
both effects by (1) strongly driving convection, (2) assuming a particularly small inner core, or (3) assuming a very large
inner core. These models still fall somewhat short of explaining the low amplitude of Mariner 10 observations, but the incorporation
of an additional effect helps to reach this goal: The subadiabatic heat flow through Mercury’s core–mantle boundary may cause
the outer part of the core to be stably stratified, which would largely exclude convective motions in this region. The magnetic
field, which is small scale, strong, and very time dependent in the lower convective part of the core, must diffuse through
the stagnant layer. Here, the electromagnetic skin effect filters out the more rapidly varying high-order contributions and
mainly leaves behind the weaker and slower varying dipole and quadrupole components (Christensen in Nature 444:1056–1058,
2006). Messenger and BepiColombo data will allow us to discriminate between the various models in terms of the magnetic fields
spatial structure, its degree of axisymmetry, and its secular variation. 相似文献