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921.
金属间化合物TiAl(W,Si)合金的蠕变行为和机制 总被引:1,自引:0,他引:1
研究了 Ti-47Al-2 W-0.5 Si合金在 650~ 750℃区间的蠕变行为和变形机制。结果表明,合金 650℃蠕变寿命与施加应力之间符合线性的双对数关系,可用表达式 lgtf=10 lgR+30来描述。蠕变寿命与最小蠕变速率之间满足 Monkman-Grant关系的修正式。合金的比蠕变强度与抗热腐蚀镍基高温合金 K438G相当。在700℃变载荷下蠕变时具有与恒载荷下蠕变相类似的特征。 800℃长期时效粗化合金组织,降低蠕变寿命。位错滑移和形变孪生是合金蠕变的主要变形机制。 相似文献
922.
923.
航空发动机用金属橡胶隔振器动静态性能的研究 总被引:14,自引:1,他引:14
以某型号航空发动机阻尼减振需求为背景,对开发研制的金属橡胶隔振器与现用的橡胶隔振器进行了动、静态实验研究。研究结果表明:金属橡胶隔振器的能量耗散性能、静态承载能力、过临界的能力及提供振动防护的区域都远远大于橡胶隔振器,而且通过改变金属橡胶隔振器的结构参数和预压缩量可以优化其隔振效果。研究结果为利用金属橡胶隔振器来改善航空发动机的振动状况提供了依据。 相似文献
924.
Streamer evaporation is the consequence of heating in ideal MHD models because plasma is weakly contained by the magnetic
field. Heating causes inflation, opening of field lines, and release of solar wind. It was discovered in simulations and,
due to the absence of loss mechanisms, the ultimate end point is the complete evaporation of the streamer. Of course streamers
do not behave in this way because of losses by thermal conduction and radiation. Heating is also expected to depend on ambient
conditions. We use a global MHD model with thermal conduction to examine the effect of changing the heating scale height.
We also extend an analytic model of streamers developed by Pneuman (1968) to show that steady streamers are unable to contain
plasma for temperatures near the cusp greater than ∼ 2 × 106 K.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
925.
We present results derived from the analysis of an equatorial streamer structure as observed by the UVCS instrument aboard
SOHO. From observations of the H I Lyα and Lyβ lines we infer the density and temperature of the plasma. We develop a preliminary
axisymmetric, magnetostatic model of the corona which includes the effects of gas pressure gradients on the magnetic structure.
We infer a coronal plasma β > 1 in the closed field regions and near the cusp of the streamer. We add to the model a parallel
velocity field assuming mass flux conservation along magnetic flux tubes. We then compute the Lyα emissivity and the line-of-sight
integrals to obtain images of Lyα intensity, taking into account projection effects and Doppler dimming. The images we obtain
from this preliminary model are in good general agreement with the UVCS observations, both qualitatively and quantitatively.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
926.
The Electric Antennas for the STEREO/WAVES Experiment 总被引:1,自引:0,他引:1
S. D. Bale R. Ullrich K. Goetz N. Alster B. Cecconi M. Dekkali N. R. Lingner W. Macher R. E. Manning J. McCauley S. J. Monson T. H. Oswald M. Pulupa 《Space Science Reviews》2008,136(1-4):529-547
The STEREO/WAVES experiment is designed to measure the electric component of radio emission from interplanetary radio bursts and in situ plasma waves and fluctuations in the solar wind. Interplanetary radio bursts are generated from electron beams at interplanetary shocks and solar flares and are observed from near the Sun to 1 AU, corresponding to frequencies of approximately 16 MHz to 10 kHz. In situ plasma waves occur in a range of wavelengths larger than the Debye length in the solar wind plasma λ D ≈10 m and appear Doppler-shifted into the frequency regime down to a fraction of a Hertz. These phenomena are measured by STEREO/WAVES with a set of three orthogonal electric monopole antennas. This paper describes the electrical and mechanical design of the antenna system and discusses efforts to model the antenna pattern and response and methods for in-flight calibration. 相似文献
927.
The Plasma and Suprathermal Ion Composition (PLASTIC) Investigation on the STEREO Observatories 总被引:1,自引:0,他引:1
A. B. Galvin L. M. Kistler M. A. Popecki C. J. Farrugia K. D. C. Simunac L. Ellis E. Möbius M. A. Lee M. Boehm J. Carroll A. Crawshaw M. Conti P. Demaine S. Ellis J. A. Gaidos J. Googins M. Granoff A. Gustafson D. Heirtzler B. King U. Knauss J. Levasseur S. Longworth K. Singer S. Turco P. Vachon M. Vosbury M. Widholm L. M. Blush R. Karrer P. Bochsler H. Daoudi A. Etter J. Fischer J. Jost A. Opitz M. Sigrist P. Wurz B. Klecker M. Ertl E. Seidenschwang R. F. Wimmer-Schweingruber M. Koeten B. Thompson D. Steinfeld 《Space Science Reviews》2008,136(1-4):437-486
The Plasma and Suprathermal Ion Composition (PLASTIC) investigation provides the in situ solar wind and low energy heliospheric ion measurements for the NASA Solar Terrestrial Relations Observatory Mission, which consists of two spacecraft (STEREO-A, STEREO-B). PLASTIC-A and PLASTIC-B are identical. Each PLASTIC is a time-of-flight/energy mass spectrometer designed to determine the elemental composition, ionic charge states, and bulk flow parameters of major solar wind ions in the mass range from hydrogen to iron. PLASTIC has nearly complete angular coverage in the ecliptic plane and an energy range from ~0.3 to 80 keV/e, from which the distribution functions of suprathermal ions, including those ions created in pick-up and local shock acceleration processes, are also provided. 相似文献
928.
S. B. Mende S. E. Harris H. U. Frey V. Angelopoulos C. T. Russell E. Donovan B. Jackel M. Greffen L. M. Peticolas 《Space Science Reviews》2008,141(1-4):357-387
The NASA Time History of Events and Macroscale Interactions during Substorms (THEMIS) project is intended to investigate magnetospheric substorm phenomena, which are the manifestations of a basic instability of the magnetosphere and a dominant mechanism of plasma transport and explosive energy release. The major controversy in substorm science is the uncertainty as to whether the instability is initiated near the Earth, or in the more distant >20 Re magnetic tail. THEMIS will discriminate between the two possibilities by using five in-situ satellites and ground-based all-sky imagers and magnetometers, and inferring the propagation direction by timing the observation of the substorm initiation at multiple locations in the magnetosphere. An array of stations, consisting of 20 all-sky imagers (ASIs) and 30-plus magnetometers, has been developed and deployed in the North American continent, from Alaska to Labrador, for the broad coverage of the nightside magnetosphere. Each ground-based observatory (GBO) contains a white light imager that takes auroral images at a 3-second repetition rate (“cadence”) and a magnetometer that records the 3 axis variation of the magnetic field at 2 Hz frequency. The stations return compressed images, “thumbnails,” to two central databases: one located at UC Berkeley and the other at the University of Calgary, Canada. The full images are recorded at each station on hard drives, and these devices are physically returned to the two data centers for data copying. All data are made available for public use by scientists in “browse products,” accessible by using internet browsers or in the form of downloadable CDF data files (the “browse products” are described in detail in a later section). Twenty all-sky imager stations are installed and running at the time of this publication. An example of a substorm was observed on the 23rd of December 2006, and from the THEMIS GBO data, we found that the substorm onset brightening of the equatorward arc was a gradual process (>27 seconds), with minimal morphology changes until the arc breaks up. The breakup was timed to the nearest frame (<3 s) and located to the nearest latitude degree at about ±3oE in longitude. The data also showed that a similar breakup occurred in Alaska ~10 minutes later, highlighting the need for an array to distinguish prime onset. 相似文献
929.
Leslie A. Young S. Alan Stern Harold A. Weaver Fran Bagenal Richard P. Binzel Bonnie Buratti Andrew F. Cheng Dale Cruikshank G. Randall Gladstone William M. Grundy David P. Hinson Mihaly Horanyi Donald E. Jennings Ivan R. Linscott David J. McComas William B. McKinnon Ralph McNutt Jeffery M. Moore Scott Murchie Catherine B. Olkin Carolyn C. Porco Harold Reitsema Dennis C. Reuter John R. Spencer David C. Slater Darrell Strobel Michael E. Summers G. Leonard Tyler 《Space Science Reviews》2008,140(1-4):93-127
The New Horizons spacecraft will achieve a wide range of measurement objectives at the Pluto system, including color and panchromatic maps, 1.25–2.50 micron spectral images for studying surface compositions, and measurements of Pluto’s atmosphere (temperatures, composition, hazes, and the escape rate). Additional measurement objectives include topography, surface temperatures, and the solar wind interaction. The fulfillment of these measurement objectives will broaden our understanding of the Pluto system, such as the origin of the Pluto system, the processes operating on the surface, the volatile transport cycle, and the energetics and chemistry of the atmosphere. The mission, payload, and strawman observing sequences have been designed to achieve the NASA-specified measurement objectives and maximize the science return. The planned observations at the Pluto system will extend our knowledge of other objects formed by giant impact (such as the Earth–moon), other objects formed in the outer solar system (such as comets and other icy dwarf planets), other bodies with surfaces in vapor-pressure equilibrium (such as Triton and Mars), and other bodies with N2:CH4 atmospheres (such as Titan, Triton, and the early Earth). 相似文献
930.
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