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21.
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对铸态ZA2 7Ce合金进行固溶处理 ,获得单一均匀的固溶体后 ,分别进行 96℃ ,180℃和 2 5 0℃人工时效。采用悬挂弯曲共振法测量阻尼性能Q-1值 (阻尼本领 ) ,结果是 ,96℃人工时效后阻尼性能好于 180℃以及 2 5 0℃人工时效后的阻尼性能。利用SEM研究时效后微观组织 ,结果发现 ,96℃人工时效获得粒状组织 ,180℃以及2 5 0℃人工时效获得层片状组织。利用等轴晶界面滑动内耗机理分析认为 ,ZA2 7Ce合金粒状组织的阻尼性能好于层片状组织的阻尼性能 相似文献
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The synodic recurrence of the Mt. Wilson plage index (MPSI) and the Calgary cosmic ray (CR) intensity is investigated, using
the wavelet power spectra in the range of 18–38 days, during the last three solar cycles. The unique temporal coincidence
between the quasi–synodic MPSI and the CR periods is detected in 1978–1982 (the 21st solar cycle). In the 22nd cycle there
is a very strong MPSI synodic recurrence, from 1989.5 to 1990.5, but it is absent in the CR data. In 1992.5–1993.5 the MPSI
and CR recurrence phenomenon is in good accordance with the solar wind speed and cosmic ray modulation as measured during
the first Ulysses passage around the Sun. The Gnevyshev gap is present in the 27-day recurrence of CR, in agreement with Kudela
et al. (1999).
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
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26.
流动控制技术在航空涡轮推进系统上的应用 总被引:13,自引:3,他引:13
方昌德 《燃气涡轮试验与研究》2003,16(2):1-6
介绍了主动流动控制在风扇/压气机、主燃烧室、涡轮和排气系统中的应用情况。阐明了流动控制在大幅度地提高发动机的性能、增加发动机的稳定性、减轻发动机的重量等方面的巨大潜力。同时指出分步实施流动控制的过程也就是应对其重大技术挑战的过程。 相似文献
27.
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
28.
This paper presents an auto-tuning method for a proportion plus integral(PI) controller for permanent magnet synchronous motor(PMSM) drives, which is supposed to be embedded in electro-mechanical actuator(EMA) control module in aircraft. The method, based on a relay feedback with variable delay time, explores different critical points of the system frequency response.The Nyquist points of the plant can then be derived from the delay time and filter time constant.The coefficients of the PI controller can then be obtained by calculation while shifting the Nyquist point to a specific position to obtain the required phase margin. The major advantage of the autotuning method is that it can provide a series of tuning results for different system bandwidths and damping ratios, corresponding to the specification for delay time and phase margin. Simulation and experimental results for the PMSM controller verify the performance of both the current loop and the speed loop auto-tuning. 相似文献
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H. Mészárosová H.S. Sawant J.R. Cecatto J. Rybák M. Karlický F.C.R. Fernandes M.C. de Andrade K. Jiřička 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2009
The 22 min long decimetric type IV radio event observed during the decay phase of the June 6, 2000 flare simultaneously by the Brazilian Solar Spectroscope (BSS) and the Ond?ejov radiospectrograph in frequency range 1200–4500 MHz has been analyzed. We have found that the characteristic periods of about 60 s belong to the long-period spectral component of the fast wave trains with a tadpole pattern in their wavelet power spectra. We have detected these trains in the whole frequency range 1200–4500 MHz. The behavior of individual wave trains at lower frequencies is different from that at higher frequencies. These individual wave trains have some common as well as different properties. In this paper, we focus on two examples of wave trains in a loop segment and the main statistical parameters in their wavelet power and global spectra are studied and discussed. 相似文献