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411.
412.
交流变频调速系统的SPWM波形生成方法的谐波分析 总被引:1,自引:0,他引:1
本文简述了交流变频调速系统常用的四种SPWM波形生成的方法,并研究了各种方法的SPWM开关点计算公式及其推导,利用这些公式计算了一系列开关点数据,同时提出了一种以开关点数据分析SPWM波形各次谐波的方法,通过谐波分析证实自然采样法优于其他方法。 相似文献
413.
We review the physical processes of particle acceleration, injection, propagation, trapping, and energy loss in solar flare
conditions. An understanding of these basic physical processes is inexorable to interpret the detailed timing and spectral
evolution of the radiative signatures caused by nonthermal particles in hard X-rays, gamma-rays, and radio wavelengths. In
contrast to other more theoretically oriented reviews on particle acceleration processes, we aim here to capitalize on the
numerous observations from recent spacecraft missions, such as from the Compton Gamma Ray Observatory (CGRO), the Yohkoh Hard X-Ray Telescope (HXT) and Soft X-Ray Telescope (SXT), and the Transition Region and Coronal Explorer (TRACE). High-precision energy-dependent time delay measurements from CGRO and spatial imaging with Yohkoh and TRACE provide invaluable observational constraints on the topology of the acceleration region, the reconstruction of magnetic reconnection
processes, the resulting electromagnetic fields, and the kinematics of energized (nonthermal) particles.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
414.
We use energy spectra of anomalous cosmic rays (ACRs) measured with the Cosmic Ray instrument on the Voyager 1 and 2 spacecraft during the period 1994/157-313 to determine several parameters of interest to heliospheric studies. We estimate that the strength of the solar wind termination shock is 2.42 (–0.08, +0.04). We determine the composition of ACRs by estimating their differential energy spectra at the shock and find the following abundance ratios: H/He = 5.6 (–0.5, +0.6), C/He = 0.00048 ± 0.00011, N/He = 0.011 ± 0.001, O/He = 0.075 ± 0.006, and Ne/He = 0.0050 ± 0.0004. We correlate our observations with those of pickup ions to deduce that the long-term ionization rate of neutral nitrogen at 1 AU is 8.3 × 10–7 s–1 and that the charge-exchange cross section for neutral N and solar wind protons is 1.0 × 10–15 cm2 at 1.1 keV. We estimate that the neutral C/He ratio in the outer heliosphere is 1.8(–0.7, +0.9) × 10–5. We also find that heavy ions are preferentially injected into the acceleration process at the termination shock. 相似文献
415.
汪恩松 《北京航空航天大学学报》1994,20(4):446-451
研究了卫星太阳阵展开的动力学问题,将卫星太阳阵的结构视为树形多体系统,利用给出的自由形式树形多刚体系统运动微分方程建立太阳阵系统的动力学方程,应用为该系统动力学方程编制的计算程序,可对太阳阵展开过程中卫星本体姿态的改变量以及太阳帆板在展开过程中的运动参数进行数值计算。 相似文献
416.
非接触式光纤外差干涉位移传感器是将半导体激光器线性调频技术和光纤传感技术相结合制成的1种新型外差干涉仪。它的位移测量范围可达26mm,分辨率为0.02μm;对不同材料、不同粗糙度的对象面,有着几乎相同的测量灵敏度和测量精度;探头和对象面无需严格垂直。 相似文献
417.
刘素洁 《沈阳航空工业学院学报》1994,(1):31-34
TFM(可控调频)是近几年发展起来的一种新的调频体制.此技术的最大优点是信号功率谱主瓣窄,频带利用率高,邻道干扰小,又可获得最好的数字传输质量,这是一般调频技术所无法比拟的,本文详细论述了TFM技术的工作原理,实现方法. 相似文献
418.
L. Golub 《Space Science Reviews》2006,124(1-4):23-33
We provide a brief overview of present-day studies of inner corona dynamics, with examples of mass ejections (CME), flares
and active region dynamics. While the names of the topics have not changed in several decades, the internal details and the
language used to express the nature of the problem have changed considerably. We conclude with a short discussion of the contribution
to studies of coronal dynamics to be expected from the Atmospheric Imager Assembly (AIA) on the Solar Dynamics Observatory. 相似文献
419.
Energetic proton precipitation occurring during solar events can increase the production of odd nitrogen in the upper stratosphere
and mesosphere. A very intense solar proton event (SPE) occurred on 28 October 2003. Its impact on the composition of the
middle atmosphere was observed in details due to the availability of several space instruments. Here we present GOMOS observations
of a strong NO2increase and a related ozone decrease in the upper stratosphere at north polar latitude. The perturbation of the chemical
composition of the stratosphere was observed until the middle of December 2003. A strong NO2 increase was also observed in the south polar vortex in June-July 2003. It is tentatively attributed to the effect of an
SPE with protons of moderate energy occurring on 29 May 2003. If this hypothesis is confirmed, it will imply that the global
effect of SPEs on the composition of the stratosphere is underestimated when only strong energy SPEs are considered. 相似文献
420.