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921.
赵志伟 《南京气象学院学报》2002,25(6):853-858
提出了一种具有零电流关断(ZCS)的反激式单级功率因数校正(PFC)变换器。这种变换器工作在完全能量转换方式(DCM)下,综合了电流谐振技术与PFC技术。分析了这种变换器的工作原理,并在输出30W条件下进行了实验验证。 相似文献
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E.?Terradellas M.?R.?SolerEmail author E.?Ferreres M.?Bravo 《Boundary-Layer Meteorology》2005,114(3):489-518
A wavelet method is used to estimate kinetic energy and fluxes from data collected under stable conditions during the CASES-99 field campaign. Results in the high frequency range are compared with those obtained by the traditional method used to estimate turbulent moments, which is based on the Reynolds decomposition of variables into a mean and a turbulent part. The fact that the wavelet transform performs much better as a filter than the averaging process accounts for most of the disagreements between results. Since the wavelet method can be applied at very different spectral ranges, it is also used to analyse two different coherent structures: a density current and a train of internal gravity waves. The strong burst of turbulence related to the density current reflects the complexity of the first event. The wavelet method discriminates the different scales of motion, which are present in the perturbation, and is therefore an ideal tool for assessing the interactions between them. A method based on the phase difference between wavelet-transformed time series is then applied to the analysis of the horizontal and vertical structure of the gravity waves, and a three-dimensional image of the oscillations is provided. 相似文献
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冬季黑潮区域SSTA的时空演变及其与大气环流的联系 总被引:9,自引:3,他引:9
采用海温资料和NCEP/NCAR 40a再分析的海平面气压场(SLP)、高度场、风场资料,利用REOF、相关分析和合成分析方法,研究了冬季黑潮区域海温异常(SSTA)的时空演变,结果显示:冬季黑潮SSTA具有整体一致的空间变化特征,并具有明显的年际、年代际变化趋势。划分了冬季黑潮海温的正、负异常年,分析了相应年份若干气象要素场的分布特征,结果表明:负异常年时,黑潮海域SLP和700hPa高度场为负距平,冬季风加强,正异常年则反之;冬季黑潮区域SSTA与850 hPa风场距平的分布形态关系密切。 相似文献
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利用2007年祁连山地形云的观测试验资料,分析了祁连山夏季西南气流背景下地形云的演化过程,得到了祁连山地形云发展和演变的概念模型。(1)祁连山地形云的水汽主要分布在3500~6500m的范围内,对流层中层的西南气流将水汽由南向北输送到祁连山区。(2)祁连山区水汽比较丰沛,凝结高度和自由对流高度均较低,当湿气团抬升到凝结高度以上时对流有效位能很容易释放,形成有利于产生降水的云系。(3)祁连山每个山峰南北侧昼间的谷风会在山峰辐合抬升,众多山峰形成的祁连山群谷风的抬升作用下容易形成沿山脊排列的中β对流云带,在高空西南气流的推动下移到北侧,是造成北侧降水比南侧大的原因之一。 相似文献
930.
The spectra with wavelength range of 390 nm to 660 nm of triggered lightning were observed in Guangdong Area using a slitless spectrograph. The characteristics of the lightning spectra during the initial continuous current and return strokes were analyzed, and the differences between the metal section and air section of the lightning channel were compared. The results showed that the metal spectra were contained in the metal section during the initial continuous current. As for the lightning channel of the return strokes, the line spectra for both the metal section and the air section were identical; neither of the two sections contained the metal spectra, but the relative intensity of its emission spectrum was different. Owing to different radiation mechanisms, the spectral structures and luminance of the two sections were not the same. Combined with the current data, it was found that there was a good positive correlation between the total spectral strength and the transferred charge. The total intensity of the lightning channel spectrum increased with the height of the channel, indicating that the radiation sequence of the lightning channel was different. High temporal resolution observations showed that the spectral line duration could be divided into three categories, in which the lines with higher excitation energy appear first and decay rapidly, while those with lower excitation energy appear later but last longer. 相似文献