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The identification rate of UHF RFID system was restricted by multipath propagation effects.The system identification performance was studied considering the correlation coefficient between forward and reverse channels.Based on the generalized Rician fading channel model,the analytical expression of identification rate was derived under independent,full correlation and correlation cases.Compared with the existing analysis,the proposed uniform calculation formula of identification rate was for any correlation coefficient and kinds of channel conditions.The numerical computation and Monte-carlo simulations show that the influences of different correlation coefficients,channel conditions,sensitivity and distance on the identification rate. 相似文献
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Interpretation of scatterometer ocean surface wind vector EOFs over the Northwestern Pacific 总被引:1,自引:0,他引:1
Jiayi Pan Xiao-Hai Yan Quanan ZhengW.Timothy Liu Victor V Klemas 《Remote sensing of environment》2003,84(1):53-68
Satellite scatterometer winds over the northwestern Pacific were analyzed with the vector empirical orthogonal function (VEOF) method. The Hilbert-Huang transform (HHT), a newly developed non-linear and non-stationary time series data processing method, was also employed in the analysis. A combination of European Remote Sensing Satellite (ERS) −1/2 scatterometer, NASA Scatterometer (NSCAT) and NASA's Quick Scatterometer (QuikSCAT) winds covering the period from January 1992 to April 2000 and the area of 0-50°N, 100-148°E constitutes the baseline for this study. The results indicate that annual cycles dominate the two leading VEOF modes. The first VEOF shows the East Asian monsoon features and the second represents a spring-autumn oscillation. We removed the annual signal from the data set and calculated the interannual VEOFs. The first interannual VEOF represents the interannual variability existing in the spring-autumn oscillation. The temporal mode is correlated with the Southern Oscillation Index (SOI), but has a half-year lag with respect to the SOI. The spatial mode of the first interannual VEOF reflects the response of the tropical and extratropical winds to ENSO events. The second interannual VEOF is another ENSO related mode, and the temporal VEOF mode is correlated with the SOI with a correlation coefficient of 0.78, revealing the wind variability over mid-latitudes, which is associated with ENSO events. Further analysis indicated that the wind variability over the coast of East Asia represents anomalies of a Hadley cell. The quasi-biennial oscillation (QBO) was found in the temporal mode, indicating and verifying that the QBO in the wind fields is related to ENSO events. The third VEOF shows the interannaul variability in the winter-summer mode and displays the interannual variability of the East Asian monsoon. The three leading interannual VEOFs are statistically meaningful as confirmed by a significance test. 相似文献
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1 引言纯镍是在工业生产中各种苛刻腐蚀环境下采用的金属材料。鉴于石油化工生产过程中高温、高压和介质强腐蚀性的特点 ,石油化工装置设备选材的要求很高 ,烧碱装置的关键设备碱蒸发器就是采用纯镍制造的。我国石化行业烧碱装置的碱蒸发器过去基本是随装置从国外引进的 ,近年来 ,该设备已初步进行国产化。由于碱蒸发器的制造涉及到纯镍材料的焊接 ,因此 ,如何对纯镍材料进行焊接工艺优化 ,成为保证设备制造质量的关键。由于纯镍材料本身固有的物理、化学特性 ,在焊接过程中极易出现裂纹、气孔及晶粒粗大等缺陷 ,严重影响到设备的制造质量… 相似文献