贵州高原具有少日照、多云雨和复杂下垫面的山地特殊气候和地形,准确探究该区域生态系统水分利用效率(WUE)的时空分异特征对进一步了解喀斯特地区碳水循环过程具有重要意义。本文气象站点数据用ANUSPLIN软件进行插值处理,与使用时间序...贵州高原具有少日照、多云雨和复杂下垫面的山地特殊气候和地形,准确探究该区域生态系统水分利用效率(WUE)的时空分异特征对进一步了解喀斯特地区碳水循环过程具有重要意义。本文气象站点数据用ANUSPLIN软件进行插值处理,与使用时间序列谐波分析法和质量控制文件重新构建高质量的MODIS-NDVI数据作为CASA模型的输入数据模拟植被NPP,再结合MOD16-ET数据估算WUE。综合利用Theil-Sen Median趋势分析、Mann-Kendall检验和稳定性分析等统计方法,对贵州高原2000—2014年各地貌区、植被类型WUE的时空分异特征进行对比分析。研究表明:(1)研究区近15年来WUE均值和趋势的空间格局都呈西部高于东部的特点, WUE趋势呈显著增加态势( R^2 =0.63, P <0.001)。(2)从各地貌区来看,多年WUE均值排序为:断陷盆地>岩溶峡谷>峰丛洼地>非喀斯特地貌>岩溶高原>岩溶槽谷,其中断陷盆地和岩溶峡谷呈显著( P <0.05)增加趋势。(3)从不同植被类型来看, WUE大小呈混交林>阔叶林>耕地>针叶林>草地>灌丛排序。针叶林和灌丛变异系数(CV)值较高,但前者对气候波动的抵挡能力更强,增加速率更快。草地CV值最低,变化速率最慢,不易受气候波动的影响。由于退耕还林等生态工程的实施效果显著,使耕地WUE的变化速率最快。展开更多
A novel approach for improving the spectral performance of sinusoidal Pulse Width Modulation (SPWM) inverter is presented. By varying the carrier frequency according to chaotic time-sequence, the discrete spectrum of ...A novel approach for improving the spectral performance of sinusoidal Pulse Width Modulation (SPWM) inverter is presented. By varying the carrier frequency according to chaotic time-sequence, the discrete spectrum of the output voltage is transformed into the continuous spectrum, which could reduce the acoustic noise concentrated at specific tones in an inverter-driven electric machine. Fourier analysis shows that the harmonic at the fixed frequency has been restrained effectively and the distribution of the spectrum is in a wider range. Besides, a novel variable is introduced for the evaluation of the output voltage spectrum in SPWM inverter. Simulations and experiments with DSP confirm the advantages of the novel approach. Experimental results show the annoying acoustic noise has been translated into some enjoyable sound like a fall or water flowing when this novel method is applied.展开更多
An in-situ GC-ECD system was used to measure halocarbons at Shangdianzi （SDZ） GAW regional station. In this paper, we reported observational results of atmospheric CFC- 11 （CCI3F） mixing ratios from April 2007 to ...An in-situ GC-ECD system was used to measure halocarbons at Shangdianzi （SDZ） GAW regional station. In this paper, we reported observational results of atmospheric CFC- 11 （CCI3F） mixing ratios from April 2007 to March 2008. The CFC- 11 time series showed large variability. Approximately 62% observed values were filtered as non-background data. The median, 10% and 90% percentiles of CFC-11 background mixing ratios were 245.4 ppt （10-12 mol/mol）, 244.6 ppt and 246.1 ppt, respectively; whereas those of non-background CFC- 11 mixing ratios were 254.7, 246.6 and 272.1 ppt, respectively. Significant differences in background and non-background CFC-11 mixing ratios were observed between summer and autumn, mainly because of the CFC-11 stored in loam being prone to atmospheric release in hot seasons. Comparison of tile SDZ data with the five AGAGE stations suggested agreement with mid-high latitude Northern Hemisphere stations MHD, THD and RPB. The SDZ data were higher than that of Southern Hemisphere stations CGO and SMO. Higher CFC-11 mixing ratios measured in different seasons were always associated with winds from the W-WSW-SW sector, indicating that the airflow coming from this wind sector has a positive contribution to CFC- 11 concentrations. The CFC-11 mixing ratios were higher in autumn and summer than in spring and winter, in which its mixing ratios were very close to the atmospheric background level. This was happened especially when airflow originated from the NNE-NE-ENE-E sector, indicating the air masses coming from these wind directions was relatively clean.展开更多
文摘贵州高原具有少日照、多云雨和复杂下垫面的山地特殊气候和地形,准确探究该区域生态系统水分利用效率(WUE)的时空分异特征对进一步了解喀斯特地区碳水循环过程具有重要意义。本文气象站点数据用ANUSPLIN软件进行插值处理,与使用时间序列谐波分析法和质量控制文件重新构建高质量的MODIS-NDVI数据作为CASA模型的输入数据模拟植被NPP,再结合MOD16-ET数据估算WUE。综合利用Theil-Sen Median趋势分析、Mann-Kendall检验和稳定性分析等统计方法,对贵州高原2000—2014年各地貌区、植被类型WUE的时空分异特征进行对比分析。研究表明:(1)研究区近15年来WUE均值和趋势的空间格局都呈西部高于东部的特点, WUE趋势呈显著增加态势( R^2 =0.63, P <0.001)。(2)从各地貌区来看,多年WUE均值排序为:断陷盆地>岩溶峡谷>峰丛洼地>非喀斯特地貌>岩溶高原>岩溶槽谷,其中断陷盆地和岩溶峡谷呈显著( P <0.05)增加趋势。(3)从不同植被类型来看, WUE大小呈混交林>阔叶林>耕地>针叶林>草地>灌丛排序。针叶林和灌丛变异系数(CV)值较高,但前者对气候波动的抵挡能力更强,增加速率更快。草地CV值最低,变化速率最慢,不易受气候波动的影响。由于退耕还林等生态工程的实施效果显著,使耕地WUE的变化速率最快。
文摘A novel approach for improving the spectral performance of sinusoidal Pulse Width Modulation (SPWM) inverter is presented. By varying the carrier frequency according to chaotic time-sequence, the discrete spectrum of the output voltage is transformed into the continuous spectrum, which could reduce the acoustic noise concentrated at specific tones in an inverter-driven electric machine. Fourier analysis shows that the harmonic at the fixed frequency has been restrained effectively and the distribution of the spectrum is in a wider range. Besides, a novel variable is introduced for the evaluation of the output voltage spectrum in SPWM inverter. Simulations and experiments with DSP confirm the advantages of the novel approach. Experimental results show the annoying acoustic noise has been translated into some enjoyable sound like a fall or water flowing when this novel method is applied.
基金supported by Non-profit Research Project to Serve the Public Interest (Grant No. GYHY200806026)International S&T Cooperation Program of MOST (Grant No. 2007DFA20650)Research Fund for Returned Overseas Chinese Scholars of the State Education Ministry (Grant No. [2009]1108)
文摘An in-situ GC-ECD system was used to measure halocarbons at Shangdianzi （SDZ） GAW regional station. In this paper, we reported observational results of atmospheric CFC- 11 （CCI3F） mixing ratios from April 2007 to March 2008. The CFC- 11 time series showed large variability. Approximately 62% observed values were filtered as non-background data. The median, 10% and 90% percentiles of CFC-11 background mixing ratios were 245.4 ppt （10-12 mol/mol）, 244.6 ppt and 246.1 ppt, respectively; whereas those of non-background CFC- 11 mixing ratios were 254.7, 246.6 and 272.1 ppt, respectively. Significant differences in background and non-background CFC-11 mixing ratios were observed between summer and autumn, mainly because of the CFC-11 stored in loam being prone to atmospheric release in hot seasons. Comparison of tile SDZ data with the five AGAGE stations suggested agreement with mid-high latitude Northern Hemisphere stations MHD, THD and RPB. The SDZ data were higher than that of Southern Hemisphere stations CGO and SMO. Higher CFC-11 mixing ratios measured in different seasons were always associated with winds from the W-WSW-SW sector, indicating that the airflow coming from this wind sector has a positive contribution to CFC- 11 concentrations. The CFC-11 mixing ratios were higher in autumn and summer than in spring and winter, in which its mixing ratios were very close to the atmospheric background level. This was happened especially when airflow originated from the NNE-NE-ENE-E sector, indicating the air masses coming from these wind directions was relatively clean.
