Global surface temperature has dramatically increased in the past decades.It is critical to evaluate such a change using appropriate approaches.The previous studies for assessment of the change usually used overall tr...Global surface temperature has dramatically increased in the past decades.It is critical to evaluate such a change using appropriate approaches.The previous studies for assessment of the change usually used overall trends of temperature series(i.e.slopes of simple linear regression of temperature versus year based on a least-square analysis) for entire study period.Temperature trends,however,differ among different periods,i.e.there are often breakpoints in the temperature series.Therefore,the overall linear trend of a temperature series may conceal some of the temporal characteristics of the temperature change.To precisely characterize the temporal and spatial patterns of air temperature change in China,we analyze the annual mean temperature series between the year of 1961?2004 for 536 meteorological stations across China,using piecewise linear regression approach.We found remarkable breakpoints in the annual mean temperature during the study period across the country.The annual mean temperature started to increase in 1984 at a rate of 0.058°C/a at the country level.The year when warming started appeared to be gradually later from the north to the south:temperature increased since the 1970s in the north(north of 40°N),and did not rise until the 1980s in most areas of the south(south of 40°N),with warming starting in 1983 in the Tibetan Plateau.The trends in annual mean temperatures showed a large spatial heterogeneity across China:a relatively small rising with a rate of 0.025-0.05°C/a in the Sichuan Basin,Central China and South China;the greatest increase in some parts of northwest China(i.e.Xinjiang) with up to a rate of 0.1°C/a;and rising at a rate of >0.05°C/a for most regions of the country.The feedbacks of cold waves and snow may be responsible for such regional differences in the timing and rates of warming in China.展开更多
As a mono-sodium salt form of alendronic acid,alendronate sodium presents multi-level ionization for the dissociation of its four hydroxyl groups.The dissociation constants of alendronate sodium were determined in thi...As a mono-sodium salt form of alendronic acid,alendronate sodium presents multi-level ionization for the dissociation of its four hydroxyl groups.The dissociation constants of alendronate sodium were determined in this work by studying the piecewise linear relationship between volume of titrant and p H value based on acidbase potentiometric titration reaction.The distribution curves of alendronate sodium were drawn according to the determined p Ka values.There were 4 dissociation constants(pKa_1=2.43,pKa_2=7.55,pKa_3=10.80,pKa_4=11.99,respectively) of alendronate sodium,and 12 existing forms,of which 4 could be ignored,existing in different p H environments.展开更多
Recent developments in database technology have seen a wide variety of data being stored in huge collections. The wide variety makes the analysis tasks of a generic database a strenuous task in knowledge discovery. On...Recent developments in database technology have seen a wide variety of data being stored in huge collections. The wide variety makes the analysis tasks of a generic database a strenuous task in knowledge discovery. One approach is to summarize large datasets in such a way that the resulting summary dataset is of manageable size. Histogram has received significant attention as summarization/representative object for large database. But, it suffers from computational and space complexity. In this paper, we propose an idea to transform the histogram object into a Piecewise Linear Regression (PLR) line object and suggest that PLR objects can be less computational and storage intensive while compared to those of histograms. On the other hand to carry out a cluster analysis, we propose a distance measure for computing the distance between the PLR lines. Case study is presented based on the real data of online education system LMS. This demonstrates that PLR is a powerful knowledge representative for very large database.展开更多
本研究旨在探讨1983-2008年间印度植被净初级生产力(NPP)的时空变化格局及其与温度降水的关系。基于遥感数据和GLOPEM-CEVSA模型估算区域植被NPP,利用分段线性回归,分析了过去26年印度植被NPP的时空格局与变化特征。结果表明:(1)过去26...本研究旨在探讨1983-2008年间印度植被净初级生产力(NPP)的时空变化格局及其与温度降水的关系。基于遥感数据和GLOPEM-CEVSA模型估算区域植被NPP,利用分段线性回归,分析了过去26年印度植被NPP的时空格局与变化特征。结果表明:(1)过去26年间印度植被年均NPP为414.29 g C·m-2·a-1,森林、农田和草地的NPP平均值分别为1002.32、485.98和631.39 g C·m-2·a-1。(2)分段线性回归结果显示,1983-2008年间,印度植被总平均NPP呈先上升后下降的趋势,趋势转折点在1996年。占印度面积比例最大的农田植被类型的平均NPP也呈先上升后下降的趋势,趋势转折点在1996年,与总平均NPP的趋势转折点一致。(3)在空间上,印度大部分地区,发生了趋势转折,趋势转折点集中在1991-2000年间,大部分地区NPP在趋势转折点前呈上升趋势,其后呈下降趋势,与区域平均NPP的变化趋势一致。(4)印度西北部干旱地区植被NPP与温度呈负相关,与降水呈正相关。喜马拉雅山南部森林NPP则与温度呈正相关。降雨量较大的印度南部地区NPP与降水呈负相关。展开更多
植被碳储量对生态系统碳平衡具有重要调节作用,对植被碳储量进行模拟并分析其对气候变化的响应是全球陆地生态系统碳循环和气候变化研究的重要内容。基于全球植被动态模型模拟的全球植被碳储量,分析植被碳储量在1901年-2000年间的时空...植被碳储量对生态系统碳平衡具有重要调节作用,对植被碳储量进行模拟并分析其对气候变化的响应是全球陆地生态系统碳循环和气候变化研究的重要内容。基于全球植被动态模型模拟的全球植被碳储量,分析植被碳储量在1901年-2000年间的时空变化趋势,及其与气温和降水的时空关系。将LPJ-DGVM(Lund-Potsdam-Jena Dynamic Global Vegetation Model)模型对植被碳储量的模拟结果与国际上被广泛接受的其他研究结果进行了对比后得出,该模型对植被碳储量具有较好的模拟能力。对植被碳储量的模拟结果表明:全球过去100年的植被碳储量在整体上呈增加趋势,增加率为0.0016kgC/(m2a),通过分段线性回归方法得出植被碳储量时间变化趋势存在显著的转折点,20世纪50年代初以前,植被碳储量具有下降趋势,线性斜率为-0.0014kgC/(m2a),之后植被碳储量呈现显著的增加趋势,增加率为0.0055kgC/(m2a),是整体增加率的3倍多,因此整体增加率显著低估了近半个世纪以来植被碳储量的实际增加率。在空间栅格尺度上的分析表明,植被碳储量对气候变化的响应具有很大的区域差异,在不同地区,温度和降水的变化对植被碳储量的变化趋势贡献不同,并与各地区植物生长所受的环境条件约束的状况有关。研究结论进一步说明LPJ能够较好的模拟植物生长与气候之间的相关关系、揭示植被碳储量变化规律和特征,另外为了更好地研究气候变化对植被碳储量的影响,下一步需要对LPJ进行改进,增强其对人类活动如土地利用变化和农业灌溉行为等的模拟能力。展开更多
基金supported by the National Natural Science Foundation of China (30721140306 and 90711002)
文摘Global surface temperature has dramatically increased in the past decades.It is critical to evaluate such a change using appropriate approaches.The previous studies for assessment of the change usually used overall trends of temperature series(i.e.slopes of simple linear regression of temperature versus year based on a least-square analysis) for entire study period.Temperature trends,however,differ among different periods,i.e.there are often breakpoints in the temperature series.Therefore,the overall linear trend of a temperature series may conceal some of the temporal characteristics of the temperature change.To precisely characterize the temporal and spatial patterns of air temperature change in China,we analyze the annual mean temperature series between the year of 1961?2004 for 536 meteorological stations across China,using piecewise linear regression approach.We found remarkable breakpoints in the annual mean temperature during the study period across the country.The annual mean temperature started to increase in 1984 at a rate of 0.058°C/a at the country level.The year when warming started appeared to be gradually later from the north to the south:temperature increased since the 1970s in the north(north of 40°N),and did not rise until the 1980s in most areas of the south(south of 40°N),with warming starting in 1983 in the Tibetan Plateau.The trends in annual mean temperatures showed a large spatial heterogeneity across China:a relatively small rising with a rate of 0.025-0.05°C/a in the Sichuan Basin,Central China and South China;the greatest increase in some parts of northwest China(i.e.Xinjiang) with up to a rate of 0.1°C/a;and rising at a rate of >0.05°C/a for most regions of the country.The feedbacks of cold waves and snow may be responsible for such regional differences in the timing and rates of warming in China.
基金the support of Key Laboratory of Chinese Medicine Preparation of Solid Dispersion,Gansu Longshenrongfa Pharmaceutical Industry Co.,Ltd.,Gansu Province,China
文摘As a mono-sodium salt form of alendronic acid,alendronate sodium presents multi-level ionization for the dissociation of its four hydroxyl groups.The dissociation constants of alendronate sodium were determined in this work by studying the piecewise linear relationship between volume of titrant and p H value based on acidbase potentiometric titration reaction.The distribution curves of alendronate sodium were drawn according to the determined p Ka values.There were 4 dissociation constants(pKa_1=2.43,pKa_2=7.55,pKa_3=10.80,pKa_4=11.99,respectively) of alendronate sodium,and 12 existing forms,of which 4 could be ignored,existing in different p H environments.
文摘Recent developments in database technology have seen a wide variety of data being stored in huge collections. The wide variety makes the analysis tasks of a generic database a strenuous task in knowledge discovery. One approach is to summarize large datasets in such a way that the resulting summary dataset is of manageable size. Histogram has received significant attention as summarization/representative object for large database. But, it suffers from computational and space complexity. In this paper, we propose an idea to transform the histogram object into a Piecewise Linear Regression (PLR) line object and suggest that PLR objects can be less computational and storage intensive while compared to those of histograms. On the other hand to carry out a cluster analysis, we propose a distance measure for computing the distance between the PLR lines. Case study is presented based on the real data of online education system LMS. This demonstrates that PLR is a powerful knowledge representative for very large database.
文摘本研究旨在探讨1983-2008年间印度植被净初级生产力(NPP)的时空变化格局及其与温度降水的关系。基于遥感数据和GLOPEM-CEVSA模型估算区域植被NPP,利用分段线性回归,分析了过去26年印度植被NPP的时空格局与变化特征。结果表明:(1)过去26年间印度植被年均NPP为414.29 g C·m-2·a-1,森林、农田和草地的NPP平均值分别为1002.32、485.98和631.39 g C·m-2·a-1。(2)分段线性回归结果显示,1983-2008年间,印度植被总平均NPP呈先上升后下降的趋势,趋势转折点在1996年。占印度面积比例最大的农田植被类型的平均NPP也呈先上升后下降的趋势,趋势转折点在1996年,与总平均NPP的趋势转折点一致。(3)在空间上,印度大部分地区,发生了趋势转折,趋势转折点集中在1991-2000年间,大部分地区NPP在趋势转折点前呈上升趋势,其后呈下降趋势,与区域平均NPP的变化趋势一致。(4)印度西北部干旱地区植被NPP与温度呈负相关,与降水呈正相关。喜马拉雅山南部森林NPP则与温度呈正相关。降雨量较大的印度南部地区NPP与降水呈负相关。
文摘植被碳储量对生态系统碳平衡具有重要调节作用,对植被碳储量进行模拟并分析其对气候变化的响应是全球陆地生态系统碳循环和气候变化研究的重要内容。基于全球植被动态模型模拟的全球植被碳储量,分析植被碳储量在1901年-2000年间的时空变化趋势,及其与气温和降水的时空关系。将LPJ-DGVM(Lund-Potsdam-Jena Dynamic Global Vegetation Model)模型对植被碳储量的模拟结果与国际上被广泛接受的其他研究结果进行了对比后得出,该模型对植被碳储量具有较好的模拟能力。对植被碳储量的模拟结果表明:全球过去100年的植被碳储量在整体上呈增加趋势,增加率为0.0016kgC/(m2a),通过分段线性回归方法得出植被碳储量时间变化趋势存在显著的转折点,20世纪50年代初以前,植被碳储量具有下降趋势,线性斜率为-0.0014kgC/(m2a),之后植被碳储量呈现显著的增加趋势,增加率为0.0055kgC/(m2a),是整体增加率的3倍多,因此整体增加率显著低估了近半个世纪以来植被碳储量的实际增加率。在空间栅格尺度上的分析表明,植被碳储量对气候变化的响应具有很大的区域差异,在不同地区,温度和降水的变化对植被碳储量的变化趋势贡献不同,并与各地区植物生长所受的环境条件约束的状况有关。研究结论进一步说明LPJ能够较好的模拟植物生长与气候之间的相关关系、揭示植被碳储量变化规律和特征,另外为了更好地研究气候变化对植被碳储量的影响,下一步需要对LPJ进行改进,增强其对人类活动如土地利用变化和农业灌溉行为等的模拟能力。
