Runoff observation uncertainty is a key unsolved issue in the hydrology community.Existing studies mainly focused on observation uncertainty sources and their impacts on simulation performance,but the impacts on chang...Runoff observation uncertainty is a key unsolved issue in the hydrology community.Existing studies mainly focused on observation uncertainty sources and their impacts on simulation performance,but the impacts on changes of flow regime characteristics remained rare.This study detects temporal changes in 16 flow regime metrics from five main components(i.e.,magnitude,frequency of events,variability,duration,and timing),and evaluates the effects of observation uncertainty on trends of flow regime metrics by adopting a normal distribution error model and using uncertainty width,significant change rate of slopes,coefficient of variation,and degree of deviation.The daily runoff series from 1971 to 2020 at five hydrological stations(i.e.,Huangheyan,Tangnaihai,and Lanzhou in the Yellow River Source Region,Xianyang in the Weihe River Catchment,and Heishiguan in the Yiluo River Catchment)in the water conservation zone of Yellow River are collected for our study.Results showed that:(1)Flow regimes showed significant increases in the low flow magnitude,and significant decreases in the high and average flow magnitude,variability and duration at all the five stations.The magnitude,variability and duration metrics decreased significantly,and the frequency metrics increased significantly at Heishiguan.The low flow magnitude and timing metrics increased significantly,while the high flow magnitude,frequency and variability metrics decreased significantly at Xianyang.The low flow magnitude and high flow timing metrics increased significantly,while the low flow frequency,high flow magnitude and variability metrics decreased significantly in the Yellow River Source Region.(2)Observation uncertainty remarkably impacted the changes of 28.75% of total flow regime metrics at all the stations.The trends of 11.25% of total metrics changed from significance to insignificance,while those of 17.5% of total metrics changed from insignificance to significance.For the rest metrics,the trends remained the same,i.e.,significant(18.75%)and insignificant(52.50%)trends.(3)Observation uncertainty had the greatest impacts on the frequency metrics,especially at Xianyang,followed by duration,variability,timing and magnitude metrics.展开更多
In a stainless steel autoclave,the synthesis kinetics of dimethyl carbonate(DMC) from urea and methanol was separately investigated without catalyst and with Zn-containing catalyst.Without catalyst,for the first react...In a stainless steel autoclave,the synthesis kinetics of dimethyl carbonate(DMC) from urea and methanol was separately investigated without catalyst and with Zn-containing catalyst.Without catalyst,for the first reaction of DMC synthesis(the reaction of urea with methanol to methyl carbamate(MC)),the reaction kinetics can be described as the first order with respect to the concentrations of both methanol and urea.For the second reaction of DMC synthesis(the reaction of MC with methanol to DMC),the results exhibit characteristics of zero-order reaction.For Zn-containing catalyst,the first reaction is neglected in the kinetics model since its rate is much faster than the second reaction.The macro-kinetic parameters of the second reaction are obtained by fitting the experimental data to a pseudo-homogenous model,in which a side reaction in forming process of DMC is incorporated since it decreases the yield of DMC drastically at high temperature.The activation energy of the reaction from MC to DMC is 104 kJ/mol while that of the side reaction of DMC is 135 kJ/mol.The highest yield of DMC is 23%.展开更多
基金National Key Research and Development Program of China,No.2021YFC3201102National Natural Science Foundation of China,No.42071041,No.42171047。
文摘Runoff observation uncertainty is a key unsolved issue in the hydrology community.Existing studies mainly focused on observation uncertainty sources and their impacts on simulation performance,but the impacts on changes of flow regime characteristics remained rare.This study detects temporal changes in 16 flow regime metrics from five main components(i.e.,magnitude,frequency of events,variability,duration,and timing),and evaluates the effects of observation uncertainty on trends of flow regime metrics by adopting a normal distribution error model and using uncertainty width,significant change rate of slopes,coefficient of variation,and degree of deviation.The daily runoff series from 1971 to 2020 at five hydrological stations(i.e.,Huangheyan,Tangnaihai,and Lanzhou in the Yellow River Source Region,Xianyang in the Weihe River Catchment,and Heishiguan in the Yiluo River Catchment)in the water conservation zone of Yellow River are collected for our study.Results showed that:(1)Flow regimes showed significant increases in the low flow magnitude,and significant decreases in the high and average flow magnitude,variability and duration at all the five stations.The magnitude,variability and duration metrics decreased significantly,and the frequency metrics increased significantly at Heishiguan.The low flow magnitude and timing metrics increased significantly,while the high flow magnitude,frequency and variability metrics decreased significantly at Xianyang.The low flow magnitude and high flow timing metrics increased significantly,while the low flow frequency,high flow magnitude and variability metrics decreased significantly in the Yellow River Source Region.(2)Observation uncertainty remarkably impacted the changes of 28.75% of total flow regime metrics at all the stations.The trends of 11.25% of total metrics changed from significance to insignificance,while those of 17.5% of total metrics changed from insignificance to significance.For the rest metrics,the trends remained the same,i.e.,significant(18.75%)and insignificant(52.50%)trends.(3)Observation uncertainty had the greatest impacts on the frequency metrics,especially at Xianyang,followed by duration,variability,timing and magnitude metrics.
基金Project(2010ZC034) supported by the Science Foundation of Yunnan Province,ChinaProject(20105314120005) supported by the Research Fund for Doctor Program of Higher Education of China+2 种基金Project(11-12-609) supported by the Open Foundation of State Key Laboratory of Coal Conversion,ChinaProject(KKJD201051012) supported by the Scientific Research Fund of Yunnan Provincial Education Department,ChinaProject(2009-096) supported by the Analysis and Measure Foundation of Kunming University of Scienceand Technology,China
文摘In a stainless steel autoclave,the synthesis kinetics of dimethyl carbonate(DMC) from urea and methanol was separately investigated without catalyst and with Zn-containing catalyst.Without catalyst,for the first reaction of DMC synthesis(the reaction of urea with methanol to methyl carbamate(MC)),the reaction kinetics can be described as the first order with respect to the concentrations of both methanol and urea.For the second reaction of DMC synthesis(the reaction of MC with methanol to DMC),the results exhibit characteristics of zero-order reaction.For Zn-containing catalyst,the first reaction is neglected in the kinetics model since its rate is much faster than the second reaction.The macro-kinetic parameters of the second reaction are obtained by fitting the experimental data to a pseudo-homogenous model,in which a side reaction in forming process of DMC is incorporated since it decreases the yield of DMC drastically at high temperature.The activation energy of the reaction from MC to DMC is 104 kJ/mol while that of the side reaction of DMC is 135 kJ/mol.The highest yield of DMC is 23%.
