A simple and convenient method has been developed for the pre-concentration and separation of inorganic selenium species from environmental water samples using anion exchange chromatographic column combined with high ...A simple and convenient method has been developed for the pre-concentration and separation of inorganic selenium species from environmental water samples using anion exchange chromatographic column combined with high resolution inductively coupled plasma mass spectrometry(HR-ICP-MS)measurement.^(75)Se(Ⅳ) and ^(75)Se(Ⅵ)were prepared and used as tracers during the experiments.The volatility of selenium during solution evaporation was investigated to establish a reliable water samples pretreatment procedure.The parameters which affect the uptake of Se(Ⅳ)and Se(Ⅵ)on Dowex1×8 resin was optimized and the procedure for Se(Ⅳ)and Se(Ⅵ)separation was proposed.Both Se(Ⅳ)and Se(Ⅵ)are retained on the column in natural or alkaline solution with high distribution coefficient.The successive gradient elution of pre-concentrated species of selenium with HNO_(3)solution allows to differentiate between them.Se(Ⅳ)and Se(Ⅵ)finally were eluted with 0.05 mol/L HNO_(3) and 5.0 mol/L HNO_(3),respectively.The proposed method has been successfully verified using the certified reference materials(CRMs)of real water samples,and spiked recoveries for real samples were 98%-104%with 5%relative standard deviations(RSDs).The developed procedure is proved to be reliable and can be used for the rapid determination of selenium species in environmental water samples.展开更多
Controlled islanding is an important approach to prevent instability in power grids.In this paper,a novel approach is proposed for power system separation,which consists of two steps:1)Finding multiple islanding scena...Controlled islanding is an important approach to prevent instability in power grids.In this paper,a novel approach is proposed for power system separation,which consists of two steps:1)Finding multiple islanding scenarios;2)Choosing the best option to obtain the most desirable island.In the first step,different islanding solutions are determined by a proposed hierarchical clustering method.In this algorithm,which is based on a minimum active power flow disruption objective function,the generator coherency constraints are considered in the clustering process.In the second step,the best separation scenario is chosen based on an arbitrary objective function.Particularly,in this paper,the amount of load shedding and the voltage profile deviation after separation are considered as the final criteria to select the best solution among available options.In so doing,the degree of load importance is also taken into account.The proposed two-step method is applied on an IEEE 9-bus test system and it is also evaluated on an IEEE 39-bus grid.The simulation results on the IEEE 39-bus grid and the comparative analysis with a state-of-the-art method confirm that the final islanding solution is more optimized based on the secondary criteria,which have not been addressed in the existing approaches.Moreover,the proposed method is computationally efficient and can be employed in real-scale power grids.展开更多
基金The financial support from National Natural Science Foundation of China(Nos.22061132004,U21A20442,22106059,22106057,21771093)Fundamental Research Funds for the Central Universities of China(No.lzujbky-2021-kb11,lzujbky-2021-sp41)Gansu guiding program of Science and Technology Innovation(No.20JR10RA610)are gratefully appreciated。
文摘A simple and convenient method has been developed for the pre-concentration and separation of inorganic selenium species from environmental water samples using anion exchange chromatographic column combined with high resolution inductively coupled plasma mass spectrometry(HR-ICP-MS)measurement.^(75)Se(Ⅳ) and ^(75)Se(Ⅵ)were prepared and used as tracers during the experiments.The volatility of selenium during solution evaporation was investigated to establish a reliable water samples pretreatment procedure.The parameters which affect the uptake of Se(Ⅳ)and Se(Ⅵ)on Dowex1×8 resin was optimized and the procedure for Se(Ⅳ)and Se(Ⅵ)separation was proposed.Both Se(Ⅳ)and Se(Ⅵ)are retained on the column in natural or alkaline solution with high distribution coefficient.The successive gradient elution of pre-concentrated species of selenium with HNO_(3)solution allows to differentiate between them.Se(Ⅳ)and Se(Ⅵ)finally were eluted with 0.05 mol/L HNO_(3) and 5.0 mol/L HNO_(3),respectively.The proposed method has been successfully verified using the certified reference materials(CRMs)of real water samples,and spiked recoveries for real samples were 98%-104%with 5%relative standard deviations(RSDs).The developed procedure is proved to be reliable and can be used for the rapid determination of selenium species in environmental water samples.
文摘Controlled islanding is an important approach to prevent instability in power grids.In this paper,a novel approach is proposed for power system separation,which consists of two steps:1)Finding multiple islanding scenarios;2)Choosing the best option to obtain the most desirable island.In the first step,different islanding solutions are determined by a proposed hierarchical clustering method.In this algorithm,which is based on a minimum active power flow disruption objective function,the generator coherency constraints are considered in the clustering process.In the second step,the best separation scenario is chosen based on an arbitrary objective function.Particularly,in this paper,the amount of load shedding and the voltage profile deviation after separation are considered as the final criteria to select the best solution among available options.In so doing,the degree of load importance is also taken into account.The proposed two-step method is applied on an IEEE 9-bus test system and it is also evaluated on an IEEE 39-bus grid.The simulation results on the IEEE 39-bus grid and the comparative analysis with a state-of-the-art method confirm that the final islanding solution is more optimized based on the secondary criteria,which have not been addressed in the existing approaches.Moreover,the proposed method is computationally efficient and can be employed in real-scale power grids.
