This paper introduces a quasi-natural experimental framework into trade policy evaluation and reassesses China s trade liberalization through the survival of export products.We use propensity score matching and China ...This paper introduces a quasi-natural experimental framework into trade policy evaluation and reassesses China s trade liberalization through the survival of export products.We use propensity score matching and China s dual trade system to design a quasi-natural experiment based on Chinese industrial enterprises,customs import and export,and tariff data over the period of 2000-2006;we then use survival analysis to study the impacts of China s trade liberalization on the export duration of manufacturing firms9 products.We find that the substantial reduction in import tariffs after China s accession to the World Trade Organization enhances the export duration of firm products,indicating that trade liberalization ameliorates the survival of export products.The promotion effects of tariff reduction on export duration are obviously stronger for core products than for noncore products.展开更多
In addition to increasing penetration of distributed generation(DG),the distribution system power flow may be significantly impacted by direction and magnitude.This paper proposes a method for optimal placement of win...In addition to increasing penetration of distributed generation(DG),the distribution system power flow may be significantly impacted by direction and magnitude.This paper proposes a method for optimal placement of wind DG considering the unbalanced operation of distribution systems.The objective function includes static voltage stability index,three-phase unbalance index,system reliability index,and DG investment cost.The untransposed distribution lines and unbalanced load are modelled,and corresponding static voltage stability index and system reliability considering DG penetrations are derived.The expected and stochastic daily distributed generation and demand profiles in four seasons are calculated to improve the accuracy.To solve this multi-objective optimization model,a fuzzy membership function is used to integrate the four individual objectives,and a sensitivity-based method is proposed to solve the model efficiently.Case study on IEEE 13-bus distribution 3-phase networks and 123-node test feeder successfully verifies the performance of the proposed approach.展开更多
This study investigated the interaction between Cu^2+and nano zero-valent iron(NZVI)coated with three types of stabilizers(i.e., polyacrylic acid [PAA], Tween-20 and starch) by examining the Cu^2+ uptake, coll...This study investigated the interaction between Cu^2+and nano zero-valent iron(NZVI)coated with three types of stabilizers(i.e., polyacrylic acid [PAA], Tween-20 and starch) by examining the Cu^2+ uptake, colloidal stability and mobility of surface-modified NZVI(SM-NZVI) in the presence of Cu^2+. The uptake of Cu^2+ by SM-NZVI and the colloidal stability of the Cu-bearing SM-NZVI were examined in batch tests. The results showed that NZVI coated with different modifiers exhibited different affinities for Cu^2+, which resulted in varying colloidal stability of different SM-NZVI in the presence of Cu^2+. The presence of Cu^2+ exerted a slight influence on the aggregation and settling of NZVI modified with PAA or Tween-20. However, the presence of Cu^2+caused significant aggregation and sedimentation of starch-modified NZVI, which is due to Cu^2+complexation with the starch molecules coated on the surface of the particles. Column experiments were conducted to investigate the co-transport of Cu^2+ in association with SM-NZVI in water-saturated quartz sand. It was presumed that a physical straining mechanism accounted for the retention of Cu-bearing SM-NZVI in the porous media. Moreover, the enhanced aggregation of SM-NZVI in the presence of Cu^2+ may be contributing to this straining effect.展开更多
基金This work was supported by the National Social Science Fund of China(No.71172020)the Natural Science Foundation of Hunan Province of China(No.2018JJ2069).
文摘This paper introduces a quasi-natural experimental framework into trade policy evaluation and reassesses China s trade liberalization through the survival of export products.We use propensity score matching and China s dual trade system to design a quasi-natural experiment based on Chinese industrial enterprises,customs import and export,and tariff data over the period of 2000-2006;we then use survival analysis to study the impacts of China s trade liberalization on the export duration of manufacturing firms9 products.We find that the substantial reduction in import tariffs after China s accession to the World Trade Organization enhances the export duration of firm products,indicating that trade liberalization ameliorates the survival of export products.The promotion effects of tariff reduction on export duration are obviously stronger for core products than for noncore products.
基金supported in part by the 2015 Science and Technology Project of China Southern Power Grid(WYKJ00000027)in part by funding from mid-career researcher development scheme,the Faculty of Engineering&Information Technologies,The University of Sydney.
文摘In addition to increasing penetration of distributed generation(DG),the distribution system power flow may be significantly impacted by direction and magnitude.This paper proposes a method for optimal placement of wind DG considering the unbalanced operation of distribution systems.The objective function includes static voltage stability index,three-phase unbalance index,system reliability index,and DG investment cost.The untransposed distribution lines and unbalanced load are modelled,and corresponding static voltage stability index and system reliability considering DG penetrations are derived.The expected and stochastic daily distributed generation and demand profiles in four seasons are calculated to improve the accuracy.To solve this multi-objective optimization model,a fuzzy membership function is used to integrate the four individual objectives,and a sensitivity-based method is proposed to solve the model efficiently.Case study on IEEE 13-bus distribution 3-phase networks and 123-node test feeder successfully verifies the performance of the proposed approach.
基金supported by the Fundamental Research Funds for the Central Universities (531107040788)the National Natural Science Foundation of China (Nos. 51409100, 51039001, 51378190)the Program for Changjiang Scholars and Innovative Research Team in University (IRT-13R17)
文摘This study investigated the interaction between Cu^2+and nano zero-valent iron(NZVI)coated with three types of stabilizers(i.e., polyacrylic acid [PAA], Tween-20 and starch) by examining the Cu^2+ uptake, colloidal stability and mobility of surface-modified NZVI(SM-NZVI) in the presence of Cu^2+. The uptake of Cu^2+ by SM-NZVI and the colloidal stability of the Cu-bearing SM-NZVI were examined in batch tests. The results showed that NZVI coated with different modifiers exhibited different affinities for Cu^2+, which resulted in varying colloidal stability of different SM-NZVI in the presence of Cu^2+. The presence of Cu^2+ exerted a slight influence on the aggregation and settling of NZVI modified with PAA or Tween-20. However, the presence of Cu^2+caused significant aggregation and sedimentation of starch-modified NZVI, which is due to Cu^2+complexation with the starch molecules coated on the surface of the particles. Column experiments were conducted to investigate the co-transport of Cu^2+ in association with SM-NZVI in water-saturated quartz sand. It was presumed that a physical straining mechanism accounted for the retention of Cu-bearing SM-NZVI in the porous media. Moreover, the enhanced aggregation of SM-NZVI in the presence of Cu^2+ may be contributing to this straining effect.