Antibiotics are widely used in humans and animals,but their transformation from surface water to groundwater and the impact of land uses on them remain unclear.In this study,14 antibioticswere systematically surveyed ...Antibiotics are widely used in humans and animals,but their transformation from surface water to groundwater and the impact of land uses on them remain unclear.In this study,14 antibioticswere systematically surveyed in a complex agricultural area in Central China.Results indicated that the selected antibiotic concentrations in surface waters were higher in winter(average:32.7 ng/L)than in summer(average:17.9 ng/L),while the seasonal variation in groundwaters showed an opposite trend(2.2 ng/L in dry winter vs.8.0 ng/L in summer).Macrolides were the predominant antibiotics in this area,with a detected frequency of over 90%.A significant correlation between surface water and groundwater antibiotics was only observed in winter(R^(2)=0.58).This study further confirmed the impact of land uses on these contaminants,with optimal buffer radii of 2500 m in winter and 500 m in summer.Risk assessment indicated that clarithromycin posed high risks in this area.Overall,this study identified the spatiotemporal variability of antibiotics in a typical agricultural area in Central China and revealed the impact of land uses on antibiotic pollution in aquatic environments.展开更多
The volatility of financial markets has driven the diversification of investment instruments,encouraging investors to keep improving their portfolio-picking techniques.While numerous studies based on Modern Portfolio ...The volatility of financial markets has driven the diversification of investment instruments,encouraging investors to keep improving their portfolio-picking techniques.While numerous studies based on Modern Portfolio Theory(MPT)have developed accepted methods for determining optimal portfolios,not enough research has been done on the visual graphical analysis of risk preferences to accommodate diverse investors.Furthermore,by including risk-free assets in the analysis,this study presents an innovative methodology.This study's main goal is to find and analyze the risk portfolio frontier while examining the complementing of risk-free investments.Under idealized assumptions,portfolio returns and risks are formulated and solved as equality-constrained optimization problems,yielding frontier portfolios.The risk-efficient frontier and preference levels are depicted graphically,with explicit discussion of unfettered short-selling possibilities.The inclusion of risk-free assets further broadens the model's practical applicability.The framework's viability is empirically validated using historical data from twelve stocks.These results illustrate investors can use the efficient frontier as a foundation to match portfolio selections to their own risk tolerances,providing practical guidance for adaptable wealth management.展开更多
基金supported by the Key Project of Hubei Province Natural Science Foundation(Nos.2020CFA110,2015CFA132)the National Natural Science Foundation of China(Nos:41601545,41571202,41671512)the Youth Innovation Promotion Association,Chinese of Academy of Sciences(No.2018369).
文摘Antibiotics are widely used in humans and animals,but their transformation from surface water to groundwater and the impact of land uses on them remain unclear.In this study,14 antibioticswere systematically surveyed in a complex agricultural area in Central China.Results indicated that the selected antibiotic concentrations in surface waters were higher in winter(average:32.7 ng/L)than in summer(average:17.9 ng/L),while the seasonal variation in groundwaters showed an opposite trend(2.2 ng/L in dry winter vs.8.0 ng/L in summer).Macrolides were the predominant antibiotics in this area,with a detected frequency of over 90%.A significant correlation between surface water and groundwater antibiotics was only observed in winter(R^(2)=0.58).This study further confirmed the impact of land uses on these contaminants,with optimal buffer radii of 2500 m in winter and 500 m in summer.Risk assessment indicated that clarithromycin posed high risks in this area.Overall,this study identified the spatiotemporal variability of antibiotics in a typical agricultural area in Central China and revealed the impact of land uses on antibiotic pollution in aquatic environments.
文摘The volatility of financial markets has driven the diversification of investment instruments,encouraging investors to keep improving their portfolio-picking techniques.While numerous studies based on Modern Portfolio Theory(MPT)have developed accepted methods for determining optimal portfolios,not enough research has been done on the visual graphical analysis of risk preferences to accommodate diverse investors.Furthermore,by including risk-free assets in the analysis,this study presents an innovative methodology.This study's main goal is to find and analyze the risk portfolio frontier while examining the complementing of risk-free investments.Under idealized assumptions,portfolio returns and risks are formulated and solved as equality-constrained optimization problems,yielding frontier portfolios.The risk-efficient frontier and preference levels are depicted graphically,with explicit discussion of unfettered short-selling possibilities.The inclusion of risk-free assets further broadens the model's practical applicability.The framework's viability is empirically validated using historical data from twelve stocks.These results illustrate investors can use the efficient frontier as a foundation to match portfolio selections to their own risk tolerances,providing practical guidance for adaptable wealth management.
