The microreactor based hydroxylation process of 1,2,4-trichlorobezene for producing 2,5-dichlorphenol,the key intermediate of dicamba,is energy efficient and cost effective.But the 2,5-dicholorphneol is present in a m...The microreactor based hydroxylation process of 1,2,4-trichlorobezene for producing 2,5-dichlorphenol,the key intermediate of dicamba,is energy efficient and cost effective.But the 2,5-dicholorphneol is present in a mixed state after production.The reaction mixture contained the main by-product 2,4-dichlorophneol,low-content by-product 3,4-dichlorophneol,and other impurities.The difficulty in separation and analysis limits the application of this process widely.The current work aimed at establishing effective analysis methods by gas chromatography(GC)and high performance liquid chromatography(HPLC).The GC method was not able to separate 2,5-dichlorophenol and 2,4-dichlorophenol completely,but the developed HPLC method worked efficiently.The linear correlation coefficients of 2,5-dichlorophenol and 2,4-dichlorophenol were both higher than 0.999,and the average recovery was 100.33% for 2,5-dichlorophenol and 100.13% for 2,4-dichlorophenol,respectively.The relative standard deviations from precision tests were both less than 1%.The contents of 2,5-dichlorophenol and 2,4-dichlorophenol were determined with external standard method.The HPLC method has the advantages of simple operation,good separation efficiency,high accuracy and precision,and was successfully applied for both qualitative and quantitative analysis of 2,5-dichlorophenol and 2,4-dichlorophenol of the sample solution.展开更多
With few available soil organic carbon(SOC)profiles and the heterogeneity of those that do exist, the estimation of SOC pools in karst areas is highly uncertain.Based on the spatial heterogeneity of SOC content of 23,...With few available soil organic carbon(SOC)profiles and the heterogeneity of those that do exist, the estimation of SOC pools in karst areas is highly uncertain.Based on the spatial heterogeneity of SOC content of 23,536 samples in a karst watershed, a modified estimation method was determined for SOC storage that exclusively applies to karst areas. The method is a "soil-type method" based on revised calculation indexes for SOC storage. In the present study, the organic carbon contents of different soil types varied greatly, but generally decreased with increasing soil depth. The organic carbon content decreased nearly linearly to a depth of 0–50 cm and then varied at depths of 50–100 cm. Because of the large spatial variability in the karst area, we were able to determine that influences of the different indexes on the estimation of SOC storage decreased as follows: soil thickness > boulder content > rock fragment content > SOC content > bulk density. Using the modified formula, the SOC content in the Houzhai watershed in Puding was estimated to range from 3.53 to 5.44 kg m^(-2), with an average value of 1.24 kg m^(-2) to a depth of 20 cm, and from 4.44 to 14.50 kg m^(-2), with an average value of 12.12 kg m^(-2) to a depth of 100 cm. The total SOC content was estimated at 5.39*10^(5) t.展开更多
Particulate matter diameter ≤ 2.5 μm(PM2.5) causes direct harm to human health. Finding forms of urban forest systems that with the ability to reduce the amount of particulate matter in air effectively is the aim of...Particulate matter diameter ≤ 2.5 μm(PM2.5) causes direct harm to human health. Finding forms of urban forest systems that with the ability to reduce the amount of particulate matter in air effectively is the aim of this study. Five commonly cultivated kinds of urban forest types were studied in Beijing city at three stages of leaf growth. Results show that the urban forest system is capable of storing and capturing dust from the air. The types of shrubs and broadleaf trees that have the ability to capture PM2.5from the air are most effective when leaves have fully developed. In the leafless season, the conifer and mixed tree types are the most effective in removing dust from the air. For all kinds of forest types and stages of leaf growth, the PM2.5concentration is highest in the morning but lower in the afternoon and evening. Grassland cannot control particles suspended in the air,but can reduce dust pollution caused by dust from the ground blown by the wind back into the air.展开更多
To increase the knowledge on the particulate matter of a wetland in Beijing, an experimental study on the concentration and composition of PM10 and PM2.5was implemented in Beijing Olympic Forest Park from 2013 to 2014...To increase the knowledge on the particulate matter of a wetland in Beijing, an experimental study on the concentration and composition of PM10 and PM2.5was implemented in Beijing Olympic Forest Park from 2013 to 2014. This study analyzed the meteorological factors and deposition fluxes at different heights and in different periods in the wetlands. The results showed that the mean mass concentrations of PM10 and PM2.5were the highest at 06:00–09:00 and the lowest at 15:00–18:00. And the annual concentration of PM10 and PM2.5in the wetland followed the order of dry period(winter) > normal water period(spring and autumn) > wet period(summer), with the concentration in the dry period significantly higher than that in the normal water and wet periods. The chemical composition of PM2.5in the wetlands included NH4+, K+, Na+, Mg2+, SO42-, NO3-, and Cl-, which respectively accounted for 12.7%, 1.0%, 0.8%, 0.7%, 46.6%, 33.2%, and 5.1% of the average annual composition. The concentration of PM10 and PM2.5in the wetlands had a significant positive correlation with relative humidity, a negative correlation with wind speed, and an insignificant negative correlation with temperature and radiation. The daily average dry deposition amount of PM10 in the different periods followed the order of dry period >normal water period > wet period, and the daily average dry deposition amount of PM2.5in the different periods was dry period > wet period > normal water period.展开更多
Proper supply of spares is critical to guarantee safe operation,improve service quality and reduce maintenance costs.This paper proposes a condition-based spare ordering model for a two-stage degrading system,which co...Proper supply of spares is critical to guarantee safe operation,improve service quality and reduce maintenance costs.This paper proposes a condition-based spare ordering model for a two-stage degrading system,which consists of inflection point transfer process and two-stage degradation process with continuous degradation process and random external shocks.External shocks itself does not directly lead to system failure,but it will speed up the degradation process.In turn,degradation can also make the system more vulnerable to shocks.In general,the degradation rate at the defective stage is greater than that at the normal stage.The proposed model depends on system degradation process and spare lead-time.In order to achieve accurate maintenance and deal with emergency maintenance caused by system rapid degradation after inflection point transfer time,the model considers both the regular lead-time and expedited lead-time.Before inflection point transfer time,regular spare ordering policy is performed.After inflection point transfer time,expedited spare ordering policy is implemented.The decision variable of the model is the ordering time.The objective of this study is to determine the optimal ordering time such that the expected cost rate is minimized.Finally,a numerical example is presented to illustrate the proposed model and sensitivity analysis on critical parameters is carried out.展开更多
基金This work was supported by National Key Research Development Program of China(2017YFB1103002,2018YFB0604304)National Natural Science Foundation of China(51821004).
文摘The microreactor based hydroxylation process of 1,2,4-trichlorobezene for producing 2,5-dichlorphenol,the key intermediate of dicamba,is energy efficient and cost effective.But the 2,5-dicholorphneol is present in a mixed state after production.The reaction mixture contained the main by-product 2,4-dichlorophneol,low-content by-product 3,4-dichlorophneol,and other impurities.The difficulty in separation and analysis limits the application of this process widely.The current work aimed at establishing effective analysis methods by gas chromatography(GC)and high performance liquid chromatography(HPLC).The GC method was not able to separate 2,5-dichlorophenol and 2,4-dichlorophenol completely,but the developed HPLC method worked efficiently.The linear correlation coefficients of 2,5-dichlorophenol and 2,4-dichlorophenol were both higher than 0.999,and the average recovery was 100.33% for 2,5-dichlorophenol and 100.13% for 2,4-dichlorophenol,respectively.The relative standard deviations from precision tests were both less than 1%.The contents of 2,5-dichlorophenol and 2,4-dichlorophenol were determined with external standard method.The HPLC method has the advantages of simple operation,good separation efficiency,high accuracy and precision,and was successfully applied for both qualitative and quantitative analysis of 2,5-dichlorophenol and 2,4-dichlorophenol of the sample solution.
基金provided by National Key Basic Research Development Program (Grant No.2013CB956702)
文摘With few available soil organic carbon(SOC)profiles and the heterogeneity of those that do exist, the estimation of SOC pools in karst areas is highly uncertain.Based on the spatial heterogeneity of SOC content of 23,536 samples in a karst watershed, a modified estimation method was determined for SOC storage that exclusively applies to karst areas. The method is a "soil-type method" based on revised calculation indexes for SOC storage. In the present study, the organic carbon contents of different soil types varied greatly, but generally decreased with increasing soil depth. The organic carbon content decreased nearly linearly to a depth of 0–50 cm and then varied at depths of 50–100 cm. Because of the large spatial variability in the karst area, we were able to determine that influences of the different indexes on the estimation of SOC storage decreased as follows: soil thickness > boulder content > rock fragment content > SOC content > bulk density. Using the modified formula, the SOC content in the Houzhai watershed in Puding was estimated to range from 3.53 to 5.44 kg m^(-2), with an average value of 1.24 kg m^(-2) to a depth of 20 cm, and from 4.44 to 14.50 kg m^(-2), with an average value of 12.12 kg m^(-2) to a depth of 100 cm. The total SOC content was estimated at 5.39*10^(5) t.
基金supported by the Forestry Public Welfare Project of China (No. 201304301)
文摘Particulate matter diameter ≤ 2.5 μm(PM2.5) causes direct harm to human health. Finding forms of urban forest systems that with the ability to reduce the amount of particulate matter in air effectively is the aim of this study. Five commonly cultivated kinds of urban forest types were studied in Beijing city at three stages of leaf growth. Results show that the urban forest system is capable of storing and capturing dust from the air. The types of shrubs and broadleaf trees that have the ability to capture PM2.5from the air are most effective when leaves have fully developed. In the leafless season, the conifer and mixed tree types are the most effective in removing dust from the air. For all kinds of forest types and stages of leaf growth, the PM2.5concentration is highest in the morning but lower in the afternoon and evening. Grassland cannot control particles suspended in the air,but can reduce dust pollution caused by dust from the ground blown by the wind back into the air.
基金supported by the Forestry Special Funds for Public Welfare projects of China(No.201304301)Beijing Municipal Science and Technology Project(No.Z141100006014031)the Youth Foundation of Beijing Municipal Bureau of Landscape and Forestry(No.2014-4-7)
文摘To increase the knowledge on the particulate matter of a wetland in Beijing, an experimental study on the concentration and composition of PM10 and PM2.5was implemented in Beijing Olympic Forest Park from 2013 to 2014. This study analyzed the meteorological factors and deposition fluxes at different heights and in different periods in the wetlands. The results showed that the mean mass concentrations of PM10 and PM2.5were the highest at 06:00–09:00 and the lowest at 15:00–18:00. And the annual concentration of PM10 and PM2.5in the wetland followed the order of dry period(winter) > normal water period(spring and autumn) > wet period(summer), with the concentration in the dry period significantly higher than that in the normal water and wet periods. The chemical composition of PM2.5in the wetlands included NH4+, K+, Na+, Mg2+, SO42-, NO3-, and Cl-, which respectively accounted for 12.7%, 1.0%, 0.8%, 0.7%, 46.6%, 33.2%, and 5.1% of the average annual composition. The concentration of PM10 and PM2.5in the wetlands had a significant positive correlation with relative humidity, a negative correlation with wind speed, and an insignificant negative correlation with temperature and radiation. The daily average dry deposition amount of PM10 in the different periods followed the order of dry period >normal water period > wet period, and the daily average dry deposition amount of PM2.5in the different periods was dry period > wet period > normal water period.
基金The authors are grateful to the anonymous reviewers and the editor for their critical as well as constructive review of the manuscript.This research is supported by the National Natural Science Foundation of China under Grant Nos.51575055 and 51975058 and the National Science and Technology Major Project of China under Grant No.2015ZX04001002.
文摘Proper supply of spares is critical to guarantee safe operation,improve service quality and reduce maintenance costs.This paper proposes a condition-based spare ordering model for a two-stage degrading system,which consists of inflection point transfer process and two-stage degradation process with continuous degradation process and random external shocks.External shocks itself does not directly lead to system failure,but it will speed up the degradation process.In turn,degradation can also make the system more vulnerable to shocks.In general,the degradation rate at the defective stage is greater than that at the normal stage.The proposed model depends on system degradation process and spare lead-time.In order to achieve accurate maintenance and deal with emergency maintenance caused by system rapid degradation after inflection point transfer time,the model considers both the regular lead-time and expedited lead-time.Before inflection point transfer time,regular spare ordering policy is performed.After inflection point transfer time,expedited spare ordering policy is implemented.The decision variable of the model is the ordering time.The objective of this study is to determine the optimal ordering time such that the expected cost rate is minimized.Finally,a numerical example is presented to illustrate the proposed model and sensitivity analysis on critical parameters is carried out.
