5-Alkenyl-2,2-butylidene-1,3-dioxane-4,6-diones were synthesized by the Knoevenagel condensation reaction of aromatic aldehydes with 2,2-butylidene-1,3-dioxane-4,6-dione using o-phthalimide-N-sulfonic acid as catalyst...5-Alkenyl-2,2-butylidene-1,3-dioxane-4,6-diones were synthesized by the Knoevenagel condensation reaction of aromatic aldehydes with 2,2-butylidene-1,3-dioxane-4,6-dione using o-phthalimide-N-sulfonic acid as catalyst, without solvent under ultrasonic irradiation. The present method has some notable advantages such as mild reaction conditions, short reaction times, less catalyst dosage and high yields with the green aspects by avoiding toxic catalysts and solvents. Further, the catalyst can be reused for five times without any noticeable decrease in the catalytic activity.展开更多
Extreme events have become increasingly frequent worldwide which are reflected in diverse changes in the shape of the temperature probability density function.However,few studies have paid attention to the heterogenei...Extreme events have become increasingly frequent worldwide which are reflected in diverse changes in the shape of the temperature probability density function.However,few studies have paid attention to the heterogeneity of temperature at the scale of climate zones.Here,we use the ERA5-land data set to explore interdecadal summer temperature changes and the distribution across different climate zones from 1981 to 2019.Comparing the minimum(Tmin)and maximum(Tmax)temperature of 1982–1991 and 2010–2019,the results imply that Tmin and Tmax in summer maintained a notable upward trend over the past 40 years,especially Tmin.The effects of a simple shift toward a warmer climate contributed most to all climate zones,while the standard deviation,skewness and kurtosis had minor effects on extreme temperature except for tropics.Quantile analysis shows that the probability of extreme events in all climate zones is increasing in frequency and intensity,especially Tmin and Tmax in temperate climate zone.Understanding diverse reasons for climate change can assist us with taking different measures to address extreme climate in distinct climate zones.展开更多
Extreme heat is among the deadliest of weather-related hazards,exerting far-reaching impacts on the natural environment and human society globally.Its risk has been rising worldwide over the past decades,particularly ...Extreme heat is among the deadliest of weather-related hazards,exerting far-reaching impacts on the natural environment and human society globally.Its risk has been rising worldwide over the past decades,particularly in densely populated urban settlements in which more than half the world’s population live.1,2 This rise is primarily attributed to anthropogenic greenhouse gas(GHG)emissions,of which the dominant share is contributed by the Global North.1 The Global North comprises economically developed countries with higher levels of industrialization,technology,infrastructures,energy consumption,and GHG emissions(e.g.,North America and West Europe)whose cities are major emission hotspots.1 Besides,emission transfers via international trade from the Global South,encompassing countries with lower economic development and energy consumption,higher poverty,and more vulnerable infrastructures(e.g.,India and Brazil)compared with the Global North,contribute a nonnegligible share of GHGs.展开更多
The North American Soil Moisture Database (NASMD) was initiated in 2011 to assemble and homogenize in situ soil moisture measurements from 32 observational networks in the United States and Canada encompassing more th...The North American Soil Moisture Database (NASMD) was initiated in 2011 to assemble and homogenize in situ soil moisture measurements from 32 observational networks in the United States and Canada encompassing more than 1800 stations. Although statistical quality control (QC) procedures have been applied in the NASMD, the soil moisture content tends to be systematically underestimated by in situ sensors in frozen soils, and using a single maximum threshold (i.e., 0.6 m3 m-3) may not be sufficient for robust QC because of the diverse soil textures in North America. In this study, based on the in situ soil porosity and North American Land Data Assimilation System phase 2 (NLDAS-2) Noah soil temperature, the simple automated QC method is revised to supplement the existing QC approach. This revised QC method is first validated based on the assessment at 78 of the Soil Climate Analysis Network (SCAN) stations where the manually checked data are available, and is then applied to all stations in the NASMD to produce a more strict quality-controlled dataset. The results show that the revised automated QC procedure can flag the spurious and erroneous soil moisture measurements for the SCAN stations, especially for those located in high altitudes and latitudes. Relative to station measurements in the original NASMD, the quality-controlled data show a slightly better agreement with the manually checked soil moisture content. It should be noted that this quality-controlled dataset may be over-flagged for some valid soil moisture measurements due to potential errors of the soil temperature and soil porosity data, and validation in this study is limited by the availability of benchmark soil moisture data. The updated QC and additional validation will be desirable to boost confidence in the product when high-quality data become available in the future.展开更多
文摘5-Alkenyl-2,2-butylidene-1,3-dioxane-4,6-diones were synthesized by the Knoevenagel condensation reaction of aromatic aldehydes with 2,2-butylidene-1,3-dioxane-4,6-dione using o-phthalimide-N-sulfonic acid as catalyst, without solvent under ultrasonic irradiation. The present method has some notable advantages such as mild reaction conditions, short reaction times, less catalyst dosage and high yields with the green aspects by avoiding toxic catalysts and solvents. Further, the catalyst can be reused for five times without any noticeable decrease in the catalytic activity.
基金funded by the National Natural Science Foundation of China(Grant Nos.41901327 and 42075070)the Guangdong Basic and Applied Basic Research Foundation(No.2019A1515010823).
文摘Extreme events have become increasingly frequent worldwide which are reflected in diverse changes in the shape of the temperature probability density function.However,few studies have paid attention to the heterogeneity of temperature at the scale of climate zones.Here,we use the ERA5-land data set to explore interdecadal summer temperature changes and the distribution across different climate zones from 1981 to 2019.Comparing the minimum(Tmin)and maximum(Tmax)temperature of 1982–1991 and 2010–2019,the results imply that Tmin and Tmax in summer maintained a notable upward trend over the past 40 years,especially Tmin.The effects of a simple shift toward a warmer climate contributed most to all climate zones,while the standard deviation,skewness and kurtosis had minor effects on extreme temperature except for tropics.Quantile analysis shows that the probability of extreme events in all climate zones is increasing in frequency and intensity,especially Tmin and Tmax in temperate climate zone.Understanding diverse reasons for climate change can assist us with taking different measures to address extreme climate in distinct climate zones.
基金National Natural Science Foundation of China(grant no.41871029)Innovation Project of LREIS(grant no.KPI002)The authors are thankful to Nicholas Grubic at the University of Toronto for editing the manuscript.
文摘Extreme heat is among the deadliest of weather-related hazards,exerting far-reaching impacts on the natural environment and human society globally.Its risk has been rising worldwide over the past decades,particularly in densely populated urban settlements in which more than half the world’s population live.1,2 This rise is primarily attributed to anthropogenic greenhouse gas(GHG)emissions,of which the dominant share is contributed by the Global North.1 The Global North comprises economically developed countries with higher levels of industrialization,technology,infrastructures,energy consumption,and GHG emissions(e.g.,North America and West Europe)whose cities are major emission hotspots.1 Besides,emission transfers via international trade from the Global South,encompassing countries with lower economic development and energy consumption,higher poverty,and more vulnerable infrastructures(e.g.,India and Brazil)compared with the Global North,contribute a nonnegligible share of GHGs.
基金the National Key Research&Development Program of China(2019YFA0607203,2017YFA0604404)the National Natural Science Foundation of China(41901327,41671398,41871318)+2 种基金the Guangdong Basic and Applied Basic Research Foundation(2019A1515010823)the Fundamental Research Funds for the Central Universities(19lgpy41)Natural Resources of the People’s Republic of China(GS(2020)2879)。
基金Supported by the National Key Research and Development Program of China(2017YFA0604300)National Natural Science Foundation of China(51779278,51379224,and 41671398)NOAA/CPO Modeling,Analyses,Predictions,and Projections(MAP) Program
文摘The North American Soil Moisture Database (NASMD) was initiated in 2011 to assemble and homogenize in situ soil moisture measurements from 32 observational networks in the United States and Canada encompassing more than 1800 stations. Although statistical quality control (QC) procedures have been applied in the NASMD, the soil moisture content tends to be systematically underestimated by in situ sensors in frozen soils, and using a single maximum threshold (i.e., 0.6 m3 m-3) may not be sufficient for robust QC because of the diverse soil textures in North America. In this study, based on the in situ soil porosity and North American Land Data Assimilation System phase 2 (NLDAS-2) Noah soil temperature, the simple automated QC method is revised to supplement the existing QC approach. This revised QC method is first validated based on the assessment at 78 of the Soil Climate Analysis Network (SCAN) stations where the manually checked data are available, and is then applied to all stations in the NASMD to produce a more strict quality-controlled dataset. The results show that the revised automated QC procedure can flag the spurious and erroneous soil moisture measurements for the SCAN stations, especially for those located in high altitudes and latitudes. Relative to station measurements in the original NASMD, the quality-controlled data show a slightly better agreement with the manually checked soil moisture content. It should be noted that this quality-controlled dataset may be over-flagged for some valid soil moisture measurements due to potential errors of the soil temperature and soil porosity data, and validation in this study is limited by the availability of benchmark soil moisture data. The updated QC and additional validation will be desirable to boost confidence in the product when high-quality data become available in the future.