Compacted clay liners are extensively used as barriers to control the upward diffusion of vapors of volatile or semi-volatile organic contaminants released from unsaturated contaminated soils at industrycontaminated s...Compacted clay liners are extensively used as barriers to control the upward diffusion of vapors of volatile or semi-volatile organic contaminants released from unsaturated contaminated soils at industrycontaminated sites.This study aimed to investigate the gas diffusion barrier performance of compacted clayey soils amended with three agents including attapulgite and diatomite individually,and attapulgite/diatomite mixture.The properties including water retention,volumetric shrinkage,gas diffusion,and unconfined compressive strength were evaluated through a series of laboratory tests of amended compacted clayey soils.The results demonstrate that the decrease in volume proportions of interaggregate pores leads to an increase in unconfined compressive strength(qu).Both hydrophilic groups and microstructures of attapulgite and diatomite result in an increase in water retention percent(Wt)of compacted clayey soil specimens after amendment regardless of the type of agent or initial water content(w0).Furthermore,the ratio of the gas diffusion coefficient(De)to the gas diffusion coefficient in the air(Da)was significantly reduced owing to a decrease in volume proportions of inter-aggregate pores,hydrophilic group,and microstructures of attapulgite and diatomite.Scanning electron microscope analyses revealed that rod-shaped attapulgite filled the inter-aggregate pores formed by clay particles,whereas the disc-shaped diatomite particles,characterized by micropores,failed to obstruct the interaggregate pores due to their larger particle size.Mercury intrusion porosimetry(MIP)analyses showed a reduction in pore volume in the inter-aggregate pores,leading to a reduction in the total pore volume for both the attapulgite and attapulgite/diatomite mixture amended clays,which is in accordance with the scanning electron microscope(SEM)results.The findings are pertinent to the practical application of compacted clay liners as gas barriers against the upward migration of volatile or semi-volatile organic contaminants at contaminated sites.展开更多
The severe acute respiratory syndrome coronavirus 2(SARS-CoV-2)pandemic,which has lasted for nearly a year,has made people deeply aware of the strong transmissibility and pathogenicity of SARS-CoV-2 since its outbreak...The severe acute respiratory syndrome coronavirus 2(SARS-CoV-2)pandemic,which has lasted for nearly a year,has made people deeply aware of the strong transmissibility and pathogenicity of SARS-CoV-2 since its outbreak in December 2019.By December 2020,SARS-CoV-2 had infected over 65 million people globally,resulting in more than 1 million deaths.At present,the exact animal origin of SARS-CoV-2 remains unclear and antiviral vaccines are now undergoing clinical trials.Although the social order of human life is gradually returning to normal,new confirmed cases continue to appear worldwide,and the majority of cases are sporadic due to environmental factors and lax self-protective consciousness.This article provides the latest understanding of the epidemiology and risk factors of nosocomial and community transmission of SARS-CoV-2,as well as strategies to diminish the risk of transmission.We believe that our review will help the public correctly understand and cope with SARS-CoV-2.展开更多
基金the funding support from the National Natural Science Foundation of China(Grant No.42177133)the Primary Research and Development Plan of Jiangsu Province(Grant No.BE2022830)the Primary Research and Development Plan of Anhui Province(Grant No.2023t07020018).
文摘Compacted clay liners are extensively used as barriers to control the upward diffusion of vapors of volatile or semi-volatile organic contaminants released from unsaturated contaminated soils at industrycontaminated sites.This study aimed to investigate the gas diffusion barrier performance of compacted clayey soils amended with three agents including attapulgite and diatomite individually,and attapulgite/diatomite mixture.The properties including water retention,volumetric shrinkage,gas diffusion,and unconfined compressive strength were evaluated through a series of laboratory tests of amended compacted clayey soils.The results demonstrate that the decrease in volume proportions of interaggregate pores leads to an increase in unconfined compressive strength(qu).Both hydrophilic groups and microstructures of attapulgite and diatomite result in an increase in water retention percent(Wt)of compacted clayey soil specimens after amendment regardless of the type of agent or initial water content(w0).Furthermore,the ratio of the gas diffusion coefficient(De)to the gas diffusion coefficient in the air(Da)was significantly reduced owing to a decrease in volume proportions of inter-aggregate pores,hydrophilic group,and microstructures of attapulgite and diatomite.Scanning electron microscope analyses revealed that rod-shaped attapulgite filled the inter-aggregate pores formed by clay particles,whereas the disc-shaped diatomite particles,characterized by micropores,failed to obstruct the interaggregate pores due to their larger particle size.Mercury intrusion porosimetry(MIP)analyses showed a reduction in pore volume in the inter-aggregate pores,leading to a reduction in the total pore volume for both the attapulgite and attapulgite/diatomite mixture amended clays,which is in accordance with the scanning electron microscope(SEM)results.The findings are pertinent to the practical application of compacted clay liners as gas barriers against the upward migration of volatile or semi-volatile organic contaminants at contaminated sites.
基金National Key Research and Development Program of China,No.2018YFC2001900National Natural Science Foundation of China,No.81873952 and No.81670770.
文摘The severe acute respiratory syndrome coronavirus 2(SARS-CoV-2)pandemic,which has lasted for nearly a year,has made people deeply aware of the strong transmissibility and pathogenicity of SARS-CoV-2 since its outbreak in December 2019.By December 2020,SARS-CoV-2 had infected over 65 million people globally,resulting in more than 1 million deaths.At present,the exact animal origin of SARS-CoV-2 remains unclear and antiviral vaccines are now undergoing clinical trials.Although the social order of human life is gradually returning to normal,new confirmed cases continue to appear worldwide,and the majority of cases are sporadic due to environmental factors and lax self-protective consciousness.This article provides the latest understanding of the epidemiology and risk factors of nosocomial and community transmission of SARS-CoV-2,as well as strategies to diminish the risk of transmission.We believe that our review will help the public correctly understand and cope with SARS-CoV-2.
