Poyang Lake in the Changjiang(Yangtze)River catchment has undergone frequent spring drought since 2003,and some researchers attributed this phenomenon to sand mining and the lakebed deformation in the outlet channel l...Poyang Lake in the Changjiang(Yangtze)River catchment has undergone frequent spring drought since 2003,and some researchers attributed this phenomenon to sand mining and the lakebed deformation in the outlet channel linking the lake with Changjiang River main channel.However,there is still a lack of high-resolution subaqueous geomorphological evidence of how sand mining led to lakebed deformation in the outlet channel.We examined the bed morphology and sub-bottom sedimentary structure of the outlet channel,using a multibeam echo sounder and sub-bottom profi ler in Poyang Lake.We found that:(1)the subaqueous micro-topography types of the outlet channel are characterized by sand mining disturbance,natural erosional topography,and fl at bed and dunes,accounting for 44.9%,21.4%,28.6%,and 5.1%of the channel area,respectively;and(2)sand mining activity aff ects the local bed topography extensively and signifi cantly.The depth of sandpits caused by sand mining varied from 1.4 m to 12 m deeper than the surrounding bed surface,with 4.41 m of depth increase on average.Hence,the large-scale high-intensity sand mining activities and their signifi cant geomorphic eff ects demand for an improved assessment for future management and longer-term sustainability.Because of the large-scale and ongoing high-intensity sand mining activities in the Poyang Lake outlet channel,these eff ects should raise caution in the future and contribute to monitoring eff orts that are essential to implement sustainable management solutions.The present study and techniques implemented can serve as a scientifi c reference for dam construction and sand mining within the Poyang Lake basin.展开更多
Al-Mg alloys are an important class of non-heat treatable alloys in which Mg solute and grain size play essential role in their mechanical properties and plastic deformation behaviors.In this work,a cyclical continuou...Al-Mg alloys are an important class of non-heat treatable alloys in which Mg solute and grain size play essential role in their mechanical properties and plastic deformation behaviors.In this work,a cyclical continuous expanded extrusion and drawing(CCEED)process was proposed and implemented on an Al-3Mg alloy to introduce large plastic deformation.The results showed that the continuous expanded extrusion mainly improved the ductility,while the cold drawing enhanced the strength of the alloy.With the increased processing CCEED passes,the multi-pass cross shear deformation mechanism progressively improved the homogeneity of the hardness distributions and refined grain size.Continuous dynamic recrystallization played an important role in the grain refinement of the processed Al-3Mg alloy rods.Besides,the microstructural evolution was basically influenced by the special thermomechanical deformation conditions during the CCEED process.展开更多
The Yihe River Basin is a key area for water conservation and soil erosion control in northern China.The excessive development of land resources is a major factor causing soil erosion and ecological degradation.Howeve...The Yihe River Basin is a key area for water conservation and soil erosion control in northern China.The excessive development of land resources is a major factor causing soil erosion and ecological degradation.However,the impacts of land use change on soil erosion in the basin are not yet clearly.Understanding the complex relationship between land use and soil erosion is an important way to promote the development of land resources utilization and ecological construction from cognition to decision-making.This study simulated the temporal-spatial changes of soil erosion in the basin from 1956 to 2020 using Integrated Valuation of Ecosystem Services and Tradeoffs(InVEST)model,and evaluated the changes of soil erosion under different land use scenarios from 2020 to 2050 using Future Land Use Simulation(FLUS)model.From 1956 to 2020,the overall soil erosion intensity showed a slight decreasing trend,and the average annual soil erosion modulus was 38.21 t/ha/year.Soil erosion intensity was higher in the central and northern mountainous areas,while it was lower in the flat alluvial plains in the south.Arable land(4.07 t/ha/year)was the largest contributor to the amount of soil erosion,and land use changes caused the soil erosion intensity to fluctuate and decrease after 1995.From 2020 to 2050,soil erosion varied widely under different land use scenarios,and the land use pattern targeting ecological priority development would effectively mitigate soil erosion.Therefore,optimizing land use patterns and structures are critical initiatives to prevent soil erosion.展开更多
Changes of subaqueous topography in shallow offshore water pose safety risks for embankments,navigation,and ports.This study conducted measurements of subaqueous topography between Datong and Xuliujing in the Yangtze ...Changes of subaqueous topography in shallow offshore water pose safety risks for embankments,navigation,and ports.This study conducted measurements of subaqueous topography between Datong and Xuliujing in the Yangtze River using a Sea Bat 7125 multi-beam echo sounder,and the channel change from 1998 to 2013 was calculated using historical bathymetry data.The study revealed several important results:(1)the overall pattern of changes through the studied stretch of the river was erosion–deposition–erosion.Erosion with a volume 700×10~6m^3occurred in the upper reach,deposition of about 204×10~6m^3occurred in the middle reach,and erosion of about 602×10~6m^3occurred in the lower reach.(2)Dunes are the most common microtopographic feature,accounting for 64.3%of the Datong to Xuliujing reach,followed by erosional topography and flat river topography,accounting for 27.6%and 6.6%,respectively.(3)Human activities have a direct impact on the development of the microtopography.For instance,the mining of sand formed holes on the surface of dunes with lengths of 20–35 m and depths of 3–5 m.We concluded that the overall trend of erosion(net erosion volume of 468×10~6m^3)occurred in the study area mainly because of the decreased sediment discharge following the closure of the Three Gorges Dam.However,other human activities were also impact factors of topographic change.Use of embankments and channel management reduced channel width,restricted river meandering,and exacerbated the erosion phenomenon.展开更多
Mesenchymal stromal cells(MSCs)have been considered a promising alternative for treatment of acute respiratory distress syndrome(ARDS).However,there is significant heterogeneity in their therapeutic efficacy,largely o...Mesenchymal stromal cells(MSCs)have been considered a promising alternative for treatment of acute respiratory distress syndrome(ARDS).However,there is significant heterogeneity in their therapeutic efficacy,largely owing to the incomplete understanding of the mechanisms underlying the therapeutic activities of MSCs.Here,we hypothesize that the cholinergic antiinflammatory pathway(CAP),which is recognized as a neuroimmunological pathway,may be involved in the therapeutic mechanisms by which MSCs mitigate ARDS.Using lipopolysaccharide(LPS)and bacterial lung inflammation models,we found that inflammatory cell infiltration and Evans blue leakage were reduced and that the expression levels of choline acetyltransferase(ChAT)and vesicular acetylcholine transporter(VAChT)in lung tissue were significantly increased 6 hours after MSC infusion.When the vagus nerve was blocked orα7 nicotinic acetylcholine(ACh)receptor(α7nAChR)-knockout mice were used,the therapeutic effects of MSCs were significantly reduced,suggesting that the CAP may play an important role in the effects of MSCs in ARDS treatment.Our results further showed that MSC-derived prostaglandin E2(PGE2)likely promoted ACh synthesis and release.Additionally,based on the efficacy of nAChR andα7nAChR agonists,we found that lobeline,the nicotinic cholinergic receptor excitation stimulant,may attenuate pulmonary inflammation and alleviate respiratory symptoms of ARDS patients in a clinical study(ChiCTR2100047403).In summary,we reveal a previously unrecognized MSC-mediated mechanism of CAP activation as the means by which MSCs alleviate ARDS-like syndrome,providing insight into the clinical translation of MSCs or CAP-related strategies for the treatment of patients with ARDS.展开更多
In the present work,a double-pass continuous expansion extrusion forming(CEEF) process was proposed for an Al-Mg-Si alloy,in which the diameter of rods was gradually expanded.The microstructural evolution,mechanical p...In the present work,a double-pass continuous expansion extrusion forming(CEEF) process was proposed for an Al-Mg-Si alloy,in which the diameter of rods was gradually expanded.The microstructural evolution,mechanical properties and deformation characteristics were investigated by utilizing microstructural observations,mechanical testing and a finite element method coupled with a cellular automata model.The results showed that the strength and ductility of the double-pass CEEF processed Al-Mg-Si alloys were improved synchronously,especially in artificially aged alloys.The grain size of the processed Al-Mg-Si alloy rods was refined remarkably by continuous dynamic recrystallization(CDRX)and geometric dynamic recrystallization(GDRX),and the homogeneity of microstructure was gradually improved with increasing number of processing passes.The artificially aged alloy processed with double-pass CEEF and water quenching contained fine(sub)grains and high-density dislocations,which resulted in more needle-shaped β" precipitates and a larger precipitate aspect ratio than the as-received and air-cooled CEEF alloys owing to the different precipitation kinetics.The severe cumulate strain and microshear bands were found to accelerate CDRX and GDRX for grain refinement between adjacent positions of the parabolic metal flow due to the special temperature characteristics and la rge shear straining during the CEEF process.展开更多
基金Supported by the Comprehensive survey of the geological environment along the Changjiang River(No.DD20190260)the Natural Science Foundation of Shandong Province(No.ZR2020QD083)the Postdoctoral Science Foundation(No.2018M642693)。
文摘Poyang Lake in the Changjiang(Yangtze)River catchment has undergone frequent spring drought since 2003,and some researchers attributed this phenomenon to sand mining and the lakebed deformation in the outlet channel linking the lake with Changjiang River main channel.However,there is still a lack of high-resolution subaqueous geomorphological evidence of how sand mining led to lakebed deformation in the outlet channel.We examined the bed morphology and sub-bottom sedimentary structure of the outlet channel,using a multibeam echo sounder and sub-bottom profi ler in Poyang Lake.We found that:(1)the subaqueous micro-topography types of the outlet channel are characterized by sand mining disturbance,natural erosional topography,and fl at bed and dunes,accounting for 44.9%,21.4%,28.6%,and 5.1%of the channel area,respectively;and(2)sand mining activity aff ects the local bed topography extensively and signifi cantly.The depth of sandpits caused by sand mining varied from 1.4 m to 12 m deeper than the surrounding bed surface,with 4.41 m of depth increase on average.Hence,the large-scale high-intensity sand mining activities and their signifi cant geomorphic eff ects demand for an improved assessment for future management and longer-term sustainability.Because of the large-scale and ongoing high-intensity sand mining activities in the Poyang Lake outlet channel,these eff ects should raise caution in the future and contribute to monitoring eff orts that are essential to implement sustainable management solutions.The present study and techniques implemented can serve as a scientifi c reference for dam construction and sand mining within the Poyang Lake basin.
基金This work was financially supported by the National Nat-ural Science Foundation of China(No.51774124)the Hun-an Provincial Natural Science Foundation of China(No.2019JJ40017)+1 种基金the Key Technologies R&D in Strategic Emerging Industries and Transformation in High-tech Achievements Program of Hunan Province,China(No.2019GK4045)the Graduate Training and Innovation Practice Base of Hunan Province,China.
文摘Al-Mg alloys are an important class of non-heat treatable alloys in which Mg solute and grain size play essential role in their mechanical properties and plastic deformation behaviors.In this work,a cyclical continuous expanded extrusion and drawing(CCEED)process was proposed and implemented on an Al-3Mg alloy to introduce large plastic deformation.The results showed that the continuous expanded extrusion mainly improved the ductility,while the cold drawing enhanced the strength of the alloy.With the increased processing CCEED passes,the multi-pass cross shear deformation mechanism progressively improved the homogeneity of the hardness distributions and refined grain size.Continuous dynamic recrystallization played an important role in the grain refinement of the processed Al-3Mg alloy rods.Besides,the microstructural evolution was basically influenced by the special thermomechanical deformation conditions during the CCEED process.
基金supported by the Natural Science Foundation of Shandong Province(ZR2020MD008)the National Natural Science Foundation of China(41101079).
文摘The Yihe River Basin is a key area for water conservation and soil erosion control in northern China.The excessive development of land resources is a major factor causing soil erosion and ecological degradation.However,the impacts of land use change on soil erosion in the basin are not yet clearly.Understanding the complex relationship between land use and soil erosion is an important way to promote the development of land resources utilization and ecological construction from cognition to decision-making.This study simulated the temporal-spatial changes of soil erosion in the basin from 1956 to 2020 using Integrated Valuation of Ecosystem Services and Tradeoffs(InVEST)model,and evaluated the changes of soil erosion under different land use scenarios from 2020 to 2050 using Future Land Use Simulation(FLUS)model.From 1956 to 2020,the overall soil erosion intensity showed a slight decreasing trend,and the average annual soil erosion modulus was 38.21 t/ha/year.Soil erosion intensity was higher in the central and northern mountainous areas,while it was lower in the flat alluvial plains in the south.Arable land(4.07 t/ha/year)was the largest contributor to the amount of soil erosion,and land use changes caused the soil erosion intensity to fluctuate and decrease after 1995.From 2020 to 2050,soil erosion varied widely under different land use scenarios,and the land use pattern targeting ecological priority development would effectively mitigate soil erosion.Therefore,optimizing land use patterns and structures are critical initiatives to prevent soil erosion.
基金supported by the National Natural Science Foundation of China (Grant Nos. 51761135023 & 41476075)the China Geological Survey (Grant No. DD20160246)
文摘Changes of subaqueous topography in shallow offshore water pose safety risks for embankments,navigation,and ports.This study conducted measurements of subaqueous topography between Datong and Xuliujing in the Yangtze River using a Sea Bat 7125 multi-beam echo sounder,and the channel change from 1998 to 2013 was calculated using historical bathymetry data.The study revealed several important results:(1)the overall pattern of changes through the studied stretch of the river was erosion–deposition–erosion.Erosion with a volume 700×10~6m^3occurred in the upper reach,deposition of about 204×10~6m^3occurred in the middle reach,and erosion of about 602×10~6m^3occurred in the lower reach.(2)Dunes are the most common microtopographic feature,accounting for 64.3%of the Datong to Xuliujing reach,followed by erosional topography and flat river topography,accounting for 27.6%and 6.6%,respectively.(3)Human activities have a direct impact on the development of the microtopography.For instance,the mining of sand formed holes on the surface of dunes with lengths of 20–35 m and depths of 3–5 m.We concluded that the overall trend of erosion(net erosion volume of 468×10~6m^3)occurred in the study area mainly because of the decreased sediment discharge following the closure of the Three Gorges Dam.However,other human activities were also impact factors of topographic change.Use of embankments and channel management reduced channel width,restricted river meandering,and exacerbated the erosion phenomenon.
基金supported by the National Key Research and Development Program of China,Stem Cell and Translational Research(2018YFA0107200,2019YFA0110303,2021YFA1100600)National Natural Science Foundation of China(81730005,32130046,81900075,81970109,82170540,81721003)+2 种基金Natural Science Foundation of Guangdong Province(2018A0303130305,2021A1515011759,2022A1515012452,2022A1515011919)Key Research and Development Program of Guangdong Province(2019B020236002)Key Scientific and Technological Program of Guangzhou City(201803040011),and Pearl River S&T Nova Program of Guangzhou(201906010095).
文摘Mesenchymal stromal cells(MSCs)have been considered a promising alternative for treatment of acute respiratory distress syndrome(ARDS).However,there is significant heterogeneity in their therapeutic efficacy,largely owing to the incomplete understanding of the mechanisms underlying the therapeutic activities of MSCs.Here,we hypothesize that the cholinergic antiinflammatory pathway(CAP),which is recognized as a neuroimmunological pathway,may be involved in the therapeutic mechanisms by which MSCs mitigate ARDS.Using lipopolysaccharide(LPS)and bacterial lung inflammation models,we found that inflammatory cell infiltration and Evans blue leakage were reduced and that the expression levels of choline acetyltransferase(ChAT)and vesicular acetylcholine transporter(VAChT)in lung tissue were significantly increased 6 hours after MSC infusion.When the vagus nerve was blocked orα7 nicotinic acetylcholine(ACh)receptor(α7nAChR)-knockout mice were used,the therapeutic effects of MSCs were significantly reduced,suggesting that the CAP may play an important role in the effects of MSCs in ARDS treatment.Our results further showed that MSC-derived prostaglandin E2(PGE2)likely promoted ACh synthesis and release.Additionally,based on the efficacy of nAChR andα7nAChR agonists,we found that lobeline,the nicotinic cholinergic receptor excitation stimulant,may attenuate pulmonary inflammation and alleviate respiratory symptoms of ARDS patients in a clinical study(ChiCTR2100047403).In summary,we reveal a previously unrecognized MSC-mediated mechanism of CAP activation as the means by which MSCs alleviate ARDS-like syndrome,providing insight into the clinical translation of MSCs or CAP-related strategies for the treatment of patients with ARDS.
基金supported by the National Natural Science Foundation of China(51774124,51671083,52074114)Hunan Provincial Natural Science Foundation of China(2019JJ40017)+1 种基金Key Technologies R&D in Strategic Emerging Industries and Transformation in High-tech Achievements Program of Hunan Province(2019GK4045)Graduate Training and Innovation Practice Base of Hunan Province。
文摘In the present work,a double-pass continuous expansion extrusion forming(CEEF) process was proposed for an Al-Mg-Si alloy,in which the diameter of rods was gradually expanded.The microstructural evolution,mechanical properties and deformation characteristics were investigated by utilizing microstructural observations,mechanical testing and a finite element method coupled with a cellular automata model.The results showed that the strength and ductility of the double-pass CEEF processed Al-Mg-Si alloys were improved synchronously,especially in artificially aged alloys.The grain size of the processed Al-Mg-Si alloy rods was refined remarkably by continuous dynamic recrystallization(CDRX)and geometric dynamic recrystallization(GDRX),and the homogeneity of microstructure was gradually improved with increasing number of processing passes.The artificially aged alloy processed with double-pass CEEF and water quenching contained fine(sub)grains and high-density dislocations,which resulted in more needle-shaped β" precipitates and a larger precipitate aspect ratio than the as-received and air-cooled CEEF alloys owing to the different precipitation kinetics.The severe cumulate strain and microshear bands were found to accelerate CDRX and GDRX for grain refinement between adjacent positions of the parabolic metal flow due to the special temperature characteristics and la rge shear straining during the CEEF process.
