Danjiangkou Reservoir is water source of Middle Route Project of the South-to-North Water Diversion(SNWD)Project,research on the dynamic changes in vegetation cover and its influencing factors is of great significance...Danjiangkou Reservoir is water source of Middle Route Project of the South-to-North Water Diversion(SNWD)Project,research on the dynamic changes in vegetation cover and its influencing factors is of great significance for understanding the ecological environment of the water diversion area and formulating protection measures.In this study,the normalized difference in vegetation index(NDVI)was used to analyze the dynamic changes and influencing factors of vegetation in the upstream and downstream of Danjiangkou Dam from 1982 to 2018.The results showed that the NDVI exhibited an upward trend of 0.017 year−1(P<0.05),and that the significantly increased area was located near the valley upstream of the dam,while the significantly decreased area was mainly distributed in the basin downstream of the dam and around the central city.The comprehensive contributions of climate and human activity factors to NDVI changes were 92.03%and 7.97%,respectively.The human activities in the upstream of the dam were mainly reflected in the ecological measures such as returning farmland to forest;the human activities at the downstream of the dam were mainly reflected in urban expansion,occupation of cultivated land and forest land by construction land.展开更多
A new spinning method to manufacture the cylindrical parts with nano/ultrafine grained structures is proposed, which consists of quenching, power spinning and recrystallization annealing. The microstructural evolution...A new spinning method to manufacture the cylindrical parts with nano/ultrafine grained structures is proposed, which consists of quenching, power spinning and recrystallization annealing. The microstructural evolution during the different process stages and macroforming quality of the spun parts made of ASTM 1020 steel are investigated. The results show that the microstructures of the ferrites and pearlites in the ASTM 1020 steel are transformed to the lath martensites after quenching. The martensite laths obtained by quenching are refined to 87 nm and a small amount of nanoscale deformation twins with an average thickness of 20 nm is generated after performing a 3-pass stagger spinning with 55% thinning ratio of wall thickness, where the equivalent strain required is only 0.92. The equiaxial ferritic grains with an average size of 160 nm and nano-carbides are generated by subsequent recrystallization annealing at 480°C for 30 min. The spun parts with high dimensional precision and low surface roughness are obtained by the forming method developed in this work, combining quenching with 3-pass stagger spinning and recrystallization annealing.展开更多
基金This research was financially supported by National Key Research and Development Program of China(2018YFC1506500)National Natural Science Foundation of China(41971402).
文摘Danjiangkou Reservoir is water source of Middle Route Project of the South-to-North Water Diversion(SNWD)Project,research on the dynamic changes in vegetation cover and its influencing factors is of great significance for understanding the ecological environment of the water diversion area and formulating protection measures.In this study,the normalized difference in vegetation index(NDVI)was used to analyze the dynamic changes and influencing factors of vegetation in the upstream and downstream of Danjiangkou Dam from 1982 to 2018.The results showed that the NDVI exhibited an upward trend of 0.017 year−1(P<0.05),and that the significantly increased area was located near the valley upstream of the dam,while the significantly decreased area was mainly distributed in the basin downstream of the dam and around the central city.The comprehensive contributions of climate and human activity factors to NDVI changes were 92.03%and 7.97%,respectively.The human activities in the upstream of the dam were mainly reflected in the ecological measures such as returning farmland to forest;the human activities at the downstream of the dam were mainly reflected in urban expansion,occupation of cultivated land and forest land by construction land.
基金supported by National Natural Science Foundation of China(Grant No.51075153)Natural Science Foundation of Guangdong Province(Grant No.10151040301000000)+1 种基金Key Laboratory of Precision Equipment and Manufacturing Technology of Guangdong Province(Grant No.PEMT1202)the EU FP7 Marie Curie International Research Staff Exchange Scheme(IRSES)Mat Pro Future Project(Grant No.318968)
文摘A new spinning method to manufacture the cylindrical parts with nano/ultrafine grained structures is proposed, which consists of quenching, power spinning and recrystallization annealing. The microstructural evolution during the different process stages and macroforming quality of the spun parts made of ASTM 1020 steel are investigated. The results show that the microstructures of the ferrites and pearlites in the ASTM 1020 steel are transformed to the lath martensites after quenching. The martensite laths obtained by quenching are refined to 87 nm and a small amount of nanoscale deformation twins with an average thickness of 20 nm is generated after performing a 3-pass stagger spinning with 55% thinning ratio of wall thickness, where the equivalent strain required is only 0.92. The equiaxial ferritic grains with an average size of 160 nm and nano-carbides are generated by subsequent recrystallization annealing at 480°C for 30 min. The spun parts with high dimensional precision and low surface roughness are obtained by the forming method developed in this work, combining quenching with 3-pass stagger spinning and recrystallization annealing.
