By combining living trees and archaeological wood, the annual mean temperatures were reconstructed based on ring-width indices of the mid-eastern Tibetan Plateau for the past 2485 years. The climate variations reveale...By combining living trees and archaeological wood, the annual mean temperatures were reconstructed based on ring-width indices of the mid-eastern Tibetan Plateau for the past 2485 years. The climate variations revealed by the reconstruction indicate that there were four periods to have average tem- peratures similar to or even higher than that mean of 1970 to 2000 AD. A particularly notable rapid shift from cold to warm, we call it the "Eastern Jin Event", occurred from 348 AD to 413 AD. Calculation re- sults show that the temperature variations over the mid-eastern Tibetan Plateau are not only repre- sentative for large parts of north-central China, but also closely correspond to those of the entire Northern Hemisphere over long time scales. During the last 2485 years, the downfall of most major dynasties in China coincides with intervals of low temperature. Compared with the temperature records in other regions of China during the last 1000 years, this reconstruction from the Tibetan Plateau shows a significant warming trend after the 1950s.展开更多
In this paper, we generalize Clifford semirings to left Clifford semirings bymeans of the so-called band semirings. We also discuss a special case of this kind of semirings,that is, strong distributive lattices of lef...In this paper, we generalize Clifford semirings to left Clifford semirings bymeans of the so-called band semirings. We also discuss a special case of this kind of semirings,that is, strong distributive lattices of left rings.展开更多
Inspired by helical or spiral veins,which endow plants with excellent fexibility and elasticity to withstand storms,we present novel hollow microsprings with ionic liquid encapsulation for fexible and stretchable elec...Inspired by helical or spiral veins,which endow plants with excellent fexibility and elasticity to withstand storms,we present novel hollow microsprings with ionic liquid encapsulation for fexible and stretchable electronics.Te microsprings were generated by using a coaxial capillary microfuidic device to consecutively spin poly(vinylidene fuoride)(PVDF)presolution and an ionic liquid,which formed laminar fows in the coaxial injection microfuidic channels.Te fast phase inversion of PVDF helps to form the core-shell structure of a microfber and guarantees the in situ encapsulation of ionic liquid.Te hybrid microfber can then spiral and be further solidifed to maintain the helical structure with increasing fow rates of the injection fuids.Because of the feasible and precise control of the injection fuids during the microfuidic spinning,the resultant microsprings have controlled core-shell structures,helical pitches,and corresponding electromechanical properties.By further embedding them into stretchable flms,the simple paradigm of a fexible device shows great conductive performance in tensile tests and even motion cycles,which could be explored as a promising candidate in stretchable sensors,fexible electronics,and electronic skins.展开更多
The large 2219 Al alloy rings used to connect propellant tank components of a satellite launch vehicle to each other are conventionally manufactured by radial-axial ring rolling at 460°C with 50% deformation,but ...The large 2219 Al alloy rings used to connect propellant tank components of a satellite launch vehicle to each other are conventionally manufactured by radial-axial ring rolling at 460°C with 50% deformation,but often suffer from coarse elongated grain and low ductility. An improved process(hot ring rolling at460°C with 30% deformation, then air cooling to 240°C, followed by ring rolling at 240°C with 20% deformation) was tested for ring manufacturing. The corresponding microstructure evolution and mechanical properties of the produced rings were studied. The results show that the improved process can successfully be applied to manufacture the large 2219 Al alloy rings without formation of macroscopic defects,resulting in a product with fine and uniform grains after heat treatment. The fracture mechanism of both rings was mainly intergranular fracture. With the resulting grain size refinement due to the improved process, more homogeneous slip occured and the crack propagation path became more tortuous during the tensile testing process. Thus, the elongation in all three orthogonal directions was greatly improved,and the axial elongation increased from 3.5% to 10.0%.展开更多
Let R be an arbitrary commutative ring with identity. Denote by t the Lie algebra over R consisting of all upper triangular n by n matrices and let b be the Lie subalgebra of t consisting of all matrices of trace 0. T...Let R be an arbitrary commutative ring with identity. Denote by t the Lie algebra over R consisting of all upper triangular n by n matrices and let b be the Lie subalgebra of t consisting of all matrices of trace 0. The aim of this paper is to give an explicit description of the derivation algebras of the Lie algebras t and b, respectively.展开更多
We present a composite tree-ring chronology from two sites of Qilian Juniper （Sabina przewalskii） in the northwestern Qilian Mountains （QM）, Northwestern China. Precipitation in June was found to be the main limit...We present a composite tree-ring chronology from two sites of Qilian Juniper （Sabina przewalskii） in the northwestern Qilian Mountains （QM）, Northwestern China. Precipitation in June was found to be the main limiting factor for tree-growth. The tree rings are also significantly and positively correlated with June precipitation over large areas of the northern Tibetan Plateau （TP）. The authors thus consider that the treering based drought reconstruction from 1803-2006 is representative of a large area drought history. During the reconstruction period, persistent and severe dry epochs occurred in the 1820s-1830s, 1870s-1880s, 1920s, and 1950s 1960s, and persistent wet periods were found from 1803-1810s, 1890s-1920s, and 1970s-1980s. The severe dry and wet periods are similar to those found over the northeastern TP, indicating the potential linkages of the drought regimes between them. Comparison with global SST indicates that the drought variability is closely related to the tropical Pacific and Arctic Ocean SSTs, suggesting the connection of regional moisture variations to the Asian monsoon and westerly belt circulations, respectively.展开更多
Our understanding of the long-term hydroclimate variations in South China is prohibited by the shortness of me- teorological records. Paleoclimatic proxies, such as tree-rings, can be pursued to extend the meteorologi...Our understanding of the long-term hydroclimate variations in South China is prohibited by the shortness of me- teorological records. Paleoclimatic proxies, such as tree-rings, can be pursued to extend the meteorological records back for centuries to help us better understand hydroclimatic conditions. In this study, we reconstructed the July--Au- gust standardized precipitafio^evapotranspiration index （SPEIjut Aug） based on a newly developed 127-yr adjusted latewood width chronology from Tsuga longibracteata, South China. The chronology explained 40% of the actual SPEIjul Aug variance in the period 1953-2014. The reconstructed SPEIjuI Aug can represent large-scale July-August SPEI variations over South China, including northern Guangxi, Hunan, and Guizhou provinces. From the perspec- tive of the past 127 years, the extreme summer drought in 2013 was not unusual because more extreme drought events occurred in the first half of the 20th century. A significant 2.0-3.6-yr hydroclimatic cycle existed in the recon- struction, which indicated that the SPEIjulug might be driven by El Nifio-Southern Oscillation （ENSO）. We further checked the time-dependency of the relationship between SPEIJuI_Aug and ENSO and found that it was unstable. Their relationship was weak before the 1950s, became significant from the 1950s to early 1990s, and then dropped to be weak again and even out of phase since the early 1990s, which may be attributable to the significant westward exten- sion of the western Pacific subtropical high.展开更多
The Populus euphratica floodplain forests along the lower reaches of the Tarim River in continental-arid Xinjiang （northwest China） have been declining in recent decades as a result of dam constructions and the with...The Populus euphratica floodplain forests along the lower reaches of the Tarim River in continental-arid Xinjiang （northwest China） have been declining in recent decades as a result of dam constructions and the withdrawal of water from the river. Since 2000, controlled flooding has been carried out to counteract this process of degradation. However, the consequences of a changing water regime for the floodplain ecosystem are not yet sufficiently investigated. In 2004 we sampled a total of 150 P. euphratica trees along two transects at the middle and lower reaches of the Tarim River to compare the age structure and growth of these two tree populations. The anthropogenic drawdown of the groundwater table had no effect on the average growth of the trees at the lower reaches. However, tree growth abruptly increased after controlled flooding, thus showing distinct signs of recovery.展开更多
The annual growth rings of ten trees and the soils near the tree roots were sampled from the mining area of lead-and zinc-dominant metals in the Xixia Mountain, Nanjing, for the determination of chemical element conte...The annual growth rings of ten trees and the soils near the tree roots were sampled from the mining area of lead-and zinc-dominant metals in the Xixia Mountain, Nanjing, for the determination of chemical element contents. The study results showed that the elemental contents in the tree rings were correlated with those in the soils, i. e., the elemental contents in the tree rings increased with those in the soils, even in the cases of different environments and different tree species. Therefore, a time-concentration sequence could be set up on the basis of determining the elemental contents in the successive annual growth rings of trees to qualitatively reflect the annual variations of relevant elements in the soils, and a time-concentration sequence of elemental contents in soils could also be established in terms of related model to reproduce the dynamic changes of the surroundings.展开更多
Aims Forest growth and recruitment and their relationships to climate are complex.The aims of our study are(i)to examine the patterns in tree radial growth and recruitment along an altitudinal gradient in Mt.Everest r...Aims Forest growth and recruitment and their relationships to climate are complex.The aims of our study are(i)to examine the patterns in tree radial growth and recruitment along an altitudinal gradient in Mt.Everest region and(ii)to identify the climatic factors that are responsible to the observed patterns in tree growth and recruitment.Methods Four plots,each 30360 m in size,were established from the lower to upper limits of the eastern Himalayan fir forest in Dingjie County of the Mt.Everest Nature Reserve,China.Dendrochronological techniques were applied to obtain information about the radial growth and age of the trees in the plots.Correlation analysis was used to identify the relationships between radial growth and recruitment of trees and climatic variables,i.e.monthly mean temperature and Palmer Drought Severity Index(PDSI).The population age structure was analyzed to investigate the recruitment history.Important Findings The timberline plot was characterized by significant tree recruitments in the recent three decades and sporadic recruitments in earlier periods.The other three plots showed recruitment pulses during 1880–1910 in Plot 3700 m,during 1870–80 and 1920–30 in Plot 3520 m and during 1900–40 in Plot 3410 m.The recruitment of fir trees in the timberline was sensitive to summer(June–September)temperatures,but it was mainly controlled by episodic disturbances in lower altitudes.Fir radial growth in the upper two plots was positively correlated with previous winter and current August temperature.Fir radial growth at the two lower plots was positively correlated with PDSI from previous September to current September.展开更多
A ring is said to be UR if every element can be written as the sum of a unit and a regular element. These rings are shown to be a unifying generalization of regular rings, clean rings and （S, 2）-ring~. Some relation...A ring is said to be UR if every element can be written as the sum of a unit and a regular element. These rings are shown to be a unifying generalization of regular rings, clean rings and （S, 2）-ring~. Some relations of these rings are studied and several properties of clean rings and （S, 2）-rings are extended. PAng extensions of UR-rings are also investigated.展开更多
Let U = Tri（fit, M, B） be a triangular ring, where A and B are unital rings, and M is a faithful （A, B）-bimodule. It is shown that an additive map φ on U is centralized at zero point （i.e., ,φ（A）B = A,φ（B）...Let U = Tri（fit, M, B） be a triangular ring, where A and B are unital rings, and M is a faithful （A, B）-bimodule. It is shown that an additive map φ on U is centralized at zero point （i.e., ,φ（A）B = A,φ（B） = 0 whenever AB = 0） if and only if it is a centralizer. Let 5 ： U →U be an additive map. It is also shown that the following four conditions are equivalent： （1） 5 is specially generalized derivable at zero point, i.e., 5（AB） = δ（A）B ＋ AS（B） - Aδ（I）B whenever AB = 0; （2） 5 is generalized derivable at zero point, i.e., there exist additive maps τ1 and τ2 on U derivable at zero point such that δ（AB） = δ（A）B ＋ Aτ1（B） = τ2（A）B ＋ Aδ（B） whenever AB = 0; （3） δ is a special generalized derivation; （4） δ is a generalized derivation. These results are then applied to nest algebras of Banach space展开更多
基金Supported by National Natural Science Foundation of China (Grant Nos. 40525004, 40599420, 40890051)National Basic Research Program of China (Grant Nos. 2007BAC30B00, 2004CB720200, 2006CB400503)the Swedish International Development Cooperation Agency (SIDA, Grant to Hans W. Linderholm)
文摘By combining living trees and archaeological wood, the annual mean temperatures were reconstructed based on ring-width indices of the mid-eastern Tibetan Plateau for the past 2485 years. The climate variations revealed by the reconstruction indicate that there were four periods to have average tem- peratures similar to or even higher than that mean of 1970 to 2000 AD. A particularly notable rapid shift from cold to warm, we call it the "Eastern Jin Event", occurred from 348 AD to 413 AD. Calculation re- sults show that the temperature variations over the mid-eastern Tibetan Plateau are not only repre- sentative for large parts of north-central China, but also closely correspond to those of the entire Northern Hemisphere over long time scales. During the last 2485 years, the downfall of most major dynasties in China coincides with intervals of low temperature. Compared with the temperature records in other regions of China during the last 1000 years, this reconstruction from the Tibetan Plateau shows a significant warming trend after the 1950s.
文摘In this paper, we generalize Clifford semirings to left Clifford semirings bymeans of the so-called band semirings. We also discuss a special case of this kind of semirings,that is, strong distributive lattices of left rings.
基金This work was supported by the National Key Research and Development Program of China[2017YFA0700404]the NSAF Foundation of China[Grant No.U1530260]+1 种基金the Natural Science Foundation of Jiangsu[Grant No.BE2018707]the Scientifc Research Foundation of Southeast University,and the Scientifc Research Foundation of the Graduate School of Southeast University[Grant No.YBJJ1779].
文摘Inspired by helical or spiral veins,which endow plants with excellent fexibility and elasticity to withstand storms,we present novel hollow microsprings with ionic liquid encapsulation for fexible and stretchable electronics.Te microsprings were generated by using a coaxial capillary microfuidic device to consecutively spin poly(vinylidene fuoride)(PVDF)presolution and an ionic liquid,which formed laminar fows in the coaxial injection microfuidic channels.Te fast phase inversion of PVDF helps to form the core-shell structure of a microfber and guarantees the in situ encapsulation of ionic liquid.Te hybrid microfber can then spiral and be further solidifed to maintain the helical structure with increasing fow rates of the injection fuids.Because of the feasible and precise control of the injection fuids during the microfuidic spinning,the resultant microsprings have controlled core-shell structures,helical pitches,and corresponding electromechanical properties.By further embedding them into stretchable flms,the simple paradigm of a fexible device shows great conductive performance in tensile tests and even motion cycles,which could be explored as a promising candidate in stretchable sensors,fexible electronics,and electronic skins.
基金supported financially by the Joint Funds of the National Natural Science Foundation of China(No.U1637601)the Fund of Jiangsu Province for the Transformation of Scientific and Technological Achievements(No.BA2015075)the Project of Innovation-driven Plan for Postgraduate in Central South University(No.2016ZZTS048)
文摘The large 2219 Al alloy rings used to connect propellant tank components of a satellite launch vehicle to each other are conventionally manufactured by radial-axial ring rolling at 460°C with 50% deformation,but often suffer from coarse elongated grain and low ductility. An improved process(hot ring rolling at460°C with 30% deformation, then air cooling to 240°C, followed by ring rolling at 240°C with 20% deformation) was tested for ring manufacturing. The corresponding microstructure evolution and mechanical properties of the produced rings were studied. The results show that the improved process can successfully be applied to manufacture the large 2219 Al alloy rings without formation of macroscopic defects,resulting in a product with fine and uniform grains after heat treatment. The fracture mechanism of both rings was mainly intergranular fracture. With the resulting grain size refinement due to the improved process, more homogeneous slip occured and the crack propagation path became more tortuous during the tensile testing process. Thus, the elongation in all three orthogonal directions was greatly improved,and the axial elongation increased from 3.5% to 10.0%.
基金the National Natural Scieace Foundation of China(10071078).
文摘Let R be an arbitrary commutative ring with identity. Denote by t the Lie algebra over R consisting of all upper triangular n by n matrices and let b be the Lie subalgebra of t consisting of all matrices of trace 0. The aim of this paper is to give an explicit description of the derivation algebras of the Lie algebras t and b, respectively.
基金supported by the National Natural Science Foundation of China In-novation Team Project(Grant No.40721061)the Na-tional Natural Science Foundation of China(Grant Nos.40671191 and 90502008)+1 种基金the Chinese 111 Project(Grant No.B06026)the One Hundred Talents Program of CAS(Grant No.29O827B11)
文摘We present a composite tree-ring chronology from two sites of Qilian Juniper （Sabina przewalskii） in the northwestern Qilian Mountains （QM）, Northwestern China. Precipitation in June was found to be the main limiting factor for tree-growth. The tree rings are also significantly and positively correlated with June precipitation over large areas of the northern Tibetan Plateau （TP）. The authors thus consider that the treering based drought reconstruction from 1803-2006 is representative of a large area drought history. During the reconstruction period, persistent and severe dry epochs occurred in the 1820s-1830s, 1870s-1880s, 1920s, and 1950s 1960s, and persistent wet periods were found from 1803-1810s, 1890s-1920s, and 1970s-1980s. The severe dry and wet periods are similar to those found over the northeastern TP, indicating the potential linkages of the drought regimes between them. Comparison with global SST indicates that the drought variability is closely related to the tropical Pacific and Arctic Ocean SSTs, suggesting the connection of regional moisture variations to the Asian monsoon and westerly belt circulations, respectively.
基金Supported by the National Natural Science Foundation of China(41271210)Global Change Program(2016YFA0600503)+1 种基金Priority Academic Program Development of Jiangsu Higher Education InstitutionsJiangsu Collaborative Innovation Center for Climate Change
文摘Our understanding of the long-term hydroclimate variations in South China is prohibited by the shortness of me- teorological records. Paleoclimatic proxies, such as tree-rings, can be pursued to extend the meteorological records back for centuries to help us better understand hydroclimatic conditions. In this study, we reconstructed the July--Au- gust standardized precipitafio^evapotranspiration index （SPEIjut Aug） based on a newly developed 127-yr adjusted latewood width chronology from Tsuga longibracteata, South China. The chronology explained 40% of the actual SPEIjul Aug variance in the period 1953-2014. The reconstructed SPEIjuI Aug can represent large-scale July-August SPEI variations over South China, including northern Guangxi, Hunan, and Guizhou provinces. From the perspec- tive of the past 127 years, the extreme summer drought in 2013 was not unusual because more extreme drought events occurred in the first half of the 20th century. A significant 2.0-3.6-yr hydroclimatic cycle existed in the recon- struction, which indicated that the SPEIjulug might be driven by El Nifio-Southern Oscillation （ENSO）. We further checked the time-dependency of the relationship between SPEIJuI_Aug and ENSO and found that it was unstable. Their relationship was weak before the 1950s, became significant from the 1950s to early 1990s, and then dropped to be weak again and even out of phase since the early 1990s, which may be attributable to the significant westward exten- sion of the western Pacific subtropical high.
文摘The Populus euphratica floodplain forests along the lower reaches of the Tarim River in continental-arid Xinjiang （northwest China） have been declining in recent decades as a result of dam constructions and the withdrawal of water from the river. Since 2000, controlled flooding has been carried out to counteract this process of degradation. However, the consequences of a changing water regime for the floodplain ecosystem are not yet sufficiently investigated. In 2004 we sampled a total of 150 P. euphratica trees along two transects at the middle and lower reaches of the Tarim River to compare the age structure and growth of these two tree populations. The anthropogenic drawdown of the groundwater table had no effect on the average growth of the trees at the lower reaches. However, tree growth abruptly increased after controlled flooding, thus showing distinct signs of recovery.
基金Project supported by the National Natural Science Foundation of China.
文摘The annual growth rings of ten trees and the soils near the tree roots were sampled from the mining area of lead-and zinc-dominant metals in the Xixia Mountain, Nanjing, for the determination of chemical element contents. The study results showed that the elemental contents in the tree rings were correlated with those in the soils, i. e., the elemental contents in the tree rings increased with those in the soils, even in the cases of different environments and different tree species. Therefore, a time-concentration sequence could be set up on the basis of determining the elemental contents in the successive annual growth rings of trees to qualitatively reflect the annual variations of relevant elements in the soils, and a time-concentration sequence of elemental contents in soils could also be established in terms of related model to reproduce the dynamic changes of the surroundings.
基金Natural Science Foundation of China(30670365,40631002 and 30870461)the Chinese Academy of Sciences(KSCXYW-Z-1022).
文摘Aims Forest growth and recruitment and their relationships to climate are complex.The aims of our study are(i)to examine the patterns in tree radial growth and recruitment along an altitudinal gradient in Mt.Everest region and(ii)to identify the climatic factors that are responsible to the observed patterns in tree growth and recruitment.Methods Four plots,each 30360 m in size,were established from the lower to upper limits of the eastern Himalayan fir forest in Dingjie County of the Mt.Everest Nature Reserve,China.Dendrochronological techniques were applied to obtain information about the radial growth and age of the trees in the plots.Correlation analysis was used to identify the relationships between radial growth and recruitment of trees and climatic variables,i.e.monthly mean temperature and Palmer Drought Severity Index(PDSI).The population age structure was analyzed to investigate the recruitment history.Important Findings The timberline plot was characterized by significant tree recruitments in the recent three decades and sporadic recruitments in earlier periods.The other three plots showed recruitment pulses during 1880–1910 in Plot 3700 m,during 1870–80 and 1920–30 in Plot 3520 m and during 1900–40 in Plot 3410 m.The recruitment of fir trees in the timberline was sensitive to summer(June–September)temperatures,but it was mainly controlled by episodic disturbances in lower altitudes.Fir radial growth in the upper two plots was positively correlated with previous winter and current August temperature.Fir radial growth at the two lower plots was positively correlated with PDSI from previous September to current September.
基金the National -Natural Science Foundation of China （No. 10571026） the Natural Science Foundation of Jiangsu Province （No. 2005207）.
文摘A ring is said to be UR if every element can be written as the sum of a unit and a regular element. These rings are shown to be a unifying generalization of regular rings, clean rings and （S, 2）-ring~. Some relations of these rings are studied and several properties of clean rings and （S, 2）-rings are extended. PAng extensions of UR-rings are also investigated.
基金supported by National Natural Science Foundation of China (Grant No. 11101250)supported by National Natural Science Foundation of China (Grant No. 11171249)Youth Foundation of Shanxi Province (Grant No. 2012021004)
文摘Let U = Tri（fit, M, B） be a triangular ring, where A and B are unital rings, and M is a faithful （A, B）-bimodule. It is shown that an additive map φ on U is centralized at zero point （i.e., ,φ（A）B = A,φ（B） = 0 whenever AB = 0） if and only if it is a centralizer. Let 5 ： U →U be an additive map. It is also shown that the following four conditions are equivalent： （1） 5 is specially generalized derivable at zero point, i.e., 5（AB） = δ（A）B ＋ AS（B） - Aδ（I）B whenever AB = 0; （2） 5 is generalized derivable at zero point, i.e., there exist additive maps τ1 and τ2 on U derivable at zero point such that δ（AB） = δ（A）B ＋ Aτ1（B） = τ2（A）B ＋ Aδ（B） whenever AB = 0; （3） δ is a special generalized derivation; （4） δ is a generalized derivation. These results are then applied to nest algebras of Banach space
