The creep strain of conventionally treated 2195 alloy is very low,increasing the difficulty of manufacturing Al-Cu-Li alloy sheet parts by creep age forming.Therefore,finding a solution to improve the creep formabilit...The creep strain of conventionally treated 2195 alloy is very low,increasing the difficulty of manufacturing Al-Cu-Li alloy sheet parts by creep age forming.Therefore,finding a solution to improve the creep formability of Al-Cu-Li alloy is vital.A thorough comparison of the effects of cryo-deformation and ambient temperature large pre-deformation(LPD)on the creep ageing response in the 2195 alloy sheet at 160℃with different stresses has been made.The evolution of dislocations and precipitates during creep ageing of LPD alloys are revealed by X-ray diffraction and transmission electron microscopy.High-quality 2195 alloy sheet largely pre-deformed by 80%without edge-cracking is obtained by cryo-rolling at liquid nitrogen temperature,while severe edge-cracking occurs during room temperature rolling.The creep formability and strength of the 2195 alloy are both enhanced by introducing pre-existing dislocations with a density over 1.4×10^(15)m^(−2).At 160℃and 150 MPa,creep strain and creep-aged strength generally increases by 4−6 times and 30−50 MPa in the LPD sample,respectively,compared to conventional T3 alloy counterpart.The elongation of creep-aged LPD sample is low but remains relevant for application.The high-density dislocations,though existing in the form of dislocation tangles,promote the formation of refined T1 precipitates with a uniform dispersion.展开更多
Microstructure evolution and dislocation configurations in nanostructured Al–Mg alloys processed by high pressure torsion （HPT） were analyzed by transmission electron microscopy （TEM） and high-resolution TEM （HR...Microstructure evolution and dislocation configurations in nanostructured Al–Mg alloys processed by high pressure torsion （HPT） were analyzed by transmission electron microscopy （TEM） and high-resolution TEM （HRTEM）. The results show that the grains less than 100 nm have sharp grain boundaries （GBs） and are completely free of dislocations. In contrast, a high density of dislocation as high as 1017 m^-2 exists within the grains larger than 200 nm and these larger grains are usually separated into subgrains and dislocation cells. The dislocations are 60° full dislocations with Burgers vectors of 1/2〈110〉and most of them appear as dipoles and loops. The microtwins and stacking faults （SFs） formed by the Shockley partials from the dissociation of both the 60° mixed dislocation and 0° screw dislocation in ultrafine grains were simultaneously observed by HRTEM in the HPT Al–Mg alloys. These results suggest that partial dislocation emissions, as well as the activation of partial dislocations could also become a deformation mechanism in ultrafine-grained aluminum during severe plastic deformation. The grain refinement mechanism associated with the very high local dislocation density, the dislocation cells and the non-equilibrium GBs, as well as the SFs and microtwins in the HPT Al-Mg alloys were proposed.展开更多
A new combined soft switching technique and a novel topology of aeronautical static inverter with high frequency pulse dc link are proposed in this paper, namely an electrical isolated converter can realize soft swi...A new combined soft switching technique and a novel topology of aeronautical static inverter with high frequency pulse dc link are proposed in this paper, namely an electrical isolated converter can realize soft switching of two stage cascade converters. It lays technical foundation for high power density, high efficiency and low cost aeronautical static inverter. The operation and design approach of this topology are carefully analyzed and studied. The validity of this topology is verified by simulation and test.展开更多
Using NCEP/NCAR daily reanalysis data and SCSMEX data, an investigation is carried out of the relationship between the position variation of the west Pacific subtropical high （WPSH） and the apparcnt heating in June ...Using NCEP/NCAR daily reanalysis data and SCSMEX data, an investigation is carried out of the relationship between the position variation of the west Pacific subtropical high （WPSH） and the apparcnt heating in June 1998 based on the complete vertical vorticlty equation. It is tbund that the non-adiabatic heating plays an important role in the position variation of WPSH. In comparison with climatic mean status, the vertical change of non-adiabatic heating is stronger in the north side of WPSH in June 1998, but weaker in the south side of WPSH. The anomalous non-uniform heating induces anomalous cyclonic vorticity in South China, areas to lhe south of the Yangtze and its mid-lower valleys, but anomalous anticyclonic vorticity in the Indo-China Peninsula and South China Sea areas lead to the more southward position of WPSH than the mean.展开更多
Using datasets on high-tech industries in Beijing as empirical studies, this paper attempts to interpret spatial shift of high-tech manufacturing firms and to examine the main determinants that have had the greatest e...Using datasets on high-tech industries in Beijing as empirical studies, this paper attempts to interpret spatial shift of high-tech manufacturing firms and to examine the main determinants that have had the greatest effect on this spatial evolution. We aimed at merging these two aspects by using firm level databases in 1996 and 2010. To explain spatial change of the high-tech firms in Beijing, the Kernel density estimation method was used for hotspot analysis and detection by comparing their locations in 1996 and 2010, through which spatial features and their temporal changes could be approximately plotted. Furthermore, to provide quantitative results, Ripley′s K-function was used as an instrument to reveal spatial shift and the dispersion distance of high-tech manufacturing firms in Beijing. By employing a negative binominal regression model, we evaluated the main determinants that have significantly affected the spatial evolution of high-tech manufacturing firms and compared differential influence of these locational factors on overall high-tech firms and each sub-sectors. The empirical analysis shows that high-tech industries in Beijing, in general, have evident agglomeration characteristics, and that the hotspot has shifted from the central city to suburban areas. In combination with the Ripley index, this study concludes that high-tech firms are now more scattered in metropolitan areas of Beijing as compared with 1996. The results of regression model indicate that the firms′ locational decisions are significantly influenced by the spatial planning and regulation policies of the municipal government. In addition, market processes involving transportation accessibility and agglomeration economy have been found to be important in explaining the dynamics of locational variation of high-tech manufacturing firms in Beijing. Research into how markets and the government interact to determine the location of high-tech manufacturing production will be helpful for policymakers to enact effective policies toward a more efficient urban spatial structure.展开更多
Low-grade invasive ductal carcinoma is almost diploid, and has frequent losses of chromosome 16q, which is shared by other precancerous lesions of the mammary gland such as flat epithelial atypia （FEA）, atypical duc...Low-grade invasive ductal carcinoma is almost diploid, and has frequent losses of chromosome 16q, which is shared by other precancerous lesions of the mammary gland such as flat epithelial atypia （FEA）, atypical ductal hyperplasia （ADH）, and lownuclear grade ductal carcinoma in situ （DCIS）. The genetic alterations accumulate in a stepwise fashion as the precancerous lesions progress to invasve ductal carcinoma. This supports the linear progression model of breast cancer from FEA, through ADH, to low- nuclear grade DCIS as non-obligate early events in low-grade IDC evolution. In contrast, high-grade carcinoma tends to aneuploidy with complex genetic alterations--most importantly, frequent gains at chromosome 16q. Frequent losses at chromosome 16q in low-grade IDC and gains in the same arm of the same chromosome in high-grade IDC imply that these lesions are two end outcomes of different disease processes and that they do not lie in the same continuum of a process. Therefore, low-grade and high-grade IDC are two distinct diseases with a divergent route of progression.展开更多
Aimed at the problem that the state estimation in the measurement update of the simultaneous localization and mapping(SLAM)method is incorrect or even not convergent because of the non-Gaussian measurement noise,outli...Aimed at the problem that the state estimation in the measurement update of the simultaneous localization and mapping(SLAM)method is incorrect or even not convergent because of the non-Gaussian measurement noise,outliers,or unknown and time-varying noise statistical characteristics,a robust SLAM method based on the improved variational Bayesian adaptive Kalman filtering(IVBAKF)is proposed.First,the measurement noise covariance is estimated using the variable Bayesian adaptive filtering algorithm.Then,the estimated covariance matrix is robustly processed through the weight function constructed in the form of a reweighted average.Finally,the system updates are iterated multiple times to further gradually correct the state estimation error.Furthermore,to observe features at different depths,a feature measurement model containing depth parameters is constructed.Experimental results show that when the measurement noise does not obey the Gaussian distribution and there are outliers in the measurement information,compared with the variational Bayesian adaptive SLAM method,the positioning accuracy of the proposed method is improved by 17.23%,20.46%,and 17.76%,which has better applicability and robustness to environmental disturbance.展开更多
Current phase comparison based pilot protection had been generally utilized as primary protection of the transmission lines in China from the 1950＇s to the 1980＇ s, Comentional phase comparison pilot protection has ...Current phase comparison based pilot protection had been generally utilized as primary protection of the transmission lines in China from the 1950＇s to the 1980＇ s, Comentional phase comparison pilot protection has a long phase comparison time, which results in a longer fault-clearing time. This paper proposes a new current phase comparison, pilot protection scheme that is based on non-power frequency fauh eun＇ent component. The phase of the fourth harmonic eun＇ent of each end of the protected line has heen abstracted hy utilizing complex wavelet transformation and then compared in order to determine whether the inner fauh occurs or not. This way can greatly deerease fauh-elearing time and improve performances of this pilot protection when fault occurs under the heavy-load current and asymmetrical operation eonditions, Many EMTP simulations have verified the proposed scheme＇s correctness and effectiveness.展开更多
The dynamics of high-altitude inland lakes in the Tibetan Plateau are sensitive indicators of climate change. Due to the remoteness and hard access, satellite altimetry becomes an effective approach to obtaining large...The dynamics of high-altitude inland lakes in the Tibetan Plateau are sensitive indicators of climate change. Due to the remoteness and hard access, satellite altimetry becomes an effective approach to obtaining largescale and temporally continuous information of lake-level changes. The CryoSat-2 altimetry is expected to solve the current problem that earlier radar altimeters are only practical for monitoring large water bodies, while ICESat laser altimetry is available only for the period 2003-2009. In this study, the comparison of CryoSat-2 altimetry for Namco with in situ water-level data suggests a high cor- relation coefficient of 0.71 （P 〈 0.01）, with the mean error of -0.12 m and root-mean-square error of 0.18 m. Further, the combination of ICESat and CryoSat-2 altimetry data and in situ lake-level observations reveals a rapid water- level rise of 0.24 4- 0.04 m/year during 2003-2008 and then a slightly decreasing trend of -0.09 4- 0.04 m/year during 2009-2013. This study suggests that the CryoSat-2 altimetry has the potential of sustaining the fine observa- tions on Tibetan lakes, following the ICESat mission. Besides, the examination of four key climatic variables （temperature, precipitation, potential evapotranspiration, and relative humidity） during 1990-2013 indicates that the wetting climate over Namco Basin stagnated or even reversed around 2006, which may be tightly related to the slowing lake growth.展开更多
Using the temperature profiles retrieved from the Mars Climate Sounder（MCS） instrument onboard Mars Reconnaissance Orbiter（MRO） satellite between November 2006 and April 2013, we studied the seasonal and interannu...Using the temperature profiles retrieved from the Mars Climate Sounder（MCS） instrument onboard Mars Reconnaissance Orbiter（MRO） satellite between November 2006 and April 2013, we studied the seasonal and interannual variability of QuasiStationary Planetary Waves（QSPWs） in the Martian middle atmosphere. The QSPW amplitudes in the Southern Hemisphere（SH） high latitudes are significantly stronger than those in the Northern Hemisphere（NH）. Seasonal variation with maximum amplitude near winter solstice of each hemisphere is clearly seen. The vertical structure of the QSPW in temperature shows double-layer feature with one peak near 50 Pa and the other peak near 1 Pa. The QSPW in geopotential height is clearly maximized in the region between two temperature peaks. The maximum amplitude of QSPW for s=1 is ~8–10 K in temperature and ~1 km in geopotential height in the SH high latitudes. The maximum amplitude at the SH high latitudes in Mars Year（MY） 31 is ~2 K stronger than those in other MYs, suggesting the clear interannual variability. We compared the satellite results with those obtained from the Mars Climate Database（MCD） simulation version 5.0; a reasonable agreement was found. The MCD simulation further suggested that the variability of dust might partially contribute to the interannual variability of QSPW amplitude.展开更多
基金Projects(52274404,52305441,U22A20190)supported by the National Natural Science Foundation of ChinaProjects(2022JJ20065,2023JJ40739)supported by the Natural Science Foundation of Hunan Province,China+2 种基金Project(2022RC1001)supported by the Science and Technology Innovation Program of Hunan Province,ChinaProject(2023ZZTS0972)supported by the Fundamental Research Funds for the Central Universities,ChinaProject(2021YFB3400903)supported by the National Key R&D Program of China。
文摘The creep strain of conventionally treated 2195 alloy is very low,increasing the difficulty of manufacturing Al-Cu-Li alloy sheet parts by creep age forming.Therefore,finding a solution to improve the creep formability of Al-Cu-Li alloy is vital.A thorough comparison of the effects of cryo-deformation and ambient temperature large pre-deformation(LPD)on the creep ageing response in the 2195 alloy sheet at 160℃with different stresses has been made.The evolution of dislocations and precipitates during creep ageing of LPD alloys are revealed by X-ray diffraction and transmission electron microscopy.High-quality 2195 alloy sheet largely pre-deformed by 80%without edge-cracking is obtained by cryo-rolling at liquid nitrogen temperature,while severe edge-cracking occurs during room temperature rolling.The creep formability and strength of the 2195 alloy are both enhanced by introducing pre-existing dislocations with a density over 1.4×10^(15)m^(−2).At 160℃and 150 MPa,creep strain and creep-aged strength generally increases by 4−6 times and 30−50 MPa in the LPD sample,respectively,compared to conventional T3 alloy counterpart.The elongation of creep-aged LPD sample is low but remains relevant for application.The high-density dislocations,though existing in the form of dislocation tangles,promote the formation of refined T1 precipitates with a uniform dispersion.
基金Project(BK2012715)supported by the Basic Research Program(Natural Science Foundation)of Jiangsu Province,ChinaProject(14KJA430002)supported by the Key University Science Research Project of Jiangsu Province,China+3 种基金Project(50971087)supported by the National Natural Science Foundation of China,ChinaProjects(11JDG070,11JDG140)supported by the Senior Talent Research Foundation of Jiangsu University,ChinaProject(hsm1301)supported by the Foundation of the Jiangsu Province Key Laboratory of High-end Structural Materials,ChinaProject(Kjsmcx2011004)supported by the Foundation of the Jiangsu Province Key Laboratory of Materials Tribology,China
文摘Microstructure evolution and dislocation configurations in nanostructured Al–Mg alloys processed by high pressure torsion （HPT） were analyzed by transmission electron microscopy （TEM） and high-resolution TEM （HRTEM）. The results show that the grains less than 100 nm have sharp grain boundaries （GBs） and are completely free of dislocations. In contrast, a high density of dislocation as high as 1017 m^-2 exists within the grains larger than 200 nm and these larger grains are usually separated into subgrains and dislocation cells. The dislocations are 60° full dislocations with Burgers vectors of 1/2〈110〉and most of them appear as dipoles and loops. The microtwins and stacking faults （SFs） formed by the Shockley partials from the dissociation of both the 60° mixed dislocation and 0° screw dislocation in ultrafine grains were simultaneously observed by HRTEM in the HPT Al–Mg alloys. These results suggest that partial dislocation emissions, as well as the activation of partial dislocations could also become a deformation mechanism in ultrafine-grained aluminum during severe plastic deformation. The grain refinement mechanism associated with the very high local dislocation density, the dislocation cells and the non-equilibrium GBs, as well as the SFs and microtwins in the HPT Al-Mg alloys were proposed.
文摘A new combined soft switching technique and a novel topology of aeronautical static inverter with high frequency pulse dc link are proposed in this paper, namely an electrical isolated converter can realize soft switching of two stage cascade converters. It lays technical foundation for high power density, high efficiency and low cost aeronautical static inverter. The operation and design approach of this topology are carefully analyzed and studied. The validity of this topology is verified by simulation and test.
基金Innovation Plans for Postgraduates of Higher Education Colleges in Jiangsu Province(E30000008098-3)Natural Science Foundation of China (40575045)+1 种基金National Key Fundamental ResearchDevelopment Plans (2004CB418302 2004CB418303)
文摘Using NCEP/NCAR daily reanalysis data and SCSMEX data, an investigation is carried out of the relationship between the position variation of the west Pacific subtropical high （WPSH） and the apparcnt heating in June 1998 based on the complete vertical vorticlty equation. It is tbund that the non-adiabatic heating plays an important role in the position variation of WPSH. In comparison with climatic mean status, the vertical change of non-adiabatic heating is stronger in the north side of WPSH in June 1998, but weaker in the south side of WPSH. The anomalous non-uniform heating induces anomalous cyclonic vorticity in South China, areas to lhe south of the Yangtze and its mid-lower valleys, but anomalous anticyclonic vorticity in the Indo-China Peninsula and South China Sea areas lead to the more southward position of WPSH than the mean.
基金Under the auspices of National Natural Science Foundation of China(No.40971075)
文摘Using datasets on high-tech industries in Beijing as empirical studies, this paper attempts to interpret spatial shift of high-tech manufacturing firms and to examine the main determinants that have had the greatest effect on this spatial evolution. We aimed at merging these two aspects by using firm level databases in 1996 and 2010. To explain spatial change of the high-tech firms in Beijing, the Kernel density estimation method was used for hotspot analysis and detection by comparing their locations in 1996 and 2010, through which spatial features and their temporal changes could be approximately plotted. Furthermore, to provide quantitative results, Ripley′s K-function was used as an instrument to reveal spatial shift and the dispersion distance of high-tech manufacturing firms in Beijing. By employing a negative binominal regression model, we evaluated the main determinants that have significantly affected the spatial evolution of high-tech manufacturing firms and compared differential influence of these locational factors on overall high-tech firms and each sub-sectors. The empirical analysis shows that high-tech industries in Beijing, in general, have evident agglomeration characteristics, and that the hotspot has shifted from the central city to suburban areas. In combination with the Ripley index, this study concludes that high-tech firms are now more scattered in metropolitan areas of Beijing as compared with 1996. The results of regression model indicate that the firms′ locational decisions are significantly influenced by the spatial planning and regulation policies of the municipal government. In addition, market processes involving transportation accessibility and agglomeration economy have been found to be important in explaining the dynamics of locational variation of high-tech manufacturing firms in Beijing. Research into how markets and the government interact to determine the location of high-tech manufacturing production will be helpful for policymakers to enact effective policies toward a more efficient urban spatial structure.
文摘Low-grade invasive ductal carcinoma is almost diploid, and has frequent losses of chromosome 16q, which is shared by other precancerous lesions of the mammary gland such as flat epithelial atypia （FEA）, atypical ductal hyperplasia （ADH）, and lownuclear grade ductal carcinoma in situ （DCIS）. The genetic alterations accumulate in a stepwise fashion as the precancerous lesions progress to invasve ductal carcinoma. This supports the linear progression model of breast cancer from FEA, through ADH, to low- nuclear grade DCIS as non-obligate early events in low-grade IDC evolution. In contrast, high-grade carcinoma tends to aneuploidy with complex genetic alterations--most importantly, frequent gains at chromosome 16q. Frequent losses at chromosome 16q in low-grade IDC and gains in the same arm of the same chromosome in high-grade IDC imply that these lesions are two end outcomes of different disease processes and that they do not lie in the same continuum of a process. Therefore, low-grade and high-grade IDC are two distinct diseases with a divergent route of progression.
基金Primary Research and Development Plan of Jiangsu Province(No.BE2022389)Jiangsu Province Agricultural Science and Technology Independent Innovation Fund Project(No.CX(22)3091)the National Natural Science Foundation of China(No.61773113)。
文摘Aimed at the problem that the state estimation in the measurement update of the simultaneous localization and mapping(SLAM)method is incorrect or even not convergent because of the non-Gaussian measurement noise,outliers,or unknown and time-varying noise statistical characteristics,a robust SLAM method based on the improved variational Bayesian adaptive Kalman filtering(IVBAKF)is proposed.First,the measurement noise covariance is estimated using the variable Bayesian adaptive filtering algorithm.Then,the estimated covariance matrix is robustly processed through the weight function constructed in the form of a reweighted average.Finally,the system updates are iterated multiple times to further gradually correct the state estimation error.Furthermore,to observe features at different depths,a feature measurement model containing depth parameters is constructed.Experimental results show that when the measurement noise does not obey the Gaussian distribution and there are outliers in the measurement information,compared with the variational Bayesian adaptive SLAM method,the positioning accuracy of the proposed method is improved by 17.23%,20.46%,and 17.76%,which has better applicability and robustness to environmental disturbance.
基金Sponsored by the Power Electrical Science and Technology Foundation of XJ Group and the Shanghai University Foundation for Excellent Young Teacher.
文摘Current phase comparison based pilot protection had been generally utilized as primary protection of the transmission lines in China from the 1950＇s to the 1980＇ s, Comentional phase comparison pilot protection has a long phase comparison time, which results in a longer fault-clearing time. This paper proposes a new current phase comparison, pilot protection scheme that is based on non-power frequency fauh eun＇ent component. The phase of the fourth harmonic eun＇ent of each end of the protected line has heen abstracted hy utilizing complex wavelet transformation and then compared in order to determine whether the inner fauh occurs or not. This way can greatly deerease fauh-elearing time and improve performances of this pilot protection when fault occurs under the heavy-load current and asymmetrical operation eonditions, Many EMTP simulations have verified the proposed scheme＇s correctness and effectiveness.
基金supported by the National Special Basic Research Project of the Ministry of Science and Technology(2013FY111400-2,2009CB723901)the National Natural Science Foundation of China(41120114001,41125003,41071254,40971048)+3 种基金the European Space Agency(ESA AO 2605)the Knowledge Innovation Foundation Program for outstanding Young Scholar of Chinese Academy of Sciences(CAS)(KZCX2-EWQN104)supported by Open Research Fund of Key Laboratory of Tibetan Environmental Changes and Land Surface Processes in Chinese Academy of SciencesOpen Fund of State Key Laboratory of Remote Sensing Science
文摘The dynamics of high-altitude inland lakes in the Tibetan Plateau are sensitive indicators of climate change. Due to the remoteness and hard access, satellite altimetry becomes an effective approach to obtaining largescale and temporally continuous information of lake-level changes. The CryoSat-2 altimetry is expected to solve the current problem that earlier radar altimeters are only practical for monitoring large water bodies, while ICESat laser altimetry is available only for the period 2003-2009. In this study, the comparison of CryoSat-2 altimetry for Namco with in situ water-level data suggests a high cor- relation coefficient of 0.71 （P 〈 0.01）, with the mean error of -0.12 m and root-mean-square error of 0.18 m. Further, the combination of ICESat and CryoSat-2 altimetry data and in situ lake-level observations reveals a rapid water- level rise of 0.24 4- 0.04 m/year during 2003-2008 and then a slightly decreasing trend of -0.09 4- 0.04 m/year during 2009-2013. This study suggests that the CryoSat-2 altimetry has the potential of sustaining the fine observa- tions on Tibetan lakes, following the ICESat mission. Besides, the examination of four key climatic variables （temperature, precipitation, potential evapotranspiration, and relative humidity） during 1990-2013 indicates that the wetting climate over Namco Basin stagnated or even reversed around 2006, which may be tightly related to the slowing lake growth.
基金support from the National Natural Science Foundation of China(Grants Nos.41225017,41127901,41025016,and 41121003)the Chinese Academy of Sciences Key Research Program(Grant No.KZZD-EW-01)+1 种基金the National Basic Research Program of China(Grant No.2012CB825605)the Fundamental Research Funds for the Central Universities
文摘Using the temperature profiles retrieved from the Mars Climate Sounder（MCS） instrument onboard Mars Reconnaissance Orbiter（MRO） satellite between November 2006 and April 2013, we studied the seasonal and interannual variability of QuasiStationary Planetary Waves（QSPWs） in the Martian middle atmosphere. The QSPW amplitudes in the Southern Hemisphere（SH） high latitudes are significantly stronger than those in the Northern Hemisphere（NH）. Seasonal variation with maximum amplitude near winter solstice of each hemisphere is clearly seen. The vertical structure of the QSPW in temperature shows double-layer feature with one peak near 50 Pa and the other peak near 1 Pa. The QSPW in geopotential height is clearly maximized in the region between two temperature peaks. The maximum amplitude of QSPW for s=1 is ~8–10 K in temperature and ~1 km in geopotential height in the SH high latitudes. The maximum amplitude at the SH high latitudes in Mars Year（MY） 31 is ~2 K stronger than those in other MYs, suggesting the clear interannual variability. We compared the satellite results with those obtained from the Mars Climate Database（MCD） simulation version 5.0; a reasonable agreement was found. The MCD simulation further suggested that the variability of dust might partially contribute to the interannual variability of QSPW amplitude.
