High concentrations of PM_(2.5) are universally considered as a main cause for haze formation. Therefore, it is important to identify the spatial heterogeneity and influencing factors of PM_(2.5) concentrations for re...High concentrations of PM_(2.5) are universally considered as a main cause for haze formation. Therefore, it is important to identify the spatial heterogeneity and influencing factors of PM_(2.5) concentrations for regional air quality control and management. In this study, PM_(2.5) data from 2000 to 2015 was determined from an inversion of NASA atmospheric remote sensing images. Using geo-statistics, geographic detectors, and geo-spatial analysis methods, the spatio-temporal evolution patterns and driving factors of PM_(2.5) concentration in China were evaluated. The main results are as follows.(1) In general, the average concentration of PM_(2.5) in China increased quickly and reached its peak value in 2006; subsequently, concentrations remained between 21.84 and 35.08 μg/m3.(2) PM_(2.5) is strikingly heterogeneous in China, with higher concentrations in the north and east than in the south and west. In particular, areas with relatively high PM_(2.5) concentrations are primarily in four regions, the Huang-Huai-Hai Plain, Lower Yangtze River Delta Plain, Sichuan Basin, and Taklimakan Desert. Among them, Beijing-Tianjin-Hebei Region has the highest concentration of PM_(2.5).(3) The center of gravity of PM_(2.5) has generally moved northeastward, which indicates an increasingly serious haze in eastern China. High-value PM_(2.5) concentrations have moved eastward, while low-value PM_(2.5) has moved westward.(4) Spatial autocorrelation analysis indicates a significantly positive spatial correlation. The "High-High" PM_(2.5) agglomeration areas are distributed in the Huang-Huai-Hai Plain, Fenhe-Weihe River Basin, Sichuan Basin, and Jianghan Plain regions. The "Low-Low" PM_(2.5) agglomeration areas include Inner Mongolia and Heilongjiang, north of the Great Wall, Qinghai-Tibet Plateau, and Taiwan, Hainan, and Fujian and other southeast coastal cities and islands.(5) Geographic detection analysis indicates that both natural and anthropogenic factors account for spatial variations in PM_(2.5) concentration. Geographica展开更多
Methane (CH4) and nitrous oxide (N2O) saturation concentration and gas-water interface emission flux in surface water of the Yangtze Delta plain river net were investigated in summer at representative sites including ...Methane (CH4) and nitrous oxide (N2O) saturation concentration and gas-water interface emission flux in surface water of the Yangtze Delta plain river net were investigated in summer at representative sites including the upper reaches of the Huangpu River and the rivers in the Chongming Island. The results show that the CH4 concentration in river water ranged from 0.30±0.03 to 6.66±0.14 μmol.L-1, and N2O concentration ranged from 13.8±2.33 to 435±116 nmol.L-1. River surface water had a very high satura- tion level of CH4 (from 468±49.0% to 11560±235%) and that of N2O (from 175±29.5% to 4914±1304%). Dissolved oxygen (DO) was the primary factor controlling the CH4 concentration in water. N2O concentration had significant negative correlation with salinity and a significant positive correlation with nitrate (NO3-), nitrite (NO2-), chemical oxygen demand (CODcr) concentration and pH of river water. CH4 and N2O of river water were brought about mainly by methanogenesis and denitrification in river bottom sediment that diffused through sediment-water interface into the water body and then into atmosphere through the gas-water interface. The emission flux of CH4 and N2O at river gas-water interface reached 778±59.8 and 236±63.6 μmol.m-2.h-1, respectively in summer. The river net was a potential source of atmospheric CH4 and N2O because of eutrophication of the water body.展开更多
The rice endosperm plays crucial roles in nourishing the embryo during embryogenesis and seed germination. Although previous studies have provided the general information about rice endosperm, a systematic investigati...The rice endosperm plays crucial roles in nourishing the embryo during embryogenesis and seed germination. Although previous studies have provided the general information about rice endosperm, a systematic investigation throughout the entire endosperm developmental process is still lacking. In this study, we examined in detail rice endosperm development on a daily basis throughout the 3o-day period of post-fertilization development. We observed that coenocytic nuclear division occurred in the first 2 days after pollination （DAP）, cellularization occurred between 3 and 5 DAP, differentiation of the aleurone and starchy endosperm occurred between 6 and 9 DAP, and accumulation of storage products occurred concurrently with the aleurone/starchy endosperm differentiation from 6 DAP onwards and was accomplished by 21 DAP. Changes in cytoplasmic membrane permeability, possibly caused by programmed cell death, were observed in the central region of the starchy endosperm at 8 DAP, and expanded to the whole starchy endosperm at 21 DAP when the aleurone is the only living component in the endosperm. Further, we observed that a distinct multi-layered dorsal aleurone formed near the dorsal vascular bundle, while the single- or occasionally two-cell layered aleurone was located in the lateral and ventral positions of endosperm. Our results provide in detail the dynamic changes in mitotic divisions, cellularization, cell differentiation, storage product accumulation, and programmed cell death that occur during rice endosperm development.展开更多
The environmental quality of heavy metals （Pb, Cd, Cr, As, Hg） in agricultural surface soil of Chongming Island was assessed by national, local and professional standards based on a large scale investigation, in whi...The environmental quality of heavy metals （Pb, Cd, Cr, As, Hg） in agricultural surface soil of Chongming Island was assessed by national, local and professional standards based on a large scale investigation, in which 28 samples from vegetable plots, 65 samples from paddy fields and 9 samples from watermelon fields were collected from whole island area. Results showed that the average concentration of Pb, Cd, Cr, As and Hg was 21.6 mg.kg^-l,0.176 mg.kg^-1, 69.4 mg.kg^-1, 9.209 mg.kg^-1 and 0.128 mg.kg^-1, respectively. Compared with the background value of Shanghai City soil, except for Pb and Cr, all the other heavy metals average concentrations in Chongming Island agricultural surface soil exceeded their corresponding natural-background values. The concentrations of Cd, As and Hg were 33.0%, 1.2% and 26.3% higher than the background value of Shanghai City, respectively. In addition, inverse distance interpolation （IDW） tool of GIS was also applied to study the spatial variation of heavy metals. The results indicated that most of agricultural soil quality was good, and the ratio of ecological, good soil, certified soil and disqualified soil were 1.26%, 97.1%, 1.47% and 0.12%, respectively. About 10.1%, 85.7%, 27.0%, 55.4% and 55.2% soil samples exceeded the Pb, Cd, Cr, As and Hg background value of Shanghai City, respectively. Among these three land use type soils, vegetable soil was most seriously polluted by heavy metals, which is probably related to the over-application of pesticides. The annual deposition fluxes of Pb, Cd, As and Hg were 7736μg·m^-2·a^-1, 208μg·m^-2·a^-1, 2238μg·m^-2·a^-1 and 52.8 μg·m^-2·a^-1 respectively. Crop straw burning was the important source of heavy metals of atmospheric deposition, and atmospheric deposition contributed a lot to heavy metals in agricultural soil in Chongming Island.展开更多
Three ice cores recovered from the Himalayas (i.e. the East Rongbuk Glacier and the Far East Rongbuk Glacier at Mt. Qomolangma (Everest), and the Dasuopu Glacier at Xixiabangma) show a sharp decline in the accumulatio...Three ice cores recovered from the Himalayas (i.e. the East Rongbuk Glacier and the Far East Rongbuk Glacier at Mt. Qomolangma (Everest), and the Dasuopu Glacier at Xixiabangma) show a sharp decline in the accumulation rates since the 1950s, which is consistent with the precipitation fluctuation over India and the low northern latitude zone (5°-35癗). Correspondingly, an increasing trend is observed for the ice core accumulations from the central and northern Qinghai-Tibetan Plateau (i.e. the Xiao Dongkemadi Glacier in the central Tanggula Mountains, the Guliya Ice Cap in the western Kunlun Mountains, and the Dunde Ice Cap in the Qilian Mountains) since the 1950s, which is consistent with the precipitation fluctuation over the middle-high northern latitude zone (35°-70°N). However, the variation magnitude of the high-elevation ice core accumulations is more significant than that of precipitation at the low-eleva- tion places, suggesting its extra sensitivity of high-elevation areas to climatic change.展开更多
Changes in metal concentrations in the litter of Potamogeton crispus were monitored during a consecutive 40-day in situ decomposition experiment using the litterbag method.The accumulation index was calculated and use...Changes in metal concentrations in the litter of Potamogeton crispus were monitored during a consecutive 40-day in situ decomposition experiment using the litterbag method.The accumulation index was calculated and used to indicate the changes in the metals in litter.The results showed that the concentrations of Al,Cd,Cr,Fe,Mn,and Pb in litter increased significantly during the decomposition,while Cu and Zn concentrations decreased dramatically.Significant positive correlations were found between the concentrations of Al,Cr,Fe,and Mn and between Cu and Zn.Moreover,Cu and Zn both negatively correlated with Al and Fe.The remaining dry mass was negatively correlated with Al and Fe concentrations but positively correlated with Cu and Zn concentrations.Generally the accumulation index values of metals other than Al were less than one,indicating that the litter of P.crispus acted as a source of metals to the surrounding water body.Al was the only metal that showed continuous net accumulation in litter.The net accumulation of Fe and Mn in litter during the last 10 days of the experiment may indicate the precipitation of Feand Mn-oxides.It was estimated that 160 g/m^2（dry weight）P.crispus was decomposed in40 days.This was equivalent to releasing the following amounts of metals：0.01 mg Cd,0.03 mg Cr,0.71 mg Cu,0.55 mg Mn,0.02 mg Pb and 13.8 mg Zn into surrounding water,and accumulating 149 mg Al and 11 mg Fe,in a 1 m^2 area.展开更多
A nationally representative sample of 1640 Chinese urban adolescents (mean age=14.5 years) and their parents and teachers were surveyed to examine the associations between relationships with teachers and parents and a...A nationally representative sample of 1640 Chinese urban adolescents (mean age=14.5 years) and their parents and teachers were surveyed to examine the associations between relationships with teachers and parents and adolescents' developmental outcomes such as academic performance, psychological well-being, altruistic behaviors, and misconduct. Results showed that the quality of adolescents' relationships with teachers was highly correlated with adolescent outcomes, in most cases more so than for relationships with parents. Furthermore, such associations were the same across both genders and three grade levels. These findings suggest that teachers may play an especially significant role in Chinese adolescent development. This study adds to the small but growing literature on the importance of teachers as well as other non-parental adults in adolescent psychosocial development.展开更多
Abstract Industrial robots are used for automatic drilling and riveting. The absolute position accuracy of an industrial robot is one of the key performance indexes in aircraft assembly, and can be improved through er...Abstract Industrial robots are used for automatic drilling and riveting. The absolute position accuracy of an industrial robot is one of the key performance indexes in aircraft assembly, and can be improved through error compensation to meet aircraft assembly requirements. The achiev- able accuracy and the difficulty of accuracy compensation implementation are closely related to the choice of sampling points. Therefore, based on the error similarity error compensation method, a method for choosing sampling points on a uniform grid is proposed. A simulation is conducted to analyze the influence of the sample point locations on error compensation. In addition, the grid steps of the sampling points are optimized using a statistical analysis method. The method is used to generate grids and optimize the grid steps of a Kuka KR-210 robot. The experimental results show that the method for planning sampling data can be used to effectively optimize the sampling grid. After error compensation, the position accuracy of the robot meels the position accuracy require- ments.展开更多
The future development of new-type urbanization has drawn great attention from both the government and public alike. In this context, the present study had three related research aims. Firstly, it sought to predict th...The future development of new-type urbanization has drawn great attention from both the government and public alike. In this context, the present study had three related research aims. Firstly, it sought to predict the urbanization and population dynamics in China at both national and provincial levels for the period of 2015 to 2030. Secondly, on this basis, it sought to examine the spatial variation of urbanization given the predicted national urbaniza- tion rate of 70.12%. Thirdly, it sought to estimate and evaluate the national and provincial demands of investment in the development of new-type urbanization. The main conclusions from this study were as follows： （1） The population size and urbanization rate will reach 1.445 billion and 70.12%, respectively, from 2015 to 2030. （2） The demographic dividend will vanish when the population pressure reaches its maximum. During this period, there will be 70.16 million urban population born. The suburban population that becomes urbanized will be 316.7 million, and thus the net increase in urban population will reach 386 million. （3） Although the urbanization rate of every Chinese province will increase during 2015-2030, it will do so un- equally, while differences in urbanization quality among provinces will also be substantial. In some provinces, moreover, the urbanization quality is not compatible with their eco-social development. （4）A total of 4,105,380 billion yuan is required to fund new-type urbanization and the investment demand for each province varies greatly; for example, Guangdong prov- ince requires the most funding, amounting to approximately 148 times that required by Tibet, the province in least need of funding. In the final part of this study, policy suggestions con- cerning the investment of the new-type urbanization are put forward and discussed.展开更多
The morphology and electronic structure of a Li4Ti5012 anode are known to determine its electrical and electrochemical properties in lithium rechargeable batteries. Ag-Li4Ti5012 nanofibers have been rationally designe...The morphology and electronic structure of a Li4Ti5012 anode are known to determine its electrical and electrochemical properties in lithium rechargeable batteries. Ag-Li4Ti5012 nanofibers have been rationally designed and synthesized by an electrospinning technique to meet the requirements of one-dimensional （1D） morphology and superior electrical conductivity. Herein, we have found that the 1D Ag-Li4Ti5012 nanofibers show enhanced specific capacity, rate capability, and cycling stability compared to bare Li4Ti5012 nanofibers, due to the Ag nanoparticles （〈5 nm）, which are mainly distributed at interfaces between Li4Ti5O12 primary particles. This structural morphology gives rise to 20% higher rate capability than bare Li4Ti5O12 nanofibers by facilitating the charge transfer kinetics. Our findings provide an effective way to improve the electrochemical performance of Li4Ti5O12 anodes for lithium rechargeable batteries.展开更多
Achieving good recognition results for License plates is challenging due to multiple adverse factors. For instance, in Malaysia, where private vehicle （e.g., cars） have numbers with dark background, while public veh...Achieving good recognition results for License plates is challenging due to multiple adverse factors. For instance, in Malaysia, where private vehicle （e.g., cars） have numbers with dark background, while public vehicle （taxis/cabs） have numbers with white background. To reduce the complexity of the problem, we propose to classify the above two types of images such that one can choose an appropriate method to achieve better results. Therefore, in this work, we explore the combination of Convolutional Neural Networks （CNN） and Recurrent Neural Networks namely, BLSTM （Bi-Directional Long Short Term Memory）, for recognition. The CNN has been used for feature extraction as it has high discriminative ability, at the same time, BLSTM has the ability to extract context information based on the past information. For classification, we propose Dense Cluster based Voting （DCV）, which separates foreground and background for successful classification of private and public. Experimental results on live data given by MIMOS, which is funded by Malaysian Government and the standard dataset UCSD show that the proposed classification outperforms the existing methods. In addition, the recognition results show that the recognition performance improves significantly after classification compared to before classification.展开更多
Seasonal variation in surface ozone and the relationship between the background ozone concentration and wind were evaluated at Zhongshan Station,Antarctica using 2008 data.The wind frequency from the station area was ...Seasonal variation in surface ozone and the relationship between the background ozone concentration and wind were evaluated at Zhongshan Station,Antarctica using 2008 data.The wind frequency from the station area was only 2%,while the prevailing wind frequency was much larger (79.2%).This indicates that the surface ozone observations were not affected by the human activities at the station,and therefore could be counted as background concentrations of surface ozone along Antarctic coast.The concentration of surface ozone shows a distinct annual variation with the yearly mean of 25.0 nmol mol-1 and the maximum in winter,the minimum in summer.The surface ozone concentration had a strong negative correlation with ultraviolet radiation,and the mean values during polar night were one to two times higher than those in summer.These results imply that photochemical destruction of ozone dominates over Antarctica.The ozone depletion events at Zhongshan Station were obviously related to lower temperatures and higher BrO concentrations.Backward trajectory analysis reveals that the ozone depletion events are predominately caused by the high BrO concentrations.展开更多
Carbon nanofibers with hollow structures have an excellent application prospect in various fields be-cause of their high specific surface area and abundant active sites.PAN-based hollow carbon nanofiber doped with Co/...Carbon nanofibers with hollow structures have an excellent application prospect in various fields be-cause of their high specific surface area and abundant active sites.PAN-based hollow carbon nanofiber doped with Co/CoO(H-Co/CoO-CNF)was successfully prepared and used as a catalyst to activate perox-ymonosulfate(PMS)and degrade Rhodamine B(RhB).The catalyst showed a surprising degradation rate(98.89%)of RhB within 15 min and had good degradation performance in a wide pH range(pH 1.5-11.2).Compared with solid fibers,H-Co/CoO-CNF shows better cyclic characteristics.The catalyst is also mag-netic and recoverable easily due to the addition of Co/CoO.Two pathways of both radical(SO_(4)·^(−))and non-radical(^(1)O_(2))exist during the RhB degradation process are confirmed through electron paramagnetic resonance(EPR)analysis and radical quenching experiments.This work provides a new idea for hollow fibers loaded with metals and their oxides and can guide the development of catalysts for advanced oxi-dation processes in the future.展开更多
Rice caryopsis as one of the most important food sources for humans has a complex structure that is composed of maternal tissues including the pericarp and testa and filial tissues including the endosperm and embryo. ...Rice caryopsis as one of the most important food sources for humans has a complex structure that is composed of maternal tissues including the pericarp and testa and filial tissues including the endosperm and embryo. Although rice caryopsis studies have been conducted previously, a system- atic characterization throughout the entire developmental process is still lacking. In this study, detailed morphological examinations of caryopses were made during the entire 30- day developmental process. We observed some rapid changes in cell differentiation events and cataloged how cellular degeneration processes occurred in maternal tissues. The differentiations of tube cells and cross cells were achieved by 9 days after pollination （DAP）. In the testa, the outer integument was degenerated by 3 DAP, while the outer layer of the inner integument degenerated by 7 DAP. In the nucellus, all tissues with the exception of the nucellar projection and the nucellar epidermis degenerated in the first 5 DAP. By 21 DAP, all maternal tissues, including vascular bundles, the nucellar projection and the nucellar epidermal cells were degenerated. In summary, this study provides a complete atlas of the dynamic changes in cell differentiation and degeneration for individual maternal cell layers of rice caryopsis.展开更多
BACKGROUND:Early identifi cation of patients requiring ventilator support will be benefi cial for the outcomes of botulism.The present study aimed to establish a new scoring system to predict mechanical ventilation(MV...BACKGROUND:Early identifi cation of patients requiring ventilator support will be benefi cial for the outcomes of botulism.The present study aimed to establish a new scoring system to predict mechanical ventilation(MV)for botulism patients.METHODS:A single-center retrospective study was conducted to identify risk factors associated with MV in botulism patients from 2007 to 2022.Univariate analysis and multivariate logistic regression analysis were used to screen out risk factors for constructing a prognostic scoring system.The area under the receiver operating characteristic(ROC)curve was calculated.RESULTS:A total of 153 patients with botulism(66 males and 87 females,with an average age of 43 years)were included.Of these,49 patients(32.0%)required MV,including 21(13.7%)with invasive ventilation and 28(18.3%)with non-invasive ventilation.Multivariate analysis revealed that botulinum toxin type,pneumonia,incubation period,degree of hypoxia,and severity of muscle involvement were independent risk factors for MV.These risk factors were incorporated into a multivariate logistic regression analysis to establish a prognostic scoring system.Each risk factor was scored by allocating a weight based on its regression coeffi cient and rounded to whole numbers for practical utilization([botulinum toxin type A:1],[pneumonia:2],[incubation period≤1 day:2],[hypoxia<90%:2],[severity of muscle involvement:grade II,3;grade III,7;grade IV,11]).The scoring system achieved an area under the ROC curve of 0.82(95%CI 0.75-0.89,P<0.001).At the optimal threshold of 9,the scoring system achieved a sensitivity of 83.7%and a specifi city of 70.2%.CONCLUSION:Our study identified botulinum toxin type,pneumonia,incubation period,degree of hypoxia,and severity of muscle involvement as independent risk factors for MV in botulism patients.A score≥9 in our scoring system is associated with a higher likelihood of requiring MV in botulism patients.This scoring system needs to be validated externally before it can be applied in clinical settings.展开更多
The sulfated CeO_(2)/Al_(2)O_(3) catalysts with different sizes of CeO_(2)nanoparticles were prepared by using pure H_2O or acetic acid solution as impregnation solvent, and the influence of sizes of CeO_(2) nanoparti...The sulfated CeO_(2)/Al_(2)O_(3) catalysts with different sizes of CeO_(2)nanoparticles were prepared by using pure H_2O or acetic acid solution as impregnation solvent, and the influence of sizes of CeO_(2) nanoparticles on the catalytic performances of the sulfated CeO_(2)/Al_(2)O_(3) catalyst was studied. The catalytic performance tests show that the sulfated CeO_(2)/Al_(2)O_(3) catalyst using acetic acid solution as impregnation solvent has better catalytic activity and the resistance to K+poisoning than the sulfated CeO_(2)/Al_(2)O_(3) catalyst using pure H_(2)O as impregnation solvent. The excellent catalytic performances can be ascribed to the smaller sizes of CeO_(2) nanoparticles in CeO_(2)/Al_(2)O_(3) catalyst using acetic acid solution, which results in larger amount of adsorbed sulfate species, surface acid sites, surface active oxygen species and excellent redox property. These features are helpful for improving the catalytic performances of sulfated CeO_(2)/Al_(2)O_(3) catalyst using smaller amount of CeO_(2) to cut the costs.展开更多
What is already known about this topic?Fatal poisonings caused by wild mushrooms containing amanita toxins pose a significant threat in the southern regions of China.These toxins primarily induce gastrointestinal symp...What is already known about this topic?Fatal poisonings caused by wild mushrooms containing amanita toxins pose a significant threat in the southern regions of China.These toxins primarily induce gastrointestinal symptoms initially,which are then followed by potentially life-threatening acute liver damage.What is added by this report?This report contributes to the existing knowledge on these cases of poisoning by documenting the second occurrences in Hebei Province and the first occurrences in Xingtai City.Five individuals reported consuming wild mushrooms from the same origin,and laboratory tests confirmed the presence ofα-amanitin in their blood samples.What are the implications for public health practice?This underscores the risk associated with the collection and consumption of amanita toxin-containing mushrooms in Hebei.It is important to note that the identification of toxic and non-toxic mushrooms should not solely rely on personal experience or appearance.展开更多
The vertical structure of the atmospheric ozone and temperature as well as the seasonal variations is presented by using ozone sounding data at Zhongshan Station over East Antarctica from February, 2008 to February, 2...The vertical structure of the atmospheric ozone and temperature as well as the seasonal variations is presented by using ozone sounding data at Zhongshan Station over East Antarctica from February, 2008 to February, 2009. The results show that the heights of thermal tropopause and ozone tropopause are mostly the same with yearly mean 7.9 and 7.4 km separately above the station. There is obvious seasonal variation in the pressure and temperature of the tropopause, manifested by the clear one-wave pattern with an opposite phase. As the turning point of the tropopause temperature is visible in autumn and faint in spring and winter, the tropopause height can be better confirmed by utilization of the changes of ozone. Seasonal variation of the tropospheric ozone of vertical distribution is not clear, relative to stratosphere. In the spring, ozone in the low level of stratosphere lost seriously. The minimum partial ozone in 14 km was 1.57 MPa only and the maximum partial ozone occurred in the up level stratosphere. In the rest of the season the ozone increases with height rising in the low level of stratosphere. The evidence shows that ozone lost in spring is closely related with low temperature of polar night and the process of PSC photochemical destruction ozone in the stratosphere. From the vertical characteristics and seasonal variation of ozone and temperature, it is meaningful to understand formation and development of Antarctic ozone deletion.展开更多
For the first time,this work comprehensively studied the effectiveness of precipitation hardening achieved by aging treatment in improving the tensile superelasticity of NiTi alloys fabricated by elec-tron beam wire-f...For the first time,this work comprehensively studied the effectiveness of precipitation hardening achieved by aging treatment in improving the tensile superelasticity of NiTi alloys fabricated by elec-tron beam wire-feed additive manufacturing(EBAM),which possesses inherent advantages in producing dense and oxidation-free structures.Aging treatments under three temperatures(450,350,and 250℃)and different durations were conducted,and the resultant performance of tensile superelasticity,together with the corresponding evolution of precipitation and phase transformation behavior were investigated for the EBAM-fabricated NiTi alloys.Results showed that by appropriate aging treatment,EBAM fabricated NiTi alloys could achieve excellent recovery rates of approximately 95%and 90%after the 1st and 10th load/unload cycle for a maximum tensile strain of 6%,which were almost the highest achieved so far by AM processed NiTi alloys and close to those of some conventional NiTi alloys.The improvement of tensile superelasticity benefited from the fine and dispersive Ni4Ti3 precipitates,which could be introduced by aging at 350℃ for 4 h or at 250℃ for 200 h.Moreover,the large amount of Ni4Ti3 precipitates would promote the intermediate R-phase transformation and bring a two-stage or three-stage transformation sequence,which depended on whether the distribution of the precipitation was homogeneous or not.This work could provide guidance for the production of NiTi alloys with good tensile superelasticity by EBAM or other additive manufacturing processes.展开更多
基金The Strategic Priority Research Program of the Chinese Academy of Sciences,No.XDA19040401China Postdoctoral Science Foundation,No.2016M600121+1 种基金National Natural Science Foundation of China,No.41701173,No.41501137The State Key Laboratory of Resources and Environmental Information System
文摘High concentrations of PM_(2.5) are universally considered as a main cause for haze formation. Therefore, it is important to identify the spatial heterogeneity and influencing factors of PM_(2.5) concentrations for regional air quality control and management. In this study, PM_(2.5) data from 2000 to 2015 was determined from an inversion of NASA atmospheric remote sensing images. Using geo-statistics, geographic detectors, and geo-spatial analysis methods, the spatio-temporal evolution patterns and driving factors of PM_(2.5) concentration in China were evaluated. The main results are as follows.(1) In general, the average concentration of PM_(2.5) in China increased quickly and reached its peak value in 2006; subsequently, concentrations remained between 21.84 and 35.08 μg/m3.(2) PM_(2.5) is strikingly heterogeneous in China, with higher concentrations in the north and east than in the south and west. In particular, areas with relatively high PM_(2.5) concentrations are primarily in four regions, the Huang-Huai-Hai Plain, Lower Yangtze River Delta Plain, Sichuan Basin, and Taklimakan Desert. Among them, Beijing-Tianjin-Hebei Region has the highest concentration of PM_(2.5).(3) The center of gravity of PM_(2.5) has generally moved northeastward, which indicates an increasingly serious haze in eastern China. High-value PM_(2.5) concentrations have moved eastward, while low-value PM_(2.5) has moved westward.(4) Spatial autocorrelation analysis indicates a significantly positive spatial correlation. The "High-High" PM_(2.5) agglomeration areas are distributed in the Huang-Huai-Hai Plain, Fenhe-Weihe River Basin, Sichuan Basin, and Jianghan Plain regions. The "Low-Low" PM_(2.5) agglomeration areas include Inner Mongolia and Heilongjiang, north of the Great Wall, Qinghai-Tibet Plateau, and Taiwan, Hainan, and Fujian and other southeast coastal cities and islands.(5) Geographic detection analysis indicates that both natural and anthropogenic factors account for spatial variations in PM_(2.5) concentration. Geographica
基金Supported by the National Natural Science Foundation of China (Grant No. 40730526)the Science & Technology Department of Shanghai (Grant No. 07DZ12037)+1 种基金the National Great Water Issue Project of China (Grant No. 2008ZX07317-006)China Postdoctoral Science Foundation (Grant No. 20060400635)
文摘Methane (CH4) and nitrous oxide (N2O) saturation concentration and gas-water interface emission flux in surface water of the Yangtze Delta plain river net were investigated in summer at representative sites including the upper reaches of the Huangpu River and the rivers in the Chongming Island. The results show that the CH4 concentration in river water ranged from 0.30±0.03 to 6.66±0.14 μmol.L-1, and N2O concentration ranged from 13.8±2.33 to 435±116 nmol.L-1. River surface water had a very high satura- tion level of CH4 (from 468±49.0% to 11560±235%) and that of N2O (from 175±29.5% to 4914±1304%). Dissolved oxygen (DO) was the primary factor controlling the CH4 concentration in water. N2O concentration had significant negative correlation with salinity and a significant positive correlation with nitrate (NO3-), nitrite (NO2-), chemical oxygen demand (CODcr) concentration and pH of river water. CH4 and N2O of river water were brought about mainly by methanogenesis and denitrification in river bottom sediment that diffused through sediment-water interface into the water body and then into atmosphere through the gas-water interface. The emission flux of CH4 and N2O at river gas-water interface reached 778±59.8 and 236±63.6 μmol.m-2.h-1, respectively in summer. The river net was a potential source of atmospheric CH4 and N2O because of eutrophication of the water body.
基金funded by the National Basic Research Program of China (2016ZX08009)the National High-Tech R&D Program of China (2012AA02A707)
文摘The rice endosperm plays crucial roles in nourishing the embryo during embryogenesis and seed germination. Although previous studies have provided the general information about rice endosperm, a systematic investigation throughout the entire endosperm developmental process is still lacking. In this study, we examined in detail rice endosperm development on a daily basis throughout the 3o-day period of post-fertilization development. We observed that coenocytic nuclear division occurred in the first 2 days after pollination （DAP）, cellularization occurred between 3 and 5 DAP, differentiation of the aleurone and starchy endosperm occurred between 6 and 9 DAP, and accumulation of storage products occurred concurrently with the aleurone/starchy endosperm differentiation from 6 DAP onwards and was accomplished by 21 DAP. Changes in cytoplasmic membrane permeability, possibly caused by programmed cell death, were observed in the central region of the starchy endosperm at 8 DAP, and expanded to the whole starchy endosperm at 21 DAP when the aleurone is the only living component in the endosperm. Further, we observed that a distinct multi-layered dorsal aleurone formed near the dorsal vascular bundle, while the single- or occasionally two-cell layered aleurone was located in the lateral and ventral positions of endosperm. Our results provide in detail the dynamic changes in mitotic divisions, cellularization, cell differentiation, storage product accumulation, and programmed cell death that occur during rice endosperm development.
基金National Natural Science Foundation of China, No.40701164, No.40730526 Public Project of Ministry of Environmental Protection of China, No.WFLY-2009-1-SK-06-03 National Key Water Program during the 1 lth Five-Year Plan Period, No.2009ZX07317-006
文摘The environmental quality of heavy metals （Pb, Cd, Cr, As, Hg） in agricultural surface soil of Chongming Island was assessed by national, local and professional standards based on a large scale investigation, in which 28 samples from vegetable plots, 65 samples from paddy fields and 9 samples from watermelon fields were collected from whole island area. Results showed that the average concentration of Pb, Cd, Cr, As and Hg was 21.6 mg.kg^-l,0.176 mg.kg^-1, 69.4 mg.kg^-1, 9.209 mg.kg^-1 and 0.128 mg.kg^-1, respectively. Compared with the background value of Shanghai City soil, except for Pb and Cr, all the other heavy metals average concentrations in Chongming Island agricultural surface soil exceeded their corresponding natural-background values. The concentrations of Cd, As and Hg were 33.0%, 1.2% and 26.3% higher than the background value of Shanghai City, respectively. In addition, inverse distance interpolation （IDW） tool of GIS was also applied to study the spatial variation of heavy metals. The results indicated that most of agricultural soil quality was good, and the ratio of ecological, good soil, certified soil and disqualified soil were 1.26%, 97.1%, 1.47% and 0.12%, respectively. About 10.1%, 85.7%, 27.0%, 55.4% and 55.2% soil samples exceeded the Pb, Cd, Cr, As and Hg background value of Shanghai City, respectively. Among these three land use type soils, vegetable soil was most seriously polluted by heavy metals, which is probably related to the over-application of pesticides. The annual deposition fluxes of Pb, Cd, As and Hg were 7736μg·m^-2·a^-1, 208μg·m^-2·a^-1, 2238μg·m^-2·a^-1 and 52.8 μg·m^-2·a^-1 respectively. Crop straw burning was the important source of heavy metals of atmospheric deposition, and atmospheric deposition contributed a lot to heavy metals in agricultural soil in Chongming Island.
基金This work was supported by the KnowledgeInnovation Projects of the Chinese Academy of Sciences (CAS) (Grant Nos. KZCX1-1-10-02 and KZCX2-108 and 301)the Cold and Arid Regions Environmental and Engineering Research Institute of the CAS (Grant No. CACX
文摘Three ice cores recovered from the Himalayas (i.e. the East Rongbuk Glacier and the Far East Rongbuk Glacier at Mt. Qomolangma (Everest), and the Dasuopu Glacier at Xixiabangma) show a sharp decline in the accumulation rates since the 1950s, which is consistent with the precipitation fluctuation over India and the low northern latitude zone (5°-35癗). Correspondingly, an increasing trend is observed for the ice core accumulations from the central and northern Qinghai-Tibetan Plateau (i.e. the Xiao Dongkemadi Glacier in the central Tanggula Mountains, the Guliya Ice Cap in the western Kunlun Mountains, and the Dunde Ice Cap in the Qilian Mountains) since the 1950s, which is consistent with the precipitation fluctuation over the middle-high northern latitude zone (35°-70°N). However, the variation magnitude of the high-elevation ice core accumulations is more significant than that of precipitation at the low-eleva- tion places, suggesting its extra sensitivity of high-elevation areas to climatic change.
基金supported by the National Natural Science Foundation of China(Nos.41401563,41301544,41201094)the Natural Science Foundation of Shandong Province(Nos.ZR2014JL028+2 种基金ZR2012DQ003)the China Postdoctoral Science Foundation(No.2015M571830)the Taishan Scholar Program of Shandong Province for supporting his research
文摘Changes in metal concentrations in the litter of Potamogeton crispus were monitored during a consecutive 40-day in situ decomposition experiment using the litterbag method.The accumulation index was calculated and used to indicate the changes in the metals in litter.The results showed that the concentrations of Al,Cd,Cr,Fe,Mn,and Pb in litter increased significantly during the decomposition,while Cu and Zn concentrations decreased dramatically.Significant positive correlations were found between the concentrations of Al,Cr,Fe,and Mn and between Cu and Zn.Moreover,Cu and Zn both negatively correlated with Al and Fe.The remaining dry mass was negatively correlated with Al and Fe concentrations but positively correlated with Cu and Zn concentrations.Generally the accumulation index values of metals other than Al were less than one,indicating that the litter of P.crispus acted as a source of metals to the surrounding water body.Al was the only metal that showed continuous net accumulation in litter.The net accumulation of Fe and Mn in litter during the last 10 days of the experiment may indicate the precipitation of Feand Mn-oxides.It was estimated that 160 g/m^2（dry weight）P.crispus was decomposed in40 days.This was equivalent to releasing the following amounts of metals：0.01 mg Cd,0.03 mg Cr,0.71 mg Cu,0.55 mg Mn,0.02 mg Pb and 13.8 mg Zn into surrounding water,and accumulating 149 mg Al and 11 mg Fe,in a 1 m^2 area.
文摘A nationally representative sample of 1640 Chinese urban adolescents (mean age=14.5 years) and their parents and teachers were surveyed to examine the associations between relationships with teachers and parents and adolescents' developmental outcomes such as academic performance, psychological well-being, altruistic behaviors, and misconduct. Results showed that the quality of adolescents' relationships with teachers was highly correlated with adolescent outcomes, in most cases more so than for relationships with parents. Furthermore, such associations were the same across both genders and three grade levels. These findings suggest that teachers may play an especially significant role in Chinese adolescent development. This study adds to the small but growing literature on the importance of teachers as well as other non-parental adults in adolescent psychosocial development.
基金co-supported by the National Natural Science Foundation of China(No.51475225)the Aeronautical Science Foundation of China(No.2013ZE52067)
文摘Abstract Industrial robots are used for automatic drilling and riveting. The absolute position accuracy of an industrial robot is one of the key performance indexes in aircraft assembly, and can be improved through error compensation to meet aircraft assembly requirements. The achiev- able accuracy and the difficulty of accuracy compensation implementation are closely related to the choice of sampling points. Therefore, based on the error similarity error compensation method, a method for choosing sampling points on a uniform grid is proposed. A simulation is conducted to analyze the influence of the sample point locations on error compensation. In addition, the grid steps of the sampling points are optimized using a statistical analysis method. The method is used to generate grids and optimize the grid steps of a Kuka KR-210 robot. The experimental results show that the method for planning sampling data can be used to effectively optimize the sampling grid. After error compensation, the position accuracy of the robot meels the position accuracy require- ments.
基金National Natural Science Foundation of China, No.41501137, No.41530634, No.41271186
文摘The future development of new-type urbanization has drawn great attention from both the government and public alike. In this context, the present study had three related research aims. Firstly, it sought to predict the urbanization and population dynamics in China at both national and provincial levels for the period of 2015 to 2030. Secondly, on this basis, it sought to examine the spatial variation of urbanization given the predicted national urbaniza- tion rate of 70.12%. Thirdly, it sought to estimate and evaluate the national and provincial demands of investment in the development of new-type urbanization. The main conclusions from this study were as follows： （1） The population size and urbanization rate will reach 1.445 billion and 70.12%, respectively, from 2015 to 2030. （2） The demographic dividend will vanish when the population pressure reaches its maximum. During this period, there will be 70.16 million urban population born. The suburban population that becomes urbanized will be 316.7 million, and thus the net increase in urban population will reach 386 million. （3） Although the urbanization rate of every Chinese province will increase during 2015-2030, it will do so un- equally, while differences in urbanization quality among provinces will also be substantial. In some provinces, moreover, the urbanization quality is not compatible with their eco-social development. （4）A total of 4,105,380 billion yuan is required to fund new-type urbanization and the investment demand for each province varies greatly; for example, Guangdong prov- ince requires the most funding, amounting to approximately 148 times that required by Tibet, the province in least need of funding. In the final part of this study, policy suggestions con- cerning the investment of the new-type urbanization are put forward and discussed.
文摘The morphology and electronic structure of a Li4Ti5012 anode are known to determine its electrical and electrochemical properties in lithium rechargeable batteries. Ag-Li4Ti5012 nanofibers have been rationally designed and synthesized by an electrospinning technique to meet the requirements of one-dimensional （1D） morphology and superior electrical conductivity. Herein, we have found that the 1D Ag-Li4Ti5012 nanofibers show enhanced specific capacity, rate capability, and cycling stability compared to bare Li4Ti5012 nanofibers, due to the Ag nanoparticles （〈5 nm）, which are mainly distributed at interfaces between Li4Ti5O12 primary particles. This structural morphology gives rise to 20% higher rate capability than bare Li4Ti5O12 nanofibers by facilitating the charge transfer kinetics. Our findings provide an effective way to improve the electrochemical performance of Li4Ti5O12 anodes for lithium rechargeable batteries.
基金This research work was supported by the Faculty of Computer Science and Information Technology, the University of Malaya under a special allocation of Post Graduate Funding for the RP036B-15AET project. The work described in this paper was supported by the Natural Science Foundation of China under grant no. 61672273, and the Science Foundation for Distinguished Young Scholars of Jiangsu under grant no. BK20160021.
文摘Achieving good recognition results for License plates is challenging due to multiple adverse factors. For instance, in Malaysia, where private vehicle （e.g., cars） have numbers with dark background, while public vehicle （taxis/cabs） have numbers with white background. To reduce the complexity of the problem, we propose to classify the above two types of images such that one can choose an appropriate method to achieve better results. Therefore, in this work, we explore the combination of Convolutional Neural Networks （CNN） and Recurrent Neural Networks namely, BLSTM （Bi-Directional Long Short Term Memory）, for recognition. The CNN has been used for feature extraction as it has high discriminative ability, at the same time, BLSTM has the ability to extract context information based on the past information. For classification, we propose Dense Cluster based Voting （DCV）, which separates foreground and background for successful classification of private and public. Experimental results on live data given by MIMOS, which is funded by Malaysian Government and the standard dataset UCSD show that the proposed classification outperforms the existing methods. In addition, the recognition results show that the recognition performance improves significantly after classification compared to before classification.
基金supported by the National Natural Science Foundation of China(41076132)the MOST Program of China(2006BAB18B05)
文摘Seasonal variation in surface ozone and the relationship between the background ozone concentration and wind were evaluated at Zhongshan Station,Antarctica using 2008 data.The wind frequency from the station area was only 2%,while the prevailing wind frequency was much larger (79.2%).This indicates that the surface ozone observations were not affected by the human activities at the station,and therefore could be counted as background concentrations of surface ozone along Antarctic coast.The concentration of surface ozone shows a distinct annual variation with the yearly mean of 25.0 nmol mol-1 and the maximum in winter,the minimum in summer.The surface ozone concentration had a strong negative correlation with ultraviolet radiation,and the mean values during polar night were one to two times higher than those in summer.These results imply that photochemical destruction of ozone dominates over Antarctica.The ozone depletion events at Zhongshan Station were obviously related to lower temperatures and higher BrO concentrations.Backward trajectory analysis reveals that the ozone depletion events are predominately caused by the high BrO concentrations.
基金financially supported by the National Natural Science Foundation of China(No.52072193)the Shandong Provin-cial Natural Science Foundation(Nos.ZR2021JQ16,ZR2019YQ19 and ZR2019BEM018)+2 种基金the Project of Shandong Province Higher Ed-ucational Science and Technology Program(No.2019KJA026)the Shandong Provincial College Students’Innovative Entrepreneurial Training(Nos.S202111065214 andS202211065062)State Key Laboratory for Modification of Chemical Fibers and Polymer Mate-rials(No.KF2217).
文摘Carbon nanofibers with hollow structures have an excellent application prospect in various fields be-cause of their high specific surface area and abundant active sites.PAN-based hollow carbon nanofiber doped with Co/CoO(H-Co/CoO-CNF)was successfully prepared and used as a catalyst to activate perox-ymonosulfate(PMS)and degrade Rhodamine B(RhB).The catalyst showed a surprising degradation rate(98.89%)of RhB within 15 min and had good degradation performance in a wide pH range(pH 1.5-11.2).Compared with solid fibers,H-Co/CoO-CNF shows better cyclic characteristics.The catalyst is also mag-netic and recoverable easily due to the addition of Co/CoO.Two pathways of both radical(SO_(4)·^(−))and non-radical(^(1)O_(2))exist during the RhB degradation process are confirmed through electron paramagnetic resonance(EPR)analysis and radical quenching experiments.This work provides a new idea for hollow fibers loaded with metals and their oxides and can guide the development of catalysts for advanced oxi-dation processes in the future.
基金funded by the 863 National High-Tech R&D Program of China (2012AA02A707)the National Transgenic Science and Technology Program (2014ZX08009003-005)
文摘Rice caryopsis as one of the most important food sources for humans has a complex structure that is composed of maternal tissues including the pericarp and testa and filial tissues including the endosperm and embryo. Although rice caryopsis studies have been conducted previously, a system- atic characterization throughout the entire developmental process is still lacking. In this study, detailed morphological examinations of caryopses were made during the entire 30- day developmental process. We observed some rapid changes in cell differentiation events and cataloged how cellular degeneration processes occurred in maternal tissues. The differentiations of tube cells and cross cells were achieved by 9 days after pollination （DAP）. In the testa, the outer integument was degenerated by 3 DAP, while the outer layer of the inner integument degenerated by 7 DAP. In the nucellus, all tissues with the exception of the nucellar projection and the nucellar epidermis degenerated in the first 5 DAP. By 21 DAP, all maternal tissues, including vascular bundles, the nucellar projection and the nucellar epidermal cells were degenerated. In summary, this study provides a complete atlas of the dynamic changes in cell differentiation and degeneration for individual maternal cell layers of rice caryopsis.
基金funded by the Medical Science Research Project of Hebei Provincial Health and Health Commission(20221073).
文摘BACKGROUND:Early identifi cation of patients requiring ventilator support will be benefi cial for the outcomes of botulism.The present study aimed to establish a new scoring system to predict mechanical ventilation(MV)for botulism patients.METHODS:A single-center retrospective study was conducted to identify risk factors associated with MV in botulism patients from 2007 to 2022.Univariate analysis and multivariate logistic regression analysis were used to screen out risk factors for constructing a prognostic scoring system.The area under the receiver operating characteristic(ROC)curve was calculated.RESULTS:A total of 153 patients with botulism(66 males and 87 females,with an average age of 43 years)were included.Of these,49 patients(32.0%)required MV,including 21(13.7%)with invasive ventilation and 28(18.3%)with non-invasive ventilation.Multivariate analysis revealed that botulinum toxin type,pneumonia,incubation period,degree of hypoxia,and severity of muscle involvement were independent risk factors for MV.These risk factors were incorporated into a multivariate logistic regression analysis to establish a prognostic scoring system.Each risk factor was scored by allocating a weight based on its regression coeffi cient and rounded to whole numbers for practical utilization([botulinum toxin type A:1],[pneumonia:2],[incubation period≤1 day:2],[hypoxia<90%:2],[severity of muscle involvement:grade II,3;grade III,7;grade IV,11]).The scoring system achieved an area under the ROC curve of 0.82(95%CI 0.75-0.89,P<0.001).At the optimal threshold of 9,the scoring system achieved a sensitivity of 83.7%and a specifi city of 70.2%.CONCLUSION:Our study identified botulinum toxin type,pneumonia,incubation period,degree of hypoxia,and severity of muscle involvement as independent risk factors for MV in botulism patients.A score≥9 in our scoring system is associated with a higher likelihood of requiring MV in botulism patients.This scoring system needs to be validated externally before it can be applied in clinical settings.
基金Project supported by the National Natural Science Foundation of China(21607019)the Scientific and Technological Research Program of Chongqing Municipal Education Commission(KJQN202101242,KJQN202001227)the Open Project Program of Key Laboratory of Water Environment Evolution and Pollution Control in the Three Gorges Reservoir(WEPKL2019ZD-04)。
文摘The sulfated CeO_(2)/Al_(2)O_(3) catalysts with different sizes of CeO_(2)nanoparticles were prepared by using pure H_2O or acetic acid solution as impregnation solvent, and the influence of sizes of CeO_(2) nanoparticles on the catalytic performances of the sulfated CeO_(2)/Al_(2)O_(3) catalyst was studied. The catalytic performance tests show that the sulfated CeO_(2)/Al_(2)O_(3) catalyst using acetic acid solution as impregnation solvent has better catalytic activity and the resistance to K+poisoning than the sulfated CeO_(2)/Al_(2)O_(3) catalyst using pure H_(2)O as impregnation solvent. The excellent catalytic performances can be ascribed to the smaller sizes of CeO_(2) nanoparticles in CeO_(2)/Al_(2)O_(3) catalyst using acetic acid solution, which results in larger amount of adsorbed sulfate species, surface acid sites, surface active oxygen species and excellent redox property. These features are helpful for improving the catalytic performances of sulfated CeO_(2)/Al_(2)O_(3) catalyst using smaller amount of CeO_(2) to cut the costs.
文摘What is already known about this topic?Fatal poisonings caused by wild mushrooms containing amanita toxins pose a significant threat in the southern regions of China.These toxins primarily induce gastrointestinal symptoms initially,which are then followed by potentially life-threatening acute liver damage.What is added by this report?This report contributes to the existing knowledge on these cases of poisoning by documenting the second occurrences in Hebei Province and the first occurrences in Xingtai City.Five individuals reported consuming wild mushrooms from the same origin,and laboratory tests confirmed the presence ofα-amanitin in their blood samples.What are the implications for public health practice?This underscores the risk associated with the collection and consumption of amanita toxin-containing mushrooms in Hebei.It is important to note that the identification of toxic and non-toxic mushrooms should not solely rely on personal experience or appearance.
基金supported by National Natural Science Foundation of China (Grant No. 41076132)the Program of China Polar Environment Investigation and Assessment (2011–2015)
文摘The vertical structure of the atmospheric ozone and temperature as well as the seasonal variations is presented by using ozone sounding data at Zhongshan Station over East Antarctica from February, 2008 to February, 2009. The results show that the heights of thermal tropopause and ozone tropopause are mostly the same with yearly mean 7.9 and 7.4 km separately above the station. There is obvious seasonal variation in the pressure and temperature of the tropopause, manifested by the clear one-wave pattern with an opposite phase. As the turning point of the tropopause temperature is visible in autumn and faint in spring and winter, the tropopause height can be better confirmed by utilization of the changes of ozone. Seasonal variation of the tropospheric ozone of vertical distribution is not clear, relative to stratosphere. In the spring, ozone in the low level of stratosphere lost seriously. The minimum partial ozone in 14 km was 1.57 MPa only and the maximum partial ozone occurred in the up level stratosphere. In the rest of the season the ozone increases with height rising in the low level of stratosphere. The evidence shows that ozone lost in spring is closely related with low temperature of polar night and the process of PSC photochemical destruction ozone in the stratosphere. From the vertical characteristics and seasonal variation of ozone and temperature, it is meaningful to understand formation and development of Antarctic ozone deletion.
基金This work was financially supported by the Tribology Science Fund of the State Key Laboratory of Tribology(No.SKLT2022C20)the National Natural Science Foundation of China(Nos.51875309 and 51905310)the Natural Science Foundation of Shandong Province(No.ZR2020YQ39).
文摘For the first time,this work comprehensively studied the effectiveness of precipitation hardening achieved by aging treatment in improving the tensile superelasticity of NiTi alloys fabricated by elec-tron beam wire-feed additive manufacturing(EBAM),which possesses inherent advantages in producing dense and oxidation-free structures.Aging treatments under three temperatures(450,350,and 250℃)and different durations were conducted,and the resultant performance of tensile superelasticity,together with the corresponding evolution of precipitation and phase transformation behavior were investigated for the EBAM-fabricated NiTi alloys.Results showed that by appropriate aging treatment,EBAM fabricated NiTi alloys could achieve excellent recovery rates of approximately 95%and 90%after the 1st and 10th load/unload cycle for a maximum tensile strain of 6%,which were almost the highest achieved so far by AM processed NiTi alloys and close to those of some conventional NiTi alloys.The improvement of tensile superelasticity benefited from the fine and dispersive Ni4Ti3 precipitates,which could be introduced by aging at 350℃ for 4 h or at 250℃ for 200 h.Moreover,the large amount of Ni4Ti3 precipitates would promote the intermediate R-phase transformation and bring a two-stage or three-stage transformation sequence,which depended on whether the distribution of the precipitation was homogeneous or not.This work could provide guidance for the production of NiTi alloys with good tensile superelasticity by EBAM or other additive manufacturing processes.
