Based on the GIMMS AVHRR NDVI data （8 km spatial resolution） for 1982-2000, the SPOT VEGETATION NDVI data （1 km spatial resolution） for 1998-2009, and observa- tional plant biomass data, the CASA model was used to...Based on the GIMMS AVHRR NDVI data （8 km spatial resolution） for 1982-2000, the SPOT VEGETATION NDVI data （1 km spatial resolution） for 1998-2009, and observa- tional plant biomass data, the CASA model was used to model changes in alpine grassland net primary production （NPP） on the Tibetan Plateau （TP）. This study will help to evaluate the health conditions of the alpine grassland ecosystem, and is of great importance to the pro- motion of sustainable development of plateau pasture and to the understanding of the func- tion of the national ecological security shelter on the TP. The spatio-temporal characteristics of NPP change were investigated using spatial statistical analysis, separately on the basis of physico-geographical factors （natural zone, altitude, latitude and longitude）, river basin, and county-level administrative area. Data processing was carried out using an ENVI 4.8 platform, while an ArcGIS 9.3 and ANUSPLIN platform was used to conduct the spatial analysis and mapping. The primary results are as follows： （1） The NPP of alpine grassland on the TP gradually decreases from the southeast to the northwest, which corresponds to gradients in precipitation and temperature. From 1982 to 2009, the average annual total NPP in the TP alpine grassland was 177.2x1012 gC yrl（yr represents year）, while the average annual NPP was 120.8 gC m^-2 yr^-1. （2） The annual NPP in alpine grassland on the TP fluctuates from year to year but shows an overall positive trend ranging from 114.7 gC m^-2 yr^-1 in 1982 to 129.9 gC m^-2 yr^-1 in 2009, with an overall increase of 13.3%; 32.56% of the total alpine grassland on the TP showed a significant increase in NPP, while only 5.55% showed a significant decrease over this 28-year period. （3） Spatio-temporal characteristics are an important control on an- nual NPP in alpine grassland： a） NPP increased in most of the natural zones on the TP, only showing a slight decrease in the Ngari montane desert-steppe and desert zone. The positive 展开更多
Based on the NOAA AVHRR-NDVI monthly data from 1981 to 2001, the spatial distribution and dynamic change of land cover along the Qinghai-Tibet Highway and Railway were studied. The results of the analytical data indic...Based on the NOAA AVHRR-NDVI monthly data from 1981 to 2001, the spatial distribution and dynamic change of land cover along the Qinghai-Tibet Highway and Railway were studied. The results of the analytical data indicate that the NDVI values in July, August and September are rather high during a year, and a linear trend by calculating NDVI of each pixel computed based on the average values of NDVI in July, August and September were obtained. The results are as follows： 1） Land cover of the study area by NDVI displays high at two sides of the area and low in the center, and agriculture area 〉 alpine meadow 〉 alpine grassland 〉 desert grassland. 2） In the study area, the amount ofpixels with high increase, slight increase, no change, slight decrease and high decrease account for 0.29%, 14.86%, 67.61%, 16.7% and 0.57% of the whole area, respectively. The increase of land cover pixels is mainly in the agriculture and alpine meadow and the decrease pixels mainly in the alpine grassland, desert grassland and hungriness. Grassland and hungriness contribute to the decrease mostly and artificial land and meadow contribute to the increase mostly. 3） In the area where human beings live, the changing trend is obvious, such as the valleys of Lhasa River and Huangshui River and area along the Yellow River; in the high altitude area with fewer people living, the changing trend is relatively low, like the area of Hoh Xil. 4） Human being＇s behaviors are a key factor followed by the climate changes affecting land cover.展开更多
Ever since hematopoietic stem cells(HSCs)were first identified half a century ago,their differentiation roadmap has been extensively studied.The classical model of hematopoiesis has long held as a dogma that HSCs resi...Ever since hematopoietic stem cells(HSCs)were first identified half a century ago,their differentiation roadmap has been extensively studied.The classical model of hematopoiesis has long held as a dogma that HSCs reside at the top of a hierarchy in which HSCs possess self-renewal capacity and can progressively give rise to all blood lineage cells.However,over the past several years,with advances in single cell technologies,this developmental scheme has been challenged.In this review,we discuss the evidence supporting heterogeneity within HSC and progenitor populations as well as the hierarchical models revised by novel approaches mainly in mouse system.These evolving views provide further understanding of hematopoiesis and highlight the complexity of hematopoietic differentiation.展开更多
The Circular Electron Positron Collider(CEPC)is a large scientific project initiated and hosted by China,fostered through extensive collaboration with international partners.The complex comprises four accelerators:a 3...The Circular Electron Positron Collider(CEPC)is a large scientific project initiated and hosted by China,fostered through extensive collaboration with international partners.The complex comprises four accelerators:a 30 GeV Linac,a 1.1 GeV Damping Ring,a Booster capable of achieving energies up to 180 GeV,and a Collider operating at varying energy modes(Z,W,H,and tt).The Linac and Damping Ring are situated on the surface,while the subterranean Booster and Collider are housed in a 100 km circumference underground tunnel,strategically accommodating future expansion with provisions for a potential Super Proton Proton Collider(SPPC).The CEPC primarily serves as a Higgs factory.In its baseline design with synchrotron radiation(SR)power of 30 MW per beam,it can achieve a luminosity of 5×10^(34)cm^(-2)s^(-1)per interaction point(IP),resulting in an integrated luminosity of 13 ab^(-1)for two IPs over a decade,producing 2.6 million Higgs bosons.Increasing the SR power to 50 MW per beam expands the CEPC's capability to generate 4.3 million Higgs bosons,facilitating precise measurements of Higgs coupling at sub-percent levels,exceeding the precision expected from the HL-LHC by an order of magnitude.This Technical Design Report(TDR)follows the Preliminary Conceptual Design Report(Pre-CDR,2015)and the Conceptual Design Report(CDR,2018),comprehensively detailing the machine's layout,performance metrics,physical design and analysis,technical systems design,R&D and prototyping efforts,and associated civil engineering aspects.Additionally,it includes a cost estimate and a preliminary construction timeline,establishing a framework for forthcoming engineering design phase and site selection procedures.Construction is anticipated to begin around 2027-2028,pending government approval,with an estimated duration of 8 years.The commencement of experiments and data collection could potentially be initiated in the mid-2030s.展开更多
Smart textiles with high sensitivity and rapid response for various external stimuli have gained tremendous attentions in human healthcare monitoring,personal heat management,and wearable electronics.However,the curre...Smart textiles with high sensitivity and rapid response for various external stimuli have gained tremendous attentions in human healthcare monitoring,personal heat management,and wearable electronics.However,the current smart textiles only acquire desired signal passively,regularly lacking subsequent on-demand therapy actively.Herein,a robust,breathable,and flexible smart textiles as multi-function sensor and wearable heater for human health monitoring and gentle thermotherapy in real time is constructed.The composite fiber as strain sensor(CFY@PU)was fabricated via warping carbon fiber yarns(CFY)onto polyurethane fibers(PU),which endowed composite fiber with high conductivity,excellent sensitivity(GF=76.2),and fantastic dynamic durability(7500 cycles)in strain sensing.In addition,CFY@PU can detect various degrees of human movements such as elbow bending,swallowing and pulse,which can provide effective information for disease diagnosis.More surprisingly,weaving CFY@PU into a fabric can assemble highly sensitive pressure sensor for remote communication and information encryption.Warping CFY onto Kevlar would obtain temperature-sensitive composite fiber(CFY@Kevlar)as temperature sensor and wearable heater for on-demand thermotherapy,which provided unique opportunities in designing smart textiles with ultrahigh sensitivity,rapid response,and great dynamic durability.展开更多
On-surface Ullmann coupling has been intensely utilized for the tailor-made fabrication of conjugated frameworks towards molecular electronics, however, reaction mechanisms are still limitedly understood. Herein, we p...On-surface Ullmann coupling has been intensely utilized for the tailor-made fabrication of conjugated frameworks towards molecular electronics, however, reaction mechanisms are still limitedly understood. Herein, we provide a comprehensive elucidation of the surface Ullmann coupling of 2,7-dibromopyrene (Br2Py) on Ag(111) by scanning tunnelling microscopy (STM), X-ray photoelectron spectroscopy (XPS) and density function theory (DFT), and reveal that the Ullmann reaction path is unique regardless of predesigned assembled structures. By manipulating deposition conditions, diverse assembled architectures have been constructed for Br2Py on Ag(111), including the ladder phase, parallel arrangement, hexagonal patterns from monomers or Kagome lattices based on organometallic (OM) dimers. Intriguingly, stepwise annealing leads to an identical reaction diagram for the surface Ullmann coupling from individual assembled structures convergent into the brick-wall-pattern OM dimers first, which is deemed to be a stable phase, and then into elongated OM chains in order and eventually long-range polymers with direct C-C coupling. While the reaction mechanism is demonstrated to be dominated by the metal coordinated and halogen bonding motifs, interestingly, it has also been revealed that surface adatoms and dissociated Br atoms play a crucial role in coupling reactions. In contrast to previous reports demonstrating the manipulation of Ullmann reactions by preassembled strategy, herein, weak intermolecular interaction in assembled nanostructures is immediately suppressed by strong covalent bonding during reactions. Importantly, our report proposes essential insights on fundamental understanding of surface Ullmann coupling towards high-yield surface synthesis.展开更多
Estimating the global state of a networked system is an important problem in many application domains.The classical approach to tackling this problem is the periodic(observation)method,which is inefficient because it ...Estimating the global state of a networked system is an important problem in many application domains.The classical approach to tackling this problem is the periodic(observation)method,which is inefficient because it often observes states at a very high frequency.This inefficiency has motivated the idea of event-based method,which leverages the evolution dynamics in question and makes observations only when some rules are triggered(i.e.,only when certain conditions hold).This paper initiates the investigation of using the event-based method to estimate the equilibrium in the new application domain of cybersecurity,where equilibrium is an important metric that has no closed-form solutions.More specifically,the paper presents an event-based method for estimating cybersecurity equilibrium in the preventive and reactive cyber defense dynamics,which has been proven globally convergent.The presented study proves that the estimated equilibrium from our trigger rule i)indeed converges to the equilibrium of the dynamics and ii)is Zeno-free,which assures the usefulness of the event-based method.Numerical examples show that the event-based method can reduce 98%of the observation cost incurred by the periodic method.In order to use the event-based method in practice,this paper investigates how to bridge the gap between i)the continuous state in the dynamics model,which is dubbed probability-state because it measures the probability that a node is in the secure or compromised state,and ii)the discrete state that is often encountered in practice,dubbed sample-state because it is sampled from some nodes.This bridge may be of independent value because probability-state models have been widely used to approximate exponentially-many discrete state systems.展开更多
Heterogeneous catalysis taking place at solid interfaces plays a crucial role not only in industrial chemical production, energy conversion but also in fundamental research. The dynamic evolution of surface morphology...Heterogeneous catalysis taking place at solid interfaces plays a crucial role not only in industrial chemical production, energy conversion but also in fundamental research. The dynamic evolution of surface morphology and composition requires full understanding especially under realistic reaction conditions. To this end, conventional scanning tunneling microscopy(STM) has been integrated with high pressure cell and electrochemical cell, forming high pressure(HP) STM and electrochemical(EC) STM for the in-situ/operando characterization at solid-gas and solid-liquid interfaces with atomic resolution, respectively. In this review, we attempt to give a brief introduction to the development and working principle of these two techniques and subsequently summarize several representative progresses in recent days. The dynamic changes in active sites, surface reconstruction, absorbates alteration and products formation are directly characterized in a combination with other surface sensitive technologies. The correlation between surface structures and catalytic performance as well as the underlying mechanism can thus be unraveled, which provides insights into the rational design and optimization of catalysts.展开更多
基金National Basic Research Program of China,No.2010CB951704Strategic Priority Research Program of the Chinese Academy of Sciences,No.XDB03030501No.XDA05060704
文摘Based on the GIMMS AVHRR NDVI data （8 km spatial resolution） for 1982-2000, the SPOT VEGETATION NDVI data （1 km spatial resolution） for 1998-2009, and observa- tional plant biomass data, the CASA model was used to model changes in alpine grassland net primary production （NPP） on the Tibetan Plateau （TP）. This study will help to evaluate the health conditions of the alpine grassland ecosystem, and is of great importance to the pro- motion of sustainable development of plateau pasture and to the understanding of the func- tion of the national ecological security shelter on the TP. The spatio-temporal characteristics of NPP change were investigated using spatial statistical analysis, separately on the basis of physico-geographical factors （natural zone, altitude, latitude and longitude）, river basin, and county-level administrative area. Data processing was carried out using an ENVI 4.8 platform, while an ArcGIS 9.3 and ANUSPLIN platform was used to conduct the spatial analysis and mapping. The primary results are as follows： （1） The NPP of alpine grassland on the TP gradually decreases from the southeast to the northwest, which corresponds to gradients in precipitation and temperature. From 1982 to 2009, the average annual total NPP in the TP alpine grassland was 177.2x1012 gC yrl（yr represents year）, while the average annual NPP was 120.8 gC m^-2 yr^-1. （2） The annual NPP in alpine grassland on the TP fluctuates from year to year but shows an overall positive trend ranging from 114.7 gC m^-2 yr^-1 in 1982 to 129.9 gC m^-2 yr^-1 in 2009, with an overall increase of 13.3%; 32.56% of the total alpine grassland on the TP showed a significant increase in NPP, while only 5.55% showed a significant decrease over this 28-year period. （3） Spatio-temporal characteristics are an important control on an- nual NPP in alpine grassland： a） NPP increased in most of the natural zones on the TP, only showing a slight decrease in the Ngari montane desert-steppe and desert zone. The positive
基金National Natural Science Foundation of China No.90202012+1 种基金 National Basic Research Program of China, No.2005CB422006 No. 2002CB412507
文摘Based on the NOAA AVHRR-NDVI monthly data from 1981 to 2001, the spatial distribution and dynamic change of land cover along the Qinghai-Tibet Highway and Railway were studied. The results of the analytical data indicate that the NDVI values in July, August and September are rather high during a year, and a linear trend by calculating NDVI of each pixel computed based on the average values of NDVI in July, August and September were obtained. The results are as follows： 1） Land cover of the study area by NDVI displays high at two sides of the area and low in the center, and agriculture area 〉 alpine meadow 〉 alpine grassland 〉 desert grassland. 2） In the study area, the amount ofpixels with high increase, slight increase, no change, slight decrease and high decrease account for 0.29%, 14.86%, 67.61%, 16.7% and 0.57% of the whole area, respectively. The increase of land cover pixels is mainly in the agriculture and alpine meadow and the decrease pixels mainly in the alpine grassland, desert grassland and hungriness. Grassland and hungriness contribute to the decrease mostly and artificial land and meadow contribute to the increase mostly. 3） In the area where human beings live, the changing trend is obvious, such as the valleys of Lhasa River and Huangshui River and area along the Yellow River; in the high altitude area with fewer people living, the changing trend is relatively low, like the area of Hoh Xil. 4） Human being＇s behaviors are a key factor followed by the climate changes affecting land cover.
基金supported by grants from the National Key Research and Development Program of China(2016YFA0100600,2017YFA0103400)the National Natural Science Foundation of China(81421002,81730006,81430004,81670106,81870086,8181101081)+1 种基金CAMS Initiative for Innovative Medicine(2017-I2M-3-009,2016-I2M-1-017)and the CAMS Fundamental Research Funds for Central Research Institutes(2016GH3100001,2018PT31005).
文摘Ever since hematopoietic stem cells(HSCs)were first identified half a century ago,their differentiation roadmap has been extensively studied.The classical model of hematopoiesis has long held as a dogma that HSCs reside at the top of a hierarchy in which HSCs possess self-renewal capacity and can progressively give rise to all blood lineage cells.However,over the past several years,with advances in single cell technologies,this developmental scheme has been challenged.In this review,we discuss the evidence supporting heterogeneity within HSC and progenitor populations as well as the hierarchical models revised by novel approaches mainly in mouse system.These evolving views provide further understanding of hematopoiesis and highlight the complexity of hematopoietic differentiation.
基金support from diverse funding sources,including the National Key Program for S&T Research and Development of the Ministry of Science and Technology(MOST),Yifang Wang's Science Studio of the Ten Thousand Talents Project,the CAS Key Foreign Cooperation Grant,the National Natural Science Foundation of China(NSFC)Beijing Municipal Science&Technology Commission,the CAS Focused Science Grant,the IHEP Innovation Grant,the CAS Lead Special Training Programthe CAS Center for Excellence in Particle Physics,the CAS International Partnership Program,and the CAS/SAFEA International Partnership Program for Creative Research Teams.
文摘The Circular Electron Positron Collider(CEPC)is a large scientific project initiated and hosted by China,fostered through extensive collaboration with international partners.The complex comprises four accelerators:a 30 GeV Linac,a 1.1 GeV Damping Ring,a Booster capable of achieving energies up to 180 GeV,and a Collider operating at varying energy modes(Z,W,H,and tt).The Linac and Damping Ring are situated on the surface,while the subterranean Booster and Collider are housed in a 100 km circumference underground tunnel,strategically accommodating future expansion with provisions for a potential Super Proton Proton Collider(SPPC).The CEPC primarily serves as a Higgs factory.In its baseline design with synchrotron radiation(SR)power of 30 MW per beam,it can achieve a luminosity of 5×10^(34)cm^(-2)s^(-1)per interaction point(IP),resulting in an integrated luminosity of 13 ab^(-1)for two IPs over a decade,producing 2.6 million Higgs bosons.Increasing the SR power to 50 MW per beam expands the CEPC's capability to generate 4.3 million Higgs bosons,facilitating precise measurements of Higgs coupling at sub-percent levels,exceeding the precision expected from the HL-LHC by an order of magnitude.This Technical Design Report(TDR)follows the Preliminary Conceptual Design Report(Pre-CDR,2015)and the Conceptual Design Report(CDR,2018),comprehensively detailing the machine's layout,performance metrics,physical design and analysis,technical systems design,R&D and prototyping efforts,and associated civil engineering aspects.Additionally,it includes a cost estimate and a preliminary construction timeline,establishing a framework for forthcoming engineering design phase and site selection procedures.Construction is anticipated to begin around 2027-2028,pending government approval,with an estimated duration of 8 years.The commencement of experiments and data collection could potentially be initiated in the mid-2030s.
基金supported by Outstanding Youth Project of Zhejiang Provincial Natural Science Foundation(LR22E030002)the Key Research and Development Program of Zhejiang Province(2022C01049)+1 种基金Zhejiang Provincial Natural Science Key Foundation of China(LZ20E030003)National Natural Science Foundation of China(52273095).
文摘Smart textiles with high sensitivity and rapid response for various external stimuli have gained tremendous attentions in human healthcare monitoring,personal heat management,and wearable electronics.However,the current smart textiles only acquire desired signal passively,regularly lacking subsequent on-demand therapy actively.Herein,a robust,breathable,and flexible smart textiles as multi-function sensor and wearable heater for human health monitoring and gentle thermotherapy in real time is constructed.The composite fiber as strain sensor(CFY@PU)was fabricated via warping carbon fiber yarns(CFY)onto polyurethane fibers(PU),which endowed composite fiber with high conductivity,excellent sensitivity(GF=76.2),and fantastic dynamic durability(7500 cycles)in strain sensing.In addition,CFY@PU can detect various degrees of human movements such as elbow bending,swallowing and pulse,which can provide effective information for disease diagnosis.More surprisingly,weaving CFY@PU into a fabric can assemble highly sensitive pressure sensor for remote communication and information encryption.Warping CFY onto Kevlar would obtain temperature-sensitive composite fiber(CFY@Kevlar)as temperature sensor and wearable heater for on-demand thermotherapy,which provided unique opportunities in designing smart textiles with ultrahigh sensitivity,rapid response,and great dynamic durability.
基金Fruitful discussions with Dr.Qitang Fan are greatly appreciated.This work was financially supported by National Natural Science Foundation of China(Nos.11874380,11874427,and U1732267)the National Key Research and Development Program of China(No.2016YFA040130201)the Hundred Talents Program of Chinese Academy of Sciences.
文摘On-surface Ullmann coupling has been intensely utilized for the tailor-made fabrication of conjugated frameworks towards molecular electronics, however, reaction mechanisms are still limitedly understood. Herein, we provide a comprehensive elucidation of the surface Ullmann coupling of 2,7-dibromopyrene (Br2Py) on Ag(111) by scanning tunnelling microscopy (STM), X-ray photoelectron spectroscopy (XPS) and density function theory (DFT), and reveal that the Ullmann reaction path is unique regardless of predesigned assembled structures. By manipulating deposition conditions, diverse assembled architectures have been constructed for Br2Py on Ag(111), including the ladder phase, parallel arrangement, hexagonal patterns from monomers or Kagome lattices based on organometallic (OM) dimers. Intriguingly, stepwise annealing leads to an identical reaction diagram for the surface Ullmann coupling from individual assembled structures convergent into the brick-wall-pattern OM dimers first, which is deemed to be a stable phase, and then into elongated OM chains in order and eventually long-range polymers with direct C-C coupling. While the reaction mechanism is demonstrated to be dominated by the metal coordinated and halogen bonding motifs, interestingly, it has also been revealed that surface adatoms and dissociated Br atoms play a crucial role in coupling reactions. In contrast to previous reports demonstrating the manipulation of Ullmann reactions by preassembled strategy, herein, weak intermolecular interaction in assembled nanostructures is immediately suppressed by strong covalent bonding during reactions. Importantly, our report proposes essential insights on fundamental understanding of surface Ullmann coupling towards high-yield surface synthesis.
基金supported in part by the National Natural Sciences Foundation of China(62072111)。
文摘Estimating the global state of a networked system is an important problem in many application domains.The classical approach to tackling this problem is the periodic(observation)method,which is inefficient because it often observes states at a very high frequency.This inefficiency has motivated the idea of event-based method,which leverages the evolution dynamics in question and makes observations only when some rules are triggered(i.e.,only when certain conditions hold).This paper initiates the investigation of using the event-based method to estimate the equilibrium in the new application domain of cybersecurity,where equilibrium is an important metric that has no closed-form solutions.More specifically,the paper presents an event-based method for estimating cybersecurity equilibrium in the preventive and reactive cyber defense dynamics,which has been proven globally convergent.The presented study proves that the estimated equilibrium from our trigger rule i)indeed converges to the equilibrium of the dynamics and ii)is Zeno-free,which assures the usefulness of the event-based method.Numerical examples show that the event-based method can reduce 98%of the observation cost incurred by the periodic method.In order to use the event-based method in practice,this paper investigates how to bridge the gap between i)the continuous state in the dynamics model,which is dubbed probability-state because it measures the probability that a node is in the secure or compromised state,and ii)the discrete state that is often encountered in practice,dubbed sample-state because it is sampled from some nodes.This bridge may be of independent value because probability-state models have been widely used to approximate exponentially-many discrete state systems.
基金financially supported by the National Natural Science Foundation of China (22002183, 11874380)the Photon Science Center for Carbon Neutrality of Chinese Academy of SciencesCAS Key Laboratory of Low-carbon Conversion Science and Engineering,Chinese Academy of Sciences。
文摘Heterogeneous catalysis taking place at solid interfaces plays a crucial role not only in industrial chemical production, energy conversion but also in fundamental research. The dynamic evolution of surface morphology and composition requires full understanding especially under realistic reaction conditions. To this end, conventional scanning tunneling microscopy(STM) has been integrated with high pressure cell and electrochemical cell, forming high pressure(HP) STM and electrochemical(EC) STM for the in-situ/operando characterization at solid-gas and solid-liquid interfaces with atomic resolution, respectively. In this review, we attempt to give a brief introduction to the development and working principle of these two techniques and subsequently summarize several representative progresses in recent days. The dynamic changes in active sites, surface reconstruction, absorbates alteration and products formation are directly characterized in a combination with other surface sensitive technologies. The correlation between surface structures and catalytic performance as well as the underlying mechanism can thus be unraveled, which provides insights into the rational design and optimization of catalysts.
