The redistribution of cropland to areas of higher elevation in China has long affected agricultural development and could seriously threaten national food security.However,there is currently little research reported o...The redistribution of cropland to areas of higher elevation in China has long affected agricultural development and could seriously threaten national food security.However,there is currently little research reported on this phenomenon,which may limit the improvement of cropland protection policies.To fill this gap,we analyzed the spatiotemporal characteristics and driving mechanisms of increased cropland elevation in China during the period 1980-2020.The average cropland elevation in China increased by 17.38 m from 1980 to 2020.The gravity center of the cropland area and average cropland elevation in China moved to the northwest by 81.00 km and 51.47 km,respectively.The amount of newly added cropland in eastern China was less than that in occupied regions;however,the average elevation of newly added cropland was greater than that of occupied cropland,though the opposite phenomenon was observed in western China.Slope,temperature,land-use intensity,population,economic density,and distance to main roads were the main factors affecting the redistribution of cropland to areas of higher elevation.The effects of these major driving factors exhibited significant spatial and temporal variations in China.This study has important implications for improving existing cropland protection policies and developing more effective cropland management systems in China.展开更多
Spectroscopic characterization of CO activation on multiple metal-containing catalysts remains an important and challenging goal for identifying the structure and nature of active site in many industrial processes suc...Spectroscopic characterization of CO activation on multiple metal-containing catalysts remains an important and challenging goal for identifying the structure and nature of active site in many industrial processes such as Fischer-Tropsch chemistry and alcohol synthesis.Here,we use mass-selected photoelectron velocity-map imaging spectroscopy and quantum chemical calculations to study the reactions of CO molecules with several heterobinuclear transition metal-iron clusters M-Fe(M=Ti,V,Cr).The mass spectra reveal the favorable formation of MFe(CO)_(4)^(-)with relatively high thermodynamic stability.The MFe(CO)_(4)^(-)(M=Ti,V,Cr) complexes are established to have a metal-Fe bonded M-Fe(CO)_(4) structure with C_(3 v) geometry.While the positive charge and unpaired electrons are mainly located on the M atom,the natural charge of Fe(CO)_(4) is about-2 e.The MFe(CO)_(4)^(-)(M=Ti,V,Cr) can be seen as being formed via the interactions between the M^(+)fragment and the [Fe(CO)_(4)]^(2-)core,which satisfies the 18-electron rule.The CO molecules are remarkably activated in these MFe(CO)_(4)^(-).These results shed insight into the structure-reactivity relationship of heterobinuclear transition metal carbonyls and would have important implications for understanding of CO activation on alloy surfaces.展开更多
A neural network classification method,and a batch-learning self-organizing map(BLSOM),was established using trinucleotide and tetranucleotide in the hemagglutinin gene sequences of 25 avian influenza viruses isolated...A neural network classification method,and a batch-learning self-organizing map(BLSOM),was established using trinucleotide and tetranucleotide in the hemagglutinin gene sequences of 25 avian influenza viruses isolated in Guangdong Province. Statistical analysis and normalization of the fragment number were done and MATLAB function was used to simulate the human brain thinking for self-organizing learning. When the number of training steps was 100 and above,the strains could be successfully clustered. H_1,H_3,H_5,H_7 and H_9 subtype strains fell within different classes,respectively,and the HA gene cluster map of H_3N_2 and H_7N_9strains was quite similar,suggesting that these strains shared the same origin; H_5N_1 strain was quite different in different years; H_1N_1 and H_9N_2 strains could be clustered into one group,indicating the natural recombinant variation in the two kinds of viruses,thereby providing a reference for high-risk strain screening and traceability.展开更多
The series of heterodinuclear metal oxide carbonyls in the form of TaNiO(CO)_(n)(n=5-8) are generated in the pulsed-laser vaporization source and characterized by mass-selected photoelectron velocity-map spectroscopy....The series of heterodinuclear metal oxide carbonyls in the form of TaNiO(CO)_(n)(n=5-8) are generated in the pulsed-laser vaporization source and characterized by mass-selected photoelectron velocity-map spectroscopy.During the consecutive CO adsorption,the μ^(2)-O-bent structure initially is the most favorable for TaNiO(CO)_(5),and subsequently both μ^(2)-O-bent and μ^(2)-O-linear structures are degenerate for TaNiO(CO)_(6),then the μ^(2)-O-linear structure is most preferential for TaNiO(CO)_(7),and finally the η^(2)-CO_(2)-tagged structure is the most ene rgetically competitive one for TaNiO(CO)_(8),i.e., the CO oxidation occurs at n=8.ln contrast to the literature reported CO oxidation on heteronuclear metal oxide complexes generally proceeding via Langmuir-Hinshelwood-like mechanism,complementary theo retical calculations suggest that both Langmuir-Hinshelwood-like and Eley-Rideal-like mechanisms prevail for the CO oxidation reaction on TaNiO(CO)_(8) complex.Our findings provide new insight into the composition-selective mechanism of CO oxidation on heteronuclear metal complexes,of which the composition be tailored to fulfill the desired chemical behaviors.展开更多
基金the National Natural Science Foundation of China(Grant No.42001187)the Scientific Research Project of Education Department of Hubei Province(Grant No.B2022262)the Philosophy and Social Sciences Research Project of Education Department of Hubei Province(Grant No.22G024).
文摘The redistribution of cropland to areas of higher elevation in China has long affected agricultural development and could seriously threaten national food security.However,there is currently little research reported on this phenomenon,which may limit the improvement of cropland protection policies.To fill this gap,we analyzed the spatiotemporal characteristics and driving mechanisms of increased cropland elevation in China during the period 1980-2020.The average cropland elevation in China increased by 17.38 m from 1980 to 2020.The gravity center of the cropland area and average cropland elevation in China moved to the northwest by 81.00 km and 51.47 km,respectively.The amount of newly added cropland in eastern China was less than that in occupied regions;however,the average elevation of newly added cropland was greater than that of occupied cropland,though the opposite phenomenon was observed in western China.Slope,temperature,land-use intensity,population,economic density,and distance to main roads were the main factors affecting the redistribution of cropland to areas of higher elevation.The effects of these major driving factors exhibited significant spatial and temporal variations in China.This study has important implications for improving existing cropland protection policies and developing more effective cropland management systems in China.
基金supported by the National Natural Science Foundation of China (21688102, 21873097, and 92061203)the Youth Innovation Promotion Association of the Chinese Academy of Sciences (CAS)(2020187)+3 种基金the Strategic Priority Research Program of CAS (XDB17000000)CAS (GJJSTD20190002)the International Partnership Program of CAS (121421KYSB20170012)the K.C.Wong Education Foundation (GJTD-2018-06)。
文摘Spectroscopic characterization of CO activation on multiple metal-containing catalysts remains an important and challenging goal for identifying the structure and nature of active site in many industrial processes such as Fischer-Tropsch chemistry and alcohol synthesis.Here,we use mass-selected photoelectron velocity-map imaging spectroscopy and quantum chemical calculations to study the reactions of CO molecules with several heterobinuclear transition metal-iron clusters M-Fe(M=Ti,V,Cr).The mass spectra reveal the favorable formation of MFe(CO)_(4)^(-)with relatively high thermodynamic stability.The MFe(CO)_(4)^(-)(M=Ti,V,Cr) complexes are established to have a metal-Fe bonded M-Fe(CO)_(4) structure with C_(3 v) geometry.While the positive charge and unpaired electrons are mainly located on the M atom,the natural charge of Fe(CO)_(4) is about-2 e.The MFe(CO)_(4)^(-)(M=Ti,V,Cr) can be seen as being formed via the interactions between the M^(+)fragment and the [Fe(CO)_(4)]^(2-)core,which satisfies the 18-electron rule.The CO molecules are remarkably activated in these MFe(CO)_(4)^(-).These results shed insight into the structure-reactivity relationship of heterobinuclear transition metal carbonyls and would have important implications for understanding of CO activation on alloy surfaces.
基金Supported by National Entry-Exit Inspection and Quarantine Research Project(2015IK054)Special Project of Ministry of Science and Technology for Development of Major Scientific Instruments and Equipments(2012YQ0901-9705)
文摘A neural network classification method,and a batch-learning self-organizing map(BLSOM),was established using trinucleotide and tetranucleotide in the hemagglutinin gene sequences of 25 avian influenza viruses isolated in Guangdong Province. Statistical analysis and normalization of the fragment number were done and MATLAB function was used to simulate the human brain thinking for self-organizing learning. When the number of training steps was 100 and above,the strains could be successfully clustered. H_1,H_3,H_5,H_7 and H_9 subtype strains fell within different classes,respectively,and the HA gene cluster map of H_3N_2 and H_7N_9strains was quite similar,suggesting that these strains shared the same origin; H_5N_1 strain was quite different in different years; H_1N_1 and H_9N_2 strains could be clustered into one group,indicating the natural recombinant variation in the two kinds of viruses,thereby providing a reference for high-risk strain screening and traceability.
基金supported by the National Natural Science Foundation of China (Nos.21603130,21673231,21688102 and 21873097)the Key Research Program (No.KGZD-EW-T05)+2 种基金the Strategic Priority Research Program (No.XDB17000000) of the Chinese Academy of Sciencethe Shanxi Province Science Foundation for Youths (No. 201901D211395)the 1331 Engineering of Shanxi Province and the Start-up Fund from Shanxi Normal University for support。
文摘The series of heterodinuclear metal oxide carbonyls in the form of TaNiO(CO)_(n)(n=5-8) are generated in the pulsed-laser vaporization source and characterized by mass-selected photoelectron velocity-map spectroscopy.During the consecutive CO adsorption,the μ^(2)-O-bent structure initially is the most favorable for TaNiO(CO)_(5),and subsequently both μ^(2)-O-bent and μ^(2)-O-linear structures are degenerate for TaNiO(CO)_(6),then the μ^(2)-O-linear structure is most preferential for TaNiO(CO)_(7),and finally the η^(2)-CO_(2)-tagged structure is the most ene rgetically competitive one for TaNiO(CO)_(8),i.e., the CO oxidation occurs at n=8.ln contrast to the literature reported CO oxidation on heteronuclear metal oxide complexes generally proceeding via Langmuir-Hinshelwood-like mechanism,complementary theo retical calculations suggest that both Langmuir-Hinshelwood-like and Eley-Rideal-like mechanisms prevail for the CO oxidation reaction on TaNiO(CO)_(8) complex.Our findings provide new insight into the composition-selective mechanism of CO oxidation on heteronuclear metal complexes,of which the composition be tailored to fulfill the desired chemical behaviors.
