Ratoon rice,which refers to a second harvest of rice obtained from the regenerated tillers originating from the stubble of the first harvested crop,plays an important role in both food security and agroecology while r...Ratoon rice,which refers to a second harvest of rice obtained from the regenerated tillers originating from the stubble of the first harvested crop,plays an important role in both food security and agroecology while requiring minimal agricultural inputs.However,accurately identifying ratoon rice crops is challenging due to the similarity of its spectral features with other rice cropping systems(e.g.,double rice).Moreover,images with a high spatiotemporal resolution are essential since ratoon rice is generally cultivated in fragmented croplands within regions that frequently exhibit cloudy and rainy weather.In this study,taking Qichun County in Hubei Province,China as an example,we developed a new phenology-based ratoon rice vegetation index(PRVI)for the purpose of ratoon rice mapping at a 30 m spatial resolution using a robust time series generated from Harmonized Landsat and Sentinel-2(HLS)images.The PRVI that incorporated the red,near-infrared,and shortwave infrared 1 bands was developed based on the analysis of spectro-phenological separability and feature selection.Based on actual field samples,the performance of the PRVI for ratoon rice mapping was carefully evaluated by comparing it to several vegetation indices,including normalized difference vegetation index(NDVI),enhanced vegetation index(EVI)and land surface water index(LSWI).The results suggested that the PRVI could sufficiently capture the specific characteristics of ratoon rice,leading to a favorable separability between ratoon rice and other land cover types.Furthermore,the PRVI showed the best performance for identifying ratoon rice in the phenological phases characterized by grain filling and harvesting to tillering of the ratoon crop(GHS-TS2),indicating that only several images are required to obtain an accurate ratoon rice map.Finally,the PRVI performed better than NDVI,EVI,LSWI and their combination at the GHS-TS2 stages,with producer's accuracy and user's accuracy of 92.22 and 89.30%,respectively.These results demonstrate that the proposed PRVI based on HLS data can effectively identify ratoon rice in fragmented croplands at crucial phenological stages,which is promising for identifying the earliest timing of ratoon rice planting and can provide a fundamental dataset for crop management activities.展开更多
The paper investigates the positive feedback trading phenomenon of individual stocks in China’s stock market.Heterogeneous regression models and a non-parametric Sentana-Wadhwani model are developed and applied to pr...The paper investigates the positive feedback trading phenomenon of individual stocks in China’s stock market.Heterogeneous regression models and a non-parametric Sentana-Wadhwani model are developed and applied to prove the existence of rise-favor asymmetric feedback trading.This result is consistent with the reality of China’s stock market,that is,the herding behavior of irrational retail investors has a significant influence on the market.However,the result is in contrast with the stylized findings using market indices.Further empirical research shows that this distinction could be explained by the average effect of indices.The asymmetries of positive feedback trading caused by heterogeneous feedback trading and the uneven distributed retail trading in individual stocks,are covered by the weighted average effect in indices.Therefore,the indices exhibit a different asymmetric pattern from that of individual stocks.展开更多
The harmonic index of a graph?G? is defined as where d(u) denotes the degree of a vertex u in G . In this work, we give another expression for the Harmonic index. Using this expression, we give the minimum value of th...The harmonic index of a graph?G? is defined as where d(u) denotes the degree of a vertex u in G . In this work, we give another expression for the Harmonic index. Using this expression, we give the minimum value of the harmonic index for any triangle-free graphs with order n and minimum degree δ ≥ k for k≤ n/2? and show the corresponding extremal graph is the complete graph.展开更多
The harmonic index of a graph G is defined as , where d(u) denotes the degree of a vertex u in G. It has been found that the harmonic index correlates well with the Randi c' index and with the π-electronic energy...The harmonic index of a graph G is defined as , where d(u) denotes the degree of a vertex u in G. It has been found that the harmonic index correlates well with the Randi c' index and with the π-electronic energy of benzenoid hydrocarbons. In this work, we give several relations between the harmonic index and diameter of graphs.展开更多
Hydrogen isotopes of n-alkanes in grasses, tree leaves and reeds from six regions with latitudes of 20° to 39°N in China are measured by GC-TC-IRMS analytical technique in order to understand their hy- droge...Hydrogen isotopes of n-alkanes in grasses, tree leaves and reeds from six regions with latitudes of 20° to 39°N in China are measured by GC-TC-IRMS analytical technique in order to understand their hy- drogen isotopic compositions and environmental significance. The results show that a difference in δ D values (from -42.1‰ to -66.6‰) of n-alkanes exists among the same kinds of plants from various re- gions. Hydrogen isotopic compositions of most even carbon numbered n-alkanes in every plant are slightly heavier than that of the odd homologues. A trend toward D-enrichment with increasing chain length of n-alkanes in most plant samples is observed. Mean δ D values of n-alkanes in the studied plants range from -202.6‰ to -130.7‰ and the reed from a salt marsh has the largest value. The mean δ D values of individual n-alkanes among the same kinds of plants from various regions have the characteristics of leaf > reed > grass. The hydrogen isotopic compositions of n-alkanes are apparently distinct among various kinds of plants from the same region and the mean δ D values exhibit a distri- bution of tree leaf > reed > grass. It is observed that the mean δ D values of n-alkanes and δ D values of C27 and C29 n-alkanes in the grasses and tree leaves from these studied regions correlate clearly nega- tively with latitude and positively with temperature, indicating that these values can be used as excel- lent indicators of environment and climate. These results provide important basic data for under- standing the distributional law of hydrogen isotopes of individual n-alkanes and their applied research.展开更多
基金supported by the National Natural Science Foundation of China(42271360 and 42271399)the Young Elite Scientists Sponsorship Program by China Association for Science and Technology(CAST)(2020QNRC001)the Fundamental Research Funds for the Central Universities,China(2662021JC013,CCNU22QN018)。
文摘Ratoon rice,which refers to a second harvest of rice obtained from the regenerated tillers originating from the stubble of the first harvested crop,plays an important role in both food security and agroecology while requiring minimal agricultural inputs.However,accurately identifying ratoon rice crops is challenging due to the similarity of its spectral features with other rice cropping systems(e.g.,double rice).Moreover,images with a high spatiotemporal resolution are essential since ratoon rice is generally cultivated in fragmented croplands within regions that frequently exhibit cloudy and rainy weather.In this study,taking Qichun County in Hubei Province,China as an example,we developed a new phenology-based ratoon rice vegetation index(PRVI)for the purpose of ratoon rice mapping at a 30 m spatial resolution using a robust time series generated from Harmonized Landsat and Sentinel-2(HLS)images.The PRVI that incorporated the red,near-infrared,and shortwave infrared 1 bands was developed based on the analysis of spectro-phenological separability and feature selection.Based on actual field samples,the performance of the PRVI for ratoon rice mapping was carefully evaluated by comparing it to several vegetation indices,including normalized difference vegetation index(NDVI),enhanced vegetation index(EVI)and land surface water index(LSWI).The results suggested that the PRVI could sufficiently capture the specific characteristics of ratoon rice,leading to a favorable separability between ratoon rice and other land cover types.Furthermore,the PRVI showed the best performance for identifying ratoon rice in the phenological phases characterized by grain filling and harvesting to tillering of the ratoon crop(GHS-TS2),indicating that only several images are required to obtain an accurate ratoon rice map.Finally,the PRVI performed better than NDVI,EVI,LSWI and their combination at the GHS-TS2 stages,with producer's accuracy and user's accuracy of 92.22 and 89.30%,respectively.These results demonstrate that the proposed PRVI based on HLS data can effectively identify ratoon rice in fragmented croplands at crucial phenological stages,which is promising for identifying the earliest timing of ratoon rice planting and can provide a fundamental dataset for crop management activities.
基金supported by the National Natural Science Funds with Grant numbers(71431008,71532013,71528001 and 71501170)Zhejiang Provincial National Science Funds(No.LQ16G010001)Zhejiang Provincial Key Research Base for Humanities and Social Science Research(Applied Economics in Zhejiang Gongshang University).
文摘The paper investigates the positive feedback trading phenomenon of individual stocks in China’s stock market.Heterogeneous regression models and a non-parametric Sentana-Wadhwani model are developed and applied to prove the existence of rise-favor asymmetric feedback trading.This result is consistent with the reality of China’s stock market,that is,the herding behavior of irrational retail investors has a significant influence on the market.However,the result is in contrast with the stylized findings using market indices.Further empirical research shows that this distinction could be explained by the average effect of indices.The asymmetries of positive feedback trading caused by heterogeneous feedback trading and the uneven distributed retail trading in individual stocks,are covered by the weighted average effect in indices.Therefore,the indices exhibit a different asymmetric pattern from that of individual stocks.
文摘The harmonic index of a graph?G? is defined as where d(u) denotes the degree of a vertex u in G . In this work, we give another expression for the Harmonic index. Using this expression, we give the minimum value of the harmonic index for any triangle-free graphs with order n and minimum degree δ ≥ k for k≤ n/2? and show the corresponding extremal graph is the complete graph.
文摘The harmonic index of a graph G is defined as , where d(u) denotes the degree of a vertex u in G. It has been found that the harmonic index correlates well with the Randi c' index and with the π-electronic energy of benzenoid hydrocarbons. In this work, we give several relations between the harmonic index and diameter of graphs.
基金Supported by National Natural Science Foundation of China (Grant Nos. 40642007 and 40772069)National Basic Research Program of China (Grant No. 2005CB422105)Special Project for Winners of CAS President Award
文摘Hydrogen isotopes of n-alkanes in grasses, tree leaves and reeds from six regions with latitudes of 20° to 39°N in China are measured by GC-TC-IRMS analytical technique in order to understand their hy- drogen isotopic compositions and environmental significance. The results show that a difference in δ D values (from -42.1‰ to -66.6‰) of n-alkanes exists among the same kinds of plants from various re- gions. Hydrogen isotopic compositions of most even carbon numbered n-alkanes in every plant are slightly heavier than that of the odd homologues. A trend toward D-enrichment with increasing chain length of n-alkanes in most plant samples is observed. Mean δ D values of n-alkanes in the studied plants range from -202.6‰ to -130.7‰ and the reed from a salt marsh has the largest value. The mean δ D values of individual n-alkanes among the same kinds of plants from various regions have the characteristics of leaf > reed > grass. The hydrogen isotopic compositions of n-alkanes are apparently distinct among various kinds of plants from the same region and the mean δ D values exhibit a distri- bution of tree leaf > reed > grass. It is observed that the mean δ D values of n-alkanes and δ D values of C27 and C29 n-alkanes in the grasses and tree leaves from these studied regions correlate clearly nega- tively with latitude and positively with temperature, indicating that these values can be used as excel- lent indicators of environment and climate. These results provide important basic data for under- standing the distributional law of hydrogen isotopes of individual n-alkanes and their applied research.
