This study utilizes panel data from 293 Chinese cities at the prefecture level or above,spanning from 2013 to 2022,to empirically examine the net effects and underlying mechanisms of establishing pilot free trade zone...This study utilizes panel data from 293 Chinese cities at the prefecture level or above,spanning from 2013 to 2022,to empirically examine the net effects and underlying mechanisms of establishing pilot free trade zones(FTZs)on integration into the digital global value chain(DGVC).The results demonstrate that the establishment of pilot FTZs positively promotes integration into the DGVC and generates a spatial spillover effect.Compared to coastal areas and small-and medium-sized cities,pilot FTZs have a more significant impact on the integration of inland regions and large cities into the DGVC.Mechanism tests reveal that pilot FTZs drive integration into the DGVC primarily by promoting digital industry agglomeration and enhancing the technological content of exports.Furthermore,bilateral foreign direct investment and digital trade rules positively amplify the impact of pilot FTZs on integration into the DGVC.Therefore,this study recommends comprehensively deepening the development of pilot FTZs,consistently enhancing the technological content of exports,and proactively establishing a sound digital trade regulatory framework.These recommendations offer valuable insights for DGVC integration and the construction of a high-standard free trade network.展开更多
Validation studies of global Digital Elevation Models(DEMs)in the existing literature are limited by the diversity and spread of landscapes,terrain types considered and sparseness of groundtruth.Moreover,there are kno...Validation studies of global Digital Elevation Models(DEMs)in the existing literature are limited by the diversity and spread of landscapes,terrain types considered and sparseness of groundtruth.Moreover,there are knowledge gaps on the accuracy variations in rugged and complex landscapes,and previous studies have often not relied on robust internal and external validation measures.Thus,there is still only partial understanding and limited perspective of the reliability and adequacy of global DEMs for several applications.In this study,we utilize a dense spread of LiDAR groundtruth to assess the vertical accuracies of four medium-resolution,readily available,free-access and global coverage 1 arc-second(30 m)DEMs:NASADEM,ASTER GDEM,Copernicus GLO-30,and ALOS World 3D(AW3D).The assessment is carried out at landscapes spread across Cape Town,Southern Africa(urban/industrial,agricultural,mountain,peninsula and grassland/shrubland)and forested national parks in Gabon,Central Africa(low-relief tropical rainforest and high-relief tropical rainforest).The statistical analysis is based on robust accuracy metrics that cater for normal and non-normal elevation error distribution,and error ranking.In Cape Town,Copernicus DEM generally had the least vertical error with an overall Mean Error(ME)of 0.82 m and Root Mean Square Error(RMSE)of 2.34 m while ASTER DEM had the poorest performance.However,ASTER GDEM and NASADEM performed better in the low-relief and high-relief tropical forests of Gabon.Generally,the DEM errors have a moderate to high positive correlation in forests,and a low to moderate positive correlation in mountains and urban areas.Copernicus DEM showed superior vertical accuracy in forests with less than 40%tree cover,while ASTER and NASADEM performed better in denser forests with tree cover greater than 70%.This study is a robust regional assessment of these global DEMs.展开更多
Tropical mountainous areas not only provide substantial carbon storage and play an important role in global biological diversity, but also provide basic livelihood for a large number of poor ethnic minorities. However...Tropical mountainous areas not only provide substantial carbon storage and play an important role in global biological diversity, but also provide basic livelihood for a large number of poor ethnic minorities. However, there is no unified and explicit definition for mountainous areas. The local elevation range(LER) is a crucial structural parameter for delineating mountainous areas. However, current LER products are limited by the subjective selection of an optimum statistical window or coarser spatial resolution of topographical data. In this study, we presented an approach using thresholds for three topographic parameters, elevation, slope, and LER, derived from the Advanced Spaceborne Thermal Emission and Reflection Radiometer Global Digital Elevation Model(ASTER GDEM) to redelineate the vast mountainous areas of mainland Southeast Asia(MSEA). The mean change-point analysis method was applied to determine the optimum statistical window of the 1 arc second(approximately 30 m)-resolution GDEM LER. The results showed that: First, the optimum statistical window is 38 × 38 cell units(width × height) in a rectangular neighborhood, or an area of about 1.30 km^2 for calculating GDEM LER in MSEA. Second, the LER of more than 80% of the area ranges from 30 m to 499 m in MSEA. The LERs in the northern and northwestern MSEA are greater than their counterparts in the south and east. Third, the area of the re-delineated mountainous areas was 83.52 × 10~4 km^2, about 38.71% of the total area. Spatially, the mountainous areas are mainly distributed in the north and northeast of MSEA. The re-delineated 30-m resolution map of the mountainous areas will serve as a topographical dataset for monitoring mountainrelated land surface changes in MSEA. The parameter-modified mountain extraction procedure can be expanded to delineate global mountainous areas.展开更多
Global solar radiation（GSR） is the most direct source and form of global energy, and calculation of its quantity is highly complex due to influences of local topography and terrain inter-shielding. Digital elevation...Global solar radiation（GSR） is the most direct source and form of global energy, and calculation of its quantity is highly complex due to influences of local topography and terrain inter-shielding. Digital elevation model（DEM） data as a representation of the complex terrain and multiplicity condition produces a series of topographic factors（e.g. slope, aspect, etc.）. Based on 1 km resolution DEM data, meteorological observations and NOAA-AVHRR remote sensing data, a distributed model for the calculation of GSR over rugged terrain within the Yangtze River Basin has been developed. The overarching model permits calculation of astronomical solar radiation for rugged topography and comprises a distributed direct solar radiation model, a distributed diffuse radiation model and a distributed terrain reflectance radiation model. Using the developed model, a quantitative simulation of the GSR space distribution and visualization has been undertaken, with results subsequently analyzed with respect to locality and terrain. Analyses suggest that GSR magnitude is seasonally affected, while the degree of influence was found to increase in concurrence with increasing altitude. Moreover, GSR magnitude exhibited clear spatial variation with respect to the dominant local aspect; GSR values associated with the sunny southern slopes were significantly greater than those associated with shaded slopes. Error analysis indicates a mean absolute error of 12.983 MJm-2 and a mean relative error of 3.608%, while the results based on a site authentication procedure display an absolute error of 22.621 MJm-2 and a relative error of 4.626%.展开更多
We know that SME’s that trade online grow faster and create more jobs than those that only operate in their domestic markets.The Internet is breaking down many traditional barriers to global trade,but there is still ...We know that SME’s that trade online grow faster and create more jobs than those that only operate in their domestic markets.The Internet is breaking down many traditional barriers to global trade,but there is still much governments can do to speed and enable SME digitization and ecommerce.The opportunity is huge at展开更多
The propagation of the lightning-radiated electromagnetic field along the real irregular terrain around Yangzhou Direction Finder(DF)site(119°42′E,32°39′N)and Nanjing DF site(118°46′E,32°03′N)o...The propagation of the lightning-radiated electromagnetic field along the real irregular terrain around Yangzhou Direction Finder(DF)site(119°42′E,32°39′N)and Nanjing DF site(118°46′E,32°03′N)of Jiangsu Province in China is estimated.The results show that the rough irregular terrain results in the rapid magnitude attenuation and the increase of the rise-time of the field waveform.For example,for the Yangzhou DF site as the circumference of a radius of 45 km,the root-mean-squared height(RMSH)of the real irregular terrain varies from 7 to 33 m;the extra field attenuation relative to the ideal ground surface ranges from 1%to 11%,and the extra rise-time increment varies from 0.1 to 0.6μs.Therefore,the extracted current peak of lightning return stroke may be underestimated from the remotely measured electromagnetic field,and the error varies along with different azimuths.展开更多
基金supported by the Key Project of the Hainan Province Marxist Theory Research and Development Program,titled“Research on the Opportunities and Challenges of the Digital Economy Partnership Agreement(DEPA)for the Construction of the Hainan Free Trade Port”(Grant Number:2023HNMGC02).
文摘This study utilizes panel data from 293 Chinese cities at the prefecture level or above,spanning from 2013 to 2022,to empirically examine the net effects and underlying mechanisms of establishing pilot free trade zones(FTZs)on integration into the digital global value chain(DGVC).The results demonstrate that the establishment of pilot FTZs positively promotes integration into the DGVC and generates a spatial spillover effect.Compared to coastal areas and small-and medium-sized cities,pilot FTZs have a more significant impact on the integration of inland regions and large cities into the DGVC.Mechanism tests reveal that pilot FTZs drive integration into the DGVC primarily by promoting digital industry agglomeration and enhancing the technological content of exports.Furthermore,bilateral foreign direct investment and digital trade rules positively amplify the impact of pilot FTZs on integration into the DGVC.Therefore,this study recommends comprehensively deepening the development of pilot FTZs,consistently enhancing the technological content of exports,and proactively establishing a sound digital trade regulatory framework.These recommendations offer valuable insights for DGVC integration and the construction of a high-standard free trade network.
基金supported by the(i)Commonwealth Scholarship Commission and the Foreign,Commonwealth and Development Office in the UK[Grant number NGCN-2021-239](ii)University of Cape Town Postgraduate Funding Office.
文摘Validation studies of global Digital Elevation Models(DEMs)in the existing literature are limited by the diversity and spread of landscapes,terrain types considered and sparseness of groundtruth.Moreover,there are knowledge gaps on the accuracy variations in rugged and complex landscapes,and previous studies have often not relied on robust internal and external validation measures.Thus,there is still only partial understanding and limited perspective of the reliability and adequacy of global DEMs for several applications.In this study,we utilize a dense spread of LiDAR groundtruth to assess the vertical accuracies of four medium-resolution,readily available,free-access and global coverage 1 arc-second(30 m)DEMs:NASADEM,ASTER GDEM,Copernicus GLO-30,and ALOS World 3D(AW3D).The assessment is carried out at landscapes spread across Cape Town,Southern Africa(urban/industrial,agricultural,mountain,peninsula and grassland/shrubland)and forested national parks in Gabon,Central Africa(low-relief tropical rainforest and high-relief tropical rainforest).The statistical analysis is based on robust accuracy metrics that cater for normal and non-normal elevation error distribution,and error ranking.In Cape Town,Copernicus DEM generally had the least vertical error with an overall Mean Error(ME)of 0.82 m and Root Mean Square Error(RMSE)of 2.34 m while ASTER DEM had the poorest performance.However,ASTER GDEM and NASADEM performed better in the low-relief and high-relief tropical forests of Gabon.Generally,the DEM errors have a moderate to high positive correlation in forests,and a low to moderate positive correlation in mountains and urban areas.Copernicus DEM showed superior vertical accuracy in forests with less than 40%tree cover,while ASTER and NASADEM performed better in denser forests with tree cover greater than 70%.This study is a robust regional assessment of these global DEMs.
基金supported by the Strategic Priority Research Program of Chinese Academy of Sciences (Grant No. XDA20010203)
文摘Tropical mountainous areas not only provide substantial carbon storage and play an important role in global biological diversity, but also provide basic livelihood for a large number of poor ethnic minorities. However, there is no unified and explicit definition for mountainous areas. The local elevation range(LER) is a crucial structural parameter for delineating mountainous areas. However, current LER products are limited by the subjective selection of an optimum statistical window or coarser spatial resolution of topographical data. In this study, we presented an approach using thresholds for three topographic parameters, elevation, slope, and LER, derived from the Advanced Spaceborne Thermal Emission and Reflection Radiometer Global Digital Elevation Model(ASTER GDEM) to redelineate the vast mountainous areas of mainland Southeast Asia(MSEA). The mean change-point analysis method was applied to determine the optimum statistical window of the 1 arc second(approximately 30 m)-resolution GDEM LER. The results showed that: First, the optimum statistical window is 38 × 38 cell units(width × height) in a rectangular neighborhood, or an area of about 1.30 km^2 for calculating GDEM LER in MSEA. Second, the LER of more than 80% of the area ranges from 30 m to 499 m in MSEA. The LERs in the northern and northwestern MSEA are greater than their counterparts in the south and east. Third, the area of the re-delineated mountainous areas was 83.52 × 10~4 km^2, about 38.71% of the total area. Spatially, the mountainous areas are mainly distributed in the north and northeast of MSEA. The re-delineated 30-m resolution map of the mountainous areas will serve as a topographical dataset for monitoring mountainrelated land surface changes in MSEA. The parameter-modified mountain extraction procedure can be expanded to delineate global mountainous areas.
基金National Natural Science Foundation of China,No.41175077 National Natural Science Foundation for Young Scholars,No.S0508016001 Guizhou Branch Major Projects[2011],No.6003
文摘Global solar radiation（GSR） is the most direct source and form of global energy, and calculation of its quantity is highly complex due to influences of local topography and terrain inter-shielding. Digital elevation model（DEM） data as a representation of the complex terrain and multiplicity condition produces a series of topographic factors（e.g. slope, aspect, etc.）. Based on 1 km resolution DEM data, meteorological observations and NOAA-AVHRR remote sensing data, a distributed model for the calculation of GSR over rugged terrain within the Yangtze River Basin has been developed. The overarching model permits calculation of astronomical solar radiation for rugged topography and comprises a distributed direct solar radiation model, a distributed diffuse radiation model and a distributed terrain reflectance radiation model. Using the developed model, a quantitative simulation of the GSR space distribution and visualization has been undertaken, with results subsequently analyzed with respect to locality and terrain. Analyses suggest that GSR magnitude is seasonally affected, while the degree of influence was found to increase in concurrence with increasing altitude. Moreover, GSR magnitude exhibited clear spatial variation with respect to the dominant local aspect; GSR values associated with the sunny southern slopes were significantly greater than those associated with shaded slopes. Error analysis indicates a mean absolute error of 12.983 MJm-2 and a mean relative error of 3.608%, while the results based on a site authentication procedure display an absolute error of 22.621 MJm-2 and a relative error of 4.626%.
文摘We know that SME’s that trade online grow faster and create more jobs than those that only operate in their domestic markets.The Internet is breaking down many traditional barriers to global trade,but there is still much governments can do to speed and enable SME digitization and ecommerce.The opportunity is huge at
基金Supported by the Application of the Forecasting Warning System for Lightning Disaster in Yunan Plateau(YNKJXM20190733)National Natural Science Foundation of China(41775006,41575004).
文摘The propagation of the lightning-radiated electromagnetic field along the real irregular terrain around Yangzhou Direction Finder(DF)site(119°42′E,32°39′N)and Nanjing DF site(118°46′E,32°03′N)of Jiangsu Province in China is estimated.The results show that the rough irregular terrain results in the rapid magnitude attenuation and the increase of the rise-time of the field waveform.For example,for the Yangzhou DF site as the circumference of a radius of 45 km,the root-mean-squared height(RMSH)of the real irregular terrain varies from 7 to 33 m;the extra field attenuation relative to the ideal ground surface ranges from 1%to 11%,and the extra rise-time increment varies from 0.1 to 0.6μs.Therefore,the extracted current peak of lightning return stroke may be underestimated from the remotely measured electromagnetic field,and the error varies along with different azimuths.
