Here,we quantitatively determine temporal and spatial distribution characteristics of main grain crops in the West Liaohe River basin,Inner Mongolia,China,from 2000 to 2010 based on MODIS remote sensing data and NDVI ...Here,we quantitatively determine temporal and spatial distribution characteristics of main grain crops in the West Liaohe River basin,Inner Mongolia,China,from 2000 to 2010 based on MODIS remote sensing data and NDVI time series information for the years 2000,2005 and 2010.Phenological calendars and a decisionmaking tree extraction model were also used to obtain spatial distribution information of spring maize,spring wheat and soybean.We found that in 2010,the sown area of the main grain crops in the West Liaohe River basin was 11 965.08km2,of which,the sown area for spring maize accounted for 92.28%and was concentrated in the lower reaches of the region.Spring wheat accounted for 3.14% and was mainly in the middle reaches.Soybean accounted for 4.58% and was predominantly in the upper reaches.From 2000 to 2005,the sown area of these grain crops in the West Liaohe River basin grew by 29.77%,mainly in the lower reaches： spring maize grew by 38.99%,spring wheat by 39.04% and soybean by 21.27%.From 2005 to 2010,growth in the sown area of these crops was slow（5.18% growth） and mainly in the lower reaches of the basin.The sown area of spring maize increased,but decreased for both spring wheat and soybean.展开更多
[Objective] Study on the spatial distribution of summer precipitation patterns and interannual and interdecadal variability. [Method] The summer precipitation patterns were obtained from standard field of summer preci...[Objective] Study on the spatial distribution of summer precipitation patterns and interannual and interdecadal variability. [Method] The summer precipitation patterns were obtained from standard field of summer precipitation data for 160 observation stations in China during 1951 -2000 by the utilization of empirical orthogonal function （EOF）, and characteristics of interannual and interdecadal variability were analyzed. [Result] The summer precipitation mainly distributes in eastern part of China; The 1 st, 2nd and 3rd EOF modes of spatial distribution are especially remarkable as well consistent with the results of previous reports about three rainfall patterns from analysis on the percentages of precipitation anomaly of summer. [Conclusion] There exists interannual and interdecadal variability for summer precipitation in China.展开更多
Travel time through a ring road with a total length of 80 km has been predicted by a viscoelastic traffic model(VEM), which is developed in analogous to the non-Newtonian fluid flow. The VEM expresses a traffic pressu...Travel time through a ring road with a total length of 80 km has been predicted by a viscoelastic traffic model(VEM), which is developed in analogous to the non-Newtonian fluid flow. The VEM expresses a traffic pressure for the unfree flow case by space headway, ensuring that the pressure can be determined by the assumption that the relevant second critical sound speed is exactly equal to the disturbance propagation speed determined by the free flow speed and the braking distance measured by the average vehicular length. The VEM assumes that the sound speed for the free flow case depends on the traffic density in some specific aspects, which ensures that it is exactly identical to the free flow speed on an empty road. To make a comparison, the open Navier-Stokes type model developed by Zhang(ZHANG, H. M. Driver memory, traffic viscosity and a viscous vehicular traffic flow model. Transp. Res. Part B, 37, 27–41(2003)) is adopted to predict the travel time through the ring road for providing the counterpart results.When the traffic free flow speed is 80 km/h, the braking distance is supposed to be 45 m,with the jam density uniquely determined by the average length of vehicles l ≈ 5.8 m. To avoid possible singular points in travel time prediction, a distinguishing period for time averaging is pre-assigned to be 7.5 minutes. It is found that the travel time increases monotonically with the initial traffic density on the ring road. Without ramp effects, for the ring road with the initial density less than the second critical density, the travel time can be simply predicted by using the equilibrium speed. However, this simpler approach is unavailable for scenarios over the second critical.展开更多
山地植被垂直变化和分布历来是山地生态学研究的重点内容。本文从文献计量统计和文献分析两个方面,对山地植被的垂直分布格局研究进展进行了述评。文献统计分析主要基于CNKI和Web of Science数据库平台,检索了该研究领域1915年1月至2020...山地植被垂直变化和分布历来是山地生态学研究的重点内容。本文从文献计量统计和文献分析两个方面,对山地植被的垂直分布格局研究进展进行了述评。文献统计分析主要基于CNKI和Web of Science数据库平台,检索了该研究领域1915年1月至2020年12月的国内外期刊论文,分析了山地植被垂直格局的研究历程、现状、进展和趋势。结果表明:国内外研究的文献、作者、国家和机构数量均呈增长趋势,全球范围的研究主要涵盖了美国、德国、中国、西班牙和法国等85个国家,共计34.7%的文献集中在25个主要期刊。基于CiteSpace进行文献关键词共现聚类,分析了国内外山地植被垂直分布的热点领域,并对理论与假说、研究方法和主要研究领域等进行了述评。山地植被垂直格局历经了从单因子描述、多因子分析到机理和假说的求证,代表性理论包括:时间学说、空间异质性学说、竞争共存理论、中性理论及生态位理论等;从传统研究方法、数量分类与环境解释、遥感影像信息技术、模型及数字信息技术等进行了研究方法概述;并对热点研究领域进行了分析和述评,主要包括:山地植被垂直分布与驱动因素、山地植被生产力垂直变化、植物群落的谱系结构、基于生态位理论的植被分布预测等。总之,在全球气候变化背景下,山地植被及生态系统响应敏感且变化剧烈,山地植被对气候变化的响应、植被垂直带谱的数字信息化、水土耦合下的山地生态循环与生态系统服务等领域受到更广泛的重视;多尺度、多学科融合是本领域研究的发展趋势。展开更多
基金National Natural Science Foundation of China(41271541)
文摘Here,we quantitatively determine temporal and spatial distribution characteristics of main grain crops in the West Liaohe River basin,Inner Mongolia,China,from 2000 to 2010 based on MODIS remote sensing data and NDVI time series information for the years 2000,2005 and 2010.Phenological calendars and a decisionmaking tree extraction model were also used to obtain spatial distribution information of spring maize,spring wheat and soybean.We found that in 2010,the sown area of the main grain crops in the West Liaohe River basin was 11 965.08km2,of which,the sown area for spring maize accounted for 92.28%and was concentrated in the lower reaches of the region.Spring wheat accounted for 3.14% and was mainly in the middle reaches.Soybean accounted for 4.58% and was predominantly in the upper reaches.From 2000 to 2005,the sown area of these grain crops in the West Liaohe River basin grew by 29.77%,mainly in the lower reaches： spring maize grew by 38.99%,spring wheat by 39.04% and soybean by 21.27%.From 2005 to 2010,growth in the sown area of these crops was slow（5.18% growth） and mainly in the lower reaches of the basin.The sown area of spring maize increased,but decreased for both spring wheat and soybean.
文摘[Objective] Study on the spatial distribution of summer precipitation patterns and interannual and interdecadal variability. [Method] The summer precipitation patterns were obtained from standard field of summer precipitation data for 160 observation stations in China during 1951 -2000 by the utilization of empirical orthogonal function （EOF）, and characteristics of interannual and interdecadal variability were analyzed. [Result] The summer precipitation mainly distributes in eastern part of China; The 1 st, 2nd and 3rd EOF modes of spatial distribution are especially remarkable as well consistent with the results of previous reports about three rainfall patterns from analysis on the percentages of precipitation anomaly of summer. [Conclusion] There exists interannual and interdecadal variability for summer precipitation in China.
基金Project supported by the Russian Foundation for Basic Research(No.18-07-00518)the National Natural Science Foundation of China(No.10972212)
文摘Travel time through a ring road with a total length of 80 km has been predicted by a viscoelastic traffic model(VEM), which is developed in analogous to the non-Newtonian fluid flow. The VEM expresses a traffic pressure for the unfree flow case by space headway, ensuring that the pressure can be determined by the assumption that the relevant second critical sound speed is exactly equal to the disturbance propagation speed determined by the free flow speed and the braking distance measured by the average vehicular length. The VEM assumes that the sound speed for the free flow case depends on the traffic density in some specific aspects, which ensures that it is exactly identical to the free flow speed on an empty road. To make a comparison, the open Navier-Stokes type model developed by Zhang(ZHANG, H. M. Driver memory, traffic viscosity and a viscous vehicular traffic flow model. Transp. Res. Part B, 37, 27–41(2003)) is adopted to predict the travel time through the ring road for providing the counterpart results.When the traffic free flow speed is 80 km/h, the braking distance is supposed to be 45 m,with the jam density uniquely determined by the average length of vehicles l ≈ 5.8 m. To avoid possible singular points in travel time prediction, a distinguishing period for time averaging is pre-assigned to be 7.5 minutes. It is found that the travel time increases monotonically with the initial traffic density on the ring road. Without ramp effects, for the ring road with the initial density less than the second critical density, the travel time can be simply predicted by using the equilibrium speed. However, this simpler approach is unavailable for scenarios over the second critical.
文摘山地植被垂直变化和分布历来是山地生态学研究的重点内容。本文从文献计量统计和文献分析两个方面,对山地植被的垂直分布格局研究进展进行了述评。文献统计分析主要基于CNKI和Web of Science数据库平台,检索了该研究领域1915年1月至2020年12月的国内外期刊论文,分析了山地植被垂直格局的研究历程、现状、进展和趋势。结果表明:国内外研究的文献、作者、国家和机构数量均呈增长趋势,全球范围的研究主要涵盖了美国、德国、中国、西班牙和法国等85个国家,共计34.7%的文献集中在25个主要期刊。基于CiteSpace进行文献关键词共现聚类,分析了国内外山地植被垂直分布的热点领域,并对理论与假说、研究方法和主要研究领域等进行了述评。山地植被垂直格局历经了从单因子描述、多因子分析到机理和假说的求证,代表性理论包括:时间学说、空间异质性学说、竞争共存理论、中性理论及生态位理论等;从传统研究方法、数量分类与环境解释、遥感影像信息技术、模型及数字信息技术等进行了研究方法概述;并对热点研究领域进行了分析和述评,主要包括:山地植被垂直分布与驱动因素、山地植被生产力垂直变化、植物群落的谱系结构、基于生态位理论的植被分布预测等。总之,在全球气候变化背景下,山地植被及生态系统响应敏感且变化剧烈,山地植被对气候变化的响应、植被垂直带谱的数字信息化、水土耦合下的山地生态循环与生态系统服务等领域受到更广泛的重视;多尺度、多学科融合是本领域研究的发展趋势。
