[目的]评价黄河下游水资源生态承载状态,为地区水资源管理与规划提供理论依据。[方法]运用水资源生态足迹理论结合对数均值迪式指数分解法(logarithmic mean divisia index,LMDI)对2007—2020年黄河下游水资源生态足迹的时空分布特征及...[目的]评价黄河下游水资源生态承载状态,为地区水资源管理与规划提供理论依据。[方法]运用水资源生态足迹理论结合对数均值迪式指数分解法(logarithmic mean divisia index,LMDI)对2007—2020年黄河下游水资源生态足迹的时空分布特征及驱动机制进行核算分析,并通过灰色预测模型GM(1,1)对2021—2030年的水资源生态足迹变化趋势进行预测。[结果]黄河下游历年水资源生态足迹远高于生态承载力,水资源生态赤字现象严重;水资源生态足迹与生态赤字年际间均呈波动降低趋势,用水效率逐渐提高,农业用水是最大的水资源生态足迹账户;黄河三角洲是黄河下游水资源生态压力最大的区域,淄博、济南、郑州和泰安4市的生态压力相对较小;经济效应对黄河下游水资源生态足迹变化起正向主导作用,技术效应起负向主导作用;预测结果表明,2021—2030年黄河下游人均水资源生态赤字由0.387 hm^(2)/人降至0.359 hm^(2)/人。[结论]在生产力快速发展和用水结构优化调整等综合作用下,黄河下游地区用水效率逐渐提高,水资源生态压力有一定幅度的缓解。但由于该区域水资源生态赤字基数较大,未来水资源可持续利用形势依旧十分严峻,亟待进一步加强水资源的统筹管理,助力黄河下游地区高质量可持续发展。展开更多
随着海平面上升和人类活动加剧,潮滩正面临着严重威胁,掌握其形态变化规律是研究潮滩系统对外在条件响应的直接手段。以江苏斗龙港潮滩为研究对象,利用无人机倾斜摄影测量技术,结合运动恢复结构(Structure from Motion,SfM)算法,重建潮...随着海平面上升和人类活动加剧,潮滩正面临着严重威胁,掌握其形态变化规律是研究潮滩系统对外在条件响应的直接手段。以江苏斗龙港潮滩为研究对象,利用无人机倾斜摄影测量技术,结合运动恢复结构(Structure from Motion,SfM)算法,重建潮滩三维点云,生成数字高程模型和正射影像,分析潮滩滩面及潮沟系统年内变化规律。研究结果表明:潮滩高程测量精度优于9 cm,水平精度优于2 cm;高程年内变化较大,变幅高达±0.5 m;潮沟短历时变化剧烈,无明显季节性变化特征;潮沟发育过程中,宽深比范围为10~25。无人机技术不仅可以监测粉砂淤泥质潮滩滩面变化趋势,还可以观测到卫星难以捕获的中小型潮沟短历时发育过程,可为监测河口海岸短周期动力地貌过程提供有力的技术支持。展开更多
公司创业投资是公司创业、创业投资、战略管理和创新等多个领域的关键话题。文章在概括1980—2020年Web of Science数据库收录的公司创业投资文献特征的基础上,追溯公司创业投资内涵与定义的发展,梳理和提炼该领域研究的主题内容。文章...公司创业投资是公司创业、创业投资、战略管理和创新等多个领域的关键话题。文章在概括1980—2020年Web of Science数据库收录的公司创业投资文献特征的基础上,追溯公司创业投资内涵与定义的发展,梳理和提炼该领域研究的主题内容。文章将公司创业投资研究划分为初始萌芽、平稳发展和深化发展三个阶段,系统归纳分析了公司创业投资的目标与动机、影响因素、绩效效应以及其与其他公司创业方式的关系四个主题的研究内容。最后,在评述现有研究进展和不足的基础上,展望公司创业投资研究的未来方向。展开更多
It is common to obtain the topography of tidal flats by the Unmanned Aerial Vehicle(UAV)photogrammetry,but this method is not applicable in tidal creeks.The residual water will lead to inaccurate depth inversion resul...It is common to obtain the topography of tidal flats by the Unmanned Aerial Vehicle(UAV)photogrammetry,but this method is not applicable in tidal creeks.The residual water will lead to inaccurate depth inversion results,and the topography of tidal creeks mainly depends on manual survey.The present study took the tidal creek of Chuandong port in Jiangsu Province,China,as the research area and used UAV oblique photogrammetry to reconstruct the topography of the exposed part above the water after the ebb tide.It also proposed a Trend Prediction Fitting(TPF)method for the topography of the unexposed part below the water to obtain a complete 3D topography.The topography above the water measured by UAV has the vertical precision of 12 cm.When the TPF method is used,the cross-section should be perpendicular the central axis of the tidal creek.A polynomial function can be adapted to most shape of sections,while a Fourier function obtains better results in asymmetrical sections.Compared with the two-order function,the three-order function lends itself to more complex sections.Generally,the TPF method is more suitable for small,straight tidal creeks with clear texture and no vegetation cover.展开更多
文摘公司创业投资是公司创业、创业投资、战略管理和创新等多个领域的关键话题。文章在概括1980—2020年Web of Science数据库收录的公司创业投资文献特征的基础上,追溯公司创业投资内涵与定义的发展,梳理和提炼该领域研究的主题内容。文章将公司创业投资研究划分为初始萌芽、平稳发展和深化发展三个阶段,系统归纳分析了公司创业投资的目标与动机、影响因素、绩效效应以及其与其他公司创业方式的关系四个主题的研究内容。最后,在评述现有研究进展和不足的基础上,展望公司创业投资研究的未来方向。
基金China National Funds for Distinguished Young Scientists,No.51925905National Natural Science Foundation of China,No.41401371。
文摘It is common to obtain the topography of tidal flats by the Unmanned Aerial Vehicle(UAV)photogrammetry,but this method is not applicable in tidal creeks.The residual water will lead to inaccurate depth inversion results,and the topography of tidal creeks mainly depends on manual survey.The present study took the tidal creek of Chuandong port in Jiangsu Province,China,as the research area and used UAV oblique photogrammetry to reconstruct the topography of the exposed part above the water after the ebb tide.It also proposed a Trend Prediction Fitting(TPF)method for the topography of the unexposed part below the water to obtain a complete 3D topography.The topography above the water measured by UAV has the vertical precision of 12 cm.When the TPF method is used,the cross-section should be perpendicular the central axis of the tidal creek.A polynomial function can be adapted to most shape of sections,while a Fourier function obtains better results in asymmetrical sections.Compared with the two-order function,the three-order function lends itself to more complex sections.Generally,the TPF method is more suitable for small,straight tidal creeks with clear texture and no vegetation cover.
