Fine root turnover plays a key role in carbon （C） budgets and nutrients cycles in forest ecosystems. However, the difference between branch-order-based and diameter-based approaches in estimating fine root turnover ...Fine root turnover plays a key role in carbon （C） budgets and nutrients cycles in forest ecosystems. However, the difference between branch-order-based and diameter-based approaches in estimating fine root turnover is still unclear. We studied root biomass turnover based on multiplying root standing biomass by turnover rate （inverse of median root longevity） in two Chinese temperate tree species, Fraxinus mand- shurica Rupr. and Larix gmelinii Rupr. The minirhizotron （MR） tech- nique was used to estimate longevities for first and second order roots, and total roots （R,o,al） apparent on the MR tube surface. The correspond- ing biomass for each root group was estimated by soil monolith. The difference in biomass turnover between Rtotal and the sum of the first and second order roots was used to represent the discrepancy between di- ameter- and order-based approaches. First order roots had shorter life spans and higher biomass turnover rates than the second order roots in both species. Biomass turnover estimated by the order-based method for F. mandshurica and L. gmelinii were 155.4 g.m2.aland 158.9 g.m2.a-1, respectively, in comparison with 99.5 g.m^-2-a^-1 and 117.7 g.m^-2.a^-1 estimated by the diameter-based method, indicating that the diameter-based approach underestimated biomass turnover. The most probable reason was that the order-based method enhanced separation of the heterogeneous root population into relatively homogenous root groups with varying turnover rates. We conclude that separating fine root pool into different branch orders can improve the accuracy of estimates for fine root turnover, as well as the understanding of the belowground C allocation and nutrient cycling at ecosystem level.展开更多
As far as the weight digraph is considered, based on the table instead of the weightdigraph, an optimal spanning tree method called the Table Operations Method (TOM) is proposed.And the optimality is proved and a nume...As far as the weight digraph is considered, based on the table instead of the weightdigraph, an optimal spanning tree method called the Table Operations Method (TOM) is proposed.And the optimality is proved and a numerical example is demonstrated.展开更多
文章提出了一种基于旋转成像平台的作物根系三维重构方法,用于实现高通量、低成本的作物根系表型特征采集。首先利用基于多视图立体视觉的运动恢复结构(Structure from Motion with Multi View Stereo,SFM-MVS)算法将一组图像生成根系...文章提出了一种基于旋转成像平台的作物根系三维重构方法,用于实现高通量、低成本的作物根系表型特征采集。首先利用基于多视图立体视觉的运动恢复结构(Structure from Motion with Multi View Stereo,SFM-MVS)算法将一组图像生成根系稠密点云,其次采用Dijkstra最小生成树算法实现对根系骨架的初始化,再次经过简化和平滑处理后提取出根系三维骨架模型,最后通过圆柱体拟合算法和蒙皮渲染技术实现作物根系的三维重构。结果表明,由该方法构建的作物根系三维模型可以较好地体现作物根系表型特征,与手工测量值对比相对误差在5%以内。展开更多
在500 k V变电构架的设计中,目前国内人字形构架柱和单钢管悬臂支架柱应用较为成熟,角钢格构式变电构架应用较少。在海外工程中,角钢运输具有较大优势。结合实际工程,以埃塞俄比亚某500 k V变电构架为实例,通过根开的有效组合,对21种不...在500 k V变电构架的设计中,目前国内人字形构架柱和单钢管悬臂支架柱应用较为成熟,角钢格构式变电构架应用较少。在海外工程中,角钢运输具有较大优势。结合实际工程,以埃塞俄比亚某500 k V变电构架为实例,通过根开的有效组合,对21种不同根开的变电构架进行了全面的计算,以用钢量和混凝土用量为依据进行工程造价比较分析,得出了类似工程条件下的最优根开,以指导工程设计。当构架柱高约为30 m时,结合构架所处地理位置气候等条件,最优根开建议值为6.1 m×3.1 m,即长向根开约取为柱高的1/5,短向根开约取为柱高的1/10时,结构整体力学性能较好且最为经济。展开更多
基金supported by the grants of the National Natural Science Foundation of China (No. 31100470)the Ministry of Science and Technology of China (No. 2011BAD37B02-2)
文摘Fine root turnover plays a key role in carbon （C） budgets and nutrients cycles in forest ecosystems. However, the difference between branch-order-based and diameter-based approaches in estimating fine root turnover is still unclear. We studied root biomass turnover based on multiplying root standing biomass by turnover rate （inverse of median root longevity） in two Chinese temperate tree species, Fraxinus mand- shurica Rupr. and Larix gmelinii Rupr. The minirhizotron （MR） tech- nique was used to estimate longevities for first and second order roots, and total roots （R,o,al） apparent on the MR tube surface. The correspond- ing biomass for each root group was estimated by soil monolith. The difference in biomass turnover between Rtotal and the sum of the first and second order roots was used to represent the discrepancy between di- ameter- and order-based approaches. First order roots had shorter life spans and higher biomass turnover rates than the second order roots in both species. Biomass turnover estimated by the order-based method for F. mandshurica and L. gmelinii were 155.4 g.m2.aland 158.9 g.m2.a-1, respectively, in comparison with 99.5 g.m^-2-a^-1 and 117.7 g.m^-2.a^-1 estimated by the diameter-based method, indicating that the diameter-based approach underestimated biomass turnover. The most probable reason was that the order-based method enhanced separation of the heterogeneous root population into relatively homogenous root groups with varying turnover rates. We conclude that separating fine root pool into different branch orders can improve the accuracy of estimates for fine root turnover, as well as the understanding of the belowground C allocation and nutrient cycling at ecosystem level.
文摘As far as the weight digraph is considered, based on the table instead of the weightdigraph, an optimal spanning tree method called the Table Operations Method (TOM) is proposed.And the optimality is proved and a numerical example is demonstrated.
文摘文章提出了一种基于旋转成像平台的作物根系三维重构方法,用于实现高通量、低成本的作物根系表型特征采集。首先利用基于多视图立体视觉的运动恢复结构(Structure from Motion with Multi View Stereo,SFM-MVS)算法将一组图像生成根系稠密点云,其次采用Dijkstra最小生成树算法实现对根系骨架的初始化,再次经过简化和平滑处理后提取出根系三维骨架模型,最后通过圆柱体拟合算法和蒙皮渲染技术实现作物根系的三维重构。结果表明,由该方法构建的作物根系三维模型可以较好地体现作物根系表型特征,与手工测量值对比相对误差在5%以内。
文摘在500 k V变电构架的设计中,目前国内人字形构架柱和单钢管悬臂支架柱应用较为成熟,角钢格构式变电构架应用较少。在海外工程中,角钢运输具有较大优势。结合实际工程,以埃塞俄比亚某500 k V变电构架为实例,通过根开的有效组合,对21种不同根开的变电构架进行了全面的计算,以用钢量和混凝土用量为依据进行工程造价比较分析,得出了类似工程条件下的最优根开,以指导工程设计。当构架柱高约为30 m时,结合构架所处地理位置气候等条件,最优根开建议值为6.1 m×3.1 m,即长向根开约取为柱高的1/5,短向根开约取为柱高的1/10时,结构整体力学性能较好且最为经济。
