Diversity-biomass relationships(DBRs)in terrestrial ecosystems tend to vary across spatial scales,but,particularly in hyperdiverse forests,the mechanisms driving these trends remain uncertain.Until now,few have simult...Diversity-biomass relationships(DBRs)in terrestrial ecosystems tend to vary across spatial scales,but,particularly in hyperdiverse forests,the mechanisms driving these trends remain uncertain.Until now,few have simultaneously investigated the connections between tree species diversity,stand structural diversity,mycorrhizal associations,and ecosystem functioning.In addition,DBRs have only been studied at limited spatial scales,with limited focus on the direct and indirect effects of environmental factors.We addressed these research gaps using a 30-ha forest dynamics plot located in Pu'er City,Southwest China.Through piecewise structural equation models,we quantified the direct effects of tree species diversity(α,β,γ),stand structural diversity,mycorrhizal associations(AM,EcM),and the environmental factors(soil fertility and topography),as well as the indirect effects of the environmental factors on aboveground tree biomass across spatial scales ranging from 400 to 230,400 m^(2).We hypothesized that complex interactions among these factors underpin the variation in DBRs in natural ecosystems across spatial scales.Our results showed that environmental conditions indirectly affected the tree biomass via changes in tree species diversity,and these effects became stronger as the spatial scale increased.At small to moderate spatial scales,environmental factors were more predictive of tree biomass than tree species diversity(or its components);the effects of stand structural diversity on biomass also gradually increased with spatial scale.Conversely,from the intermediate to the largest spatial scales,mycorrhizal associations gradually became the best predictors of DBR dynamics.Our research offers novel empirical evidence demonstrating the importance of environmental conditions,structural diversity,and mycorrhizal associations in shaping cross-scale DBRs.Future comprehensive studies should consider these factors to assess the mechanisms shaping scale-dependent DBRs in complex natural ecosystems.展开更多
This article analyzes The Kite Runner with the help of spactial narrative. The novel will be analyzed from three angles—the function of spatial narrative, the basic unit of spatial narrative, the periphery of spatial...This article analyzes The Kite Runner with the help of spactial narrative. The novel will be analyzed from three angles—the function of spatial narrative, the basic unit of spatial narrative, the periphery of spatial narrative and the overall effect presented in the novel by using these narrative techniques.展开更多
针对在复杂背景下输电线路多尺度缺陷目标检测精度较低的问题,文中提出一种基于改进YOLOv7(You Only Look Once version 7)的输电线路多类缺陷目标检测模型。对于复杂背景造成缺陷目标较低的问题,在Backbone部分引入改进的Swin Transfor...针对在复杂背景下输电线路多尺度缺陷目标检测精度较低的问题,文中提出一种基于改进YOLOv7(You Only Look Once version 7)的输电线路多类缺陷目标检测模型。对于复杂背景造成缺陷目标较低的问题,在Backbone部分引入改进的Swin Transformer模块,通过使用多头注意力机制提升对全局特征的提取效果来提高模型的检测精度。对于待检测目标的多尺度特性,在特征金字塔基础上引入自适应特征融合模块,提升了Neck部分特征融合网络对多类不同尺度缺陷目标的检测能力。使用SIoU(Structured Intersection over Union)损失函数在提高预测框回归精度的同时加快了模型的收敛。实验结果表明,相较于YOLOv5、YOLOv7和Faster R-CNN(Faster Region with Convolutional Neural Network)模型,改进YOLOv7模型具有较高的检测精度,其平均检测精度可达96.4%,检测速度为29.6 frame·s^(-1),能够为输电线路多类缺陷目标检测提供参考。展开更多
The resolution characteristic can be obtained by the modulation transfer function （MTF） of a GaAs/GaA1As photocathode. After establishing the theoretical model of GaAs（100）-oriented atomic configuration and the fo...The resolution characteristic can be obtained by the modulation transfer function （MTF） of a GaAs/GaA1As photocathode. After establishing the theoretical model of GaAs（100）-oriented atomic configuration and the formula for the ionized impurity scattering of the non-equilibrium carriers, this paper calculates the trajectories of photoelectrons in a photocathode. Thus the distribution of photoelectron spots on the emit-face is obtained, which is namely the point spread function. The MTF is obtained by Fourier transfer of the line spread function obtained from the point spread function. The MTF obtained from these calculations is shown to depend heavily on the electron diffusion length, and enhanced considerably by decreasing the electron diffusion length and increasing the doping concentration. Furthermore, the resolution is enhanced considerably by increasing the active-layer thickness, especially at high spatial frequencies. The best spatial resolution is 860 lp/mm, for the GaAs photocathode of doping concentration 1 ×10^19 cm 3 electron diffusion length 3.6 μm and the active-layer thickness 2 μm, under the 633-nm light irradiated. This research will contribute to the future improvement of the cathode＇s resolution for preparing a high performance GaAs photocathode, and improve the resolution of a low light level image intensifier.展开更多
Spatial distribution is fundamental for understanding species coexistence mechanisms in forest communities.Here we comprehensively explored fine-scale spatial patterns of tree species in a secondary warm-temperate dec...Spatial distribution is fundamental for understanding species coexistence mechanisms in forest communities.Here we comprehensively explored fine-scale spatial patterns of tree species in a secondary warm-temperate deciduous broad-leaved forest community in north China.Aggregated distribution patterns were predominant.Species functional traits had no significant effects on their spatial patterns.The aggregation intensity decreased with increasing DBH and abundance.The multivariate linear stepwise regression showed that abundance and maximum DBH were correlated with the aggregation intensity.Our results partially confirm that species attributes(abundance,DBH)and habitat heterogeneity may primarily contribute to spatial patterns and species coexistence in this secondary forest.展开更多
The spatial resolution of a position sensitive gamma-ray detector configuration based on plastic scintillation fiber array was measured using a Monte Carlo simulation method. Both point spread function and modulation ...The spatial resolution of a position sensitive gamma-ray detector configuration based on plastic scintillation fiber array was measured using a Monte Carlo simulation method. Both point spread function and modulation transfer function (MTF) were presented. The factors that influence the spatial resolution were also discussed. The results of the simulation showed that the intrinsic spatial resolution was consistent with the size of the physical pixels and a few centimeters spatial resolution could be obtained under certain circumstances.展开更多
Formulae for determining Green strain of an initially curved and twisted rod with circular cross-sections are derived by using the natural (curvilinear) coordinate system. Finite element analyses are performed for the...Formulae for determining Green strain of an initially curved and twisted rod with circular cross-sections are derived by using the natural (curvilinear) coordinate system. Finite element analyses are performed for the flexural buckling of initially curved and twisted thin rods under simultaneous action of axial force and torque. Numerical examples demonstrate that the given formulae are correcte. Some numerical results are compared with existing analytical solutions and data obtained by commercial FE software. The convergence of the proposed curved element is better than that of elements in the commercial FE software. It is shown that good accuracy and convergency are achieved by solving three-dimensional problems.展开更多
基金funded by Fundamental Research Funds of Chinese Academy of Forestry(No.CAFYBB2021ZA002).
文摘Diversity-biomass relationships(DBRs)in terrestrial ecosystems tend to vary across spatial scales,but,particularly in hyperdiverse forests,the mechanisms driving these trends remain uncertain.Until now,few have simultaneously investigated the connections between tree species diversity,stand structural diversity,mycorrhizal associations,and ecosystem functioning.In addition,DBRs have only been studied at limited spatial scales,with limited focus on the direct and indirect effects of environmental factors.We addressed these research gaps using a 30-ha forest dynamics plot located in Pu'er City,Southwest China.Through piecewise structural equation models,we quantified the direct effects of tree species diversity(α,β,γ),stand structural diversity,mycorrhizal associations(AM,EcM),and the environmental factors(soil fertility and topography),as well as the indirect effects of the environmental factors on aboveground tree biomass across spatial scales ranging from 400 to 230,400 m^(2).We hypothesized that complex interactions among these factors underpin the variation in DBRs in natural ecosystems across spatial scales.Our results showed that environmental conditions indirectly affected the tree biomass via changes in tree species diversity,and these effects became stronger as the spatial scale increased.At small to moderate spatial scales,environmental factors were more predictive of tree biomass than tree species diversity(or its components);the effects of stand structural diversity on biomass also gradually increased with spatial scale.Conversely,from the intermediate to the largest spatial scales,mycorrhizal associations gradually became the best predictors of DBR dynamics.Our research offers novel empirical evidence demonstrating the importance of environmental conditions,structural diversity,and mycorrhizal associations in shaping cross-scale DBRs.Future comprehensive studies should consider these factors to assess the mechanisms shaping scale-dependent DBRs in complex natural ecosystems.
文摘This article analyzes The Kite Runner with the help of spactial narrative. The novel will be analyzed from three angles—the function of spatial narrative, the basic unit of spatial narrative, the periphery of spatial narrative and the overall effect presented in the novel by using these narrative techniques.
文摘针对在复杂背景下输电线路多尺度缺陷目标检测精度较低的问题,文中提出一种基于改进YOLOv7(You Only Look Once version 7)的输电线路多类缺陷目标检测模型。对于复杂背景造成缺陷目标较低的问题,在Backbone部分引入改进的Swin Transformer模块,通过使用多头注意力机制提升对全局特征的提取效果来提高模型的检测精度。对于待检测目标的多尺度特性,在特征金字塔基础上引入自适应特征融合模块,提升了Neck部分特征融合网络对多类不同尺度缺陷目标的检测能力。使用SIoU(Structured Intersection over Union)损失函数在提高预测框回归精度的同时加快了模型的收敛。实验结果表明,相较于YOLOv5、YOLOv7和Faster R-CNN(Faster Region with Convolutional Neural Network)模型,改进YOLOv7模型具有较高的检测精度,其平均检测精度可达96.4%,检测速度为29.6 frame·s^(-1),能够为输电线路多类缺陷目标检测提供参考。
基金Project supported by the National Natural Science Foundation of China (Grant No. 60678043)the Research and Innovation Plan for Graduate Students of Jiangsu Higher Education Institutions,China (Grant No. CX09B 096Z)
文摘The resolution characteristic can be obtained by the modulation transfer function （MTF） of a GaAs/GaA1As photocathode. After establishing the theoretical model of GaAs（100）-oriented atomic configuration and the formula for the ionized impurity scattering of the non-equilibrium carriers, this paper calculates the trajectories of photoelectrons in a photocathode. Thus the distribution of photoelectron spots on the emit-face is obtained, which is namely the point spread function. The MTF is obtained by Fourier transfer of the line spread function obtained from the point spread function. The MTF obtained from these calculations is shown to depend heavily on the electron diffusion length, and enhanced considerably by decreasing the electron diffusion length and increasing the doping concentration. Furthermore, the resolution is enhanced considerably by increasing the active-layer thickness, especially at high spatial frequencies. The best spatial resolution is 860 lp/mm, for the GaAs photocathode of doping concentration 1 ×10^19 cm 3 electron diffusion length 3.6 μm and the active-layer thickness 2 μm, under the 633-nm light irradiated. This research will contribute to the future improvement of the cathode＇s resolution for preparing a high performance GaAs photocathode, and improve the resolution of a low light level image intensifier.
基金This study was supported by the National Key R&D Program of China(2017YFC0505601)the National Natural Science Foundation of China(31570630)State Key Laboratory of Forest and Soil Ecology(LFSE2015-13).
文摘Spatial distribution is fundamental for understanding species coexistence mechanisms in forest communities.Here we comprehensively explored fine-scale spatial patterns of tree species in a secondary warm-temperate deciduous broad-leaved forest community in north China.Aggregated distribution patterns were predominant.Species functional traits had no significant effects on their spatial patterns.The aggregation intensity decreased with increasing DBH and abundance.The multivariate linear stepwise regression showed that abundance and maximum DBH were correlated with the aggregation intensity.Our results partially confirm that species attributes(abundance,DBH)and habitat heterogeneity may primarily contribute to spatial patterns and species coexistence in this secondary forest.
基金Supported by Natural Science Foundation of China (No.60602065)Innovation Funds of USTC for Graduate Student (No.KD2006009)
文摘The spatial resolution of a position sensitive gamma-ray detector configuration based on plastic scintillation fiber array was measured using a Monte Carlo simulation method. Both point spread function and modulation transfer function (MTF) were presented. The factors that influence the spatial resolution were also discussed. The results of the simulation showed that the intrinsic spatial resolution was consistent with the size of the physical pixels and a few centimeters spatial resolution could be obtained under certain circumstances.
文摘Formulae for determining Green strain of an initially curved and twisted rod with circular cross-sections are derived by using the natural (curvilinear) coordinate system. Finite element analyses are performed for the flexural buckling of initially curved and twisted thin rods under simultaneous action of axial force and torque. Numerical examples demonstrate that the given formulae are correcte. Some numerical results are compared with existing analytical solutions and data obtained by commercial FE software. The convergence of the proposed curved element is better than that of elements in the commercial FE software. It is shown that good accuracy and convergency are achieved by solving three-dimensional problems.
