In this paper, we identify a space-dependent source for a fractional diffusion equation. This problem is ill-posed, i.e., the solution （if it exists） does not depend continuously on the data. The generalized Tikhono...In this paper, we identify a space-dependent source for a fractional diffusion equation. This problem is ill-posed, i.e., the solution （if it exists） does not depend continuously on the data. The generalized Tikhonov regularization method is proposed to solve this problem. An a priori error estimate between the exact solution and its regularized approximation is obtained. Moreover, an a posteriori parameter choice rule is proposed and a stable error estimate is also obtained, Numerical examples are presented to illustrate the validity and effectiveness of this method.展开更多
Ecological patterns and processes in dune ecosystems have been a research focus in recent years, however the information on how dune stabilization influences the spatial scale dependence of plant diversity is still la...Ecological patterns and processes in dune ecosystems have been a research focus in recent years, however the information on how dune stabilization influences the spatial scale dependence of plant diversity is still lacking. In this study, we measured the plant species richness, soil properties and altitude across four spatial scales （1, 10, 100 and 1,000 m2） at three different dune stabilization stages （mobile dune, semi-fixed dune and fixed dune） in Horqin Sandy Land, Northern China. We also examined the relationships between plant species richness, community composition and environmental factors along the gradient of dune stabilization. Our results showed that plant species richness increased with the increase of spatial scales in each dune stabilization stage, as well as with the increase of dune stabilization degrees. Canonical correspondence analysis （CCA） showed that plant distribu- tions in the processes of dune stabilization were determined by the combined environmental gradient in relation to soil organic carbon （SOC）, total nitrogen （TN）, carbon/nitrogen （C/N）, pH, electrical conductivity （EC）, soil water content （SWC）, fine sand （FS）, very fine sand （VFS）, silt and clay （SC）, and altitude. Plant species richness was significantly and positively correlated to SOC and TN in mobile dune, and significantly and positively correlated to SOC, TN, C/N, VFS and SC in semi-fixed dune. However, no significant correlation between plant species richness and environmental factors was observed in fixed dune. In addition, plant species richness in different dune stabili- zation stages was also determined by the combined gradient of soil properties and altitude. These results suggest that plant species richness has obvious scale dependence along the gradient of dune stabilization. Soil resources depending on dune habitats and environmental gradients caused by dune stabilization are important factors to de- termine the scale dependence of species diversity in sand dune ecosyst展开更多
H.264是最新的视频压缩标准,帧内预测是其中一个重要组成部分。JVT(Joint Video Team)提供的参考软件采用全搜索算法进行帧内预测,算法复杂度很高,无法满足实时视频的需求。为了降低帧内预测算法的复杂度,提高编码效率,根据灰度共生矩...H.264是最新的视频压缩标准,帧内预测是其中一个重要组成部分。JVT(Joint Video Team)提供的参考软件采用全搜索算法进行帧内预测,算法复杂度很高,无法满足实时视频的需求。为了降低帧内预测算法的复杂度,提高编码效率,根据灰度共生矩阵及其逆差距提取宏块的纹理特征,对宏块的平坦程度和纹理方向进行预判,提出了一种新的快速帧内预测算法。基于参考软件JM13.2的实验结果表明本算法与全搜索算法相比在信噪比和码率变化极小的情况下,编码速度有显著提高。展开更多
外商直接投资(Foreign Direct Investment,简称FDI)的空间依赖性已得到越来越多文献的证实,但FDI区位选择决定因素实证研究方面,大多数文献都忽略了这种空间依赖性,直接导致模型估计结果无法令人信服。文章利用最新发展的空间面板数据...外商直接投资(Foreign Direct Investment,简称FDI)的空间依赖性已得到越来越多文献的证实,但FDI区位选择决定因素实证研究方面,大多数文献都忽略了这种空间依赖性,直接导致模型估计结果无法令人信服。文章利用最新发展的空间面板数据模型研究中国区域FDI决定因素的动态演变,在模型中纳入空间效应后,发现:①模型的估计结果比OLS估计更为稳健;②吸引FDI的传统因素依然存在,但作用已弱化,然而新经济地理所揭示的贸易成本、集聚效应等传导机制的作用日益凸现;③相邻省份的空间溢出效应显著地影响FDI的区域分布,一省FDI的增加对相邻地区FDI流入有正向影响。展开更多
基金supported by the National Natural Science Foundation of China(11171136, 11261032)the Distinguished Young Scholars Fund of Lan Zhou University of Technology (Q201015)the basic scientific research business expenses of Gansu province college
文摘In this paper, we identify a space-dependent source for a fractional diffusion equation. This problem is ill-posed, i.e., the solution （if it exists） does not depend continuously on the data. The generalized Tikhonov regularization method is proposed to solve this problem. An a priori error estimate between the exact solution and its regularized approximation is obtained. Moreover, an a posteriori parameter choice rule is proposed and a stable error estimate is also obtained, Numerical examples are presented to illustrate the validity and effectiveness of this method.
基金financially supported by the National Natural Science Foundation of China (41171414)the Knowledge Innovation Program of the Chinese Academy of Sciences (KZCX2-EW-QN313)+1 种基金the Chinese Academy of Sciences Visiting Professorships for Senior International Scientists (2011T2Z36)the Key Project of Scientific and Technical Supporting Programs (2011BAC07B02-09), and the National Basic Research Program of China (2009CB421303)
文摘Ecological patterns and processes in dune ecosystems have been a research focus in recent years, however the information on how dune stabilization influences the spatial scale dependence of plant diversity is still lacking. In this study, we measured the plant species richness, soil properties and altitude across four spatial scales （1, 10, 100 and 1,000 m2） at three different dune stabilization stages （mobile dune, semi-fixed dune and fixed dune） in Horqin Sandy Land, Northern China. We also examined the relationships between plant species richness, community composition and environmental factors along the gradient of dune stabilization. Our results showed that plant species richness increased with the increase of spatial scales in each dune stabilization stage, as well as with the increase of dune stabilization degrees. Canonical correspondence analysis （CCA） showed that plant distribu- tions in the processes of dune stabilization were determined by the combined environmental gradient in relation to soil organic carbon （SOC）, total nitrogen （TN）, carbon/nitrogen （C/N）, pH, electrical conductivity （EC）, soil water content （SWC）, fine sand （FS）, very fine sand （VFS）, silt and clay （SC）, and altitude. Plant species richness was significantly and positively correlated to SOC and TN in mobile dune, and significantly and positively correlated to SOC, TN, C/N, VFS and SC in semi-fixed dune. However, no significant correlation between plant species richness and environmental factors was observed in fixed dune. In addition, plant species richness in different dune stabili- zation stages was also determined by the combined gradient of soil properties and altitude. These results suggest that plant species richness has obvious scale dependence along the gradient of dune stabilization. Soil resources depending on dune habitats and environmental gradients caused by dune stabilization are important factors to de- termine the scale dependence of species diversity in sand dune ecosyst
文摘H.264是最新的视频压缩标准,帧内预测是其中一个重要组成部分。JVT(Joint Video Team)提供的参考软件采用全搜索算法进行帧内预测,算法复杂度很高,无法满足实时视频的需求。为了降低帧内预测算法的复杂度,提高编码效率,根据灰度共生矩阵及其逆差距提取宏块的纹理特征,对宏块的平坦程度和纹理方向进行预判,提出了一种新的快速帧内预测算法。基于参考软件JM13.2的实验结果表明本算法与全搜索算法相比在信噪比和码率变化极小的情况下,编码速度有显著提高。
文摘外商直接投资(Foreign Direct Investment,简称FDI)的空间依赖性已得到越来越多文献的证实,但FDI区位选择决定因素实证研究方面,大多数文献都忽略了这种空间依赖性,直接导致模型估计结果无法令人信服。文章利用最新发展的空间面板数据模型研究中国区域FDI决定因素的动态演变,在模型中纳入空间效应后,发现:①模型的估计结果比OLS估计更为稳健;②吸引FDI的传统因素依然存在,但作用已弱化,然而新经济地理所揭示的贸易成本、集聚效应等传导机制的作用日益凸现;③相邻省份的空间溢出效应显著地影响FDI的区域分布,一省FDI的增加对相邻地区FDI流入有正向影响。
