软件定义网络(software defined networking,简称SDN)是分离了网络的控制平面和数据平面新兴网络技术,该技术为研发新的网络应用和未来互联网技术提供了一种全新的解决方案。本文综述了基于OpenFlow的SDN网络安全技术发展现状,首先介绍...软件定义网络(software defined networking,简称SDN)是分离了网络的控制平面和数据平面新兴网络技术,该技术为研发新的网络应用和未来互联网技术提供了一种全新的解决方案。本文综述了基于OpenFlow的SDN网络安全技术发展现状,首先介绍了OpenFlow协议版本和OpenFlow的流表结构,并分析了如何通过扩展流标结构来增强SDN网络安全性。由于扩展了流标结构,增大了SDN网络的运算负担,简述如何通过人工神经网络方法SOM(self organizing map)对OpenFlow的流表进行降维处理来减轻SDN网络的运算负担,最后探讨了SDN网络安全未来的发展和研究趋势。展开更多
Large scale harvest of Korean pine （Pinus koraiensis） seeds as a food product in the mixed Korean pine-hardwood forest of northeastern China poses a serious threat to the sustainability and restoration of this endan...Large scale harvest of Korean pine （Pinus koraiensis） seeds as a food product in the mixed Korean pine-hardwood forest of northeastern China poses a serious threat to the sustainability and restoration of this endangered regional ecosystem. Seed collection over past decades greatly reduced the seed bank and subsequent seedling and sapling re- cruitment, and impacting a wide array of granivorous animals that rely on the pine seeds. We surveyed Korean pine seeds, including solid seeds （SS）, insect consumed seeds （ICS） and other （animal） consumed （OCS） kernels, of the seed bank （forest floor and the top 10 cm of mineral soil）, the seedlings and saplings from 1 m： sample plots in five forest types in Liangshui Nature Reserve （LNR） of the southern Xiao Xing＇an Moun- tains in northeastern China to provide accurate information for assessing the Korean pine regeneration potential. The average number of pine seeds in the seed bank were 11.2 seeds/m2, 9.1 seeds/m2, 4.6 seeds/m2, 1.1 seeds/m2, and 0.2 seeds/m2 in Korean pine-basswood forest, mixed Korean pine-hardwood forest, mixed conifer-hardwood forest, white birch forests, and oak forests, respectively. In the first three forest types, percentages of SS （potentially viable seeds） were 11.2%, 3.5% and 27.8%, respectively. The percentages of ICS （not viable seeds） were consistent at around 35%. The higher but variable percentages of OCS （not viable seeds） indicated high seed predation in these forests. Com- pared with other studies, we recorded higher percentages of seed damage, probably due to our survey approach and the increased depth of seed bank sampled in our study. Depletion of pine seeds in the seed bank greatly reduced seedling and sapling recruitment. Densities of pine seed- lings varied from about 180 trees/ha in the mixed Korean pine-hardwood forest to about 5,400 trees/ha in the mixed conifer-hardwood forests and showed a high degree of spatial variation. Saplings were rare in the mixed Korean pine-hardwood forest, but ranged in the thousands in other forests. Large scale pine seed harvest has seriously threatened the sustainability of the mixed Korean pine-hardwood forest ecosystem. Scaling down the seed harvest or supplemental planting of pine saplings are urgently needed to maintain the health of the existing Korean pine forests and to restore this endangered ecosystem.展开更多
文摘软件定义网络(software defined networking,简称SDN)是分离了网络的控制平面和数据平面新兴网络技术,该技术为研发新的网络应用和未来互联网技术提供了一种全新的解决方案。本文综述了基于OpenFlow的SDN网络安全技术发展现状,首先介绍了OpenFlow协议版本和OpenFlow的流表结构,并分析了如何通过扩展流标结构来增强SDN网络安全性。由于扩展了流标结构,增大了SDN网络的运算负担,简述如何通过人工神经网络方法SOM(self organizing map)对OpenFlow的流表进行降维处理来减轻SDN网络的运算负担,最后探讨了SDN网络安全未来的发展和研究趋势。
基金supported by the National Science Foundation of China (NSFC) grant (grants 30830024,30770330)
文摘Large scale harvest of Korean pine （Pinus koraiensis） seeds as a food product in the mixed Korean pine-hardwood forest of northeastern China poses a serious threat to the sustainability and restoration of this endangered regional ecosystem. Seed collection over past decades greatly reduced the seed bank and subsequent seedling and sapling re- cruitment, and impacting a wide array of granivorous animals that rely on the pine seeds. We surveyed Korean pine seeds, including solid seeds （SS）, insect consumed seeds （ICS） and other （animal） consumed （OCS） kernels, of the seed bank （forest floor and the top 10 cm of mineral soil）, the seedlings and saplings from 1 m： sample plots in five forest types in Liangshui Nature Reserve （LNR） of the southern Xiao Xing＇an Moun- tains in northeastern China to provide accurate information for assessing the Korean pine regeneration potential. The average number of pine seeds in the seed bank were 11.2 seeds/m2, 9.1 seeds/m2, 4.6 seeds/m2, 1.1 seeds/m2, and 0.2 seeds/m2 in Korean pine-basswood forest, mixed Korean pine-hardwood forest, mixed conifer-hardwood forest, white birch forests, and oak forests, respectively. In the first three forest types, percentages of SS （potentially viable seeds） were 11.2%, 3.5% and 27.8%, respectively. The percentages of ICS （not viable seeds） were consistent at around 35%. The higher but variable percentages of OCS （not viable seeds） indicated high seed predation in these forests. Com- pared with other studies, we recorded higher percentages of seed damage, probably due to our survey approach and the increased depth of seed bank sampled in our study. Depletion of pine seeds in the seed bank greatly reduced seedling and sapling recruitment. Densities of pine seed- lings varied from about 180 trees/ha in the mixed Korean pine-hardwood forest to about 5,400 trees/ha in the mixed conifer-hardwood forests and showed a high degree of spatial variation. Saplings were rare in the mixed Korean pine-hardwood forest, but ranged in the thousands in other forests. Large scale pine seed harvest has seriously threatened the sustainability of the mixed Korean pine-hardwood forest ecosystem. Scaling down the seed harvest or supplemental planting of pine saplings are urgently needed to maintain the health of the existing Korean pine forests and to restore this endangered ecosystem.
