As well known, the magnetic cross-tail component By in the magnetotail is in direct proportion to the in-terplanetary magnetic field (IMF) By component. And the polarity of IMF and plasmoid / flux rope By components d...As well known, the magnetic cross-tail component By in the magnetotail is in direct proportion to the in-terplanetary magnetic field (IMF) By component. And the polarity of IMF and plasmoid / flux rope By components do indeed agree. This results indicate that the IMF By penetrates plasmoids and the magnetic structures must therefore be three-dimensional. In this note, the dynamical processes of magnetotail in the course of a substorm are studied using a MHD code with two-dimensions and three components on the basis of two types of initial equilibrium solutions of the quiet magnetotail. The numerical results of two cases illustrate various features of time evolution of By component that correspond to two kinds of plasmoid-like structures: one is associated with a flux rope core and the other resembles a 'closed loop' plamoid. Therefore, the occurrence of various magnetic structures in the magnetotail might be related to nonsteady driven reconnection with different distributions of the By component.展开更多
Listed by UNESCO in 1987 as a World Heritage site,the world-famous Ming Great Wall stretches several thousands of kilometers across northern China,and served as a massive military defensive system which in recent time...Listed by UNESCO in 1987 as a World Heritage site,the world-famous Ming Great Wall stretches several thousands of kilometers across northern China,and served as a massive military defensive system which in recent times has a unique historical,artistic and scientific value.Due to historical reasons and lack of advanced technologies,construction resources and conservation status of Ming Great Wall have not been investigated in any systematic manner;indeed,the extent of the Great Wall has not even been measured.This has resulted in a shortage of reliable first-hand scientific information on actual size,spatially resource distribution and preservation status of this World Heritage site.Driven by the urgent need to establish protection,research,renovation and management of Ming Great Wall,a comprehensive investigation and spatial mapping was jointly organized and completed by the State Bureau of Survey and Mapping and State Administration of Culture Heritage.High resolution digital stereo models at 1:10000 map scale covering the whole length of the Ming Great Wall have been created by photogrammetric reconstruction using nearly ten thousand aerial images.Spatial distribution and attributes of the wall sections,trenches and various subsidiary facilities in the surroundings of the Great Wall were measured with the help of digital photogrammetry workstations and results from field studies.Reliable and precise information about the Ming Great Wall has now been obtained and documented,including surface lengths,resource distribution,and preservation status.For example,the total length of Ming Great Wall is 8851.8 km,of which 6259.6 km is of actual wall,2232.5 km of natural terrain,and 359.7 km of trenches.In category lengths,1828.8 km is constructed of stone,3411.3 km of earth,249.6 km in brick,197.5 km of cliff wall and the rest 572.4 km of other means.Such information provides the scientific basis and strong platform in helping to delineate areas needing protection,in planning conservation and renovation programs,as well as digital archiving for posterity and web-based applications for modern promotions of one of the world's great attractions,the Ming Great Wall.展开更多
基金This work was supported by the National Natural Science Foundation of China (Grant Nos. 49874035 and 49834040) and the Space Physics Fund of the First-rate University Program.
文摘As well known, the magnetic cross-tail component By in the magnetotail is in direct proportion to the in-terplanetary magnetic field (IMF) By component. And the polarity of IMF and plasmoid / flux rope By components do indeed agree. This results indicate that the IMF By penetrates plasmoids and the magnetic structures must therefore be three-dimensional. In this note, the dynamical processes of magnetotail in the course of a substorm are studied using a MHD code with two-dimensions and three components on the basis of two types of initial equilibrium solutions of the quiet magnetotail. The numerical results of two cases illustrate various features of time evolution of By component that correspond to two kinds of plasmoid-like structures: one is associated with a flux rope core and the other resembles a 'closed loop' plamoid. Therefore, the occurrence of various magnetic structures in the magnetotail might be related to nonsteady driven reconnection with different distributions of the By component.
文摘Listed by UNESCO in 1987 as a World Heritage site,the world-famous Ming Great Wall stretches several thousands of kilometers across northern China,and served as a massive military defensive system which in recent times has a unique historical,artistic and scientific value.Due to historical reasons and lack of advanced technologies,construction resources and conservation status of Ming Great Wall have not been investigated in any systematic manner;indeed,the extent of the Great Wall has not even been measured.This has resulted in a shortage of reliable first-hand scientific information on actual size,spatially resource distribution and preservation status of this World Heritage site.Driven by the urgent need to establish protection,research,renovation and management of Ming Great Wall,a comprehensive investigation and spatial mapping was jointly organized and completed by the State Bureau of Survey and Mapping and State Administration of Culture Heritage.High resolution digital stereo models at 1:10000 map scale covering the whole length of the Ming Great Wall have been created by photogrammetric reconstruction using nearly ten thousand aerial images.Spatial distribution and attributes of the wall sections,trenches and various subsidiary facilities in the surroundings of the Great Wall were measured with the help of digital photogrammetry workstations and results from field studies.Reliable and precise information about the Ming Great Wall has now been obtained and documented,including surface lengths,resource distribution,and preservation status.For example,the total length of Ming Great Wall is 8851.8 km,of which 6259.6 km is of actual wall,2232.5 km of natural terrain,and 359.7 km of trenches.In category lengths,1828.8 km is constructed of stone,3411.3 km of earth,249.6 km in brick,197.5 km of cliff wall and the rest 572.4 km of other means.Such information provides the scientific basis and strong platform in helping to delineate areas needing protection,in planning conservation and renovation programs,as well as digital archiving for posterity and web-based applications for modern promotions of one of the world's great attractions,the Ming Great Wall.
