The attack angle may greatly affect the hypersonic plasma sheaths around the re-entry vehicle,thereby affecting the transmission characteristics of electromagnetic(EM)waves in the sheaths.In this paper,we propose an i...The attack angle may greatly affect the hypersonic plasma sheaths around the re-entry vehicle,thereby affecting the transmission characteristics of electromagnetic(EM)waves in the sheaths.In this paper,we propose an integrated three-dimensional(3D)model with various attack angles and realistic flying conditions of radio attenuation measurement C-II(RAM C-II)re-entry tasks for analyzing the effect of the attack angle on the transmission characteristics of EM waves in the sheaths.It is shown that the electron density and collision frequency of the sheath on the windward side can be increased by an order of magnitude with the increase of the attack angle.Meanwhile,the thickness of the sheath on the leeward side is increased where the electron density and collision frequency are reduced.The EM waves are mainly reflected on the windward plasma sheath due to the cutoff effect,and the radio-frequency(RF)blackout is mitigated if the antenna is positioned on the leeward side.Thus,by planning the trajectory properly and installing the antenna accordingly during the re-entry,it is possible to provide an approach for mitigation of the RF blackout problem to an extent.展开更多
生态空间为城市提供所需的生态系统服务,同时也受到城市发展的影响。如何在让生态空间发挥生态价值的同时,平衡人类社会对生态系统提供服务的需求成为近年来城市生态空间规划的重点。生态系统服务可以评估生态和社会价值,顺应其间的协...生态空间为城市提供所需的生态系统服务,同时也受到城市发展的影响。如何在让生态空间发挥生态价值的同时,平衡人类社会对生态系统提供服务的需求成为近年来城市生态空间规划的重点。生态系统服务可以评估生态和社会价值,顺应其间的协同关系并缓解权衡有利于进行兼顾生态和社会目标的生态空间规划。以北京市生态涵养区为例,分析关键性生态系统服务间的权衡协同关系,为不同区域分配优先保护特征,并通过低权衡、低协同和高协同3种情景,以不同灵活程度进行生态系统服务保护目标空间分配。使用Marxan with zones模型得到满足各服务保护目标的管理区划,并比较3个情景的分区结果,验证规划体系对协同权衡作用的影响。得到了3种情景下的管理区分布:低权衡情景布局偏紧凑,实现了生态系统服务间权衡最小化;从低协同到高协同情景,生态系统服务间的协同性增加;从低权衡情景到低、高协同情景,重点保护区的面积逐渐增加,生态缓冲区增加了连接性,控制发展区和集中建设区变化相对稳定,实现了生态空间多层次空间优化。最终得到的更详细的管理区划有助于指导未来生态—社会多目标生态空间规划政策的制定:即对重点保护区严格保护,加强生态缓冲区生态整治和廊道建设,以促进生态效益协同发展。在集中建设区与控制发展区引导城镇节约集约建设,减量增绿,实现社会经济绿色发展。展开更多
基金supported by National Natural Science Foundation of China(Nos.92271202 and 92371105)。
文摘The attack angle may greatly affect the hypersonic plasma sheaths around the re-entry vehicle,thereby affecting the transmission characteristics of electromagnetic(EM)waves in the sheaths.In this paper,we propose an integrated three-dimensional(3D)model with various attack angles and realistic flying conditions of radio attenuation measurement C-II(RAM C-II)re-entry tasks for analyzing the effect of the attack angle on the transmission characteristics of EM waves in the sheaths.It is shown that the electron density and collision frequency of the sheath on the windward side can be increased by an order of magnitude with the increase of the attack angle.Meanwhile,the thickness of the sheath on the leeward side is increased where the electron density and collision frequency are reduced.The EM waves are mainly reflected on the windward plasma sheath due to the cutoff effect,and the radio-frequency(RF)blackout is mitigated if the antenna is positioned on the leeward side.Thus,by planning the trajectory properly and installing the antenna accordingly during the re-entry,it is possible to provide an approach for mitigation of the RF blackout problem to an extent.
文摘生态空间为城市提供所需的生态系统服务,同时也受到城市发展的影响。如何在让生态空间发挥生态价值的同时,平衡人类社会对生态系统提供服务的需求成为近年来城市生态空间规划的重点。生态系统服务可以评估生态和社会价值,顺应其间的协同关系并缓解权衡有利于进行兼顾生态和社会目标的生态空间规划。以北京市生态涵养区为例,分析关键性生态系统服务间的权衡协同关系,为不同区域分配优先保护特征,并通过低权衡、低协同和高协同3种情景,以不同灵活程度进行生态系统服务保护目标空间分配。使用Marxan with zones模型得到满足各服务保护目标的管理区划,并比较3个情景的分区结果,验证规划体系对协同权衡作用的影响。得到了3种情景下的管理区分布:低权衡情景布局偏紧凑,实现了生态系统服务间权衡最小化;从低协同到高协同情景,生态系统服务间的协同性增加;从低权衡情景到低、高协同情景,重点保护区的面积逐渐增加,生态缓冲区增加了连接性,控制发展区和集中建设区变化相对稳定,实现了生态空间多层次空间优化。最终得到的更详细的管理区划有助于指导未来生态—社会多目标生态空间规划政策的制定:即对重点保护区严格保护,加强生态缓冲区生态整治和廊道建设,以促进生态效益协同发展。在集中建设区与控制发展区引导城镇节约集约建设,减量增绿,实现社会经济绿色发展。
