以昆明市某露天矿区为例,在地理信息系统(geographic information system,GIS)技术支持下,结合移动窗口分析法,利用2007—2017年间3期遥感影像数据,探究采矿背景下的区域景观格局时空演变模式。在获取景观类型与确定合适窗口尺度的基础...以昆明市某露天矿区为例,在地理信息系统(geographic information system,GIS)技术支持下,结合移动窗口分析法,利用2007—2017年间3期遥感影像数据,探究采矿背景下的区域景观格局时空演变模式。在获取景观类型与确定合适窗口尺度的基础上,提取研究区景观破碎化与多样性指数空间分布图,将其与矿区中心两两连接建立的剖面线进行空间叠置分析。结果表明,在最适宜尺度950 m的窗口下,10 a间景观破碎化与多样性高值区由区域边缘向中心扩散;矿区内部的斑块团聚效应与周边1~2 km处的景观异质性程度均逐年提高,而离矿区中心2.5 km以外的区域则基本不受采矿活动影响。研究结果直观显示出了采矿活动影响下矿区的景观格局时空演变规律,能够为后续生态监测与制定工作计划提供依据。展开更多
Heavy-ion fusion reactions between light nuclei such as carbon and oxygen isotopes have been studied becauseof their importance in a wide variety of stellar burning scenarios. However, due to extremely low cross secti...Heavy-ion fusion reactions between light nuclei such as carbon and oxygen isotopes have been studied becauseof their importance in a wide variety of stellar burning scenarios. However, due to extremely low cross sectionsand signal/background ratio, all the measurements could only be carried out at energies well above the regionof astrophysical interest. The reaction rates in stellar environment could be estimated only by extrapolating theexisted cross sections or the astrophysical S-factors at higher energies. The situation is even more complicated bythe strong, relatively narrow resonances in some reactions, such as 12C+12C, 12C+16O. Traditionally, optical modelor equivalent square-well optical model (ESW) were used to fit the average cross section and predict the reactioncross sections at the energies of astrophysical interest[1]. Recently, a new model, the hindrance model, was proposedto provide systematic fits to fusion reaction data at extreme sub-barrier energies[2]. Lacking of experimental datawithin this energy range, large discrepancies exist among different nuclear reaction models.展开更多
文摘Heavy-ion fusion reactions between light nuclei such as carbon and oxygen isotopes have been studied becauseof their importance in a wide variety of stellar burning scenarios. However, due to extremely low cross sectionsand signal/background ratio, all the measurements could only be carried out at energies well above the regionof astrophysical interest. The reaction rates in stellar environment could be estimated only by extrapolating theexisted cross sections or the astrophysical S-factors at higher energies. The situation is even more complicated bythe strong, relatively narrow resonances in some reactions, such as 12C+12C, 12C+16O. Traditionally, optical modelor equivalent square-well optical model (ESW) were used to fit the average cross section and predict the reactioncross sections at the energies of astrophysical interest[1]. Recently, a new model, the hindrance model, was proposedto provide systematic fits to fusion reaction data at extreme sub-barrier energies[2]. Lacking of experimental datawithin this energy range, large discrepancies exist among different nuclear reaction models.
文摘慢速中子俘获过程(s过程)是合成比铁重元素的重要途径之一。^(22)Ne(α, n)^(25)Mg反应是大质量AGB星中s过程主要的中子源,其中的^(22)Ne主要通过14N(α,γ)18F(β+)18O(α,γ)^(22)Ne反应链合成。该反应链中关键反应18O(α,γ)^(22)Ne在天体物理感兴趣能区的截面非常低,其天体反应率主要来自于^(22)Neα分离阈附近低能共振态的贡献,但目前相关能级的共振参数严重缺失。在HI-13串列加速器的Q3D磁谱仪上,通过测量18O(6Li, d)^(22)Ne反应的角分布,利用DWBA分析确定了^(22)Ne分离阈附近共振能级Eα=470 ke V的自旋宇称为0+,为后续计算18O(α,γ)^(22)Ne的天体反应率打下了基础。
