Subjects: Geosciences >> Atmospheric Sciences submitted time 2019-09-02 Cooperative journals: 《干旱区研究》
Abstract： 本文以东亚夏季风北部边缘的达里诺尔湖(以下简称“达里湖”)为研究对象，通过沉积物岩芯的采集与测试分析，利用正构烷烃及相关指标讨论达里湖区域近2 400 a以来的环境演变及其气候响应。结果显示了达里湖沉积物中正构烷烃的碳数分布为C17~C33。其中，以C25为主峰的单峰形分布约占总样品量的57%；以C19、C25为主峰的双峰形分布约占30%；以C25、C27为主峰的双峰形分布约占13%。正构烷烃的指标参数变化显示，近2 400 a以来达里湖区域环境演变不仅与全球气候事件具有明显的一致性，而且受东亚夏季风降水变化及湖区冷暖变化的影响。将其变化分为6个阶段，其中阶段1、3、5 (75 a BP至今、985~600 a BP、2 180~1 550 a BP)为暖湿气候阶段，该阶段湖区有效湿度高，木本植物占据优势，水生植物生长茂盛，湖泊营养状态较好；阶段2、4、6 (600~75 a BP、1 550~985 a BP、2 355~2 180 a BP)为冷干气候阶段，该阶段菌藻类繁殖较快，草本植物比例增加，湖泊初级生产力较低。整体上，近2400 a以来达里湖区域的气候变化由暖湿向冷干转变。
Subjects: Geosciences >> Space Physics submitted time 2016-04-22
Abstract： Schmidt and Angel lobster-eye X-ray imaging system can realize total reflection focusing and imaging by simulating lobster-eye microchannel structure. Compared with traditional way of X-ray imaging, it is provided with large field of detection view, high resolution and energy acquisition ability. This paper studies on two lobster-eye basic structures. Based on the principle of grazing incidence, we analyzed Angel and Schmidt structure of light entering focal plane and space resolution. We use tracepro simulation software to model and verify the several focusing and imaging property parameters of these two lobster-eye structures, such as receiving/transmitting light, maximum/cross arm, maximum/background, cross arm/background. The theoretical analysis and simulation results show, when the focal length is longer and channel length-width ratio is about 50. Due to multiple reflection, focusing and imaging signal-to-noise ratio of some main parameters of Schmidt is higher than Angel model, and the spatial resolution is lower. When the focal length is shorter and channel length-width ratio is about 10. Due to simple reflection, focusing and imaging signal-to-noise ratio of some main parameters of Schmidt is lower than Angel model, and the spatial resolution is almost the same.
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