Post-failure evolution analysis of an irrigation-induced loess landslide using multiple remote sensing approaches integrated with time-lapse ERT imaging: lessons from Heifangtai,China

The Heifangtai terrace, in Northwest China, is a typical area where loess landslides have been induced by agricultural irrigation, and many of the landslides are prone to reactivation. However, the spatiotemporal evolution and hydrological-triggering mechanisms of loess landslide reactivation are not well understood. In this research, multiple remote sensing (SBAS-InSAR, TLS, and optical remote sensing), integrated with time-lapse ERT (tl-ERT) imaging, was used to monitor the post-failure evolution of the Luojiapo landslide in Heifangtai during the period of May 2015 to Nov. 2020. Pronounced temporal and spatial differences in the deformation and hydrological evolution of landslides after sliding were observed. The largest displacement rates occurred in the landslide source area, and the lateral extension of the landslide source area caused by spatial differences in reactivation is an important feature of landslide evolution. In the landslide area, the groundwater table (GWT) decreased at first ascribed to the spring hole caused by the exposure of the GWT after sliding and then increased due to the subsequent continuous irrigation, and the lag time of the GWT response to irrigation decreased significantly. Spatial differences in GWT evolution are one of the main causes of spatial differences in landslide reactivation, and reactivation was more likely to occur where the GWT fluctuated at a high level. The GWT also fell with local reactivation. Our findings highlight the potential for obtaining internal and external spatiotemporal information of loess landslide evolution using multiple remote sensing integrated with tl-ERT. Our results also help to understand the reactivation process of irrigated loess landslides and provide a reference for the monitoring and early warning of such landslides.

     

AutoCAD环境下数字栅格图到数字线划图的简易转换

数字栅格图和数字线划图是可以低成本获取的两种数字地图,而DLG是目前最普遍的矢量数据格式,是GIS的主要数据来源。在缺乏专业矢量化软件的条件下,利用AutoCAD环境对DRG图像经纠正、缩放、加载坐标系统等过程后进行矢量化,是获取DLG数据的简单有效方法。     

食物质量和种间竞争对盔型溞(Daphnia galeata)和脆弱象鼻溞(Bosmina fatalis)种群增长的影响

竞争是调控水体浮游动物群落结构的生物因素之一.根据"大小效率假说",大型滤食性枝角类对小型枝角类有竞争优势.然而,大型滤食性枝角类体内磷含量通常高于小型枝角类,生长比小型枝角类更容易受食物磷缺乏的影响,食物的磷缺乏可能会改变大型枝角类和小型枝角类之间的竞争结果.本研究比较分析了食物碳磷比对两种常见枝角类（盔型溞（Daphnia galeata）和脆弱象鼻溞（Bosmina fatalis））的种群增长率、种群密度及种间竞争关系的影响.实验设计了3个食物质量处理组：高磷（碳：磷=105）、中磷（碳：磷=740）和低磷（碳：磷=2400）,食物浓度均为2 mg C/L蛋白核小球藻（Chlorella pyrenoidosa）;针对每一个食物质量处理组,盔型溞和脆弱象鼻溞分别单独培养或混合培养.盔型溞和脆弱象鼻溞平均最大种群密度分别为378~893和364~2399 ind./L;平均种群增长率分别为0.11~0.14和0.09~0.16 d^-1;平均体长分别为1.53~2.50和0.25~0.35 mm.种群增长率和体长均随着食物碳磷比的升高而显著下降,而最大种群密度在中磷处理组显著高于其它两个处理组.盔型溞种群增长率在单独培养和混合培养间无显著差异;脆弱象鼻溞种群增长率在混合培养时显著低于单独培养时.在高磷和中磷处理组,盔型溞最大种群密度在单独培养和混合培养间无显著差异,在低磷处理组,混合培养时最大种群密度显著低于单独培养时;在高磷处理组,脆弱象鼻溞最大种群密度在单独培养和混合培养间无显著差异,在中磷和低磷处理组,混合培养时显著低于单独培养时.结果表明,在食物碳不缺条件下,不管食物磷是否缺乏,盔型溞均比脆弱象鼻溞有竞争优势.     

跨国公司在中国研发投资的区位因素重构——决定目的城市以点带面能力的网络位置视角

针对对东道国的国际研发投资不能再无限二次分割的困境,将决定东道国目的城市以点带面能力的网络位置因素,纳入到了影响跨国公司国际研发投资一国区位决定的因素框架体系。实证研究发现,传统立足单一区域视角提出的供求因素如外商直接投资（FDI）、研发投入等未能很好反映跨国公司国际研发投资在中国的区位选择格局。跨国公司国际研发投资在中国的区位选择,不是由中国目的城市某孤立“点”上的因素决定,而是由目的城市可带动的“面”上因素决定。对跨国公司国际研发投资在中国的区位决定研究,因此不能再基于传统的“点”对“点”的视角。北京、上海等在中国国际研发投资中占据的绝对主导位置主要与它们在中国城市交通、创新等网络中所处的绝对核心位置有关。这些发现有助于跨国公司国际研发投资区位决定,并对中国的引资政策制定有一定的启示意义。