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明清时期黄河下游决泛区的时空变化及其人地关系规律
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作者 吴俊范 《中州学刊》 CSSCI 北大核心 2024年第12期121-130,共10页
明清黄河下游决泛水沙对颍河沿岸平原地区的环境和地表塑造的影响相对较轻,颍河两岸未形成显性决口扇地貌,历次黄泛水沙一般未越过颍河向西南漫溢,颍河干流长期作为黄泛水沙的良好容受体及其向西南蔓延扩张的界隔线。涡河沿岸地区受到... 明清黄河下游决泛水沙对颍河沿岸平原地区的环境和地表塑造的影响相对较轻,颍河两岸未形成显性决口扇地貌,历次黄泛水沙一般未越过颍河向西南漫溢,颍河干流长期作为黄泛水沙的良好容受体及其向西南蔓延扩张的界隔线。涡河沿岸地区受到明清黄河独流干道决口水沙向南泛滥及涡河本身被黄水夺溜时决泛水沙的双重影响,黄河主故道南岸核心决口扇的边缘带与沿涡次级决口扇相互交集,在涡河地区形成叠加型决口扇地貌,涡河干流长期作为黄泛重灾区与影响轻微地区的分界线。大型湖泊洼地的积水面通常与黄泛决口扇的前缘互为进退,鱼台县的土壤分布及农作物结构特征,较好地证明了南四湖洼地长期作为黄泛决口扇的边界,南四湖是明清时期黄泛水沙向北蔓延扩张的重要蓄洪区和调剂区。 展开更多
关键词 明清黄泛区 显性边界 决口扇 土壤 水患记忆
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Automatic modeling together with numerical simulation of the different-scale microstructures of human tooth enamels
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作者 LIU Tao DENG Qiang +3 位作者 YANG Dan ZHENG Jing LIU JianTao ZHOU ZhongRong 《Science China(Technological Sciences)》 SCIE EI CAS CSCD 2017年第9期1381-1399,共19页
The present paper aims to develop an automatical strategy for generating accurate different-scale microstructures of human tooth enamels(HTEs),and to elaborate a numerical scheme for simulating their elastic responses... The present paper aims to develop an automatical strategy for generating accurate different-scale microstructures of human tooth enamels(HTEs),and to elaborate a numerical scheme for simulating their elastic responses.At first,the strong governing formulation of these microstructures is briefly constructed,and the relevant weak formulation is then deduced based on the virtual work theorem.Afterwards,a subdividing approach,which cuts the elements intercepted by the interfaces between distinct phases automatically,is established with the aid of the level set method(LSM),and the discrete counterpart of the governing formula is obtained by combining the weak formulation derived and a discretized model.To be noted,two silent merits are found when the elaborated strategy is applied:(1) the continents constituting the microstructures of different scales can be arbitrarily-shaped and conveniently reproduced;(2) the periodic boundary condition commonly employed can be enforced on the external surfaces of representative unit cells(RUCs) with no difficulty.Besides,a boundary value problem(BVP) involving a simplified HTE nanostructure is designed,analytically solved,and hereafter applied to verify the correctness of the proposed strategy.It is observed that both the displacement and stress predictions by the computational approach are in good agreement with the relevant analytical results irrespective of the material combinations applied.Eventually,discussions are made on the influence of material organizations of both the 2D and 3D HTE microstructures at the ultrastructural and repeated rod levels,and some concluding remarks are drawn. 展开更多
关键词 tooth enamel level set method automatic modefing numerical simulation MICROSTRUCTURE
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