浙江省城市韧性及其时空变化分析

我国城市化进程高速发展,城市面临的风险趋向多元化、复杂化.从城市韧性的角度出发,构建了“规模-密度-形态-基础设施”四位一体城市韧性描述体系,分析了浙江省2000年至2020年间城市韧性的时空变化,并对城市发展方向提出了建议.结果表明:在研究期间,浙江省城市韧性整体呈下降趋势,其中城市规模韧性逐年下降,存在着城市规模安全的隐患;城市密度韧性呈下降趋势,全省常年处于生态赤字风险之中;城市形态韧性整体上有所下降,但降幅较缓;城市基础设施韧性呈螺旋上升趋势,且各城市间差距逐渐缩小.浙江省的城市韧性呈现出“西高东低”梯度化的空间格局,相同韧性类型的城市也有集中分布的空间特征.根据城市韧性描述体系的研究结果,将浙江省各城市划分为高韧性城市、中韧性城市和低韧性城市三类,并分别给出城市发展方向的建议.     

基于BP神经网络与熵值法的浙江省城市韧性评估研究

以浙江省为例, 利用BP神经网络与熵值法综合建模, 对2011—2020年间浙江省各地级市的城市韧性进行定量评价, 分析经济、社会、环境、设施4项城市单系统韧性及其复合韧性, 从而揭示浙江省城市韧性的空间分布特征与发展规律. 研究表明: 浙江省韧性发展趋势较为平稳, 韧性水平的空间分布差异较大, 内部存在发展不均衡现象; 核心地区与边缘地区的韧性水平均呈现缓慢上升势态, 且分异格局短期内不会发生改变.     

Microstructural evolution and mechanical properties of FeCoCrNiCu high entropy alloys: a microstructure-based constitutive model and a molecular dynamics simulation study

High entropy alloys(HEAs) attract remarkable attention due to the excellent mechanical performance. However, the origins of their high strength and toughness compared with those of the traditional alloys are still hardly revealed. Here, using a microstructure-based constitutive model and molecular dynamics(MD) simulation, we investigate the unique mechanical behavior and microstructure evolution of FeCoCrNiCu HEAs during the indentation. Due to the interaction between the dislocation and solution,the high dislocation density in FeCoCrNiCu leads to strong work hardening. Plentiful slip systems are stimulated, leading to the good plasticity of FeCoCrNiCu. The plastic deformation of FeCoCrNiCu is basically affected by the motion of dislocation loops. The prismatic dislocation loops inside FeCoCrNiCu are formed by the dislocations with the Burgers vectors of a/6[■] and a/6[■], which interact with each other, and then emit along the ■slip direction. In addition, the mechanical properties of FeCoCrNiCu HEA can be predicted by constructing the microstructure-based constitutive model, which is identified according to the evolution of the dislocation density and the stress-strain curve.Strong dislocation strengthening and remarkable lattice distortion strengthening occur in the deformation process of FeCoCrNiCu, and improve the strength. Therefore, the origins of high strength and high toughness in FeCoCrNiCu HEAs come from lattice distortion strengthening and the more activable slip systems compared with Cu. These results accelerate the discovery of HEAs with excellent mechanical properties, and provide a valuable reference for the industrial application of HEAs.