Pyramidal dislocations in magnesium (Mg) and other hexagonal close-packed metals play an important role in accommodating plastic strains along the c-axis.Bulk single crystal Mg only presents very limited plasticity in...Pyramidal dislocations in magnesium (Mg) and other hexagonal close-packed metals play an important role in accommodating plastic strains along the c-axis.Bulk single crystal Mg only presents very limited plasticity in c-axis compression,and this behavior was attributed to out-of-plane dissociation of pyramidal dislocations onto the basal plane and resulted in an immobile dislocation configuration.In contrast,other simulations and experiments reported in-plane dissociation of pyramidal dislocations on their slip planes.Thus,the core structure and mode of dissociation of pyramidal dislocations are still not well understood.To better understand the dissociation behavior of pyramidal dislocations in Mg at room temperature,in this work,atomistic simulations were conducted to investigate four types of pyramidal dislocations at 300 K:edge and screw Py-Ⅰ on{1011},edge and screw Py-Ⅱ on{1122}by using a modified embedded atom method (MEAM) potential for Mg and anisotropic elasticity dislocation model.The results show that when energy minimization was performed before relaxation,in-plane dissociation of edge dislocations on respective pyramidal plane could be obtained at room temperature for all four types of dislocation.Without energy minimization,the edge dislocations dissociated out-of-plane onto the basal plane.Calculations of potential energy and hydrostatic stress of individual atoms at the edge dislocation core show that the extraordinarily high energy and atomic stresses in the as-constructed dislocation structures caused the out-of-plane dissociation onto the basal plane.The core structures of all four types of pyramidal dislocation after in-plane dissociation were analyzed by computing the distribution of the Burgers vector.展开更多
Most recent studies on Meiyu over the middle and lower reaches of the Yangtze River(MLRYR)have focused on its interannual variability or the mechanism of certain abnormal events.The influence and physical mechanism of...Most recent studies on Meiyu over the middle and lower reaches of the Yangtze River(MLRYR)have focused on its interannual variability or the mechanism of certain abnormal events.The influence and physical mechanism of solar radiation intensity on the interdecadal frequency of strong Meiyu events over the MLRYR during historical periods were investigated using reconstructed precipitation data,reconstructed solar radiation data,and model simulation data.First,according to the solar radiation intensity,the Ming and Qing Dynasties(1470-1850)were divided into three periods of strong solar radiation and three periods of weak solar radiation.It was found that during the periods of strong solar radiation,the frequency of strong Meiyu events was significantly higher than that during the periods of weak solar radiation in the reconstructed precipitation data and model simulations.Mechanism analyses show that during the periods of strong solar radiation,the Western Pacific Subtropical High(WPSH)is stronger,and the blocking highs over the middle-high-latitudes are also stronger,which is conducive to the continuous convergence of the southward cold air and the northward warm and humid air flow at the MLRYR.Therefore,a circulation spatial pattern conducive to the occurrence of strong Meiyu events is then induced.The probability distributions of precipitation also show that,during periods of strong solar radiation,changes in circulation patterns cause the probability distribution of precipitation to shift significantly to the right,increasing the probability of strong Meiyu events occurring on the right side of the probability distribution.展开更多
基金the support from U.S.National Science Foundation (NSF) (CMMI-2016263,2032483)supported by National Science Foundation grant number ACI-1548562,on Bridges Pylon at Pittsburgh Supercomputing Center through TG-MAT200001the support provided by National Natural Science Foundation of China (51971168 and 52022076)。
文摘Pyramidal dislocations in magnesium (Mg) and other hexagonal close-packed metals play an important role in accommodating plastic strains along the c-axis.Bulk single crystal Mg only presents very limited plasticity in c-axis compression,and this behavior was attributed to out-of-plane dissociation of pyramidal dislocations onto the basal plane and resulted in an immobile dislocation configuration.In contrast,other simulations and experiments reported in-plane dissociation of pyramidal dislocations on their slip planes.Thus,the core structure and mode of dissociation of pyramidal dislocations are still not well understood.To better understand the dissociation behavior of pyramidal dislocations in Mg at room temperature,in this work,atomistic simulations were conducted to investigate four types of pyramidal dislocations at 300 K:edge and screw Py-Ⅰ on{1011},edge and screw Py-Ⅱ on{1122}by using a modified embedded atom method (MEAM) potential for Mg and anisotropic elasticity dislocation model.The results show that when energy minimization was performed before relaxation,in-plane dissociation of edge dislocations on respective pyramidal plane could be obtained at room temperature for all four types of dislocation.Without energy minimization,the edge dislocations dissociated out-of-plane onto the basal plane.Calculations of potential energy and hydrostatic stress of individual atoms at the edge dislocation core show that the extraordinarily high energy and atomic stresses in the as-constructed dislocation structures caused the out-of-plane dissociation onto the basal plane.The core structures of all four types of pyramidal dislocation after in-plane dissociation were analyzed by computing the distribution of the Burgers vector.
基金supported by the Strategic Priority Research Program of the Chinese Academy of Sciences(Category B)(Grant No.XDB40000000)the National Natural Science Foundation of China(Grant Nos.42130604,41971021,41971108,42075049&42111530182)Open Funds of State Key Laboratory of Loess and Quaternary Geology,Institute of Earth Environment,Chinese Academy of Sciences(Grant Nos.SKLLQG1820&SKLLQG1930)。
文摘Most recent studies on Meiyu over the middle and lower reaches of the Yangtze River(MLRYR)have focused on its interannual variability or the mechanism of certain abnormal events.The influence and physical mechanism of solar radiation intensity on the interdecadal frequency of strong Meiyu events over the MLRYR during historical periods were investigated using reconstructed precipitation data,reconstructed solar radiation data,and model simulation data.First,according to the solar radiation intensity,the Ming and Qing Dynasties(1470-1850)were divided into three periods of strong solar radiation and three periods of weak solar radiation.It was found that during the periods of strong solar radiation,the frequency of strong Meiyu events was significantly higher than that during the periods of weak solar radiation in the reconstructed precipitation data and model simulations.Mechanism analyses show that during the periods of strong solar radiation,the Western Pacific Subtropical High(WPSH)is stronger,and the blocking highs over the middle-high-latitudes are also stronger,which is conducive to the continuous convergence of the southward cold air and the northward warm and humid air flow at the MLRYR.Therefore,a circulation spatial pattern conducive to the occurrence of strong Meiyu events is then induced.The probability distributions of precipitation also show that,during periods of strong solar radiation,changes in circulation patterns cause the probability distribution of precipitation to shift significantly to the right,increasing the probability of strong Meiyu events occurring on the right side of the probability distribution.
