A long slope consisting of spatially random soils is a common geographical feature. This paper examined the necessity of three-dimensional(3 D) analysis when dealing with slope with full randomness in soil properties....A long slope consisting of spatially random soils is a common geographical feature. This paper examined the necessity of three-dimensional(3 D) analysis when dealing with slope with full randomness in soil properties. Although 3 D random finite element analysis can well reflect the spatial variability of soil properties, it is often time-consuming for probabilistic stability analysis. For this reason, we also examined the least advantageous(or most pessimistic) cross-section of the studied slope. The concept of"most pessimistic" refers to the minimal cross-sectional average of undrained shear strength. The selection of the most pessimistic section is achievable by simulating the undrained shear strength as a 3 D random field. Random finite element analysis results suggest that two-dimensional(2 D) plane strain analysis based the most pessimistic cross-section generally provides a more conservative result than the corresponding full 3 D analysis. The level of conservativeness is around 15% on average. This result may have engineering implications for slope design where computationally tractable 2 D analyses based on the procedure proposed in this study could ensure conservative results.展开更多
To investigate the strong random nature of the geometric interfaces between soil and rock, a rock-soil slope is considered as a two-phase random medium. A nonlinear translation of a Gaussian field is utilized to simul...To investigate the strong random nature of the geometric interfaces between soil and rock, a rock-soil slope is considered as a two-phase random medium. A nonlinear translation of a Gaussian field is utilized to simulate the two-phase random media, such that the soil(or rock) volume fraction and the inclination of the soil layer can be examined. The finite element method with random media incorporated as the material properties is used to determine the factor of safety of the rock-soil slope. Monte-Carlo simulations are used to estimate the statistical characteristics of the factor of safety. The failure mode of the rock-soil slope is examined by observing the maximum principal plastic strain at incipient slope failure. It is found that the critical surface of a rock-soil slope is fairly irregular, and it significantly differs from that of a pure soil slope. The factor of safety is sensitive to the soil volume faction, but it is predictable. The average factor of safety could be well predicted by the weighted harmonic average between the strength of soil and rock; the prediction model is practical and simple. Parametric studies on the inclination of the soil layer demonstrate that the most instable scenario occurs when the slope angle is consistent with the inclination of the soil layer.展开更多
Heat conductivity is studied by direct numerical simulations in a two-dimensional model with chiral Dzyaloshinskii-Moriya （DM） spin superexchange interactions for various DM strengths and finite sizes. We find that ...Heat conductivity is studied by direct numerical simulations in a two-dimensional model with chiral Dzyaloshinskii-Moriya （DM） spin superexchange interactions for various DM strengths and finite sizes. We find that when temperature is not too low, the thermal conductivity can be well described in the semi-classical spin wave picture, and connections of thermal conductivity with the specific heat and the dynamic relaxation time are verified to be suitable. In particular, the transition arising in Sr14-xCaxCu24O41 is related to a magnetic spin glass and qualitatively understood as a kind of Kosterlitz-Thouless transitions. It is shown that the critical temperature is linearly dependent on the spin-spin interactions for the relevant strong DM strength.展开更多
Effect sizes are estimated from several study designs when the subjects are individually sampled. When the samples are the aggregate cluster of individuals, the within cluster correlation must be accounted for to cons...Effect sizes are estimated from several study designs when the subjects are individually sampled. When the samples are the aggregate cluster of individuals, the within cluster correlation must be accounted for to construct correct confidence intervals, and to conduct valid statistical inference. The purpose of this article is to propose and evaluate statistical procedures for the estimation of the variance of the estimated attributable risk in parallel groups of clusters, and in a design dividing each of k clusters into two segments creating multiple sub-clusters. The estimated variance is the first order approximation and is obtained by the delta method. We apply the methodology and propose a Wald type confidence interval on the difference between two correlated attributable risks. We also construct a test on the hypothesis of equality of two correlated attributable risks. We evaluate the power of the proposed test via Monte-Carlo simulations.展开更多
短脉冲强激光产生的电子束具有源尺寸小、脉宽窄、准单能谱等特点,在放射照相诊断中具有独特作用.本文通过分析电子在材料中散射并采用蒙特卡罗方法数值模拟,研究了100 ke V到几百Me V能量电子束对有厚度起伏或存在界面的靶的透视,并与...短脉冲强激光产生的电子束具有源尺寸小、脉宽窄、准单能谱等特点,在放射照相诊断中具有独特作用.本文通过分析电子在材料中散射并采用蒙特卡罗方法数值模拟,研究了100 ke V到几百Me V能量电子束对有厚度起伏或存在界面的靶的透视,并与质子、X射线束透视结果比较,给出了电子束放射照相的特性与参数优化:基于电子在材料中非弹性散射或能量损失,选用能量使其射程与靶厚度接近的电子束来诊断靶厚度不均匀性;基于电子在材料中的弹性散射,选用射程超过靶厚度的电子束来诊断靶界面.展开更多
基金supported by the Key Research&Development Plan Science and Technology Cooperation Programme of Hainan Province,China(Grant No.ZDYF2016226)the National Natural Science Foundation of China(Grant Nos.51879203,51808421)
文摘A long slope consisting of spatially random soils is a common geographical feature. This paper examined the necessity of three-dimensional(3 D) analysis when dealing with slope with full randomness in soil properties. Although 3 D random finite element analysis can well reflect the spatial variability of soil properties, it is often time-consuming for probabilistic stability analysis. For this reason, we also examined the least advantageous(or most pessimistic) cross-section of the studied slope. The concept of"most pessimistic" refers to the minimal cross-sectional average of undrained shear strength. The selection of the most pessimistic section is achievable by simulating the undrained shear strength as a 3 D random field. Random finite element analysis results suggest that two-dimensional(2 D) plane strain analysis based the most pessimistic cross-section generally provides a more conservative result than the corresponding full 3 D analysis. The level of conservativeness is around 15% on average. This result may have engineering implications for slope design where computationally tractable 2 D analyses based on the procedure proposed in this study could ensure conservative results.
基金supported by the International Science and Technology Cooperation Programme of Hainan Province,China (Grant No.ZDYF2016226)the National Natural Science Foundation of China(Grant No.51879203)
文摘To investigate the strong random nature of the geometric interfaces between soil and rock, a rock-soil slope is considered as a two-phase random medium. A nonlinear translation of a Gaussian field is utilized to simulate the two-phase random media, such that the soil(or rock) volume fraction and the inclination of the soil layer can be examined. The finite element method with random media incorporated as the material properties is used to determine the factor of safety of the rock-soil slope. Monte-Carlo simulations are used to estimate the statistical characteristics of the factor of safety. The failure mode of the rock-soil slope is examined by observing the maximum principal plastic strain at incipient slope failure. It is found that the critical surface of a rock-soil slope is fairly irregular, and it significantly differs from that of a pure soil slope. The factor of safety is sensitive to the soil volume faction, but it is predictable. The average factor of safety could be well predicted by the weighted harmonic average between the strength of soil and rock; the prediction model is practical and simple. Parametric studies on the inclination of the soil layer demonstrate that the most instable scenario occurs when the slope angle is consistent with the inclination of the soil layer.
基金Supported by the Natural Science Foundation of Hubei Province under Grant No 2003ABA004.
文摘Heat conductivity is studied by direct numerical simulations in a two-dimensional model with chiral Dzyaloshinskii-Moriya （DM） spin superexchange interactions for various DM strengths and finite sizes. We find that when temperature is not too low, the thermal conductivity can be well described in the semi-classical spin wave picture, and connections of thermal conductivity with the specific heat and the dynamic relaxation time are verified to be suitable. In particular, the transition arising in Sr14-xCaxCu24O41 is related to a magnetic spin glass and qualitatively understood as a kind of Kosterlitz-Thouless transitions. It is shown that the critical temperature is linearly dependent on the spin-spin interactions for the relevant strong DM strength.
文摘Effect sizes are estimated from several study designs when the subjects are individually sampled. When the samples are the aggregate cluster of individuals, the within cluster correlation must be accounted for to construct correct confidence intervals, and to conduct valid statistical inference. The purpose of this article is to propose and evaluate statistical procedures for the estimation of the variance of the estimated attributable risk in parallel groups of clusters, and in a design dividing each of k clusters into two segments creating multiple sub-clusters. The estimated variance is the first order approximation and is obtained by the delta method. We apply the methodology and propose a Wald type confidence interval on the difference between two correlated attributable risks. We also construct a test on the hypothesis of equality of two correlated attributable risks. We evaluate the power of the proposed test via Monte-Carlo simulations.
文摘短脉冲强激光产生的电子束具有源尺寸小、脉宽窄、准单能谱等特点,在放射照相诊断中具有独特作用.本文通过分析电子在材料中散射并采用蒙特卡罗方法数值模拟,研究了100 ke V到几百Me V能量电子束对有厚度起伏或存在界面的靶的透视,并与质子、X射线束透视结果比较,给出了电子束放射照相的特性与参数优化:基于电子在材料中非弹性散射或能量损失,选用能量使其射程与靶厚度接近的电子束来诊断靶厚度不均匀性;基于电子在材料中的弹性散射,选用射程超过靶厚度的电子束来诊断靶界面.
