Localization due to disorder has been one of the most intriguing theoretical concepts that evolved in condensed matter physics.Here,we expand the theory of localization by considering two types of disorders at the sam...Localization due to disorder has been one of the most intriguing theoretical concepts that evolved in condensed matter physics.Here,we expand the theory of localization by considering two types of disorders at the same time,namely,the original Anderson’s disorder and the structural defect disorder,which has been suggested to be a key component in recently discovered two-dimensional amorphous materials.While increasing the degree of both disorders could induce localization of wavefunction in real space,we find that a small degree of structural defect disorder can significantly enhance the localization.As the degree of structural defect disorder increases,localized states quickly appear within the extended phase to enter a broad crossover region with mixed phases.We establish two-dimensional diagrams for the wavefunction localization and conductivity to highlight the interplay between the two types of disorders.Our theoretical model provides a comprehensive understanding of localization in two-dimensional amorphous materials and highlights the promising tunability of their transport properties.展开更多
China’s credit bond market has rapidly expanded in recent years.However,since 2014,the number of credit bond defaults has been increasing rapidly,posing enormous potential risks to the stability of the financial mark...China’s credit bond market has rapidly expanded in recent years.However,since 2014,the number of credit bond defaults has been increasing rapidly,posing enormous potential risks to the stability of the financial market.This study proposed a deep learning approach to predict credit bond defaults in the Chinese market.A convolutional neural network(CNN)was selected as the classification model and to reduce the extreme imbalance between defaulted and non-defaulted bonds,and a generative adversarial network(GAN)was used as the oversampling model.Based on 31 financial and 20 non-financial indicators,we collected Wind data on all credit bonds issued and matured or defaulted from 2014 to 2021.The experimental results showed that our GAN+CNN approach had superior predictive performance with an area under the curve(AUC)of 0.9157 and precision of 0.8871 compared to previous research and other commonly used classification models-including the logistic regression,support vector machine,and fully connected neural network models-and oversampling techniques-including the synthetic minority oversampling technique(SMOTE)and Borderline SMOTE model.For one-year predictions,indicators of solvency,capital structure,and fundamental properties of bonds are proved to be the most important indicators.展开更多
Deep underground rocks exhibit significant layered heterogeneity due to geological evolution and sedimentation.Rock fracture toughness, as one of the important indicators of hydraulic crack propagation, also exhibits ...Deep underground rocks exhibit significant layered heterogeneity due to geological evolution and sedimentation.Rock fracture toughness, as one of the important indicators of hydraulic crack propagation, also exhibits heterogeneous distribution. In order to investigate the influence of non-uniform fracture toughness of layered rockson hydraulic crack propagation, this paper establishes a planar three-dimensional hydraulic crack propagationmodel. The model is numerically solved using the 3D displacement discontinuity method (3D-DDM) and the finitedifference method. The calculation results indicate that when the distribution of the fracture toughness of layeredrocks changes from uniform to non-uniform, the fracture morphology develops from a standard circular crack toan elliptical crack. When the difference of the rock fracture toughness between adjacent rock layers and themiddle rock layer (pay zone) is large enough, the fracture morphology will develop towards a rectangular shape.In addition, when the fracture toughness of rock layers is non-uniformly distributed, the hydraulic crack not onlyrapidly expand in the softening layer (rock layer with lower fracture toughness), but also slowly propagate in thestrong layer (rock layer with higher fracture toughness). However, the propagation speed in the softening layer ismuch faster than that in the strong layer. The results indicate that the heterogeneity of rock fracture toughness hasan important impact on the morphology, propagation speed, and direction of hydraulic fractures.展开更多
The instability of retaining wall is a key factor for many geo-hazards,such as landslides.To estimate the stability of retaining wall,the distribution of earth pressure is necessary.The results of in-situ observations...The instability of retaining wall is a key factor for many geo-hazards,such as landslides.To estimate the stability of retaining wall,the distribution of earth pressure is necessary.The results of in-situ observations and indoor experiments demonstrate that the distribution of earth pressure behind the retaining wall exhibits remarkable nonlinearity.When the results are analyzed in details,the oscillation and quasi-periodicity of the distribution of earth pressure are observed,which has not been given widely concerns and cannot be described by the existing analytical models.Based on the internal variable gradient theory and operator averaging method,a gradientenhanced softening constitutive model is proposed in this paper to describe the oscillation and quasiperiodicity of the distribution of earth pressure acting on the retaining wall,by introducing the high-order gradient terms of the hydrostatic pressure into Mohr-Coulomb yield condition.In order to check the applicability of the proposed formulation,the predictions from the formulations are compared with the full-scale and laboratory-scale test results as well as the existing formulations.It is noted from the comparisons between predicted and measured values that the results of gradient-dependent softening constitutive model provides the comparable approximations for active earth pressure and describes the oscillation and quasi-periodicity very well.This model may enhance the comprehension of soil mechanics and provide a novel view for the design of the retaining wall.展开更多
基金supported by the National Natural Science Foundation of China(Grant No.92165101)the National Key R&D Program of China(Grant No.2021YFA1400500)+1 种基金the Strategic Priority Research Program of Chinese Academy of Sciences(Grant No.XDB33000000)the Beijing Natural Science Foundation(Grant No.JQ22001).We are grateful for computational resources supported by High-performance Computing Platform of Peking University.
文摘Localization due to disorder has been one of the most intriguing theoretical concepts that evolved in condensed matter physics.Here,we expand the theory of localization by considering two types of disorders at the same time,namely,the original Anderson’s disorder and the structural defect disorder,which has been suggested to be a key component in recently discovered two-dimensional amorphous materials.While increasing the degree of both disorders could induce localization of wavefunction in real space,we find that a small degree of structural defect disorder can significantly enhance the localization.As the degree of structural defect disorder increases,localized states quickly appear within the extended phase to enter a broad crossover region with mixed phases.We establish two-dimensional diagrams for the wavefunction localization and conductivity to highlight the interplay between the two types of disorders.Our theoretical model provides a comprehensive understanding of localization in two-dimensional amorphous materials and highlights the promising tunability of their transport properties.
基金supported in part by the Emerging Interdisciplinary Project of Central University of Finance and Economics,Beijing,China.
文摘China’s credit bond market has rapidly expanded in recent years.However,since 2014,the number of credit bond defaults has been increasing rapidly,posing enormous potential risks to the stability of the financial market.This study proposed a deep learning approach to predict credit bond defaults in the Chinese market.A convolutional neural network(CNN)was selected as the classification model and to reduce the extreme imbalance between defaulted and non-defaulted bonds,and a generative adversarial network(GAN)was used as the oversampling model.Based on 31 financial and 20 non-financial indicators,we collected Wind data on all credit bonds issued and matured or defaulted from 2014 to 2021.The experimental results showed that our GAN+CNN approach had superior predictive performance with an area under the curve(AUC)of 0.9157 and precision of 0.8871 compared to previous research and other commonly used classification models-including the logistic regression,support vector machine,and fully connected neural network models-and oversampling techniques-including the synthetic minority oversampling technique(SMOTE)and Borderline SMOTE model.For one-year predictions,indicators of solvency,capital structure,and fundamental properties of bonds are proved to be the most important indicators.
基金support of the National Natural Science Foundation of China(Grant Nos.12172036,51774018)QN Youth Research and Innovation Project-Young Teachers'scientific research ability improvement plan of Beijing University of Civil Engineering and Architecture(No.X22012).
文摘Deep underground rocks exhibit significant layered heterogeneity due to geological evolution and sedimentation.Rock fracture toughness, as one of the important indicators of hydraulic crack propagation, also exhibits heterogeneous distribution. In order to investigate the influence of non-uniform fracture toughness of layered rockson hydraulic crack propagation, this paper establishes a planar three-dimensional hydraulic crack propagationmodel. The model is numerically solved using the 3D displacement discontinuity method (3D-DDM) and the finitedifference method. The calculation results indicate that when the distribution of the fracture toughness of layeredrocks changes from uniform to non-uniform, the fracture morphology develops from a standard circular crack toan elliptical crack. When the difference of the rock fracture toughness between adjacent rock layers and themiddle rock layer (pay zone) is large enough, the fracture morphology will develop towards a rectangular shape.In addition, when the fracture toughness of rock layers is non-uniformly distributed, the hydraulic crack not onlyrapidly expand in the softening layer (rock layer with lower fracture toughness), but also slowly propagate in thestrong layer (rock layer with higher fracture toughness). However, the propagation speed in the softening layer ismuch faster than that in the strong layer. The results indicate that the heterogeneity of rock fracture toughness hasan important impact on the morphology, propagation speed, and direction of hydraulic fractures.
基金supported by the Beijing Municipal Natural Science Foundation(Grant No.8,222,010)Research Project for Young Scholars of BUCEA(Grant No.X2102080921019)Henan Key Laboratory of Special Protective Materials(Grant No.SZKFKT202102).
文摘The instability of retaining wall is a key factor for many geo-hazards,such as landslides.To estimate the stability of retaining wall,the distribution of earth pressure is necessary.The results of in-situ observations and indoor experiments demonstrate that the distribution of earth pressure behind the retaining wall exhibits remarkable nonlinearity.When the results are analyzed in details,the oscillation and quasi-periodicity of the distribution of earth pressure are observed,which has not been given widely concerns and cannot be described by the existing analytical models.Based on the internal variable gradient theory and operator averaging method,a gradientenhanced softening constitutive model is proposed in this paper to describe the oscillation and quasiperiodicity of the distribution of earth pressure acting on the retaining wall,by introducing the high-order gradient terms of the hydrostatic pressure into Mohr-Coulomb yield condition.In order to check the applicability of the proposed formulation,the predictions from the formulations are compared with the full-scale and laboratory-scale test results as well as the existing formulations.It is noted from the comparisons between predicted and measured values that the results of gradient-dependent softening constitutive model provides the comparable approximations for active earth pressure and describes the oscillation and quasi-periodicity very well.This model may enhance the comprehension of soil mechanics and provide a novel view for the design of the retaining wall.
