In the modal analysis and control of nonlinear dynamical systems,participation factors(PFs)of state variables with respect to a critical or selected mode serve as a pivotal tool for simplifying stability studies by fo...In the modal analysis and control of nonlinear dynamical systems,participation factors(PFs)of state variables with respect to a critical or selected mode serve as a pivotal tool for simplifying stability studies by focusing on a subset of highly influential state variables.For linear systems,PFs are uniquely determined by the mode’s composition and shape,which are defined by the system’s left and right eigenvectors,respectively.However,the uniqueness of other types of PFs has not been thoroughly addressed in literatures.This paper establishes sufficient conditions for the uniqueness of nonlinear PFs and five other PF variants,taking into account uncertain scaling factors in a mode’s shape and composition.These scaling factors arise from variations in the choice of physical units,which depend on the value ranges of real-world state variables.Understanding these sufficient conditions is essential for the correct application of PFs in practical stability analysis and control design.展开更多
With the continuous evolution of urban surface types,the impact of the urban heat island effect on the human population has intensified.Investigating the factors influencing urban thermal environments is crucial for p...With the continuous evolution of urban surface types,the impact of the urban heat island effect on the human population has intensified.Investigating the factors influencing urban thermal environments is crucial for providing theoretical support to urban planning and decision-making.In this study,Shenyang was selected to comprehensively analyse multiple factors,including topography,human activity,vegetation and landscape.Moreover,we used the random forest algorithm to explore nonlinear factors influencing land surface temperature(LST)over four years in the study area.The results revealed that from 2005 to 2020,the total areas with sub-high and high-temperature zones in northern Shenyang steadily increased.The area ratio of these zones increased from 20.18% in 2005 to 24.86% in 2020.Additionally,significant and strong correlations were observed between LST and variables such as the enhanced vegetation index(EVI),normalised difference vegetation index(NDVI),population density,proportion of cropland and proportion of impervious land.In 2010,proportion of impervious land exhibited the strongest correlation with LST at the 5 km scale,reaching 0.852(p<0.01).The 4 km grid scale was identified as the optimal grid size for this study,while the 2 km grid performed the worst.In 2020,NDVI emerged as the most significant factor influencing LST.These findings provide valuable guidance for improving urban planning and developing sustainable strategies.展开更多
Landslides pose a formidable natural hazard across the Qinghai-Tibet Plateau(QTP),endangering both ecosystems and human life.Identifying the driving factors behind landslides and accurately assessing susceptibility ar...Landslides pose a formidable natural hazard across the Qinghai-Tibet Plateau(QTP),endangering both ecosystems and human life.Identifying the driving factors behind landslides and accurately assessing susceptibility are key to mitigating disaster risk.This study integrated multi-source historical landslide data with 15 predictive factors and used several machine learning models—Random Forest(RF),Gradient Boosting Regression Trees(GBRT),Extreme Gradient Boosting(XGBoost),and Categorical Boosting(CatBoost)—to generate susceptibility maps.The Shapley additive explanation(SHAP)method was applied to quantify factor importance and explore their nonlinear effects.The results showed that:(1)CatBoost was the best-performing model(CA=0.938,AUC=0.980)in assessing landslide susceptibility,with altitude emerging as the most significant factor,followed by distance to roads and earthquake sites,precipitation,and slope;(2)the SHAP method revealed critical nonlinear thresholds,demonstrating that historical landslides were concentrated at mid-altitudes(1400-4000 m)and decreased markedly above 4000 m,with a parallel reduction in probability beyond 700 m from roads;and(3)landslide-prone areas,comprising 13%of the QTP,were concentrated in the southeastern and northeastern parts of the plateau.By integrating machine learning and SHAP analysis,this study revealed landslide hazard-prone areas and their driving factors,providing insights to support disaster management strategies and sustainable regional planning.展开更多
The robust control issue for uncertain nonlinear system is discussed by using the method of right coprime factorization.As it is difficult to obtain the inverse of the right factor due to the high nonlinearity,the pro...The robust control issue for uncertain nonlinear system is discussed by using the method of right coprime factorization.As it is difficult to obtain the inverse of the right factor due to the high nonlinearity,the proving of the Bezout identity becomes troublesome.Therefore,two sufficient conditions are derived to manage this problem with the nonlinear feedback system as well as that with the uncertain nonlinear feedback system under the definition of Lipschitz norm.A simulation of temperature control is given to demonstrate the validity of the proposed method.展开更多
The compact implicit integration factor （cIIF） method is an efficient time discretization scheme for stiff nonlinear diffusion equations in two and three spatial dimensions. In the current work, we apply the cIIF me...The compact implicit integration factor （cIIF） method is an efficient time discretization scheme for stiff nonlinear diffusion equations in two and three spatial dimensions. In the current work, we apply the cIIF method to some complex-valued nonlinear evolutionary equations such as the nonlinear SchrSdinger （NLS） equation and the complex Ginzburg-Landau （GL） equation. Detailed algorithm formulation and practical implementation of cIIF method are performed. The numerical results indicate that this method is very accurate and efficient.展开更多
Within the linear framework,the Modal Electromechanical Coupling Factor(MEMCF)is an important indicator to quantify the dynamic conversion of mechanical energy and electrical energy of piezoelectric structures.It is a...Within the linear framework,the Modal Electromechanical Coupling Factor(MEMCF)is an important indicator to quantify the dynamic conversion of mechanical energy and electrical energy of piezoelectric structures.It is also an important tool to guide the piezoelectric damping design of linear structures.Advanced aircraft often fly in maneuvers,and the variable working conditions induce drastic changes in the load level on structures.Geometric and contact nonlinearities of thin-walled structures and joint structures are often activated.To achieve a good vibration reduction effect covering all working conditions,one cannot directly use linear electromechanical coupling theory to instruct the piezoelectric damping design for nonlinear structures.Therefore,this paper defines the Nonlinear Modal Electromechanical Coupling Factor(NMEMCF)and proposes the corresponding numerical method for the first time to quantitatively evaluate the electromechanical coupling capability of nonlinear piezoelectric structures.Three candidate definitions of the NMEMCF are given,including two frequency definitions and one energy definition.The energy definition is the most promising one.It is not only applicable to both conservative and dissipative nonlinear structures but also compatible with the linear MEMCF.In addition,based on the energy formula,the NMEMCF can be obtained by only performing one nonlinear modal analysis in the open-circuit state.The analytical findings and the numerical tool are validated against two piezoelectric structures with different types of nonlinearities.A strong correlation among the NMEMCF,geometric parameters,and energy dissipation is observed.The results confirm that the proposed NMEMCF captures the physics of the electromechanical coupling phenomenon associated with nonlinear piezoelectric structures and can be used as an essential design indicator of piezoelectric damping,especially for variable working conditions.展开更多
This study investigates the asymmetric relationship between global and national fac-tors and domestic food prices in Turkey,considering the recent rapid and continuous increase in domestic food prices.In this context,...This study investigates the asymmetric relationship between global and national fac-tors and domestic food prices in Turkey,considering the recent rapid and continuous increase in domestic food prices.In this context,six global and three national explana-tory variables were included,and monthly data for the period from January 2004 to June 2021 were used.In addition,novel nonlinear time-series econometric approaches,such as wavelet coherence,Granger causality in quantiles,and quantile-on-quantile regression,were applied for examination at different times,frequencies,and quan-tiles.Moreover,the Toda-Yamamoto(TY)causality test and quantile regression(QR)approach were used for robustness checks.The empirical results revealed that(i)there is a significant relationship between domestic food prices and explanatory variables at different times and frequencies;(ii)a causal relationship exists in most quantiles,excluding the lowest quantile,some middle quantiles,and the highest quantile for some variables;(iii)the power of the effect of the explanatory variables on domestic food prices varies according to the quantiles;and(iv)the results were validated by the TY causality test and QR,which show that the results were robust.Overall,the empiri-cal results reveal that global and national factors have an asymmetric relationship with domestic food prices,highlighting the effects of fluctuations in global and national variables on domestic food prices.Thus,the results imply that Turkish policymakers should consider the asymmetric effects of global and national factors on domestic food prices at different times,frequencies,and quantiles.展开更多
Both the complex geometrical morphology of rough-walled rock fractures and the nonlinearity of fluid flow contribute to resistance in fluid flow through rock fractures.The interactions of the shear-flow process furthe...Both the complex geometrical morphology of rough-walled rock fractures and the nonlinearity of fluid flow contribute to resistance in fluid flow through rock fractures.The interactions of the shear-flow process further complicate the characterisation of flow behaviours in rock fractures.In this study,an improved friction factor model involving both the effects of viscous and inertial forces is presented based on the Forchheimer equation.The model incorporates two key variables,i.e.Reynolds number and relative roughness,which reflect the effects of flow regimes and fracture roughness,respectively.The changes in geometrical parameters induced by shearing are considered,with the peak asperity height predicted through a correlation with post-peak roughness degradation.The hydraulic aperture during shearing is estimated using a suggested equation that accounts for the mobilised contact area ratio and variable aperture distribution.The parametric sensitivity analysis reveals that shear-induced changes in fracture geometry enhance the flow nonlinearity in rock fractures.The model performs well in predicting the friction factor based on two validation criteria.Then,the proposed friction factor model is incorporated into the three-dimensional distinct element code(3DEC)in the form of the Darcy-Weisbach equation.Coupled with the numerically implemented mechanical model and hydraulic aperture prediction model,numerical simulations of coupled shear-flow processes in single rock fractures are conducted.The simulation outcomes are validated through comparison with the experimental results,showing acceptable agreement and demonstrating that the numerical model is capable of accurately evaluating the hydro-mechanical coupling behaviour during the shearing of rock fractures.展开更多
BACKGROUND Low serum albumin levels are established predictors of adverse outcomes in various cardiovascular conditions.However,the role of serum albumin in mortality among elderly patients with chronic aortic regurgi...BACKGROUND Low serum albumin levels are established predictors of adverse outcomes in various cardiovascular conditions.However,the role of serum albumin in mortality among elderly patients with chronic aortic regurgitation(AR)has not been thoroughly investigated.This study aims to assess the relationship between serum albumin levels and mortality in this specific patient population.METHODS Our analysis included 873 elderly AR patients from the China Valvular Heart Disease study,with baseline serum albumin measured at enrollment.Mortality outcomes were monitored for two years post-enrollment,employing a Cox proportional hazards model with a two-piecewise Cox proportional hazards framework to investigate the nonlinear relationship between serum albumin levels and all-cause mortality.RESULTS During the 2-year follow-up period,we observed 63 all-cause deaths.The association between serum albumin levels and all-cause mortality displayed an approximating L-shaped curve,indicating a mortality threshold at 35 g/L.For serum albumin levels below 35 g/L,each 1 g/L decrease was associated with a 25%higher risk of all-cause mortality(HR=1.25,95%CI:1.07–1.45).In contrast,no significant change in mortality risk was observed when serum albumin levels were greater than or equal to 35 g/L.Moreover,when serum albumin is classified as hypoproteinemia(serum albumin<35 g/L),the higher risks of all-cause death were observed in hypoproteinemic patients(HR=2.93,95%CI:1.50–5.74).More importantly,the association between serum albumin and death was significantly stronger in overweight/obese patients(≥24 kg/m^(2)vs.<24 kg/m^(2),Pinteraction=0.006).CONCLUSIONS In elderly patients with AR,serum albumin levels showed an approximating L-shaped relationship with all-cause death,with thresholds of 35 g/L.Body mass index was significant effect modifiers of the association.These results suggest that serum albumin,as an inexpensive and readily available biochemical marker,may further improve the stratified risk of mortality in older AR patients.展开更多
Based on the analysis of nonlinear geometric characteristics of the suspension systems and tires, a 3D nonlinear dynamic model of a typical heavy truck is established. The impact factors of dynamic tire loads, includi...Based on the analysis of nonlinear geometric characteristics of the suspension systems and tires, a 3D nonlinear dynamic model of a typical heavy truck is established. The impact factors of dynamic tire loads, including the dynamic load stress factors, and the maximal and the minimal vertical dynamic load factors, are used to evaluate the dynamic interaction between heavy vehicles and roads under the condition of random road surface roughness. Matlab/Simulink is used to simulate the nonlinear dynamic system and calculate the impact factors. The effects of different road surface conditions on the safety of vehicle movement and the durability of parts of a vehicle are analyzed, as well as the effects of different structural parameters and different vehicle speeds on road surfaces. The study results provide both the warning limits of road surface roughness and the limits of corresponding dynamic parameters for the 5-axle heavy truck.展开更多
文摘In the modal analysis and control of nonlinear dynamical systems,participation factors(PFs)of state variables with respect to a critical or selected mode serve as a pivotal tool for simplifying stability studies by focusing on a subset of highly influential state variables.For linear systems,PFs are uniquely determined by the mode’s composition and shape,which are defined by the system’s left and right eigenvectors,respectively.However,the uniqueness of other types of PFs has not been thoroughly addressed in literatures.This paper establishes sufficient conditions for the uniqueness of nonlinear PFs and five other PF variants,taking into account uncertain scaling factors in a mode’s shape and composition.These scaling factors arise from variations in the choice of physical units,which depend on the value ranges of real-world state variables.Understanding these sufficient conditions is essential for the correct application of PFs in practical stability analysis and control design.
基金National Natural Science Foundation of China,No.42204031。
文摘With the continuous evolution of urban surface types,the impact of the urban heat island effect on the human population has intensified.Investigating the factors influencing urban thermal environments is crucial for providing theoretical support to urban planning and decision-making.In this study,Shenyang was selected to comprehensively analyse multiple factors,including topography,human activity,vegetation and landscape.Moreover,we used the random forest algorithm to explore nonlinear factors influencing land surface temperature(LST)over four years in the study area.The results revealed that from 2005 to 2020,the total areas with sub-high and high-temperature zones in northern Shenyang steadily increased.The area ratio of these zones increased from 20.18% in 2005 to 24.86% in 2020.Additionally,significant and strong correlations were observed between LST and variables such as the enhanced vegetation index(EVI),normalised difference vegetation index(NDVI),population density,proportion of cropland and proportion of impervious land.In 2010,proportion of impervious land exhibited the strongest correlation with LST at the 5 km scale,reaching 0.852(p<0.01).The 4 km grid scale was identified as the optimal grid size for this study,while the 2 km grid performed the worst.In 2020,NDVI emerged as the most significant factor influencing LST.These findings provide valuable guidance for improving urban planning and developing sustainable strategies.
基金The National Key Research and Development Program of China,No.2023YFC3206601。
文摘Landslides pose a formidable natural hazard across the Qinghai-Tibet Plateau(QTP),endangering both ecosystems and human life.Identifying the driving factors behind landslides and accurately assessing susceptibility are key to mitigating disaster risk.This study integrated multi-source historical landslide data with 15 predictive factors and used several machine learning models—Random Forest(RF),Gradient Boosting Regression Trees(GBRT),Extreme Gradient Boosting(XGBoost),and Categorical Boosting(CatBoost)—to generate susceptibility maps.The Shapley additive explanation(SHAP)method was applied to quantify factor importance and explore their nonlinear effects.The results showed that:(1)CatBoost was the best-performing model(CA=0.938,AUC=0.980)in assessing landslide susceptibility,with altitude emerging as the most significant factor,followed by distance to roads and earthquake sites,precipitation,and slope;(2)the SHAP method revealed critical nonlinear thresholds,demonstrating that historical landslides were concentrated at mid-altitudes(1400-4000 m)and decreased markedly above 4000 m,with a parallel reduction in probability beyond 700 m from roads;and(3)landslide-prone areas,comprising 13%of the QTP,were concentrated in the southeastern and northeastern parts of the plateau.By integrating machine learning and SHAP analysis,this study revealed landslide hazard-prone areas and their driving factors,providing insights to support disaster management strategies and sustainable regional planning.
基金supported by the National Natural Science Foundation of China(61304093,61472195)
文摘The robust control issue for uncertain nonlinear system is discussed by using the method of right coprime factorization.As it is difficult to obtain the inverse of the right factor due to the high nonlinearity,the proving of the Bezout identity becomes troublesome.Therefore,two sufficient conditions are derived to manage this problem with the nonlinear feedback system as well as that with the uncertain nonlinear feedback system under the definition of Lipschitz norm.A simulation of temperature control is given to demonstrate the validity of the proposed method.
文摘The compact implicit integration factor （cIIF） method is an efficient time discretization scheme for stiff nonlinear diffusion equations in two and three spatial dimensions. In the current work, we apply the cIIF method to some complex-valued nonlinear evolutionary equations such as the nonlinear SchrSdinger （NLS） equation and the complex Ginzburg-Landau （GL） equation. Detailed algorithm formulation and practical implementation of cIIF method are performed. The numerical results indicate that this method is very accurate and efficient.
基金funded by Major Projects of Aero-Engines and Gas Turbines(J2019-Ⅳ-0023-0091 and J2019-Ⅳ-0005-0073)Aeronautical Science Foundation of China(2019ZB051002)+1 种基金China Postdoctoral Science Foundation(2021M700326)Advanced Jet Propulsion Creativity Center(Projects HKCX2020-02-013,HKCX2020-02-016 and HKCX2022-01009)。
文摘Within the linear framework,the Modal Electromechanical Coupling Factor(MEMCF)is an important indicator to quantify the dynamic conversion of mechanical energy and electrical energy of piezoelectric structures.It is also an important tool to guide the piezoelectric damping design of linear structures.Advanced aircraft often fly in maneuvers,and the variable working conditions induce drastic changes in the load level on structures.Geometric and contact nonlinearities of thin-walled structures and joint structures are often activated.To achieve a good vibration reduction effect covering all working conditions,one cannot directly use linear electromechanical coupling theory to instruct the piezoelectric damping design for nonlinear structures.Therefore,this paper defines the Nonlinear Modal Electromechanical Coupling Factor(NMEMCF)and proposes the corresponding numerical method for the first time to quantitatively evaluate the electromechanical coupling capability of nonlinear piezoelectric structures.Three candidate definitions of the NMEMCF are given,including two frequency definitions and one energy definition.The energy definition is the most promising one.It is not only applicable to both conservative and dissipative nonlinear structures but also compatible with the linear MEMCF.In addition,based on the energy formula,the NMEMCF can be obtained by only performing one nonlinear modal analysis in the open-circuit state.The analytical findings and the numerical tool are validated against two piezoelectric structures with different types of nonlinearities.A strong correlation among the NMEMCF,geometric parameters,and energy dissipation is observed.The results confirm that the proposed NMEMCF captures the physics of the electromechanical coupling phenomenon associated with nonlinear piezoelectric structures and can be used as an essential design indicator of piezoelectric damping,especially for variable working conditions.
基金from funding agencies in the public,commercial,or not-for-profit sectors.
文摘This study investigates the asymmetric relationship between global and national fac-tors and domestic food prices in Turkey,considering the recent rapid and continuous increase in domestic food prices.In this context,six global and three national explana-tory variables were included,and monthly data for the period from January 2004 to June 2021 were used.In addition,novel nonlinear time-series econometric approaches,such as wavelet coherence,Granger causality in quantiles,and quantile-on-quantile regression,were applied for examination at different times,frequencies,and quan-tiles.Moreover,the Toda-Yamamoto(TY)causality test and quantile regression(QR)approach were used for robustness checks.The empirical results revealed that(i)there is a significant relationship between domestic food prices and explanatory variables at different times and frequencies;(ii)a causal relationship exists in most quantiles,excluding the lowest quantile,some middle quantiles,and the highest quantile for some variables;(iii)the power of the effect of the explanatory variables on domestic food prices varies according to the quantiles;and(iv)the results were validated by the TY causality test and QR,which show that the results were robust.Overall,the empiri-cal results reveal that global and national factors have an asymmetric relationship with domestic food prices,highlighting the effects of fluctuations in global and national variables on domestic food prices.Thus,the results imply that Turkish policymakers should consider the asymmetric effects of global and national factors on domestic food prices at different times,frequencies,and quantiles.
基金supported by the China Scholarship Council(CSC)(Grant No.202006060033).
文摘Both the complex geometrical morphology of rough-walled rock fractures and the nonlinearity of fluid flow contribute to resistance in fluid flow through rock fractures.The interactions of the shear-flow process further complicate the characterisation of flow behaviours in rock fractures.In this study,an improved friction factor model involving both the effects of viscous and inertial forces is presented based on the Forchheimer equation.The model incorporates two key variables,i.e.Reynolds number and relative roughness,which reflect the effects of flow regimes and fracture roughness,respectively.The changes in geometrical parameters induced by shearing are considered,with the peak asperity height predicted through a correlation with post-peak roughness degradation.The hydraulic aperture during shearing is estimated using a suggested equation that accounts for the mobilised contact area ratio and variable aperture distribution.The parametric sensitivity analysis reveals that shear-induced changes in fracture geometry enhance the flow nonlinearity in rock fractures.The model performs well in predicting the friction factor based on two validation criteria.Then,the proposed friction factor model is incorporated into the three-dimensional distinct element code(3DEC)in the form of the Darcy-Weisbach equation.Coupled with the numerically implemented mechanical model and hydraulic aperture prediction model,numerical simulations of coupled shear-flow processes in single rock fractures are conducted.The simulation outcomes are validated through comparison with the experimental results,showing acceptable agreement and demonstrating that the numerical model is capable of accurately evaluating the hydro-mechanical coupling behaviour during the shearing of rock fractures.
基金supported by the Chinese Academy of Medical Sciences Innovation Fund for Medical Sciences(2017-12M-3-002)the Central High Level Hospital Clinical Research Operating Expenses,China(Zero Balance 2022-GSP-GG-15)the Natural Science Foundation Project of the Inner Mongolia Autonomous Region of China(2022LHQN08003).
文摘BACKGROUND Low serum albumin levels are established predictors of adverse outcomes in various cardiovascular conditions.However,the role of serum albumin in mortality among elderly patients with chronic aortic regurgitation(AR)has not been thoroughly investigated.This study aims to assess the relationship between serum albumin levels and mortality in this specific patient population.METHODS Our analysis included 873 elderly AR patients from the China Valvular Heart Disease study,with baseline serum albumin measured at enrollment.Mortality outcomes were monitored for two years post-enrollment,employing a Cox proportional hazards model with a two-piecewise Cox proportional hazards framework to investigate the nonlinear relationship between serum albumin levels and all-cause mortality.RESULTS During the 2-year follow-up period,we observed 63 all-cause deaths.The association between serum albumin levels and all-cause mortality displayed an approximating L-shaped curve,indicating a mortality threshold at 35 g/L.For serum albumin levels below 35 g/L,each 1 g/L decrease was associated with a 25%higher risk of all-cause mortality(HR=1.25,95%CI:1.07–1.45).In contrast,no significant change in mortality risk was observed when serum albumin levels were greater than or equal to 35 g/L.Moreover,when serum albumin is classified as hypoproteinemia(serum albumin<35 g/L),the higher risks of all-cause death were observed in hypoproteinemic patients(HR=2.93,95%CI:1.50–5.74).More importantly,the association between serum albumin and death was significantly stronger in overweight/obese patients(≥24 kg/m^(2)vs.<24 kg/m^(2),Pinteraction=0.006).CONCLUSIONS In elderly patients with AR,serum albumin levels showed an approximating L-shaped relationship with all-cause death,with thresholds of 35 g/L.Body mass index was significant effect modifiers of the association.These results suggest that serum albumin,as an inexpensive and readily available biochemical marker,may further improve the stratified risk of mortality in older AR patients.
基金The Science and Technology Support Program of Jiangsu Province(No.BE201047)
文摘Based on the analysis of nonlinear geometric characteristics of the suspension systems and tires, a 3D nonlinear dynamic model of a typical heavy truck is established. The impact factors of dynamic tire loads, including the dynamic load stress factors, and the maximal and the minimal vertical dynamic load factors, are used to evaluate the dynamic interaction between heavy vehicles and roads under the condition of random road surface roughness. Matlab/Simulink is used to simulate the nonlinear dynamic system and calculate the impact factors. The effects of different road surface conditions on the safety of vehicle movement and the durability of parts of a vehicle are analyzed, as well as the effects of different structural parameters and different vehicle speeds on road surfaces. The study results provide both the warning limits of road surface roughness and the limits of corresponding dynamic parameters for the 5-axle heavy truck.
