Tracking the sap flux of woody plants in savannas is essential for understanding their response to climate change and human management.Solar-induced fluorescence(SIF)has potential to predict transpiration yet its appl...Tracking the sap flux of woody plants in savannas is essential for understanding their response to climate change and human management.Solar-induced fluorescence(SIF)has potential to predict transpiration yet its applicability for estimating savanna sap flux is unclear.Using three years of tower-based far-red SIF observations and groundbased sap flow monitoring in a temperate savanna of Otindag Sandy Land,China,we investigated the relationship between far-red SIF and sap flux density and developed linear and random forest models for estimating.The results show a variable correlation between SIF and sap flux density for Ulmus pumila var.sabulosa(J.H.Xin)G.H.Zhu&D.H.Bian(U.pumila.)at an hourly scale.The strongest correlations were during the mid-growth period July and August when considering the time lag between SIF and sap flux(0-0.5 h).Photosynthetically active radiation was the primary factor driving the SIF and sap flux density relationship.Soil moisture,vapor pressure deficit,and air temperature also influenced this relationship on daily and monthly scales.Compared to SIF-based linear regression models,the SIF-based random forest model performed better in tracking the seasonal sap flux density.The results suggest the feasibility of accurately monitoring vegetation sap flux using SIF,woody fractional vegetation cover,and environmental factors in a temperate savanna.This method could also be used in modeling land surface processes in savanna-type ecosystems.展开更多
The fracture behavior of superconducting tapes with central and edge oblique cracks subject to electromagnetic forces is investigated. Maxwell's equations and the critical state-Bean model are used to analytically...The fracture behavior of superconducting tapes with central and edge oblique cracks subject to electromagnetic forces is investigated. Maxwell's equations and the critical state-Bean model are used to analytically determine the magnetic flux density and electromagnetic force distributions in superconducting tapes containing central and edge oblique cracks. The distributed dislocation technique(DDT) transforms the mixed boundary value problem into a Cauchy singular integral equation, which is then solved by the Gauss-Chebyshev quadrature method to determine the stress intensity factors(SIFs).The model's accuracy is validated by comparing the calculated electromagnetic force distribution for the edge oblique crack and the SIFs for both crack types with the existing results. The findings indicate that the current and electromagnetic forces are significantly affected by the crack length and oblique angle. Specifically, for central oblique cracks, a smaller oblique angle enhances the risk of crack propagation, and a higher initial magnetization intensity poses greater danger under field cooling(FC) excitation. In contrast, for edge oblique cracks, a larger angle increases the likelihood of tape fractures. This study provides important insights into the fracture behavior and mechanical failure mechanisms of superconducting tapes with oblique cracks.展开更多
The three-phase-lag(TPL)heat conduction model is an accurate representation of the actual heat transfer process.It would be interesting to investigate how the TPL model affects the thermal fracture behavior when there...The three-phase-lag(TPL)heat conduction model is an accurate representation of the actual heat transfer process.It would be interesting to investigate how the TPL model affects the thermal fracture behavior when there are defects existing in the medium.This paper aims to analyze the thermoelastic responses of two collinear cracks within a functionally graded half-space under thermal loadings by means of the TPL model.The thermoelastic problem is transformed into a series of singular integral equations using the integral transformation methods.The transient temperature and stress intensity factors(SIFs)are obtained through the application of Chebyshev polynomials.The effects of crack spacing and non-homogeneous parameters on the transient thermoelastic responses are presented,and the results of the TPL model are compared with those of the Fourier model,Cattaneo and Vernotte(CV)model,and dual-phase-lag(DPL)model.It is shown that crack spacing and non-homogeneous parameters have important effects on the thermoelastic responses,and the fluctuation phenomenon under the TPL model is the most pronounced due to the existence of the thermal displacement lag term.展开更多
Gross primary production(GPP)is closely associated with processes such as photosynthesis and transpiration within ecosystems,which is a vital component of the global carbon-water-energy cycle.Accurate prediction of GP...Gross primary production(GPP)is closely associated with processes such as photosynthesis and transpiration within ecosystems,which is a vital component of the global carbon-water-energy cycle.Accurate prediction of GPP in terrestrial ecosystems is essential for evaluating terrestrial carbon cycle processes.Machine learning(ML)models provide significant technical support in this domain.Presently,there is a deficiency of high-precision and robust GPP prediction variables and models.Challenges such as unclear contributions of predictive variables,extended model training durations,and limited robustness must be addressed.Solar-induced chlorophyll fluorescence(SIF),optimized multilayer perceptron neural networks,and ensemble learning models show the potential to overcome these challenges.This study aimed to develop an optimized multilayer perceptron neural network model and an ensemble learning model,while objectively assessing the capacity of SIF to predict GPP.Identifying robust models capable of enhancing the accuracy of GPP predictions was the ultimate goal.This study utilized continuous observations of SIF and meteorological data collected from 2020 to 2021 at a designated research observation station within the Populus plantation ecosystem of the Huanghuaihai agricultural protective forest system in Henan Province,China.By optimizing and evaluating the predictive accuracy and robustness of the models across different temporal scales(half-hourly and daily scales),a multi-layer perceptron(MLP)neural network optimization model based on the back propagation(BP)neural network(BPNN)algorithm(BP/MLP)and MLP and random forest(RF)integration(MLP-RF)ensemble models were constructed,utilizing SIF as the primary predictive variable for GPP.Both the BP/MLP(half-hourly scale model R^(2)=0.885,daily scale model R^(2)=0.921)and the MLP-RF(half-hourly scale model R^(2)=0.845,daily scale model R^(2)=0.914)models showed superior accuracy compared to the BPNN(half-hourly scale model R^(2)=0.841,daily scale model R^(2)=0.918)and the traditional RF(half-hourly scale model R^(2)=0.798,daily scale model R^(2)=0.867)models,with the BP/MLP model consistently outperforming the MLP-RF model.The BP/MLP model,which was optimized through particle swarm optimization(PSO),significantly enhanced the robustness of GPP predictions on a half-hourly scale and daily scale.Considering both half-hourly scale and daily scale in the PSO-BP/MLP modeling,the four indicators,light-use efficiency(LUE),photosynthetically active radiation(PAR),absorbed photosynthetically active radiation(APAR),and the variation in SIF with NIRvP(fSIF(NIRvP)),exhibited the potential for enhancing the accuracy of GPP predictions.This study employed a series of model optimization techniques to develop a GPP prediction model with enhanced performance that objectively evaluated the contributions of the predictive variables.This approach provided an innovative and effective method for assessing the carbon cycle in terrestrial ecosystems.展开更多
In this paper,we investigate the interfacial behavior of a thin,penny-shaped,one-dimensional(1D)hexagonal functionally graded(FG)piezoelectric quasicrystal(PQC)film bonded on a temperature-dependent elastic substrate ...In this paper,we investigate the interfacial behavior of a thin,penny-shaped,one-dimensional(1D)hexagonal functionally graded(FG)piezoelectric quasicrystal(PQC)film bonded on a temperature-dependent elastic substrate under thermal and electrical loads.The problem is modeled as axisymmetric based on the membrane theory,with the peeling stress and bending moment being disregarded.A potential theory method,combined with the Hankel transform technique,is utilized to derive the displacement field on the substrate surface.With perfect interfacial bonding assumption,an integral equation governing the phonon interfacial shear stress is formulated and numerically solved by the Chebyshev polynomials.Explicit expressions are derived for the interfacial shear stress,the internal stresses within the PQC film and the substrate,the axial strain,and the stress intensity factors(SIFs).Numerical simulations are conducted to investigate the effects of the film's aspect ratio,material inhomogeneity,material mismatch,and temperature-dependent material properties on its mechanical response.The results provide insights for the functional design and reliability assessment of FG PQC film/substrate systems.展开更多
基金supported by the Fundamental Research Funds of Chinese Academy of Forestry(grants No.CAFYBB2020QD002,CAFYBB2021MC002 and CAFYBB2023ZA009)National Natural Science Foundation of China(grants 32001371,32171875 and 32371960)。
文摘Tracking the sap flux of woody plants in savannas is essential for understanding their response to climate change and human management.Solar-induced fluorescence(SIF)has potential to predict transpiration yet its applicability for estimating savanna sap flux is unclear.Using three years of tower-based far-red SIF observations and groundbased sap flow monitoring in a temperate savanna of Otindag Sandy Land,China,we investigated the relationship between far-red SIF and sap flux density and developed linear and random forest models for estimating.The results show a variable correlation between SIF and sap flux density for Ulmus pumila var.sabulosa(J.H.Xin)G.H.Zhu&D.H.Bian(U.pumila.)at an hourly scale.The strongest correlations were during the mid-growth period July and August when considering the time lag between SIF and sap flux(0-0.5 h).Photosynthetically active radiation was the primary factor driving the SIF and sap flux density relationship.Soil moisture,vapor pressure deficit,and air temperature also influenced this relationship on daily and monthly scales.Compared to SIF-based linear regression models,the SIF-based random forest model performed better in tracking the seasonal sap flux density.The results suggest the feasibility of accurately monitoring vegetation sap flux using SIF,woody fractional vegetation cover,and environmental factors in a temperate savanna.This method could also be used in modeling land surface processes in savanna-type ecosystems.
基金Project supported by the National Natural Science Foundation of China (Nos. 12232005 and 12072101)the Ningxia Natural Science Foundation of China (No. 2024AAC04004)。
文摘The fracture behavior of superconducting tapes with central and edge oblique cracks subject to electromagnetic forces is investigated. Maxwell's equations and the critical state-Bean model are used to analytically determine the magnetic flux density and electromagnetic force distributions in superconducting tapes containing central and edge oblique cracks. The distributed dislocation technique(DDT) transforms the mixed boundary value problem into a Cauchy singular integral equation, which is then solved by the Gauss-Chebyshev quadrature method to determine the stress intensity factors(SIFs).The model's accuracy is validated by comparing the calculated electromagnetic force distribution for the edge oblique crack and the SIFs for both crack types with the existing results. The findings indicate that the current and electromagnetic forces are significantly affected by the crack length and oblique angle. Specifically, for central oblique cracks, a smaller oblique angle enhances the risk of crack propagation, and a higher initial magnetization intensity poses greater danger under field cooling(FC) excitation. In contrast, for edge oblique cracks, a larger angle increases the likelihood of tape fractures. This study provides important insights into the fracture behavior and mechanical failure mechanisms of superconducting tapes with oblique cracks.
基金Project supported by the Natural Science Foundation of Shandong Province of China(No.ZR2024MA085)the Science and Technology Plan Project of Zhejiang Province of China(No.2023C03143)the Fundamental Research Funds for the Central Universities of China。
文摘The three-phase-lag(TPL)heat conduction model is an accurate representation of the actual heat transfer process.It would be interesting to investigate how the TPL model affects the thermal fracture behavior when there are defects existing in the medium.This paper aims to analyze the thermoelastic responses of two collinear cracks within a functionally graded half-space under thermal loadings by means of the TPL model.The thermoelastic problem is transformed into a series of singular integral equations using the integral transformation methods.The transient temperature and stress intensity factors(SIFs)are obtained through the application of Chebyshev polynomials.The effects of crack spacing and non-homogeneous parameters on the transient thermoelastic responses are presented,and the results of the TPL model are compared with those of the Fourier model,Cattaneo and Vernotte(CV)model,and dual-phase-lag(DPL)model.It is shown that crack spacing and non-homogeneous parameters have important effects on the thermoelastic responses,and the fluctuation phenomenon under the TPL model is the most pronounced due to the existence of the thermal displacement lag term.
基金supported by the National Key R&D Program of China(No.2023YFD2200400-01)the Fundamental Scientific Research Operation of Central-level Public Welfare Scientific Research Institutes(No.CAFYBB2023MA001).
文摘Gross primary production(GPP)is closely associated with processes such as photosynthesis and transpiration within ecosystems,which is a vital component of the global carbon-water-energy cycle.Accurate prediction of GPP in terrestrial ecosystems is essential for evaluating terrestrial carbon cycle processes.Machine learning(ML)models provide significant technical support in this domain.Presently,there is a deficiency of high-precision and robust GPP prediction variables and models.Challenges such as unclear contributions of predictive variables,extended model training durations,and limited robustness must be addressed.Solar-induced chlorophyll fluorescence(SIF),optimized multilayer perceptron neural networks,and ensemble learning models show the potential to overcome these challenges.This study aimed to develop an optimized multilayer perceptron neural network model and an ensemble learning model,while objectively assessing the capacity of SIF to predict GPP.Identifying robust models capable of enhancing the accuracy of GPP predictions was the ultimate goal.This study utilized continuous observations of SIF and meteorological data collected from 2020 to 2021 at a designated research observation station within the Populus plantation ecosystem of the Huanghuaihai agricultural protective forest system in Henan Province,China.By optimizing and evaluating the predictive accuracy and robustness of the models across different temporal scales(half-hourly and daily scales),a multi-layer perceptron(MLP)neural network optimization model based on the back propagation(BP)neural network(BPNN)algorithm(BP/MLP)and MLP and random forest(RF)integration(MLP-RF)ensemble models were constructed,utilizing SIF as the primary predictive variable for GPP.Both the BP/MLP(half-hourly scale model R^(2)=0.885,daily scale model R^(2)=0.921)and the MLP-RF(half-hourly scale model R^(2)=0.845,daily scale model R^(2)=0.914)models showed superior accuracy compared to the BPNN(half-hourly scale model R^(2)=0.841,daily scale model R^(2)=0.918)and the traditional RF(half-hourly scale model R^(2)=0.798,daily scale model R^(2)=0.867)models,with the BP/MLP model consistently outperforming the MLP-RF model.The BP/MLP model,which was optimized through particle swarm optimization(PSO),significantly enhanced the robustness of GPP predictions on a half-hourly scale and daily scale.Considering both half-hourly scale and daily scale in the PSO-BP/MLP modeling,the four indicators,light-use efficiency(LUE),photosynthetically active radiation(PAR),absorbed photosynthetically active radiation(APAR),and the variation in SIF with NIRvP(fSIF(NIRvP)),exhibited the potential for enhancing the accuracy of GPP predictions.This study employed a series of model optimization techniques to develop a GPP prediction model with enhanced performance that objectively evaluated the contributions of the predictive variables.This approach provided an innovative and effective method for assessing the carbon cycle in terrestrial ecosystems.
基金Project supported by the National Natural Science Foundation of China(Nos.11902293 and 12272353)。
文摘In this paper,we investigate the interfacial behavior of a thin,penny-shaped,one-dimensional(1D)hexagonal functionally graded(FG)piezoelectric quasicrystal(PQC)film bonded on a temperature-dependent elastic substrate under thermal and electrical loads.The problem is modeled as axisymmetric based on the membrane theory,with the peeling stress and bending moment being disregarded.A potential theory method,combined with the Hankel transform technique,is utilized to derive the displacement field on the substrate surface.With perfect interfacial bonding assumption,an integral equation governing the phonon interfacial shear stress is formulated and numerically solved by the Chebyshev polynomials.Explicit expressions are derived for the interfacial shear stress,the internal stresses within the PQC film and the substrate,the axial strain,and the stress intensity factors(SIFs).Numerical simulations are conducted to investigate the effects of the film's aspect ratio,material inhomogeneity,material mismatch,and temperature-dependent material properties on its mechanical response.The results provide insights for the functional design and reliability assessment of FG PQC film/substrate systems.
