Using the order parameter of seismicity defined in natural time, we suggest a simple model for the expla- nation of Bath law, according to which a mainshock differs in magnitude from its largest aftershock by approxim...Using the order parameter of seismicity defined in natural time, we suggest a simple model for the expla- nation of Bath law, according to which a mainshock differs in magnitude from its largest aftershock by approximately 1.2 regardless of the mainshock magnitude. In addition, the validity of Bath law is studied in the Global Centroid Moment Tensor catalogue by using two different aftershock definitions. It is found that the mean of this difference, when considering all the pairs mainshock-largest aftershock, does not markedly differ from 1.2 and the corresponding distributions do not depend on the mainshock＇s magnitude threshold in a statistically significant manner. Finally, the analysis of the cumulative distribution functions provides evidence in favour of the proposed model.展开更多
In modern vehicles, electronic throttle(ET) has been widely utilized to control the airflow into gasoline engine. To solve the control difficulties with an ET, such as strong nonlinearity,unknown model parameters and ...In modern vehicles, electronic throttle(ET) has been widely utilized to control the airflow into gasoline engine. To solve the control difficulties with an ET, such as strong nonlinearity,unknown model parameters and input saturation constraints,an adaptive sliding-mode tracking control strategy for an ET is presented. Compared with the existing control strategies for an ET, input saturation constraints and parameter uncertainties are adequately considered in the proposed control strategy. At first, the nonlinear dynamic model for control of an ET is described. According to the dynamical model, the nonlinear adaptive sliding-mode tracking control method is presented,where parameter adaptive laws and auxiliary design system are employed. Parameter adaptive law is given to estimate the unknown parameter with an ET. An auxiliary system is designed,and its state is utilized in the tracking control method to handle the input saturation. Stability proof and analysis of the adaptive sliding-mode control method is performed by using Lyapunov stability theory. Finally, the reliability and feasibility of the proposed control strategy are evaluated by computer simulation.Simulation research shows that the proposed sliding-mode control strategy can provide good control performance for an ET.展开更多
The distinct element method（DEM） incorporated with a novel bond contact model was applied in this paper to shed light on the microscopic physical origin of macroscopic behaviors of weathered rock, and to achieve the...The distinct element method（DEM） incorporated with a novel bond contact model was applied in this paper to shed light on the microscopic physical origin of macroscopic behaviors of weathered rock, and to achieve the changing laws of microscopic parameters from observed decaying properties of rocks during weathering. The changing laws of macroscopic mechanical properties of typical rocks were summarized based on the existing research achievements. Parametric simulations were then conducted to analyze the relationships between macroscopic and microscopic parameters, and to derive the changing laws of microscopic parameters for the DEM model. Equipped with the microscopic weathering laws, a series of DEM simulations of basic laboratory tests on weathered rock samples was performed in comparison with analytical solutions. The results reveal that the relationships between macroscopic and microscopic parameters of rocks against the weathering period can be successfully attained by parametric simulations. In addition, weathering has a significant impact on both stressestrain relationship and failure pattern of rocks.展开更多
In [7], a general integer-valued time series model, the generalization of the model proposedby Al-Osh and Al..id[1], has been proposed. Its stationarity and spectral representation hasbeen investigated. In this paper,...In [7], a general integer-valued time series model, the generalization of the model proposedby Al-Osh and Al..id[1], has been proposed. Its stationarity and spectral representation hasbeen investigated. In this paper, we make a further study of the model. Its strong law of largenumbers and parameter estimstion are obtained. At the end of the paper, we give a few openproblems to be researched further.展开更多
Here we consider our four-point flexure and compression creep results obtained under Ar protection at 1800℃ to predict the tensile creep behavior of a ZrB_(2)-20 vol%SiC ultra-high temperature ceramic.Assuming power ...Here we consider our four-point flexure and compression creep results obtained under Ar protection at 1800℃ to predict the tensile creep behavior of a ZrB_(2)-20 vol%SiC ultra-high temperature ceramic.Assuming power law creep,and based on four-point bend data,we estimated the uniaxial creep parameters using an analytical method present in the literature.Both predicted and experimental compressive stress exponents were found to be in excellent agreement,1.85 and 1.76 respectively,while observation of the microstructure suggested a combination of diffusion and grain boundary sliding creep mechanisms in compression.Along with the microstructural evidence associated with the tensile regions of the flexure specimens,the predicted tensile stress exponent of 2.61 exceeds the measured flexural value of 2.2.We assert an increasing role of cavitation to the creep strain in pure tension.This cavitation component adds to the dominant grain boundary sliding mechanism as described below and elsewhere for flexural creep.展开更多
文摘Using the order parameter of seismicity defined in natural time, we suggest a simple model for the expla- nation of Bath law, according to which a mainshock differs in magnitude from its largest aftershock by approximately 1.2 regardless of the mainshock magnitude. In addition, the validity of Bath law is studied in the Global Centroid Moment Tensor catalogue by using two different aftershock definitions. It is found that the mean of this difference, when considering all the pairs mainshock-largest aftershock, does not markedly differ from 1.2 and the corresponding distributions do not depend on the mainshock＇s magnitude threshold in a statistically significant manner. Finally, the analysis of the cumulative distribution functions provides evidence in favour of the proposed model.
基金partially supported by the National Natural Science Foundation of China(61773189)Natural Science Fundamental of Liaoning Province(20170540443)the Program for Liaoning Innovative Research Team in University(LT2016006)
文摘In modern vehicles, electronic throttle(ET) has been widely utilized to control the airflow into gasoline engine. To solve the control difficulties with an ET, such as strong nonlinearity,unknown model parameters and input saturation constraints,an adaptive sliding-mode tracking control strategy for an ET is presented. Compared with the existing control strategies for an ET, input saturation constraints and parameter uncertainties are adequately considered in the proposed control strategy. At first, the nonlinear dynamic model for control of an ET is described. According to the dynamical model, the nonlinear adaptive sliding-mode tracking control method is presented,where parameter adaptive laws and auxiliary design system are employed. Parameter adaptive law is given to estimate the unknown parameter with an ET. An auxiliary system is designed,and its state is utilized in the tracking control method to handle the input saturation. Stability proof and analysis of the adaptive sliding-mode control method is performed by using Lyapunov stability theory. Finally, the reliability and feasibility of the proposed control strategy are evaluated by computer simulation.Simulation research shows that the proposed sliding-mode control strategy can provide good control performance for an ET.
基金funded by the National Basic Research Programs of China(Grant Nos.2011CB013504 and 2014CB046901)the National Funds for Distinguished Young Scientists of China(Grant No.51025932)the National Nature Science Foundation of China(Grant No.41372272)
文摘The distinct element method（DEM） incorporated with a novel bond contact model was applied in this paper to shed light on the microscopic physical origin of macroscopic behaviors of weathered rock, and to achieve the changing laws of microscopic parameters from observed decaying properties of rocks during weathering. The changing laws of macroscopic mechanical properties of typical rocks were summarized based on the existing research achievements. Parametric simulations were then conducted to analyze the relationships between macroscopic and microscopic parameters, and to derive the changing laws of microscopic parameters for the DEM model. Equipped with the microscopic weathering laws, a series of DEM simulations of basic laboratory tests on weathered rock samples was performed in comparison with analytical solutions. The results reveal that the relationships between macroscopic and microscopic parameters of rocks against the weathering period can be successfully attained by parametric simulations. In addition, weathering has a significant impact on both stressestrain relationship and failure pattern of rocks.
文摘In [7], a general integer-valued time series model, the generalization of the model proposedby Al-Osh and Al..id[1], has been proposed. Its stationarity and spectral representation hasbeen investigated. In this paper, we make a further study of the model. Its strong law of largenumbers and parameter estimstion are obtained. At the end of the paper, we give a few openproblems to be researched further.
基金AFOSR program monitor Ali Sayir,under grant#FA9550-09-1-0200,for partial support of this work.
文摘Here we consider our four-point flexure and compression creep results obtained under Ar protection at 1800℃ to predict the tensile creep behavior of a ZrB_(2)-20 vol%SiC ultra-high temperature ceramic.Assuming power law creep,and based on four-point bend data,we estimated the uniaxial creep parameters using an analytical method present in the literature.Both predicted and experimental compressive stress exponents were found to be in excellent agreement,1.85 and 1.76 respectively,while observation of the microstructure suggested a combination of diffusion and grain boundary sliding creep mechanisms in compression.Along with the microstructural evidence associated with the tensile regions of the flexure specimens,the predicted tensile stress exponent of 2.61 exceeds the measured flexural value of 2.2.We assert an increasing role of cavitation to the creep strain in pure tension.This cavitation component adds to the dominant grain boundary sliding mechanism as described below and elsewhere for flexural creep.
