On 12 December 2019,a novel coronavirus disease,named COVID-19,began to spread around the world from Wuhan,China.It is useful and urgent to consider the future trend of this outbreak.We establish the 4+1 penta-group m...On 12 December 2019,a novel coronavirus disease,named COVID-19,began to spread around the world from Wuhan,China.It is useful and urgent to consider the future trend of this outbreak.We establish the 4+1 penta-group model to predict the development of the COVID-19 outbreak.In this model,we use the collected data to calibrate the parameters,and let the recovery rate and mortality change according to the actual situation.Furthermore,we propose the BAT model,which is composed of three parts:simulation of the return rush(Back),analytic hierarchy process(AHP)method,and technique for order preference by similarity to an ideal solution(TOPSIS)method,to figure out the best return date for university students.We also discuss the impacts of some factors that may occur in the future,such as secondary infection,emergence of effective drugs,and population flow from Korea to China.展开更多
It is necessary to determine the degradation path model of products at first when using the method based on degradation path model to evaluate the degradation reliability of products.At present,the degradation path mo...It is necessary to determine the degradation path model of products at first when using the method based on degradation path model to evaluate the degradation reliability of products.At present,the degradation path model is mainly determined by scatter plots of degradation data.However,this method has strong subjectivity and is liable to cause the evaluation results to be inconsistent with the actual situation.In this paper,a degradation reliability analysis method based on TOPSIS(technique for order preference by similarity to an ideal solution)model selection is proposed,and its implementation process is given.The optimal degradation path model is selected according to the calculated proximity.With the help of TOPSIS method,various degradation path models can be selected and quantified,and the original degradation path method can be improved to avoid the risk of errors in product reliability evaluation caused by inaccurate subjective hypo thesis,so as to ensure the objectivity and accuracy in the process of model determination.The validity and practicability of the proposed met hod are verified by the degradation analysis of the injector of a certain type of diesel engine.展开更多
We investigate numerical approximations based on polynomials that are orthogonal with respect to a weighted discrete inner product and develop an algorithm for solving time dependent differential equations.We focus on...We investigate numerical approximations based on polynomials that are orthogonal with respect to a weighted discrete inner product and develop an algorithm for solving time dependent differential equations.We focus on the family of super Gaussian weight functions and derive a criterion for the choice of parameters that provides good accuracy and stability for the time evolution of partial differential equations.Our results show that this approach circumvents the problems related to the Runge phenomenon on equally spaced nodes and provides high accuracy in space.For time stability,small corrections near the ends of the interval are computed using local polynomial interpolation.Several numerical experiments illustrate the performance of the method.展开更多
基金the National Key Research and Development Program of China(No.2018YFB1004700)the National Natural Science Foundation of China(Nos.61872238 and 61972254)+1 种基金the Shanghai Science and Technology Fund(No.17510740200)the CCF-Huawei Database System Innovation Research Plan(No.CCF-Huawei DBIR2019002A)。
文摘On 12 December 2019,a novel coronavirus disease,named COVID-19,began to spread around the world from Wuhan,China.It is useful and urgent to consider the future trend of this outbreak.We establish the 4+1 penta-group model to predict the development of the COVID-19 outbreak.In this model,we use the collected data to calibrate the parameters,and let the recovery rate and mortality change according to the actual situation.Furthermore,we propose the BAT model,which is composed of three parts:simulation of the return rush(Back),analytic hierarchy process(AHP)method,and technique for order preference by similarity to an ideal solution(TOPSIS)method,to figure out the best return date for university students.We also discuss the impacts of some factors that may occur in the future,such as secondary infection,emergence of effective drugs,and population flow from Korea to China.
基金the National Natural Science Foundation of China(No.61463021)the Young Scientists Object Program of Jiangxi Province(No.20144BCB23037)the Natural Science Foundation of Jiangxi Province(No.20181BAB202020)
文摘It is necessary to determine the degradation path model of products at first when using the method based on degradation path model to evaluate the degradation reliability of products.At present,the degradation path model is mainly determined by scatter plots of degradation data.However,this method has strong subjectivity and is liable to cause the evaluation results to be inconsistent with the actual situation.In this paper,a degradation reliability analysis method based on TOPSIS(technique for order preference by similarity to an ideal solution)model selection is proposed,and its implementation process is given.The optimal degradation path model is selected according to the calculated proximity.With the help of TOPSIS method,various degradation path models can be selected and quantified,and the original degradation path method can be improved to avoid the risk of errors in product reliability evaluation caused by inaccurate subjective hypo thesis,so as to ensure the objectivity and accuracy in the process of model determination.The validity and practicability of the proposed met hod are verified by the degradation analysis of the injector of a certain type of diesel engine.
文摘We investigate numerical approximations based on polynomials that are orthogonal with respect to a weighted discrete inner product and develop an algorithm for solving time dependent differential equations.We focus on the family of super Gaussian weight functions and derive a criterion for the choice of parameters that provides good accuracy and stability for the time evolution of partial differential equations.Our results show that this approach circumvents the problems related to the Runge phenomenon on equally spaced nodes and provides high accuracy in space.For time stability,small corrections near the ends of the interval are computed using local polynomial interpolation.Several numerical experiments illustrate the performance of the method.
