The nonlinear and transient vibration of a rotor, which dropped onto back-up bearings when its active magnetic bearings were out of order, was investigated. After strictly deriving its equations of motion and performi...The nonlinear and transient vibration of a rotor, which dropped onto back-up bearings when its active magnetic bearings were out of order, was investigated. After strictly deriving its equations of motion and performing numerical simulations, the time-histories of rotating speed of the dropping rotor, and normal force at the rubbing contact point as well as the frequency spectrum of the vibration displacement of back-up bearings are fully analyzed. It is found that the strong and unsteady forced bending vibration of the unbalanced and, damped rotor decelerating through : its first. bending vibtation of the unbalanced and, damped rotor decelerating through its,first critical speed as well as chattering at high frequencies caused by the nonlinearity at the rubbing contact point between, the journal and back-up bearings may lead to the catastrophic damage. of the system.展开更多
本文根据Cummins et al（2002）的反应函数模型对我国财产保险公司2009～2013年的巨灾风险赔付效率进行了测算，并对影响保险公司应对巨灾风险能力差异的因素进行了分析。我们发现尽管我国财险市场有了较快的发展，但对巨灾风险的覆盖...本文根据Cummins et al（2002）的反应函数模型对我国财产保险公司2009～2013年的巨灾风险赔付效率进行了测算，并对影响保险公司应对巨灾风险能力差异的因素进行了分析。我们发现尽管我国财险市场有了较快的发展，但对巨灾风险的覆盖能力依然较弱，尤其是对极端情况下的巨灾损失覆盖效率较低。应对巨灾能力差异的因素包括保险公司的实际赔付率、承保风险、权益资本、再保险的利用率、公司规模等。我们还发现“偿二代”一方面能促进风险管理水平高的公司释放更多资本金，另一方面能促使风险管理水平较低的公司调整业务结构、提高风险管理水平，从而增加全行业应对巨灾风险的能力。展开更多
Aphids are a major global wheat,pest that can cause considerable loss of yield.Modeling of aphid population dynamics is an integral part of management strategies to manage or control aphid populations.In this paper,fi...Aphids are a major global wheat,pest that can cause considerable loss of yield.Modeling of aphid population dynamics is an integral part of management strategies to manage or control aphid populations.In this paper,first,a wheat aphid population dynamics model was developed based on a logistic model and theⅠlollingⅢfunctional response,which includes three factors:temperature,natural enemies and insecticide.Second,this model fitted with a cusp catastrophe model to describe how abrupt changes in the wheat aphid population were influenced by these factors,Finally,the system was validated with field data from 2016 to 2018.The bifurcation set of the cusp catastrophe model was deemod to be the quantified dynamic control threshold,so an outbreak of aphid's population can be explained according to the variation of control variables.In short,this aphid population model was successfully validated on survey data,which can be used to guide the prevention and control of aphids.展开更多
The Lewisian turning-point obviously increase the labor costs of Chinese manufacturing firms,it made the employee turnover to become the key problem that how to keep the enterprise human resource stability.Here,the co...The Lewisian turning-point obviously increase the labor costs of Chinese manufacturing firms,it made the employee turnover to become the key problem that how to keep the enterprise human resource stability.Here,the conceptual catastrophe model of employee turnover is built from the new perspective of empirical study and catastrophe theory.In particular,we developed a parameter estimation method of the Cusp catastrophe model based on qualitative simulation and fuzzy math,and then to demonstrate the rationality and robustness of this method by a practical case on a manufacturing enterprise.In the end,a series of virtual experiments are carried out for the employee turnover in the period of China’s economic transformation.The main results are that,how to measure the warning,critical and mutation area of employee turnover;the real relationship between the complex economic environment and the demission of employees;the control policy from the macroscopic governmental measures and microscopic enterprise ways.展开更多
Ecological security defined as the creation of a condition where the physical surroundings of a community provide for the needs of its inhabitants without diminishing its natural stock,which is important for regional ...Ecological security defined as the creation of a condition where the physical surroundings of a community provide for the needs of its inhabitants without diminishing its natural stock,which is important for regional security and social stability.In recent years,land use patterns in the Changbai Mountain region have changed significantly with intensive human activities,and consequently led to increasing problems in regional ecological security.Based on the Pressure-State-Impact-Response(PSIR) model and the mathematical method of catastrophe progression supported by geographical information system(GIS),the ecological security situation of the study area under land use and cover change(LUCC) was evaluated.The results indicated that the ecological security in Changbai Mountain region varied nonlinearly,which got better from 1990 to 2000 but became worse from 2000 to 2007,the ecological security levels in Changbai Mountain region were mainly medium and medium to low during the past 17 years,with higher values of Ecological Security Index(ESI) in the central region and lower values in the east and west,the ecological security situation was more serious in the settlements and river valleys,where the LUCC was most remarkable.展开更多
文摘The nonlinear and transient vibration of a rotor, which dropped onto back-up bearings when its active magnetic bearings were out of order, was investigated. After strictly deriving its equations of motion and performing numerical simulations, the time-histories of rotating speed of the dropping rotor, and normal force at the rubbing contact point as well as the frequency spectrum of the vibration displacement of back-up bearings are fully analyzed. It is found that the strong and unsteady forced bending vibration of the unbalanced and, damped rotor decelerating through : its first. bending vibtation of the unbalanced and, damped rotor decelerating through its,first critical speed as well as chattering at high frequencies caused by the nonlinearity at the rubbing contact point between, the journal and back-up bearings may lead to the catastrophic damage. of the system.
文摘本文根据Cummins et al（2002）的反应函数模型对我国财产保险公司2009～2013年的巨灾风险赔付效率进行了测算，并对影响保险公司应对巨灾风险能力差异的因素进行了分析。我们发现尽管我国财险市场有了较快的发展，但对巨灾风险的覆盖能力依然较弱，尤其是对极端情况下的巨灾损失覆盖效率较低。应对巨灾能力差异的因素包括保险公司的实际赔付率、承保风险、权益资本、再保险的利用率、公司规模等。我们还发现“偿二代”一方面能促进风险管理水平高的公司释放更多资本金，另一方面能促使风险管理水平较低的公司调整业务结构、提高风险管理水平，从而增加全行业应对巨灾风险的能力。
基金This research was funded by the National Key Research and Development Program of China(2018YFD0200402)Ph.D.Programs of the Foundation of Ministry of Education of China(20130204110004).
文摘Aphids are a major global wheat,pest that can cause considerable loss of yield.Modeling of aphid population dynamics is an integral part of management strategies to manage or control aphid populations.In this paper,first,a wheat aphid population dynamics model was developed based on a logistic model and theⅠlollingⅢfunctional response,which includes three factors:temperature,natural enemies and insecticide.Second,this model fitted with a cusp catastrophe model to describe how abrupt changes in the wheat aphid population were influenced by these factors,Finally,the system was validated with field data from 2016 to 2018.The bifurcation set of the cusp catastrophe model was deemod to be the quantified dynamic control threshold,so an outbreak of aphid's population can be explained according to the variation of control variables.In short,this aphid population model was successfully validated on survey data,which can be used to guide the prevention and control of aphids.
基金supported by China National Nature Science Foundation(Grant No.71271093).
文摘The Lewisian turning-point obviously increase the labor costs of Chinese manufacturing firms,it made the employee turnover to become the key problem that how to keep the enterprise human resource stability.Here,the conceptual catastrophe model of employee turnover is built from the new perspective of empirical study and catastrophe theory.In particular,we developed a parameter estimation method of the Cusp catastrophe model based on qualitative simulation and fuzzy math,and then to demonstrate the rationality and robustness of this method by a practical case on a manufacturing enterprise.In the end,a series of virtual experiments are carried out for the employee turnover in the period of China’s economic transformation.The main results are that,how to measure the warning,critical and mutation area of employee turnover;the real relationship between the complex economic environment and the demission of employees;the control policy from the macroscopic governmental measures and microscopic enterprise ways.
基金supported by the National Key Technology R&D Program of China under Grant No.2013BAK05B01the National Natural Science Foundation of China under Grant No.41371495+1 种基金the National Grand Fundamental Research 973 Program of China under Grant No.2010CB951102the National Key Technology R&D Program of China under Grant No.2011BAD32B00-04
文摘Ecological security defined as the creation of a condition where the physical surroundings of a community provide for the needs of its inhabitants without diminishing its natural stock,which is important for regional security and social stability.In recent years,land use patterns in the Changbai Mountain region have changed significantly with intensive human activities,and consequently led to increasing problems in regional ecological security.Based on the Pressure-State-Impact-Response(PSIR) model and the mathematical method of catastrophe progression supported by geographical information system(GIS),the ecological security situation of the study area under land use and cover change(LUCC) was evaluated.The results indicated that the ecological security in Changbai Mountain region varied nonlinearly,which got better from 1990 to 2000 but became worse from 2000 to 2007,the ecological security levels in Changbai Mountain region were mainly medium and medium to low during the past 17 years,with higher values of Ecological Security Index(ESI) in the central region and lower values in the east and west,the ecological security situation was more serious in the settlements and river valleys,where the LUCC was most remarkable.
