According to the characteristics of circular agricultural mode focusing on pig farming and by dint of system dynamics mode-based analysis techniques to analyze the characteristics,the operation force for the recycling...According to the characteristics of circular agricultural mode focusing on pig farming and by dint of system dynamics mode-based analysis techniques to analyze the characteristics,the operation force for the recycling agricultural system focusing on pig farming was put forward.展开更多
The economic growth of China has led to increasing growth disparities between regions. Such disparities are uncontrolled and are severely negative symptoms in the process of economic development. On the basis of syste...The economic growth of China has led to increasing growth disparities between regions. Such disparities are uncontrolled and are severely negative symptoms in the process of economic development. On the basis of system dynamics(SD) modeling and the relationship between industrial relocation and regional economic growth, we construct a model of the interrelationship between the two aforementioned phenomena. The model is an effective and creative exploration for examining effects of industrial relocation on Chinese regional economic growth disparities. The SD model is employed in this study to build an inter-regional labor migration SD model, an inter-regional capital migration SD model, an intra-industry SD model, an intra-regional population SD model, and an intra-regional SD model which are based on realities in labor and capital flow from the view of industrial relocation. VENSIM software is utilized to perform a system simulation based on the data of the eastern, middle, and western regions from 2000 to 2010. Results show that industrial relocation gradually narrows the relative disparity in GDP among the three regions. Moreover, the absolute one is enlarged continuously. The absolute and relative disparities in per capita GDP among eastern, middle, and western regions generally exhibit decreasing trends.展开更多
In this paper,under the assumption that the labor force function increases strictly and is bounded and the labor force growth rate function decreases monotonically from a positive value to zero,we obtain an improved S...In this paper,under the assumption that the labor force function increases strictly and is bounded and the labor force growth rate function decreases monotonically from a positive value to zero,we obtain an improved Solow Swan model. We prove that the per capita capital trends stabilitily to the steady state of the classical Solow Swan model with zero the labor force growth rate. Two comparison theorems,a limited theorem and a stability theorem are given. At the end of this paper,we give an example and discuss the economic meaning of this model and the theorems.展开更多
The goal of this investigation was to analyze the impact of some production variables (input) on agricultural pro- ductivity growth (output) in China from 1989~2002. We selected through random sampling Zhejiang Provi...The goal of this investigation was to analyze the impact of some production variables (input) on agricultural pro- ductivity growth (output) in China from 1989~2002. We selected through random sampling Zhejiang Province for our disaggre- gate analysis with the use of Cobb-Douglas function. The estimation results showed that all key parameters are significant and are of the expected sign. Labor and that capital and land have positive impact on agricultural productivity growth.展开更多
PV (photovoltaic) market is dominated by Europe, especially Germany and Spain. However, the PV industry leaders recently exist in Asia. The huge market growth require industry growth, but with competitive cost. The ...PV (photovoltaic) market is dominated by Europe, especially Germany and Spain. However, the PV industry leaders recently exist in Asia. The huge market growth require industry growth, but with competitive cost. The electricity shortage in Egypt makes transferring to photovoltaic technology necessary, especially with the high solar radiation. The only reason why grid parity is not yet reached in Egypt is the elevated subsidiary of conventional electricity. If this subsidy is transformed to incentives for using and manufacturing solar cells, the situation will vary. This article shows that transferring PV industry to Egypt has a potential of cost saving of 5.7%, which could be translated either into competitive price or higher return on investment. This work is not a feasibility study. However, based on the cost structure of each phase in the PV industry value chain, the benefit (5.7% cost reduction potential) of transferring the industry to Egypt is worthy to accomplish the needed feasibility study.展开更多
With population growth and increasing pressure on land resources,land carrying capacity(LCC) and food safety have been attracting great attention worldwide.From the point of man-grain relationship and by establishing ...With population growth and increasing pressure on land resources,land carrying capacity(LCC) and food safety have been attracting great attention worldwide.From the point of man-grain relationship and by establishing LCC and land carrying capacity index(LCCI) models,this article firstly analyzes the spatial-temporal dynamics of LCC of China from 1949 to 2005 at county,provincial and national levels.Choosing 2005 as a representative year,this article then evaluates the LCC of 264 pastoral regions(semipastoral regions),663 urban regions and 592 poverty stricken regions of the country.The results show that:(1) from 1949 to 2005,with the increase of grain production,the LCC of China has been improved conspicuously,but due to the rapid population growth,the production can only maintain a low level grain consumption;(2) over the past 25 years(1980-2005),the number of population overloading provinces decreased from 23 to 15 and the mangrain relationship has been improved gradually,but there were more overloading provinces than surplus provinces in China;(3) at county level,there were 1572 overloading counties in 1980 accounting for 68.26% of the total counties of the country and where were 649 million people lived,while in 1990,2000 and 2005,the number of overloading counties were 1066,1133 and 1087 respectively,which shows that the man-grain relationship has been improved obviously during the past 25 years;as for spatial distribution,the surplus counties were mainly concentrated in agriculture developed regions,such as Northeast Plain,North China Plain,middle and lower Reaches of the Yangtze River Plain,and overloading counties were mainly located in regions with poor natural environment and low grain production capacity,such as Northwest China,Tibetan Plateau and Loess Plateau and economically developed urban regions,such as Beijing,Tianjin and Shanghai;(4) animal husbandry improved greatly the LCC of pastoral and semi-pastoral regions,while urban regions were overloading for increasing population pressure and more than half of poverty stricken regions were overloading due to critical natural environment and poor economic conditions.展开更多
Strain growth is a phenomenon observed in containment vessels subjected to internal blast loading. The elastic response of the vessel may become larger in a later stage compared to its response during the initial stag...Strain growth is a phenomenon observed in containment vessels subjected to internal blast loading. The elastic response of the vessel may become larger in a later stage compared to its response during the initial stage. The dynamic responses of infinitely long cylindrical containment vessels subjected to uniformly-distributed internal blast loading are studied using LS-DYNA. The development of bending modes and the interaction between the breathing mode and bending modes are observed. The methodology developed for dynamic elastic buckling analysis is employed to study the strain growth phenomenon in explosion containment vessels. It is shown that the dynamic instable vibration of a containment vessel is the basic mechanism of strain growth.展开更多
A new technique of combining accretion by cyclone separator and scattertube for tailings dams was developed according to laboratory experiment, model experiment and spot experiment technology. Three tailings dams were...A new technique of combining accretion by cyclone separator and scattertube for tailings dams was developed according to laboratory experiment, model experiment and spot experiment technology. Three tailings dams were successfully constructed by the new technique. The results of engineering geological exploration, static and dynamic test and stability analysis on Baizhishan tailings dams prove that the new technique improves structure and stability of the dams and working conditions compared with the traditional technique. The thin layers of fine-grained soils are greatly reduced, fine tailings sand is solid to make the dam stable and seepage conditions are well improved; the immersing line of the dam descends. In addition, the stability and liquefaction resistance of tailings dams are strengthened remarkably. The interior stress is compressive stress, stress level of every element is less than 1.0 and safety coefficient of every element is greater than 1.0. The safety coefficient against liquefaction of every element of tailings dams is greater than 1.5 according to the analysis of seismic response by finite element method.展开更多
In order to eliminate the settlement underestimation in surcharge preload engineering, a study based on Bjerrum's creep diagram and the tangent slope definition of secondary consolidation coefficient was carried o...In order to eliminate the settlement underestimation in surcharge preload engineering, a study based on Bjerrum's creep diagram and the tangent slope definition of secondary consolidation coefficient was carried out to analyze the time effect of secondary consolidation coefficient of over consolidated soil, and a time–growth model for it was formulated. As Bjerrum's creep diagram is an idealized model, oedometer tests were performed to improve the above time–growth model of secondary consolidation coefficient for the purpose of achieving a better agreement with the actual ground situations. It is found that secondary consolidation coefficient of over consolidated soil not only decreases with the ratio of historical maximum to current effective stress of soil(OCR), but also increases with the development time of secondary consolidation. No matter how large OCR is, the long-term time effect of secondary consolidation coefficient of over consolidated soil is all significant. Based on the above results, a model for settlement estimation was formulated and a case study to estimate it indicates that the settlement estimated by our method is 2–5 times larger than that estimated by the previous method. Moreover, the larger the OCR is as well as the longer the service life is, the larger the difference between our method and the previous method is. Thus, the post-construction secondary settlement in surcharge preload engineering will be underestimated when neglecting the time effect of secondary consolidation coefficient in over consolidated state.展开更多
Through exploring the limitation of the neoclassical theory of economic growth,which classifies growth as a homogenous process,this paper reconciles various theories of economic development and explains the rises and ...Through exploring the limitation of the neoclassical theory of economic growth,which classifies growth as a homogenous process,this paper reconciles various theories of economic development and explains the rises and falls of economic growth under a unified framework,focusing on incentives of the accumulation of physical and human capital.This paper classifies instances of economic growth into four categories—the Malthusian poverty trap,the Lewis dual model of economic development,the Lewis turning point,and Solow neoclassical growth model.This paper conducts empirical analysis of these categories of economic development as they are relevant to Chinese economic growth and discusses policy implications therein.展开更多
Now environment is an important topic in academic field.Many researches focus on the negative outcomes of nature which are being continually created by human and much attention has been paid to how the environment is ...Now environment is an important topic in academic field.Many researches focus on the negative outcomes of nature which are being continually created by human and much attention has been paid to how the environment is protected through integrated research,movement and policy.But few studies are concentrated on population and environment and are to find out the interconnectivity and underlying mechanism that have an effect on people's preferring additional children and perception to environment.Many researchers claim that population growth is a great problem for environment but they do not provide the indepth integrated knowledge and mechanism that influence fertility trend and environmental problems.It is very crucial to develop practical and concrete initiatives to confirm a transition to reduce population growth and redirect the perception on population and environment.展开更多
China' s economic growth and the demand for electricity are to analyze two important indicators of a country' s economic situation. Some research institutions internationally determine the status of economic growth ...China' s economic growth and the demand for electricity are to analyze two important indicators of a country' s economic situation. Some research institutions internationally determine the status of economic growth through the analysis of actual consumption. The power industry has an important impact on the development of basic industries of the national economy, the development of other sectors of various industries play an essential supporting role. Production of electricity supply for economic development improves people' s livelihood and social progress, it provides a necessary condition, and power shortages, in turn it seriously affects the country' s economic development and living. Therefore, the power and economic growth (GDP) is to study the relationship, it will be under conditions of scarce resources saving energy, electric power development plan to develop the scientific and industrial policy system, and promote the healthy and rapid economic growth.展开更多
The driving force for China's industrial growth has shifted from the synergy of efficiency and factor input to the dominance of capital input alone.With the boundary of 2003,the contribution of capital to the grow...The driving force for China's industrial growth has shifted from the synergy of efficiency and factor input to the dominance of capital input alone.With the boundary of 2003,the contribution of capital to the growth of China's industrial economy increased from the annual average of 34.07%to 89.28%while the contribution of TFP dived from the annual average of 47.34%to-4.08%.Meanwhile,TFP growth rates dropped from the annual average of 4.6%to-0.05%and marginal capital output ratio went down from0.61 in 2002 to 0.28 in 2012.This indicates that the investment-driven pattern of China's industrial growth has been confronted with severe inefficiency.Further research suggests that the tendency of worsening industrial growth efficiency already became significant prior to the global financial crisis of 2008 and the eruption of the global financial crisis is not the fundamental reason for the worsening of efficiency and only exacerbated its tendency.The current government-led and investment-driven pattern of industrial growth is the root cause of such efficiency deterioration.Therefore,in order to achieve the transition towards innovation- and efficiency-driven growth pattern,the key is to make an appropriate distinction in the relationship between market and government,i.e.,the government must create a perfect institutional system where the market plays a decisive role and take proactive initiative to promote technology innovation and transfer on the basis of respecting market mechanism and the intent of market entities.展开更多
With the rapid development of the information technology and the computer network, the electronic commerce has become the economic hotspot and the development trend in today's society, and the influence of the electr...With the rapid development of the information technology and the computer network, the electronic commerce has become the economic hotspot and the development trend in today's society, and the influence of the electronic commerce on the national economy is growing. It is not only the important driving force of the economic growth, but also is a force influencing the development of the retail business and the changes of the structures of the economy.展开更多
The "migrant worker shortage" which occurred several)pears ago and the recent "labor shortage" were both caused by an imbalance between the supply and demand of migrant workers. It is a periodical outcome of spon...The "migrant worker shortage" which occurred several)pears ago and the recent "labor shortage" were both caused by an imbalance between the supply and demand of migrant workers. It is a periodical outcome of spontaneous adjustment by the migrant labor market. As rural welfare was greatly enhanced in 2009, migrant workers' opportunity cost of working outside their hometowns was raised. The connotation of migrant workers' "market price" is changing. The new generation of migrant workers, namely, those born after 1980, are becoming the mainstay of enterprises' employment. Being better educated, they have different lifestyles than previous generations. "Leisure and entertainment" have become part of their opportunity cost and reduced their labor supply. "Labor shortage" is an endogenous force that helps transform China's growth patter, upgrade the industrial structure and promote urbanization. The seasonal "return of migrant workers" and the "labor shortage" which appears around China's Spring Festival each year have grown into a unique b,t effective collective bargaining mechanism that helps increase migrant workers' wages. Facing labor shortages, governments should regulate the labor market pricing and orientate labor-intensive enterprises towards transition, continue to enhance the social security system for migrant workers and those in rural areas, and make an accurate forecast of the population trend and adjust population policies.展开更多
The effects of precipitates on the fatigue crack growth rate of AA 7055 Al alloy subjected to different ageing treatments were investigated using transmission electron microscope and fatigue crack growth testing.The r...The effects of precipitates on the fatigue crack growth rate of AA 7055 Al alloy subjected to different ageing treatments were investigated using transmission electron microscope and fatigue crack growth testing.The results show that the T77 treated samples exhibit the lowest crack growth rate,while the crack growth rate of over-aged samples is the highest.In terms of the model based on the reversibility of dislocation motion within the plastic zone close to the crack tip,the improved crack growth resistance is attributed to many precipitates that are coherent with Al matrix in the under-aged and T77 treated samples.When the precipitate is coherent with the Al matrix,the larger the precipitate is,the slower the fatigue crack grows.The effects of grain boundary precipitates and precipitate free zone on the fatigue crack growth resistance are less significant than those of precipitates within grains of the alloy.展开更多
基金Supported by National Natural Science Fund(70861004)~~
文摘According to the characteristics of circular agricultural mode focusing on pig farming and by dint of system dynamics mode-based analysis techniques to analyze the characteristics,the operation force for the recycling agricultural system focusing on pig farming was put forward.
基金Under the auspices of National Natural Science Foundation of China(No.41171099)National Key Basic Research Program of China(No.2012CB955802)National Social Science Foundation of China(No.10ZD&022)
文摘The economic growth of China has led to increasing growth disparities between regions. Such disparities are uncontrolled and are severely negative symptoms in the process of economic development. On the basis of system dynamics(SD) modeling and the relationship between industrial relocation and regional economic growth, we construct a model of the interrelationship between the two aforementioned phenomena. The model is an effective and creative exploration for examining effects of industrial relocation on Chinese regional economic growth disparities. The SD model is employed in this study to build an inter-regional labor migration SD model, an inter-regional capital migration SD model, an intra-industry SD model, an intra-regional population SD model, and an intra-regional SD model which are based on realities in labor and capital flow from the view of industrial relocation. VENSIM software is utilized to perform a system simulation based on the data of the eastern, middle, and western regions from 2000 to 2010. Results show that industrial relocation gradually narrows the relative disparity in GDP among the three regions. Moreover, the absolute one is enlarged continuously. The absolute and relative disparities in per capita GDP among eastern, middle, and western regions generally exhibit decreasing trends.
文摘In this paper,under the assumption that the labor force function increases strictly and is bounded and the labor force growth rate function decreases monotonically from a positive value to zero,we obtain an improved Solow Swan model. We prove that the per capita capital trends stabilitily to the steady state of the classical Solow Swan model with zero the labor force growth rate. Two comparison theorems,a limited theorem and a stability theorem are given. At the end of this paper,we give an example and discuss the economic meaning of this model and the theorems.
文摘The goal of this investigation was to analyze the impact of some production variables (input) on agricultural pro- ductivity growth (output) in China from 1989~2002. We selected through random sampling Zhejiang Province for our disaggre- gate analysis with the use of Cobb-Douglas function. The estimation results showed that all key parameters are significant and are of the expected sign. Labor and that capital and land have positive impact on agricultural productivity growth.
文摘PV (photovoltaic) market is dominated by Europe, especially Germany and Spain. However, the PV industry leaders recently exist in Asia. The huge market growth require industry growth, but with competitive cost. The electricity shortage in Egypt makes transferring to photovoltaic technology necessary, especially with the high solar radiation. The only reason why grid parity is not yet reached in Egypt is the elevated subsidiary of conventional electricity. If this subsidy is transformed to incentives for using and manufacturing solar cells, the situation will vary. This article shows that transferring PV industry to Egypt has a potential of cost saving of 5.7%, which could be translated either into competitive price or higher return on investment. This work is not a feasibility study. However, based on the cost structure of each phase in the PV industry value chain, the benefit (5.7% cost reduction potential) of transferring the industry to Egypt is worthy to accomplish the needed feasibility study.
基金supported by the National Basic Research Program of China (Grant no.40771204 and Grant no. 40801223)National Technology R&D Program (Grant no.2006BAC18B01)
文摘With population growth and increasing pressure on land resources,land carrying capacity(LCC) and food safety have been attracting great attention worldwide.From the point of man-grain relationship and by establishing LCC and land carrying capacity index(LCCI) models,this article firstly analyzes the spatial-temporal dynamics of LCC of China from 1949 to 2005 at county,provincial and national levels.Choosing 2005 as a representative year,this article then evaluates the LCC of 264 pastoral regions(semipastoral regions),663 urban regions and 592 poverty stricken regions of the country.The results show that:(1) from 1949 to 2005,with the increase of grain production,the LCC of China has been improved conspicuously,but due to the rapid population growth,the production can only maintain a low level grain consumption;(2) over the past 25 years(1980-2005),the number of population overloading provinces decreased from 23 to 15 and the mangrain relationship has been improved gradually,but there were more overloading provinces than surplus provinces in China;(3) at county level,there were 1572 overloading counties in 1980 accounting for 68.26% of the total counties of the country and where were 649 million people lived,while in 1990,2000 and 2005,the number of overloading counties were 1066,1133 and 1087 respectively,which shows that the man-grain relationship has been improved obviously during the past 25 years;as for spatial distribution,the surplus counties were mainly concentrated in agriculture developed regions,such as Northeast Plain,North China Plain,middle and lower Reaches of the Yangtze River Plain,and overloading counties were mainly located in regions with poor natural environment and low grain production capacity,such as Northwest China,Tibetan Plateau and Loess Plateau and economically developed urban regions,such as Beijing,Tianjin and Shanghai;(4) animal husbandry improved greatly the LCC of pastoral and semi-pastoral regions,while urban regions were overloading for increasing population pressure and more than half of poverty stricken regions were overloading due to critical natural environment and poor economic conditions.
文摘Strain growth is a phenomenon observed in containment vessels subjected to internal blast loading. The elastic response of the vessel may become larger in a later stage compared to its response during the initial stage. The dynamic responses of infinitely long cylindrical containment vessels subjected to uniformly-distributed internal blast loading are studied using LS-DYNA. The development of bending modes and the interaction between the breathing mode and bending modes are observed. The methodology developed for dynamic elastic buckling analysis is employed to study the strain growth phenomenon in explosion containment vessels. It is shown that the dynamic instable vibration of a containment vessel is the basic mechanism of strain growth.
文摘A new technique of combining accretion by cyclone separator and scattertube for tailings dams was developed according to laboratory experiment, model experiment and spot experiment technology. Three tailings dams were successfully constructed by the new technique. The results of engineering geological exploration, static and dynamic test and stability analysis on Baizhishan tailings dams prove that the new technique improves structure and stability of the dams and working conditions compared with the traditional technique. The thin layers of fine-grained soils are greatly reduced, fine tailings sand is solid to make the dam stable and seepage conditions are well improved; the immersing line of the dam descends. In addition, the stability and liquefaction resistance of tailings dams are strengthened remarkably. The interior stress is compressive stress, stress level of every element is less than 1.0 and safety coefficient of every element is greater than 1.0. The safety coefficient against liquefaction of every element of tailings dams is greater than 1.5 according to the analysis of seismic response by finite element method.
基金Project(51178419)supported by the National Natural Science Foundation of China
文摘In order to eliminate the settlement underestimation in surcharge preload engineering, a study based on Bjerrum's creep diagram and the tangent slope definition of secondary consolidation coefficient was carried out to analyze the time effect of secondary consolidation coefficient of over consolidated soil, and a time–growth model for it was formulated. As Bjerrum's creep diagram is an idealized model, oedometer tests were performed to improve the above time–growth model of secondary consolidation coefficient for the purpose of achieving a better agreement with the actual ground situations. It is found that secondary consolidation coefficient of over consolidated soil not only decreases with the ratio of historical maximum to current effective stress of soil(OCR), but also increases with the development time of secondary consolidation. No matter how large OCR is, the long-term time effect of secondary consolidation coefficient of over consolidated soil is all significant. Based on the above results, a model for settlement estimation was formulated and a case study to estimate it indicates that the settlement estimated by our method is 2–5 times larger than that estimated by the previous method. Moreover, the larger the OCR is as well as the longer the service life is, the larger the difference between our method and the previous method is. Thus, the post-construction secondary settlement in surcharge preload engineering will be underestimated when neglecting the time effect of secondary consolidation coefficient in over consolidated state.
文摘Through exploring the limitation of the neoclassical theory of economic growth,which classifies growth as a homogenous process,this paper reconciles various theories of economic development and explains the rises and falls of economic growth under a unified framework,focusing on incentives of the accumulation of physical and human capital.This paper classifies instances of economic growth into four categories—the Malthusian poverty trap,the Lewis dual model of economic development,the Lewis turning point,and Solow neoclassical growth model.This paper conducts empirical analysis of these categories of economic development as they are relevant to Chinese economic growth and discusses policy implications therein.
文摘Now environment is an important topic in academic field.Many researches focus on the negative outcomes of nature which are being continually created by human and much attention has been paid to how the environment is protected through integrated research,movement and policy.But few studies are concentrated on population and environment and are to find out the interconnectivity and underlying mechanism that have an effect on people's preferring additional children and perception to environment.Many researchers claim that population growth is a great problem for environment but they do not provide the indepth integrated knowledge and mechanism that influence fertility trend and environmental problems.It is very crucial to develop practical and concrete initiatives to confirm a transition to reduce population growth and redirect the perception on population and environment.
文摘China' s economic growth and the demand for electricity are to analyze two important indicators of a country' s economic situation. Some research institutions internationally determine the status of economic growth through the analysis of actual consumption. The power industry has an important impact on the development of basic industries of the national economy, the development of other sectors of various industries play an essential supporting role. Production of electricity supply for economic development improves people' s livelihood and social progress, it provides a necessary condition, and power shortages, in turn it seriously affects the country' s economic development and living. Therefore, the power and economic growth (GDP) is to study the relationship, it will be under conditions of scarce resources saving energy, electric power development plan to develop the scientific and industrial policy system, and promote the healthy and rapid economic growth.
文摘The driving force for China's industrial growth has shifted from the synergy of efficiency and factor input to the dominance of capital input alone.With the boundary of 2003,the contribution of capital to the growth of China's industrial economy increased from the annual average of 34.07%to 89.28%while the contribution of TFP dived from the annual average of 47.34%to-4.08%.Meanwhile,TFP growth rates dropped from the annual average of 4.6%to-0.05%and marginal capital output ratio went down from0.61 in 2002 to 0.28 in 2012.This indicates that the investment-driven pattern of China's industrial growth has been confronted with severe inefficiency.Further research suggests that the tendency of worsening industrial growth efficiency already became significant prior to the global financial crisis of 2008 and the eruption of the global financial crisis is not the fundamental reason for the worsening of efficiency and only exacerbated its tendency.The current government-led and investment-driven pattern of industrial growth is the root cause of such efficiency deterioration.Therefore,in order to achieve the transition towards innovation- and efficiency-driven growth pattern,the key is to make an appropriate distinction in the relationship between market and government,i.e.,the government must create a perfect institutional system where the market plays a decisive role and take proactive initiative to promote technology innovation and transfer on the basis of respecting market mechanism and the intent of market entities.
文摘With the rapid development of the information technology and the computer network, the electronic commerce has become the economic hotspot and the development trend in today's society, and the influence of the electronic commerce on the national economy is growing. It is not only the important driving force of the economic growth, but also is a force influencing the development of the retail business and the changes of the structures of the economy.
文摘The "migrant worker shortage" which occurred several)pears ago and the recent "labor shortage" were both caused by an imbalance between the supply and demand of migrant workers. It is a periodical outcome of spontaneous adjustment by the migrant labor market. As rural welfare was greatly enhanced in 2009, migrant workers' opportunity cost of working outside their hometowns was raised. The connotation of migrant workers' "market price" is changing. The new generation of migrant workers, namely, those born after 1980, are becoming the mainstay of enterprises' employment. Being better educated, they have different lifestyles than previous generations. "Leisure and entertainment" have become part of their opportunity cost and reduced their labor supply. "Labor shortage" is an endogenous force that helps transform China's growth patter, upgrade the industrial structure and promote urbanization. The seasonal "return of migrant workers" and the "labor shortage" which appears around China's Spring Festival each year have grown into a unique b,t effective collective bargaining mechanism that helps increase migrant workers' wages. Facing labor shortages, governments should regulate the labor market pricing and orientate labor-intensive enterprises towards transition, continue to enhance the social security system for migrant workers and those in rural areas, and make an accurate forecast of the population trend and adjust population policies.
基金Project(2005CB623700) supported by the National Basic Research Program of China
文摘The effects of precipitates on the fatigue crack growth rate of AA 7055 Al alloy subjected to different ageing treatments were investigated using transmission electron microscope and fatigue crack growth testing.The results show that the T77 treated samples exhibit the lowest crack growth rate,while the crack growth rate of over-aged samples is the highest.In terms of the model based on the reversibility of dislocation motion within the plastic zone close to the crack tip,the improved crack growth resistance is attributed to many precipitates that are coherent with Al matrix in the under-aged and T77 treated samples.When the precipitate is coherent with the Al matrix,the larger the precipitate is,the slower the fatigue crack grows.The effects of grain boundary precipitates and precipitate free zone on the fatigue crack growth resistance are less significant than those of precipitates within grains of the alloy.