This paper takes global manufacturing listed companies from 2010 to 2022 as samples and uses the difference-in-differences(DID)method to empirically examine the impact of the internationalization of ESG standards on t...This paper takes global manufacturing listed companies from 2010 to 2022 as samples and uses the difference-in-differences(DID)method to empirically examine the impact of the internationalization of ESG standards on the trade competitiveness of multinational enterprises and their mechanisms.The research finds that the internationalization of ESG standards significantly enhances the trade competitiveness of multinational manufacturing enterprises,and this effect is dynamic and sustainable.The mechanism analysis indicates that the internationalization of ESG standards exerts its influence through three pathways:reducing enterprise financing costs,promoting technological innovation,and enhancing brand reputation.The heterogeneity analysis shows that this effect is more significant in enterprises from developed countries,high-pollution industries,and larger enterprises.This paper provides micro-level evidence for understanding the economic consequences of the internationalization of ESG standards and offers policy implications for multinational enterprises to cope with the global ESG rule changes and enhance their trade competitiveness.展开更多
Purpose:In recent decades,with the availability of large-scale scientific corpus datasets,difference-in-difference(DID)is increasingly used in the science of science and bibliometrics studies.DID method outputs the un...Purpose:In recent decades,with the availability of large-scale scientific corpus datasets,difference-in-difference(DID)is increasingly used in the science of science and bibliometrics studies.DID method outputs the unbiased estimation on condition that several hypotheses hold,especially the common trend assumption.In this paper,we gave a systematic demonstration of DID in the science of science,and the potential ways to improve the accuracy of DID method.Design/methodology/approach:At first,we reviewed the statistical assumptions,the model specification,and the application procedures of DID method.Second,to improve the necessary assumptions before conducting DID regression and the accuracy of estimation,we introduced some matching techniques serving as the pre-selecting step for DID design by matching control individuals who are equivalent to those treated ones on observational variables before the intervention.Lastly,we performed a case study to estimate the effects of prizewinning on the scientific performance of Nobel laureates,by comparing the yearly citation impact after the prizewinning year between Nobel laureates and their prizewinning-work coauthors.Findings:We introduced the procedures to conduct a DID estimation and demonstrated the effectiveness to use matching method to improve the results.As a case study,we found that there are no significant increases in citations for Nobel laureates compared to their prizewinning coauthors.Research limitations:This study ignored the rigorous mathematical deduction parts of DID,while focused on the practical parts.Practical implications:This work gives experimental practice and potential guidelines to use DID method in science of science and bibliometrics studies.Originality/value:This study gains insights into the usage of econometric tools in science of science.展开更多
A mathematical model of optimal energy medium distribution in steelmaking process is formulated. In this model, three kinds of important energy mediums including byproduct gases, steam and electricity are considered, ...A mathematical model of optimal energy medium distribution in steelmaking process is formulated. In this model, three kinds of important energy mediums including byproduct gases, steam and electricity are considered, and the objective function accounts for both the change of generation and consumption of the byproduct gases and the demand of low （or middle） pressure steam and electricity for each period to maximize the benefit of products cost and minimize the consumption of energy. The results indicate that the optimal distribution scheme of byproduct gases, middle pressure steam, low pressure steam and electricity is achieved and case study shows that 6% of operation cost is reduced by using the proposed model comparing with the previous model.展开更多
In shale reservoirs,the organic pores with various structures formed during the thermal evolution of organic matter are the main storage site for adsorbed methane.However,in the process of thermal evolution,the adsorp...In shale reservoirs,the organic pores with various structures formed during the thermal evolution of organic matter are the main storage site for adsorbed methane.However,in the process of thermal evolution,the adsorption characteristics of methane in multi type and multi-scale organic matter pores have not been sufficiently studied.In this study,the molecular simulation method was used to study the adsorption characteristics of methane based on the geological conditions of Longmaxi Formation shale reservoir in Sichuan Basin,China.The results show that the characteristics of pore structure will affect the methane adsorption characteristics.The adsorption capacity of slit-pores for methane is much higher than that of cylindrical pores.The groove space inside the pore will change the density distribution of methane molecules in the pore,greatly improve the adsorption capacity of the pore,and increase the pressure sensitivity of the adsorption process.Although the variation of methane adsorption characteristics of different shapes is not consistent with pore size,all pores have the strongest methane adsorption capacity when the pore size is about 2 nm.In addition,the changes of temperature and pressure during the thermal evolution are also important factors to control the methane adsorption characteristics.The pore adsorption capacity first increases and then decreases with the increase of pressure,and increases with the increase of temperature.In the early stage of thermal evolution,pore adsorption capacity is strong and pressure sensitivity is weak;while in the late stage,it is on the contrary.展开更多
A systematic strategy for retrofit of the multi-period heat exchanger network （HEN） on the basis of the multi- objective optimization is developed. In this three-stage procedure, a simplified multi-objective optimiz...A systematic strategy for retrofit of the multi-period heat exchanger network （HEN） on the basis of the multi- objective optimization is developed. In this three-stage procedure, a simplified multi-objective optimization model of the multi-period lIEN is first established and then solved to target the retrofit, aiming to minimizing the total annual cost and total annual CO2 emissions. The obtained Pareto front represents series of retrofit targets under different emission limitations, from which the most desirable one can be selected. The matching of the existing and the required heat exchangers is further implemented to finalize the retrofit, which will meet the practical retrofit requirements and matching restrictions. The application of the proposed procedure is illustrated through a case study of a HEN in a vacuum gas oil hydro-treating unit.展开更多
In intercontinental trade and economics goods are bought from a global supplier.On occasion,the expected lot may include a fraction of defective items.These imperfect items still have worth and can be sold to customer...In intercontinental trade and economics goods are bought from a global supplier.On occasion,the expected lot may include a fraction of defective items.These imperfect items still have worth and can be sold to customers after repair.It is cost-effective and sustainable to rework such items in nearby repair workshops rather than return them.The reworked items can be returned from the workshop to the buyer when shortages are equal to the quantity of imperfect items.In the meantime,the supplier correspondingly deals a multi-period delay-in-payments strategy with purchaser.The entire profit has been maximized with paybacks for interim financing.This study aims to develop a synergic inventory model to get the most profit by making an allowance for reworking,multi-period delay-in-payments policy,and shortages.The findings of the proposed model augment inventory management performance by monitoring cycle time as well as fraction of phase with optimistic inventory for a supply chain.The results demonstrate that profit is smaller if the permitted period given by supplier to buyer is equal to or greater than the cycle time,and profit is greater if the permitted period is smaller than the cycle time.The algebraic method is engaged to make a closed system optimum solution.The mathematical experiment of this study is constructed to provide management insights and tangible practices.展开更多
Traditional multi-band frequency selective surface （FSS） approaches are hard to achieve a perfect resonance response in a wide band due to the limit of the onset grating lobe frequency determined by the array. To so...Traditional multi-band frequency selective surface （FSS） approaches are hard to achieve a perfect resonance response in a wide band due to the limit of the onset grating lobe frequency determined by the array. To solve this problem, an approach of combining elements in different period to build a hybrid array is presented. The results of series of numerical simulation show that multi-periodicity combined element FSS, which are designed using this approach, usually have much weaker grating lobes than the traditional FSS. Furthermore, their frequency response can be well predicted through the properties of their member element FSS. A prediction method for estimating the degree of expected grating lobe energy loss in designing multi-band FSS using this approach is provided.展开更多
Temperate and high-latitude forests are carbon sinks and play pivotal roles in offsetting greenhouse gas emissions of CO2.However,uncertainty still exists for subtropical forests,especially in monsoon-prevalent easter...Temperate and high-latitude forests are carbon sinks and play pivotal roles in offsetting greenhouse gas emissions of CO2.However,uncertainty still exists for subtropical forests,especially in monsoon-prevalent eastern Asia.Earlier studies have depended on remote sensing,ecosystem modeling,carbon fluxes,or single period forest surveys to estimate carbon sequestration capacities,and the results vary significantly.This study was designed to utilize multi-period forest survey data to explore spatial-dynamics of biomass storage in subtropical forests of China.Jiangxi province,a region with over 60%subtropical forest cover,was selected as the case study site and is located in central east China.Based on forest inventory data 1984-2013,and the stock-difference and biomass expansion factor methods,the carbon storage and density,of arboreal forests,economic forests,bamboo forests,woodlands and shrubberies were estimated.The results show that carbon storage increased from 159.1 Tg C in 1988 to 276.1 TgC in 2013,making up 3.1-3.8%of carbon stored throughout China.Among the four types of forests,the amount of carbon stored was as follows:arboreal forest>economic forest>bamboo forest>woodland and shrubbery.Arboreal forests accounted for 64.0-79.4%of the total.Forest carbon density increased from 21.2 Mg C ha-1 in 1984 to26.2 Mg C ha-1 in 2013,equal to 61.2-70.2%of the average carbon density of China’s forests in the same period.Forest carbon storage in Jiangxi will reach 355.5 Tg C and 535.8 Tg C in 2020 and 2030,respectively,and forest carbon density is predicted to be 31.9 Mg C ha-1and 46.4 Mg C ha-1,respectively.As one of the few studies using multi-period data tracking biomass dynamics in Jiangxi province,the findings of this study may be used as a reference for other research.Using Jiangxi as a case study underlies the fact that subtropical forests in China have great carbon sequestration potential and have fundamental significance to offset global environmental change effects.展开更多
As urbanization accelerates globally,air pollution-particularly PM_(2.5)-is becoming an increasingly significant threat,not only to public health but also the environment.In-depth research on the impact of China’s Ze...As urbanization accelerates globally,air pollution-particularly PM_(2.5)-is becoming an increasingly significant threat,not only to public health but also the environment.In-depth research on the impact of China’s Zero Waste City pilot policy on PM_(2.5)concentration offers valuable insights into the policy’s effectiveness and provides a potential model for environmental governance worldwide.This study employs panel data from 293 Chinese cities from 2014 to 2022 to systematically analyze the impact of the Zero-Waste City policy on PM_(2.5)concentration using a difference-in-differences model.The findings indicate that the policy not only directly reduces PM_(2.5)concentration but also indirectly curbs PM_(2.5)emissions by enhancing green innovation and green economic efficiency.Moreover,the policy’s effects are found to be positively moderated by urban energy dependence and digital financial inclusion,while they are negatively moderated by the government debt ratio.Based on these findings,this study suggests that cities should actively develop their digital economy,reduce government debt,promote green innovation,and improve green economic efficiency,as doing so will enhance their implementation of environmental policies and promote sustainable urban development.展开更多
Based on personality trait theory and experiential learning theory,lots of studies have revealed a reverse causal relationship between volunteering and the non-cognitive abilities of college students.Using data from a...Based on personality trait theory and experiential learning theory,lots of studies have revealed a reverse causal relationship between volunteering and the non-cognitive abilities of college students.Using data from a longitudinal survey of college students in Hunan Province,China,this study employed the difference-in-differences method to examine the causal relationship between volunteering and non-cognitive abilities,aiming to determine whether volunteering screens or cultivates the non-cognitive abilities of college students.The findings confirmed the screening effect of volunteering on extraversion and conscientiousness and the cultivating effect on agreeableness.However,there was neither a screening effect nor a cultivating effect on emotional stability and openness.It is indicated that volunteering during college primarily screens the non-cognitive abilities of students through personality trait mechanisms,with a limited cultivating effect on non-cognitive abilities.This highlights the necessity to prompt a re-evaluation of how volunteering fulfills its educational function.展开更多
Amid China’s rapid economic growth,significant regional imbalances persisted.To address this disparity,it is essential to pursue high-quality development by fostering endogenous drivers within poverty-stricken areas....Amid China’s rapid economic growth,significant regional imbalances persisted.To address this disparity,it is essential to pursue high-quality development by fostering endogenous drivers within poverty-stricken areas.In late 2011,the Chinese government introduced a new nationwide regional poverty alleviation and development program.This study examines the macroeconomic impacts and micro-level mechanisms of these policies by leveraging manually compiled policy documents and macro and micro data(county economies,enterprises,and land transactions),using a DID approach.The findings reveal that the program significantly boosted economic growth in poor regions without causing negative spillovers to neighboring or paired-assistance areas.Economic growth in the assisted regions was primarily driven by industrialization,encompassing both scale expansion and efficiency gains.A cost-benefit analysis further confirms substantial economic returns and long-term fiscal sustainability.These results provide important policy implications for refining regional poverty policies and advancing balanced development.展开更多
This study proposes a regression-based estimation method in difference-in-differences settings in the presence of time-varying covariates-a scenario commonly encountered in applications.We impose only a conditional pa...This study proposes a regression-based estimation method in difference-in-differences settings in the presence of time-varying covariates-a scenario commonly encountered in applications.We impose only a conditional parallel trends assumption with timevarying covariates and plausible assumptions on the conditional expectation functions.We show that a family of causal effect parameters is exactly the coefficient estimators from our proposed regressions even in the presence of staggered treatment timing and treatment effect heterogeneity across cohorts,time periods,and covariates.These parameters can be further aggregated to the dynamic treatment effects and the overall effect of being treated.We establish the corresponding asymptotic properties.Simulation studies suggest that our proposed regression-based estimators successfully outperform in estimating the causal parameters.Finally,we apply this method to evaluate the effect of intrastate bank deregulation on income inequality in the United States in the setting of Beck et al.(2010).We find substantially different results based on our proposed method.展开更多
The green credit policy(GCP)is an essential financial policy tool for solving the problem of environmental pollution,and urban energy conservation is an effective way to achieve the goal of carbon neutrality.However,e...The green credit policy(GCP)is an essential financial policy tool for solving the problem of environmental pollution,and urban energy conservation is an effective way to achieve the goal of carbon neutrality.However,existing research has not verified the energy-saving effects of green credit(GC)at the city level.Based on panel data from 283 cities in China,this study aims to investigate whether GC can effectively reduce urban energy intensity(EI),which is an important complement to existing research.In terms of research methods,to better evaluate the effect of the policy and exclude the influence of other relevant factors,this study considers the promulgation of the Green Credit Guideline(GCG)in 2012 as the basic event,uses the difference-in-differences(DID)model to investigate the impact of GC on EI,and discusses the main impact mechanism.The key results are follows.(1)GC can effectively reduce urban EI.(2)Public environmental demand positively regulates the negative correlation between GC and EI.(3)GC reduces EI through three main channels:government support,capital investment,and technological innovation;however,the mechanism of industrial structure has no significant effect.(4)The effect of GC is more significant in areas with large urban scales,low environmental regulation intensity,and high industrial agglomeration.Based on the above results,this study presents puts forward targeted policy recommendations to strengthen the role of GC in urban sustainable development.展开更多
Drawing on local legitimacy theory,which posits that firms seek acceptance and approval from their local community and stakeholders,we examine the effect of corporate governance(CG)quality on corporate social responsi...Drawing on local legitimacy theory,which posits that firms seek acceptance and approval from their local community and stakeholders,we examine the effect of corporate governance(CG)quality on corporate social responsibility(CSR)activities in Korea.Enhancing CG quality and engaging in CSR activities are increasingly important for firms’long-term sustainability.Using the KEJI-CSR index and the KCGS CG score,we find that CG quality positively influences CSR activities.Specifically,if the CG quality score increases by one standard deviation,CSR improves by approximately 1.6–2.3%of the mean CSR score.Furthermore,the relationship between CG and CSR is stronger for business conglomerates(chaebol-affiliated firms),suggesting that sound CG practices can promote CSR activities more effectively when the interests of management and stakeholders are better aligned.This finding supports local legitimacy theory.Our findings are robust under various tests,including difference-in-differences analysis and propensity score matching.An interesting policy implication is that multinational enterprises or foreign investors should prioritize the CG quality of their local subsidiaries or investee firms.Better CG practices can enhance CSR activities,which are essential for long-term survival in local markets.This study,however,is limited to Korea and may not be generalizable to other emerging markets with different governance structures.展开更多
Long-term exposure to fine particulate matters(PM_(2.5))has been associated with respiratory and cardiovascular diseases and the burden are potentially higher in China experiencing heavy air pollution.In this study,we...Long-term exposure to fine particulate matters(PM_(2.5))has been associated with respiratory and cardiovascular diseases and the burden are potentially higher in China experiencing heavy air pollution.In this study,we established the exposure-response association between long-term exposures to PM_(2.5)and lung function and blood pressure in Chinesemiddle-aged and older adults using linearmixed-effects and generalized additive mixedmodels based on 3 waves longitudinal health outcomes data by enrolling 19,988 participants from 121 cities across themainland of China.We also assessed the effect of Clean Air Policy(CAP)based on a quasi-experimental difference-in-differences(DID)design.A 10μg/m^(3)increase in PM_(2.5)concentration was associated with a 7.18(95%confidence interval[CI]:-8.35,-6.02)L/min decrease in PEF(peak expiratory flow)and a 0.72(95%[CI]:0.53,0.90)and a 0.30(95%[CI]:0.18,0.42)mmHg increase in systolic and diastolic blood pressure,respectively.The associations were more pronounced in males and rural areas for PEF,but similar across subgroups for blood pressure.DID results suggested that the effect of CAP on health outcomes were sensitive tomagnitudes of reduction in PM_(2.5).A 5μg/m^(3)reduction in PM_(2.5)or more generally led to 18.70(95%[CI]:0.79,36.61)higher PEF and-2.05(95%[CI]:-3.87,-0.23)lower diastolic blood pressure,respectively,compared to no reduction or increase in exposure.However,the effects were significant only in rural areas.Our analysis support CAP aiming to benefit public health and provides insights to inform future control policy for efficiently decreasing air pollution exposure burden.展开更多
Environmental protection policies(EPPs)play a pivotal role in advancing sustainable development and maintaining ecological balance by establishing clear directives and standards.However,a comprehensive methodology to ...Environmental protection policies(EPPs)play a pivotal role in advancing sustainable development and maintaining ecological balance by establishing clear directives and standards.However,a comprehensive methodology to evaluate the effectiveness of these policies remains underdeveloped.Here,we employ a difference-in-differences(DID)approach to assess the effectiveness of EPPs,using the implementation of the Resident Work(RW)policy as a quasi-natural experiment.Drawing on urban-level panel data from the Yangtze River Basin between 2016 and 2021,we demonstrate that the DID model robustly evaluates the RW policy's impact on water quality improvement.Cities that adopted the RW policy experienced a 0.0098 reduction in water pollution compared to non-adopting cities.A dynamic analysis revealed progressive water quality improvements over time,with stronger effects observed in economically disadvantaged cities.Furthermore,higher policy evaluation scores correlated with greater improvements in water quality.This study highlights the utility of the DID model in quantifying EPP effectiveness and offers a scalable framework for policy evaluation in environmental management.展开更多
Amid growing global attention to low-carbon transitions,the environmental effects of rural tourism remain theoretically underexplored.Drawing on Ecological Modernization Theory(EMT),this study examines whether and how...Amid growing global attention to low-carbon transitions,the environmental effects of rural tourism remain theoretically underexplored.Drawing on Ecological Modernization Theory(EMT),this study examines whether and how rural tourism contributes to carbon emission reduction in China.Using a quasi-natural experiment based on the designation of National Demonstration Counties for Rural Tourism,we construct panel data for 273 cities from 2006 to 2022 and employ a difference-in-differences model to identify causal effects.Results show that rural tourism significantly reduces carbon emissions,particularly through three mechanisms:improved digital infrastructure,enhanced technological innovation,and greater adoption of clean energy.Heterogeneity analysis reveals stronger effects in eastern regions,non-tourism-dominated cities,and areas with rich tourism resources.This study contributes to the literature by extending EMT into rural service economies,proposing a multi-pathway framework for understanding tourism-driven decarbonization,and providing empirical insights into the role of tourism in national climate strategies.展开更多
This paper focuses on Chengdu and Chongqing’s positioning as important economic center in western China and their evolving into an economic center of national influence.On the one hand,it uses the synthetic differenc...This paper focuses on Chengdu and Chongqing’s positioning as important economic center in western China and their evolving into an economic center of national influence.On the one hand,it uses the synthetic difference-in-differences(SDID)method to analyze the impact of policies since 2011 designed to build Chengdu and Chongqing into an important economic center in western China.On the other hand,it employs the entropy-weighted TOPSIS method to comprehensively evaluate the influences of ten core Chinese cities as economic centers within four major urban agglomerations,as well as conduct an analytical assessment of the Chengdu-Chongqing economic circle from key perspectives such as its capacity to lead,capacity to agglomerate,and capacity to radiate.From a longitudinal historical perspective,both Chengdu and Chongqing have benefited significantly from policies designed to build an important economic center in western China,and which laid a foundation for building an economic center of national influence.From a horizontal regional comparison,among the ten core cities evaluated as economic centers within the four major urban agglomerations,Chengdu and Chongqing ranked in the middle,possessing a moderate but not yet outstanding influence.Consequently,to evolve into an economic center of national influence,the Chengdu-Chongqing economic circle should leverage its relative advantages in connectivity,market size,value chain division of labor,policy attractiveness,and industry development.It can enhance its influence by strengthening the complementarity of its economic resources,overcoming the administrative inertia,accelerating the establishment of a regional innovation system,broadening the scope of its economic radiation,and promoting its comprehensive and all-dimensional opening-up.展开更多
Coal dependence and inefficient decentralized heating have significantly increased China’s energy consumption for winter heating,increasing air pollution and exacerbating the greenhouse effect.In 2017,China implement...Coal dependence and inefficient decentralized heating have significantly increased China’s energy consumption for winter heating,increasing air pollution and exacerbating the greenhouse effect.In 2017,China implemented the Pilot Policy on Clean Winter Heating in Northern China,aiming to achieve high central heating coverage and cleaner energy consumption.Studying the effects of this policy can help promote its implementation and serve as a reference for effective adjustment of the contents in the future.However,few studies have investigated this policy and its carbon reduction effects,and most focus on the provincial or city levels.Therefore,this paper considers the policy’s influence on air pollution and carbon emissions at the county level to provide a precise and comprehensive assessment of the policy effects.We use panel data from 1290 counties in 15 provinces in Northern China from 2014 to 2021,applying a multiperiod difference-in-differences model to quantify the impact of the policy on carbon emissions and air quality in the pilot area.We then conduct a series of tests to demonstrate the robustness of the results and analyze the mechanisms of the policy effects from two perspectives,namely,central heating and natural gas use,through a mediating effect model.Finally,we examine the heterogeneity of policy effects between counties based on geographic location and per capita income levels of rural residents through a moderating effect model.The results reveal that the policy significantly reduces air pollution and carbon emissions in the pilot area by increasing the central heating area and natural gas use.Compared with the central and western regions in the north and areas with low-income rural residents,the policy effects in the eastern regions in the north and areas with high-income rural residents are more pronounced.展开更多
This paper leverages the Opinions of the State Council on Further Promoting the Reform of the Household Registration System as a quasi-natural experiment to examine the impact of rural migrant urbanization on local go...This paper leverages the Opinions of the State Council on Further Promoting the Reform of the Household Registration System as a quasi-natural experiment to examine the impact of rural migrant urbanization on local government expenditures in science and technology(S&T)and education.Employing a generalized difference-in-differences(generalized-DID)approach and panel data from 271 Chinese prefecture-level and above-level cities spanning 2003–2019,we find that household registration reform driven by this urbanization process significantly increased the absolute level as well as the fiscal share of S&T and education spending.Mechanism analyses indicate that rural migrant urbanization promotes these expenditures through two channels:increasing the overall local fiscal revenue and encouraging a greater proportion of the fiscal resources to be allocated to these sectors.The findings uncover the current evolving trends in fiscal resource allocation due to rural migrant urbanization and provide empirical evidence for optimizing the provision of public services and enhancing the potential of long-term economic development.展开更多
文摘This paper takes global manufacturing listed companies from 2010 to 2022 as samples and uses the difference-in-differences(DID)method to empirically examine the impact of the internationalization of ESG standards on the trade competitiveness of multinational enterprises and their mechanisms.The research finds that the internationalization of ESG standards significantly enhances the trade competitiveness of multinational manufacturing enterprises,and this effect is dynamic and sustainable.The mechanism analysis indicates that the internationalization of ESG standards exerts its influence through three pathways:reducing enterprise financing costs,promoting technological innovation,and enhancing brand reputation.The heterogeneity analysis shows that this effect is more significant in enterprises from developed countries,high-pollution industries,and larger enterprises.This paper provides micro-level evidence for understanding the economic consequences of the internationalization of ESG standards and offers policy implications for multinational enterprises to cope with the global ESG rule changes and enhance their trade competitiveness.
基金This work was supported by grants from the National Natural Science Foundation of China,with No.NSFC62006109 and NSFC12031005.
文摘Purpose:In recent decades,with the availability of large-scale scientific corpus datasets,difference-in-difference(DID)is increasingly used in the science of science and bibliometrics studies.DID method outputs the unbiased estimation on condition that several hypotheses hold,especially the common trend assumption.In this paper,we gave a systematic demonstration of DID in the science of science,and the potential ways to improve the accuracy of DID method.Design/methodology/approach:At first,we reviewed the statistical assumptions,the model specification,and the application procedures of DID method.Second,to improve the necessary assumptions before conducting DID regression and the accuracy of estimation,we introduced some matching techniques serving as the pre-selecting step for DID design by matching control individuals who are equivalent to those treated ones on observational variables before the intervention.Lastly,we performed a case study to estimate the effects of prizewinning on the scientific performance of Nobel laureates,by comparing the yearly citation impact after the prizewinning year between Nobel laureates and their prizewinning-work coauthors.Findings:We introduced the procedures to conduct a DID estimation and demonstrated the effectiveness to use matching method to improve the results.As a case study,we found that there are no significant increases in citations for Nobel laureates compared to their prizewinning coauthors.Research limitations:This study ignored the rigorous mathematical deduction parts of DID,while focused on the practical parts.Practical implications:This work gives experimental practice and potential guidelines to use DID method in science of science and bibliometrics studies.Originality/value:This study gains insights into the usage of econometric tools in science of science.
基金Item Sponsored by Fundamental Research Funds for Central University of China(N090302010)National High-Tech Researchand Development Program of China(2008AA042901)National Key Science and Technology Support Plan of Ministry of Science and Technology of China(2006BAE03A00)
文摘A mathematical model of optimal energy medium distribution in steelmaking process is formulated. In this model, three kinds of important energy mediums including byproduct gases, steam and electricity are considered, and the objective function accounts for both the change of generation and consumption of the byproduct gases and the demand of low （or middle） pressure steam and electricity for each period to maximize the benefit of products cost and minimize the consumption of energy. The results indicate that the optimal distribution scheme of byproduct gases, middle pressure steam, low pressure steam and electricity is achieved and case study shows that 6% of operation cost is reduced by using the proposed model comparing with the previous model.
基金This work was supported by the National Natural Science Foundation of China(Nos.41772141,41972171)the Natural Science Foundation of Jiangsu Province(BK20181362),the Priority Academic Program Development of Jiangsu Higher Education Institutions(PAPD).
文摘In shale reservoirs,the organic pores with various structures formed during the thermal evolution of organic matter are the main storage site for adsorbed methane.However,in the process of thermal evolution,the adsorption characteristics of methane in multi type and multi-scale organic matter pores have not been sufficiently studied.In this study,the molecular simulation method was used to study the adsorption characteristics of methane based on the geological conditions of Longmaxi Formation shale reservoir in Sichuan Basin,China.The results show that the characteristics of pore structure will affect the methane adsorption characteristics.The adsorption capacity of slit-pores for methane is much higher than that of cylindrical pores.The groove space inside the pore will change the density distribution of methane molecules in the pore,greatly improve the adsorption capacity of the pore,and increase the pressure sensitivity of the adsorption process.Although the variation of methane adsorption characteristics of different shapes is not consistent with pore size,all pores have the strongest methane adsorption capacity when the pore size is about 2 nm.In addition,the changes of temperature and pressure during the thermal evolution are also important factors to control the methane adsorption characteristics.The pore adsorption capacity first increases and then decreases with the increase of pressure,and increases with the increase of temperature.In the early stage of thermal evolution,pore adsorption capacity is strong and pressure sensitivity is weak;while in the late stage,it is on the contrary.
基金Supported by the National Natural Science Foundation of China(21376188,21676211)
文摘A systematic strategy for retrofit of the multi-period heat exchanger network （HEN） on the basis of the multi- objective optimization is developed. In this three-stage procedure, a simplified multi-objective optimization model of the multi-period lIEN is first established and then solved to target the retrofit, aiming to minimizing the total annual cost and total annual CO2 emissions. The obtained Pareto front represents series of retrofit targets under different emission limitations, from which the most desirable one can be selected. The matching of the existing and the required heat exchangers is further implemented to finalize the retrofit, which will meet the practical retrofit requirements and matching restrictions. The application of the proposed procedure is illustrated through a case study of a HEN in a vacuum gas oil hydro-treating unit.
文摘In intercontinental trade and economics goods are bought from a global supplier.On occasion,the expected lot may include a fraction of defective items.These imperfect items still have worth and can be sold to customers after repair.It is cost-effective and sustainable to rework such items in nearby repair workshops rather than return them.The reworked items can be returned from the workshop to the buyer when shortages are equal to the quantity of imperfect items.In the meantime,the supplier correspondingly deals a multi-period delay-in-payments strategy with purchaser.The entire profit has been maximized with paybacks for interim financing.This study aims to develop a synergic inventory model to get the most profit by making an allowance for reworking,multi-period delay-in-payments policy,and shortages.The findings of the proposed model augment inventory management performance by monitoring cycle time as well as fraction of phase with optimistic inventory for a supply chain.The results demonstrate that profit is smaller if the permitted period given by supplier to buyer is equal to or greater than the cycle time,and profit is greater if the permitted period is smaller than the cycle time.The algebraic method is engaged to make a closed system optimum solution.The mathematical experiment of this study is constructed to provide management insights and tangible practices.
基金supported by the National Natural Science Foundation of China(90305026).
文摘Traditional multi-band frequency selective surface （FSS） approaches are hard to achieve a perfect resonance response in a wide band due to the limit of the onset grating lobe frequency determined by the array. To solve this problem, an approach of combining elements in different period to build a hybrid array is presented. The results of series of numerical simulation show that multi-periodicity combined element FSS, which are designed using this approach, usually have much weaker grating lobes than the traditional FSS. Furthermore, their frequency response can be well predicted through the properties of their member element FSS. A prediction method for estimating the degree of expected grating lobe energy loss in designing multi-band FSS using this approach is provided.
基金The work was supported by the National Natural Science Foundation of China(Grant Number:41463005)Key research and development program of Jiangxi province(Grant Number:20181ACG70021).
文摘Temperate and high-latitude forests are carbon sinks and play pivotal roles in offsetting greenhouse gas emissions of CO2.However,uncertainty still exists for subtropical forests,especially in monsoon-prevalent eastern Asia.Earlier studies have depended on remote sensing,ecosystem modeling,carbon fluxes,or single period forest surveys to estimate carbon sequestration capacities,and the results vary significantly.This study was designed to utilize multi-period forest survey data to explore spatial-dynamics of biomass storage in subtropical forests of China.Jiangxi province,a region with over 60%subtropical forest cover,was selected as the case study site and is located in central east China.Based on forest inventory data 1984-2013,and the stock-difference and biomass expansion factor methods,the carbon storage and density,of arboreal forests,economic forests,bamboo forests,woodlands and shrubberies were estimated.The results show that carbon storage increased from 159.1 Tg C in 1988 to 276.1 TgC in 2013,making up 3.1-3.8%of carbon stored throughout China.Among the four types of forests,the amount of carbon stored was as follows:arboreal forest>economic forest>bamboo forest>woodland and shrubbery.Arboreal forests accounted for 64.0-79.4%of the total.Forest carbon density increased from 21.2 Mg C ha-1 in 1984 to26.2 Mg C ha-1 in 2013,equal to 61.2-70.2%of the average carbon density of China’s forests in the same period.Forest carbon storage in Jiangxi will reach 355.5 Tg C and 535.8 Tg C in 2020 and 2030,respectively,and forest carbon density is predicted to be 31.9 Mg C ha-1and 46.4 Mg C ha-1,respectively.As one of the few studies using multi-period data tracking biomass dynamics in Jiangxi province,the findings of this study may be used as a reference for other research.Using Jiangxi as a case study underlies the fact that subtropical forests in China have great carbon sequestration potential and have fundamental significance to offset global environmental change effects.
基金The authors declare that fund support was received from National Social Science Fund of China[Grant No.23BJL010].
文摘As urbanization accelerates globally,air pollution-particularly PM_(2.5)-is becoming an increasingly significant threat,not only to public health but also the environment.In-depth research on the impact of China’s Zero Waste City pilot policy on PM_(2.5)concentration offers valuable insights into the policy’s effectiveness and provides a potential model for environmental governance worldwide.This study employs panel data from 293 Chinese cities from 2014 to 2022 to systematically analyze the impact of the Zero-Waste City policy on PM_(2.5)concentration using a difference-in-differences model.The findings indicate that the policy not only directly reduces PM_(2.5)concentration but also indirectly curbs PM_(2.5)emissions by enhancing green innovation and green economic efficiency.Moreover,the policy’s effects are found to be positively moderated by urban energy dependence and digital financial inclusion,while they are negatively moderated by the government debt ratio.Based on these findings,this study suggests that cities should actively develop their digital economy,reduce government debt,promote green innovation,and improve green economic efficiency,as doing so will enhance their implementation of environmental policies and promote sustainable urban development.
文摘Based on personality trait theory and experiential learning theory,lots of studies have revealed a reverse causal relationship between volunteering and the non-cognitive abilities of college students.Using data from a longitudinal survey of college students in Hunan Province,China,this study employed the difference-in-differences method to examine the causal relationship between volunteering and non-cognitive abilities,aiming to determine whether volunteering screens or cultivates the non-cognitive abilities of college students.The findings confirmed the screening effect of volunteering on extraversion and conscientiousness and the cultivating effect on agreeableness.However,there was neither a screening effect nor a cultivating effect on emotional stability and openness.It is indicated that volunteering during college primarily screens the non-cognitive abilities of students through personality trait mechanisms,with a limited cultivating effect on non-cognitive abilities.This highlights the necessity to prompt a re-evaluation of how volunteering fulfills its educational function.
基金Supported by the National Natural Science Foundation of China(NSFC)(Grant No.72173131)for“Research on New Trends and Driving Forces in China’s Labor Income Share:A Micro Perspective Based on Enterprise Behavior”the China Postdoctoral Science Foundation(Grant No.2023M743940)for“Research on the Income Distribution Effects of Transport Infrastructure Construction:Theoretical Analysis and Quantitative Assessment”.
文摘Amid China’s rapid economic growth,significant regional imbalances persisted.To address this disparity,it is essential to pursue high-quality development by fostering endogenous drivers within poverty-stricken areas.In late 2011,the Chinese government introduced a new nationwide regional poverty alleviation and development program.This study examines the macroeconomic impacts and micro-level mechanisms of these policies by leveraging manually compiled policy documents and macro and micro data(county economies,enterprises,and land transactions),using a DID approach.The findings reveal that the program significantly boosted economic growth in poor regions without causing negative spillovers to neighboring or paired-assistance areas.Economic growth in the assisted regions was primarily driven by industrialization,encompassing both scale expansion and efficiency gains.A cost-benefit analysis further confirms substantial economic returns and long-term fiscal sustainability.These results provide important policy implications for refining regional poverty policies and advancing balanced development.
基金supported by the Special Project for Training Young Science and Technology Talents in Early Career Development of Jiangxi Province,China(Grant No.20244BCE52087).
文摘This study proposes a regression-based estimation method in difference-in-differences settings in the presence of time-varying covariates-a scenario commonly encountered in applications.We impose only a conditional parallel trends assumption with timevarying covariates and plausible assumptions on the conditional expectation functions.We show that a family of causal effect parameters is exactly the coefficient estimators from our proposed regressions even in the presence of staggered treatment timing and treatment effect heterogeneity across cohorts,time periods,and covariates.These parameters can be further aggregated to the dynamic treatment effects and the overall effect of being treated.We establish the corresponding asymptotic properties.Simulation studies suggest that our proposed regression-based estimators successfully outperform in estimating the causal parameters.Finally,we apply this method to evaluate the effect of intrastate bank deregulation on income inequality in the United States in the setting of Beck et al.(2010).We find substantially different results based on our proposed method.
基金Natural Science Foundation of China(Key Program,No 72133003)Key Projects of Philosophy and Social Sciences Research,Ministry of Education,(Grant No.:22JZD008).
文摘The green credit policy(GCP)is an essential financial policy tool for solving the problem of environmental pollution,and urban energy conservation is an effective way to achieve the goal of carbon neutrality.However,existing research has not verified the energy-saving effects of green credit(GC)at the city level.Based on panel data from 283 cities in China,this study aims to investigate whether GC can effectively reduce urban energy intensity(EI),which is an important complement to existing research.In terms of research methods,to better evaluate the effect of the policy and exclude the influence of other relevant factors,this study considers the promulgation of the Green Credit Guideline(GCG)in 2012 as the basic event,uses the difference-in-differences(DID)model to investigate the impact of GC on EI,and discusses the main impact mechanism.The key results are follows.(1)GC can effectively reduce urban EI.(2)Public environmental demand positively regulates the negative correlation between GC and EI.(3)GC reduces EI through three main channels:government support,capital investment,and technological innovation;however,the mechanism of industrial structure has no significant effect.(4)The effect of GC is more significant in areas with large urban scales,low environmental regulation intensity,and high industrial agglomeration.Based on the above results,this study presents puts forward targeted policy recommendations to strengthen the role of GC in urban sustainable development.
文摘Drawing on local legitimacy theory,which posits that firms seek acceptance and approval from their local community and stakeholders,we examine the effect of corporate governance(CG)quality on corporate social responsibility(CSR)activities in Korea.Enhancing CG quality and engaging in CSR activities are increasingly important for firms’long-term sustainability.Using the KEJI-CSR index and the KCGS CG score,we find that CG quality positively influences CSR activities.Specifically,if the CG quality score increases by one standard deviation,CSR improves by approximately 1.6–2.3%of the mean CSR score.Furthermore,the relationship between CG and CSR is stronger for business conglomerates(chaebol-affiliated firms),suggesting that sound CG practices can promote CSR activities more effectively when the interests of management and stakeholders are better aligned.This finding supports local legitimacy theory.Our findings are robust under various tests,including difference-in-differences analysis and propensity score matching.An interesting policy implication is that multinational enterprises or foreign investors should prioritize the CG quality of their local subsidiaries or investee firms.Better CG practices can enhance CSR activities,which are essential for long-term survival in local markets.This study,however,is limited to Korea and may not be generalizable to other emerging markets with different governance structures.
基金supported by the National Institute of Environmental Health Sciences(NIEHS)of United States(No.R00ES027511)the National Natural Science Foundation of China(No.42201303).
文摘Long-term exposure to fine particulate matters(PM_(2.5))has been associated with respiratory and cardiovascular diseases and the burden are potentially higher in China experiencing heavy air pollution.In this study,we established the exposure-response association between long-term exposures to PM_(2.5)and lung function and blood pressure in Chinesemiddle-aged and older adults using linearmixed-effects and generalized additive mixedmodels based on 3 waves longitudinal health outcomes data by enrolling 19,988 participants from 121 cities across themainland of China.We also assessed the effect of Clean Air Policy(CAP)based on a quasi-experimental difference-in-differences(DID)design.A 10μg/m^(3)increase in PM_(2.5)concentration was associated with a 7.18(95%confidence interval[CI]:-8.35,-6.02)L/min decrease in PEF(peak expiratory flow)and a 0.72(95%[CI]:0.53,0.90)and a 0.30(95%[CI]:0.18,0.42)mmHg increase in systolic and diastolic blood pressure,respectively.The associations were more pronounced in males and rural areas for PEF,but similar across subgroups for blood pressure.DID results suggested that the effect of CAP on health outcomes were sensitive tomagnitudes of reduction in PM_(2.5).A 5μg/m^(3)reduction in PM_(2.5)or more generally led to 18.70(95%[CI]:0.79,36.61)higher PEF and-2.05(95%[CI]:-3.87,-0.23)lower diastolic blood pressure,respectively,compared to no reduction or increase in exposure.However,the effects were significant only in rural areas.Our analysis support CAP aiming to benefit public health and provides insights to inform future control policy for efficiently decreasing air pollution exposure burden.
基金supported by The Yangtze River Joint Research Phase Ⅱ Program(No.2022-LHYJ-02-0402).
文摘Environmental protection policies(EPPs)play a pivotal role in advancing sustainable development and maintaining ecological balance by establishing clear directives and standards.However,a comprehensive methodology to evaluate the effectiveness of these policies remains underdeveloped.Here,we employ a difference-in-differences(DID)approach to assess the effectiveness of EPPs,using the implementation of the Resident Work(RW)policy as a quasi-natural experiment.Drawing on urban-level panel data from the Yangtze River Basin between 2016 and 2021,we demonstrate that the DID model robustly evaluates the RW policy's impact on water quality improvement.Cities that adopted the RW policy experienced a 0.0098 reduction in water pollution compared to non-adopting cities.A dynamic analysis revealed progressive water quality improvements over time,with stronger effects observed in economically disadvantaged cities.Furthermore,higher policy evaluation scores correlated with greater improvements in water quality.This study highlights the utility of the DID model in quantifying EPP effectiveness and offers a scalable framework for policy evaluation in environmental management.
基金supported by the National Social Science Fund of China(Grant No.23BJY142).
文摘Amid growing global attention to low-carbon transitions,the environmental effects of rural tourism remain theoretically underexplored.Drawing on Ecological Modernization Theory(EMT),this study examines whether and how rural tourism contributes to carbon emission reduction in China.Using a quasi-natural experiment based on the designation of National Demonstration Counties for Rural Tourism,we construct panel data for 273 cities from 2006 to 2022 and employ a difference-in-differences model to identify causal effects.Results show that rural tourism significantly reduces carbon emissions,particularly through three mechanisms:improved digital infrastructure,enhanced technological innovation,and greater adoption of clean energy.Heterogeneity analysis reveals stronger effects in eastern regions,non-tourism-dominated cities,and areas with rich tourism resources.This study contributes to the literature by extending EMT into rural service economies,proposing a multi-pathway framework for understanding tourism-driven decarbonization,and providing empirical insights into the role of tourism in national climate strategies.
文摘This paper focuses on Chengdu and Chongqing’s positioning as important economic center in western China and their evolving into an economic center of national influence.On the one hand,it uses the synthetic difference-in-differences(SDID)method to analyze the impact of policies since 2011 designed to build Chengdu and Chongqing into an important economic center in western China.On the other hand,it employs the entropy-weighted TOPSIS method to comprehensively evaluate the influences of ten core Chinese cities as economic centers within four major urban agglomerations,as well as conduct an analytical assessment of the Chengdu-Chongqing economic circle from key perspectives such as its capacity to lead,capacity to agglomerate,and capacity to radiate.From a longitudinal historical perspective,both Chengdu and Chongqing have benefited significantly from policies designed to build an important economic center in western China,and which laid a foundation for building an economic center of national influence.From a horizontal regional comparison,among the ten core cities evaluated as economic centers within the four major urban agglomerations,Chengdu and Chongqing ranked in the middle,possessing a moderate but not yet outstanding influence.Consequently,to evolve into an economic center of national influence,the Chengdu-Chongqing economic circle should leverage its relative advantages in connectivity,market size,value chain division of labor,policy attractiveness,and industry development.It can enhance its influence by strengthening the complementarity of its economic resources,overcoming the administrative inertia,accelerating the establishment of a regional innovation system,broadening the scope of its economic radiation,and promoting its comprehensive and all-dimensional opening-up.
基金supported by the National Social Science Fund of China[Grant No.21BGL181]to Yan Chen.
文摘Coal dependence and inefficient decentralized heating have significantly increased China’s energy consumption for winter heating,increasing air pollution and exacerbating the greenhouse effect.In 2017,China implemented the Pilot Policy on Clean Winter Heating in Northern China,aiming to achieve high central heating coverage and cleaner energy consumption.Studying the effects of this policy can help promote its implementation and serve as a reference for effective adjustment of the contents in the future.However,few studies have investigated this policy and its carbon reduction effects,and most focus on the provincial or city levels.Therefore,this paper considers the policy’s influence on air pollution and carbon emissions at the county level to provide a precise and comprehensive assessment of the policy effects.We use panel data from 1290 counties in 15 provinces in Northern China from 2014 to 2021,applying a multiperiod difference-in-differences model to quantify the impact of the policy on carbon emissions and air quality in the pilot area.We then conduct a series of tests to demonstrate the robustness of the results and analyze the mechanisms of the policy effects from two perspectives,namely,central heating and natural gas use,through a mediating effect model.Finally,we examine the heterogeneity of policy effects between counties based on geographic location and per capita income levels of rural residents through a moderating effect model.The results reveal that the policy significantly reduces air pollution and carbon emissions in the pilot area by increasing the central heating area and natural gas use.Compared with the central and western regions in the north and areas with low-income rural residents,the policy effects in the eastern regions in the north and areas with high-income rural residents are more pronounced.
基金supported by the National Natural Science Foundation of China Youth Project“Research on the Mechanism and Policy Design of the Impact of Rural Migrant Urbanization on Local Government Education Investment”(Grant No.72103034)the Distinguished Young Scholar Funding Project of the University of International Business and Economics(Grant No.21JQ11).
文摘This paper leverages the Opinions of the State Council on Further Promoting the Reform of the Household Registration System as a quasi-natural experiment to examine the impact of rural migrant urbanization on local government expenditures in science and technology(S&T)and education.Employing a generalized difference-in-differences(generalized-DID)approach and panel data from 271 Chinese prefecture-level and above-level cities spanning 2003–2019,we find that household registration reform driven by this urbanization process significantly increased the absolute level as well as the fiscal share of S&T and education spending.Mechanism analyses indicate that rural migrant urbanization promotes these expenditures through two channels:increasing the overall local fiscal revenue and encouraging a greater proportion of the fiscal resources to be allocated to these sectors.The findings uncover the current evolving trends in fiscal resource allocation due to rural migrant urbanization and provide empirical evidence for optimizing the provision of public services and enhancing the potential of long-term economic development.
