The study of pressure stimulated current(PSC)changes of rocks is significant to monitor dynamic disasters in mines and rock masses.The existing studies focus on change laws and mechanism of currents generated under th...The study of pressure stimulated current(PSC)changes of rocks is significant to monitor dynamic disasters in mines and rock masses.The existing studies focus on change laws and mechanism of currents generated under the loading of rocks.An electrical and mechanics test system was established in this paper to explore the impacts of loading rates on PSCs.The results indicated that PSC curves of different rocks had different change laws under low/high loading rates.When the loading rate was relatively low,PSC curves firstly changed gently and then increased exponentially.Under high loading rates,PSC curves experienced the rapid increase stage,gentle increase stage and sudden change stage.The compressive strength could greatly affect the peak PSC in case of rock failure.The loading rate was a key factor in average PSC.Under low loading rates,the variations of PSCs conformed to the damage charge model of fracture mechanics,while they did not at the fracture moment.Under high loading rates,the PSCs at low stress didn’t fit the model due to the stress impact effects.The experimental results could provide theoretical basis for the influence of loading rates on PSCs.展开更多
With the economic development and multicultural exchange of ethnic villages,more and more ethnic villages have embarked on the road of tourism to become rich,but also brought the problem of ecological pollution.Few ex...With the economic development and multicultural exchange of ethnic villages,more and more ethnic villages have embarked on the road of tourism to become rich,but also brought the problem of ecological pollution.Few existing literatures discuss how to alleviate the ecological pollution in ethnic villages from the perspective of tourists’environmentally responsible behavior.In the context of ethnic villages,from the perspective of integration and the attitude-context-behavior theory,this paper constructs an EV-ABC-TERB model with four variables,namely environmental attitude,local atmosphere,emotional experience and tourists’environmentally responsible behavior,to explore the characteristics,influencing factors and influencing mechanism of tourists’environmental responsibility behavior in ethnic villages.Taking Xijiang Hmong Village as the research case,questionnaire survey method and structural equation model method were used.The results show that environmental attitude positively affects emotional experience and tourists’environmentally responsible behavior.Local atmosphere positively influences tourists’environmentally responsible behavior.Emotional experience negatively affects tourists’environmentally responsible behavior and plays an intermediary role in the way that environmental attitudes affect tourists’environmentally responsible behavior.The influence of environmental attitude on emotional experience is negatively regulated by local atmosphere.Finally,based on the analysis conclusion,it provides new ideas and inspiration for the sustainable development of the ethnic village tourism.展开更多
On the basis of combing domestic and foreign related literature and research practice,the influence mechanism of the construction of new liberal arts was analyzed,and the fundamental tasks of the construction of new l...On the basis of combing domestic and foreign related literature and research practice,the influence mechanism of the construction of new liberal arts was analyzed,and the fundamental tasks of the construction of new liberal arts in Tibet were summarized.Based on 173 field questionnaires in Tibet,factor analysis was used to conduct empirical analysis.It is found that the cumulative contribution of the first,second,third and fourth common factor was 24.921%,21.742%,17.331%,and 14.206%,respectively.Professional orientation,the reform of talent training mode,teacher ability,quality and level of the teaching team,curriculum system reform,teaching content reform,education training service,and other evaluation indicators are the key points of the construction of new liberal arts.The research conclusion is that the construction of new liberal arts needs to highlight the"three positions";it is needed to plan and promote various resources to focus on the ability and level of professional teachers’social services;the managers and professional teachers should be the leaders and participants of the innovation of the talent training model respectively.Finally,relevant policy recommendations were put forward.展开更多
[Objective] The research aimed to study the possible mechanism of terrain effect on cold-flow snowstorm.[Method] By using the meso-scale numerical model(WRF),a cold-flow snowstorm weather process in Shandong Peninsula...[Objective] The research aimed to study the possible mechanism of terrain effect on cold-flow snowstorm.[Method] By using the meso-scale numerical model(WRF),a cold-flow snowstorm weather process in Shandong Peninsula was carried out numerical simulation and terrain sensitivity contrast test.The possible reason of terrain effect on falling zone and strength of snowstorm was deeply analyzed from water vapor,thermodynamic field and so on.[Result] The mountain terrain in Shandong Peninsula had great influences on falling zone and strength of cold-flow snowstorm.The strength of snowstorm obviously increased,and the snowfall center obviously moved northward.The main reason was that terrain caused the low-level wind field convergence and vertical movement in the troposphere strengthened.Then,the spatial distribution of water vapor and snow water content in the cold-flow snowstorm process obviously changed.So,the whole snowstorm process was affected.[Conclusion] The mountain terrain in Shandong Peninsula was the important element which needed to be focused on considering in the forecast analysis of cold-flow snowstorm weather process.展开更多
The effective use of land in Northeast China is of great significance for ensuring national food security and regional rural revitalization.In this study,based on the survey data collected from Jilin Province,Northeas...The effective use of land in Northeast China is of great significance for ensuring national food security and regional rural revitalization.In this study,based on the survey data collected from Jilin Province,Northeast China,we analyzed the vacancy rates of rural homesteads in suburban,outer suburban,and remote villages,as well as the withdrawal intention of rural-settled farmers,urbansettled farmers,and farmers with urban and rural dual residency from vacant homesteads.From the perspective of farmers’perceptions,this study constructed a theoretical framework of the influence mechanism of their withdrawal intention and analyzed such mechanism by constructing a structural equation model.The results indicated that:1)rural homestead vacancy rates increased with distance from the village to the city.2)rural-settled farmers showed a low withdrawal intention for vacant rural homesteads,followed by urban and rural dual-residence farmers,and urban-settled farmers showed the highest withdrawal intention.3)the relative importance of the factors influencing withdrawal intention is in the following order:policy awareness>interest perception>living environment perception>family characteristics.Finally,this study discussed the reformation of the homestead system and rural homestead transition in Northeast China,which can provide policy support to increase the potential of cultivated land and promote sustainable rural development and urban-rural coordination.展开更多
The Qaidam Basin(QB)is a concentrated distribution area and chemical industrial bases of salt lakes in China.Lakes in the QB have been expanding during the past 20 years.Rapid lake expansion resulted in some considera...The Qaidam Basin(QB)is a concentrated distribution area and chemical industrial bases of salt lakes in China.Lakes in the QB have been expanding during the past 20 years.Rapid lake expansion resulted in some considerable scientific issues on the protection of salt lake resources and infrastructure,and monitoring of hydrological processes at the lake-basin scale.Although the spatial-temporal trends of lake changes on the Qinghai-Tibet Plateau(QTP)have been well documented,the underlying influencing mechanism and hydrogeological implications of rapid lake changes in the QB are not well understood.Three lakes in the northern QB were selected to investigate lake water level fluctuations on different time scales based on extensive in-situ monitoring and satellite observations.The influencing mechanism and hydrogeological implications of rapid changes of terminal lakes were discussed in combination with the reported increasing precipitation rate and mass balance of glaciers in the northern QTP.Results reveal the following:(1)the fluctuation pattern of Sugan Lake was asynchronous and out of phase with that of Xiao Qaidam and Toson lakes during the monitoring period;(2)Sugan Lake water rose gradually,and the rise interval was from late April to early July.In contrast,Xiao Qaidam and Toson lakes took on a rapid and steep rise,and the rise intervalwas from late July to September;(3)the influencing mechanisms for rapid lake fluctuations are controlled by different factors:glacier and snow melting with increasing temperature for Sugan Lake and increasing precipitation for Xiao Qaidam and Toson lakes;(4)in accordance with different intervals and influencing mechanisms of rapid lake expansions in the QB,hydrological risk precaution of lakes and corresponding river catchments was conducted in different parts of the basin.This study provided an important scientific basis for assessing the hydrological process and hydrological risk precaution,and protection of salt lake resources along with rapid lake expansions in the arid area.展开更多
Calcium salt is an important contributing factor for calcium-based biomineralization.To study the effect of calcium salt on soil biomineralization using crude soybean urease,the calcium salts,including the calcium chl...Calcium salt is an important contributing factor for calcium-based biomineralization.To study the effect of calcium salt on soil biomineralization using crude soybean urease,the calcium salts,including the calcium chloride (CaCl2 ),calcium acetate ((CH3 COO)2 Ca) and calcium nitrate (Ca(NO3 )2 ),were used to prepare the biotreatment solution to carry out the biomineralization tests in this paper.Two series of biomineralization tests in solution and sand column,respectively,were conducted.Scanning electron microscopy (SEM) and X-ray diffraction (XRD) were performed to determine the microscopic characteristics of the precipitated calcium carbonate (CaCO3 ) crystals.The experimental results indicate that the biomineralization effect is the best for the CaCl2 case,followed by (CH3 COO)2 Ca,and worst for Ca(NO3 )2 under the test conditions of this study (i.e.1 mol/L of calcium salt-urea).The mechanism for the effect of the calcium salt on the biomineralization of crude soybean urease mainly involves: (1) inhibition of urease activity,and (2) influence on the crystal size and morphology of CaCO3 .Besides Ca2+ ,the anions in solution can inhibit the activity of crude soybean urease,and NO3 − has a stronger inhibitory effect on the urease activity compared with both CH3 COO− and Cl− .The co-inhibition of Ca2+ and NO3 − on the activity of urease is the key reason for the worst biomineralization of the Ca(NO3 )2 case in this study.The difference in biomineralization between the CaCl2 and (CH3 COO)2 Ca cases is strongly correlated with the crystal morphology of the precipitated CaCO3 .展开更多
In recent years,supercritical CO_(2)flooding has become an effective method for developing lowpermeability reservoirs.In supercritical CO_(2)flooding different factors influence the mechanism of its displacement proce...In recent years,supercritical CO_(2)flooding has become an effective method for developing lowpermeability reservoirs.In supercritical CO_(2)flooding different factors influence the mechanism of its displacement process for oil recovery.Asynchronous injection-production modes can use supercritical CO_(2)to enhance oil recovery but may also worsen the injection capacity.Cores with high permeability have higher oil recovery rates and better injection capacity,however,gas channeling occurs.Supercritical CO_(2)flooding has a higher oil recovery at high pressure levels,which delays the occurrence of gas channeling.Conversely,gas injection has lower displacement efficiency but better injection capacity at the high water cut stage.This study analyzes the displacement characteristics of supercritical CO_(2)flooding with a series of experiments under different injection and production parameters.Experimental results show that the gas breakthrough stage has the fastest oil production and the supercritical CO_(2)injection capacity variation tendency is closely related to the gas-oil ratio.Further experiments show that higher injection rates represent significant ultimate oil recovery and injection index,providing a good reference for developing low-permeability reservoirs.展开更多
Amorphous and nanostructural Fe-B alloys made by mechanical alloying of elemental Fe and amorphous B powders have been studied using X-ray diffraction, differential scanning calorimetry and Mossbauer spectroscopy. It ...Amorphous and nanostructural Fe-B alloys made by mechanical alloying of elemental Fe and amorphous B powders have been studied using X-ray diffraction, differential scanning calorimetry and Mossbauer spectroscopy. It has been shown that the milling conditions have a strong effect on the alloying. The single phase amorphous alloy, which is limited at nominal composition of Fe60B40, has been produced only by milling in Ar atmosphere and in other composition range the mixture of nanostructure Fe-like phase and Fe2B compound with a little amorphous phase are obtained. While by milling in air atmosphere the introduction of oxygen in air may suppress the formation of amorphous phase, thus the compounds Fe2B may be synthesized with no trace of amorphous phase. The crystallization temperatures of amorphous phase in the resultant products are higher than those of a single amorphous alloy Fe60B40, and hardly independent of the milling conditions and the composition. In addition, it is revealed that detectable B content in the final products is lower than the nominal composition of all the initial samples, which indicates that some B atoms may be located in the disordered interfacial regions of the nanostructural alloyed mixtures.展开更多
The use of aeolian sand(AS)as an aggregate to prepare coal mine cemented filling materials can resolve the problems of gangue shortage and excessive AS deposits.Owing to the lack of research on the mechanism of cement...The use of aeolian sand(AS)as an aggregate to prepare coal mine cemented filling materials can resolve the problems of gangue shortage and excessive AS deposits.Owing to the lack of research on the mechanism of cemented AS backfill(CASB),the response surface method(RSM)was adopted in this study to analyze the influence of ordinary Portland cement(PO)content(x_(1)),fly ash(FA)-AS(FA-AS)ratio(x_(2)),and concentration(x_(3))on the mechanical and microscopic properties of the CASB.The hydration characteristics and internal pore structure of the backfill were assessed through thermogravimetric/derivative thermogravimetric analysis,mercury intrusion porosimetry,and scanning electron microscopy.The RSM results show that the influence of each factor and interaction term on the response values is extremely significant(except x_(1)x_(3),which had no obvious effect on the 28 d strength).The uniaxial compressive strength(UCS)increased with the PO content,FA-AS ratio,and concentration.The interaction effects of x_(1)x_(2),x_(1)x_(3),and x_(2)x_(3) on the UCS at 3,7,and 28 d were analyzed.In terms of the influence of interaction items,an improvement in one factor promoted the strengthening effect of another factor.The enhancement mechanism of the curing time,PO content,and FA-AS ratio on the backfill was reflected in the increase in hydration products and pore structure optimization.By contrast,the enhancement mechanism of the concentration was mainly the pore structure optimization.The UCS was positively correlated with weight loss and micropore content but negatively correlated with the total porosity.The R^(2) value of the fitting function of the strength and weight loss,micropore content,and total porosity exceeded 0.9,which improved the characterization of the enhancement mechanism of the UCS based on the thermogravimetric analysis and pore structure.This work obtained that the influence rules and mechanisms of the PO,FA-AS,concentration,and interaction terms on the mechanical properties of the CASB provided a certain theoretical and engineering guidance for CASB filling.展开更多
Digital village construction opens a new vista for fulfilling consumption capabilities and optimizing consumption patterns in rural areas.For this research,we used the microdata on rural households from the 2019 China...Digital village construction opens a new vista for fulfilling consumption capabilities and optimizing consumption patterns in rural areas.For this research,we used the microdata on rural households from the 2019 China Household Finance Survey(CHFS)to conduct an empirical examination of the impact of digital village construction on the upgrading of rural household consumption and its possible influence mechanisms in the endogenous switching regression(ESR)model.Our research findings can be summarized in three points.First,digital village construction has significantly contributed positive contributions to the improvements and upgrading of rural household consumption.Second,digital village construction can help upgrade rural household consumption by increasing their participation in online shopping and expanding online shopping channels.Third,digital village construction means different things to rural households at different levels of risk exposure,with its facilitation to consumption upgrades in proportion to income risks facing rural households.Our research findings,which came from an extensive,in-depth exploration of the factors influencing rural household consumption,are of practical significance and policy value to the stimulating and fulfilling of consumption potentials among rural households.展开更多
In recent years, India’s diplomatic activities in the Asia-Pacific region are very active. From major power diplomacy, bilateral diplomacy to multilateral diplomacy, India has been quite impressive. Especially its mu...In recent years, India’s diplomatic activities in the Asia-Pacific region are very active. From major power diplomacy, bilateral diplomacy to multilateral diplomacy, India has been quite impressive. Especially its multilateral diplomacy has become widely accepted. This paper attempts to understand India’s multilateral diplomacy in the Asia-Pacific region, with emphasis on Indian strategic considerations, underlying motivation and strategic influence of its participation in the Asia-Pacific multilateral mechanisms.展开更多
Extracellular polymeric substances(EPS)in activated sludge from wastewater treatment plants(WWTPs)could affect interactions between nanoparticles and alter their migration behavior.The influence mechanisms of silver n...Extracellular polymeric substances(EPS)in activated sludge from wastewater treatment plants(WWTPs)could affect interactions between nanoparticles and alter their migration behavior.The influence mechanisms of silver nanoparticles(Ag NPs)and silver sulfide nanoparticles(Ag_(2)S NPs)aggregated by active EPS sludge were studied in monovalent or divalent cation solutions.The aggregation behaviors of the NPs without EPS followed the Derjaguin-Landau-Verwey-Overbeek(DLVO)theory.The counterions aggravated the aggregation of both NPs,and the divalent cation had a strong neutralizing effect due to the decrease in electrostatic repulsive force.Through extended DLVO(EDLVO)model analysis,in NaNO3 and low-concentration Ca(NO_(3))_(2)(<10 mmol/L)solutions,EPS could alleviate the aggregation behaviors of Cit-Ag NPs and Ag_(2)S NPs due to the enhancement of steric repulsive forces.At high concentrations of Ca(NO_(3))_(2)(10‒100 mmol/L),exopolysaccharide macromolecules could promote the aggregation of Cit-Ag NPs and Ag_(2)S NPs by interparticle bridging.As the final transformation form of Ag NPs in water environments,Ag_(2)S NPs had better stability,possibly due to their small van der Waals forces and their strong steric repulsive forces.It is essential to elucidate the surface mechanisms between EPS and NPs to understand the different fates of metal-based and metal-sulfide NPs in WWTP systems.展开更多
Ecosystem services are the media and channels through which ecological elements, structures, functions, and products benefit human society. Regulating the utilization intensity and protection methods of society on the...Ecosystem services are the media and channels through which ecological elements, structures, functions, and products benefit human society. Regulating the utilization intensity and protection methods of society on the ecosystem according to the ecosystem service value(ESV) and its influencing mechanism is of great significance for achieving the sustainable development goals. This paper takes the Guangdong-Hong Kong-Macao Greater Bay Area(GBA) as the research object and describes the spatiotemporal evolution characteristics of ESV in the GBA from 2000 to 2015. Panel quantile regression is also implemented to increase the understanding of the influencing mechanism of ESV. The main results are as follows:(1) From 2000 to 2015, the total ESV declined with a decreasing rate. The areas of decline were mainly distributed in the central part of the GBA and areas along the Pearl River Estuary.(2) Elasticity index, indicating response of ESV to land use change, reached its peak(1.08). The spatial distribution of elasticity index showed that land use changes brought about more intense ESV variations at the junction of cities.(3) In areas with different ESV levels, the influencing factors have different effects. Land use integrity can only promote ecosystem service capabilities in low-ESV areas. The positive effect of temperature on ecosystem service capacity increases with the increase of ESV, which reflects the self-reinforcement of the ecosystem. Moreover, the negative effect of economic density on ecosystem service capacity decreases with the increase of ESV, which reflects the self-protection of the ecosystem. The combination of such self-reinforcement and self-protection will lead to an ESV gap between the high-and low-ESV areas, and induce the “natural Matthew effect.”展开更多
Under the background that economy and urbanization of China are gradually entering the stage of high-quality development,clarifying the influence of economic development on urban livability is of significant academic ...Under the background that economy and urbanization of China are gradually entering the stage of high-quality development,clarifying the influence of economic development on urban livability is of significant academic and practical value.In this paper,regarded as one“factor”,livability was introduced into the research framework of production function,and a theoretical model of the impact of economic development on urban livability was established.Based on the panel data of 40 cities in China from 2005 to 2019,the System GMM,panel threshold model and other methods were further adopted to carry out an empirical analysis.The results show that:(1)The livability level of large and medium-sized cities in China from 2005 to 2019 has been rising generally,but they present obvious characteristics of dimensional and spatial differentiation.(2)In general,economic development has an inhibiting effect on the improvement of urban livability,but this logical effect shows obvious heterogeneity in different time periods and diverse city scales.This inhibitory effect is more significant for the cities before entering the new normal phase of economy,and large-scale municipalities and economically-developed provincial capitals(namely Class-A cities).(3)There are significant threshold effects in the impact of economic development on urban livability,where the threshold variables are income level and economic development.With the increase of city dwellers’income,this effect presents an inverted N-shaped nonlinear feature.When the development of economy makes the average wage of employees between 60,000and 80,000 yuan,economic development can significantly improve urban livability.Also,there is a significant single threshold inhibitory effect when economic development is taken as a threshold variable.However,its negative impact shows a law of diminishing marginal efficiency.In addition,a similar threshold effect is found in smaller-scale Class-B cities.The findings of this research can provide some insights for urban planners and policymakers in both China and vast developing countries to understand better the relationship between economic development and urban livability.Finally,according to the research findings,we proposed the corresponding policy enlightenment from both“macro guidance”and“micro action”.展开更多
As power systems experience increased wind penetration,an effective analysis and assessment of the influence of wind energy on power system transient stability is required.This paper presents a novel center of inertia...As power systems experience increased wind penetration,an effective analysis and assessment of the influence of wind energy on power system transient stability is required.This paper presents a novel center of inertia(COI)approach to understand how integrated doubly fed induction generators(DFIGs)affect the transient dynamics of a power system.Under the COI coordinate,the influence of integrated DFIGs is separated into the COI related and individual synchronous generator related parts.Key factors that affect the COI’s dynamic motion as well as the rotor dynamics of each individual synchronous generator with respect to the DFIG integration are investigated.To further validate the analysis,comparative simulations of three different scenarios with varying DFIG capacities,access locations,and the replacement of synchronous generators are conducted.The results show that the dynamics of the COI and the individual generators are affected by the integrated DFIGs via different mechanisms,and are sensitive to different variables in the DFIG’s integration condition.展开更多
Over the past 20 years,China has experienced multiple economic transitions characterized by marketization,globalization,decentralization,and urbanization;as a result,urban land development intensity(ULDI)has become a ...Over the past 20 years,China has experienced multiple economic transitions characterized by marketization,globalization,decentralization,and urbanization;as a result,urban land development intensity(ULDI)has become a significant issue for sustainable development.As China’s largest globalized urban area,the rapid socio-economic development of the Yangtze River Delta has created a huge demand for urban land.We apply a theoretical framework for a four-dimensional analysis tool to understand the dynamic evolution of the ULDI in the context of economic transition.It reveals that marketization,globalization,decentralization,and urbanization affect the ULDI in the economic transition of Yangtze River Delta.Marketization,especially the continuous improvement of land marketization,optimizes the spatial allocation of land resources and encourages urban land users to improve ULDI.Globalization promotes the rapid growth of economy and population through an increase in foreign direct investment.In the process of decentralization,local governments rely on developing a mode of land finance,resulting in a disordered urban space and low ULDI.Population growth and agglomeration during urbanization stimulates residents’consumption capacity and promotes economic growth,thus creating a greater demand for urban land.However,a low level of development and utilization restricts the improvement of development intensity.Economic development can improve the level of land-intensive use by promoting the adjustment,optimization,and upgrade of urban industrial structures.展开更多
Background:The carbon pools of forest soils play a vital role in global carbon sequestration and emissions.Forest management can regulate the sequestration and output of forest soil carbon pools to a certain extent;ho...Background:The carbon pools of forest soils play a vital role in global carbon sequestration and emissions.Forest management can regulate the sequestration and output of forest soil carbon pools to a certain extent;however,the kinetics of the effects of forest density on soil carbon pools require further investigation.Methods:We established sample plots with stand density gradients in three different aged Larix principis-rupprechtii plantations and quantified the soil respiration,soil organic carbon(SOC),soil dissolved organic carbon(DOC),microbial biomass carbon(MBC),light fraction organic carbon(LFOC),and readily oxidized carbon(ROC).Results and conclusions:During the growth and development of plantations,stand density is an essential factor that impacts soil respiration and its associated elements.Moderate density was observed to promote both the soil and heterotrophic respiration rates and the sequestration of MBC and LFOC,whereas it inhibited the sequestration of ROC.The soil,heterotrophic,and autotrophic respiration rates of older forest stands were relatively rapid,whereas the contents of SOC,MBC,LFOC,DOC,and ROC were higher and more sensitive to changes in stand density.The MBC,LFOC,and ROC in soil labile organic carbon were closely related to both the soil and heterotrophic respiration,but not the SOC.Among them,the LFOC and MBC played the roles of“warehouse”and“tool”and were significantly correlated with soil and heterotrophic respiration.The ROC,as a“raw material”,exhibited a significantly negative correlation with the soil and heterotrophic respiration.When the soil and heterotrophic respiration rates were rapid,the ROC content in the soil maintained the low level of a“dynamically stabilized”state.The stand density regulated heterotrophic respiration by affecting the soil labile organic carbon,which provided an essential path for the stand density to regulate soil respiration.展开更多
In a variable nozzle turbine(VNT),the nozzle vane and rotor clearance can generate complicated tip leakage flow,which produces a large flow loss and results in a noticeable reduction in the VNT performance.Therefore,i...In a variable nozzle turbine(VNT),the nozzle vane and rotor clearance can generate complicated tip leakage flow,which produces a large flow loss and results in a noticeable reduction in the VNT performance.Therefore,it is necessary to study the influence of the nozzle vane and rotor clearance on the VNT performance to reveal the underlying mechanisms.In this study,the variation of VNT performance resulting from the nozzle vane and rotor clearance was studied numerically using the commercial CFD code.The numerical results were in good agreement with the experimental data.VNT performance under three varied clearance conditions under different clearance sizes,rotating speeds,and expansion ratios was analyzed.Clearance conditions included the individual effect of nozzle vane clearance,the individual effect of rotor clearance,and the combined effect of nozzle vane and rotor clearance.The results showed that the rotor clearance(clearance size equal to 0.4 mm)resulted in a certain reduction in thermal efficiency(–3.98%)and torque(–4.48%).Meanwhile,the nozzle vane hub and shroud clearance also affected the thermal efficiency(–3.66%and–13.37%,respectively)and torque(12.54%and–0.05%,respectively).Compared with the rotor clearance,the nozzle vane clearance dominated the variation in the VNT performance,and the values of the mass flow ratio,thermal efficiency,and torque increased by 12.15%,5.43%,and 8.01%,respectively(The clearance on both sides of the vane was equal to 0.2 mm.).Under the combined effect of the nozzle vane and rotor clearance,the deviation of the thermal efficiency and mass flow ratio was smaller than the sum of the values of their individual effects;when the clearance on both sides of the vane was equal to 0.2 mm and the rotor clearance was equal to 0.6 mm,the value was reduced by 2.77%and 1.71%,respectively.This study also explains the influence mechanisms of clearance at both ends of the nozzle vane and the vane/rotor clearance interaction on the VNT performance in detail.展开更多
Following climate change,changes in precipitation patterns and food security are major challenges faced by humans.However,research on how these changes in precipitation pattern impacts food supply is limited.This stud...Following climate change,changes in precipitation patterns and food security are major challenges faced by humans.However,research on how these changes in precipitation pattern impacts food supply is limited.This study aims to elucidate this impact and response mechanisms using precipitation data of a climate change-sensitive confluence zone of the southwest and southeast monsoons in Yunnan Province from 1988 to 2018.The results revealed that the precipitation pattern could be divided into three periods:abundant precipitation(Stage I,from 1988 to 2004),decreased precipitation(Stage II,from 2005 to 2015),and drought recovery(Stage III,from 2016 to 2018).Following the transition from Stage I to Stage II and from Stage II to Stage III,the area of precipitation changed significantly,accounting for 15.07%,13.87%,and 16.53%of Yunnan’s total area,for Stages I,II,and III,respectively.At the provincial level,a significant positive correlation was observed between precipitation and food production(r=0.535,P<0.01),and the correlation coefficient between precipitation and grain yield was higher than that between precipitation and meat and milk production.Based on a precipitation–grain yield transect and breakpoint detection method,key precipitation thresholds affecting grain yield were estimated as 700 and 1500 mm,respectively;when precipitation was<700,700–1500,and≥1500 mm,the correlation coefficients between precipitation and grain yield were 0.448(P<0.01),0.370(P<0.01),and–0.229(P>0.05),respectively.Based on the precipitation thresholds,Yunnan Province can be divided into precipitation surplus,precipitation equilibrium,and precipitation deficit regions,corresponding countermeasures to stabilize grain yield were proposed for each of these regions.The threshold effect of precipitation on grain yield is controlled by molecular-level water–crop mechanisms,in which reactive oxygen species,a by-product of plant aerobic metabolism,plays a key regulatory role.展开更多
基金the State Key Laboratory of Coal Resources and Safe Mining,China University of Mining and Technology(No.SKLCRSM22KF011)the National Natural Science Foundation of China(Nos.52130411,52104191,51974120,and 51904103)+1 种基金the Natural Science Foundation of Hunan Province(No.2021JJ40204)the Science and Technology Innovation Program of Hunan Province(No.2020RC3047).
文摘The study of pressure stimulated current(PSC)changes of rocks is significant to monitor dynamic disasters in mines and rock masses.The existing studies focus on change laws and mechanism of currents generated under the loading of rocks.An electrical and mechanics test system was established in this paper to explore the impacts of loading rates on PSCs.The results indicated that PSC curves of different rocks had different change laws under low/high loading rates.When the loading rate was relatively low,PSC curves firstly changed gently and then increased exponentially.Under high loading rates,PSC curves experienced the rapid increase stage,gentle increase stage and sudden change stage.The compressive strength could greatly affect the peak PSC in case of rock failure.The loading rate was a key factor in average PSC.Under low loading rates,the variations of PSCs conformed to the damage charge model of fracture mechanics,while they did not at the fracture moment.Under high loading rates,the PSCs at low stress didn’t fit the model due to the stress impact effects.The experimental results could provide theoretical basis for the influence of loading rates on PSCs.
文摘With the economic development and multicultural exchange of ethnic villages,more and more ethnic villages have embarked on the road of tourism to become rich,but also brought the problem of ecological pollution.Few existing literatures discuss how to alleviate the ecological pollution in ethnic villages from the perspective of tourists’environmentally responsible behavior.In the context of ethnic villages,from the perspective of integration and the attitude-context-behavior theory,this paper constructs an EV-ABC-TERB model with four variables,namely environmental attitude,local atmosphere,emotional experience and tourists’environmentally responsible behavior,to explore the characteristics,influencing factors and influencing mechanism of tourists’environmental responsibility behavior in ethnic villages.Taking Xijiang Hmong Village as the research case,questionnaire survey method and structural equation model method were used.The results show that environmental attitude positively affects emotional experience and tourists’environmentally responsible behavior.Local atmosphere positively influences tourists’environmentally responsible behavior.Emotional experience negatively affects tourists’environmentally responsible behavior and plays an intermediary role in the way that environmental attitudes affect tourists’environmentally responsible behavior.The influence of environmental attitude on emotional experience is negatively regulated by local atmosphere.Finally,based on the analysis conclusion,it provides new ideas and inspiration for the sustainable development of the ethnic village tourism.
基金Supported by Teaching and Research Project of Tibet Autonomous Region Education Department(XZJYKTJX18,XZJKY19417)Quality Engineering Project(5333219008)。
文摘On the basis of combing domestic and foreign related literature and research practice,the influence mechanism of the construction of new liberal arts was analyzed,and the fundamental tasks of the construction of new liberal arts in Tibet were summarized.Based on 173 field questionnaires in Tibet,factor analysis was used to conduct empirical analysis.It is found that the cumulative contribution of the first,second,third and fourth common factor was 24.921%,21.742%,17.331%,and 14.206%,respectively.Professional orientation,the reform of talent training mode,teacher ability,quality and level of the teaching team,curriculum system reform,teaching content reform,education training service,and other evaluation indicators are the key points of the construction of new liberal arts.The research conclusion is that the construction of new liberal arts needs to highlight the"three positions";it is needed to plan and promote various resources to focus on the ability and level of professional teachers’social services;the managers and professional teachers should be the leaders and participants of the innovation of the talent training model respectively.Finally,relevant policy recommendations were put forward.
基金Supported by Special Item of Public Welfare Industry (Meteorology)Science Research (GYHY201106006)Special Item of Forecaster of China Meteorological Administration (CMATG2007Y08)Key Topics of Shandong Meteorological Bureau (2010sdqxz10)
文摘[Objective] The research aimed to study the possible mechanism of terrain effect on cold-flow snowstorm.[Method] By using the meso-scale numerical model(WRF),a cold-flow snowstorm weather process in Shandong Peninsula was carried out numerical simulation and terrain sensitivity contrast test.The possible reason of terrain effect on falling zone and strength of snowstorm was deeply analyzed from water vapor,thermodynamic field and so on.[Result] The mountain terrain in Shandong Peninsula had great influences on falling zone and strength of cold-flow snowstorm.The strength of snowstorm obviously increased,and the snowfall center obviously moved northward.The main reason was that terrain caused the low-level wind field convergence and vertical movement in the troposphere strengthened.Then,the spatial distribution of water vapor and snow water content in the cold-flow snowstorm process obviously changed.So,the whole snowstorm process was affected.[Conclusion] The mountain terrain in Shandong Peninsula was the important element which needed to be focused on considering in the forecast analysis of cold-flow snowstorm weather process.
基金Under the auspices of Strategic Priority Research Program of the Chinese Academy of Sciences (No. XDA28100405,XDA28020403)National Natural Science Foundation of China (No. 41771179, 42071275)+1 种基金Talents Training Project Supported by the Central Government for the Reform and Development of Local UniversitiesYoung Scientist Group Project of Northeast Institute of Geography and Agroecology,Chinese Academy of Sciences (No. 2022QNXZ02)
文摘The effective use of land in Northeast China is of great significance for ensuring national food security and regional rural revitalization.In this study,based on the survey data collected from Jilin Province,Northeast China,we analyzed the vacancy rates of rural homesteads in suburban,outer suburban,and remote villages,as well as the withdrawal intention of rural-settled farmers,urbansettled farmers,and farmers with urban and rural dual residency from vacant homesteads.From the perspective of farmers’perceptions,this study constructed a theoretical framework of the influence mechanism of their withdrawal intention and analyzed such mechanism by constructing a structural equation model.The results indicated that:1)rural homestead vacancy rates increased with distance from the village to the city.2)rural-settled farmers showed a low withdrawal intention for vacant rural homesteads,followed by urban and rural dual-residence farmers,and urban-settled farmers showed the highest withdrawal intention.3)the relative importance of the factors influencing withdrawal intention is in the following order:policy awareness>interest perception>living environment perception>family characteristics.Finally,this study discussed the reformation of the homestead system and rural homestead transition in Northeast China,which can provide policy support to increase the potential of cultivated land and promote sustainable rural development and urban-rural coordination.
基金Supported by the Second Tibetan Plateau Scientific Expedition and Research Program(No.2019 QZKK 0805)the National Natural Science Foundation of China(No.U 21 A 2018)the Foundation of Department of Qinghai Science&Technology(No.2020-ZJ-T 06)。
文摘The Qaidam Basin(QB)is a concentrated distribution area and chemical industrial bases of salt lakes in China.Lakes in the QB have been expanding during the past 20 years.Rapid lake expansion resulted in some considerable scientific issues on the protection of salt lake resources and infrastructure,and monitoring of hydrological processes at the lake-basin scale.Although the spatial-temporal trends of lake changes on the Qinghai-Tibet Plateau(QTP)have been well documented,the underlying influencing mechanism and hydrogeological implications of rapid lake changes in the QB are not well understood.Three lakes in the northern QB were selected to investigate lake water level fluctuations on different time scales based on extensive in-situ monitoring and satellite observations.The influencing mechanism and hydrogeological implications of rapid changes of terminal lakes were discussed in combination with the reported increasing precipitation rate and mass balance of glaciers in the northern QTP.Results reveal the following:(1)the fluctuation pattern of Sugan Lake was asynchronous and out of phase with that of Xiao Qaidam and Toson lakes during the monitoring period;(2)Sugan Lake water rose gradually,and the rise interval was from late April to early July.In contrast,Xiao Qaidam and Toson lakes took on a rapid and steep rise,and the rise intervalwas from late July to September;(3)the influencing mechanisms for rapid lake fluctuations are controlled by different factors:glacier and snow melting with increasing temperature for Sugan Lake and increasing precipitation for Xiao Qaidam and Toson lakes;(4)in accordance with different intervals and influencing mechanisms of rapid lake expansions in the QB,hydrological risk precaution of lakes and corresponding river catchments was conducted in different parts of the basin.This study provided an important scientific basis for assessing the hydrological process and hydrological risk precaution,and protection of salt lake resources along with rapid lake expansions in the arid area.
基金the financial support by the National Natural Science Foundation of China(NSFC)(Grant Nos.52178319 and 52108307)the Natural Science Foundation of Fujian Province,China(Grant No.2022J05127).
文摘Calcium salt is an important contributing factor for calcium-based biomineralization.To study the effect of calcium salt on soil biomineralization using crude soybean urease,the calcium salts,including the calcium chloride (CaCl2 ),calcium acetate ((CH3 COO)2 Ca) and calcium nitrate (Ca(NO3 )2 ),were used to prepare the biotreatment solution to carry out the biomineralization tests in this paper.Two series of biomineralization tests in solution and sand column,respectively,were conducted.Scanning electron microscopy (SEM) and X-ray diffraction (XRD) were performed to determine the microscopic characteristics of the precipitated calcium carbonate (CaCO3 ) crystals.The experimental results indicate that the biomineralization effect is the best for the CaCl2 case,followed by (CH3 COO)2 Ca,and worst for Ca(NO3 )2 under the test conditions of this study (i.e.1 mol/L of calcium salt-urea).The mechanism for the effect of the calcium salt on the biomineralization of crude soybean urease mainly involves: (1) inhibition of urease activity,and (2) influence on the crystal size and morphology of CaCO3 .Besides Ca2+ ,the anions in solution can inhibit the activity of crude soybean urease,and NO3 − has a stronger inhibitory effect on the urease activity compared with both CH3 COO− and Cl− .The co-inhibition of Ca2+ and NO3 − on the activity of urease is the key reason for the worst biomineralization of the Ca(NO3 )2 case in this study.The difference in biomineralization between the CaCl2 and (CH3 COO)2 Ca cases is strongly correlated with the crystal morphology of the precipitated CaCO3 .
基金financial support from the National Natural Science Foundation of China(No.51904324,51974348,U19B6003)
文摘In recent years,supercritical CO_(2)flooding has become an effective method for developing lowpermeability reservoirs.In supercritical CO_(2)flooding different factors influence the mechanism of its displacement process for oil recovery.Asynchronous injection-production modes can use supercritical CO_(2)to enhance oil recovery but may also worsen the injection capacity.Cores with high permeability have higher oil recovery rates and better injection capacity,however,gas channeling occurs.Supercritical CO_(2)flooding has a higher oil recovery at high pressure levels,which delays the occurrence of gas channeling.Conversely,gas injection has lower displacement efficiency but better injection capacity at the high water cut stage.This study analyzes the displacement characteristics of supercritical CO_(2)flooding with a series of experiments under different injection and production parameters.Experimental results show that the gas breakthrough stage has the fastest oil production and the supercritical CO_(2)injection capacity variation tendency is closely related to the gas-oil ratio.Further experiments show that higher injection rates represent significant ultimate oil recovery and injection index,providing a good reference for developing low-permeability reservoirs.
文摘Amorphous and nanostructural Fe-B alloys made by mechanical alloying of elemental Fe and amorphous B powders have been studied using X-ray diffraction, differential scanning calorimetry and Mossbauer spectroscopy. It has been shown that the milling conditions have a strong effect on the alloying. The single phase amorphous alloy, which is limited at nominal composition of Fe60B40, has been produced only by milling in Ar atmosphere and in other composition range the mixture of nanostructure Fe-like phase and Fe2B compound with a little amorphous phase are obtained. While by milling in air atmosphere the introduction of oxygen in air may suppress the formation of amorphous phase, thus the compounds Fe2B may be synthesized with no trace of amorphous phase. The crystallization temperatures of amorphous phase in the resultant products are higher than those of a single amorphous alloy Fe60B40, and hardly independent of the milling conditions and the composition. In addition, it is revealed that detectable B content in the final products is lower than the nominal composition of all the initial samples, which indicates that some B atoms may be located in the disordered interfacial regions of the nanostructural alloyed mixtures.
基金financially supported by the National Natural Science Foundation of China (NO.52174095)。
文摘The use of aeolian sand(AS)as an aggregate to prepare coal mine cemented filling materials can resolve the problems of gangue shortage and excessive AS deposits.Owing to the lack of research on the mechanism of cemented AS backfill(CASB),the response surface method(RSM)was adopted in this study to analyze the influence of ordinary Portland cement(PO)content(x_(1)),fly ash(FA)-AS(FA-AS)ratio(x_(2)),and concentration(x_(3))on the mechanical and microscopic properties of the CASB.The hydration characteristics and internal pore structure of the backfill were assessed through thermogravimetric/derivative thermogravimetric analysis,mercury intrusion porosimetry,and scanning electron microscopy.The RSM results show that the influence of each factor and interaction term on the response values is extremely significant(except x_(1)x_(3),which had no obvious effect on the 28 d strength).The uniaxial compressive strength(UCS)increased with the PO content,FA-AS ratio,and concentration.The interaction effects of x_(1)x_(2),x_(1)x_(3),and x_(2)x_(3) on the UCS at 3,7,and 28 d were analyzed.In terms of the influence of interaction items,an improvement in one factor promoted the strengthening effect of another factor.The enhancement mechanism of the curing time,PO content,and FA-AS ratio on the backfill was reflected in the increase in hydration products and pore structure optimization.By contrast,the enhancement mechanism of the concentration was mainly the pore structure optimization.The UCS was positively correlated with weight loss and micropore content but negatively correlated with the total porosity.The R^(2) value of the fitting function of the strength and weight loss,micropore content,and total porosity exceeded 0.9,which improved the characterization of the enhancement mechanism of the UCS based on the thermogravimetric analysis and pore structure.This work obtained that the influence rules and mechanisms of the PO,FA-AS,concentration,and interaction terms on the mechanical properties of the CASB provided a certain theoretical and engineering guidance for CASB filling.
基金the“High-quality Development,Credit Assets,and Digital Economy”project(KY2023E0122)funded by the Beijing Academy of Social Sciencesthe Sichuan Philosophy and Social Science Planning project(SC21B0310)+2 种基金a technological innovation capacity building program(KTYTD202233)a college students’innovation and entrepreneurship program(202310621238,202310621243)supported by Chengdu University of Information Technology.
文摘Digital village construction opens a new vista for fulfilling consumption capabilities and optimizing consumption patterns in rural areas.For this research,we used the microdata on rural households from the 2019 China Household Finance Survey(CHFS)to conduct an empirical examination of the impact of digital village construction on the upgrading of rural household consumption and its possible influence mechanisms in the endogenous switching regression(ESR)model.Our research findings can be summarized in three points.First,digital village construction has significantly contributed positive contributions to the improvements and upgrading of rural household consumption.Second,digital village construction can help upgrade rural household consumption by increasing their participation in online shopping and expanding online shopping channels.Third,digital village construction means different things to rural households at different levels of risk exposure,with its facilitation to consumption upgrades in proportion to income risks facing rural households.Our research findings,which came from an extensive,in-depth exploration of the factors influencing rural household consumption,are of practical significance and policy value to the stimulating and fulfilling of consumption potentials among rural households.
文摘In recent years, India’s diplomatic activities in the Asia-Pacific region are very active. From major power diplomacy, bilateral diplomacy to multilateral diplomacy, India has been quite impressive. Especially its multilateral diplomacy has become widely accepted. This paper attempts to understand India’s multilateral diplomacy in the Asia-Pacific region, with emphasis on Indian strategic considerations, underlying motivation and strategic influence of its participation in the Asia-Pacific multilateral mechanisms.
基金We sincerely thank the National Natural Science Foundation of China(No.51878092 and No.52070029)for their support.
文摘Extracellular polymeric substances(EPS)in activated sludge from wastewater treatment plants(WWTPs)could affect interactions between nanoparticles and alter their migration behavior.The influence mechanisms of silver nanoparticles(Ag NPs)and silver sulfide nanoparticles(Ag_(2)S NPs)aggregated by active EPS sludge were studied in monovalent or divalent cation solutions.The aggregation behaviors of the NPs without EPS followed the Derjaguin-Landau-Verwey-Overbeek(DLVO)theory.The counterions aggravated the aggregation of both NPs,and the divalent cation had a strong neutralizing effect due to the decrease in electrostatic repulsive force.Through extended DLVO(EDLVO)model analysis,in NaNO3 and low-concentration Ca(NO_(3))_(2)(<10 mmol/L)solutions,EPS could alleviate the aggregation behaviors of Cit-Ag NPs and Ag_(2)S NPs due to the enhancement of steric repulsive forces.At high concentrations of Ca(NO_(3))_(2)(10‒100 mmol/L),exopolysaccharide macromolecules could promote the aggregation of Cit-Ag NPs and Ag_(2)S NPs by interparticle bridging.As the final transformation form of Ag NPs in water environments,Ag_(2)S NPs had better stability,possibly due to their small van der Waals forces and their strong steric repulsive forces.It is essential to elucidate the surface mechanisms between EPS and NPs to understand the different fates of metal-based and metal-sulfide NPs in WWTP systems.
基金Fundamental Research Funds for the Central Universities,No.19lgzd09Guangdong Special Support ProgramPearl River S&T Nova Program of Guangzhou,No.201806010187。
文摘Ecosystem services are the media and channels through which ecological elements, structures, functions, and products benefit human society. Regulating the utilization intensity and protection methods of society on the ecosystem according to the ecosystem service value(ESV) and its influencing mechanism is of great significance for achieving the sustainable development goals. This paper takes the Guangdong-Hong Kong-Macao Greater Bay Area(GBA) as the research object and describes the spatiotemporal evolution characteristics of ESV in the GBA from 2000 to 2015. Panel quantile regression is also implemented to increase the understanding of the influencing mechanism of ESV. The main results are as follows:(1) From 2000 to 2015, the total ESV declined with a decreasing rate. The areas of decline were mainly distributed in the central part of the GBA and areas along the Pearl River Estuary.(2) Elasticity index, indicating response of ESV to land use change, reached its peak(1.08). The spatial distribution of elasticity index showed that land use changes brought about more intense ESV variations at the junction of cities.(3) In areas with different ESV levels, the influencing factors have different effects. Land use integrity can only promote ecosystem service capabilities in low-ESV areas. The positive effect of temperature on ecosystem service capacity increases with the increase of ESV, which reflects the self-reinforcement of the ecosystem. Moreover, the negative effect of economic density on ecosystem service capacity decreases with the increase of ESV, which reflects the self-protection of the ecosystem. The combination of such self-reinforcement and self-protection will lead to an ESV gap between the high-and low-ESV areas, and induce the “natural Matthew effect.”
基金National Natural Science Foundation of China,No.41901205Natural Science Foundation of Jiangsu Province,No.BK20190482。
文摘Under the background that economy and urbanization of China are gradually entering the stage of high-quality development,clarifying the influence of economic development on urban livability is of significant academic and practical value.In this paper,regarded as one“factor”,livability was introduced into the research framework of production function,and a theoretical model of the impact of economic development on urban livability was established.Based on the panel data of 40 cities in China from 2005 to 2019,the System GMM,panel threshold model and other methods were further adopted to carry out an empirical analysis.The results show that:(1)The livability level of large and medium-sized cities in China from 2005 to 2019 has been rising generally,but they present obvious characteristics of dimensional and spatial differentiation.(2)In general,economic development has an inhibiting effect on the improvement of urban livability,but this logical effect shows obvious heterogeneity in different time periods and diverse city scales.This inhibitory effect is more significant for the cities before entering the new normal phase of economy,and large-scale municipalities and economically-developed provincial capitals(namely Class-A cities).(3)There are significant threshold effects in the impact of economic development on urban livability,where the threshold variables are income level and economic development.With the increase of city dwellers’income,this effect presents an inverted N-shaped nonlinear feature.When the development of economy makes the average wage of employees between 60,000and 80,000 yuan,economic development can significantly improve urban livability.Also,there is a significant single threshold inhibitory effect when economic development is taken as a threshold variable.However,its negative impact shows a law of diminishing marginal efficiency.In addition,a similar threshold effect is found in smaller-scale Class-B cities.The findings of this research can provide some insights for urban planners and policymakers in both China and vast developing countries to understand better the relationship between economic development and urban livability.Finally,according to the research findings,we proposed the corresponding policy enlightenment from both“macro guidance”and“micro action”.
基金supported in part by the Major Program of the National Natural Science Foundation of China under Grant 51190103the National High Technology Research and Development Program of China under Grant 2012AA050208.
文摘As power systems experience increased wind penetration,an effective analysis and assessment of the influence of wind energy on power system transient stability is required.This paper presents a novel center of inertia(COI)approach to understand how integrated doubly fed induction generators(DFIGs)affect the transient dynamics of a power system.Under the COI coordinate,the influence of integrated DFIGs is separated into the COI related and individual synchronous generator related parts.Key factors that affect the COI’s dynamic motion as well as the rotor dynamics of each individual synchronous generator with respect to the DFIG integration are investigated.To further validate the analysis,comparative simulations of three different scenarios with varying DFIG capacities,access locations,and the replacement of synchronous generators are conducted.The results show that the dynamics of the COI and the individual generators are affected by the integrated DFIGs via different mechanisms,and are sensitive to different variables in the DFIG’s integration condition.
基金Natural Science Foundation of Jiangsu Province,No.BK20200109Open Fund of Key Laboratory of Coastal Zone Exploitation and Protection+2 种基金Ministry of Natural Resources,No.2021CZEPK05National Natural Science Foundation of China,No.42101282The Project of Philosophy and Social Science Research in Colleges and Universities of Jiangsu Province,No.2022SJYB0287。
文摘Over the past 20 years,China has experienced multiple economic transitions characterized by marketization,globalization,decentralization,and urbanization;as a result,urban land development intensity(ULDI)has become a significant issue for sustainable development.As China’s largest globalized urban area,the rapid socio-economic development of the Yangtze River Delta has created a huge demand for urban land.We apply a theoretical framework for a four-dimensional analysis tool to understand the dynamic evolution of the ULDI in the context of economic transition.It reveals that marketization,globalization,decentralization,and urbanization affect the ULDI in the economic transition of Yangtze River Delta.Marketization,especially the continuous improvement of land marketization,optimizes the spatial allocation of land resources and encourages urban land users to improve ULDI.Globalization promotes the rapid growth of economy and population through an increase in foreign direct investment.In the process of decentralization,local governments rely on developing a mode of land finance,resulting in a disordered urban space and low ULDI.Population growth and agglomeration during urbanization stimulates residents’consumption capacity and promotes economic growth,thus creating a greater demand for urban land.However,a low level of development and utilization restricts the improvement of development intensity.Economic development can improve the level of land-intensive use by promoting the adjustment,optimization,and upgrade of urban industrial structures.
基金funded by the National Key Research and Development Program of China(2016YFD0600205).
文摘Background:The carbon pools of forest soils play a vital role in global carbon sequestration and emissions.Forest management can regulate the sequestration and output of forest soil carbon pools to a certain extent;however,the kinetics of the effects of forest density on soil carbon pools require further investigation.Methods:We established sample plots with stand density gradients in three different aged Larix principis-rupprechtii plantations and quantified the soil respiration,soil organic carbon(SOC),soil dissolved organic carbon(DOC),microbial biomass carbon(MBC),light fraction organic carbon(LFOC),and readily oxidized carbon(ROC).Results and conclusions:During the growth and development of plantations,stand density is an essential factor that impacts soil respiration and its associated elements.Moderate density was observed to promote both the soil and heterotrophic respiration rates and the sequestration of MBC and LFOC,whereas it inhibited the sequestration of ROC.The soil,heterotrophic,and autotrophic respiration rates of older forest stands were relatively rapid,whereas the contents of SOC,MBC,LFOC,DOC,and ROC were higher and more sensitive to changes in stand density.The MBC,LFOC,and ROC in soil labile organic carbon were closely related to both the soil and heterotrophic respiration,but not the SOC.Among them,the LFOC and MBC played the roles of“warehouse”and“tool”and were significantly correlated with soil and heterotrophic respiration.The ROC,as a“raw material”,exhibited a significantly negative correlation with the soil and heterotrophic respiration.When the soil and heterotrophic respiration rates were rapid,the ROC content in the soil maintained the low level of a“dynamically stabilized”state.The stand density regulated heterotrophic respiration by affecting the soil labile organic carbon,which provided an essential path for the stand density to regulate soil respiration.
文摘In a variable nozzle turbine(VNT),the nozzle vane and rotor clearance can generate complicated tip leakage flow,which produces a large flow loss and results in a noticeable reduction in the VNT performance.Therefore,it is necessary to study the influence of the nozzle vane and rotor clearance on the VNT performance to reveal the underlying mechanisms.In this study,the variation of VNT performance resulting from the nozzle vane and rotor clearance was studied numerically using the commercial CFD code.The numerical results were in good agreement with the experimental data.VNT performance under three varied clearance conditions under different clearance sizes,rotating speeds,and expansion ratios was analyzed.Clearance conditions included the individual effect of nozzle vane clearance,the individual effect of rotor clearance,and the combined effect of nozzle vane and rotor clearance.The results showed that the rotor clearance(clearance size equal to 0.4 mm)resulted in a certain reduction in thermal efficiency(–3.98%)and torque(–4.48%).Meanwhile,the nozzle vane hub and shroud clearance also affected the thermal efficiency(–3.66%and–13.37%,respectively)and torque(12.54%and–0.05%,respectively).Compared with the rotor clearance,the nozzle vane clearance dominated the variation in the VNT performance,and the values of the mass flow ratio,thermal efficiency,and torque increased by 12.15%,5.43%,and 8.01%,respectively(The clearance on both sides of the vane was equal to 0.2 mm.).Under the combined effect of the nozzle vane and rotor clearance,the deviation of the thermal efficiency and mass flow ratio was smaller than the sum of the values of their individual effects;when the clearance on both sides of the vane was equal to 0.2 mm and the rotor clearance was equal to 0.6 mm,the value was reduced by 2.77%and 1.71%,respectively.This study also explains the influence mechanisms of clearance at both ends of the nozzle vane and the vane/rotor clearance interaction on the VNT performance in detail.
基金National Key Research and Development Program of China,No.2018YFE0184300National Natural Science Foundation of China,No.41761115,No.41271203Key Research Projects of Graduate Students in Yunnan Normal University,No.ysdyjs2019166。
文摘Following climate change,changes in precipitation patterns and food security are major challenges faced by humans.However,research on how these changes in precipitation pattern impacts food supply is limited.This study aims to elucidate this impact and response mechanisms using precipitation data of a climate change-sensitive confluence zone of the southwest and southeast monsoons in Yunnan Province from 1988 to 2018.The results revealed that the precipitation pattern could be divided into three periods:abundant precipitation(Stage I,from 1988 to 2004),decreased precipitation(Stage II,from 2005 to 2015),and drought recovery(Stage III,from 2016 to 2018).Following the transition from Stage I to Stage II and from Stage II to Stage III,the area of precipitation changed significantly,accounting for 15.07%,13.87%,and 16.53%of Yunnan’s total area,for Stages I,II,and III,respectively.At the provincial level,a significant positive correlation was observed between precipitation and food production(r=0.535,P<0.01),and the correlation coefficient between precipitation and grain yield was higher than that between precipitation and meat and milk production.Based on a precipitation–grain yield transect and breakpoint detection method,key precipitation thresholds affecting grain yield were estimated as 700 and 1500 mm,respectively;when precipitation was<700,700–1500,and≥1500 mm,the correlation coefficients between precipitation and grain yield were 0.448(P<0.01),0.370(P<0.01),and–0.229(P>0.05),respectively.Based on the precipitation thresholds,Yunnan Province can be divided into precipitation surplus,precipitation equilibrium,and precipitation deficit regions,corresponding countermeasures to stabilize grain yield were proposed for each of these regions.The threshold effect of precipitation on grain yield is controlled by molecular-level water–crop mechanisms,in which reactive oxygen species,a by-product of plant aerobic metabolism,plays a key regulatory role.
