Understanding how the transpiration of this vegetation type responds to environmental stress is important for determining the wa-ter-balance dynamics of the riparian ecosystem threatened by groundwater depletion.Trans...Understanding how the transpiration of this vegetation type responds to environmental stress is important for determining the wa-ter-balance dynamics of the riparian ecosystem threatened by groundwater depletion.Transpiration and sap flow were measured using the heat-pulse technique.The results were then projected up to the stand level to investigate the stand’s water-use in relation to climate forcing in the desert riparian forest in an extreme arid region.This study took place from April through October 2003 and from May through October 2004.The experimental site was selected in the Populus euphratica Forest Reserve(101o10'E,41o59'N)in Ejina county,in the lower Heihe River basin,China.The sapwood area was used as a scalar to extrapolate the stand-water consumption from the whole trees’water consumption measured by the heat-pulse velocity recorder(HPVR).Scale transferring from a series of individual trees to a stand was done according to the existing natural variations between trees under given environmental conditions.The application of the biometric parameters available from individual tree and stand levels was proved suitable for this purpose.A significant correlation between the sapwood area and tree diameter at breast height(DBH)was found.The prediction model is well fitted by the power model.On the basis of the prediction model,the sapwood area can be cal-culated by DBH.The sap-flow density can then be used to extrapolate the stand-water use by means of a series of mathematical models.展开更多
The purpose of this paper is to study the energy efficiency of a local living space exposed to solar radiation in the subtropical climate of Casablanca. The study was mainly focused on the contribution of a phase chan...The purpose of this paper is to study the energy efficiency of a local living space exposed to solar radiation in the subtropical climate of Casablanca. The study was mainly focused on the contribution of a phase change material (PCM), inserted into a 7-cm thick air layer of a double brick wall, in two different locations. We note that the experimental study was conducted using two real-scale test cavities, located in the Faculty of Science Ain Chock-Casablanca. Two PCM mounting methods were used for the south and west walls, in order to test its energy efficiency as a storage and retrieval means of the solar flux coming from the outside. In the case of the southern wall, the PCM is put directly on the internal side of the outside part of the double wall (Case 1). For the west wall, the PCM is placed 1.2 cm away from the internal side of the outer part of the double wall (Case 2). The first result shows that the PCM placed to the wall allows storing the solar heat during the day and releasing it to the outside of the building at night. While in the second case, the PCM keeps the heat stored day and night.展开更多
【目的】探究农户分化对农业生产性投资的直接影响机制和间接影响机制,为解决中国当前农业生产性投资不足问题、制定农地流转等相关政策提供理论借鉴和参考。【方法】采用2012—2020年中国家庭追踪调查(China family panel studies,CFPS...【目的】探究农户分化对农业生产性投资的直接影响机制和间接影响机制,为解决中国当前农业生产性投资不足问题、制定农地流转等相关政策提供理论借鉴和参考。【方法】采用2012—2020年中国家庭追踪调查(China family panel studies,CFPS)数据,通过建立OLS模型、面板固定效应模型、中介效应模型进行计量分析,并进一步做出稳健性、内生性检验。【结果】农户分化对农业生产性投资有显著负向影响;农地流转在农户分化与农业生产投资间发挥部分中介作用,农户分化通过影响农地流转进而对农业生产性投资产生影响。【结论】要充分关注农户分化给农业生产造成粗放化、副业化甚至撂荒等潜在危害;积极采取措施发挥农地流转对农业生产投资的刺激作用。展开更多
In this paper, a kind of second-order two-scale （SOTS） computation is developed for conductive-radiative heat trans- fer problem in periodic porous materials. First of all, by the asymptotic expansion of the tempera...In this paper, a kind of second-order two-scale （SOTS） computation is developed for conductive-radiative heat trans- fer problem in periodic porous materials. First of all, by the asymptotic expansion of the temperature field, the cell problem, homogenization problem, and second-order correctors are obtained successively. Then, the corresponding finite element al- gorithms are proposed. Finally, some numerical results are presented and compared with theoretical results. The numerical results of the proposed algorithm conform with those of the FE algorithm well, demonstrating the accuracy of the present method and its potential applications in thermal engineering of porous materials.展开更多
The influence of labor migration on rural household land transfer has been hotly debated in academic circles,which focuses on whether part-time employment leads to land transfer.Using survey data on rural households i...The influence of labor migration on rural household land transfer has been hotly debated in academic circles,which focuses on whether part-time employment leads to land transfer.Using survey data on rural households in the Sichuan Province,and applying the theoretical framework of new economics of labor migration,this study explores the influences of labor migration on the direction and scale of land transfer from the perspective of rural household structure.The results indicate that:1)the quantity of laborers has significant influence on the direction and scale of land transfer.The larger the on-farm labor variable(Labor),the lesser the possibility that land will be rented-out and the amount of land rented out will also be smaller.In addition,there is a greater probability that land will be rented-in and the amount of land rented-in will be greater.2)The greater the ratio of off-farm laborers to rural household laborers(Off-farm)the greater the possibility that land will be rented-out.In addition the higher the ratio of on-farm laborers to the total household laborers(On-farm),the larger the possibility that land will be rented-in.Meanwhile,if the household has individuals at the age of 64 or older(Old)who are engaged in agriculture,there is a smaller possibility that land will be rentedout.3)the ratio of part-time laborers to rural household laborers(Pluriactivity)have significant inverse U-shaped influences on the rent-in of land as well as the amount of land rented-in.The inflection points are 33.27%and 14.10%,respectively.Such findings confirm the significance of this study in better understanding the influence of labor migration on rural household land transfer.展开更多
基金supported by the National Natural Science Foundation of China(4072500140501012)+1 种基金drought mete-orological scientific research fund projects(IAM200707)the Knowledge Innovation Program from the Chinese Academy of Sciences(KZCX2-XB2-04)
文摘Understanding how the transpiration of this vegetation type responds to environmental stress is important for determining the wa-ter-balance dynamics of the riparian ecosystem threatened by groundwater depletion.Transpiration and sap flow were measured using the heat-pulse technique.The results were then projected up to the stand level to investigate the stand’s water-use in relation to climate forcing in the desert riparian forest in an extreme arid region.This study took place from April through October 2003 and from May through October 2004.The experimental site was selected in the Populus euphratica Forest Reserve(101o10'E,41o59'N)in Ejina county,in the lower Heihe River basin,China.The sapwood area was used as a scalar to extrapolate the stand-water consumption from the whole trees’water consumption measured by the heat-pulse velocity recorder(HPVR).Scale transferring from a series of individual trees to a stand was done according to the existing natural variations between trees under given environmental conditions.The application of the biometric parameters available from individual tree and stand levels was proved suitable for this purpose.A significant correlation between the sapwood area and tree diameter at breast height(DBH)was found.The prediction model is well fitted by the power model.On the basis of the prediction model,the sapwood area can be cal-culated by DBH.The sap-flow density can then be used to extrapolate the stand-water use by means of a series of mathematical models.
文摘The purpose of this paper is to study the energy efficiency of a local living space exposed to solar radiation in the subtropical climate of Casablanca. The study was mainly focused on the contribution of a phase change material (PCM), inserted into a 7-cm thick air layer of a double brick wall, in two different locations. We note that the experimental study was conducted using two real-scale test cavities, located in the Faculty of Science Ain Chock-Casablanca. Two PCM mounting methods were used for the south and west walls, in order to test its energy efficiency as a storage and retrieval means of the solar flux coming from the outside. In the case of the southern wall, the PCM is put directly on the internal side of the outside part of the double wall (Case 1). For the west wall, the PCM is placed 1.2 cm away from the internal side of the outer part of the double wall (Case 2). The first result shows that the PCM placed to the wall allows storing the solar heat during the day and releasing it to the outside of the building at night. While in the second case, the PCM keeps the heat stored day and night.
文摘【目的】探究农户分化对农业生产性投资的直接影响机制和间接影响机制,为解决中国当前农业生产性投资不足问题、制定农地流转等相关政策提供理论借鉴和参考。【方法】采用2012—2020年中国家庭追踪调查(China family panel studies,CFPS)数据,通过建立OLS模型、面板固定效应模型、中介效应模型进行计量分析,并进一步做出稳健性、内生性检验。【结果】农户分化对农业生产性投资有显著负向影响;农地流转在农户分化与农业生产投资间发挥部分中介作用,农户分化通过影响农地流转进而对农业生产性投资产生影响。【结论】要充分关注农户分化给农业生产造成粗放化、副业化甚至撂荒等潜在危害;积极采取措施发挥农地流转对农业生产投资的刺激作用。
基金Project supported by the National Basic Research Program of China(Grant No.2010CB832702)the National Natural Science Foundation of China(Grant No.90916027)
文摘In this paper, a kind of second-order two-scale （SOTS） computation is developed for conductive-radiative heat trans- fer problem in periodic porous materials. First of all, by the asymptotic expansion of the temperature field, the cell problem, homogenization problem, and second-order correctors are obtained successively. Then, the corresponding finite element al- gorithms are proposed. Finally, some numerical results are presented and compared with theoretical results. The numerical results of the proposed algorithm conform with those of the FE algorithm well, demonstrating the accuracy of the present method and its potential applications in thermal engineering of porous materials.
基金financial supports from National Natural Science Foundation of China(Grant Nos.4157152741801221+3 种基金4160161441701622)Sichuan Center for Rural Development Research Project(Grant No.01781912)Ministry of education humanities and social science research youth fund project(No.17YJC630136)
文摘The influence of labor migration on rural household land transfer has been hotly debated in academic circles,which focuses on whether part-time employment leads to land transfer.Using survey data on rural households in the Sichuan Province,and applying the theoretical framework of new economics of labor migration,this study explores the influences of labor migration on the direction and scale of land transfer from the perspective of rural household structure.The results indicate that:1)the quantity of laborers has significant influence on the direction and scale of land transfer.The larger the on-farm labor variable(Labor),the lesser the possibility that land will be rented-out and the amount of land rented out will also be smaller.In addition,there is a greater probability that land will be rented-in and the amount of land rented-in will be greater.2)The greater the ratio of off-farm laborers to rural household laborers(Off-farm)the greater the possibility that land will be rented-out.In addition the higher the ratio of on-farm laborers to the total household laborers(On-farm),the larger the possibility that land will be rented-in.Meanwhile,if the household has individuals at the age of 64 or older(Old)who are engaged in agriculture,there is a smaller possibility that land will be rentedout.3)the ratio of part-time laborers to rural household laborers(Pluriactivity)have significant inverse U-shaped influences on the rent-in of land as well as the amount of land rented-in.The inflection points are 33.27%and 14.10%,respectively.Such findings confirm the significance of this study in better understanding the influence of labor migration on rural household land transfer.
