Naturally occurring plant compounds including tannins, saponins and essential oils are extensively assessed as natural alternatives to in-feed antibiotics.Tannins are a group of polyphenolic compounds that are widely ...Naturally occurring plant compounds including tannins, saponins and essential oils are extensively assessed as natural alternatives to in-feed antibiotics.Tannins are a group of polyphenolic compounds that are widely present in plant region and possess various biological activities including antimicrobial,anti-parasitic, anti-viral, antioxidant, anti-inflammatory, immunomodulation, etc.Therefore, tannins are the major research subject in developing natural alternative to in-feed antibiotics.Strong protein affinity is the well-recognized property of plant tannins, which has successfully been applied to ruminant nutrition to decrease protein degradation in the rumen, and thereby improve protein utilization and animal production efficiency.Incorporations of tannin-containing forage in ruminant diets to control animal pasture bloat, intestinal parasite and pathogenic bacteria load are another 3 important applications of tannins in ruminant animals.Tannins have traditionally been regarded as "anti-nutritional factor" for monogastric animals and poultry, but recent researches have revealed some of them, when applied in appropriate manner, improved intestinal microbial ecosystem, enhanced gut health and hence increased productive performance.The applicability of plant tannins as an alternative to in-feed antibiotics depends on many factors that contribute to the great variability in their observed efficacies.展开更多
A field experiment was conducted for two consecutive years in a farmer's field at Haji Mora Village, Dera Ismail Khan (D.I. Khan) in the Northwest Frontier Province (NWPP) of Pakistan to compare various management...A field experiment was conducted for two consecutive years in a farmer's field at Haji Mora Village, Dera Ismail Khan (D.I. Khan) in the Northwest Frontier Province (NWPP) of Pakistan to compare various management practices, such as the effect of various organic manures and gypsum in a rice-wheat cropping system on a saline-sodic Entisol (Zindani soil series). The treatments consisted of 1) a control (rice-wheat), 2) gypsum, 3) farmyard manure (FYM), 4) berseem (Trifolium alexzndrinum L.) as green manure (GM), and 5) dhancha (Sesbania sp.) as GM. All treatments increased yields of both rice and wheat significantly (P < 0.01) over the control, with the green manure treatments proving more economical than the others; while they decreased pH, electrical conductivity (EC), and sodium adsorption ratio (SAR) of the soil. Saturation percentage and available water of the soil were raised for all treatments due to an increase in organic matter content of the soil.展开更多
Nowadays, intensive breeding of poultry and livestock of large scale has made the treatment of its waste and wastewater an urgent environmental issue, which motivated this study. A wetland of 688 mz was constructed on...Nowadays, intensive breeding of poultry and livestock of large scale has made the treatment of its waste and wastewater an urgent environmental issue, which motivated this study. A wetland of 688 mz was constructed on an egg duck farm, and water hyacinth （Eichhornia crassipes） was chosen as an aquatic plant for the wetland and used as food for duck production. The objectives of this study were to test the role of water hyacinth in purifying nutrient-rich wastewater and its effects on the ducks＇ feed intake, egg laying performance and egg quality. This paper shows that the constructed wetland removed as much as 64.44% of chemical oxygen demand （COD）, 21.78% of total nitrogen （TN） and 23.02% of total phosphorus （TP）. Both dissolved oxygen （DO） and the transparency of the wastewater were remarkably improved, with its transparency 2.5 times higher than that of the untreated wastewater. After the ducks were fed with water hyacinth, the average daily feed intake and the egg-laying ratio in the test group were 5.86% and 9.79% higher, respectively, than in the control group; the differences were both significant at the 0.01 probability level. The egg weight in the test group was 2.36% higher than in the control group （P 〈 0.05）, but the feed conversion ratios were almost the same. The eggshell thickness and strength were among the egg qualities significantly increased in ducks fed with water hyacinth. We concluded that a water hyacinth system was effective for purifying wastewater from an intensive duck farm during the water hyacinth growing season, as harvested water hyacinth had an excellent performance as duck feed. We also discussed the limitations of the experiment.展开更多
With intermittence and stochastics of wind power largely introduced into power systems, power system stability analysis and control is in urgent need of reliable wind farm models. Considering the superiority of wide-a...With intermittence and stochastics of wind power largely introduced into power systems, power system stability analysis and control is in urgent need of reliable wind farm models. Considering the superiority of wide-area measurement systems, this paper develops a novel methodology for practical synchrophasor measurement-based modeling and parameter identification of wind farms. For the sake of preserving basic structural characteristics and control patterns simultaneously, a comprehensive wind farm model is constructed elaborately. To improve the efficiency of the identification procedure,dominant parameters are classified and selected by trajectory sensitivity analysis. Furthermore, an improved genetic algorithm is proposed to strengthen the capability of global optimization. The test results on the WECC benchmark system and the CEPRI 36-bus system demonstrate the effectiveness and reliability of the proposed modeling and identification methodology.展开更多
China has made many strides in large-scale development and centralized integration of wind power in recent years.The wind power penetration of some regions has reached a high level,which brings significant challenges ...China has made many strides in large-scale development and centralized integration of wind power in recent years.The wind power penetration of some regions has reached a high level,which brings significant challenges for power system dispatch due to the inherent variability and uncertainty of wind resources.To increase the dispatch capabilities of wind power generation,the spatial smoothing effect among adjacent wind farms needs to be fully utilized.This paper presents the concept of hierarchical coordinated dispatch for wind power based on a new concept of a virtual power generator.The spatial smoothing effect of wind power is analyzed first.Next,the virtual power generator method of a wind farm cluster is defined and established.Then,the hierarchical coordinated dispatch mode is compared with an existing wind power dispatch mode for individual wind farms.Finally,the proposed concept is implemented on a simulation case to demonstrate applicability and effectiveness.展开更多
There is more wind with less turbulence offshore compared with an onshore case,which drives the development of the offshore wind farm worldwide.Since a huge amount of money is required for constructing an offshore win...There is more wind with less turbulence offshore compared with an onshore case,which drives the development of the offshore wind farm worldwide.Since a huge amount of money is required for constructing an offshore wind farm,many types of research have been done on the optimization of the offshore wind farm with the purpose of either minimizing the cost of energy or maximizing the total energy production.There are several factors that have an impact on the performance of the wind farm,mainly the energy production of wind farm which is highly decided bythe wind condition of construction area and micro-siting of wind turbines(WTs),as well as the initial investment which is influenced by both the placement of WTs and the electrical system design,especially the scheme of cable connection layout.In this paper,a review of the state-of-the-art researches related to the wind farm layout optimization as well as electrical system design including cable connection scheme optimization is presented.The most significant factors that should be considered in the optimization work of the offshore wind farm is highlighted after reviewing the latest works,and the future needs are specified.展开更多
Inefficient use of fertilizer has caused serious environmental problems and unsustainable development of agriculture in China.To meet the increasing food demand in the future without damaging the ecological environmen...Inefficient use of fertilizer has caused serious environmental problems and unsustainable development of agriculture in China.To meet the increasing food demand in the future without damaging the ecological environment,Chinese government officially launched the Action Plan for the Zero Growth of Fertilizer Use in 2015.At the same time,China released a series of policies aiming explicitly at expanding farm size and a great number of large scale farmers emerged recently.However,whether the expansion of farm size will be beneficial for the increase of fertilizer use efficiency still remains to be investigated.In this study,we comprehensively explored the relationship between fertilizer use efficiency and farm size.Based on the 4281 farm households’survey data collected by the National Development and Reform Commission(NDRC)of China from 2004 to 2016 in Jiangsu Province,China,this paper applies a stochastic frontier production function to estimate fertilizer use efficiency across farm size and uses a regression model to analyze the influence of farm size on fertilizer use efficiency.The results show that:(1)the average fertilizer use efficiency of whole samples was only 0.60,much lower than the average technical efficiency,indicating that on average half of the fertilizer utilized are excessive in China;and(2)the smallest farm size group get the highest fertilizer use efficiency score.We also provide some possible explanations for the inverse relationship between farm size and fertilizer use efficiency.展开更多
Increased penetration of intermittent renewable energy resources is pushing the grid to prepare more reserves to meet the supply and demand balance.Demand response(DR)is an efficient strategy to reduce the overall loa...Increased penetration of intermittent renewable energy resources is pushing the grid to prepare more reserves to meet the supply and demand balance.Demand response(DR)is an efficient strategy to reduce the overall load at peak times.In order to fully utilize the application of DR and make DR capable of actively supporting grid operations at all times,this paper builds a DR and wind farm integrated economic dispatch model.The objective is to minimize the total operation costs,such as fuel cost,startup cost,greenhouse gas(GHG)emission costs,and DR cost.DR maximum participating time and DR ramp rate constraints are considered.A system with 10 traditional units,one large-scale wind farm,three types of DR,including interruptible load,direct load control,and load as capacity resource are selected to verify the proposed model.Four DR penetration rates are analyzed:0%,10%,20%and 30%.The results indicate that DR penetration can decrease total operation costs.The lower price DR resource gets the priority to be committed.The DR and wind farm integration is indispensable in the future economic dispatch.展开更多
稻鱼系统是将水稻栽培与水产养殖结合起来,以获得更多量和更多样化的食物、更友好的环境的一种种养结合模式。稻鱼系统在我国历史悠久,2000年以来发展迅速,形成了规模化、产业化、品牌化和多样化的稻鱼系统经营模式。本文以各类新型农...稻鱼系统是将水稻栽培与水产养殖结合起来,以获得更多量和更多样化的食物、更友好的环境的一种种养结合模式。稻鱼系统在我国历史悠久,2000年以来发展迅速,形成了规模化、产业化、品牌化和多样化的稻鱼系统经营模式。本文以各类新型农业经营主体发展起来的多类型稻鱼型农场为研究对象,采用成对比较法,从农场基本情况、水稻产量与水产产量、氮肥与农药使用、经济总产出等方面进行了特征分析,探讨了稻鱼种养的综合效应。结果表明:调查的153个稻鱼种养型农场主要为稻鲤、稻鳖、稻虾、稻蟹和稻鳅共5种类型,90%的农场的土地规模主要分布在1～50 hm^2之间,46.6%的农场以专业合作社形式经营,而家庭农场经营形式占29.4%,农业公司占24%;农场经营者平均年龄为44岁,受教育程度高中及以上学历占97.2%。与常规水稻单作农场相比,稻鱼种养型农场的水稻产量表现为增产或稳产效应,同时产出一定数量水产品,平均水产品产量为(1.19±0.08) t/hm^2。稻鱼种养型农场氮肥平均投入为(128.40±8.03) kg N/hm^2,比水稻单作模式平均减少33.63%;农药平均投入(6.21±0.62) kg a.i./hm^2,比水稻单作模式平均减少59.73%。稻鱼种养型农场总经济产出平均为(6.98±4.12)万元/hm^2,不同模式间差异较大;与水稻单作经济产出(2.60±0.34)万元/hm^2相比,稻鲤、稻鳖、稻虾、稻蟹和稻鳅总经济产出分别增加效益205%、78%、156%、710%和480%。稻鱼种养型农场总投入产出比为0.47±0.16,显著低于水稻单作模式总投入产出比0.66±0.17。研究表明,以农场为载体的规模化和产业化发展起来的稻鱼系统,采用标准化技术和产业化经营能使稻鱼系统的效应大大提高,也有利于稻鱼共生产业的健康发展。展开更多
The traditional rice-fish farming system is selected as a ＂globally important agricultural heritage system＂ （GIAHS） by the Food and Agriculture Organization （FAO）,United Nations Development Programme （UNDP）,an...The traditional rice-fish farming system is selected as a ＂globally important agricultural heritage system＂ （GIAHS） by the Food and Agriculture Organization （FAO）,United Nations Development Programme （UNDP）,and Global Environment Facility （GEF）,etc.In Zhejiang Province of China,where the pilot site for this GIAHS farming system is located,we compared the use of traditional rice varieties in rice-fish co-culture and rice monoculture.Further,we determined how traditional rice varieties were performed in this rice-fish system.Only 19% of the farmers who practiced rice monoculture planted traditional varieties while 52% of farmers who practiced rice-fish co-culture planted traditional varieties.Traditional varieties represented 13% of the total land cultivated under rice in the rice-fish system but only 2% in the rice monoculture system.In the rice-fish system,yield was lower for traditional rice varieties than hybrid varieties but application of fertilizers and pesticides was also lower.In a field experiment in the rice-fish system without pesticides,rice planthopper numbers and sheath blight incidence were lower from three traditional varieties than one hybrid variety;yields were 8 to 32% lower from the traditional varieties than the hybrid.Our results showed that traditional rice varieties can be preserved through conserving GIAHS rice-fish co-culture.Our study also indicated that traditional rice varieties can survive in the rice-fish system because these varieties are helpful to the whole system and beneficial to the farmers.展开更多
Using data from the farm household survey conducted in 2009,arable land use intensity(ALUI)and its influence factors at farm household level were investigated by the Tobit model.Suyu District of Suqian City and Taixin...Using data from the farm household survey conducted in 2009,arable land use intensity(ALUI)and its influence factors at farm household level were investigated by the Tobit model.Suyu District of Suqian City and Taixing City of Jiansu Province,China were chosen as the regions for comparison.The results show that:1)On the average, the ALUI,labor intensity,yield-increasing input,and labor-saving input are 15 238.14 yuan(RMB)/ha,192 d/ha, 7233.01 yuan/ha,and 2451.32 yuan/ha in the less economically developed Suyu District,and 13 020.65 yuan/ha,181 d/ha,5871.82 yuan/ha,and 2625.97 yuan/ha in more economically developed Taixing City.The figures indicate that Suyu District has higher ALUI and labor intensity input but lower labor-saving input.2)Comparing all the influence factors,the total arable land area in available and average plot size have bigger effects on arable land intensive use;to a small degree,family′s non-farm income affects labor intensity,yield-increasing input,and labor-saving input;the yield-increasing input decreases significantly when the householder has higher education attainment;the commercialization rates of agricultural products and the planting proportion of cash crops both have unstable influence on ALUI; the share of arable land rented in has few impacts on labor intensity,yield-increasing input,and labor-saving input. 3)There are no differences found in the internal impact mechanism of influence factors on the arable land intensive use behaviors of farm households.However,there are conspicuous disparities in the impact degrees and statistical significance based on varying economic levels.4)Using the results as bases,this study proposes that the government should implement land management and agricultural policies according to local condition.And these policies should decrease land fragmentation to promote scale management of land and arable land use intensification.展开更多
Offshore wind farms(OWFs)have received widespread attention for their abundant unexploited wind energy poten-tial and convenient locations conditions.They are rapidly developing towards having large capacity and being...Offshore wind farms(OWFs)have received widespread attention for their abundant unexploited wind energy poten-tial and convenient locations conditions.They are rapidly developing towards having large capacity and being located further away from shore.It is thus necessary to explore effective power transmission technologies to connect large OWFs to onshore grids.At present,three types of power transmission technologies have been proposed for large OWF integration.They are:high voltage alternating current(HVAC)transmission,high voltage direct current(HVDC)transmission,and low-frequency alternating current(LFAC)or fractional frequency alternating current transmission.This work undertakes a comprehensive review of grid connection technologies for large OWF integration.Compared with previous reviews,a more exhaustive summary is provided to elaborate HVAC,LFAC,and five HVDC topologies,consisting of line-commutated converter HVDC,voltage source converter HVDC,hybrid-HVDC,diode rectifier-based HVDC,and all DC transmission systems.The fault ride-through technologies of the grid connection schemes are also presented in detail to provide research references and guidelines for researchers.In addition,a comprehensive evalu-ation of the seven grid connection technologies for large OWFs is proposed based on eight specific indicators.Finally,eight conclusions and six perspectives are outlined for future research in integrating large OWFs.展开更多
Food safety issues constitute an international topic discussed by many scholars. Although there is an extensive body of literature on comparisons of food safety control practices across different governance structures...Food safety issues constitute an international topic discussed by many scholars. Although there is an extensive body of literature on comparisons of food safety control practices across different governance structures, these studies have been conducted mainly in terms of qualitative and descriptive analysis. In addition, little attention has been given to family farms. This study addresses the food safety control practices adopted by firms with different governance structures in China. Food safety control is expressed by the following aspects, i.e., pollution-free, green, organic, and/or geographical indication prod- ucts certification, establishment of production records, and pesticide residue testing. Three types of governance structures that engage in agricultural production are distinguished： farmer cooperatives, agricultural companies, and family farms. The food safety control practices of various governance structures are investigated based on a database that comprises 600 vegetable and fruit enterprises in Zhejiang, China. The results show that （1） pesticide residue testing is adopted by the most firms, followed by products certification, and production records are adopted by the fewest firms, and （2） agricul- tural companies adopt more food safety control practices than family farms, while farmer cooperatives adopt the fewest food safety control practices. Governance structure features of a cooperative in terms of ownership, decision-making, and income distribution are the main reasons for the low level of food safety control in the cooperative.展开更多
基金partially funded by Alberta Agriculture and Forestry,Agriculture and Agri-Food Canadaprojects of China Postdoctoral Science Foundation (Grant No.:2017M611930)+1 种基金Natural Science Foundation of Jiangsu Province of China (No.:BK20170494)China Agriculture Research System (CARS-36)
文摘Naturally occurring plant compounds including tannins, saponins and essential oils are extensively assessed as natural alternatives to in-feed antibiotics.Tannins are a group of polyphenolic compounds that are widely present in plant region and possess various biological activities including antimicrobial,anti-parasitic, anti-viral, antioxidant, anti-inflammatory, immunomodulation, etc.Therefore, tannins are the major research subject in developing natural alternative to in-feed antibiotics.Strong protein affinity is the well-recognized property of plant tannins, which has successfully been applied to ruminant nutrition to decrease protein degradation in the rumen, and thereby improve protein utilization and animal production efficiency.Incorporations of tannin-containing forage in ruminant diets to control animal pasture bloat, intestinal parasite and pathogenic bacteria load are another 3 important applications of tannins in ruminant animals.Tannins have traditionally been regarded as "anti-nutritional factor" for monogastric animals and poultry, but recent researches have revealed some of them, when applied in appropriate manner, improved intestinal microbial ecosystem, enhanced gut health and hence increased productive performance.The applicability of plant tannins as an alternative to in-feed antibiotics depends on many factors that contribute to the great variability in their observed efficacies.
文摘A field experiment was conducted for two consecutive years in a farmer's field at Haji Mora Village, Dera Ismail Khan (D.I. Khan) in the Northwest Frontier Province (NWPP) of Pakistan to compare various management practices, such as the effect of various organic manures and gypsum in a rice-wheat cropping system on a saline-sodic Entisol (Zindani soil series). The treatments consisted of 1) a control (rice-wheat), 2) gypsum, 3) farmyard manure (FYM), 4) berseem (Trifolium alexzndrinum L.) as green manure (GM), and 5) dhancha (Sesbania sp.) as GM. All treatments increased yields of both rice and wheat significantly (P < 0.01) over the control, with the green manure treatments proving more economical than the others; while they decreased pH, electrical conductivity (EC), and sodium adsorption ratio (SAR) of the soil. Saturation percentage and available water of the soil were raised for all treatments due to an increase in organic matter content of the soil.
文摘Nowadays, intensive breeding of poultry and livestock of large scale has made the treatment of its waste and wastewater an urgent environmental issue, which motivated this study. A wetland of 688 mz was constructed on an egg duck farm, and water hyacinth （Eichhornia crassipes） was chosen as an aquatic plant for the wetland and used as food for duck production. The objectives of this study were to test the role of water hyacinth in purifying nutrient-rich wastewater and its effects on the ducks＇ feed intake, egg laying performance and egg quality. This paper shows that the constructed wetland removed as much as 64.44% of chemical oxygen demand （COD）, 21.78% of total nitrogen （TN） and 23.02% of total phosphorus （TP）. Both dissolved oxygen （DO） and the transparency of the wastewater were remarkably improved, with its transparency 2.5 times higher than that of the untreated wastewater. After the ducks were fed with water hyacinth, the average daily feed intake and the egg-laying ratio in the test group were 5.86% and 9.79% higher, respectively, than in the control group; the differences were both significant at the 0.01 probability level. The egg weight in the test group was 2.36% higher than in the control group （P 〈 0.05）, but the feed conversion ratios were almost the same. The eggshell thickness and strength were among the egg qualities significantly increased in ducks fed with water hyacinth. We concluded that a water hyacinth system was effective for purifying wastewater from an intensive duck farm during the water hyacinth growing season, as harvested water hyacinth had an excellent performance as duck feed. We also discussed the limitations of the experiment.
基金supported by National Basic Research Program of China(No.2012CB215206)National Natural Science Foundation of China(No.51107061)
文摘With intermittence and stochastics of wind power largely introduced into power systems, power system stability analysis and control is in urgent need of reliable wind farm models. Considering the superiority of wide-area measurement systems, this paper develops a novel methodology for practical synchrophasor measurement-based modeling and parameter identification of wind farms. For the sake of preserving basic structural characteristics and control patterns simultaneously, a comprehensive wind farm model is constructed elaborately. To improve the efficiency of the identification procedure,dominant parameters are classified and selected by trajectory sensitivity analysis. Furthermore, an improved genetic algorithm is proposed to strengthen the capability of global optimization. The test results on the WECC benchmark system and the CEPRI 36-bus system demonstrate the effectiveness and reliability of the proposed modeling and identification methodology.
基金supported in part by Chinese National Key Technologies R&D Program(2013BAA01B03)National Natural Science Foundation of China(51190101)industrial project of State Grid Corporation of China(No.NY71-13-043).
文摘China has made many strides in large-scale development and centralized integration of wind power in recent years.The wind power penetration of some regions has reached a high level,which brings significant challenges for power system dispatch due to the inherent variability and uncertainty of wind resources.To increase the dispatch capabilities of wind power generation,the spatial smoothing effect among adjacent wind farms needs to be fully utilized.This paper presents the concept of hierarchical coordinated dispatch for wind power based on a new concept of a virtual power generator.The spatial smoothing effect of wind power is analyzed first.Next,the virtual power generator method of a wind farm cluster is defined and established.Then,the hierarchical coordinated dispatch mode is compared with an existing wind power dispatch mode for individual wind farms.Finally,the proposed concept is implemented on a simulation case to demonstrate applicability and effectiveness.
文摘There is more wind with less turbulence offshore compared with an onshore case,which drives the development of the offshore wind farm worldwide.Since a huge amount of money is required for constructing an offshore wind farm,many types of research have been done on the optimization of the offshore wind farm with the purpose of either minimizing the cost of energy or maximizing the total energy production.There are several factors that have an impact on the performance of the wind farm,mainly the energy production of wind farm which is highly decided bythe wind condition of construction area and micro-siting of wind turbines(WTs),as well as the initial investment which is influenced by both the placement of WTs and the electrical system design,especially the scheme of cable connection layout.In this paper,a review of the state-of-the-art researches related to the wind farm layout optimization as well as electrical system design including cable connection scheme optimization is presented.The most significant factors that should be considered in the optimization work of the offshore wind farm is highlighted after reviewing the latest works,and the future needs are specified.
基金supported by the National Social Science Fund of China (14ZDA037)the National Natural Science Foundation of China (71333008)+1 种基金the Postdoctoral Science Foundation of China (2018M631508)the Fundamental Research Funds for the Central University, China (2662018QD008)
文摘Inefficient use of fertilizer has caused serious environmental problems and unsustainable development of agriculture in China.To meet the increasing food demand in the future without damaging the ecological environment,Chinese government officially launched the Action Plan for the Zero Growth of Fertilizer Use in 2015.At the same time,China released a series of policies aiming explicitly at expanding farm size and a great number of large scale farmers emerged recently.However,whether the expansion of farm size will be beneficial for the increase of fertilizer use efficiency still remains to be investigated.In this study,we comprehensively explored the relationship between fertilizer use efficiency and farm size.Based on the 4281 farm households’survey data collected by the National Development and Reform Commission(NDRC)of China from 2004 to 2016 in Jiangsu Province,China,this paper applies a stochastic frontier production function to estimate fertilizer use efficiency across farm size and uses a regression model to analyze the influence of farm size on fertilizer use efficiency.The results show that:(1)the average fertilizer use efficiency of whole samples was only 0.60,much lower than the average technical efficiency,indicating that on average half of the fertilizer utilized are excessive in China;and(2)the smallest farm size group get the highest fertilizer use efficiency score.We also provide some possible explanations for the inverse relationship between farm size and fertilizer use efficiency.
基金This work was supported in part by the National High Technology Research and Development Program(863 Program)under Grant 2014AA051901National Natural Science Foundation of China under Grant 51261130473.
文摘Increased penetration of intermittent renewable energy resources is pushing the grid to prepare more reserves to meet the supply and demand balance.Demand response(DR)is an efficient strategy to reduce the overall load at peak times.In order to fully utilize the application of DR and make DR capable of actively supporting grid operations at all times,this paper builds a DR and wind farm integrated economic dispatch model.The objective is to minimize the total operation costs,such as fuel cost,startup cost,greenhouse gas(GHG)emission costs,and DR cost.DR maximum participating time and DR ramp rate constraints are considered.A system with 10 traditional units,one large-scale wind farm,three types of DR,including interruptible load,direct load control,and load as capacity resource are selected to verify the proposed model.Four DR penetration rates are analyzed:0%,10%,20%and 30%.The results indicate that DR penetration can decrease total operation costs.The lower price DR resource gets the priority to be committed.The DR and wind farm integration is indispensable in the future economic dispatch.
文摘稻鱼系统是将水稻栽培与水产养殖结合起来,以获得更多量和更多样化的食物、更友好的环境的一种种养结合模式。稻鱼系统在我国历史悠久,2000年以来发展迅速,形成了规模化、产业化、品牌化和多样化的稻鱼系统经营模式。本文以各类新型农业经营主体发展起来的多类型稻鱼型农场为研究对象,采用成对比较法,从农场基本情况、水稻产量与水产产量、氮肥与农药使用、经济总产出等方面进行了特征分析,探讨了稻鱼种养的综合效应。结果表明:调查的153个稻鱼种养型农场主要为稻鲤、稻鳖、稻虾、稻蟹和稻鳅共5种类型,90%的农场的土地规模主要分布在1～50 hm^2之间,46.6%的农场以专业合作社形式经营,而家庭农场经营形式占29.4%,农业公司占24%;农场经营者平均年龄为44岁,受教育程度高中及以上学历占97.2%。与常规水稻单作农场相比,稻鱼种养型农场的水稻产量表现为增产或稳产效应,同时产出一定数量水产品,平均水产品产量为(1.19±0.08) t/hm^2。稻鱼种养型农场氮肥平均投入为(128.40±8.03) kg N/hm^2,比水稻单作模式平均减少33.63%;农药平均投入(6.21±0.62) kg a.i./hm^2,比水稻单作模式平均减少59.73%。稻鱼种养型农场总经济产出平均为(6.98±4.12)万元/hm^2,不同模式间差异较大;与水稻单作经济产出(2.60±0.34)万元/hm^2相比,稻鲤、稻鳖、稻虾、稻蟹和稻鳅总经济产出分别增加效益205%、78%、156%、710%和480%。稻鱼种养型农场总投入产出比为0.47±0.16,显著低于水稻单作模式总投入产出比0.66±0.17。研究表明,以农场为载体的规模化和产业化发展起来的稻鱼系统,采用标准化技术和产业化经营能使稻鱼系统的效应大大提高,也有利于稻鱼共生产业的健康发展。
基金supported by the National Basic Research Program of China (2011CB100406)the Science and Technology Department of Zhejiang Province,China(2008C12064)+2 种基金the Ministry of Environment Protection of China (201090020)the Wenzhou Bureau of Science and Technology of Zhejiang Province,China(N20080024)the Key Laboratory of Non-Point Sources Pollution Control,Ministry of Agriculture of China (KYJD09021)
文摘The traditional rice-fish farming system is selected as a ＂globally important agricultural heritage system＂ （GIAHS） by the Food and Agriculture Organization （FAO）,United Nations Development Programme （UNDP）,and Global Environment Facility （GEF）,etc.In Zhejiang Province of China,where the pilot site for this GIAHS farming system is located,we compared the use of traditional rice varieties in rice-fish co-culture and rice monoculture.Further,we determined how traditional rice varieties were performed in this rice-fish system.Only 19% of the farmers who practiced rice monoculture planted traditional varieties while 52% of farmers who practiced rice-fish co-culture planted traditional varieties.Traditional varieties represented 13% of the total land cultivated under rice in the rice-fish system but only 2% in the rice monoculture system.In the rice-fish system,yield was lower for traditional rice varieties than hybrid varieties but application of fertilizers and pesticides was also lower.In a field experiment in the rice-fish system without pesticides,rice planthopper numbers and sheath blight incidence were lower from three traditional varieties than one hybrid variety;yields were 8 to 32% lower from the traditional varieties than the hybrid.Our results showed that traditional rice varieties can be preserved through conserving GIAHS rice-fish co-culture.Our study also indicated that traditional rice varieties can survive in the rice-fish system because these varieties are helpful to the whole system and beneficial to the farmers.
基金Under the auspices of National Natural Science Foundation of China(No.40971104,40801063,41101160)National Social Science Foundation of China(No.10ZD&M030)Non-profit Industry Financial Program of Ministry of Land and Resources of China(No.200811033)
文摘Using data from the farm household survey conducted in 2009,arable land use intensity(ALUI)and its influence factors at farm household level were investigated by the Tobit model.Suyu District of Suqian City and Taixing City of Jiansu Province,China were chosen as the regions for comparison.The results show that:1)On the average, the ALUI,labor intensity,yield-increasing input,and labor-saving input are 15 238.14 yuan(RMB)/ha,192 d/ha, 7233.01 yuan/ha,and 2451.32 yuan/ha in the less economically developed Suyu District,and 13 020.65 yuan/ha,181 d/ha,5871.82 yuan/ha,and 2625.97 yuan/ha in more economically developed Taixing City.The figures indicate that Suyu District has higher ALUI and labor intensity input but lower labor-saving input.2)Comparing all the influence factors,the total arable land area in available and average plot size have bigger effects on arable land intensive use;to a small degree,family′s non-farm income affects labor intensity,yield-increasing input,and labor-saving input;the yield-increasing input decreases significantly when the householder has higher education attainment;the commercialization rates of agricultural products and the planting proportion of cash crops both have unstable influence on ALUI; the share of arable land rented in has few impacts on labor intensity,yield-increasing input,and labor-saving input. 3)There are no differences found in the internal impact mechanism of influence factors on the arable land intensive use behaviors of farm households.However,there are conspicuous disparities in the impact degrees and statistical significance based on varying economic levels.4)Using the results as bases,this study proposes that the government should implement land management and agricultural policies according to local condition.And these policies should decrease land fragmentation to promote scale management of land and arable land use intensification.
基金National Natural Science Foundation of China (61963020)National Natural Science Foundation of China (52022035)+2 种基金Key Program of National Natural Science Foundation of China (52037003)Major Special Project of Yunnan Province of China (202002AF080001)Curriculum ideological and political connotation construction project (2021KS037).
文摘Offshore wind farms(OWFs)have received widespread attention for their abundant unexploited wind energy poten-tial and convenient locations conditions.They are rapidly developing towards having large capacity and being located further away from shore.It is thus necessary to explore effective power transmission technologies to connect large OWFs to onshore grids.At present,three types of power transmission technologies have been proposed for large OWF integration.They are:high voltage alternating current(HVAC)transmission,high voltage direct current(HVDC)transmission,and low-frequency alternating current(LFAC)or fractional frequency alternating current transmission.This work undertakes a comprehensive review of grid connection technologies for large OWF integration.Compared with previous reviews,a more exhaustive summary is provided to elaborate HVAC,LFAC,and five HVDC topologies,consisting of line-commutated converter HVDC,voltage source converter HVDC,hybrid-HVDC,diode rectifier-based HVDC,and all DC transmission systems.The fault ride-through technologies of the grid connection schemes are also presented in detail to provide research references and guidelines for researchers.In addition,a comprehensive evalu-ation of the seven grid connection technologies for large OWFs is proposed based on eight specific indicators.Finally,eight conclusions and six perspectives are outlined for future research in integrating large OWFs.
基金supported by the National Social Science Fund of China (13AZD079)the Zhejiang Provincial Natural Science Foundation of China (LQ14G030041 and LZ12G03003)the National Natural Science Foundation of China (71333011 and 71273234)
文摘Food safety issues constitute an international topic discussed by many scholars. Although there is an extensive body of literature on comparisons of food safety control practices across different governance structures, these studies have been conducted mainly in terms of qualitative and descriptive analysis. In addition, little attention has been given to family farms. This study addresses the food safety control practices adopted by firms with different governance structures in China. Food safety control is expressed by the following aspects, i.e., pollution-free, green, organic, and/or geographical indication prod- ucts certification, establishment of production records, and pesticide residue testing. Three types of governance structures that engage in agricultural production are distinguished： farmer cooperatives, agricultural companies, and family farms. The food safety control practices of various governance structures are investigated based on a database that comprises 600 vegetable and fruit enterprises in Zhejiang, China. The results show that （1） pesticide residue testing is adopted by the most firms, followed by products certification, and production records are adopted by the fewest firms, and （2） agricul- tural companies adopt more food safety control practices than family farms, while farmer cooperatives adopt the fewest food safety control practices. Governance structure features of a cooperative in terms of ownership, decision-making, and income distribution are the main reasons for the low level of food safety control in the cooperative.
