This work studies the problem of control design for linear systems with input saturation.It is well known that integral quadratic constraints(IQC) can be used to describe input saturation and that the use of IQC in an...This work studies the problem of control design for linear systems with input saturation.It is well known that integral quadratic constraints(IQC) can be used to describe input saturation and that the use of IQC in analysis can lead to less conservative performance bound and larger domain of attraction.In this work,it is shown that a class of commonly used IQCs may not help in control synthesis.That is,the use of these IQCs does not enlarge the guaranteed domain of performance for synthesis.展开更多
Agricultural inputs are necessities in a production process just as food is a necessity for human survival. Production comes with the use of inputs. The cultivation of maize in Cameroon is predominantly dominated by s...Agricultural inputs are necessities in a production process just as food is a necessity for human survival. Production comes with the use of inputs. The cultivation of maize in Cameroon is predominantly dominated by smallholder farmers who use traditional methods and face drudgery. The current production level of maize in the country is declining and to meet consumption requirements, huge quantities of the commodity are imported. This study questions the impacts of variable input costs on maize production. Inputs are building blocks of production costs;it is therefore important for maize farmers to be alerted on the effective use of farm inputs in order to obtain higher returns. Data were collected with the use of a structured questionnaire. They were analysed using descriptive statistics and OLS Regression techniques. Results show that on average per hectare, each maize farmer spends USD10.12 on seeds, USD28.90 on fertilizer, USD8.90 on labour, and USD13.28 on herbicides. The regression results show that estimated coefficients of unit costs of fertilizer, herbicides and labour were negative but insignificant while land and hybrid seeds were positive. Input subsidy is recommended as a policy instrument to lower prices paid by farmers.展开更多
In this paper, a laboratory study has been made to develop low cost high performance steel plates with superior HAZ toughness for large heat input welding. Simulated results show that the absorbed impact energy of hea...In this paper, a laboratory study has been made to develop low cost high performance steel plates with superior HAZ toughness for large heat input welding. Simulated results show that the absorbed impact energy of heat-affected zone (HAZ) at -20℃reaches above 200J when large heat inputs of 100 to 400kJ/cm were applied, suggestive of superior HAZ toughness for large heat input welding of developed steel plate. The microstructures in HAZ are transformed from mainly fine ferrite and bainite at 100kJ/cm, through an intermediate stage of ferrite, bainite and pearlite at 200 and 300kJ/cm, to nearly fine ferrite and pearlite at 400kJ/cm. The prior austenite grain size and ferrite grain size in HAZ are controlled to ～50 and ～20μm, respectively. The high HAZ toughness is due to the inhibition of prior austenite grain size at high temperatures and the formation of beneficial microstructures to HAZ toughness during continuous cooling.展开更多
为定量化设施果类蔬菜养分投入,实现设施果蔬优质高产、绿色高效生产,本研究以山东省典型设施果类蔬菜为研究对象,基于通过农户调研与土壤样品采集测定收集的数据,结合对现有文献的综述,使用生命周期评价方法,系统分析研究区域设施果类...为定量化设施果类蔬菜养分投入,实现设施果蔬优质高产、绿色高效生产,本研究以山东省典型设施果类蔬菜为研究对象,基于通过农户调研与土壤样品采集测定收集的数据,结合对现有文献的综述,使用生命周期评价方法,系统分析研究区域设施果类蔬菜生产的施肥现状、土壤养分状况和环境代价及其相关关系。结果表明:山东省主栽设施果类蔬菜养分投入量高,设施番茄、黄瓜、辣椒、茄子的氮(以N计)、磷(以P2O5计)、钾(以K2O计)投入量平均达到743、600、740 kg·hm^(-2),施肥变异系数较大(CV=30.3%~43.9%),大量的肥料投入造成了较高的养分盈余,进而导致表层土壤(0~30 cm)养分含量显著升高,同时导致了较高的环境代价。设施果类蔬菜的单位面积上活性氮损失、温室气体排放、富营养化效应和酸化效应均以黄瓜生产系统最高,分别达225 kg·hm^(-2)、10058 kg CO_(2e)·hm^(-2)、124 kg PO_(4e)·hm^(-2)和63.4 kg SO_(2e)·hm^(-2),其次是茄子、番茄和辣椒。氮素盈余是导致活性氮损失的最主要因素,氮、磷、钾肥料的生产过程和施用过程是设施果类蔬菜温室气体排放、富营养化效应和酸化效应的主要贡献因子,贡献率高达80%以上。因此,为保证设施果类蔬菜产业绿色优质高质量发展,应通过优化设施蔬菜养分资源综合管理策略来减少养分盈余、降低环境代价。展开更多
Rising labor opportunity cost is one of the most important characteristics of farmers' economic environment in present China,and brings great agricultural land use changes correspondingly.Based on the stratified r...Rising labor opportunity cost is one of the most important characteristics of farmers' economic environment in present China,and brings great agricultural land use changes correspondingly.Based on the stratified random sample of rural households in Sui County,this paper estimates the opportunity cost of farm labors,and then analyzes its effect on farmers' agricultural land use decisions.The findings show that the households with higher labor opportunity cost are more likely to reduce labor intensity and increase labor-saving input in their land use decisions.From the descriptive analysis,we also find these households always prefer grain crop planting,reduce yield-raising input or even rent out their cultivated land.As labor and yield-raising input are two essential positive factors for grain production,continuous declining of labor input and yield-raising input caused by rising labor opportunity cost may influence the grain yield per unit area in the future.展开更多
文摘This work studies the problem of control design for linear systems with input saturation.It is well known that integral quadratic constraints(IQC) can be used to describe input saturation and that the use of IQC in analysis can lead to less conservative performance bound and larger domain of attraction.In this work,it is shown that a class of commonly used IQCs may not help in control synthesis.That is,the use of these IQCs does not enlarge the guaranteed domain of performance for synthesis.
文摘Agricultural inputs are necessities in a production process just as food is a necessity for human survival. Production comes with the use of inputs. The cultivation of maize in Cameroon is predominantly dominated by smallholder farmers who use traditional methods and face drudgery. The current production level of maize in the country is declining and to meet consumption requirements, huge quantities of the commodity are imported. This study questions the impacts of variable input costs on maize production. Inputs are building blocks of production costs;it is therefore important for maize farmers to be alerted on the effective use of farm inputs in order to obtain higher returns. Data were collected with the use of a structured questionnaire. They were analysed using descriptive statistics and OLS Regression techniques. Results show that on average per hectare, each maize farmer spends USD10.12 on seeds, USD28.90 on fertilizer, USD8.90 on labour, and USD13.28 on herbicides. The regression results show that estimated coefficients of unit costs of fertilizer, herbicides and labour were negative but insignificant while land and hybrid seeds were positive. Input subsidy is recommended as a policy instrument to lower prices paid by farmers.
文摘In this paper, a laboratory study has been made to develop low cost high performance steel plates with superior HAZ toughness for large heat input welding. Simulated results show that the absorbed impact energy of heat-affected zone (HAZ) at -20℃reaches above 200J when large heat inputs of 100 to 400kJ/cm were applied, suggestive of superior HAZ toughness for large heat input welding of developed steel plate. The microstructures in HAZ are transformed from mainly fine ferrite and bainite at 100kJ/cm, through an intermediate stage of ferrite, bainite and pearlite at 200 and 300kJ/cm, to nearly fine ferrite and pearlite at 400kJ/cm. The prior austenite grain size and ferrite grain size in HAZ are controlled to ～50 and ～20μm, respectively. The high HAZ toughness is due to the inhibition of prior austenite grain size at high temperatures and the formation of beneficial microstructures to HAZ toughness during continuous cooling.
文摘为定量化设施果类蔬菜养分投入,实现设施果蔬优质高产、绿色高效生产,本研究以山东省典型设施果类蔬菜为研究对象,基于通过农户调研与土壤样品采集测定收集的数据,结合对现有文献的综述,使用生命周期评价方法,系统分析研究区域设施果类蔬菜生产的施肥现状、土壤养分状况和环境代价及其相关关系。结果表明:山东省主栽设施果类蔬菜养分投入量高,设施番茄、黄瓜、辣椒、茄子的氮(以N计)、磷(以P2O5计)、钾(以K2O计)投入量平均达到743、600、740 kg·hm^(-2),施肥变异系数较大(CV=30.3%~43.9%),大量的肥料投入造成了较高的养分盈余,进而导致表层土壤(0~30 cm)养分含量显著升高,同时导致了较高的环境代价。设施果类蔬菜的单位面积上活性氮损失、温室气体排放、富营养化效应和酸化效应均以黄瓜生产系统最高,分别达225 kg·hm^(-2)、10058 kg CO_(2e)·hm^(-2)、124 kg PO_(4e)·hm^(-2)和63.4 kg SO_(2e)·hm^(-2),其次是茄子、番茄和辣椒。氮素盈余是导致活性氮损失的最主要因素,氮、磷、钾肥料的生产过程和施用过程是设施果类蔬菜温室气体排放、富营养化效应和酸化效应的主要贡献因子,贡献率高达80%以上。因此,为保证设施果类蔬菜产业绿色优质高质量发展,应通过优化设施蔬菜养分资源综合管理策略来减少养分盈余、降低环境代价。
基金Under the auspices of National Science Foundation of China(Grant no.40971062)
文摘Rising labor opportunity cost is one of the most important characteristics of farmers' economic environment in present China,and brings great agricultural land use changes correspondingly.Based on the stratified random sample of rural households in Sui County,this paper estimates the opportunity cost of farm labors,and then analyzes its effect on farmers' agricultural land use decisions.The findings show that the households with higher labor opportunity cost are more likely to reduce labor intensity and increase labor-saving input in their land use decisions.From the descriptive analysis,we also find these households always prefer grain crop planting,reduce yield-raising input or even rent out their cultivated land.As labor and yield-raising input are two essential positive factors for grain production,continuous declining of labor input and yield-raising input caused by rising labor opportunity cost may influence the grain yield per unit area in the future.
