Through the research into college students' English autonomous learning ability of the non-English major students. That the cause why university students' English autonomous learning ability is weak is proved to be ...Through the research into college students' English autonomous learning ability of the non-English major students. That the cause why university students' English autonomous learning ability is weak is proved to be that they do not value the use of learning strategies. The use of learning strategies can promote the formation and enhancement of autonomous learning ability of the learners. Metacognitive strategy is a high-level management skill which can enable the learners to plan, regulate, monitor and evaluate actively their own learning process. Massive researches have proved whether metacognitive strategy is used successfully or not can directly affect the student learning result. So, it is necessary for teachers to cultivate and train the students to use metacogitive strategy in the university English teaching.展开更多
Contagious bovine pleuro-pneumonia (CBPP) is one of the endemic and life-threatening livestock diseases in the arid and semi-arid land areas (ASALs) of Kenya, which justify the case for the control of livestock di...Contagious bovine pleuro-pneumonia (CBPP) is one of the endemic and life-threatening livestock diseases in the arid and semi-arid land areas (ASALs) of Kenya, which justify the case for the control of livestock diseases to avoid the spread of such diseases from the ASALs to the rest of the country, and a CBPP control quarantine line (CQL) that to help prevent the spread of CBPP from the ASALs of North-eastern Kenya to the rest of the country has been in existence since the colonial (pre-1963) times in Kenya. However, the livestock keepers in the ASALs view the CQL as an impediment to their main source of livelihoods because it entails livestock movement restrictions, thus constraining unfettered livestock marketing. Available literature shows that there is a dearth of information on the economics of livestock diseases control in Kenya in terms of its impacts on social welfare. Employing the CQL as a case study, this study shows that an application of analytic techniques that combine disease risk analysis and conventional cost-benefit modelling that incorporates some aspects that are specific to livestock diseases and their control strategies can generate indices of economic impacts of livestock diseases control on social welfare. The study finds that the livestock keepers and traders in Kenya do not consider CBPP a major problem to warrant livestock movement restrictions, yet the official records of the veterinary authorities indicate that CBPP is a major threat to the cattle industry in Kenya. Annually, the government spends substantial resources on the CQL operation and maintenance and also on CBPP surveillance and monitoring to contain the CBPP menace in Kenya. This study shows that such expenditures are economically and socially justifiable. Nevertheless, the study finds some operational inefficiencies in the enforcement of the CQL requirements. The authors, therefore, undertake an evaluation of alternative CBPP control strategies and conclude that it would be more cost effective to shift the CQL from its current location to the international borders of the arid districts, provided that this action is preceded by adequate CBPP control preparatory measures, as described in the paper.展开更多
Cymbopogon nardus is an invasive grass weed in the grazing lands of Uganda affecting growth of desirable species and impeding movement of livestock. Farmers have for long used manual removal with a hand hoe to control...Cymbopogon nardus is an invasive grass weed in the grazing lands of Uganda affecting growth of desirable species and impeding movement of livestock. Farmers have for long used manual removal with a hand hoe to control the weed to allow growth of palatable species. In order to reduce on the drudgery associated with the hand hoe, a trial was set up to evaluate removal with a hand hoe, use of fire and spraying the weed with glyphosate herbicide to control Cymbopogon nardus. Eight treatments associated with the different control strategies were replicated on four sites in the land use system. Both manual removal with a hand hoe and spraying with glyphosate herbicide were effective in controlling Cymbopogon nardus with 95% and 92% kill of Cymbopogon tussocks, respectively. The differences between the two control methods were not significant. Plant species biodiversity recovery was faster in the manually controlled plots than in those sprayed with glyphosate, but the number of species was not significantly different. The frequency of occurrence of species was however significantly different with manually controlled plots registering a higher frequency of the species. Fire had no effect as a control strategy, but instead increased the number of tussocks, growth vigour of the re-growth, flowering and hence seed setting. After three seasons, no significant difference was observed in species biodiversity between manual and herbicide control. These results suggest that herbicides could effectively be used to control Cymbopogon nardus to cut on costs and avoid the drudgery normally associated with manual control.展开更多
Organic Rankine Cycles(ORCs) are an effective way to produce electricity from low-grade heat sources, which cannot be effectively obtained using conventional high-temperature Rankine cycles. Due to the lack of availab...Organic Rankine Cycles(ORCs) are an effective way to produce electricity from low-grade heat sources, which cannot be effectively obtained using conventional high-temperature Rankine cycles. Due to the lack of available information regarding the real Organic Rankine Cycle units on industrial level, off-design simulation under diversified operating conditions plays a significant role for both the system performance prediction and control strategy design. This paper summarizes the theoretical basis, modeling approaches and tools for ORC off-design simulations. Firstly, a review was conducted on the individual state-of-the-art convective heat transfer correlations and void fraction models. Secondly, different kinds of modeling approaches and simulation tools were proposed, highlighting their relevant characteristics, and were categorized for their specific applications. Moreover, an in-depth analysis of technical challenges related to various applications and focusing on the model accuracy and complexity, computational efficiency, as well as the model compatibility were extensively described and discussed. Finally, the current research trends in this field and the development for further investigations were presented.展开更多
Heavy-duty legged robots have been regarded as one of the important developments in the field of legged robots because of their high payload-total mass ratio,terrain adaptability,and multitasking.The problems associat...Heavy-duty legged robots have been regarded as one of the important developments in the field of legged robots because of their high payload-total mass ratio,terrain adaptability,and multitasking.The problems associated with the development and use of heavy-duty legged robots have motivated researchers to conduct many important studies,covering topics related to the mechanical structure,force distribution,control strategy,energy efficiency,etc.Overall,heavy-duty legged robots have three main characteristics:greater body masses,larger body sizes,and higher payload-total mass ratios.Thus,various heavy-duty legged robots and their performances are reviewed here.This review presents the current developments with regard to heavy-duty legged robots.Also,the main characteristics of high-performance heavy-duty legged robots are determined and conclusions are drawn.Furthermore,the current research of key techniques of heavy-duty legged robots,including the mechanical structure,force distribution,control method,and power source,is described.To assess the transportation capacity of heavy-duty legged robots,performance evaluation parameters are proposed.Finally,problems that need further research are addressed.展开更多
United Nations Political Declaration 2011 on HIV and AIDS calls to reduce the sexual transmission and the transmission of HIV among people, who inject drugs by 50% by 2015, through different control strategies and pre...United Nations Political Declaration 2011 on HIV and AIDS calls to reduce the sexual transmission and the transmission of HIV among people, who inject drugs by 50% by 2015, through different control strategies and precautionary measures. In this paper, we propose and study a simple SI type model that considers the effect of various precaution- ary measures to control HIV epidemic. We show, unlike conventional epidemic models, that the basic reproduction number which essentially considered as the disease eradica- tion condition is no longer sufficient to eliminate HIV infection. In particular, we show that even when the basic reproduction number is made less than unity, the disease may persist if the initial outbreak is not low. Eradication of disease is however guaranteed if the ensemble control measure exceeds some upper critical value. It is also shown that an epidemic model with mass action incidence may exhibit backward bifurcation and bistability if density-dependent demography is considered. Our theoretical study thus indicates that extra attention should be given in controlling HIV epidemic to achieve the desired result.展开更多
文摘Through the research into college students' English autonomous learning ability of the non-English major students. That the cause why university students' English autonomous learning ability is weak is proved to be that they do not value the use of learning strategies. The use of learning strategies can promote the formation and enhancement of autonomous learning ability of the learners. Metacognitive strategy is a high-level management skill which can enable the learners to plan, regulate, monitor and evaluate actively their own learning process. Massive researches have proved whether metacognitive strategy is used successfully or not can directly affect the student learning result. So, it is necessary for teachers to cultivate and train the students to use metacogitive strategy in the university English teaching.
文摘Contagious bovine pleuro-pneumonia (CBPP) is one of the endemic and life-threatening livestock diseases in the arid and semi-arid land areas (ASALs) of Kenya, which justify the case for the control of livestock diseases to avoid the spread of such diseases from the ASALs to the rest of the country, and a CBPP control quarantine line (CQL) that to help prevent the spread of CBPP from the ASALs of North-eastern Kenya to the rest of the country has been in existence since the colonial (pre-1963) times in Kenya. However, the livestock keepers in the ASALs view the CQL as an impediment to their main source of livelihoods because it entails livestock movement restrictions, thus constraining unfettered livestock marketing. Available literature shows that there is a dearth of information on the economics of livestock diseases control in Kenya in terms of its impacts on social welfare. Employing the CQL as a case study, this study shows that an application of analytic techniques that combine disease risk analysis and conventional cost-benefit modelling that incorporates some aspects that are specific to livestock diseases and their control strategies can generate indices of economic impacts of livestock diseases control on social welfare. The study finds that the livestock keepers and traders in Kenya do not consider CBPP a major problem to warrant livestock movement restrictions, yet the official records of the veterinary authorities indicate that CBPP is a major threat to the cattle industry in Kenya. Annually, the government spends substantial resources on the CQL operation and maintenance and also on CBPP surveillance and monitoring to contain the CBPP menace in Kenya. This study shows that such expenditures are economically and socially justifiable. Nevertheless, the study finds some operational inefficiencies in the enforcement of the CQL requirements. The authors, therefore, undertake an evaluation of alternative CBPP control strategies and conclude that it would be more cost effective to shift the CQL from its current location to the international borders of the arid districts, provided that this action is preceded by adequate CBPP control preparatory measures, as described in the paper.
文摘Cymbopogon nardus is an invasive grass weed in the grazing lands of Uganda affecting growth of desirable species and impeding movement of livestock. Farmers have for long used manual removal with a hand hoe to control the weed to allow growth of palatable species. In order to reduce on the drudgery associated with the hand hoe, a trial was set up to evaluate removal with a hand hoe, use of fire and spraying the weed with glyphosate herbicide to control Cymbopogon nardus. Eight treatments associated with the different control strategies were replicated on four sites in the land use system. Both manual removal with a hand hoe and spraying with glyphosate herbicide were effective in controlling Cymbopogon nardus with 95% and 92% kill of Cymbopogon tussocks, respectively. The differences between the two control methods were not significant. Plant species biodiversity recovery was faster in the manually controlled plots than in those sprayed with glyphosate, but the number of species was not significantly different. The frequency of occurrence of species was however significantly different with manually controlled plots registering a higher frequency of the species. Fire had no effect as a control strategy, but instead increased the number of tussocks, growth vigour of the re-growth, flowering and hence seed setting. After three seasons, no significant difference was observed in species biodiversity between manual and herbicide control. These results suggest that herbicides could effectively be used to control Cymbopogon nardus to cut on costs and avoid the drudgery normally associated with manual control.
基金financially supported by the National Key Basic Research Program of China 973 Program(Grant No.2014CB249201)
文摘Organic Rankine Cycles(ORCs) are an effective way to produce electricity from low-grade heat sources, which cannot be effectively obtained using conventional high-temperature Rankine cycles. Due to the lack of available information regarding the real Organic Rankine Cycle units on industrial level, off-design simulation under diversified operating conditions plays a significant role for both the system performance prediction and control strategy design. This paper summarizes the theoretical basis, modeling approaches and tools for ORC off-design simulations. Firstly, a review was conducted on the individual state-of-the-art convective heat transfer correlations and void fraction models. Secondly, different kinds of modeling approaches and simulation tools were proposed, highlighting their relevant characteristics, and were categorized for their specific applications. Moreover, an in-depth analysis of technical challenges related to various applications and focusing on the model accuracy and complexity, computational efficiency, as well as the model compatibility were extensively described and discussed. Finally, the current research trends in this field and the development for further investigations were presented.
基金supported by the National Basic Research Program of China("973" Program)(Grant No.2013CB035502)the International Sci-ence and Technology Cooperation Project with Russia(Grant No.2010DFR70270)+2 种基金the National Natural Science Foundation of China(Grant No.51275106)the"111" Project(Grant No.B07018)the Key Laboratory Opening Funding of Aerospace Mechanism and Control(Grant No.HIT.KLOF.2010057)
文摘Heavy-duty legged robots have been regarded as one of the important developments in the field of legged robots because of their high payload-total mass ratio,terrain adaptability,and multitasking.The problems associated with the development and use of heavy-duty legged robots have motivated researchers to conduct many important studies,covering topics related to the mechanical structure,force distribution,control strategy,energy efficiency,etc.Overall,heavy-duty legged robots have three main characteristics:greater body masses,larger body sizes,and higher payload-total mass ratios.Thus,various heavy-duty legged robots and their performances are reviewed here.This review presents the current developments with regard to heavy-duty legged robots.Also,the main characteristics of high-performance heavy-duty legged robots are determined and conclusions are drawn.Furthermore,the current research of key techniques of heavy-duty legged robots,including the mechanical structure,force distribution,control method,and power source,is described.To assess the transportation capacity of heavy-duty legged robots,performance evaluation parameters are proposed.Finally,problems that need further research are addressed.
文摘United Nations Political Declaration 2011 on HIV and AIDS calls to reduce the sexual transmission and the transmission of HIV among people, who inject drugs by 50% by 2015, through different control strategies and precautionary measures. In this paper, we propose and study a simple SI type model that considers the effect of various precaution- ary measures to control HIV epidemic. We show, unlike conventional epidemic models, that the basic reproduction number which essentially considered as the disease eradica- tion condition is no longer sufficient to eliminate HIV infection. In particular, we show that even when the basic reproduction number is made less than unity, the disease may persist if the initial outbreak is not low. Eradication of disease is however guaranteed if the ensemble control measure exceeds some upper critical value. It is also shown that an epidemic model with mass action incidence may exhibit backward bifurcation and bistability if density-dependent demography is considered. Our theoretical study thus indicates that extra attention should be given in controlling HIV epidemic to achieve the desired result.