The optimal path planning for fixed-wing unmanned aerial vehicles(UAVs) in multi-target surveillance tasks(MTST) in the presence of wind is concerned.To take into account the minimal turning radius of UAVs,the Dubins ...The optimal path planning for fixed-wing unmanned aerial vehicles(UAVs) in multi-target surveillance tasks(MTST) in the presence of wind is concerned.To take into account the minimal turning radius of UAVs,the Dubins model is used to approximate the dynamics of UAVs.Based on the assumption,the path planning problem of UAVs in MTST can be formulated as a Dubins traveling salesman problem(DTSP).By considering its prohibitively high computational cost,the Dubins paths under terminal heading relaxation are introduced,which leads to significant reduction of the optimization scale and difficulty of the whole problem.Meanwhile,in view of the impact of wind on UAVs' paths,the notion of virtual target is proposed.The application of the idea successfully converts the Dubins path planning problem from an initial configuration to a target in wind into a problem of finding the minimal root of a transcendental equation.Then,the Dubins tour is derived by using differential evolution(DE) algorithm which employs random-key encoding technique to optimize the visiting sequence of waypoints.Finally,the effectiveness and efficiency of the proposed algorithm are demonstrated through computational experiments.Numerical results exhibit that the proposed algorithm can produce high quality solutions to the problem.展开更多
Reducing cost of service is an important goal for resource discovery and interaction technologies. The shortcomings of transhipment-method and hibernation-method are to increase holistic cost of service and to slower ...Reducing cost of service is an important goal for resource discovery and interaction technologies. The shortcomings of transhipment-method and hibernation-method are to increase holistic cost of service and to slower resource discovery respectively. To overcome these shortcomings, a context-aware computing-based method is developed. This method, firstly, analyzes the courses of devices using resource discovery and interaction technologies to identify some types of context related to reducing cost of service, then, chooses effective methods such as stopping broadcast and hibernation to reduce cost of service according to information supplied by the context but not the transhipment-method’s simple hibernations. The results of experiments indicate that under the worst condition this method overcomes the shortcomings of transhipment-method, makes the “poor” devices hibernate longer than hibernation-method to reduce cost of service more effectively, and discovers resources faster than hibernation-method; under the best condition it is far better than hibernation-method in all aspects.展开更多
Payments for ecosystem service （PES） schemes have spread all over developing countries in the last 20 years or so. PES schemes often have high opportunity costs in terms of foregone uses of goods and services offere...Payments for ecosystem service （PES） schemes have spread all over developing countries in the last 20 years or so. PES schemes often have high opportunity costs in terms of foregone uses of goods and services offered by the environment. It is within this scope that economic evaluation of environmental goods and services plays a role. In this paper we surveyed articles and studies that report application of economic environmental valuation procedures in PES schemes. Special attention was paid to data collection and analysis, to theoretical robustness of its procedures and to the aggregation of estimated value. We also scrutinize how these estimates had been incorporated into PES schemes, in particularly in the assessment phase of these schemes. Empirical data from Brazil and other Latin American countries were used, particularly those in the Amazon Basis. Our results reveal a frequent overestimation of the values of ecosystem services calculated through the use of economic valuation methods. Values have been estimated by production function methods （opportunity cost, preventive expenditures, recovering cost or dose-response methods）. As a consequence, estimated values reflect much more willingness to accept compensation by supplier and rarely willingness to pay by consumer of these ecosystem services. Besides this distance between supply and demand, application of valuation methods did not account for problems such as uncertainty, risks, and lack of information. All these limitations have led to wrong decision-making.展开更多
基金Project(61120106010)supported by the Projects of Major International(Regional)Joint Research Program Nature Science Foundation of ChinaProject(61304215,61203078)supported by National Natural Science Foundation of China+1 种基金Project(2013000704)supported by the Beijing Outstanding Ph.D.Program Mentor,ChinaProject(61321002)supported by the Foundation for Innovative Research Groups of the National Natural Science Foundation of China
文摘The optimal path planning for fixed-wing unmanned aerial vehicles(UAVs) in multi-target surveillance tasks(MTST) in the presence of wind is concerned.To take into account the minimal turning radius of UAVs,the Dubins model is used to approximate the dynamics of UAVs.Based on the assumption,the path planning problem of UAVs in MTST can be formulated as a Dubins traveling salesman problem(DTSP).By considering its prohibitively high computational cost,the Dubins paths under terminal heading relaxation are introduced,which leads to significant reduction of the optimization scale and difficulty of the whole problem.Meanwhile,in view of the impact of wind on UAVs' paths,the notion of virtual target is proposed.The application of the idea successfully converts the Dubins path planning problem from an initial configuration to a target in wind into a problem of finding the minimal root of a transcendental equation.Then,the Dubins tour is derived by using differential evolution(DE) algorithm which employs random-key encoding technique to optimize the visiting sequence of waypoints.Finally,the effectiveness and efficiency of the proposed algorithm are demonstrated through computational experiments.Numerical results exhibit that the proposed algorithm can produce high quality solutions to the problem.
文摘Reducing cost of service is an important goal for resource discovery and interaction technologies. The shortcomings of transhipment-method and hibernation-method are to increase holistic cost of service and to slower resource discovery respectively. To overcome these shortcomings, a context-aware computing-based method is developed. This method, firstly, analyzes the courses of devices using resource discovery and interaction technologies to identify some types of context related to reducing cost of service, then, chooses effective methods such as stopping broadcast and hibernation to reduce cost of service according to information supplied by the context but not the transhipment-method’s simple hibernations. The results of experiments indicate that under the worst condition this method overcomes the shortcomings of transhipment-method, makes the “poor” devices hibernate longer than hibernation-method to reduce cost of service more effectively, and discovers resources faster than hibernation-method; under the best condition it is far better than hibernation-method in all aspects.
文摘Payments for ecosystem service （PES） schemes have spread all over developing countries in the last 20 years or so. PES schemes often have high opportunity costs in terms of foregone uses of goods and services offered by the environment. It is within this scope that economic evaluation of environmental goods and services plays a role. In this paper we surveyed articles and studies that report application of economic environmental valuation procedures in PES schemes. Special attention was paid to data collection and analysis, to theoretical robustness of its procedures and to the aggregation of estimated value. We also scrutinize how these estimates had been incorporated into PES schemes, in particularly in the assessment phase of these schemes. Empirical data from Brazil and other Latin American countries were used, particularly those in the Amazon Basis. Our results reveal a frequent overestimation of the values of ecosystem services calculated through the use of economic valuation methods. Values have been estimated by production function methods （opportunity cost, preventive expenditures, recovering cost or dose-response methods）. As a consequence, estimated values reflect much more willingness to accept compensation by supplier and rarely willingness to pay by consumer of these ecosystem services. Besides this distance between supply and demand, application of valuation methods did not account for problems such as uncertainty, risks, and lack of information. All these limitations have led to wrong decision-making.
