A two-agent dynamic model with an invasive weed diffusion externality: an application to Yellow Starthistle (Centaurea solstitialis L.) in New Mexico

This paper presents a bioeconomic model for two agents, a cattle rancher and a non-rancher, with interdependencies between their individual effort of invasive weed management and profitability. Dynamic simulations allow us to find numerically the optimal effort of weed control over a 5-year time horizon under a variety of beginning infestation levels. In a base-case scenario without governmental cost-share of control costs, we find that efforts to control the weed are not profitable. The base-case scenarios also indicate that grazing contributes to giving the invasive weed a competitive edge. A second series of simulations include incentive payments for weed control which are set at the minimum level required to have a net positive impact on the rancher's profitability. From these simulations, we find that the level of infestation impacts the size of the incentive necessary to get the agent to control the weeds and that the incentive payments impact the level of effort of the rancher. In addition, results reveal that the higher incentive payments for lower levels of weed infestations reduce the total cumulative incentive payments over time. Efficient policies directed towards management of invasive weeds may need to be adjusted for each individual case.     

When is overfishing underfishing?

The term overfishing is being used with increasing frequency to designate an undesirable level of fisheries exploitation. All too often, however, the term is taken as being self-evident. This article demonstrates that many definitions of overfishing are possible, depending essentially on what objective is being pursued for the fishery. Various possible biological and economic objectives are considered, both in a static and dynamic model of the fishery. Consideration is given to the best utilization of the fish stock from the viewpoint of the individual fishermen as well as that of society. It is shown that overfishing by one definition may be underfishing by another, and it is concluded therefore that anyone using the term overfishing ought, as a matter of course, to define it.     

Assessing the demand of solid waste disposal in urban region by urban dynamics modelling in a GIS environment

The twentieth century saw a dramatic increase in the production of urban solid waste, reflecting unprecedented global levels of economic activity. Despite some efforts to reduce and recover the waste, disposal in landfills is still the most usual destination. However, landfill has become more difficult to implement because of its increasing cost, community opposition to landfill siting, and more restrictive environmental regulations regarding the siting and operation of landfills. Moreover, disposal in landfill is the waste destination method with the largest demand for land, while land is a resource whose availability has been decreasing in urban systems. Shortage of land for landfills is a problem frequently cited in the literature as a physical constraint. Nonetheless, the shortage of land for waste disposal has not been fully studied and, in particular, quantified. This paper presents a method to quantify the relationship between the demand and supply of suitable land for waste disposal over time using a geographic information system and modelling techniques. Based on projections of population growth, urban sprawl and waste generation the method can allow policy and decision-makers to measure the dimension of the problem of shortage of land into the future. The procedure can provide information to guide the design and schedule of programs to reduce and recover waste, and can potentially lead to a better use of the land resource. Porto Alegre City, Brazil was used as the case study to illustrate and analyse the approach. By testing different waste management scenarios, the results indicated that the demand for land for waste disposal overcomes the supply of suitable land for this use in the study area before the year 2050.     

The time-varying factors influencing the recycling rate of products

In Europe targets have been laid down by EU legislation for the recycling rate of end-of-life vehicles to be achieved within the nearby future. It is illustrated in this paper that the definition of the recycling rate and the realisation of the imposed targets are very much dependent on different parameters such as the changing lifetime of the product and product design. It may seem obvious that the recycling rate is determined by various time-varying factors, however, this paper endeavours to describe and quantify the role of these factors on the recycling rate over time by the use of a dynamic systems model. This model permits the prediction of the recycling rate as a function of the numerous presented parameters, changing design scenarios etc. In addition, different definitions of the recycling rate will be presented and discussed. This will lead to a better understanding of the parameters affecting the recycling system and a more precise understanding of the recycling targets and their realisation as imposed by EU legislation. This paper focuses on cars, but the discussion and the definitions derived are equally valid for any end-of-life product.     

大吨位桥式起重机主梁静刚度检测方法

探索了一种基于弹性理论的桥式起重机静刚度的近似测量方法,可大幅度减轻配重工作的难度并在现场检测中得到应用。     

基于高速列车作用引起的铁道线路垂向动态响应的研究

研究了在高速列车作用下,由运行质量变化和沿线路方向的弹性基础支撑的非均匀性等所引起的对铁道线路的垂向动态响应.在时域内使用FEA法推导建立了高速列车/线路系统相互作用的运动方程,通过使用数值积分算法,分析了车辆运行速度、移动质量、线路的弹性基础支撑及其非均匀性等参数变化对铁道线路动态性能的影响, 通过与通用分析模型结果进行的对比显示了良好的一致性.研究表明轨枕失效区域对钢轨的动态响应影响显著,在非均匀弹性基础支撑上钢轨的变形与移动质量的大小成反比,但在均匀基础支撑上钢轨的变形则与移动质量的大小无关.     

锚杆支护巷道安全监测技术

锚杆支护巷道顶板冒落具有突发性和冒落面积大的特点,安全监测非常必要.笔者介绍了国内近年来最新研制的CM-200型测力锚杆、GYS-300型锚杆(索)测力计、LBY-3型顶板离层指示仪、ZW-4型遥测多点位移计等监测仪器;提出锚杆支护巷道动态信息施工方法:监测施工、监测信息反馈、检验和修正设计,循环往复,以达到最佳施工效果.