排序方式: 共有27条查询结果,搜索用时 31 毫秒
11.
Economists have proved that the exclusion of the effects of irreversibility from a decision-making framework is a specification error which leads to sub-optimal solutions. Consequently, in any cost-benefit framework, the effects of an irreversibility are included in the form of an option value. Unfortunately, in the real world, there exist certain potential irreversibilities that jeopardize the very existence of the decision-making entity, were they to occur. We demonstrate that if the effects of such irreversibilities are modeled in terms of a finite option value (in cost-benefit analysis) then the optimal solutions derived therefrom may be unable to avert a potential catastrophe. In theory, an infinite option value should lead to catastrophe-averting decisions in such situations. However, in practice, such mathematical formulations tend to be intractable. In many situations, irreversible catastrophes proceed from a positive reinforcement of fluctuations in system behavior, primarily due to sympathetic responses in sub-systems. Engineers have designed relatively low-cost methods to dampen similar oscillations in physical systems. We demonstrate how such engineering type analysis can be used successfully to identify catastrophe-averting policies for a model ecosystem that faces irreversible famine that must be avoided as a precondition for survival. 相似文献
12.
Robert U. Ayres Steven M. Miller 《Journal of Environmental Economics and Management》1980,7(4):353-371
We develop an optimal growth model that includes several important new features. First, technological change is endogenously related to the growth of “knowledge.” Investment may be directed either towards physical capital or knowledge (or both). Knowledge becomes an effective substitute for scarce resources by increasing the technical efficiency of resource utilization both for consumption and in capital. Nevertheless, a finite quantity resource must be embodied in capital and a finite flow is required for depreciation. Thus, there is an upper limit to technical efficiency and economic growth is thus ultimately limited by the availability of renewable resources. For a simple aggregate production function it is shown that technical efficiency never approaches unity on an optimal path. 相似文献
13.
Robert U. Ayres 《Environmental Modeling and Assessment》1997,2(3):107-128
There are four major elements that are required by the biosphere in significantly greater quantities than they are available in nature. These four are carbon (C), nitrogen (N), sulfur (S) and phosphorus (P). (Hydrogen and oxygen, the other two major ingredients of organic materials, are not scarce in the earth's crust, though oxygen is also recycled along with carbon.) These natural cycles are driven by geological, hydrological, atmospheric and biological processes. In effect, the geo‐biosphere is a dissipative system (in the sense of Prigogine) in a quasi steady state, far from thermodynamic equilibrium. This steady state is maintained by the influx of solar exergy. Interruption or disturbance of these natural cycles as a consequence of human industrial/economic activity could adversely affect the stability of the biosphere, and might possibly reduce its productivity. Indeed, because the more complex long‐lived organisms such as large mammals (including man), birds and even trees evolve more slowly than smaller short‐lived organisms, the very nature of an altered steady state might not be favorable to many existing species. Thus there is even a potential threat to human survival itself. Unfortunately, the interactions among these cycles have received relatively little attention up to now. 相似文献
14.
Van Zwieten L Ayres MR Morris SG 《Environmental pollution (Barking, Essex : 1987)》2003,124(2):331-339
The impacts of arsenic co-contamination on the natural breakdown of 1,1,l1-trichloro-2,2-bis(4-chlorophenyl)ethane (DDT) in soil are investigated in a study of 12 former cattle dip sites located in northeastern NSW, Australia. This study examines the relationship between the intrinsic breakdown of DDT to 1,1 -dichloro-2,2-bis(4-chlorophenyl)ethane (DDD) and 1,l-dichloro-2,2-bis(4-chlorophenyl)ethylene (DDE), and the impacts of arsenic co-contamination on this breakdown. Between-site analysis demonstrated that arsenic at 2000 mg/kg gave a 50% reduction in the concentration of DDD compared to background arsenic of 5 mg/kg.Within-site analysis also showed the ratio of DDT:DDD increased in soils as arsenic concentrations increased. This within-site trend was also apparent with the DDT:DDE ratio, suggesting inhibition of DDT breakdown by arsenic co-contamination. Microbial activity was inhibited as residues of total DDTs and arsenic increased. Hence arsenic co-contamination and high concentrations of DDT in soil may result in an increased persistence of DDT in the environment studied. 相似文献
15.
Studies of collaborative watershed groups show that effective leadership is an important factor for success. This research
uses data from in-depth interviews and meeting observation to qualitatively examine leadership in a Midwestern collaborative
watershed group operating with government funding. One major finding was a lack of role definition for volunteer steering-committee
members. Lack of role clarity and decision-making processes led to confusion regarding project management authority among
the group, paid project staff members, and agency personnel. Given the important role of government grants for funding projects
to protect water quality, this study offers insight into leadership issues that groups with Clean Water Act Section 319 (h)
funds may face and suggestions on how to resolve them. 相似文献
16.
17.
18.
Jacquelyn Orlando Donna Branson George Ayres Richard Leavitt 《Journal of environmental science and health. Part. B》2013,48(5):617-628
Abstract A technique for comparing pesticide penetration through fabric was devised. It involved passing fabric swatches through a controlled spray system and measuring the pesticide residue transferring on and through the tested fabric. Six variations in fabric were selected for testing: 100% cotton woven chambray, Scotch‐guard® treated chambray, Tyvek® , Crowntex® , and two variations of Gore Tex®. Guthion® (azinphos‐methyl) was chosen as the insecticide for controlled use in this experiment because of its widespread use and relatively high toxicity. Gas Chromatographie analysis of the amount of Guthion® transferred through the outer fabric was made by the use of analysis of variance (ANOVA) and Duncan's multiple range test. The ANOVA for experiment replication showed no significant difference among the replications of each fabric. The treatment ANOVA was highly significant at the 0.01 level. Duncan's multiple range test further analyzed the differences in the treatment, and three groups were found to be significantly different from each other. The two types of Gore Tex®, Tyvek® and Crowntex® comprised the group permitting the least penetration. Scotch‐guard® treated chambray followed, and untreated chambray allowed the greatest penetration. 相似文献
19.
Van Zwieten L Ahmad N Marolt RS Ayres M Morris S 《Journal of environmental science and health. Part. B》2001,36(5):501-516
Soil taken from a former cattle tick dip site in NSW Australia, was remediated with a chemical leaching technology. The pre- and post-remediated soil (20g) was dispersed in water (100mL) and subjected to passive diffusion using polymeric membranes. The remediation reduced tDDT from 1174.3 microg/g to 102.9 microg/g (ash weight basis), which was further reduced to 43.2 microg/g with composting. The membranes accumulated 41.3 microg tDDT/g from the dip soil, 49.2 microg tDDT/g from the chemically leached soil and 3.1 microg tDDT/g from the leached composted soil. The chemical leaching removed over 90% of the tDDT, but released soil bound DDT, which was converted to DDE, while 2.99 microg/g was accumulated by the membranes from dip soil, 37.52 microg/g was accumulated from remediated soil. Composting, however, almost eliminated the availability for passive diffusion by the membranes from 50-60 microg/g in remediated soil to 3 -3.5 microg/g in composted soil. Variability studies of the membranes using eight replicates demonstrated that the accumulation by the membranes was reproducible with an average relative error of 20.3% for p,p'-DDT in soil type two, whilst the lowest average relative error for p,p'-DDE was 4.3%, suggesting that triplicate analyses will achieve acceptable accuracy. 相似文献
20.
The results of analyses for polychlorodibenzofuran (PCDF) content in two samples of polychlorobiphenyl (PCB) from used electrical transformers are presented and discussed. In neither sample was there evidence for enhanced PCDF concentrations even though one of them had been subjected to overheating while in service. 相似文献