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排序方式: 共有112条查询结果,搜索用时 578 毫秒
61.
参照《水质化学需氧量的测定重铬酸盐法》(HJ 828—2017)标准,设计出三水平四因素正交试验方案,考察水样体积、消解温度、消解时间和硫酸银-硫酸溶液加入量对化学需氧量(COD;)测量值的影响。研究表明:测定COD_(Cr)质量浓度>50 mg/L的样品时,影响COD;测定值的主次因素排序为:水样体积、硫酸银-硫酸溶液加入量、消解时间和消解温度;COD_(Cr)测定的最优试验条件为:水样体积5 m L、消解温度200℃、消解时间90 min、硫酸银-硫酸溶液加入量10 m L。与《HJ 828—2017》标准中的监测条件相比,该方法分析时间更短、加入的硫酸银-硫酸溶液体积更少,在应急监测中具有更高的参考价值。 相似文献
62.
We present a simple dynamic model to get some key insights about the substitution of renewable for nonrenewable resources and the consequences for sustainability. We highlight the role of the elasticity of substitution (technological component) to determine the adjustment of production as a response to scarcity and growing ability of resources (environmental component). In some cases, the model predicts a smooth substitution of renewable for nonrenewable resources, but this process could work in the opposite direction if renewable resources are temporarily beyond their maximum sustainable yield, so that their marginal natural growth is negative. If substitution possibilities are high enough, it may be optimal to suspend the extraction of a resource to allow the biomass to regenerate. A production process is more likely to be sustainable the more heavily it depends on renewable, rather than nonrenewable resources. 相似文献
63.
Comparison of labour productivities and wage-to-price ratios suggests that the Coal Board's behaviour was not profit-maximizing. This does not make the use of production functions to determine optimal scale very relevant. In particular, the current debates about efficiency and closures cannot be approached solely or mainly from production function analysis. 相似文献
64.
Yannick Outreman Anne Le Ralec Eric Wajnberg Jean-Sébastien Pierre 《Behavioral ecology and sociobiology》2005,58(2):208-217
The present study aimed to address how an insect parasitoid makes patch-departure decisions from various types of host patches and how previous patch experiences in the environment modify this decision-making process. Experiments were done with the parasitic wasp Aphidius rhopalosiphi attacking the grain aphid Sitobion avenae. In the experiments, wasps were observed in a laboratory environment containing several patches of various host densities, and behavioural records were analysed using a Coxs proportional hazards model. Consideration of the effect of the within-patch experience gave a classic pattern of patch-leaving decision rules in parasitoids: A. rhopalosiphi used local information on host quality (i.e. numbers of ovipositions or rejections) and availability (i.e. patch density) to determine departure decision. However, consideration of previous patch experiences provided evidence that these departure rules are fundamentally dynamic, responding to the physiological state of the animal and the information it has about its environment. Results showed that A. rhopalosiphi decreased its tendency to leave the visited patch after an oviposition. However, when a female has already laid several other eggs in the environment, such an incremental mechanism gradually switched to a decremental one. Hence, A. rhopalosiphi responded to egg-load depletion by leaving the visited patches sooner and by depositing a smaller number of eggs in those patches, which probably led to a decreased level of superparasitism. Results also indicated that previous experiences enabled wasps to estimate spatial host distribution and then to adjust their behavioural decisions accordingly. Thus, A. rhopalosiphi was shown to adjust its patch residence time according to the quality and the number of the patches previously visited. These proximate mechanistic rules adopted by A. rhopalosiphi females are discussed in the context of general predictions from optimality models.Communicated by D. Gwynne 相似文献
65.
分析了主成份子集合选择法的应用过程,指出该方法只考虑了各测点的污染随机变化信息.而忽略了各测点的污染水平信息;用该方法所得到的优化点集不能正确地反映地区大气污染水平.因而主成份子集合选择法不宜应用于大气例行监测的优化布点研究中. 相似文献
66.
Guillaume Rieucau William L. Vickery G. Jean Doucet 《Behavioral ecology and sociobiology》2009,63(6):891-897
The giving-up density of food (GUD), the amount of food remaining in a patch when a forager ceases foraging there, can be
used to compare the costs of foraging in different food patches. But, to draw inferences from GUDs, specific effects of foraging
costs (predation risk, metabolic and missed opportunities costs) on GUDs have to be identified. As high predation risk, high
metabolic costs and abundant food all should produce high GUDs, this does not allow us to infer directly the quality of a
habitat. In order to separate the effect of each foraging cost, we developed an optimal foraging model based on food supplementation.
We illustrate the use of our model in a study where we assessed the impact of a power line right-of-way in a white-tailed
deer (Odocoileus virginianus) winter yard by determining whether the negative effects of cover loss outweigh the positive effects of browse regeneration. 相似文献
67.
68.
Marco Antonio Leonel Caetano Douglas Francisco Marcolino Gherardi 《Ecological modelling》2011,222(15):2835-2840
The Brazilian government has already acknowledged the importance of investing in the development and application of technologies to reduce or prevent CO2 emissions resulting from human activities in the Legal Brazilian Amazon (BA). The BA corresponds to a total area of 5 × 106 km2 from which 4 × 106 km2 was originally covered by the rain forest. One way to interfere with the net balance of greenhouse gases (GHG) emissions is to increase the forest area to sequester CO2 from the atmosphere. The single most important cause of depletion of the rain forest is cattle ranching. In this work, we present an effective policy to reduce the net balance of CO2 emissions using optimal control theory to obtain a compromising partition of investments in reforestation and promotion of clear technology to achieve a CO2 emission target for 2020. The simulation indicates that a CO2 emission target for 2020 of 376 million tonnes requires an estimated forest area by 2020 of 3,708,000 km2, demanding a reforestation of 454,037 km2. Even though the regional economic growth can foster the necessary political environment for the commitment with optimal emission targets, the reduction of 38.9% of carbon emissions until 2020 proposed by Brazilian government seems too ambitious. 相似文献
69.
The solar energy received by a flat plate collector is calculated for various tracking modes: fixed, inclination depending on the season or the month; variable inclination with fixed azimuth, variable azimuth with fixed inclination and double tracking. At first, we take into account only the sun position and then, we use validated radiation models for estimating the ground solar radiation. Using a tracker is questionable particularly if the additional costs are taken into account. A good solution to increase the available solar energy is to change seasonally the inclination, that is, 4 times per year. 相似文献
70.
Over the past 65 years, forest tenure in China has oscillated unpredictably between private and village property regimes. This policy-induced uncertainty has distorted the harvesting decisions of individuals granted rights to grow trees and has lowered the value of China׳s forest output. We provide an analytical framework for assessing these effects quantitatively. Understanding the consequences of this policy-induced uncertainty is particularly important since China is currently engaged in an ambitious plan to increase its domestic supply of timber. To conduct this analysis, we extend the literature on forestry economics when there is a risk of loss due to forest fire or pests. We (1) take account of the possibility that replanting can only resume after an interval of uncertain length (with immediate replanting as a special Case); (2) investigate the effects of compensation for such losses based only on the net value of the stand of trees at the time of the loss; and (3) compare it to compensation that would leave the wealth and rotation decisions of the farmer unaffected by the presence of uncertainty. 相似文献