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701.
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为了探讨3种化合物对温石棉致人胚肺(HEL)细胞DNA链断裂的影响,用不同浓度的柠檬酸铝、混合稀土或亚硒酸钠溶液浸泡温石棉1h后,再将其与HEL细胞共同孵育,利用单细胞凝胶电泳技术,测定了HEL细胞的DNA链断裂程度.结果显示,温石棉可致HEL细胞DNA链断裂,并呈明显的剂量反应关系(r=0.992,P<0.01),其中80μg/mL石棉所致DNA链断裂为对照组的7倍.与未处理温石棉组相比,经3种化合物预处理的温石棉所致HEL细胞DNA链断裂均明显减少,其中用等量柠檬酸铝、混合稀土或亚硒酸钠处理过的石棉,其所致DNA链断裂分别降低了38.3%、61.5%、30.1%,这表明,用上述3种化合物预处理温石棉,有可能减轻温石棉对人类的致癌危害性. 相似文献
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运用生态学原理,从结构元、结构链和结构网3个层次对石辛庄村级农业生态经济系统结构进行调控,并从生态效益、资源利用效益、环境效益和经济效益4个方面对该生态经济系统的调控效果作了评价. 相似文献
705.
Abstract: The bushmeat trade is perceived as a major threat to wild animal populations in the tropics. Little is known of how the trade is organized, however, or of the actors involved in it, impeding the development of effective conservation policy. We investigated the structure and operation of a bushmeat commodity chain in West Africa that supplies a typical urban market, the city of Takoradi in southwestern Ghana. Data were collected from January through February 2000, describing 2430 bushmeat transactions encompassing 17 different taxa from 70 different actors, through a combination of direct observation and semistructured interviews. Five different types of actor traded along the commodity chain: commercial hunters, farmer hunters, wholesalers, market traders, and chopbar (cafe) owners. Bushmeat was traded freely among all these actors, although the primary trade route for terrestrial mammals was from commercial hunters via wholesalers to chopbars. In contrast, invertebrates were only traded by farmer hunters, market traders, and chopbars. Wholesalers captured the largest per capita share of the market (4% of all sales were handled by each wholesaler), whereas the most important vendors were chopbars, which as a group made 85% of all bushmeat sales to the public. Variation in the price of bushmeat was largely explained by transport costs and taste preferences. Transport costs were most significant for hunters and greatest on long journeys involving large loads. Nevertheless, hunters obtained the greatest income per kilogram of bushmeat sold of all actor groups. Our results suggest that there is no single best entry point along the bushmeat commodity chain for conservation intervention. On the contrary, the successful monitoring and management of the bushmeat trade is likely to require a multiactor approach that encompasses most or all actor groups. 相似文献
706.
Bayes methods for combining disease and exposure data in assessing environmental justice 总被引:1,自引:0,他引:1
Waller LANCE A. Louis THOMAS A. Carlin BRADLEY P. 《Environmental and Ecological Statistics》1997,4(4):267-281
Environmental justice reflects the equitable distribution of the burden of environmental hazards across various sociodemographic groups. The issue is important in environmental regulation, siting of hazardous waste repositories and prioritizing remediation of existing sources of exposure. We propose a statistical framework for assessing environmental justice. The framework includes a quantitative assessment of environmental equity based on the cumulative distribution of exposure within population subgroups linked to disease incidence through a dose-response function. This approach avoids arbitrary binary classifications of individuals solely as 'exposed' or 'unexposed'. We present a Bayesian inferential approach, implemented using Markov chain Monte Carlo methods, that accounts for uncertainty in both exposure and response. We illustrate our method using data on leukaemia deaths and exposure to toxic chemical releases in Allegheny County, Pennsylvania. 相似文献
707.
Markov Chain Monte Carlo on optimal adaptive sampling selections 总被引:1,自引:0,他引:1
Chang-Tai Chao 《Environmental and Ecological Statistics》2003,10(1):129-151
Under a Bayesian population model with a given prior distribution, the optimal sampling strategy with a fixed sample size n is an n-phase adaptive one. That is, the selection of the next sampling units should sequentially depend on the information obtained from the previously selected units, including the observed values of interest. Such an optimal strategy is in general not executable in practice due to its intensive computation. In many survey sampling situations, an important problem is that one would like to select a set of units in addition to a certain number of sampling units which have been observed. If the optimal strategy is an adaptive one, the selection of the additional units should take both the labels and the observed values of the already selected units into account. Hence, a simpler optimal two-phase adaptive sampling strategy under a Bayesian population model is proposed in this article for practical interest. A Markov chain Monte Carlo method is used to approximate the posterior joint distribution of the unobserved population units after the first phase sampling, for the optimal selection of the second phase sample. This approximation method is found to be successful to select the optimal second-phase sample. Finally, this optimal strategy is applied to a set of data from a study of geothermal CO2 emissions in Yellowstone National Park as a practical illustrative example. 相似文献
708.
For modeling the distribution of plant species in terms of climate covariates, we consider an autologistic regression model for spatial binary data on a regularly spaced lattice. This model belongs to the class of autologistic models introduced by Besag (1974). Three estimation methods, the coding method, maximum pseudolikelihood method and Markov chain Monte Carlo method are studied and comparedvia simulation and real data examples. As examples, we use the proposed methodology to model the distributions of two plant species in the state of Florida. 相似文献
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