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11.
Walker JC  Sloan LC 《Geotimes》1992,37(6):16-18
We frequently forget that there is more to science than the making of a more precise measurement or a more elaborate calculation. It is even more than applying to new problems the methods that worked on old problems. These activities, which keep most of us busy most of the time, are important, but the new and unexpected discoveries are more important. And many radically new discoveries arise from scientific puzzles, the "anomalies." We believe that studies of past climates have exposed an anomaly that deserves attention and that may result in a fundamentally new understanding of the climate system. The poles have been much warmer throughout much of Earth's history than they are now. Ice-age episodes with durations of millions of years have been separated by periods of hundreds of millions of years that have left little or no evidence of polar ice sheets. The data are best for the most recent of these ice-free episodes so we will concentrate on the Eocene.  相似文献   
12.
Chang LC  Hsiao CT 《Ground water》2002,40(5):481-490
In time-varying ground water remediation, the lack of an optimal control algorithm to simultaneously consider fixed costs and time-varying operating costs makes it nearly impossible to obtain an optimal solution. This study presents a novel algorithm that integrates a genetic algorithm (GA) and constrained differential dynamic programming (CDDP) to solve this time-varying ground water remediation problem. A GA can easily incorporate the fixed costs associated with the installation of wells. However, using a GA to solve for time-varying policies would dramatically increase the computational resources required. Therefore, the CDDP is used to handle the subproblems associated with time-varying operating costs. A hypothetical case study that incorporates fixed and time-varying operating costs is presented to demonstrate the effectiveness of the proposed algorithm. Simulation results indicate that the fixed costs can significantly influence the number and locations of wells, and a notable total cost savings can be realized by applying the novel algorithm herein.  相似文献   
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Two factors determine whether pollution is likely to affect a population indirectly through loss of prey: firstly, the sensitivity of the prey to the pollutants, and secondly, the sensitivity of the predator population to loss of prey at the given life stage. We here apply a statistical recruitment model for Northeast Arctic cod to evaluate the sensitivity of cod cohorts to loss of zooplankton prey, for example following an oil spill. The calculations show that cod cohorts are highly sensitive to possible zooplankton biomass reductions in the distribution area of the cod larvae, and point to a need for more knowledge about oil-effects on zooplankton. Our study illustrates how knowledge about population dynamics may guide which indirect effects to consider in environmental impact studies.  相似文献   
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"Using survey data from high school students of Scotland's Shetland and Orkney Islands (affected by North Sea oil development), we explore relations between intentions to migrate and individual background, aspirations, and attitudes. Attitudes toward oil development do not predict migration intentions. Instead, migration intentions are predicted by essentially the same variables identified in other studies, in areas where energy development was not occurring. Thus, we found no evidence that oil development fundamentally changed young people's thoughts about leaving."  相似文献   
17.
A variety of anthropogenic chemicals are capable of binding to the estrogen receptor of vertebrate species. Binding of these compounds can interfere with homeostasis by disrupting normal gene expression patterns. The purpose of this study was to investigate the feasibility of applying array technology as a monitoring tool for detecting the presence and distribution of estrogenic compounds in coastal habitats using sheepshead minnows as our model. cDNA clones that were isolated from differential display, including vitellogenin alpha and beta, vitelline envelope protein (ZP2), and transferrin, among others, were spotted on the macroarray. The results of these experiments demonstrate a characteristic expression pattern of estrogen responsive genes in sheepshead minnows exposed to 17 beta-estradiol (E2).  相似文献   
18.
Hepatic concentrations of metallothionein [MT] and three metals (Cu, Zn, Cd) were determined in 242 European flounders (Pleuronectes flesus) collected from power stations at Oldbury-upon-Severn and Hinkley Point, located in Severn Estuary and Bristol Channel, UK, respectively, between March 1996 and February 1998. A model involving three-factor analysis of variance (ANOVA) was used to examine variation in MT and metal concentrations with respect to season, year and site; with age-class included as a covariate in the analysis. Hepatic concentrations of MT and Cd (and to some degree, Cu, but not Zn) increased significantly with age. The model explained 38, 25, 17 and 26% of the variation in MT, Cu, Zn and Cd, respectively, with significant effects due to season, and to a lesser extent, to year. Site was only a significant factor for Cd which was higher in fish from Hinkley. Correlation between the individual concentration of MT and each metal alone, or in combination, was poor, and explained only an additional 3.0% of the residual variation in MT, most of which was attributable to Cu (2.7%). Compared to other industrialised estuaries, Cd concentrations were high (>20 micro g-1 in some individuals). The study emphasises the importance of seasonal variation and other factors in biomonitoring programmes and highlights the limitations of using [MT] as a biomarker for metal contamination in flounders from the Severn Estuary.  相似文献   
19.
Increased oceanic heat transport has often been cited as a means of maintaining warm high-latitude surface temperatures in many intervals of the geologic past, including the early Eocene. Although the excess amount of oceanic heat transport required by warm high latitude sea surface temperatures can be calculated empirically, determining how additional oceanic heat transport would take place has yet to be accomplished. That the mechanisms of enhanced poleward oceanic heat transport remain undefined in paleoclimate reconstructions is an important point that is often overlooked. Using early Eocene climate as an example, we consider various ways to produce enhanced poleward heat transport and latitudinal energy redistribution of the sign and magnitude required by interpreted early Eocene conditions. Our interpolation of early Eocene paleotemperature data indicate that an approximately 30% increase in poleward heat transport would be required to maintain Eocene high-latitude temperatures. This increased heat transport appears difficult to accomplish by any means of ocean circulation if we use present ocean circulation characteristics to evaluate early Eocene rates. Either oceanic processes were very different from those of the present to produce the early Eocene climate conditions or oceanic heat transport was not the primary cause of that climate. We believe that atmospheric processes, with contributions from other factors, such as clouds, were the most likely primary cause of early Eocene climate.  相似文献   
20.
Hypoxia and benthic community recovery in Korean coastal waters   总被引:1,自引:0,他引:1  
Low dissolved oxygen (hypoxia and/or anoxia) has become a major cause of change to the benthic component of ecosystems around the world. We present the response of a benthic community to hypoxia in organically enriched environments in Korean coastal waters. Disturbances due to low dissolved oxygen (DO), and organic enrichment altered community dynamics, result in defaunation during summer hypoxia with delayed recolonization occurring in winter. As DO decreased, the number of taxa, their abundance and biomass of macrofauna dropped significantly at inner bay stations in Chinhae Bay and Youngsan River estuarine bay affected by hypoxia. With the return of normoxic conditions in Chinhae Bay, recolonization was initiated by opportunistic species, with a 1-4months lag. The polychaetes, Sigambra tentaculata, Mesochaetopterus sp., and Lumbrineris longifolia, were most persistent under hypoxia. The first recolonizers were the polychaetes Paraprionospio pinnata, S. tantaculata, Glycinde gurjanovae and Nectoneanthes multignatha and the bivalve Theora fragilis. The second group of colonizers included the polychaetes Capitella capitata, Mesochaetopterus sp. and L. longifolia, and the bivalve Raetellops pulchella. Hypoxic and near anoxic conditions resulted in mass mortality in Chinhae Bay and Youngsan River estuarine bay, but communities did partially recover after return to normoxic conditions despite delayed recolonization.  相似文献   
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