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31.
Roman Krzysztofowicz 《Journal of the American Water Resources Association》1992,28(1):193-200
ABSTRACT: The performance of a flood warning system can be characterized statistically by three variables: the expected number of detections per year, ND; the expected number of false warnings per year, NP; and the expected lead time of a warning, LT. The Performance Tradeoff Characteristic (PTC) of a warning system is a set of all combinations (ND, NP, and LT) that are feasible to attain in a given system. The concept of PTC is an evolution of the concept of ROC (Relative Operating Characteristic) widely used in detection theory. Each characteristic, ROC and PTC, can be displayed graphically in the form of a family of curves. The displays offer an aid to engineering planning and design of flood warning systems. (KEY TERMS: flood forecasts; flood warnings; reliability; detection; Relative Operating Characteristic; Performance Tradeoff Characteristic.) 相似文献
32.
This research extends recent studies of the relationship between characteristics of jobs and patterns of workers' alcohol consumption. Working within a ‘generalization perspective ’whereby job conditions are seen as having important effects on the mental health and behaviors of workers in non-work settings, the current research derives and tests a model of four job-related factors as they influence three aspects of alcohol use; the simple frequency—quantity of drinking, escapist-oriented reasons for drinking, and a combination of heavier drinking with escapist-oriented definitions which is labeled ‘self-medication’. Analyses of data drawn from the 1973 Quality of Employment Survey (QES) indicate that the relationship between jobs and drinking behavior is more complex than previously conceptualized. Specifically, we find evidence that for working men characteristics of jobs affect levels of alcohol consumption and the incidence of self-medicating drinking. These findings support and refine job-based explanations of drinking behavior. The implications of these findings for subsequent research and model-specification are discussed. 相似文献
33.
34.
The copepod Acartia tonsa and the reef mysid Mysidium integrum ingest stained coral mucus. Ingestion rates determined with radioisotope-labeled mucus ranged from 4 to 81% body carbon · 24 h-1 for the copepods and I to 70% body carbon · 24 h-1 for the mysids. Incorporation was measured by comparing the organic composition of fecal material and by the incorporation of isotope-labeled mucus. A. tonsa incorporated 47% of ingested ash-free material, 68% of carbon and 36% of nitrogen. M. integrum incorporated 44% of ingested ash-free matter, 57% of carbon and 55% of nitrogen. Incorporation estimates using 14C-labeled mucus were 65% and 39% for incorporation by A. tonsa and M. integrum respectively. A. tonsa and M. integrum incorporated both the mucus substrate and the epiphytic bacteria of the mucus-detritus. 相似文献
35.
Longauer R Gömöry D Paule L Blada I Popescu F Mankovska B Müller-Starck G Schubert R Percy K Szaro RC Karnosky DF 《Environmental pollution (Barking, Essex : 1987)》2004,130(1):85-92
The effects of air pollution on the genetic structure of Norway spruce, European silver fir and European beech were studied at four polluted sites in Slovakia, Romania and Czech Republic. In order to reduce potential effects of site heterogeneity on the health condition, pair-wise sampling of pollution-tolerant and sensitive trees was applied. Genotypes of sampled trees were determined at 21 isozyme gene loci of spruce, 18 loci of fir and 15 loci of beech. In comparison with Norway spruce, fewer genetic differences were revealed in beech and almost no differentiation between pollution-tolerant and sensitive trees was observed in fir. In adult stands of Norway spruce, sensitive trees exhibited higher genetic multiplicity and diversity. The decline of pollution-sensitive trees may result thus in a gradual genetic depletion of pollution-exposed populations of Norway spruce through the loss of less frequent alleles with potential adaptive significance to altered stressing regimes in the future. Comparison of the subsets of sensitive and tolerant Norway spruce individuals as determined by presence or absence of discolorations ("spruce yellowing") revealed different heterozygosity at 3 out of 11 polymorphic loci. 相似文献
36.
Concentrations of dioxin-like PCB congeners in unweathered Aroclors by HRGC/HRMS using EPA Method 1668A 总被引:6,自引:0,他引:6
Rushneck DR Beliveau A Fowler B Hamilton C Hoover D Kaye K Berg M Smith T Telliard WA Roman H Ruder E Ryan L 《Chemosphere》2004,54(1):79-87
We have determined the congener compositions of nine commercial Aroclor products of polychlorinated biphenyls (PCBs) to the sub-part-per-million level using high-resolution gas chromatography combined with high-resolution mass spectrometry according to US Environmental Protection Agency (EPA) Method 1668A. These Aroclor composition data should allow improved characterization and risk assessment of PCB contamination at hazardous waste sites, particularly for dioxin-like PCB congeners. By combining the data on the concentrations of each dioxin-like congener with its World Health Organization toxicity equivalency factor, we have established dioxin toxic equivalent concentrations for each pure Aroclor product. 相似文献
37.
In the conceptualization of thriving at work, it is emphasized that employees' learning and vitality are two equally important components of thriving and that thriving is facilitated by contextual features and available resources. In this study, we examined the effects of two challenge stressors (time pressure and learning demands) on thriving at work. Based on the literature on challenge and hindrance stressors, we proposed that challenge stressors positively affect learning and negatively affect vitality. To uncover underlying mechanisms, we measured challenge appraisal and hindrance appraisal of work situations in a diary study. A sample of 124 knowledge workers responded to three daily surveys (before the lunch break, during the afternoon, and at the end of the workday) for a period of five workdays. Results indicate that the indirect effects of learning demands and time pressure on learning are mediated by challenge appraisal, whereas indirect effects of learning demands on vitality are mediated by hindrance appraisal. Overall, our study shows that challenge stressors have a positive total effect on learning but no total effect on vitality. These differential relationships call for a finer distinction between the two components of thriving at work in future research. Copyright © 2016 The Authors Journal of Organizational Behavior Published by John Wiley & Sons Ltd. 相似文献
38.
Clyde J. Dial Janet M. Houthoofd Eugene F. Harris 《Journal of the Air & Waste Management Association (1995)》2013,63(10):1393-1396
An overview of activities of the Risk Reduction Engineering Laboratory in response to the Environmental Protection Agency’s Treatability Initiative are described and a summary of the information in the first ten Engineering Bulletins, which are a component of the initiative, is provided. 相似文献
39.
Interactions of bacteria and fungi on decomposing litter: differential extracellular enzyme activities 总被引:10,自引:0,他引:10
Fungi and bacteria are key agents in plant litter decomposition in freshwater ecosystems. However, the specific roles of these two groups and their interactions during the decomposition process are unclear. We compared the growth and patterns of degradative enzymes expressed by communities of bacteria and fungi grown separately and in coexistence on Phragmites leaves. The two groups displayed both synergistic and antagonistic interactions. Bacteria grew better together with fungi than alone. In addition, there was a negative effect of bacteria on fungi, which appeared to be caused by suppression of fungal growth and biomass accrual rather than specifically affecting enzyme activity. Fungi growing alone had a high capacity for the decomposition of plant polymers such as lignin, cellulose, and hemicellulose. In contrast, enzyme activities were in general low when bacteria grew alone, and the activity of key enzymes in the degradation of lignin and cellulose (phenol oxidase and cellobiohydrolase) was undetectable in the bacteria-only treatment. Still, biomass-specific activities of most enzymes were higher in bacteria than in fungi. The low total activity and growth of bacteria in the absence of fungi in spite of apparent high enzymatic efficiency during the degradation of many substrates suggest that fungi provide the bacteria with resources that the bacteria were not able to acquire on their own, most probably intermediate decomposition products released by fungi that could be used by bacteria. 相似文献
40.
Fenton''s type reaction and chemical pretreatment of PCBs 总被引:3,自引:0,他引:3
This study evaluates the effects of Fenton's reagent (FR) on the rate and extent of the oxidative degradation of individual mono, di-, tri- and tetrachlorobiphenyls in the commercial mixture DELOR 103, equivalent to AROCLOR 1248. The oxidation effect of FR strongly increased with increasing the molar ratio of Fe2+/H2O2. The most effective oxidation of DELOR 103 (10 μg.ml−1) was achieved in a solution containing 1M H2O2 and 1 mM Fe2+. The FR elimination rate constants of PCB congeners decrease with increasing number of chlorine substituents in the biphenyl molecule and show a good correlation with the values of molecular weights of the PCB congeners and their 1-octanol/water partition coefficients. 相似文献