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61.
The advantages of using radionuclides for laboratory studies of environmental processes include the wide range of element concentrations that can be studied, the capability to simultaneously study several isotopes in a single experiment, the direct applicability to the behaviour of radioactive waste or fallout, and the ability to study the mechanisms, reversibility and kinetics of environmental reactions under controlled conditions. These attributes are demonstrated using specific examples drawn from case studies in Australia, including radionuclide fallout onto tropical soils, the association of trace metals with harbour sediments and the behaviour of uranium in natural and contaminated systems.  相似文献   
62.
A laboratory experiment was performed to evaluate the effects of intermittent suspended solids exposure on the unionid clams Quadrula pustolosa, Fusconaia cerina and Pleurobema beadleanum. Intermittent impacts of this type are important effects of commercial navigation traffic in freshwater. Clams were cyclically exposed to turbulence alone or accompanied by 600-750 mg litre(-1) of suspended inorganic solids for 9 days. Clams exposed to suspended solids every 3 h reduced their metabolic rate but did not shift from the mainly protein based catabolism of controls. Feeding impairment was apparently compensated for by a reduction in metabolic demand. Conversely, clams exposed every 0.5 h to suspended solids shifted to virtually complete reliance on non-protein body stores as indicated by O:N values averaging 197.  相似文献   
63.
Gas chromatography was used to analyse the gases released by growing cultures of the denitrifying marine bacterium Pseudomonas perjectomarinus. When nitrate was provided as final oxidant, CO2 was the first detectable gas released. Following the peak rate of release of CO2 at approximately 16 h, N2 liheration began and peaked at 30 h. When N2O was provided as terminal oxidant, CO2 and N2 release began within a few hours and the rate of liberation of both increased for 45 to 50 h before leveling. Cell-free extracts of bacteria from denitrifying cultures of P. perfectomarinus were incubated anaerobically with nitrate, malic acid and electron transfer cofactors provided, and the gases in the atmosphere above the reaction mixtures were analysed. NO was found to be present transiently, and N2O was discerned after prolonged incubation. The applicability of gas chromatography to analyses of marine ecosystems and the need for better means of sampling the atmosphere above enzymatic reaction mixtures were disoussed.  相似文献   
64.
This study explores the notion that many existing studies which show moderate relationships between role variables and stress symptoms are doing so because of the operational similarity of independent and dependent variables. It was predicted that the removal of such an artefact by clearly separating the two sets of variables would result in a nil relationship. Matched ‘cases’ and ‘controls’ were compared in two different organizations. The independent judgments of occupational health specialists were used to measure stress on a number of agreed dimensions, and role measurements were taken by the researchers in three different ways. On all comparisons made there was a strong trend suggesting no role/stress associations. The implications of the results for role stress studies are discussed.  相似文献   
65.
66.
Adsorption of radionuclides on soils and sediments is commonly quantified by distribution coefficients (Kd values). This paper examines the relationship between Kd values for uranium(VI) adsorption and the specific surface area (SSA) of geologic materials. We then investigate the potential applicability of normalising uranium (U) Kd measurements using the SSA, to produce ‘Ka values’ as a generic expression of the affinity of U for the surface. The data for U provide a reasonably coherent set of Ka values on various solid phases, both with and without ligands. The Ka representation provides a way of harmonising datasets obtained for materials having different specific surface areas, and accounting for the effects of ligands in different systems. In addition, this representation may assist in developing U sorption models for complex materials. However, a significant limitation of the Ka concept is that sorption of radionuclides at trace levels can be dominated by interactions with specific surface sites, whose abundances are not reflected by the SSA. Therefore, calculated Ka values should be interpreted cautiously.  相似文献   
67.
This paper theorizes how and why safety climate can be conceived as both a leading and a lagging indicator of safety events (i.e., accidents, injuries). When safety climate is conceived as a leading indicator, a prospective design is utilized and safety climate data are correlated with accidents/injuries that occur in the future. When safety climate is conceived as a lagging indicator, retrospective designs are used in which safety climate data are correlated with prior accidents/injuries. We examine the research literature to reveal that safety climate has been investigated as both a leading and a lagging indicator, but it is usually only examined as one or the other within a given study and has been examined as a lagging indicator most frequently. Consistent with our theorizing, prospective designs yield stronger relationships than retrospective designs, suggesting that safety climate is a better leading indicator than lagging indicator; however, it is clearly both. Implications for safety climate research and study design are discussed.  相似文献   
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