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Among the manifestations of radioactive decay which can be etched to optical visibility on the surface of mica are tracks from nuclei recoiling from alpha emission, called ‘alpha-recoil tracks’. If, beforeetching, the mica is heated to temperatures of the order of 600°C, all evidence of these tracks is annealed from muscovite mica in a few minutes. Alpha activity observed on mica from pot sherds, from stones surrounding fire places, from fire pits, and fired daub may constitute an alpha-recoil track clock which started at the moment of the last firing of the artifacts. 相似文献
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Research on policy impact has increasingly focused on the practical application of social science research. This paper outlines four roles—substantive expert, information processor, change agent, and scholar—which have helped to increase the potential usefulness of our research while maintaining linkages to the academic community. This paper suggests the general nature of these roles and suggests specific implementation strategies, which need to be pursued as an early and continuing aspect of the research enterprise. Balancing these multiple roles presents several analytical and ethical difficulties, but helps to establish credibility in both the scientific and policymaking communities. 相似文献
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It is argued that variation in uncertainty about social program goals and causal processes should influence the selection of evaluation designs and methods. Eighteen prominent evaluation reports are examined to contrast predicted evaluation strategies derived from theory about organizational uncertainty with the actual evaluation methods used. It was found that the actual design, measurement, and analysis procedures were frequently different from procedures that were compatible with the kinds of program uncertainty described in the evaluation reports. It is suggested that theory and practice in program evaluation can be improved by systematically incorporating organizational concepts that would contribute to the selection of evaluation methods. 相似文献
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