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J. A. J. Gowlett 《Journal of World Prehistory》1987,1(2):127-170
Accelerator mass spectrometry (AMS) allows radiocarbon dating to be carried out by direct counting of14C atoms, rather than the conventional counting of radioactive disintegrations. The result is that samples up to 1000 times smaller can be handled. The approach was tested in principle by 1977 and for archaeological operation by 1983. More than 2000 samples per year are now being dated worldwide. The machines can now operate to about ± 80 years or better. Dates older than 40,000 years have not yet been achieved, but the ability to use small samples has already had considerable impact on dating the period 10,000–30,000 years ago. Bone is an ideal material for the new technique, since amino acids can normally be isolated and purified from gram-size samples. Studies of the origins of domestication are aided by the dating of individual grains and seeds. Because small samples can be mobile in the soil, careful sample selection strategies and procedures are required. The full impact of the technique can be assessed only through the rapid and comprehensive publication of archaeological results. 相似文献
84.
The upper Mersey Valley was glaciated on three occasions during the Pleistocene. The youngest, Rowallan Claciation, probably commenced after 28000 years B.P. The maximum ice limit was attained before 13500 years B.P., and retreat occurred before 10000years B.P. Deposits associated with Rowallan Glaciation are weakly weathered chemically. They overlie moderately weathered deposits that were formed during the Arm Glaciation, which is inferred from relative dating data to have occurred before the Last Interglacial Stage. North of the deposits and ice limits of the Arm Glaciation extremely weathered tills and rhythmites occur. They were formed by ice of the Croesus Glaciation which is inferred to be of Early Pleistocene age or older. 相似文献
85.
A. D. KNIGHTON 《Geographical Research》1987,25(1):83-97
Tin mining, based largely on alluvial tin deposited along the line of the ancestral Ringarooma, began in 1875 and reached a peak in the period 1905-9. Output declined thereafter and, following a brief recovery during the Second World War, had virtually ceased by 1981. Neither the methods, location nor level of production remained constant during the mining era. The widespread use of hydraulic sluicing and the proximity of many mines to the main river were major factors contributing to the high rate of sediment supply, with the Briseis mine at Derby being the dominant source. Based on data from published and unpublished papers, and mine records, the variable nature of that supply was estimated using a procedure which takes account of the effects of storage and changing practices. Many input points supplied material but the overall pattern is one in which downstream reaches made later starts and reached later peaks, suggesting that they will continue to experience the effects of an increased sediment load for some time. 相似文献
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The p-median problem is a powerful tool in analyzing facility location options when the goal of the location scheme is to minimize the average distance that demand must traverse to reach its nearest facility. It may be used to determine the number of facilities to site, as well as the actual facility locations. Demand data are frequently aggregated in p-median location problems to reduce the computational complexity of the problem. Demand data aggregation, however, results in the loss of locational information. This loss may lead to suboptimal facility location configurations (optimality errors) and inaccurate measures of the resulting travel distances (cost errors). Hillsman and Rhoda (1978) have identified three error components: Source A, B, and C errors, which may result from demand data aggregation. In this article, a method to measure weighted travel distances in p-median problems which eliminates Source A and B errors is proposed. Test problem results indicate that the proposed measurement scheme yields solutions with lower optimality and cost errors than does the traditional distance measurement scheme. 相似文献
88.
This paper is concerned with the reciprocal relationship between migration and development in Third World settings. Using individual-level data for Venezuela, migration behavior is related to a person's age, educational attainment, gender, and characteristics of his/her place(s) of residence as an out-migrant, in-migrant, or stayer. Place characteristics are in terms of four groups based on employment patterns: the core, regional centers, resource frontiers, and traditional rural areas. Four questions are of concern. First, does development influence migration? All analyses indicate this is so. Second, does migration influence development? Findings are ambiguous in that places experiencing improvement in their mix of human capital lagged in the net number of persons obtained through migration whereas a gain in numbers was accompanied by deterioriation in human capital profiles. Third, was incipient polarization reversal occurring in Venezuela in the late 1960s, early 1970s? This paper departs from the usual approach by addressing this question in terms of human capital attributes instead of population aggregates. On this basis, polarization reversal is in evidence, particularly in regional centers. Finally, this study answers in the affirmative that places with different development characteristics generate migration streams differing in type, magnitude, explanation, and impact. 相似文献
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Sarah A. Bendall 《Gender & history》2023,35(1):42-67
This article examines the visual and material culture of sixteenth-century elite ceremonial armours and the paradoxes inherent in using images of women to decorate them between 1525 and 1550. It argues that foreign invading forces and their allies exploited or inverted traditional gender binaries associated with the classical and humanist iconography of the Italian Renaissance, particularly its female allegorical forms, to visually signify power relationships between combatants during the Italian Wars. Rather than simply embodying masculinity, elaborate ceremonial armours with images of women are revealing of both ideals of masculinity and femininity during times of war. These portrayals were part of wider conversations about gender and power, about the strength and weaknesses of women, and, ultimately, women's inferior status to men, which were utilised in allegorical forms to make claims to authority on these elite forms of male dress. 相似文献