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91.
The possibility of lead isotope fractionation in ancient lead production is examined. Kinetic theory relating to isotopic fractionation in non-equilibrium evaporation is considered and the feasibility of the alteration of lead isotope abundance ratios in ore roasting and smelting is assessed. Previous experimental work is shown to have been inconclusive and conclusions are drawn on the need for further research to quantify the possible extent of fractionation in practice. 相似文献
92.
D. E. NELSON G. CHALOUPKA C. CHIPPINDALE M. S. ALDERSON J. R. SOUTHON 《Archaeometry》1995,37(1):151-156
Accelerator mass spectrometry radiocarbon ages have been taken for a test suite of small samples of material removed from some of the ‘beeswax’art figures found in rock shelters in northern Australia. The results indicate that we can reliably date this unique form of rock art with no noticeable damage. We had not expected to find figures of any great antiquity, and so we were surprised to find that the ages obtained spanned the time period from the recent past to about 4000 BP. 相似文献
93.
A Roman archaeological site in northern Spain (La Maja, province of La Rioja) includes pottery workshops, part of an important ceramic industry that developed from about the first century BC to the first century AD. A geophysical study was planned to determine the extent of the industrial complex in the vicinity of an excavated kiln. Magnetic observations were done on a grid of 30 × 36m, with a sampling interval of 1m. Two dipolar-shaped anomalies were found: one in the north-east and the other in the south-west of the area. Low-pass and band-pass filters were used in the Fourier domain to enhance the characteristics of the magnetic data and to remove noise and undesirable shallow features. Three-dimensional polygonal prisms were used to model the magnetic anomalies based on palaeomagnetic measurements performed over an uncovered kiln that helped to constrain the induced and remanent parameters of the magnetizing fields. 相似文献
94.
The localization or representation of mental abilities in the brain have always been considered as key questions for understanding the organization of the human nervous system. Particularly with the advent of modern electrophysiological and imaging techniques that provide maps of electromagnetic fields and metabolic processes on the living central nervous system, the representation theory is experiencing a scientific renaissance in neurology, but is only one theory, however, in the succession of a long philosophical tradition dealing with the possible identification of mental phenomena and brain processes. This dichotomy was formulated at the latest in the Cartesian dualism of res cogitans and res extensa of the mind-body problem. Nowadays philosophical discussion, on the contrary, is dominated by monistic concepts that attempt to explain the mental realm on an organic foundation in order not to succumb to the problem of a psychophysical dualism. Of these, the identity theory offers a philosophically plausible concept postulating that the identity of brain conditions and mental phenomena is based on organic foundations. In this theory, the efforts of brain research converge on the representations of mental phenomena in the human nervous system. In a comprehensive approach, both concepts could complement each other. 相似文献
95.
ABSTRACT. Data for 28 metropolitan areas over a 15-year period are used to determine the impacts of government spending, taxes, and public infrastructure on total employment and disaggregated employment. After carefully controlling for the government budget constraint we find that taxes are negatively related to total employment and education spending is positively related to total employment. Nevertheless, we find that it is difficult for metropolitan areas to influence the composition of their employment with government tax and expenditure policies. Moreover, at current levels of public infrastructure, marginal changes in infrastructure have no strong effect on employment. 相似文献
96.
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98.
Morphological Impacts and Implications of a Trial Release on the Wingecarribee River,New South Wales
A trial, monitored release on the Wingecarribee River over 27 days had a peak discharge below the Wingecarribee Dam of 1090 ML/d, which had a flow duration of 0.95 per cent. Morphological impacts on 29 km of channel below the dam included bank erosion, concentrated neck overflow, bed degradation and channel widening at recent cutoffs, sedimentation in weir pools and overbank flow, particularly at discharges greater than 800 ML/d. Prolonged operational releases at bankfull discharge (400–800 ML/d) will have the greatest morphologic impacts and should be avoided. Pulses which dissipate stream power over a broad, well-vegetated floodplain should be incorporated in the operational release policy, provided such pulses are phased to facilitate channel and vegetation recovery. 相似文献
99.
Acid sulphate soils form when iron pyrite oxidises to sulphuric acid on atmospheric exposure, lowering soil pH below 4. In the Richmond River estuary, northern New South Wales, flood mitigation, drainage works and floodplain excavations have augmented acid sulphate soil formation by increasing pyrite availability for oxidation. These engineering works have facilitated the transport of acidified water and have impeded recovery from tributary acidification. The increased frequency and duration of acidification are associated with elevated concentrations of inorganic monomeric aluminium and dissolved iron, and major iron hydroxide precipitation, with deleterious effects on exposed aquatic biota and habitat. Fish kills and an outbreak of epizootic ulcerative syndrome (EUS) have been recorded from acidified sites in the estuary. 相似文献
100.
G.J.R. LINGE 《Geographical Research》1995,33(1):116-132
The sovereignty of the bleak Kurile islands, off northern Japan, has long been the subject of a bitter stand-off between Russia and Japan. This has not only prevented their signing a post-1945 Peace Treaty but has retarded the flow of official financial assistance and corporate investment funds across the few hundred kilometre-wide Sea of Japan. As a result the reconstruction of the Russian Far East has been made more difficult, thus exacerbating the economic and social hardship there. Examples like this should cause us to reflect on the dangers of making simplistic explanations about the spatial organisation of economic activity as well as the need to rediscover political geography. 相似文献