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71.
Pan-STARRS, a funded project to repeatedly survey the entire visiblesky to faint limiting magnitudes (mR~ 24), will have asubstantial impact on the study of the Kuiper Belt and outer solarsystem. We briefly review the Pan-STARRS design philosophy and sketchsome of the planetary science areas in which we expect this facility tomake its mark. Pan-STARRS will find ~20,000 Kuiper Belt Objectswithin the first year of operation and will obtain accurate astrometryfor all of them on a weekly or faster cycle. We expect that it willrevolutionise our knowledge of the contents and dynamical structure ofthe outer solar system.  相似文献   
72.
A palaeotemperature reconstruction based on periglacial phenomena in Europe north of approximately 51 °N, is compared with high‐resolution regional climate model simulations of the marine oxygen isotope Stage 3 (Stage 3) palaeoclimate. The experiments represent Stage 3 warm (interstadial), Stage 3 cold (stadial) and Last Glacial Maximum climatic conditions. The palaeotemperature reconstruction deviates considerably for the Stage 3 cold climate experiments, with mismatches up to 11 °C for the mean annual air temperature and up to 15 °C for the winter temperature. However, in this reconstruction various factors linking climate and permafrost have not been taken into account. In particular a relatively thin snow cover and high climatic variability of the glacial climate could have influenced temperature limits for ice‐wedge growth. Based on modelling the 0 °C mean annual ground temperature proves to be an appropriate upper temperature limit. Using this limit, mismatches with the Stage 3 cold climate experiments have been reduced but still remain. We therefore assume that the Stage 3 ice wedges were generated during short (decadal time‐scale) intervals of extreme cold climate, below the mean temperatures indicated by the Stage 3 cold climate model simulations. Copyright © 2003 John Wiley & Sons, Ltd.  相似文献   
73.
Efficiency and sustainability of grain production are now important in China. In this study, the grain production systems of Jiangsu and Shaanxi Provinces were compared, to analyze their efficiency and sustainability in terms of utilization of natural resources, inputs of purchased energy and materials, and outputs. Flows of energy and materials between environment and human society were identified, and the natural and human work involved in generating inputs as materials or energy were valued in terms of equivalent amount of solar energy required for their production using emergy method. The results showed environmental resources were continually playing a less important role in the systems, when inorganic subsidiary emergy inputs increased drastically while organic ones decreased or increased little. Deterioration of input emergy structure affected the systems‘ efficiency and sustainability, resulting in emergy investment ratios and environmental loading ratios increasing while yield ratios and sustainability indices decreasing. In general, efficiency and sustainability of grain production in Jiangsu are worse than those in Shaanxi. This analysis also suggested that inorganic subsidiary emergy should be introduced properly, and peasants in Jiangsu should utilize natural conditions wisely while those in Shaanxi pay enough attention to soil and surface water conservation.  相似文献   
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The Quaternary fills of the buried valleys of southern Alberta and Saskatchewan have provided a wealth of information for the reconstruction of the glacial-interglacial record of the western plains of Canada, and this paper reports on the previously unstudied stratigraphy of the buried Calgary Valley and its former tributaries in the lower Red Deer River area. We attempt to differentiate Empress Group sediments, which potentially relate to pre-glacial, interglacial/ interstadial and post-glacial lake and river deposition, using sedimentology, stratigraphy and palaeoecology. Twenty-nine stratigraphical logs indicate that Empress Group sediments have infilled a considerably large area of badlands and tributary coulees that once drained into the Calgary Valley, located 15 km to the north of Dinosaur Provincial Park. Radiocarbon dates of 52.4 ka, 27.4 ka and > 42.4 ka and glacially modified quartz grains suggest that at least some of the valley fills date to interglacial or interstadial periods and may be mid-Wisconsinan in age. However, outcrops of an older till overlying other valley fills suggest that the buried valleys were only partially excavated during interglacials/interstadials and that older (even pre-glacial) sediments could have survived. Subglacial channels, recognisable on air photographs, largely coincide with buried valley positions due to the preferential excavation of the Quaternary sediment by meltwater and are filled with post-glacial lake sediment from which a radiocarbon date of 16 ka BP was obtained. Pre-glacial and glacial/post-glacial Empress Group sediments are lithologically indistinct but cover a large time span in southern Alberta.  相似文献   
77.
1IN T R O D U C T IO NAn image isa setofbelief,s ideasand impressionsthatapersonholdsaboutan object(KOTLER,1991).Similar-lydefinitionistheimage of a destinationas thesum ofbelief,sideasand impressionsthatpeoplehave ofa placeor destination(CROMPTON,1979;KO…  相似文献   
78.
Uranium was measured by fission track analysis in meteoritic troilite and graphite. The distribution is extremely heterogeneous, with a few high-U grains dominating the total abundances. U/He ages cannot be estimated from such a distribution pattern, and therefore previously reported excessive ages are not valid.  相似文献   
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This study on the distribution features of petroleum hydrocarbon in water and sedi-ment off the Fujian shore using data obtained from the baseline research on oceanic contamination in Fujian showed that:during the research preiod,petroleum hydrocarbon concentrations in water varied from 5.77μg/L to 37.28μg/L,averaged 14.48 μg/L;was lower in the wet seasson than in the dry season;and was highest in the Minjiang Estuary and Jiulong Estuary in both seasons ,The petorleum hydrocarbon concentrations in shore sediment varied from 14.48 mg/kg to 784.36 mg/kg,averaged 133.3 mg/kg ,and was closely related to sediment types (granularity).  相似文献   
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