Calculations,according to some open-system models,point out that while a statistically significant discrepancy between the results of two U-series methods,^230Th/^234U and ^227Th/^220Th(or ^231Pa/^235U),attests a relatively recent and important uranium migration,concordant dates cannot guarantee closes-system behavior of sample.The results of 20 fossil bones from 10 Chinese sites,19 of which are determined by two U-series methods,are given,Judging from independent age controls,8 out of the 11 concordant age sets are unacceptable,The results in this paper suggest that uranium may cycle into or out of fossil bones,such geochemical events may take place at any time and no known preserving condition may securely protect them from being affected.So for the sitew we have studied,the U-series dating of fossil bones is of limited reliability. 相似文献
We report the results of the first laser beacon experiment at the astronomical site of La Palma (Canary Islands). A continuous wave low‐power laser (a few hundred mW) system has been set up. The laser, tuned on the sodium D2 line at 589 nm, is launched close to the zenith angle. The emission of the mesospheric sodium layer is observed from a telescope located 160 m away from the laser. The layer is therefore resolved in altitude and the different features of its dynamics are investigated. 相似文献
Horashim East is a newly discovered Middle Palaeolithic open-air occurrence in central Israel, revealed during a thematic prehistoric survey. Hundreds of lithic items were found, including an early-stage biface, Levallois cores and products. As only a few open-air settlements are known from the Middle Palaeolithic Levant, the discovery of Horashim East sheds new light on human land-use patterns during this period and reinforces the notion that central-eastern Israel was favourable for human settlement throughout the Palaeolithic. 相似文献