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/230Th (or 231Pa/235U), attests a relat...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/230Th (or 231Pa/235U), attests a relatively recent and important uranium migration,concordant dates cannot guarantee closed-system behavior of a 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 sites we have studied, the U-series dating of fossil bones is of limited reliability.展开更多
防火墙技术已成为近年来保护计算机网络安全的技术性措施。它是位于两个信任程度不同的网络之间的软件或硬件设备的组合。文章从防火墙技术具体实现原理上,介绍工作在开放系统互联(OSI,Open System Interconnection)参考模型网络层的网...防火墙技术已成为近年来保护计算机网络安全的技术性措施。它是位于两个信任程度不同的网络之间的软件或硬件设备的组合。文章从防火墙技术具体实现原理上,介绍工作在开放系统互联(OSI,Open System Interconnection)参考模型网络层的网络级防火墙、工作在 OSI 参考模型应用层的应用级网关、工作在 OSI 参考模型会话层的电路级网关和状态检测防火墙。展开更多
文摘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/230Th (or 231Pa/235U), attests a relatively recent and important uranium migration,concordant dates cannot guarantee closed-system behavior of a 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 sites we have studied, the U-series dating of fossil bones is of limited reliability.
文摘防火墙技术已成为近年来保护计算机网络安全的技术性措施。它是位于两个信任程度不同的网络之间的软件或硬件设备的组合。文章从防火墙技术具体实现原理上,介绍工作在开放系统互联(OSI,Open System Interconnection)参考模型网络层的网络级防火墙、工作在 OSI 参考模型应用层的应用级网关、工作在 OSI 参考模型会话层的电路级网关和状态检测防火墙。
