特权约束系统职责隔离问题研究

特权控制操作系统最重要的资源，需要应用职责隔离原则，确保特权安全．与现有研究不同，从特权隐式授权方面探讨对职责隔离的支持问题．通过分析特权来源，将特权定义分解为约束规则与执行规则，弥补了现有访问控制研究中对权限效果描述不足的缺陷．两类规则间的逻辑推导说明授权间的推导关系，即特权问存在隐式授权，可能不满足职责隔离要求．利用授权推导关系图准确而全面地反映了特权机制的所有隐式授权．从特权的职责隔离属性，及职责隔离对特权的机制要求两方面探讨上层职责隔离需求与底层特权控制实施的一致性问题．以目前广泛应用的POSIX权能机制为例，给出其形式化模型BMPS模型的定义，指出该机制支持职责隔离存在的问题，并对该机制进行了改进，给出满足职责隔离要求的特权策略实施方案．

High electrical-to-green efficiency high stability intracavity-frequency-doubled Nd:YAG-LBO QCW 532 nm laser with a straight cavity

An electrical-to-green efficiency of more than 10% was demonstrated by intracavity-frequency-doubling a Q-switched diode-side-pumped Nd:YAG laser with a type II lithium triborate (LBO) crystal in a straight plano-concave cavity. An average power of 69.2 W at 532 nm was generated when electrical input power was 666 W. The corresponding electrical-to-green conversion efficiency is 10.4%. To the best of our knowledge, this is the highest electrical-to-green efficiency of second harmonic generation laser systems with side-pumped laser modules, ever reported. At about 66 W of green output power, the power fluctuation over 4 hours was better than +/-0.86%.

O~-离子单电子解离过程的研究

采用交叉束方法,利用兰州大学串列加速器的负离子源提供的4—19keV的O~-与惰性气体靶原子He、Ne、Ar碰撞,通过静电偏转和位置灵敏探测器区分碰撞后中性粒子束和负离子束,测量了不同碰撞系统的中性粒子计数与相应入射负离子计数的比值R(E),讨论了R(E)与入射负离子能量E和靶原子种类的依赖关系。