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 无论是从理论基础上还是具体步骤上,中值淘汰法与分支学家常用的方法都不相同。在构建分支图之前识别祖征与反向进化,直接衍征与环极向衍征有悖于分支学的基本原则;而在具体运算过程中仅以2个分类单元求取中值又会掩盖反向进化;新的中值必须全部包括分支图上下面的中值的原则事实上是不承认反向进化。中值淘汰法产生的分支图不及Farris方法产生的分支图简约。  相似文献   

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AACS是一种内容散布和数字版权管理的标准,通过吊销设备密钥来吊销非法的设备,并且采用子集差分树技术对数量庞大的设备密钥进行管理.根据子集差分树原理,每个设备需要存储大量的设备密钥.在被吊销设备的分布是随机和均匀的这一合理假设条件下,对AACS的设备密钥存储方案进行了改进.改进后,每个设备存储的密钥数量减少,并且合法设备被划分的子集个数仅仅稍微增加.  相似文献   

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While literature reviews with a large-scale scope are nowadays becoming a staple element of modern research practice, there are many challenges in taking on such an endeavour, yet little evidence of previous studies addressing these challenges exists. This paper introduces a practical and efficient review framework for extremely large corpora of literature, refined by five parallel implementations within a multi-disciplinary project aiming to map out the research and practice landscape of modelling, simulation, and management methods, spanning a variety of sectors of application where such methods have made a significant impact. Centred on searching and screening techniques along with the use of some emerging IT-assisted analytic and visualisation tools, the proposed framework consists of four key methodological elements to deal with the scale of the reviews, namely: (a) an incremental and iterative review structure, (b) a 3-stage screening phase including filtering, sampling and sifting, (c) use of visualisation tools, and (d) reference chasing (both forward and backward). Five parallel implementations of systematically conducted literature search and screening yielded a total initial search result of 146 087 papers, ultimately narrowed down to a final set of 1383 papers which was manageable within the limited time and other constraints of this research work.  相似文献   

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