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首页> 外文期刊>Acta crystallographica.Section D. Biological crystallography >New ways of looking at experimental phasing.
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New ways of looking at experimental phasing.

机译：观察实验定相的新方法。

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In the original work by Blow and Crick, experimental phasing was formulated as a least-squares problem. For good data on good derivatives this approach works reasonably well, but we now attempt to extract more information from poorer data than in the past. As in many other crystallographic problems, the assumptions underlying the use of least squares for phasing are not satisfied, particularly for poor derivatives. The introduction of maximum likelihood (and more powerful computers) has led to substantial improvements. For computational convenience, these new methods still make many assumptions about the independence of different measurements and sources of error. A more general formulation for the probability distributions underlying likelihood-based methods for both experimental phasing and molecular-replacement phasing is reviewed. In the new formulation, all the structure factors associated with a particular hkl are considered to be related by a complex multivariate normal distribution. When it is assumed that certain errors are independent, the general formulation reduces to current likelihood targets. However, the new formulation makes the necessary assumptions more explicit and points the way to improving phasing using both isomorphous and anomalous differences.
机译：在打击和克里克的原创作品,实验分阶段是制定最小二乘问题。衍生品这一方法工作得相当好,但我们现在试图提取更多的信息来自贫困数据比过去。其他晶体问题,假设潜在的使用最小二乘法进行不满意,特别是对贫困衍生品。(和更强大的计算机)导致了可能性实质性的改进。方便,这些新方法仍然使许多关于不同的独立性假设测量和误差的来源。概率分布的公式底层基于可能性的方法实验分阶段和molecular-replacement分阶段研究进展。结构因素有关特定hkl被认为是相关的复杂的多元正态分布。假定某些错误是独立的,一般配方降低电流目标的可能性。使更明确的和必要的假设点的方法改善逐步使用同晶型和异常差异。

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