Re: [ccp4bb]: Problems with low mosaicity crystals

[<gb10@globalphasing.com>]

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     This is an interesting discussion. In relation to this vibration problem, 
I recall seeing a poster by Norma Duke et al. (from APS) at the last ACA 
meeting pointing to the same conclusion: even lysozyme crystals gave bad 
merging statistics in an apparently erratic manner, which was in the end 
correlated with the fact that they had been mounted on long loops. 

     Concerning Pete's remark that vibration would lead to high mosaicity, 
a possible twist is that vibration would occur in certain crystal orientations 
but not in others, so that the compensation by increased mosaicity would only 
come into play if that quantity was tracked as a function of rotation angle, 
which may not always be the case. This variability would also tend to confuse 
the post-refinement process. 

     Perhaps more attention needs to be paid to the mechanics of holding 
frozen crystals in loops.


     With best wishes,

          Gerard.

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     * Gerard Bricogne                     gb10@GlobalPhasing.com  *
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