Full metadata
Title
The indexing ambiguity in serial femtosecond crystallography (SFX) resolved using an expectation maximization algorithm
Description
Crystallographic auto-indexing algorithms provide crystal orientations and unit-cell parameters and assign Miller indices based on the geometric relations between the Bragg peaks observed in diffraction patterns. However, if the Bravais symmetry is higher than the space-group symmetry, there will be multiple indexing options that are geometrically equivalent, and hence many ways to merge diffraction intensities from protein nanocrystals. Structure factor magnitudes from full reflections are required to resolve this ambiguity but only partial reflections are available from each XFEL shot, which must be merged to obtain full reflections from these `stills'. To resolve this chicken-and-egg problem, an expectation maximization algorithm is described that iteratively constructs a model from the intensities recorded in the diffraction patterns as the indexing ambiguity is being resolved. The reconstructed model is then used to guide the resolution of the indexing ambiguity as feedback for the next iteration. Using both simulated and experimental data collected at an X-ray laser for photosystem I in the P63 space group (which supports a merohedral twinning indexing ambiguity), the method is validated.
Date Created
2014-09-23
Contributors
- Liu, Haiguang (Author)
- Spence, John (Author)
- College of Liberal Arts and Sciences (Contributor)
- Department of Physics (Contributor)
Resource Type
Extent
9 pages
Language
eng
Copyright Statement
In Copyright
Primary Member of
Identifier
Digital object identifier: 10.1107/S2052252514020314
Identifier Type
International standard serial number
Identifier Value
2052-2525
Series
IUCrJ
Handle
https://hdl.handle.net/2286/R.I.44846
Preferred Citation
Liu, H., & Spence, J. C. (2014). The indexing ambiguity in serial femtosecond crystallography (SFX) resolved using an expectation maximization algorithm. IUCrJ, 1(6), 393-401. doi:10.1107/s2052252514020314
Level of coding
minimal
Cataloging Standards
Note
View the article as published at http://journals.iucr.org/m/issues/2014/06/00/it5003/index.html
System Created
- 2017-07-14 12:43:33
System Modified
- 2021-08-16 02:23:30
- 3 years 3 months ago
Additional Formats