title: Aspects of direct phasing in femtosecond nanocrystallography.
abstract: X-ray free-electron laser diffraction patterns from protein nanocrystals provide information on the diffracted amplitudes between the Bragg reflections, offering the possibility of direct phase retrieval without the use of ancillary experimental data. Proposals for implementing direct phase retrieval are reviewed. These approaches are limited by the signal-to-noise levels in the data and the presence of different and incomplete unit cells in the nanocrystals. The effects of low signal to noise can be ameliorated by appropriate selection of the intensity data samples that are used. The effects of incomplete unit cells may be small in some cases, and a unique solution is likely if there are four or fewer molecular orientations in the unit cell.
authors.affiliation: Computational Imaging Group, Department of Electrical and Computer Engineering, University of Canterbury, Christchurch, New Zealand rick.millane@canterbury.ac.nz.
authors.forename: Rick P
authors.initials: RP
authors.lastname: Millane
authors.affiliation: Computational Imaging Group, Department of Electrical and Computer Engineering, University of Canterbury, Christchurch, New Zealand.
authors.forename: Joe P J
authors.initials: JP
authors.lastname: Chen
mesh_terms: D018360:Crystallography, X-Ray / Q000379:methods*; D004583:Electrons; D007834:Lasers; D053758:Nanoparticles / Q000737:chemistry* / Q000648:ultrastructure; D059629:Signal-To-Noise Ratio; D013997:Time Factors; D014961:X-Ray Diffraction / Q000379:methods*
keywords: X-ray free-electron lasers; crystallography; imaging; phase retrieval