Single molecule imaging by XFEL-s
Event details
| Date | 17.01.2014 |
| Hour | 14:15 |
| Speaker | Gyula Faigel, Wigner Research Centre for Physics, Institute for Solid State Physics and Optics, Budapest, Hungary |
| Location | |
| Category | Conferences - Seminars |
We study the possibility of imaging single molecules by intense and short XFEL pulses. Lately, the first hard XFEL source (LCLS) came into operation. Pilot experiments on single molecules have been done. In these, 20-50 nm resolution has been reported. This is far from the ultimate goal, the atomic resolution, but it is a promising start. Three main obstacles have to be solved before full exploitation of this method: 1. the radiation damage; which at 20 nm resolution is not a problem. However, at the Å range, the motion of atoms during the x-ray pulse has to be taken into account. 2. Determination of the orientation of 2D diffraction patterns taken at unknown orientations of the samples. This step is hindered by the low statistics of individual measurements. This can be circumvented by sorting the patterns into classes, in which every particle has the same orientation and adding them, or by applying sophisticated self organizing map type algorithms for finding the proper orientations. The third problem is the phase retrieval of the continuous 3D pattern. There are many approaches to solve the phase problem; all are based on Fourier recycling.
We studied all of the above questions. Using our special molecular dynamics tool we modeled the motion of atoms in biological specimens, and we gave limits to pulse parameters. Concerning the classification problem, we worked out a quality threshold approach, which allows the classification of realistic large data sets. Further, we developed an „Expansion expectation Maximization and Compression” (EMC) type algorithm for the orientation of 2D diffraction patterns, and we applied the “Charge flipping” algorithm (developed also in our lab) for phase retrieval. In the talk I will summarize the above results.
We studied all of the above questions. Using our special molecular dynamics tool we modeled the motion of atoms in biological specimens, and we gave limits to pulse parameters. Concerning the classification problem, we worked out a quality threshold approach, which allows the classification of realistic large data sets. Further, we developed an „Expansion expectation Maximization and Compression” (EMC) type algorithm for the orientation of 2D diffraction patterns, and we applied the “Charge flipping” algorithm (developed also in our lab) for phase retrieval. In the talk I will summarize the above results.
Links
Practical information
- Informed public
- Free
Organizer
- ICMP (Arnaud Magrez and Raphael Butté)
Contact
- Arnaud Magrez