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SUMMARY:Single molecule imaging by XFEL-s
DTSTART:20140117T141500
DTSTAMP:20260407T064102Z
UID:904104d6f2cdfc755de946661298c3a0bacfafd3f729ba77d8d98a99
CATEGORIES:Conferences - Seminars
DESCRIPTION:Gyula Faigel\, Wigner Research Centre for Physics\, Institute 
 for Solid State Physics and Optics\, Budapest\, Hungary\nWe study the poss
 ibility of imaging single molecules by intense and short XFEL pulses. Late
 ly\, the first hard XFEL source (LCLS) came into operation. Pilot experime
 nts 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 bef
 ore full exploitation of this method: 1. the radiation damage\; which at 2
 0 nm resolution is not a problem. However\, at the Å range\, the motion o
 f atoms during the x-ray pulse has to be taken into account. 2. Determinat
 ion of the orientation of 2D diffraction patterns taken at unknown orienta
 tions of the samples. This step is hindered by the low statistics of indiv
 idual 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 fi
 nding the proper orientations. The third problem is the phase retrieval of
  the continuous 3D pattern. There are many approaches to solve the phase p
 roblem\; all are based on Fourier recycling.\nWe 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 threshol
 d approach\, which allows the classification of realistic large data sets.
  Further\, we developed an „Expansion expectation Maximization and Compr
 ession” (EMC) type algorithm for the orientation of 2D diffraction patte
 rns\, and we applied the “Charge flipping” algorithm (developed also i
 n our lab) for phase retrieval. In the talk I will summarize the above res
 ults.
LOCATION:PH L1 503 http://plan.epfl.ch/?room=PHL1503
STATUS:CONFIRMED
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