Thon rings are present (see table 2.4). Too to analyze careful correction of the CTF requires such data over the first Thon ring outside. In the most fundamental approach this through simply obtains reversal of the phase of each odd Thon of ring; a komplettere approach requires additional correction of the extent. This changes the contrast of the picture details so that the picture then an applicable projection of the three-dimensional represents reliably objects you and can are used, in order to produce a more reliable reconstruction. Improvement is the procedure, which is used, in order the breakdownsignaling thing to increase (S/N) relationship of the pictures by the calculation of average values. For all kinds copy, gives it local to fluctuations strength of the ice film, in the concentration of the buffer salts and other contaminants and impurities as denatured proteins. Change of the occasional noises develops also from the supporting film and from effects of the radiation damage on the ensemble. If table of 2.4 pictures of a carbon film (taken with 200 KV on one PROTECT T-20 FEG-EM) to defocus evaluated indicated and their appropriate Fourier converts.
The bright and dark volumes are Thon of rings, which result from the contrast transient response, those by the objective objective the microscopes IMAGE ANALYSIS 17 are imposed micro graphs become on film, which add photographic emulsion Schhrotrau noted; A CCD camera more /Fotovervielfacher produces also something auxiliary noise. Although crystals and not periodic copies become different than, the substantial are simply calculation of average values of treat similar particle pictures. For two-dimensional crystals can be taken place the calculation of average values using Fourier-Spektrum of the crystal via extracting the periodic part of the spectrum and abolition of the background. The back Fourier transform supplies then an average picture, in which the unit cell of the crystal with a increased S/N relationship is seen. For the individual particles, average calculating is accomplished in the material area, in that the pictures first is agreed and into different groups according to their different characteristics then classified. The acceptance is formed that the sample contains identical subunits, embedded everyone with an arbitrary determining position in an ice film. Determination of the determining position of the different projections is a substantial step prior for the computation of a full three-dimensional diagram. In some cases something information knows its reached during the data acquisition, e.g. the inclination to of the goniometer the pictures can in the tomographischen analysis by two-dimensional be first used notes crystals. For individual particles the task is many more difficult. Today there are two main beginnings to projection-bring general lines together and. The COMM on lines approach basedly on the fact that any two, 2 measure projections of a structure have you at least, 1 measure projection in the Common. Knowledge of the angles between these lines for three at least, supplies necessary orientational parameters to 2 measure projections with. The method first in the mutual area applied by Crowther and later in the material area by van Heel. In the projection, the one comparison brings together between the molecular pictures and all possible projections of the model is formed. Determining position of the projection, which has the nähste similarity to the molecular picture, is assigned the picture. This approach is in the material area for particles also at most uses low symmetry and in the Fourier area for particles with icosahedral symmetry.
In the reconstruction of the three-dimensional distribution of the molecular densities, there are two main beginnings. First is a material space approach and second a Fourier closes you approach, which is similar to the crystallographic method. In the material area `back projection the technology is used, in order to waive the enterprise of the receipt of a projection. A projection represents simply the sum total of all densities of the three-dimensional article in individual surface (a little like a medical X-ray). By the densities of the three-dimensional article to repair the densities of the projections in the reverse must be extended by projection of direction. There are some algorithms, which would drive through this procedure. The Fourier method basedly on the central section theorem, that indicates Fourier transform of a projection is a central section in the Fourier area. This is called that projections in the different angles makes available then sections of the Fourier area at these angle and therefore the area can be filled up. We can achieve the complete three-dimensional Fourier transform of the article therefore. The Rückfourier transformation of such a volume produces the three-dimensional density distribution of the article inside material area. For particles with icosahedral or screw-like symmetry, a Fourier Bessel transformation there can avoid you some Interpolationstörungen at most the use of a cylinder co-ordination system is used.
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