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Dear Smith Liu<br>
<br>
Solving a 3D reconstruction problem is an optimization problem
over a relevant resolution range ('RRR' :) ): finding the best
possible 3D reconstruction, given a set of noisy molecular images.
The very low frequency information in the cryo-EM images are not
relevant to the 3D structure and can be removed by a high-pass
filter. Similarly, the very high frequency information may be
associated with noise only and may interfere with the structure
determination; this can be suppressed by a low-pass filter. One
can thus concentrate the analysis on the RRR by band-pass
filtering the input data. However, even within the RRR, the power
distribution associated with the structural information we are
after is not distributed homogeneously. Typically the
low-frequency side of the structural information is
over-represented compared to the high-frequency side of things due
to all kinds of experimental reasons. This effect is described by
an ad-hoc Gaussian low-pass filter called "the B-factor".
Compensating for an estimated B-factor implies boosting the high
frequency data components with respect to the low-frequency data
components within the RRR. In any refinement/optimization of the
structure, after this inverse B-factor filter, the relative
influence of the high frequency components increases, which, in
turn, results in a 3D reconstruction solution that is more focused
on the fine structural details.<br>
<br>
How to make use of this knowledge? That depends on the software
being used and above all on the level of understanding that the
user has over what is going on in the processing.<br>
<br>
Hope this helps,<br>
<br>
Marin van Heel<br>
<br>
<br>
On 24/05/2015 07:15, Smith Liu wrote:<br>
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cite="mid:4878aa34.d393.14d845944ef.Coremail.smith_liu123@163.com"
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<div>Dear All,</div>
<div> </div>
<div>It was said the resolution of the EM map can be improved by
modifying the b-factor level. Will you please tell me the
reason behind it and how to process it?</div>
<div> </div>
<div>Smith</div>
</div>
<br>
<br>
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<pre class="moz-signature" cols="72">--
================================================================
Prof Dr Ir Marin van Heel
Professor of Cryo-EM Data Processing
Leiden University
NeCEN Building Room 05.27
Einsteinweg 55
2333 CC Leiden
The Netherlands
Tel. NL: +31(0)715271424 // Mobile NL: +31(0)652736618
Skype: Marin.van.Heel
email: marin.vanheel(A_T)gmail.com
and: mvh.office(A_T)gmail.com
----------------------------------------------
Emeritus Professor of Structural Biology
Imperial College London
Faculty of Natural Sciences
Biochemistry Building (Room 512)
South Kensington Campus
London SW7 2AZ, UK
email: m.vanheel(A_T)ic.ac.uk
Tel. UK: +44(0)2075945316 //Mobile: +44(0)7941540625
----------------------------------------------
Visiting Professor at:
Laboratório Nacional de Nanotecnologia - LNNano
CNPEM/ABTLuS, Campinas, Brazil
Brazilian mobile phone +55-19-983189143
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