Re: [ccp4bb] Refining against images instead of only reflections

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CCP4bb <-- 1999 <-- November 1999 <-- 30 November 1999

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Subject: Re: Refining against images instead of only reflections
From: Dirk Kostrewa kostrewa {- at -} GENZENTRUM {- dot -} LMU {- dot -} DE
Date: 2010-01-28

Dear James,

Am 27.01.10 10:08, schrieb James Holton:

> I'm still not really sure what the difference is between a Bragg spot
> and a feature "under" it. Why not define a "Bragg intensity"
> operationally? Subtracting local background with a least-squares
> plane is pretty much universally done, and as long as the disorder is
> uncorrelated, the intensities obtained this way really are those of
> the partial-occupancy models we currently build. It is when this
> assumption breaks down that we need a "correction factor".

Since diffuse scattering leads to long tails around the Bragg spots,
there was an interesting approach by Bob Blessing some time ago to fit a
kind of triangular background under the (2D-)spots from an empirical
least-squares analysis of the diffuse scattering in these long tails and
subtract this background from the total intensities. To my knowledge,
his approach hasn't gone into any data processing program (maybe in Bob
Blessing's DREAR - but I don't use it). Here is the reference:

"Data reduction and error analysis for accurate singel crystal
diffraction intensities", Robert H. Blessing, Cryst. Rev., Vol. 1, pp 3-58

Best regards,

Dirk.

*******************************************************
Dirk Kostrewa
Gene Center, A 5.07
Ludwig-Maximilians-University
Feodor-Lynen-Str. 25
81377 Munich
Germany
Phone: +49-89-2180-76845
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E-mail: kostrewa@genzentrum.lmu.de
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CCP4bb navigation

CCP4bb <-- 1999 <-- November 1999 <-- 30 November 1999

Previous message:
Subject: Re: DSSP server
From: Robbie Joosten robbie_joosten {- at -} HOTMAIL {- dot -} COM
Date: 2010-01-28

Next message:
Subject: Very high B-factors of some atoms of ligand in Refmac
From: Sangeetha Vedula sangeetha {- dot -} bb {- at -} GMAIL {- dot -} COM
Date: 2010-01-28