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Re: [ccp4bb] phasing power ofatoms
 

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CCP4bb <-- 2007 <-- March 2007 <-- 28 March 2007
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Subject: Re: phasing power ofatoms
From: Bernhard Rupp bernhardrupp {- at -} SBCGLOBAL {- dot -} NET
Date: 2007-03-28 		Next message:
Subject: Director of Protein Production
From: Steve Almo almo {- at -} MEDUSA {- dot -} BIOC {- dot -} AECOM {- dot -} YU {- dot -} EDU
Date: 2007-03-28


Subject: Re: phasing power ofatoms
From: Peter Zwart PHZwart {- at -} LBL {- dot -} GOV
Date: 2007-03-28
Hi all,

It is good to keep in mind that


2*[ <
Iplus - Imin
> / < Imean > ]
approx
[ < (
Iplus - Imin
) / Imean > ]


i.e.

/ is NOT equal to



In fact, might be closer to what one is interested in from an
experimental point of view, as that talks about 'average signal' rather
than the 'signal average'.

Also, when reporting these ratios, it is important to stipulate what is
reported. Some flavours are:
<
dI
>/
<
dI
/I >
<
dF
>
<
dF
/F >
< dF^2 >^1/2 / ^1/2
.
.
. etc etc etc

They are all related of course, but all have slightly different values.

In the end, what matters is data quality anyway. Having good Bijvoet
ratios on paper doesn't help much if you don't have good data.

Some thoughts on these issues can be found in Acta Cryst. (2005). D61,
1437–1448 and references therein. The simulation tool described in this
paper is available on request.


HTH

Peter





--
Peter Zwart
Beamline Scientist,
Physical Biosciences Division
Berkeley Center for Structural Biology

Building 6, Room 2134
Tel: 510-486-4214, Fax: 510-486-5664
http://bcsb.lbl.gov

Lawrence Berkeley Laboratory
1 Cyclotron Road
BLDG 6R2100
Berkeley, CA 94720, USA.
--



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