Re: [ccp4bb] twinned?

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Subject: difference betwen blue confocal max-flux and osmic confocal max-flux
From: "Karthikeyan S {- dot -} " skarthik {- at -} IMTECH {- dot -} RES {- dot -} IN
Date: 2008-04-02

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Subject: Re: Inverse 3D profile/threading
From: Mensur Dlakic mdlakic {- at -} MONTANA {- dot -} EDU
Date: 2008-04-02

Subject: Re: twinned?
From: Bart Hazes bart {- dot -} hazes {- at -} UALBERTA {- dot -} CA
Date: 2008-04-02

Hi Qiang,

A normal data set has a unimodal intensity distribution with a
predictable shape. When there is twinning the distribution remains
unimodal but becomes sharper and this is picked up in the twinning
analysis. When there is pseudo-translational symmetry, as you indicate
you have, then the intensity distribution becomes bimodal with one set
of reflections systematically strengthened and another systematically
weakened. This makes the whole distribution broader, just the opposite
of what twinning does, and therefore shows up as "negative twinning" in
the analysis.

Bart

Qiang Chen wrote:
> Hi all,
>
> The data I am working on has a strong translation vector. The space group
> is C2221 and resolution is 2.3 angstrom. There are two molecules per AU
> with a pseudo-2-fold axis.
> On the cumulative intensity distribution plot, the theor and obser curves
> totally do not overlap. I did "detect_twinning" from CNS, and there is the
> result:
>
> <
I
^2>/(<
I
>)^2 = 3.2236 (2.0 for untwinned, 1.5 for twinned)
> (<
F
>)^2/<
F
^2> = 0.6937 (0.785 for untwinned, 0.865 for twinned)
> Does the result mean my data is not twinned?
>
> Any suggestion will be highly appreciated.
> Thank you!
>
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--

==============================================================================

Bart Hazes (Assistant Professor)
Dept. of Medical Microbiology & Immunology
University of Alberta
1-15 Medical Sciences Building
Edmonton, Alberta
Canada, T6G 2H7
phone: 1-780-492-0042
fax: 1-780-492-7521

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CCP4bb <-- 2008 <-- April 2008 <-- 02 April 2008

Next message:
Subject: Re: Inverse 3D profile/threading
From: Mensur Dlakic mdlakic {- at -} MONTANA {- dot -} EDU
Date: 2008-04-02