Re: Rex value -- March 10, 2009 - 18:23

Hi Ed,

PY is next to me and we discussed this issue together.

This seems very strange since values of the AICc criterion (extracted
during model selection) are not equal for models with or without these
10e-19 Rex... If this is in s-1, then the criterion should be almost
equal as a Rex of 10e-19 s-1 would be negligible.

Moreover, if using the latex_mf_table.py script, the Rex values are
reported and associated to the 800 MHz field strength with values in s-1
between 1 and 6... These values correspond to those we would obtain by
multiplying the Rex values in the xml results file by (2 pi frq)**2...

Hence, I would think values extracted in the xml file, that is values
one gets with the command "value.display('Rex')", are in the field
independent format obtained from Rex/omega**2.

Are we wrong ?

Thank you Ed.


Séb  :)





Edward d'Auvergne wrote:
> On Mon, Mar 9, 2009 at 6:58 PM, Pierre-Yves Savard
> <Pierre-Yves.Savard@xxxxxxxxxxxxx> wrote:
>   
> > Hi,
> >
> > I would like to know if the Rex values given in the xml result file of
> > relax 1.3 are expressed in s-1 or if it is the result of the following
> > formula: Rex/(2 * π * freq)**2?
> >     
>
> The value is in 1/seconds (note this is actually rad/s but the rad is
> hidden - hence why you don't call it Hertz).  The field strength is
> also noted in the results file, indicating that it is not the
> field-strength free value of sigma_ex = Rex/omega**2.
>
>
>   
> > The values I get (~3E-19) seem to come from the scaling equation, but in
> > the result file, these values are associated with a field strength:
> >
> > <rex desc="Chemical exchange relaxation (800 MHz)"
> > ieee_754_byte_array="[197, 23, 28, 207, 173, 151, 0, 60]">
> >                        1.124351254e-19
> >
> > Maybe the field strength associated with the values in the result file
> > are remnants of relax 1,.2, where Rex were given in s-1...
> >     
>
> No, I would call that no very much chemical exchange at all.  Model
> selection should get rid of this model - unless of course the
> equivalent model without Rex failed!
>
> Regards,
>
> Edward
>
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-- 
Sébastien Morin
PhD Student
S. Gagné NMR Laboratory
Université Laval & PROTEO
Québec, Canada