On 5 November 2015 at 15:53, Edward d'Auvergne <edward@xxxxxxxxxxxxx> wrote:
On 5 November 2015 at 14:05, Christina Möller <c.moeller@xxxxxxxxxxxxx>
wrote:
I know that the relaxation data can also be back calculated using the
equations 7.3a - 7.8 in the relax manual (PDF), although it is not that
trivial for an ellipsoid model because I need to determine the weights. Is
there a reason why you define c=1/3(ωH*∆σ)^2 (eq. 7.5) instead of
c=2/15(ωN*∆σ)^2 like it can be found in literature?
These two factors come from using CGS vs. SI units. I have mentioned
this issue before (see
http://thread.gmane.org/gmane.science.nmr.relax.devel/1023/focus=1034
). I have also started a stub wiki article to help explain these
differences - http://wiki.nmr-relax.com/CGS_versus_SI . In SI units
the correct unit (squared) is (ω·∆σ)^2 / 3, and SI units are used
throughout relax. This has made some parts of relax more difficult to
implement as there are many equations in the literature in CGS units,
and the authors will often not identify this older system. Some
stubborn people just prefer the magnetic constant to be 1 rather than
µ0/(4π), and will not shift from the CGS metric system to the SI
metric system.
Hi Christina,
The wiki article http://wiki.nmr-relax.com/CGS_versus_SI is now
somewhat improved. However it doesn't cover all of the NMR constants
yet, as that will be a lot of work to derive. Anyway, I hope that
helps a little to understand the equation differences seen in the NMR
literature.
Regards,
Edward
Re: back calculation of relaxation data