On 5 November 2015 at 15:53, Edward d'Auvergne <edw...@nmr-relax.com> wrote: > On 5 November 2015 at 14:05, Christina Möller <c.moel...@fz-juelich.de> 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 _______________________________________________ relax (http://www.nmr-relax.com) This is the relax-users mailing list relax-users@gna.org To unsubscribe from this list, get a password reminder, or change your subscription options, visit the list information page at https://mail.gna.org/listinfo/relax-users
