No Rex

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The relaxation dispersion model for no chemical exchange. This if for all SQ CPMG-type data, MMQ CPMG-type data, and R1rho-type data. This model is labelled as No Rex in relax.


The No Rex model has the parameter R20 or R' depending on the data type.

Equation for No Exchange in CPMG

[math] R_{2,\textrm{eff}} = R_2^0 [/math]

Equation for No Exchange in R1rho

[math] \mathrm{R}_{1\rho}= \mathrm{R}_1\cos^2\theta + \mathrm{R}_{1\rho}{´} \sin^2\theta [/math]

If no R1 values has been loaded, but the R1_fit flag has been turned on, the R1 will be fitted as well.

For data without a loaded offset, (see also  relax disp.spin lock offset+field ), if
[math] \bar{\Omega}_{S,i} = 0.0 [/math] then the Rotating frame tilt angle θ is set to: [math] \theta = \frac{\pi}{2} [/math]

and as such
[math] cos^2\theta = cos^2\left( \frac{\pi}{2} \right) = 0.0 [/math]

Therefore the fitted R1 values have no meaning for "No Rex" model, if there is no offset.


These is no reference for the No Rex model.


The implementation of the No Rex model in relax can be seen in the:

See also