# No Rex

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.

## Contents

## Parameters

The No Rex model has the parameter R_{2}^{0} or R_{1ρ}' 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 R_{1} values has been loaded, but the `R1_fit`

flag has been turned on, the R_{1} 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 R_{1} values have no meaning for "No Rex" model, if there is no offset.

## Reference

These is no reference for the No Rex model.

## Links

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