Hi,
In relax, the Rex reported will be that of the first input field
strength. The frequency of the Rex value is documented in the header
line of the results file. This is a deliberate design to increase the
flexibility of relax - Rex is automatically handled for you. If you
would like to convert to a different field strength, just divide by
the proton frequency in Hz, squared, then multiply by the new
frequency squared. relax could be modified to report the value for
the highest field, this will of course also be fully automatic from
the user's perspective, but the current design allows an advanced user
to choose which frequency the Rex is reported for.
Regards,
Edward
On Feb 18, 2008 4:57 AM, Sebastien Morin <sebastien.morin.1@xxxxxxxxx> wrote:
Hi,
I have a question concerning Rex and its magnetic field dependence vs
how it is treated in relax.
Rex, the contribution from us-ms motions on the transversal relaxation
rate (R2), is scaled quadratically with the magnetic field. When doing
an analysis with relax, one gets a value for Rex.
When working with data from multiple magnetic fields, I realized that
the dataset to which this Rex is associated changes as a function of the
order with which datasets are input into relax. In fact, the Rex value
is associated with the first dataset input.
Here are some results I had with the full_analysis.py script modified to
minimize only tm3 (for a rapid test) :
================================================================
Input_order Association Rex__residue_25
=========== =========== =======================
500-600-800 500 7.0885287044805514
500-800-600 500 7.0885287044182812
600-800-500 600 2.7486344907905164e-13
600-500-800 600 2.7486344897092221e-13
800-500-600 800 -2.1641012543284559e-17
800-600-500 800 -5.3169783493616144e-21
================================================================
As you can see, the Rex value changes with the input order. Most change
comes from the first dataset input, but there is also a small influence
from the subsequent datasets input...
Is this normal ?
Would it be better to always input datasets so Rex gets associated with
the highest magnetic field ? With the lowest ?
Thanks for clarifying this issue !
Cheers,
Séb
--
Sebastien Morin
Etudiant au PhD en biochimie
Laboratoire de resonance magnetique nucleaire
Dr Stephane Gagne
CREFSIP (Universite Laval, Quebec, CANADA)
1-418-656-2131 #4530
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Re: Rex vs magnetic field