r20030 - /branches/relax_disp/lib/dispersion/it99.py -- June 11, 2013 - 12:01

Author: bugman
Date: Tue Jun 11 12:01:56 2013
New Revision: 20030

URL: http://svn.gna.org/viewcvs/relax?rev=20030&view=rev
Log:
Fixes for the lib.dispersion.it99 module.

This is mainly because the omega_1eff parameter was not being correctly 
converted from the nu_cpmg
values.


Modified:
    branches/relax_disp/lib/dispersion/it99.py

Modified: branches/relax_disp/lib/dispersion/it99.py
URL: 
http://svn.gna.org/viewcvs/relax/branches/relax_disp/lib/dispersion/it99.py?rev=20030&r1=20029&r2=20030&view=diff
==============================================================================
--- branches/relax_disp/lib/dispersion/it99.py (original)
+++ branches/relax_disp/lib/dispersion/it99.py Tue Jun 11 12:01:56 2013
@@ -27,7 +27,7 @@
 
     Ishima R. and Torchia D.A. (1999).  Estimating the time scale of 
chemical exchange of proteins from measurements of transverse relaxation 
rates in solution.  J. Biomol. NMR, 14, 369-372.  (U{DOI: 
10.1023/A:1008324025406<http://dx.doi.org/10.1023/A:1008324025406>}).
 
-The equation used is:
+The equation used is::
 
               phi_ex * tex
     Rex ~= ------------------- ,
@@ -35,11 +35,17 @@
 
     phi_ex = pA * pB * delta_omega^2 ,
     
-    omega_a^2 = sqrt(omega_1^4 + pA^2*delta_omega^4) ,
+    omega_a^2 = sqrt(omega_1eff^4 + pA^2*delta_omega^4) ,
 
     R2eff = R20 + Rex ,
 
-where tex = 1/(2kex), kex is the chemical exchange rate constant, pA and pB 
are the populations of states A and B, and delta_omega is the chemical shift 
difference between the two states.
+where tex = 1/(2kex), kex is the chemical exchange rate constant, pA and pB 
are the populations of states A and B, and delta_omega is the chemical shift 
difference between the two states.  The effective rotating frame field for a 
CPMG-type experiment is given by::
+
+    omega_1eff = 2*sqrt(3) * nu_cpmg
+
+and therefore::
+
+    omega_1eff^4 = 144 * nu_cpmg^4
 """
 
 # Python module imports.
@@ -82,8 +88,11 @@
             back_calc[i] = r20
             continue
 
+        # The effective rotating frame field.
+        omega_1eff4 = 144 * (2.0*pi*cpmg_frqs[i])**4
+
         # Denominator.
-        omega_a2 = sqrt((2.0*pi*cpmg_frqs[i])**4 + pa2dw4)
+        omega_a2 = sqrt(omega_1eff4 + pa2dw4)
         denom = 1.0 + omega_a2 * tex2
 
         # Avoid divide by zero.