"Artificial" vs. "real" B-factors?

San Martin, Carmen carmen at wistar.upenn.edu
Tue Jun 1 14:59:45 EST 1999


  Dear all,

  I am trying to use X-plor rigid body refinement to fit an atomic
resolution model into an electron microscopy density (~15 Angstrom
resolution). I know that I have to consider quite high B-factor values, to
account for the low resolution of the EM density and to avoid truncation
artifacts. I see that I can do this in Xplor in two different ways:

1. Use the vector statement

vector do (b=125.) 

2. Use an artificial B value in the FFT statement

   fft 
      bscalefactor=125.
      memory=2000000  
   end                

  My question is, what is the difference between these two ways of setting
artificial B factor values? My first impression was that using either of
them would give the same results, but no, they give different R values.
Can anybody explain the difference, or point to some reference where it is
explained?

  Thanks for your time,

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