[MMTK] Question about neutron scattering in nMoldyn

Konrad Hinsen hinsen at cnrs-orleans.fr
Fri Oct 17 13:28:58 UTC 2008


On Oct 17, 2008, at 9:38, Ramon Crehuet wrote:

> This information helps, but raises new questions...
> 1) Given that experimental results do not state the angular  
> resolution of the apparatus, is the default value in nmoldyn a  
> reasonable choice? (for more details, we are trying to compare with  
> results obtained in the IN13 at the ILL)

I don't know much about angular resolution of spectrometers either. I  
suspect it is better than what you can get from nMOLDYN calculations  
on realistic system sizes. As I said before, the finite width of the  
Q shells is there for computational reasons, not to model  
spectrometer properties. Nevertheless, I don't remember any case  
where it turned out to be a problem. Such a hypothetical case would  
require a quantity that varies strongly as a function of Q.

> 2) How can the energy resolution be introduced? Jeremy Smith has a  
> interesting paper (Biophys. J, 82, p. 1216) showing that this  
> parameter influences the measured <u^2>. And he does it with nmoldyn!

Energy resolution is related to the length of the time series being  
analyzed. nMOLDYN lets you specify a Gaussian window function when  
Fourier-transforming time series; the width of this window can be  
chosen to correspond to the spectrometer's energy resolution.

Konrad.
--
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Konrad Hinsen
Centre de Biophysique Moléculaire, CNRS Orléans
Synchrotron Soleil - Division Expériences
Saint Aubin - BP 48
91192 Gif sur Yvette Cedex, France
Tel. +33-1 69 35 97 15
E-Mail: hinsen at cnrs-orleans.fr
Web: http://dirac.cnrs-orleans.fr/~hinsen/
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