From: Dr A.J. Rowe <ajr@leicester.ac.uk>
  To  : rasmb@bbri.harvard.edu
  Date: Fri, 5 Sep 1997 15:13:42 +0100 (BST)

Wiener skewing - what it is

Emory -

Wiener skewing arises physically from the fact that a ray of light entering the
cell at the region of the highest dn will - for finite optical pathlength - be
refracted *away* from the maximum dn region for its travers. In other words, the
apparent maximum in dn/dr will be *distorted* away from the true maximum. Or, if
you like, the Schlieren peak will be *skewed*. For optics focussed on the mid
point of the cell, the effect is quite easy to see in a g(s*) profile. You would
not notice it by visual inspection in an equilibrium trace - buts its effects
would be there in your results.

There are ways of avoiding/minimising it, none of them perfect (see my mail to
Les Holladay which I have asked him to post).

All bet

Arthur

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Dr Arthur J Rowe
Director
UK National Centre for Macromolecular Hydrodynamics
Leicester Laboratory
Adrian Building
University of Leicester
Leicester LE1 7RH    UK

Tel: +44 (0)116 252 3448
Fax: +44 (0)116 252 5602
ajr@leicester.ac.uk
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