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  From: Thomas M Laue <>
  To  : Borries Demeler/Biophysics <>
  Date: Mon, 9 May 1994 14:29:13 -0400 (EDT)

Re: Bo Demeler's Wavelength Suggestion

Bo and others-
The Rayleigh slits do not help with sloping baselines or any other 
absorbance characteristics. They merely cut the light intensity. I agree 
that the wavelength impurity could cause the trouble, but also agree that 
it is probably not the cause of what Jack and John are describing. 
Gregg's suggestion that it is window holders is a possibility (DON'T USE 
ANY HOLDERS EXCEPT THE WIDE-OPEN ONES!), but I doubt that it is the problem 
here, either. It could be a timing problem where the edge of the 
reference sector is being caught at low radii, but not at higher radii 
(or, conversely, the sample sector is partially occluded at higher radii, 
but not at lower). However, this is obvious in the intensity profiles, and I 
doubt is the cause for the problems in either of these two labs. Besides, 
in this case, you'd expect to find some negatively sloped plateaus, and 
that hasn't been reported by anyone so far.

Hopefully, an explanation will come along soon.

Re: the high temperature XLA. This sounds like a real challenge! I am 
willing to put some time and effort into seeing what can be done to up 
the temperature range, but the fundamental problem seems to be the drive 
overheating (electronics could be moved and other pieces manufactured 
from more thermally-stable materials). The drive could be cooled, but 
even then, I'd not want to be the one to fire the machine up to 60000 
rpm for the first time at 100 C.

I'll put together a list of the problem spots and some possible remedies. 
Clearly, this will be a bigger and longer term project than it first 

Tom Laue 

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