From: Holger Strauss <strauss@fmp-berlin.de>
  To  : rasmb@bbri.harvard.edu
  Date: Fri, 6 Apr 2001 20:09:06 +0200 (MEDT)

reliability at high speeds

Dear RASMBers,

this is a question concerning the reliability of the instruments, both
XL-A and -I, at high speeds. 

Recently, we had some trouble with the absorption optics of the XL-I
(extremely noisy radial scans, OK for wavelengths and intensities),
which now seem to have subsisted, because of reasons currently not very
well understood by us (some problems just disappear...?). However, we did
a sedimentation velocity run at 60k, 3.5hs, 5mins between scans. 

a) some scans show less absorption than the following ones.
b) the spacing between the scans is not even (some are nearly overlaid,
but at least in one case, a scan seems to have been utterly omitted

There seem to be two possibilities:

- problems just pop up again, then our optics are faulty
- or there is a problem because we are operating at the upper limit of
what is certified

As we don't have much experience at the maximum speed of the
instrument, we are wondering how well the reproduceability of radial
position and lamp firing actually is at such high speeds, and wether it is
sustained over an extended period of time (however, 3.5hs is not much).
Based on trial and error, some scans do give reasonably good results when
using them in programs based on the Lamm equation; there is however a
problem using methods like vanHolde-Weischet, 2nd moment and dc/dt. 

Although the instrument is certified up to 60k, is the quality of the
data as good as, say, 50k or 45k?
Is there a difference between interference and absorption optics at
high speeds?
How much stress is put on the material? This is difficult to estimate, but
something like doubling operating speed reduces lifespan of
windows/cells/centerpieces/rotors/centrifuge by x would be helpful.

Thanks a lot in advance. 

Holger

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Holger Strauss 

Forschungsinstitut fuer Molekulare Pharmakologie (FMP)
Robert-Roessle Strasse 10

13125 Berlin/Germany

Tel: +49 (0)30 94793 - 223 (office)
                     - 316 (lab)

Fax: +49 (0)30 94793 - 169 


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Die Situation des Haustieres zieht die des Schlachttieres nach sich.