[RASMB] Temperature control

[Peter Schuck]

Hi all, 
I agree with the previous comments about the temperature stability.  However, I
believe there's another aspect to the question of what's an acceptable
temperature drift during the run, which is the level of detail one wants to
analyze the data.  

Whole boundary fitting (e.g. with Lamm equation solutions, or c(s) applied to
the entire set of scans from the beginning of sedimentation to complete
depletion) appears more sensitive to the effects of temperature changes than,
let's say, just an average s-value obtained from the boundary midpoint. 
Probably the same is true for any other method that takes into account more of
the details of the boundary shape.  My experience with Lamm equation and c(s)
is that a few tenth of a degree temperature change is tolerable (and frequently
unavoidable), but if it's more than 1 degree, the ability to model the data and
the quality of the analysis can suffer significantly.  

I suspect that there are more subtle effects of temperature fluctuations on
sedimentation than just the obviously visible macroscopic convection process
that stretches over a spatial scale of few millimeters.  As we're improving
detection systems, use larger data sets, and more detailed modeling, we may be
picking up temperature effects that are not affecting much the overall average
boundary stability and average sedimentation, and therefore were not much of a
concern before, in particular with the earliest AUCs.  

Best regards,
Peter

At 01:35 PM 4/4/02 +0000, you wrote: 
>
> Hi all -
>
> The issue of temperature control raised by Jack Kornblatt is an important
> one. The absolute temperature of the rotor is probably not defined (or
> claimed) to better than a few tenths of a degree, but at least once the thing
> has settled down the constancy seems acceptable (better than 0.1 deg
> usually). For most velocity work this is fine. Although if you happen to want
> to study the effect of varying temperature one would like to know the true
> temperatures, not just to have the reassurance that whatever they are, they
> are steady !
>
> As Peter Schuck says, there is no escape from pre-equilibration if you want
> to be really sure you have no effects caused by minor changes in temperature.
> However, I doubt that in most cases the stability of the boundary is in
> question if we are merely talking of the odd degree or fractions of a degree.
> Convective stirring is pretty unlikely. After all - temperature control
> systems were absent from the earliest AUCs, and people got stable boundaries
> and s values similar to modern ones, even with a temperature drift amounting
> to whole degrees !
>
> One can of course evaluate s values use the integral  of f(T)*(omega)^2.dt in
> place of (omega)^2, where f(T) is the temperature correction factor at the
> temperature T appertaining at time t.  Assuming that no component in the
> system shows significant temperature-dependent effects, that's valid. I
> recall that years ago I did this - no doubt for some good (but un-remembered)
> reason . . .
>
> Best wishes for your project, Jack - and kind regards to all on RASMB
>
> Arthur
>
> --
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> Arthur J Rowe
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***********************************************************
Peter Schuck, PhD
Molecular Interactions Resource
Division of Bioengineering and Physical Science, ORS
National Institutes of Health
Bldg. 13 Rm. 3N17
13 South Drive 
Bethesda, MD 20892 - 5766
Tel: (301) 435-1950
Fax: (301) 480-1242
email: Peter_Schuck at nih.gov
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