[RASMB] (no subject)

[Peter Schuck]

Yi-Ming,

I think it doesn't really matter because the data acquisition software 
won't take any scans anyway until the rotor is at full speed.

The other question is the data analysis.  The option in Sedfit is just to 
take into account the fact that the rotor wasn't at full speed at time 0 
(the clock for counting the sedimentation time starts when you push the 
start button), but arrived at full speed only a few minutes later.  If you 
have a look at the interference patterns, you can sometimes clearly see 
that material is moving away from the meniscus while the rotor is still 
accelerating, and with this option the Lamm equation will mimic this 
behavior.  Note that although you can't get scans during this period, the 
history of this will be relevant for all subsequent scans.

The Sedfit option for rotor acceleration is an alternative data treatment 
to the usual way of approximately accounting for the acceleration by just 
taking the w^2*t to consider an 'effective sedimentation time'.  The latter 
is OK if you don't worry about diffusion (for which the true elapsed time 
is relevant, not this w^2*t time-scale).  Taking into account the 
acceleration phase of the rotor in the Lamm equation modeling, c(s) or 
other, is a little bit more precise, although the differences are normally 
not very significant.  There can be situations, however, where the 
difference is more noticeable.

Peter




At 11:16 AM 2/13/2004 -0500, you wrote:
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>Hi:
>
>I am runing sedimentation velocity experiment. I would like to know when I
>should "start method scan" if I am going to use "Sedfit" to analyse the
>data. Should I start method scan during the acceleration stage or start
>method scan after the rotor speed reach the set speed. Sedfit can "include
>the acceleration phase of the rotor into the modeling by clicking on
>Loading Options--------ramp rotor speed" . Dose this mean that I should
>start method scan in the acceleration stage?
>
>I would appreciate very much if someone can help me for this question!
>
>Thanks!
>
>Yi-Ming Li
>
>
>
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