[RASMB] question about Sedfit

[Peter Schuck]

Satinder,

Sedfit and sedphat are designed to handle this using the algebraic 
decomposition of systematic noise. You can calculate the amount of vertical 
shifts and the radial-dependent baseline while you're fitting the data, and 
then subtract it from the raw data to better inspect the shape of the 
boundary and the quality of fit.

You will find information on how this works at the sedfit website in the 
tutorial
http://www.analyticalultracentrifugation.com/systematic_noise_analysis.htm

How do actually do this in sedfit is described in detail in the 
step-by-step tutorial
http://www.analyticalultracentrifugation.com/tutorial_sizedistributions.htm
(there are screenshots how to do this) and in the menu help section
http://www.analyticalultracentrifugation.com/sedfit_help_subtract_calculated_noise.htm

With regard to the centerpieces, we use the charcoal-filled Epon double 
sector centerpieces routinely at 50,000 and 60,000 rpm without having any 
problem, despite their rating.  You need to be careful, though, that 
there's no leak in the cell, which may cause it to break.  There is a 
description how we do this in our lab in the experimental protocol

http://www.nih.gov/od/ors/dbeps/PBR/Applications/Protocols.pdf

in the sedimentation velocity protocol Step II.

Peter


At 11:15 AM 1/26/2005 -0500, you wrote:
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>Hello,
>
>I am trying to use Sedfit to analyze some velocity data taken with
>interference optics. The problem I have is that the fringes keep
>jumping around from scan to scan. Can Sedfit handle this, i.e,
>align all the scans. If so, how do you do it? I noticed there was
>something about it on Peter Schuck's
>"analyticalultracentrifugation.com" website under IgG sample. I
>tried this method with my data and nothing shifted. Does anyone
>have any suggestions as to what I may be doing wrong?
>
>Also, what is the maximum speed the Beckman 2-sector centerpieces
>can withstand? I think it's 40,000 rpm, but I am not sure. Anyone
>know?
>
>Thanks in advance for your help.
>
>Sincerely yours,
>Satinder
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