[RASMB] Abrupt change in intensity

[Maluf, Nasib K]

Dear All,
 
I would like to clarify the experiment I did that I sent as an attachment yesterday.  In this experiment, I had loaded samples in both the sample and reference chambers of the cell; the data I sent was for the sample chamber.  The experiment was to use the noise deconvolution features in sedfit to do a cofs analysis on the transformed intensity data, as has been described many times.
 
The consensus explanation for the abrupt change in intensity I observed in my data is that the gain setting of the XLI detector automatically changed to improve signal to noise.  If you put a sample in the reference chamber that has a high starting intensity/absorbance (at R = 6.5 cm) then the gain is automatically set lower; as the reference sample sediments, eventually the intensity at 6.5 cm will decrease, which will eventually result in an increase in the gain.  To avoid this, one would make sure the starting intensity (in the reference chamber) starts off low so the gain setting remains the same throughout the run.  
 
Thanks to everyone for the explanations.  If I have said anything incorrect, please let me know!  I wrote this email since several people replyed to me privately and I thought this would be of general interest.
 
Thanks,
 
Karl

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