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<TITLE>Re: [RASMB] "wavy" interference optics residuals</TITLE>
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<BLOCKQUOTE><FONT COLOR="#800000">Hi Debra (again)<BR>
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Checking back my records - which I should have done before mailing - I see that the frequency of the wave noise I saw was only around 1 cycle (2¼) in 2 mm radial distance. <BR>
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I have quickly done a computer simulation of the situation, taking a non-ideal system with sigma(monomer) = 1.5, BM = 0.0015 (fringe units) loading concentration 3 fringes (~1 mg/ml), with ±0.007 SD of stochastic noise added to each data point. Floating BM, c(reference) and baseline (E) without wave noise, fitting* gave an estimate for BM = 0.001501. Whereas doing the same fit with 1 cycle of wave noise added (amplitude 0.005) returned a value BM = 0.001498!<BR>
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So - given that for a globular protein at ~1 mg/ml you are pushing it to get a reliable value for the second virial term (BM), I think that for most purposes wave noise of this level of amplitude can be tolerated, mysterious though it may be. But what do you reckon IS the amplitude of your wave? Actually I would predict that for 7 cycles within the domain of the data set you are better off than the situation which I have simulated, since 1 noise cycle (sine wave) is skewed and thus in not an un-biased addition<BR>
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Regards<BR>
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Arthur<BR>
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*using our INVEQ software<BR>
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<BLOCKQUOTE><FONT SIZE="2"><FONT FACE="Arial">Hi All,</FONT></FONT> <BR>
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<FONT SIZE="2"><FONT FACE="Arial">We have been experiencing a problem with our interference data in which after data fitting, the residuals frequently have a systematic ³wavy² look to them where they rise above and below zero multiple times >7 across the fitted data. Subtracting a water blank does not fix the problem, and it has occurred an several different samples. In real time, the fringes also ³jump² during centrifugation. Is this an indication of an equipment problem, perhaps that there is something unstable in the centrifuge and/or optical system that is leading to the movement of the fringe pattern detected by the camera? If so, is there a likely culprit? If not, what is likely to cause this?</FONT></FONT> <BR>
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<FONT SIZE="2"><FONT FACE="Arial">Thanks for the help, <BR>
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<FONT FACE="Times New Roman">Debra M. Eckert, Ph.D.</FONT> <BR>
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<FONT FACE="Times New Roman">Research Assistant Professor of Biochemistry</FONT> <BR>
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<FONT FACE="Times New Roman">University</FONT> of Utah <BR>
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<FONT FACE="Times New Roman">deckert@biochem.utah.edu</FONT> <BR>
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