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<p class=MsoNormal><font size=2 face="Times New Roman"><span style='font-size:
11.0pt'>I attached the wrong file to the last message please disregard the
prior attachment and use this one.<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face="Times New Roman"><span style='font-size:
11.0pt'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 face="Times New Roman"><span style='font-size:
11.0pt'>Dear RASMB members,<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face="Times New Roman"><span style='font-size:
11.0pt'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 face="Times New Roman"><span style='font-size:
11.0pt'>I have recently been struggling with a recurring problem when I
centrifuge 10 and 20nm gold particles that causes my XLA to generate poorly
formed OD data scans that cannot be fit by Sedfit. I had initially been getting
well formed scans that were easily fit by Sedfit using the continuous c(s)
model however after half of the sample side in one cell (in a 4 cell rotor)
leaked out during a run I was no longer able to get the nice sigmoidal scans
that I originally had even though I tightened and refilled the leaking cell. I
asked the Beckman service rep to investigate and he cleaned the optics and told
me to have the XLA perform a radial calibration and the scans were back to a
sigmoidal shape using the same sample of gold nanoparticles and Sedfit could
fit the data well again. However after another cell leaked in the centrifuge,
the scans could not be fit with Sedfit even though the cell was tightened and
refilled and no longer leaked. I have been performing a radial calibration
before each run and have not turned off the delay calibration hoping the
instrument will recalibrate and improve the scans however, this has not
happened. I have attached screen shots showing the quality of the data before
and after the cell leak. It looks like it could be the optics but I am not
convinced this is the whole story since it seems extreme that one cell leak can
alter the XLA performance this much until the optics are cleaned.<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face="Times New Roman"><span style='font-size:
11.0pt'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 face="Times New Roman"><span style='font-size:
11.0pt'><o:p> </o:p></span></font></p>
<p class=MsoAutoSig><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'>James B. Falabella<o:p></o:p></span></font></p>
<p class=MsoAutoSig><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'>Process Sensing Group<o:p></o:p></span></font></p>
<p class=MsoAutoSig><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'>National <st1:PlaceType w:st="on">Institute</st1:PlaceType> of <st1:PlaceName
w:st="on">Standards</st1:PlaceName> and Technology <st1:place w:st="on"><st1:City
w:st="on">Gaithersburg</st1:City>, <st1:State w:st="on">MD</st1:State></st1:place><o:p></o:p></span></font></p>
<p class=MsoAutoSig><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'>Tel: 301-975-5041<o:p></o:p></span></font></p>
<p class=MsoAutoSig><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'>Fax: 301-975-2643<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'><o:p> </o:p></span></font></p>
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