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<p class="MsoNormal"><span style="font-size:14.0pt;font-family:"Times New Roman",serif">Hi-<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:14.0pt;font-family:"Times New Roman",serif">Good to know. On the Optima, the problem will appear during a heating cycle. I believe the Optima does not use PID (proportional) thermal control, so the heating pulses
can be large enough and long enough to not dissipate sufficiently before reaching the cells.
<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:14.0pt;font-family:"Times New Roman",serif">In the XLI, the expectation is the opposite. Since the TE modules are towards the center of the rotor, a destabilizing thermal gradient can be produced during the cooling
cycle.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:14.0pt;font-family:"Times New Roman",serif">In both cases, allowing a long enough equilibration time minimizes (but does not eliminate) the potential for convection.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:14.0pt;font-family:"Times New Roman",serif">Best wishes,<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:14.0pt;font-family:"Times New Roman",serif">Tom<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:14.0pt;font-family:"Times New Roman",serif"><o:p> </o:p></span></p>
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<p class="MsoNormal"><b>From:</b> RASMB <rasmb-bounces@list.rasmb.org> <b>On Behalf Of
</b>Walter, Johannes<br>
<b>Sent:</b> Wednesday, March 10, 2021 4:17 AM<br>
<b>To:</b> rasmb@rasmb.org<br>
<b>Subject:</b> Re: [RASMB] Boundary convection problem in the Optima ultracentrifuge<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal" style="margin-bottom:12.0pt"><strong><span lang="DE" style="font-family:"Calibri",sans-serif;color:red">Caution - External Email</span></strong><span lang="DE"><br>
<br>
<o:p></o:p></span></p>
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<p class="MsoNormal"><span lang="DE" style="color:#1F497D">Dear Tom,<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="DE" style="color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D">Thank you very much for that very interesting paper. Fortunately, we do not observe any convection issues with our Optima as long as the temperature equilibration is at least 6 h (below that, we see severe issues
for many analytes). By the way, there is a very interesting study by Sloutskin et al.:<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D"><a href="https://nam12.safelinks.protection.outlook.com/?url=https%3A%2F%2Fwww.sciencedirect.com%2Fscience%2Farticle%2Fpii%2FS0927775715003180&data=04%7C01%7Ctom.laue%40unh.edu%7C93dc6a5704344ae4039708d8e3a57776%7Cd6241893512d46dc8d2bbe47e25f5666%7C0%7C0%7C637509647557566997%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000&sdata=t6Wm%2F9ayKAMipjL1faJaAK%2F4ryYDdWf7aNMRmFyHenw%3D&reserved=0">https://www.sciencedirect.com/science/article/pii/S0927775715003180</a><o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D">They studied convection and layering effects in analytical centrifugation, where similar issues are observed due to the cooling system.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D">Best wishes,<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D">Johannes<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="DE"><o:p> </o:p></span></p>
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<p class="MsoNormal"><b><span lang="DE">Von:</span></b><span lang="DE"> RASMB <<a href="mailto:rasmb-bounces@list.rasmb.org">rasmb-bounces@list.rasmb.org</a>>
<b>Im Auftrag von </b>Laue, Thomas<br>
<b>Gesendet:</b> Dienstag, 9. März 2021 21:41<br>
<b>An:</b> RASMB <<a href="mailto:rasmb@rasmb.org">rasmb@rasmb.org</a>><br>
<b>Betreff:</b> [RASMB] Boundary convection problem in the Optima ultracentrifuge<o:p></o:p></span></p>
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<p class="MsoNormal"><span lang="DE"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:14.0pt;font-family:"Times New Roman",serif">Dear all-<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:14.0pt;font-family:"Times New Roman",serif">Data acquired using the Optima ultracentrifuge may exhibit boundary convection, thus confounding the precision and accuracy of data analysis and interpretation from this
instrument. Not all instruments exhibit the phenomenon, and the problem is intermittent on others. The root cause are thermal ‘waves’ that travel from the rotor edge towards the center. These waves produce density gradients in the solution which, in turn,
may be driven by the gravitational field to cause turbulent flow and consequent mixing between adjacent sample regions. The problem is most pronounced in low-concentration buffers where little-to-no stabilizing density gradient forms due to solvent component
redistribution.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:14.0pt;font-family:"Times New Roman",serif">There is a paper available describing the problem, its causes, how to detect it and ways to minimize its occurrence:
<a href="https://nam12.safelinks.protection.outlook.com/?url=https%3A%2F%2Fbiorxiv.org%2Fcgi%2Fcontent%2Fshort%2F2021.03.08.434487v1&data=04%7C01%7Ctom.laue%40unh.edu%7C93dc6a5704344ae4039708d8e3a57776%7Cd6241893512d46dc8d2bbe47e25f5666%7C0%7C0%7C637509647557576957%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000&sdata=20rLmmSF2IZFA2tLrXBFOiUxhWQQwu4jE0G9Bw6YdIs%3D&reserved=0">
https://biorxiv.org/cgi/content/short/2021.03.08.434487v1</a><o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:14.0pt;font-family:"Times New Roman",serif">Best wishes,<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:14.0pt;font-family:"Times New Roman",serif">Tom<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:14.0pt;font-family:"Times New Roman",serif"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:14.0pt;font-family:"Times New Roman",serif"><o:p> </o:p></span></p>
<p class="MsoNormal">Professor Emeritus<o:p></o:p></p>
<p class="MsoNormal">University of New Hampshire<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
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