[RASMB] Strange AUC noise

[Laue, Thomas]

Hi-
Were these Spin60 or Spin50 cells? If they were Spin60, it might be that the lamp timing on the ‘noisy’ machine is causing the light pulse to partially hit the centerpiece wall. This is a machine-to-machine problem, consistent with what you are seeing. However, the telltale for the timing problem is increased noise in the scans, often at the top of the cell, not a wave.  Consequently, I vote for the slit assembly lifting (John’s suggestion).
Tom


From: RASMB [mailto:rasmb-bounces at list.rasmb.org] On Behalf Of John Philo
Sent: Monday, October 19, 2015 5:00 PM
To: 'David Hayes'; 'RASMB'
Subject: Re: [RASMB] Strange AUC noise

David, I will speculate that you have a problem with the slit assembly. You might see something like that if the foil on the bottom side has come partially loose. Or perhaps there is some dirt or a burr causing the whole assembly to lift up at certain radial positions.
I once had the foil come loose in a way that produced wild outlier scans, but only every once in while (a few per run). Intermittently the foil would actually catch on something (probably the ring on top of the PMT) and fold completely back on itself.
And by the way, you should remind your people to fill the cells much more. You want the meniscus to be up near 5.9 cm, not at ~6.25 cm.
John
From: RASMB [mailto:rasmb-bounces at list.rasmb.org] On Behalf Of David Hayes
Sent: Monday, October 19, 2015 11:14 AM
To: RASMB <rasmb at rasmb.org<mailto:rasmb at rasmb.org>>
Subject: [RASMB] Strange AUC noise

Hi all,

We had some strange AUC noise in a recent experiment.  In the pictures below from SEDFIT, the first two runs produced data as in the picture NNBekman1 (the IT guys name our instruments and they pruposely mispelled Beckman as Bekman years ago). A strange noise pattern showed up in the scans that were produced on day one.  Then the sample was loaded into a new cell and run again on the same centrifuge producing the strange noise pattern in the picture called NNBekman1.   the filled cell was taken and gently mixed and then run on another centrifuge Bekman17 and made a perfectly fine patter shown in picture Beckman17.

We have seen the strange noise before on our NNBekman1 centrifuge, but this is the first time on NNBekman2.

Has anyone seen noise like this?
Any theories on the cause of the noise?

It certainly looks like an optical artifact of some kind, but the time dependence is hard to explain.

Kind Regards,

David Hayes



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