[RASMB] Abrupt change in intensity

[pjgb at mrc-lmb.cam.ac.uk]

Dear Holger/Karl,

>From the description it seems that there may be some change in intensity of 
the light coming from your lamp - I would have thought unlikely to be the 
lamp itself suddenly getting brighter (losing intensity would be more 
likely), but it could be something moving out of the lightpath.  This would 
not affect absorbance scans, since both I and I0 would change 
proportionately, so the ratio I/I0 would not alter - compatible with what 
Holger says.

Jo

--On Friday, August 11, 2006 9:40 am +0200 Holger Strauss 
<Holger.Strauss at mpikg.mpg.de> wrote:

> Karl,
>
> though I don't know what's going on, I have also observed this phenomenon
> for intensity data at different wavelengths and at different absolute
> values for the intensity (and much lower than your 23 000 counts), so it
> is also machine-independent. It is not always present though but I
> couldn't find out what really causes it. Strangely enough, recording
> absorbance instead of intensity seems to work fine. The analysis is OK if
> you set the fitting limit after this cutoff, or if you exclude the first
> eighteen scans, so it really seems to be a cutoff and not a systematic
> error affecting the other data points.
>
> Any more input is greatly appreciated!
>
> Cheers, Holger
>
>> Dear All,
>>
>> I have attached the raw intensity data for a recent sedimentation
>> velocity experiment.  The first 18 scans showed a baseline intensity
>> around 23000 counts (for both air and buffer).  Then for scan 19,
>> the intensity suddenly increased to around 35000 counts and
>> contained much more systematic noise.  According to the header files
>> for every scan, the wavelength was set at 260 nm.  What is going on?
>>
>> Thanks for any help,
>>
>> Karl Maluf
>
>
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P.J.G. Butler,
MRC Laboratory of Molecular Biology,
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