> Then I went into the Follow Shift Changes dialog to take a look at what
> that did (obviously not a typical set of data to put into it but it
> seemed to immediately be offering to calculate shift changes as a
> function of delay time so I thought I would carry on. So I tried it and
> seem to get strange results. According to the graphs (one is shown) the
> shift changes of all peaks seem to be monotonically increasing with
> delay time (so I thought maybe there is a temperature effect in the
> pulse program). But if I look at the raw shifts reported in the peak
> selection table the evidence is for a much more chaotic variation.
>
> A screenshot is attached. What is going on ? Is there a difference
> between the crosspeak positions reported in the peak selection table and
> those used for the shift change calculations ? Am I misinterpreting what
> is being shown ? Is there a help page for this popup - I could not find one.
The Follow Shift Changes popup is plotting the cumulative shift distance
for the peaks groups against time, so even if the peaks are scattered and
not in a line there will almost always be some distance between one peak
and the next in the series.
If the peaks were already grouped together after the rate analysis, then
the grouping for the shift changes is also defined. Thus, there was no
need for Analysis to try to find peak groups following a linear
trajectory. ( Which works to optimise fit of shift distance to the series
value, as well as positional linearity )
This system was built in this way so as to try and treat all points of a
series with the same significance (although there has to be some reference
for assignments) and to not assume that every trajectory is always in a
straight line in every conceivable situation. Also, it means that if you
ever had a situation where peak groups could not be discerned by the
trajectory search you can still manually propagate assignments and still
be able to measure the shift changes.
I could include a 'linearity of trajectory' column in the future if
absolutely essential.
It should be noted that if you started from unassigned peaks and set a low
value for the Shift Error (how much grace points have to defy a linear
trajectory when they are on top of one another) then most peaks would not
be groupable.
In general however, this system was not built to look at such things.
> (When I did group peaks it told me that "Experiments in series do not
> have individual shift lists. Link each experiment to its own shift list
> ?". I usually said "no", but also go the same result if I say "yes").
Indeed, this should make no difference. Only if the shifts were changing
significantly would one opt to have separate shift lists, but that would
be the case in most circumstances.
T.
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Dr Tim Stevens Email: [log in to unmask]
Department of Biochemistry [log in to unmask]
University of Cambridge Phone: +44 1223 766018 (office)
80 Tennis Court Road +44 7816 338275 (mobile)
Old Addenbrooke's Site +44 1223 364613 (home)
Cambridge CB2 1GA WWWeb: http://www.bio.cam.ac.uk/~tjs23
United Kingdom http://www.pantonia.co.uk
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