Dear Veronica,
At first glance, it looks as if you have a textbook example of
progressive radiation damage, i.e. the structure is changing between
the start and the end of your experiment, and the scaling gets skewed
towards finding a best compromise between all the measurements at
medium (rather than low) resolution. The "smiley" shape in the Rmeas
is something that Zbyszek Dauter identified many years ago as a
tell-tale sign of progressive radiation damage.
You say that each of your 6 datasets is "taken from a fresh spot
on the crystal", but how big is your beam relative to the crystal? How
far apart are these spots? Most of all: at room temperature, free
radicals will diffuse much more readily than in a frozen crystal, so
that your later datasets may not in fact come from truly fresh spots.
I hope this is helpful.
With best wishes,
Gerard.
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On Fri, Feb 27, 2015 at 03:40:38PM -0500, Veronica Pillar wrote:
> Hi all,
>
> I have a data set from a large room-temperature lysozyme crystal consisting
> of 6 90-degree sweeps, each taken from a fresh spot on the crystal. When I
> scale & merge the first sweep by itself, the R[meas/merge] vs. resolution
> trace as reported by aimless looks fairly normal (lowest values in the
> 6-2.5 A range and steadily increasing at higher resolution). However, as I
> look at the subsequent sweeps individually, the traces get progressively
> stranger until the final sweep's R vs. resolution trace looks like a smiley
> face, lowest around 2.5 A and about the same in the lowest and highest
> resolution bins. The overall Rmeas is about the same for all sweeps
> (3.0-3.2%). Do you have any ideas on what has happened (either during data
> collection or data processing) to cause this?
>
> Thanks,
> Veronica
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