The most extreme degree of confusion (or at least of requirement for fast
mental arithmetic) I have come across in relation to this topic is the habit
of small-molecule crystallographers working on accurate density studies to
characterise the resolution limit of their datasets by quoting the maximum
value of sin(theta)/lambda in Angstrom^-1. Upon being told of a dataset
with a resolution of 1.25 in sin(theta)/lambda you have to quickly deduce
that the maximum d* value is 2.50 and therefore, in protein crystallographer
lingo, the resolution limit dmin is 0.40 Angstrom. Then, you start feeling
very envious.
With best wishes,
Gerard.
--
On Thu, Jun 30, 2011 at 02:07:28PM -0400, Richard Edward Gillilan wrote:
This has been a point of confusion
Here are the conventions used in a few of the classic SAXS text vs. recent
reviews:
--
I believe Guinier actually used the variable u in his thesis, but must have
changed at some point (I don't have it handy to check at the moment).
Guinier Fournet (1955) h = 4pi Sin(theta)/lambda where 2*theta =
scattering angle
Glatter Kratky (1982) (including chapters by Porod and other authors)
h = 4pi Sin(theta)/lambda
--- so h makes sense if one is familiar with crystallography derivations.
Feigin Svergun (1987) s = 4pi Sin(theta)/lambda
The notation s seems to come from the notation for scattering vectors.
Svergun publications consistently use s this way, though the software can
define s with or without the 2pi and in either inverse nanometers or inverse
Angstroms. In my experience very few use 2Sin(theta)/lambda, though it is
more familiar to crystallographers as the inverse of the d-spacing.
But q is widely used in BioSAXS:
Putnam, Hammel, Hura Tainer (2007) q = 4 pi Sin(theta)/lambda
Jacques and Trewhella (2010)q = 4 pi Sin(theta)/lambda
Why q? I haven't traced it back yet. From generalized coordinate of classical
mechanics maybe?
On Jun 30, 2011, at 3:37 AM, James Stroud wrote:
Hello All,
Is there precedent or a conventional shorthand (e.g. greek letter) for
sin(theta)/lambda?
Thanks in advance for any help or suggestions.
James
--
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