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
--
===============================================================
* *
* Gerard Bricogne g...@globalphasing.com *
* *
* Global Phasing Ltd. *
* Sheraton House, Castle Park Tel: +44-(0)1223-353033 *
* Cambridge CB3 0AX, UK Fax: +44-(0)1223-366889 *
* *
===============================================================
