Investigate core shell bicelle model

[richardh]

Looking at the c kernel code, I suspect that L in the model is actually the half length of the core, NOT the full length.

The equation in the description is not what is actually calculated.

I am not convinced yet that results are correct if sld of face is different to sld of rim.

The manual needs a diagram for the geometry of the bicelle. (The part with sld_face has radius Rcore)

[richardh]

The Length is OK (of course), as it got halved elsewhere.

[richardh]

The limiting cases of:

(a) SLDface = SLDrim does generate a core/shell cylinder as expected.

(b) SLDcore=SLDface=SLDsolvent does generate a hollow cylinder (i.e. tube or pipe), as expected.

© SLDrim=SLDsolvent=SLDcore ought to generate two discs with a gap of L between them, I don't think this happens, suspect some horrible cross terms are missing.

[butler]

regarding the graphic — the current graphic is taken from an RSC journal articles. While it is cited question is whether this constitutes "fair use" or would be a copyright infringement?

[richardh]

Generated new graphics.

I(Q) equations look OK in code, need to check docs page now.

[richardh]

Have generated two new images from scratch.

Edited equation in "description" box.

Starting parameters look a little odd? - hand over to Paul

[butler]

In adc753dbe4450955415a1427496ad3341a93896e/sasmodels:

bicelle model documentation standardized, ref to original derivation and
equations added to rst documentation. re #696 and #646