Model a distribution of SLDs in a composite shape

[pkienzle]

A user presented a core-shell model with a fixed shell but a variable volume fraction of material in the core.

Simulating with sasmodels:

python -m sasmodels.compare core_shell_sphere -q=0.005:0.5 -nq=1000 radius=90 radius_pd=0.2 thickness=30 sld_core=5,10 sld_shell=7.4 sld_solvent=4.47

Orange has core Vf = 100%, blue has core Vf = 0%

Sasmodels only allows polydispersity on shape parameters not on material parameters, so modeling this system would require a custom plugin.

Do we want to allow polydispersity on SLD for models with multiple components?

[butlerpd]

I am very confused. I don't understand what a polydispers SLD means? or how it helps in this instance if it did? To me the issue is about the long standing question of whether we include the variety of molecularly constrained models to the sasmodels package or keep only the physics based models (what the probe actually sees) or some restricted combination.

Other wise is this not a classic example of why one would use the reparameterization editor. (a rather simple one in this case with radius of core replaced by vf of core?)

[pkienzle]

The sample preparation is creating vesicles then inserting varying amounts of material inside them, so the volume fraction of material in the core is a distribution rather than a single value. To model this we would need to do form the incoherent sum across a distribution of volume fractions. We cannot model this with a single average core SLD.

[butlerpd]

Yes .. hummm... some thought required now 😄