swollen sphere parameterization (Trac #605) #737
Description
Improve description of ''phi'' and ''x'' parameters. Is ''phi'' supposed to be volume fraction of spheres, and ''x'' the solvent fraction within spheres? The redundant ''scale'' parameter is automatically included in all models, and has been removed.
Documentation, including equations, needs to reflect the additional parameters.
''phi'' need not be polydisperse; the integral over a polydisperse scale factor is indistinguishable from a monodisperse scale factor equal to the weighted average of the polydisperse scale factor.
Is solvent fraction ''x'' supposed to be polydisperse? In which case with different spheres absorbing different amounts of solvent, shouldn't the underlying ''radius'' be increased and ''sld'' adjusted toward ''sld_solvent'' as solvent fraction increases? As it is now, being a scale factor on the sphere form, there is no reason to make it polydisperse.
As contrast is reduced by solvent fraction in the sphere, shouldn't the sphere form factor be reduced by the squared fraction? This would occur automatically if ''sld'' were adjusted toward ''sld_solvent'' by factor ''(1-x)''.
Migrated from http://trac.sasview.org/ticket/605
{
"status": "closed",
"changetime": "2016-10-10T21:52:22",
"_ts": "2016-10-10 21:52:22.851332+00:00",
"description": "Improve description of ''phi'' and ''x'' parameters. Is ''phi'' supposed to be volume fraction of spheres, and ''x'' the solvent fraction within spheres? The redundant ''scale'' parameter is automatically included in all models, and has been removed.\n\nDocumentation, including equations, needs to reflect the additional parameters.\n\n''phi'' need not be polydisperse; the integral over a polydisperse scale factor is indistinguishable from a monodisperse scale factor equal to the weighted average of the polydisperse scale factor.\n\nIs solvent fraction ''x'' supposed to be polydisperse? In which case with different spheres absorbing different amounts of solvent, shouldn't the underlying ''radius'' be increased and ''sld'' adjusted toward ''sld_solvent'' as solvent fraction increases? As it is now, being a scale factor on the sphere form, there is no reason to make it polydisperse.\n\nAs contrast is reduced by solvent fraction in the sphere, shouldn't the sphere form factor be reduced by the squared fraction? This would occur automatically if ''sld'' were adjusted toward ''sld_solvent'' by factor ''(1-x)''.\n",
"reporter": "pkienzle",
"cc": "",
"resolution": "obsolete",
"workpackage": "SasView Bug Fixing",
"time": "2016-07-31T22:31:16",
"component": "SasView",
"summary": "swollen sphere parameterization",
"priority": "major",
"keywords": "",
"milestone": "SasView Next Release +1",
"owner": "",
"type": "defect"
}