Changeset 96153e4 in sasmodels for sasmodels/models/core_shell_parallelepiped.py
 Timestamp:
 May 20, 2018 11:22:28 PM (4 years ago)
 Branches:
 master, core_shell_microgels, magnetic_model, ticket1257vesicleproduct, ticket_1156, ticket_1265_superball, ticket_822_more_unit_tests
 Children:
 fc7bcd5
 Parents:
 c64a68e
 File:

 1 edited
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sasmodels/models/core_shell_parallelepiped.py
r5bc6d21 r96153e4 4 4 5 5 Calculates the form factor for a rectangular solid with a coreshell structure. 6 The thickness and the scattering length density of the shell or 7 "rim" can be different on each (pair) of faces. 6 The thickness and the scattering length density of the shell or "rim" can be 7 different on each (pair) of faces. The three dimensions of the core of the 8 parallelepiped (strictly here a cuboid) may be given in *any* size order as 9 long as the particles are randomly oriented (i.e. take on all possible 10 orientations see notes on 2D below). To avoid multiple fit solutions, e 11 specially with MonteCarlo fit methods, it may be advisable to restrict their 12 ranges. There may be a number of closely similar "best fits", so some trial and 13 error, or fixing of some dimensions at expected values, may help. 8 14 9 15 The form factor is normalized by the particle volume $V$ such that … … 18 24 pulled out of the form factor term due to the multiple slds in the model. 19 25 20 The core of the solid is defined by the dimensions $A$, $B$, $C$ such that21 $A < B < C$.26 The core of the solid is defined by the dimensions $A$, $B$, $C$ here shown 27 such that $A < B < C$. 22 28 23 29 .. figure:: img/parallelepiped_geometry.jpg … … 104 110 ~~~~~~~~~~~~~ 105 111 106 If the scale is set equal to the particle volume fraction, $\phi$, the returned107 value is the scattered intensity per unit volume, $I(q) = \phi P(q)$. However,108 **no interparticle interference effects are included in this calculation.**109 110 112 There are many parameters in this model. Hold as many fixed as possible with 111 113 known values, or you will certainly end up at a solution that is unphysical. 112 114 113 The returned value is in units of cm^1, on absolute scale.114 115 115 116 NB: The 2nd virial coefficient of the core_shell_parallelepiped is calculated … … 120 121 121 122 For 2d data the orientation of the particle is required, described using 122 angles $\theta$, $\phi$ and $\Psi$ as in the diagrams below. For further 123 details of the calculation and angular dispersions see :ref:`orientation`. 124 The angle $\Psi$ is the rotational angle around the *long_c* axis. For example, 125 $\Psi = 0$ when the *short_b* axis is parallel to the *x*axis of the detector. 123 angles $\theta$, $\phi$ and $\Psi$ as in the diagrams below, for further details 124 of the calculation and angular dispersions see :ref:`orientation` . 125 126 The angle $\Psi$ is the rotational angle around the $C$ axis. 127 For $\theta = 0$ and $\phi = 0$, $\Psi = 0$ corresponds to the $B$ axis 128 oriented parallel to the yaxis of the detector with $A$ along the xaxis. 129 For other $\theta$, $\phi$ values, the parallelepiped has to be first rotated 130 $\theta$ degrees in the $zx$ plane and then $\phi$ degrees around the $z$ axis, 131 before doing a final rotation of $\Psi$ degrees around the resulting $C$ axis 132 of the particle to obtain the final orientation of the parallelepiped. 126 133 127 134 .. note:: For 2d, constraints must be applied during fitting to ensure that the
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