source: sasmodels/sasmodels/models/core_shell_sphere.py @ 7d4b2ae

core_shell_microgelscostrafo411magnetic_modelrelease_v0.94release_v0.95ticket-1257-vesicle-productticket_1156ticket_1265_superballticket_822_more_unit_tests
Last change on this file since 7d4b2ae was 7d4b2ae, checked in by piotr, 8 years ago

Added fractal_core_shell

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1r"""
2This model provides the form factor, $P(q)$, for a spherical particle with a core-shell structure.
3The form factor is normalized by the particle volume.
4
5Definition
6----------
7
8The 1D scattering intensity is calculated in the following way (Guinier, 1955)
9
10.. math::
11
12    P(q) = \frac{\text{scale}}{V} F^2(q) + \text{background}
13
14where
15
16.. math::
17
18    F^2(q)=\frac{3}{V_s}\left[V_c(\rho_c-\rho_s)\frac{\sin(qr_c)-qr_c\cos(qr_c)}{(qr_c)^3}+
19    V_s(\rho_s-\rho_{solv})\frac{\sin(qr_s)-qr_s\cos(qr_s)}{(qr_s)^3}\right]
20
21where $V_s$ is the volume of the outer shell, $V_c$ is
22the volume of the core, $r_s$ is the radius of the shell, $r_c$ is the radius of the
23core, $\rho_c$ is the scattering length density of the core, $\rho_s$ is the scattering length
24density of the shell, $\rho_{solv}$ is the scattering length density of the solvent.
25
26The 2D scattering intensity is the same as $P(q)$ above, regardless of the
27orientation of the $q$ vector.
28
29NB: The outer most radius (ie, = radius + thickness) is used as the
30effective radius for $S(Q)$ when $P(Q) \cdot S(Q)$ is applied.
31
32Reference
33---------
34
35A Guinier and G Fournet, *Small-Angle Scattering of X-Rays*, John Wiley and Sons, New York, (1955)
36
37Validation
38----------
39
40Validation of our code was done by comparing the output of the 1D model to the output of
41the software provided by NIST (Kline, 2006). Figure 1 shows a comparison of the output of
42our model and the output of the NIST software.
43
44.. figure:: img/core_shell_sphere_1d.jpg
45
46    Comparison of the SasView scattering intensity for a core-shell sphere with
47    the output of the NIST SANS analysis software. The parameters were set to:
48    *scale* = 1.0, *radius* = 60 , *contrast* = 1e-6 |Ang^-2|, and
49    *background* = 0.001 |cm^-1|.
50"""
51
52from numpy import pi, inf
53
54name = "core_shell_sphere"
55title = "Form factor for a monodisperse spherical particle with particle with a core-shell structure."
56description = """
57    F^2(q) = 3/V_s [V_c (core_sld-shell_sld) (sin(q*radius)-q*radius*cos(q*radius))/(q*radius)^3
58                   + V_s (shell_sld-solvent_sld) (sin(q*r_s)-q*r_s*cos(q*r_s))/(q*r_s)^3]
59
60            V_s: Volume of the sphere shell
61            V_c: Volume of the sphere core
62            r_s: Shell radius = radius + thickness
63"""
64category = "shape:sphere"
65
66# pylint: disable=bad-whitespace, line-too-long
67#             ["name", "units", default, [lower, upper], "type","description"],
68parameters = [["radius",      "Ang",        60.0, [0, inf],    "volume", "Sphere core radius"],
69              ["thickness",   "Ang",        10.0, [0, inf],    "volume", "Sphere shell thickness"],
70              ["core_sld",    "1e-6/Ang^2", 1.0,  [-inf, inf], "",       "Sphere core scattering length density"],
71              ["shell_sld",   "1e-6/Ang^2", 2.0,  [-inf, inf], "",       "Sphere shell scattering length density"],
72              ["solvent_sld", "1e-6/Ang^2", 3.0,  [-inf, inf],  "",      "Solvent scattering length density"]]
73# pylint: enable=bad-whitespace, line-too-long
74
75source = ["lib/sph_j1c.c", "lib/core_shell.c", "core_shell_sphere.c"]
76
77demo = dict(scale=1, background=0, radius=60, thickness=10,
78            core_sld=1.0, shell_sld=2.0, solvent_sld=0.0)
79
80oldname = 'CoreShellModel'
81oldpars = {}
82
83def ER(radius, thickness):
84    """
85        Equivalent radius
86        @param radius: core radius
87        @param thickness: shell thickness
88    """
89    return radius + thickness
90
91def VR(radius, thickness):
92    """
93        Volume ratio
94        @param radius: core radius
95        @param thickness: shell thickness
96    """
97    whole = 4.0 * pi / 3.0 * pow((radius + thickness), 3)
98    core = 4.0 * pi / 3.0 * radius * radius * radius
99    return whole, whole - core
100
101tests = [[{'radius': 20.0, 'thickness': 10.0}, 'ER', 30.0],
102         [{'radius': 20.0, 'thickness': 10.0}, 'VR', 0.703703704],
103
104         # The SasView test result was 0.00169, with a background of 0.001
105         [{'radius': 60.0,
106           'thickness': 10.0,
107           'core_sld': 1.0,
108           'shell_sld':2.0,
109           'solvent_sld':3.0,
110           'background':0.0
111          }, 0.4, 0.000698838]]
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