1 | # rectangular_prism model |
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2 | # Note: model title and parameter table are inserted automatically |
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3 | r""" |
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4 | Definition |
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5 | ---------- |
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6 | |
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7 | |
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8 | This model provides the form factor, $P(q)$, for a hollow rectangular |
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9 | prism with infinitely thin walls. It computes only the 1D scattering, not the 2D. |
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10 | The 1D scattering intensity for this model is calculated according to the |
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11 | equations given by Nayuk and Huber\ [#Nayuk2012]_. |
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12 | |
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13 | Assuming a hollow parallelepiped with infinitely thin walls, edge lengths |
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14 | $A \le B \le C$ and presenting an orientation with respect to the |
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15 | scattering vector given by $\theta$ and $\phi$, where $\theta$ is the angle |
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16 | between the $z$ axis and the longest axis of the parallelepiped $C$, and |
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17 | $\phi$ is the angle between the scattering vector (lying in the $xy$ plane) |
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18 | and the $y$ axis, the form factor is given by |
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19 | |
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20 | .. math:: |
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21 | |
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22 | P(q) = \frac{1}{V^2} \frac{2}{\pi} \int_0^{\frac{\pi}{2}} |
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23 | \int_0^{\frac{\pi}{2}} [A_L(q)+A_T(q)]^2 \sin\theta\,d\theta\,d\phi |
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24 | |
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25 | where |
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26 | |
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27 | .. math:: |
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28 | |
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29 | V &= 2AB + 2AC + 2BC \\ |
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30 | A_L(q) &= 8 \times \frac{ |
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31 | \sin \left( \tfrac{1}{2} q A \sin\phi \sin\theta \right) |
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32 | \sin \left( \tfrac{1}{2} q B \cos\phi \sin\theta \right) |
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33 | \cos \left( \tfrac{1}{2} q C \cos\theta \right) |
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34 | }{q^2 \, \sin^2\theta \, \sin\phi \cos\phi} \\ |
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35 | A_T(q) &= A_F(q) \times |
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36 | \frac{2\,\sin \left( \tfrac{1}{2} q C \cos\theta \right)}{q\,\cos\theta} |
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37 | |
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38 | and |
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39 | |
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40 | .. math:: |
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41 | |
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42 | A_F(q) = 4 \frac{ \cos \left( \tfrac{1}{2} q A \sin\phi \sin\theta \right) |
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43 | \sin \left( \tfrac{1}{2} q B \cos\phi \sin\theta \right) } |
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44 | {q \, \cos\phi \, \sin\theta} + |
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45 | 4 \frac{ \sin \left( \tfrac{1}{2} q A \sin\phi \sin\theta \right) |
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46 | \cos \left( \tfrac{1}{2} q B \cos\phi \sin\theta \right) } |
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47 | {q \, \sin\phi \, \sin\theta} |
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48 | |
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49 | The 1D scattering intensity is then calculated as |
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50 | |
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51 | .. math:: |
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52 | |
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53 | I(q) = \text{scale} \times V \times (\rho_\text{p} - \rho_\text{solvent})^2 \times P(q) |
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54 | |
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55 | where $V$ is the surface area of the rectangular prism, $\rho_\text{p}$ |
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56 | is the scattering length density of the parallelepiped, $\rho_\text{solvent}$ |
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57 | is the scattering length density of the solvent, and (if the data are in |
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58 | absolute units) *scale* is related to the total surface area. |
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59 | |
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60 | **The 2D scattering intensity is not computed by this model.** |
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61 | |
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62 | |
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63 | Validation |
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64 | ---------- |
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65 | |
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66 | Validation of the code was conducted by qualitatively comparing the output |
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67 | of the 1D model to the curves shown in (Nayuk, 2012\ [#Nayuk2012]_). |
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68 | |
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69 | |
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70 | References |
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71 | ---------- |
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72 | |
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73 | .. [#Nayuk2012] R Nayuk and K Huber, *Z. Phys. Chem.*, 226 (2012) 837-854 |
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74 | .. [#] L. Onsager, *Ann. New York Acad. Sci.*, 51 (1949) 627-659 |
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75 | |
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76 | Source |
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77 | ------ |
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78 | |
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79 | `hollow_rectangular_prism_thin_walls.py <https://github.com/SasView/sasmodels/blob/master/sasmodels/models/hollow_rectangular_prism_thin_walls.py>`_ |
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80 | |
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81 | `hollow_rectangular_prism_thin_walls.c <https://github.com/SasView/sasmodels/blob/master/sasmodels/models/hollow_rectangular_prism_thin_walls.c>`_ |
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82 | |
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83 | Authorship and Verification |
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84 | ---------------------------- |
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85 | |
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86 | * **Author:** Miguel Gonzales **Date:** February 26, 2016 |
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87 | * **Last Modified by:** Paul Kienzle **Date:** October 15, 2016 |
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88 | * **Last Reviewed by:** Paul Butler **Date:** September 07, 2018 |
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89 | * **Source added by :** Steve King **Date:** March 25, 2019 |
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90 | """ |
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91 | |
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92 | import numpy as np |
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93 | from numpy import inf |
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94 | |
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95 | name = "hollow_rectangular_prism_thin_walls" |
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96 | title = "Hollow rectangular parallelepiped with thin walls." |
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97 | description = """ |
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98 | I(q)= scale*V*(sld - sld_solvent)^2*P(q)+background |
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99 | with P(q) being the form factor corresponding to a hollow rectangular |
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100 | parallelepiped with infinitely thin walls. |
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101 | """ |
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102 | category = "shape:parallelepiped" |
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103 | |
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104 | # ["name", "units", default, [lower, upper], "type","description"], |
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105 | parameters = [["sld", "1e-6/Ang^2", 6.3, [-inf, inf], "sld", |
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106 | "Parallelepiped scattering length density"], |
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107 | ["sld_solvent", "1e-6/Ang^2", 1, [-inf, inf], "sld", |
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108 | "Solvent scattering length density"], |
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109 | ["length_a", "Ang", 35, [0, inf], "volume", |
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110 | "Shorter side of the parallelepiped"], |
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111 | ["b2a_ratio", "Ang", 1, [0, inf], "volume", |
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112 | "Ratio sides b/a"], |
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113 | ["c2a_ratio", "Ang", 1, [0, inf], "volume", |
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114 | "Ratio sides c/a"], |
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115 | ] |
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116 | |
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117 | source = ["lib/gauss76.c", "hollow_rectangular_prism_thin_walls.c"] |
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118 | have_Fq = True |
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119 | radius_effective_modes = [ |
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120 | "equivalent cylinder excluded volume", "equivalent outer volume sphere", |
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121 | "half length_a", "half length_b", "half length_c", |
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122 | "equivalent outer circular cross-section", |
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123 | "half ab diagonal", "half diagonal", |
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124 | ] |
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125 | |
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126 | |
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127 | def random(): |
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128 | """Return a random parameter set for the model.""" |
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129 | a, b, c = 10**np.random.uniform(1, 4.7, size=3) |
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130 | pars = dict( |
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131 | length_a=a, |
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132 | b2a_ratio=b/a, |
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133 | c2a_ratio=c/a, |
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134 | ) |
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135 | return pars |
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136 | |
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137 | |
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138 | # parameters for demo |
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139 | demo = dict(scale=1, background=0, |
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140 | sld=6.3, sld_solvent=1.0, |
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141 | length_a=35, b2a_ratio=1, c2a_ratio=1, |
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142 | length_a_pd=0.1, length_a_pd_n=10, |
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143 | b2a_ratio_pd=0.1, b2a_ratio_pd_n=1, |
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144 | c2a_ratio_pd=0.1, c2a_ratio_pd_n=1) |
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145 | |
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146 | tests = [[{}, 0.2, 0.837719188592], |
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147 | [{}, [0.2], [0.837719188592]], |
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148 | ] |
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