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 | |
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5 | This model provides the form factor, $P(q)$, for a hollow rectangular |
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6 | prism with infinitely thin walls. It computes only the 1D scattering, not the 2D. |
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7 | |
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8 | |
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9 | Definition |
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10 | ---------- |
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11 | |
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12 | The 1D scattering intensity for this model is calculated according to the |
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13 | equations given by Nayuk and Huber (Nayuk, 2012). |
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14 | |
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15 | Assuming a hollow parallelepiped with infinitely thin walls, edge lengths |
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16 | $A \le B \le C$ and presenting an orientation with respect to the |
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17 | scattering vector given by $\theta$ and $\phi$, where $\theta$ is the angle |
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18 | between the $z$ axis and the longest axis of the parallelepiped $C$, and |
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19 | $\phi$ is the angle between the scattering vector (lying in the $xy$ plane) |
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20 | and the $y$ axis, the form factor is given by |
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21 | |
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22 | .. math:: |
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23 | |
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24 | P(q) = \frac{1}{V^2} \frac{2}{\pi} \int_0^{\frac{\pi}{2}} |
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25 | \int_0^{\frac{\pi}{2}} [A_L(q)+A_T(q)]^2 \sin\theta\,d\theta\,d\phi |
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26 | |
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27 | where |
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28 | |
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29 | .. math:: |
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30 | |
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31 | V &= 2AB + 2AC + 2BC \\ |
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32 | A_L(q) &= 8 \times \frac{ |
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33 | \sin \left( \tfrac{1}{2} q A \sin\phi \sin\theta \right) |
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34 | \sin \left( \tfrac{1}{2} q B \cos\phi \sin\theta \right) |
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35 | \cos \left( \tfrac{1}{2} q C \cos\theta \right) |
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36 | }{q^2 \, \sin^2\theta \, \sin\phi \cos\phi} \\ |
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37 | A_T(q) &= A_F(q) \times |
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38 | \frac{2\,\sin \left( \tfrac{1}{2} q C \cos\theta \right)}{q\,\cos\theta} |
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39 | |
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40 | and |
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41 | |
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42 | .. math:: |
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43 | |
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44 | A_F(q) = 4 \frac{ \cos \left( \tfrac{1}{2} q A \sin\phi \sin\theta \right) |
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45 | \sin \left( \tfrac{1}{2} q B \cos\phi \sin\theta \right) } |
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46 | {q \, \cos\phi \, \sin\theta} + |
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47 | 4 \frac{ \sin \left( \tfrac{1}{2} q A \sin\phi \sin\theta \right) |
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48 | \cos \left( \tfrac{1}{2} q B \cos\phi \sin\theta \right) } |
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49 | {q \, \sin\phi \, \sin\theta} |
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50 | |
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51 | The 1D scattering intensity is then calculated as |
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52 | |
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53 | .. math:: |
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54 | |
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55 | I(q) = \text{scale} \times V \times (\rho_\text{p} - \rho_\text{solvent})^2 \times P(q) |
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56 | |
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57 | where $V$ is the volume of the rectangular prism, $\rho_\text{p}$ |
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58 | is the scattering length of the parallelepiped, $\rho_\text{solvent}$ |
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59 | is the scattering length of the solvent, and (if the data are in absolute |
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60 | units) *scale* represents the volume fraction (which is unitless). |
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61 | |
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62 | **The 2D scattering intensity is not computed by this model.** |
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63 | |
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64 | |
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65 | Validation |
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66 | ---------- |
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67 | |
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68 | Validation of the code was conducted by qualitatively comparing the output |
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69 | of the 1D model to the curves shown in (Nayuk, 2012). |
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70 | |
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71 | |
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72 | References |
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73 | ---------- |
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74 | |
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75 | R Nayuk and K Huber, *Z. Phys. Chem.*, 226 (2012) 837-854 |
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76 | """ |
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77 | |
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78 | import numpy as np |
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79 | from numpy import pi, inf, sqrt |
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80 | |
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81 | name = "hollow_rectangular_prism_thin_walls" |
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82 | title = "Hollow rectangular parallelepiped with thin walls." |
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83 | description = """ |
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84 | I(q)= scale*V*(sld - sld_solvent)^2*P(q)+background |
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85 | with P(q) being the form factor corresponding to a hollow rectangular |
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86 | parallelepiped with infinitely thin walls. |
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87 | """ |
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88 | category = "shape:parallelepiped" |
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89 | |
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90 | # ["name", "units", default, [lower, upper], "type","description"], |
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91 | parameters = [["sld", "1e-6/Ang^2", 6.3, [-inf, inf], "sld", |
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92 | "Parallelepiped scattering length density"], |
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93 | ["sld_solvent", "1e-6/Ang^2", 1, [-inf, inf], "sld", |
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94 | "Solvent scattering length density"], |
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95 | ["length_a", "Ang", 35, [0, inf], "volume", |
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96 | "Shorter side of the parallelepiped"], |
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97 | ["b2a_ratio", "Ang", 1, [0, inf], "volume", |
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98 | "Ratio sides b/a"], |
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99 | ["c2a_ratio", "Ang", 1, [0, inf], "volume", |
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100 | "Ratio sides c/a"], |
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101 | ] |
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102 | |
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103 | source = ["lib/gauss76.c", "hollow_rectangular_prism_thin_walls.c"] |
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104 | |
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105 | def ER(length_a, b2a_ratio, c2a_ratio): |
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106 | """ |
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107 | Return equivalent radius (ER) |
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108 | """ |
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109 | b_side = length_a * b2a_ratio |
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110 | c_side = length_a * c2a_ratio |
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111 | |
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112 | # surface average radius (rough approximation) |
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113 | surf_rad = sqrt(length_a * b_side / pi) |
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114 | |
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115 | ddd = 0.75 * surf_rad * (2 * surf_rad * c_side + (c_side + surf_rad) * (c_side + pi * surf_rad)) |
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116 | return 0.5 * (ddd) ** (1. / 3.) |
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117 | |
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118 | def VR(length_a, b2a_ratio, c2a_ratio): |
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119 | """ |
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120 | Return shell volume and total volume |
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121 | """ |
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122 | b_side = length_a * b2a_ratio |
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123 | c_side = length_a * c2a_ratio |
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124 | vol_total = length_a * b_side * c_side |
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125 | vol_shell = 2.0 * (length_a*b_side + length_a*c_side + b_side*c_side) |
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126 | return vol_shell, vol_total |
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127 | |
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128 | |
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129 | def random(): |
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130 | a, b, c = 10**np.random.uniform(1, 4.7, size=3) |
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131 | pars = dict( |
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132 | length_a=a, |
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133 | b2a_ratio=b/a, |
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134 | c2a_ratio=c/a, |
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135 | ) |
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136 | return pars |
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137 | |
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138 | |
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139 | # parameters for demo |
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140 | demo = dict(scale=1, background=0, |
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141 | sld=6.3, sld_solvent=1.0, |
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142 | length_a=35, b2a_ratio=1, c2a_ratio=1, |
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143 | length_a_pd=0.1, length_a_pd_n=10, |
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144 | b2a_ratio_pd=0.1, b2a_ratio_pd_n=1, |
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145 | c2a_ratio_pd=0.1, c2a_ratio_pd_n=1) |
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146 | |
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147 | tests = [[{}, 0.2, 0.837719188592], |
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148 | [{}, [0.2], [0.837719188592]], |
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149 | ] |
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