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11 | <p class=MsoNormal><h3><span style='font-family:"Times New Roman","serif"'>Polydisperisty |
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12 | and Angular Distributions</span></h3></p> |
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13 | |
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14 | <p class=MsoNormal><span style='font-family:"Times New Roman","serif"'>Calculates |
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15 | the form factor for a polydisperse and/or angular population of particles with |
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16 | uniform scattering length density. The resultant form factor is normalized by |
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17 | the average particle volume such that P(q) = scale*<F*F>/Vol + bkg, where |
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18 | F is the scattering amplitude and the < > denote an average over the size |
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19 | distribution. Users should use PD (polydispersity: this definition is different from the typical definition in polymer science) |
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20 | for a size distribution and Sigma for an |
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21 | angular distribution (see below).</span></p> |
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22 | <p> Note that this computation is very time intensive thus applying polydispersion/angular distrubtion for |
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23 | more than one paramters or increasing Npts values might need extensive patience to complete the computation. Also |
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24 | note that even though it is time consuming, it is safer to have larger values of Npts and Nsigmas.</p> |
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25 | |
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26 | <p class=MsoNormal style='margin-bottom:0in;margin-bottom:.0001pt'><span |
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27 | style='font-family:"Times New Roman","serif"'>The following five distribution |
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28 | functions are provided;</span></p> |
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29 | <ul> |
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30 | <li><a href="#Rectangular">Rectangular distribution</a></li> |
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31 | <li><a href="#Array">Array distribution</a></li> |
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32 | <li><a href="#Gaussian">Gaussian distribution</a></li> |
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33 | <li><a href="#Lognormal">Lognormal distribution</a></li> |
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34 | <li><a href="#Schulz">Schulz distribution</a></li> |
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35 | </ul> |
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36 | <p> </p> |
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37 | <p><a name="Rectangular"><h4>Rectangular distribution</a></h4></p> |
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38 | <p><img src="./img/pd_image001.png"></p> |
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39 | <p> </p> |
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40 | <p>The x<sub>mean</sub> is the mean |
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41 | of the distribution, w is the half-width, and Norm is a normalization factor |
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42 | which is determined during the numerical calculation. Note that the Sigma and |
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43 | the half width <i>w</i> are different.</p> |
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44 | <p>The standard deviation is </p> |
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45 | <p><img src="./img/pd_image002.png"></p> |
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46 | <p> </p> |
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47 | <p>The PD (polydispersity) is </p> |
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48 | <p><img src="./img/pd_image003.png"></p> |
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49 | <p> </p> |
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50 | <p><img width=511 height=270 |
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51 | id="Picture 1" src="./img/pd_image004.jpg" alt=flat.gif></p> |
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52 | <p> </p> |
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53 | <p> </p> |
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54 | <p><a name="Array"><h4>Array distribution</h4></a></p> |
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55 | |
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56 | <p>This distribution is to be given |
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57 | by users as a txt file where the array should be defined by two columns in the |
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58 | order of x and f(x) values. The f(x) will be normalized by SansView during the |
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59 | computation.</p> |
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60 | |
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61 | <p>Example of an array in the file;</p> |
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62 | |
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63 | <p>30 0.1</p> |
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64 | |
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65 | <p>32 0.3</p> |
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66 | |
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67 | <p>35 0.4</p> |
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68 | |
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69 | <p>36 0.5</p> |
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70 | |
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71 | <p>37 0.6</p> |
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72 | |
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73 | <p>39 0.7</p> |
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74 | |
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75 | <p>41 0.9</p> |
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76 | |
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77 | <p'> </p> |
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78 | |
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79 | <p>We use only these array values in |
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80 | the computation, therefore the mean value given in the control panel, for |
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81 | example radius = 60, will be ignored.</p> |
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82 | <p> </p> |
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83 | |
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84 | |
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85 | <p><a name="Gaussian"><h4>Gaussian distribution</h4></a></p> |
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86 | <p> </p> |
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87 | |
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88 | <p><img src="./img/pd_image005.png"></p> |
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89 | |
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90 | <p> </p> |
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91 | |
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92 | <p>The x<sub>mean</sub> is the mean |
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93 | of the distribution and Norm is a normalization factor which is determined |
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94 | during the numerical calculation.</p> |
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95 | |
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96 | <p> </p> |
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97 | |
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98 | <p>The PD (polydispersity) is </p> |
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99 | |
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100 | <p><img src="./img/pd_image003.png"></p> |
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101 | |
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102 | <p> </p> |
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103 | |
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104 | <p><img width=518 height=275 |
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105 | id="Picture 2" src="./img/pd_image006.jpg" alt=gauss.gif></p> |
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106 | |
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107 | <p> </p> |
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108 | |
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109 | <p><a name="Lognormal"><h4>Lognormal distribution</h4></a></p> |
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110 | |
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111 | <p> </p> |
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112 | |
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113 | <p><img src="./img/pd_image007.png"></p> |
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114 | |
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115 | <p> </p> |
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116 | |
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117 | <p>The μ = ln(x<sub>med</sub>), x<sub>med</sub> |
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118 | is the median value of the distribution, and Norm is a normalization factor |
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119 | which will be determined during the numerical calculation. The median value is |
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120 | the value given in the size parameter in the control panel, for example, |
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121 | radius = 60.</p> |
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122 | |
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123 | <p > </p> |
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124 | |
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125 | <p>The PD (polydispersity) is given |
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126 | by σ,</p> |
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127 | |
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128 | <p><img src="./img/pd_image008.png"></p> |
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129 | |
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130 | <p> </p> |
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131 | |
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132 | <p>For the angular distribution,</p> |
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133 | |
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134 | <p><img src="./img/pd_image009.png"></p> |
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135 | |
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136 | <p> </p> |
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137 | |
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138 | <p>The mean value is given by x<sub>mean</sub> |
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139 | =exp(μ+p<sup>2</sup>/2).</p> |
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140 | |
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141 | <p>The peak value is given by x<sub>peak</sub>=exp(μ-p<sup>2</sup>).</span></p> |
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142 | |
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143 | <p> </p> |
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144 | |
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145 | <p><img width=450 height=239 |
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146 | id="Picture 7" src="./img/pd_image010.jpg" alt=lognormal.gif></p> |
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147 | |
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148 | <p> </p> |
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149 | |
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150 | <p>This distribution function |
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151 | spreads more and the peak shifts to the left as the p increases, requiring |
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152 | higher values of Nsigmas and Npts.</p> |
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153 | |
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154 | <p> </p> |
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155 | |
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156 | <p><a name="Schulz"><h4>Schulz distribution</h4></a></p> |
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157 | |
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158 | <p> </p> |
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159 | |
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160 | <p><img src="./img/pd_image011.png"></p> |
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161 | |
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162 | <p> </p> |
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163 | |
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164 | <p>The x<sub>mean</sub> is the mean |
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165 | of the distribution and Norm is a normalization factor which is determined |
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166 | during the numerical calculation. </p> |
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167 | |
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168 | <p>The z = 1/p<sup>2</sup> 1.</p> |
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169 | <p> </p> |
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170 | |
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171 | <p>The PD (polydispersity) is </p> |
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172 | <p'><img src="./img/pd_image012.png"></p> |
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173 | <p>Note that the higher PD (polydispersity) |
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174 | might need higher values of Npts and Nsigmas. For example, at PD = 0.7 and radisus = 60 A, |
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175 | Npts >= 160, and Nsigmas >= 15 at least.</p> |
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176 | <p/> |
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177 | <p><img width=438 height=232 |
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178 | id="Picture 4" src="./img/pd_image013.jpg" alt=schulz.gif></p> |
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179 | |
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180 | </div> |
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181 | <br> |
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182 | </body> |
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