1 | r""" |
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2 | Definition |
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3 | ---------- |
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4 | |
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5 | This model calculates the SAS signal of a phase separating solution |
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6 | under spinodal decomposition. The scattering intensity $I(q)$ is calculated as |
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7 | |
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8 | .. math:: |
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9 | I(q) = I_{max}\frac{(1+\gamma/2)x^2}{\gamma/2+x^{2+\gamma}}+B |
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10 | |
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11 | where $x=q/q_0$ and $B$ is a flat background. The characteristic structure |
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12 | length scales with the correlation peak at $q_0$. The exponent $\gamma$ is |
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13 | equal to $d+1$ with d the dimensionality of the off-critical concentration |
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14 | mixtures. A transition to $\gamma=2d$ is seen near the percolation threshold |
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15 | into the critical concentration regime. |
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16 | |
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17 | References |
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18 | ---------- |
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19 | |
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20 | H. Furukawa. Dynamics-scaling theory for phase-separating unmixing mixtures: |
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21 | Growth rates of droplets and scaling properties of autocorrelation functions. |
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22 | Physica A 123,497 (1984). |
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23 | |
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24 | Authorship and Verification |
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25 | ---------------------------- |
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26 | |
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27 | * **Author:** Dirk Honecker **Date:** Oct 7, 2016 |
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28 | """ |
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29 | |
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30 | import numpy as np |
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31 | from numpy import inf, errstate |
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32 | |
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33 | name = "spinodal" |
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34 | title = "Spinodal decomposition model" |
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35 | description = """\ |
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36 | I(q) = scale ((1+gamma/2)x^2)/(gamma/2+x^(2+gamma))+background |
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37 | |
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38 | List of default parameters: |
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39 | scale = scaling |
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40 | gamma = exponent |
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41 | x = q/q_0 |
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42 | q_0 = correlation peak position [1/A] |
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43 | background = Incoherent background""" |
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44 | category = "shape-independent" |
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45 | |
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46 | # pylint: disable=bad-whitespace, line-too-long |
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47 | # ["name", "units", default, [lower, upper], "type", "description"], |
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48 | parameters = [["gamma", "", 3.0, [-inf, inf], "", "Exponent"], |
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49 | ["q_0", "1/Ang", 0.1, [-inf, inf], "", "Correlation peak position"] |
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50 | ] |
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51 | # pylint: enable=bad-whitespace, line-too-long |
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52 | |
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53 | def Iq(q, |
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54 | gamma=3.0, |
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55 | q_0=0.1): |
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56 | """ |
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57 | :param q: Input q-value |
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58 | :param gamma: Exponent |
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59 | :param q_0: Correlation peak position |
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60 | :return: Calculated intensity |
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61 | """ |
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62 | with errstate(divide='ignore'): |
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63 | x = q/q_0 |
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64 | inten = ((1 + gamma / 2) * x ** 2) / (gamma / 2 + x ** (2 + gamma)) |
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65 | return inten |
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66 | Iq.vectorized = True # Iq accepts an array of q values |
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67 | |
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68 | def random(): |
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69 | pars = dict( |
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70 | scale=10**np.random.uniform(1, 3), |
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71 | gamma=np.random.uniform(0, 6), |
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72 | q_0=10**np.random.uniform(-3, -1), |
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73 | ) |
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74 | return pars |
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75 | |
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76 | demo = dict(scale=1, background=0, |
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77 | gamma=1, q_0=0.1) |
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