[7ed702f] | 1 | r""" |
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| 2 | |
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| 3 | A number of natural and commercial processes form high-surface area materials |
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| 4 | as a result of the vapour-phase aggregation of primary particles. |
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| 5 | Examples of such materials include soots, aerosols, and fume or pyrogenic |
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| 6 | silicas. These are all characterised by cluster mass distributions (sometimes |
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| 7 | also cluster size distributions) and internal surfaces that are fractal in |
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| 8 | nature. The scattering from such materials displays two distinct breaks in |
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| 9 | log-log representation, corresponding to the radius-of-gyration of the primary |
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| 10 | particles, $rg$, and the radius-of-gyration of the clusters (aggregates), |
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| 11 | $Rg$. Between these boundaries the scattering follows a power law related to |
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| 12 | the mass fractal dimension, $Dm$, whilst above the high-Q boundary the |
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| 13 | scattering follows a power law related to the surface fractal dimension of |
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| 14 | the primary particles, $Ds$. |
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| 15 | |
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| 16 | Definition |
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| 17 | ---------- |
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| 18 | |
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| 19 | The scattered intensity I(q) is calculated using a modified |
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| 20 | Ornstein-Zernicke equation |
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| 21 | |
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| 22 | .. math:: |
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| 23 | |
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| 24 | I(q) = scale \times P(q) + background |
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| 25 | |
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| 26 | P(q) = \left\{ \left[ 1+(q^2a)\right]^{D_m/2} \times |
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| 27 | \left[ 1+(q^2b)\right]^{(6-D_s-D_m)/2} |
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| 28 | \right\}^{-1} |
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| 29 | |
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| 30 | a = R_{g}^2/(3D_m/2) |
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| 31 | |
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| 32 | b = r_{g}^2/[-3(D_s+D_m-6)/2] |
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| 33 | |
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| 34 | scale = scale\_factor \times NV^2 (\rho_{particle} - \rho_{solvent})^2 |
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| 35 | |
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| 36 | where $R_g$ is the size of the cluster, $r_g$ is the size of the primary |
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| 37 | particle, $D_s$ is the surface fractal dimension, $D_m$ is the mass fractal |
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| 38 | dimension, $\rho_{solvent}$ is the scattering length density of the solvent, |
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| 39 | and $\rho_{particle}$ is the scattering length density of particles. |
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| 40 | |
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| 41 | .. note:: |
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| 42 | |
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| 43 | The surface ( $D_s$ ) and mass ( $D_m$ ) fractal dimensions are only |
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[9418d75] | 44 | valid if $0 < surface\_dim < 6$ , $0 < mass\_dim < 6$ , and |
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| 45 | $(surface\_dim + mass\_dim ) < 6$ . |
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[7ed702f] | 46 | |
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| 47 | |
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[95441ff] | 48 | References |
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| 49 | ---------- |
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[7ed702f] | 50 | |
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| 51 | P Schmidt, *J Appl. Cryst.*, 24 (1991) 414-435 Equation(19) |
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| 52 | |
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[168052c] | 53 | A J Hurd, D W Schaefer, J E Martin, *Phys. Rev. A*, |
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| 54 | 35 (1987) 2361-2364 Equation(2) |
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[7ed702f] | 55 | |
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| 56 | """ |
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| 57 | |
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| 58 | from numpy import inf |
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| 59 | |
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| 60 | name = "mass_surface_fractal" |
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| 61 | title = "Mass Surface Fractal model" |
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| 62 | description = """ |
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| 63 | The scattering intensity I(x) = scale*P(x)*S(x) + background, where |
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| 64 | p(x)= {[1+(x^2*a)]^(Dm/2) * [1+(x^2*b)]^(6-Ds-Dm)/2}^(-1) |
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| 65 | a = Rg^2/(3*Dm/2) |
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| 66 | b = rg^2/(3*(6-Ds-Dm)/2) |
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| 67 | scale = scale factor * N*Volume^2*contrast^2 |
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[a807206] | 68 | fractal_dim_mass = Dm (mass fractal dimension) |
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| 69 | fractal_dim_surf = Ds |
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| 70 | rg_cluster = Rg |
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[30fbe2e] | 71 | rg_primary = rg |
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[7ed702f] | 72 | background = background |
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| 73 | Ref: Schmidt, J Appl Cryst, eq(19), (1991), 24, 414-435 |
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| 74 | Hurd, Schaefer, Martin, Phys Rev A, eq(2),(1987),35, 2361-2364 |
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| 75 | Note that 0 < Ds< 6 and 0 < Dm < 6. |
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| 76 | """ |
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| 77 | category = "shape-independent" |
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| 78 | |
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[168052c] | 79 | # pylint: disable=bad-whitespace, line-too-long |
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[6d96b66] | 80 | # ["name", "units", default, [lower, upper], "type","description"], |
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| 81 | parameters = [ |
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| 82 | ["fractal_dim_mass", "", 1.8, [0.0, 6.0], "", "Mass fractal dimension"], |
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| 83 | ["fractal_dim_surf", "", 2.3, [0.0, 6.0], "", "Surface fractal dimension"], |
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| 84 | ["rg_cluster", "Ang", 86.7, [0.0, inf], "", "Cluster radius of gyration"], |
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| 85 | ["rg_primary", "Ang", 4000., [0.0, inf], "", "Primary particle radius of gyration"], |
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| 86 | ] |
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[168052c] | 87 | # pylint: enable=bad-whitespace, line-too-long |
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[7ed702f] | 88 | |
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[9c461c7] | 89 | source = ["mass_surface_fractal.c"] |
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[7ed702f] | 90 | |
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| 91 | demo = dict(scale=1, background=0, |
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[a807206] | 92 | fractal_dim_mass=1.8, |
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| 93 | fractal_dim_surf=2.3, |
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| 94 | rg_cluster=86.7, |
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[30fbe2e] | 95 | rg_primary=4000.0) |
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[7ed702f] | 96 | |
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[07a6700] | 97 | tests = [ |
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[168052c] | 98 | |
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| 99 | # Accuracy tests based on content in test/utest_other_models.py |
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[a807206] | 100 | [{'fractal_dim_mass': 1.8, |
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| 101 | 'fractal_dim_surf': 2.3, |
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| 102 | 'rg_cluster': 86.7, |
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[30fbe2e] | 103 | 'rg_primary': 4000.0, |
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[6dd90c1] | 104 | 'background': 0.0, |
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[168052c] | 105 | }, 0.05, 1.77537e-05], |
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| 106 | |
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| 107 | # Additional tests with larger range of parameters |
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[a807206] | 108 | [{'fractal_dim_mass': 3.3, |
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| 109 | 'fractal_dim_surf': 1.0, |
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| 110 | 'rg_cluster': 90.0, |
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[30fbe2e] | 111 | 'rg_primary': 4000.0, |
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[6dd90c1] | 112 | }, 0.001, 0.18562699016], |
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[168052c] | 113 | |
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[a807206] | 114 | [{'fractal_dim_mass': 1.3, |
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| 115 | 'fractal_dim_surf': 1.0, |
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| 116 | 'rg_cluster': 90.0, |
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[30fbe2e] | 117 | 'rg_primary': 2000.0, |
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[168052c] | 118 | 'background': 0.8, |
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| 119 | }, 0.001, 1.16539753641], |
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| 120 | |
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[a807206] | 121 | [{'fractal_dim_mass': 2.3, |
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| 122 | 'fractal_dim_surf': 1.0, |
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| 123 | 'rg_cluster': 90.0, |
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[30fbe2e] | 124 | 'rg_primary': 1000.0, |
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[168052c] | 125 | 'scale': 10.0, |
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[6dd90c1] | 126 | 'background': 0.0, |
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[168052c] | 127 | }, 0.051, 0.000169548800377], |
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| 128 | ] |
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