[dc02af0] | 1 | # Note: model title and parameter table are inserted automatically |
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| 2 | r""" |
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[a5d0d00] | 3 | This model provides the scattering intensity, $I(q) = P(q) S(q)$, for a |
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| 4 | lamellar phase where a random distribution in solution are assumed. |
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| 5 | Here a Caille $S(Q)$ is used for the lamellar stacks. |
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[dc02af0] | 6 | |
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[a5d0d00] | 7 | The scattering intensity $I(q)$ is |
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[dc02af0] | 8 | |
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[a5d0d00] | 9 | .. math: |
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| 10 | |
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| 11 | I(q) = 2\pi \frac{P(q)S(q)}{\delta q^2} |
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[dc02af0] | 12 | |
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| 13 | The form factor is |
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| 14 | |
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[a5d0d00] | 15 | .. math: |
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| 16 | |
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| 17 | P(q) = \frac{2\Delta\rho^2}{q^2}\left(1-\cos q\delta \right) |
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[dc02af0] | 18 | |
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| 19 | and the structure factor is |
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| 20 | |
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[a5d0d00] | 21 | .. math: |
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| 22 | |
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| 23 | S(q) = 1 + 2 \sum_1^{N-1}\left(1-\frac{n}{N}\right) |
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| 24 | \cos(qdn)\exp\left(-\frac{2q^2d^2\alpha(n)}{2}\right) |
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[dc02af0] | 25 | |
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| 26 | where |
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| 27 | |
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[a5d0d00] | 28 | .. math: |
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[dc02af0] | 29 | |
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[a5d0d00] | 30 | \begin{eqnarray} |
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| 31 | \alpha(n) &=& \frac{\eta_{cp}}{4\pi^2} \left(\ln(\pi n)+\gamma_E\right) \\ |
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| 32 | \gamma_E &=& 0.5772156649 && \text{Euler's constant} \\ |
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| 33 | \eta_{cp} &=& \frac{q_o^2k_B T}{8\pi\sqrt{K\overline{B}}} && \text{Caille constant} |
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| 34 | \end{eqnarray} |
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[dc02af0] | 35 | |
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[a5d0d00] | 36 | Here $d$ = (repeat) spacing, $\delta$ = bilayer thickness, |
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| 37 | the contrast $\Delta\rho$ = SLD(headgroup) - SLD(solvent), |
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| 38 | $K$ = smectic bending elasticity, $B$ = compression modulus, and |
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| 39 | $N$ = number of lamellar plates (*n_plates*). |
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[dc02af0] | 40 | |
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[a5d0d00] | 41 | NB: **When the Caille parameter is greater than approximately 0.8 to 1.0, the |
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| 42 | assumptions of the model are incorrect.** And due to a complication of the |
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| 43 | model function, users are responsible for making sure that all the assumptions |
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| 44 | are handled accurately (see the original reference below for more details). |
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[dc02af0] | 45 | |
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[a5d0d00] | 46 | Non-integer numbers of stacks are calculated as a linear combination of |
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| 47 | results for the next lower and higher values. |
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| 48 | |
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| 49 | The 2D scattering intensity is calculated in the same way as 1D, where the |
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| 50 | $q$ vector is defined as |
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[dc02af0] | 51 | |
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| 52 | .. math:: |
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| 53 | |
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[a5d0d00] | 54 | q = \sqrt{q_x^2 + q_y^2} |
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[dc02af0] | 55 | |
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| 56 | The returned value is in units of |cm^-1|, on absolute scale. |
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| 57 | |
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[a5d0d00] | 58 | .. image:: img/lamellarCaille_1d.jpg |
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[dc02af0] | 59 | |
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| 60 | *Figure. 1D plot using the default values (w/6000 data point).* |
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| 61 | |
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[a5d0d00] | 62 | Our model uses the form factor calculations as implemented in a c library |
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| 63 | provided by the NIST Center for Neutron Research (Kline, 2006). |
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[dc02af0] | 64 | |
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| 65 | REFERENCE |
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[a5d0d00] | 66 | --------- |
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[dc02af0] | 67 | |
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| 68 | F Nallet, R Laversanne, and D Roux, J. Phys. II France, 3, (1993) 487-502 |
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| 69 | |
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| 70 | also in J. Phys. Chem. B, 105, (2001) 11081-11088 |
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| 71 | """ |
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[3c56da87] | 72 | from numpy import inf |
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[dc02af0] | 73 | |
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| 74 | name = "lamellarPS" |
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| 75 | title = "Random lamellar sheet with Caille structure factor" |
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| 76 | description = """\ |
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| 77 | [Random lamellar phase with Caille structure factor] |
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| 78 | randomly oriented stacks of infinite sheets |
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| 79 | with Caille S(Q), having polydisperse spacing. |
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| 80 | sld = sheet scattering length density |
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| 81 | sld_solvent = solvent scattering length density |
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| 82 | background = incoherent background |
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| 83 | scale = scale factor |
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| 84 | """ |
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[a5d0d00] | 85 | category = "shape:lamellae" |
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[dc02af0] | 86 | |
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[3e428ec] | 87 | # ["name", "units", default, [lower, upper], "type","description"], |
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| 88 | parameters = [["thickness", "Ang", 30.0, [0, inf], "volume", "sheet thickness"], |
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| 89 | ["Nlayers", "", 20, [0, inf], "", "Number of layers"], |
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| 90 | ["spacing", "Ang", 400., [0.0,inf], "volume", "d-spacing of Caille S(Q)"], |
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| 91 | ["Caille_parameter", "1/Ang^2", 0.1, [0.0,0.8], "", "Caille parameter"], |
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| 92 | ["sld", "1e-6/Ang^2", 6.3, [-inf,inf], "", |
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| 93 | "layer scattering length density"], |
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| 94 | ["solvent_sld", "1e-6/Ang^2", 1.0, [-inf,inf], "", |
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| 95 | "Solvent scattering length density"], |
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| 96 | ] |
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| 97 | |
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| 98 | source = ["lamellarCaille_kernel.c"] |
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[dc02af0] | 99 | |
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| 100 | # No volume normalization despite having a volume parameter |
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| 101 | # This should perhaps be volume normalized? |
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| 102 | form_volume = """ |
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| 103 | return 1.0; |
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| 104 | """ |
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| 105 | |
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| 106 | Iqxy = """ |
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[bfb195e] | 107 | return Iq(sqrt(qx*qx+qy*qy), IQ_PARAMETERS); |
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[dc02af0] | 108 | """ |
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| 109 | |
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| 110 | # ER defaults to 0.0 |
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| 111 | # VR defaults to 1.0 |
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| 112 | |
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[3e428ec] | 113 | demo = dict(scale=1, background=0, |
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| 114 | thickness=67.,Nlayers=3.75,spacing=200., |
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| 115 | Caille_parameter=0.268,sld=1.0, solvent_sld=6.34, |
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| 116 | thickness_pd= 0.1, thickness_pd_n=100, |
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| 117 | spacing_pd= 0.05, spacing_pd_n=40) |
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[dc02af0] | 118 | |
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| 119 | oldname = 'LamellarPSModel' |
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[3e428ec] | 120 | oldpars = dict(thickness='delta', Nlayers='N_plates', Caille_parameter='caille', |
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| 121 | sld='sld_bi',solvent_sld='sld_sol') |
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