1 | # Note: model title and parameter table are inserted automatically |
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2 | r""" |
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3 | This model provides the scattering intensity, *I(q)*, for a lyotropic lamellar |
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4 | phase where a random distribution in solution are assumed. The SLD of the head |
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5 | region is taken to be different from the SLD of the tail region. |
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6 | |
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7 | *2.1.31.1. Definition* |
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8 | |
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9 | The scattering intensity *I(q)* is |
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10 | |
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11 | .. math:: |
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12 | |
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13 | I(Q) = 2\pi{P(Q) \over (2(|delta|\ H +|delta|\ T) Q^2) |
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14 | |
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15 | The form factor is |
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16 | |
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17 | .. image:: img/lamellarFFHG_.jpg |
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18 | |
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19 | where |delta|\ T = tail length (or *tail_length*), |delta|\ H = head thickness |
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20 | (or *h_thickness*), |drho|\ H = SLD(headgroup) - SLD(solvent), |
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21 | and |drho|\ T = SLD(tail) - SLD(solvent). |
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22 | |
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23 | The 2D scattering intensity is calculated in the same way as 1D, where |
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24 | the *q* vector is defined as |
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25 | |
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26 | .. math:: |
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27 | |
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28 | Q = \sqrt{Q_x^2 + Q_y^2} |
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29 | |
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30 | The returned value is in units of |cm^-1|, on absolute scale. In the |
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31 | parameters, *sld_tail* = SLD of the tail group, and *sld_head* = SLD |
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32 | of the head group. |
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33 | |
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34 | .. image:: img/lamellarFFHG_138.jpg |
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35 | |
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36 | *Figure. 1D plot using the default values (w/1000 data point).* |
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37 | |
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38 | Our model uses the form factor calculations implemented in a C library |
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39 | provided by the NIST Center for Neutron Research (Kline, 2006). |
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40 | |
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41 | REFERENCE |
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42 | |
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43 | F Nallet, R Laversanne, and D Roux, J. Phys. II France, 3, (1993) 487-502 |
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44 | |
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45 | also in J. Phys. Chem. B, 105, (2001) 11081-11088 |
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46 | |
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47 | *2014/04/17 - Description reviewed by S King and P Butler.* |
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48 | """ |
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49 | |
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50 | from numpy import inf |
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51 | |
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52 | name = "lamellar_FFHG" |
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53 | title = "Random lamellar phase with Head Groups " |
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54 | description = """\ |
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55 | [Random lamellar phase with Head Groups] |
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56 | I(q)= 2*pi*P(q)/(2(H+T)*q^(2)), where |
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57 | P(q)= see manual |
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58 | layer thickness =(H+T+T+H) = 2(Head+Tail) |
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59 | sld = Tail scattering length density |
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60 | sld_head = Head scattering length density |
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61 | sld_solvent = solvent scattering length density |
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62 | background = incoherent background |
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63 | scale = scale factor |
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64 | """ |
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65 | category = "shape:lamellae" |
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66 | |
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67 | # ["name", "units", default, [lower, upper], "type","description"], |
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68 | parameters = [["tail_length", "Ang", 15, [0, inf], "volume", |
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69 | "Tail thickness"], |
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70 | ["head_length", "Ang", 10, [0, inf], "volume", |
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71 | "head thickness"], |
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72 | ["sld", "1e-6/Ang^2", 0.4, [-inf,inf], "", |
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73 | "Tail scattering length density"], |
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74 | ["head_sld", "1e-6/Ang^2", 3.0, [-inf,inf], "", |
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75 | "Head scattering length density"], |
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76 | ["solvent_sld", "1e-6/Ang^2", 6, [-inf,inf], "", |
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77 | "Solvent scattering length density"], |
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78 | ] |
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79 | |
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80 | # No volume normalization despite having a volume parameter |
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81 | # This should perhaps be volume normalized? |
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82 | form_volume = """ |
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83 | return 1.0; |
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84 | """ |
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85 | |
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86 | Iq = """ |
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87 | const double qsq = q*q; |
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88 | const double drh = head_sld - solvent_sld; |
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89 | const double drt = sld - solvent_sld; //correction 13FEB06 by L.Porcar |
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90 | const double qT = q*tail_length; |
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91 | double Pq, inten; |
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92 | Pq = drh*(sin(q*(head_length+tail_length))-sin(qT)) + drt*sin(qT); |
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93 | Pq *= Pq; |
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94 | Pq *= 4.0/(qsq); |
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95 | |
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96 | inten = 2.0e-4*M_PI*Pq/qsq; |
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97 | |
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98 | // normalize by the bilayer thickness |
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99 | inten /= 2.0*(head_length+tail_length); |
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100 | |
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101 | return inten; |
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102 | """ |
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103 | |
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104 | Iqxy = """ |
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105 | return Iq(sqrt(qx*qx+qy*qy), IQ_PARAMETERS); |
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106 | """ |
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107 | |
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108 | # ER defaults to 0.0 |
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109 | # VR defaults to 1.0 |
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110 | |
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111 | demo = dict(scale=1, background=0, |
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112 | tail_length=15,head_length=10, |
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113 | sld=0.4, head_sld=3.0, solvent_sld=6.0, |
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114 | tail_length_pd= 0.2, tail_length_pd_n=40, |
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115 | head_length_pd= 0.01, head_length_pd_n=40) |
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116 | |
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117 | oldname = 'LamellarFFHGModel' |
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118 | oldpars = dict(head_length='h_thickness', sld='sld_tail', |
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119 | head_sld='sld_head', solvent_sld='sld_solvent') |
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120 | |
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