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QENS fit functions - jump diffusion
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andyfaff
#pragma rtGlobals=1 // Use modern global access method. //Jobic, H. & Theodorou, D. //"Quasi-elastic neutron scattering and molecular dynamics simulation // as complementary techniques for studying diffusion in zeolites", // Microporous and Mesoporous Materials, 2007, 102, 21-50 //note that we are fitting FWHM, NOT HWHM, so there are factors of two difference. Function chudleyelliot(w, y, x):fitfunc wave w, y, x //eqn 51 //w[0] = tau //w[1] = d y = sin(x * w[1]) / (x * w[1]) y = 1 - y y /= w[0] / 2 End Function hallross(w, y, x):fitfunc wave w, y, x //eqn 53 //w[0] = tau //w[1] = <r^2> y = exp(-1 * x^2 * w[1] / 6) y = 1 - y y /= w[0] / 2 End Function singwisjolander(w, y, x):fitfunc wave w, y, x //eqn 55 //w[0] = tau //w[1] = <r^2> y = x^2 * w[1] y /= 1 + x^2 * w[1] / 6 y /= w[0] * 6 / 2 End
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