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Indirect Fourier transform (IFT) is a solution of ill-posed given by Fourier transform of noisy data (as from biological small-angle scattering) proposed by Glatter. IFT is used instead of direct Fourier transform of noisy data, since a direct FT would give large systematic errors. Transform is computed by linear fit to a subfamily of functions corresponding to constraints on a reasonable solution. If a result of the transform is distance distribution function, it is common to assume that the function is non-negative, and is zero at ''P''(0) = 0 and ''P''(''D''max)≥;0, where Dmax is a maximum diameter of the particle. It is approximately true, although it disregards inter-particle effects. IFT is also performed in order to regularize noisy data. == Fourier transformation in small angle scattering == see Lindner et al. for a thorough introduction 〔Neutrons, X-rays and Light: Scattering Methds Applied to Soft Condensed Matter by P. Lindner and Th.Zemb (chapter 3 by Olivier Spalla)〕 The intensity ''I'' per unit volume ''V'' is expressed as: : where is the scattering length density. We introduce the correlation function by: : That is, taking the fourier transformation of the correlation function gives the intensity. The probability of finding, within a particle, a point at a distance from a given point is given by the distance probability function . And the connection between the correlation function and the distance probability function is given by: :, where is the scattering length of the point . That is, the correlation function is weighted by the scattering length. For X-ray scattering, the scattering length is directly proportional to the electron density . 抄文引用元・出典: フリー百科事典『 ウィキペディア(Wikipedia)』 ■ウィキペディアで「Indirect Fourier transform」の詳細全文を読む スポンサード リンク
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