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Indirect Bayes
Provides Bayesian analysis routines primarily for use with QENS data.
This tab creates a group ‘normalisation’ file by taking a resolution file and
fitting it to all the groups in the resolution (vanadium) data file which has
the same grouping as the sample data of interest.
The routine fits the width of the resolution file to give a ‘stretch factor’
and the area provides an intensity normalisation factor.
The fitted parameters are in the group workspace with suffix _ResNorm with
additional suffices of _Intensity & _Stretch.
The processing on this tab is provided by the ResNorm
algorithm.
- Vanadium File
- Either a reduced file created using the Energy Transfer tab or an
\(S(Q, \omega)\) file.
- Resolution File
- A resolution file created using the Calibrtion tab.
- EMin & EMax
- The energy range to perform fitting within.
- Preview Spectrum
- Changes the spectrum displayed in the preview plot.
- Plot Current Preview
- Plots the currently selected preview plot in a separate external window
- Run
- Runs the processing configured on the current tab.
- Plot
- Plots the selected parameter stored in the result workspaces.
- Save Result
- Saves the result in the default save directory.
Warning
This interface is only available on Windows
The model that is being fitted is that of a \(\delta\)-function (elastic component)
of amplitude \(A(0)\) and Lorentzians of amplitude \(A(j)\) and HWHM
\(W(j)\) where \(j=1,2,3\). The whole function is then convolved with
the resolution function. The -function and Lorentzians are intrinsically
normalised to unity so that the amplitudes represent their integrated areas.
For a Lorentzian, the Fourier transform does the conversion:
\(1/(x^{2}+\delta^{2}) \Leftrightarrow exp[-2\pi(\delta k)]\). If \(x\)
is identified with energy \(E\) and \(2\pi k\) with \(t/\hbar\)
where t is time then: \(1/[E^{2}+(\hbar / \tau)^{2}] \Leftrightarrow exp[−t
/\tau]\) and \(\sigma\) is identified with \(\hbar / \tau\). The program
estimates the quasielastic components of each of the groups of spectra and
requires the resolution file and optionally the normalisation file created by
ResNorm.
For a Stretched Exponential, the choice of several Lorentzians is replaced with
a single function with the shape : \(\psi\beta(x) \Leftrightarrow
exp[-2\pi(\sigma k)\beta]\). This, in the energy to time FT transformation, is
\(\psi\beta(E) \Leftrightarrow exp[-(t/\tau)\beta]\). So \(\sigma\) is
identified with \((2\pi)\beta\hbar/\tau\) . The model that is fitted is
that of an elastic component and the stretched exponential and the program gives
the best estimate for the \(\beta\) parameter and the width for each group
of spectra.
- Sample
- Either a reduced file created using the Energy Transfer tab or an
\(S(Q, \omega)\) file.
- Resolution
- A resolution file created using the Calibration tab.
- Program
- The curve fitting program to use.
- Background
- The background fitting program to use.
- Elastic Peak
- If an elastic peak should be used.
- Sequential Fit
- Enables multiple fitting iterations.
- Fix Width
- Allows selection of a width file.
- Use ResNorm
- Allows selection of a ResNorm output file or workspace to use with fitting.
- EMin & EMax
- The energy range to perform fitting within.
- Sample Binning
- Sample binning to use.
- Resolution Binning
- Resolution binning to use.
- Preview Spectrum
- Changes the spectrum displayed in the preview plot.
- Plot Current Preview
- Plots the currently selected preview plot in a separate external window
- Run
- Runs the processing configured on the current tab.
- Plot
- Plots the selected parameter stored in the result workspaces.
- Save Result
- Saves the result in the default save directory.
Warning
This interface is only available on Windows
This is a variation of the stretched exponential option of Quasi. For each
spectrum, a fit is performed for a grid of β and σ values. The distribution of
goodness of fit values is plotted.
- Sample
- Either a reduced file created using the Energy Transfer tab or an
\(S(Q, \omega)\) file.
- Resolution
- A resolution file created using the Calibration tab.
- Background
- The background fitting program to use.
- Elastic Peak
- If an elastic peak should be used.
- Sequential Fit
- Enables multiple fitting iterations.
- EMin & EMax
- The energy range to perform fitting within.
- Sample Binning
- Sample binning to use.
- Sigma
- Value of Sigma to use.
- Beta
- Value of Beta to use.
- Preview Spectrum
- Changes the spectrum displayed in the preview plot.
- Plot Current Preview
- Plots the currently selected preview plot in a separate external window
- Run
- Runs the processing configured on the current tab.
- Plot
- Plots the selected parameter stored in the result workspaces.
- Plot Contour
- Produces a contour plot of the selected workspace.
- Save Result
- Saves the result in the default save directory.
Categories: Interfaces | Indirect