QLines v1

../_images/QLines-v1_dlg.png

QLines dialog.

Summary

The program estimates the quasielastic components of each of the groups of spectra and requires the resolution file (.RES file) and optionally the normalisation file created by ResNorm.

Properties

Name Direction Type Default Description
InputType Input string File Origin of data input - File (.nxs) or Workspace. Allowed values: [‘File’, ‘Workspace’]
Instrument Input string iris Instrument. Allowed values: [‘irs’, ‘iris’, ‘osi’, ‘osiris’]
Analyser Input string graphite002 Analyser & reflection. Allowed values: [‘graphite002’, ‘graphite004’]
Program Input string QL Name of program to run. Allowed values: [‘QL’, ‘QSe’]
SamNumber Input string Mandatory Sample run number
ResInputType Input string File Origin of res input - File (_res.nxs) or Workspace. Allowed values: [‘File’, ‘Workspace’]
ResType Input string Res Format of Resolution file. Allowed values: [‘Res’, ‘Data’]
ResNumber Input string Mandatory Resolution run number
ResNorm Input boolean False Use ResNorm output file
ResNormInputType Input string File Origin of ResNorm input - File (_red.nxs) or Workspace. Allowed values: [‘File’, ‘Workspace’]
ResNormNumber Input string   ResNorm run number
BackgroundOption Input string Sloping Form of background to fit. Allowed values: [‘Sloping’, ‘Flat’, ‘Zero’]
ElasticOption Input boolean True Include elastic peak in fit
FixWidth Input boolean False Fix one of the widths
WidthFile Input string   Name of file containing fixed width values
EnergyMin Input number -0.5 Minimum energy for fit. Default=-0.5
EnergyMax Input number 0.5 Maximum energy for fit. Default=0.5
SamBinning Input number 1 Binning value (integer) for sample. Default=1
ResBinning Input number 1 Binning value (integer) for resolution - QLd only. Default=1
Sequence Input boolean True Switch Sequence Off/On
Plot Input string None Plot options. Allowed values: [‘None’, ‘ProbBeta’, ‘Intensity’, ‘FwHm’, ‘Fit’, ‘All’]
Verbose Input boolean True Switch Verbose Off/On
Save Input boolean False Switch Save result to nxs file Off/On

Description

The model that is being fitted is that of a δ-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.

This routine was originally part of the MODES package.

Usage

Example - a basic example using QLines to fit a reduced workspace.

def createSampleWorkspace(name, random=False):
        """ Creates a sample workspace with a single lorentzian that looks like IRIS data"""
        import os
        function = "name=Lorentzian,Amplitude=8,PeakCentre=5,FWHM=0.7"
        ws = CreateSampleWorkspace("Histogram", Function="User Defined", UserDefinedFunction=function, XUnit="DeltaE", Random=True, XMin=0, XMax=10, BinWidth=0.01)
        ws = CropWorkspace(ws, StartWorkspaceIndex=0, EndWorkspaceIndex=9)
        ws = ScaleX(ws, -5, "Add")
        ws = ScaleX(ws, 0.1, "Multiply")

        #load instrument and instrument parameters
        LoadInstrument(ws, InstrumentName='IRIS', RewriteSpectraMap=True)
        path = os.path.join(config['instrumentDefinition.directory'], 'IRIS_graphite_002_Parameters.xml')
        LoadParameterFile(ws, Filename=path)
        ws = RenameWorkspace(ws, OutputWorkspace=name)
        return ws


ws = createSampleWorkspace("irs26176_graphite002_red", random=True)
res = createSampleWorkspace("irs26173_graphite002_res")

QLines(SamNumber='26176', ResNumber='26173', InputType='Workspace', ResInputType='Workspace', Instrument='irs', Analyser='graphite002', Plot='None')

Categories: Algorithms | Workflow\MIDAS