QLines v1¶

QLines dialog.

Table of Contents

Summary
Properties
Description
Usage
Source

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

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')
        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 | PythonAlgorithms

Source ¶

Python: QLines.py

QLines v1¶

Summary¶

Properties¶

Description¶

Usage¶

Source¶

Summary ¶

Properties ¶

Description ¶

Usage ¶

Source ¶