[ec392464] | 1 | .. resolution_calculator_help.rst |
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| 2 | |
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| 3 | .. This is a port of the original SasView html help file to ReSTructured text |
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| 4 | .. by S King, ISIS, during SasView CodeCamp-III in Feb 2015. |
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| 5 | |
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| 6 | Q Resolution Estimator |
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| 7 | ====================== |
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| 8 | |
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| 9 | Description |
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| 10 | ----------- |
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| 11 | |
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| 12 | This tool is to approximately estimate the resolution of Q based on the SAS |
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| 13 | instrumental parameter values assuming that the detector is flat and vertical |
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| 14 | to the incident beam direction. |
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| 15 | |
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| 16 | .. ZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZ |
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| 17 | |
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| 18 | How To |
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| 19 | ------ |
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| 20 | |
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| 21 | 1. Select the source and source type (Monochromatic or TOF). Note that the |
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| 22 | computational difference between the sources is only the gravitational |
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| 23 | contribution due to the mass. |
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| 24 | |
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| 25 | 2. Change the default values of the instrumental parameters as desired. |
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| 26 | |
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| 27 | 3. The input formats of wavelength and its spread (=FWHM/wavelength) depend on |
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| 28 | the source type.For monochromatic wave, the inputs are just one values as shown |
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| 29 | with the defaults.For TOF, the min and max values should be separated by "-" |
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| 30 | to describe the wavelength band range. Optionally, the input of the wavelength |
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| 31 | (NOT of the wavelength spread) could be extended by adding "; --" where the -- |
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| 32 | is the number of the bins for the numerical integration. Otherwise, the |
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| 33 | default value "10" bins will be used. The same number of bins will be used |
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| 34 | for the corresponding wavelength spread in either cases. |
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| 35 | |
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| 36 | 4. For TOF, the default wavelength spectrum is flat. The custom spectrum file |
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| 37 | (with 2 column text: wavelength(A) vs. intensity) can also be loaded by |
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| 38 | selecting "Add new" in the combobox. |
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| 39 | |
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| 40 | 5. Once set all the input values, click the compute button. Depending on |
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| 41 | computation loads the calculation time will vary. |
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| 42 | |
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| 43 | 6. 1D and 2D dQ will be displayed in the text-box at the bottom of the panel. |
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| 44 | Two dimensional resolution weight distribution (2D elliptical Gaussian |
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| 45 | function) will also be displayed in the plot panel even if the Q inputs are |
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| 46 | outside of the detector limit. The red lines indicate the limits of the |
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| 47 | detector (if a green lines appear (for TOF), it indicates the limits of the |
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| 48 | maximum q range for the largest wavelength due to the size of the detector). |
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| 49 | Note that the effect from the beam block is ignored, so in the small q region |
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| 50 | near the beam block |
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| 51 | |
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| 52 | [ie., q<2*pi*(beam block diameter) / (sample to detector distance) / lamda_min] |
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| 53 | |
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| 54 | the variance is slightly under estimated. |
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| 55 | |
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| 56 | 7. The summary can be accessed by clicking the 'light-bulb' icon at the bottom |
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| 57 | of the SasView main window. |
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| 58 | |
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| 59 | .. image:: resolution_tutor.gif |
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| 60 | |
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| 61 | .. ZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZ |
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| 62 | |
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| 63 | Theory |
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| 64 | ------ |
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| 65 | |
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| 66 | The scattering wave transfer vector is by definition |
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| 67 | |
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| 68 | .. image:: q.gif |
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| 69 | |
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| 70 | In the limit of the small angle, the variance of q in the first order |
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| 71 | approximation is |
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| 72 | |
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| 73 | .. image:: sigma_q.gif |
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| 74 | |
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| 75 | In summary, the geometric and gravitational contributions depending on the |
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| 76 | shape of each factors can be expressed as shown the table. |
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| 77 | |
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| 78 | .. image:: sigma_table.gif |
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| 79 | |
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| 80 | Finally, we use a Gaussian function to describe the 2D weighting distribution |
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| 81 | of the uncertainty in q. |
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| 82 | |
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| 83 | .. ZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZ |
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| 84 | |
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| 85 | References |
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| 86 | ---------- |
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| 87 | D.F.R. Mildner and J.M. Carpenter, J. Appl. Cryst. 17, 249-256 (1984) |
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| 88 | |
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| 89 | D.F.R. Mildner, J.M. Carpenter and D.L. Worcester, J. Appl. Cryst. 19, 311-319 |
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| 90 | (1986) |
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