71 lines
2.7 KiB
HTML
71 lines
2.7 KiB
HTML
<HTML>
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<HEAD>
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<TITLE>The Online UB Calculation Routine</TITLE>
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</HEAD>
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<BODY>
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<H1>The Online UB Calculation Routine</H1>
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<P>
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This module allows to calculate the UB matrix from either two reflections and the
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cell constants or standalone from three reflections. A little aid for
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indexing is implemented too. As usual when dealing with calculations
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the common rule: shit in, shit out holds true. In this case this
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means that the quality of the UB matrix obtained increases when:
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<ul>
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<li>Reflections have been centered as accuratly as possible, i.e. with
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slits closed and collimators in.
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<li>Two theta has been calibrated against a standard beforehand.
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<li> The crystal under investigation has been properly centered.
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<li>Cell constants and wavelength are accurate.
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</ul>
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This module is for classic four circle diffraction only.
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</P>
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<p>
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A range of commands allows for reflection and data input and
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calculations. For the following discussion it is assumed that the UB
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matrix calculation object has been configured into the system under
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the name ubcalc.
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<dl>
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<dt>ubcalc ref1, ref2, ref3 h k l two_theta omega chi phi
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<dd>Reflection input for up to three reflections. Miller indices must
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be given. When angles are not given, the current position of motors
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stt, om, chi, phi is read.
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<dt>ubcalc cell a b c alpha beta gamma
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<dd>Input of cell constants
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<dt>ubcalc ub2ref
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<dt>Calculate the UB matrix from ref1, ref2 and the cell constants.
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<dt>ubcalc ub3ref
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<dd>Calculate the UB matrix from the three reflections ref1, ref2 and
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ref3.
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<dt>ubcalc listub
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<dd>Print the calculated UB matrix
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<dt>ubcalc cellub
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<dd>Caclulate and print the cell constants as calculated from the UB matrix.
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<dt>ubcalc activate
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<dd>Copies the UB matrix to the hkl module. The positions of new
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reflections can then be calculated with hkl.
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<dt>ubcalc index two_theta
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<dd>Makes suggestions for possible miller indices matching
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two_theta. If two_theta is omitted, the current value of two theta is
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read from the motor stt. A brute force search through the space of
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possible indices is undertaken using the cell constants given and the
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wavelength from the hkl module. This routine is controlled by three
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parameters within ubcalc:
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<ul>
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<li>difftheta, The maximum permissible difference in two_theta
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<li>maxindex, The maximum value for miller indices in any direction.
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<li>maxlist, The maximum number of suggestions to list.
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</ul>
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<dt>ubcalc difftheta, maxindex, maxlist value
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<dd>Inquire or set the above parameters. For inquiry, give no value,
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for setting the parameter give tha name and the value.
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<dt>ubcalc list
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<dd>Print all the data in ubcalc.
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<dt>ubcalc listcell
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<dd>Print the cell constants.
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<dt>ubcalc listref1, listref2, listref2
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<dd>Print reflections 1, 2 or 3
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</dl>
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</p>
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</BODY>
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</HTML>
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