Changeset 244

Dec 4, 2009 5:02:48 PM (13 years ago)

# on 2000/07/28 20:16:33, toby did:
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  • trunk/doc/expgui7.html

    • Property rcs:date changed from 2000/07/03 21:41:08 to 2000/07/28 20:16:33
    • Property rcs:rev changed from 1.1 to 1.2
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    3030The Preferential Orientation Pane is used to control parameters related
    3131to fitting parameters using the March-Dollase formulation
    32 for preferred orientation. In this model one or more axes are designated
     32or the spherical harmonic formulation
     33for preferred orientation. Note that GSAS allows both sets of terms to be
     34used at the same time, but it seems unlikely that anyone would
     35actually want to try this.
     38<h4>A.7.a March-Dollase</H4>
     40In this model one or more axes are designated
    3341as directions [designated by (<i>hkl</i>)] where crystallites are over
    3442(Ratio > 1) or underrepresented (Ratio < 1).
    4957"Off", all terms are displayed for all selected histograms.
    5058No attempt is made to group terms or flags.
    51 <P>
    52 Note that the other model for treating preferred orientation -- the orientation
    53 distribution function (spherical harmonics) is not yet implemented
    54 in EXPGUI and must be accessed from EXPEDT.
     61<H4>A.7.b Spherical harmonic</H4>
     63The spherical harmonic formulation, also referred to as an "orientation
     64distribution function" defines a set of terms to treat preferential
     65orientation as a function of the sample symmetry and as a function of
     66the Laue phase symmetry of the phase and the selected order expansion.
     67Note that only one set of terms
     68is used for each phase, so this function should not be used when the
     69different types of powder data,
     70for example neutron and x-ray data, are used in a single refinement.
     71The setting angles define the orientation of the sample with respect to
     72the detectors and are typically used for texture analysis using TOF data
     76<img SRC="po3.gif" align=TEXTTOP>
     78When more than one phase is present, the phase is selected with the buttons
     79in the upper left. Note that
     80when additional terms are added by increasing the spherical harmonic order,
     81the new parameters default to zero. Thus, is the order is set to zero
     82and then reset to the previous non-zero value, all terms will be
     83reset to zero.
     84Also, as in EXPEDT, when the sample symmetry is changed, the
     85order is reset to zero.
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