| 1 | <html> |
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| 2 | <head> |
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| 3 | <META NAME="Author" CONTENT="Brian H. Toby"> |
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| 4 | <title>EXPGUI</title> |
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| 5 | </head> |
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| 6 | <BODY BGCOLOR="#FFFFFF"> |
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| 7 | |
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| 8 | <A HREF=http://www.ncnr.nist.gov> |
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| 16 | <CENTER> |
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| 17 | <A Href="http://www.ncnr.nist.gov/programs/crystallography/software/tclpkgs.html"> |
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| 18 | <IMG SRC="tcltklogo100.gif" |
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| 19 | alt="Link to Tcl/Tk information"> |
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| 20 | </CENTER></A> |
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| 21 | <hr> |
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| 22 | |
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| 23 | <center><h1> |
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| 24 | EXPGUI |
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| 25 | </h1></center> |
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| 26 | <A Href="expgui.html">EXPGUI top</A> |
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| 27 | |
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| 28 | <h3>A.7 Preferential Orientation Pane</h3></a> |
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| 29 | <DL><DL> |
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| 30 | The Preferential Orientation Pane is used to control parameters related |
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| 31 | to fitting parameters using the March-Dollase formulation |
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| 32 | or the spherical harmonic formulation |
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| 33 | for preferred orientation. Note that GSAS allows both sets of terms to be |
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| 34 | used at the same time, but it seems unlikely that anyone would |
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| 35 | actually want to try this. |
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| 36 | |
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| 37 | </DL></DL> |
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| 38 | <h4>A.7.a March-Dollase</H4> |
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| 39 | <DL><DL> |
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| 40 | In this model one or more axes are designated |
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| 41 | as directions [designated by (<i>hkl</i>)] where crystallites are over |
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| 42 | (Ratio > 1) or underrepresented (Ratio < 1). |
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| 43 | The checkbox to the right of the Ratio value determines if it will |
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| 44 | be refined. |
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| 45 | </DL></DL> |
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| 46 | <img SRC="po1.gif" align=TEXTTOP> |
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| 47 | <DL><DL> |
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| 48 | If more than one axis is present, one must define the relative fraction |
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| 49 | of preferred orientation for each direction. These fractions are normalized, |
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| 50 | so do not vary the fractions for all directions in a phase. |
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| 51 | </DL></DL> |
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| 52 | <img SRC="po2.gif" align=TEXTTOP> |
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| 53 | <DL><DL> |
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| 54 | If |
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| 55 | <A href="expgui.html#multiplehistogram"> |
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| 56 | "Multiple Histogram Selection" mode</A> is set to any value other than |
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| 57 | "Off", all terms are displayed for all selected histograms. |
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| 58 | No attempt is made to group terms or flags. |
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| 59 | |
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| 60 | </DL></DL> |
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| 61 | <H4>A.7.b Spherical harmonic</H4> |
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| 62 | <DL><DL> |
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| 63 | The spherical harmonic formulation, also referred to as an "orientation |
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| 64 | distribution function" defines a set of terms to treat preferential |
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| 65 | orientation as a function of the sample symmetry and as a function of |
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| 66 | the Laue phase symmetry of the phase and the selected order expansion. |
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| 67 | Note that only one set of terms |
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| 68 | is used for each phase, so this function should not be used when the |
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| 69 | different types of powder data, |
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| 70 | for example neutron and x-ray data, are used in a single refinement. |
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| 71 | The setting angles define the orientation of the sample with respect to |
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| 72 | the detectors and are typically used for texture analysis using TOF data |
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| 73 | only. |
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| 74 | |
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| 75 | </DL></DL> |
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| 76 | <img SRC="po3.gif" align=TEXTTOP> |
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| 77 | <DL><DL> |
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| 78 | When more than one phase is present, the phase is selected with the buttons |
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| 79 | in the upper left. Note that |
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| 80 | when additional terms are added by increasing the spherical harmonic order, |
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| 81 | the new parameters default to zero. Thus, is the order is set to zero |
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| 82 | and then reset to the previous non-zero value, all terms will be |
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| 83 | reset to zero. |
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| 84 | Also, as in EXPEDT, when the sample symmetry is changed, the |
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| 85 | order is reset to zero. |
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| 86 | </DL></DL> |
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| 87 | |
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| 88 | <hr> |
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| 89 | <A Href="expgui.html">EXPGUI top</A> |
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| 90 | |
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| 91 | <p><a href="http://www.ncnr.nist.gov/staff/toby/">Brian Toby</a> (<a href="mailto:brian.toby@nist.gov">Brian.Toby@NIST.GOV</a>) |
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| 92 | <br> |
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| 93 | $Revision: 244 $ $Date: 2009-12-04 23:02:48 +0000 (Fri, 04 Dec 2009) $ |
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| 94 | </body> |
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| 95 | </html> |
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