source: trunk/doc/expgui7.html @ 246

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1<html>
2<head>
3   <META NAME="Author" CONTENT="Brian H. Toby">
4   <title>EXPGUI</title>
5</head>
6<BODY BGCOLOR="#FFFFFF">
7
8<A HREF=http://www.ncnr.nist.gov>
9<IMG SRC="http://www.ncnr.nist.gov/images/ncnrtrans.gif" 
10alt="Link to NIST Center for Neutron Research home page"
11ALIGN=RIGHT></A>
12<A HREF=http://www.nist.gov>
13<IMG SRC="http://www.ncnr.nist.gov/images/webidblue_2lineright.gif" 
14alt="Link to National Institute of Standards & Technology home page"
15ALIGN=LEFT></A>
16<CENTER>
17<A Href="http://www.ncnr.nist.gov/programs/crystallography/software/tclpkgs.html">
18<IMG SRC="tcltklogo100.gif" 
19alt="Link to Tcl/Tk information">
20</CENTER></A>
21<hr>
22
23<center><h1>
24EXPGUI
25</h1></center>
26<A Href="expgui.html">EXPGUI top</A>
27
28<h3>A.7 Preferential Orientation Pane</h3></a>
29<DL><DL>
30The Preferential Orientation Pane is used to control parameters related
31to fitting parameters using the March-Dollase formulation
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.
36
37</DL></DL>
38<h4>A.7.a March-Dollase</H4>
39<DL><DL>
40In this model one or more axes are designated
41as directions [designated by (<i>hkl</i>)] where crystallites are over
42(Ratio > 1) or underrepresented (Ratio < 1).
43The checkbox to the right of the Ratio value determines if it will 
44be refined.
45</DL></DL>
46<img SRC="po1.gif" align=TEXTTOP>
47<DL><DL>
48If more than one axis is present, one must define the relative fraction
49of preferred orientation for each direction. These fractions are normalized,
50so do not vary the fractions for all directions in a phase.
51</DL></DL>
52<img SRC="po2.gif" align=TEXTTOP>
53<DL><DL>
54If
55<A href="expgui.html#multiplehistogram">
56"Multiple Histogram Selection" mode</A> is set to any value other than
57"Off", all terms are displayed for all selected histograms.
58No attempt is made to group terms or flags.
59
60</DL></DL>
61<H4>A.7.b Spherical harmonic</H4>
62<DL><DL>
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
73only.
74
75</DL></DL>
76<img SRC="po3.gif" align=TEXTTOP>
77<DL><DL>
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.
86</DL></DL>
87
88<hr>
89<A Href="expgui.html">EXPGUI top</A>
90
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>)
92<br>
93$Revision: 244 $ $Date: 2009-12-04 23:02:48 +0000 (Fri, 04 Dec 2009) $
94</body>
95</html>
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