source: trunk/doc/expgui7.html

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1<html>
2<head>
3   <title>EXPGUI</title>
4   <meta name="keywords" content="crystallography, Rietveld, diffraction,
5   GSAS, EXPGUI">
6</HEAD>
7<style>
8A:link {text-decoration:none}
9A:vlink {text-decoration:none}
10</style>
11
12<BODY BGCOLOR="#FFFFFF"
13      topmargin="0" leftmargin="0" marginwidth="0" marginheight="0" 
14      text="#000000" link="#0033ff" vlink="#0033ff" alink="#0033ff">
15
16<?
17   include("/var/www/include/navigation.inc");
18   include("/var/www/include/utility.inc");
19?>
20<blockquote><font face="arial, helvetica, sans-serif">
21
22<TABLE BORDER BGCOLOR="#FFFF40" ALIGN=RIGHT>
23<TR><TH><A  Href="expgui.html">EXPGUI top</A> 
24</TH><TH><A Href="expguic.html">Next page (Menus)</A>
25</TH><TH><A Href="expgui6A.html">Previous page</A>
26</TH></TR></TABLE><BR CLEAR=ALL>
27
28<center><h1>
29<HR noshade width="75%" size="2" align="center">
30EXPGUI, part 9
31<HR noshade width="75%" size="2" align="center">
32</h1></center>
33
34<h3>A.9 Preferential Orientation Panel</h3></a>
35<DL><DL>
36The Preferential Orientation Panel is used to control parameters related
37to fitting parameters using the March-Dollase formulation
38or the spherical harmonic formulation
39for preferred orientation. Note that GSAS allows both sets of terms to be
40used at the same time, but it seems unlikely that anyone would
41actually want to try this.
42
43</DL></DL>
44<a name="MD"></a>
45<h4>A.9.a March-Dollase</H4>
46<DL><DL>
47In this model one or more axes are designated
48as directions [designated by (<i>hkl</i>)] where crystallites are over
49(Ratio > 1) or underrepresented (Ratio < 1).
50The checkbox to the right of the Ratio value determines if it will 
51be refined.
52</DL></DL>
53<img SRC="po1.gif" align=TEXTTOP alt="EXPGUI Screen snapshot">
54<DL><DL>
55If more than one axis is present, one must define the relative fraction
56of preferred orientation for each direction. These fractions are normalized,
57so do not vary the fractions for all directions in a phase.
58</DL></DL>
59<img SRC="po2.gif" align=TEXTTOP alt="EXPGUI Screen snapshot">
60<DL><DL>
61If
62<A href="expgui.html#multiplehistogram">
63"Multiple Histogram Selection" mode</A> is set to any value other than
64"Off", all terms are displayed for all selected histograms.
65No attempt is made to group terms or flags.
66
67</DL></DL>
68<a name="ODF"></a>
69<H4>A.9.b Spherical harmonic</H4>
70<DL><DL>
71The spherical harmonic formulation, also referred to as an "orientation
72distribution function" defines a set of terms to treat preferential
73orientation as a function of the sample symmetry and as a function of
74the Laue phase symmetry of the phase and the selected order expansion.
75Note that only one set of terms
76is used for each phase, so this function should not be used when the
77different types of powder data,
78for example neutron and x-ray data, are used in a single refinement.
79The setting angles define the orientation of the sample with respect to
80the detectors and are typically used for texture analysis using TOF data
81only.
82
83</DL></DL>
84<img SRC="po3.gif" align=TEXTTOP  alt="EXPGUI Screen snapshot">
85<DL><DL>
86When more than one phase is present, the phase is selected with the buttons
87in the upper left. Note that
88when additional terms are added by increasing the spherical harmonic order,
89the new parameters default to zero. Thus, is the order is set to zero
90and then reset to the previous non-zero value, all terms will be
91reset to zero.
92Also, as in EXPEDT, when the sample symmetry is changed, the
93order is reset to zero.
94</DL></DL>
95
96<hr>
97<TABLE BORDER BGCOLOR="#FFFF40" ALIGN=RIGHT>
98<TR><TH><A  Href="expgui.html">EXPGUI top</A> 
99</TH><TH><A Href="expguic.html">Next page (Menus)</A>
100</TH><TH><A Href="expgui6A.html">Previous page</A>
101</TH></TR></TABLE>
102
103</blockquote>
104</body>
105</html>
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