| 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" |
|---|
| 10 | alt="Link to NIST Center for Neutron Research home page" |
|---|
| 11 | ALIGN=RIGHT></A> |
|---|
| 12 | <A HREF=http://www.nist.gov> |
|---|
| 13 | <IMG SRC="http://www.ncnr.nist.gov/images/webidblue_2lineright.gif" |
|---|
| 14 | alt="Link to National Institute of Standards & Technology home page" |
|---|
| 15 | ALIGN=LEFT></A> |
|---|
| 16 | <CENTER> |
|---|
| 17 | <A Href="http://www.ncnr.nist.gov/programs/crystallography/software/tclpkgs.html"> |
|---|
| 18 | <IMG SRC="tcltklogo100.gif" |
|---|
| 19 | alt="Link to Tcl/Tk information"> |
|---|
| 20 | </CENTER></A> |
|---|
| 21 | <hr> |
|---|
| 22 | |
|---|
| 23 | <TABLE BORDER BGCOLOR="#FFFF40" ALIGN=RIGHT> |
|---|
| 24 | <TR><TH><A Href="expgui.html">EXPGUI top</A> |
|---|
| 25 | </TH><TH><A Href="expguic.html">Menu contents</A> |
|---|
| 26 | </TH><TH><A Href="expgui6.html">Previous page</A> |
|---|
| 27 | </TH></TR></TABLE><BR CLEAR=ALL> |
|---|
| 28 | |
|---|
| 29 | <center><h1> |
|---|
| 30 | EXPGUI, part 7 |
|---|
| 31 | </h1></center> |
|---|
| 32 | |
|---|
| 33 | <h3>A.7 Preferential Orientation Pane</h3></a> |
|---|
| 34 | <DL><DL> |
|---|
| 35 | The Preferential Orientation Pane is used to control parameters related |
|---|
| 36 | to fitting parameters using the March-Dollase formulation |
|---|
| 37 | or the spherical harmonic formulation |
|---|
| 38 | for preferred orientation. Note that GSAS allows both sets of terms to be |
|---|
| 39 | used at the same time, but it seems unlikely that anyone would |
|---|
| 40 | actually want to try this. |
|---|
| 41 | |
|---|
| 42 | </DL></DL> |
|---|
| 43 | <h4>A.7.a March-Dollase</H4> |
|---|
| 44 | <DL><DL> |
|---|
| 45 | In this model one or more axes are designated |
|---|
| 46 | as directions [designated by (<i>hkl</i>)] where crystallites are over |
|---|
| 47 | (Ratio > 1) or underrepresented (Ratio < 1). |
|---|
| 48 | The checkbox to the right of the Ratio value determines if it will |
|---|
| 49 | be refined. |
|---|
| 50 | </DL></DL> |
|---|
| 51 | <img SRC="po1.gif" align=TEXTTOP> |
|---|
| 52 | <DL><DL> |
|---|
| 53 | If more than one axis is present, one must define the relative fraction |
|---|
| 54 | of preferred orientation for each direction. These fractions are normalized, |
|---|
| 55 | so do not vary the fractions for all directions in a phase. |
|---|
| 56 | </DL></DL> |
|---|
| 57 | <img SRC="po2.gif" align=TEXTTOP> |
|---|
| 58 | <DL><DL> |
|---|
| 59 | If |
|---|
| 60 | <A href="expgui.html#multiplehistogram"> |
|---|
| 61 | "Multiple Histogram Selection" mode</A> is set to any value other than |
|---|
| 62 | "Off", all terms are displayed for all selected histograms. |
|---|
| 63 | No attempt is made to group terms or flags. |
|---|
| 64 | |
|---|
| 65 | </DL></DL> |
|---|
| 66 | <H4>A.7.b Spherical harmonic</H4> |
|---|
| 67 | <DL><DL> |
|---|
| 68 | The spherical harmonic formulation, also referred to as an "orientation |
|---|
| 69 | distribution function" defines a set of terms to treat preferential |
|---|
| 70 | orientation as a function of the sample symmetry and as a function of |
|---|
| 71 | the Laue phase symmetry of the phase and the selected order expansion. |
|---|
| 72 | Note that only one set of terms |
|---|
| 73 | is used for each phase, so this function should not be used when the |
|---|
| 74 | different types of powder data, |
|---|
| 75 | for example neutron and x-ray data, are used in a single refinement. |
|---|
| 76 | The setting angles define the orientation of the sample with respect to |
|---|
| 77 | the detectors and are typically used for texture analysis using TOF data |
|---|
| 78 | only. |
|---|
| 79 | |
|---|
| 80 | </DL></DL> |
|---|
| 81 | <img SRC="po3.gif" align=TEXTTOP> |
|---|
| 82 | <DL><DL> |
|---|
| 83 | When more than one phase is present, the phase is selected with the buttons |
|---|
| 84 | in the upper left. Note that |
|---|
| 85 | when additional terms are added by increasing the spherical harmonic order, |
|---|
| 86 | the new parameters default to zero. Thus, is the order is set to zero |
|---|
| 87 | and then reset to the previous non-zero value, all terms will be |
|---|
| 88 | reset to zero. |
|---|
| 89 | Also, as in EXPEDT, when the sample symmetry is changed, the |
|---|
| 90 | order is reset to zero. |
|---|
| 91 | </DL></DL> |
|---|
| 92 | |
|---|
| 93 | <hr> |
|---|
| 94 | <TABLE BORDER BGCOLOR="#FFFF40" ALIGN=RIGHT> |
|---|
| 95 | <TR><TH><A Href="expgui.html">EXPGUI top</A> |
|---|
| 96 | </TH><TH><A Href="expguic.html">Menu contents</A> |
|---|
| 97 | </TH><TH><A Href="expgui6.html">Previous page</A> |
|---|
| 98 | </TH></TR></TABLE> |
|---|
| 99 | |
|---|
| 100 | <a href="http://www.ncnr.nist.gov/staff/toby/">Brian Toby</a> (<a href="mailto:brian.toby@nist.gov">Brian.Toby@NIST.GOV</a>) |
|---|
| 101 | <br> |
|---|
| 102 | $Revision: 277 $ $Date: 2009-12-04 23:03:22 +0000 (Fri, 04 Dec 2009) $ |
|---|
| 103 | </body> |
|---|
| 104 | </html> |
|---|
