some doc improvements for Darwin Widths, front-page links

doc/examples.rst

@@ -389,11 +389,17 @@ which follows very closely the description from chapter 6.4 in
   * `crystal`: the atomic symbol for the crystal: 'Si', 'Ge', or 'C'. ['Si']
   * `hkl`: a tuple with (h, k, l) of the reflection used. [(1, 1, 1)]
   * `a`: lattice constant [`None` - use nominal value for crystal]
-  * `polarization`: `s` or `p` to specify the monochromator polarization  relative to the X-ray source [`s`]
+  * `polarization`: `s`, `p`, or `u` to specify the X-ray polarization relative to the crystal [`s`] 
   * `m`: the order of the reflection. [1]
   * `ignore_f1`: whether to ignore `f1`. [False]
   * `ignore_f2`: whether to ignore `f2`. [False]
 
+Polarization of `s` should be used for vertically deflecting monochromators
+at most synchrotron sources (which will normally be horizontally
+polarized), and `p` should be used for horizontally deflecting
+monochromators.  For crystals used to analyzed unpolarized X-ray emission,
+use `u`, which will give the average of `s` and `p` polarization.
+
 As with :func:`ionchamber_fluxes`, the output here is complicated enough
 that it is put into a named `DarwinWidth` tuple that will contain the
 following fields:

doc/index.rst

@@ -6,17 +6,16 @@ X-ray DB: X-ray Reference Data in SQLite
 .. _XrayDB Github Page:  https://github.com/xraypy/XrayDB
 .. _FFAST webpage:       https://www.nist.gov/pml/data/ffast/index.cfm
 .. _PDF Version of this documentation:  https://xraypy.github.io/XrayDB/xraydb.pdf
-.. _XrayDB Web App (beta!):  https://millenia.cars.aps.anl.gov/xraydb
+.. _XrayDB Web App (CARS, U Chicago):  https://millenia.cars.aps.anl.gov/xraydb
+.. _XrayDB Web App (xrayabsorption.org):  https://xraydb.xrayabsorption.org/
 
 XrayDB provides atomic data, characteristic X-ray energies, and X-ray cross
 sections for the elements in an SQLite3 database, ``xraydb.sqlite``.  This
 file can be used directly with SQLite :cite:`sqlite` using standard SQL, or
-from the many programming language that suppor SQLite.  A Python module
-providing such an interface is provided here.
-
-Because some of the components of the database hold arrays of numbers
-(for example, coefficients for interpolation), the arrays are stored in the
+from the many programming language that support SQLite.  Some of the
+components of the database hold arrays of numbers which are stored in the
 database as JSON-encoded strings, and will need to be unpacked to be used.
+A Python module providing such an interface is provided here.
 
 The project began with the data from the compilation of basic atomic
 properties and X-ray absorption edge energies, emission energies, and
@@ -29,27 +28,27 @@ scattering cross sections :math:`f'(E)` and :math:`f''(E)` and absorption
 cross sections from :cite:`Chantler` as from the `FFAST webpage`_ (but on
 a finer energy grid, data from :cite:`Chantler2016`) are also included.
 
-In general, the values here use units that are SI and in common usage in
-X-ray work.  Cross sections are in cm^2/gr, and energies are in eV.
-Energy-dependent data for cross-sections are typically most reliable
-between about 250 eV to about 250,000 eV.  Elements from Z=1 to 92 are
-supported, with some data are included for elements between Z=93 and Z=98.
+The values here use units that are SI and commonly used in X-ray work.
+Cross sections are in cm^2/gr, and energies are in eV.  Energy-dependent
+data for cross-sections are typically most reliable between about 250 eV to
+about 250,000 eV.  Elements from Z=1 to 92 are supported, with some data
+are included for elements between Z=93 and Z=98.
 
 The current version of the XrayDB is **8.1**, and the version of the Python
-module is |release|.
+module is |release|.   See Also:
 
-See Also:
+   * `XrayDB Web App (CARS, U Chicago)`_ and `XrayDB Web App
+     (xrayabsorption.org)`_ are interactive web applications to browse the
+     data in this database and make plots of X-ray attenuation, scattering
+     factors, mirror reflectivity, and more.
 
-   * `PDF Version of this documentation`_
+   * Printable Poster-sized :ref:`periodic_tables`.
 
    * `XrayDB Github Page`_ has data sources, code, development and issues.
 
-   * `XrayDB Web App (beta!)`_ is an interactive web page to browse some of
-     the data in this database and make plots of X-ray attenuation,
-     mirror reflectivity, and more.
-
-   * :ref:`periodic_tables`.
+   * `PDF Version of this documentation`_
 
+
 Table of Contents
 -----------------------