.. _irena-anisotropy-analysis:
.. _AnisotropyAnalysis:

.. index::
   Irena; Anisotropy analysis
   Hermans orientational parameter

Anisotropy Analysis — HOP
==========================

This tool analyzes the anisotropy of an oriented scattering peak using the
Hermans orientational parameter (HOP) from Nika-generated intensity versus
azimuthal angle data, according to formula 8 in:

   P. C. van der Heijden, L. Rubatat, O. Diat, *Macromolecules* 2004, 37,
   5327. https://pubs.acs.org/doi/10.1021/ma035642w

See also: L. E. Alexander, R. J. Roe, et al.

The tool accepts angular dependence of scattered intensity at a specific Q
value. The simplest way to generate suitable input data is to use Nika's
:ref:`Line profile <LineProfileTool>` tool to compute the intensity profile
along a circle at the Q value of interest, yielding intensity as a function of
azimuthal angle. Nika stores these data as triplets of waves named
``az_Dataname``, ``r_Dataname``, and ``s_Dataname``, where ``az_Dataname``
contains the azimuthal angle in degrees.

.. note::

   Proper calibration and background subtraction are essential before using
   this tool; otherwise the results will be incorrect.

Main GUI
--------

.. Figure:: media/AnisotropySys1.jpg
   :align: center
   :height: 480px

The top section contains :ref:`standard data selection tools <DataSelection>`.
Data can be selected using the standard Irena selection system. When the
"*Nika Az data*" checkbox is checked, Nika-generated ``az_dataName`` and
``r_dataName`` pairs are used (uncertainty wave is optional). When unchecked,
arbitrarily named data can be selected. The azimuthal angle wave must be in
**degrees**.

Select data and click "*Graph data*" to generate the graph:

.. Figure:: media/AnisotropySys2.jpg
   :align: center
   :width: 580px

Set cursors to bracket the peak region — place each cursor below the half-
maximum point on each side of the peak. The peak maximum must not fall exactly
at 0° or 360°. The code internally extends the data to either side as needed,
so the peak can be close to 0° or 360°, but enough of the peak must be visible
for the position fit to succeed.

Select the peak profile shape (Gaussian or Lorentzian) and click "*Fit Peak*".
The complete analysis runs and fills the results table:

.. Figure:: media/AnisotropySys3.jpg
   :align: center
   :width: 680px

Results appear in both the table and the graph.

"*Save results (notebook)*" saves the results and graph to the Irena
:ref:`Results notebook <ResultsNotebook>`, which can be exported as RTF for use
in any word processor.

This tool cannot currently be scripted. Additional analysis options can be added
on request — contact the developer with your requirements.