Changes in src/sas/invariant/media/invariant_help.rst [0d66541:23a9beb] in sasview

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• src/sas/invariant/media/invariant_help.rst (modified) (1 diff)

src/sas/invariant/media/invariant_help.rst

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-..invariant_help.rst
+.. invariant_help.rst
 
-Placeholder for invariant help
+.. This is a port of the original SasView html help file to ReSTructured text
+.. by S King, ISIS, during SasView CodeCamp-III in Feb 2015.
+
+Invariant Calculation Perspective
+=================================
+
+Scattering_Invariant_
+
+Volume_Fraction_
+
+Specific_Surface_Area_
+
+Definitions_
+
+Reference_
+
+How_to_Use_
+
+.. ZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZ
+
+.. _Scattering_Invariant:
+
+Scattering Invariant
+--------------------
+
+The scattering invariant (Q*) is a model-independent quantity that can be 
+easily calculated from scattering data.
+
+For two phase systems, the scattering invariant, Q*, is defined as the 
+integral of the square of the wave transfer (q) multiplied by the scattering 
+cross section over the full range of q.
+
+Q* is given by the following equation
+
+.. image:: image001.gif
+
+This model independent quantity (Q*) is calculated from the scattering data 
+that can be used to determine the volume fraction and the specific area of the 
+sample under consideration.
+
+These quantities are useful in their own right and can be used in further 
+analysis. With this scattering invariant module users will also be able to 
+determine the consistency of those properties between data. There is no real 
+data defined from zero to infinity, there usually have limited range.
+
+Q* is not really computed from zero to infinity. Our maximum q range is 
+1e-5 ~ 10 (1/Angstrom). The lower and/or higher q range than data given can be 
+extrapolated by fitting some data nearby.
+
+The scattering invariant is computed as follows
+
+*I(q)* = *I(q)*  w/o background : If the data includes a background, user sets 
+the value to subtract the background for the Q* computation.
+
+Reset *I(q)* = *I(q)* scaling factor* , delta *I(q) =*  delta *I(q)*scaling 
+factor* : If non-zero scaling factor is given, it will be considered.
+
+Invariant
+
+.. image:: image001.gif
+
+where *g =q*  for the pinhole geometry and *g =qv*  (the slit height) for the 
+slit geometry which can be given in data or as a value.
+
+Higher q-region (\>= qmax in data)
+
+Power law (w/o background term) function = C/q4will be used
+
+where the constant C(=2pi(delta(rho))Sv) is to be found by fitting part of 
+data with the range of qN-mto qN(m\<N).
+
+Lower q-region (\<= qmin in data):
+
+Guinier function = *I0exp(-Rg2q2/3)*  where I0and Rgare obtained by fitting,
+
+similarly to the high q region above.
+
+Power law can also be used.
+
+.. ZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZ
+
+.. _Volume_Fraction:
+
+Volume Fraction
+---------------
+
+.. image:: image002.gif
+
+where delta(rho) is the SLD contrast of which value is given by users.
+
+.. image:: image003.gif
+
+Thus
+
+where 0 =\< *A*  =\<1/4 in order for these values to be physically valid.
+
+.. ZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZ
+
+.. _Specific_Surface_Area:
+
+Specific Surface Area
+---------------------
+
+.. image:: image004.gif
+
+where *A*  and *Q**  are obtained from previous sections, and the Porod 
+constant *Cp*  is given by users.
+
+.. ZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZ
+
+.. _Definitions:
+
+Definitions
+-----------
+
+Q: the magnitude of neutron (or X-ray) momentum transfer vector.
+
+I(Q): the scattering intensity as a function of the momentum transfer Q.
+
+Invariant total is the sum of the invariant calculated from datas q range and
+the invariant resulting from extrapolation at low q range and at high q range 
+if considered.
+
+.. ZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZ
+
+.. _Reference:
+
+References
+----------
+
+Chapter 2 in O. Glatter and O. Kratky, "Small Angle X-Ray Scattering", Academic 
+Press, New York, 1982
+
+http://physchem.kfunigraz.ac.at/sm/
+
+.. ZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZZ
+
+.. _How_to_Use:
+
+How to Use
+----------
+
+1. Loading data to the panel: Open the data file from File in the menu bar. 
+Select loaded data from a plot panel by highlighting that it until its color 
+turns yellow. Then right click on that the data and selects the option Compute 
+Invariant. The application automatically computes the invariant value if the 
+data loaded is valid.
+
+2. To subtract a background or/and to rescale the data, type the values in 
+Customized Input box.
+
+3. If you want to calculate the volume fraction and the specific surface 
+area, type the optional inputs in the customized input box, and then press 
+'Compute' button.
+
+4. The invariant can also be calculated including the outside of the data Q 
+range:  To include the lower Q and/or the higher Q range, check in the enable 
+extrapolation check box in 'Extrapolation' box. If the power low is chosen,
+the power (exponent) can be either held or fitted by checking the 
+corresponding radio button.  The Npts that is being used for the extrapolation 
+can be specified.
+
+5. If the invariant calculated from the extrapolated region is too large, it 
+will be warn in red at the top of the panel, which means that your data is not 
+proper to calculate the invariant.
+
+6. The details of the calculation is available by clicking the 'Details'
+button in the middle of the panel.
+
+.. image:: image005.gif