# Changeset a2ca6e5 in sasmodels

Ignore:
Timestamp:
Feb 15, 2018 7:01:45 AM (6 years ago)
Branches:
master, core_shell_microgels, magnetic_model, ticket-1257-vesicle-product, ticket_1156, ticket_1265_superball, ticket_822_more_unit_tests
Children:
547c6f0
Parents:
13bd583
Message:

Updated help doc for polymer_excl_volume model in wake of Ticket 1073

File:
1 edited

### Legend:

Unmodified
 r2d81cfe $a$ is the statistical segment length of the polymer chain, and $n$ is the degree of polymerization. This integral was later put into an almost analytical form as follows (Hammouda, 1993) .. math:: P(Q)=\frac{1}{\nu U^{1/2\nu}}\gamma\left(\frac{1}{2\nu},U\right) - \frac{1}{U^{1/2\nu}}\gamma\left(\frac{1}{\nu},U\right) later recast as (for example, Hore, 2013; Hammouda & Kim, 2017) .. math:: U=\frac{Q^2a^2n^{2\nu}}{6} = \frac{Q^2R_{g}^2(2\nu+1)(2\nu+2)}{6} The two analytic forms are equivalent. In the 1993 paper .. math:: \frac{1}{\nu U^{1/2\nu}} has been factored out. **SasView implements the 1993 expression**. The square of the radius-of-gyration is defined as R_{g}^2 = \frac{a^2n^{2\nu}}{(2\nu+1)(2\nu+2)} Note that this model applies only in the mass fractal range (ie, $5/3<=m<=3$ ) and **does not apply** to surface fractals ( \$3