Editing Appendix/Ramblings/PatrickMotl (section)

==May 4 (from Patrick)==

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Hi Joel,

Replying to your web page

The models have xi_interface values of 2.39184 and 2.44016

For the evolutions, I used passive scalars to identify fluids as
core or envelope and use effective polytropic indices and exponents
based on the proportion of the fluid in a given cell that is core or
envelope.

There is slightly more to it than that as the “vacuum” is n = 1.5 
and a third fluid type.

When I do that, the stars are definitely convectively unstable.

<font color="red">'''s.ps'''</font> is a quick plot of entropy vs radial cell number. The fluid 
in the envelope is lower in entropy than fluid in the core.

The entropy plotted is c_p ln( tau / rho) = R (gamma/(gamma-1)) ln (tau / rho)
where R is the gas constant.

The movie shows the meridional cross section of density through the
star, the core envelope boundary corrugates pretty quickly in the
run and then everything goes off the rails. There may be more
than one problem but the convective instability is definitely 
one problem.

cheers,
Patrick
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<tr><td align="center">[[File:Figure s.ps.png|400px|Motl Figure s.ps]]</td></tr>
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