[FLASH-USERS] confusion regarding abar and zbar

[Jonathan Slavin]

Yes, that's exactly what I said.  How does one get FLASH to use zbar?  I
just tried again after running setup with the added argument
-with-unit=physics/Eos/EosMain/Gamma
but I still get that d*T/P * kboltz/amu_cgs = 1.28 (= abar) instead of
0.612 (= abar/(1 + zbar)) like I would expect.

Jon

On Wed, Sep 16, 2015 at 10:23 AM, Tomasz Plewa <tplewa at fsu.edu> wrote:

> Hi Jon -
>
> It is frequently assumed electron pressure is negligible compared to ions,
> which is true for a nonionized gas. Obviously, the correct formula should
> take into account contributions from both ions and electrons. For a fully
> ionized gas,
>
> \mu = \frac{\sum_j n_j A_j }{\sum_j n_j ( 1 + Z_j) }
>
> Tomek
> --
>
> On 09/16/15 10:00, Jonathan Slavin wrote:
>
> Hi all,
>
> I'm doing simulations aimed at understanding aspects of supernova remnant
> evolution.  Since the SNR is expanding the general interstellar medium, the
> proper mean mass per atom (i.e. neutrals and ions) is about 1.28 amu, given
> 90% H and 10% He by number.  As I understand it, this is set by the runtime
> parameter eos_singleSpeciesA, which corresponds to abar.  If I want to
> assume constant, uniform, complete ionization then, as I understand it, I
> need to set zbar via the runtime parameter eos_singleSpeciesZ, to a value
> of ~1.091 = 1.2/1.1 = (n(H+) + 2*n(He++))/(n(H) + n(He)).  At least that's
> what I thought from the docs where at one point it's stated that n(e) =
> zbar*n(ion).  However, when I look at density*temperature/pressure*kB/amu,
> I get abar.  So it seems that zbar is not used.  What I expect is that
> P = (1 + zbar)/abar*kB*density*temperature
> Where P is the total pressure (electron pressure + atom pressure).  Is
> this not true?  Do I need to specify some extra unit for zbar to be used
> (maybe -with-unit=physics/Eos/EosMain/Gamma)?  Am I misunderstanding the
> meaning of zbar?  Any help would be appreciated.
>
> Thanks,
> Jon
>
> --
> ________________________________________________________
> Jonathan D. Slavin                 Harvard-Smithsonian CfA
> jslavin at cfa.harvard.edu       60 Garden Street, MS 83
> phone: (617) 496-7981       Cambridge, MA 02138-1516
> cell: (781) 363-0035             USA
> ________________________________________________________
>
>
>


-- 
________________________________________________________
Jonathan D. Slavin                 Harvard-Smithsonian CfA
jslavin at cfa.harvard.edu       60 Garden Street, MS 83
phone: (617) 496-7981       Cambridge, MA 02138-1516
cell: (781) 363-0035             USA
________________________________________________________
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