Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: The equilibrium-diffusion limit for radiation hydrodynamics   The equilibrium-diffusion approximation (EDA) is used to describe certain
radiation-hydrodynamic (RH) environments. When this is done the RH equations
reduce to a simplified set of equations. The EDA can be derived by
asymptotically analyzing the full set of RH equations in the
equilibrium-diffusion limit. We derive the EDA this way and show that it and
the associated set of simplified equations are both first-order accurate with
transport corrections occurring at second order. Having established the EDA's
first-order accuracy we then analyze the grey nonequilibrium-diffusion
approximation and the grey Eddington approximation and show that they both
preserve this first-order accuracy. Further, these approximations preserve the
EDA's first-order accuracy when made in either the comoving-frame (CMF) or the
lab-frame (LF). While analyzing the Eddington approximation, we found that the
CMF and LF radiation-source equations are equivalent when neglecting ${\cal
O}(\beta^2)$ terms and compared in the LF. Of course, the radiation pressures
are not equivalent. It is expected that simplified physical models and
numerical discretizations of the RH equations that do not preserve this
first-order accuracy will not retain the correct equilibrium-diffusion
solutions. As a practical example, we show that nonequilibrium-diffusion
radiative-shock solutions devolve to equilibrium-diffusion solutions when the
asymptotic parameter is small.

36
The categories of this paper are: cmp-lg
14
The categories of this paper are: math-ph
34
The categories of this paper are: chem-ph
37
The categories of this paper are: supr-con
4
The categories of this paper are: cond-mat
23
The categories of this paper are: solv-int
21
The categories of this paper are: adap-org
7
The categories of this paper are: hep-th
35
The categories of this paper are: mtrl-th
18
The categories of this paper are: econ
24
The categories of this paper are: dg-ga
28
The categories of this paper are: alg-geom
9
The categories of this paper are: nlin
20
The categories of this paper are: acc-phys
31
The categories of this paper are: ao-sci
0
The categories of this paper are: hep-ph