Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: The Evolution and Efficiency of Oblique MHD Cosmic-Ray Shocks: Two-Fluid
  Simulations   Using a new, second-order accurate numerical method we present dynamical
simulations of oblique MHD cosmic ray (CR) modified plane shock evolution using
the two-fluid model for diffusive particle acceleration. The numerical shocks
evolve to published analytical steady state properties. In order to probe the
dynamical role of magnetic fields we have explored for these time asymptotic
states the parameter space of upstream fast mode Mach number, $M_f$, and plasma
$\beta$, compiling the results into maps of dynamical steady state CR
acceleration efficiency, $\epsilon_c$. These maps, along with additional
numerical experiments, show that $\epsilon_c$ is reduced through the action of
compressive work on tangential magnetic fields in CR-MHD shocks. Thus
$\epsilon_c$ in low $\beta$, moderate $M_f$ shocks tends to be smaller in quasi
perpendicular shocks than it would be high $\beta$ shocks of the same $M_f$.
This result supports earlier conclusions that strong, oblique magnetic fields
inhibit diffusive shock acceleration. For quasi parallel shocks with $\beta <
1$, on the other hand, $\epsilon_c$ seems to be increased at a given $M_f$ when
compared to high $\beta$ shocks. The apparent contradiction to the first
conclusion results, however, from the fact that for small $\beta$ quasi
parallel shocks, the fast mode Mach number is not a good measure of compression
through the shock. That is better reflected in the sonic Mach number, which is
greater. Acceleration efficiencies for high and low $\beta$ having comparable
sonic Mach numbers are more similar. Time evolution of CR-MHD shocks is
qualitatively similar to CR-gasdynamical shocks. However, several potentially
interesting differences are apparent.

31
The categories of this paper are: ao-sci
11
The categories of this paper are: hep-lat
3
The categories of this paper are: physics
8
The categories of this paper are: hep-ex
10
The categories of this paper are: q-bio
5
The categories of this paper are: gr-qc
19
The categories of this paper are: eess
36
The categories of this paper are: cmp-lg
17
The categories of this paper are: q-fin
28
The categories of this paper are: alg-geom
20
The categories of this paper are: acc-phys
30
The categories of this paper are: q-alg
7
The categories of this paper are: hep-th
37
The categories of this paper are: supr-con
24
The categories of this paper are: dg-ga
27
The categories of this paper are: comp-gas