Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Global simulations of magnetorotational turbulence I: convergence and
  the quasi-steady state   Magnetorotational turbulence provides a viable mechanism for angular momentum
transport in accretion disks. We present global, three dimensional (3D), MHD
accretion disk simulations that investigate the dependence of the turbulent
stresses on resolution. Convergence in the time-and-volume-averaged
stress-to-gas-pressure ratio, at a value of $\sim0.04$, is found for a model
with radial, vertical, and azimuthal resolution of 12-51, 27, and 12.5 cells
per scale-height (the simulation mesh is such that cells per scale-height
varies in the radial direction). A control volume analysis is performed on the
main body of the disk (|z|<2H) to examine the production and removal of
magnetic energy. Maxwell stresses in combination with the mean disk rotation
are mainly responsible for magnetic energy production, whereas turbulent
dissipation (facilitated by numerical resistivity) predominantly removes
magnetic energy from the disk. Re-casting the magnetic energy equation in terms
of the power injected by Maxwell stresses on the boundaries of, and by Lorentz
forces within, the control volume highlights the importance of the boundary
conditions (of the control volume). The different convergence properties of
shearing-box and global accretion disk simulations can be readily understood on
the basis of choice of boundary conditions and the magnetic field
configuration. Periodic boundary conditions restrict the establishment of
large-scale gradients in the magnetic field, limiting the power that can be
delivered to the disk by Lorentz forces and by stresses at the surfaces. The
factor of three lower resolution required for convergence in turbulent stresses
for our global disk models compared to stratified shearing-boxes is explained
by this finding. (Abridged)

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The categories of this paper are: hep-ex
25
The categories of this paper are: patt-sol
37
The categories of this paper are: supr-con
33
The categories of this paper are: plasm-ph
17
The categories of this paper are: q-fin
3
The categories of this paper are: physics
20
The categories of this paper are: acc-phys
15
The categories of this paper are: nucl-ex
0
The categories of this paper are: hep-ph
18
The categories of this paper are: econ
16
The categories of this paper are: stat
10
The categories of this paper are: q-bio
28
The categories of this paper are: alg-geom
1
The categories of this paper are: cs
19
The categories of this paper are: eess
12
The categories of this paper are: nucl-th