MHD turbulence is generally believed to have two important functions in accretion disks: it transports angular momentum outward, and the energy in its shortest wavelength modes is dissipated into the heat that the disks radiate. In this paper we examine a pair of mechanisms which may play an important role in regulating the amplitude and spectrum of this turbulence: photon diffusion and viscosi...

Magnetohydrodynamics (MHD) studies the dynamics of electrically conducting fluids, involving Navier-Stokes equations coupled with Maxwell equations via Lorentz force and Ohm’s law. Monolithic methods, which solve fully coupled MHD systems, are computationally expensive. Partitioned methods, on the other hand, decouple the full system and solve subproblems in parallel, and thus reduce the comput...

We introduce Gradient Particle Magnetohydrodynamics (GPM), a new Lagrangian method for magnetohydrodynamics based on gradients corrected for the locally disordered particle distribution. The development of a numerical code for MHD simulation using the GPM algorithm is outlined. Validation tests simulating linear and nonlinear sound waves, linear MHD waves, advection of magnetic fields in a magn...

We report the discovery of a family of stationary magnetohydrodynamic (MHD) outÑows from a disk found by time-dependent, axisymmetric MHD simulations. The initial poloidal magnetic Ðeld threading the disk was taken to be a tapered monopole Ðeld, with the Ðeld strength on the disk decreasing outwardly to small values. At the disk surface, matter was given a small initial push with a speed less t...

We present a model for nonlinear decay of the weak wave in three-dimensional incompressible magnetohydrodynamic (MHD) turbulence. We show that the decay rate is different for parallel and perpendicular waves. We provide a general formula for arbitrarily directed waves and discuss particular limiting cases known in the literature. We test our predictions with direct numerical simulations of wave...

MHD turbulence is generally believed to have two important functions in accretion disks: it transports angular momentum outward, and the energy in its shortest wavelength modes is dissipated into the heat that the disks radiate. In this paper we examine a pair of mechanisms which may play an important role in regulating the amplitude and spectrum of this turbulence: photon diffusion and viscosi...

We suggest an explanation for the twin kilohertz quasi-periodic oscillations (kHz QPOs) in low-mass X-ray binaries (LMXBs) based on magnetohydrodynamics (MHD) oscillation modes in neutron star magnetospheres. Including the effect of the neutron star spin, we derive several MHD wave modes by solving the dispersion equations, and propose that the coupling of the two resonant MHD modes may lead to...

In this, the second of a series of three papers, we continue a detailed description of ZEUS-2D, a numerical code for the simulation of uid dynamical ows in astrophysics including a self-consistent treatment of the e ects of magnetic elds and radiation transfer. In this paper, we give a detailed description of the magnetohydrodynamical (MHD) algorithms in ZEUS-2D. The recently developed constrai...

Results from the Swarthmore Spheromak Experiment ~SSX! @M. R. Brown, Phys. Plasmas 6, 1717 ~1999!# indicate that formation and partial merging of two spheromak plasmas can be described well by a magnetohydrodynamic ~MHD! picture in which there is substantial evolution towards force free states within each vessel, while reconnection activity, also described reasonably well by MHD, occurs in the ...

Background During Cardiac Magnetic Resonance Imaging (CMR), blood plasma electrolytes ejected into the aorta during early systole interact with the static magnetic field of the MR scanner (B0) to produce a Magnetohydrodynamic (MHD) Effect [1]. Electrocardiograms (ECGs) recorded in the presence of B0 are overlaid with induced MHD voltages (VMHD), leading to non-robustly synchronized imaging [2],...