403 research outputs found
Boundary Between Stable and Unstable Regimes of Accretion
We investigated the boundary between stable and unstable regimes of accretion
and its dependence on different parameters. Simulations were performed using a
"cubed sphere" code with high grid resolution (244 grid points in the azimuthal
direction), which is twice as high as that used in our earlier studies. We
chose a very low viscosity value, with alpha-parameter alpha=0.02. We observed
from the simulations that the boundary strongly depends on the ratio between
magnetospheric radius r_m (where the magnetic stress in the magnetosphere
matches the matter stress in the disk) and corotation radius r_cor (where the
Keplerian velocity in the disk is equal to the angular velocity of the star).
For a small misalignment angle of the dipole field, Theta=5 degrees, accretion
is unstable if r_cor/r_m>1.35, and is stable otherwise. In cases of a larger
misalignment angle of the dipole, Theta=20 degrees, instability occurs at
slightly larger values, r_cor/r_m>1.41.Comment: 4 pages, 4 figures, conference proceedings: "Physics at the
Magnetospheric Boundary", Geneva, Switzerland, 25-28 June, 201
Experimental realization of a Dirac monopole through the decay of an isolated monopole
We experimentally observe the decay dynamics of deterministically created
isolated monopoles in spin-1 Bose-Einstein condensates. As the condensate
undergoes a change between magnetic phases, the isolated monopole gradually
evolves into a spin configuration hosting a Dirac monopole in its synthetic
magnetic field. We characterize in detail the Dirac monopole by measuring the
particle densities of the spin states projected along different quantization
axes. Importantly, we observe the spontaneous emergence of nodal lines in the
condensate density that accompany the Dirac monopole. We also demonstrate that
the monopole decay accelerates in weaker magnetic field gradients.Comment: 10 pages, 7 figure
MHD Simulations of Magnetospheric Accretion, Ejection and Plasma-field Interaction
We review recent axisymmetric and three-dimensional (3D) magnetohydrodynamic
(MHD) numerical simulations of magnetospheric accretion, plasma-field
interaction and outflows from the disk-magnetosphere boundary.Comment: 11 pages, 8 figures, conference proceedings: "Physics at the
Magnetospheric Boundary", Geneva, Switzerland, 25-28 June, 201
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