78 research outputs found
Gravitational Capture of Cosmic Strings by a Black Hole
The gravitational interaction of an infinitely long cosmic string with a
Schwarzschild black hole is studied. We consider a straight string that is
initially at a great distance and moving at some initial velocity v (0 < v < c)
towards the black hole. The equations of motion of the string are solved
numerically to obtain the dependence of the capture impact parameter on the
initial velocity.Comment: 15 pages, 2 figures, submitted to Phys Rev
Retrospective comparison of hydrostatic and pneumatic reduction of childhood intussusception at Red Cross Children's Hospital (1989-1997)
In accordance with consensus of the current literature, we have been using pneumatic reduction by preference at Red Cross Children's Hospital (RCCH) since the early 1990's. The aim of this study is to evaluate the results of our experience since 1989 as we have gradually moved from the hydrostatic method to the pneumatic method. This study will present results of 100 cases seen over a seven year period at the Red Cross Children's Hospital. The results of the respective reduction techniques will be discussed with special attention on complication rates, efficiency and cost implications
Numerical simulations of self-gravitating magnetized disks
We present the first global simulations of self-gravitating magnetized tori.
The simulations are performed with Zeus-2D and GLOBAL. We find the
magnetorotational instability (MRI) to behave similarly in a self-gravitating
environment as in previous simulations of non self-gravitating systems:
enhancement of turbulent angular momentum transport follows the linear phase.
The torus quickly develops a two component structure composed of an inner thick
disk in Keplerian rotation and an outer massive disk. We compare this result
with zero mass global simulations in 2D, and also present preliminary results
of 3D simulations.Comment: 6 pages, 6 figures, kluwer.cls, To appear in the proceedings of
"Magnetic fields and star formation: Theory versus observations",
Madrid,April 21-25 200
Evolution of massive and magnetized protoplanetary disks
We present global 2D and 3D simulations of self-gravitating magnetized tori.
We used the 2D calculations to demonstrate that the properties of the MRI are
not affected by the presence of self-gravity: MHD turbulence and enhanced
angular momentum transport follow the linear growth of the instability. In 3D,
we have studied the interaction between an gravitational instability and
MHD turbulence. We found its strength to be significantly decreased by the
presence of the latter, showing that both instabilities strongly interact in
their non-linear phases. We discuss the consequences of these results.Comment: 8 pages, 7 figures, to appear in the proceedings of the XIXth IAP
colloquium "Extrasolar Planets: Today and Tomorrow" held in Paris, France,
2003, June 30 - July 4, ASP Conf. Serie
Evolution of self-gravitating magnetized disks. I- Axisymmetric simulations
In this paper and a companion work, we report on the first global numerical
simulations of self-gravitating magnetized tori, subject in particular to the
influence of the magnetorotational instability (MRI). In this work, paper I, we
restrict our calculations to the study of the axisymmetric evolution of such
tori. Our goals are twofold: (1) to investigate how self-gravity influences the
global structure and evolution of the disks; and (2) to determine whether
turbulent density inhomogeneities can be enhanced by self-gravity in this
regime.
As in non self-gravitating models, the linear growth of the MRI is followed
by a turbulent phase during which angular momentum is transported outward. As a
result, self-gravitating tori quickly develop a dual structure composed of an
inner thin Keplerian disk fed by a thicker self-gravitating disk, whose
rotation profile is close to a Mestel disk. Our results show that the effects
of self-gravity enhance density fluctuations much less than they smooth the
disk, and giving it more coherence. We discuss the expected changes that will
occur in 3D simulations, the results of which are presented in a companion
paper.Comment: 20 pages, 7 figures, accepted for publication in Ap
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