2,448 research outputs found
Spherical Harmonic Decomposition on a Cubic Grid
A method is described by which a function defined on a cubic grid (as from a
finite difference solution of a partial differential equation) can be resolved
into spherical harmonic components at some fixed radius. This has applications
to the treatment of boundary conditions imposed at radii larger than the size
of the grid, following Abrahams, Rezzola, Rupright et al.(gr-qc/9709082}. In
the method described here, the interpolation of the grid data to the
integration 2-sphere is combined in the same step as the integrations to
extract the spherical harmonic amplitudes, which become sums over grid points.
Coordinates adapted to the integration sphere are not needed.Comment: 5 pages, LaTeX uses cjour.cls (supplied
Carter's constant revealed
A new formulation of Carter's constant for geodesic motion in Kerr black
holes is given. It is shown that Carter's constant corresponds to the total
angular momentum plus a precisely defined part which is quadratic in the linear
momenta. The characterization is exact in the weak field limit obtained by
letting the gravitational constant go to zero. It is suggested that the new
form can be useful in current studies of the dynamics of extreme mass ratio
inspiral (EMRI) systems emitting gravitational radiation.Comment: Minor changes to match published versio
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