2,581 research outputs found
Approximate dynamics of dark matter ellipsoids
The collapse of non-collisional dark matter and the formation of pancake
structures in the Universe are investigated approximately. Collapse is
described by a system of ordinary differential equations, in the model of a
uniformly rotating, three-axis, uniform density ellipsoid. Violent relaxation,
mass and angular momentum losses are taken into account phenomenologically. The
formation of the equilibrium configuration, secular instability and the
transition from a spheroid to a three-axis ellipsoid are investigated
numerically and analytically in this dynamical model.Comment: 11 pages, 8 figure
Possible evolution of dim radio quiet neutron star 1E 1207.4-5209 based on a B-decay model
Dim radio-quiet neutron star (DRQNS) 1E 1207.4-5209 is one of the most
heavily examined isolated neutron stars. Wide absorption lines were observed in
its spectrum obtained by both XMM-Newton and Chandra X-ray satellites. These
absorption lines can be interpreted as a principal frequency centered at 0.7
keV and its harmonics at 1.4, 2.1 and possibly 2.8 keV. The principal line can
be formed by resonant proton cyclotron scattering leading to a magnetic field
which is two orders of magnitude larger than the perpendicular component of the
surface dipole magnetic field (B) found from the rotation period (P) and the
time rate of change in the rotation period (\.{P}) of 1E 1207.4-5209. Besides,
age of the supernova remnant (SNR) G296.5+10.0 which is physically connected to
1E 1207.4-5209 is two orders of magnitude smaller than the characteristic age
(=P/2\.{P}) of the neutron star. These huge differences between the
magnetic field values and the ages can be explained based on a B-decay model.
If the decay is assumed to be exponential, the characteristic decay time turns
out to be several thousand years which is three orders of magnitude smaller
than the characteristic decay time of radio pulsars represented in an earlier
work. The lack of detection of radio emission from DRQNSs and the lack of point
sources and pulsar wind nebulae in most of the observed SNRs can also be partly
explained by such a very rapid exponential decay. The large difference between
the characteristic decay times of DRQNSs and radio pulsars must be related to
the differences in the magnetic fields, equation of states and masses of these
isolated neutron stars.Comment: 13 pages, 1 figur
National Health Insurance Proposals: An Ethical Perspective
Presented to the WMU Center for the Study of Ethics in Society, January 31, 1992
Dynamical chaos in the problem of magnetic jet collimation
We investigate dynamics of a jet collimated by magneto-torsional
oscillations. The problem is reduced to an ordinary differential equation
containing a singularity and depending on a parameter. We find a parameter
range for which this system has stable periodic solutions and study
bifurcations of these solutions. We use Poincar\'e sections to demonstrate
existence of domains of regular and chaotic motions. We investigate transition
from periodic to chaotic solutions through a sequence of period doublings.Comment: 11 pages, 29 figures, 1 table, MNRAS (published online
Gravitational lensing by gravitational waves
Gravitational lensing by gravitational wave is considered. We notice that
although final and initial direction of photons coincide, displacement between
final and initial trajectories occurs. This displacement is calculated
analytically for the plane gravitational wave pulse. Estimations for
observations are discussed.Comment: 9 pages, 3 figure
A Closer Look at Two Branes in an Bulk
We investigate a scenario with two branes in an bulk. In this
scenario there are two gravitons and we investigate the role played by each of
them for different positions of the second brane. We show that both gravitons
play a significant role only when the turn-around point in the warp factor is
approximately equidistant from both branes. We find that the ultralight mode
becomes heavy as the second brane approaches the turn-around point, and the
physics begins to resemble that of the RS model. Thus we demonstrate the
crucial role played by the turn-around in the warp factor in enabling the
presence of both gravitons.Comment: 21 pages, late
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