9,068 research outputs found
TIDAL AND TIDAL-RESONANT EFFECTS IN COALESCING BINARIES
Tidal and tidal-resonant effects in coalescing compact binary systems are
investigated by direct numerical integration of the equations of motion. For
the stars polytropic models are used. The tidal effects are found to be
dominated by the (non-resonant) -modes. The effect of the -mode-tidal
resonances is obtained. The tidal interaction is shown to be of interest
especially for low-mass binaries. There exists a characteristic final plunge
orbit beyond which the system cannot remain stable even if radiation reaction
is not taken into account; in agreement with results obtained by Lai et al.
\shortcite{Lai93}. The importance of the investigated effects for the
observation of gravitational waves on Earth is discussed.Comment: 17 pages, latex (mn.sty), 5 figures, M.N.R.A.S. in pres
On the Einstein-Vlasov system with hyperbolic symmetry
It is shown that a spacetime with collisionless matter evolving from data on
a compact Cauchy surface with hyperbolic symmetry can be globally covered by
compact hypersurfaces on which the mean curvature is constant and by compact
hypersurfaces on which the area radius is constant. Results for the related
cases of spherical and plane symmetry are reviewed and extended. The prospects
of using the global time coordinates obtained in this way to investigate the
global geometry of the spacetimes concerned are discussed.Comment: 23 pages LaTeX2
Efficient Evaluation of the Probability Density Function of a Wrapped Normal Distribution
The wrapped normal distribution arises when a the density of a
one-dimensional normal distribution is wrapped around the circle infinitely
many times. At first look, evaluation of its probability density function
appears tedious as an infinite series is involved. In this paper, we
investigate the evaluation of two truncated series representations. As one
representation performs well for small uncertainties whereas the other performs
well for large uncertainties, we show that in all cases a small number of
summands is sufficient to achieve high accuracy
Directly Indecomposables in Semidegenerate Varieties of Connected po-Groupoids
We study varieties with a term-definable poset structure, "po-groupoids". It
is known that connected posets have the "strict refinement property" (SRP). In
[arXiv:0808.1860v1 [math.LO]] it is proved that semidegenerate varieties with
the SRP have definable factor congruences and if the similarity type is finite,
directly indecomposables are axiomatizable by a set of first-order sentences.
We obtain such a set for semidegenerate varieties of connected po-groupoids and
show its quantifier complexity is bounded in general
Recursive Estimation of Orientation Based on the Bingham Distribution
Directional estimation is a common problem in many tracking applications.
Traditional filters such as the Kalman filter perform poorly because they fail
to take the periodic nature of the problem into account. We present a recursive
filter for directional data based on the Bingham distribution in two
dimensions. The proposed filter can be applied to circular filtering problems
with 180 degree symmetry, i.e., rotations by 180 degrees cannot be
distinguished. It is easily implemented using standard numerical techniques and
suitable for real-time applications. The presented approach is extensible to
quaternions, which allow tracking arbitrary three-dimensional orientations. We
evaluate our filter in a challenging scenario and compare it to a traditional
Kalman filtering approach
A Practical Attack on the MIFARE Classic
The MIFARE Classic is the most widely used contactless smart card in the
market. Its design and implementation details are kept secret by its
manufacturer. This paper studies the architecture of the card and the
communication protocol between card and reader. Then it gives a practical,
low-cost, attack that recovers secret information from the memory of the card.
Due to a weakness in the pseudo-random generator, we are able to recover the
keystream generated by the CRYPTO1 stream cipher. We exploit the malleability
of the stream cipher to read all memory blocks of the first sector of the card.
Moreover, we are able to read any sector of the memory of the card, provided
that we know one memory block within this sector. Finally, and perhaps more
damaging, the same holds for modifying memory blocks
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