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A niching memetic algorithm for simultaneous clustering and feature selection
Clustering is inherently a difficult task, and is made even more difficult when the selection of relevant features is also an issue. In this paper we propose an approach for simultaneous clustering and feature selection using a niching memetic algorithm. Our approach (which we call NMA_CFS) makes feature selection an integral part of the global clustering search procedure and attempts to overcome the problem of identifying less promising locally optimal solutions in both clustering and feature selection, without making any a priori assumption about the number of clusters. Within the NMA_CFS procedure, a variable composite representation is devised to encode both feature selection and cluster centers with different numbers of clusters. Further, local search operations are introduced to refine feature selection and cluster centers encoded in the chromosomes. Finally, a niching method is integrated to preserve the population diversity and prevent premature convergence. In an experimental evaluation we demonstrate the effectiveness of the proposed approach and compare it with other related approaches, using both synthetic and real data
A fully-coherent all-sky search for gravitational-waves from compact binary coalescences
We introduce a fully-coherent method for searching for gravitational wave
signals generated by the merger of black hole and/or neutron star binaries.
This extends the coherent analysis previously developed and used for targeted
gravitational wave searches to an all-sky, all-time search. We apply the search
to one month of data taken during the fifth science run of the LIGO detectors.
We demonstrate an increase in sensitivity of 25% over the coincidence search,
which is commensurate with expectations. Finally, we discuss prospects for
implementing and running a coherent search for gravitational wave signals from
binary coalescence in the advanced gravitational wave detector data.Comment: 17 pages, 12 figure
Distorted Black Holes with Charge
We present new solutions to the Einstein-Maxwell equations representing a
class of charged distorted black holes. These solutions are static-axisymmetric
and are generalizations of the distorted black hole solutions studied by Geroch
and Hartle. Physically, they represent a charged black hole distorted by
external matter fields. We discuss the zeroth and first law for these black
holes. The first law is proved in two different forms, one motivated by the
isolated horizon framework and the other using normalizations at infinity.Comment: 18 pages, LaTe
Isolated, slowly evolving, and dynamical trapping horizons: geometry and mechanics from surface deformations
We study the geometry and dynamics of both isolated and dynamical trapping
horizons by considering the allowed variations of their foliating two-surfaces.
This provides a common framework that may be used to consider both their
possible evolutions and their deformations as well as derive the well-known
flux laws. Using this framework, we unify much of what is already known about
these objects as well as derive some new results. In particular we characterize
and study the "almost-isolated" trapping horizons known as slowly evolving
horizons. It is for these horizons that a dynamical first law holds and this is
analogous and closely related to the Hawking-Hartle formula for event horizons.Comment: 39 pages, 6 figures, version to appear in PRD : a few minor changes
and many typos corrected in equation
When can gravitational-wave observations distinguish between black holes and neutron stars?
Gravitational-wave observations of compact binaries have the potential to
uncover the distribution of masses and angular momenta of black holes and
neutron stars in the universe. The binary components' physical parameters can
be inferred from their effect on the phasing of the gravitational-wave signal,
but a partial degeneracy between the components' mass ratio and their angular
momenta limits our ability to measure the individual component masses. At the
typical signal amplitudes expected by the Advanced Laser Interferometer
Gravitational-wave Observatory (signal-to-noise ratios between 10 and 20), we
show that it will in many cases be difficult to distinguish whether the
components are neutron stars or black holes. We identify when the masses of the
binary components could be unambiguously measured outside the range of current
observations: a system with a chirp mass M
would unambiguously contain the smallest-mass neutron star observed, and a
system with \mathcal{M} \ge 2.786 \Msun must contain a black hole. However,
additional information would be needed to distinguish between a binary
containing two 1.35 M neutron stars and an exotic
neutron-star--black-hole binary. We also identify those configurations that
could be unambiguously identified as black-hole binaries, and show how the
observation of an electromagnetic counterpart to a neutron-star--black-hole
binary could be used to constrain the black-hole spin.Comment: 5 pages, 4 figures. Final version to be published in Ap.J.Let
Improved methods for detecting gravitational waves associated with short gamma-ray bursts
In the era of second generation ground-based gravitational wave detectors,
short gamma-ray bursts (GRBs) will be among the most promising astrophysical
events for joint electromagnetic and gravitational wave observation. A targeted
search for gravitational wave compact binary merger signals in coincidence with
short GRBs was developed and used to analyze data from the first generation
LIGO and Virgo instruments. In this paper, we present improvements to this
search that enhance our ability to detect gravitational wave counterparts to
short GRBs. Specifically, we introduce an improved method for estimating the
gravitational wave background to obtain the event significance required to make
detections; implement a method of tiling extended sky regions, as required when
searching for signals associated to poorly localized GRBs from Fermi Gamma-ray
Burst Monitor or the InterPlanetary Network; and incorporate astrophysical
knowledge about the beaming of GRB emission to restrict the search parameter
space. We describe the implementation of these enhancements and demonstrate how
they improve the ability to observe binary merger gravitational wave signals
associated with short GRBs.Comment: 13 pages, 6 figure
Host Galaxies Catalog Used in LIGO Searches for Compact Binary Coalescence Events
An up-to-date catalog of nearby galaxies considered as hosts of binary
compact objects is provided with complete information about sky position,
distance, extinction-corrected blue luminosity and error estimates. With our
current understanding of binary evolution, rates of formation and coalescence
for binary compact objects scale with massive-star formation and hence the
(extinction-corrected) blue luminosity of host galaxies. Coalescence events in
binary compact objects are among the most promising gravitational-wave sources
for ground-based gravitational-wave detectors such as LIGO. Our catalog and
associated error estimates are important for the interpretation of analyses,
carried out for LIGO, to constrain the rates of compact binary coalescence,
given an astrophysical population model for the sources considered. We discuss
how the notion of effective distance, created to account for the antenna
pattern of a gravitational-wave detector, must be used in conjunction with our
catalog. We note that the catalog provided can be used on other astronomical
analysis of populations that scale with galaxy blue luminosity.Comment: 29 pages, 7 figures, Accepted to Astrophysical Journal. To appear in
March 20 2008 Astrophysical Journa
Horizon energy and angular momentum from a Hamiltonian perspective
Classical black holes and event horizons are highly non-local objects,
defined in terms of the causal past of future null infinity. Alternative,
(quasi)local definitions are often used in mathematical, quantum, and numerical
relativity. These include apparent, trapping, isolated, and dynamical horizons,
all of which are closely associated to two-surfaces of zero outward null
expansion. In this paper we show that three-surfaces which can be foliated with
such two-surfaces are suitable boundaries in both a quasilocal action and a
phase space formulation of general relativity. The resulting formalism provides
expressions for the quasilocal energy and angular momentum associated with the
horizon. The values of the energy and angular momentum are in agreement with
those derived from the isolated and dynamical horizon frameworks.Comment: 39 pages, 3 figures, Final Version : content essentially unchanged
but many small improvements made in response to referees, a few references
adde
The Loudest Event Statistic: General Formulation, Properties and Applications
The use of the loudest observed event to generate statistical statements
about rate and strength has become standard in searches for gravitational waves
from compact binaries and pulsars. The Bayesian formulation of the method is
generalized in this paper to allow for uncertainties both in the background
estimate and in the properties of the population being constrained. The method
is also extended to allow rate interval construction. Finally, it is shown how
to combine the results from multiple experiments and a comparison is drawn
between the upper limit obtained in a single search and the upper limit
obtained by combining the results of two experiments each of half the original
duration. To illustrate this, we look at an example case, motivated by the
search for gravitational waves from binary inspiral.Comment: 11 pages, 8 figure
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