2,461 research outputs found
Gravitomagnetic Resonance Shift due to a Slowly Rotating Compact Star
The effect of a slowly rotating mass on a forced harmonic oscillator with two
degrees of freedom is studied in the weak field approximation. It is found that
according to the general theory of relativity there is a shift in the resonat
frequency of the oscillator which depends on the density and rotational
frequency of the gravitational source. The proposed shift is quite small under
normal physical situations however it is estimated that for compact x-ray
sources such as white dwarfs, pulsars, and neutron stars the shift is quite
appreciable.Comment: 8 pages, 2 figures, Accepted for Publication in Inter. Journal of
Modern Physics
Evidence of the Boyer Model of Scholarship in Counselor Education
This study delineated how the Boyer (1990) model of scholarship has been implemented in counselor education. The taxonomy of scholarship was delineated: Scholarship of Discovery, Scholarship of Teaching, Scholarship of Application, and Scholarship of Integration. The Journal of Counseling and Development and Counselor Education and Supervision were examined from 2000 to 2008. Examples of scholarship from each journal were identified. Evidence of the Boyer model in premier counseling journals suggests a consistency of approach between this model and scholarly activities in counselor education. An expanded view of scholarship may have positive implications for scholarly activity in graduate education and pretenured faculty
An AUC-based Permutation Variable Importance Measure for Random Forests
The random forest (RF) method is a commonly used tool for classification with high dimensional data as well as for ranking candidate predictors based on the so-called random forest variable importance measures (VIMs). However the classification performance of RF is known to be suboptimal in case of strongly unbalanced data, i.e. data where response class sizes differ considerably. Suggestions were made to obtain better classification performance based either on sampling procedures or on cost sensitivity analyses. However to our knowledge the performance of the VIMs has not yet been examined in the case of unbalanced response classes. In this paper we explore the performance of the permutation VIM for unbalanced data settings and introduce an alternative permutation VIM based on the area under the curve (AUC) that is expected to be more robust towards class imbalance. We investigated the performance of the standard permutation VIM and of our novel AUC-based permutation VIM for different class imbalance levels using simulated data and real data. The results suggest that the standard permutation VIM loses its ability to discriminate between associated predictors and predictors not associated with the response for increasing class imbalance. It is outperformed by our new AUC-based permutation VIM for unbalanced data settings, while the performance of both VIMs is very similar in the case of balanced classes. The new AUC-based VIM is implemented in the R package party for the unbiased RF variant based on conditional inference trees. The codes implementing our study are available from the companion website: http://www.ibe.med.uni-muenchen.de/organisation/mitarbeiter/070_drittmittel/janitza/index.html
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The UK WTC 9/11 evacuation study: methodologies used in the elicitation and storage of human factors data
This paper describes the methodologies employed in the collection and storage of first-hand accounts of evacuation experiences derived from face-to-face interviews with evacuees from the World Trade Center (WTC) Twin Towers complex on 11 September 2001. In particular the paper describes the development of the High-rise Evacuation Evaluation Database (HEED). This is a flexible qualitative research tool which contains the full transcribed interview accounts and coded evacuee experiences extracted from those transcripts. The data and information captured and stored in the HEED database is not only unique, but it provides a means to address current and emerging issues relating to human factors associated with the evacuation of high-rise buildings
The Challenges in Gravitational Wave Astronomy for Space-Based Detectors
The Gravitational Wave (GW) universe contains a wealth of sources which, with
the proper treatment, will open up the universe as never before. By observing
massive black hole binaries to high redshifts, we should begin to explore the
formation process of seed black holes and track galactic evolution to the
present day. Observations of extreme mass ratio inspirals will allow us to
explore galactic centers in the local universe, as well as providing tests of
General Relativity and constraining the value of Hubble's constant. The
detection of compact binaries in our own galaxy may allow us to model stellar
evolution in the Milky Way. Finally, the detection of cosmic (super)strings and
a stochastic background would help us to constrain cosmological models.
However, all of this depends on our ability to not only resolve sources and
carry out parameter estimation, but also on our ability to define an optimal
data analysis strategy. In this presentation, I will examine the challenges
that lie ahead in GW astronomy for the ESA L3 Cosmic Vision mission, eLISA.Comment: 12 pages. Plenary presentation to appear in the Proceedings of the
Sant Cugat Forum on Astrophysics, Sant Cugat, April 22-25, 201
Gravitational Waves in Brans-Dicke Theory : Analysis by Test Particles around a Kerr Black Hole
Analyzing test particles falling into a Kerr black hole, we study
gravitational waves in Brans-Dicke theory of gravity. First we consider a test
particle plunging with a constant azimuthal angle into a rotating black hole
and calculate the waveform and emitted energy of both scalar and tensor modes
of gravitational radiation. We find that the waveform as well as the energy of
the scalar gravitational waves weakly depends on the rotation parameter of
black hole and on the azimuthal angle.
Secondly, using a model of a non-spherical dust shell of test particles
falling into a Kerr black hole, we study when the scalar modes dominate. When a
black hole is rotating, the tensor modes do not vanish even for a ``spherically
symmetric" shell, instead a slightly oblate shell minimizes their energy but
with non-zero finite value, which depends on Kerr parameter . As a result,
we find that the scalar modes dominate only for highly spherical collapse, but
they never exceed the tensor modes unless the Brans-Dicke parameter
\omega_{BD} \lsim 750 for or unless \omega_{BD} \lsim 20,000
for , where is mass of black hole.
We conclude that the scalar gravitational waves with \omega_{BD} \lsim
several thousands do not dominate except for very limited situations
(observation from the face-on direction of a test particle falling into a
Schwarzschild black hole or highly spherical dust shell collapse into a Kerr
black hole). Therefore observation of polarization is also required when we
determine the theory of gravity by the observation of gravitational waves.Comment: 24 pages, revtex, 18 figures are attached with ps file
Merger of binary neutron stars of unequal mass in full general relativity
We present results of three dimensional numerical simulations of the merger
of unequal-mass binary neutron stars in full general relativity. A -law
equation of state is adopted, where , ,
\varep, and are the pressure, rest mass density, specific internal
energy, and the adiabatic constant, respectively. We take and the
baryon rest-mass ratio to be in the range 0.85--1. The typical grid size
is for . We improve several implementations since the
latest work. In the present code, the radiation reaction of gravitational waves
is taken into account with a good accuracy. This fact enables us to follow the
coalescence all the way from the late inspiral phase through the merger phase
for which the transition is triggered by the radiation reaction. It is found
that if the total rest-mass of the system is more than times of the
maximum allowed rest-mass of spherical neutron stars, a black hole is formed
after the merger irrespective of the mass ratios. The gravitational waveforms
and outcomes in the merger of unequal-mass binaries are compared with those in
equal-mass binaries. It is found that the disk mass around the so formed black
holes increases with decreasing rest-mass ratios and decreases with increasing
compactness of neutron stars. The merger process and the gravitational
waveforms also depend strongly on the rest-mass ratios even for the range --1.Comment: 32 pages, PRD68 to be publishe
Frequency-domain P-approximant filters for time-truncated inspiral gravitational wave signals from compact binaries
Frequency-domain filters for time-windowed gravitational waves from
inspiralling compact binaries are constructed which combine the excellent
performance of our previously developed time-domain P-approximants with the
analytic convenience of the stationary phase approximation without a serious
loss in event rate. These Fourier-domain representations incorporate the ``edge
oscillations'' due to the (assumed) abrupt shut-off of the time-domain signal
caused by the relativistic plunge at the last stable orbit. These new analytic
approximations, the SPP-approximants, are not only `effectual' for detection
and `faithful' for parameter estimation, but are also computationally
inexpensive to generate (and are `faster' by factors up to 10, as compared to
the corresponding time-domain templates). The SPP approximants should provide
data analysts the Fourier-domain templates for massive black hole binaries of
total mass m less than about 40 solar mases, the most likely sources for LIGO
and VIRGO.Comment: 50 Pages, 10 Postscript figures, 7 Tables, Revtex, Typos corrected,
References updated, Additions on pages 25, 26 and 3
Nonlinear Gravitational Waves: Their Form and Effects
A gravitational wave must be nonlinear to be able to transport its own
source, that is, energy and momentum. A physical gravitational wave, therefore,
cannot be represented by a solution to a linear wave equation. Relying on this
property, the second-order solution describing such physical waves is obtained.
The effects they produce on free particles are found to consist of nonlinear
oscillations along the direction of propagation.Comment: 15 pages, no figures. v2: presentation changes aiming at clarifying
the text; matches published versio
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