141 research outputs found
Conformal classes of asymptotically flat, static vacuum data
We show that time-reflection symmetric, asymptotically flat, static vacuum
data which admit a non-trivial conformal rescaling which leads again to such
data must be axi-symmetric and admit a conformal Killing field. Moreover, it is
shown that there exists a 3-parameter family of such data.Comment: 23 page
Radiation-reaction-induced evolution of circular orbits of particles around Kerr Black Holes
It is demonstrated that, in the adiabatic approximation, non-Equatorial
circular orbits of particles in the Kerr metric (i.e. orbits of constant
Boyer-Lindquist radius) remain circular under the influence of gravitational
radiation reaction. A brief discussion is given of conditions for breakdown of
adiabaticity and of whether slightly non-circular orbits are stable against the
growth of eccentricity.Comment: 23 pages. Revtex 3.0. Inquiries to [email protected]
Approximating the inspiral of test bodies into Kerr black holes
We present a new approximate method for constructing gravitational radiation
driven inspirals of test-bodies orbiting Kerr black holes. Such orbits can be
fully described by a semi-latus rectum , an eccentricity , and an
inclination angle ; or, by an energy , an angular momentum component
, and a third constant . Our scheme uses expressions that are exact
(within an adiabatic approximation) for the rates of change (,
, ) as linear combinations of the fluxes (,
, ), but uses quadrupole-order formulae for these fluxes.
This scheme thus encodes the exact orbital dynamics, augmenting it with
approximate radiation reaction. Comparing inspiral trajectories, we find that
this approximation agrees well with numerical results for the special cases of
eccentric equatorial and circular inclined orbits, far more accurate than
corresponding weak-field formulae for (, , ). We
use this technique to study the inspiral of a test-body in inclined, eccentric
Kerr orbits. Our results should be useful tools for constructing approximate
waveforms that can be used to study data analysis problems for the future LISA
gravitational-wave observatory, in lieu of waveforms from more rigorous
techniques that are currently under development.Comment: 15 pages, 5 figures, submitted to PR
Study of the Relation between the Spiral Arm Pitch Angle and the Kinetic Energy of Random Motions of the Host Spiral Galaxies, A
In this work, we report a relation between the kinetic energy of random motions of the corresponding host galaxies and spiral arm pitch angles (Mdynσ2- P), (M*σ2- P) where Mdyn is the bulge dynamical mass, M* is bulge stellar mass, and σ is the velocity dispersion of the host galaxy bulge. We measured the spiral arm pitch angle (P) for a sample of Spitzer/IRAC 3.6-μm images of 54 spiral galaxies, estimated by using a 2D Fast Fourier Transform decomposition technique (2DFFT). We selected a sample of nearly face-on spiral galaxies and used IRAF ellipse to determine the ellipticity and major-axis position angle in order to deproject the images to face-on, and using a 2D Fast Fourier Transform decomposition technique, we determined the spiral arm pitch angles. We estimated the kinetic energy of random motions of the corresponding host galaxies (Mdynσ, M*σ2) by using Mdyn, M*, and σ, where the stellar velocity dispersion (σ) of the bulge was taken from the literature. We determined the bulge dynamical mass (Mdyn) using the virial theorem, and the bulge stellar mass (M*) was estimated by using the bulge 3.6-μm luminosity with the appropriate stellar mass-to-light ratio (M/L)
Peer-review in a world with rational scientists: Toward selection of the average
One of the virtues of peer review is that it provides a self-regulating
selection mechanism for scientific work, papers and projects. Peer review as a
selection mechanism is hard to evaluate in terms of its efficiency. Serious
efforts to understand its strengths and weaknesses have not yet lead to clear
answers. In theory peer review works if the involved parties (editors and
referees) conform to a set of requirements, such as love for high quality
science, objectiveness, and absence of biases, nepotism, friend and clique
networks, selfishness, etc. If these requirements are violated, what is the
effect on the selection of high quality work? We study this question with a
simple agent based model. In particular we are interested in the effects of
rational referees, who might not have any incentive to see high quality work
other than their own published or promoted. We find that a small fraction of
incorrect (selfish or rational) referees can drastically reduce the quality of
the published (accepted) scientific standard. We quantify the fraction for
which peer review will no longer select better than pure chance. Decline of
quality of accepted scientific work is shown as a function of the fraction of
rational and unqualified referees. We show how a simple quality-increasing
policy of e.g. a journal can lead to a loss in overall scientific quality, and
how mutual support-networks of authors and referees deteriorate the system.Comment: 5 pages 4 figure
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