428 research outputs found
Analysis of the Environmental Factors Affecting the Growth Traits of Iran-Black Sheep
A study was conducted to evaluate the effects of non-genetic factors on the growth behavior of Iran-Black sheep. The data of growth performances, birth weight (BW), weaning weight (W3), weight at 6, 9and 12 months of age (W6, W9 and W12, respectively), were taken from 1522 lambs belonging to data bank from Abbas Abad Sheep Breeding Station located at the North-east of Iran during a period of five years. Statistical analyses were performed using a general linear model including non-genetic factors: lamb sex, birth year and litter size as main effects, the lamb's age when weighed as covariate, and the interactions between these factors. Results showed that all traits were significantly (
Metric of a tidally perturbed spinning black hole
We explicitly construct the metric of a Kerr black hole that is tidally
perturbed by the external universe in the slow-motion approximation. This
approximation assumes that the external universe changes slowly relative to the
rotation rate of the hole, thus allowing the parameterization of the
Newman-Penrose scalar by time-dependent electric and magnetic tidal
tensors. This approximation, however, does not constrain how big the spin of
the background hole can be and, in principle, the perturbed metric can model
rapidly spinning holes. We first generate a potential by acting with a
differential operator on . From this potential we arrive at the metric
perturbation by use of the Chrzanowski procedure in the ingoing radiation
gauge. We provide explicit analytic formulae for this metric perturbation in
spherical Kerr-Schild coordinates, where the perturbation is finite at the
horizon. This perturbation is parametrized by the mass and Kerr spin parameter
of the background hole together with the electric and magnetic tidal tensors
that describe the time evolution of the perturbation produced by the external
universe. In order to take the metric accurate far away from the hole, these
tidal tensors should be determined by asymptotically matching this metric to
another one valid far from the hole. The tidally perturbed metric constructed
here could be useful in initial data constructions to describe the metric near
the horizons of a binary system of spinning holes. This perturbed metric could
also be used to construct waveforms and study the absorption of mass and
angular momentum by a Kerr black hole when external processes generate
gravitational radiation.Comment: 17 pages, 3 figures. Final PRD version, minor typos, etc corrected.
v3: corrected typo in Eq. (35) and (57
Spin-induced scalarized black holes
It was recently shown that a scalar field suitably coupled to the
Gauss-Bonnet invariant can undergo a spin-induced linear
tachyonic instability near a Kerr black hole. This instability appears only
once the dimensionless spin is sufficiently large, that is, . A tachyonic instability is the hallmark of spontaneous scalarization.
Focusing, for illustrative purposes, on a class of theories that do exhibit
this instability, we show that stationary, rotating black hole solutions do
indeed have scalar hair once the spin-induced instability threshold is
exceeded, while black holes that lie below the threshold are described by the
Kerr solution. Our results provide strong support for spin-induced black hole
scalarization.publishe
Three new triterpenes from the resinous bark of Protium kleinii and their antinociceptive activity
Three novel pentacyclic triterpenes have been isolated from the resin of Protium kleinii and their structures elucidated by NMR spectroscopy as 3-oxo-11beta,16beta-dihydroxy-urs-12-ene (1), 3-oxo-11beta-hydroxy-urs-12-ene (2) and 3-oxo-11beta-hydroxy-olean-12-ene (3). The systemic administration of the above compounds (10-100 mg kg-1, i.p.) was able to inhibited both first and second phase of the formalin-induced nociception in mice. The known triterpenes 3beta,16beta-dihydroxy-olean-12-ene (brein) (4) and a mixture of alpha (5)- and beta-amyrin (6) were also found. Três triterpenos pentacíclicos inéditos foram isolados da resina de Protium kleinii. Suas estruturas, 3-oxo-11beta,16beta-diidróxi-urs-12-eno (1), 3-oxo-11beta-hidróxi-urs-12-eno (2) e 3-oxo-11beta-hidróxi-olean-12-eno (3), foram elucidadas por espectroscopia de RMN. A administração sistêmica destes compostos (10-100 mg kg-1, i.p.) foi capaz de inibir tanto a primeira quanto a segunda fase da nocicepção induzida pela formalina em camundongos. Em adição, foram isolados os triterpenos conhecidos 3beta,16beta-dihidróxi-urs-12-eno (breina) (4) e uma mistura de alfa (5)- e beta-amirina (6)
Extreme mass ratio inspiral rates: dependence on the massive black hole mass
We study the rate at which stars spiral into a massive black hole (MBH) due
to the emission of gravitational waves (GWs), as a function of the mass M of
the MBH. In the context of our model, it is shown analytically that the rate
approximately depends on the MBH mass as M^{-1/4}. Numerical simulations
confirm this result, and show that for all MBH masses, the event rate is
highest for stellar black holes, followed by white dwarfs, and lowest for
neutron stars. The Laser Interferometer Space Antenna (LISA) is expected to see
hundreds of these extreme mass ratio inspirals per year. Since the event rate
derived here formally diverges as M->0, the model presented here cannot hold
for MBHs of masses that are too low, and we discuss what the limitations of the
model are.Comment: Accepted to CQG, special LISA issu
Two approaches to testing general relativity in the strong-field regime
Observations of compact objects in the electromagnetic spectrum and the
detection of gravitational waves from them can lead to quantitative tests of
the theory of general relativity in the strong-field regime following two very
different approaches. In the first approach, the general relativistic field
equations are modified at a fundamental level and the magnitudes of the
potential deviations are constrained by comparison with observations. In the
second approach, the exterior spacetimes of compact objects are parametrized in
a phenomenological way, the various parameters are measured observationally,
and the results are finally compared against the general relativistic
predictions. In this article, I discuss the current status of both approaches,
focusing on the lessons learned from a large number of recent investigations.Comment: To appear in the proceedings of the conference New Developments in
Gravit
Generalized Chern-Simons Modified Gravity in First-Order Formalism
We propose a generalization of Chern-Simons (CS) modified gravity in
first-order formalism. CS modified gravity action has a term that comes from
the chiral anomaly which is Pontryagin invariant. First-order CS modified
gravity is a torsional theory and in a space-time with torsion the chiral
anomaly includes a torsional topological term called Nieh-Yan invariant. We
generalize the CS modified gravity by adding the Nieh-Yan term to the action
and find the effective theory. We compare the generalized theory with the
first-order CS modified gravity and comment on the similarities and
differences.Comment: 8 pages, an author added, new paragraphs, comments and references
added, published in Gen. Relativ. Gravi
Renormalized spin coefficients in the accumulated orbital phase for unequal mass black hole binaries
We analyze galactic black hole mergers and their emitted gravitational waves.
Such mergers have typically unequal masses with mass ratio of the order 1/10.
The emitted gravitational waves carry the inprint of spins and mass quadrupoles
of the binary components. Among these contributions, we consider here the
quasi-precessional evolution of the spins. A method of taking into account
these third post-Newtonian (3PN) effects by renormalizing (redefining) the 1.5
PN and 2PN accurate spin contributions to the accumulated orbital phase is
developed.Comment: 10 pages, to appear in Class. Quantum Grav. GWDAW13 Proceedings
Special Issue, v2: no typos conjectur
How do Black Holes Spin in Chern-Simons Modified Gravity?
No Kerr-like exact solution has yet been found in Chern-Simons modified
gravity. Intrigued by this absence, we study stationary and axisymmetric
metrics that could represent the exterior field of spinning black holes. For
the standard choice of the background scalar, the modified field equations
decouple into the Einstein equations and additional constraints. These
constraints eliminate essentially all solutions except for Schwarzschild. For
non-canonical choices of the background scalar, we find several exact solutions
of the modified field equations, including mathematical black holes and
pp-waves. We show that the ultrarelativistically boosted Kerr metric can
satisfy the modified field equations, and we argue that physical spinning black
holes may exist in Chern-Simons modified gravity only if the metric breaks
stationarity, axisymmetry or energy-momentum conservation.Comment: 20 pages, 1 figure. Submitted to PR
Environmental effects for gravitational-wave astrophysics
The upcoming detection of gravitational waves by terrestrial interferometers will usher in the era of gravitational-wave astronomy. This will be particularly true when space-based detectors will come of age and measure the mass and spin of massive black holes with exquisite precision and up to very high redshifts, thus allowing for better understanding of the symbiotic evolution of black holes with galaxies, and for high-precision tests of General Relativity in strong-field, highly dynamical regimes. Such ambitious goals require that astrophysical environmental pollution of gravitational-wave signals be constrained to negligible levels, so that neither detection nor estimation of the source parameters are significantly affected. Here, we consider the main sources for space-based detectors the inspiral, merger and ringdown of massive black-hole binaries and extreme mass-ratio inspirals - and account for various effects on their gravitational waveforms, including electromagnetic fields, cosmological evolution, accretion disks, dark matter, "firewalls" and possible deviations from General Relativity. We discover that the black-hole quasinormal modes are sharply different in the presence of matter, but the ringdown signal observed by interferometers is typically unaffected. The effect of accretion disks and dark matter depends critically OH their geometry and density profile, but is negligible for most sources, except for few special extreme mass-ratio inspirals. Electromagnetic fields and cosmological effects are always negligible. We finally explore the implications of our findings for proposed tests of General Relativity with gravitational waves, and conclude that environmental effects will not prevent the development of precision gravitational-wave astronomy
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