195 research outputs found
Gravitational waves from axisymmetrically oscillating neutron stars in general relativistic simulations
Gravitational waves from oscillating neutron stars in axial symmetry are
studied performing numerical simulations in full general relativity. Neutron
stars are modeled by a polytropic equation of state for simplicity. A
gauge-invariant wave extraction method as well as a quadrupole formula are
adopted for computation of gravitational waves. It is found that the
gauge-invariant variables systematically contain numerical errors generated
near the outer boundaries in the present axisymmetric computation. We clarify
their origin, and illustrate it possible to eliminate the dominant part of the
systematic errors. The best corrected waveforms for oscillating and rotating
stars currently contain errors of magnitude in the local wave
zone. Comparing the waveforms obtained by the gauge-invariant technique with
those by the quadrupole formula, it is shown that the quadrupole formula yields
approximate gravitational waveforms besides a systematic underestimation of the
amplitude of where and denote the mass and the radius of
neutron stars. However, the wave phase and modulation of the amplitude can be
computed accurately. This indicates that the quadrupole formula is a useful
tool for studying gravitational waves from rotating stellar core collapse to a
neutron star in fully general relativistic simulations. Properties of the
gravitational waveforms from the oscillating and rigidly rotating neutron stars
are also addressed paying attention to the oscillation associated with
fundamental modes
Polymorphisms in pattern recognition receptors and their relationship to infectious disease susceptibility in pigs
<p>Abstract</p> <p>Background</p> <p>Pattern recognition receptors (PRRs), including Toll-like receptors (TLRs), are censoring receptors for molecules derived from bacteria, viruses, and fungi. The PRR system is a prerequisite for proper responses to pathogens, for example by cytokine production, resulting in pathogen eradication. Many cases of polymorphisms in PRR genes affecting the immune response and disease susceptibility are known in humans and mice.</p> <p>Methods</p> <p>We surveyed polymorphisms in pig genes encoding PRRs and investigated the relationship between some of the detected polymorphisms and molecular function or disease onset.</p> <p>Results</p> <p>Nonsynonymous polymorphisms abounded in pig TLR genes, particularly in the region corresponding to the ectodomains of TLRs expressed on the cell surface. Intracellular TLRs such as TLR3, TLR7, and TLR8, and other intracellular PRRs, such as the peptidoglycan receptor NOD2 and viral RNA receptors RIG-I and MDA5, also possessed nonsynonymous polymorphisms. Several of the polymorphisms influenced molecular functions such as ligand recognition. Polymorphisms in the PRR genes may be related to disease susceptibility in pigs: pigs with a particular allele of <it>TLR2</it> showed an increased tendency to contract pneumonia.</p> <p>Conclusions</p> <p>We propose the possibility of pig breeding aimed at disease resistance by the selection of PRR gene alleles that affect pathogen recognition.</p
Gravitational radiation from infall into a black hole: Regularization of the Teukolsky equation
The Teukolsky equation has long been known to lead to divergent integrals
when it is used to calculate the gravitational radiation emitted when a test
mass falls into a black hole from infinity. Two methods have been used in the
past to remove those divergent integrals. In the first, integrations by parts
are carried out, and the infinite boundary terms are simply discarded. In the
second, the Teukolsky equation is transformed into another equation which does
not lead to divergent integrals. The purpose of this paper is to show that
there is nothing intrinsically wrong with the Teukolsky equation when dealing
with non-compact source terms, and that the divergent integrals result simply
from an incorrect choice of Green's function. In this paper, regularization of
the Teukolsky equation is carried out in an entirely natural way which does not
involve modifying the equation.Comment: ReVTeX, 23 page
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
The radial infall of a highly relativistic point particle into a Kerr black hole along the symmetry axis
In this Letter we consider the radial infall along the symmetry axis of an
ultra-relativistic point particle into a rotating Kerr black hole. We use the
Sasaki-Nakamura formalism to compute the waveform, energy spectra and total
energy radiated during this process. We discuss possible connections between
these results and the black hole-black hole collision at the speed of light
process.Comment: 1 figur
Computing radiation from Kerr black holes: Generalization of the Sasaki-Nakamura equation
As shown by Teukolsky, the master equation governing the propagation of weak
radiation in a black hole spacetime can be separated into four ordinary
differential equations, one for each spacetime coordinate. (``Weak'' means the
radiation's amplitude is small enough that its own gravitation may be
neglected.) Unfortunately, it is difficult to accurately compute solutions to
the separated radial equation (the Teukolsky equation), particularly in a
numerical implementation. The fundamental reason for this is that the Teukolsky
equation's potentials are long ranged. For non-spinning black holes, one can
get around this difficulty by applying transformations which relate the
Teukolsky solution to solutions of the Regge-Wheeler equation, which has a
short-ranged potential. A particularly attractive generalization of this
approach to spinning black holes for gravitational radiation (spin weight s =
-2) was given by Sasaki and Nakamura. In this paper, I generalize Sasaki and
Nakamura's results to encompass radiation fields of arbitrary integer spin
weight, and give results directly applicable to scalar (s = 0) and
electromagnetic (s = -1) radiation. These results may be of interest for
studies of astrophysical radiation processes near black holes, and of programs
to compute radiation reaction forces in curved spacetime.Comment: 10 pages, no figures, to appear in Phys. Rev. D. Present version
updates the references, fixes some typos, and corrects some of the
Introductory tex
Doped two orbital chains with strong Hund's rule couplings - ferromagnetism, spin gap, singlet and triplet pairings
Different models for doping of two-orbital chains with mobile
fermions and strong, ferromagnetic (FM) Hund's rule couplings stabilizing the
S=1 spins are investigated by density matrix renormalization group (DMRG)
methods. The competition between antiferromagnetic (AF) and FM order leads to a
rich phase diagram with a narrow FM region for weak AF couplings and strongly
enhanced triplet pairing correlations. Without a level difference between the
orbitals, the spin gap persists upon doping, whereas gapless spin excitations
are generated by interactions among itinerant polarons in the presence of a
level difference. In the charge sector we find dominant singlet pairing
correlations without a level difference, whereas upon the inclusion of a
Coulomb repulsion between the orbitals or with a level difference, charge
density wave (CDW) correlations decay slowest. The string correlation functions
remain finite upon doping for all models.Comment: 9pages, 9figure
Gravitational signals emitted by a point mass orbiting a neutron star: a perturbative approach
We compute the energy spectra of the gravitational signals emitted when a
pointlike mass moves on a closed orbit around a non rotating neutron star,
inducing a perturbation of its gravitational field and its internal structure.
The Einstein equations and the hydrodynamical equations are perturbed and
numerically integrated in the frequency domain. The results are compared with
the energy spectra computed by the quadrupole formalism which assumes that both
masses are pointlike, and accounts only for the radiation emitted because the
orbital motion produces a time dependent quadrupole moment. The results of our
perturbative approach show that, in general, the quadrupole formalism
overestimates the amount of emitted radiation, especially when the two masses
are close. However, if the pointlike mass is allowed to move on an orbit so
tight that the keplerian orbital frequency resonates with the frequency of the
fundamental quasi-normal mode of the star (2w_K=w_f), this mode can be excited
and the emitted radiation can be considerably larger than that computed by the
quadrupole approach.Comment: 36 pages, 7 figures, submimtted to Phys. Rev.
Phylogenetic groups and cephalosporin resistance genes of Escherichia coli from diseased food-producing animals in Japan
A total of 318 Escherichia coli isolates obtained from different food-producing animals affected with colibacillosis between 2001 and 2006 were subjected to phylogenetic analysis: 72 bovine isolates, 89 poultry isolates and 157 porcine isolates. Overall, the phylogenetic group A was predominant in isolates from cattle (36/72, 50%) and pigs (101/157, 64.3%) whereas groups A (44/89, 49.4%) and D (40/89, 44.9%) were predominant in isolates from poultry. In addition, group B2 was not found among diseased food-producing animals except for a poultry isolate. Thus, the phylogenetic group distribution of E. coli from diseased animals was different by animal species. Among the 318 isolates, cefazolin resistance (minimum inhibitory concentrations: ≥32 μg/ml) was found in six bovine isolates, 29 poultry isolates and three porcine isolates. Of them, 11 isolates (nine from poultry and two from cattle) produced extended spectrum β-lactamase (ESBL). The two bovine isolates produced blaCTX-M-2, while the nine poultry isolates produced blaCTX-M-25 (4), blaSHV-2 (3), blaCTX-M-15 (1) and blaCTX-M-2 (1). Thus, our results showed that several types of ESBL were identified and three types of β-lactamase (SHV-2, CTX-M-25 and CTX-M-15) were observed for the first time in E. coli from diseased animals in Japan
Extreme Mass Ratio Inspirals: LISA's unique probe of black hole gravity
In this review article I attempt to summarise past and present-ongoing-work
on the problem of the inspiral of a small body in the gravitational field of a
much more massive Kerr black hole. Such extreme mass ratio systems, expected to
occur in galactic nuclei, will constitute prime sources of gravitational
radiation for the future LISA gravitational radiation detector. The article's
main goal is to provide a survey of basic celestial mechanics in Kerr spacetime
and calculations of gravitational waveforms and backreaction on the small
body's orbital motion, based on the traditional `flux-balance' method and the
Teukolsky black hole perturbation formalism.Comment: Invited review article, 45 pages, 23 figure
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