287 research outputs found
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
Time-frequency detection algorithm for gravitational wave bursts
An efficient algorithm is presented for the identification of short bursts of
gravitational radiation in the data from broad-band interferometric detectors.
The algorithm consists of three steps: pixels of the time-frequency
representation of the data that have power above a fixed threshold are first
identified. Clusters of such pixels that conform to a set of rules on their
size and their proximity to other clusters are formed, and a final threshold is
applied on the power integrated over all pixels in such clusters. Formal
arguments are given to support the conjecture that this algorithm is very
efficient for a wide class of signals. A precise model for the false alarm rate
of this algorithm is presented, and it is shown using a number of
representative numerical simulations to be accurate at the 1% level for most
values of the parameters, with maximal error around 10%.Comment: 26 pages, 15 figures, to appear in PR
Primary health care facility infrastructure and services and the nutritional status of children 0 to 71 months old and their caregivers attending these facilities in four rural districts in the Eastern Cape and KwaZulu-Natal provinces, South Africa
Objective: To assess primary health care (PHC) facility infrastructure and services, and the nutritional status of 0 to 71-month-old children and their caregivers attending PHC facilities in the Eastern Cape (EC) and KwaZulu-Natal (KZN) provinces in South Africa. Design: Cross-sectional survey. Setting: Rural districts in the EC (OR Tambo and Alfred Nzo) and KZN (Umkhanyakude and Zululand). Subjects: PHC facilities and nurses (EC: n = 20; KZN: n = 20), and 0 to 71-month-old children and their caregivers (EC: n = 994; KZN: n = 992). Methods: Structured interviewer-administered questionnaires and anthropometric survey. Results: Of the 40 PHC facilities, 14 had been built or renovated after 1994. The PHC facilities had access to the following: safe drinking water (EC: 20%; KZN: 25%); electricity (EC: 45%; KZN: 85%); flush toilets (EC: 40%; KZN: 75%); and operational telephones (EC: 20%; KZN: 5%). According to more than 80% of the nurses, problems with basic resources and existing cultural practices influenced the quality of services. Home births were common (EC: 41%; KZN: 25%). Social grants were reported as a main source of income (EC: 33%; KZN: 28%). Few households reported that they had enough food at all times (EC: 15%; KZN: 7%). The reported prevalence of diarrhoea was high (EC: 34%; KZN: 38%). Undernutrition in 0 to younger than 6 month-olds was low; thereafter, however, stunting in children aged 6 to 59 months (EC: 22%; KZN: 24%) and 60 to 71 months (EC: 26%; KZN: 31%) was medium to high. Overweight and obese adults (EC: 49%; KZN: 42%) coexisted. Conclusion: Problems regarding infrastructure, basic resources and services adversely affected PHC service delivery and the well-being of rural people, and therefore need urgent attention.Keywords: primary health care facilities; nutritional status; children; caregiversâ rural; South Afric
The rat androgen receptor gene promoter
The androgen receptor (AR) is activated upon binding of testosterone or
dihydrotestosterone and exerts regulatory effects on gene expression in
androgen target cells. To study transcriptional regulation of the rat AR
gene itself, the 5' genomic region of this gene was cloned from a genomic
library and the promoter was identified. S1-nuclease protection analysis
showed two major transcription start sites, located between 1010 and 1023
bp upstream from the translation initiation codon. The area surrounding
these start sites was cloned in both orientations in a CAT reporter
plasmid. Upon transfection of the constructs into COS cells, part of the
promoter stimulated transcription in an orientation-independent manner,
but the full promoter showed a higher and unidirectional activity. In the
promoter/reporter gene constructs, transcription initiated from the same
positions as in the native gene. Sequence analysis showed that the
promoter of the rat AR gene lacks typical TATA and CCAAT box elements, but
one SP1 site is located at about 60 bp upstream from the major start site
of transcription. Other possible promoter elements are TGTYCT sequences at
positions -174 to -179, -434 to -439., -466 to -471, and -500 to -505,
resembling half-sites of the glucocorticoid-responsive element (GRE).
Furthermore, a homopurine stretch containing a total of 8 GGGGA elements
and similar to sequences that are present in several other GC-rich
promoters, is located between -89 and -146 bp upstream from the major
start site of transcriptio
High heart rate associated early repolarization causes Jâwaves in both zebra finch and mouse
Animal science
Radio precursors to neutron star binary mergings
We discuss a possible generation of radio bursts preceding final stages of
binary neutron star mergings which can be accompanied by short gamma-ray
bursts. Detection of such bursts appear to be advantageous in the low-frequency
radio band due to a time delay of ten to several hundred seconds required for
radio signal to propagate in the ionized intergalactic medium. This delay makes
it possible to use short gamma-ray burst alerts to promptly monitor specific
regions on the sky by low-frequency radio facilities, especially by LOFAR. To
estimate the strength of the radio signal, we assume a power-law dependence of
the radio luminosity on the total energy release in a magnetically dominated
outflow, as found in millisecond pulsars. Based on the planned LOFAR
sensitivity at 120 MHz, we estimate that the LOFAR detection rate of such radio
transients could be about several events per month from redshifts up to
in the most optimistic scenario. The LOFAR ability to detect such
events would crucially depend on exact efficiency of low-frequency radio
emission mechanism.Comment: 6 pages, 2 figures, Accepted for publication in Astrophysics & Space
Science. Largely extended version of ArXiv:0912.521
Gravitational-wave astronomy: the high-frequency window
This contribution is divided in two parts. The first part provides a
text-book level introduction to gravitational radiation. The key concepts
required for a discussion of gravitational-wave physics are introduced. In
particular, the quadrupole formula is applied to the anticipated
``bread-and-butter'' source for detectors like LIGO, GEO600, EGO and TAMA300:
inspiralling compact binaries. The second part provides a brief review of high
frequency gravitational waves. In the frequency range above (say) 100Hz,
gravitational collapse, rotational instabilities and oscillations of the
remnant compact objects are potentially important sources of gravitational
waves. Significant and unique information concerning the various stages of
collapse, the evolution of protoneutron stars and the details of the
supranuclear equation of state of such objects can be drawn from careful study
of the gravitational-wave signal. As the amount of exciting physics one may be
able to study via the detections of gravitational waves from these sources is
truly inspiring, there is strong motivation for the development of future
generations of ground based detectors sensitive in the range from hundreds of
Hz to several kHz.Comment: 21 pages, 5 figures, Lectures presented at the 2nd Aegean Summer
School on the Early Universe, Syros, Greece, September 200
Stellar populations of classical and pseudo-bulges for a sample of isolated spiral galaxies
In this paper we present the stellar population synthesis results for a
sample of 75 bulges in isolated spiral Sb-Sc galaxies, using the spectroscopic
data from the Sloan Digital Sky Survey and the STARLIGHT code. We find that
both pseudo-bulges and classical bulges in our sample are predominantly
composed of old stellar populations, with mean mass-weighted stellar age around
10 Gyr. While the stellar population of pseudo-bulges is, in general, younger
than that of classical bulges, the difference is not significant, which
indicates that it is hard to distinguish pseudo-bulges from classical bulges,
at least for these isolated galaxies, only based on their stellar populations.
Pseudo-bulges have star formation activities with relatively longer timescale
than classical bulges, indicating that secular evolution is more important in
this kind of systems. Our results also show that pseudo-bulges have a lower
stellar velocity dispersion than their classical counterparts, which suggests
that classical bulges are more dispersion-supported than pseudo-bulges.Comment: 10 pages, 8 figures. Accepted for publication in Astrophysics & Space
Scienc
Various features of quasiequilibrium sequences of binary neutron stars in general relativity
Quasiequilibrium sequences of binary neutron stars are numerically calculated
in the framework of the Isenberg-Wilson-Mathews (IWM) approximation of general
relativity. The results are presented for both rotation states of synchronized
spins and irrotational motion, the latter being considered as the realistic one
for binary neutron stars just prior to the merger. We assume a polytropic
equation of state and compute several evolutionary sequences of binary systems
composed of different-mass stars as well as identical-mass stars with adiabatic
indices gamma=2.5, 2.25, 2, and 1.8. From our results, we propose as a
conjecture that if the turning point of binding energy (and total angular
momentum) locating the innermost stable circular orbit (ISCO) is found in
Newtonian gravity for some value of the adiabatic index gamma_0, that of the
ADM mass (and total angular momentum) should exist in the IWM approximation of
general relativity for the same value of the adiabatic index.Comment: Text improved, some figures changed or deleted, new table, 38 pages,
31 figures, accepted for publication in Phys. Rev.
Relativistic Hydrodynamic Evolutions with Black Hole Excision
We present a numerical code designed to study astrophysical phenomena
involving dynamical spacetimes containing black holes in the presence of
relativistic hydrodynamic matter. We present evolutions of the collapse of a
fluid star from the onset of collapse to the settling of the resulting black
hole to a final stationary state. In order to evolve stably after the black
hole forms, we excise a region inside the hole before a singularity is
encountered. This excision region is introduced after the appearance of an
apparent horizon, but while a significant amount of matter remains outside the
hole. We test our code by evolving accurately a vacuum Schwarzschild black
hole, a relativistic Bondi accretion flow onto a black hole, Oppenheimer-Snyder
dust collapse, and the collapse of nonrotating and rotating stars. These
systems are tracked reliably for hundreds of M following excision, where M is
the mass of the black hole. We perform these tests both in axisymmetry and in
full 3+1 dimensions. We then apply our code to study the effect of the stellar
spin parameter J/M^2 on the final outcome of gravitational collapse of rapidly
rotating n = 1 polytropes. We find that a black hole forms only if J/M^2<1, in
agreement with previous simulations. When J/M^2>1, the collapsing star forms a
torus which fragments into nonaxisymmetric clumps, capable of generating
appreciable ``splash'' gravitational radiation.Comment: 17 pages, 14 figures, submitted to PR
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