1,741 research outputs found
Horizon-absorption effects in coalescing black-hole binaries: An effective-one-body study of the non-spinning case
We study the horizon absorption of gravitational waves in coalescing,
circularized, nonspinning black hole binaries. The horizon absorbed fluxes of a
binary with a large mass ratio (q=1000) obtained by numerical perturbative
simulations are compared with an analytical, effective-one-body (EOB) resummed
expression recently proposed. The perturbative method employs an analytical,
linear in the mass ratio, effective-one-body (EOB) resummed radiation reaction,
and the Regge-Wheeler-Zerilli (RWZ) formalism for wave extraction.
Hyperboloidal (transmitting) layers are employed for the numerical solution of
the RWZ equations to accurately compute horizon fluxes up to the late plunge
phase. The horizon fluxes from perturbative simulations and the EOB-resummed
expression agree at the level of a few percent down to the late plunge. An
upgrade of the EOB model for nonspinning binaries that includes horizon
absorption of angular momentum as an additional term in the resummed radiation
reaction is then discussed. The effect of this term on the waveform phasing for
binaries with mass ratios spanning 1 to 1000 is investigated. We confirm that
for comparable and intermediate-mass-ratio binaries horizon absorbtion is
practically negligible for detection with advanced LIGO and the Einstein
Telescope (faithfulness greater than or equal to 0.997)
Early star formation traced by the highest redshift quasars
The iron abundance relative to alpha-elements in the circumnuclear region of
quasars is regarded as a clock of the star formation history and, more
specifically, of the enrichment by SNIa. We investigate the iron abundance in a
sample of 22 quasars in the redshift range 3.0<z<6.4 by measuring their rest
frame UV FeII bump, which is shifted into the near-IR, and by comparing it with
the MgII 2798 flux. The observations were performed with a device that can
obtain near-IR spectra in the range 0.8-2.4 um in one shot, thereby enabling an
optimal removal of the continuum underlying the FeII bump. We detect iron in
all quasars including the highest redshift (z=6.4) quasar currently known. The
uniform observational technique and the wide redshift range allows a reliable
study of the trend of the FeII/MgII ratio with redshift. We find the FeII/MgII
ratio is nearly constant at all redshifts, although there is marginal evidence
for a higher FeII/MgII ratio in the quasars at z~6. If the FeII/MgII ratio
reflects the Fe/alpha abundance, this result suggests that the z~6 quasars have
already undergone a major episode of iron enrichment. We discuss the possible
implications of this finding for the star formation history at z>6. We also
detect a population of weak iron emitters at z~4.5, which are possibly hosted
in systems that evolved more slowly. Alternatively, the trend of the FeII/MgII
ratio at high redshift may reflect significantly different physical conditions
of the circumnuclear gas in such high redshift quasars.Comment: Replaced to match the accepted version (ApJL in press), 5 page
Molecular Gas, Dust and Star Formation in Galaxies: II. Dust properties and scalings in \sim\ 1600 nearby galaxies
We aim to characterize the relationship between dust properties. We also aim
to provide equations to estimate accurate dust properties from limited
observational datasets.
We assemble a sample of 1,630 nearby (z<0.1) galaxies-over a large range of
Mstar, SFR - with multi-wavelength observations available from wise, iras,
planck and/or SCUBA. The characterization of dust emission comes from SED
fitting using Draine & Li dust models, which we parametrize using two
components (warm and cold ). The subsample of these galaxies with global
measurements of CO and/or HI are used to explore the molecular and/or atomic
gas content of the galaxies.
The total Lir, Mdust and dust temperature of the cold component (Tc) form a
plane that we refer to as the dust plane. A galaxy's sSFR drives its position
on the dust plane: starburst galaxies show higher Lir, Mdust and Tc compared to
Main Sequence and passive galaxies. Starburst galaxies also show higher
specific Mdust (Mdust/Mstar) and specific Mgas (Mgas/Mstar). The Mdust is more
closely correlated with the total Mgas (atomic plus molecular) than with the
individual components. Our multi wavelength data allows us to define several
equations to estimate Lir, Mdust and Tc from one or two monochromatic
luminosities in the infrared and/or sub-millimeter.
We estimate the dust mass and infrared luminosity from a single monochromatic
luminosity within the R-J tail of the dust emission, with errors of 0.12 and
0.20dex, respectively. These errors are reduced to 0.05 and 0.10 dex,
respectively, if the Tc is used. The Mdust is correlated with the total Mism
(Mism \propto Mdust^0.7). For galaxies with Mstar 8.5<log(Mstar/Msun) < 11.9,
the conversion factor \alpha_850mum shows a large scatter (rms=0.29dex). The SF
mode of a galaxy shows a correlation with both the Mgass and Mdust: high
Mdust/Mstar galaxies are gas-rich and show the highest SFRs.Comment: 24 pages, 28 figures, 6 tables, Accepted for publication in A&
NGC 5506 Unmasked as a Narrow Line Seyfert 1: A Direct View of the Broad Line Region using Near-IR Spectroscopy
This letter presents incontrovertible evidence that NGC5506 is a Narrow Line
Seyfert 1 (NLSy1). Our new 0.9-1.4 micron spectrum of its nucleus clearly shows
the permitted OI 1.1287 micron line (with full width at half maximum <2000
km/s) and the `1 micron FeII lines'. These lines can only originate in the
optically-thick broad line region (BLR) and, among Seyfert nuclei the latter
series of lines are seen only in NLSy1s. The obscuration to the BLR, derived
from a rough estimate of the OI 1.1287 micron / OI 8446 Angstrom ratio and from
the reddening of the near-IR Paschen lines, is A_v > 5. Together, these results
make NGC5506 the first identified case of an optically-obscured NLSy1. This new
classification helps explain its radio to X-ray properties, which until now
were considered highly anomalous. However, interesting new concerns are raised:
e.g., NGC5506 is unusual in hosting both a `type 1' AGN and a nuclear water
vapor megamaser. As the brightest known NLSy1, NGC5506 is highly suitable for
study at wavebands less affected by obscuration.Comment: 4 pages, to appear in A&A Letter
Adaptive multi-stage integration schemes for Hamiltonian Monte Carlo
Hamiltonian Monte Carlo (HMC) is a powerful tool for Bayesian statistical inference due to its potential to rapidly explore high dimensional state space, avoiding the random walk behavior typical of many Markov Chain Monte Carlo samplers. The proper choice of the integrator of the Hamiltonian dynamics is key to the efficiency of HMC. It is becoming increasingly clear that multi-stage splitting integrators are a good alternative to the Verlet method, traditionally used in HMC. Here we propose a principled way of finding optimal, problem-specific integration schemes (in terms of the best conservation of energy for harmonic forces/Gaussian targets) within the families of 2- and 3-stage splitting integrators. The method, which we call Adaptive Integration Approach for statistics, or s-AIA, uses a multivariate Gaussian model and simulation data obtained at the HMC burn-in stage to identify a system-specific dimensional stability interval and assigns the most appropriate 2-/3-stage integrator for any user-chosen simulation step size within that interval. s-AIA has been implemented in the in-house software package HaiCS without introducing computational overheads in the simulations. The efficiency of the s-AIA integrators and their impact on the HMC accuracy, sampling performance and convergence are discussed in comparison with known fixed-parameter multi-stage splitting integrators (including Verlet). Numerical experiments on well-known statistical models show that the adaptive schemes reach the best possible performance within the family of 2-, 3-stage splitting schemes.PID2019-104927GB-C21
MCIN/AEI/10.13039/501100011033
ERDF (“A way of making Europe”)
KK-2022/00006
KK-2021/00022
KK-2021/00064
LCF/BQ/DI20/1178002
Condensation transition in a model with attractive particles and non-local hops
We study a one dimensional nonequilibrium lattice model with competing
features of particle attraction and non-local hops. The system is similar to a
zero range process (ZRP) with attractive particles but the particles can make
both local and non-local hops. The length of the non-local hop is dependent on
the occupancy of the chosen site and its probability is given by the parameter
. Our numerical results show that the system undergoes a phase transition
from a condensate phase to a homogeneous density phase as is increased
beyond a critical value . A mean-field approximation does not predict a
phase transition and describes only the condensate phase. We provide heuristic
arguments for understanding the numerical results.Comment: 11 Pages, 6 Figures. Published in Journal of Statistical Mechanics:
Theory and Experimen
Binary black hole merger in the extreme mass ratio limit
We discuss the transition from quasi-circular inspiral to plunge of a system
of two nonrotating black holes of masses and in the extreme mass
ratio limit . In the spirit of the Effective One Body
(EOB) approach to the general relativistic dynamics of binary systems, the
dynamics of the two black hole system is represented in terms of an effective
particle of mass moving in a (quasi-)Schwarzschild
background of mass and submitted to an
radiation reaction force defined by Pad\'e resumming high-order Post-Newtonian
results. We then complete this approach by numerically computing, \`a la
Regge-Wheeler-Zerilli, the gravitational radiation emitted by such a particle.
Several tests of the numerical procedure are presented. We focus on
gravitational waveforms and the related energy and angular momentum losses. We
view this work as a contribution to the matching between analytical and
numerical methods within an EOB-type framework.Comment: 14 pages, six figures. Revised version. To appear in the CQG special
issue based around New Frontiers in Numerical Relativity conference, Golm
(Germany), July 17-21 200
Recommended from our members
Molecular models should not be published without the corresponding atomic coordinates.
In PNAS, Romero et al. (1) present models of how glucocerebrosidase (GCase) interacts with saposin C (SAPC) and membranes. Unfortunately, the authors do not publish representative atomic coordinates or molecular dynamics trajectories for their models, denying researchers the opportunity to scrutinize the data Romero et al. (1) use to draw their functional conclusions. Access to these data is an important issue for
structural biologists (2), and the open release of experimentally determined structural data has been the accepted practice for many years (3). Indeed, Romero et al. rely on several such publically available structures to carry out their study.J.E.D. is supported by a Royal Society University Research Fellowship (UF100371). S.C.G. is supported by a Sir Henry Dale Fellowship co-funded by the Royal Society and Wellcome Trust (098406/Z/12/B)
The menstruation experience: Attitude dimensions among South African students
This study aimed to investigate the attitudes and experiences regarding menstruation among undergraduate women at a historically disadvantaged South African university. A total of 255 women participated in the study. The majority of participants were black women (coloured = 55%; African = 29 .2%). They responded to the Menstrual Attitudes Questionnaire (MAQ) and a demographic questionnaire. Data were analysed using descriptive statistics and ANOVA with post-hoc tests. The majority of women in the study (78%) had positive attitudes towards menstruation, viewing it as a natural event that can be anticipated and predicted. However, many of the women (51–58%) perceived it as debilitating and bothersome to everyday living. Menstruation was perceived by women as impacting on participation and performance in higher education, suggesting that the provision of tertiary education for previously disadvantaged groups needs to consider the needs of women who experience difficulty managing menstruation. The provision of material resources, education in self-care strategies and distribution of information to normalise menstruation may assist the adverse impact of menstruation on their higher education experience .DHE
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