1,672 research outputs found
Reconstructing the Thermal Sunyaev-Zel'dovich Effect in 3D
The thermal Sunyaev-Zel'dovich (tSZ) effect measures the line-of-sight
projection of the thermal pressure of free electrons and lacks any redshift
information. By cross correlating the tSZ effect with an external cosmological
tracer we can recover a good fraction of this lost information. Weak lensing
(WL) is thought to provide an unbiased probe of the dark Universe, with many WL
surveys having sky coverage that overlaps with tSZ surveys. Generalising the
tomographic approach, we advocate the use of the spherical Fourier-Bessel (sFB)
expansion to perform an analysis of the cross-correlation between the projected
(2D) tSZ Compton -parameter maps and 3D weak lensing convergence maps. We
use redshift dependent linear biasing and the halo model as a tool to
investigate the tSZ-WL cross-correlations in 3D. We use the Press-Schechter
(PS) and the Sheth-Tormen (ST) mass-functions in our calculations, finding that
the results are quite sensitive to detailed modelling. We provide detailed
analysis of surveys with photometric and spectroscopic redshifts. The
signal-to-noise (S/N) of the cross-spectra for
individual 3D modes, defined by the radial and tangential wave numbers
, remains comparable to, but below, unity though optimal binning is
expected to improve this. The results presented can be generalised to analyse
other CMB secondaries, such as the kinetic Sunyaev-Zel'dovich (kSZ) effect.Comment: 27 pages, 12 Figures. Published in MNRA
Impact of Numerical Relativity information on effective-one-body waveform models
We present a comprehensive comparison of the spin-aligned effective-one-body
(EOB) waveform model of Nagar et al. [Phys. Rev. D93, 044046 (2016)], informed
using 40 numerical-relativity (NR) datasets, against a set of 149, ,
NR waveforms freely available through the Simulation Extreme Spacetime (SXS)
catalog. We find that, without further calibration, these EOBNR waveforms have
unfaithfulness (at design Advanced-LIGO sensitivity and evaluated with total
mass varying as ) always below
against all NR waveforms except for three outliers, that still never exceed the
level; with a minimal retuning of the (effective)
next-to-next-to-next-to-leading-order spin-orbit coupling parameter for the
non-equal-mass and non-equal-spin sector, that only needs three more NR
waveforms, one is left with another two (though different) outliers, with
maximal unfaithfulness of up to only for a total mass of . We
show this is the effect of slight inaccuracies in the phenomenological
description of the postmerger waveform of Del Pozzo and Nagar
[arXiv:1606.03952] that was constructed by interpolating over only 40NR
simulations. We argue that this is easily fixed by using either an alternative
ringdown description (e.g., the superposition of quasi-normal-modes) or an
improved version of the phenomenological representation. By analyzing a NR
waveform with mass ratio and dimensionless spins obtained with the
BAM code, we conclude that the model would benefit from NR simulations
specifically targeted at improving the postmerger-ringdown phenomenological
fits for mass ratios and spins .Comment: 24 pages, 20 figures, submitted to Phys. Rev.
Gravitational-Wave Asteroseismology with Fundamental Modes from Compact Binary Inspirals
The first detection of gravitational waves (GWs) from the binary neutron star
(NS) inspiral GW170817 has opened a unique channel for probing the fundamental
properties of matter at supra-nuclear densities inaccessible elsewhere in the
Universe. This observation yielded the first constraints on the equation of
state (EoS) of NS matter from the GW imprint of tidal interactions. Tidal
signatures in the GW arise from the response of a matter object to the
spacetime curvature sourced by its binary companion. They crucially depend on
the EoS and are predominantly characterised by the tidal deformability
parameters , where denotes the quadrupole and
octupole respectively. As the binary evolves towards merger, additional
dynamical tidal effects become important when the orbital frequency approaches
a resonance with the stars' internal oscillation modes. Among these modes, the
fundamental (-)modes have the strongest tidal coupling and can give
rise to a cumulative imprint in the GW signal even if the resonance is not
fully excited. Here we present the first direct constraints on fundamental
oscillation mode frequencies for GW170817 using an inspiral GW phase model with
an explicit dependence on the -mode frequency and without assuming any
relation between and . We rule out anomalously small
values of and, for the larger companion, determine a lower bound on
the -mode (-mode) frequency of kHz ( kHz) at
the 90\% credible interval (CI). We then show that networks of future GW
detectors will be able to measure -mode frequencies to within tens of Hz
from the inspiral alone. Such precision astroseismology will enable novel tests
of fundamental physics and the nature of compact binaries.Comment: 8 pages, 5 figure
A Multipolar Effective One Body Model for Non-Spinning Black Hole Binaries
We introduce \TEOBiResumSM{}, a nonspinning inspiral-merger-ringdown waveform
model built within the effective one body (EOB) framework that includes
gravitational waveform modes beyond the dominant quadrupole . The model incorporates: (i) an improved Pad\'e resummation of the
factorized waveform amplitudes entering the
EOB-resummed waveform where the 3PN, mass-ratio dependent, terms are hybridized
with test-mass limit terms up to 6PN relative order for most of the multipoles
up to included; (ii) an improved determination of the effective 5PN
function entering the EOB interaction potential done using the
most recent, error-controlled, nonspinning numerical relativity (NR) waveforms
from the Simulating eXtreme Spacetimes (SXS) collaboration; and (iii) a
NR-informed phenomenological description of the multipolar ringdown. Such
representation stems from 19 NR waveforms with mass ratios up to
as well as test-mass waveform data, although it does not incorporate
mode-mixing effects. The NR-completed higher modes through merger and ringdown
considered here are: . For simplicity, the other subdominant modes,
up to , are approximated by the corresponding, purely analytical,
factorized and resummed EOB waveform. To attempt an estimate of (some of) the
underlying analytic uncertainties of the model, we also contrast the effect of
the 6PN-hybrid Pad\'e-resummed 's with the standard PN,
Taylor-expanded, ones used in previous EOB works. The maximum unfaithfulness
against the SXS waveforms including all NR-completed modes up to
is always for binaries with total mass as .Comment: 24 pages, 18 figures. Improved figures and presentation. Submitted to
Phys. Rev.
Validity of common modelling approximations for precessing binary black holes with higher-order modes
The current paradigm for constructing waveforms from precessing compact
binaries is to first construct a waveform in a non-inertial, co-precessing
binary source frame followed by a time-dependent rotation to map back to the
physical, inertial frame. A key insight in the construction of these models is
that the co-precessing waveform can be effectively mapped to some equivalent
aligned spin waveform. Secondly, the time-dependent rotation implicitly
introduces -mode mixing, necessitating an accurate description of
higher-order modes in the co-precessing frame. We assess the efficacy of this
modelling strategy in the strong field regime using Numerical Relativity
simulations. We find that this framework allows for the highly accurate
construction of modes in our data set, while for higher order
modes, especially the and modes, we find rather
large mismatches. We also investigate a variant of the approximate map between
co-precessing and aligned spin waveforms, where we only identify the slowly
varying part of the time domain co-precessing waveforms with the aligned-spin
one, but find no significant improvement. Our results indicate that the simple
paradigm to construct precessing waveforms does not provide an accurate
description of higher order modes in the strong-field regime, and demonstrate
the necessity for modelling mode asymmetries and mode-mixing to significantly
improve the description of precessing higher order modes.Comment: Improved version: correcting typos, adding acknowledgement and more
reference
Collective Employee Representation and the Impact of Law: Initial Response to the Employment Relations Act 1999.
Using data gathered primarily during interviews with managers and trade union officials, this article examines how trade unions and employers have reacted to the introduction of the statutory procedure for union recognition in the Employment Relations Act 1999 (ERA). Findings indicate that the ERA and the drift of EU influence have had a substantial effect in shifting the balance of employer attitudes towards greater approval of trade unions and have accelerated the rate at which employers are redesigning their relationships with unions. Although employers are tending to restrict unions' influence over traditional issues such as pay-setting, they are increasingly seeking their assistance in implementing difficult organisational changes. The article explores the impact of such changes on trade union activity and collective representation more broadly.Collective bargaining, employee representation, trade union recognition labour legislation
Assessing gravitational-wave binary black hole candidates with Bayesian odds
Gravitational waves from the coalescence of binary black holes can be
distinguished from noise transients in a detector network through Bayesian
model selection by exploiting the coherence of the signal across the network.
We present a Bayesian framework for calculating the posterior probability that
a signal is of astrophysical origin, agnostic to the specific search strategy,
pipeline or search domain with which a candidate is identified. We apply this
framework under \textit{identical} assumptions to all events reported in the
LIGO-Virgo GWTC-1 catalog, GW190412 and numerous event candidates reported by
independent search pipelines by other authors. With the exception of GW170818,
we find that all GWTC-1 candidates, and GW190412, have odds overwhelmingly in
favour of the astrophysical hypothesis, including GW170729, which was assigned
significantly different astrophysical probabilities by the different search
pipelines used in GWTC-1. GW170818 is de-facto a single detector trigger, and
is therefore of no surprise that it is disfavoured as being produced by an
astrophysical source in our framework. We find \textit{three} additional event
candidates, GW170121, GW170425 and GW170727, that have significant support for
the astrophysical hypothesis, with a probability that the signal is of
astrophysical origin of 0.53, 0.74 and 0.64 respectively. We carry out a
hierarchical population study which includes these three events in addition to
those reported in GWTC-1, finding that the main astrophysical results are
unaffected.Comment: 23 pages, 11 figures, comments and feedback welcome
Reciprocal Learning: An Intergenerational Computer Training Model for Young Adults Working with Elders Follow-Up Evaluation: Summer 2006 - Report Series # 15
The goal of this evaluation, conducted in the summer of 2006, was to capture the experiences of young adults who participated as âsenior tech tutorsâ for elders in the computer training program. The training was piloted in the Internet CafĂ© at the Sheridan Elder Research Centre (SERC) in the fall of 2005. Twelve young adults participated in the training to become âsenior tech tutors. An additional three participated in tutoring without having attended the training but were provided with instructional hand-outs. These three tech tutors had prior education and experience in the field of gerontology. Feedback interviews were conducted over the telephone. These interviews took place over an eight-week period. The relationships that tech tutors formed with their âstudentâ elders had an impact on tech tutorsâ goals, their views about aging and their career aspirations
Relational Expressions for Data Transformation and Computation
Separate programming models for data transformation (declarative) and
computation (procedural) impact programmer ergonomics, code reusability and
database efficiency. To eliminate the necessity for two models or paradigms, we
propose a small but high-leverage innovation: the introduction of complete
relations into the relational database. Complete relations and the discipline
of constraint programming, which concerns them, are founded on the same algebra
as relational databases. We claim that by synthesising the relational database
of Codd and Date, with the results of the constraint programming community, the
relational model holistically offers programmers a single declarative paradigm
for both data transformation and computation, reusable code with computations
that are indifferent to what is input and what is output, and efficient
applications with the query engine optimising and parallelising all levels of
data transformation and computation.Comment: 12 pages, 4 tables. To be published in the proceedings of the
Shepherding Track of the 2023 Australasian Database Conference Melbourne (Nov
1-3
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