369 research outputs found
Positioning Childrenâs Voice in Clinical Trials Research: A New Model for Planning, Collaboration, and Reflection
Following the United Nations Convention on the Rights of the Child, there has been considerable growth in research with children about health and services that affect them. Creative methods to engage with children have also been developed. One area where progress has been slower is the inclusion of childrenâs perspectives in qualitative research in the context of clinical trials or feasibility studies. Addressing this gap, this article discusses experiences of, and reflections on, the process of researching childrenâs views as part of a clinical feasibility study. The article considers what worked well and highlights remaining dilemmas. A new continuum of childrenâs engagement in research is presented, designed to assist researchers to make explicit the contingent demands on their research, and to suggest a range of techniques from within the broader fields of health, childhood studies, and education research that could be used to forward qualitative research in clinical contexts
The Paired-Paddock Model as an Agent for Change on Grazing Properties Across Southeast Australia
From the mid 1970s to the mid 1990s the low productivity of wool and beef producing farms in the high rainfall zone (\u3e550 mm annual rainfall) in south east Australia has been a major contributing factor to the difficulties faced by farmers in this region. This was despite research from the Long-term Phosphate Experiment at Hamilton in south west Victoria indicating that there is considerable potential to increase the productivity and profitability of wool production (Saul, 1994). By implementing the productive pasture technology (PPT) that involves increased rates of fertiliser on pastures containing productive species and increased stocking rates to utilise the extra pasture grown (Trompf & Sale, 2000), gains in excess of $A200/ha on a gross margin basis can be regularly achieved. However wool and beef producers were reluctant to adopt the technology. In 1993 the Grassland\u27s Productivity Program (GPP) was initiated to assist producers to develop skills and gain confidence in their ability to manage more productive pastures on their farms. In brief, groups of 4-6 farmers were assisted by an experienced facilitator to compare current management practice in one paddock with PPT in an adjacent paddock. Over 500 wool and beef producers in south east Australia have been exposed to the paired-paddock model, firstly in the GPP from 1993 to 1997 and more recently in the Triple P Program. This paper reports on the effectiveness of the paired-paddock model in assisting pastoral producers to adopt PPT
Farmer Adoption; Ten Years of Productive Pasture Systems in Southern Australia
n Southern Australian sheep and beef farmers have been slow to adopt technology related to grazing management and pasture utilisation despite clear evidence of a strong link between utilisation (stock per ha) and profitability. Between 1971-95, the average stocking rate on farms was 10-12 dry sheep equivalent per hectare (dse/ha) (Anon 2004). Results from the Hamilton Long-term Phosphate Experiment (Cayley et al., 2002) show higher pasture production, herbage digestibility, stocking rates and profitability as phosphorus fertiliser applications increase. In 1993, the Grassland Productivity Program (GPP) started in the winter rainfall areas of southern Australia (Trompf & Sale 2000), initiated by the Grassland Society of Southern Australia, funded by the wool industry. In brief, groups of 4-6 farmers were assisted by experienced advisors to compare current management practice in one paddock with productive pasture technology (PPT) in an adjacent paddock. PPT consisted of appropriate fertiliser application; pasture manipulation to balance grass and legume content and higher stocking rates to ensure utilisation of the herbage grown. Over 300 farmers participated in GPP between 1993-2003. This paper reports the impact on the grazing industry 10 years after PPT was introduced
Periastron Advance in Spinning Black Hole Binaries: Gravitational Self-Force from Numerical Relativity
We study the general relativistic periastron advance in spinning black hole
binaries on quasi-circular orbits, with spins aligned or anti-aligned with the
orbital angular momentum, using numerical-relativity simulations, the
post-Newtonian approximation, and black hole perturbation theory. By imposing a
symmetry by exchange of the bodies' labels, we devise an improved version of
the perturbative result, and use it as the leading term of a new type of
expansion in powers of the symmetric mass ratio. This allows us to measure, for
the first time, the gravitational self-force effect on the periastron advance
of a non-spinning particle orbiting a Kerr black hole of mass M and spin S =
-0.5 M^2, down to separations of order 9M. Comparing the predictions of our
improved perturbative expansion with the exact results from numerical
simulations of equal-mass and equal-spin binaries, we find a remarkable
agreement over a wide range of spins and orbital separations.Comment: 18 pages, 12 figures; matches version to appear in Phys. Rev.
Are different approaches to constructing initial data for binary black hole simulations of the same astrophysical situation equivalent?
Initial data for numerical evolutions of binary-black holes have been dominated by âconformally flatâ (CF) data (i.e., initial data where the conformal background metric is chosen to be flat) because they are easy to construct. However, CF initial data cannot simulate nearly extremal spins, while more complicated âconformally curvedâ initial data (i.e., initial data in which the background metric is not explicitly chosen to be flat), such as initial data where the spatial metric is chosen to be proportional to a weighted superposition of two Kerr-Schild black holes can. Here we establish the consistency between the astrophysical results of these two initial data schemes for nonspinning binary systems. We evolve the inspiral, merger, and ringdown of two equal-mass, nonspinning black holes using superposed Kerr-Schild initial data and compare with an analogous simulation using CF initial data. We find that the resultant gravitational-waveform phases agree to within ÎŽÏâČ10^(-2) radians and the amplitudes agree to within ÎŽA/AâČ5Ă10^(-3), which are within the numerical errors of the simulations. Furthermore, we find that the final mass and spin of the remnant black hole agree to one part in 10^5
Modeling the source of GW150914 with targeted numerical-relativity simulations
In fall of 2015, the two LIGO detectors measured the gravitational wave
signal GW150914, which originated from a pair of merging black holes. In the
final 0.2 seconds (about 8 gravitational-wave cycles) before the amplitude
reached its maximum, the observed signal swept up in amplitude and frequency,
from 35 Hz to 150 Hz. The theoretical gravitational-wave signal for merging
black holes, as predicted by general relativity, can be computed only by full
numerical relativity, because analytic approximations fail near the time of
merger. Moreover, the nearly-equal masses, moderate spins, and small number of
orbits of GW150914 are especially straightforward and efficient to simulate
with modern numerical-relativity codes. In this paper, we report the modeling
of GW150914 with numerical-relativity simulations, using black-hole masses and
spins consistent with those inferred from LIGO's measurement. In particular, we
employ two independent numerical-relativity codes that use completely different
analytical and numerical methods to model the same merging black holes and to
compute the emitted gravitational waveform; we find excellent agreement between
the waveforms produced by the two independent codes. These results demonstrate
the validity, impact, and potential of current and future studies using
rapid-response, targeted numerical-relativity simulations for better
understanding gravitational-wave observations.Comment: 11 pages, 3 figures, submitted to Classical and Quantum Gravit
SubmilliJansky Transients in Archival Radio Observations
[ABRIDGED] We report the results of a 944-epoch survey for transient sources
with archival data from the Very Large Array spanning 22 years with a typical
epoch separation of 7 days. Observations were obtained at 5 or 8.4 GHz for a
single field of view with a full-width at half-maximum of 8.6' and 5.1',
respectively, and achieved a typical point-source detection threshold at the
beam center of ~300 microJy per epoch. Ten transient sources were detected with
a significance threshold such that only one false positive would be expected.
Of these transients, eight were detected in only a single epoch. Two transients
were too faint to be detected in individual epochs but were detected in
two-month averages. None of the ten transients was detected in longer-term
averages or associated with persistent emission in the deep image produced from
the combination of all epochs. The cumulative rate for the short timescale
radio transients above 370 microJy at 5 and 8.4 GHz is 0.07 < R < 40 deg^-2
yr^-1, where the uncertainty is due to the unknown duration of the transients,
20 min < t_char < 7 days. A two-epoch survey for transients will detect 1.5 +/-
0.4 transient per square degrees above a flux density of 370 microJy. Two
transients are associated with galaxies at z=0.040 and z=0.249. These may be
similar to the peculiar Type Ib/c radio supernova SN 1998bw associated with GRB
980428. Six transients have no counterparts in the optical or infrared (R=27,
Ks=18). The hosts and progenitors of these transients are unknown.Comment: Accepted for ApJ; full quality figures available at
http://astro.berkeley.edu/~gbower/ps/rt.pd
Dynamical excision boundaries in spectral evolutions of binary black hole spacetimes
Simulations of binary black hole systems using the Spectral Einstein Code (SpEC) are done on a computational domain that excises the regions inside the black holes. It is imperative that the excision boundaries are outflow boundaries with respect to the hyperbolic evolution equations used in the simulation. We employ a time-dependent mapping between the fixed computational frame and the inertial frame through which the black holes move. The time-dependent parameters of the mapping are adjusted throughout the simulation by a feedback control system in order to follow the motion of the black holes, to adjust the shape and size of the excision surfaces so that they remain outflow boundaries, and to prevent large distortions of the grid. We describe in detail the mappings and control systems that we use. We show how these techniques have been essential in the evolution of binary black hole systems with extreme configurations, such as large spin magnitudes and high mass ratios, especially during the merger, when apparent horizons are highly distorted and the computational domain becomes compressed. The techniques introduced here may be useful in other applications of partial differential equations that involve time-dependent mappings
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