2,909 research outputs found
Correlation of Low z Lyman-alpha Absorbers with HI-selected Galaxies
In this work, observational evidence for the connection between low column
density Lyman-alpha absorbers and large-scale structure traced by gas-rich
galaxies is investigated. The HI Parkes All Sky Survey (HIPASS) galaxy
catalogue is cross-correlated with known low redshift, low column density
Lyman-alpha absorbers from the literature. The absorber-galaxy
cross-correlation function shows that on scales from 1 to 10 h^-1 Mpc,
absorbers are imbedded in halos with masses similar to that of galaxy groups.
This statistical evidence suggests that galaxy groups could be the dominant
environment of low column density Lyman-alpha absorbers at z=0.Comment: 3 pages, 1 figure, to appear in IAU 199 conf. proc.: "Probing
Galaxies through Quasar Absorption Lines," eds. Williams, Shu, Menar
Cross correlation of Lyman-alpha absorbers with gas-rich galaxies
The HI Parkes All Sky Survey (HIPASS) galaxy catalogue is cross-correlated
with known low redshift, low column density (N_HI <10^15 cm^-2) Lyman-alpha
absorbers from the literature. The redshift-space correlation is found to be
similar in strength to HIPASS galaxy self-clustering (correlation length
s_0,ag=6+/-4 and s_0,gg=3.1+/-0.5 h^-1 Mpc respectively). In real-space the
cross-correlation is stronger than the galaxy auto-correlation (correlation
length r_0,ag=7.2+/-1.4 and r_0,gg=3.5+/-0.7 h^-1 Mpc respectively) on scales
from 1-10 h^-1 Mpc, ruling out the mini-halo model for the confinement
Lyman-alpha absorbers at the 99 percent confidence level. Provided that the
cause of the strong cross-correlation is purely gravitational, the ratio of
correlation lengths suggest that absorbers are embedded in dark matter haloes
with masses log(M/Msun)=14.2 h^-1, similar to those of galaxy groups. The
flattening of the cross-correlation at separations less than ~600 h^-1 kpc
could correspond to the thickness of filaments in which absorbers are embedded.
This work provides indirect statistical evidence for the notion that galaxy
groups and large-scale filaments, particularly those that comprise gas-rich
galaxies, are the dominant environments of low column density Lyman-alpha
absorbers at z=0.Comment: 10 pages, 10 figures, accepted for publication in MNRAS, minor typos
fixed and references update
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Clinical legal education in the United Kingdom: Origins, growth and the technological innovations and challenges of its future
Connectivity, confidentiality and confidence: Key issues in the provision of online pro bono activities
The provision of pro bono activities for law students has become an established feature of the undergraduate legal education landscape in Law Schools in the United Kingdom (“UK”) and beyond, providing the experiential elements of clinical legal education programmes. Pro bono activities conducted online, or utilising and enhanced by technologies in other ways (for example, through the development of a mobile phone application providing legal guidance), are increasingly becoming a part of this offering, reflecting wider shifts within legal practice and society and an increasing recognition of the importance of digital literacy skills. This paper will situate these forms of online and technologically-enhanced pro bono activities both within the wider context of contemporary clinical legal education and also as a part of broader professional and societal shifts. It will explore a variety of innovative approaches being taken internationally, including work done by The Open University’s Open Justice Centre in the UK, before moving on to focus on a number of key challenges and opportunities which may arise through the increasing provision of these new forms of pro bono activities by Law Schools. These include the potential and pitfalls of the technology involved, issues with confidentiality (particularly in the context of online legal advice) and the issue of how to foster trust in the online environment. The paper will conclude with a number of suggestions for areas requiring further research and discussion to enable contemporary clinicians to fully utilise the potential of online and technologically-enhanced pro bono activities
A comparison of the effects of oral vs. intravenous hydration on subclinical acute kidney injury: a protocol of a randomised controlled trial
Background:
Optimal treatment for established renal failure is living donor kidney transplantation. However this pathway exposes healthy individuals to significant reduction in nephron mass via major surgical procedure. Laparoscopic donor nephrectomy is now the most common method for live donor transplantation, reducing both donor post-operative pain and recovery time. However this procedure exposes kidneys to additional haemodynamic stresses. It has been suggested that donor hydration—particularly the use of preoperative intravenous fluids—may counteract these stresses, reducing subclinical acute kidney injury and ultimately improving long-term renal function. This may be important in both preservation of donor renal function and recipient graft longevity.
Methods/Design:
A prospective single-centre single-blinded randomized controlled trial will be carried out to determine the effects of donor preoperative intravenous fluids. The primary outcome is donor subclinical acute kidney injury (defined as plasma NGAL, >153 ng/ml) on day 1 postoperatively. Secondary outcomes include intraoperative haemodynamics, recipient subclinical acute kidney injury, perioperative complications and donor sleep quality.
Donors will be randomised into two groups: the intervention group will receive active pre-hydration consisting of three litres of intravenous Hartmann’s solution between midnight and 8 am before morning kidney donation, while the control group will not receive this. Both groups will receive unlimited oral fluids until midnight, as is routine. Plasma NGAL will be measured at pre-specified perioperative time points, intraoperative haemodynamic data will be collected using non-invasive cardiac output monitoring and clinical notes will be used to obtain demographic and clinical data. The researcher will be blinded to the donor fluid hydration status. Blinded statistical analysis will be performed on an intention-to-treat basis. A prospective power calculation estimates a required sample size of 86 patients.
Discussion:
This study will provide important data, as there is currently little evidence about the use of donor preoperative fluids in laparoscopic nephrectomy. It is hoped that the results obtained will guide future clinical practice
The Column Density Distribution Function at z=0 from HI Selected Galaxies
We have measured the column density distribution function, f(N), at z=0 using
21-cm HI emission from galaxies selected from a blind HI survey. f(N) is found
to be smaller and flatter at z=0 than indicated by high-redshift measurements
of Damped Lyman-alpha (DLA) systems, consistent with the predictions of
hierarchical galaxy formation. The derived DLA number density per unit
redshift, dn/dz =0.058, is in moderate agreement with values calculated from
low-redshift QSO absorption line studies. We use two different methods to
determine the types of galaxies which contribute most to the DLA cross-section:
comparing the power law slope of f(N) to theoretical predictions and analysing
contributions to dn/dz. We find that comparison of the power law slope cannot
rule out spiral discs as the dominant galaxy type responsible for DLA systems.
Analysis of dn/dz however, is much more discriminating. We find that galaxies
with log M_HI < 9.0 make up 34% of dn/dz; Irregular and Magellanic types
contribute 25%; galaxies with surface brightness > 24 mag arcsec^{-2} account
for 22% and sub-L* galaxies contribute 45% to dn/dz. We conclude that a large
range of galaxy types give rise to DLA systems, not just large spiral galaxies
as previously speculated.Comment: 13 pages, low resolution figures in the appendix, MNRAS accepte
Local Column Density Distribution Function from HI selected galaxies
The cross-section of sky occupied by a particular neutral hydrogen column
density provides insight into the nature of Lyman-alpha absorption systems. We
have measured this column density distribution at z=0 using 21-cm HI emission
from a blind survey. A subsample of HI Parkes All Sky Survey (HIPASS) galaxies
have been imaged with the Australia Telescope Compact Array (ATCA). The
contribution of low HI mass galaxies 10^7.5 to 10^8 M_solar is compared to that
of M_star (10^10 to 10^10.5 M_solar) galaxies. We find that the column density
distribution function is dominated by low HI mass galaxies with column
densities in the range 3x10^18 to 2x10^20 cm^-2. This result is not intuitively
obvious. M_star galaxies may contain the bulk of the HI gas, but the
cross-section presented by low HI mass galaxies 10^7.5 to 10^8 M_solar is
greater at moderate column densities. This result implies that moderate column
density Lyman-alpha absorption systems may be caused by a range of galaxy types
and not just large spiral galaxies as originally thought.Comment: 5 pages, including 1 figure. To appear in "Extragalactic Gas at Low
Redshift" (ASP Conf. Series, Weymann Conf.
Evolution of damped Lyman alpha kinematics and the effect of spatial resolution on 21-cm measurements
We have investigated the effect of spatial resolution on determining
pencil-beam like velocity widths and column densities in galaxies. Three 21-cm
datasets are used, the HIPASS galaxy catalogue, a subset of HIPASS galaxies
with ATCA maps and a high-resolution image of the LMC. Velocity widths measured
from 21-cm emission in local galaxies are compared with those measured in
intermediate redshift Damped Lyman alpha (DLA) absorbers. We conclude that
spatial resolution has a severe effect on measuring pencil-beam like velocity
widths in galaxies. Spatial smoothing by a factor of 240 is shown to increase
the median velocity width by a factor of two. Thus any difference between
velocity widths measured from global profiles or low spatial resolution 21-cm
maps at z=0 and DLAs at z>1 cannot unambiguously be attributed to galaxy
evolution. The effect on column density measurements is less severe and the
values of dN/dz from local low-resolution 21-cm measurements are expected to be
overestimated by only ~10 per cent.Comment: 5 pages, 6 figures, accepted for publication in MNRAS letter
Optimization of NANOGrav's Time Allocation for Maximum Sensitivity to Single Sources
Pulsar Timing Arrays (PTAs) are a collection of precisely timed millisecond
pulsars (MSPs) that can search for gravitational waves (GWs) in the nanohertz
frequency range by observing characteristic signatures in the timing residuals.
The sensitivity of a PTA depends on the direction of the propagating
gravitational wave source, the timing accuracy of the pulsars, and the
allocation of the available observing time. The goal of this paper is to
determine the optimal time allocation strategy among the MSPs in the North
American Nanohertz Observatory for Gravitational Waves (NANOGrav) for a single
source of GW under a particular set of assumptions. We consider both an
isotropic distribution of sources across the sky and a specific source in the
Virgo cluster. This work improves on previous efforts by modeling the effect of
intrinsic spin noise for each pulsar. We find that, in general, the array is
optimized by maximizing time spent on the best-timed pulsars, with sensitivity
improvements typically ranging from a factor of 1.5 to 4.Comment: Accepted by Astrophyiscal Journa
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