1,806 research outputs found
Designing a Green Roof for Ireland
A model is presented for the gravity-driven flow of rainwater descending through the soil layer of a green roof, treated as a porous medium on a at permeable surface representing an efficient drainage layer. A fully saturated zone is shown to occur. It is typically a thin layer, relative to the total soil thickness, and lies at the bottom of the soil layer. This provides a bottom boundary condition for the partially saturated upper zone. It is shown that after the onset of rainfall, well-defined fronts of water can descend through the soil layer. Also the rainwater flow is relatively quick compared with the moisture uptake by the roots of the plants in the roof. In a separate model the exchanges of water are described between the (smaller-scale) porous granules of soil, the roots and the rainwater in the inter-granule pores
The cluster abundance in cosmic string models for structure formation
We use the present observed number density of large X-ray clusters to
constrain the amplitude of matter density perturbations induced by cosmic
strings on the scale of Mpc (), in both open cosmologies
and flat models with a non-zero cosmological constant. We find a slightly lower
value of than that obtained in the context of primordial Gaussian
fluctuations generated during inflation. This lower normalization of
results from the mild non-Gaussianity on cluster scales, where the one point
probability distribution function is well approximated by a
distribution. We use our estimate of to constrain the string linear
energy density and show that it is consistent with the COBE
normalization.Comment: 5 pages, 2 figure
Social franchising primary healthcare clinics â a model for South African National Health Insurance?
This article describes the first government social franchise initiative in the world to deliver a âbrandâ of quality primary healthcare (PHC) clinic services. Quality and standards of care are not uniformly and reliably delivered across government PHC clinics in North West Province, South Africa, despite government support, numerous policies, guidelines and in-service training sessions provided to staff. Currently the strongest predictor of good-quality service is the skill and dedication of the facility manager. A project utilising the social franchising business model, harvesting best practices, has been implemented with the aim of developing a system to ensure reliably excellent healthcare service provision in every facility in North West. The services of social franchising consultants have been procured to develop the business model to drive this initiative. Best practices have been benchmarked, and policies, guidelines and clinic support systems have been reviewed, evaluated and assessed, and incorporated into the business plan. A pilot clinic has been selected to refine and develop a working social franchise model. This will then be replicated in one clinic to confirm proof of concept before further scale-up. The social franchise business model can provide solutions to a reliable and recognisable âbrandâ of quality universal coverage of healthcare services.
ISOPHOT 95 micron observations in the Lockman Hole - The catalogue and an assessment of the source counts
We report results from a new analysis of a deep 95 micron imaging survey with
ISOPHOT on board the Infrared Space Observatory, over a ~1 square degree area
within the Lockman Hole, which extends the statistics of our previous study
(Rodighiero et al. 2003). Within the survey area we detect sixty-four sources
with S/N>3 (roughly corresponding to a flux limit of 16 mJy). Extensive
simulations indicate that the sample is almost complete at fluxes > 100 mJy,
while the incompleteness can be quantified down to ~30 mJy. The 95 micron
galaxy counts reveal a steep slope below 100 mJy (alpha~1.6), in excess of that
expected for a non-evolving source population. In agreement with counts data
from ISO at 15 and 175 micron, this favours a model where the IR populations
evolve both in number and luminosity densities. We finally comment on some
differences found with other ISO results in this area.Comment: 4 pages, accepted by Astronomy and Astrophysics Lette
Association of Self-reported High-Risk Allergy History With Allergy Symptoms After COVID-19 Vaccination
Allergic history in individuals with confirmed anaphylaxis to a messenger RNA (mRNA) COVID-19 vaccine is common. However, the risk factors for allergy symptoms after receiving the vaccine are unknown
Evolution of the Mass Function of Dark Matter Haloes
We use a high resolution CDM numerical simulation to calculate the
mass function of dark matter haloes down to the scale of dwarf galaxies, back
to a redshift of fifteen, in a 50 Mpc volume containing 80 million
particles. Our low redshift results allow us to probe low density
fluctuations significantly beyond the range of previous cosmological
simulations. The Sheth and Tormen mass function provides an excellent match to
all of our data except for redshifts of ten and higher, where it overpredicts
halo numbers increasingly with redshift, reaching roughly 50 percent for the
10^{10}-10^{11} \msun haloes sampled at redshift 15. Our results confirm
previous findings that the simulated halo mass function can be described solely
by the variance of the mass distribution, and thus has no explicit redshift
dependence. We provide an empirical fit to our data that corrects for the
overprediction of extremely rare objects by the Sheth and Tormen mass function.
This overprediction has implications for studies that use the number densities
of similarly rare objects as cosmological probes. For example, the number
density of high redshift (z 6) QSOs, which are thought to be hosted by
haloes at 5 peaks in the fluctuation field, are likely to be
overpredicted by at least a factor of 50%. We test the sensitivity of our
results to force accuracy, starting redshift, and halo finding algorithm.Comment: v2: 9 pages, 11 figures, accepted by MNRAS with revisions. Includes
additional numerical tests and error discussion, clarifications, and referee
suggestion
Quasar Feedback: the Missing Link in Structure Formation
We consider the impact of quasar outflows on structure formation. Such
outflows are potentially more important than galactic winds, which appear
insufficient to produce the level of preheating inferred from X-ray
observations of galaxy clusters. Using a simple analytical model for the
distribution of quasars with redshift, coupled with a one-dimensional
Sedov-Taylor model for outflows, we are able to make robust statements about
their impact of on structure formation. As large regions of the IGM are heated
above a critical entropy of approximately 100 keV cm^2, cooling become
impossible within them, regardless of changes in density. On quasar scales,
this has the effect of inhibiting further formation, resulting in the observed
fall-off in their number densities below z = 2. On galaxy scales, quasar
feedback fixes the turn-over scale in the galaxy luminosity function (L_*) as
the nonlinear scale at the redshift of strong feedback. The galaxy luminosity
function then remains largely fixed after this epoch, consistent with recent
observations and in contrast to the strong evolution predicted in more standard
galaxy-formation models. Finally, strong quasar feedback explains why the
intracluster medium is observed to have been pre-heated to entropy levels just
above S_crit, the minimum excess that would not have been erased by cooling.
The presence of such outflows is completely consistent with the observed
properties of the Lyman-alpha forest at z ~ 2, but is expected to have a
substantial and detectable impact on Compton distortions observed in the
microwave background and the multiphase properties of the "warm-hot" (z=0)
circumgalactic medium.Comment: 20 pages, 11 figures, ApJ, accepted (minor changes made, two plots
updated
Extending PLE models into the mid-IR, far-IR & sub-mm
Simple pure luminosity evolution (PLE) models, in which galaxies brighten at
high redshift due to increased star-formation rates (SFRs), are known to
provide a good fit to the colours and number counts of galaxies throughout the
optical and near-infrared. We show that optically defined PLE models, where
dust reradiates absorbed optical light into infrared spectra composed of local
galaxy templates, fit galaxy counts and colours out to 8um and to at least
z=2.5. At 24-70um, the model is able to reproduce the observed source counts
with reasonable success if 16% of spiral galaxies show an excess in mid-IR flux
due to a warmer dust component and a higher SFR, in line with observations of
local starburst galaxies. There remains an under-prediction of the number of
faint-flux, high-z sources at 24um, so we explore how the evolution may be
altered to correct this. At 160um and longer wavelengths, the model fails, with
our model of normal galaxies accounting for only a few percent of sources in
these bands. However, we show that a PLE model of obscured AGN, which we have
previously shown to give a good fit to observations at 850um, also provides a
reasonable fit to the Herschel/BLAST number counts and redshift distributions
at 250-500um. In the context of a LCDM cosmology, an AGN contribution at
250-870um would remove the need to invoke a top-heavy IMF for high-redshift
starburst galaxies, although the excellent fit of the galaxy PLE model at
shorter wavelengths would still need to be explained.Comment: 14 pages, 11 figures; submitted to MNRA
The Mass Function of an X-Ray Flux-Limited Sample of Galaxy Clusters
A new X-ray selected and X-ray flux-limited galaxy cluster sample is
presented. Based on the ROSAT All-Sky Survey the 63 brightest clusters with
galactic latitude |bII| >= 20 deg and flux fx(0.1-2.4 keV) >= 2 * 10^{-11}
ergs/s/cm^2 have been compiled. Gravitational masses have been determined
utilizing intracluster gas density profiles, derived mainly from ROSAT PSPC
pointed observations, and gas temperatures, as published mainly from ASCA
observations, assuming hydrostatic equilibrium. This sample and an extended
sample of 106 galaxy clusters is used to establish the X-ray
luminosity--gravitational mass relation. From the complete sample the galaxy
cluster mass function is determined and used to constrain the mean cosmic
matter density and the amplitude of mass fluctuations. Comparison to
Press--Schechter type model mass functions in the framework of Cold Dark Matter
cosmological models and a Harrison--Zeldovich initial density fluctuation
spectrum yields the constraints OmegaM = 0.12^{+0.06}_{-0.04} and sigma8 =
0.96^{+0.15}_{-0.12} (90% c.l.). Various possible systematic uncertainties are
quantified. Adding all identified systematic uncertainties to the statistical
uncertainty in a worst case fashion results in an upper limit OmegaM < 0.31.
For comparison to previous results a relation sigma8 = 0.43 OmegaM^{-0.38} is
derived. The mass function is integrated to show that the contribution of mass
bound within virialized cluster regions to the total matter density is small,
i.e., OmegaCluster = 0.012^{+0.003}_{-0.004} for cluster masses larger than
6.4^{+0.7}_{-0.6} * 10^{13} h_{50}^{-1} Msun.Comment: 35 pages; accepted for publication in The Astrophysical Journal; this
and related papers, supplementary information, as well as electronic files of
the tables given in this paper are available at
http://www.astro.virginia.edu/~thr4f
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