609 research outputs found
Variations in hospital standardised mortality ratios (HSMR) as a result of frequent readmissions
BACKGROUND: We investigated the impact that variations in the frequency of readmissions had upon a hospital's standardised mortality ratio (HSMR). An adapted HSMR model was used in the study. Our calculations were based on the admissions of 70 hospitals in The Netherlands during the years 2005 to 2009. METHODS: Through a retrospective analysis of routinely collected hospital data, we calculated standardised in-hospital mortality ratios both by hospital and by diagnostic group (H/SMRs) using two different models. The first was the Dutch 2010 model while the second was the same model but with an additional adjustment for the readmission frequency. We compared H/SMR outcomes and the corresponding quality metrics in order to test discrimination (c-statistics), calibration (Hosmer-Lemeshow) and explanatory power (pseudo-R2 statistic) for both models. RESULTS: The SMR outcomes for model 2 compared to model 1, varied between -39% and +110%. On the HSMR level these variations ranged from -12% to +11%. There was a substantial disagreement between the models with respect to significant death on the SMR level as well as the HSMR level (~ 20%). All quality metrics comparing both models were in favour of model 2. The susceptibility to adjustment for readmission increased for longer review periods. CONCLUSIONS: The 2010 HSMR model for the Netherlands was sensitive to adjustment for the frequency of readmissions. A model without this adjustment, as opposed to a model with the adjustment, produced substantially different HSMR outcomes. The uncertainty introduced by these differences exceeded the uncertainty indicated by the 95% confidence intervals. Therefore an adjustment for the frequency of readmissions should be considered in The Netherlands, since such a model showed more favourable quality metric characteristics compared to a model without such an adjustment. Other countries could well benefit from a similar adjustment to their models. A review period of the data collected over the last three years, at least, is advisable. (aut.ref.
An Over-Massive Black Hole in the Compact Lenticular Galaxy NGC1277
All massive galaxies likely have supermassive black holes at their centers,
and the masses of the black holes are known to correlate with properties of the
host galaxy bulge component. Several explanations have been proposed for the
existence of these locally-established empirical relationships; they include
the non-causal, statistical process of galaxy-galaxy merging, direct feedback
between the black hole and its host galaxy, or galaxy-galaxy merging and the
subsequent violent relaxation and dissipation. The empirical scaling relations
are thus important for distinguishing between various theoretical models of
galaxy evolution, and they further form the basis for all black hole mass
measurements at large distances. In particular, observations have shown that
the mass of the black hole is typically 0.1% of the stellar bulge mass of the
galaxy. The small galaxy NGC4486B currently has the largest published fraction
of its mass in a black hole at 11%. Here we report observations of the stellar
kinematics of NGC 1277, which is a compact, disky galaxy with a mass of 1.2 x
10^11 Msun. From the data, we determine that the mass of the central black hole
is 1.7 x 10^10 Msun, or 59% its bulge mass. Five other compact galaxies have
properties similar to NGC 1277 and therefore may also contain over-sized black
holes. It is not yet known if these galaxies represent a tail of a
distribution, or if disk-dominated galaxies fail to follow the normal black
hole mass scaling relations.Comment: 7 pages. 6 figures. Nature. Animation at
http://www.mpia.de/~bosch/blackholes.htm
Galaxy Clustering & Galaxy-Galaxy Lensing: A Promising Union to Constrain Cosmological Parameters
Galaxy clustering and galaxy-galaxy lensing probe the connection between
galaxies and their dark matter haloes in complementary ways. On one hand, the
halo occupation statistics inferred from the observed clustering properties of
galaxies are degenerate with the adopted cosmology. Consequently, different
cosmologies imply different mass-to-light ratios for dark matter haloes. On the
other hand, galaxy-galaxy lensing yields direct constraints on the actual
mass-to-light ratios and it can be used to break this degeneracy, and thus to
constrain cosmological parameters. In this paper we establish the link between
galaxy luminosity and dark matter halo mass using the conditional luminosity
function (CLF). We constrain the CLF parameters using the galaxy luminosity
function and the luminosity dependence of the correlation lengths of galaxies.
The resulting CLF models are used to predict the galaxy-galaxy lensing signal.
For a cosmology with , the model
accurately fits the galaxy-galaxy lensing data obtained from the SDSS. For a
comparison cosmology with , however, we
can accurately fit the luminosity function and clustering properties of the
galaxy population, but the model predicts mass-to-light ratios that are too
high, resulting in a strong overprediction of the galaxy-galaxy lensing signal.
We conclude that the combination of galaxy clustering and galaxy-galaxy lensing
is a powerful probe of the galaxy-dark matter connection, with the potential to
yield tight constraints on cosmological parameters. Since this method mainly
probes the mass distribution on non-linear scales, it is complementary to
constraints obtained from the galaxy power-spectrum, which mainly probes the
large-scale (linear) matter distribution.Comment: 20 pages, 11 figures, submitted to MNRA
Cosmological Constraints from a Combination of Galaxy Clustering and Lensing -- III. Application to SDSS Data
We simultaneously constrain cosmology and galaxy bias using measurements of
galaxy abundances, galaxy clustering and galaxy-galaxy lensing taken from the
Sloan Digital Sky Survey. We use the conditional luminosity function (which
describes the halo occupation statistics as function of galaxy luminosity)
combined with the halo model (which describes the non-linear matter field in
terms of its halo building blocks) to describe the galaxy-dark matter
connection. We explicitly account for residual redshift space distortions in
the projected galaxy-galaxy correlation functions, and marginalize over
uncertainties in the scale dependence of the halo bias and the detailed
structure of dark matter haloes. Under the assumption of a spatially flat,
vanilla {\Lambda}CDM cosmology, we focus on constraining the matter density,
{\Omega}m, and the normalization of the matter power spectrum, {\sigma}8, and
we adopt WMAP7 priors for the spectral index, the Hubble parameter, and the
baryon density. We obtain that \Omegam = 0.278_{-0.026}^{+0.023} and {\sigma}8
= 0.763_{-0.049}^{+0.064} (95% CL). These results are robust to uncertainties
in the radial number density distribution of satellite galaxies, while allowing
for non-Poisson satellite occupation distributions results in a slightly lower
value for {\sigma}8 (0.744_{-0.047}^{+0.056}). These constraints are in
excellent agreement (at the 1{\sigma} level) with the cosmic microwave
background constraints from WMAP. This demonstrates that the use of a realistic
and accurate model for galaxy bias, down to the smallest non-linear scales
currently observed in galaxy surveys, leads to results perfectly consistent
with the vanilla {\Lambda}CDM cosmology.Comment: 21 pages, 9 figures, 5 tables, submitted to MNRA
Cosmological Constraints from a Combination of Galaxy Clustering and Lensing -- I. Theoretical Framework
We present a new method that simultaneously solves for cosmology and galaxy
bias on non-linear scales. The method uses the halo model to analytically
describe the (non-linear) matter distribution, and the conditional luminosity
function (CLF) to specify the halo occupation statistics. For a given choice of
cosmological parameters, this model can be used to predict the galaxy
luminosity function, as well as the two-point correlation functions of
galaxies, and the galaxy-galaxy lensing signal, both as function of scale and
luminosity. In this paper, the first in a series, we present the detailed,
analytical model, which we test against mock galaxy redshift surveys
constructed from high-resolution numerical -body simulations. We demonstrate
that our model, which includes scale-dependence of the halo bias and a proper
treatment of halo exclusion, reproduces the 3-dimensional galaxy-galaxy
correlation and the galaxy-matter cross-correlation (which can be projected to
predict the observables) with an accuracy better than 10 (in most cases 5)
percent. Ignoring either of these effects, as is often done, results in
systematic errors that easily exceed 40 percent on scales of \sim 1
h^{-1}\Mpc, where the data is typically most accurate. Finally, since the
projected correlation functions of galaxies are never obtained by integrating
the redshift space correlation function along the line-of-sight out to
infinity, simply because the data only cover a finite volume, they are still
affected by residual redshift space distortions (RRSDs). Ignoring these, as
done in numerous studies in the past, results in systematic errors that easily
exceed 20 perent on large scales (r_\rmp \gta 10 h^{-1}\Mpc). We show that it
is fairly straightforward to correct for these RRSDs, to an accuracy better
than percent, using a mildly modified version of the linear Kaiser
formalism
The Merger Rates and Mass Assembly Histories of Dark Matter Haloes in the Two Millennium Simulations
We construct merger trees of dark matter haloes and quantify their merger
rates and mass growth rates using the joint dataset from the Millennium and
Millennium-II simulations. The finer resolution of the Millennium-II Simulation
has allowed us to extend our earlier analysis of halo merger statistics to an
unprecedentedly wide range of descendant halo mass (10^10 < M0 < 10^15 Msun),
progenitor mass ratio (10^-5 < xi < 1), and redshift (0 < z < 15). We update
our earlier fitting form for the mean merger rate per halo as a function of
M_0, xi, and z. The overall behavior of this quantity is unchanged: the rate
per unit redshift is nearly independent of z out to z~15; the dependence on
halo mass is weak (M0^0.13); and it is nearly a power law in the progenitor
mass ratio (xi^-2). We also present a simple and accurate fitting formula for
the mean mass growth rate of haloes as a function of mass and redshift. This
mean rate is 46 Msun/yr for 10^12 Msun haloes at z=0, and it increases with
mass as M^{1.1} and with redshift as (1+z)^2.5 (for z > 1). When the fit for
the mean mass growth rate is integrated over a halo's history, we find
excellent match to the mean mass assembly histories of the simulated haloes. By
combining merger rates and mass assembly histories, we present results for the
number of mergers over a halo's history and the statistics of the redshift of
the last major merger.Comment: 12 pages, 9 figures, accepted in MNRA
The Evolution of the Dark Halo Spin Parameters lambda and lambda' in a LCDM Universe: The Role of Minor and Major Mergers
The evolution of the spin parameter of dark halos and the dependence on the
halo merging history in a set of dissipationless cosmological LCDM simulations
is investigated. Special focus is placed on the differences of the two commonly
used versions of the spin parameter, namely lambda=J*E^1/2/(G*M^5/2) (Peebles
80) and lambda'=J/(sqrt(2)*M_vir*R_vir*V_vir) (Bullock et al. 01). Though the
distribution of the spin transfer rate defined as the ratio of the spin
parameters after and prior to a merger is similar to a high degree for both,
lambda and lambda', we find considerable differences in the time evolution:
while lambda' is roughly independent of redshift, lambda turns out to increase
significantly with decreasing redshift. This distinct behaviour arises from
small differences in the spin transfer during accretion events. The evolution
of the spin parameter is strongly coupled with the virial ratio
eta:=2*E_kin/|E_pot| of dark halos. Major mergers disturb halos and increase
both their virial ratio and spin parameter for 1-2 Gyrs. At high redshifts
(z=2-3) many halos are disturbed with an average virial ratio of eta = 1.3
which approaches unity until z=0. We find that the redshift evolution of the
spin parameters is dominated by the huge number of minor mergers rather than
the rare major merger events.Comment: 10 pages, 11 figures, submitted to MNRA
Subjective cognitive decline and self-reported sleep problems: The SCIENCe project
We aim to investigate the frequency and type of sleep problems in memory clinic patients with subjective cognitive decline (SCD) and their association with cognition, mental health, brain magnetic resonance imaging (MRI), and cerebrospinal fluid (CSF) biomarkers. Three hundred eight subjects (65 ± 8 years, 44% female) were selected from the Subjective Cognitive Impairment Cohort (SCIENCe) project. All subjects answered two sleep questionnaires, Berlin Questionnaire (sleep apnea) and Pittsburgh Sleep Quality Index (sleep quality) and underwent a standardized memory clinic work-up. One hundred ninety-eight (64%) subjects reported sleep problems, based on 107 (35%) positive screenings on sleep apnea and 162 (53%) on poor sleep quality. Subjects with sleep problems reported more severe depressive symptoms, more anxiety, and more severe SCD. Cognitive tests, MRI, and CSF biomarkers did not differ between groups. Our results suggest that improvement of sleep quality and behaviors are potential leads for treatment in many subjects with SCD to relieve the experienced cognitive complaints
Detection of IMBHs from microlensing in globular clusters
Globular clusters have been alternatively predicted to host intermediate-mass
black holes (IMBHs) or nearly impossible to form and retain them in their
centres. Over the last decade enough theoretical and observational evidence
have accumulated to believe that many galactic globular clusters may host IMBHs
in their centres, just like galaxies do. The well-established correlations
between the supermassive black holes and their host galaxies do suggest that,
in extrapolation, globular clusters (GCs) follow the same relations. Most of
the attempts in search of the central black holes (BHs) are not direct and
present enormous observational difficulties due to the crowding of stars in the
GC cores. Here we propose a new method of detection of the central BH -- the
microlensing of the cluster stars by the central BH. If the core of the cluster
is resolved, the direct determination of the lensing curve and lensing system
parameters are possible; if unresolved, the differential imaging technique can
be applied. We calculate the optical depth to central BH microlensing for a
selected list of Galactic GCs and estimate the average time duration of the
events. We present the observational strategy and discuss the detectability of
microlensing events using a 2-m class telescope.Comment: 10 pages, 11 figures, accepted in New Astronom
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