877 research outputs found
Chemical and physical influences on aerosol activation in liquid clouds: a study based on observations from the Jungfraujoch, Switzerland
A simple statistical model to predict the number of aerosols which activate to form cloud droplets in warm clouds has been established, based on regression analysis of data from four summertime Cloud and Aerosol Characterisation Experiments (CLACE) at the high-altitude site Jungfraujoch (JFJ). It is shown that 79 % of the observed variance in droplet numbers can be represented by a model accounting only for the number of potential cloud condensation nuclei (defined as number of particles larger than 80 nm in diameter), while the mean errors in the model representation may be reduced by the addition of further explanatory variables, such as the mixing ratios of O3, CO, and the height of the measurements above cloud base. The statistical model has a similar ability to represent the observed droplet numbers in each of the individual years, as well as for the two predominant local wind directions at the JFJ (northwest and southeast). Given the central European location of the JFJ, with air masses in summer being representative of the free troposphere with regular boundary layer in-mixing via convection, we expect that this statistical model is generally applicable to warm clouds under conditions where droplet formation is aerosol limited (i.e. at relatively high updraught velocities and/or relatively low aerosol number concentrations). A comparison between the statistical model and an established microphysical parametrization shows good agreement between the two and supports the conclusion that cloud droplet formation at the JFJ is predominantly controlled by the number concentration of aerosol particles
Environmental dependence of X-ray and optical properties of galaxy clusters
Galaxy clusters are widely used to constrain cosmological parameters through their properties, such as masses, luminosity, and temperature distributions. One should take into account all kind of biases that could affect these analyses in order to obtain reliable constraints. In this work, we study the difference in the properties of clusters residing in different large-scale environments, defined by their position within or outside of voids, and the density of their surrounding space. We use both observational and simulation cluster and void catalogues, i.e. XMM Cluster Survey (XCS) and redMaPPer clusters, Baryon Oscillation Spectroscopic Survey (BOSS) voids, and Magneticum simulations. We devise two different environmental proxies for the clusters and study their redshift, richness, mass, X-ray luminosity, and temperature distributions, as well as some properties of their galaxy populations. We use the Kolmogorov–Smirnov two-sample test to discover that richer and more massive clusters are more prevalent in overdense regions and outside of voids. We also find that clusters of matched richness and mass in overdense regions and outside voids tend to have higher X-ray luminosities and temperatures. These differences could have important implications for precision cosmology with clusters of galaxies, since cluster mass calibrations can vary with environment
Observations of mealtimes in hospital aged care rehabilitation wards
Malnutrition is common in long-stay elderly hospitalized patients and their dietary intakes are often poor, despite the provision of adequate quantities of food to meet patient needs. The aim of this study was to identify environmental factors that were associated with achieving adequate food consumption in a hospital context. This study observed the daily routines of 30 elderly patients over 2 days in rehabilitation wards in three Australian hospitals. All activities associated with mealtimes were recorded, from the commencement of breakfast to the conclusion of supper at the end of the day. Four key themes emerged: the eating location; assistance given at meals; negative and positive interruptions. The time taken to eat meals averaged 22 min, ranging from 3 to 55 min. Food intakes appeared to be better when meals were consumed communally in a dining room. There were many occasions when patients needed more assistance to eat than was available. The most common factors negatively affecting meal consumption were medication rounds, inappropriate placement of trays, packaging being hard to open, and patient showering. The presence of visitors, dietitians and nutrition assistants appeared to improve dietary intakes. Trials of protected mealtimes in Australian hospitals are certainly important and timely
Origin of Life
The evolution of life has been a big enigma despite rapid advancements in the
fields of biochemistry, astrobiology, and astrophysics in recent years. The
answer to this puzzle has been as mind-boggling as the riddle relating to
evolution of Universe itself. Despite the fact that panspermia has gained
considerable support as a viable explanation for origin of life on the Earth
and elsewhere in the Universe, the issue remains far from a tangible solution.
This paper examines the various prevailing hypotheses regarding origin of life
like abiogenesis, RNA World, Iron-sulphur World, and panspermia; and concludes
that delivery of life-bearing organic molecules by the comets in the early
epoch of the Earth alone possibly was not responsible for kick-starting the
process of evolution of life on our planet.Comment: 32 pages, 8 figures,invited review article, minor additio
Improved curve fits to summary survival data: application to economic evaluation of health technologies
addresses: Peninsula College of Medicine and Dentistry, Veysey Building, Salmon Pool Lane, Exeter, EX2 4SG, UK. [email protected]: PMCID: PMC3198983types: Journal Article; Research Support, Non-U.S. Gov't© 2011 Hoyle and Henley; licensee BioMed Central Ltd.
This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.Mean costs and quality-adjusted-life-years are central to the cost-effectiveness of health technologies. They are often calculated from time to event curves such as for overall survival and progression-free survival. Ideally, estimates should be obtained from fitting an appropriate parametric model to individual patient data. However, such data are usually not available to independent researchers. Instead, it is common to fit curves to summary Kaplan-Meier graphs, either by regression or by least squares. Here, a more accurate method of fitting survival curves to summary survival data is described
Pathways to massive black holes and compact star clusters in pre-galactic dark matter haloes with virial temperatures > 10000K
Large dynamic range numerical simulations of atomic cooling driven collapse
of gas in pre-galactic DM haloes with T_vir ~ 10000 K show that the gas loses
90% and more of its angular momentum before rotational support sets in. In a
fraction of these haloes where the metallicity is low and UV radiation
suppresses H_2 cooling, conditions are thus very favourable for the rapid
build-up of massive black holes. Depending on the progression of metal
enrichment, the continued suppression of H_2 cooling by external and internal
UV radiation and the ability to trap the entropy produced by the release of
gravitational energy, the gas at the centre of the halo is expected to form a
supermassive star, a stellar-mass black hole accreting at super-Eddington
accretion rates or a compact star-cluster undergoing collisional run-away of
massive stars at its centre. In all three cases a massive black hole of
initially modest mass finds itself at the center of a rapid inflow of gas with
inflow rates of ~ 1 M_solar\yr. The massive black hole will thus grow quickly
to a mass of 10^5 to 10^6 M_solar until further inflow is halted either by
consumption of gas by star formation or by the increasing energy and momentum
feedback from the growing massive black hole. Conditions for the formation of
massive seed black holes in this way are most favourable in haloes with T_vir ~
15000 K and V_vir ~ 20 km\s with less massive haloes not allowing collapse of
gas by atomic cooling and more massive haloes being more prone to
fragmentation. This should imprint a characteristic mass on the mass spectrum
of an early population of massive black hole seeds in pre-galactic haloes which
will later grow into the observed population of supermassive black holes in
galactic bulges.Comment: 13 pages, 8 figures. Submitted to MNRA
On High-Energy Behavior of Cross Sections in Theories with Large Extra Dimensions
We discuss the high-energy behavior of cross sections in theories with large
extra dimensions and low-scale quantum gravity, addressing two particular
issues: (i) the tension of the D-branes, and (ii) bounds on the cross section
and their relation to approximations in the mode sum over Kaluza-Klein-graviton
exchanges.Comment: 6 pages, late
Infrared emission towards SN 1987A 11 years after outburst: Measurements with ISOCAM
We present measurements of the mid-infrared (MIR) emission from SN 1987A,
made using the Infrared Space Observatory (ISO) 11 years after outburst. They
are the only late epoch detections of this source in the thermal IR regime. The
position of the source, determined from an offset to an IR-emitting star,
suggests that the emission is associated with SN 1987A or its extended
supernova remnant (SNR). A predominantly circumstellar origin is however
suggested by the size and orientation of the IR-emitting region, which is
comparable with the extension of the inner ring seen with the Hubble Space
Telescope (HST). The emission is most probably from collisionally-heated
circumstellar grains embedded in shocked gas downstream of the blast wave. The
MIR extent is consistent with the hypothesis that the blast wave was
propagating into material of moderate density interior to the thick inner ring
at the epoch of the ISOCAM observations
Gravitational recoils of supermassive black holes in hydrodynamical simulations of gas rich galaxies
We study the evolution of gravitationally recoiled supermassive black holes
(BHs) in massive gas-rich galaxies by means of high-resolution hydrodynamical
simulations. We find that the presence of a massive gaseous disc allows
recoiled BHs to return to the centre on a much shorter timescale than for
purely stellar discs. Also, BH accretion and feedback can strongly modify the
orbit of recoiled BHs and hence their return timescale, besides affecting the
distribution of gas and stars in the galactic centre. However, the dynamical
interaction of kicked BHs with the surrounding medium is in general complex and
can facilitate both a fast return to the centre as well as a significant delay.
The Bondi-Hoyle-Lyttleton accretion rates of the recoiling BHs in our simulated
galaxies are favourably high for the detection of off-centred AGN if kicked
within gas-rich discs -- up to a few per cent of the Eddington accretion rate
-- and are highly variable on timescales of a few 10^7 yrs. In major merger
simulations of gas-rich galaxies, we find that gravitational recoils increase
the scatter in the BH mass -- host galaxy relationships compared to simulations
without kicks, with the BH mass being more sensitive to recoil kicks than the
bulge mass. A generic result of our numerical models is that the clumpy massive
discs suggested by recent high-redshift observations, as well as the remnants
of gas-rich mergers, exhibit a gravitational potential that falls steeply in
the central regions, due to the dissipative concentration of baryons. As a
result, supermassive BHs should only rarely be able to escape from massive
galaxies at high redshifts, which is the epoch where the bulk of BH recoils is
expected to occur.[Abridged]Comment: 16 pages, 13 figures, minor revisions, MNRAS accepte
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