278 research outputs found
Freshwater Sponges and their Interaction with Bacteria Through Filtration, Retention and Antimicrobial Properties
Impact of dietary protein content on growth of white-clawed crayfish <i>Austropotamobius pallipes </i>Lereboullet, 1858 (Decapoda: Astacidae) in captive rearing for conservation
The same, but different: Stochasticity in binary destruction
Observations of binaries in clusters tend to be of visual binaries with
separations of 10s - 100s au. Such binaries are 'intermediates' and their
destruction or survival depends on the exact details of their individual
dynamical history. We investigate the stochasticity of the destruction of such
binaries and the differences between the initial and processed populations
using N-body simulations. We concentrate on Orion Nebula Cluster-like clusters,
where the observed binary separation distribution ranges from 62 - 620 au.
We find that, starting from the same initial binary population in
statistically identical clusters, the number of intermediate binaries that are
destroyed after 1 Myr can vary by a factor of >2, and that the resulting
separation distributions can be statistically completely different in initially
substructured clusters. We also find that the mass ratio distributions are
altered (destroying more low mass ratio systems), but not as significantly as
the binary fractions or separation distributions. We conclude that finding very
different intermediate (visual) binary populations in different clusters does
not provide conclusive evidence that the initial populations were different.Comment: 11 pages, 7 figures, accepted for publication in MNRA
Effects of freshwater sponge Ephydatia fluviatilis on conjugative transfer of antimicrobial resistance in Enterococcus faecalis strains in aquatic environments
The evolution of binary populations in cool, clumpy star clusters
Observations and theory suggest that star clusters can form in a subvirial
(cool) state and are highly substructured. Such initial conditions have been
proposed to explain the level of mass segregation in clusters through dynamics,
and have also been successful in explaining the origin of trapezium-like
systems. In this paper we investigate, using N-body simulations, whether such a
dynamical scenario is consistent with the observed binary properties in the
Orion Nebula Cluster (ONC). We find that several different primordial binary
populations are consistent with the overall fraction and separation
distribution of visual binaries in the ONC (in the range 67 - 670 au), and that
these binary systems are heavily processed. The substructured, cool-collapse
scenario requires a primordial binary fraction approaching 100 per cent. We
find that the most important factor in processing the primordial binaries is
the initial level of substructure; a highly substructured cluster processes up
to 20 per cent more systems than a less substructured cluster because of
localised pockets of high stellar density in the substructure. Binaries are
processed in the substructure before the cluster reaches its densest phase,
suggesting that even clusters remaining in virial equilibrium or undergoing
supervirial expansion would dynamically alter their primordial binary
population. Therefore even some expanding associations may not preserve their
primordial binary population.Comment: 12 pages, 7 figures; accepted for publication in MNRA
Properties of hierarchically forming star clusters
We undertake a systematic analysis of the early (< 0.5 Myr) evolution of
clustering and the stellar initial mass function in turbulent fragmentation
simulations. These large scale simulations for the first time offer the
opportunity for a statistical analysis of IMF variations and correlations
between stellar properties and cluster richness. The typical evolutionary
scenario involves star formation in small-n clusters which then progressively
merge; the first stars to form are seeds of massive stars and achieve a
headstart in mass acquisition. These massive seeds end up in the cores of
clusters and a large fraction of new stars of lower mass is formed in the outer
parts of the clusters. The resulting clusters are therefore mass segregated at
an age of 0.5 Myr, although the signature of mass segregation is weakened
during mergers. We find that the resulting IMF has a smaller exponent
(alpha=1.8-2.2) than the Salpeter value (alpha=2.35). The IMFs in subclusters
are truncated at masses only somewhat larger than the most massive stars (which
depends on the richness of the cluster) and an universal upper mass limit of
150 Msun is ruled out. We also find that the simulations show signs of the
IGIMF effect proposed by Weidner & Kroupa, where the frequency of massive stars
is suppressed in the integrated IMF compared to the IMF in individual clusters.
We identify clusters through the use of a minimum spanning tree algorithm which
allows easy comparison between observational survey data and the predictions of
turbulent fragmentation models. In particular we present quantitative
predictions regarding properties such as cluster morphology, degree of mass
segregation, upper slope of the IMF and the relation between cluster richness
and maximum stellar mass. [abridged]Comment: 21 Pages, 25 Figure
Primordial mass segregation in simulations of star formation?
We take the end result of smoothed particle hydrodynamics (SPH) simulations of star formation which include feedback from photoionization and stellar winds and evolve them for a further 10 Myr using N-body simulations. We compare the evolution of each simulation to a control run without feedback, and to a run with photoionization feedback only. In common with previous work, we find that the presence of feedback prevents the runaway growth of massive stars, and the resulting star-forming regions are less dense, and preserve their initial substructure for longer. The addition of stellar winds to the feedback produces only marginal differences compared to the simulations with just photoionization feedback. We search for mass segregation at different stages in the simulations; before feedback is switched on in the SPH runs, at the end of the SPH runs (before N-body integration) and during the N-body evolution. Whether a simulation is primordially mass segregated (i.e. before dynamical evolution) depends extensively on how mass segregation is defined, and different methods for measuring mass segregation give apparently contradictory results. Primordial mass segregation is also less common in the simulations when star formation occurs under the influence of feedback. Further dynamical mass segregation can also take place during the subsequent (gas-free) dynamical evolution. Taken together, our results suggest that extreme caution should be exercised when interpreting the spatial distribution of massive stars relative to low-mass stars in simulations
On the mass segregation of stars and brown dwarfs in Taurus
We use the new minimum spanning tree (MST) method to look for mass
segregation in the Taurus association. The method computes the ratio of MST
lengths of any chosen subset of objects, including the most massive stars and
brown dwarfs, to the MST lengths of random sets of stars and brown dwarfs in
the cluster. This mass segregation ratio (Lambda_MSR) enables a quantitative
measure of the spatial distribution of high-mass and low-mass stars, and brown
dwarfs to be made in Taurus.
We find that the most massive stars in Taurus are inversely mass segregated,
with Lambda_MSR = 0.70 +/- 0.10 (Lambda_MSR = 1 corresponds to no mass
segregation), which differs from the strong mass segregation signatures found
in more dense and massive clusters such as Orion. The brown dwarfs in Taurus
are not mass segregated, although we find evidence that some low-mass stars
are, with an Lambda_MSR = 1.25 +/- 0.15. Finally, we compare our results to
previous measures of the spatial distribution of stars and brown dwarfs in
Taurus, and briefly discuss their implications.Comment: 10 pages, 8 figures, accepted for publication in MNRA
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A RCT of telehealth for COPD patient's Quality of life: The Whole System Demonstrator Evaluation
INTRODUCTION/OBJECTIVES: Despite some concerns that the introduction of telehealth (TH) may lead to reductions in quality of life (QoL), lower mood and increased anxiety in response to using assistive technologies to reduce health care utilisation and manage long term conditions, this research focuses on the extent to which providing people with tools to monitor their condition can improve QoL.
METHODS: The Chronic Obstructive Pulmonary Disease cohort of the Whole Systems Demonstrator Trial is a pragmatic General Practitioner (GP) clustered RCT evaluating TH in the UK from three regions in England. All patients at a participating GP practice were deemed eligible for inclusion in the study if they were diagnosed with COPD.
RESULTS: 447 participants completed baseline and either a short (4 months) or long term (12 months) follow up. There was a trend of improved QoL and mood in the TH group at longer-term follow up, but not short term follow up. Emotional functioning (g= 0.280 95% CI, 0.051- 0.510) and mastery reached (g= 2.979 95%CI, 0- 0.46) significance at P<0.05 (all Hedges g <0.3).
CONCLUSIONS: TH showed minimal benefit to QoL in COPD patients who were not preselected to be at increased risk of acute exacerbations. Benefits were more likely in disease specific measures at longer term follow up. TH is a complex intervention and should be embedded in a service that is evidenced based. Outcome measures must be sensitive enough to detect changes in the target population for the specific intervention. This article is protected by copyright. All rights reserved
On the spatial distributions of dense cores in Orion B
We quantify the spatial distributions of dense cores in three spatially distinct areas of the Orion
B star-forming region. For L1622, NGC 2068/NGC 2071, and NGC 2023/NGC 2024, we measure
the amount of spatial substructure using the Q-parameter and find all three regions to be
spatially substructured (Q < 0.8). We quantify the amount of mass segregation using MSR
and find that the most massive cores are mildly mass segregated in NGC 2068/NGC 2071
(MSR ∼ 2), and very mass segregated in NGC 2023/NGC 2024 (MSR = 28+13
−10 for the
four most massive cores). Whereas the most massive cores in L1622 are not in areas
of relatively high surface density, or deeper gravitational potentials, the massive cores in
NGC 2068/NGC 2071 and NGC 2023/NGC 2024 are significantly so. Given the low density
(10 cores pc−2) and spatial substructure of cores in Orion B, the mass segregation cannot be
dynamical. Our results are also inconsistent with simulations in which the most massive stars
form via competitive accretion, and instead hint that magnetic fields may be important in
influencing the primordial spatial distributions of gas and stars in star-forming regions
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