637 research outputs found
Are dumbbell brightest cluster members signposts to galaxy cluster activity?
We assemble a sample of galaxy clusters whose brightest members are dumbbell
galaxies and compare them with a control sample in order to investigate if they
are the result of recent mergers. We show that the dumbbell sample is no more
likely than other clusters to exhibit subclustering. However, they are much
more likely to have at least one dumbbell component possessing a significant
peculiar velocity with respect to the parent cluster than a non-dumbbell
brightest cluster member. We interpret this in the context of seeing the
clusters at various stages of post-merger relaxation.Comment: 10 pages, 2 figures, accepted for publication in PAS
Structure of the magnetoionic medium around the FR Class I radio galaxy 3C 449
The goal of this work is to constrain the strength and structure of the
magnetic field associated with the environment of the radio source 3C 449,
using observations of Faraday rotation, which we model with a structure
function technique and by comparison with numerical simulations. We assume that
the magnetic field is a Gaussian, isotropic random variable and that it is
embedded in the hot intra-group plasma surrounding the radio source. For this
purpose, we present detailed rotation measure images for the polarized radio
source 3C 449, previously observed with the Very Large Array at seven
frequencies between 1.365 and 8.385 GHz. We quantify the statistics of the
magnetic-field fluctuations by deriving rotation measure structure functions,
which we fit using models derived from theoretical power spectra. We quantify
the errors due to sampling by making multiple two-dimensional realizations of
the best-fitting power spectrum.We also use depolarization measurements to
estimate the minimum scale of the field variations. We then make
three-dimensional models with a gas density distribution derived from X-ray
observations and a random magnetic field with this power spectrum. Under these
assumptions we find that both rotation measure and depolarization data are
consistent with a broken power-law magnetic-field power spectrum, with a break
at about 11 kpc and slopes of 2.98 and 2.07 at smaller and larger scales
respectively. The maximum and minimum scales of the fluctuations are around 65
and 0.2 kpc, respectively. The average magnetic field strength at the cluster
centre is 3.5 +/-1.2 micro-G, decreasing linearly with the gas density within
about 16 kpc of the nucleus.Comment: 19 pages; 14 figures; accepted for publication on A&A. For a high
quality version use ftp://ftp.eso.org/pub/general/guidetti
The ATESP 5 GHz radio survey. II. Physical properties of the faint radio population
One of the most debated issues about sub-mJy radio sources, which are
responsible for the steepening of the 1.4 GHz source counts, is the origin of
their radio emission. Particularly interesting is the possibility of combining
radio spectral index information with other observational properties to assess
whether the sources are triggered by star formation or nuclear activity. The
aim of this work is to study the optical and near infrared properties of a
complete sample of 131 radio sources with S>0.4 mJy, observed at both 1.4 and 5
GHz as part of the ATESP radio survey. We use deep multi-colour (UBVRIJK)
images, mostly taken in the framework of the ESO Deep Public Survey, to
optically identify and derive photometric redshifts for the ATESP radio
sources. Deep optical coverage and extensive colour information are available
for 3/4 of the region covered by the radio sample. Typical depths of the images
are U~25, B~26, V~25.4, R~25.5, I~24.3, 19.5<K_s<20.2, J<22.2. Optical/near
infrared counterparts are found for ~78% (66/85) of the radio sources in the
region covered by the deep multi-colour imaging, and for 56 of these reliable
estimates of the redshift and type are derived. We find that many of the
sources with flat radio spectra are characterised by high radio-to-optical
ratios (R>1000), typical of classical powerful radio galaxies and quasars.
Flat-spectrum sources with low R values are preferentially identified with
early type galaxies, where the radio emission is most probably triggered by
low-luminosity active galactic nuclei. Considering both early type galaxies and
quasars as sources with an active nucleus, such sources largely dominate our
sample (78%). Flat-spectrum sources associated with early type galaxies are
quite compact (d<10-30 kpc), suggesting core-dominated radio emission.Comment: 15 pages, 13 figures, accepted for pubblication in A&
The ATESP Radio Survey II. The Source Catalogue
This paper is part of a series reporting the results of the Australia
Telescope ESO Slice Project (ATESP) radio survey obtained at 1400 MHz with the
Australia Telescope Compact Array (ATCA) over the region covered by the ESO
Slice Project (ESP) galaxy redshift survey. The survey consists of 16 radio
mosaics with ~8"x14" resolution and uniform sensitivity (1sigma noise level ~79
microJy) over the whole area of the ESP redshift survey (~26 sq. degrees at
decl. -40 degr). Here we present the catalogue derived from the ATESP survey.
We detected 2960 distinct radio sources down to a flux density limit of ~0.5
mJy (6sigma), 1402 being sub-mJy sources. We describe in detail the procedure
followed for the source extraction and parameterization. The internal accuracy
of the source parameters was tested with Monte Carlo simulations and possible
systematic effects (e.g. bandwidth smearing) have been quantified.Comment: 14 pages, 14 Postscript figures, Accepted for publication in A&A
Suppl. Corrected typos and added Journal Referenc
Pasture Chemoscapes and Their Ecological Services
Ruminant livestock-production systems are between a rock and a hard place; they are experiencing increasing societal pressure to reduce environmental impacts in a world that demands increased food supply. Recent improvements in the understanding of the nutritional ecology of livestock by scientists may help livestock producers respond to these seemingly contradictory demands. Forages are nutrition and pharmacy centers with primary (nutrients) and plant secondary compounds (PSC; pharmaceuticals, nutraceuticals), which can provide multiple services for the proper functioning of agroecosystems. Legumes with lower contents of fiber and higher contents of nonstructural carbohydrates, coupled with different types and concentrations of PSC (e.g., condensed tannins, terpenes), create a diverse array of chemicals in the landscape (i.e., the âchemoscapeâ) with the potential to enhance livestock nutrition, health and welfare relative to foodscapes dominated by grasses and other conventional feeds. These PSC-containing plants may reduce methane emissions and nitrogen (N) excretion from animals while increasing animal growth rate compared with swards dominated by grasses, and provide meat quality that appeals to consumers. Condensed tannins from sainfoin and saponins from alfalfa and manure of cattle consuming these forages also reduce N mobilization in soils, reduce nutrient leaching, and increase plant-available N stores for future use. The challenge for future pastoral production systems is to design multifunctional spatiotemporal arrangements of forages with âidealâ chemical diversity for specific ecoregions, aiming to achieve sustainability while increasing production goals and improving ecosystem services. Thus, the objective of this review is to stimulate the quest for chemically and taxonomically diverse pastoral feeding systems that optimize overall productivity; reduce environmental impacts; and enhance livestock, soil, and human health
Shape of the Galactic Orbits in Clusters
A kinematical analysis applied to a sample of galaxy clusters indicates that
the differences between the velocity distribution of elliptical and spiral
galaxies are associated with the shape of their orbit families. The orbital
anisotropies present on each morphological population could be measured with
the use of a parameter which is the ratio of the radial and tangential velocity
dispersions, and can be recovered through the observed line-of-sight velocity
distribution. When a Gaussian velocity distribution is assumed, having
different dispersions along the radial and tangential directions, we conclude
that the orbits of elliptical galaxies in clusters are close to radial, while
spirals have more circular shaped or isotropic orbits. Lenticulars galaxies
shares an intermediate orbital parameter, between spirals and ellipticals.Comment: 23 pages including 6 EPS-figures, and 4 tables. Accepted for
publication by ApJ, April 199
Thermal hydraulic analysis of Alfred bayonet tube steam generator
The paper analyzes the performance of ALFRED steam generator from the thermal-hydraulic point of view highlighting the effect of some design features. The parameters object of the study are the regenerative heat transfer, the dimension of the inner tube and the length of the bayonet. The system code RELAP5-3D/2.4.2 has been chosen for the analysis. Sensitivities analysis allowed the determination of the different design parameters influence, here briefly summarized. The increase of regenerative heat transfer affects the efficiency of the steam generator through a degradation of the outlet steam quality: the number of bayonet tubes required to remove the nominal power increases with the increase of the global heat transfer coefficient of the inner tube. A higher inner diameter results in a larger surface area for the regenerative heat transfer and in a higher heat transfer coefficient in the annular region because of the reduction of the cross section. The result is an improvement of the performances of the steam generator thanks to the dimension reduction of the annular gap. Finally, if the height of the bayonet tube is reduced by 1 meter, the number of bayonet tubes required to remove the nominal power increases up to 20%
A review on the effects of part-time grazing herbaceous pastures on feeding behaviour and intake of cattle, sheep and horses
Part-time grazing (PTG) is the grazing technique based on the time-restricted access to pasture of farmed herbivores, usually supplemented indoors. This review evaluates the effects of the duration of access to pasture on the functional responses of grazing time and herbage intake rate in cattle, sheep and horses and the implications of these responses on diet selection, diet digestibility, energy expenditure, animal welfare, the performance of ruminants and the quality of their products (milk and meat).
Ruminants with restricted access time to pasture display compensatory behaviour through increased intake rate, achieving similar levels of intake and performance compared with 24 h-grazing ruminants, particularly if access time is in the range 6-8 h/d. This can depend on the reduction of locomotion energy expenditure, and, sometimes, on the selection of a better quality diet than that on offer. Nevertheless, due to lower ingestive fibre trituration, fibre digestibility could be reduced, particularly with access time <4 h/d. Moreover, milk content of FA regarded as beneficial for consumers' health, such as n-3 PUFA and rumenic acid, is usually higher in PTG than stall-fed ruminants, with a minimum access to grass pasture of 6 h/d in cows supplemented with total mixed rations or 4 h/d in sheep supplemented with concentrate and hay. Timing the grazing session of ruminants in the afternoon and evening hours is a good strategy to match pasture quality and animal attitude to forage intensively and efficiently, favouring intake, performance and produce quality.
Horses show on average lower intake rates scaled to metabolic weight than ruminants, probably due to their lower energy requirements but also for the need to spend part of the time outdoor performing physical activity and social behavior. Therefore, they probably need longer access time than ruminants. However, access should be time restricted or avoided during periods of the year and day hours (from midday to evening) when herbage content of non structural carbohydrates (sum of starch and water soluble carbohydrates) is high (> 15 % DM) since it can be conducive to equine metabolic syndrome and laminitis.
In general, PTG can improve ruminant and horse welfare as compared with stall-feeding with reference to appropriate behavior and freedom from some pathologies, although further research is needed to quantify these effects on a wider range of animal species and welfare indicators
Livestock in evolving foodscapes and thoughtscapes
Humanityâs main societal and epistemic transitions also mirror changes in its approach to the food system. This particularly holds true for humanâanimal interactions and the consumption of animal source foods (red meat especially, and to a lesser degree dairy, eggs, poultry, and fish). Hunter-gathering has been by far the longest prevailing form of human sustenance, followed by a diffuse transition to crop agriculture and animal husbandry. This transition eventually stabilized as a state-controlled model based on the domestication of plants, animals, and humans. A shift to a post-domestic paradigm was initiated during the 19th century in the urbanizing populations of the Anglosphere, which was characterized by the rise of agri-food corporations, an increased meat supply, and a disconnect of most of its population from the food chain. While this has improved undernutrition, various global threats have been emerging in parallel. The latter include, among others, a public health crisis, climate change, pandemics, and societal class anxieties. This state of affairs is an unstable one, setting the conditions of possibility for a new episteme that may evolve beyond mere adjustments within the business-as-usual model. At least two disruptive scenarios have been described in current food discourses, both by scientists and mass media. Brought to its extreme, the first scenario relates to the radical abolishment of livestock, rewilding, a âplants-onlyâ diet, and vegan ideology. A second option consists of a holistic approach to animal husbandry, involving more harmonic and richer types of humanâanimalâland interactions. We argue that â instead of reactive pleas for less or none â future thoughtscapes should emphasize âmore of the better.
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