609 research outputs found
Recent star formation in nearby 3CR radio-galaxies from UV HST observations
We analyzed HST images of 31 nearby (z <~ 0.1) 3CR radio-galaxies. We
compared their UV and optical images to detect evidence of recent star
formation. Six objects were excluded because they are highly nucleated or had
very low UV count rates. After subtracting the emission from their nuclei
and/or jets, 12 of the remaining 25 objects, presenting an UV/optical colors
NUV - r < 5.4, are potential star-forming candidates. Considering the
contamination from other AGN-related processes (UV emission lines, nebular
continuum, and scattered nuclear light), there are 6 remaining star-forming
"blue" galaxies.
We then divide the radio galaxies, on the basis of the radio morphology,
radio power, and diagnostic optical line ratios, into low and high excitation
galaxies, LEG and HEG. While there is no correlation between the FR type (or
radio power) and color, the FR type is clearly related to the spectroscopic
type. In fact, all HEG (with one possible exception) show morphological
evidence of recent star formation in UV compact knots, extended over 5-20 kpc.
Conversely, there is only 1 "blue" LEG out of 19, including in this class also
FR I galaxies.
The picture that emerges, considering color, UV, optical, and dust
morphology, is that only in HEG recent star formation is associated with these
relatively powerful AGN, which are most likely triggered by a recent, major,
wet merger. Conversely, in LEG galaxies the fraction of actively star-forming
objects is not enhanced with respect to quiescent galaxies. The AGN activity in
these sources can be probably self-sustained by their hot interstellar medium.Comment: Accepted for publication in A&
On the almost sure convergence of adaptive allocation procedures
In this paper, we provide some general convergence results for adaptive
designs for treatment comparison, both in the absence and presence of
covariates. In particular, we demonstrate the almost sure convergence of the
treatment allocation proportion for a vast class of adaptive procedures, also
including designs that have not been formally investigated but mainly explored
through simulations, such as Atkinson's optimum biased coin design, Pocock and
Simon's minimization method and some of its generalizations. Even if the large
majority of the proposals in the literature rely on continuous allocation
rules, our results allow to prove via a unique mathematical framework the
convergence of adaptive allocation methods based on both continuous and
discontinuous randomization functions. Although several examples of earlier
works are included in order to enhance the applicability, our approach provides
substantial insight for future suggestions, especially in the absence of a
prefixed target and for designs characterized by sequences of allocation rules.Comment: Published at http://dx.doi.org/10.3150/13-BEJ591 in the Bernoulli
(http://isi.cbs.nl/bernoulli/) by the International Statistical
Institute/Bernoulli Society (http://isi.cbs.nl/BS/bshome.htm
Multi-objective optimal designs in comparative clinical trials with covariates: The reinforced doubly adaptive biased coin design
The present paper deals with the problem of allocating patients to two
competing treatments in the presence of covariates or prognostic factors in
order to achieve a good trade-off among ethical concerns, inferential precision
and randomness in the treatment allocations. In particular we suggest a
multipurpose design methodology that combines efficiency and ethical gain when
the linear homoscedastic model with both treatment/covariate interactions and
interactions among covariates is adopted. The ensuing compound optimal
allocations of the treatments depend on the covariates and their distribution
on the population of interest, as well as on the unknown parameters of the
model. Therefore, we introduce the reinforced doubly adaptive biased coin
design, namely a general class of covariate-adjusted response-adaptive
procedures that includes both continuous and discontinuous randomization
functions, aimed to target any desired allocation proportion. The properties of
this proposal are described both theoretically and through simulations.Comment: Published in at http://dx.doi.org/10.1214/12-AOS1007 the Annals of
Statistics (http://www.imstat.org/aos/) by the Institute of Mathematical
Statistics (http://www.imstat.org
High-resolution VLA observations of FR0 radio galaxies: properties and nature of compact radio sources
We present the results of Karl G. Jansky Very Large Array (VLA) observations
to study the properties of FR0 radio galaxies, the compact radio sources
associated with early-type galaxies which represent the bulk of the local
radio-loud AGN population. We obtained A-array observations at 1.5, 4.5, and
7.5 GHz for 18 FR0s from the FR0CAT sample: these are sources at ,
unresolved in the FIRST images and spectroscopically classified as low
excitation galaxies (LEG). Although we reach an angular resolution of 0.3
arcsec, the majority of the 18 FR0s is still unresolved. Only four objects show
extended emission. Six have steep radio spectra, 11 are flat cores, while one
shows an inverted spectrum. We find that 1) the ratio between core and total
emission in FR0s is 30 times higher than in FRI and 2) FR0s share the
same properties with FRIs from the nuclear and host point of view. FR0s differ
from FRIs only for the paucity of extended radio emission. Different scenarios
were investigated: 1) the possibility that all FR0s are young sources
eventually evolving into extended sources is ruled out by the distribution of
radio sizes; 2) similarly, a time-dependent scenario, where a variation of
accretion or jet launching prevents the formation of large-scales radio
structures, appears to be rather implausible due to the large abundance of
sub-kpc objects 3) a scenario in which FR0s are produced by mildly relativistic
jets is consistent with the data but requires observations of a larger sample
to be properly tested.Comment: accepted for publication on MNRAS (12 pages, 8 figures
Discovery of a FR0 radio galaxy emitting at -ray energies
We present supporting evidence for the first association of a Fermi source,
3FGLJ1330.0-3818, with the FR0 radio galaxy Tol1326-379. FR0s represent the
majority of the local radio loud AGN population but their nature is still
unclear. They share the same properties of FRIs from the point of view of the
nuclear and host properties, but they show a large deficit of extended radio
emission. Here we show that FR0s can emit photons at very high energies.
Tol1326-379 has a GeV luminosity of erg
s, typical of FRIs, but with a steeper -ray spectrum
(). This could be related to the intrinsic jet properties
but also to a different viewing angle.Comment: 7 pages, 5 figures , accepted for publication on MNRA
Voluntary Traceability and Transaction Costs: An Empirical Analysis in the Italian Meat Processing Supply Chain
This paper analyses voluntary traceability effects on the coordination of the food supply chain from the transaction cost perspective. The analysis concerns Italian firms and makes particular reference to the meat sector. A survey was conducted by questionnaire to assess the changes in key transaction factors and costs after the introduction of traceability. The results underline an increase in the degree of human, material and site asset specificity, and reveal a reduction in the degree of uncertainty in transactions. Growth in some transaction costs related to monitoring is also observed. Factorial and cluster analysis were used to underline the different organisational solutions of the firms.traceability, trust, transaction cost, vertical relationships, meat chain, Agribusiness, Livestock Production/Industries,
Mass, shape and thermal properties of A1689 by a multi-wavelength X-ray, lensing and Sunyaev-Zel'dovich analysis
Knowledge of mass and concentration of galaxy clusters is crucial to
understand their formation and evolution. Unbiased estimates require the
understanding of the shape and orientation of the halo as well as its
equilibrium status. We propose a novel method to determine the intrinsic
properties of galaxy clusters from a multi-wavelength data set spanning from
X-ray spectroscopic and photometric data to gravitational lensing to the
Sunyaev-Zel'dovich effect (SZe). The method relies on two quite non informative
geometrical assumptions: the distributions of total matter or gas are
approximately ellipsoidal and co-aligned; they have different, constant axial
ratios but share the same degree of triaxiality. Weak and strong lensing probe
the features of the total mass distribution in the plane of the sky. X-ray data
measure size and orientation of the gas in the plane of the sky. Comparison
with the SZ amplitude fixes the elongation of the gas along the line of sight.
These constraints are deprojected thanks to Bayesian inference. The mass
distribution is described as a Navarro-Frenk-White halo with arbitrary
orientation, gas density and temperature are modelled with parametric profiles.
We applied the method to Abell 1689. Independently of the priors, the cluster
is massive, M_{200}=(1.3+-0.2)*10^{15}M_sun, and over-concentrated,
c_{200}=8+-1, but still consistent with theoretical predictions. The total
matter is triaxial (minor to major axis ratio ~0.5+-0.1 exploiting priors from
N-body simulations) with the major axis nearly orientated along the line of
sight. The gas is rounder (minor to major axis ratio ~0.6+-0.1) and deviates
from hydrostatic equilibrium. The contribution of non-thermal pressure is
~20-50 per cent in inner regions, <~ 300 kpc, and ~25+-5 per cent at ~1.5 Mpc.Comment: 14 pages; MNRAS, in pres
Self-similarity of temperature profiles in distant galaxy clusters: the quest for a Universal law
We present the XMM-Newton temperature profiles of 12 bright clusters of
galaxies at 0.4<z<0.9, with 5<kT<11 keV. The normalized temperature profiles
(normalized by the mean temperature T500) are found to be generally
self-similar. The sample was subdivided in 5 cool-core (CC) and 7 non cool-core
(NCC) clusters, by introducing a pseudo-entropy ratio
sigma=(T_IN/T_OUT)X(EM_IN/EM_OUT)^-1/3 and defining the objects with sigma<0.6
as CC clusters and those with sigma>=0.6 as NCC clusters. The profiles of CC
and NCC clusters differ mainly in the central regions, with the latters
exhibiting a marginally flatter central profile. A significant dependence of
the temperature profiles on the pseudo-entropy ratio sigma is detected by
fitting a function of both r and sigma, showing an indication that the outer
part of the profiles becomes steeper for higher values of sigma (i.e.
transitioning towards the NCC clusters). No significant evidence of redshift
evolution could be found within the redshift range sampled by our clusters
(0.4<z<0.9). A comparison of our high-z sample with intermediate clusters at
0.1<z<0.3, showed how both the CC and NCC clusters temperature profiles have
experienced some sort of evolution. This can be due by the fact that higher z
clusters are at less advanced stage of their formation and did not have enough
time to create a relaxed structure, characterized by a central temperature dip
in CC clusters and by flatter profiles in NCC clusters. This is the first time
that a systematic study of the temperature profiles of galaxy clusters at z>0.4
has been attempted, as we were able to define the closest possible relation to
a Universal law for the temperature profiles of galaxy clusters at 0.1<z<0.9,
showing a dependence on both the state of relaxation of the clusters and the
redshift.Comment: 14 pages, 8 figures, A&A in press, minor changes (language editing
X-ray study of a sample of FR0 radio galaxies: unveiling the nature of the central engine
FR0s are compact radio sources that represent the bulk of the Radio-Loud (RL)
AGN population, but they are still poorly understood. Pilot studies on these
sources have been already performed at radio and optical wavelengths: here we
present the first X-ray study of a sample of 19 FR0 radio galaxies selected
from the SDSS/NVSS/FIRST sample of Best & Heckman (2012), with redshift
0.15, radio size 10 kpc and optically classified as low-excitation
galaxies (LEG). The X-ray spectra are modeled with a power-law component
absorbed by Galactic column density with, in some cases, a contribution from
thermal extended gas. The X-ray photons are likely produced by the jet as
attested by the observed correlation between X-ray (2-10 keV) and radio (5 GHz)
luminosities, similar to FRIs. The estimated Eddington-scaled luminosities
indicate a low accretion rate. Overall, we find that the X-ray properties of
FR0s are indistinguishable from those of FRIs, thus adding another similarity
between AGN associated with compact and extended radio sources. A comparison
between FR0s and low luminosity BL Lacs, rules out important beaming effects in
the X-ray emission of the compact radio galaxies. FR0s have different X-ray
properties with respect to young radio sources (e.g. GPS/CSS sources),
generally characterized by higher X-ray luminosities and more complex spectra.
In conclusion, the paucity of extended radio emission in FR0s is probably
related to the intrinsic properties of their jets that prevent the formation of
extended structures, and/or to intermittent activity of their engines.Comment: Accepted for publication in MNRAS (18 pages, 4 figures
An LCA model to assess the environmental improvement of new farming systems
The environmental impact of new farming practices is compared with that of conventional one. The approach is that of LCA and the assessing procedure is based on two cross-interaction matrices relating system inputs with emissions and impacts. With the aim to allow its application also at farm level by non-expert users, the procedure has been implemented in software that facilitate it use. Furthermore, the definition of standard impact values and a total environmental effects index make it easier to compare different systems and to evaluate the improvement achieved with a new agricultural practice. As an example, the model has been applied to compare the environmental effects generated in the production of sunflower using ecological, integrated and conventional farming techniques. Both Ecological and Integrated technique present lower impact than conventional even if for some specific impact the results are inverted. The application highlights the importance of the functional unit: when environmental effects are referred to the unit of production (ton), the total impact of the integrated technique is higher than the conventional one. Energy and CO2 efficiency are also computed, which are resulted to be good indicators of the overall environmental impact of a cultivation syste
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