1,229 research outputs found
Kinetic Luminosity and Composition of Active Galactic Nuclei Jets
We present a new method how to discriminate the matter content of
parsec-scale jets of active galactic nuclei. By constraining the kinetic
luminosity of a jet from the observed core size at a single very long baseline
interferometry frequency, we can infer the electron density of a radio-emitting
component as a function of the composition. Comparing this density with that
obtained from the theory of synchrotron self-absorption, we can determine the
composition. We apply this procedure to the five components in the 3C~345 jet
and find that they are likely pair-plasma dominated at 11 epochs out of the
total 21 epochs, provided that the bulk Lorentz factor is less than 15
throughout the jet. We also investigate the composition of the 3C~279 jet and
demonstrate that its two components are likely pair-plasma dominated at three
epochs out of four epochs, provided that their Doppler factors are less than
10, which are consistent with observations. The conclusions do not depend on
the lower cutoff energy of radiating particles.Comment: 6 figures, 2 tables; accepted to Astroph.
INTENSE THERMAL NEUTRON FIELDS FROM A MEDICAL-TYPE LINAC: THE E_LIBANS PROJECT
The e_LiBANS project aims at producing intense thermal neutron fields for diverse interdisciplinary irradiation purposes. It makes use of a reconditioned medical electron LINAC, recently installed at the Physics Department and INFN in Torino, coupled to a dedicated photo-converter, developed within this collaboration, that uses (\u3b3,n) reaction within high Z targets. Produced neutrons are then moderated to thermal energies and concentrated in an irradiation volume. To measure and to characterize in real time the intense field inside the cavity new thermal neutron detectors were designed with high radiation resistance, low noise and very high neutron-to-photon discrimination capability. This article offers an overview of the e_LiBANS project and describes the results of the benchmark experiment
Development of gamma insensitive silicon carbide diagnostics to qualify intense thermal and epithermal neutron fields
The e_LiBANS project aims at creating accelerator based compact neutron
facilities for diverse interdisciplinary applications. After the successful
setting up and characterization of a thermal neutron source based on a medical
electron LINAC, a similar assembly for epithermal neutrons has been developed.
The project is based on an Elekta 18 MV LINAC coupled with a
photoconverter-moderator system which deploys the ({\gamma},n) photonuclear
reaction to convert a bremsstrahlung photon beam into a neutron field. This
communication describes the development of novel diagnostics to qualify the
thermal and epithermal neutron fields that have been produced. In particular, a
proof of concept for the use of silicon carbide photodiodes as a thermal
neutron rate detector is presented.Comment: 10 pages, 10 figures, accepted for publication to JINST on the 17th
April 202
The Pearson-Readhead Survey of Compact Extragalactic Radio Sources From Space. II. Analysis of Source Properties
We have performed a multi-dimensional correlation analysis on the observed
properties of a statistically complete core-selected sample of compact
radio-loud active galactic nuclei, based on data from the VLBI Space Observing
Programme (Paper I) and previously published studies. Our sample is drawn from
the well-studied Pearson-Readhead (PR) survey, and is ideally suited for
investigating the general effects of relativistic beaming in compact radio
sources. In addition to confirming many previously known correlations, we have
discovered several new trends that lend additional support to the beaming
model. These trends suggest that the most highly beamed sources in
core-selected samples tend to have a) high optical polarizations; b) large
pc/kpc-scale jet misalignments; c) prominent VLBI core components; d)
one-sided, core, or halo radio morphology on kiloparsec scales; e) narrow
emission line equivalent widths; and f) a strong tendency for intraday
variability at radio wavelengths. We have used higher resolution space and
ground-based VLBI maps to confirm the bi-modality of the jet misalignment
distribution for the PR survey, and find that the sources with aligned parsec-
and kiloparsec-scale jets generally have arcsecond-scale radio emission on both
sides of the core. The aligned sources also have broader emission line widths.
We find evidence that the BL Lacertae objects in the PR survey are all highly
beamed, and have very similar properties to the high-optically polarized
quasars, with the exception of smaller redshifts. A cluster analysis on our
data shows that after partialing out the effects of redshift, the luminosities
of our sample objects in various wave bands are generally well-correlated with
each other, but not with other source properties.Comment: 21 pages, 10 figures. Accepted for publication in the Astrophysical
Journal. Part I can be found at astro-ph/010227
Modeling nuclei of radio galaxies from VLBI radio observations. Application to the BL Lac Object S5 1803+784
We present a new method to fit the variations of both coordinates of a VLBI
component as a function of time, assuming that the nucleus of the radio source
contains a binary black hole system (BBH system). The presence of a BBH system
produces 2 perturbations of the trajectory of the ejected VLBI components. By
using only the VLBI coordinates, the problem we have to solve reduces to an
astrometric problem. Knowledge of the variations of the VLBI coordinates as a
function of time contains the kinematical information, thus we are able to
deduce the inclination angle of the source and the bulk Lorentz factor of the
ejected component. Generally, there is a family of the BBH system producing the
same fit to our data. To illustrate this method, we apply it to the source
1807+784. We find that the inclination of the source is i = 5.8+-1.8 degrees
and the VLBI component is ejected with a bulk Lorentz factor of 3.7+-0.3. We
determine the family of the BBH system which provides the best fit, assuming at
first that the masses of the 2 black holes are equal and then that the masses
are different. Each family of BBH systems is characterized by Tp/Tb~1.967,
where Tp and Tb are the precession period of the accretion disk of the black
hole ejecting the VLBI component and the orbiting period of the BBH system.Comment: 15 pages, 12 figure
Association of Systemic Lupus Erythematosus Clinical Features with European Population Genetic Substructure
Systemic Lupus Erythematosus (SLE) is an autoimmune disease with a very varied spectrum of clinical manifestations that could be partly determined by genetic factors. We aimed to determine the relationship between prevalence of 11 clinical features and age of disease onset with European population genetic substructure. Data from 1413 patients of European ancestry recruited in nine countries was tested for association with genotypes of top ancestry informative markers. This analysis was done with logistic regression between phenotypes and genotypes or principal components extracted from them. We used a genetic additive model and adjusted for gender and disease duration. Three clinical features showed association with ancestry informative markers: autoantibody production defined as immunologic disorder (Pâ=â6.8Ă10(-4)), oral ulcers (Pâ=â6.9Ă10(-4)) and photosensitivity (Pâ=â0.002). Immunologic disorder was associated with genotypes more common in Southern European ancestries, whereas the opposite trend was observed for photosensitivity. Oral ulcers were specifically more common in patients of Spanish and Portuguese self-reported ancestry. These results should be taken into account in future research and suggest new hypotheses and possible underlying mechanisms to be investigated. A first hypothesis linking photosensitivity with variation in skin pigmentation is suggested
WEBT and XMM-Newton observations of 3C 454.3 during the post-outburst phase. Detection of the little and big blue bumps
The blazar 3C 454.3 underwent an unprecedented optical outburst in spring
2005. This was first followed by a mm and then by a cm radio outburst, which
peaked in February 2006. We report on follow-up observations by the WEBT to
study the multiwavelength emission in the post-outburst phase. XMM-Newton
observations on July and December 2006 added information on the X-ray and UV
fluxes. The source was in a faint state. The radio flux at the higher
frequencies showed a fast decreasing trend, which represents the tail of the
big radio outburst. It was followed by a quiescent state, common at all radio
frequencies. In contrast, moderate activity characterized the NIR and optical
light curves, with a progressive increase of the variability amplitude with
increasing wavelength. We ascribe this redder-when-brighter behaviour to the
presence of a "little blue bump" due to line emission from the broad line
region, which is clearly visible in the source SED during faint states.
Moreover, the data from the XMM-Newton OM reveal a rise of the SED in the UV,
suggesting the existence of a "big blue bump" due to thermal emission from the
accretion disc. The X-ray spectra are well fitted with a power-law model with
photoelectric absorption, possibly larger than the Galactic one. However, the
comparison with previous X-ray observations would imply that the amount of
absorbing matter is variable. Alternatively, the intrinsic X-ray spectrum
presents a curvature, which may depend on the X-ray brightness. In this case,
two scenarios are possible.Comment: 9 pages, 7 figures, accepted for publication in A&
Highlights from the Pierre Auger Observatory
The Pierre Auger Observatory is the world's largest cosmic ray observatory.
Our current exposure reaches nearly 40,000 km str and provides us with an
unprecedented quality data set. The performance and stability of the detectors
and their enhancements are described. Data analyses have led to a number of
major breakthroughs. Among these we discuss the energy spectrum and the
searches for large-scale anisotropies. We present analyses of our X
data and show how it can be interpreted in terms of mass composition. We also
describe some new analyses that extract mass sensitive parameters from the 100%
duty cycle SD data. A coherent interpretation of all these recent results opens
new directions. The consequences regarding the cosmic ray composition and the
properties of UHECR sources are briefly discussed.Comment: 9 pages, 12 figures, talk given at the 33rd International Cosmic Ray
Conference, Rio de Janeiro 201
Lysine pathway metabolites and the risk of type 2 diabetes and cardiovascular disease in the PREDIMED study: results from two case-cohort studies
Background: The pandemic of cardiovascular disease (CVD) and type 2 diabetes (T2D) requires the identifcation
of new predictor biomarkers. Biomarkers potentially modifable with lifestyle changes deserve a special interest. Our
aims were to analyze: (a) The associations of lysine, 2-aminoadipic acid (2-AAA) or pipecolic acid with the risk of T2D
or CVD in the PREDIMED trial; (b) the efect of the dietary intervention on 1-year changes in these metabolites, and (c)
whether the Mediterranean diet (MedDiet) interventions can modify the efects of these metabolites on CVD or T2D
risk.
Methods: Two unstratifed case-cohort studies nested within the PREDIMED trial were used. For CVD analyses, we
selected 696 non-cases and 221 incident CVD cases; for T2D, we included 610 non-cases and 243 type 2 diabetes
incident cases. Metabolites were quantifed using liquid chromatographyâtandem mass spectrometry, at baseline and
after 1-year of intervention.
Results: In weighted Cox regression models, we found that baseline lysine (HR+1 SD increase=1.26; 95% CI 1.06â1.51)
and 2-AAA (HR+1 SD increase=1.28; 95% CI 1.05â1.55) were both associated with a higher risk of T2D, but not with CVD.
A signifcant interaction (p=0.032) between baseline lysine and T2D on the risk of CVD was observed: subjects with
prevalent T2D and high levels of lysine exhibited the highest risk of CVD. The intervention with MedDiet did not have
a signifcant efect on 1-year changes of the metabolites.
Conclusions: Our results provide an independent prospective replication of the association of 2-AAA with future
risk of T2D. We show an association of lysine with subsequent CVD risk, which is apparently diabetes-dependent. No
evidence of efects of MedDiet intervention on lysine, 2-AAA or pipecolic acid changes was found
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