5,736 research outputs found
Enabling the Autonomic Management of Federated Identity Providers
The autonomic management of federated authorization infrastructures (federations) is seen as a means for improving the monitoring and use of a service providerâs resources. However, federations are comprised of independent management domains with varying scopes of control and data ownership. The focus of this paper is on the autonomic management of federated identity providers by service providers located in other domains, when the identity providers have been diagnosed as the source of abuse. In particular, we describe how an autonomic controller, external to the domain of the identity provider, exercises control over the issuing of privilege attributes. The paper presents a conceptual design and implementation of an effector for an identity provider that is capable of enabling cross-domain autonomic management. The implementation of an effector for a SimpleSAMLphp identity provider is evaluated by demonstrating how an autonomic controller, together with the effector, is capable of responding to malicious abuse
Dual Screening the Political:Media Events, Social Media, and Citizen Engagement
Dual screeningâthe complex bundle of practices that involve integrating, and switching across and between, live broadcast media and social mediâis now routine for many citizens during important political media events. But do these practices shape political engagement, and if so, why? We devised a unique research design combining a large-scale Twitter dataset and a custom-built panel survey focusing on the broadcast party leadersâ debates held during the 2014 European Parliament elections in the United Kingdom. We find that relatively active, âlean-forwardâ practices, such as commenting live on social media as the debate unfolded, and engaging with conversations via Twitter hashtags, have the strongest and most consistent positive associations with political engagement
Majorana and the quasi-stationary states in Nuclear Physics
A complete theoretical model describing artificial disintegration of nuclei
by bombardment with alpha-particles, developed by Majorana as early as in 1930,
is discussed in detail alongside the basic experimental evidences that
motivated it. By following the quantum dynamics of a state resulting from the
superposition of a discrete state with a continuum one, whose interaction is
described by a given potential term, Majorana obtained (among the other
predictions) the explicit expression for the integrated cross section of the
nuclear process, which is the direct measurable quantity of interest in the
experiments. Though this is the first application of the concept of
quasi-stationary states to a Nuclear Physics problem, it seems also that the
unpublished Majorana's work anticipates by several years the related seminal
paper by Fano on Atomic Physics.Comment: latex, amsart, 13 page
Photohadronic modelling of the 2010 gamma-ray flare from Mrk 421
Blazars are a subclass of active galactic nuclei (AGNs) that have a relativistic jet with a small viewing angle towards the observer. Recent results based on hadronic scenarios have motivated an ongoing discussion of how a blazar can produce high energy neutrinos during a flaring state and which scenario can successfully describe the observed gamma-ray behaviour. Markarian 421 is one of the closest and brightest objects in the extragalactic gamma-ray sky and showed flaring activity over a 14-days period in 2010 March. In this work, we describe the performed analysis of Fermi-LAT data from the source focused on the MeV range (100 MeVâ1 GeV), and study the possibility of a contribution coming from the pÎł interactions between protons and MeV SSC target photons to fit the very high energy (VHE) gamma-ray emission. The fit results were compared with two leptonic models (one-zone and two-zone) using the Akaike Information Criteria (AIC) test, which evaluates goodness-of-fit alongside the simplicity of the model. In all cases, the photohadronic model was favoured as a better fit description in comparison to the one-zone leptonic model, and with respect to the two-zone model in the majority of cases. Our results show the potential of a photohadronic contribution to a lepto-hadronic origin of gamma-ray flux of blazars. Future gamma-ray observations above tens of TeV and below 100 MeV in energy will be crucial to test and discriminate between models
Characterization of an INVS Model IV Neutron Counter for High Precision () Cross-Section Measurements
A neutron counter designed for assay of radioactive materials has been
adapted for beam experiments at TUNL. The cylindrical geometry and 60% maximum
efficiency make it well suited for () cross-section measurements near
the neutron emission threshold. A high precision characterization of the
counter has been made using neutrons from several sources. Using a combination
of measurements and simulations, the absolute detection efficiency of the
neutron counter was determined to an accuracy of 3% in the neutron energy
range between 0.1 and 1 MeV. It is shown that this efficiency characterization
is generally valid for a wide range of targets.Comment: 22 pages, 13 figure
Role of the stage-regulated nucleoside transporter TbNT10 in differentiation and adenosine uptake in Trypanosoma brucei
Neutrinos from the pulsar wind nebulae
In the recent paper we calculated the -ray spectra from pulsar wind
nebulae (PWNe), assuming that a significant amount of the pulsar rotational
energy is converted into relativistic nuclei. These nuclei accelerate leptons
which are responsible for most of the observed electromagnetic emission from
PWNe. Small part of nuclei also interact with the matter of the supernova
producing -rays, which can also contribute to the observed spectra of
young nebulae. Here we calculate the spectra of neutrinos from the interaction
of nuclei inside the nebula and the expected neutrino event rates in the 1
km neutrino detector from: the Crab Nebula (PSR 0531+21), the Vela SNR (PSR
0833-45), G 343.1-2.3 (PSR 1706-44), MSH15-52 (PSR 1509-58), 3C58 (PSR
J0205+6449), and CTB80 (PSR 1951+32). It is shown that only the Crab Nebula can
produce the neutrino event rate above the sensitivity limit of the 1 km
neutrino detector, provided that nuclei take most of the rotational energy lost
by the pulsar. The neutrino event rate expected from the Vela SNR is comparable
to that from the Crab Nebula but these neutrinos are less energetic and emitted
from a much larger region on the sky. Therefore it may be difficult to subtract
the Vela SNR signal from the higher background of the atmospheric neutrinos.Comment: 7 pages, 3 figures, A&A style, accepted to A&
X-rays and Gamma-rays from Cataclysmic Variables: The example case of Intermediate Polar V1223 Sgr
The accretion of matter onto intermediate polar White Dwarfs (IPWDs) seems to
provide attractive conditions for acceleration of particles to high energies in
a strongly magnetized turbulent region at the accretion disk inner radius. We
consider possible acceleration of electrons and hadrons in such region and
investigate their high energy radiation processes. It is concluded that
accelerated electrons loose energy mainly on synchrotron process producing
non-thermal X-ray emission. On the other hand, accelerated hadrons are
convected onto the WD surface and interact with dense matter. As a result, high
energy -rays from decay of neutral pions and secondary leptons from
decay of charged pions appear. We show that GeV-TeV -rays can escape
from the vicinity of the WD. Secondary leptons produce synchrotron radiation in
the hard X-rays and soft -rays. As an example, we predict the X-ray and
-ray emission from IPWD V1223 Sgr. Depending on the spectral index of
injected particles, this high energy emission may be detected by the -LAT telescope and/or the future Cherenkov Telescope Array (CTA)
observatory.Comment: 16 pages, 1 figure, accepted to MNRA
TeV neutrinos and gamma rays from pulsars
Recent studies suggest that pulsars could be strong sources of TeV muon
neutrinos provided positive ions are accelerated by pulsar polar caps to PeV
energies. In such a situation muon neutrinos are produced through the delta
resonance in interactions of pulsar accelerated ions with its thermal radiation
field. High energy gamma rays also should be produced simultaneously in pulsar
environment as both charged and neutral pions are generated in the interactions
of energetic hadrons with the ambient photon fields. Here we estimate TeV gamma
ray flux at Earth from few nearby young pulsars. When compared with the
observations we find that proper consideration of the effect of polar cap
geometry in flux calculation is important. Incorporating such an effect we
obtain the (revised) event rates at Earth due to few potential nearby pulsars.
The results suggest that pulsars are unlikely to be detected by the upcoming
neutrino telescopes. We also estimate TeV gamma ray and neutrino fluxes from
pulsar nebulae for the adopted model of particle acceleration.Comment: Six pages, accepted in MNRA
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