11,427 research outputs found
High-energy -ray emission from GRBs
GRBs are nowadays a rather well understood phenomenon in the soft (KeV-MeV)
-ray energy band, while only a few GRBs have been observed at high
photon energies (E_{\gamma} \ut > 1 GeV). It is also widely recognized that
GRBs accelerate protons to relativistic energies and that dense media are often
present nearby the sources. Within this framework we compute in detail the
high-energy -ray flux from the decay of neutral pions produced through
the interaction of accelerate protons with nucleons in the surrounding medium.
We also take into account the local and intergalactic -ray absorption.
The presence of magnetic fields around the GRB sources causes the deflection of
the accelerated protons and so a temporal spread of the produced high-energy
-rays with respect to the signal in the soft -ray band.
Moreover, we analyze the possibility to detect the -ray signal in the
GeV-TeV energy range by the ARGO detector under construction in Tibet.Comment: 9 pages, 7 figures, abstract shortened, to appear in Astronomy and
Astrophysic
Mass Accretion Processes in Young Stellar Objects: Role of Intense Flaring Activity
According to the magnetospheric accretion scenario, young low-mass stars are
surrounded by circumstellar disks which they interact with through accretion of
mass. The accretion builds up the star to its final mass and is also believed
to power the mass outflows, which may in turn have a significant role in
removing the excess angular momentum from the star-disk system. Although the
process of mass accretion is a critical aspect of star formation, some of its
mechanisms are still to be fully understood. On the other hand, strong flaring
activity is a common feature of young stellar objects (YSOs). In the Sun, such
events give rise to perturbations of the interplanetary medium. Similar but
more energetic phenomena occur in YSOs and may influence the circumstellar
environment. In fact, a recent study has shown that an intense flaring activity
close to the disk may strongly perturb the stability of circumstellar disks,
thus inducing mass accretion episodes (Orlando et al. 2011). Here we review the
main results obtained in the field and the future perspectives.Comment: 4 pages, 2 Figures; accepted for publication on Acta Polytechnica
(Proceedings of the Frascati Workshop 2013
The X-ray cycle in the solar-type star HD 81809
(abridged) Our long-term XMM-Newton program of long-term monitoring of a
solar-like star with a well-studied chromospheric cycle, HD 81809 aims to study
whether an X-ray cycle is present, along with studying its characteristics and
its relation to the chromospheric cycle. Regular observations of HD 81809 were
performed with XMM-Newton, spaced by 6 months from 2001 to 2007. We studied the
variations in the resulting coronal luminosity and temperature, and compared
them with the chromospheric CaII variations. We also modeled the observations
in terms of a mixture of active regions, using a methodology originally
developed to study the solar corona. Our observations show a well-defined cycle
with an amplitude exceeding 1 dex and an average luminosity approximately one
order of magnitude higher than in the Sun. The behavior of the corona of HD
81809 can be modeled well in terms of varying coverage of solar-like active
regions, with a larger coverage than for the Sun, showing it to be compatible
with a simple extension of the solar case.Comment: In press, Astronomy & Astrophysic
Open Innovation, ambiguity and technological convergence
Objectives. Current paper aims to provide a fresh conceptual framework on the relationship among open innovation, decision ambiguity, and technological convergence. We argue that there is a curvilinear relationship between open innovation and both technological convergence and ambiguity. Contained level of convergence and ambiguity foster open innovation, whilst an excess of them is an impediment to collaboration. Technological convergence further acts as a moderator for ambiguity, in light of the benefits of isomorphism.
Methodology. We propose a conceptual framework for open innovation decisions after accurately reviewing the main literature antecedents.
Findings. We suggest an inverse u-shaped relationship between open innovation and either ambiguity or technological convergence.
Research limits. In future, the theoretical framework proposed by thus study has to be tested with robust and proper statistical techniques on large scale samples.
Practical implications. The model offers a heuristic for open innovation decisions under ambiguity.
Originality of the study. To the best of our knowledge, the relationship linking open innovation, technological convergence and ambiguity emerges as a literature gap. This study tackles this issue, proposing an interpretation for the analysis of alliances decision in innovation
Challenging times for insurance, banking and financial supervision in Saudi Arabia
The financial system in the Kingdom of Saudi Arabia (KSA) has a history of relative soundness, particularly in banking, due to comparatively strict and enforced domestic supervision, and supported by what has been for the most part a reasonably robust economy. However, the sector is facing challenges of a sluggish economy, need for reform and negative effects of the COVID-19 pandemic. This paper strives to assess how well the government thus far has responded to the challenges in the financial sector. The working hypothesis is that the insurance industry has improved its position, resulting in higher efficiency and profitability and lower risk. This is an industry historically plagued by too many players, financial issues and less than adequate controls. The analysis undertaken bears out the hypothesis, as revealed by the enhanced contribution made by the industry since the pandemic. Analysis suggests that strides have been made in that industry in terms of helping to diversify the economy with the onset of the pandemic. Moreover, evidence is provided that the sensitivity to changes in oil volumes (rather than to changes in oil prices) is a key risk factor for the financial sector in the KSA. These findings have implications for policy makers in terms of leveraging the pandemic conditions as an opportunity to drive further reform and diversify the economy with lower risk
Hydrodynamic modelling of ejecta shrapnel in the Vela supernova remnant
Many supernova remnants (SNRs) are characterized by a knotty ejecta
structure. The Vela SNR is an excellent example of remnant in which detached
clumps of ejecta are visible as X-ray emitting bullets that have been observed
and studied in great detail. We aim at modelling the evolution of ejecta
shrapnel in the Vela SNR, investigating the role of their initial parameters
(position and density) and addressing the effects of thermal conduction and
radiative losses. We performed a set of 2-D hydrodynamic simulations describing
the evolution of a density inhomogeneity in the ejecta profile. We explored
different initial setups. We found that the final position of the shrapnel is
very sensitive to its initial position within the ejecta, while the dependence
on the initial density contrast is weaker. Our model also shows that moderately
overdense knots can reproduce the detached features observed in the Vela SNR.
Efficient thermal conduction produces detectable effects by determining an
efficient mixing of the ejecta knot with the surrounding medium and shaping a
characteristic elongated morphology in the clump.Comment: Accepted for publication in Monthly Notices of the Royal Astronomical
Societ
KATRIN Sensitivity to Sterile Neutrino Mass in the Shadow of Lightest Neutrino Mass
The presence of light sterile neutrinos would strongly modify the energy
spectrum of the Tritium \beta-electrons. We perform an analysis of the KATRIN
experiment's sensitivity by scanning almost all the allowed region of neutrino
mass-squared difference and mixing angles of the 3+1 scenario. We consider the
effect of the unknown absolute mass scale of active neutrinos on the
sensitivity of KATRIN to the sterile neutrino mass. We show that after 3 years
of data-taking, the KATRIN experiment can be sensitive to mixing angles as
small as sin^2 (2\theta_s) ~ 10^-2. Particularly we show that for small mixing
angles, sin^2 (2\theta_s) < 0.1, the KATRIN experiment can gives the strongest
limit on active-sterile mass-squared difference.Comment: 4 pages, 2 figures, matches the published versio
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