High-energy γ\gamma-ray emission from GRBs

GRBs are nowadays a rather well understood phenomenon in the soft (KeV-MeV) $\gamma$-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 $\gamma$-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 $\gamma$-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 $\gamma$-rays with respect to the signal in the soft $\gamma$-ray band. Moreover, we analyze the possibility to detect the $\gamma$-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