12,753 research outputs found
How isotropic can the UHECR flux be?
Modern observatories of ultra-high energy cosmic rays (UHECR) have collected
over 10^4 events with energies above 10 EeV, whose arrival directions appear to
be nearly isotropically distributed. On the other hand, the distribution of
matter in the nearby Universe -- and, therefore, presumably also that of UHECR
sources -- is not homogeneous. This is expected to leave an imprint on the
angular distribution of UHECR arrival directions, though deflections by cosmic
magnetic fields can confound the picture. In this work, we investigate
quantitatively this apparent inconsistency. To this end we study observables
sensitive to UHECR source inhomogeneities but robust to uncertainties on
magnetic fields and the UHECR mass composition. We show, in a rather
model-independent way, that if the source distribution tracks the overall
matter distribution, the arrival directions at energies above 30 EeV should
exhibit a sizeable dipole and quadrupole anisotropy, detectable by UHECR
observatories in the very near future. Were it not the case, one would have to
seriously reconsider the present understanding of cosmic magnetic fields and/or
the UHECR composition. Also, we show that the lack of a strong quadrupole
moment above 10 EeV in the current data already disfavours a pure proton
composition, and that in the very near future measurements of the dipole and
quadrupole moment above 60 EeV will be able to provide evidence about the UHECR
mass composition at those energies.Comment: 9 pages, 8 figures; accepted versio
Non-Commutative Geometry and Twisted Conformal Symmetry
The twist-deformed conformal algebra is constructed as a Hopf algebra with
twisted co-product. This allows for the definition of conformal symmetry in a
non-commutative background geometry. The twisted co-product is reviewed for the
Poincar\'e algebra and the construction is then extended to the full conformal
algebra. It is demonstrated that conformal invariance need not be viewed as
incompatible with non-commutative geometry; the non-commutativity of the
coordinates appears as a consequence of the twisting, as has been shown in the
literature in the case of the twisted Poincar\'e algebra.Comment: 8 pages; REVTeX; V2: Reference adde
Education and Skills Mismatch in the Italian Graduate Labour Market
This paper focuses on education and skills mismatch amongst Italian graduates. Indicators for over and under-utilisation of education and under-utilisation of skills are included in a grouped data lognormal wage equation, allowing us to test a number of theories which could explain the effect of over-schooling on wages. We find little evidence to support assignment theory and also identify a relatively weak wage effect arising from educational mismatch associated with the formal requirements of a job, when compared to that associated with an employeeÕs perception of the job requirements. Our interpretation is that employers may be mis-specifying jobs as ÔgraduateÕ jobs in order to take advantage of an excess supply of graduates.over-education, skill under-utilisation, wages, on-the-job search
Energy-Aware Wireless Relay Selection in Load-Coupled OFDMA Cellular Networks
We investigate transmission energy minimization via optimizing wireless relay
selection in orthogonal-frequency-division multiple access (OFDMA) networks. We
take into account the impact of the load of cells on transmission energy. We
prove the NP-hardness of the energy-aware wireless relay selection problem. To
tackle the computational complexity, a partial optimality condition is derived
for providing insights in respect of designing an effective and efficient
algorithm. Numerical results show that the resulting algorithm achieves high
energy performance.Comment: 4 pages, 2 figure
In vivo therapeutic efficacy of frog skin-derived peptides against Pseudomonas aeruginosa-induced pulmonary infection
Pseudomonas aeruginosa is an opportunistic and frequently drug-resistant pulmonary pathogen especially in cystic fibrosis sufferers. Recently, the frog skin-derived antimicrobial peptide (AMP) Esc(1-21) and its diastereomer Esc(1-21)-1c were found to possess potent in vitro antipseudomonal activity. Here, they were first shown to preserve the barrier integrity of airway epithelial cells better than the human AMP LL-37. Furthermore, Esc(1-21)-1c was more efficacious than Esc(1-21) and LL-37 in protecting host from pulmonary bacterial infection after a single intra-tracheal instillation at a very low dosage of 0.1 mg/kg. The protection was evidenced by 2-log reduction of lung bacterial burden and was accompanied by less leukocytes recruitment and attenuated inflammatory response. In addition, the diastereomer was more efficient in reducing the systemic dissemination of bacterial cells. Importantly, in contrast to what reported for other AMPs, the peptide was administered at 2 hours after bacterial challenge to better reflect the real life infectious conditions. To the best of our knowledge, this is also the first study investigating the effect of AMPs on airway-epithelia associated genes upon administration to infected lungs. Overall, our data highly support advanced preclinical studies for the development of Esc(1-21)-1c as an efficacious therapeutic alternative against pulmonary P. aeruginosa infection
- …