Precision limits of the twin-beam multiband URSULA

URSULA is a multiband astronomical photoelectric photometer which minimizes errors introduced by the presence of the atmosphere. It operates with two identical channels, one for the star to be measured and the other for a reference star. After a technical description of the present version of the apparatus, some measurements of stellar sources of different brightness, and in different atmospheric conditions are presented. These measurements, based on observations made with the 91 cm Cassegrain telescope of the Catania Astrophysical Observatory, are used to check the photometer accuracy and compare its performance with that of standard photometers

Widespread abiotic methane in chromitites

Recurring discoveries of abiotic methane in gas seeps and springs in ophiolites and peridotite massifs worldwide raised the question of where, in which rocks, methane was generated. Answers will impact the theories on life origin related to serpentinization of ultramafic rocks, and the origin of methane on rocky planets. Here we document, through molecular and isotopic analyses of gas liberated by rock crushing, that among the several mafic and ultramafic rocks composing classic ophiolites in Greece, i.e., serpentinite, peridotite, chromitite, gabbro, rodingite and basalt, only chromitites, characterized by high concentrations of chromium and ruthenium, host considerable amounts of 13C-enriched methane, hydrogen and heavier hydrocarbons with inverse isotopic trend, which is typical of abiotic gas origin. Raman analyses are consistent with methane being occluded in widespread microfractures and porous serpentine- or chlorite-filled veins. Chromium and ruthenium may be key metal catalysts for methane production via Sabatier reaction. Chromitites may represent source rocks of abiotic methane on Earth and, potentially, on Mars

Bridge's vehicular loads characterization through Weight-In-Motion (WIM) systems. The case study of Brescia

The growing traffic flow and the increase in transported masses negatively affect infrastructural safety. Several authors have characterized traffic loads on bridges in the American and Chinese context using Weigh-in-Motion (WIM) systems. Conversely, very few studies have been carried out in Europe and, as far as the authors know, none in Italy. This study covers this gap by providing a statistical analysis of raw WIM data collected on a main bridge near the city of Brescia (Italy). First, the traffic flow and the characteristics of vehicles were gathered by a WIM device. Second, some descriptive statistics were performed by computing the probabilistic distributions of numerous vehicular attributes. Third, as a novelty element, a K-means based Clustering technique was adopted on a wide set of vehicular features to detect heavy vehicle clusters. The results showed the existence of three main clusters: two predominately composed by lightly overloaded ordinary vehicles and construction machinery, respectively, and one by mass exceptional vehicles. This study considers a broader set of vehicular parameters than previous ones and then, provides a deeper understanding. Moreover, it shows that axle mass limits violations are noteworthy among mass exceptional vehicles in Italy highlighting the need of improving weight enforcement. These knowledges will be crucial for a rational organisation of the existing assets

Warm Inflation, Neutrinos and Dark matter: a minimal extension of the Standard Model

We show that warm inflation can be realized within a minimal extension of the Standard Model with three right-handed neutrinos, three complex scalars and a gauged lepton/B-L U(1) symmetry. This simple model can address all the shortcomings of the Standard Model that are not related to fine-tuning, within general relativity, with distinctive experimental signatures that can be probed in the near future. The inflaton field emerges from the collective breaking of the U(1) symmetry, and interacts with two of the right-handed neutrinos, sustaining a high-temperature radiation bath during inflation. The discrete interchange symmetry of the model protects the scalar potential against large thermal corrections and leads to a stable inflaton remnant at late times which can account for dark matter. Consistency of the model and agreement with Cosmic Microwave Background observations naturally yield light neutrino masses below 0.1 eV, while thermal leptogenesis occurs naturally after a smooth exit from inflation into the radiation era.Comment: 43 pages (30 main + 13 appendices), 8 figures. Comments are welcom

The early evolution of Globular Clusters: the case of NGC 2808

Enhancement and spread of helium among globular cluster stars have been recently suggested as a way to explain the horizontal branch blue tails, in those clusters which show a primordial spread in the abundances of CNO and other elements involved in advanced CNO burning (D'Antona et al. 2002). In this paper we examine the implications of the hypothesis that, in many globular clusters, stars were born in two separate events: an initial burst (first generation), which gives origin to probably all high and intermediate mass stars and to a fraction of the cluster stars observed today, and a second, prolonged star formation phase (second generation) in which stars form directly from the ejecta of the intermediate mass stars of the first generation. In particular, we consider in detail the morphology of the horizontal branch in NGC 2808 and argue that it unveils the early cluster evolution, from the birth of the first star generation to the end of the second phase of star formation. This framework provides a feasible interpretation for the still unexplained dichotomy of NGC 2808 horizontal branch, attributing the lack of stars in the RR Lyr region to the gap in the helium content between the red clump, whose stars are considered to belong to the first stellar generation and have primordial helium, and the blue side of the horizontal branch, whose minimum helium content reflects the helium abundance in the smallest mass (~4Msun)contributing to the second stellar generation. This scenario provides constraints on the required Initial Mass Function, in a way that a great deal of remnant neutron stars and stellar mass black holes might have been produced.Comment: 23 pages, 7 figures, in press on The Astrophysical Journa

Seismic isolation of buildings using composite foundations based on metamaterials

Metamaterials can be engineered to interact with waves in entirely new ways, finding application on the nanoscale in various fields such as optics and acoustics. In addition, acoustic metamaterials can be used in large-scale experiments for filtering and manipulating seismic waves (seismic metamaterials). Here, we propose seismic isolation based on a device that combines some properties of seismic metamaterials (e.g., periodic mass-in-mass systems) with that of a standard foundation positioned right below the building for isolation purposes. The concepts on which this solution is based are the local resonance and a dual-stiffness structure that preserves large (small) rigidity for compression (shear) effects. In other words, this paper introduces a different approach to seismic isolation by using certain principles of seismic metamaterials. The experimental demonstrator tested on the laboratory scale exhibits a spectral bandgap that begins at 4.5 Hz. Within the bandgap, it filters more than 50% of the sei..

Electrical current-driven pinhole formation and insulator-metal transition in tunnel junctions

Current Induced Resistance Switching (CIS) was recently observed in thin tunnel junctions (TJs) with ferromagnetic (FM) electrodes and attributed to electromigration of metallic atoms in nanoconstrictions in the insulating barrier. The CIS effect is here studied in TJs with two thin (20 \AA) non-magnetic (NM) Ta electrodes inserted above and below the insulating barrier. We observe resistance (R) switching for positive applied electrical current (flowing from the bottom to the top lead), characterized by a continuous resistance decrease and associated with current-driven displacement of metallic ions from the bottom electrode into the barrier (thin barrier state). For negative currents, displaced ions return into their initial positions in the electrode and the electrical resistance gradually increases (thick barrier state). We measured the temperature (T) dependence of the electrical resistance of both thin- and thick-barrier states ($R_b$ and R$_B$ respectively). Experiments showed a weaker R(T) variation when the tunnel junction is in the $R_b$ state, associated with a smaller tunnel contribution. By applying large enough electrical currents we induced large irreversible R-decreases in the studied TJs, associated with barrier degradation. We then monitored the evolution of the R(T) dependence for different stages of barrier degradation. In particular, we observed a smooth transition from tunnel- to metallic-dominated transport. The initial degradation-stages are related to irreversible barrier thickness decreases (without the formation of pinholes). Only for later barrier degradation stages do we have the appearance of metallic paths between the two electrodes that, however, do not lead to metallic dominated transport for small enough pinhole radius.Comment: 10 pages, 3 figure

Comparing the vibrational behaviour of e-kick scooters and e-bikes: Evidence from Italy

E-kick scooters are currently among the most popular emerging electric-powered Personal micro–Mobility Vehicles (e-PMVs) and have recently been equated to e-bikes. However, even if the dynamic behaviour of e-bikes is well studied, much less has been done to understand the behaviour of e-kick scooters. Furthermore, comparisons between the two vehicles have rarely been investigated and only based on mechanical models. This study covers this gap by proposing a novel framework that evaluates the vibrational behaviours of both vehicles when driven by different users and exposed to the pavement irregularities, using both real and simulated data. The experimental data are collected equipping an e-kick scooter and an e-bike with Inertial Measurement Units, and then processed by ISO 2631–1 method to obtain an objective evaluation of the comfort. Next, the experimental data are expanded to include uncertainty applying a Monte Carlo Simulation based on a two-layer feed-forward Artificial Neural Network. Afterwards, several statistical analyses are performed to understand the key factors affecting the vibrational magnitude (and their extent) for each vehicle. This framework was tested in an Italian city (Brescia) along urban paths with five different pavement surfaces. The results showed that the e-kick scooter appears to be globally more solicited than the e-bike in terms of vibrational magnitude. Moreover, pavement surface, sensor position, user gender, user height, and travel speed are identified as crucial factors explaining the vibrational magnitude for both vehicles. The overall findings challenge the recent European regulations that equated e-kick scooters with bikes. These findings may help public administrations in planning the circulation of e-bikes and e-kick scooters in cities and recommend that manufacturers improve the e-kick scooter design by including shock absorbers to increase comfort

Berry connections calculated from first principles

Berry connections can be very useful for the determination of electronic properties of materials. Yet they are particularly difficult to calculate from first principles. The main problems in so calculating are the randomness of the wavefunction phase for different points in the reciprocal space that is given by numerical calculations and the band crossing at points of degeneracy. In this letter we show how this can be overcome and applied to the simple case of two dimensional semiconductor hexagonal boron nitride. To demonstrate the effectiveness of the process, we calculate the linear and second harmonic generation conductivities from the Berry connections obtained directly from density functional theory