Probabilistic evaluation of n traces with no putative source: A likelihood ratio based approach in an investigative framework

Analysis of marks recovered from different crime scenes can be useful to detect a linkage between criminal cases, even though a putative source for the recovered traces is not available. This particular circumstance is often encountered in the early stage of investigations and thus, the evaluation of evidence association may provide useful information for the investigators. This association is evaluated here from a probabilistic point of view: a likelihood ratio based approach is suggested in order to quantify the strength of the evidence of trace association in the light of two mutually exclusive propositions, namely that the n traces come from a common source or from an unspecified number of sources. To deal with this kind of problem, probabilistic graphical models are used, in form of Bayesian networks and object-oriented Bayesian networks, allowing users to intuitively handle with uncertainty related to the inferential problem

Reconnection-driven particle acceleration in relativistic shear flows

Particle energization in shear flows is invoked to explain non-thermal emission from the boundaries of relativistic astrophysical jets. Yet, the physics of particle injection, i.e., the mechanism that allows thermal particles to participate in shear-driven acceleration, remains unknown. With particle-in-cell simulations, we study the development of Kelvin-Helmholtz (KH) instabilities seeded by the velocity shear between a relativistic magnetically-dominated electron-positron jet and a weakly magnetized electron-ion ambient plasma. We show that, in their nonlinear stages, KH vortices generate kinetic-scale reconnection layers, which efficiently energize the jet particles, thus providing a first-principles mechanism for particle injection into shear-driven acceleration. Our work lends support to spine-sheath models of jet emission - with a fast core/spine surrounded by a slower sheath - and can explain the origin of radio-emitting electrons at the boundaries of relativistic jets.Comment: 8 pages, 6 figures, 1 appendi

First optical validation of a Schwarzschild Couder telescope: the ASTRI SST-2M Cherenkov telescope

The Cherenkov Telescope Array (CTA) represents the most advanced facility designed for Cherenkov Astronomy. ASTRI SST-2M has been developed as a demonstrator for the Small Size Telescope in the context of the upcoming CTA. Its main innovation consists in the optical layout which implements the Schwarzschild-Couder configuration and is fully validated for the first time. The ASTRI SST-2M optical system represents the first qualified example for two mirrors telescope for Cherenkov Astronomy. This configuration permits to (i) maintain a high optical quality across a large FoV (ii) de-magnify the plate scale, (iii) exploit new technological solutions for focal plane sensors. The goal of the paper is to present the optical qualification of the ASTRI SST-2M telescope. The qualification has been obtained measuring the PSF sizes generated in the focal plane at various distance from the optical axis. These values have been compared with the performances expected by design. After an introduction on the Gamma Astronomy from the ground, the optical design and how it has been implemented for ASTRI SST-2M is discussed. Moreover the description of the setup used to qualify the telescope over the full field of view is shown. We report the results of the first--light optical qualification. The required specification of a flat PSF of $\sim 10$ arcmin in a large field of view ~10 deg has been demonstrated. These results validate the design specifications, opening a new scenario for Cherenkov Gamma ray Astronomy and, in particular, for the detection of high energy (5 - 300 TeV) gamma rays and wide-field observations with CTA.Comment: 6 pages, 5 figure

Spectral Index of the Diffuse Radio Background Measured From 100 to 200 MHz

The mean absolute brightness temperature of the diffuse radio background was measured as a function of frequency in a continuous band between 100 and 200 MHz over an effective solid angle of ~pi str at high Galactic latitude. A spectral brightness temperature index of beta = 2.5 +/- 0.1 (alpha_s = 0.5) was derived from the observations, where the error limits are 3-sigma and include estimates of the instrumental systematics. Zenith drift scans with central declinations of -26.5 degrees and spanning right ascensions 0 to 10 hours yielded little variation in the mean spectral index. The mean absolute brightness temperature at 150 MHz was found to reach a minimum of T = 237 +/- 10 K at a right ascension of 2.5 hours. Combining these measurements with those of Haslam et al. 1982 yields a spectral index of beta = 2.52 +/- 0.04 between 150 and 408 MHz.Comment: 8 pages including 7 figures and 4 tables. Accepted by A

Particle Acceleration in Pulsar Wind Nebulae: PIC modelling

We discuss the role of particle-in-cell (PIC) simulations in unveiling the origin of the emitting particles in PWNe. After describing the basics of the PIC technique, we summarize its implications for the quiescent and the flaring emission of the Crab Nebula, as a prototype of PWNe. A consensus seems to be emerging that, in addition to the standard scenario of particle acceleration via the Fermi process at the termination shock of the pulsar wind, magnetic reconnection in the wind, at the termination shock and in the Nebula plays a major role in powering the multi-wavelength signatures of PWNe.Comment: 32 pages, 16 figures, to appear in the book "Modelling Nebulae" edited by D. Torres for Springer, based on the invited contributions to the workshop held in Sant Cugat (Barcelona), June 14-17, 201

Sulphur Compounds: Comparison of Different Sorbent Tubes for their Detection

Different techniques have been developed for the analysis of gaseous sulphur pollutants, to maximize the analytical signals. In a complex matrix, such as odorous emissions, the detection of sulphur compounds can be critical in GC analysis, due to the lower concentration of these pollutants and the disturbing effect of co-eluting hydrocarbons. However, their detection is fundamental because they have a non-negligible odour impact. In the field of gaseous emissions analytics, it is common to use sorbent tubes for the sampling step. This technology uses different adsorbent materials, with different selectivity depending on the nature of the gas to be analysed. This work aims to evaluate the ability of three different sorbent tubes to collect different sulphur compounds, belonging to the classes of mercaptans, thioethers and aromatic heterocyclic compounds. A standard solution of 10 sulphur compounds was prepared by diluting in methanol 50 µL of each liquid standard into a 10 mL flask. Subsequently, this solution was diluted in methanol to obtain sulphur standards at five different concentrations (approximately 5-500 ng/µL). The tubes were loaded with the standard solutions with an aliquot of each solution, using a gas chromatograph packed column injector and subsequently analysed by TD-GC-MS. By the results obtained - average Response Factor (RF) and its Relative Standard Deviation (% RSD), it is possible to conduct a comparison among these tubes and evaluate their performance. From the comparison of the tubes, discussing % RSD, it is possible to highlight a slightly better performance, in terms of the number of compounds with % RSD ≤ 30%, for tubes specific for sulphur compounds. Focusing on RF values, multi-sorbent bed tubes show slightly higher RFs for very volatile sulphur compounds, but Sulphur tubes present higher RF values for 6 compounds out of 10 compounds considered. The performance of Tenax TA tubes, instead, appears strictly correlated with the compound’s volatility and therefore they don’t appear useful for sorption of very volatile compounds