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

Expeditious Calibration Method for Quantification of Odorous Mixtures via GC

An odour sample is generally a complex matrix consisting of numerous molecules (mostly volatile organic compounds, VOCs) chemically different from each other, and which can be perceived by the human nose. In order to chemically characterize this complex gaseous matrix, gas-chromatography (GC) is commonly used. By this analytical technique, it is possible to obtain the resolution of odour gaseous mixtures in order to qualify and quantify the compounds. However, the quantification is a tricky operation based on the comparison of the sample under examination with purpose-made gas mixtures containing a compound, chosen as a standard, at known concentration. Commonly, these mixtures are obtained from cylinders of compressed gases, the use of which involves problems relating to their management, thermodynamic equilibrium feasibility, considerable economic outlay and not-negligible procurement times. This paper describes a method, proposed as a versatile and simple alternative to the use of such cylinders, for preparing gaseous calibration standards at known concentration. The method involves the continuous injection of VOC in liquid form, by means of a syringe pump, into a stream of neutral gas, such as air or nitrogen, which acts as diluent gas, controlled by a mass flow meter. Exploiting the volatility of the compounds used, it is possible to generate a continuous gas stream, exiting the system, containing the selected VOC at the desired concentration, which can be directly used as calibration standard

Analysis of Odorous VOCs using TD-GC-MS/FID/PFPD: Development and Applications to Real Samples

This work aims to present the applicability of a gas chromatograph equipped with three detectors for the analysis of odorous mixtures. An Agilent gas chromatograph (mod. 8890), equipped with a mass spectrometer (Agilent 5977B MSD), a Flame Ionization Detector (FID, Agilent) and a Pulsed Flame Photometric Detector (PFPD, OI Analytical mod. 5833) was adopted, obtaining simultaneous acquisition with MS, FID and PFPD detectors. The splitting of the sample into the three detectors was carried out at the end of the chromatographic column, by a capillary flow technology splitter (Agilent Splitter CFT). By using this system, it is, therefore, possible to achieve the specific detection and quantification of organic compounds by FID analysis, sulphur compounds by PFPD and the identification of the compounds by MS analysis, via comparison with mass spectra. Based on the preliminary outcomes obtained,the application of this system in the analysis of odour samples enabled the determination of specific classes, even in traces: by this, the subsequent identification of these compounds during a single chromatographic run is possible. This combination provides significant time and costs savings in the calibration and analysis of chromatographic data

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