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Digital radiographic imaging systems cover a wide range of clinical applications and can produce adequate image quality using a broad span of exposure levels. Over exposure may generate higher dose levels without an affective increasing of the images quality; thus experimental data analysis is an ongoing process useful to provide information about adequacy of radiation exposure. The main purpose of this work is the assessment of quality performance of digital radiographic systems by using objective image quality tests. To this aim, the influence of radiographic parameters has been investigated in order to reduce radiation dose to patients by assuring a good quality of the images.

DEMETRA, the 'DEMonstrator of Egnss services based on Time Reference Architecture', is an European Project funded by the European Union in the Horizon 2020 program. The main aim of the project was to develop and test a prototype of Time Service Provider based the European Global Navigation Satellite System (GNSS) providing innovative or improved time services based on different technologies and embedded in a modular architecture. The main innovative features are time certification, non-repudiation, integrity, reliability, resilience. The demonstrator has been developed and tested during the years 2015-2016. Nine different time services were developed and tested also in real environment at users premises. The paper reports the results of the experimental campaigns and the main lesson learned also by the trials with potential users.

During 2015-2016, a European Consortium of 15 partners from 8 different countries, developed the DEMETRA (DEMonstrator of EGNSS services based on Time Reference Architecture), a project funded by the European Union in the frame of the Horizon 2020 program. This project aims at developing and experimenting time dissemination services dedicated to specific users like traffic control, energy distribution, finance, telecommunication, and scientific institutions. Nine services have been developed. These services provide time dissemination with accuracy levels from millisecond to the sub-ns, and also additional services like certification, calibration, or integrity. Five of these services are based on the European GNSS. After a development phase (see PTTI 2016 presentation) the full DEMETRA system has been working during six months for demonstration. The paper will report about the experimentation results, showing performances and limits of the proposed time dissemination services, aiming to foster the exploitation of the European GNSS for timing applications.

The H2020 research project, DEMETRA (DEMonstrator of EGNSS services based on Time Reference Architecture) is funded by the European Union and aims to develop and test several time services based on the European Global Navigation Satellite System (GNSS) and introducing important new features such as certified time stamping, improved accuracy, or integrity, not yet provided by GNSS systems. The demonstrator has been successfully assembled at INRIM premises by the end of February 2016, and it will be tested with two validation test campaigns. The first closed loop test finished in May 2016, the first experimental results to validate the time services performances are here reported. The second test campaign will be conducted in a realistic case at user premises, to test the real advantages and feasibility of the proposed time services.

DEMETRA aims to be a prototype of an European time dissemination service, based on the timing signal of the European Galileo system, adding particular features like - among the others - certification, calibration, or integrity, that could be of interest to a wide range of users belonging to different sectors as traffic control, energy distribution, finance, telecommunication, and scientific institutions. Nine time dissemination services are proposed. The paper will report about the development status and the first experimentation results of the system, showing potentialities and limits of the proposed time dissemination services, aiming to foster the exploitation of the European GNSS for timing applications.

DEMETRA (DEMonstrator of EGNSS services based on Time Reference Architecture) is a project co-funded by the EU through the research and innovation programme 'Horizon 2020'. The DEMETRA project started in January 2015 and lasts 24 months. Based on the current practice of national metrological laboratories, identifying the additional necessities of the timing users, DEMETRA will define and develop a prototype of a European time disseminator, based on EGNSS. Nine different time services are proposed for demonstration by consortium partners. The DEMETRA partnership, including Scientific Institutions, GNSS Industries, and a Service Provider cover the different faces of the project, including an analysis of commercial potential in terms of market and business development.

The Fe related density of states of Cd 1−x Fe x Se has been investigated by means of synchrotron radiation photoemission. Energy distribution curves of the ternary compound Cd 1−x Fe x Se are presented and compared with those of the binary compound CdSe. Two Fe related structures are easily observed for all photon energies investigated (30 eV – 60 eV), whereas a third structure could be found only in the resonant photoemission region. An analysis of the costant initial state spectra suggests an atomic like interpretation of the experimental observations.

The room temperature (RT) formation of the interface between metals (Cr, Sn, Ag) and the SnO 2 surface was studied by Synchrotron Radiation induced UPS. The Sn4 d core level and the Valence Band were monitored as a function of metal growth starting from submonolayer regime. At low monolayer coverages a redox reaction with different rate and evolution depending on metal reactivity, arises between the Cr and Sn atoms and the SnO 2 surface, oxidizing the overlayer and reducing the Sn cation at the interface. Deposition of less reactive Ag film leaves the stoichiometry of the substrate unchanged. However, in this case as well as for Cr, at high metal coverage the metallic tin segregation is observed.

Tin oxide films were deposited by ArF excimer laser induced photolysis of Sn(CH3)4/O2 mixtures. The “in situ” Auger analysis was used to determine the effect of the gas-phase oxygen concentration on the film composition. The surface properties of the films were investigated by synchrotron radiation UV photoemission spectroscopy. To this aim samples were transferred to a synchrotron radiation facility, without any exposure to air and kept in dynamical high vacuum. The results obtained showed that the valence-band spectrum was characteristic for SnO2 and that the Sn 4d core peak did not have any contribution due to metallic tin. Furthermore, by tuning the synchrotron radiation photon energy, in order to vary the photoelectron escape depth, we got the indication that the oxygen vacancies responsible for the weak emission in the band-gap region were localized at the sample surface.

The composition of films deposited by dissociating pure tetramethyltin (TMT) or TMT/O2 mixtures at 193 nm, was monitored by ‘‘in situ’’ Auger spectroscopy. The presence of C contamination, which was considerable in films obtained from the pure organometallic, was greatly reduced by the occurrence of oxidation and carbon‐free films were achieved when the gas phase concentration of TMT was sufficiently small. The dependence of the O/Sn Auger electron spectroscopy peak‐to‐peak height ratio on the p(O2)/p(TMT) ratio in the precursor mixture showed a saturation for large concentration of oxygen. The surface properties of the tin oxide films were investigated by synchrotron radiation ultraviolet photoemission spectroscopy (UPS). To this aim samples were transferred to a synchrotron radiation facility, without any exposure to air and kept in dynamical high vacuum. The UPS demonstrated that the films were essentially made of SnO2: in fact the valence band exhibited the typical features of SnO2 and the analysis of...

By using the transfer matrix approach we exactly solve the quantum mechanical counterpart of the Langevin equation for a double barrier heterostructure (DBH) system containing scattering centers in the well, and we investigate the effect of scattering on the electron tunneling mechanism. From a model calculation, we show how the scattering affects the phase coherence of the carrier wave inside the quantum well. We consider both the elastic and inelastic collision processes in the well of the DBH. The linewidth in the tunneling transmission probability is related to: intrinsic resonant linewidth (due to the electron leaking out of the barrier), elastic collision broadening and inelastic broadening. The scattering effect also results in a peak shift. Moreover, we show that the presence of an elastic scattering center modifies the peak-to-valley ratio in the I–V characteristics: in particular we demonstrate that this ratio increases whenever a particular distribution of scattering center inside the well is present.

The room temperature oxidation of a tin metal foil up to O2 exposures of 8 × 1011 L (1 L = 10−6 Torr · s) has been studied by synchrotron radiation photoemission spectroscopy. Valence band (VB) and Sn 4d core level energy distribution curves (EDC have been measured at photon energies of 50 and 90 eV. It resulted that the oxide film formed on tin after oxygen chemisorbtion contained Sn2+ and Sn4+ with relative concentrations determined by the stage of the oxidation. The VB, that at 500 L of O2 had the characteristic profile of the SnO VB, showed at higher exposures the appearance of spectral features due to SnO2. The analysis of the Sn4d core levels allowed us to identify the presence of a chemical shift of 0.73 ± 0.05 eV between the Sn4+ and Sn2+ peaks. In fact the curves obtained by subtracting the metallic contribution due to the substrate from the Sn 4d peaks measured at increasing O2 exposure, appeared progressively shifted towards higher binding energies, because of the change in the composition of the oxide layer. Best fit curves of the previous peaks, deconvoluted using doublets of Gaussians for the Sn2+ and Sn4+ 4d 3 2 and 4d 5 2 spin orbit components, were used to evaluate the concentration of the two phases. Only the Sn2+ component was found by the fitting program in the peak observed at 500 L, whereas increasing concentrations of Sn4+ (up to 71% at 8 × 1011 L) showed up at heavier oxidation. Photoemission spectra, taken at different depths in the oxide layer, etched by low energy (200 eV) Ar+ sputtering, showed the presence of a composition gradient; SnO2 being an overlayer lying above a film containing mostly SnO. The thickness of the oxide film present on the tin foil dosed with 8 × 1011 L of oxygen was evaluated to be about 17 A.

A theoretical analysis of the resonant tunneling contribution and of the effect of scattering centers on current for structures like Schottky Barriers (SB), Metal-Oxide-Semiconductor junctions (MOS), and Double Barrier Heterostructures (DBH) is presented in terms of the transfer matrix and Airy functions uni-dimensional approaches. The scattering is simulated to arise from localized states, with δ-type potential, within the well or the barrier. We show how the scattering affects the phase coherence of the carrier wave inside the quantum well, and the electron tunneling mechanism through the barrier. In particular we evidence the opposite effects of elastic scattering centers: a decrease of the peak-to-valley ratio in the I-V characteristics of DBH if the centers are randomly distributed in spatial position, or a increase whenever a particular distribution inside the well or the barrier is present.

A theoretical analysis of the effect of scattering centers on tunneling current in amorphous (a-SiC:H/a-Si:H/a-SiC:H) double barrier heterostructures (DBH) is presented in terms of the transfer matrix and Airy function approaches. We consider one localized center in the well of the DBH and take into account the random distribution of its position by making configurational average. We use the δ-type function to describe the perturbation potential of the centers. In agreement with experimental observations, we find resonant peaks arising from quantized states in the well even in the case of the presence of scattering centers. The effect of scattering is to lower the transmission probability and to shift and broaden the peak of the resonant tunneling spectrum. For the I–V characteristics the effect of scattering is to shift the resonance shoulders.

In this paper we use the transfer matrix approach to investigate the effect of scattering in the well on resonant tunneling in double‐barrier heterostructures. We consider a double‐barrier heterostructure, in which there is a uniform distribution of scattering centers throughout the well, and use the δ‐type function to describe the perturbation potential of the centers. For simplicity, we only consider one dimension. From model calculations of the transmission probability of the system we find, in agreement with experimental observations, that resonant peaks arising from the quantized states in the well are always present, provided the concentration of the scattering centers is not too high. The effect of scattering is to lower the tunneling current and to shift and broaden the peak of the resonant tunneling spectrum.

A theoretical analysis of the effect of resonant tunneling via localized tail states on the photocurrent yield in Pd/hydrogenated amorphous silicon (a-Si:H) Schottky barriers is presented in terms of the transfer matrix approach. We use a single empty state with δ-type potential within the barrier. By adjusting the strength ( Ω 1 ) of the δ function, the barrier height θb and the position χ1 of the localized state, we fit the curves of the square root of the photocurrent yield as a function of photon energies for samples with different density of states in the gap. We find that the contribution of the resonant tunneling to the photocurrent yield is remarkable, in particular for the low photon energy region. It implies that the resonant tunneling effect is very important on the experimentally determined value of the barrier height.

In this work we use transfer matrix and Airy function approaches to investigate the distribution of carriers within thin SiO2 films containing localized states for Si/SiO2/Si structure in detail. We show that the distribution of the probability density ‖ψ‖2 within oxide films has a shape with, at first, a monotonically exponential decrease from the Si/SiO2 interface, then arriving at a valley, and followed by a peak at the center for the case of ‘‘off’’ resonance. When the carrier energy matches that of the eigenstate the probability density is exponentially decreased from the localized center on both sides. We show that there are two kinds of probability densities corresponding to resonant tunneling via a localized state within the barrier. On increasing the reverse applied field, the localization degree of the wave function decreases.

Recently an European Consortium of 15 partners from 7 different countries, started to work on a research project, DEMETRA (DEMonstrator of EGNSS services based on Time Reference Architecture), funded by the European Union in the frame of the Horizon 2020 program, aiming to develop and experiment time services based on the European Global Navigation Satellite System (GNSS). DEMETRA aims to be a prototype of an European time dissemination service, based on the timing signal of the European Galileo system, adding particular features like certification, calibration, or integrity, that could be of interest to some specific users like traffic control, energy distribution, finance, telecommunication, and scientific institutions.