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Unravelling Resistive Switching Mechanism in ZnO NW Arrays: The Role of the Polycrystalline Base Layer
No full textThe physical mechanism involved in resistive switching phenomena occurring in devices based on ZnO nanowire (NW) arrays may vary considerably, also depending on the structure of the switching layer. In particular, it is shown here that the formation of a ZnO base layer between the metallic catalyst substrate and the NW, which is typical of CVD-grown ZnO NW arrays, should not be neglected when explaining the switching physical mechanism. The structural and electrical properties of this layer are investigated after the mechanical removal of NWs. Electrical measurements were performed in the presence of NWs and, after their removal, showed that the base alone exhibits resistive switching properties. The proposed switching mechanism is based on the creation/rupture of an oxygen vacancies conductive path along grain boundaries of the polycrystalline base. The creation of the filament is facilitated by the high concentration of vacancies at the grain boundaries that are oriented perpendicularly to the electrodes, as a direct consequence of the ZnO growth along the c-axis of the wurtzite lattice
Checking the consistency of the solution in ordinal semi-democratic decision making problems
No full textAn interesting decision-making problem is that of aggregating multi-agent preference orderings into a consensus ordering, in the case the agents' importance is expressed in the form of a rank-ordering. Due to the specificity of the problem, the scientific literature encompasses a relatively small number of aggregation techniques. For the aggregation to be effective, it is important that the consensus ordering well reflects the input data, i.e., the agents' preference orderings and importance rank-ordering. The aim of this paper is introducing a new quantitative tool - represented by the so-called p indicators - which allows to check the degree of consistency between consensus ordering and input data, from several perspectives. This tool is independent from the aggregation technique in use and applicable to a wide variety of practical contexts, e.g., problems in which preference orderings include omissions and/or incomparabilities between some alternatives. Also, the p indicators are simple, intuitive and practical for comparing the results obtained from different techniques. The description is supported by various application examples
Full-core coupled neutronic/thermal-hydraulic modelling of the EBR-II SHRT-45R transient
No full textDuring the last decade the European activities in the field of nuclear fission research include the design of fast reactors cooled by liquid metals. Within this framework, the Fast REactor NEutronics/Thermal-hydraulICs (FRENETIC) code is being developed at Politecnico di Torino over the last few years. It implements a full-core coupled neutronic/thermalhydraulic model of a liquid-metal-cooled fast reactor as relevant for two of the six options currently under study within the framework of the Generation-IV International Forum, namely the lead-cooled fast reactors and the sodium-cooled fast reactors. The code validation process involves the participation in a coordinated research project of the International Atomic Energy Agency, aiming at testing different computational tools against the shutdown heat removal tests performed many years ago in the sodium-cooled Experimental Breeder Reactor-II (EBR-II) at Argonne National Laboratory, USA. In this paper, results of the FRENETIC analysis of one of the transients considered in the project, the unprotected EBR-II shutdown heat removal test SHRT-45R, are presented and compared to the measurements, providing the first validation of the coupled neutronic/thermal-hydraulic features of the FRENETIC code
Analysis of laminated composites and sandwich structures by trigonometric, exponential and miscellaneous polynomials and a MITC9 plate element
No full textComparison of ITRF2014 station coordinate input time series of DORIS, VLBI and GNSS
No full textIn this paper station coordinate time series from three space geodesy techniques that have contributed to the realization of the International Terrestrial Reference Frame 2014 (ITRF2014) are compared. In particular the height component time series extracted from official combined intra-technique solutions submitted for ITRF2014 by DORIS, VLBI and GNSS Combination Centers have been investigated. The main goal of this study is to assess the level of agreement among these three space geodetic techniques. A novel analytic method, modeling time series as discrete-time Markov processes, is presented and applied to the compared time series. The analysis method has proven to be particularly suited to obtain quasi-cyclostationary residuals which are an important property to carry out a reliable harmonic analysis. We looked for common signatures among the three techniques. Frequencies and amplitudes of the detected signals have been reported along with their percentage of incidence. Our comparison shows that two of the estimated signals, having one-year and 14 days periods, are common to all the techniques. Different hypotheses on the nature of the signal having a period of 14 days are presented. As a final check we have compared the estimated velocities and their Standard Deviations (STD) for the sites that co-located the VLBI, GNSS and DORIS stations, obtaining a good agreement among the three techniques both in the horizontal (1.0 mm/yr mean STD) and in the vertical (0.7 mm/yr mean STD) component, although some sites show larger STDs, mainly due to lack of data, different data spans or noisy observation
The effect of heavy tars (toluene and naphthalene) on the electrochemical performance of an anode-supported SOFC running on bio-syngas
No full textThe effect of heavy tar compounds on the performance of a Ni-YSZ anode supported solid oxide fuel cell was investigated. Both toluene and naphthalene were chosen as model compounds and tested separately with a simulated bio-syngas. Notably, the effect of naphthalene is almost negligible with pure H2 feed to the SOFC, whereas a severe degradation is observed when using a bio-syngas with an H2:CO = 1. The tar compound showed to have a remarkable effect on the inhibition of the WGS shift-reaction, possibly also on the CO direct electro-oxidation at the three-phase-boundary. An interaction through adsorption of naphthalene on nickel catalytic and electrocatalytic active sites is a plausible explanation for observed degradation and strong performance loss. Different sites seem to be involved for H2 and CO electro-oxidation and also with regard to catalytic water gas shift reaction. Finally, heavy tars (C ≥ 10) must be regarded as a poison more than a fuel for SOFC applications, contrarily to lighter compounds such benzene or toluene that can directly reformed within the anode electrode. The presence of naphthalene strongly increases the risk of anode re-oxidation in a syngas stream as CO conversion to H2 is inhibited and also CH4 conversion is blocked
Hierarchical theories of structures based on Legendre polynomial expansions with finite element applications
No full textFormal verification of LTE-UMTS and LTE-LTE handover procedures
No full textAbstract Long Term Evolution (LTE) is the most recent standard in mobile communications, introduced by 3rd Generation Partnership Project (3GPP). Most of the works in literature about LTE security analyze authentication procedures, while handover procedures are far less considered. This paper focuses on the procedures that are activated when a mobile device moves between different LTE cells and between LTE and the older Universal Mobile Telecommunications System (UMTS) networks and completes previous results with a deeper formal analysis of these procedures. The analysis shows that security properties (secrecy of keys, including backward/forward secrecy, immunity from off-line guessing attacks, and network components authentication) hold almost as expected in nominal conditions, i.e. when all backhaul links are secured and all backhaul nodes are trusted. The paper also analyses how these security properties are affected by possible anomalous situations, such as a compromised backhaul node or a misconfiguration by which a backhaul link becomes not protected and can be accessed by an attacker. The analysis shows that some security properties hold even in these adverse cases while other properties are compromised
PLA and P3HB-3HH-based bio-composites made with cotton fabric
No full textComposite panels were produced using film stacking procedure: a dry layer of fabric and two layers of matrix were piled up alternately and compression molded. The matrices used were PLA or PHB and the fabric was a cotton twill fabric without any chemical pre-treatment or treated with an epoxy functional oligomeric acrylic polymer (J). The PLA-based composite had clearly better mechanical properties than the pure matrix, namely +75%, +39% and +45% for elastic modulus, elongation at break and tensile strength, respectively. The PHB gave dramatic results reaching increases of +103%, +83%,+104% of the same three parameters. The J additive employed in the PLA gave no substantial changes but reduced the elongation at break. The same J additive in the PHB-based composite apparently increased the adeshion between matrix and fabric, showing an modulus and strenght increase with a reduction of elongation at break
PVInGrid: A Distributed Infrastructure for evaluating the integration of Photovoltaic systems in Smart Grid
No full textPlanning and developing the future Smart City is becoming mandatory due to the need of moving forward to a more sustainable society. To foster this transition an accurate simulation of energy production from renewable sources, such as Photovoltaic Panels (PV), is necessary to evaluate the impact on the grid. In this paper, we present a distributed infrastructure that simulates the PV production and evaluates the integration of such systems in the grid considering data provided by smart-meters. The proposed solution is able to model the behaviour of PV systems solution exploiting GIS representation of rooftops and real meteorological data. Finally, such information is used to feed a real-time distribution network simulator