Monolithic Bidirectional Switch Based on GaN Gate Injection Transistors

The paper deals with a bi-directional switch based on N-channel enhancement-mode GaN FET. The proposed device is a Gate Injection Transistor monolithic solution to reduce the volume of the switch with high current density and blocking voltage of 600V. It features a dual-gate control pin and two power terminal. In the paper, the main characteristics of the bi-directional switch and the performance in the four-quadrant of operation are examined and discussed. The device characteristics are compared with the traditional MOSFET and IGBT solutions. The gate driver design issues are considered to optimize the switching transient of the GaN-based switch. Finally, an experimental evaluation of the GaN FET as the bidirectional circuit breaker is carried out in an AC power supply system to validate the effectiveness of the proposed monolithic new device

Fibre Reinforced Geopolymers as Inorganic Strengthening Composites for Masonry Structures

The study presents an assessment of externally bonded Fibre-Reinforced GeoPolymers (FRGPs) as strengthening material for masonry structures. Thanks to their tailored chemical and mechanical characteristics, geopolymer matrices can fulfil the restoration criteria for Built Heritage (BH) with the benefit of heat-resistant performances better than those of organic and inorganic matrices used in Externally Bonded Fibre Reinforced Polymers (EB-FRP) and Fabric-Reinforced Cementitious Matrix (FRCM) materials, respectively. This work is built on the outcomes of a previous investigation that proved the suitability of the developed geopolymer matrix for applications on clay bricks, revealing a good adhesion to masonry substrates and to embedded reinforcements. The behaviour of three FRGPs, including either a bi-directional basalt mesh, a bi-directional carbon mesh or a unidirectional Ultra High Strength Steel (UHSS) fabric, was explored by means of local tests on masonry sub-assemblages made of soft-mud clay bricks and hydraulic lime mortar. In overall, 9 single-lap shear tests on single bricks with a bonded length of 200 mm and 9 three-point bending tests on 2-brick slices, connected by a mortar joint and reinforced at the bottom face, were carried out. Lastly, the behaviour in alkaline environments of each reinforcement was investigated through tensile tests on coupons immersed for 28 days in alkaline solutions simulating the conditions of the geopolimeric matrices. Results confirmed the interesting potential of FRGPs for strengthening masonry elements, highlighting a good performance of steel and carbon reinforcements. On the other hand, precautions should be taken with basalt meshes that, as expected, were more sensitive to alkaline environment

A comparison of electrochemical degradation of phenol on boron doped diamond and lead dioxide anodes

This work compares two electrode materials used to mineralize phenol contained in waste waters. Two disks covered with either boron doped diamond (BDD) or PbO2 were used as anodes in a one compartment flow cell under the same hydrodynamic conditions. Efficiencies of galvanostatic electrolyses are compared on the basis of measurements of Total Organic Carbon (TOC) and Chemical Oxygen Demand (COD). Galvanostatic electrolyses were monitored by analysis of phenol and of its oxidation derivatives to evaluate the operating time needed for complete elimination of toxic aromatics. The experimental current efficiency is close to the theoretical value for the BDD electrode. Other parameters being equal, phenol species disappeared at the same rate using the two electrode materials but the BDD anode showed better efficiency to eliminate TOC and COD. Moreover, during the electrolysis less intermediates are formed with BDD compared to PbO2 whatever the current density. A comparison of energy consumption is given based on the criterion of 99% removal of aromatic compounds

Volcanic hazard assessment at the Campi Flegrei caldera

Previous and new results from probabilistic approaches based on available volcanological data from real eruptions of Campi Flegrei, are assembled in a comprehensive assessment of volcanic hazards at the Campi Flegrei caldera, in order to compare the volcanic hazards related to the different types of events. Hazard maps based on a very wide set of numerical simulations, produced using field and laboratory data as input parameters relative to the whole range of fallout and pyroclastic-flow events and their relative occurrence, are presented. The results allow us to quantitatively evaluate and compare the hazard related to pyroclastic fallout and density currents (PDCs) in the Campi Flegrei area and its surroundings, including the city of Naples. Due to the dominant wind directions, the hazard from fallout mostly affects the area east of the caldera, and the caldera itself, with the level of probability and expected thickness decreasing with distance from the caldera and outside the eastern sectors. The hazard from PDCs decrease roughly radially with distance from the caldera centre and is strongly controlled by the topographic relief, which produces an effective barrier to propagation of PDCs to the east and northeast, areas which include metropolitan Naples. The main result is that the metropolitan area of Naples would be directly exposed to both fallout and PDCs. Moreover, the level of probability for critical tephra accumulation by fallout is relatively high, even for moderate-scale events, while, due to the presence of topographic barriers, the hazard from PDCs is only moderate and mostly associated with the largest events

Debt levels, debt composition, and sovereign spreads in emerging and advanced economies

This paper studies the relationship between sovereign spreads and the interaction between debt composition and debt levels in advanced and emerging market countries. It finds that in emerging market countries there is a significant correlation between spreads and debt levels. This correlation, however, is not statistically significant in countries where most public debt is denominated in local currency. In advanced economies, the magnitude of the correlation between debt levels and spreads is about one fifth of the corresponding correlation for emerging market economies. In Eurozone countries, however, the correlation between spreads and debt ratios is similar to that of emerging market countries. The paper also shows that the financial crisis amplified the relationship between spreads and debt levels within the Eurozone but had no effect on the relationship between spreads and debt in standalone countries. Finally, the paper shows that the relationship between debt levels and spreads is amplified by the presence of large net foreign liabilities. This amplifying effect of net foreign liabilities is larger in the Eurozone than in standalone advanced economies. The paper concludes that debt composition matters and corroborates the original sin hypothesis that, rather than being a mere reflection of institutional weaknesses, the presence of foreign currency debt increases financial fragility and leads to suboptimal macroeconomic policies

Characterisation of La0.6Sr0.4Co0.2Fe0.8O3-\u3b4- Ba0.5Sr0.5Co0.8Fe0.2O3-\u3b4composite as cathode for solid oxide fuel cells

Mixture of La0.6Sr0.4Co0.2Fe0.8O3-\u3b4 and Ba0.5Sr0.5Co0.8Fe0.2O3-\u3b4, was investigated as promising cathode for intermediate temperature solid oxide fuel cells (IT-SOFCs). The two perovskites possess high catalytic activity for the oxygen reduction (ORR), although some problems related to their chemical and structural stability have still to be overcome in view of improving durability of the cell performance. The achievement of a stable and high-performing composite material is the aim of this study. In principle, chemical equilibrium at the LSCF-BSCF interface may be reached through ions interdiffusion during the sintering process, resulting in the chemical stabilization of the material. The composite-cathode deposited on Ce0.8Sm0.2O2-\u3b4 electrolyte was then investigated by Electrochemical Impedance Spectroscopy (EIS) as a function of temperature, overpotential and time. The results exhibited an interesting electrochemical behavior of the electrode toward oxygen reduction reaction. XRD analysis was performed to detect structural modification during thermal or operation stages and it was found that after the sintering the two starting perovskites were no longer present; a new phase with a rhombohedral La0,4Sr0,6FeO3-type structure (LSF) is formed. An improvement in composite cathode durability has been detected under the considered operating conditions (200 mAcm-2, 700 \ub0C) in comparison with the pure BSCF electrode. The results confirmed this new electrode as promising system for further investigation as IT-SOFC cathode

A Comprehensive Approach to Improve Performance and Stability of State-of-the- Art Air Electrodes for Intermediate Temperature Reversible Cells: An Impedance Spectroscopy Analysis

Solid oxide fuel cells (SOFC) are devices for the transformation of chemical energy in electrical energy. SOFC appear very promising for their very high efficiency, in addition to the capability to work in reverse mode, which makes them suitable for integration in production units powered with renewables. Research efforts are currently addressed to find chemically and structurally stable materials, in order to improve performance stability during long-term operation. In this work, we examine different approaches for improving stability of two state-of-the-art perovskite materials, La0.6Sr0.4Co0.2Fe0.8O3-\uf064 (LSCF) and Ba0.5Sr0.5Co0.8Fe0.2O3-\uf064 (BSCF), very promising as air electrodes. Two different systems are considered: (i) LSCF and BSCF porous electrodes impregnated by a nano-sized La0.8Sr0.2MnO3-\uf064 layer and (ii) LSCF-BSCF composites with the two phases in different volume proportions. The study considers the results obtained by electrochemical impedance spectroscopy investigation, observing the polarisation resistance (Rp) of each system to evaluate performance in typical SOFC operating conditions. Furthermore, the behaviour of polarisation resistance under the effect of a net current load (cathodic) circulating for hundreds of hours is examined, as parameter to evaluate long-term performance stability

Planting time for maximization of yield of vinegar plant calyx (Hibiscus sabdariffa L.)

Objetivou-se avaliar a produtividade de cálices de Hibiscus sabdariffa L., planta medicinal, em quatro épocas de plantio em Lavras M.G. Os tratamentos foram quatro épocas de plantio (18 de outubro; 15 de novembro; 18 de dezembro de 2001 e 15 de janeiro de 2002) e realizada uma colheita quando praticamente não existiam cálices em desenvolvimento, quase no final do ciclo da planta. Foram considerados os números de cálices por planta, as fitomassas frescas e secas dos cálices e a qualidade. Concluiu-se que a época de plantio influenciou o rendimento por planta e as fitomassas frescas e secas dos cálices, diferindo entre si pelo teste de Tukey a 5%. No plantio de outubro, houve maior rendimento (2.522 kg/ha), com produção de 5,24 vezes a mais em relação ao plantio do mês de janeiro (481 kg/ha). Os plantios nos meses de novembro e dezembro tiveram produções de 1.695 e 1.093 kg.ha-1 de cálices secos, respectivamente, e em relação ao mês de janeiro, a produção foi 3,52 e 2,27 vezes a mais.Deve-se realizar a colheita assim que os cálices estiverem maduros, a fim de preservar a qualidade