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A Phase Variable Model of Aircraft Brushless Exciter Based on Finite Element Analysis and Its Coupling with the Rotating Rectifier Circuit
No full textThis paper presents the phase variable model of brushless exciter employed by aircraft integrated starter/generators. The model uses current-flux linkage functions obtained by finite element analysis. Since the developed model contains the exciter machine and its connected rotating rectifier, a particular attention is paid to adequately considering coupling effects between the exciter and the rotating rectifier which govern operation of the rectifier. One important parameter of this coupling is the inductance which contributes in commutation process of the rectifier (commutation inductance). In this regard, a simple finite element analysis technique is proposed to identify the commutation inductance. Finally, the developed model is validated by comparing its results with finite element analysis
Addressing the controversial mechanism of Na+ reversible storage in TiO2 nanotube arrays: amorphous, anatase and rutile TiO2
No full textTitanium dioxide (TiO2), in its amorphous as well as most common polyphases including anatase, rutile, brookite and various metastable phases, is under intense investigation as anode candidate for advanced sodium-ion electrochemical energy storage. Na-ion batteries (NiB) are attracting the widespread interest of the scientific community because they may offer the most convenient alternative to current leading-edge Li-ion technology (LiB) for large-scale grid energy storage, where size does not matter and cost, safety and reliability are the most stringent requirements. In the recent years, various hypotheses have been proposed on the real mechanism of reversible insertion of sodium ions into the TiO2 structure and literature reports are often controversial in this respect. Interestingly, we experienced peculiar, intrinsically different electrochemical response between amorphous, rutile and anatase TiO2 nanotubular arrays, obtained by simple anodic oxidation, when tested as binder- and conducting additive-free electrodes in lab-scale sodium cells. In particular, after the initial electrochemical activation, anatase TiO2 showed excellent high rate capability and very stable long-term cycling performance at larger specific capacity values, thus definitely outperforming the amorphous and rutile counterparts. To reach deepen insights into the subject, materials were thoroughly characterized by means of scanning electron microscopy and ex-situ X-ray diffraction, and the mechanism of sodium ion insertion in the TiO2 bulk phases was systematically modelled by density functional theory (DFT) calculations. The results we obtained may significantly contribute to get a more systematic selection of proper active material configurations for highly efficient sodium-based energy storage systems
Innovative polymer electrolytes for safe, low-cost and durable sodium-ion batteries
No full textIn the recent years, large-scale and high-energy storage systems are becoming extremely important to realize the load leveling of intermittent renewable energy sources, such as wind and solar, into the grid. Secondary (rechargeable) sodium-based batteries represent the most promising technology in this respect, because of their high-energy density, low-cost, simple design, and easiness in maintenance. However, standard batteries use liquid electrolytes as ion transport media; these are based on toxic and volatile organic carbonate solvents, and their flammability clearly raises safety concerns. The most striking solution at present is to switch on all solid-state designs exploiting polymer materials, films, ceramics, etc. Here, we offer an overview of our recent developments on innovative polymer electrolytes for sodium-ion batteries. Polymer electrolytes were prepared through different techniques, including simple solvent casting and UV-induced photopolymerization (UV-curing), being simple, low-cost and easily scalable to an industrial level. All samples were thoroughly characterized in the physico-chemical and electrochemical viewpoint. They exhibited excellent ionic conductivity and wide electrochemical stability window, which ensure safe operation at ambient conditions. Electrochemical performances in lab-scale devices were evaluated by means of cyclic voltammetry and galvanostatic charge/discharge cycling exploiting different electrode materials (prepared by water-based procedures exploiting green carboxymethylcellulose as binder). Work on Na-ion polymer batteries for moderate temperature application is at an early stage, only lab-scale cells were demonstrated so far. Nevertheless, with the appropriate choice and optimisation of electrode/electrolyte materials (and successful combination thereof), the intriguing characteristics of the newly developed polymer electrolytes here presented postulates the possibility of their effective implementation in safe, durable and high energy density secondary Na-based solid-state devices conceived for green-grid storage and operating at ambient and/or sub-ambient temperatures
Glass-ceramic oxidation protection of higher manganese silicide thermoelectrics
No full textA higher manganese silicide (HMS) thermoelectric, with composition MnSi1.74, densified by spark plasma sintering, was successfully coated with a glass-ceramic, in order to be used at temperatures higher than 500°C. Compositional changes in both the HMS substrate and the glass-ceramic coating are reviewed and discussed with respect to the electrical properties of the uncoated and coated HMS before and after thermal cycles from RT to 600°C in air. The formation of a Si-deficient layer (MnSi) on the uncoated HMS surface is due to the reaction between the HMS and oxygen at 600°C, thus contributing to a lower power factor in comparison with the as-sintered HMS. Coated HMS samples (after thermal cycles RT-600°C) show a lower electrical resistivity and a significantly higher power factor in comparison with the uncoated ones. The glass-ceramic coating is self-reparable at 600°C, as demonstrated by the complete sealing of an induced scratch on its surface
Gruppo pedivella con inserto porta-pedale estendibile e recupero di coppia
No full textUn gruppo pedivella (1) per un ciclo, preferibilmente una bicicletta, comprende un corpo (2, 13) rotante intorno a un primo asse (A) e avente almeno una guida (3) trasversale rispetto al primo asse (A), un inserto porta-pedale (4) traslante lungo la guida (3), e un manovellismo girevole intorno a un secondo asse (B) parallelo al primo asse (A) e avente una biella (6) incernierata all'inserto porta-pedale (4) e una manovella 10 (7) collegata in trasmissione di coppia al corpo (2, 13) in modo che un carico applicato da un utente durante una pedalata per estrarre o ritrarre l'inserto porta-pedale (4) lungo la guida (3) sia trasferito come coppia al corpo (2, 13)
Study of the Microstructure and Cracking Mechanisms of Hastelloy X Produced by Laser Powder Bed Fusion
No full textHastelloy X (HX) is a Ni-based superalloy which suffers from high crack susceptibility during the laser powder bed fusion (LPBF) process. In this work, the microstructure of as-built HX samples was rigorously investigated to understand the main mechanisms leading to crack formation. The microstructural features of as-built HX samples consisted of very fine dendrite architectures with dimensions typically less than 1 µm, coupled with the formation of sub-micrometric carbides, the largest ones were mainly distributed along the interdendritic regions and grain boundaries. From the microstructural analyses, it appeared that the formation of intergranular carbides provided weaker zones, which combined with high thermal residual stresses resulted in hot cracks formation along the grain boundaries. The carbides were extracted from the austenitic matrix and characterized by combining different techniques, showing the formation of various types of Mo-rich carbides, classified as M6C, M12C and MnCm type. The first two types of carbides are typically found in HX alloy, whereas the last one is a metastable carbide probably generated by the very high cooling rates of the process
A Single Point, Multi-Parameter, Fiber Optic Sensor Based on a Combination of Interferometry and LSPR
No full textWe demonstrate a new single point, multiparameter, fiber optic sensor concept based on a combination of interferometric and plasmonic sensor modalities on an optical fiber end face. The sensor consists of an extrinsic Fabry-Perot interferometer in the form of a hemispherical stimuli-responsive hydrogel with immobilized gold nanoparticles (GNPs). The GNPs exhibit local surface plasmon resonance (LSPR) that is sensitive towards the local refractive index (RI) of the surrounding environment, while the stimuli-responsive hydrogel is sensitive towards specific chemical compounds. We evaluate the quality of the interferometric and LSPR signals as function of GNP concentration and of hydrogel swelling degree stimulated by ethanol solutions. The GNPs have little influence on the visibility of the Fabry-Perot etalon. The swelling degree of the hydrogel, with corresponding bulk RI changes, have little influence on the local surface RI of the GNPs. We expect this novel sensor concept to be of great value for biosensors for medical applications
Advances in the design of solid lipid nanoparticles and nanostructured lipid carriers for targeting brain diseases
No full textChecking the Consistency of Solutions in Decision-Making Problems with Multiple Weighted Agents
No full textA decision-making problem diffused in various practical contexts is that of aggregating multi-agent judgements into a consensus ordering, in the case the agents' importance is expressed through a set of weights. A crucial point in this aggregation is that the consensus ordering well reflects the input data, i.e., agents' judgements and importance. The scientific literature encompasses several aggregation techniques, even if it does not include a versatile tool for a quantitative assessment and comparison of their performance. The aim of this paper is introducing a new indicator (p), which allows to verify the degree of consistency between consensus ordering and input data. This indicator is simple, intuitive and independent from the aggregation technique in use; for this reason, it can be applied to a variety of practical contexts and used to compare the results obtained through different aggregation techniques, when applied to a specific problem. The description is supported by various application examples
