Multidisciplinary design and optimization of innovative electrical power systems for aerospace applications

La tesi ha riguardato lo sviluppo di modelli a parametri concentrati di sistemi basati su cella a combustibile PEM e su elettrolizzatori alcalini e PEM. Secondariamente, è stata considerata anche la calibrazione e ottimizzazione di modelli a parametri distribuiti (in CFD) sviluppati durante la tesi di laurea specialistica. I modelli a parametri concentrati, sviluppati in ambiente Matlab-Simulink, hanno considerato tutti gli elementi principali costituenti tale tipo di sistemi, facendo uso di approcci differenti rispetto a quanto disponibile in letteratura. In particolare, sono stati modellati gli stack di cella a combustibile ed elettrolizzatori, gli umidificatori gas-gas e liquido-gas a membrana, gli scambiatori di calore, lo stoccaggio dei reagenti, i compressori e motori elettrici, così come il controllo termico e fluidico degli stack. I modelli sono di tipo dinamico, non isotermo, con modellazione dei flussi bi-fase e multi-componente. Tutti i principali aspetti della fisica coinvolti in tale tipo di sistemi sono stati considerati. I modelli sono stati calibrati e validati con dati sperimentali per ogni tipologia di componente del sistema. Sono inoltre stati applicati metodi di sensitivity analysis ed ottimizzazione con modelli surrogati al modello di cella PEM a parametri distribuiti sviluppato durante la tesi di laurea specialistica

VLT spectroscopy of globular clusters in the Sombrero galaxy

We have obtained intermediate-resolution VLT spectroscopy of 75 globular cluster candidates around the Sa galaxy M104 (NGC4594). Fifty-seven candidates out to ~ 40 kpc in the halo of the galaxy were confirmed to be bona-fide globular clusters, 27 of which are new. A first analysis of the velocities provides only marginal evidence for rotation of the cluster system. From Hbeta line strengths, almost all of the clusters in our sample have ages that are consistent, within the errors, with Milky Way globular clusters. Only a few clusters may be 1-2 Gyr old, and bulge and halo clusters appear coeval. The absorption line indices follow the correlations established for the Milky Way clusters. Metallicities are derived based upon new empirical calibrations with Galactic globular clusters taking into account the non-linear behavior of some indices (e.g., Mg2). Our sample of globular clusters in NGC4594 spans a metallicity range of -2.13 < [Fe/H] < +0.26 dex, and the median metallicity of the system is [Fe/H] = -0.85. Thus, our data provide evidence that some of the clusters have super-solar metallicity. Overall, the abundance distribution of the cluster system is consistent with a bimodal distribution with peaks at [Fe/H] ~- 1.7 and -0.7. However, the radial change in the metallicity distribution of clusters may not be straightforwardly explained by a varying mixture of two sub-populations of red and blue clusters.Comment: 6 pages (incl. 4 figures) to appear in the proceedings of the ESO workshop "Extragalactic Globular Cluster Systems", ESO Astrophysics Symp., Garching bei Muenchen (Germany), ed. Kissler-Patig M., Springer-Verlag: Heidelber

On the secrecy of compressive cryptosystems under finite-precision representation of sensing matrices

In recent years, the Compressed Sensing (CS) framework has been shown to be an effective private key cryptosystem. If infinite precision is available, then it has been shown that spherical secrecy can be achieved. However, despite its theoretically proven secrecy properties, the only practically feasible implementations involve the use of Bernoulli sensing matrices. In this work, we show that different distributions employing a much larger finite alphabet can be considered. More in detail, we consider the use of quantized Gaussian sensing matrices and experimentally show that, besides being suitable for practical implementation, they can achieve higher secrecy with respect to Bernoulli sensing matrices. Furthermore, we show that this approach can be used to tune the secrecy of the CS cryptosystems based on the available machine precision

Comparison between 1-D and grey-box models of a SOFC

Solid Oxide Fuel Cells (SOFCs) have shown unique performance in terms of greater electrical efficiency and thermochemical integrity with the power systems compared to gas turbines and internal combustion engines. Nonetheless, simple and reliable models still must be defined. In this paper, a comparison between a grey-box model and a 1-D model of a SOFC is performed to understand the impact of the heat transfer inside the cell on the internal temperature distribution of the solid electrolyte. Hence, a significant internal temperature peak of the solid electrolyte is observed for a known difference between anode and cathode inlet temperatures. Indeed, it highlights the difference between the 1-D model and the grey-box model regarding the thermal conditioning of the SOFC. Therefore, the results of this study can be used to investigate the reliability of the thermal results of box models in system-level simulations

Strambo: alcuni appunti sulla parola e sul personaggio

Il contributo prende in esame l’etimologia del lemma “strambo” e offre un excursus di carattere storico-linguistico e letterario sulle attestazioni di questo aggettivo nella letteratura italiana e sui vari significati che esso assume a seconda dei sostantivi a cui è di volta in volta associato