Non-linear Coulomb blockade microscopy of a correlated one-dimensional quantum dot

We evaluate the chemical potential of a one-dimensional quantum dot, coupled to an atomic force microscope tip. The dot is described within the Luttinger liquid framework and the conductance peaks positions as a function of the tip location are calculated in the linear and non-linear transport regimes for an arbitrary number of particles. The differences between the chemical potential oscillations induced by Friedel and Wigner terms are carefully analyzed in the whole range of interaction strength. It is shown that Friedel oscillations, differently from the Wigner ones, are sensitive probes to detect excited spin states and collective spin density waves involved in the transport.Comment: 4 figure

Mathematical Models of ice stream dynamics and supraglacial drainage

Patterning is a recurrent feature of glacial systems, which characterizes as much subglacial and supraglacial environments as the flow of ice itself. Some examples include bedforms developing at the contact between ice and bed, spatial organization in subglacial and supraglacial drainage networks, the narrow corridors of fast flowing ice known as ice streams that form the arterial drainage system of large ice sheets, and temporal switches between slow and fast flow regimes in glacier and ice stream flow. This thesis focusses on two types of glacial patterns, namely ice streams and channelization in supraglacial drainage networks. Ice flow within ice sheets is far from uniform, with the narrow bands known as ice streams flowing at velocity two order of magnitude larger than the rest of the ice sheet. In the Siple Coast region of West Antarctica ice streams experiance weak topographic confinement, thus suggesting that they may originate spontaneously from an otherwise uniform flow as a fingering instability. Motivated by observations suggesting that the marked contrast in velocity between ice streams and surrounding ice is due to a transition from frozen, thus sticky bed underneath slow flowing regions, to molten, thus well lubricated bed under ice streams, we investigate the role of basal thermal transitions in relation to the onset of ice streams. Our findings suggest that basal transitions from frozen to molten bed (or vice versa) can undergo an instability potentially leading to the onset of streaming. An asymptotic analysis for short wavelenght perturbations shows that, at wavelengths of few ice thicknesses, such instability is controlled by the interplay between strain heating and heat advection from the region upstream of the transition. We also find that the background structure of the ice sheet is key to pattern formation. In particular, in the case of ice flowing from molten to frozen regions we find an instability at the ice sheet thickness scale or smaller, which is not resolved by most ice sheet models. Observations reveal that ice streams experience significant temporal variability on a variety of time scales, ranging from decadal to multi-millennial ones. As much as spatial patterning, such variability holds implications for the future of ice sheets, sea level change, and the interpretation of geological records. Recent work \citep{robel} shows that the switch between steady streaming conditions and self-sustained oscillations with multi-millennial periodicity can be understood as a Hopf bifurcation. Little is presently known about shorter scale variability, which however appears more likely to originate from external forcing. In chapter \ref{ch:stoch} we explore the effects of a specific type of forcing, i.e. stochastically-varying climatic conditions, on the temporal dynamics of ice stream flow. We find that data-based climate fluctuations alter the deterministic dynamics substantially, and are capable of introducing widespread, short-scale oscillations even in ranges of the parametric regime where the deterministic dynamics predict steady streaming. We thus conclude that noise-induced transitions may play a role in the observed temporal dynamics of ice stream flow. In part \ref{drain} we turn to patterning in drainage networks on the surface of glaciers. Supraglacial drainage networks route meltwater originating on the surface of glaciers towards moulins and crevasses, through which it eventually reaches the base of the ice. Therefore, understanding the physical controls on the structure of the drainage network has implications for how surface melt influences the motion of ice. Here we focus on the physical controls on the formation of evenly spaced channels on the surface of glaciers. In particular, we find that the flow of meltwater on bare ice is capable of carving evenly spaced channels as a result of a morphological instability. We show that in certain conditions the network is shaped solely by the hydrodynamics of meltwater regardless of ice thermal conditions, which justifies widely-observed regular patterns in drainage networks. Finally, comparison of our results with the geometrical feature of supraglacial networks reported in the literature shows good agreement between model's predictions and observations

Experimental determination of satellite bolted joints thermal resistance

The thermal resistance was experimentally determined of the bolted joints of the first Brazilian satellite (SCD 01). These joints, used to connect the satellite structural panels, are reproduced in an experimental apparatus, keeping, as much as possible, the actual dimensions and materials. A controlled amount of heat is forced to pass through the joint and the difference of temperature between the panels is measured. The tests are conducted in a vacuum chamber with liquid nitrogen cooled walls, that simulates the space environment. Experimental procedures are used to avoid much heat losses, which are carefully calculated. Important observations about the behavior of the joint thermal resistance with the variation of the mean temperature are made

Performance analysis and dynamics of innovative SOFC hybrid systems based on turbocharger-derived machinery

La crescente consapevolezza su temi quali il cambiamento climatico e l\u2019inquinamento atmosferico ha portato a politiche nazionali ed internazionali mirate allo sviluppo di sistemi energetici innovativi e sostenibili. Tra di essi, le fuel cell sono uno dei pi\uf9 promettenti, essendo caratterizzate da alte efficienze e basse emissioni. In particolare, i sistemi ibridi basati sull\u2019integrazione di fuel cell ad alta temperatura con dispositivi derivati da turbocompressori hanno attirato l\u2019attenzione del mondo accademico e dell\u2019industria negli ultimi decenni. Tuttavia, la complessit\ue0, la fragilit\ue0 e l\u2019alto costo di questi impianti ha rallentato il loro sviluppo, e solo poche grandi aziende sono state in grado di realizzare prototipi completi. Le difficolt\ue0 tecniche affrontate dalla comunit\ue0 scientifica hanno messo in luce l\u2019importanza delle simulazioni per progettare, testare, controllare e analizzare i sistemi ibridi a fuel cell. Sulla base di tale esperienza, questa tesi mira ad espandere la attuale conoscenza sui sistemi ibridi a fuel cell a ossidi solidi, ponendo una particolare attenzione su un innovativo sistema turbocompresso di piccola taglia, alimentato con biogas e recentemente introdotto all\u2019interno del progetto europeo Bio-HyPP. Lo scopo principale della tesi \ue8 determinare se questo tipo di sistema possa essere una valida alternativa ai sistemi basati su microturbine a gas, analizzando il suo comportamento in relazione a diversi scenari, sia stazionari, sia transitori. Per fare ci\uf2, \ue8 necessario definire i vincoli operativi del sistema e sviluppare un sistema di controllo in grado di rispettarli, ottimizzando al tempo stesso le prestazioni dell\u2019impianto. Inoltre, l\u2019affidabilit\ue0 dei sistemi ibridi pu\uf2 essere migliorata grazie all\u2019implementazione di strumenti diagnostici e di procedure per prevenire il pompaggio del compressore. La parte finale della tesi \ue8 mirata allo studio di tali strumenti, al loro sviluppo e alla loro integrazione con il sistema di controllo. Tutte le attivit\ue0 presentate in questa tesi sono state svolte facendo affidamento su strumenti di simulazione. Ci\uf2 \ue8 stato possibile grazie alla collaborazione tra il Laboratorio di Matematica Applicata, Simulazione e Modellistica Matematica e il Thermochemical Power Group dell\u2019Universit\ue0 degli Studi di Genova. Dopo aver presentato il layout del sistema a fuel cell con turbocompressore, un dettagliato modello stazionario dell\u2019impianto sviluppato in Matlab\uae-Simulink\uae \ue8 stato utilizzato per progettare una strategia, basata sul controllo di valvole installate sull\u2019impianto, in grado di rispettare tutti i suoi vincoli operativi. Successivamente, \ue8 stata svolta un\u2019analisi di prestazioni in off-design, considerando allo stesso tempo diverse condizioni di carico di potenza e di temperatura ambiente. Tale analisi \ue8 stata utilizzata per confermare l\u2019efficacia della strategia di controllo proposta, e per valutare le capacit\ue0 del sistema con turbocompressore. Successivamente \ue8 stato creato un modello dinamico utilizzando lo strumento TRANSEO, in modo da studiare il comportamento del sistema durante i transitori. Avendo adottato una strategia di controllo basata sulla valvola di cold bypass, \ue8 stata analizzata la risposta del sistema ad una sua apertura a gradino, al fine di progettare un sistema di controllo efficace e reattivo, in grado di mantenere la massima temperatura di cella costante e, allo stesso tempo, di rispettare i vincoli del sistema. Sono stati progettati quattro diversi controllori, che successivamente sono stati testati su due diversi scenari di variazione di carico e confrontati sulla base di vari parametri operativi. La parte finale della tesi ha riguardato lo sviluppo di innovativi strumenti che possano aumentare l\u2019affidabilit\ue0 dei sistemi ibridi a fuel cell a ossidi solidi, in particolare tecniche di prevenzione del pompaggio e sistemi di diagnostica basati su reti Bayesiane. Un modello semplificato del sistema con turbocompressore \ue8 stato sviluppato in TRANSEO e sono state testate diverse tecniche di prevenzione del pompaggio: condizionamento del flusso d\u2019aria, iniezione di acqua, ricircolo e bleed, installazione di un eiettore all\u2019imbocco del compressore. Le soluzioni pi\uf9 efficaci sono state integrate con il controllore del sistema ibrido e sono state testate durante un transitorio per evitare che il punto operativo del compressore si avvicinasse al pompaggio. Infine, grazie ad una collaborazione tra l\u2019Universit\ue0 degli Studi di Genova e la M\ue4lardalens H\uf6gskola di V\ue4ster\ue5s, in Svezia, sono state sviluppate delle reti Bayesiane per la diagnostica di sistemi ibridi a fuel cell a ossidi solidi con microturbina a gas. Questa attivit\ue0 \ue8 stata svolta simulando il sistema su Matlab\uae-Simulink\uae e creando le reti Bayesiane su Hugin Expert. Due sistemi di diagnostica, uno per la microturbina e uno per la fuel cell, sono stati sviluppati e testati in condizioni stazionarie. Il secondo \ue8 stato anche testato in condizioni dinamiche e integrato con il sistema di controllo per prevenire l\u2019usura della cella. In conclusione, questa tesi ha messo in luce il grande potenziale dei sistemi ibridi SOFC-turbocompressore, mostrando la loro alta efficienza in un ampio intervallo di condizioni operative in termini di carico elettrico e temperatura ambiente. La tesi ha anche dimostrato che \ue8 possibile garantire il corretto funzionamento di questi sistemi durante diversi scenari transitori, implementando controllori a cascata progettati per agire sulla valvola di bypass freddo per controllare la massima temperatura della cella. Per quanto riguarda la possibilit\ue0 di migliorare l\u2019affidabilit\ue0 di tali sistemi, le tecniche basate sul ricircolo del compressore sono risultate essere le pi\uf9 efficaci per allontanare il sistema da una condizione di pompaggio. I risultati delle simulazioni mostrano come la loro integrazione con strumenti di monitoraggio possa prevenire diverse situazioni di pericolo. La parte finale della tesi ha mostrato come il deterioramento dei sistemi ibridi a SOFC possa essere limitato grazie a reti Bayesiane, che sono state utilizzate per diagnosticare accuratamente le condizioni di un sistema SOFC-microturbina a gas, ma potrebbero ugualmente essere applicate su impianti con turbocompressore.The growing awareness on climate change and pollution has brought to national and international policies aimed at promoting the development of innovative and environmentally sustainable energy systems. Among these systems, fuel cells are one of the most promising technologies, characterized by high energy conversion efficiencies and low emissions. In particular, hybrid systems based on the integration of a high temperature fuel cell with turbocharger-derived machinery have drawn the interest of academia and industry over the past decades. However, the complexity, fragility and high cost of these plants have slowed down their development, and only a few big companies were able to build complete prototypes. The technological challenges faced by the scientific community have highlighted the importance of simulations to design, test, control and analyse fuel cell hybrid systems. Based on this experience, this thesis wants to expand the current knowledge on solid oxide fuel cell hybrid systems, with a particular focus on an innovative small-scale biofueled turbocharged layout, which was introduced recently within the Bio-HyPP European project. The main goal of this thesis is to determine if this kind of system can be a viable alternative to micro gas turbine-based systems, analysing its steady-state and transient behaviour in various operating conditions. To do this, it is necessary to define the system operative constraints, and to develop a control system capable of ensuring their compliance, while optimizing the plant performance. The possibility of increasing the reliability of solid oxide fuel cell hybrid systems is finally investigated, considering the implementation of surge prevention techniques and diagnostic tools. All these activities strongly relying on simulation tools. This was possible thanks to the collaboration between the Laboratory of Applied Mathematics, Simulation and Mathematical Modelling with the Thermochemical Power Group of the University of Genoa. After introducing the layout of the turbocharged fuel cell system, a detailed steady-state model of the plant is developed in Matlab\uae-Simulink\uae and used to design a strategy, based on the control of valves installed on the plant, able to comply with its many operative constraints. Then, an off-design performance analysis of the system is performed, considering simultaneously various conditions of power load and ambient temperature. This analysis is used to confirm the effectiveness of the proposed control strategy and to assess the capabilities of the turbocharged system. A dynamic model is created using the TRANSEO tool to study the transient behaviour of the system. Having adopted a control strategy based on the cold bypass valve, the response of the system to a valve opening step change is analysed in order to design an effective and responsive control system, able to keep the fuel cell maximum temperature constant while complying with the system constraints. Four different controllers are designed, tested on two different load variation scenarios and compared on the basis of many parameters. The final part of the thesis regards the development of innovative tools aimed at improving the reliability of solid oxide fuel cell hybrid system, in particular surge prevention techniques and Bayesian belief network-based diagnosis systems. A simplified dynamic model of the turbocharged SOFC system is developed in TRANSEO, and various surge prevention techniques are tested on it: intake air conditioning, water spray at compressor inlet, air bleed and recirculation, and installation of an ejector at the compressor intake. The most effective procedures are integrated with the controller of the hybrid system and tested during a transient scenario to prevent the compressor operative point from approaching a surge condition. Bayesian belief networks aimed at diagnosing the status of SOFC hybrid systems are developed thanks to a collaboration between the University of Genoa and the M\ue4lardalens H\uf6gskola of V\ue4ster\ue5s, Sweden. A micro gas turbine \u2013 solid oxide fuel cell system is considered for this study, but the methodology could be easily extended to turbocharged plants. The activity is carried out simulating the system on Matlab\uae-Simulink\uae and designing the Bayesian networks on Hugin Expert. Two different diagnosis systems, one for the turbomachinery and one for the fuel cell stack, are developed and tested on stationary conditions. The second one is also tested during transients and integrated with the control system to prevent degradation of the fuel cells. In conclusion, this thesis highlighted the great potential of turbocharged SOFC hybrid systems, showing high energy conversion efficiencies in a wide operative range in terms of load and ambient conditions. It also showed that the proper operation of the system is possible during various transient scenarios, implementing cascade controllers designed to act on a cold bypass valve to control the SOFC maximum temperature. Regarding the possibility of improving the reliability of these systems, surge prevention techniques based on compressor recirculation appeared as the most effective ones. Simulation results suggest that their integration with a surge precursors detection tool could avoid the occurrence of many potentially dangerous scenarios. The final part of this thesis showed that the durability of SOFC hybrid systems could be further improved thanks to Bayesian belief networks, which were proved to effectively diagnose the status of SOFC-MGT systems but could be applied to turbocharged plants as well

The Unsung Kingdom Translation Project Designing an Effective and Sustainable Classroom Activity for a Japanese Video Game Translation

This paper presents the experience of the design of a didactic activity for the translation of a Japanese video game in Italian, carried out in 2020 during the first year of the Japanese language course of the Master’s Degree Programme in Language and Civilisation of Asia and Mediterranean Africa at Ca’ Foscari University. The described protocol allows the design of video game translation sessions as a teaching activity, overcoming some typical technical and organisational problems. One important issue this paper addresses involves the possibility of reviewing the translation within the game, which is fundamental to understanding how to translate texts for this medium. The paper will also give an overview of the translation issues that students encountered during the activity and of how they solved them. Finally, the results of a survey will show whether the implemented protocol and classroom activity were satisfactory for the students and how they can be improved

Learning Japanese through VR technology. The case of altspace VR

Through this paper, I intend to analyse the state of Japanese learning through virtual reality technologies, avoiding as much as possible the analysis of prototypes and laboratory experiments, focusing instead on a case study that implements software and hardware already present on the consumer market. After analysing the VR technology currently available to end-users and its hardware, which has lately increased in popularity due to the COVID-19 pandemic, and the specificities of virtual reality compared to other communication technologies, I will proceed to the analysis of the case study Altspace VR, a social VR software used also by an active Japanese learning community, to try to identify the characteristics that could make this technology particularly suitable for language learning

Sex hormones in allergic conjunctivitis: altered levels of circulating androgens and estrogens in children and adolescents with vernal keratoconjunctivitis

PURPOSE: Vernal keratoconjunctivitis (VKC) is a chronic allergic disease mainly affecting boys in prepubertal age and usually recovering after puberty. To evaluate a possible role of sex hormones in VKC, serum levels of sex hormones in children and adolescents with VKC were assessed. METHODS: 12 prepubertal and 7 early pubertal boys with active VKC and 6 male patients with VKC in remission phase at late pubertal age and 48 healthy age and sex-matched subjects were included. Serum concentration of estrone, 17 beta-estradiol, dehydroepiandrosterone-sulfate, total testosterone and free testosterone, dihydrotestosterone (DHT), cortisol, delta-4-androstenedione, follicle-stimulating hormone, luteinizing hormone, and sex-hormones binding globuline (SHBG) were evaluated. RESULTS: Serum levels of Estrone were significantly increased in all groups of patients with VKC when compared to healthy controls (P < 0.001). Prepubertal and early pubertal VKC showed a significant decrease in DHT (P = 0.007 and P = 0.028, resp.) and SHBG (P = 0.01 and P = 0.002, resp.) when compared to controls and serum levels of SHBG were increased in late pubertal VKC in remission phase (P = 0.007). CONCLUSIONS AND RELEVANCE: VKC patients have different circulating sex hormone levels in different phases of the disease and when compared to nonallergic subjects. These findings suggest a role played by sex hormones in the pathogenesis and/or activity of VKC