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Production of strengthened copper materials by Mechanical Milling-Mechanical Alloying and Spark Plasma Sintering
Get PDFCopper is widely used in many applications demanding high thermal and electrical conductivity, unfortunately its low hardness and wear resistance limit its performance. Work hardening has been proposed as a successful strengthening mechanism for the production of harder copper material, keeping the intrinsic conductivities. In this PhD thesis initially mechanical milling (MM) has been considered as suited strengthening technique due to the severe strain hardening and microstructural refinement induced by severe plastic deformation during the process. Then an enhanced hardening has been obtained by dispersion of a second harder phase in the copper matrix by mechanical alloying (MA), leading to the production of metal matrix composites (MMC). In this PhD thesis strain hardened and dispersion hardened copper materials have been sintered by Spark Plasma Sintering (SPS). Firstly the MM behaviour of Cu as function of milling time has been studied, it consists in three stages: flaking, welding and fracturing process. Since stearic acid has been added as process control agent (PCA), its decomposition has been analysed to limit the residual porosity in sintered samples. Several focused attempts have been made and the best results have been obtained by using a fine particle size, decreasing the heating rate and applying the SPS pressure once the decomposition of PCA was completed. However the presence of copper oxide and microstructure defects induced by the severe strain hardening hinder the densification. The residual porosity is responsible of a decrease of hardness in sintered sample and consequently to a limited wear resistance, to a decrease of thermal conductivity and to a loss of ductility. For the production of MMC a ceramic reinforcement (0.5wt% of TiB2) has been selected. Increasing milling time the dispersion of the hard phase among the matrix becomes more homogeneous and refinement of TiB2 is highlighted. The evolution of particle size and morphology during MA is similar to MM; also the densification mechanism during SPS are the same consisting in powder rearrangement, local and bulk deformation. The final density generally decreases by increasing milling time, by the way an increasing hardness confirms that strain hardening and dispersion hardening abundantly compensate the negative effect of porosity. Has been proved that the hard particles successfully enhanced sliding and abrasion wear meanwhile the copper matrix guarantees high thermal conductivity, satisfying the requirements.
Therefore considering the characteristics of the initial copper powder, promising results have been obtained for MMCs showing an increased hardness combined with a high wear resistance and a thermal conductivity comparable to atomized copper and much higher than the commercial Cu-Be alloy. On the other side mechanical milled samples exhibited some limits, but they allowed a deep understanding of the MM process of copper
Preparation and characterization of Cu2-xZn1+ySnS4 for thin films solar cells
No full textCZTS non-stoichiometric thin films [Cu2-xZn1+xSnS4)] for solar cells applications have been successfully deposited on glass substrates using two different types of synthesis and two effective deposition methods: dip coating into a sol or drop-wise ink spin-coating. For dip-coating, a sol was prepared by mixing a solution of metal chlorides dissolved in methanol together with thiourea dissolved in ethylene glycol; tin chloride (either pentahydrate or anhydrous) was used as a tin source. The ink for spin-coating was prepared by hot-injection, starting from metal (copper, tin and zinc) chlorides like in the previous synthesis: the salts, dissolved in oleylamine, were heated at 130 °C, when a solution of pure sulfur in oleylamine was injected. The CZTS thin films samples from both methods have been recrystallized by two thermal treatments, respectively with and without an extra sulfur powder at 550 °C in Ar atmosphere. Treatment duration was shown to affect both structure and microstructure of CZTS coatings. Moreover, the optical properties of the final absorbing layers were also deeply affected by the type and length of thermal treatments. Spurious phases like SnO2, SnS and ZnS, were produced in some cases, and identified as a possible culprit for poor CZTS photovoltaic device efficiency. Based on the extensive evidence collected during this research work, the present Thesis provides a rationale for an effective preparation of kesterite thin films for photovoltaic applications
Recovering the Sight to blind People in indoor Environments with smart Technologies
No full textThe methodologies presented in this thesis address the problem of blind people rehabilitation through assistive technologies. In overall terms, the basic and principal needs that a blind individual might be concerned with can be confined to two components, namely (i) navigation/ obstacle avoidance, and (ii) object recognition. Having a close look at the literature, it seems clear that the former category has been devoted the biggest concern with respect to the latter one. Moreover, the few contributions on the second concern tend to approach the recognition task on a single predefined class of objects. Furthermore, both needs, to the best of our knowledge, have not been embedded into a single prototype. In this respect, we put forth in this thesis two main contributions. The first and main one tackles the issue of object recognition for the blind, in which we propose a ‘coarse recognition’ approach that proceeds by detecting objects in bulk rather than focusing on a single class. Thus, the underlying insight of the coarse recognition is to list the bunch of objects that likely exist in a camera-shot image (acquired by the blind individual with an opportune interface, e.g., voice recognition synthesis-based support), regardless of their position in the scene. It thus trades the computational time with object information details as to lessen the processing constraints. As for the second contribution, we further incorporate the recognition algorithm, along with an implemented navigation system that is supplied with a laser-based obstacle avoidance module. Evaluated on image datasets acquired in indoor environments, the recognition schemes have exhibited, with little to mild disparities with respect to one another, interesting results in terms of either recognition rates or processing gap. On the other hand, the navigation system has been assessed in an indoor site and has revealed plausible performance and flexibility with respect to the usual blind people’s mobility speed. A thorough experimental analysis is hereby provided alongside laying the foundations for potential future research lines, including object recognition in outdoor environments
Machine Learning for Tract Segmentation in dMRI data
No full textDiffusion MRI (dMRI) data allows to reconstruct the 3D pathways of axons within the white matter of the brain as a set of streamlines, called tractography. A streamline is a vectorial representation of thousands of neuronal axons expressing structural connectivity. An important task is to group the same functional streamlines into one tract segmentation. This work is extremely helpful for neuro surgery or diagnosing brain disease. However, the
segmentation process is difficult and time consuming due to the large number of streamlines (about 3 × 10 5 in a normal brain) and the variability of the brain anatomy among different subjects. In our project, the goal is to design an effective method for tract segmentation task based on machine learning techniques and to develop an interactive tool to assist medical practitioners to perform this
task more precisely, more easily, and faster. First, we propose a design of interactive segmentation process by presenting the user a clustered version of the tractography in which user selects some of the clusters to identify a superset of the streamlines of interest. This superset is then re-clustered at a finer scale and again the user is requested to select the relevant clusters. The process of
re-clustering and manual selection is iterated until the remaining streamlines faithfully represent the desired anatomical structure of interest. To solve the computational issue of clustering a large number of streamlines under the strict time constraints requested by the interactive use, we present a solution which consists in embedding the streamlines into a Euclidean space (call dissimilarity representation), and then in adopting a state-of-the art scalable implementation of the k-means algorithm. The dissimilarity representation is defined by selecting a set of streamlines called prototypes and then mapping any new streamline to the vector of distances from prototypes. Second, an algorithm is proposed to find the correspondence/mapping between streamlines in tractographies among two different samples, without requiring any transformation as the traditional tractography registration usually does. In other words, we try to find a mapping between the tractographies. Mapping is very useful for studying tractography data across subjects. Last but not least, by exploring the mapping in the context of dissimilarity representation, we also propose the algorithmic solution to build the common vectorial representation of streamlines across subject. The core of the proposed solution combines two state-of-the-art
elements: first using the recently proposed tractography mapping approach to align the prototypes across subjects; then applying the dissimilarity representation to build the common vectorial representation for streamline. Preliminary
results of applying our methods in clinical use-cases show evidence that our proposed algorithm is greatly beneficial (in terms of time efficiency, easiness.etc.) for the study of white matter tractography in clinical applications
Growth Study and Characterization of TiO2 Based Thin Films for Low Temperature Synthesis of Transparent Conductive Films
No full textTransparent conductive oxides (TCOs) are of increasing importance for displays, photovoltaics, architectural and window glass technologies. The most utilized TCOs are tin-doped indium oxide (ITO), which is suffering from scarcity, lower transmittance in the near infrared region, poor chemical stability in hydrogen atmosphere and toxicity. Due to these limitations, there is a huge interest to develop alternative TCOs which possess higher conductivity than indium or that use less scarce elements than indium. Currently, many potential candidates are under the extensive study to replace ITO including doped ZnO, SnO2 and TiO2.
The core objectives of the work presented in this thesis were: (i) to develop a method for the low temperature (≤350 °C) synthesis of TiO2-based transparent conductive films, which is chemically stable, inexpensive and non-toxic material; and (ii) to investigate the growth-properties relationship to understand the factors dictating the doping process and properties of Nb-doped TiO2 films (TNO). The approach was to explore three doping methods of the films: intrinsic doping, extrinsic doping and, with the aim to combine the benefits of both, intrinsic-extrinsic co-doping. TNO films were deposited by RF sputtering on various substrates including glass, silicon and Kapton polyimide under different plasma power conditions in Ar and Ar-O2 discharge. Two types of niobium containing targets, Nb metal and Nb2O5 oxide were employed simultaneously with ceramic TiO2 target for the films growth. Thermal and laser annealing processes were carried out for the films crystallization and doping. The structural analysis by x-ray diffraction (XRD) revealed a poor control over the anatase phase (mixed anatase and rutile phase formation) when the substrate was heated during the films growth, which degraded the films transport properties. The adjustment of the process pressure and substrate temperature enhanced the conductivity of the annealed TNO films and allowed to tune the resistivity over a wide range (10-1-10-4 Ω.cm). The resistivity measured for the intrinsically and extrinsically doped films were of the order of 10-2 Ω.cm, which is higher than that of ITO (< 10-3 Ω.cm). The lowest resistivity was obtained for intrinsically-extrinsically co-doped TiO2 (7.45×10-4 Ω.cm) with optical transparency of 65-90 % in the wavelength range 400-750 nm. The findings of this work show that the conductivity of the films is strongly correlated with the crystalline structure particularly on the amount of anatase phase with respect to rutile and with the oxygen vacancies in the films. The approach adopted in this work for the generation of oxygen vacancies could be useful for other oxide-based films, where the oxygen vacancies-dependent properties are crucial, for room temperature ferromagnetism and photocatalytic applications. The obtained results can significantly contribute to the development of transparent electrodes by RF sputtering, a suitable technique for coating on large area substrates
Democracy and Development in the Making: Civic Participation in Armenia; Challenges, Opportunities
No full textThis research focuses on civic participation and its role in an emerging democracy context, and examines the forms, patterns, trends, obstacles to and opportunities for civic participation, as well as the impact of civic participation on democratization and development processes in Armenia, a post-soviet country in the South Caucasus, that has embarked on simultaneous transition toward democracy and free market economy since its independence in 1991.
The dissertation suggests that civic participation is a key ingredient for successful transformations and effective reforms in both political and economic sectors in the post-soviet context of Armenia, and, therefore, more attention, as well as more vigorous efforts and resources should be directed to building civic capacity of the people and organizations in this setting. It is argued, that while, obviously, not a panacea for all development and democratization related challenges, civic engagement has a strong potential to foster those processes and contribute to the achievement of more effective, inclusive and sustainable solutions in the areas of democracy promotion and development in the transition countries. The original contribution of the thesis is an empirical study of civic participation in Armenia and assessment of its determinants and the impact on democracy and development related outcomes in the country. The primary research includes a study of civic participation in 10 rural and small urban communities across the country, and provides comprehensive information and insights into civic participation forms, pattern, determinants, obstacles and opportunities at the community level. Civic participation is further studied by examining the major civic initiatives and campaigns that took place in the country over the recent five years (2010-2015) and assessment of their outcomes and impact. The study looks closely at the determinants of civic participation, both the individual level factors and the obstacles and opportunities provided by the institutional context, and, in particular, examines the relationship of civic participation with social capital, civic education, and use of internet and communication technology (ICT). Civic participation habits and trends among the youth are explored by means of surveys conducted in 2013 and 2014. An innovative measure – a Civic Participation Score (CP Score) is introduced and computed, based on a pre-defined and operationalized set of indicators, and a Civic Participation Index (CP Index) is calculated for monitoring the changes, in separate indicator categories and overall, and analysing civic participation trends over time. The research sheds light on civic participation practice and trends in Armenia and builds a framework for analysis of civic engagement in an emerging democracy context, by identifying the participants, their motives, forms of civic engagement, its impact, as well as challenges and opportunities for participation. The study highlights the specific needs and opportunities for further civic capacity building and lays down a roadmap for further research and action in this direction
Modelling water budget at a basin scale using JGrass-NewAge system
No full textWater resources availability and its variability is one of the most pressing global problems. Hydrological models are useful to understand the water balance of a basin, providing information for water resource forecast, assessment, and management. The effectiveness of the models in estimating the freshwater space-time availability and variability, however, depends on concurrent and explicitly modelling of all water budget components instead of a single component estimation and optimization. The whole water budget modelling at basin scale requires a combined solution from hydrological and spatial information tools, in-situ and remote sensing data. The present dissertation describes an effort to improve estimation of each water budget component, and water budget closure at various spatial and temporal scales, by combining JGrass-NewAge model system, GIS spatial toolbox, in-situ and remote sensing data. JGrass-NewAge is a system which deploys modern informatics to facilitate models maintainability and reproducible research. It integrates advanced GIS features and the Object Modelling System version 3 infrastructures, which allow for a component-based modelling experience. This means that JGrass-NewAGE is not actually a model, but a set of elements (the components) that can be combined just before runtime to produce various modelling solutions. Topics like calibration of processes, the interpolation forcing and the assessment of forecasting errors can therefore be faced with consistent and solid approaches. In this context also the use of some remote sensing resources can be inserted appropriately and with new techniques. For all the analysis, two significantly different basins, in terms of size and hydrological processes, are considered as case studies. These are Posina river basin in northeast Italy (small size basin) and Upper Blue Nile basin(large size basin) are used as case study.
The uDig Spatial Toolbox (uST) GIS infrastructure that is used for generating the hydromorphological parameters is described in the second chapter. A large number of tools are included in uST for terrain analysis, river network delineation, and basin topology characterisation. In addition, the geomorphological settings necessary to run JGrass-NewAGE are shown. The third chapter studies the effect of spatial discretisation and the hillslope size on basin responses. The possible epistemic uncertainty exerted by the use of sub basin spatial discretisation of topographic information in the semi-distributed hydrological modelling has been studied. The use of different spatial representation in hydrological modelling context has been also studied by comparing JGrass-NewAGE with a model configuration called PeakFlow. The latter is an implementation of the geomorphological unit hydrograph based on the width function. The experiment indicates that the Peak-Flow model, with a more accurate spatial representation, reproduce the storm events slightly better than the JGrass-NewAGE model. In the fourth chapter, the thesis set-up JGrass-Newage modelling solution for the estimation of hydrological modelling inputs (rainfall, snow, temperature data) and estimates them, as well as with their errors. Regards to the meteorological forcings (mainly temperature and precipitation), in Posina river basin where there are relatively dense meteorological stations, the effects of different interpolation schemes were evaluated. Since the hydrological processes from rainfall is different from snowfall, a new method of separating rainfall and snowfall was introduced using MODIS imagery data.
In the fifth chapter, JGrass-NewAGE was used to estimate the whole set of water balance components. For evapotranspiration (ET) estimation, the Priestley-Taylor component of JGrass-NewAGE is used. In order to calibrate its parameter a new method based on the water budget was implemented. This method uses two different hypothesis on available data (budget stationarity "Budyko hypothesis", and local proportionality of actual evapotranspiration to soil moisture availability). Finally the spatial and temporal dynamics of water budget closure of Posina river basin is presented. The sixth chapter concerns about the inputs data, particularly precipitation, for water balance modelling in a region where ground-based gauge data are scarce. Five high-resolution satellite rainfall estimation (SRE) products were compared and analysed using the available rain gauge. The basin rainfall is investigated systematically, and it was found that, at some locations, the difference in mean annual rainfall estimates between these SREs very high. In addition to the identification of the best performing products, the chapter shows that a simple empirical cumulative distribution (ecdf) mapping bias correction method can provide a means to improve the rainfall estimation of all SREs, and the highest improvement is obtained for CMORPH.
In the seventh chapter, using the capability of JGrass-NewAGE components and different remote sensing data, the spatio-temporal water budget of Upper Blue Nile basin is simulated. The water budget components (rainfall, discharge evapotranspiration, and storage) were analysed for about 16 years at daily time step using the modelling solution and remote sensing data set. For the verification of the approaches followed, wide ranges of remote sensing data (MODIS ET product MOD16, GRACE, and EUMETSAT CM SAF cloud fractional cover) are used
Leaving Home Sooner or Later: Co-residence and Parent-Adult Child Relations in Italy and Sweden
No full textThe present dissertation examines whether the heterogeneity of co-residence experiences and the nest-leaving process have consequences for later parent-adult child relationships in Italy and Sweden. Three aspects of intergenerational linkages are analyzed: residential proximity, the frequency of parent-child contact, and the downward flow of economic resources from parents to their adult children. By devoting particular attention to these three dimensions of intergenerational solidarity, the first chapter presents an overview of the literature on parent-adult child relationships and describes long-standing cultural differences between Italy and Sweden.
In the second chapter, I ask whether in Italy the time spent in the parental home promotes the frequency of contacts between generations, and whether violating social norms regarding the socially accepted time for leaving home is related to less frequent interactions with parents in later life. The findings show that the longer the time adult children spent in their parents’ home, the higher the propensity to reside near, and maintain frequent interaction with parents in later life is. In addition, spending longer time in the parental home appears to provide much less benefit for Italian daughters than for sons. Age norms appear to prescribe the socially accepted ‘age deadline’ for fulfilling expectations for normal adult development. Considering the reasons for leaving home, marriage continues to be the normative occasion to leave the parental family, particularly among adult daughters, who are subject to greater cultural expectations about family ties.
The third chapter devotes particular attention to union dissolution and family conflict during childhood and adolescence as possible mechanisms behind the relationship between nest-leaving processes and later parent-child relationships. The findings reveal that the duration of co-residence is likely to foster family interactions also in Sweden, and this positive relationship is only marginally explained by childhood family experiences. However, late home leavers tend to maintain frequent contacts with parents in part owing to having moved shorter geographical distances, and this is more evident for adult daughters than for sons. In addition, adult daughters who stay at home for longer have more opportunities to form binding relationships with mothers than with fathers.
The fourth study aims to extend the findings of the previous two chapters, by analyzing intergenerational financial transfers and using a within-family approach (or a sibling design). The findings show that in Italy and other southern European countries late home leavers are more likely to receive economic support from their parents, compared to their siblings who move out of the family nest at an earlier age. But this effect is completely mediated by the time since leaving the parental home, indicating that parents tend to facilitate the transition to independence of their young adult children.
The last chapter discusses the findings in the light of previous research. The results of the present dissertation supports the idea that family members’ life courses are deeply interconnected, and that previous family history has important long-term consequences for later intergenerational relationships. I provide new insights into how co-residence experiences and events in early adulthood shape later family relations throughout the life course
Implicit Human-computer Interaction: Two complementary Approaches
No full textOne of the main goals of Human Computer Interaction (HCI) is to improve the interface between users and computers: interfacing should be effortless and easy to learn. In this thesis, we pursue this goal, aiming to reduce the stress of users and increase their wellbeing. We work on two different but complementary approaches: (i) Automatic assessment of user’s inner psychological state, so as to enhance computer-human interaction; and (ii) Information presentation in a comprehensive manner, with no stress added by devices and applications when delivering information. Not only computers should understand their users, but also users should easily understand the information given by computers.
For the first approach we collected physiological and psychological data from people exposed to emotional stimuli. We created a database, and made it freely available to the community, for further use in research on automated detection of the differences in the inner states of users. We employed the data for predicting both the emotional state of users and their personality traits. For the second approach, we investigated two devices that intend to provide comprehensible feedback easily. First we discuss how to utilize a breathing sensor that informs its users on their current physiological state and on how to decrease the stress in daily life by adapting their breathing patterns. Here we investigated general criteria on how to develop systems that are easily understandable. The second device was a tactile belt. We analyze the belt as a solution that provides comprehensive guidance information in navigation contexts, and that does not require cognitive effort. The belt uses localized tactile stimulation to transmit directional information. By employing the tactile sense it can augment or even replace the information normally received through eyes and ears. Finally, we discuss opportunities for future applications of our research, and conclude with a summary of our contributions to HCI: transmitting information from humans to machines and vice versa
Il Single Supervisory Mechanism. Funzioni e modelli di integrazione amministrativa
Get PDFAvvalendosi degli “strumenti” del diritto amministrativo europeo, il presente lavoro intende esplorare alcuni tra i principali temi e problemi sollevati dalla recente istituzione del Single Supervisory Mechanism (SSM) o Meccanismo unico di vigilanza, nel quadro del più ampio progetto di realizzazione dell’Unione bancaria europea.
Dopo una breve ricostruzione dei processi evolutivi che hanno segnato l’incrementale “europeizzazione” delle funzioni di regolazione e di vigilanza nel settore del credito, la ricerca si propone di analizzare il quadro istituzionale entro cui si inserisce il Meccanismo unico di vigilanza, di individuarne la base giuridica, gli obiettivi e l’ambito di applicazione. La ricerca esamina, inoltre, le strutture organizzative e relazionali del SSM, la natura e la composizione dei nuovi organi di vigilanza, i rapporti tra la Banca centrale europea e le autorità di vigilanza nazionali. Particolare attenzione è dedicata, poi, agli aspetti dell’indipendenza e dell’accountability del sistema settoriale. L’indagine prosegue con lo studio della normativa sostanziale applicabile da parte BCE nell’esercizio dei compiti di vigilanza e ne evidenzia alcuni tratti affatto peculiari. Inoltre, ampia attenzione è dedicata all’analisi dei compiti e dei poteri di vigilanza attribuiti alla BCE e alla questione – centrale per la comprensione del funzionamento del SSM – relativa alle tecniche di allocazione e distribuzione dei compiti tra le autorità componenti il sistema comune, dei numerosi strumenti di coordinamento, dei vari moduli di esecuzione della normativa bancaria sostanziale, delle sequenze procedimentali che sorreggono l’esercizio dei poteri di vigilanza. L’ultima parte è dedicata al tema della tutela dei soggetti privati destinatari dell’azione amministrativa, nella prospettiva delle garanzie procedimentali, dei rimedi amministrativi interni alla BCE e della tutela giurisdizionale.
L’indagine si propone di ricostruire i diversi modelli di integrazione amministrativa che strutturano l’architettura istituzionale del Meccanismo unico, di esplorarne le novità e di evidenziarne le logiche. In definitiva, ci si chiede se – al di là della estrema varietà delle forme di esecuzione, degli strumenti di coordinamento e delle tecniche di integrazione organizzativa, funzionale e procedimentale utilizzate per “tenere insieme” le componenti del Meccanismo – sia possibile individuare alcuni elementi che, in una prospettiva sintetica, risultino in grado di identificare in termini unitari un nuovo modello di integrazione amministrativa europea