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Solid-state single-photon Detectors and CMOS Readaout Circuits for Positron Emission Tomography Applications
No full textIn recent years, Silicon Photomultipliers (SiPMs) have been increasingly used as photo-detectors in Positron Emission Tomography (PET) application, which is a nuclear imaging tech-nique that is used to accurately image biochemical processes inside the human body. A SiPM is composed by an array of parallel connected micro-cells of Single Photon Avalanche Diodes (SPADs), and can be classified mainly into two categories Digital-SiPMs (D-SiPMs) and Analog-SiPMs (A-SiPMs). In A-SiPMs, all the microcells share the same bias voltage and have a common readout line. Through custom manufacturing process, the performance of A-SiPMs can be exten-sively optimized. With respect to A-SiPMs, D-SiPMs are composed by many SPAD pixels, each one containing one SPAD and local front-end circuitry. The digital SiPM takes advantage of CMOS technology to perform a 1-b direct A/D conversion per SPAD thus providing a fully digi-tal implementation. On the other hand, SPADs fabricated in CMOS process typically suffer high noise since the critical SPAD implants can hardly be optimized by using the standard CMOS process flow. The main activities carried out within this PhD thesis have been focused on two critical as-pects relevant for the optimization of PET systems performance: (I) the improvement of the per-formance of SPAD in D-SiPMs and (II) the development of high-performance A-SiPM readout application specific integrated circuit (ASIC).
Concerning the first point, novel SPADs have been fabricated in CMOS 150-nm technology targeting at low noise, high sensitivity and excellent timing jitter. Three structures with different shapes, geometries and diameters, have been implemented in three test chips. Measurement re-sults of one p+/n-well SPAD array show a 0.4Hz/µm2 dark count noise, 0.85% afterpulsing for a dead time of 150ns at 3V excess bias. The photon detection probability is about 31% at 450nm wavelength at 5V excess bias. The SPAD exhibits a timing jitter of 82ps (FWHM) under a blue laser, which is potentially suitable for D-SiPMs in PET application.
The second objective of this PhD work was to develop A-SiPM readout ASIC for PET appli-cation. To utilize the high intrinsic time resolution of A-SiPMs, the development of specialized, highly integrated readout electronics is required. Therefore, two ASICs, first chip with test struc-tures and 16 channels and the second chip with 32 channels, have been developed in 150-nm CMOS technology, with the aim of developing a compact A-SiPM module. The performance of the second chip has been validated by using 3 × 3 × 5 mm3 LYSO crystals coupled to 4 × 4 mm2 SiPMs (FBK-NUV-HD). The measurements show an energy resolution of 14.7% FWHM for the detection of 511 keV photons and the coincidence time resolution is 433ps (FWHM). To improve the timing resolution, part of the PhD work was carried on Stanford University, focused on char-acterization of A-SiPMs and analysis of noise contribution
Computational Aesthetics in HCI: Towards a Predictive Model of Graphical User Interface Aesthetics
No full textThis thesis describes the development and validation of a predictive model of graphical user interface (GUI) aesthetics. The development was informed by the processing-fluency theory of aesthetic pleasure and involved outlining several visual dimensions of GUI designs, which could affect aesthetics impression. Each of the dimensions was grounded in theory and represents a unique visual aspect of GUI design. The resulting model automatically evaluates the design dimensions and combines them in an estimate of the average impression that GUI appearance would make on the user population. The model was validated in a number of user studies proving high validity and reliability. The model outputs an aesthetics score ofuser impression and could inform the creation of more beautiful GUIs by highlighting which of the design dimensions could be improved. The thesis describes the studies that validated the model on several types of GUIs and demonstrated a potential application of the model in future research and practice
Tracing bedload transport in Alpine mountain streams by means of PIT-tagged particles: interplay between sediment supply and hydro-meteorological forcing
No full textConceptual models of first-order controls governing river channel dynamics in mountain streams have been rarely tested in the field. In this Ph.D. thesis we examine the effects of hydro-meteorological forcing and sediment supply on the bedload transport dynamics of mountain streams. To this purpose we select three step-pool mountain streams that share identical granitic lithology, but exhibit contrasting sediment supply and hydro-climatic conditions. The three study sites, which are located in Trentino, Eastern Italian Alps, include the Ussaia Creek (2.3 km2) in Val di Sole, and the Grigno and Tolvà Creeks (7 km2) in Valsugana. The former is characterized by high, sand-rich sediment supply delivered by some 20 m-thick glacigenic deposits. The latter two, which flow through glacially carved bedrock terrain, are disconnected from colluvial sediment inputs so that sediment sources are limited to channel banks and bars during high flows. Mean annual precipitation is respectively 844 mm in Ussaia Creek and 1511 mm in Grigno and Tolvà Creeks. All study streams experience, to variable extents, snowmelt and rainfall-induced bedload transporting flows.
To estimate quantitatively the effects and the interactions associated with sediment supply and hydro-meteorological forcing, we monitor precipitation and atmospheric temperature. Hydrological levels at instrumented sections are recorded via pressure transducers. Bedload transport is monitored by tagging and tracking 632 stones (b-axis: 30 to 131 mm; weight 88-4004 g). The tracking of these PIT-tagged tracers was conducted from December 2013 to December 2015 by means of an RFID portable pole antenna. Cumulatively, a total of 16, 11 and 19 bedload events were monitored respectively at Grigno, Tolvà and Ussaia Creek. We measured displacement lengths occurred during inter-survey periods, induced by peak flows associated to snowmelt, rainfall or a combination of the two (mixed-type). Active channel depth was evaluated via direct digging tests at the three study sites finding a median burial depth of 0.1 m at Grigno and Tolvà Creeks, and 0.25 m at Ussaia Creek; recent findings (Schneider et al., 2014), show that ordinary bedload events of boulder-bed streams in the Alps, active layer thickness is comprised within 0.01 and 0.22 m; Houbrechts et al. (2012) demonstrated that in mountain streams the active layer thickness is lower than D50. The active layer width was evaluated via orthophoto maps obtained through Structure-from-Motion. To characterize the streambed roughness and the channel slope we conducted topographic and morphologic surveys. To evaluate event-based bedload sediment volumes we applied the virtual velocity approach (Haschenburger and Church, 1998). In particular, to assess the minimum discharge able to entrain clasts, determining the virtual transport duration of each tracer weight class, we used the competence flow method. In order to evaluate the uncertainty associated with methodology that has been customarily applied in the literature, we performed a sensitivity analysis of the evaluation of bedload transfer proposing three scenarios varying the assumptions that (i) virtual velocities are normally distributed and therefore justifying the adoption of median virtual velocities instead of the average virtual velocity, (ii) that active channel width is constant in time, hence replacing bankfull width with site-specific active widths, evaluated on the base of PIT-tagged particles displacements.
The monitoring year 2014 was characterized by a total annual precipitation two times larger than the historical mean, associated to a prolonged snowmelt and to heavy storm front events. By contrast, in 2015 we observed no snowmelt and no precipitation occurred in November and December. At Grigno and Tolvà Creeks, the majority of sediment is transported during autumn storm fronts (median travel distance: 30 m) and secondarily by summer convective storms (median travel distance: 4.5 m). At Ussaia Creek, snowmelt-related events induced 17% of the observed displacement lengths (median travel distance: 2 m), but the primary source of sediment transport is associated chiefly with prolonged storm fronts (median travel distance: 200 m). The mass of tracers does not affect virtual velocities, that are instead affected by seasonal distribution of hydro-meteorological events. In fact, at Grigno and Tolvà Creeks we observe a stratification of velocities according to hydro-meteorological forcing, with the largest values observed during rainfall season, commonly associated to highest values of peak discharge. Variability of virtual velocities at Ussaia Creek does not depend on seasonal hydro-climatic forcing and peak discharge values, with distributions of virtual velocities partly overlapping among snowmelt- and rainfall-related events. The seasonal pattern is translated to bedload transport volumes, with Ussaia Creek transporting by the end of the snowmelt period in 2014, three times more sediment than Grigno Creek. This is testified by a prolonged autumn rainfall that hit simultaneously the study sites, caused a debris-flow that transported 1084 m3 at Ussaia Creek, a much larger quantity compared to the 32.2 m3 evaluated at Grigno and the 62.5 m3 at Tolvà Creek.
The definition of rainfall intensity-duration thresholds of precipitation events triggering bedload at our sites shows that transport-limited systems (i.e., Ussaia Creek) result sensitive to precipitation inputs characterized by low rainfall intensity (below 5 mm hr-1) and large duration. Conversely, supply-limited systems (i.e., Grigno and Tolvà Creeks) exhibit armoured beds and interlocked, resilient structures that limit entrainment processes, mobilizing bedload only in response to short-duration/high-intensity rainfall (10 mm hr-1). These channels preserve their morphological structure even under high flow events, triggering sediment transport processes limitedly to peaked storm hydrographs.
In the present study we show that the variability in bedload transport among different study reaches is linked to sediment supply conditions and to peculiar hydro-climatic settings. An additional study site characterized by dry conditions, Strimm Creek (Alto Adige, Italy), allows us to obtain a latitudinal transect from dry to wet conditions across the Eastern Italian Alps. By monitoring tracer displacements from 2011 to 2015 at this formerly-glaciated, high-elevation mountain basin, we observe that limited sediment-supply conditions exert a strong control on bedload, chiefly triggered by snowmelt events that account for 73% of the overall travel distances. At Grigno and Tolvà Creeks, also characterized by limited sediment supply, transport is dominated by rainfall events, responsible of driving 95% of the overall travel distances. Sediment availability at Ussaia Creek is responsible for triggering the largest observed bedload events, associated to prolonged autumn precipitation and secondarily to snowmelt events
River temperature behaviour in changing environments: trends, patterns at different spatial and temporal scales and role as a stressor
No full textRiver/stream water temperature is one of the master water quality parameters as it controls several key iogeochemical, physical and ecological processes and river ecosystem functioning. Thermal regimes of several rivers have been substantially altered by climate change and other anthropogenic impacts resulting in deleterious impacts on river health. Given its importance, several studies have been conducted to understand the key processes defining water temperature, its controls and drivers of change. Temporal and spatial river temperature changes are a result of complex interactions between climate, hydrology and landscape/basin properties, making it difficult to identify and quantify the effect of individual controls. There is a need to further improve our understanding of the causes of spatiotemporal heterogeneity in river temperatures and the governing processes altering river temperatures. Furthermore, to assess the impacts of changing river temperatures on the river ecosystem, it is crucial to better understand the responses of freshwater biota to simultaneously acting stressors such as changing river temperatures, hydrology and river quality aspects (e.g. dissolved oxygen levels). So far, only a handful of studies have explored the impacts of multiple stressors, including changing river temperature, on river biota and, thus, are not well known. This thesis, thus, analysed the changes in river temperature behaviour at different scales and its effects on freshwater organisms. Firstly, at a regional scale, temporal changes in river temperature within long (25 years) and short time periods (10 years) were quantified and the roles of climatic, hydrological and landscape factors were identified for North German rivers. Secondly, at a reach scale, spatial temperature heterogeneity in a sixth-order lowland river (River Spree) was quantified and the role of landscape factors in inducing such heterogeneity was elucidated. Thirdly, at a site scale, short-term behavioural responses (namely drift) of three benthic invertebrate species to varying levels of water temperature, flow, and dissolved oxygen, and to combinations of those factors were experimentally investigated.
Results from this thesis showed that, at a regional scale, the majority of investigated rivers in Germany have undergone significant annual and seasonal warming in the past decades. Air temperature change was found to be the major control of increasing river temperatures and of its temporal variability, with increasing influence for increasing catchment area and lower altitudes (lowland rivers). Strongest river temperature increase was observed in areas with low water availability. Other hydro-climatological variables such as flow, baseflow, NAO, had significant contributions in river temperature variability. Spatial variability in river temperature trend rates was mainly governed by ecoregion, altitude and catchment area via affecting the sensitivity of river temperature to its local climate. At a reach scale as well, air temperature was the major control of the temporal variability in river temperature over a period of nine months within a 200 km lowland river reach. The spatial heterogeneity of river temperature in this reach was most apparent during warm months and was mainly a result of the local landscape settings namely, urban areas and lakes. The influence of urban areas was independent of its distance from the river edge, at least when present within 1 km. Heat advected from upstream reaches determined the base river temperature while climatological controls induced river temperature variations around that base temperature, especially below lakes. Riparian buffers were not found to be effective in substantially moderating river temperature in reaches affected by lake warming due to the dominant advected heat from the upstream lake. Experimental investigation indicated that increasing water temperature had a stronger short-term effect on behavioural responses of benthic invertebrates, than simultaneous changes in flow or dissolved oxygen. Also, increases in water temperature was shown to affect benthic invertebrates more severely if accompanied by concomitant low dissolved oxygen and flow levels, while interactive effects among variables vary much among taxa.
These results support findings of other studies that river warming, similar to climate change, might be a global phenomenon. Within Germany, lowland rivers are the most vulnerable to future warming, with reaches affected by urbanization and shallow lentic structures being more vulnerable and, therefore, requiring urgent attention. Furthermore, river biota in lowland rivers is particularly susceptible to short-term increases in river temperature such as heat waves. Plantation of riparian buffers, a widely recognized practice to manage climate change effects, in the headwater reaches can be suggested to mitigate and prevent future warming of lowland rivers in general and also throughout river basins, as river temperature response in lowland catchments is a culmination of local and upstream conditions. However, further river temperature increase in lowland river reaches within or close to urban areas and shallow lentic structures will be more difficult to mitigate only via riparian shading and would require additional measure
Adaptive Quality Estimation for Machine Translation and Automatic Speech Recognition
No full textQuality estimation (QE) approaches aim to predict the quality of an automatically generated output without relying on manually-crafted references. Having access only to the system's input and output, a QE module assigns a score or a label to each (input, output) pair. In this thesis we develop approaches to predict the quality of outputs of
two types of natural language processing (NLP) systems: machine translation (MT) and automatic speech recognition (ASR). The work presented here can be divided into three parts. The first part presents advances on the standard approaches to MT QE. We describe a general feature extraction framework, several quality indicators dependent and independent from MT systems that generate the translations, and new quality indicators that approximate the cross-lingual mapping between the meaning of source and translated sentences. Such advances result in state-of-the-art performance in two official evaluation campaigns on the MT QE problem. In the second part we show that the standard MT QE approaches suffer from domain drift problems due to the high specificity of labeled data currently available. In the standard MT QE framework, models are trained on data from a specific text type, with translations produced by one MT system and with labels obtained over the work of specific individual translators. Such models present poor performance when one or more of these conditions change. The ability of a system to adapt and cope with such changes is a facet of the QE problem that so far has been disregarded. To address these issues and deal with the noisy conditions of real-world translation workflows, we propose adaptive approaches to QE that are robust to both the diverse nature of translation jobs and differences between training and test data. In the third part, we propose and define an ASR QE framework. We identify useful quality indicators and show that ASR QE can be performed without having access to the ASR system, by only exploring information of its inputs and outputs. We apply a subset of the same adaptive techniques developed for MT QE and show that the ASR QE setting can also benefit from robust adaptive learning algorithms
I poteri signorili in un'area di confine. L'Appenino tosco-emiliano tra l'XI e il XIV secolo.
No full textLa presente ricerca si propone di studiare l’evoluzione dei poteri signorili nel contesto geografico dell’Appennino tosco-emiliano attraverso l’analisi, in chiave comparativa, di tre signorie rurali (conti Alberti, Ubaldini, conti di Panico ) inerenti quello specifico ambito territoriale. Dal punto di vista cronologico l’indagine ha inizio a partire dall’XI secolo – con la comparsa, nelle fonti, dei poteri signorili di banno – e termina intorno agli anni Trenta del XIV secolo – quando la contestazione delle prerogative signorili in quella zona era un fatto ormai consolidato sia in termini politici, sia in termini territoriali. Mediante lo studio della documentazione disponibile – dispersa in vari fondi archivistici, pubblici e privati – si è perciò tentato di approfondire alcune tematiche di carattere generale tra le più frequentate e discusse dalla storiografia, quali il rapporto tra città e contado, i processi di ricomposizione politica dei territori, lo sviluppo dell’aristocrazia rurale e delle prerogative ad essa connesse. La scelta di studiare le vicende relative alle tre famiglie dei conti Alberti, degli Ubaldini e dei conti di Panico risponde a precise opportunità di metodo e di ricerca. Riguardo alle prime si è tenuto conto dell’omogeneità territoriale delle zone d’influenza signorile, collocate, per la maggior parte, a ridosso delle montagne e delle colline delle attuali province di Firenze, Pistoia, Prato e Bologna. Riguardo alle seconde, invece, si è inteso privilegiare alcuni dominati signorili solo in parte studiati dalla storiografia e dall’erudizione locale, così da rendere più proficuo il confronto con realtà aristocratiche differenti che hanno goduto di maggior considerazione da parte degli storici (ad esempio, i conti Guidi). La ricerca è articolata in tre sezioni. Nella prima vengono analizzate le forme del potere esistenti nell’area che sta tra l’Emilia e la Toscana nel pieno medioevo discutendo la terminologia utilizzata per descrivere l’organizzazione dello spazio ed evidenziando il ruolo che ebbero alcune città (Firenze, Pistoia, Prato e Bologna) nel disciplinamento del territorio. Nella seconda sezione vengono indagati i presupposti del potere signorile, considerando quali “prerequisiti strutturali” prima il radicamento patrimoniale e il possesso degli uomini, poi la rete delle relazioni intessute con l’impero, con il papato, con i marchesi di Tuscia, con i vescovi, con gli enti ecclesiastici e con le città. Nella terza sezione la tesi descrive l’esercizio dei poteri signorili mostrando come questi si manifestassero nell’amministrazione della giustizia, nel controllo di determinati diritti di natura economica (in particolare quelli di derivazione pubblica), nell’attività militare e più in generale nell’uso della coercizione e della violenza. Ciascuno di questi aspetti è quindi posto in relazione con le pretese e le richieste provenienti dalle città comunali, nel tentativo di offrire una panoramica del tema quanto più possibile completa ed esaustiva
The Aesthetics of Sustainability. Systemic thinking and self-organization in the evolution of cities
No full textSustainability while being definitely a new form of humanity, as it has been proposed and dealt with in many urban and landscape projects lacks often of an essential characteristic of the anthropic space: seduction. We believe that Sustainability has to find its own power of seduction if it is to compete successfully with the ambiguous but established charms of the unsustainable city. From all the above it is clear the importance of the ‘Aesthetic of Sustainability’ as fundamental for the success of a new model of green planning not just from an environmental and economic point of view, but, perhaps and most importantly, from a social and mental one. This research investigates the possibility to look at Sustainability and Aesthetics through the lens of evolutive processes and the complexity theory to inform a new Bottom Up/Self Organized approach as a possible morphogenetic process for sustainable city design.
Often criticized as the theory of ‘out of control’ the complexity theory applied to the urban could instead be the enabler of a new paradigm where the notion of single authorship with intellectual ownership and his aesthetic language is substituted by the concept of a collective and a new aesthetics of choice where the Aesthetics of Sustainability is that action on the psyche, negotiating between personal subjectivity and collective subjectivity, as a form of knowledge, a process, and a tool for aesthetic creation that cannot be separated from the socius and the environment
Costellazione Tempesta. Immaginare Shakespeare tra Riscritture e Iconografia
No full textThe essay analyses the evolution through the centuries XVII-XX of a number of different adaptations of Shakespeare's The Tempest. The analysis is enriched by cross-medial references to the history of Shakespearean iconography, that intersecates and sometimes guides the development of new readings and rewritings of The Tempest
The Psychophysiological Effects of Touch and Odor
No full textIn everyday life, the emotional perception often occurred in different modalities at once but knowledge about multisensory perception on emotion was minimal. To understand emotional integration, odors and touch were used in two experiments. The first experiment was conducted to distinguish the emotional effects of different odors and to examine the effect of gender difference with respect to emotional perception. The aim of the second experiment was to determine the emotional integration of bimodal stimuli. The self-report and psychophysiological responses from forty-five participants were computed. Data were analyzed by two-way mixed ANOVA and two-way repeated measures ANOVA, statistical significance at the .05 level. The findings highlight that there was no crossed interaction between olfactory and tactile modalities in the aspect of emotion. The bimodal stimuli did not enhance the emotional perception of unimodal stimuli. Civet oil markedly elicited an unpleasantness. Michelia oil elicited objective arousal, meanwhile, Lavender oil elicited a pleasant feeling. In addition, 3 cm/s stroking touch elicited subjective pleasantness with moderate arousal, and 30 cm/s stroking touch elicited high arousal without the feeling of pleasantness. Moreover, men are more sensitive to some type of odor than women especially unpleasant odors and arousing odors. This was the first work that studied the bimodal emotional perception between olfactory and tactile modalities and was a first study that revealed the peripheral psychophysiological effect of CT afferents. A further study should investigate an impact of gender and culture to emotional integration and a consistency of finding
Essays on Firm Boundaries and Firm Organization in Transition countries
No full textFor a long time economic theory argued that the level of economic development depends on the allocation of production factors both between and within economies. However, it is rarely underlined that allocation depends on organizational decisions and management, especially on organizational decisions within and across firms. Understanding such decisions through both empirical studies and theory is highly important. It may enable us to understand the microeconomic roots of macroeconomic patterns. This thesis conducts at the empirical analysis of organizational decisions that may potentially influence aggregate performance. It shows connection of the organizational decisions with both the economic environment and firm characteristics. The focus is on transition countries, after the massive privatization period. The reasons are threefold: i) essential differences that emerged in performances of countries with similar heritages and starting points ii) the need to quantify the impact of “complementary” reforms after privatization iii) the mis-match between the expectations and the results of building a market-oriented environment.
Following a first chapter overviewing the economic context, theoretical positioning and empirical framework, the thesis contains four studies. The first two studies (Chapter 2 and Chapter 3) are devoted to firm boundaries decisions as one of the key organizational decisions. By using the cross-section data of the EBRD-World Bank Business Environment Enterprise Survey (BEEPS III) and utilizing the predictions of Antràs and Helpman's global sourcing modelling, I study the industry-level incidence of integration and firm-level decisions to redefine firm boundaries. Both studies highlight the importance of both technological and institutional factors. Moreover, the second study presents the firm-level perspective and highlights the importance of firm propensity to change.
The third study (Chapter 4) is focused on changes of internal firm organization and their connection with international trade liberalization. It provides preliminary answers to the following questions: (i) what drives flattening decisions, and (ii) whether flatter structures may be associated with a higher degree of control. By using the Management, Organization and Innovation (MOI) Survey, this study provides new evidence on the positive connection between increased competition from imports and firm flattening in transition countries. It also suggests that flattening may have more centralization features than is usually assumed.
The fourth study (Chapter 5) explores the connection between management quality and corruption. By using the BEEPS V cross-section data, I underline the general negative connection between the management quality and different kinds of corruption over the period 2011-2014. However, the results also indicate the existence of idiosyncratic links between corruption and quality of management in some transition countries.
As a result, the thesis contributes to the literature by advancing the state-of-the-art knowledge on firm organization in transition countries over the period 2005-2014. First, it identifies significant differences between country groups, namely EU and non-EU transition countries. The differences are persistent and characteristic for all the types of organizational change considered in the thesis, as well as the link between management and corruption. In particular, in non EU-transition countries, these differences are due to country-level and firm-level idiosyncrasy. Second, the thesis evidences that, regardless of numerous reforms of the business environment, firms in transition countries are rarely subject to organizational changes. However, a small number of firms subject to organizational changes significantly out-perform their counterparts. Consequently, it is important to understand what features of the economic environment or characteristics of firms prevent such efficiency-enhancing changes.
Third, the thesis shows that firms in transition countries differ in their internal organizational structures, which they adjust to changes in product market competition. However, the intensity of these adjustments is heterogeneous across countries and industries. Fourth, a negative connection between management quality and corruption indicates that further simplification of business regulations and anti-corruption measures would unquestionably enhance the quality of management in EU transition countries both at the firm and at the country level. However, similar measures are not equally efficient for non-EU transition countries, because the link is idiosyncratic in these countries at the firm level.
This thesis provides new evidence on the significant role of contractual links, technology complexity, product market competition and corruption in explaining the gap between micro-behavior and macro-objectives. However, the results put forward the need for i) a bottom-up approach, with firm behavior being analyzed and considered as an underlying force of aggregate and international performance, and ii) theories that account for firm organizational adjustments, because such adjustments may significantly alter our understanding of international trade gains and the channels through which efficiency enhancing reforms act and affect industrial reorganization