Design Modelling and Mechanical/Acoustic Characterization of Piezoelectric Micro Ultrasound Transducers

This master thesis is realized in STMicroelectronics thanks to a collaboration between the company and Politecnico di Milano. The activity is aimed at modelling and experimentally characterizing a Piezoelectric Micro-machined Ultrasound Transducer (PMUT). This is a new generation MEMS (Micro Electro Mechanical System) able to send and receive ultrasound waves by exploiting the piezoelectric effect: here the attention will be focused on the sending mode only. Throughout all the activity a continuous comparison between numerical simulation and experimental results is proposed. This approach is the typical work flow to launch a product into the market. The design modelling is done by using the finite element software COMSOL Multiphysics 5.6 while the laboratory campaign is carried out through Polytec MSA500 and other electronic equipment. The analysis performed are mainly focused on investigating the static and dynamic mechanical behavior of the device and only as a closing section the emitted acoustic field has been considered. Concerning the mechanical characterization, the main fields of investigation are the deformed configurations both of the single membrane and the whole device, the resonance frequencies of the membranes, the dynamic oscillation and the cross-talk phenomena through which the membranes within the same die can interact. Starting from the distorted geometry of the membranes, this is due to the fabrication process which introduces residual stresses and in turn causes a non flat configuration of the membrane: it is noted that the initial upward deformation flattens by applying an increasing DC voltage. Similarly, even the deformation of the die is caused by the presence of residual stresses. Going on, the modal analysis is performed: the first six modes are evaluated to have a complete characterization but the only one exploited in applications is the first one, having a frequency equal to 140kHz. Once the frequency is known, a dynamic analysis is carried out. The membranes are activated by means of a single sinusoidal voltage signal at the resonance frequency and the oscillation ring down is analyzed. Thanks to these measurements, it has been possible to measure the damping of the device by computing the Q factor. This is carried out in presence of Air and Vacuum and the values obtained are respectively 22 and 182: in this way the fluid and mechanic contributions to the damping are divided. Furthermore, by studying the oscillation ring down it appears the need to develop a non linear hysterical piezoelectric model to simulate the dynamic behavior of PZT layer: it will be part of the future activity. Subsequently, the presence of the undesired phenomena of cross-talk has been experimentally investigated. Because of this effect, the membranes can interact each other and the oscillation of one membrane can put in motion the close ones. The analysis has been performed in vacuum and air: it is noted that the acoustic contribution to the cross-talk has a higher influence and in particular the communication occurs through the back cavities. The last part of the thesis is devoted to the acoustic measurements of the emitted field in terms of directionality and sound pressure level. The radiation pattern of the emitted acoustic field by the membrane is simulated by means of a 2D axysimmetric model. Moreover, the pressure intensity has been evaluated at 2cm over the membrane both through simulation and experimentally: a mismatch is noted and it is due to the inability of the model to consider the oscillation cross-talk of the other membranes. From here comes the second future development to be investigated: the emitted acoustic field considering the oscillation of the other membranes or avoid the cross-talk by changing the design of the device, i.e closing the cavity at the bottom of the membranes. This thesis is the starting point of future activities aimed at modelling the non linear hysterical piezoelectric behavior to better match the dynamic response and studying the cross-talk effect in the acoustic emission.Universidad de Sevilla. Máster en Ingeniería Industria

The problem of “working for someone”: debt, dependence and labour exploitation in Chad

Precolonial elites used to enslave the farmers of rural Chad, now they hold them in debt bondage. How much has changed, how much has not

“Citizens of a chief”. State building, emancipation and control by elites in the Guéra region

Despite the recent decentralization reforms, citizenship and freedom are still problematic in many Sahel countries. This paper focuses on the topic of citizenship in the Guéra region of central Chad. It opens with a brief history of the region, from its long days as a slave-reservoir for neighbouring Muslim sultanates until colonization by the French at the beginning of the 20th century. It then focuses on the way the French organised the area administratively, facilitating the creation of a local elite through the customary authority system. This arrangement led to the creation of a system in which people could fully enjoy their rights only under the protection of one of the customary authorities recognized by the state. In this process, people previously labelled as the descendants of slaves were able to gain in status and thus become part of the ruling elites. The post-colonial state suffered a long period of instability that preserved and reinforced this system of governance, which was then further strengthened by the recent policies of decentralization. Three cases are presented in order to explain this system of governance and its effects: the stories of David and Abdel, the case of the land around Kuju village and the resettlement of Ibis village. These cases show how local people’s ability to exert their rights depends on the protection of a recognized customary authority. Nowadays, if they are to fully enjoy their rights, Guéra people need to be “citizens of a chief”. The local elites that emerged during the colonial period are still in political control and individuals need to negotiate with them when building their own life projects

Memories and legacies of enslavement in Chad

Memories of slavery affect contemporary political life in many Sahelian countries, but how do stigmatised groups use those memories as a tool for integration

Climate change impact on the cryosphere: from local to global scale

La criosfera, la porzione della superficie terrestre dove l'acqua è immagazzinata allo stato solido, svolge un ruolo di fondamentale importanza nella regolazione del bilancio energetico terrestre e del ciclo idrologico, fornendo risorse idriche a molte regioni del pianeta. La criosfera, regolando ed allo stesso tempo essendo influenzata dalle condizioni climatiche, è una importante sentinella dei cambiamenti climatici, subendone gli effetti e scaturendone ulteriori a scala globale e locale. In questo studio vengono analizzate diverse tematiche legate alla criosfera, dalle Alpi italiane alla Groenlandia. Viene studiata in primo luogo la climatologia di altezza ed equivalente in acqua del manto nevoso (SWE) tramite l'analisi statistica di altezza e densità della neve raccolte tra il 1967 ed il 2020 in un'ampia regione delle Alpi italiane. Dall'analisi statistica è emerso che l'altezza neve è diminuita di 12 cm e lo SWE di 37 mm per decade dal 1967. L'altezza media della neve si è ridotta del 33\% nel periodo 1994-2020 rispetto al periodo 1967-1993, mentre lo SWE del 37\%. Gli effetti del cambiamento climatico risultano essere più intensi a basse altitudini, con una riduzione dell'altezza del manto nevoso del 63\% al di sotto dei 1500 m. Questi risultati sono ulteriormente confermati dal change-point trovato a fine anni 1980. L'analisi del dataset HISTALP mostra la forte dipendenza dell'evoluzione del manto nevoso dalla temperatura, influenzando lo stato di precipitazione e regolando l'inizio della fusione. Gli effetti del manto nevoso a scala locale sono stati studiati analizzando il contributo della fusione nivale nel caso di eventi di precipitazione intensa con presenza di neve al suolo. L'analisi è stata limitata alle stazioni di Aprica e Pantano d'Avio, in Lombardia, dove sono stati raccolti i dati di temperatura, precipitazione ed altezza neve dal 1996. Con i dati osservati è stato calibrato un modello gradi-giorno tramite il quale è stato possibile ricostruire la serie temporale della somma di precipitazione e fusione nivale per le durate di 1, 3, 6, 12 e 24 ore. L'analisi degli annual maxima ha mostrato che la fusione nivale contribuisce ad un incremento medio dei quantili di circa il 2.2\%, aumentando con la durata fino a raggiungere, in un solo caso, il 10\%. Ad una più larga scala, lo studio della fusione superficiale della Groenlandia è di fondamentale importanza nella stima del contributo della calotta di ghiaccio all'innalzamento del livello medio degli oceani. Sono stati raccolti ed intercalibrati i dati satellitari a microonde passive raccolti da sensori montati su cinque diversi satelliti tra il 1979 ed il 2019. Il confronto con dati misurati da stazioni meteorologiche e con simulazioni del modello climatico regionale MAR hanno mostrato che un algoritmo basato sul modello di emissione elettromagnetica MEMLS riesce a cogliere l'evoluzione spaziale e temporale della fusione superficiale. L'analisi dei trend di lungo periodo ha mostrato che la superficie di fusione è aumentata tra il 3.6 ed il 6.9\% dell'intera area della Groenlandia per decennio durante il periodo di osservazione. Inoltre, la stagione di fusione è iniziata tra i 3 ed i 4 giorni prima e si è conclusa tra i 3 ed i 7 giorni dopo ogni decennio. Il numero totale medio di giorni di fusione è aumentato di circa 3-5 giorni per decennio. Per l'area della Groenlandia è stato poi implementato un algoritmo di downscaling statistico per il modello MAR. Il confronto con le misure di temperatura delle stazioni meteorologiche e con i dati di temperatura superficiale rilevati dal satellite Lansat-8 mostra come il dataset ad elevata risoluzione riesca meglio a cogliere la distribuzione spaziale della temperatura, senza perdere accuratezza a livello locale. Il confronto con le misure di bilancio di massa superficiale mostra invece un sostanziale miglioramento rispetto all'output originale a bassa risoluzioneThe cryosphere, the region of the Earth where water is stored in its solid form, plays a crucial role in regulating Earth’s energy balance and contributes to moisture fluxes and freshwater storage and release, providing water resources to many regions of the world. The cryosphere affects and is affected by climate conditions, being a driver and a sentinel of climate change, and playing a role of paramount importance from global to local scale processes. Here, different topics related to the cryosphere are investigated, spanning from the Greenland ice sheet to the Italian alps. A climatology of snow depth and snow water equivalent is carried out using a dataset of snow depth and snow density measurements collected at 299 sites between 1967 and 2020 over a wide portion of the Italian Alps. By performing different statistical analyses, a decrease of 12 cm every decade in snow depth and 37 mm every decade in SWE has been found since 1967. Average snow depth in the period 1994-2020 has been 33% lower than in the period 1967-1993, with stronger effects at low altitudes (reduction of 63% below 1500 m asl). The average SWE in 1994-2020 has been 36% lower than in 1967-1993. These results are confirmed by the increased elevation of the computed null snow depth elevation and the detected change-points at the end of the 1980s. The analysis of the HISTALP dataset confirmed the strong dependency of snow accumulation and melt on air temperature, impacting liquid/solid precipitation separation and timing of melt onset. The influence of snow on ground at local scale has been investigated evaluating the contribution of snowmelt to intense rain-on-snow events in Lombardy. By means of measured temperature, precipitation and snow depth data and the calibration of a snowmelt model, the timeseries of the combination of precipitation and melt has been obtained for the fixed durations 1, 3, 6, 12 and 24 h. The annual maxima analysis revealed that snowmelt increases the quantiles obtained from the selected extreme values distributions of about 2.2%, with stronger impacts for longer durations, up to 10%. At a larger scale, the analysis of surface melting over the Greenland ice sheet is of paramount importance to better estimate the ice sheet contribution to sea level rise. The cross-calibration of five different sensors collecting satellite data over the Greenland ice sheet between 1979 and 2019 has been performed. The comparison with in-situ observation and the output of the regional climate model MAR revealed that a threshold-based melt detection algorithm based on the electromagnetic emission model MEMLS shows the best performances in capturing surface melting evolution. The long-term trends analysis showed an increase of surface melting areal extension of about 3.6-6.9% of the Greenland ice sheet every decade. The melting season has started between 3 and 4 days earlier and between 3 and 7 days later every decade. The total number of melting days has increase by 3-5 days every decade. A statistical downscaling algorithm for the regional climate model MAR has been implemented. The comparison with in-situ observations and satellite measurements revealed that the downscaled dataset can well capture temperature temporal evolution and spatial distribution. It better captures at local scale the cumulated surface mass balance, exhibiting lower errors when compared with measured surface mass balance with respect to the original modelled outpu

Exploratory Research for the Identification of a Decision-Making Model for the Adoption and Implementation of Emerging Technology in Healthcare Operations

OBJECTIVES The most promising medical innovations appear to take a long time to be used in healthcare practice. This research has two main objectives: to understand the factors that limit or promote the adoption of Emerging Technologies (ET) in healthcare and to provide a model for understanding, codifying and improving the current situation. METHODOLOGY A case study is used to shed light on the process of adopting ET in healthcare between a teaching hospital (adopter) and a manufacturer of innovation (producer). The primary data, investigated through thematic analysis and literary evidence, consists of nine semi-structured interviews from ET experts on the side of the adopter and the producer. The Attitude, Decision, and Implementation (ADI) decision-making model is used as the theoretical lens for this study. This framework is a modification of the process described in the theory of Diffusion of Innovation (DoI) (Rogers, 2003) adapted to the peculiarities of the healthcare environment. RESULTS From the analysis of the interviews, it is clear that innovation in medicine has several limitations (financial resources, free time of healthcare professionals, correct identification and know-how of the professionals involved, communication, healthcare resistance) against few facilitators (Innovation Champions, appropriate marketing, medical conferences). This study also highlights the absence of a shared and codified model for the adoption of innovation in medicine. DISCUSSION The impediments and the facilitating factors that emerged in the analysis of the primary data have been confirmed in literature. Furthermore, the primary data analysis with literary evidence supports the ADI model as a possible decision-making process for the adoption of ET in healthcare. Its three cyclical phases: the creation of an attitude (A) towards the ET, the decision to continue the collaboration between the parties (D), and the implementation of innovation (I) are sustained by primary data and literary evidence. CONCLUSIONS The ADI model could improve the efficiency and pace of adoption of ET in healthcare by limiting barriers, exploiting facilitating factors and building a beneficial relationship between users and producers of ET

Investigating the physiological mechanisms of the oxygen consumption \u201cslow component\u201d.

The study of the oxygen consumption (VO2) kinetics is focused on the understanding of how human metabolism adjusts during the transition from a condition of resting/movement to another in order to satisfy the new energetic demand. As an integrated index of pulmonary, cardiovascular and muscles capacity VO2 kinetics have gained progressively increasing interests during the XX and the early XXI centuries. Thanks to the development of new technologies as well as an always increasing community of interested scientists in this subject, the knowledge in this field has been expanded considerably. However, some of the topics related to VO2 kinetics remain debated and call for further research. One of these topics is the loss of efficiency of human locomotion that occurs at the higher metabolic intensities, after the transitory period in which a new steady-state in VO2 should be achieved. This phenomenon is typically called VO2 \u201cslow component\u201d, as representative of a further increase in VO2 after the expected steady-state. The importance of the VO2 slow component lies in its link with exercise tolerance and on the understanding of the adaptations of the human body during physical activity. Therefore, researchers have tried to define the physiological underpinning of the slow component and to develop intervention strategies to reduce its amplitude. Nevertheless, a number of physiological uncertainties regarding the mechanistic bases of the slow component exist and require to be clarified. The purpose of this thesis was to deal with this gap and to study the origins of the VO2 slow component, and the loss of efficiency of locomotion that the slow component represents. In chapter one, a brief explanation of the VO2 response during exercise and the current explanatory theories for the VO2 slow component are provided. In chapter two, the experimental aims of the thesis are explained. Then, the results of four different studies are presented in chapters three, four, five, and six. Finally, chapter seven summarizes the main findings of this research work

Migration, Urbanization and Development: A Case Study of Mexico

A group of scholars at IIASA is studying national processes of structural transformation, seeing to further our understanding of the relationships between agriculture, industry, and urbanization in economic development. An integral component of this activity is a collection of national case studies of urbanization and development experiences, among them Mexico's

An intensity-dependent slow component of HR interferes with accurate exercise implementation in postmenopausal women

Heart rate (HR) targets are commonly used to administer exercise intensity in sport and clinical practice. Yet, as exercise protracts, a time-dependent dissociation between HR and metabolism can lead to a mis-prescription of the intensity ingredient of the exercise dose. Purpose: we tested the hypothesis that a slow component of HR (i.e. scHR) occurs in all intensity domains, greater than the slow component of oxygen uptake (scV[Combining Dot Above]O2), and we developed an equation to predict it across exercise intensities. Method: 18 healthy, postmenopausal women (54 ± 4 years) performed on a cycle-ergometer: i) a ramp incremental test for thresholds and V[Combining Dot Above]O2max detection; ii) 30-min constant-work exercise at 40, 50, 60, 70, and 80 %V[Combining Dot Above]O2max for the measurement of scHR, scV[Combining Dot Above]O2, stroke volume (SV) and body temperature (T°). scHR and scV[Combining Dot Above]O2 were compared by two-way RM-ANOVA (intensity and variable); Pearson correlation was calculated between the slow component of all variables, relative intensity, and domain; scHR (b·min-2) was predicted with a linear model based on exercise intensity relative to the respiratory compensation point (RCP). Results: A positive scHR was present in all domains, twice the size of scV[Combining Dot Above]O2 (p < 0.001) and significantly correlated with the slow components of V[Combining Dot Above]O2 (r2 = 0.46), T° (r2 = 0.52) and with relative intensity (r2 = 0.66). A linear equation accurately predicts scHR based on %RCP (r2 = 0.66, SEE = 0.15). Discussion: A mismatch exists between the slow components of HR and metabolic intensity. Whenever exercise is prescribed based on HR, target values should be adjusted over time to grant that the desired metabolic stimulus is maintained throughout the exercise session

“Peasants and accomplices”: a dialogue with Ermanno Olmi

Responding to suggestions offered by Giorgio Ferraresi, in a dense dialogue/interview Ermanno Olmi, great artist and high witness of the past and present of rural civilisation, explains the sense that returning a new centrality to agriculture - and in particular to the ‘peasant way’ to its rediscovery - assumes within a general movement of redemption of nature from the subjugation and abandonment in which the industrialist and ‘developmentalist’ post-war choices seemed to have inexorably thrown it, in our country as elsewhere; showing how a mature and aware return to earth, with its matrix and prospects both territorial, but also cultural, social, economic and emotional, represents today the only possible escape from the general crisis of human settlement on Earth.In risposta agli spunti offerti da Giorgio Ferraresi, in un denso dialogo/intervista Ermanno Olmi, grande artista ed alto testimone del passato e del presente della civilizzazione rurale, spiega il senso che la restituzione di una nuova centralità all’agricoltura - ed in particolare alla ‘via contadina’ alla sua riscoperta - assume entro un generale movimento di riscatto della natura dallo stato di soggezione e di abbandono in cui le scelte industrialiste e ‘sviluppiste’ del dopoguerra sembravano averla inesorabilmente gettata, nel nostro Paese come altrove; mostrando come un ritorno consapevole e maturo alla terra, con le sue matrici e le sue prospettive territoriali (ma anche culturali, sociali, economiche ed emozionali), sia oggi l’unica possibile via di fuga dalla crisi generalizzata dell’insediamento umano sulla Terra