Development and analysis of Magnetic Resonance Imaging acquisition and reconstruction methods for functional and structural investigation of cardiac and lung tissues.

The imaging of the lung and of the heart are often challenging in magnetic resonance due to the motion of the organs. In order to avoid motion artifacts it is possible to make the acquisition fast enough to fit in the breath-hold, or use some motion management methods in free breathing. A fast image acquisition can be obtained with non-Cartesian acquisition schemes, which require specialized reconstruction methods. In this work the least-squares non-uniform fast Fourier transform (LS-NUFFT) was compared to the standard gridding (GR) taking the direct summation method (DS) as reference. LS-NUFFT obtained lower root mean square error (RMSE), but heavier geometric information loss. The performance improvement of the LS-NUFFT was studied using three regularization methods. The truncated SVD reduced the RMSE of the simple regularization-free LS-NUFFT. Alternatively, the scan time can be shortened with some FOV reduction techniques. For cardiac imaging, the inner volume (IV) reduced-FOV selection was explored for the myocardial T2 mapping. The FOV reduction successfully avoided aliasing and provided a scan time reduction from about 23s to 15s. However, undesired stimulated echoes caused an overestimation in the T2 of about 20%. The effects of the inner volume excitation on the T2 mapping were described and clarified. Finally, motion management was explored for lung imaging in free-breathing, using a non-Cartesian acquisition trajectory. The rotating ultra-fast sequence (RUFIS) was demonstrated to be very suitable for the short T2* lung tissue. The respiratory motion was addressed with three methods: prospective triggering (PT), prospective gating (PG) and retrospective gating (RG). All methods were able to reconstruct a 3D high-resolution dataset. PG and RG could achieve 1.2 mm isotropic resolution in clinically reasonable scan time (~6min). The RG sequence could reconstruct multiple phases of the respiration cycle at cost of higher scan time

Automatic Extraction of Measurement-Based Large-Signal FET Models by Nonlinear Function Sampling.

A new method is proposed for the accurate experimental characterization and fully automated extraction of compact nonlinear models for Field-Effect Transistors (FETs). The approach, which leads to a charge-conservative description, is based on a single large-signal measurement under a two-tone sinusoidal wave excitation. A suitable choice of tone frequencies, amplitudes, and bias allows to adequately characterize the transistor over the whole safe operating region. The voltage controlled nonlinear functions describing the two-port FET model can be computed over an arbitrarily dense voltage domain by solving an overdetermined system of linear equations. These equations are expressed in terms of a new Nonlinear Function Sampling operator based on a bi-periodic Fourier series description of the acquired frequency spectra. The experimental validation is carried out on a 0.25-μm Gallium Nitride (GaN) on Silicon Carbide (SiC) High-Electron Mobility Transistor (HEMT) under continuous-wave (CW) and two-tone excitation (intermodulation distortion test).This project was partially supported by the Spanish Ministerio de Ciencia, Innovación y Universidades in the frame of ‘Salvador de Madariaga’ Program PRX18/00108

« De scientia Dei ». Aquinas' Commentary on Sentences I, dist. 35. : A Doctrinal Investigation and a Critical Edition

Cette thèse est consacrée à une analyse doctrinale et philologique du commentaire de Thomas d'Aquin sur la distinction 35 du premier Livre des Sentences de Pierre Lombard. Le sujet de cette distinction est la science que Dieu a de lui-même et des autres choses. La première partie de notre travail est une présentation conceptuelle et historique de l'arrière-fond de cette distinction. Elle est divisée en quatre étapes. Dans la première, nous nous sommes interrogé sur la science divine dans une perspective linguistique. Dans la seconde, nous avons discuté le rôle de l'autre, en tant qu'objet, dans la connaissance divine. Dans la troisième,nous avons étudié la synthèse chez Thomas des éléments aristotéliciens et pseudo-dionysiens, comme la notion d'actus purus et la notion d'esse. La quatrième étape, présente brièvement le contexte historique pour comprendre la méthode du commentaire des Sentences, ainsi qu'un bref panorama de l'Université de Paris au XIIIe siècle. La deuxième partie de la thèse offre une édition critique de la distinction 35. Après avoir collationné les témoins manuscrits selon les critères de la Commission Léonine, nous avons présenté le texte avec une introduction où nous établissons les différentes familles de la transmission textuelle.This dissertation provides a doctrinal and philological study of Aquinas' Commentary on Book I, dist. 35 ofPeter Lombard's Sentences. At issue is the knowledge that God has of Himself and of the things other thanHimself. The first part of the dissertation investigates the conceptual and historical background of dist. 35. Itdivides into four sections. First, we approach the topic of the divine science from a linguistic perspective.Secondly, we examine the role of things other than God as objects of the divine knowledge. Thirdly, we drawattention to Aquinas' synthesis of Aristotelian and pseudo-Dionysian elements, namely the notions of actuspurus and esse. The fourth section provides an overview of the historical context and the XIIIth-centuryUniversity of Paris, in order to better understand the method of commentaries on the Sentences. The secondpart of the dissertation intends to provide, for the first time, the critical edition of Aquinas' Commentary onBook I, dist. 35 of Peter Lombard's Sentences. The manuscripts are collated according to LeonineCommission's criteria. The critical text is introduced by a philological study in which we investigate the textualtransmission of dist. 35 and we propose a stemma

STUDIO SUGLI EFFETTI DEGLI ULTRASUONI NEI TESSUTI E MODELLAZIONE DEL FENOMENO DI CAVITAZIONE

Il presente lavoro di tesi è volto allo studio degli effetti che gli ultrasuoni hanno sui tessuti biologici, con particolare riferimento alle applicazioni biomediche in cui gli ultrasuoni sono usati. Lo scopo principale è quello di cercare di mettere in evidenza i possibili danni provocati dalle tecniche diagnostiche o terapeutiche che fanno uso degli ultrasuoni e studiare in modo più approfondito il fenomeno della cavitazione. Il primo capitolo descrive tutti i possibili effetti, osservati in letteratura fino ai tempi odierni, provocati dagli ultrasuoni sul mezzo in cui si propagano. Gli effetti descritti sono in primo luogo quelli termici, che si verificano qualora i tessuti siano sottoposti ad un campo ultrasonico per un tempo prolungato. È poi preso in considerazione il fenomeno della cavitazione che è, di fatto, il più rilevante in ambito diagnostico e di conseguenza la maggior parte dell’attenzione sarà rivolta ad esso. Sono poi elencati anche dei fenomeni di natura più macroscopica, imputabili sempre all’applicazione di un campo acustico ultrasonico. Infine per completezza sono anche elencati alcuni fenomeni la cui origine non è ancora ben chiara, ma è comunque correlata all’esposizione agli ultrasuoni. Nel secondo capitolo invece si concentra l’attenzione esclusivamente sul fenomeno della cavitazione, dando la dimostrazione matematica del modello di Rayleigh-Plesset che descrive la dinamica di bolle senza rivestimento e immerse in una soluzione acquosa. Successivamente è implementata una simulazione software della dinamica di una bolla di cavitazione sottoposta ad un campo ultrasonico. Tale simulazione è stata realizzata facendo uso principalmente della piattaforma di sviluppo MATLAB ed è stato discusso quale fosse il metodo di integrazione numerica più appropriato per implementare il modello della bolla, mettendo in luce le difficoltà di trattazione di un sistema non lineare. È stato provato il metodo di Verlet per l’integrazione numerica, implementato sia in MATLAB che in Python, per poi far ricadere la scelta su un metodo della famiglia Runge-Kutta, in particolare di ordine cinque. È inoltre eseguita l’identificazione del modello che si implementa, ossia la determinazione dei valori dei parametri usati. Il terzo capitolo inizia mettendo in evidenza quali siano i limiti del modello Rayleigh-Plesset e proponendo alcune possibili soluzioni per il loro superamento. È volta poi l’attenzione alle bolle usate in medicina più frequentemente, descrivendo anche i possibili utilizzi dei mezzo di contrasto per ecografia sia in ambito della diagnosi, sia in quello della terapia. È proposta una correzione del modello Rayleigh-Plesset in modo da riuscire a simulare anche bolle dotate di uno shell di rivestimento come quelle di cui si fa uso in medicina. Sono infine descritti i risultati, ossia i diversi modi in cui il modello ottenuto è stato applicato negli ambiti della diagnosi in medicina. È stata proposta una modifica del modello con lo scopo di determinare quando la bolla vada incontro a implosione con una semplice operazione di soglia dipendente dal contesto considerato. Tale soglia è stata reperita in un caso da letteratura, mentre in un altro è stata determinata sperimentalmente. È stato poi messo in luce come il modello sia capace di studiare il comportamento in frequenza delle bolle, anche in dipendenza del mechanical index, e come tale comportamento sia differente a seconda dell’ambito di sperimentazione considerato. È stata fatta un’analisi spettrale dell’andamento simulato del raggio della bolla nel tempo, con lo scopo di determinare i contributi frequenziali più importanti del segnale che arriverà alla sonda ecografica dalle bolle stesse. È poi mostrata l’utilità del modello nella determinazione di pressione e temperatura raggiunte dall’interno della bolla, con lo scopo di poter correlare tali valori agli effetti biologici che il mezzo di contrasto o le bolle di cavitazione possono indurre

De scientia Dei La distinction 35 du commentaire de Thomas d'Aquin sur le Ier livre des Sentences Étude doctrinale et édition critique

Cette thèse est consacrée à une analyse doctrinale et philologique du commentaire de Thomas d'Aquin sur la distinction 35 du premier Livre des Sentences de Pierre Lombard. Le sujet de cette distinction est la science que Dieu a de lui-même et des autres choses. La première partie de notre travail est une présentation conceptuelle et historique de l'arrière-fond de cette distinction. Elle est divisée en quatre étapes. Dans la première, nous nous sommes interrogé sur la science divine dans une perspective linguistique. Dans la seconde, nous avons discuté le rôle de l'autre, en tant qu'objet, dans la connaissance divine. Dans la troisième,nous avons étudié la synthèse chez Thomas des éléments aristotéliciens et pseudo-dionysiens, comme la notion d'actus purus et la notion d'esse. La quatrième étape, présente brièvement le contexte historique pour comprendre la méthode du commentaire des Sentences, ainsi qu'un bref panorama de l'Université de Paris au XIIIe siècle. La deuxième partie de la thèse offre une édition critique de la distinction 35. Après avoir collationné les témoins manuscrits selon les critères de la Commission Léonine, nous avons présenté le texte avec une introduction où nous établissons les différentes familles de la transmission textuelle.This dissertation provides a doctrinal and philological study of Aquinas' Commentary on Book I, dist. 35 ofPeter Lombard's Sentences. At issue is the knowledge that God has of Himself and of the things other thanHimself. The first part of the dissertation investigates the conceptual and historical background of dist. 35. Itdivides into four sections. First, we approach the topic of the divine science from a linguistic perspective.Secondly, we examine the role of things other than God as objects of the divine knowledge. Thirdly, we drawattention to Aquinas' synthesis of Aristotelian and pseudo-Dionysian elements, namely the notions of actuspurus and esse. The fourth section provides an overview of the historical context and the XIIIth-centuryUniversity of Paris, in order to better understand the method of commentaries on the Sentences. The secondpart of the dissertation intends to provide, for the first time, the critical edition of Aquinas' Commentary onBook I, dist. 35 of Peter Lombard's Sentences. The manuscripts are collated according to LeonineCommission's criteria. The critical text is introduced by a philological study in which we investigate the textualtransmission of dist. 35 and we propose a stemma.PARIS4-Bib. électronique (751059905) / SudocSudocFranceF

A GaN HEMT Global Large-Signal Model Including Charge Trapping for Multibias Operation

This paper presents a novel empirical model for gallium nitride on silicon carbide high-electron mobility transistors. A global state-space formulation describes charge trapping effects by means of suitable 2-D nonlinear lag functions of the applied voltages, extracted from a reduced set of double-pulse current-voltage characteristics. The implementation in CAD tools involves a simple equivalent circuit and lookup tables, making the model well suited for power amplifier design in the presence of signals of practical interest. An extensive validation at both low (4 MHz) and radio frequencies (5.5 GHz) exhibits good accuracy and a robust performance prediction for the operation above the cut-off of dispersive phenomena, across different operating classes and loads, in terms of output power, power-added efficiency, and third-order intermodulation distortion. These results show that traps with both linear and nonlinear dynamics are stimulated in large-signal operation, and that these must be taken into account for global model predictions

Two-Input Nonlinear Dynamic Model Inversion for the Linearization of Envelope-Tracking RF PAs

none4siWe present an algorithm for the real-time inversion of a two-input behavioral model applicable to supply-modulated radio-frequency (RF) power amplifiers (PAs). This approach includes the nonlinear dynamic effects on the RF output due to the mutual interactions between the modulated supply and the RF input. The model inversion consists of an iterative procedure that only relies on the model, which has been empirically identified. It results in an open loop linearization algorithm fully implementable in a digital architecture. The method allows exploiting the trade-off between the power-added efficiency (PAE) and the digital predistortion (DPD) computational load for a given linearity target.mixedGibiino, Gian Piero; Santarelli, Alberto; Schreurs, Dominique; Filicori, FabioGibiino, Gian Piero; Santarelli, Alberto; Schreurs, Dominique; Filicori, Fabi

Global modeling of GaN HEMT resistive current including charge trapping and self-heating for multi-bias multi-class PA performance prediction

An empirical Gallium Nitride (GaN) HEMT model, suitable for multi-bias and multi-class power amplifier (PA) performance prediction, is formulated. In addition to the fast dynamically-nonlinear capture mechanisms normally considered for local modeling, dynamically-linear charge trapping is taken into account here. A straightforward empirical identification procedure based on tailored double-pulsed IV measurements is described. Validation experiments carried out on a 8 7125 pm (gate length: 0.25 pm) GaN-on-SiC HEMT show good model prediction capabilities under different drain bias conditions and class AB, B, and C large-signal PA operation at both low-frequency (f = 4 MHz) and RF (f = 2.5 GHz)

Behavioral modeling of RF PAs under wideband load modulation

This work proposes a behavioral modeling approach suitable for power amplifier (PA) operation under dynamic load modulation. The model accounts for the PA nonlinear dynamic effects by means of 1st order kernel functions of the modified Volterra formulation, extracted from automated Nonlinear Vector Network Analyzer (NVNA) measurements. Validation experiments under wideband load modulation are reported for a commercial PA concurrently excited by an RF multi-tone at the input, and by another multi-tone actively injected at the output in order to generate a dynamic load. The experiment is performed at 2.4 GHz with 20 MHz bandwidth signals