La Ricostruzione 3D di Bologna nel XVI Secolo

Il lavoro presentato ha come oggetto la ricostruzione tridimensionale della città di Bologna nella sua fase rinascimentale. Tale lavoro vuole fornire un modello 3D delle architetture e degli spazi urbani utilizzabile sia per scopi di ricerca nell’ambito della storia delle città sia per un uso didattico-divulgativo nel settore del turismo culturale. La base del lavoro è una fonte iconografica di grande importanza: l’affresco raffigurante Bologna risalente al 1575 e situato in Vaticano; questa è una veduta a volo d’uccello di grandi dimensioni dell’intero tessuto urbano bolognese all’interno della terza cerchia di mura. In esso sono rappresentate in maniera particolareggiata le architetture civili e ecclesiastiche, gli spazi ortivi e cortilivi interni agli isolati e alcune importanti strutture urbane presenti in città alla fine del Cinquecento, come l’area portuale e i canali interni alla città, oggi non più visibili. La ricostruzione tridimensionale è stata realizzata tramite Blender, software per la modellazione 3D opensource, attraverso le fasi di modellazione, texturing e creazione materiali (mediante campionamento delle principali cromie presenti nell’affresco), illuminazione e animazione. Una parte della modellazione è stata poi testata all’interno di un GIS per verificare l’utilizzo delle geometrie 3D come elementi collegabili ad altre fonti storiche relative allo sviluppo urbano e quindi sfruttabili per la ricerca storica. Grande attenzione infine è stata data all’uso dei modelli virtuali a scopo didattico-divulgativo e per il turismo culturale. La modellazione è stata utilizzata all’interno di un motore grafico 3D per costruire un ambiente virtuale interattivo nel quale un utente anche non esperto possa muoversi per esplorare gli spazi urbani della Bologna del Cinquecento. In ultimo è stato impostato lo sviluppo di un’applicazione per sistemi mobile (Iphone e Ipad) al fine di fornire uno strumento per la conoscenza della città storica in mobilità, attraverso la comparazione dello stato attuale con quello ricostruito virtualmente.

L'area dei Lungarni di Pisa nel tardo Medioevo (XIV-XV secolo). un tentativo di ricostruzione in 3D.

Lo scopo di questa ricerca è la ricostruzione dei Lungarni di Pisa nel Tardo Medioevo (XIV-XV secolo); lo studio intende sottolineare le trasformazioni urbanistiche che hanno cambiato il volto di Pisa nel corso del tempo e ricordare che l’area fluviale ebbe un ruolo di primo piano come baricentro commerciale ed economico della città, vocazione che si è in gran parte persa con l’età moderna e contemporanea. La metodologia seguita, affinata e perfezionata durante la partecipazione al progetto Nu.M.E. (Nuovo Museo Elettronico della Città di Bologna), si basa sull’analisi e il confronto di fonti eterogenee ma complementari, che includono precedenti studi di storia dell’urbanistica, un corpus di documentazione di epoca medievale (provvedimenti amministrativi come gli Statuti del Comune di Pisa, ma anche descrizioni di cronisti e viaggiatori), fonti iconografiche, tra cui vedute e mappe cinquecentesche o successive, e fonti materiali, come le persistenze medievali ancora osservabili all’interno degli edifici ed i reperti rinvenuti durante alcune campagne di scavo archeologiche. Il modello 3D non è concepito come statico e “chiuso”, ma è liberamente esplorabile all’interno di un engine tridimensionale; tale prodotto può essere destinato a livelli di utenza diversi, che includono sia studiosi e specialisti interessati a conoscere un maggior numero di informazioni e ad approfondire la ricerca, sia semplici cittadini appassionati di storia o utenti più giovani, come studenti di scuole medie superiori e inferiori.

Classical limit of the Nelson model

Since the development of quantum mechanics it has been natural to analyze the connection between classical and quantum mechanical descriptions of physical systems. In particular one should expect that in some sense when quantum mechanical effects becomes negligible the system will behave like it is dictated by classical mechanics. One famous relation between classical and quantum theory is due to Ehrenfest. This result was later developed and put on firm mathematical foundations by Hepp. He proved that matrix elements of bounded functions of quantum observables between suitable coherents states (that depend on Planck's constant h) converge to classical values evolving according to the expected classical equations when h goes to zero. His results were later generalized by Ginibre and Velo to bosonic systems with infinite degrees of freedom and scattering theory. In this thesis we study the classical limit of Nelson model, that describes non relativistic particles, whose evolution is dictated by Schrödinger equation, interacting with a scalar relativistic field, whose evolution is dictated by Klein-Gordon equation, by means of a Yukawa-type potential. The classical limit is a mean field and weak coupling limit. We proved that the transition amplitude of a creation or annihilation operator, between suitable coherent states, converges in the classical limit to the solution of the system of differential equations that describes the classical evolution of the theory. The quantum evolution operator converges to the evolution operator of fluctuations around the classical solution. Transition amplitudes of normal ordered products of creation and annihilation operators between coherent states converge to suitable products of the classical solutions. Transition amplitudes of normal ordered products of creation and annihilation operators between fixed particle states converge to an average of products of classical solutions, corresponding to different initial conditions.

Theoretical studies of fluid membrane mechanics

Biologische Membranen sind Fettmolekül-Doppelschichten, die sich wie zweidimensionale Flüssigkeiten verhalten. Die Energie einer solchen fluiden Oberfläche kann häufig mit Hilfe eines Hamiltonians beschrieben werden, der invariant unter Reparametrisierungen der Oberfläche ist und nur von ihrer Geometrie abhängt. Beiträge innerer Freiheitsgrade und der Umgebung können in den Formalismus mit einbezogen werden. Dieser Ansatz wird in der vorliegenden Arbeit dazu verwendet, die Mechanik fluider Membranen und ähnlicher Oberflächen zu untersuchen. Spannungen und Drehmomente in der Oberfläche lassen sich durch kovariante Tensoren ausdrücken. Diese können dann z. B. dazu verwendet werden, die Gleichgewichtsposition der Kontaktlinie zu bestimmen, an der sich zwei aneinander haftende Oberflächen voneinander trennen. Mit Ausnahme von Kapillarphänomenen ist die Oberflächenenergie nicht nur abhängig von Translationen der Kontaktlinie, sondern auch von Änderungen in der Steigung oder sogar Krümmung. Die sich ergebenden Randbedingungen entsprechen den Gleichgewichtsbedingungen an Kräfte und Drehmomente, falls sich die Kontaktlinie frei bewegen kann. Wenn eine der Oberflächen starr ist, muss die Variation lokal dieser Fläche folgen. Spannungen und Drehmomente tragen dann zu einer einzigen Gleichgewichtsbedingung bei; ihre Beiträge können nicht mehr einzeln identifiziert werden. Um quantitative Aussagen über das Verhalten einer fluiden Oberfläche zu machen, müssen ihre elastischen Eigenschaften bekannt sein. Der "Nanotrommel"-Versuchsaufbau ermöglicht es, Membraneigenschaften lokal zu untersuchen: Er besteht aus einer porenüberspannenden Membran, die während des Experiments durch die Spitze eines Rasterkraftmikroskops in die Pore gedrückt wird. Der lineare Verlauf der resultierenden Kraft-Abstands-Kurven kann mit Hilfe der in dieser Arbeit entwickelten Theorie reproduziert werden, wenn der Einfluss von Adhäsion zwischen Spitze und Membran vernachlässigt wird. Bezieht man diesen Effekt in die Rechnungen mit ein, ändert sich das Resultat erheblich: Kraft-Abstands-Kurven sind nicht länger linear, Hysterese und nichtverschwindende Trennkräfte treten auf. Die Voraussagen der Rechnungen könnten in zukünftigen Experimenten dazu verwendet werden, Parameter wie die Biegesteifigkeit der Membran mit einer Auflösung im Nanometerbereich zu bestimmen. Wenn die Materialeigenschaften bekannt sind, können Probleme der Membranmechanik genauer betrachtet werden. Oberflächenvermittelte Wechselwirkungen sind in diesem Zusammenhang ein interessantes Beispiel. Mit Hilfe des oben erwähnten Spannungstensors können analytische Ausdrücke für die krümmungsvermittelte Kraft zwischen zwei Teilchen, die z. B. Proteine repräsentieren, hergeleitet werden. Zusätzlich wird das Gleichgewicht der Kräfte und Drehmomente genutzt, um mehrere Bedingungen an die Geometrie der Membran abzuleiten. Für den Fall zweier unendlich langer Zylinder auf der Membran werden diese Bedingungen zusammen mit Profilberechnungen kombiniert, um quantitative Aussagen über die Wechselwirkung zu treffen. Theorie und Experiment stoßen an ihre Grenzen, wenn es darum geht, die Relevanz von krümmungsvermittelten Wechselwirkungen in der biologischen Zelle korrekt zu beurteilen. In einem solchen Fall bieten Computersimulationen einen alternativen Ansatz: Die hier präsentierten Simulationen sagen voraus, dass Proteine zusammenfinden und Membranbläschen (Vesikel) bilden können, sobald jedes der Proteine eine Mindestkrümmung in der Membran induziert. Der Radius der Vesikel hängt dabei stark von der lokal aufgeprägten Krümmung ab. Das Resultat der Simulationen wird in dieser Arbeit durch ein approximatives theoretisches Modell qualitativ bestätigt.

Finite-element discretization of 3D energy-transport equations for semiconductors

In this thesis a mathematical model was derived that describes the charge and energy transport in semiconductor devices like transistors. Moreover, numerical simulations of these physical processes are performed. In order to accomplish this, methods of theoretical physics, functional analysis, numerical mathematics and computer programming are applied. After an introduction to the status quo of semiconductor device simulation methods and a brief review of historical facts up to now, the attention is shifted to the construction of a model, which serves as the basis of the subsequent derivations in the thesis. Thereby the starting point is an important equation of the theory of dilute gases. From this equation the model equations are derived and specified by means of a series expansion method. This is done in a multi-stage derivation process, which is mainly taken from a scientific paper and which does not constitute the focus of this thesis. In the following phase we specify the mathematical setting and make precise the model assumptions. Thereby we make use of methods of functional analysis. Since the equations we deal with are coupled, we are concerned with a nonstandard problem. In contrary, the theory of scalar elliptic equations is established meanwhile. Subsequently, we are preoccupied with the numerical discretization of the equations. A special finite-element method is used for the discretization. This special approach has to be done in order to make the numerical results appropriate for practical application. By a series of transformations from the discrete model we derive a system of algebraic equations that are eligible for numerical evaluation. Using self-made computer programs we solve the equations to get approximate solutions. These programs are based on new and specialized iteration procedures that are developed and thoroughly tested within the frame of this research work. Due to their importance and their novel status, they are explained and demonstrated in detail. We compare these new iterations with a standard method that is complemented by a feature to fit in the current context. A further innovation is the computation of solutions in three-dimensional domains, which are still rare. Special attention is paid to applicability of the 3D simulation tools. The programs are designed to have justifiable working complexity. The simulation results of some models of contemporary semiconductor devices are shown and detailed comments on the results are given. Eventually, we make a prospect on future development and enhancements of the models and of the algorithms that we used.

Anwendung der geoelektrischen 3D-Tomographie für die Analyse thermisch induzierter Strömungen im Labor

Sowohl in der Natur als auch in der Industrie existieren thermisch induzierte Strömungen. Von Interesse für diese Forschungsarbeit sind dabei die Konvektionen im Erdmantel sowie in den Glasschmelzwannen. Der dort stattfindende Materialtransport resultiert aus Unterschieden in der Dichte, der Temperatur und der chemischen Konzentration innerhalb des konvektierenden Materials. Um das Verständnis für die ablaufenden Prozesse zu verbessern, werden von zahlreichen Forschergruppen numerische Modellierungen durchgeführt. Die Verifikation der dafür verwendeten Algorithmen erfolgt meist über die Analyse von Laborexperimenten. Im Vordergrund dieser Forschungsarbeit steht die Entwicklung einer Methode zur Bestimmung der dreidimensionalen Temperaturverteilung für die Untersuchung von thermisch induzierten Strömungen in einem Versuchsbecken. Eine direkte Temperaturmessung im Inneren des Versuchsmaterials bzw. der Glasschmelze beeinflusst allerdings das Strömungsverhalten. Deshalb wird die geodynamisch störungsfrei arbeitende Impedanztomographie verwendet. Die Grundlage dieser Methode bildet der erweiterte Arrhenius-Zusammenhang zwischen Temperatur und spezifischer elektrischer Leitfähigkeit. Während der Laborexperimente wird ein zähflüssiges Polyethylenglykol-Wasser-Gemisch in einem Becken von unten her erhitzt. Die auf diese Weise generierten Strömungen stellen unter Berücksichtigung der Skalierung ein Analogon sowohl zu dem Erdmantel als auch zu den Schmelzwannen dar. Über mehrere Elektroden, die an den Beckenwänden installiert sind, erfolgen die geoelektrischen Messungen. Nach der sich anschließenden dreidimensionalen Inversion der elektrischen Widerstände liegt das Modell mit der Verteilung der spezifischen elektrischen Leitfähigkeit im Inneren des Versuchsbeckens vor. Diese wird mittels der erweiterten Arrhenius-Formel in eine Temperaturverteilung umgerechnet. Zum Nachweis der Eignung dieser Methode für die nichtinvasive Bestimmung der dreidimensionalen Temperaturverteilung wurden mittels mehrerer Thermoelemente an den Beckenwänden zusätzlich direkte Temperaturmessungen durchgeführt und die Werte miteinander verglichen. Im Wesentlichen sind die Innentemperaturen gut rekonstruierbar, wobei die erreichte Messgenauigkeit von der räumlichen und zeitlichen Auflösung der Gleichstromgeoelektrik abhängt.

3D nanostructured microcarriers for cell therapy in regenerative medicine

Supercritical Emulsion Extraction technology (SEE-C) was proposed for the production of poly-lactic-co-glycolic acid microcarriers. SEE-C operating parameters as pressure, temperature and flow rate ratios were analyzed and the process performance was optimized in terms of size distribution and encapsulation efficiency. Microdevices loaded with bovine serum insulin were produced with different sizes (2 and 3 µm) or insulin charges (3 and 6 mg/g) and with an encapsulation efficiency of 60%. The microcarriers were characterized in terms of insulin release profile in two different media (PBS and DMEM) and the diffusion and degradation constants were also estimated by using a mathematical model. PLGA microdevices were also used in a cultivation of embryonic ventricular myoblasts (cell line H9c2 obtained from rat) in a FBS serum free medium to monitor cell viability and growth in dependence of insulin released. Good cell viability and growth were observed on 3 µm microdevices loaded with 3 mg/g of insulin. PLGA microspheres loaded with growth factors (GFs) were charged into alginate scaffold with human Mesenchimal Steam Cells (hMSC) for bone tissue engineering with the aim of monitoring the effect of the local release of these signals on cells differentiation. These “living” 3D scaffolds were incubated in a direct perfusion tubular bioreactor to enhance nutrient transport and exposing the cells to a given shear stress. Different GFs such as, h-VEGF, h-BMP2 and a mix of two (ratio 1:1) were loaded and alginate beads were recovered from dynamic (tubular perfusion system bioreactor) and static culture at different time points (1st, 7th, 21st days) for the analytical assays such as, live/dead; alkaline phosphatase; osteocalcin; osteopontin and Van Kossa Immunoassay. The immunoassay confirmed always a better cells differentiation in the bioreactor with respect to the static culture and revealed a great influence of the BMP-2 released in the scaffold on cell differentiation.

3D-electron microscopy of different conformations of cephalopod hemocyanins

Die Hämocyanine der Cephalopoden Nautilus pompilius und Sepia officinalis sorgen für den Sauerstofftransport zwischen den Kiemen und den Geweben. Sie bestehen aus einem zylindrischen Dekamer mit interner Kragenstruktur. Während eine Untereinheit (also eine Polypeptidkette) bei NpH aus sieben paralogen funktionellen Domänen (FU-a bis FU-g) besteht, führte ein Genduplikationsereignis der FU-d zu acht FUs in SoH (a, b, c, d, d´, e, f, g). In allen Mollusken Hämocyaninen bilden sechs dieser FUs den äußeren Ring und die restlichen die interne Kragenstruktur. rnrnIn dieser Arbeit wurde ein dreidimensionales Modell des Hämocyanins von Sepia officinalis (SoH) erstellt. Die Rekonstruktion, mit einer Auflösung von 8,8Å (FSC=0,5), erlaubt das Einpassen von Homolologiemodellen und somit das Erstellen eines molekularen Modells mit pseudo atomarer Auflösung. Des Weiteren wurden zwei Rekonstruktionen des Hämocyanins von Nautilus pompilius (NpH) in verschiedenen Oxygenierungszuständen erstellt. Die auf 10 und 8,1Å aufgelösten Modelle zeigen zwei verschiedene Konformationen des Proteins. Daraus ließ sich eine Modellvorstellung über die allosterische Funktionsweise ableiten. Die hier erreichte Auflösung von 8Å ist die momentan höchste eines Molluskenhämocyanins. rnAuf Grundlage des molekularen Modells von SoH konnte die Topologie des Proteins aufgeklärt werden. Es wurde gezeigt, dass die zusätzliche FU-d´ in den Kragen integriert ist und somit die prinzipielle Wandarchitektur aller Mollusken Hämocyanine identisch ist. Wie die Analyse des erstellten molekularen Modells zeigt werden sind die beiden Isoformen (SoH1 und SoH2) in den Bereichen der Interfaces nahezu identisch; auch der Vergleich mit NpH zeigt grosse Übereinstimmungen. Des weiteren konnte eine Fülle von Informationen bezüglich der allosterischen Signalübertragung innerhalb des Moleküls gewonnen werden. rnDer Versuch, NpH in verschiedenen Oxygenierungszuständen zu zeigen, war erfolgreich. Die Datensätze, die unter zwei atmosphärischen Bedingungen präpariert wurden, führten reproduzierbar zu zwei unterschiedlichen Rekonstruktionen. Dies zeigt, daß der hier entwickelte experimentelle Ansatz funktioniert. Er kann nun routinemäßig auf andere Proteine angewandt werden. Wie der strukturelle Vergleich zeigte, verändert sich die Orientierung der FUs durch die Oxygenierung leicht. Dies wiederum beeinflusst die Anordnung innerhalb der Interfaces sowie die Abstände zwischen den beteiligten Aminosäuren. Aus dieser Analyse konnte eine Modellvorstellung zum allosterischen Signaltransfer innerhalb des Moleküls abgeleitet werden, die auf einer Umordnung von Salzbrücken basiert.

3D-Strukturanalyse von Molluskenhämocyaninen aus elektronenmikroskopischen Bildern

Diese Arbeit präsentiert die bislang höchst aufgelösten KryoEM-Strukturen für ein Cephalopoden hämocyanin Dekamer (Nautilus pompilus Hämocyanin, NpH) und ein Gastropoden Hämocyanin Didekamer (keyhole limpet hemocyanin isoform 1). Durch die Methoden des “molecular modelling” und “rigid-body-fiting” wurde auch eine detaillierte Beschreibung beider Strukturen auf atomarem Niveau erstmalig möglich. Hämocyanine sind kupferhaltige Sauerstoff-Transportproteine die frei gelöst in Blut zahlreicher Arthropoden und Mollusken vorkommen. Allgemein sind Molluskenhämocyanine als Dekamere (Hohlzylinder aus 5 Untereinheiten-dimere) oder Didecamere (Zusammenlagerung von zwei Dekameren) zu finden. Durch Anlagerung weiterer Dekamere bilden sich teilweise tubuläre Multidekamere. Hämocyanine der Cephalopoden bestehen ausschließlich aus solitären Decameren. In Octopus und Nautilus bestehen die 10 Untereinheiten aus 7 funktionellen Einheiten(FU-a bis FU-g), wobei jede FU ein Sauerstoffmolekül binden kann. FUs a-f bilden die Wand des ringförmigen Moleküls und 10 Kopien der FU-g bilden einen sogenannten „inneren Kragenkomplex“. Das im Rahmen dieser Arbeit erstelltes molekulares Modell von NpH klärt die Struktur des Dekamers vollständig auf. Wir waren zum ersten Mal in der Lage das Untereinheiten-dimer, den Verlauf der Polypeptidkette und 15 unterschiedliche Kontaktstellen zwischen FUs zu identifizieren. Viele der inter-FU-Kontakte weisen Aminosäurenkonstellationen auf, die die Basis für die Übertragung allosterischer Wechselwirkungen zwischen FUs darstellen könnten und Hinweise für den Aufbau der allosterische Einheit geben. Potentielle Bindungsstellen für N-glykosidische Zucker und bivalente Kationen wurden auch identifiziert. Im Gegensatz zu NpH, kommen Gastropoden Hämocyanine (inkl. KLH) hauptsächlich als Didekamere vor und der Kragenkomplex wird in diesem Fall aus 2 FUs gebildet (Fu-g und FU-h). Die zusätzliche C'-terminale FU-h zeichnet sich durch eine spezielle Verlängerung von ~ 100 Aminosäuren aus. KLH stammt aus der kalifornische Schnecke Megathura crenulata und kommt seit mehreren Jahrzehnten als Immunostimulator in der immunologischen Grundlagenforschung und klinischen Anwendung zum Einsatz. KLH weist zwei Isoformen auf, KLH1 und KLH2. Das vorliegende Modell von KLH1 erlaubt die komplexe Architektur dieses riesigen Proteins in allen Details zu verstehen, sowie einen Vergleich zum dem NpH Dekamer auf atomare Ebene. Es wurde gefunden, dass das Untereinheitensegment a-b-c-d-e-f-g, sowie die equivalenten Kontaktstellen zwichen FUs stark konserviert sind. Dies deutet darauf hin, dass in Bezug auf die Übertragung allosterische Signale zwischen benachbarten FUs, grundlegende Mechanismen in beiden Molekülen beibehalten wurden. Weiterhin, konnten die Verbindungen zwischen den zwei Dekameren ertsmalig identifiziert werden. Schließlich, wurde die Topologie der N-glycosidischen Zucker, welche für die immunologische Eigenschaften von KLH1 von großer Bedeutung sind, auch aufgeklärt. Somit leistet die vorliegende Arbeit einen wesentlichen Schritt zum Verständnis der Quartärstruktur und Funktion der Molluskenhämocyanine.rn

Numerical modeling of the Alto Tiberina low angle normal fault

The aim of this Thesis is to obtain a better understanding of the mechanical behavior of the active Alto Tiberina normal fault (ATF). Integrating geological, geodetic and seismological data, we perform 2D and 3D quasi-static and dynamic mechanical models to simulate the interseismic phase and rupture dynamic of the ATF. Effects of ATF locking depth, synthetic and antithetic fault activity, lithology and realistic fault geometries are taken in account. The 2D and 3D quasi-static model results suggest that the deformation pattern inferred by GPS data is consistent with a very compliant ATF zone (from 5 to 15 km) and Gubbio fault activity. The presence of the ATF compliant zone is a first order condition to redistribute the stress in the Umbria-Marche region; the stress bipartition between hanging wall (high values) and footwall (low values) inferred by the ATF zone activity could explain the microseismicity rates that are higher in the hanging wall respect to the footwall. The interseismic stress build-up is mainly located along the Gubbio fault zone and near ATF patches with higher dip (30°models demonstrate that the magnitude expected, after that an event is simulated on the ATF, can decrease if we consider the fault plane roughness.

Estimation of Quasi-Rational DSGE Models

Small-scale dynamic stochastic general equilibrium have been treated as the benchmark of much of the monetary policy literature, given their ability to explain the impact of monetary policy on output, inflation and financial markets. One cause of the empirical failure of New Keynesian models is partially due to the Rational Expectations (RE) paradigm, which entails a tight structure on the dynamics of the system. Under this hypothesis, the agents are assumed to know the data genereting process. In this paper, we propose the econometric analysis of New Keynesian DSGE models under an alternative expectations generating paradigm, which can be regarded as an intermediate position between rational expectations and learning, nameley an adapted version of the "Quasi-Rational" Expectatations (QRE) hypothesis. Given the agents' statistical model, we build a pseudo-structural form from the baseline system of Euler equations, imposing that the length of the reduced form is the same as in the `best' statistical model.

Numerical and Analytical Methods for Laser-Plasma Acceleration Physics

Theories and numerical modeling are fundamental tools for understanding, optimizing and designing present and future laser-plasma accelerators (LPAs). Laser evolution and plasma wave excitation in a LPA driven by a weakly relativistically intense, short-pulse laser propagating in a preformed parabolic plasma channel, is studied analytically in 3D including the effects of pulse steepening and energy depletion. At higher laser intensities, the process of electron self-injection in the nonlinear bubble wake regime is studied by means of fully self-consistent Particle-in-Cell simulations. Considering a non-evolving laser driver propagating with a prescribed velocity, the geometrical properties of the non-evolving bubble wake are studied. For a range of parameters of interest for laser plasma acceleration, The dependence of the threshold for self-injection in the non-evolving wake on laser intensity and wake velocity is characterized. Due to the nonlinear and complex nature of the Physics involved, computationally challenging numerical simulations are required to model laser-plasma accelerators operating at relativistic laser intensities. The numerical and computational optimizations, that combined in the codes INF&RNO and INF&RNO/quasi-static give the possibility to accurately model multi-GeV laser wakefield acceleration stages with present supercomputing architectures, are discussed. The PIC code jasmine, capable of efficiently running laser-plasma simulations on Graphics Processing Units (GPUs) clusters, is presented. GPUs deliver exceptional performance to PIC codes, but the core algorithms had to be redesigned for satisfying the constraints imposed by the intrinsic parallelism of the architecture. The simulation campaigns, run with the code jasmine for modeling the recent LPA experiments with the INFN-FLAME and CNR-ILIL laser systems, are also presented.

Towards the 3D attenuation imaging of active volcanoes: methods and tests on real and simulated data

The purpose of my PhD thesis has been to face the issue of retrieving a three dimensional attenuation model in volcanic areas. To this purpose, I first elaborated a robust strategy for the analysis of seismic data. This was done by performing several synthetic tests to assess the applicability of spectral ratio method to our purposes. The results of the tests allowed us to conclude that: 1) spectral ratio method gives reliable differential attenuation (dt*) measurements in smooth velocity models; 2) short signal time window has to be chosen to perform spectral analysis; 3) the frequency range over which to compute spectral ratios greatly affects dt* measurements. Furthermore, a refined approach for the application of spectral ratio method has been developed and tested. Through this procedure, the effects caused by heterogeneities of propagation medium on the seismic signals may be removed. The tested data analysis technique was applied to the real active seismic SERAPIS database. It provided a dataset of dt* measurements which was used to obtain a three dimensional attenuation model of the shallowest part of Campi Flegrei caldera. Then, a linearized, iterative, damped attenuation tomography technique has been tested and applied to the selected dataset. The tomography, with a resolution of 0.5 km in the horizontal directions and 0.25 km in the vertical direction, allowed to image important features in the off-shore part of Campi Flegrei caldera. High QP bodies are immersed in a high attenuation body (Qp=30). The latter is well correlated with low Vp and high Vp/Vs values and it is interpreted as a saturated marine and volcanic sediments layer. High Qp anomalies, instead, are interpreted as the effects either of cooled lava bodies or of a CO2 reservoir. A pseudo-circular high Qp anomaly was detected and interpreted as the buried rim of NYT caldera.

Soil-structure interaction during tunnelling in urban area: observations and 3D numerical modelling

This work illustrates a soil-tunnel-structure interaction study performed by an integrated,geotechnical and structural,approach based on 3D finite element analyses and validated against experimental observations.The study aims at analysing the response of reinforced concrete framed buildings on discrete foundations in interaction with metro lines.It refers to the case of the twin tunnels of the Milan (Italy) metro line 5,recently built in coarse grained materials using EPB machines,for which subsidence measurements collected along ground and building sections during tunnelling were available.Settlements measured under freefield conditions are firstly back interpreted using Gaussian empirical predictions. Then,the in situ measurements’ analysis is extended to include the evolving response of a 9 storey reinforced concrete building while being undercrossed by the metro line.In the finite element study,the soil mechanical behaviour is described using an advanced constitutive model. This latter,when combined with a proper simulation of the excavation process, proves to realistically reproduce the subsidence profiles under free field conditions and to capture the interaction phenomena occurring between the twin tunnels during the excavation. Furthermore, when the numerical model is extended to include the building, schematised in a detailed manner, the results are in good agreement with the monitoring data for different stages of the twin tunnelling. Thus, they indirectly confirm the satisfactory performance of the adopted numerical approach which also allows a direct evaluation of the structural response as an outcome of the analysis. Further analyses are also carried out modelling the building with different levels of detail. The results highlight that, in this case, the simplified approach based on the equivalent plate schematisation is inadequate to capture the real tunnelling induced displacement field. The overall behaviour of the system proves to be mainly influenced by the buried portion of the building which plays an essential role in the interaction mechanism, due to its high stiffness.

HCl gas gettering of 3d transition metals for crystalline silicon solar cell concepts

In order to reduce the costs of crystalline silicon solar cells, low-cost silicon materials like upgraded metallurgical grade (UMG) silicon are investigated for the application in the photovoltaic (PV) industry. Conventional high-purity silicon is made by cost-intensive methods, based on the so-called Siemens process, which uses the reaction to form chlorosilanes and subsequent several distillation steps before the deposition of high-purity silicon on slim high-purity silicon rods. UMG silicon in contrast is gained from metallurgical silicon by a rather inexpensive physicochemical purification (e.g., acid leaching and/or segregation). However, this type of silicon usually contains much higher concentrations of impurities, especially 3d transition metals like Ti, Fe, and Cu. These metals are extremely detrimental in the electrically active part of silicon solar cells, as they form recombination centers for charge carriers in the silicon band gap. This is why simple purification techniques like gettering, which can be applied between or during solar cell process steps, will play an important role for such low-cost silicon materials. Gettering in general describes a process, whereby impurities are moved to a place or turned into a state, where they are less detrimental to the solar cell. Hydrogen chloride (HCl) gas gettering in particular is a promising simple and cheap gettering technique, which is based on the reaction of HCl gas with transition metals to form volatile metal chloride species at high temperatures.rnThe aim of this thesis was to find the optimum process parameters for HCl gas gettering of 3d transition metals in low-cost silicon to improve the cell efficiency of solar cells for two different cell concepts, the standard wafer cell concept and the epitaxial wafer equivalent (EpiWE) cell concept. Whereas the former is based on a wafer which is the electrically active part of the solar cell, the latter uses an electrically inactive low-cost silicon substrate with an active layer of epitaxially grown silicon on top. Low-cost silicon materials with different impurity grades were used for HCl gas gettering experiments with the variation of process parameters like the temperature, the gettering time, and the HCl gas concentration. Subsequently, the multicrystalline silicon neighboring wafers with and without gettering were compared by element analysis techniques like neutron activation analysis (NAA). It was demonstrated that HCl gas gettering is an effective purification technique for silicon wafers, which is able to reduce some 3d transition metal concentrations by over 90%. Solar cells were processed for both concepts which could demonstrate a significant increase of the solar cell efficiency by HCl gas gettering. The efficiency of EpiWE cells could be increased by HCl gas gettering by approximately 25% relative to cells without gettering. First process simulations were performed based on a simple model for HCl gas gettering processes, which could be used to make qualitative predictions.