Existence of solutions and asymtptotic limits of the Euler-Poisson and the quantum drift-diffusion systems

My work concerns two different systems of equations used in the mathematical modeling of semiconductors and plasmas: the Euler-Poisson system and the quantum drift-diffusion system. The first is given by the Euler equations for the conservation of mass and momentum, with a Poisson equation for the electrostatic potential. The second one takes into account the physical effects due to the smallness of the devices (quantum effects). It is a simple extension of the classical drift-diffusion model which consists of two continuity equations for the charge densities, with a Poisson equation for the electrostatic potential. Using an asymptotic expansion method, we study (in the steady-state case for a potential flow) the limit to zero of the three physical parameters which arise in the Euler-Poisson system: the electron mass, the relaxation time and the Debye length. For each limit, we prove the existence and uniqueness of profiles to the asymptotic expansion and some error estimates. For a vanishing electron mass or a vanishing relaxation time, this method gives us a new approach in the convergence of the Euler-Poisson system to the incompressible Euler equations. For a vanishing Debye length (also called quasineutral limit), we obtain a new approach in the existence of solutions when boundary layers can appear (i.e. when no compatibility condition is assumed). Moreover, using an iterative method, and a finite volume scheme or a penalized mixed finite volume scheme, we numerically show the smallness condition on the electron mass needed in the existence of solutions to the system, condition which has already been shown in the literature. In the quantum drift-diffusion model for the transient bipolar case in one-space dimension, we show, by using a time discretization and energy estimates, the existence of solutions (for a general doping profile). We also prove rigorously the quasineutral limit (for a vanishing doping profile). Finally, using a new time discretization and an algorithmic construction of entropies, we prove some regularity properties for the solutions of the equation obtained in the quasineutral limit (for a vanishing pressure). This new regularity permits us to prove the positivity of solutions to this equation for at least times large enough.

Sicurezza nelle reti di sensori wireless UWB: generazione di chiavi simmetriche da parametri fisici

Le reti di oggetti intelligenti costituiscono una realtà che si sta affermando nel mondo quotidiano. Dispositivi capaci di comunicare tra loro, oltre che svolgere la propria funzione primaria, possono comporre una nuvola che faccia riferimento al legittimo proprietario. Un aspetto fondamentale di questo scenario riguarda la sicurezza, in particolar modo per garantire una comunicazione protetta. Il soddisfacimento di questo requisito è fondamentale anche per altri punti come l'integrità dell'informazione condivisa e l'autenticazione. Lo strumento più antico e tutt'ora adatto alla riservatezza di una comunicazione è costituito dalla crittografia. Una tecnica crittografica è schematicamente composta da un algoritmo che, a seconda di una chiave e del messaggio in ingresso, restituisce in uscita un messaggio cifrato, il crittogramma. Questo viene poi inviato e al legittimo destinatario che, essendo in possesso della chiave e dell'algoritmo, lo converte nel messaggio originale. L'obiettivo è rendere impossibile ad un utente malevolo - non dotato di chiave - la ricostruzione del messaggio. L'assunzione che l'algoritmo possa essere noto anche a terze parti concentra l'attenzione sul tema della chiave. La chiave deve essere sufficientemente lunga e casuale, ma soprattutto deve essere nota ai due utenti che intendono instaurare la comunicazione. Quest'ultimo problema, noto come distribuzione della chiave, è stato risolto con il sistema RSA a chiave pubblica. Il costo computazionale di questa tecnica, specialmente in un contesto di dispositivi non caratterizzati da grandi potenze di calcolo, suggerisce però la ricerca di strade alternative e meno onerose. Una soluzione promettente ed attualmente oggetto di studio sembra essere costituita dalle proprietà del canale wireless. Un ponte radio è caratterizzato da una funzione di trasferimento che dipende dall'ambiente in cui ci si trova e, per il teorema di reciprocità, risulta essere lo stesso per i due utenti che l'hanno instaurato. Oggetto della tesi è lo studio ed il confronto di alcune delle tecniche possibili per estrarre una chiave segreta da un mezzo condiviso, come quello del canale wireless. Si presenterà il contesto in cui verrà sviluppato l'elaborato. Si affronteranno in particolare due casi di interesse, costituiti dalla attuale tecnologia di propagazione del segnale a banda stretta (impiegata per la maggior parte delle trasmissioni senza fili) per passare a quella relativamente più recente della banda Ultra-larga (UWB). Verranno poi illustrate delle tecniche per ottenere stringhe di bit dai segnali acquisiti, e saranno proposti dei metodi per la loro correzione da eventuali discordanze. Saranno infine riportate le conclusioni sul lavoro svolto e le possibili strade future.

Comportamento dinamico fuori del piano di pareti murarie: influenza della deformabilità degli impalcati

The aim of this study was to investigate the influence of the diaphragm flexibility on the behavior of out-of-plane walls in masonry buildings. Simplified models have been developed to perform kinematic and dynamic analyses in order to compare the response of walls with different restraint conditions. Kinematic non linear analyses of assemblages of rigid blocks have been performed to obtain the acceleration-displacement curves for walls with different restraint conditions at the top. A simplified 2DOF model has been developed to analyse the dynamic response of the wall with an elastic spring at the top, following the Housner rigid behaviour hypothesis. The dissipation of energy is concentrated at every impact at the base of the wall and is modelled through the introduction of the coefficient of restitution. The sets of equations of the possible configurations of the wall, depending on the different positions of the centre of rotation at the base and at the intermediate hinge have been obtained. An algorithm for the numerical integration of the sets of the equations of motion in the time domain has been developed. Dynamic analyses of a set of walls with Gaussian impulses and recorded accelerograms inputs have been performed in order to compare the response of the simply supported wall with the one of the wall with elastic spring at the top. The influence of diaphragm stiffness Kd has been investigated determining the variation of maximum displacement demand with the value of Kd. A more regular trend has been obtained for the Gaussian input than for the recorded accelerograms.

Analytical methods for evaluating the quality and the genuineness of olive oils

This Ph.D. thesis focuses on the investigation of some chemical and sensorial analytical parameters linked to the quality and purity of different categories of oils obtained by olives: extra virgin olive oils, both those that are sold in the large retail trade (supermarkets and discounts) and those directly collected at some Italian mills, and lower-quality oils (refined, lampante and “repaso”). Concurrently with the adoption of traditional and well-known analytical procedures such as gas chromatography and high-performance liquid chromatography, I carried out a set-up of innovative, fast and environmentally-friend methods. For example, I developed some analytical approaches based on Fourier transform medium infrared spectroscopy (FT-MIR) and time domain reflectometry (TDR), coupled with a robust chemometric elaboration of the results. I investigated some other freshness and quality markers that are not included in official parameters (in Italian and European regulations): the adoption of such a full chemical and sensorial analytical plan allowed me to obtain interesting information about the degree of quality of the EVOOs, mostly within the Italian market. Here the range of quality of EVOOs resulted very wide, in terms of sensory attributes, price classes and chemical parameters. Thanks to the collaboration with other Italian and foreign research groups, I carried out several applicative studies, especially focusing on the shelf-life of oils obtained by olives and on the effects of thermal stresses on the quality of the products. I also studied some innovative technological treatments, such as the clarification by using inert gases, as an alternative to the traditional filtration. Moreover, during a three-and-a-half months research stay at the University of Applied Sciences in Zurich, I also carried out a study related to the application of statistical methods for the elaboration of sensory results, obtained thanks to the official Swiss Panel and to some consumer tests.

Nanoporous alumina based hypersonic phononic hybrid structures studied by brillouin spectroscopy

Phononische Kristalle sind strukturierte Materialien mit sich periodisch ändernden elastischen Moduln auf der Wellenlängenskala. Die Interaktion zwischen Schallwellen und periodischer Struktur erzeugt interessante Interferenzphänomene, und phononische Kristalle erschließen neue Funktionalitäten, die in unstrukturierter Materie unzugänglich sind. Hypersonische phononische Kristalle im Speziellen, die bei GHz Frequenzen arbeiten, haben Periodizitäten in der Größenordnung der Wellenlänge sichtbaren Lichts und zeigen daher die Wege auf, gleichzeitig Licht- und Schallausbreitung und -lokalisation zu kontrollieren, und dadurch die Realisierung neuartiger akusto-optischer Anordnungen. Bisher bekannte hypersonische phononische Kristalle basieren auf thermoplastischen Polymeren oder Epoxiden und haben nur eingeschränkte thermische und mechanische Stabilität und mechanischen Kontrast. Phononische Kristalle, die aus mit Flüssigkeit gefüllten zylindrischen Kanälen in harter Matrix bestehen, zeigen einen sehr hohen elastischen Kontrast und sind bislang noch unerforscht. In dieser Dissertation wird die experimentelle Untersuchung zweidimensionaler hypersonischer phononischer Kristalle mit hexagonaler Anordnung zylindrischer Nanoporen basierend auf der Selbstorganisation anodischen Aluminiumoxids (AAO) beschrieben. Dazu wird die Technik der hochauflösenden inelastischen Brillouin Lichtstreuung (BLS) verwendet. AAO ist ein vielsetiges Modellsystem für die Untersuchung reicher phononischer Phänomene im GHz-Bereich, die eng mit den sich in den Nanoporen befindlichen Flüssigkeiten und deren Interaktion mit der Porenwand verknüpft sind. Gerichteter Fluss elastischer Energie parallel und orthogonal zu der Kanalachse, Lokalisierung von Phononen und Beeinflussung der phononischen Bandstruktur bei gleichzeitig präziser Kontrolle des Volumenbruchs der Kanäle (Porosität) werden erörtert. Außerdem ermöglicht die thermische Stabilität von AAO ein temperaturabhängiges Schalten phononischer Eigenschaften infolge temperaturinduzierter Phasenübergänge in den Nanoporen. In monokristallinen zweidimensionalen phononischen AAO Kristallen unterscheiden sich die Dispersionsrelationen empfindlich entlang zweier hoch symmetrischer Richtungen in der Brillouinzone, abhängig davon, ob die Poren leer oder gefüllt sind. Alle experimentellen Dispersionsrelationen werden unter Zuhilfenahme theoretische Ergebnisse durch finite Elemente Analyse (FDTD) gedeutet. Die Zuordnung der Verschiebungsfelder der elastischen Wellen erklärt die Natur aller phononischen Moden.

High-Speed Laser Processing of Thin Single and Multi-Layer Films

Theoretical models are developed for the continuous-wave and pulsed laser incision and cut of thin single and multi-layer films. A one-dimensional steady-state model establishes the theoretical foundations of the problem by combining a power-balance integral with heat flow in the direction of laser motion. In this approach, classical modelling methods for laser processing are extended by introducing multi-layer optical absorption and thermal properties. The calculation domain is consequently divided in correspondence with the progressive removal of individual layers. A second, time-domain numerical model for the short-pulse laser ablation of metals accounts for changes in optical and thermal properties during a single laser pulse. With sufficient fluence, the target surface is heated towards its critical temperature and homogeneous boiling or "phase explosion" takes place. Improvements are seen over previous works with the more accurate calculation of optical absorption and shielding of the incident beam by the ablation products. A third, general time-domain numerical laser processing model combines ablation depth and energy absorption data from the short-pulse model with two-dimensional heat flow in an arbitrary multi-layer structure. Layer removal is the result of both progressive short-pulse ablation and classical vaporisation due to long-term heating of the sample. At low velocity, pulsed laser exposure of multi-layer films comprising aluminium-plastic and aluminium-paper are found to be characterised by short-pulse ablation of the metallic layer and vaporisation or degradation of the others due to thermal conduction from the former. At high velocity, all layers of the two films are ultimately removed by vaporisation or degradation as the average beam power is increased to achieve a complete cut. The transition velocity between the two characteristic removal types is shown to be a function of the pulse repetition rate. An experimental investigation validates the simulation results and provides new laser processing data for some typical packaging materials.

Influenza della conservazione delle olive sulla qualita dell'olio vergine prodotto

Il primo scopo di questo progetto sperimentale è stato quello di valutare la qualità chimica e sensoriale di oli vergini d’oliva ottenuti da olive conservate per tempi diversi prima della loro lavorazione. Spesso, infatti, quando le olive arrivano in frantoio, la loro trasformazione può essere ritardata a causa della ridotta capacità di lavorazione degli impianti rispetto alla quantità di prodotto da lavorare. Il tempo e le modalità di conservazione delle drupe risultano fattori molto importanti ai fini della qualità organolettica dell’olio prodotto. Per questa finalità sono state acquistate olive di due diverse varietà (Correggiolo e Canino) e divise in due aliquote. La prima aliquota di ogni partita di olive è stata franta al momento della consegna (tempo 0), la seconda invece è stata stoccata in condizioni non ideali di conservazione ed umidità per 7 giorni (varietà Correggiolo) e 15 giorni (varietà Canino), quindi franta. Per tutti i campioni sono stati valutati i parametri di qualità stabiliti dal Reg. CEE n. 2568/91 e successive modifiche: acidità libera e numero di perossidi con valutazioni titrimetriche, estinzioni specifiche nell'ultravioletto mediante spettrofotometria, determinazione gascromatografica degli alchil esteri degli acidi grassi ed analisi sensoriale secondo “Panel test”. Sono stati inoltre valutati parametri compositivi che attualmente non sono contemplati nei regolamenti ufficiali: il profilo qualitativo e quantitativo gascromatografico in digliceridi e quello in componenti volatili (SPME). I risultati ottenuti per i campioni ottenuti da olive “fresche” e da olive conservate per tempi diversi sono stati comparati con i limiti di legge che definiscono l'appartenenza alle categorie merceologiche degli oli di oliva vergini (extravergine, vergine o lampante) e, per i parametri non normati, sono state valutate le principali differenze in relazione alla qualità del prodotto. Il secondo scopo del progetto è stato quello di valutare la possibilità di una rapida discriminazione di oli d’oliva caratterizzati da differenti concentrazioni di alchil esteri degli acidi grassi mediante Riflettometria nel Dominio del Tempo (TDR, Time Domain Reflectometry). Il metodo chimico proposto dal Reg. UE n. 61/2011 risulta, infatti, lungo e dispendioso prevedendo una separazione preparativa seguita da analisi gascromatografica. La TDR si presenta, invece, come un metodo alternativo rapido, economico e non distruttivo per la valutazione e discriminazione degli oli d’oliva sulla base di questo parametro qualitativo.

Dynamic analysis of the motorcycle chattering behaviour by means of symbolic multibody modelling

Aim of this research is the development and validation of a comprehensive multibody motorcycle model featuring rigid-ring tires, taking into account both slope and roughness of road surfaces. A novel parametrization for the general kinematics of the motorcycle is proposed, using a mixed reference-point and relative-coordinates approach. The resulting description, developed in terms of dependent coordinates, makes it possible to efficiently include rigid-ring kinematics as well as road elevation and slope. The equations of motion for the multibody system are derived symbolically and the constraint equations arising from the dependent-coordinate formulation are handled using a projection technique. Therefore the resulting system of equations can be integrated in time domain using a standard ODE algorithm. The model is validated with respect to maneuvers experimentally measured on the race track, showing consistent results and excellent computational efficiency. More in detail, it is also capable of reproducing the chatter vibration of racing motorcycles. The chatter phenomenon, appearing during high speed cornering maneuvers, consists of a self-excited vertical oscillation of both the front and rear unsprung masses in the range of frequency between 17 and 22 Hz. A critical maneuver is numerically simulated, and a self-excited vibration appears, consistent with the experimentally measured chatter vibration. Finally, the driving mechanism for the self-excitation is highlighted and a physical interpretation is proposed.

In vivo konditionale Depletion von latentem murinen Cytomegalovirus

Die Lunge stellt einen Hauptort der CMV-Latenz dar. Die akute CMV-Infektion wird durch infiltrierende antivirale CD8 T-Zellen terminiert. Das virale Genom verbleibt jedoch im Lungengewebe in einem nicht replikativen Zustand, der Latenz, erhalten. Es konnte bereits gezeigt werden, dass während der Latenz die Major Immediate Early- (MIE) Gene ie1- und ie2 sporadisch transkribiert werden. Bisher konnte diese beginnende Reaktivierung latenter CMV-Genome nur in einer Momentaufnahme gezeigt werden (Kurz et al., 1999; Grzimek et al., 2001; Simon et al., 2005; zur Übersicht: Reddehase et al., 2008). Die sporadische Expression der MIE-Gene führt jedoch zur Präsentation eines antigenen IE1-Peptids und somit zur Stimulation antiviraler IE1-Peptid-spezifischer CD8 T-Zellen, die durch ihre Effektorfunktion die beginnende Reaktivierung wieder beenden. Dies führte uns zu der Hypothese, dass MIE-Genexpression über einen Zeitraum betrachtet (period prevalence) häufiger stattfindet als es in einer Momentaufnahme (point prevalence) beobachtet werden kann.rnrnUm die Häufigkeit der MIE-Genexpression in der Dynamik in einem definierten Zeitraum zu erfassen, sollte eine Methode entwickelt werden, welche es erstmals ermöglicht, selektiv und konditional transkriptionell aktive Zellen sowohl während der akuten Infektion als auch während der Latenz auszulöschen. Dazu wurde mit Hilfe der Zwei-Schritt BAC-Mutagenese ein rekombinantes death-tagged Virus hergestellt, welches das Gen für den Diphtherie Toxin Rezeptor (DTR) unter Kontrolle des ie2-Promotors (P2) enthält. Ist der P2 transkriptionell aktiv, wird der DTR an der Zelloberfläche präsentiert und die Zelle wird suszeptibel für den Liganden Diphtherie Toxin (DT). Durch Gabe von DT werden somit alle Zellen ausgelöscht, in denen virale Genome transkriptionell aktiv sind. Mit zunehmender Dauer der DT-Behandlung sollte also die Menge an latenten viralen Genomen abnehmen.rnrnIn Western Blot-Analysen konnte das DTR-Protein bereits 2h nach der Infektion nachgewiesen werden. Die Präsentation des DTR an der Zelloberfläche wurde indirekt durch dessen Funktionalität bewiesen. Das rekombinante Virus konnte in Fibroblasten in Gegenwart von DT nicht mehr replizieren. In akut infizierten Tieren konnte die virale DNA-Menge durch eine einmalige intravenöse (i.v.) DT-Gabe signifikant reduziert werden. Verstärkt wurde dieser Effekt durch eine repetitive i.v. DT-Gabe. Auch während der Latenz gelang es, die Zahl der latenten viralen Genome durch repetitive i.v. und anschließende intraperitoneale (i.p.) DT-Gabe zu reduzieren, wobei wir abhängig von der Dauer der DT-Gabe eine Reduktion um 60\% erreichen konnten. Korrespondierend zu der Reduktion der DNA-Menge sank auch die Reaktivierungshäufigkeit des rekombinanten Virus in Lungenexplantatkulturen. rnrnrnUm die Reaktivierungshäufigkeit während der Latenz berechnen zu können, wurde durch eine Grenzverdünnungsanalyse die Anzahl an latenten viralen Genomen pro Zelle bestimmt. Dabei ergab sich eine Kopienzahl von 9 (6 bis 13). Ausgehend von diesen Ergebnissen lässt sich berechnen, dass, bezogen auf die gesamte Lunge, in dem getesteten Zeitraum von 184h durch die DT-Behandlung 1.000 bis 2.500 Genome pro Stunde ausgelöscht wurden. Dies entspricht einer Auslöschung von 110 bis 280 MIE-Gen-exprimierenden Lungenzellen pro Stunde. Damit konnte in dieser Arbeit erstmals die Latenz-assoziierte Genexpression in ihrer Dynamik dargestellt werden.rn

Identifizierung, Quantifizierung und Hemmung von ausgewählten Hefen im Wein

Hefen stellen einen großen und wichtigen Teil der Mikrobiota während der Weinbereitung dar, da ohne ihre alkoholische Fermentation die Umwandlung von Most und Wein nicht möglich wäre. Ferner ist es ihre Vielzahl an Stoffwechselprodukten, die dem Aroma des fertigen Weines eine zusätzliche Komplexität verleihen. Auf der anderen Seite steht durch den Metabolismus verschiedenster so genannter Wildhefen die Gefahr von Qualitätsabstufungen der Weine, was allgemein als „Weinfehler“ betrachtet wird. Ziel dieser Arbeit war zum einen die taxonomische Einordnung von Saccharomyces-Spezies, sowie die Quantifizierung und Hemmung von ausgewählten Wildhefen während der Weinbereitung.rnEin Teil dieser Arbeit umfasste die Identifizierung der nahverwandten Mitglieder der Saccharomyces sensu stricto-Gruppe. Durch den Einsatz des DNA-Fingerpinting-Systems SAPD-PCR konnten alle die Gruppe umfassenden Spezies anhand spezifischer Bandenmuster nachgewiesen werden, wodurch eine Einordnung dieser schwer zu differenzierenden Arten möglich war. Die Differenzierung zwischen den einzelnen Spezies war in jedem Fall deutlicher als dies die Sequenzierung der 5.8S rDNA und ihre flankierenden ITS-Regionen vermochte. Die SAPD-PCR zeichnete sich zudem durch eine geringe Muster-Varianz bei verschiedenen Stämmen einer Art aus und konnte zuverlässig unbekannte Stämme bestimmen und bereits hinterlegte Stämme neu klassifizieren. Zudem konnte mit Hilfe dieses Systems Hybride aus Saccharomyces cerevisiae und S. bayanus bzw. S. cerevisiae und S. kudriavzevii detektiert werden, wenn diese Hybride aus relativ gleichen genomischen Anteilen der Eltern bestanden. rnZusätzlich wurde ein quantitatives PCR-System entwickelt, um die Gattungen Saccharomyces, Hanseniaspora und Brettanomyces in Most und Wein detektieren und quantifizieren zu können. Die hierfür entwickelten Primer zeigten sich spezifisch für die untersuchten Arten. Durch die serielle Verdünnung definierter DNA-Mengen konnte für alle drei Systeme eine Kalibrierungskurve erstellt werden, mit Hilfe derer die tatsächlichen Quantifizierungen durchgeführt wurden. Die qPCR-Analyse lieferte ähnliche Zellzahlen wie Lebendzellzahl-Bestimmungen und wurde nicht von anderen Spezies und von Traubensaft gestört. Die maximal detektierbare Zellzahl betrug 2 x 107 Zellen/ml, während die minimale Detektionsgrenze je nach Art zwischen 1 x 102 Zellen/ml und 1 x 103 Zellen/ml lag. Allerdings konnte eine effektive DNA-Isolierung dieser geringen Zellzahlen nur erreicht werden, wenn die Zellzahl durch artfremde Hefen künstlich erhöht wurde. Die Analyse einer Most-Vergärung mit den drei Spezies zeigte schlussendlich, dass die quantitative PCR sicher und schnell Veränderungen und Sukzessionen detektiert und so ein geeignetes Mittel darstellt, um Populationsdynamiken während der Weinherstellung zu beobachten. rnDer letzte Teil dieser Arbeit befasste sich mit der Inhibierung von Schadhefen durch zellwand-hydrolysierende Enzyme. Es konnte hierbei eine endoglykosidisch wirkende β-1,3-Glucanase aus dem Bakterium Delftia tsuruhatensis isoliert werden. Diese besaß eine ungefähre Masse von 28 kDa, einen isolektrischen Punkt von ca. 4,3 und wirkte mit einer spezifischen Aktivität von 10 U/mg Protein gegen das Glucan Laminarin. Zudem zeigte das Enzym ein Temperaturoptimum von 50 °C und ein pH-Optimum bei pH 4,0. Weinparameter wie erhöhte Konzentrationen an Ethanol, Phenolen und Sulfit beeinflussten die Wirkung des Enzyms nicht oder nur wenig. Neben der allgemeinen Wirkung gegen β-1,3-Glucane konnte hier auch gezeigt werden, dass ebenso gut die β-1,3-Glucane in der Zellwand verschiedener Hefen hydrolysiert wurden. Fluoreszenz- und rasterelektronen-mikroskopische Aufnahmen von Hefezellen nach Inkubation mit der β-1,3-Glucanase zeigten zusätzlich die Zerstörung der Zelloberfläche der Hefen. Die lytische Wirkung des Enzyms wurde an verschiedenen weintypischen Hefen getestet. Hierbei zeigten sich stammspezifische Unterschiede in der Sensitivität gegenüber dem Enzym. Außerdem konnte festgestellt werden, dass sowohl Wachstumsphase als auch Medium der Hefen Einfluss auf deren Zellwand hat und somit auch auf die Wirkung des Enzyms.rn

New enhancement strategies for plasmon-enhanced fluorescence biosensors

This thesis investigates metallic nanostructures exhibiting surface plasmon resonance for the amplification of fluorescence signal in sandwich immunoassays. In this approach, an analyte is captured by an antibody immobilized on a plasmonic structure and detected by a subsequently bound fluorophore labeled detection antibody. The highly confined field of surface plasmons originates from collective charge oscillations which are associated with high electromagnetic field enhancements at the metal surface and allow for greatly increased fluorescence signal from the attached fluorophores. This feature allows for improving the signal-to-noise ratio in fluorescence measurements and thus advancing the sensitivity of the sensor platform. In particular, the thesis presents two plasmonic nanostructures that amplify fluorescence signal in devices that rely on epifluorescence geometry, in which the fluorophore absorbs and emits light from the same direction perpendicular to the substrate surface.rnThe first is a crossed relief gold grating that supports propagating surface plasmon polaritons (SPPs) and second, gold nanoparticles embedded in refractive index symmetric environment exhibiting collective localized surface plasmons (cLSPs). Finite-difference time-domain simulations are performed in order to design structures for the optimum amplification of established Cy5 and Alexa Fluor 647 fluorophore labels with the absorption and emission wavelengths in the red region of spectrum. The design takes into account combined effect of surface plasmon-enhanced excitation rate, directional surface plasmon-driven emission and modified quantum yield for characteristic distances in immunoassays. Homebuilt optical instruments are developed for the experimental observation of the surface plasmon mode spectrum, measurements of the angular distribution of surface plasmon-coupled fluorescence light and a setup mimicking commercial fluorescence reading systems in epifluorescence geometry.rnCrossed relief grating structures are prepared by interference lithography and multiple copies are made by UV nanoimprint lithography. The fabricated crossed diffraction gratings were utilized for sandwich immunoassay-based detection of the clinically relevant inflammation marker interleukin 6 (IL-6). The enhancement factor of the crossed grating reached EF=100 when compared to a flat gold substrate. This result is comparable to the highest reported enhancements to date, for fluorophores with relatively high intrinsic quantum yield. The measured enhancement factor excellently agrees with the predictions of the simulations and the mechanisms of the enhancement are explained in detail. Main contributions were the high electric field intensity enhancement (30-fold increase) and the directional fluorescence emission at (4-fold increase) compared to a flat gold substrate.rnCollective localized surface plasmons (cLSPs) hold potential for even stronger fluorescence enhancement of EF=1000, due to higher electric field intensity confinement. cLSPs are established by diffractive coupling of the localized surface plasmon resonance (LSPR) of metallic nanoparticles and result in a narrow resonance. Due to the narrow resonance, it is hard to overlap the cLSPs mode with the absorption and emission bands of the used fluorophore, simultaneously. Therefore, a novel two resonance structure that supports SPP and cLSP modes was proposed. It consists of a 2D array of cylindrical gold nanoparticles above a low refractive index polymer and a silver film. A structure that supports the proposed SPP and cLSP modes was prepared by employing laser interference lithography and the measured mode spectrum was compared to simulation results.rn

Analisi di algoritmi per reti di sensori radar uwb basati su misure sperimentali

In un sistema radar è fondamentale rilevare, riconoscere e cercare di seguire il percorso di un eventuale intruso presente in un’area di osservazione al fine ultimo della sicurezza, sia che si consideri l’ambito militare, che anche quello civile. A questo proposito sono stati fatti passi avanti notevoli nella creazione e sviluppo di sistemi di localizzazione passiva che possano rilevare un target (il quale ha come unica proprietà quella di riflettere un segnale inviato dal trasmettitore), in modo che esso sia nettamente distinto rispetto al caso di assenza dell’intruso stesso dall’area di sorveglianza. In particolare l’ultilizzo di Radar Multistatico (ossia un trasmettitore e più ricevitori) permette una maggior precisione nel controllo dell’area d’osservazione. Tra le migliori tecnologie a supporto di questa analisi vi è l’UWB (Ultra Wide-Band), che permette di sfruttare una banda molto grande con il riscontro di una precisione che può arrivare anche al centimetro per scenari in-door. L’UWB utilizza segnali ad impulso molto brevi, a banda larga e che quindi permettono una risoluzione elevata, tanto da consentire, in alcune applicazioni, di superare i muri, rimuovendo facilmente gli elementi presenti nell’ambiente, ossia il clutter. Quindi è fondamentale conoscere algoritmi che permettano la detection ed il tracking del percorso compiuto dal target nell’area. In particolare in questa tesi vengono elaborati nuovi algoritmi di Clustering del segnale ricevuto dalla riflessione sull’intruso, utilizzati al fine di migliorare la visualizzazione dello stesso in post-processing. Infine questi algoritmi sono stati anche implementati su misure sperimentali attuate tramite nodi PulsOn 410 Time Domain, al fine ultimo della rilevazione della presenza di un target nell’area di osservazione dei nodi.

Dielectric relaxation in biological materials

The study of dielectric properties concerns storage and dissipation of electric and magnetic energy in materials. Dielectrics are important in order to explain various phenomena in Solid-State Physics and in Physics of Biological Materials. Indeed, during the last two centuries, many scientists have tried to explain and model the dielectric relaxation. Starting from the Kohlrausch model and passing through the ideal Debye one, they arrived at more com- plex models that try to explain the experimentally observed distributions of relaxation times, including the classical (Cole-Cole, Davidson-Cole and Havriliak-Negami) and the more recent ones (Hilfer, Jonscher, Weron, etc.). The purpose of this thesis is to discuss a variety of models carrying out the analysis both in the frequency and in the time domain. Particular attention is devoted to the three classical models, that are studied using a transcendental function known as Mittag-Leffler function. We highlight that one of the most important properties of this function, its complete monotonicity, is an essential property for the physical acceptability and realizability of the models. Lo studio delle proprietà dielettriche riguarda l’immagazzinamento e la dissipazione di energia elettrica e magnetica nei materiali. I dielettrici sono importanti al fine di spiegare vari fenomeni nell’ambito della Fisica dello Stato Solido e della Fisica dei Materiali Biologici. Infatti, durante i due secoli passati, molti scienziati hanno tentato di spiegare e modellizzare il rilassamento dielettrico. A partire dal modello di Kohlrausch e passando attraverso quello ideale di Debye, sono giunti a modelli più complessi che tentano di spiegare la distribuzione osservata sperimentalmente di tempi di rilassamento, tra i quali modelli abbiamo quelli classici (Cole-Cole, Davidson-Cole e Havriliak-Negami) e quelli più recenti (Hilfer, Jonscher, Weron, etc.). L’obiettivo di questa tesi è discutere vari modelli, conducendo l’analisi sia nel dominio delle frequenze sia in quello dei tempi. Particolare attenzione è rivolta ai tre modelli classici, i quali sono studiati utilizzando una funzione trascendente nota come funzione di Mittag-Leffler. Evidenziamo come una delle più importanti proprietà di questa funzione, la sua completa monotonia, è una proprietà essenziale per l’accettabilità fisica e la realizzabilità dei modelli.

Mission synthesis of sine-on-random excitations for accelerated vibration qualification testing

In most real-life environments, mechanical or electronic components are subjected to vibrations. Some of these components may have to pass qualification tests to verify that they can withstand the fatigue damage they will encounter during their operational life. In order to conduct a reliable test, the environmental excitations can be taken as a reference to synthesize the test profile: this procedure is referred to as “test tailoring”. Due to cost and feasibility reasons, accelerated qualification tests are usually performed. In this case, the duration of the original excitation which acts on the component for its entire life-cycle, typically hundreds or thousands of hours, is reduced. In particular, the “Mission Synthesis” procedure lets to quantify the induced damage of the environmental vibration through two functions: the Fatigue Damage Spectrum (FDS) quantifies the fatigue damage, while the Maximum Response Spectrum (MRS) quantifies the maximum stress. Then, a new random Power Spectral Density (PSD) can be synthesized, with same amount of induced damage, but a specified duration in order to conduct accelerated tests. In this work, the Mission Synthesis procedure is applied in the case of so-called Sine-on-Random vibrations, i.e. excitations composed of random vibrations superimposed on deterministic contributions, in the form of sine tones typically due to some rotating parts of the system (e.g. helicopters, engine-mounted components, …). In fact, a proper test tailoring should not only preserve the accumulated fatigue damage, but also the “nature” of the excitation (in this case the sinusoidal components superimposed on the random process) in order to obtain reliable results. The classic time-domain approach is taken as a reference for the comparison of different methods for the FDS calculation in presence of Sine-on-Random vibrations. Then, a methodology to compute a Sine-on-Random specification based on a mission FDS is presented.

Optical properties of a nanomatch-like plasmonic structure

The optical properties of a match-like plasmonic nanostructure are numerically investigated using full-wave finite-difference time-domain analysis in conjunction with dispersive material models. This work is mainly motivated by the developed technique enabling reproducible fabrication of nanomatch structures as well as the growing applications that utilize the localized field enhancement in plasmonic nanostructures. Our research revealed that due to the pronounced field enhancement and larger resonance tunabilities, some nanomatch topologies show potentials for various applications in the field of, e.g., sensing as well as a novel scheme for highly reproducible tips in scanning near field optical microscopy, among others. Despite the additional degrees of freedom that are offered by the composite nature of the proposed nanomatch topology, the paper also reflects on a fundamental complication intrinsic to the material interfaces especially in the nanoscale: stoichiometric mixing. We conclude that the specificity in material modeling will become a significant issue in future research on functionalized composite nanostructures.