Diese Arbeit beschreibt eine ausfŸhrliche Untersuchung der physikalischen Eigenschaften von Mikrokugelresonatoren aus Quarzglas. Diese Resonatoren unterstŸtzen sogennante whispering-gallery Moden (WGM), die GŸten so hoch bis 109 bieten. Als experimentelle Hilfsmittel wurden ein Nahfeld- und ein Konfokalmikroskop benutzt, um die Struktur der Moden bezŸglich der Topographie des Resonators eindeutig zu identifizieren, oder um einzelne Quantenemitter zu detektieren und anzuregen. Die resonante †berhšhung des elektromagnetischen Feldes in den Moden des Resonators wurde ausgenutzt, um stimulierte Raman-Streuung mit extrem niedrigem Schwellenwert im Quarzglas zu beobachten. Ein Rekordschwellenwert von 4.5 Mikrowatts wurde gemessen. Mittels einer Nahfeldsonde wurde die Modenstruktur des Mikro-Ramanlasers gemessen. Mikroresonatoren stellen einen Grundbaustein der Resonator-Quantenelektrodynamik dar. In dieser Arbeit wurde die Kopplung von einem einzelnen strahlenden Dipol an die WGM sowohl theoretisch als auch experimentell untersucht. Die kontrollierte Kopplung von einem einzelnen Nanoteilchen an die WGM eines Mikrokugelresonators wurde nachgewiesen. Erste Ergebnisse in der Kopplung eines einzelnen Emitters an die Moden des Resonators wurden erzielt. Die resonante Wechselwirkung mit Resonatormoden wurde ausgenutzt, um den Photonentransfer zwischen zwei Nanoteilchen dramatisch zu verstŠrken. Schlie§lich wurde die bislang unbeachtete Analogie zwischen dem Quantensystem eines einzelnen Emitters in Wechselwirkung mit einer einzelnen Resonatormode und dem klassischen System zweier gekoppelten Moden experimentell untersucht. Es wurde bewiesen, wie die aus der Resonatorquantenelektrodynamik bekannten Kopplungsregime der starken und schwachen Kopplung in Analogie auch an einem klassischen System beobachtet werden kšnnen. Der †bergang von schwacher zu starker Kopplung wurde beobachtet, und bislang gemessene unerwartet hohe Kopplungsraten konnten einfach erklŠrt werden. / This work presents an extensive study of the physical properties of silica microsphere resonators, which support whispering-gallery modes (WGMs). These modes feature Q-factors as high as 109 corresponding to a finesse of 3 millions for spheres with a diameter of about 80 micrometers. These are to date among the highest available Q-factors, leading to cavity lifetimes of up to few microseconds. A near-field microscope and a confocal microscope are used as tools to unequivocally identify the mode structure related to the sphere topography, and for excitation and detection of single quantum emitters. The high field enhancement of the cavity modes is exploited to observe ultra-low threshold stimulated Raman scattering in silica glass. A record ultra-low threshold of 4.5 microwatts was recorded. The mode structure of the laser is investigated by means of a near-field probe, and the interaction of the probe itself with the lasing properties is investigated in a systematic way. Microcavities also one of the building blocks of Cavity QED. Here, the coupling of a radiative dipole to the whispering-gallery modes has been studied both theoretically and experimentally. The controlled coupling of a single nanoparticle to the WGMs is demonstrated, and first results in coupling a single quantum emitter to the modes of a microsphere are reported. The resonant interaction with these modes is exploited to enhance photon exchange between two nanoparticles. Finally a novel analogy between a system composed of a single atom interacting with one cavity mode on one side and intramodal coupling in microsphere resonators induced by a near-field probe on the other side is presented and experimentally explored. The induced coupling regimes reflect the different regimes of weak and strong coupling typical of Cavity QED. The transition between the two coupling regimes is observed, and a previously observed unexpectedly large coupling rate is explained.

Diese Arbeit leistet einen Beitrag zum Verständnis optischer Anregungen in metallischen Nanostrukturen. Am Beispiel ausgewählter Strukturen werden experimentell die Dynamik dieser Anregungen mit Femtosekunden-Zeitauflösung und ihre elektromagnetischen Moden auf der Nanometer-Längenskala untersucht. Anhand winkel- und zeitaufgelöster Transmissionsexperimente an metallischen Dünnfilmgittern wird gezeigt, dass resonante Oberflächenplasmon-Polaritonen (OPPen) wesentlich die optischen Eigenschaften dieser Strukturen beeinflussen. Die Lebensdauer solcher Anregungen wird ermittelt und damit nachgewiesen, dass Kopplungen zwischen OPP-Resonanzen drastische Lebensdauer-Modifikationen zur Folge haben. In einem eigens konstruierten, spektral auflösenden optischen Nahfeldmikroskop werden die elektromagnetischen Feldverteilungen der OPPen direkt abgebildet. Derartige Experimente erlauben erstmals eine Zuordnung der räumlichen Moden zur zeitlichen Dynamik verschiedener OPP-Resonanzen. Diese Erkenntnisse ermöglichen zudem eine Interpretation des nahfeldmikroskopischen Bildkontrasts bezüglich der Beiträge verschiedener vektorieller Komponenten des optischen Nahfeldes. Die selektive Abbildung unterschiedlicher elektrischer und magnetischer Feldkomponenten in Abhängigkeit vom Sondentyp wird demonstriert. Darüberhinaus wird die OPP-Erzeugung in einem Gitter auf dem Schaft einer Nahfeldspitze ausgenutzt, um propagierende OPPen im Apex zu konzentrieren. Ein weiterer Teil der Arbeit nutzt elektrische Feldüberhöhungen an scharfen Metallspitzen für die lokalisierte Erzeugung nichtlinearer optischer Signale. Die Beobachtung intensiver Multiphoton-Elektronenemission nach Femtosekundenanregung stellt ein zentrales Ergebnis dar. Dieser Prozess wird umfangreich charakterisiert und findet seine erste Anwendung in einer neuartigen Rastersondentechnik, in der die örtlich variierende Elektronenemission der Bildgebung dient. / This thesis contributes to the understanding of optical excitations in metallic nanostructures. In experiments on selected model structures, the dynamics of these excitations and their electromagnetic spatial modes are investigated with femtosecond temporal and nanometer spatial resolution, respectively. Angle- and time-resolved transmission experiments on metallic thin film gratings demonstrate the dominant role resonant surface plasmon polaritons (SPPs) play in the optical properties of such structures. The lifetimes of these excitations are determined, and it is shown that coherent couplings among SPP-resonances result in drastic lifetime modifications. The spatial SPP mode profiles are imaged using a custom-built near-field optical microscope. The experiments reveal a direct correlation between the spatial mode structure and the dynamics of different SPP resonances. These findings allow for an interpretation of the near-field optical image contrast in terms of the contributions of different vectorial components of the electromagnetic near-field. A selective imaging of different electric and magnetic field components is demonstrated for various types of near-field probes. Furthermore, the excitation of SPPs in periodic structures is employed in a novel type of near-field tip. The resonant excitation of SPPs in a nanofabricated grating on the shaft of a sharp metallic tip results in their concentration at the tip apex. The final part of the thesis highlights the importance of optical field enhancements for the local generation of nonlinear optical signals at the apex of sharp metallic tips. Specifically, the observation of intense multiphoton electron emission after femtosecond excitation is a major result. This process is thoroughly characterized, and a novel scanning microscopy application based on this effect is presented. In this technique, an image contrast with nanometer resolution arises from spatially varying electron emission rates.

[pt] No presente trabalho de tese, se faz uma avaliação de moduladores de amplitude baseados no efeito de electro-absorção. As estruturas usadas para a fabricação dos dispositivos foram estruturas com poços quânticos múltiplos de InAlAs/InGaAs e AlGaAs/GaAs. As estruturas de InAlAs/InGaAs foram projetadas para trabalhar na faixa comercial das telecomunicações (1.55 µm). Por isto a importância de aperfeiçoar os parâmetros de desempenho do dispositivo, tais como Stark shift, chirp, razão de contraste, perda por inserção, entre outros. Um estudo sistemático prévio destas estruturas foi realizado por Pires [Pires,1998]. Ele propõe variar a concentração de gálio na liga para produzir uma leve tensão na estrutura e modificar desta forma as propriedades ópticas do material. O estudo de [Pires,1998] propôs uma faixa de valores para variar a concentração de gálio (entre 46 por cento e 52 por cento) onde pode ser encontrada a melhor condição de operação do dispositivo. Cabe a esta tese aprofundar o estudo nesta faixa de valores, e decidir os parâmetros mais adequados para operação. No referente às estruturas de AlGaAs/GaAs, se toma como partida uma proposta teórica de [Batty et al, 1993], e estudada posteriormente por [Tribuzy, 2001], onde se sugere usar finas camadas de dopagem delta nos poços de GaAs para melhorar o deslocamento Stark em 87% para um campo aplicado de 40 kV/cm. O dispositivo foi desenhado e fabricado, obtendo-se um valor de 78 por cento para o mesmo campo aplicado, resultado relevante, pois é a verificação experimental de uma proposta teórica. / [en] In this thesis work, is made an evaluation of modulators of amplitude based in the electrum-absorption effect. The structures used for the devices were multiple quantum wells of InAlAs/InGaAs and AlGaAs/GaAs. The structures of InAlAs/InGaAs are used to work in the commercial band of the telecommunications (1,55 µm). This is the reason it is important to optimize the parameters of performance of the device, such as the Stark shift, chirp, contrast reason, insertion loss, etc. Previously, a systematic study of these structures was made by [Pires, 1998], the gallium concentration was varied to produce a strain in the structure and to modify the optic properties of the material. In the study of [Pires, 1998] considered the Gallium concentration was varied between 46 percent and 52 percent in which range the best condition to operate the device can be found. This is part of the work here presented. In this thesis this range of values was studied in more detail. For the structures of AlGaAs/GaAs, a theoretical proposal of [Batty et al, 1993] was experimentally investigated. It was suggested a nipi structure to use a fine delta doped in the GaAs wells, this delta doped will improve in 87 percent the Stark shift for a field of 40 KV/cm. The device was simulated and manufactured, obtaining a value of 78 percent for the same field applied, this is a excellent result, because this confirm the theoretical prediction.

La technologie NFC (Near Field Communication) est une nouvelle technique de communication basée sur la technologie RFID (Radio-Fréquence IDentification). La NFC utilise le couplage magnétique entre deux antennes afin de transférer les données et / ou l'énergie entre deux dispositifs électroniques. Elle exploite la fréquence de 13,56 MHz. En raison de la large gamme de dispositifs et d'applications, une définition de la géométrie de l'antenne et de ses paramètres électriques associés est très difficile. En effet, chaque dispositif présente des caractéristiques physiques différentes. En revanche, le circuit intégré (CI) de contrôle NFC est générique et indépendant d'une antenne où d'un dispositif. C'est pourquoi, chaque intégrateur associe le circuit intégré NFC avec une antenne pour chaque dispositif. Or le module de transmission du système NFC nécessite une bonne adaptation de l'antenne à son circuit intégré (IC). Actuellement, cette adaptation est effectuée à la main pour chaque dispositif selon un processus itératif chronophage. En outre, l'adaptation est effectuée une seule fois au moment de la conception du dispositif, quel que soit le mode de communication (lecteur, carte ou peer-to-peer) et à vide c'est-à-dire sans considérer l'influence du dispositif secondaire. Dans ce manuscrit, nous proposons une description détaillée des performances électriques des systèmes NFC. Ensuite un modèle électrique analytique complet et précis de l'antenne NFC est proposé. Enfin, nous développons une nouvelle technique d'adaptation automatique d'impédance afin d'optimiser les performances électriques dans la phase d'émission en termes de transfert d'énergie entre le lecteur et le transpondeur. / Near Field Communication (NFC) is a standardized communication technology derived from Radio Frequency Identification (RFID). NFC uses magnetic induction between two antennas in order to transfer data and/or energy between two electronic devices. NFC operating frequency is 13.56 MHz.Due to the wide range of devices and applications, a predefinition of antenna geometry and corresponding electrical parameters is difficult. In fact, each device shows different antennaphysical characteristics ; On the Other hand, the NFC control integrated circuit (IC) is generic and does not depend on antenna nor a device. Therefore, each integrator associates the NFC IC with a specific antenna for each device. Current NFC transmission modules require the antenna circuitry to be matched with the integrated circuit. Nowadays, the matching is performed manually using a time consuming iterative procedure for each device. Moreover, the matchingcan be done only once at the device design level, regardless of the communication mode (reader, card or peer-to-peer) and regardless of the secondary device influence on the primary antenna characteristics.In this manuscript, we propose a detailed description of the electrical performances of NFC Systems. Then an accurate and complete analytical electrical model of NFC antennas is proposed.Finally, we develop a new technic of automatic adaptation of the matching network in order to optimize the electrical performances in the transmission phase in terms of energy transfer from the reader to the transponder.

L'objectif de ce projet de thèse est de mettre en évidence des phénomènes de chiralité optique induits dans des systèmes plasmoniques. La manipulation des différents degrés de liberté de la lumière est mise en évidence par le biais de techniques expérimentales complémentaires basées sur la tomographie en polarisation, la microscopie à fuites radiatives et la microscopie en champ proche optique (SNOM). D'une part, nous rapportons une méthode de caractérisation non-invasive afin de révéler la présence conjointe de chiralité planaire et volumique au sein de métasurfaces plasmoniques. Pour décrire cette chiralité mixte, une généralisation du modèle de Kuhn est développée. D'autre part, nous démontrons deux dispositifs plasmoniques exploitant le couplage spin-orbite optique pour contrôler les moments angulaires de spin et orbitaux de la lumière. En particulier, le mécanisme réciproque de l'effet spin Hall optique est démontré à l'aide de nano-ouvertures en forme de T: la trajectoire des plasmons de surface est adressée dans le moment angulaire de spin des photons. Cette fonctionnalité est ensuite mise en œuvre dans une expérience de brouillage d'interférence. La génération de vortex plasmoniques est également réalisée par le biais de cavités spirales, dont la chiralité conditionne l'intensité et le moment angulaire orbital des vortex. Enfin, une preuve de concept sur la mesure de la densité locale d’états optique, façonnée par un environnement chiral, est démontrée à l'aide d'une sonde SNOM classique et quantique. Ce travail permet de connecter les grandeurs de densité et de flux de chiralité aux interactions lumière-matière. L'étude de la chiralité dans le contexte de la plasmonique ouvre des perspectives prometteuses dans la nano-manipulation optique, la séparation de molécules chirales et le contrôle de sources quantiques. / In this thesis, we aim at demonstrating chiral optical effects in plasmonic systems. The manipulation of the different degrees of freedom of light is evidenced by complementary experimental approaches based on polarisation tomography, leakage radiation microscopy and scanning near-field optical microscopy (SNOM). On one hand, we report on a non-invasive method to reveal the coexistence of surface and bulk chirality in plasmonic metasurfaces. Specifically, we extend the model of Kuhn to describe this chirality mixture. On the other hand, we demonstrate two plasmonic devices which rely on the optical spin-orbit coupling to control the spin and the orbital angular momentum of light. In particular, the reciprocal mechanism of the spin-Hall effect of light is shown using T-shaped nano-apertures: the trajectory of surface plasmons can be encoded in the spin of the photons. This which-path marker is then implemented in an interference erazer experiment. Plasmonic vortex generation is also reported in spiral cavities. The spiral chirality rules the intensity as well as the angular orbital momentum of the singular fields. Finally, as a proof of concept, we demonstrate using a conventional and quantum SNOM probe that the local density of optical states can be structured by a chiral environment. We also connect the density and flux chirality to light-matter interactions. Studying chirality in the context of plasmonics opens promising prospects in the optical nano-manipulation, chiral molecules discrimination and the control of quantum sources.

Les données accumulées sur les mouvements du sol apportent des connaissances très importantes sur les processus de rupture des séismes, les caractéristiques du milieu de propagation, la relation entre le mouvement du sol et les dommages des structures... Cependant, les séismes de faible et moyenne amplitude étant plus fréquents que les grands événements sismiques, les bases de données de mouvements de sol utilisées dans le développement de modèles de prédiction du mouvement du sol ne contiennent pas beaucoup de données de forts séismes. Le point le plus critique concerne les stations proches de la rupture de la faille, pour lesquelles les bases de données restent mal échantillonnées. Les pays à sismicité modérée ou élevée pour lesquels des failles majeures peuvent se briser à proximité de ses grandes villes, sont donc confrontés à un risque sismique majeur, mais le manque d’enregistrements du mouvement ne permet pas une bonne prédiction des mouvements fort du sol. Il est donc nécessaire de simuler le mouvement fort en champ proche. Cette thèse est divisée en 2 parties. La partie 1 se concentre sur une meilleure compréhension de la rupture sismique et de son rapport avec le mouvement du sol proche de la faille. Les mécanismes de génération des valeurs de pics du mouvement du sol sont étudiés pour des ruptures homogènes et hétérogènes. Une analyse quantitative de sensibilité du mouvement du sol aux paramètres cinématiques de la rupture est présentée, pour des sites au voisinage de la rupture ainsi qu’en champ lointain. Un second chapitre est consacré à un effet de source majeur en champ proche: l’effet de directivité. Ce phénomène se produit lorsque la rupture se propage vers un site, avec une vitesse de rupture proche de la vitesse de l'onde de cisaillement Vs; les ondes se propageant vers le sites interfèrent de manière constructive et génèrent une onde de grande amplitude appelée pulse. Les caractéristiques de ce pulse, notamment sa durée, représentent des paramètres d’intérêt pour le génie parasismique. Une équation simple est présentée pour relier la durée du pulse à la configuration géométrique de la rupture et du site d'intérêt et aux paramètres de la source. La partie 2 est consacrée à une meilleure estimation de l’aléa sismique au Liban en simulant le mouvement fort pour des sites proches de la faille principale: la faille de Yammouneh. Le Liban est situé dans un environnement tectonique actif où le risque sismique est considéré comme modéré à élevé. Historiquement, des tremblements de terre destructifs se sont produits dans le passé, le dernier remontant à 1202. Cependant, en raison de la sismicité de grande ampleur actuellement peu fréquente, aucun mouvement fort n'a jamais été enregistré au Liban à ce jour. La faille de Yammouneh est une grande faille en décrochement traversant le Liban du Nord au Sud, situant toutes les villes et infrastructures à moins de 25km de la faille. Une tomographie de la structure de la croûte du Liban, en termes de vitesse des ondes de cisaillement Vs, est réalisée en utilisant le bruit ambiant. À notre connaissance, il s’agit de la première étude de la tomographie Vs 3D au Liban. Par la suite, une approche hybride est utilisée pour simuler le mouvement du sol en champ proche sur une large bande de fréquences (0.1-10Hz). Aux basses fréquences (≤1Hz), des ruptures potentielles de M7 sont simulées (comme définie dans les chapitres précédents), et les fonctions sources obtenues sont convoluées aux fonctions de Green calculées pour le modèle de propagation des ondes issu de la tomographie Vs afin d’estimer le mouvement du sol à proximité de la faille. Le mouvement du sol est complété par un contenu haute fréquence (jusqu’à 10 Hz), en utilisant un modèle stochastique calibré par des enregistrements en champ proche, et en tenant compte de la phase impulsive due à la directivité de la rupture. / Accumulated data of strong ground motions have been providing us very important knowledge about rupture processes of earthquakes, propagation-path, site-amplification effects on ground motion, the relation between ground motion and damage... However, most of the ground motion databases used in the development of ground motion prediction models are primarily comprised of accelerograms produced by small and moderate earthquakes. Hence, as magnitude increases, the sets of ground motions become sparse. Ground motion databases are poorly sampled for short source-to-site distance ranges (‘Near-fault’ ranges). However, the strongest ground shaking generally occurs close to earthquake fault rupture. Countries of moderate to high seismicity for which major faults can break in the vicinity of its major cities are facing a major seismic risk, but the lack of earthquake recordings makes it difficult to predict ground motion. Strong motion simulations may then be used instead. One of the current challenges for seismologists is the development of reliable methods for simulating near-fault ground motion taking into account the lack of knowledge about the characteristics of a potential rupture. This thesis is divided into 2 parts. Part 1 focuses on better understanding the seismic rupture process and its relation with the near-fault ground motion. The mechanisms of peak ground motion generating are investigated for homogeneous as well as for heterogeneous ruptures. A quantitative sensitivity analysis of the ground motion to the source kinematic parameters is presented, for sites located in the vicinity of the fault rupture, as well as far from the rupture. A second chapter is dedicated to a major near-fault source effect: the directivity effect. This phenomenon happens when the rupture propagates towards a site of interest, with a rupture speed close to the shear-wave speed (Vs); the waves propagating towards the site adds up constructively and generates a large amplitude wave called the pulse. The features of this pulse are of interest for the earthquake engineering community. In this chapter, a simple equation is presented that relates the period of the pulse to the geometric configuration of the rupture and the site of interest, and to the source parameters.Part 2 is dedicated to better estimate the seismic hazard in Lebanon by simulating the strong ground motion at sites near the main fault (the Yammouneh fault). Lebanon is located in an active tectonic environment where the seismic hazard is considered moderate to high. Historically, destructive earthquakes occurred in the past, the last one dates back to 1202. However, strong motion has never been recorded in Lebanon till now due to the presently infrequent large-magnitude seismicity, and therefore facing an alarming note of potential new ruptures. The Yammouneh fault is a large strike-slip fault crossing Lebanon, making all its regions located within 25km away from the fault. At first, the crustal structure tomography of Lebanon, in terms of Vs, is performed using the ambient noise, in order to characterise the wave propagation from the rupture to the ground surface. To our knowledge, this is the first study of the 3D Vs tomography in Lebanon. Afterwards, a hybrid approach is presented to simulate broadband near-fault ground motion . At low-frequencies (≤1Hz), potential ruptures of M7 are simulated (as defined in the previous chapters), and the generated slip rate functions are convolved with the Green’s functions computed for the propagation medium defined by the Vs tomography. The ground-motion is complemented by a high-frequency content (up to 10Hz), using a stochastic model calibrated by near-fault recordings and accounting for the presence of the directivity pulse. The computed peak ground acceleration is compared to the design acceleration in Lebanon.

Counterfeit products, especially in the pharmaceutical sector, have plagued the international community for decades. To combat this problem, many anti-counterfeiting approaches have been proposed. They use either Radio Frequency Identification (RFID) or Near Field Communication (NFC) physical tags affixed to the products. Current anti-counterfeiting approaches detect two counterfeiting attacks: (1) modifications to a product's tag details, such as changing the expiration date; and (2) cloning of a genuine product's details to reuse on counterfeit products. In addition, these anti-counterfeiting approaches track-and-trace the physical locations of products as the products flow through supply chains. Existing approaches suffer from two main drawbacks. They cannot detect tag reapplication attacks, wherein a counterfeiter removes a legitimate tag from a genuine product and reapplies it to a counterfeit or expired product. Second, most existing approaches typically rely on a central server to authenticate products. This is not scalable and creates tremendous processing burden on the server, since significant volumes of products flood through the supply chain's nodes. In addition, centralized supply chains require substantial data storage to store authentication records for all products. Moreover, as with centralized systems, traditional supply chains inherently have the problem of a single-point of failure. The thesis of this dissertation is that a robust, scalable, counterfeiting-resistant supply chain that addresses the above drawbacks and can be simultaneously achieved by (i) using a combination of NFC tags on products and a distributed ledger such as blockchain for reapplication-proof, decentralized, and transparent product authentication (ii) a novel game-theoretical consensus protocol for enforcing true decentralization, and enhancing the protocol's security and performance. In this dissertation, we first propose a new Tag Reapplication Detection (TRD) system to detect reapplication attacks using low-cost NFC tags and public key cryptography. To detect reapplication attacks, TRD tracks the number of times a tag has been read in the supply chain using a 'central' authentication server. Second, leveraging the blockchain technology, we propose the Block-Supply Chain, a transformation of TRD into a decentralized supply chain. In this chain, each node maintains a blockchain (distributed public ledger) per product. This blockchain comprises chained blocks, where each is an authentication event. The Block-Supply Chain can detect tag reapplication attacks and can replace the centralized supply chain design, thus overcoming the centralization issues. One of the fundamental characteristics of blockchain technology is the consensus protocol. Consensus protocols ensure that all nodes in the blockchain network agree on the validity of a block to be included in the public ledger. The first and most popular of the existing consensus protocols is Proof of Work (PoW). However, PoW requires massive computational effort, resulting in high energy and computing resources consumption. Alternatively, Byzantine Fault Tolerance (BFT) protocols, such as Tendermint, were adapted in blockchain technology to be efficient and easy to implement. Nevertheless, not all of BFT protocols guarantee true decentralization, and they are mostly based on fixed-validators. BFT fixed-validators protocols typically rely on fixed, static validators responsible for validating all newly proposed blocks. This opens the door for adversaries to launch several attacks on these validators, such as Distributed Denial of Service (DDoS) and Eclipse attacks. In contrast, a truly decentralized protocol ensures that variable sets of anonymous validators execute the blocks' validations. Building on this observation, we propose the TrueBFT, a truly decentralized BFT-based consensus protocol that does not require PoW and randomly employs a different set of validators on each block's proposal. TrueBFT is designed for permissioned blockchains (in such blockchains, the participants who can transact on the blockchain are limited, and each participant is required to have permission to join the system). Our simulations show that TrueBFT offers remarkable performance with a satisfactory level of security compared to the state-of-the-art protocol Tendermint. Another issue with current consensus protocols, particularly the BFT, is that the majority of them do not take the number of employed validators into consideration. The number of validators in a blockchain network influences its security and performance substantially. In response, we integrate a game theoretical model into TrueBFT that analyzes the risk likelihood of each proposer (i.e., the node that creates and proposes the new block). Consequently, each time a new block is proposed, the 'number of validators' becomes proportional to the risk likelihood block's proposer. Additionally, the game model reinforces the honest behavior of the validators by rewarding honest validators and punishing dishonest ones. Together, TRD, Block-Supply Chain, and the game-theoretical TrueBFT consensus protocol enable robust, scalable, decentralized anti-counterfeiting supply chain that is resistant to tag reapplication attacks, as well as attacks to consensus protocols such as DDoS and Eclipse attacks.

The thesis aims to improve treatment dose accuracy in brachytherapy using a high dose rate (HDR) Ir-192 stepping source and in external beam therapy using intensity modulated radiation therapy (IMRT). For HDR brachytherapy, this has been achieved by investigating dose errors in the near field and the transit dose of the HDR brachytherapy stepping source. For IMRT, this study investigates the volume effect of detectors in the dosimetry of small fields, and the clinical implementation and dosimetric verification of a 6MV photon beam for IMRT. For the study of dose errors in the near field of an HDR brachytherapy stepping source, the dose rate at point P at 0.25 cm in water from the transverse bisector of a straight catheter was calculated with Monte Carlo code MCNP 4.A. The Monte Carlo (MC) results were used to compare with the results calculated with the Nucletron Brachytherapy Planning System (BPS) formalism. Using the MC calculated radial dose function and anisotropy function with the BPS formalism, 1% dose calculation accuracy can be achieved even in the near field with negligible extra demand on computation time. A video method was used to analyse the entrance, exit and the inter-dwell transit speed of the HDR stepping source for different path lengths and step sizes ranging from 2.5 mm to 995 mm. The transit speeds were found to be ranging from 54 to 467 mm/s. The results also show that the manufacturer has attempted to compensate for the effects of inter-dwell transit dose by reducing the actual dwell time of the source. A well-type chamber was used to determine the transit doses. Most of the measured dose differences between stationary and stationary plus inter-dwell source movement were within 2%. The small-field dosimetry study investigates the effect of detector size in the dosimetry of small fields and steep dose gradients with a particular emphasis on IMRT measurements. Due to the finite size of the detector, local discrepancies of more than 10 % are found between calculated cross profiles of intensity modulated beams and intensity modulated profiles measured with film. A method to correct for the spatial response of finite sized detectors and to obtain the

InGaN based blue and near-ultraviolet light emitting diodes and laser diodes have been successfully commercialized for many applications such as general lighting, display backlighting and high density optical storage devices. Despite having a comparably high defect density, these devices are known for their efficient operation, which is attributed to localization in potential fluctuations preventing carriers from reaching the centers of nonradiative recombination. Nitride research is currently headed towards improving deep ultraviolet AlGaN and green InGaN emitters with higher Al and In molar fractions. The efficiency of these devices trails behind the blue counterparts as the carrier localization does not seem to aid in supressing nonradiative losses. In addition, the operation of ternary nitride heterostructure based devices is further complicated by the presence of large built-in electric fields. Although the problem can be ameliorated by growing structures in nonpolar or semipolar directions, the step from research to production still awaits. In this thesis, carrier dynamics and localization effects have been studied in three different nitride ternary compounds: AlGaN epitaxial layers and quantum wells with high Al content, nonpolar m-plane InGaN/GaN quantum wells and lattice matched AlInN/GaN heterostructures. The experimental methods of this work mainly consist of spectroscopy techniques such as time-resolved photoluminescence and differential transmission pump-probe measurements as well as spatial photoluminescence mapping by means of scanning near-field microscopy. The comparison of luminescence and differential transmission measurements has allowed estimating the localization depth in AlGaN quantum wells. Additionally, it has been demonstrated that the polarization degree of luminescence from m-InGaN quantum wells decreases as carriers diffuse to localization centers.What is more, dual-scale localization potential has been evidenced by near-field measurements in both AlGaN and m-InGaN. Larger scale potential fluctuation have been observed directly and the depth of nanoscopic localization has been estimated theoretically from the recorded linewidth of the near-field spectra. Lastly, efficient carrier transport has been observed through AlInN layer despite large alloy inhomogeneities evidenced by broad luminescence spectra and the huge Stokes shift. Inhomogeneous luminescence from the underlying GaN layer has been linked to the fluctuations of the built-in electric field at the AlInN/GaN interface. / <p>QC 20121101</p>

Radiative heat transfer in nanostructures with sub-wavelength dimensions can exceed that predicted by Planck&#039 / s blackbody distribution. This increased effect is due to the tunneling of infrared radiation between nanogaps, and can allow the eventual development of nano-thermo-photo-voltaic (Nano-TPV) cells for energy generation from low temperature heat sources. Although near field radiation effects have been discussed for many years, experimental verification of these effects is very limited so far. In this study, silica coated silicon wafer sample chips have been manufactured by using MEMS fabrication methods for testing the near field radiation effects. A variety of samples with 1&times / 1, 2&times / 2 and 5&times / 5 mm2 area, and with 25 nm, 50 nm, 100 nm and 200 nm (nano-gap) separations have been prepared. 3D structures with vacuum gaps have been obtained by bonding of the silica coated wafers. The samples have been tested in an experimental setup by a collaborative group at &Ouml / zyegin University, Istanbul. An increase in the net radiation heat transfer with decreasing nano-gap size has been reported by the &Ouml / zyegin group who used these samples in a parallel study. The thesis outlines the micro-fabrication techniques used for the sample preparation. Also, the manufacturing problems we have faced during this research program are discussed.