Dissertations / Theses on the topic 'Delayed coupling'

Thesis: Ph. D. in Organic Chemistry, Massachusetts Institute of Technology, Department of Chemistry, 2014.
Cataloged from PDF version of thesis.
Includes bibliographical references.
The studies in the present dissertation were aimed at developing and applying synthetic methods mediated by palladium catalysis. In Chapters 1 and 2, the palladium-catalyzed amidation and amination of five-membered heterocyclic bromides containing multiple heteroatoms are described. These methods provide efficient access to N-arylated imidazoles and pyrazoles in moderate to excellent yields. In Chapter 3, a series of novel triptycene-based compounds were synthesized using a palladium-catalyzed C-N, C-C, C-N cross-coupling sequence. Experimental results suggest that this series of compounds could potentially be used as delayed singlet emitters for organic light emitting devices. Chapter 1. Palladium-Catalyzed Amidation of Five-Membered Heterocyclic Bromides Palladium-catalyzed C-N cross-coupling between primary amides and five-membered heterocyclic bromides that contain multiple heteroatoms was achieved for the first time using the Pd/AdBrettPhos catalyst system. This system allows for efficient access to Narylated imidazoles, pyrazoles, thiazoles, pyrroles, and thiophenes in moderate to excellent yield. Experimental results and DFT calculations point to the need for electronrich and especially sterically demanding biaryl dialkylphosphine ligands to promote these difficult cross-coupling reactions. The same protocol was also extended to forming tertiary amides from secondary amides and five-membered heterocyclic bromides. Preliminary studies showed promising results using a Pd/AdRockPhos catalyst system. Chapter 2. Palladium-Catalyzed Amination of Unprotected Five-Membered Heterocyclic Bromides An efficient method for the palladium-catalyzed amination of unprotected bromoimidazoles and bromopyrazoles is presented. The transformation is facilitated by the use of our newly developed Pd-precatalyst based on the bulky biarylphosphine ligand, tBuBrettPhos. The mild reaction conditions employed allow for the preparation of a broad scope of aminoimidazoles and aminopyrazoles in moderate to excellent yields. Chapter 3. Synthesis of Delayed Singlet Emitters for OLED Development The development of novel thermally activated delayed fluorescence (TADF) materials for use in organic light emitting devices (OLEDs) is reported. A series of triptycenebased delayed singlet emitters have been synthesized using a palladium-catalyzed C-N, C-C, C-N cross-coupling sequence. Preliminary investigations have demonstrated that these compounds could serve as delayed singlet emitters at a range of wavelengths from orange to blue, which is highly desirable for organic electronics applications.
by Mingjuan Su.
Ph. D. in Organic Chemistry

Organic Light-Emitting Diodes (OLEDs) technology has matured over recent years, reaching the commercialization level and being used in various applications. The required efficiency can be achieved by transforming triplet excitons into singlet states via Reverse InterSystem Crossing (RISC), which a general mechanism called thermally activated delayed fluorescence (TADF). Two prototypical molecules in the field, 2CzBN and 4CzBN, Carbazole Benzonitrile (donor-acceptor) derivatives, possess similar energy gap between singlet and triplet (∆EST, a key parameter in the RISC rate), but different TADF performance. In this sense, other parameter must be considered to explain these different behaviors. In this work, we theoretically investigate 2CzBN and 4CzBN and address the problem of how flexible donor-acceptor (D-A) or donor-acceptor-donor (D-A-D) molecular architectures affect the nature of excited state, and the oscillator strength. Furthermore, we analyze the RISC rates as a function of the conformation of the carbazole side groups, considering the S0, S1, T1 and T2 states. The oscillator strength of 4CzBN is higher than of 2CzBN, which, in turn, is almost vanishing, resulting in only 4CzBN being a TADF active molecule. We also note the presence of a second triplet state T2 lower in energy than S1, and that the reorganization energies, associated to the RISC processes involving T1 and T2, are both important factor in differentiating the rates in 2CzBN and 4CzBN. However, the 4CzBN RISC rate from T2 to S1 is surprisingly high with respect to the one from T1 to S1, although, according to EL-Sayed rules, since T2 (CT/LE) is more similar to S1 (CT) than in 2CzBN (LE, CT), this transition should be less favored. These insights are important to understand the photophysics of the TADF process and to design novel TADF emitters based on the benzo-carbazole architecture.

Oscillations are present at many different levels of biological organization. The cell cycle that directs the division of individual cells, the regular depolarization of neurons in the sinu-atrial node which underlies the regular beating of the heart, the circadian rhythms that govern the daily activity cycles of virtually all organisms, and the clocks that make entire populations of fireflies flash on and off in unison feature as prominent examples of biological clocks. During development, biological clocks regulate the patterning of growing tissues, as is the case in vertebrate somitogenesis, and potentially also in vertebrate limb outgrowth and axial segmentation of invertebrate embryos. During vertebrate segmentation, the embryonic axis is subdivided along its anterior-posterior axis into epithelial spheres of cells called somites. This rhythmic process is thought to be driven by a multicellular oscillatory gene network, the so-called segmentation clock. Oscillations of hairy and enhancer of split gene products have been proposed to constitute the core clockwork in individual cells, and these oscillators are coupled to each other by Delta-Notch intercellular signaling. The interaction of the segmentation clock with a posteriorly-moving arrest wavefront then translates the temporal information encoded by the clock into a spatial pattern of segments. In the framework of this Clock and Wavefront model, segment length is determined by both clock period and arrest wavefront velocity. How the period of the segmentation clock is regulated is presently unknown, and understanding the mechanism of period setting might yield insight into the nature and function of the segmentation clock. In this study, two different but complementary approaches were pursued to investigate how period is regulated in the zebrafish segmentation clock. First, it has been reported that zebrafish mind bomb (mib) mutant embryos form somites more slowly than their wt siblings, suggesting that Mib might be implicated in period setting. Mib is an E3 ubiquitin ligase required for ubiquitination and endocytosis of the Notch ligand Delta, and Notch signaling is impaired in mutants with defective Mib. It has been suggested that the mechanistic basis for the requirement of Delta endocytosis in Notch signaling is a need for Delta to enter a particular endocytic compartment, potentially a recycling endosome, in a ubiquitin-dependent manner, where its signaling ability might be established or amplified by an as yet unknown posttranslational modification. In the present study, Delta trafficking through the endocytic pathway was analyzed in the PSM of wt and mib embryos through colocalization studies with endocytic markers. The rationale of this approach was that if Delta gained access to a particular endocytic compartment through Mib-dependent endocytosis, the presence of Delta in this compartment would be expected to be reduced in mutants with defective Mib, thereby revealing the compartment’s identity. However, no qualitative changes in colocalization with different endocytic markers could be detected in mib mutants, and the methods available did not allow for quantification of colocalization in wt or mutant backgrounds. However, Delta colocalized with 13 markers of recycling endosomes, consistent with the hypothesis that these are functionally important in Notch signaling. More refined techniques will be necessary for a quantitative analysis of normal as compared to impaired Delta trafficking. A genetic approach to period regulation proved to be successful for the Drosophila circadian clock, where the identification of period mutants advanced the understanding of the clock’s genetic circuitry. This motivated a screen for period mutants of the segmentation clock, which was carried out by measuring somitogenesis period, segment length and arrest wavefront velocity in a pool of candidate mutants. A subset of Delta-Notch mutants, and embryos treated with a small-molecule inhibitor that impairs Notch signaling, displayed correlated increases in somitogenesis period and segment length, while there was no detectable change in arrest wavefront velocity. Combined, these findings suggested that segmentation clock period is increased in experimental conditions with impaired Delta-Notch signaling. Using a theoretical description of the segmentation clock as an array of coupled phase oscillators, the delay in the coupling and the autonomous frequency of individual cells were estimated from the direction and magnitude of the period changes. The mutants presented here are the first candidates for segmentation clock period mutants in any vertebrate. The nature of the molecular lesions in these mutants, all of which affect genes implicated in intercellular Delta-Notch signaling, suggests that communication between oscillating PSM cells is a key factor responsible for setting the period of the segmentation clock.

Cette thèse porte sur la conception, la synthèse et la caractérisation de nouveaux dérivés accepteurs d'électrons. Elle se concentre sur l’étude des dérivés de la 1,2,4,5-tétrazine, mais contient également l’étude de dérivés du benzonitrile, précurseurs typiques de la préparation des 1,2,4,5-tétrazines et de dérivés de la pyridazine, les produits dérivés de la réaction de Diels – Alder à Demande Inverse (IEDDA) des dérivés de la tétrazine. De plus, les dérivés de 1,2,3,4-thiatriazole, en tant que produits imprévus de la synthèse de Pinner modifiée, sont également étudiés de manière approfondie. En raison des états de transfert de charge (CT) introduits dans le système donneur-accepteur, les dérivés préparés accepteur d'électrons présentent en général des propriétés photophysiques et électrochimiques intéressantes, et ont donc un intérêt particulier pour l'électronique organique.Le point culminant de cette thèse est le développement de méthodologies synthétiques dans chaque chapitre. En résumé, le chapitre 2 met en évidence une nouvelle approche synthétique sans métal pour les 1,2,4,5-tétrazines 3-monosubstituées, qui sont très utiles pour la chimie du click bioorthogonal. Le chapitre 3 décrit une stratégie de synthèse élaborée pour de nouveaux dérivés de benzonitrile donneur-accepteur qui présentent de la TADF, de l’ AIE et du mécanochromisme. Le chapitre 4 présente une étude détaillée de la réaction de couplage croisé Buchwald – Hartwig en tant que méthodologie de synthèse importante dans la synthèse de molécules de tétrazine. Le chapitre 5 décrit l'étude de la réaction à l'IEDDA comme un outil synthétique utile pour préparer des dérivés de pyridazine. Le chapitre 6 présente une nouvelle synthèse pratique de 1,2,3,4-thiatriazoles à partir de composés nitriles
This PhD thesis deals with the design, synthesis and characterization of novel electron-acceptor derivatives. It is focused on the study of 1,2,4,5-tetrazine derivatives, but also involves the study of benzonitrile derivatives which are the typical precursors for the preparation of 1,2,4,5-tetrazines, and pyridazine derivatives which are the products derived from Inverse Electron Demand Diels–Alder (IEDDA) reaction of tetrazine derivatives. Moreover, 1,2,3,4-thiatriazole derivatives, as unpredicted products from modified Pinner synthesis, are also elaborately investigated. Due to the charge-transfer (CT) states introduced in the donor-acceptor system, the prepared electron-acceptor derivatives exhibit interesting photophysical and electrochemical properties, and therefore are of particular interest in organic electronics.The highlight of this thesis is the development of synthetic methodologies in each chapter. To sum up, Chapter 2 demonstrates a novel metal-free synthetic approach to 3-monosubstituted 1,2,4,5-tetrazines, which are highly useful for bioorthogonal click chemistry. Chapter 3 describes an elaborative synthetic strategy for novel donor-acceptor benzonitrile derivatives which exhibit TADF, AIE and mechanochromism. Chapter 4 presents a detailed study of Buchwald–Hartwig cross-coupling reaction as an important synthetic methodology in the synthesis of tetrazine molecules. Chapter 5 described the study of IEDDA reaction as a useful synthetic tool to prepare pyridazine derivatves. Chapter 6 presented a novel convenient one-pot synthesis of 1,2,3,4-thiatriazoles directly from nitrile compounds

Ce travail de recherche a pour but d’étudier des matériaux cimentaires soumis à des attaques sulfatiques selon trois différentes conditions : attaques sulfatiques externes (ASE), formation différée d’ettringite communément appelée attaque sulfatique interne et l’effect couplé des deux réactions, ainsi que de proposer un mécanisme uniforme pour les dégradations causées par ces réactions. En se basant sur le mécanisme proposé, un model poro-mécanique est proposé pour simuler l’expansion induite par les produits expansifs néoformés pendant la dégradation. Cette étude inclut trois parties : dans la première partie, les dégradations des éprouvettes de pâte de ciment correspondant à deux types de ciments (CEM I et CEM III) et deux dimensions exposées à trois différents types d’attaques sulfatiques (ASE, ASI, et le couplage des deux réactions), sont étudiés et comparés : variations de longueur, de masse, ainsi que des observations visuelles. Les éprouvettes exposées au couplage ASE-ASI montrent la cinétique d’expansion la plus rapide et le degré de dégradation le plus important, comparé aux autres cas. Ensuite, la structure poreuse des pâtes de ciment avant et après les attaques sulfatiques est caractérisée en utilisant différentes techniques : porosimétrie à mercure (MIP), sorption dynamique de vapeur (DVS), porosité accessible à l’eau ou essais de dissolution par traitement thermique. En comparant les variations de la distribution de la taille des pores des pâtes de ciment exposées à différentes conditions, les cristaux néoformés se trouvent précipités à la fois dans les pores capillaires et les pores des C-S-H. En plus de l’évolution de la distribution de la taille des pores pendant l’ASI, un mécanisme de dégradation est proposé : les cristaux néoformés (l’ettringite) sont précipités dans les grands pores, sans provoquer une expansion manifeste, et ils sont ensuite précipités dans les pores capillaires et les pores des C-S-H, ce qui induit un gonflement. Par ailleurs, le volume des pores occupé par les produits de l’ASI sont libérés après des essais de dissolution par traitement thermique, ce qui confirme la formation de produits d’expansion dans cette gamme de pores. Enfin, en se basant sur les résultats expérimentaux montrant que l’ettringite se forme en allant des grands pores vers les plus petits, un model poro-mécanique est proposé pour simuler l’expansion des matériaux cimentaires soumis à des attaques sulfatiques. Le modèle est basé sur la croissance contrôlée en surface et les propriétés physicochimiques pour l’ASE et l’ASI, malgré les différences entre ces deux réactions. Deux constantes indépendantes : ai et ap sont proposées pour représenter la cinétique de l’invasion des cristaux et la déformation. De plus, le modèle peut être couplé avec toutes les théories mécaniques, par exemple : l’élasticité, la plasticité, la théorie de l’endommagement ou autres. Le modèle illustre bien le processus de cristallisation et il prédit l’expansion correspondante à la fois à l’ASE et l’ASI
This work aims to study cement-based materials subjected to sulfate attacks in three different conditions: External Sulfate Attack (ESA), Delayed Ettringite Formation (DEF) and the Coupling effect of both, and to propose the same damage mechanism for all of them. Based on the proposed mechanism, a poromechanical model is established to simulate the expansion induced by expansive crystals during the degradation. The study includes the following three parts. In the first part, the degradation of cement paste specimens with two kinds of cement type (CEM I and CEM III) and two dimensions (2 2 12 cm3 and 11 11 22 cm3) exposed to three sulfate attack conditions (ESA, DEF, and Coupling effect) are studied and compared, including the length variation, mass variations, and observations. The specimens exposed to the coupling effect show the fastest kinetics and the most serious degree of degradation compared to the other cases. Then, the pore structure of cement pastes before and after sulfate attacks is characterized via different techniques: MIP, DVS, water accessible tests and heat-based dissolution tests. By comparing the variation of pore size distribution of cement pastes exposed to different conditions, the generated crystals are found to be precipitated both in capillary and gel pores. In addition to the evolution of pore size distribution during DEF, a damage mechanism is proposed: the generated crystals (ettringite) precipitate in the big pores without inducing an obvious expansion, and then penetrate into capillary and gel pores, which leads to a swelling. Moreover, the pore volume occupied by DEF induced products is released after heat-based dissolutiontests, which further confirms the formation of expansive products in that porerange. Finally, based on the experimental conclusion that ettringite forms through the large to small pores in all cases, a poromechanical model is proposed to simulate the expansion of cement-based materials submitted to sulfate attacks. The model is based on the surface-controlled growth and physicochemical properties both for ESA and DEF, despite the different source of sulfate ions. Two independent constants, ai and ap, are proposed to represent the kinetics of crystal invasion and deformation. Moreover, the model could be coupled with any mechanical theories, e.g. elasticity, plasticity, damage theory or any other. The model well illustrates the crystallization process and well predicts the corresponding expansion both in ESA and DEF

The stability of synchronization and control in networks of dynamical systems with strongly delayed connections is investigated. Strict conditions for both, synchronization of stable periodic and equilibrium solutions , and control of unstable equilibrium are obtained. With a network model including self-feedback delay, the existence of a critical coupling strength kc is demonstrated, which is related to the network structure, isolated vector field and coupling function, such that for large delay and coupling strength k < kc the network undergoes to stable synchronization. Moreover, it is derived that for heterogeneous networks, kc $\rightarrow$ 0 as the network size grows to infinity, unless the coupling parameter scales with the maximum degree. In contrast, for random networks, the interval of coupling strengths that leads to stable synchronization is the maximum possible when the connectivity threshold is crossed making the network connected. Based on the network structure, the scaling of the coupling parameter, which allows for a synchronization, is derived. And, with a network model consisting of instantaneous self-connections, it is shown that it is possible to stabilize synchronous equilibrium that is unstable in an isolated system. Such a control close to a Hopf bifurcation is studied in details and strict conditions for the stability are obtained. In particular, it is demonstrated that the stabilization domains in parameter space are reappearing periodically and decreasing in size with the increase of time-delays. Also, the frequency of the reappearance of the control domains and the number spectral roots of the adjacency matrix are closely dependent, for instance, the number of cycle multi-partitions of the graph indicates the reappearance frequency of the control domains.
Nesta tese investiga-se a estabilidade da sincronização e o controle em redes de sistemas dinâmicos onde o acoplamento se dá com atraso grande. São obtidas condições analíticas para ambos, a saber, sincronização de soluções periódicas e equilíbrios estáveis e controle de equilíbrio instáveis. Com um modelo de rede que inclui atraso com auto-alimentação, mostra-se a existência de um parâmetro crítico de acoplamento, kc, que depende apenas da estrutura da rede, do campo de vetores e da função de acoplamento, tal que para atraso grande e parâmetro de acoplamento k < kc a rede apresenta uma sincronização estável. Além disso, mostra-se que para redes heterogêneas, kc $\rightarrow$ 0 ao passo que o número de nós da rede cresce ao infinito, a menos que o parâmetro de acoplamento é escalonado com o grau máximo da rede. Em contrapartida, evidencia-se que para redes aleatórias, o intervalo de parâmetros de acoplamento que induzem sincronização estável é o máximo possível quando o limiar de conectividade da rede é atingindo fazendo com que a mesma se torne conectada. Baseando-se na estrutura da rede, propriedades de escalonamento do parâmetro de acoplamento são derivadas, permitindo sincronização estável. E, com um modelo de rede consistindo de auto-alimentação instantânea, verifica-se que é possível estabilizar soluções de equilíbrio que são instáveis no sistema isolado. Este cenário de controle quando o sistema isolado está próximo da bifurcação de Hopf é estudado em detalhes e então condições analíticas para a estabilidade são obtidas. Em particular, demonstra-se que os domínios de estabilização no espaço de parâmetros são periódicos e decrescentes ao passo que o atraso cresce. Além disso, evidencia-se como a frequência de reaparecimento de tais domínios é influenciada pelo número de raízes espectrais da matriz de adjacência do grafo, que por sua vez está relacionado com, por exemplo, as multipartições cíclicas do grafo.

In dieser Dissertation werden wir die Wirkung der Verzögerung Kupplung auf Netzwerke von chaotischen erkunden dynamischer Systeme mit dem Rahmen der Master Stabilität Formalismus. Wir werden untersuchen das Phänomen der Verzögerung-verstärkter und Verzögerungen-induzierte stabile Synchronisation in einer willkürlichen Verzögerung gekoppelt Netzwerk von zeitkontinuierlichen dynamischen Systemen. Wir demonstrieren, dass es immer existieren eine erweiterte Regime des stabilen synchronen Zustand als eine Funktion der Kopplungsstärke geeignete Verbindung Verzögerungen, die nicht ohne Verzögerung in die Kupplung beobachtet werden kann. Wir schlagen eine partielle verzögerung Verbindung als eine Kombination von sowohl den momentanen und der komplett Verzögerung Verbindung mit gewissen Gewichten Bestimmung ihrer Beiträgen. Wir werden zeigen, dass die partielle Verzögerung Verbindung beide Grenzfälle des momentanen und der komplett Verzögerung Kupplung am synchronizabilit von Netzwerken übertrifft. Der Rahmen fuer Master Stabilität Formalismus ist mit einem Netzwerk von intrinsischen Zeitverzögerung Systeme, deren Knoten Dynamik durch Verzögerung Differentialgleichungen beschrieben erweitert, zum ersten Mal in der Literatur und veranschaulicht das allgemeine Verhalten des Master-Stabilisierungsfunktion in Netzwerken skalare Zeit Einschaltverzögerung Systeme auf den Synchronisations-Eigenschaften des Netzes. Außerdem untersuchen wir das Zusammenspiel von Lärm und verzögert in das Phänomen der Lärmverstärkter Phasensynchronisierung in beiden unidirektional und bidirektional gekoppelt zeitverzögerung systeme.
In this thesis, we will explore the effect of delay coupling on networks of chaotic dynamical systems using the framework of master stability formalism. We will investigate the phenomenon of delay-enhanced and delay-induced stable synchronization in an arbitrary delay coupled network of time-continuous dynamical systems. We will demonstrate that there always exist an extended regime of stable synchronous state as a function of coupling strength for appropriate coupling delays, which cannot be observed without any delay in the coupling. We will also propose a partial delay coupling as a combination of both the instantaneous and the completely delay coupling with certain weights determining their contributions. We will show that the partial delay coupling outperforms both limiting cases of the instantaneous and the completely delay coupling on the synchronizability of networks. The framework of master stability formalism is extended to a network of intrinsic time-delay systems, whose node dynamics are described by delay differential equations, for the first time in the literature and illustrated the generic behavior of the master stability function in networks of scalar time-delay systems based on the synchronization properties of the network. We also investigate the interplay of noise and delay in the phenomenon of noise-enhanced phase synchronization in both unidirectionally and bidirectionally coupled time-delay systems.

Kyoto University (京都大学)
0048
新制・課程博士
博士(情報学)
甲第11158号
情博第133号
新制||情||30(附属図書館)
22727
UT51-2004-R33
京都大学大学院情報学研究科通信情報システム専攻
(主査)教授 小野寺 秀俊, 教授 富田 眞治, 教授 松山 隆司
学位規則第4条第1項該当

La Réaction Sulfatique Interne (RSI) est une pathologie du béton pouvant affecter les matériaux soumis à un échauffement au-delà de 65°C. Elle consiste en une formation d'ettringite dans le matériau durci et conduit à son gonflement. Il s'en suit une fissuration et une dégradation des performances mécaniques pouvant poser des problèmes d'intégrité structurelle à l'instar de la Réaction Alcali-Granulat (RAG) à laquelle elle est fréquemment couplée in situ. Lorsqu'un ouvrage est atteint, il convient de poser un diagnostic, évaluer son aptitude au service, prédire son évolution et mettre en uvre des méthodes de réparation. Ceci nécessite une compréhension fine des effets de la RSI à l'échelle microscopique et à l'échelle de l'ouvrage. De nombreuses études expérimentales et théoriques ont été menées pour déterminer les mécanismes mis en uvre et les paramètres influençant la RSI. Toutefois, la complexité des phénomènes rend délicate la transposition de ces connaissances à l'échelle de la structure. Les approches macroscopiques semblent donc plus adaptées à ce type de problème. Pour mettre au point ces approches, il est nécessaire de comprendre en détail les effets de la pathologie à l'échelle du matériau et de la structure. Cette thèse décrit les résultats d'une étude de laboratoire basée sur des essais sur éprouvettes pour caractériser les couplages entre les gonflements et l'humidité, la température et l'état de contraintes. Ces travaux ont également été l'occasion d'étudier les couplages entre RAG et RSI. En parallèle, des suivis dimensionnels et hydriques de poutres soumises à des conditions d'exposition à l'humidité contrôlées ont permis de constituer une base de données des effets structurels de la RSI. La confrontation de ces essais menés conjointement à l'échelle du matériau et de la structure fournit des données permettant de mettre au point des méthodes de re-calcul des ouvrages et de les valider en confrontant leurs prédictions aux résultats expérimentaux

Ce travail concerne les transistors bipolaires à hétérogène TBH SiGe. En particulier, l'auto-échauffement des transistors unitaires et le couplage thermique avec leurs plus proches voisins périphériques sont caractérisés et modélisés. La rétroaction électrothermique intra- et inter-transistor est largement étudiée. En outre, l’impact des effets thermiques sur la performance de deux circuits analogiques est évalué. L'effet d'autoéchauffement est évalué par des mesures à basse fréquence et des mesures impulsionnelles DC et AC. L'auto-échauffement est diminué de manière significative en utilisant des petites largeurs d'impulsion. Ainsi la dépendance fréquentielle de l’autoéchauffementa été étudiée en utilisant les paramètres H et Y. De nouvelles structures de test ont été fabriqués pour mesurer l'effet de couplage. Les facteurs de couplage thermique ont été extraits à partir de mesures ainsi que par simulations thermiques 3D. Les résultats montrent que le couplage des dispositifs intra est très prononcé. Un nouvel élément du modèle de résistance thermique récursive ainsi que le modèle de couplage thermique a été inclus dans un simulateur de circuit commercial. Une simulation transitoire entièrement couplée d'un oscillateur en anneau de 218 transistors a été effectuée. Ainsi, un retard de porte record de 1.65ps est démontré. À la connaissance des auteurs, c'est le résultat le plus rapide pour une technologie bipolaire. Le rendement thermique d'un amplificateur de puissance à 60GHz réalisé avec un réseau multi-transistor ou avec un transistor à plusieurs doigts est évalué. La performance électrique du transistor multidoigt est dégradée en raison de l'effet de couplage thermique important entre les doigts de l'émetteur. Un bon accord est constaté entre les mesures et les simulations des circuits en utilisant des modèles de transistors avec le réseau de couplage thermique. Enfin, les perspectives sur l'utilisation des résultats sont données
The power generate by modern silicon germanium (SiGe) heterojunction bipolar transistors (HBTs) can produce large thermal gradients across the silicon substrate. The device opering temperature modifies model parameters and can significantly affect circuit operation. This work characterizes and models self-heating and thermal coupling in SiGe HBTs. The self-heating effect is evaluated with low frequency and pulsed measurements. A novel pulse measurement system is presented that allows isothermal DC and RF measurements with 100ns pulses. Electrothermal intra- and inter-device feedback is extensively studied and the impact on the performance of two analog circuits is evaluated. Novel test structures are designed and fabricated to measure thermal coupling between single transistors (inter-device) as well as between the emitter stripes of a multi-finger transistor (intra-device). Thermal coupling factors are extracted from measurements and from 3D thermal simulations. Thermally coupled simulations of a ring oscillator (RO) with 218 transistors and of a 60GHz power amplifier (PA) are carried out. Current mode logic (CML) ROs are designed and measured. Layout optimizations lead to record gate delay of 1.65ps. The thermal performance of a 60GHz power amplifier is compared when realized with a multi-transistor array (MTA) and with a multi-finger trasistor (MFT). Finally, perspectives of this work within a CAD based circuit design environment are discussed

We consider a system of two identical Morris-Lecar neurons coupled via electrical coupling. We focus our study on the effects that the coupling strength, γ , and the coupling time delay, τ , cause on the dynamics of the system. For small γ we use the phase model reduction technique to analyze the system behavior. We determine the stable states of the system with respect to γ and τ using the appropriate phase models, and we estimate the regions of validity of the phase models in the γ , τ plane using both analytical and numerical analysis. Next we examine asymptotic of the arbitrary conductance-based neuronal model for γ → +∞ and γ → −∞. The theory of nearly linear systems developed in [30] is extended in the special case of matrices with non-positive eigenvalues. The asymptotic analysis for γ > 0 shows that with appropriate choice of γ the voltages of the neurons can be made arbitrarily close in finite time and will remain that close for all subsequent time, while the asymptotic analysis for γ < 0 suggests the method of estimation of the boundary between “weak” and “strong” coupling.

This thesis deals with the chaotic dynamics of nonlinear networks consisting of semiconductor lasers which have time-delayed self-feedbacks or mutual couplings. These semiconductor lasers are simulated numerically by the Lang-Kobayashi equations. The central issue is how the chaoticity of the lasers, measured by the maximal Lyapunov exponent, changes when the delay time is changed. It is analysed how this change of chaoticity with increasing delay time depends on the reflectivity of the mirror for the self-feedback or the strength of the mutal coupling, respectively. The consequences of the different types of chaos for the effect of chaos synchronization of mutually coupled semiconductor lasers are deduced and discussed. At the beginning of this thesis, the master stability formalism for the stability analysis of nonlinear networks with delay is explained. After the description of the Lang-Kobayashi equations and their linearizations as a model for the numerical simulation of semiconductor lasers with time-delayed couplings, the artificial sub-Lyapunov exponent $\lambda_{0}$ is introduced. It is explained how the sign of the sub-Lyapunov exponent can be determined by experiments. The notions of "strong chaos" and "weak chaos" are introduced and distinguished by their different scaling properties of the maximal Lyapunov exponent with the delay time. The sign of the sub-Lyapunov exponent $\lambda_{0}$ is shown to determine the occurence of strong or weak chaos. The transition sequence "weak to strong chaos and back to weak chaos" upon monotonically increasing the coupling strength $\sigma$ of a single laser's self-feedback is shown for numerical calculations of the Lang-Kobayashi equations. At the transition between strong and weak chaos, the sub-Lyapunov exponent vanishes, $\lambda_{0}=0$, resulting in a special scaling behaviour of the maximal Lyapunov exponent with the delay time. Transitions between strong and weak chaos by changing $\sigma$ can also be found for the Rössler and Lorenz dynamics. The connection between the sub-Lyapunov exponent and the time-dependent eigenvalues of the Jacobian for the internal laser dynamics is analysed. Counterintuitively, the difference between strong and weak chaos is not directly visible from the trajectory although the difference of the trajectories induces the transitions between the two types of chaos. In addition, it is shown that a linear measure like the auto-correlation function cannot unambiguously reveal the difference between strong and weak chaos either. Although the auto-correlations after one delay time are significantly higher for weak chaos than for strong chaos, it is not possible to detect a qualitative difference. If two time-scale separated self-feedbacks are present, the shorter feedback has to be taken into account for the definition of a new sub-Lyapunov exponent $\lambda_{0,s}$, which in this case determines the occurence of strong or weak chaos. If the two self-feedbacks have comparable delay times, the sub-Lyapunov exponent $\lambda_{0}$ remains the criterion for strong or weak chaos. It is shown that the sub-Lyapunov exponent scales with the square root of the effective pump current $\sqrt{p-1}$, both in its magnitude and in the position of the critical coupling strengths. For networks with several distinct sub-Lyapunov exponents, it is shown that the maximal sub-Lyapunov exponent of the network determines whether the network's maximal Lyapunov exponent scales strongly or weakly with increasing delay time. As a consequence, complete synchronization of a network is excluded for arbitrary networks which contain at least one strongly chaotic laser. Furthermore, it is demonstrated that the sub-Lyapunov exponent of a driven laser depends on the number of the incoherently superimposed inputs from unsynchronized input lasers. For networks of delay-coupled lasers operating in weak chaos, the condition $|\gamma_{2}|<\mathrm{e}^{-\lambda_{\mathrm{m}}\,\tau}$ for stable chaos synchronization is deduced using the master stability formalism. Hence, synchronization of any network depends only on the properties of a single laser with self-feedback and the eigenvalue gap of the coupling matrix. The characteristics of the master stability function for the Lang-Kobayashi dynamics is described, and consequently, the master stability function is refined to allow for precise practical prediction of synchronization. The prediction of synchronization with the master stability function is demonstrated for bidirectional and unidirectional networks. Furthermore, the master stability function is extended for two distinct delay times. Finally, symmetries and resonances for certain values of the ratio of the delay times are shown for the master stability function of the Lang-Kobyashi equations
Die vorliegende Arbeit beschäftigt sich mit der chaotischen Dynamik von nichtlinearen Netzwerken, die aus Halbleiterlasern bestehen, welche ihrerseits eine zeitverzögerte Selbstrückkopplung oder gegenseitige Kopplungen aufweisen. Diese Halbleiterlaser werden numerisch mit Hilfe der Lang-Kobayashi-Gleichungen simuliert. Die zentrale Fragestellung ist dabei, wie sich die Chaotizität der Laser, die in Form des größten Lyanpunov-Exponenten gemessen wird, mit der Verzögerungszeit ändert. Des Weiteren wird untersucht, wie diese Veränderung der Chaotizität bei Zunahme der zeitlichen Verzögerung entweder von der Reflektivität des Spiegels der Selbstrückkopplung oder aber von der Stärke der gegenseitigen Kopplungen abhängt. Die Folgen der unterschiedlichen Arten von Chaos für den Effekt der Chaossynchronisation gegenseitig gekoppelter Halbleiterlaser werden hergeleitet und diskutiert. Zu Beginn dieser Arbeit wird zunächst der Master-Stability-Formalismus für die Stabilitätsanalyse von nichtlinearen Netzwerken mit Zeitverzögerung erklärt. Nach der Beschreibung der Lang-Kobayshi-Gleichungen und deren Linearisierungen als Modell für die numerische Simulation von Halbleiterlasern mit zeitverzögerten Kopplungen wird der künstliche Sub-Lyapunov-Exponent $\lambda_{0}$ eingeführt. Es wird erläutert, wie das Vorzeichen des Sub-Lyapunov-Exponenten in Experimenten bestimmt werden kann. Die Termini "starkes Chaos" und "schwaches Chaos" werden eingeführt. Diese werden auf Basis der unterschiedlichen Skalierungseigenschaften des größten Lyapunov-Exponenten mit der Verzögerungszeit unterschieden. Es wird gezeigt, dass das Vorzeichen des Sub-Lyapunov-Exponenten $\lambda_{0}$ das Auftreten von starkem oder schwachem Chaos bestimmt. Die Übergangssequenz "schwaches zu starkem Chaos und wieder zurück zu schwachem Chaos" bei monotoner Erhöhung der Kopplungsstärke $\sigma$ eines einzelnen Lasers mit Selbstrückkopplung wird für numerische Berechnungen der Lang-Kobayashi-Gleichungen dargestellt. Beim Übergang zwischen starkem und schwachem Chaos verschwindet der Sub-Lyapunov-Exponent, $\lambda_{0}=0$, was zu einem speziellen Skalierungsverhalten des größten Lyapunov-Exponenten mit der Verzögerungszeit führt. Übergänge zwischen starkem und schwachem Chaos durch Änderung von $\sigma$ können auch für die Rössler- und Lorenz-Dynamik gefunden werden. Der Zusammenhang zwischen dem Sub-Lyapunov-Exponenten und den zeitabhängigen Eigenwerten der Jacobi-Matrix der internen Laserdynamik wird analysiert. Anders als intuitiv erwartet, ist der Unterschied zwischen starkem und schwachem Chaos nicht unmittelbar anhand der Trajektorie ersichtlich, obwohl der Unterschied der Trajektorien die Übergänge zwischen den beiden Chaosarten induziert. Darüber hinaus wird gezeigt, dass ein lineares Maß wie die Autokorrelationsfunktion den Unterschied zwischen starkem und schwachem Chaos auch nicht eindeutig aufzeigen kann. Obwohl die um eine Verzögerungszeit verschobenen Autokorrelationen für schwaches Chaos signifikant größer als für starkes Chaos sind, ist es nicht möglich, einen qualitativen Unterschied festzustellen. Bei Vorliegen zweier zeitskalenseparierter Selbstrückkopplungen muss die kürzere Rückkopplung bei der Definition eines neuen Sub-Lyapunov-Exponenten $\lambda_{0,s}$ berücksichtigt werden, welcher dann das Auftreten von starkem oder schwachem Chaos bestimmt. Falls die beiden Selbstrückkopplungen vergleichbare Verzögerungszeiten aufweisen, so ist der Sub-Lyapunov-Exponent $\lambda_{0}$ nach wie vor das Kriterium für starkes oder schwaches Chaos. Es wird gezeigt, dass der Sub-Lyapunov-Exponent mit der Quadratwurzel des effektiven Pumpstroms $\sqrt{p-1}$ skaliert, und zwar sowohl bezüglich seiner Größe als auch bezüglich der Position der kritischen Kopplungsstärken. Für Netzwerke mit mehreren unterschiedlichen Sub-Lyapunov-Exponenten wird gezeigt, dass der größte Sub-Lyapunov-Exponent des Netzwerks bestimmt, ob der größte Lyapunov-Exponent des Netzwerks mit zunehmender Verzögerungszeit stark oder schwach skaliert. Folglich ist vollständige Synchronisation eines Netzwerks für beliebige Netzwerke, die wenigstens einen stark chaotischen Laser beinhalten, ausgeschlossen. Zudem wird gezeigt, dass der Sub-Lyapunov-Exponent eines getriebenen Lasers von der Anzahl der inkohärent superponierten Eingangssignale der nicht synchronisierten Eingangslaser abhängt. Für Netzwerke aus zeitverzögert gekoppelten Lasern, die im schwachen Chaos betrieben werden, wird die Bedingung $|\gamma_{2}|<\mathrm{e}^{-\lambda_{\mathrm{m}}\,\tau}$ für stabile Chaossynchronisation mit Hilfe des Master-Stability-Formalismus hergeleitet. Folglich hängt die Synchronisation eines jeden Netzwerks nur von den Eigenschaften eines einzelnen Lasers mit Selbstrückkopplung und von der Eigenwertlücke der Kopplungsmatrix ab. Die spezifischen Eigenschaften der Master-Stability-Funktion der Lang-Kobayashi-Dynamik werden beschrieben, und dementsprechend wird die Master-Stability-Funktion angepasst, um eine präzise praktische Vorhersage von Synchronisation zu ermöglichen. Die Vorhersage von Synchronisation mittels der Master-Stability-Funktion wird für bidirektionale und unidirektionale Netzwerke demonstriert. Ferner wird die Master-Stability-Funktion für den Fall zweier unterschiedlicher Verzögerungszeiten erweitert. Schließlich werden Symmetrien und Resonanzen bei bestimmten Werten des Verhältnisses der Verzögerungszeiten für die Master-Stability-Funktion der Lang-Kobyashi-Gleichungen aufgezeigt

碩士
元智大學
資訊工程學系
92
Advance in process technologies has led to decrease in feature size of the transistors. With reduced wires spacing, coupling capacitance between wires increases significant. The coupling capacitance becomes a critical factor in deciding circuit delay. Since coupling delay depends on many factors such as the use of driving gates, driving strengths, input signal switching direction, input slew rate, and the interconnect length and width. It is difficult to obtain accurate coupling delay without resort to SPICE simulation. However, it is utmost important for a static timing analysis tool to compute coupling delay efficiently. To achieve this goal, the coupling delay should be pre-characterized and formed an easily accessible database. In this thesis, we perform coupling delay characterization. We use the curve fitting method to obtain the closed-form equations for computing coupling delay. The R-Square of these closed-form equations are higher than 0.99. We then verify the accuracy of closed-from equation using the 200 results obtained by HSPICE. We use the closed-from equations to calculate coupling delay and transition time with same circuit parameters as that used by HSPICE. In the coupling delays, the maximum relative error is 22.46% and the maximum average of absolute error is 6.04E-12s. In the transition times, the maximum relative error is 27.90% and the maximum average of absolute errors is 9.11E-12s. We also employ the closed-form equation s to calculate delay on several circuit instances. We compare the results calculated by closed-form equations with the results obtain by HSPICE. In a noiseless circuit, the maximum relative error is 14.76% of delay and the maximum relative error is 13.05% of the transition time. In the circuit with a single aggressor, the maximum relative error for the delay at output is 101% and the maximum relative error of transition time at the output is 81.83%. In the circuit with multi-aggressors, the maximum relative error is 259.4% of delay and the maximum relative error is 87.03% of the transition time. In the circuit with global crosstalk problem, the maximum relative error is 97.59% of delay and the maximum relative error is 80.59% of the transition time. When the closed-from equations are used to calculate the delay in static timing analysis, the high relative error does not matter when the absolute error is extremely small. The higher relative errors in each case described above are acceptable, because the absolute errors are extremely small.

碩士
國立交通大學
應用數學系所
96
We study the interaction between coupling strengths, delay and concavity for a pair of two Mirollo-Strogatz-type oscillators. For a pair of two concave oscillators with a nonzero delay, the complete phase diagrams with respect to both inhibitory and excitatory coupling are given. In particular, we prove that the delay and excitatory coupling induce multistable synchronization for such system. On the other hand, the in-phase synchronization is shown to be unstable for inhibitory coupling if the delay is not zero.

碩士
國立清華大學
電機工程學系
95
Memory fault simulator is an important tool for memory test sequence optimization. Traditional sequential fault simulation algorithm has time complexity O(N3) (N: number of cells in memory), which may be too slow to simulate a large number of memory words. Therefore, we had developed a fault simulator called Random Access Memory Simulator for Error Screening (RAMSES). RAMSES uses fault descriptors to describe fault models' behaviors, which can reduce the time complexity to O(N2) and support new fault models. Delay fault plays a more and more important role in memory testing. In this thesis, we adopt new delay fault models targeting DRAM timing parameters and modify RAMSES that is now called RAMSES-D. Finally, the concept of weighted coupling fault is proposed. Fault count itself cannot accurately represent the real coupling fault distribution. Even if the same fault model is concerned, cells in diRerent positions will have diRerent fault occurrence probability. We propose a weight function and assign a weight to each coupling fault, and modify the fault coverage calculation method. The weighted fault coverage shows the effectiveness of the weight function, and that different coupling fault ratio varies with diRerent memory configuraitons. We propose a 23N March test pattern for delay fault models, which reduces 23.3% test length from originally proposed delay fault test patterns. With the weight function, we can use physical information to calculate coupling fault coverage. Experimental result shows that the weight of intra-word coupling fault can be 10% to 14%; while the original fault count method cannot distinguish the degree of importance between diRerent memory configurations.

碩士
國立臺灣科技大學
電子工程系
97
The channel parameters such as directions of arrival (DOAs) or multipath delays are of importance in wireless communication systems. The precise information of these two parameters not only are crucial in the localization of mobil stations, but also enhances the accuracy of channel estimation, which in turn improves the communication link quality. It is thus of interest to simultaneously estimate the DOAs and delays of the impinging rays based on the signals received by an antenna array. However, most of the existing algorithms either do not take the mutual coupling, incurred due to closely spaced antennas, into consideration or are too complicated to admit practical implementations. Since the subspace based algorithms in general strike a better tradeoff between performance and complexity. In this thesis, we extend two widespread Multiple-SIgnal-Classification (MUSIC) based algorithms for joint DOA-delay estimation, namely the JADE-MUSIC and CTST-MUSIC, to the scenarios in the presence of mutual coupling. It is justified that when the mutual coupling is known, the extensions take the same form as the original ones, except a slight modification of the spatial response vectors. Also, with the addition of auxiliary sensors on both sides of the antenna array, it is shown that both algorithms can be extended to the scenarios when the mutual coupling is unknown. Our focus is put on the CTST approach which uses three stages of one-dimensional (1-D) MUSIC algorithms along with a constrained spatial filtering process and a constrained temporal filtering process in between to render high resolution parameter estimates, yet with low computational overhead. Simulations are provided to verify the resilience of the extended algorithms against the mutual coupling and their superiority compared with previous works.

Capacitive crosstalk between adjacent signal wires in integrated circuits may lead to noise or a speedup or slowdown in signal transitions. These in turn may lead to circuit failure or reduced operating speed. This thesis focuses on generating test patterns to induce crosstalk-induced signal delays, in order to determine whether the circuit can still meet its timing specification. A timing-driven test generator is developed to sensitize multiple aligned aggressors coupled to a delay-sensitive victim path to detect the combination of a delay spot defect and crosstalk-induced slowdown. The framework uses parasitic capacitance information, timing windows and crosstalk-induced delay estimates to screen out unaligned or ineffective aggressors coupled to a victim path, speeding up crosstalk pattern generation. In order to induce maximum crosstalk slowdown along a path, aggressors are prioritized based on their potential delay increase and timing alignment. The test generation engine introduces the concept of alignment-driven path sensitization to generate paths from inputs to coupled aggressor nets that meet timing alignment and direction requirements. By using path delay information obtained from circuit preprocessing, preferred paths can be chosen during aggressor path propagation processes. As the test generator sensitizes aggressors in the presence of victim path necessary assignments, the search space is effectively reduced for aggressor path generation. This helps in reducing the test generation time for aligned aggressors. In addition, two new crosstalk-driven dynamic test compaction algorithms are developed to control the increase in test pattern count. The proposed test generation algorithm is applied to ISCAS85 and ISCAS89 benchmark circuits. SPICE simulation results demonstrate the ability of the alignment-driven test generator to increase crosstalk-induced delays along victim paths.

Delay variability poses a formidable challenge in both design and test of nanometer circuits. While process parameter variability is increasing with technology scaling, as circuits are becoming more complex, the dynamic or vector dependent variability is also increasing steadily. In this research, we develop solutions to incorporate the effect of delay variability in delay testing. We focus on two different applications of delay testing. In the first case, delay testing is used for testing the timing performance of a circuit using path based fault models. We show that if dynamic delay variability is not accounted for during the path selection phase, then it can result in targeting a wrong set of paths for test. We have developed efficient techniques to model the effect of two different dynamic effects namely multiple-input switching noise and coupling noise. The basic strategy to incorporate the effect of dynamic delay variability is to estimate the maximum vector delay of a path without being too pessimistic. In the second case, the objective was to increase the defect coverage of reliability defects in the presence of process variations. Such defects cause very small delay changes and hence can easily escape regular tests. We develop a circuit that facilitates accurate control over the capture edge and thus enable faster than at-speed testing. We further develop an efficient path selection algorithm that can select a path that detects the smallest detectable defect at any node in the presence of process variations.
text

As the third generation of luminescent materials, thermally activated delayed fluorescence (TADF)-type compounds have great potential as emitter molecules in OLEDs allowing for electro-fluorescence with 100 % internal quantum efficiency. For organic electronics, the general wide range of applications from OLEDs, bio-fluorescence imaging to sensor technologies and photonic energy storages roots on the enormous variety of organic materials. Especially in the field of metal- free aromatic designs, the range of possible materials showing diverse triplet harvesting effects is immense, making material development a highly complex task. Firstly, initial efforts in the understanding of the basic concepts behind TADF will be highlighted. A rational design strategy for TADF materials will be illustrated on an innovative material series based on phenylcarbazoles. A reasonable branch of isomers are theoretically constructed and slight stoichiometric modifications are performed to understand how molecular structure and intramolecular steric hindrance affects reverse intersystem crossing (RISC), while simultaneously revealing the strategy for deep blue TADF. The rational design of a bluish green TADF material called 5CzCF3Ph providing CIEy ≤ 0.4 is demonstrated, enabling peak EQE values of 12.1 % with a promising LT50 of 2 hrs at 500 cd∙m-2. Subsequently, the photophysics of five newly designed trimeric donor (D)-acceptor (A)-donor (D) type material compounds, analogue concepts to archetypical TADF designs, highlight the importance of intramolecular electronic couplings between adjacent triplet states for adiabatically-driven TADF, revealing the mechanism of local type triplet state perturbations on 3CT states. The most promising candidate (DMAC-PTO-DMAC) is disclosed and in turn optimized to meet required conditions for deep blue TADF emission. Ultimately, a deep blue luminescent material called isoDMAC-PTO is developed, featuring CIE coordinates of (0.16, 0.14) with an overall quantum yield of (86.4 ± 0.5) %. The focus switches to the fundamental understanding of the underlying mechanism giving rise to TADF in small molecules, leaving the scope of deep blue emission. While investigating the photophysical properties of a synthesized donor (D)-acceptor (A) type thermally activated delayed fluorescence (TADF) emitter named methyl 2-(9,9-dimethylacridin-10-yl)benzoate (DMAC-MB), it is possible to identify the excited state dynamics mediating the spin-flip process and hence the reutilization of non-radiative triplet states allowing for an internal quantum efficiency approaching unity. As experimentally observed by detailed temperature- and time-dependent transient photoluminescence (PL) measurements and consolidated by comprehensive quantum-chemical considerations, excited state configuration interaction by non-adiabatic couplings are anticipated as key property behind triplet up-conversion in the vicinity of conical intersections, contributing to recent research facing the exciton management within the auspicious field of TADF. For the first time, this thesis reports that even a TADF-silent molecule can be converted into efficient TADF systems by increasing the donor π- conjugation length through polymerization of the building block itself. With a total photoluminescence quantum yield up to 71 %, comprehensible research illustrates an efficient thermally activated delayed fluorescence polymer P1, based solely on non-TADF chromophores represented by a model compound 2 (PLQY of 3 % at RT). Finally, as predicted by TDDFT calculations and shown for the first time in the aspiring field of TADF, a thermally activated delayed fluorescence polymer based on a merely radiative, solely phosphorescent repeating unit is demonstrated. Intramolecular π-conjugation is exploited to trigger the charge-transfer excited state energy, revealing a general design tool to provoke TADF, reserved in particular for polymers. While the introduced twisted methyl 2-(9,9-dimethylacridin-10-yl) benzoate (DMAC-MB) reveals efficient thermally activated delayed fluorescence (TADF), a modified analogue 9,9-Dimethyl-5H,9H-quinolino[3,2,1-de]acridin-5-one (DMAC-ACR) shows emerging room temperature phosphorescence (RTP). As for TADF, intramolecular non-adiabatic couplings are unlocked as key feature actuating persistent RTP, linking photophysical analogies between TADF and RTP to structural self-similarities. Last but not least, degradation processes in TADF materials will be addressed. A correlation between theoretically calculated bond-dissociation energies (BDEs) and phenomenological observations reveals that low BDEs, in particular along pronounced charge-transfer bonds, ultimately lead to irreversible TADF material degradation induced by bi-molecular processes comprising TPQ as well as TTA. Finally, this thesis reveals the photophysics of 24 newly designed, synthesized and characterized TADF materials and demonstrates a fundamentally new approach for RTP, based on structural analogues to TADF. Far reaching design principles as conjugation induced TADF in polymers, as well as new design strategies selectively incorporating virbonic couplings yield device performances comprising LT50 of 2 hrs at 500 cd∙m-2 and targeted deep blue emission with CIE (0.16, 0.14). While lighting the way for TADF as future luminescent OLED materials, intrinsic material instabilities due to low bond-dissociation energies are disclosed as key-issues for tomorrows research.

The electromagnetic coupling of a microstrip transmission line (MS-TL) to a metamaterial backward wave Negative-Refractive-Index transmission line (NRI-TL) is the primary investigation of this dissertation. The coupling of forward waves in the MS-TL to the backward waves in the NRI-TL results in the formation of complex modes, characterized by simultaneous phase progression and attenuation along the lossless lines. Through network-theoretic considerations, we investigate the properties of these modes in the complex-frequency plane of the Laplace domain to help unravel the confusion that has existed in the literature regarding the independent excitation of a pair of conjugate complex modes. We show that it is possible to arbitrarily suppress one of the modes over a finite bandwidth and completely eliminate it at a discrete set of frequencies using proper source and load impedances. Hence we use conjugate modes with independent amplitudes in our eigenmode expansion when we analyse various coupling configurations between the two types of lines (MS/NRI-TL coupler). We derive approximate closed-form expression for the scattering parameters of the MS/NRI-TL coupler and these are complemented by design charts that allow the synthesis of a wide range of specifications. Moreover, these expressions reveal that such couplers allow for arbitrary backward coupling levels along with very high-isolation when they are made half a guided wavelength long. The MS/NRI-TL coupler offers some interesting applications which we highlight through the design and testing of a 3-dB power splitter, a high-directivity signal monitor and a compact corporate power divider. We have included design, simulation and experimental data for the fabricated prototypes exhibiting good agreement and thereby justifying the theory that has been developed in this work to explain the coupling between a right-handed MS-TL and a left-handed NRI-TL.

The degree by which a species can adapt to the demands of its changing environment defines how well it can exploit the resources of new ecological niches. Since the nervous system is the seat of an organism's behavior, studying adaptation starts from there. The nervous system adapts through neuronal plasticity, which may be considered as the brain's reaction to environmental perturbations. In a natural setting, these perturbations are always changing. As such, a full understanding of how the brain functions requires studying neuronal plasticity under temporally varying stimulation conditions, i.e., studying the role of plasticity in carrying out spatiotemporal computations. It is only then that we can fully benefit from the full potential of neural information processing to build powerful brain-inspired adaptive technologies. Here, we focus on homeostatic plasticity, where certain properties of the neural machinery are regulated so that they remain within a functionally and metabolically desirable range. Our main goal is to illustrate how homeostatic plasticity interacting with associative mechanisms is functionally relevant for spatiotemporal computations. The thesis consists of three studies that share two features: (1) homeostatic and synaptic plasticity act on a dynamical system such as a recurrent neural network. (2) The dynamical system is nonautonomous, that is, it is subject to temporally varying stimulation. In the first study, we develop a rigorous theory of spatiotemporal representations and computations, and the role of plasticity. Within the developed theory, we show that homeostatic plasticity increases the capacity of the network to encode spatiotemporal patterns, and that synaptic plasticity associates these patterns to network states. The second study applies the insights from the first study to the single node delay-coupled reservoir computing architecture, or DCR. The DCR's activity is sampled at several computational units. We derive a homeostatic plasticity rule acting on these units. We analytically show that the rule balances between the two necessary processes for spatiotemporal computations identified in the first study. As a result, we show that the computational power of the DCR significantly increases. The third study considers minimal neural control of robots. We show that recurrent neural control with homeostatic synaptic dynamics endows the robots with memory. We show through demonstrations that this memory is necessary for generating behaviors like obstacle-avoidance of a wheel-driven robot and stable hexapod locomotion.