The methods and principles of cybernetics are applied to a discussion of stability and regulation in social systems taking a global viewpoint. The fundamental but still classical notion of stability as applied to homeostatic and ultrastable systems is discussed, with a particular reference to a specific well-studied example of a closed social group (the Tsembaga studied by Roy Rappaport in New Guinea). The discussion extends to the problem of evolution in large systems and the question of regulating evolution is addressed without special qualifications. A more comprehensive idea of stability is introduced as the argument turns to the problem of evolution for viability in general. Concepts pertaining to the problem of evolution are exemplified by a computer simulation model of an abstractly defined ecosystem in which various dynamic processes occur allowing the study of adaptive and evolutionary behaviour. In particular, the role of coalition formation and cooperative behaviour is stressed as a key factor in the evolution of complexity. The model consists of a population of several species of dimensionless automata inhabiting a geometrically defined environment in which a commodity essential for metabolic requirements (food) appears. Automata can sense properties of their environment, move about it, compete for food, reproduce or combine into coalitions thus forming new and more complex species. Each species is associated with a specific genotype from which the species’ behavioural characteristics (its phenotype) are derived. Complexity and survival efficiency of species increases through coalition formation, an event which occurs when automata are faced with an “undecidable” situation that is resolvable only by forming a new and more complex organization. Exogenous manipulation of the food distribution pattern and other critical factors produces different environmental conditions resulting in different behaviour patterns of automata and in different evolutionary “pathways.” Eve-1, the computer program developed to implement this model, accepts a high-level command language which allows for the setting of parameters, definition of initial configurations, and control of output formats. Results of simulation are produced graphically and include various pertinent tables. The program was given a modular hierarchical structure which allows easy generation of new versions incorporating different sets of rules. The model strives to capture the essence of the evolution of complexity viewed as a general process rather than to describe the evolution of a particular “real” system. In this respect it is not context-specific, and the behaviours which are observable in different runs can receive various interpretation depending on specific identifications. Of these, biological, ecological, and sociological interpretations are the most obvious and the latter, in particular, is stressed.

Organic Light-Emitting Diodes (OLEDs) currently advance in the display market due to their unique image quality. Innovations profit from further extraordinary properties such as mechanical flexibility, optical transparency and large area coverage. Despite considerable progress in development, high costs and moderate efficiencies hamper the entry into the lighting market. However, there still is enormous potential for efficiency improvement. Current problems are the work-intensive search for best material combinations and large amounts of trapped light in the flat OLED geometry. This thesis develops novel concepts for improving the efficiency of OLEDs: An optimized fabrication, a systematic evaluation of light outcoupling structures by proposing a new metric, and an examination of efficiency limitations with optical simulations to identify options for action. The optimization of OLEDs is closely related to the properties of the individual molecules, while the fabrication process is often neglected. However, literature has shown that vapor deposited organic glasses can exhibit extraordinary high stabilities when fabricated at the right conditions. The substrate temperature is therefore set to 85 % of the materials conventional glass transition temperature Tg while the deposition rates are kept below < 0.1 nm/s. This concept is adapted and the glass forming molecule TPBi is fabricated as stable host and electron transporter in a simple OLED. Efficiency and lifetime improvement could be achieved with four different phosphorescent emitters. For Ir(ppy)2(acac) the External Quantum Efficiency (EQE) at 100 cd/m² is enhanced from 19.4 to 24.0 % and the lifetime LT 70 at 1,000 cd/m² from 14.8 to 74.2 h, i.e. the time in which the initial luminance drops to 70 % is five times higher. The origin is found in improved radiative and electrical efficiency. This fabrication concept enables an additional optimization path besides material development. Next, the high refractive index of organic materials lead to light confinement through total internal reflection. Many light outcoupling strategies have been developed, but their direct comparison is difficult through the diversity of used structures and OLEDs. This thesis proposes a new efficiency metric, the Efficiency of Light Outcoupling Structures (ELOS), that states the effectiveness of a light outcoupling structure. It weights experimental efficiency enhancement to theoretically maximal gain that is simulated. It was found that a glass half-sphere extracts about 80 % photons from the OLED substrate, while a combination of a diffraction grating with the half-sphere extracts at best 43 % from the whole OLED. The corresponding EQEs are 32.5 % and 36.5 %. The ELOS promotes a systematic search for a universally efficient light outcoupling structures, because it removes misinterpretation through the specifically used OLED. Lastly, optical investigations have found the following statements for bottom-emitting OLEDs: Highest EQEs with external light outcoupling structures are reached for 3/4 λ cavities. EQEs of more than 90 % could be reached with a low refractive index electron transport layer in combination with a high refractive index substrate and ideal external light outcoupling. For top-emitting OLEDs, the thin film interference can be exploited to shift the emission color of sky-blue emitter towards blue. Commission Internationale de l’Éclairage (CIE) color coordinates of (0.127/0.168) could experimentally be achieved with an emitter that has (0.213/0.374). The color tuning reduces EQE, but therefore exploits higher lifetimes of sky-blue emitters. This opens an alternative to reach deep blue emission besides material development, which is a current challenge for displays. / Organische Leuchtdioden (OLEDs) etablieren sich derzeit im Display-Markt aufgrund ihrer einzigartigen Bildqualität. Innovationen profitieren zudem von weiteren außergewöhnlichen Eigenschaften wie z.B. mechanische Flexibilität, optische Transparenz und Großflächigkeit. Obwohl es bereits beträchtliche Weiterentwicklungen gab, erschweren hohe Kosten und moderate Effizienzen den Markteintritt in den Beleuchtungssektor. Dabei gibt es noch enormes Potential für Effizienzsteigerungen. Derzeitige Probleme sind die aufwändige Suche nach den besten Material(-kombinationen) und große Verluste durch Licht, welches im flachen Bauteil verbleibt. In dieser Dissertation werden deshalb neuartige Konzepte entwickelt, um die Effizienzsteigerung voranzutreiben: Eine optimierte Herstellung, eine systematische Untersuchung von Lichtauskoppelstrukturen mittels einer neuen Metrik und die Untersuchung von Effizienzlimitierungen mithilfe von optischen Simulationen, um weitere Möglichkeiten zur Verbesserung zu identifizieren. Die Optimierung von OLEDs ist eng verbunden mit der Materialsuche, wobei der Herstellungsprozess oft vernachlässigt wird. Allerdings konnte in der Literatur gezeigt werden, dass aufgedampfte organische Gläser außergewöhnlich stabil sein können, wenn die Herstellungsbedingungen optimiert werden. Dafür muss die Substrattemperatur auf etwa 85 % der gewöhnlichen Glasübergangstemperatur Tg gesetzt werden, während das Material mit niedrigen Raten von < 0,1 nm/s aufgetragen wird. Dieses Konzept wird übernommen für das Glasformer Molekül TPBi, welches als stabile Matrix und Elektronentransporter in einer einfachen OLED realisiert wird. Damit wird eine Effizienz- und Lebensdauerverbessung für vier phosphoreszente Emittermoleküle erreicht. Für Ir(ppy)2(acac) wird die externe Quanteneffizienz (EQE) bei 100 cd/m² von 19,4 auf 24,0 % erhöht und die Lebensdauer LT 70 bei 1000 cd/m² von 14,8 auf 74,2 h, d.h. die Zeit, bis die ursprüngliche Helligkeit auf 70 % fällt, wird verfünffacht. Ursache dafür ist eine verbesserte elektrische Effizienz und Strahlungseffizienz. Diese Herstellungsoptimierung eröffnet neben der Materialsuche eine weitere Möglichkeit für OLED Verbesserungen. Weiterhin führt der hohe Brechungsindex organischer Materialien zu Lichteinschluss im Bauteil durch totale interne Reflexion. Um zusätzliches Licht zu extrahieren, wurden viele Lichtauskoppelstrukturen entwickelt, welche sich jedoch aufgrund der Vielfalt der Strukturen und OLEDs nur schwer vergleichen lassen. Diese Arbeit schlägt eine neue Effizienzgröße vor, die sogenannte Effizienz von Lichtauskoppelstrukturen (ELOS), welche die Effektivität von den Strukturen angibt. Sie vergleicht die experimentell bestimmte mit der maximal erwartbaren Verbesserung, welche mit optischen Simulationen berechnet wird. Damit konnte gezeigt werden, dass eine Glashalbkugel etwa 80 % aller Photonen vom OLED Substrat extrahiert, während eine Kombination von Streugittern mit Glashalbkugel bestenfalls 43 % der verbleibenden Photonen in der gesamten OLED extrahiert. Die jeweiligen EQEs sind 32,5 % und 36,5 %. Die ELOS fördert eine systematische Suche nach den universell am besten funktionierenden Lichtauskoppelstrukturen, weil Missinterpretationen durch die jeweilig verwendeten OLEDs verringert werden. Letztendlich haben die optischen Untersuchungen folgende Aussagen für bottom emittierenden OLEDs gefunden: Die höchste EQE mit externen Lichtauskoppelstrukturen werden mit 3/4 λ Kavitäten erreicht. EQEs von mehr als 90 % könnten erreicht werden durch Kombination von niedrigbrechenden Elektronentransportschichten, hochbrechenden Substraten und idealen Lichtauskoppelstrukturen. Für top emittierende OLEDs kann Dünnschichtinterferenz ausgenutzt werden, um die Farbe von himmelblauen Emittern zu tiefblau zu verschieben. CIE Farbkoordinaten von (0.127/0.168) konnten experimentell erreicht werden mit einem Emitter von (0.213/0.374). Die Farbverschiebung verringert zwar die EQE, allerdings kann so die höhere Lebensdauer von himmelblauen Emittern ausgenutzt werden. Damit wird eine Alternative zur Materialsuche geschaffen, um tiefblaue Farbe zu erreichen, was eine derzeitige Herausforderung für Displays ist.

Depuis plusieurs années, le département Temps-Fréquence de l’institut FEMTO-ST mène une étude sur le comportement des résonateurs à ondes acoustiques de volume à énergie piégée dans des cristaux à quartz à température cryogénique, typiquement proche de 4 K. Les performances en termes de coefficient de qualité mécanique relevé à ces températures, plusieurs milliards à quelques dizaines de MHz, font des cavités acoustiques en quartz de bons candidats pour des sources de fréquences cryogéniques ultrastables.Les travaux présentés dans ce manuscrit s’inscrivent dans la continuité de ce programme d’étude. Ils visent à consolider l’intérêt du quartz mais aussi à envisager des solutions alternatives à base de matériaux à très faibles pertes acoustiques mais non piézoélectriques pour lesquels l’excitation optique est une alternative crédible. Les présents travaux peuvent être résumés en trois parties majeures :- La première partie a été réalisée dans le but de déterminer une coupe de quartz possédant un point d’inversion sur sa caractéristique fréquence-température aux températures cryogéniques. La seule régulation de température du résonateur d’une source de fréquence ultrastable est en effet insuffisante sans l’existence d’un tel point qui doit servir de point de fonctionnement à la régulation thermique. La recherche d’une coupe compensée a nécessité une campagne préliminaire de mesure des coefficients de température des coefficients élastiques du matériau, inconnus à basses températures. Il a alors été possible, à partir de la connaissance de ces coefficients, d’identifier par le calcul puis de réaliser une coupe remplissant les conditions recherchées.- La seconde partie a pour objectif de faire la preuve de concept consistant à utiliser une cavité acoustique en quartz en cavité optique. Dans sa version de base, le résonateur à quartz à onde de volume piégée est plan-convexe (pour assurer le piégeage) et à électrodes (métalliques pour assurer l’excitation électrique !) déposées sur chacune de ses faces. Il est démontré, théoriquement et expérimentalement, qu’une telle géométrie fonctionne en cavité optique, avec son avantage de simplicité mais avec ses limites. Cette structure de base doit être mise à profit pour le couplage optomécanique abordé en troisième partie et constitue le socle de conception de dispositifs optomécaniques plus performants.- La troisième partie est consacrée à l’évaluation de la pertinence du couplage optomécanique de tels dispositifs fonctionnant à température cryogénique. Une étude portant sur la quantification théorique du couplage optomécanique que peut atteindre une telle cavité a été réalisée. / For a few years, the Time and Frequency department in FEMTO-ST Insitute has been leading research about the behavior of Bulk Acoustic Wave (BAW) trapped in quartz crystal at cryogenic temperatures (near 4K).The measured quality factor are around a few billions at few tens of MHz for such temperatures. Acoustical quartz cavities are therefore good candidates for ultrastable cryogenic frequency sources. The work presented here is in the natural continuation of the research cited above. They aim at strenghtening the interest for quartz crystal, but also to consider alternative solutions with non-piezoelectric material with very-low acoustical losses, for which optical excitation is an option. The following work can be summed up in three main parts:- The first part is about the determination of a quartz crystal cut for which a turnover point exists in the frequency-temperature curve in the cryogenic region. Indeed, it is not enough to barely control the temperature in an ultrastable frequency source. Such a turnover point needs to be the operation point for thermal regulation. Searching a compensated cut arose the need for a preliminary measurements campaign of thermal coefficients of elastics coefficients of the material, which were unknown at low temperature. It was then possible, based on these coefficients, to calculate and even realize a cut fulfilling the required condition.- The second part had the objective to demonstrate conceptually that using a quartz acoustical cavity as an optical cavity was feasible. In its basic scheme, a BAW quartz resonator is plano-convex (to ensure the trapping of the acoustic wave) and has electrodes (metal-made to ensure electrical excitation) deposited on each face. It has been demonstrated, both theoretically and experimentally, that such a geometry works fine as an optical cavity, with its corresponding advantages and limitations. This scheme is used for the optomechanical coupling discussed in the third part and constitutes the very base for more efficient optomechanical devices.- The third part is dedicated to the evaluation of how efficient will such devices be while functioning at cryogenic temperature. A theoretical quantification of the optomechanical coupling that these cavities might reach is also presented.

Magister Scientiae (Medical Bioscience) - MSc(MBS) / The South African economy relies heavily on mining. The residues of these activities contain harmful metals that are discharged into the environment as industrial wastes, contaminating the air, soil, surface and ground water. A lot of people who live in remote areas in South Africa rely on ground water to drink and cook. They also cultivate their own vegetables increasing the risk of metal toxicity. Some of these metals are very toxic and can cause adverse effects upon being ingested. Toxic metals are well known to be harmful to humans. Some of these metals are carcinogenic or nephrotoxic when a large amount is accumulated in the human body causing cancer and destroying tissues such as the kidneys. The detrimental health effects of these metals may take months to years before manifestation causing people to sideline them as hazards. One of the major toxic elements that are discharged into the environment is lead. A natural zeolite called clinoptilolite has been widely used as an adsorbent for toxic metals from contaminated water and from the human body because of its properties such as ion-exchange capacity and pore size. However, this natural zeolite clinoptilolite is not pure and may contain traces of toxic elements of which the nature and concentration depend on the origin of clinoptilolite. The structural stability of clinoptilolite in acidic or alkaline media is not well documented. The lack of documented information about the leachates of clinoptilolite and their long term effects on the human body may cause harm to people who ingest this zeolite. This has led to investigation of synthetic zeolites such as faujasite which has already been used for decontamination of sludge, industrial effluents and other waste water by removing toxic metals such as Pb, Cd, Cu, Zn and As. This study focuses on comparing the toxic metal removal efficiency of natural zeolite clinoptilolite (C), clinoptilolite-based faujasite (FAU3) and clinoptilolite-based ultrastable Y zeolite (USY3), from contaminated water and simulated gastric juice containing lead and cadmium and to evaluate the extent of leaching of other elements from these zeolites. Clinoptilolite was used as a starting material for the synthesis of faujasite (FAU3) which was further treated with oxalic acid to get an ultrastable Y zeolite (USY3). Various techniques were used to characterise the as-received clinoptilolite, faujasite zeolite and USY, namely XRD, SEMEDS, FTIR, solid state NMR (27Al and 29Si) and BET-N2. These characterisation techniques confirmed that clinoptilolite was successfully transformed into faujasite and that the treatment of faujasite with oxalic acid yielded USY3. A comparative adsorption study was conducted using three zeolite samples: namely Clinoptilolite (C), clinoptilolite-based faujasite (FAU3) and ultrastable Y zeolite (USY3). ICP was used to characterise the liquid samples and it was concluded that zeolites were efficient in removing lead and cadmium from contaminated water samples as well as from simulated gastric juice. Some leachates from these zeolites were also observed. A contaminated water sample containing lead and cadmium was used as a medium where the removal capacity and percentage removal with C, FAU3 and USY3 was investigated. It was observed that the optimum dosage varied from one zeolite to the other and also from one metal to the other. The optimum dosage for C, FAU3 and USY3 for the uptake of lead was found to be 0.2 g, 0.2 g and 0.05 g respectively while for cadmium it was 0.4 g, 005 g and 0.1 g, respectively. It was also shown in this study that the removal capacity for lead and cadmium could be hindered by the Na content in FAU3 and USY3 due to the fact that these metals could be in an uptake competition with Na and other cations that leached out or exchanged from the zeolites. It was observed that the optimum metal concentration for lead uptake as well as for cadmium with few metals being released back into the solution was 0.1 mg/L. The optimum contact time for both lead and cadmium was 15 minutes. The factor that varied depending on the type of metal was pH, which was at its optimum at 3.5 for lead and at 5.5 for cadmium. A simulated gastric juice was contaminated with toxic metals (lead and cadmium) and the zeolites were used to treat the contaminated samples. It was shown that the removal capacity of these zeolites increased with the increase in initial concentration of the metal. Time proved to be one factor that affected the behaviour of zeolites. The modification of the synthesised faujasite into an ultrastable Y zeolite proved to have played a role in increasing the removal of toxic metals and in preventing the high leaching of some elements out of the zeolite. / 2018-12-14

Les meilleurs oscillateurs dans le domaine micro-onde sont souvent des systèmes encombrants ou requérant une maintenance fastidieuse ce qui freine leur utilisation pour des applications mobiles ou dans des environnements aux conditions difficiles. L'avènement des peignes de fréquences optiques, récompensés par un prix Nobel en 2005, a ouvert de nouvelles perspectives en permettant un transfert des qualités inégalées des sources optiques vers le domaine micro-onde. Dans la technique utilisée au LNE-SYRTE, la division de fréquence optique, un signal micro-onde peut être extrait d'un laser ultra-stable dans l'infrarouge proche par photodétection, ce qui s'accompagne d'une réduction du bruit égale au carré du rapport des fréquences initiale et finale, soit plus de 8 ordres de grandeurs. Ce bénéfice est cependant réduit par différents processus collatéraux qui augmentent le niveau de bruit final. Le travail décrit dans cette thèse est la génération et la caractérisation du signal micro-onde le plus pur généré jusqu'à présent. Les différents processus introduisant un excès de bruit lors de la conversion opto-éléctronique sont étudiés et en partie surmontés. En particulier la conversion du bruit d'amplitude du laser femtoseconde vers la porteuse micro-onde est analysée en détail et son effet grandement réduit. Les résultats obtenus laissent penser que les techniques optiques de génération de micro-ondes vont bouleverser l'état de l'art. Les niveaux de pureté atteints et les techniques développées peuvent bénéficier un vaste éventail de domaines comme les radars mobiles, la métrologie temps-fréquence ou les prochaines générations de télécommunications à ultra-haut débit. / State-of-the-art microwave oscillators are typically bulky systems requiring tedious maintenance which is hindering their use in mobile applications or in demanding environments. The invention of the optical frequency combs, which was awarded a Nobel prize in 2005, was a game-changer as it enabled a high-fidelity transfer of the unrivalled properties of optical oscillators to the microwave domain. In the technique used at SYRTE, the optical frequency division, a microwave signal can be extracted from a near-infrared ultra-stable laser using photodetection. The transfer is accompanied by a reduction of phase noise equal to the microwave-to-optical frequency ratio squared, i.e. more than eight order of magnitudes. This benefit is however reduced by several processes producing excess noise during the transfer. The work described in this thesis is the generation of the lowest phase noise microwave signal ever reported. The different processes inducing excess noise are analyzed and, in part, overcome. Specifically, the conversion of the femtosecond laser intensity noise to the microwave phase noise is studied thoroughly and its effect significantly reduced. The results augur that the optical approaches in microwave generation are on the verge to disrupt the state-of-the-art. The noise levels demonstrated and the techniques developed can benefit a large range of applications such as mobile radars, time and frequency metrology or the next generation of ultrafast telecommunication networks.

Je présente le développement d'une expérience de production de gaz quantiques d'ytterbium. L'objectif est de réaliser des champs de jauge artificiels sur des gaz piégés dans des réseaux optiques. La combinaison de ces champs et des interactions entre atomes ouvre de nouvelles perspectives pour notre domaine comme la réalisation d'états analogues à ceux de la physique de l'effet Hall quantique fractionnaire.Tout d'abord, je présente les méthodes expérimentales développées pour produire un condensat de Bose-Einstein d'atomes (CBE) d'Yb174: un piège magnéto-optique sur la raie d'intercombinaison 1S0-3P1, son transfert dans un piège dipolaire et son transport sur une distance de 22 cm. Un condensat pur d'environ 6x10^4 est ensuite obtenu après évaporation dans un piège dipolaire croisé. Les protocoles envisagés pour réaliser des champs de jauge artificiels requièrent le couplage cohérent du niveau fondamental 1S0 et du niveau métastable 3P0 sur la transition "horloge". Nous avons construit un laser à 578nm asservi en fréquence sur une cavité de référence. En optimisant le point de fonctionnement en température de la cavité nous avons obtenu des dérives résiduelles en fréquence inférieures à 100 mHz/s. Nous avons réalisé une spectroscopie sur cette transition d'un CBE piégé ou en expansion et obtenu des largeurs de raies du l'ordre du kHz limitées par les interactions entre atomes.Enfin, je présente en détail les protocoles pour réaliser des champs de jauge artificiels dans des réseaux optiques et leur éventuelle mise en pratique et notamment un schéma pour réaliser un réseau optique bichromatique dépendant de l'état interne des atomes dans une cavité doublement résonante. / In this work I present the development of a new experiment to produce quantum degenerate gases of ytterbium. This project aims at realizing artificial gauge fields with ultracold atoms in optical lattices. Combining intense gauge fields with strong on-site interactions is expected to open a new area for ultracold quantum gases, where for instance the atomic analogs of fractional quantum Hall systems could be realized.First I describe the experimental methods for the production of a Bose-Einstein condensate (BEC) of 174Yb. This implies magneto-optical trapping on the 1S0-3P1 intercombination transition and a transport of the atomic cloud in an optical dipole trap over a distance of 22 cm. Evaporative cooling in a crossed dipole trap results in the production of pure BECs of about 6x10^4 atoms.The planned implementation of artificial gauge fields requires the coherent driving of the 1S0-3P0 clock transition of ytterbium. For this purpose an ultrastable laser system at 578 nm, frequency locked to an ultralow expansion (ULE) cavity, has been realized. A precise determination of the temperature zero-crossing point of the ULE cavity allowed us to limit laser frequency drifts below 100 mHz/s. Spectroscopic measurements of the clock transition on a trapped and free falling BEC are presented, where typical linewidths in the kHz range are observed, limited by interatomic interactions. Finally I present a detailed discussion of the methods to achieve artificial gauge fields in optical lattices and their possible experimental implementation. This includes a scheme to realize a bichromatic state-dependent optical superlattice in a doubly-resonant cavity.