Comprendre les propriétés des interfaces molécules/métaux est d’une importance capitale pour la spintronique organique. La première partie porte sur l’étude des propriétés magnétiques de molécules de phtalocyanine de manganèse. Nous avons montré que les premières couches moléculaires forment des colonnes avec un arrangement antiferromagnétique sur la surface de Co(100). Ces dernières mènent à de l’anisotropie d’échange. La seconde partie porte sur l’étude d’une molécule à transition de spin, la Fe(phen)2(NCS)2, sublimée sur différentes surfaces. Nous avons identifié les états de spin d’une molécule unique sur du Cu(100). De plus, nous avons commuté l’état de spin d’une molécule unique pourvu qu’elle soit suffisamment découplée du substrat. / Understanding the properties of molecules at the interface with metals is a fundamental issue for organic spintronics. The first part is devoted to the study of magnetic properties of planar manganese-phthalocyanine molecules and Co films. We evidenced that the first molecular layers form vertical columns with antiferromagnetic ordering on the Co(100) surface. In turn, these molecular columns lead to exchange bias. The second part is focused on the study of a spin-crossover complex, Fe(phen)2(NCS)2 sublimed on different metallic surfaces. We identified the two spin states of a single molecules on Cu(100). By applying voltages pulses, we switched the spin state of a single molecule provided that it is sufficiently decoupled from the substrate.

Thesis (PhD)--Stellenbosch University, 2013. / Bibliography / ENGLISH ABSTRACT: This study investigated a single research question, that is: How do teachers experience the implementation of the Further Education and Training (FET) National Curriculum Statement (NCS) for Physical Science? The focus of the study was on searching the inner consciousness of Physical Science teachers as they engaged with the teaching of the subject on a daily basis. It is in the inner consciousness where one finds the truth about people’s perceptions, beliefs, emotions, challenges and convictions about/towards phenomena that the study sought to determine. In so doing, this study searched for phenomenological truth about the daily realities Physical Science teachers are faced with, as they implement the NCS. Phenomenological truth is floatable, precarious in nature, and subject to an individual’s perception of truth. It is important to note that phenomenological truth makes no reference to absolute truth. At the time this study was conducted the NCS was the only policy document with legal status for schools in South Africa. As a result the NCS influences and directs the pedagogical practices of teachers. This is because the NCS has a specific expectation of Physical Science teachers with regards to their understanding of the content, the delivery of the content, the learning environment, and professionalism. Through searching the consciousness of teachers, they revealed how they experienced what they do in the Physical Science classroom. In other words, how they experience what, how, when and who they teach. Probing into the consciousness of teachers and how they experience the implementation of the NCS provides valuable insight into the quality of curriculum delivery. This study did not only focus on the implementation of the NCS, but also examined why it might be difficult for teachers to change their practices. Phenomenology is both a theory and a method. The study was guided by the ideas of Edmund Husserl - who is regarded by many phenomenologists as the father of phenomenology, Martin Heidegger, Maurice Merleau-Ponty, and many other phenomenologists. Husserl (cited in Derrida, 1967) believed that we should begin any explanation with experience, which is a scientific description that does not presuppose any significance of the existence of the metaphysical world. By delving into the complexities of experience one can locate the flowing life of an individual’s consciousness as it occurs. Husserl posited the belief returning to the things themselves (cited in, Derrida, 1967; Spanos, 1976; Groenewald, 2004) to describe the purity of experience as data. In this study I sampled three teachers and employed a phenomenological methodological framework to capture their lived experiences. I used one-on-one semi-structured face-to-face interviews to construct the data. In addition, field notes were used to turn the direct experiences and observations of the participants into vivid descriptions. In phenomenology researchers use field notes to make the voice of people heard in the text. I drew on Husserl, Heidegger and Merleau-Ponty’s philosophical pathways that a person must be understood from his position within a specific time and place to present the findings. The major finding in this study showed that the teachers’ consciousness, with respect to Physical Science teaching was negatively influenced by the legacy of apartheid-education. This negative consciousness through which they framed their thoughts and filtered their ideas became the collective mindset through which they personified their teaching. The study revealed that the delivery of the NCS (by the teachers) was mostly axiomatised by old habits and images in their thoughts engrained in their memory under apartheid education. The findings also showed that their (teachers’) consciousness with regards to the NCS unconsciously oscillated between the present and the past and that they continuously and unconsciously bring the past (old ideas and beliefs) into the present. The teachers constantly have to struggle against the phenomenological self or attitude and ceaselessly suppose and follow thoughts of pre-comprehension or preconception. / AFRIKAANSE OPSOMMING: Die doelwit van hierdie studie was om die volgende navorsingvraag te beantwoord: Hoe ervaar onderwysers die implementering van die Verdere Onderwys en Opleiding (VOO) Nasionale Kurrikulum Verklaring (NKV) vir Fisiese Wetenskap? Die hoofdoel was om meer insig te verkry oor wat binne onderwysers se psige plaasvind soos hulle op ‘n daaglikse basis hul uitleef in die Fisiese Wetenskapsklaskamer binne die raamwerk van die NKV. Dit is binne die psige waar hul persepsies, diepgewortelde waardes, emosies, en uitdagings rondom die NKV rus. Om hierdie rede is die studie geïntresseerd om die fenomenologiese waarheid van die alledaagse realiteite waarmee hulle aanhoudend gekonfronteer word, te myn. Fenominologiese waarheid is vloeibaar en verskil van persoon tot persoon en hou geen verwysing met absolute waarheid nie. Toe hierdie studie plaasgevind het, was die VOO NKV die enigste wettige beleidsdokument vir die deelnemers. Die onderwysers was dus verplig om die voorgeskrewe beginsels soos in die NKV saamgevat toe te pas in die voorbereiding en aanbieding van hul lesse. Die NKV beskryf in diepte die inhoud vir elke graad (10-12), hoe die inhoud aangebied moet word, die klaskamer atmosfeer, asook die professionalitiet van die opvoeders. Al die antwoorde soos saamgevat in laasgenoemde, lê bine die psige van die onderwysers. Die ondersoek van die psige van die onderwysers lei tot ‘n begrip van hoe, wat en waarom Fisiese Wetenskaps-onderswysers doen wat hulle doen. Alhoewel die fokus van hierdie studie op die implementering van die NKV is, dra dit ook by tot groeiende kennis aangaande hoekom onderwysers dit moeilik vind om hulle praktyke te verander wanneer dit kom by die hernuwing van ‘n kurrikulum. Fenomenologie is beide ‘n navorsingsmetode en ‘n teorie. Die literatuuroorsig van hierdie studie is geinspireer deur die idees van Edmund Husserl, wat bestempel word as die vader van fenomenolgie, asook Martin Heidegger, Maurice Merleau-Ponty, en veskeie ander fenomenoloë. Derrida (1967) is oortuig daarvan dat enige verduideliking akkuraat beskryf kan word indien geleefde ervaring in ag geneem word. Geleefde ervaring spreek direk tot die onderliggende psige van ‘n individu, en deur die psige te ondersoek, is dit moontlik om ‘n individu se oortuigings ten opsigte van sy/haar geloof, persepsies en uitdagings, asook hoe die individu reageer op hierdie aspekte te verstaan. Husserl gebruik die uitdrukking ‘returning to the things themselves’ wanneer hy verwys na die belangrikheid en oorspronlikheid van ervaring (vermeld in, Derrida, 1967; Spanos, 1976; Groenewald, 2004). Om hierdie rede is ‘n fenomenologiese metode gevolg om die lewenservaringe van drie swart onderwysers vas te vang. Hierdie fenomenologiese vertolkende ondersoek word deur veelvoudigemetodes van inligtingsinsameling gekenmerk. Inligting in hierdie studie oor die deelnemers se ervaringe is vekry deur middel van individuele onderhoude, en die ontleding van die inhoud daarvan. Addisionele inligting is verkry deur veldnotas. Die doelwit van die veldnotas was om die deelnemers se direkte ervaringe en waarnemings in besonderhede te beskryf. Die ontledingsbenadering van elke deelnemer is gedoen binne die raamwerk van Husserl, Heidegger en Merleau-Ponty wat gegrond is op teorieë wat die belangrikheid van plek en tyd uitbeeld. Die resultate van hierdie studie het getoon dat die onderliggende psige van elke deelnemer deur die nalatenskap van apartheid negatief beïnvloed is. Hierdie negatiewe denkpatrone waardeur die onderwysers se idees formuleer vorm die kollektiewe ingesteldheid waardeur hulle hul onderrigswêreld skep. Verder het die studie onthul dat hul aanbieding van die NKV meestal gedryf word deur ou gewoontes wat binne hul denke gekristalliseer het. Hulle vind dit dus moeilik om deur hierdie ou gewoontes te breek. Hul denke wissel gedurig tussen die verlede en die hede en roep die verlede voortdurend binne die hede. Alhoewel die bevindinge van hierdie studie gekoppel is aan plek en tyd is daar ‘n konstante struweling tussen die fenomenologiese self en hul ou gesette denke.

Ces dernières années, les nanocristaux (NCs) semi-conducteurs ont reçu un intérêt grandissant pour deux raisons principalement. D'une part, ces objets possèdent des tailles qui se situent entre celles des molécules et des matériaux cristallins. Leur étude d'un point de vue fondamental est par conséquent utile pour mieux comprendre les propriétés de la matière condensée en fonction de la dimension des objets étudiés . En particulier, les NCs de chalcogénures de plomb possèdent une constante diélectrique élevée (ε∞=23 pour PbSe) et des porteurs de charges ayant des faibles masses effectives, conduisant à la formation d'excitons avec un large rayon de Bohr effectif. De ce fait, ce sont des objets de choix pour étudier le régime de fort confinement quantique. D'autre part, la miniaturisation des composants électroniques nécessite l'utilisation d'objets semi-conducteurs aux dimensions de plus en plus petites, avec des coûts de fabrication les plus bas possibles. Les NCS semi-conducteurs, dont les synthèses chimiques sont généralement simples, répondent à cet enjeu et un certain nombre d'applications tirent avantage de leurs propriétés optiques. Dans la première partie de cette thèse, la méthode de synthèse des NCs de PbSe est décrite. Grâce à l'utilisation de plusieurs techniques de caractérisation (microscopies électroniques, diffraction des rayons X (XRD), diffraction électronique (SAED)), l'optimisation de cette méthode a conduit à l'obtention de NCs monodisperses en taille et possédant une structure cristalline parfaite. Dans un second temps, des études plus fines en spectroscopie Raman ont confirmé la qualité structurale des NCs. Elles ont aussi permis d'étudier les effets de confinement sur le spectre des phonons optiques longitudinaux. Enfin, les NCs de PbSe se détériorant rapidement à l'air, des structures coeur coquille ont été élaborées pour réaliser de l'ingénierie de bande dans des NCs à hétérostructures. En utilisant le rayonnement synchrotron et après avoir développé des techniques de dépôt de films ultra minces de NCs coeur-coquille PbSe/CdSe, la discontinuité de la bande de valence de ces structures a été étudiée par spectroscopie de photoélectrons.

We have studied by STM, SQUID, X-ray reflectivity, X-ray diffraction, optical absorption and XAS Fe(phen)2(NCS)2 and Fe{[3,5-dimethylpyrazolyl]3BH}2 samples deposited by thermal evaporation on Cu(100), Co(100) and SiO2 substrates, and compared with results on powder samples. We have confirmed the existence of the soft X-ray induced excited spin state trapping (SOXIESST), and investigated its properties, in particular dynamic aspects. The effect is sensitive to the intensity and the structure of the applied X-ray beam, and is non-resonant. We suggest that its efficiency is also governed by metal-ligand charge transfer states (MLCT). The study of single molecules has revealed that they could be switched by voltage pulses, and by this way building memristive devices, but only if the influence of the substrate is sufficiently reduced. We have then investigated thin films with the help from a simple thermodynamic model, and evidenced that the cooperativity was reduced and the transition temperature is modified (higher for Fe-phen, and lower for Fe-pyrz). Finally, we use these results to build multilayer vertical devices Au/Fe-phen/Au, and its electrical properties depends, according to our preliminary results, on the external stimuli (temperature, magnetic field). Notably, they present a "diode" effect at the spin transition.

>Magister Scientiae - MSc / In this study PbSe quantum dots (QDs) were successfully synthesized via the organometallic and aqueous routes. Optical characterization was carried out using photoluminescence (PL) spectroscopy, structural and morphological characterization were carried out using X-ray diffraction (XRD) and transmission electron microscopy (TEM). Energy-dispersive X-ray spectroscopy (EDS) was used to determine the composition of the QDs. All the synthesized QDs were found to have emissions within the near-infrared region of the spectrum (≥1000 nm) with most of them being less than 5 nm in size. The aqueous synthesized QDs had a perfect Gaussian emission spectrum with a FWHM of ~23 nm indicating pure band gap emission and narrow size distribution respectively. The QDs were determined to have a cubic rock-salt crystal structure consistent with bulk PbSe. The aqueous synthesized QDs were however not stable in solution with the QDs precipitating after approximately 48 h. The organometallic synthesized QDs were transferred into the aqueous phase by exchanging the surface oleic acid ligands with 11-mercaptoundecanoic acid ligands. The ligand exchanged QDs were however stable in solution for over two weeks. The effects of reaction parameters on the optical and structural properties of the organometallic synthesized QDs were investigated by varying the reaction time, temperature, ligand purity, lead and selenium sources. It was observed that larger QDs were formed with longer reaction times, with reactions proceeding faster at higher reaction temperatures than at lower temperatures. Varying the ligand purity was found to have minimal effects on the properties of the synthesized QDs. The lead and selenium sources contributed largely to the properties of the QDs with lead oxide producing spherical QDs which were smaller compared to the cubic QDs produced from lead acetate. TBPSe was seen to produce smaller QDs as compared to TOPSe. The cytotoxity of the synthesized QDs was determined following the WST-1 cell viability assay with the QDs being found to be non-toxic at all the tested concentrations

Tesis por compendio / [ES] Con esta tesis se pretende dar solución a algunos de los problemas más habituales que aparecen en los Sistemas de control basados en red (NCS) como son los retardos variables en el tiempo, las pérdidas y el desorden de paquetes, y la restricción de ancho de banda y de recursos computacionales y energéticos de los dispositivos que forman parte del sistema de control. Para ello se ha planteado la integración de técnicas de control multifrecuencial, de control basado en paquetes, de control basado en predictor y de control basado en eventos. Los diseños de control realizados se han simulado utilizando Matlab-Simulink y Truetime, se ha analizado su estabilidad mediante LMIs y QFT, y se han validado experimentalmente en un péndulo invertido, un robot cartesiano 3D y en robots móviles de bajo coste. El artículo 1 aborda el control basado en eventos, el cual minimiza el ancho de banda consumido en el NCS mediante un control basado en eventos periódicos y presenta un método para obtener sus parámetros óptimos para el sistema específico en que se utilice. Los artículos 2, 4 y 6 añaden el control basado en paquetes, así como el control multifrecuencia, que aborda problemas de falta de datos por bajo uso del sensor y los retardos, pérdidas y desórdenes de paquetes en la red. También afrontan, mediante tecnicas de predicción basadas en un filtro de Kalman multifrecuencia variable en el tiempo, los problemas de ruido y perturbaciones, así como la observación de los estados completos del sistema. El artículo 7 hace frente a un modelo no lineal que utiliza las anteriores soluciones junto con un filtro de Kalman extendido para presentar otro tipo de estructura para un vehículo autónomo que, gracias a la información futura obtenida mediante estas técnicas, puede realizar de forma remota tareas de alto nivel como es la toma de decisiones y la monitorización de variables. Los artículos 3 y 5, presentan una forma de obtener y analizar la respuesta en frecuencia de sistemas SISO multifrecuencia y estudian su comportamiento ante ciertas incertidumbres o problemas en la red haciendo uso de procedimientos QFT. / [CA] Amb aquesta tesi es pretén donar solució a alguns dels problemes més habituals que apareixen als Sistemes de Control Basats en xarxa (NCS) com son els retards d'accés i transferència variables en el temps, les pèrdues y desordenament de paquets, i la restricció d'ampli de banda així com de recursos computacionals i energètics dels dispositius que foment part del sistema de control. Per tal de resoldre'ls s'ha plantejat la integració de tècniques de control multifreqüencial, de control basat en paquets, de control basat en predictor i de control basat en events. Els dissenys de control realitzats s'han simulat fent ús de Matlab-Simulink i de TrueTime, s'ha analitzat la seua estabilitat mitjançant LMIs i QFT, i s'han validat experimentalment en un pèndul invertit, un robot cartesià 3D i en robots mòbils de baix cost. L'article 1 aborda el control basat en events, el qual minimitza l'ampli de banda consumit a l'NCS mitjançant un control basat en events periòdics i presenta un mètode per a obtindré els seus paràmetres òptims per al sistema específic en el qual s'utilitza. Els articles 2, 4 i 6 afegeixen el control basat en paquets, així com el control multifreqüència, que aborda problemes de falta de dades per el baix us del sensor i els retards, pèrdues i desordre de paquets en la xarxa. També afronten, mitjançant tècniques de predicció basades en un filtre de Kalman multifreqüència variable en el temps. Els problemes de soroll i pertorbacions, així com la observació dels estats complets del sistema. L'article 7 fa referència a un model no lineal que utilitza les anteriors solucions junt a un filtre de Kalman estès per a presentar altre tipus d'estructura per a un vehicle autònom que, gracies a la informació futura obtinguda mitjançant aquestes tècniques, pot realitzar de manera remota tasques d'alt nivell com son la presa de decisions i la monitorització de variables. Els articles 3 y 5 presenten la manera d'obtindre i analitzar la resposta en frequencia de sistemes SISO multifreqüència i estudien el seu comportament front a certes incerteses o problemes en la xarxa fent us de procediments QFT. / [EN] This thesis attempts to solve some of the most frequent issues that appear in Networked Control Systems (NCS), such as time-varying delays, packet losses and packet disorders and the bandwidth limitation. Other frequent problems are scarce computational and energy resources of the local system devices. Thus, it is proposed to integrate multirate control, packet-based control, predictor-based control and event-based control techniques. The control designs have been simulated using Matlab-Simulink and Truetime, the stability has been analysed by LMIs and QFT, and the experimental validation has been done on an inverted pendulum, a 3D cartesian robot and in low-cost mobile robots. Paper 1 addresses event-based control, which minimizes the bandwidth consumed in NCS through a periodic event-triggered control and presents a method to obtain the optimal parameters for the specific system used. Papers 2, 4 and 6 include packet-based control and multirate control, addressing problems such as network delays, packet dropouts and packet disorders, and the scarce data due to low sensor usage in order to save battery in sensing tasks and transmissions of the sensed data. Also addressed, is how despite the existence of measurement noise and disturbances, time-varying dual-rate Kalman filter based prediction techniques observe the complete state of the system. Paper 7 tackles a non-linear model that uses all the previous solutions together with an extended Kalman filter to present another type of structure for an autonomous vehicle that, due to future information obtained through these techniques, can remotely carry out high level tasks, such as decision making and monitoring of variables. Papers 3 and 5, present a method for obtaining and analyzing the SISO dual-rate frequency response and using QFT procedures to study its behavior when faced with specific uncertainties or network problems. / This work was supported by the Spanish Ministerio de Economía y Competitividad under Grant referenced TEC2012-31506. / Alcaina Acosta, JJ. (2020). Design and implementation of event-based multi-rate controllers for networked control systems [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/159884 / TESIS / Compendio

A critical evaluation of the National Curriculum Statement (NCS) was undertaken to uncover strategies for infusing values across the curricula – values that may facilitate the development of spiritual intelligence (SQ) in adolescents. A literature study was conducted to determine whether SQ may be harnessed to cultivate values within an educational context. In addition, moral and spiritual development in adolescence was explored and a case made for values-education. An empirical investigation was undertaken using both a qualitative research design and semi-structured interviews. A purposive sample was used comprising 14 education specialists, principals and Life Orientation teachers from six secondary schools in Gauteng and Mpumalanga provinces. The most important finding was the fact that values-education in the NCS was problematic. The conclusion was thus drawn that teachers should be trained to incorporate values within curriculum activities − values that could engender SQ and, thus, address the moral dilemmas in our schools. / Psychology of Education / M. Ed. (Psychology of Education)

The paradigm shift in teaching from the teacher-centred approach to the learner-centred approach in recent years has impacted on the way teachers go about their duties in the classroom. This paradigm shift necessitated this research with the aim of investigating how the Student Teams Achievement Division (STAD) technique can be used as a cooperative learning technique to teach EFAL in Kwazulu-Natal. The purpose of this study was to design a framework for the implementation of STAD as a cooperative teaching strategy for EFAL teachers by gleaning literature on teaching and learning, cooperative learning and STAD in chapters two to four of this study. Empirical research, by way of a survey and focus group discussions were also conducted in four out of the twelve districts in the Kwazulu-Natal Province to help solidify the framework designed in this study. In striving to get in-depth insight into this study, the post-positivist-constructivist paradigm, which calls for the mixed methods research design was employed for the collection and analysis of data. Specifically, the Likert scale survey questionnaire and focus group discussions were used to collect data, through the sequential mixed methods design for the quantitative and qualitative phases of this study respectively, from a sample of 220 respondents and twelve participants. The findings of this research indicated that the time spent in training teachers towards the implementation of the STAD technique was not adequate. That notwithstanding, it was indicative that teachers make efforts to implement the strategy in their teaching and the results proved to be very positive as the technique continues to help improve upon learners’ performances and builds in them qualities such as critical thinking skills, good discussion skills and positive collaborative learning. In the nutshell, the literature study, the findings of the empirical research and the recommendation of this study forms the basis for designing the framework for the implementation of STAD as a teaching strategy for EFAL teachers. / Curriculum and Instructional Studies / D. Ed. (Curriculum Studies)

The study focuses on challenges in the development of learner-centred and process-oriented teaching and learning in the learning areas, natural science (NS) and mathematics in South African schools. The aim of NS is to develop scientifically literate learners. The three Learning Outcomes (LOs) and the accompanying Assessment Standards (ASs) should enable learners to understand the science products or system of ideas such as underlying theories and principles. The LOs point out the learner’s abilities to use the sciences products or system of ideas. Educators encounter challenges in the application of the LOs and ASs in teaching and learning activities. Against this background, a mixed method study was conducted in selected schools in the Tshwane South District in Gauteng. Data were gathered by document analysis, focus groups and a questionnaire to gauge how the educators are applying the LOs and ASs. Findings indicated that lessons plans were inadequate and educators were not familiar with curriculum documents. / Science and Technology Education / M. Ed. (Natural Sciences Education)

Networked control over wireless networks is of growing importance in many application domains such as industrial control, building automation and transportation systems. Wide deployment however, requires systematic design tools to enable efficient resource usage while guaranteeing close-loop control performance. The control system may be greatly affected by the inherent imperfections and limitations of the wireless medium and malfunction of system components. In this thesis, we make five important contributions that address these issues.  In the first contribution, we consider event- and self-triggered control and investigate how to efficiently tune and execute these paradigms for appropriate control performance. Communication strategies for aperiodic control are devised, where we jointly address the selection of medium-access control and scheduling policies. Experimental results show that the best trade-off is obtained by a hybrid scheme, combining event- and self-triggered control together with contention-based and contention-free medium access control. The second contribution proposes an event-based method to select between fast and slow periodic sampling rates. The approach is based on linear quadratic control and the event condition is a quadratic function of the system state. Numerical and experimental results show that this hybrid controller is able to reduce the average sampling rate in comparison to a traditional periodic controller, while achieving the same closed-loop control performance. In the third contribution, we develop compensation methods for out-of-order communications and time-varying delays using a game-theoretic minimax control framework. We devise a linear temporal coding strategy where the sensor combines the current and previous measurements into a single packet to be transmitted. An experimental evaluation is performed in a multi-hop networked control scenario with a routing layer vulnerability exploited by a malicious application. The experimental and numerical results show the advantages of the proposed compensation schemes. The fourth contribution proposes a distributed reconfiguration method for sensor and actuator networks. We consider systems where sensors and actuators cooperate to recover from faults. Reconfiguration is performed to achieve model-matching, while minimizing the steady-state estimation error covariance and a linear quadratic control cost. The reconfiguration scheme is implemented in a room heating testbed, and experimental results demonstrate the method's ability to automatically reconfigure the faulty system in a distributed and fast manner. The final contribution is a co-simulator, which combines the control system simulator Simulink with the wireless network simulator COOJA. The co-simulator integrates physical plant dynamics with realistic wireless network models and the actual embedded software running on the networked devices. Hence, it allows for the validation of the complete wireless networked control system, including the study of the interactions between software and hardware components. / <p>QC 20140929</p>