The thesis includes two aspects. The first part includes designs and optical study of electro-absorption modulator structures. Three structures are designed near 1.5

A study of the stability of bicontinuous nanoporous metals is presented. Atomic scale simulations are used to probe the dominant mechanisms of geometric relaxation in these materials. A method is presented for generating model bicontinuous metal / void structures for use in atomistic simulations of bicontinuous nanoporous solids. The structures are generated with periodic boundary conditions using a phase-field model to simulate the spinodal decomposition of an ideal system. One phase in the model is then associated with the pore volume while the other phase is associated with the metal ligaments. Small angle neutron scattering was used to quantitatively compare experimental samples to those generated by the phase field method. EAM results using model structures with experimentally accessible length scales are presented which demonstrate the potential of such simulations in understanding the behavior of nanoporous metals. Simulated relaxations of these structures, as well as the relaxation of model spherical clusters, indicate that the surface relaxation effect dominates the overall dimensional relaxation of np-metals post processing. Capillary effects play a secondary role in the overall relaxation. The simulation results presented also identify a maximum surface area to volume ratio necessary to maintain mechanical stability beyond which the pore structure collapses. / Ph. D.

L'objectif de la thèse est d'identifier et de quantifier les paramètres régissant l'épaississement des macles dans trois métaux hexagonaux (Zr, Ti, Mg). Le mécanisme que nous étudions est le glissement de dislocations d'interfaces, i.e. les disconnections, le long des joints de macles parfaits. Nous nous intéressons alors à la germination des disconnections avant de nous concentrer sur leur migration.Une première étude en potentiel empirique permet de valider un couplage original avec la théorieélastique afin d'extraire des simulations atomiques l'énergie de cœur des disconnections. Cette méthode permet de partitionner l'énergie entre une contribution de cœur, intrinsèque à la disconnection et une partie élastique qui dépend de l'environnement de la disconnection. Cette partition faite, nous modélisons alors l'énergie de formation de dipôles de disconnections isolés, pour chacun des différents joints de macles. Cette modélisation nous permet alors de sélectionner les dipôles de disconnections les plus pertinents que nous étudions par la méthode abinitio.Nous modélisons ensuite la migration des disconnections le long des joints de macles parfaits.Pour cela, nous montrons via l'utilisation de la méthode Nudged Elastic Band, que l'énergie demigration est d'un ordre de grandeur inférieur à l'énergie de formation. Ainsi, l'énergie de formation des dipôles de disconnections apparait comme prédominant dans la croissance des macles / The aim of this thesis is to identify and quantify the parameters of importance when dealing with twin thickening in three hcp metals (Zr, Ti, Mg). The mechanism we study is the glide of twinning dislocations, i. e. the disconnection, along the perfect twin boundaries. We first focus on the nucleation of disconnection before addressing their migration. A study using an EAM potential allows us to validate an original coupling between our atomistic simulations and linear elasticity in order to extract the core energy of disconnection.We then show how this coupling permits to divide the formation energy in two terms: the core contribution, intrinsec to the disconnections, and an elastic one, which depends on the disconnection's environment. Thanks to this partition, we model the formation of isolated disconnection that may appear along the different twin planes. We select the dipoles of lowest formation energies in order to perform ab initio calculations and compare the behavior observed the three different metals. We then model the migration of disconnections along the perfect twin planes. To do so, we use the Nudged Elastic Band method, and find out that the migration energy of disconnections is one order of magnitude lower than their formation energies. We therefor conclude that the disconnection nucleation is the rate limiting factor to explain twin thickening thanks to the creation and motion of disconnection

Les réseaux d’accès sont particulièrement concernés par les montées en débit dans un contexte exigeant et compétitif. En 2013, les verrous technologiques autour des cavités auto-alimentées limitaient leur expansion. Notre propos fut de les aborder selon une approche “composant”. A partir de caractérisations croisées entre des RSOA variés et de simulations, nous avons montré: - l’importance du seuil du RSOA sur les performances globales ; - les rôles de l’émission spontanée, de la densité de porteurs, des recombinaisons Auger et de la hauteur des barrières ; - la sensibilité des RSOA fort gain au ripple. Livrés à nos partenaires, les RSOA bande O menèrent à des résultats à l’état de l’art tandis que les RSOA aluminium ne tinrent les promesses espérées. Nous cherchâmes alors à trouver des solutions alternatives. Comparativement au RSOA, Fabry-Pérot comme EAM-RSOA limitent le chirp et sont de plus grande bande passante. Toutefois, intégrés en cavité, ils ne dépassèrent pas les 2,5 Gbit/s pour un BER restreint. Pourtant, pris séparément, RSOA et EAM autorisent des débits jusqu’à 20 Gbit/s. Nous pensons qu’en remplaçant le tronçon de fibre par de l’optique en espace libre confirmerait le potentiel de ce concept / Today, access networks have to face higher data bit rates with strong constraints and competitors. In 2013, self-seeded cavities were limited by some issues that we have tried to solve from a component point of view. Thanks to experimental observations on various RSOA and thanks to simulations, we have shown: - the impact of RSOA threshold on the global performances, - the influence of the spontaneous emission, of the carrier density, of Auger recombination as well as the barrier bandgap, - how high gain RSOA were sensitive to ripple. Delivered to our partners, O band RSOA led to state-of-the-art results whereas aluminum RSOA were disappointing. We looked for short/mid-terms solutions. Compared to RSOA, both of the Fabry-Perot and the RSOA-EAM reduce the chirp and display an enhanced bandwidth. Yet, integrated in the cavity, they were limited at 2.5 Gbit/s with a high BER. Nonetheless each of the EAM and the RSOA could support up to 20 Gbit/s. We believe we could prove such data bitrates by replacing the feeder fiber between the two components by a free space link

Les télécommunications par satellite prennent aujourd’hui de en plus d’importance, et le nombre d’abonnés à travers le monde ne cesse de croître. Partout où la fibre optique ne peut être déployée, elles sont un moyen fiable de fournir des débits très élevés aux utilisateurs, dont les pratiques nécessitent des bandes passantes toujours plus importantes (vidéo HD, visioconférences, téléchargement, cloud computing, jeux en ligne...). Elles garantissent également de très vastes zones de couverture. Pour les concepteurs de charges utiles de satellite, suivre les besoins du marché revient à augmenter constamment le nombre d’équipements embarqués, ce qui affecte le volume et la masse des systèmes et donc le coût de mise en orbite. Une des solutions envisagées afin de contrer ce phénomène consiste à employer des technologies optiques. Il a été démontré par Thales Alenia Space que pour un système de distribution de signaux de référence de 1 vers 64 équipements, la réduction du poids pourrait être de 70 %. Dans ce contexte nous avons développé 7 convertisseurs de fréquence RF réalisés à partir de composants photoniques semi-conducteurs. Ces convertisseurs font partie des composants clés des charges utiles car ils permettent d’isoler les transmissions montantes (vol vers satellite) et descendantes (satellite vers sol) afin d’éviter les interférences. Les performances des 7 architectures proposées, réalisées à partir de modulateurs électro-absorbants (EAM) et d’amplificateurs optiques à semi-conducteurs (SOA) ont été évaluées au travers de différentes simulations et en calculant le gain de conversion, le facteur de bruit, les isolations RF/FI et OL/FI, les rapports C/I3 et les coordonnées du point d’interception d’ordre 3. Nous avons obtenu des performances intéressantes, premières données pour de futures études et montré que ces convertisseurs seraient compatibles avec de nombreux plans de fréquence en bandes Ku/Ku, Ku+/Ku, et Ka/Ka. Des manipulations ont également permis de valider les modèles théoriques employés dans les simulations. / Nowadays, Satellite telecommunications are becoming very popular and the number of subscribers worldwide is always growing. Wherever the optical fiber cannot be deployed, they are a reliable way to provide very high data rates to the users, whose activities are becoming more and more bandwidth-hungry (HD video, video conferencing, downloading, cloud computing, online games ...). They also guarantee very large coverage areas. In order to follow the market needs satellite payload designers have to increase the number of on-board equipment, which affects the volume and mass of the systems and therefore the launching cost. One of the solutions to solve the problem consists in using optical technologies. It has been demonstrated by Thales Alenia Space that In the case of a reference signal distribution system for 64 devices, a weight reduction of about 70% could be obtained. In this context we have developed 7 RF frequencydown-converters based on photonic semiconductor components. The down-converters are key components of satellite payloads, as their aim is to isolate uplink transmissions (ground to satellite) and downlink (satellite to ground) to avoid interference. Performance of the 7 architectures, incorporating electro-absorption modulators (EAM) and semiconductor optical amplifiers (SOA) were evaluated through various simulations and by calculating the conversion gain, noise figure, RF/IF and LO/IF isolations, the C/I3 ratio and the coordinates of the third order intercept point. We obtained interesting results, first data for futur works,and showed that these converters are compatible with many frequency plans in Ku/Ku, ku+/Ku, and Ka/Ka bands. Manipulations were also led and validated the theoretical models used in simulations.

No description available.

Challenges continue to exist in developing a comprehensive theory of diffusion in liquid metals, despite the advancement of several semi-empirical and theoretical models. One major difficulty in developing a theory is that experimental data are not available for many pure metals and binary metal systems, and when they do exist, data are often inaccurate. In addition to challenges with data quality, where deemed reliable, existing data are typically reported over limited temperature and concentration intervals. In this thesis research, interdiffusion data was obtained for the binary Al-Cu system using the solid wire long capillary technique (SWLC), and molecular dynamics (MD) simulation with a concentration-dependent embedded atom method (CD-EAM) interatomic potential. In the SWLC experiments the interdiffusion coefficient was determined at temperatures of 993 K, 1023 K, 1073 K, 1123 K, and 1193 K, over an Al-rich concentration range limited by the liquidus of the binary phase diagram at the given temperature. For liquid Al~100Cu~0 (tracer), Al80Cu20, and Al60Cu40, the interdiffusion coefficient is well described by the Arrhenius relationship D_AlCu=D_0*exp(-Q_0/RT) over the temperature range, with best fit parameter values of Q_0 = 20.85 ± 4.49 kJ/mol, D_0 = 8.21 (+5.4, -3.26) x 10^-8 m^2/s, Q_0 = 34.41 ± 3.71 kJ/mol, D_0 = 2.84 (+1.47, -0.97) x 10^-7 m^2/s, Q_0 = 38.74 ± 8.01 kJ/mol, D_0 = 4.03 (+5.89, -2.39) x 10^-7 m^2/s, respectively. For the MD simulations, a new Al-Cu CD-EAM interatomic potential was developed that is suitable for the study of diffusion phenomena in the liquid state. Self- and interdiffusion coefficients were determined over a temperature interval of 993-1493 K. Simulations are performed for liquid Al99.999Cu0.001 (tracer), Al80Cu20, and Al60Cu40, and interdiffusion is described by Q_0 = 22.81 ± 0.27 kJ/mol, D_0 = 1.04 (+0.03, -0.03) x 10^-7 m^2/s Q_0 = 30.15 ± 0.49 kJ/mol, D_0 = 1.78 (+0.08, -0.08) x 10^-7 m^2/s, Q_0 = 37.01 ± 1.48 kJ/mol, D_0 = 3.29 (+0.52, -0.45) x 10^-7 m^2/s, respectively. The calculated values of the interdiffusion coefficients from the MD simulation are in good agreement with those obtained using the SWLC technique, supporting the accuracy of these new experimental findings. / February 2017

Due to dramatic growth of capacity in optical fiber communication, the fiber dispersion has become one of major factors affecting the quality of optical signal transmission with different modulation scheme, leading to the importance in controlling optical chirp. Among the elements used for optical fiber communications, electroabsorption modulator (EAM) and semiconductor optical amplifier (SOA) are served as optical amplitude and phase modulation. In this work, EAM-integrated SOA is used to realize the pre-chirp technique through their inherently reversed phase modulation as well as amplitude modulation. In the experiment, tunable optical filter and a 10Gb/s data pattern are used for extracting the frequency chirp of the timely signal. With the positive chirp operation in EAM, it is found that the overall chirp of EAM-integrated SOA can be varied from 3GHz to -9GHz by adjusting current injection through SOA. Also, as inspecting the 10Gb/s pattern, the pattern effect can also be controlled by the reversed carrier dynamics between EAM and SOA. Finally, a 10Gb/s data transmission with 43km transmission is demonstrated by using such pre-chirp technique, showing that such technique can be applied to other type signal processing.

Submitted by Automa??o e Estat?stica (sst@bczm.ufrn.br) on 2016-03-09T23:56:23Z No. of bitstreams: 1 ClaudiaRobertoSoaresDeMacedo_DISSERT.pdf: 2359435 bytes, checksum: 05dc5297f30a0b6bd4e777dd82d7949d (MD5) / Approved for entry into archive by Arlan Eloi Leite Silva (eloihistoriador@yahoo.com.br) on 2016-03-14T23:35:11Z (GMT) No. of bitstreams: 1 ClaudiaRobertoSoaresDeMacedo_DISSERT.pdf: 2359435 bytes, checksum: 05dc5297f30a0b6bd4e777dd82d7949d (MD5) / Made available in DSpace on 2016-03-14T23:35:11Z (GMT). No. of bitstreams: 1 ClaudiaRobertoSoaresDeMacedo_DISSERT.pdf: 2359435 bytes, checksum: 05dc5297f30a0b6bd4e777dd82d7949d (MD5) Previous issue date: 2015-04-13 / A presen?a de alunos com Transtorno do Espectro Autista (TEA) na escola comum tem aumentado e, com ela, a necessidade de desenvolver estrat?gias interventivas que favore?am sua aprendizagem. Uma das ferramentas que pode viabilizar esse processo ? a Aprendizagem Mediada, compreendida como um estilo de intera??o onde o professor seleciona, modifica, amplia e/ou interpreta os est?mulos ambientais de forma a favorecer a aprendizagem do educando. Nos ?ltimos anos diversos estudos t?m utilizado a Escala de Experi?ncia de Aprendizagem Mediada (EAM; Lidz, 1991) como instrumento para avaliar o comportamento mediador. Essas pesquisas t?m sugerido que a Escala EAM pode fornecer diretrizes importantes para o planejamento de interven??es educacionais, particularmente daquelas que envolvem educandos com necessidades educacionais especiais. Com o objetivo de ampliar esses achados, o presente estudo visou avaliar os efeitos de uma proposta de interven??o baseada na Experi?ncia de Aprendizagem Mediada no desempenho social/acad?mico de uma crian?a com TEA, inserida no 4? ano do ensino fundamental. O estudo, de cunho colaborativo, foi realizado na cidade de Parnamirim, estado do Rio Grande do Norte, no decorrer do ano letivo 2014. Participaram da investiga??o um estudante, de nove anos, com TEA e sua professora titular. A pesquisa utilizou delineamento quase experimental intrassujeito do tipo A-B (linha de base e tratamento) para avaliar o comportamento da docente. Adicionalmente foram empregados procedimentos qualitativos para analisar as respostas da d?ade. Na fase de linha de base, foram observadas tr?s rotinas escolares do educando, com foco nas pr?ticas pedag?gicas e comportamentos mediadores da professora. Com base nos resultados dessa fase, foi delineado um programa de capacita??o com a docente. O comportamento da d?ade, nas tr?s rotinas, foi novamente analisado ap?s a capacita??o. Os resultados dessa fase apontaram mudan?as qualitativas e quantitativas nos n?veis de media??o da professora. Adicionalmente, foram observadas mudan?as no comportamento social do educando, como tamb?m avan?os acad?micos. / The presence of students with Autism Spectrum Disorder (ASD) in regular schools has increased and with it, the need to develop interventional strategies that enhance their learning. One of the tools that can facilitate this process is Mediated Learning, defined as an interaction style where the teacher selects, modifies, enhances, and interprets environmental stimuli in order to promote student learning. In recent years several studies have used the Mediated Learning Experience Scale (MLE; Lidz, 1991) as a tool to assess the mediator behavior. These studies have suggested that the EAM Scale can provide important guidelines for planning educational interventions, particularly those involving students with special needs. In order to extend these findings, this study aimed to evaluate the effects of an intervention based on the Mediated Learning Experience on social / academic skills of a child with ASD, enrolled in the 4th grade of a regular elementary school. This collaborative study was held in the city of Parnamirim, state of Rio Grande do Norte, in 2014. A 9-year old boy with ASD and his teacher participated in the study. The research used a quasi-experimental A-B design (baseline and treatment) to evaluate the teacher's behavior. Qualitative procedures were also used to analyze the dyad?s responses. Teacher and student behaviors were observed in three school routines during baseline. Based on the results of this phase, a training program was designed for the teacher. Dyad behavior was analyzed again after training in the same routines. The results of this phase showed qualitative and quantitative changes in levels of teacher mediation. Additionally, data indicated that the child enhanced his social and academic skills during the intervention.

Dünnfilmabscheidung wird häufig mit physikalischer Gasphasenabscheidung durchgeführt, wobei in letzter Zeit vermehrt höhere Teilchenenergien zur Steuerung des Wachstums eingesetzt werden. Dieser Abscheideprozess kann durch Multiskalensimulation optimiert werden, wofür die Oberflächeninteraktionen von Kupferteilchen bis 800 eV benötigt werden. Die Interaktionen sind jedoch bisher nur für geringe Teilchenenergien unterhalb von 300 eV bekannt. Die vorliegende Arbeit schließt diese Lücke, indem mit Molekulardynamik-Methoden (MD) die Oberflächeninteraktionen von Kupferteilchen bis 800 eV simuliert werden. Die dabei erhaltenen Ergebnisse zeigen eine deutliche Verbesserung der Genauigkeit und Zuverlässigkeit im Vergleich mit der Literatur, sowie im Vergleich mit Ergebnissen aus der zur Simulation der Wechselwirkung von hochenergetischen Ionen mit Materie etablierten Simulationsmethode TRIM. Es wird auch die Abhängigkeit der Oberflächeninteraktionen und der Verteilungen der gesputterten Teilchen von der Netzebene gezeigt. Außerdem konnten erstmals Ergebnisse für den für das Substratsputtern hochenergetischen Bereich von 300 eV bis 800 eV gewonnen werden. Diese stehen nun für die Simulation des Abscheideprozesses zur Verfügung.:Inhaltsverzeichnis Abbildungsverzeichnis Abkürzungsverzeichnis Symbolverzeichnis 1 Einführung 2 Grundlagen 2.1 Oberflächeninteraktionen 2.1.1 Sorption 2.1.2 Reflexion 2.1.3 Sputtern 2.2 Physikalische Grundlagen 2.2.1 Klassische Betrachtungsweise 2.2.2 Newtonsche Axiome 2.2.3 Statistische Physik 2.2.4 Festkörperphysik 2.3 Binary Collision Approximation 2.3.1 Grundlagen 2.3.2 TRIM 2.3.3 Erweiterungen von TRIM 2.3.4 Grenzen 2.4 Molekulardynamik 2.4.1 Allgemeines 2.4.2 Kraftfelder 2.4.3 Integrationsalgorithmen 2.4.4 Thermostate 2.4.5 Randbedingungen 2.4.6 LAMMPS 2.5 Materialsystem und Stand der Forschung 2.5.1 Materialsystem 2.5.2 Stand der Forschung 3. Methoden und Modelle 3.1 Modellsystem für die MD-Simulation 3.1.1 Aufbau des Modellsystems 3.1.2 Festzulegende Systemparameter 3.1.3 Projektilparameter 3.2 Ablauf der Simulation 3.2.1 Erstellen des Substrates 3.2.2 Weg des Projektils zum Substrat 3.2.3 Wechselwirkung und Zeit bis zum Gleichgewicht 3.3 Auswertungsverfahren 3.3.1 Auswertung der einzelnen Simulationen 3.3.2 Stochastische Betrachtung 3.3.3 Erstellen der Interaktionstabellen 4. Ergebnisse und Diskussion 4.1 Simulation mit TRIM 4.2 Vorversuche zur MD-Simulation 4.2.1 Potential 4.2.2 Thermostat 4.2.3 Thermostatanteil 4.2.4 Temperatur 4.2.5 Substratgröße 4.2.6 Netzebene 4.2.7 Erhaltene Systemparameter 4.3 Oberflächeninteraktionen 4.3.1 Auswertung (111)-Netzebene 4.3.2 Vergleich mit experimentellen Ergebnissen 4.3.3 Vergleich der Netzebenen 4.4 Energie- und Richtungsverteilungen 4.4.1 Reflektierte Teilchen 4.4.2 Gesputterte Teilchen 4.5 Vergleich der Methoden 4.6 Anwendung 5. Zusammenfassung und Ausblick 5.1 Zusammenfassung 5.2 Ausblick Literaturverzeichnis Danksagung Selbstständigkeitserklärung