O projeto e o desenvolvimento de circuitos integrados é um dos mais importantes e aquecidos segmentos da indústria eletrônica da atualidade. Neste cenário, ferramentas de automação têm possibilitado aos projetistas manipular uma elevada quantidade de transistores em circuitos cada vez mais complexos, diminuindo, assim, o tempo de projeto. Em especial, ferramentas de síntese lógica têm contribuído significativamente para reduzir o ciclo de desenvolvimento. Na metodologia de projeto full-custom, cada bloco funcional tem sua geração realizada de forma manual, desde a implementação das redes de transistores até a geração do leiaute. Entretanto, esta tarefa é extremamente custosa em tempo de projeto. Neste contexto, torna-se confortável ter a disposição algoritmos dedicados para derivar redes de transistores automaticamente. Diversos tipos de arranjos de transistores são encontrados na literatura. Estas diferentes redes de transistores apresentam diferentes comportamentos em termos de consumo de área, consumo de potência e velocidade. Desta forma, não apenas a geração automática de redes de transistores é importante, mas também técnicas automatizadas para avaliar e comparar estas distintas redes de chaves é de fundamental importância para guiar o projetista que deseja alcançar implementações de circuitos eficientes. Estas avaliações não precisam ser necessariamente processos custosos de caracterização elétrica. Elas podem ser realizadas através de estimativas capazes de fornecer informações acuradas sobre o comportamento das redes. Esta idéia pode ser utilizada por projetistas que desejam gerar e avaliar potenciais soluções em redes de transistores para alimentar fluxos standard-cell (utilizando bibliotecas de células), ou por aqueles que utilizam a abordagem de mapeamento tecnológico library-free (fazendo uso de geradores de células). Neste contexto, este trabalho apresenta um gerador automático de redes de transistores capaz de fornecer diferentes tipos de redes em diversos estilos lógicos. Para comparar as redes geradas, algumas técnicas de estimativa são empregadas. Comparações são realizadas sobre conjuntos distintos de funções Booleanas, demonstrando as vantagens da utilização de lógicas alternativas em relação ao difundido padrão CMOS. / Currently, VLSI design has established a dominant role in the electronics industry. Automated tools have enabled designers to manipulate more transistors on a design project and shorten the design cycle. In particular, logic synthesis tools have contributed significantly to reduce the design cycle time. In full-custom designs, manual generation of transistor netlists for each functional block is performed, but this is an extremely time-consuming task. In this sense, it becomes comfortable to have efficient algorithms to derive transistor networks automatically. There are several kinds of transistor networks arrangements. These different networks present different behaviors in terms of area, delay and power consumption. Thus, not only automatic transistor networks generation is important, but also an automated technique to evaluate and to compare the distinct switch networks is fundamental to guide designers that need to achieve efficient circuit implementations. This evaluation not necessarily needs to be an expensive electrical characterization process. It can be obtained through estimation processes capable of delivering good information about the logic cells behavior. This idea is useful for those designers that desire to generate and to evaluate potential transistor network implementations to feed standard-cell flow designs (using cell libraries), or for those designers who target the use of library-free technology mapping concept (using automatic cells generators). In this context, this work presents an automated transistor network generator able to delivery different kinds of networks in several logic styles. In order to compare the obtained networks, some estimation techniques are employed. A comparison is done over a set of Boolean function benchmarks, showing the advantages of using alternative logic styles over the traditional Complementary Series-Parallel CMOS (CSP CMOS).

Submitted by Irene Nascimento (irene.kessia@ufpe.br) on 2016-11-08T17:29:28Z No. of bitstreams: 2 license_rdf: 1232 bytes, checksum: 66e71c371cc565284e70f40736c94386 (MD5) Dissertacao_Felipe_Correa_CD.pdf: 5991890 bytes, checksum: bf897f6d56367daee94655b05dc520e3 (MD5) / Made available in DSpace on 2016-11-08T17:29:28Z (GMT). No. of bitstreams: 2 license_rdf: 1232 bytes, checksum: 66e71c371cc565284e70f40736c94386 (MD5) Dissertacao_Felipe_Correa_CD.pdf: 5991890 bytes, checksum: bf897f6d56367daee94655b05dc520e3 (MD5) Previous issue date: 2015-07-31 / Capes / O conversor nove chaves (Nine-Switch Inverter - NSI) foi proposto recentemente e, desde então, um grande número de aplicações foi explorado para esta nova topologia, especialmente como um possível substituto do tradicional conversor back-to-back. A principal vantagem do NSI é o menor número de chaves (nove em vez de doze do conversor back-to-back), que, como consequência, acarreta em restrições nas amplitudes de saída do inversor. Na literatura, foram propostas diferentes técnicas de modulação por largura de pulso (Pulse Width Modulation - PWM) que respeitam estas restrições. Diante deste cenário, o presente trabalho propõe duas abordagens para a generalização da modulação no NSI: a modulação escalar quasi generalizada e a generalizada, que são baseadas no conceito de generalização para o inversor trifásico fonte de tensão (VSI) convencional e que podem ser facilmente implementadas com um reduzido esforço computacional. Este conceito propicia, através de uma abordagem sistemática e direta, a geração de qualquer técnica de PWM, seja ela contínua ou descontínua, através do ajuste de graus de liberdade específicos. Objetivando a redução de perdas, são apresentados os graus de liberdade específicos que, quando aplicados nas modulações propostas, aumentam o rendimento do inversor. Resultados de simulação confirmam a funcionalidade das modulações. / The nine-switch inverter (NSI) has been proposed recently and, since then, a large number of applications were explored for this new topology, specially as a possible substitute to the traditional back-to-back converter. The main advantage of the NSI is its lesser number of switches (nine instead of twelve of the back-to-back converter), which, as a consequence, leads to some restrictions in the total attainable amplitude at its outputs. In literature, many pulse width modulation (PWM) techniques were proposed respecting those restrictions. In this scenario, this paper proposes two generalization approaches for the modulation of the NSI: the quasi generalized scalar modulation and the generalized scalar modulation, which are based on the generalization concept for the voltage source inverter (VSI), easily implemented with a reduced computational effort. Such concept leads to a systematic and straight approach to the generation of any continuous or discontinuous PWM technique for the NSI, simply adjusting a few degrees of freedom of the modulation strategy. Aiming the reduction of the power losses, specific degrees of freedom are presented, for the proposed modulations. Simulation results confirm the validity of the proposed methods.

Submitted by Geandra Rodrigues (geandrar@gmail.com) on 2018-03-27T17:53:34Z No. of bitstreams: 1 nielsonsoares.pdf: 4342256 bytes, checksum: bcb08c0e8cbff9d4ed4b60f92f7715b2 (MD5) / Approved for entry into archive by Adriana Oliveira (adriana.oliveira@ufjf.edu.br) on 2018-03-27T18:03:27Z (GMT) No. of bitstreams: 1 nielsonsoares.pdf: 4342256 bytes, checksum: bcb08c0e8cbff9d4ed4b60f92f7715b2 (MD5) / Made available in DSpace on 2018-03-27T18:03:27Z (GMT). No. of bitstreams: 1 nielsonsoares.pdf: 4342256 bytes, checksum: bcb08c0e8cbff9d4ed4b60f92f7715b2 (MD5) Previous issue date: 2018-02-27 / CAPES - Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / As máquinas de chave são equipamentos eletromecânicos de grande importância em uma malha ferroviária. A ocorrência de falhas nesses equipamentos pode ocasionar interrupções das ferrovias e acarretar potenciais prejuízos econômicos. Assim, um diagnóstico precoce dessas falhas pode representar uma redução de custos e um aumento de produtividade. Essa dissertação tem como objetivo propor um modelo preditivo, baseado em técnicas de inteligência computacional, para a solução desse problema. A metodologia aplicada compreende o uso de técnicas de extração e seleção de características baseada em testes de hipóteses e modelos de aprendizado de máquina não supervisionado. O modelo proposto foi testado em uma base de dados disponibilizada por uma empresa ferroviária brasileira e se mostrou eficiente ao constatar como críticas as operações realizadas próximas à operação classificada como falha. / Railroad switch machines are important electromechanical equipment in a railway network, and the occurrence of failures in such equipment can cause railroad interruptions and lead to potential economic losses. Thus, an early diagnosis of these failures can represent a reduction of costs and an increase in productivity. This dissertation aims to propose a predictive model, based on computational intelligence techniques, to solve this problem. The applied methodology includes the use of features extraction and selection techniques based on hypothesis tests and unsupervised machine learning models. The proposed model was tested in a database made available by a Brazilian railway company and proved to be efficient when considering as critical the operations performed close to the operation classified as failure.

Abstract Although avalanche switching has been known since the 1950s, a trustworthy one-dimensional physical interpretation of the practically interesting high-current mode ("secondary breakdown") in a Si avalanche transistor has appeared only within the last decade and thanks to numerical one-dimensional and two-dimensional physics-based device modelling. A good fit with experimental waveforms has been achieved only for high-current, long-duration pulses (~100 A/7 ns), however, and modelling fails in the case of shorter pulses in a range that is of greater practical importance. One significant finding in this thesis is that reliable modelling of a Si avalanche transistor is in general impossible without taking account of three-dimensional effects. The task is a challenging one, as it is being put forward for the first time and state-of-the-art simulators are unable to model three-dimensional avalanche dynamics with an external circuit included (i.e. in “MixedMode”). Thus a smart approach was adopted which allowed the main features of the three-dimensional transient to be explained using a two-dimensional simulator and compared with the experimental data. The focus was on a trade-off of between high switching efficiency in an avalanche transistor (high-speed switching with a lower residual voltage as occurs at extremely high current densities) and device reliability as determined by local overheating during a single pulse, similarly resulting from high current density. This denotes the practical importance of the work performed here, as the current density is directly affected by three-dimensional dynamic processes. The second task performed in this thesis concerns the reliability of the GaAs avalanche transistors developed recently in the Electronics Laboratory and demonstrated of unique (superfast) switching and high-power-density sub-THz emission for mm-wave imaging and radars. Critically important for this new device is the limitation originating from premature breakdown at the surface of the GaAs p-n junction with a high density of surface states. Two of the results of this work are also fairly challenging: (i) the mechanism of "soft" surface breakdown intrinsic to all GaAs transistor mesas was interpreted in terms of the surface trapping of avalanche-generated electrons as suggested here, and (ii) passivation of the surface with a chalcogenide glass was suggested, as this allows the premature surface breakdown to be suppressed completely, an effect that has proved to be caused by a large negative surface charge formed on the “U centres” intrinsic to a chalcogenide glass. / Tiivistelmä Vaikka avalanche läpilyönti pii-transistoreissa on tunnettu jo 1950-luvulta lähtien, luotettava 1-dimensionaalinen fysikaalinen tulkinta ilmiöstä käytännön sovellusten kannalta kiinnostavilla suurilla virtatasoilla (ns. “secondary breakdown”) on esitetty vasta viime vuosikymmenen aikana 1- ja 2-dimensionaalisiin numeerisiin simulointeihin ja fysikaaliseen mallinnukseen perustuen. Kokeellisten mittausten ja simulointien välille on saatu hyvä sovitus kuitenkin vain sellaisessa ohjaustilanteessa, jossa transistori toimii suurella virtatasolla ja tuottaa leveitä virtapulsseja (~100  A / 7 ns); mallinnus ei vastaa mittaustuloksia lyhyillä virtapulsseilla, jotka kuitenkin ovat tärkeitä käytännön sovellusten kannalta. Yksi tämän työn keskeisiä havaintoja on se, että piipohjaisen avalanche transistorin luotettava mallintaminen ei ole käytännössä yleisesti mahdollista ottamatta huomioon 3-dimensionaalisia (3D) efektejä. Tällainen mallinnus, jota tässä työssä on kehitetty ensimmäistä kertaa, on vaikeaa, koska kaupalliset simulointiohjelmistot eivät kykene käsittelemään avalanche ilmiön dynamiikka 3-dimensionaalisesti tilanteessa, jossa transistoriin on kytketty ulkoinen piiri (ns. mixed-mode -simulointitilanne). Tähän kehitettiin tekniikka, joka mahdollistaa 3-dimensionaalisen kytkentätransientin tärkeimpien piirteiden selittämisen ja mittaustuloksiin vertaamisen 2-dimensionaalisten simulointien perusteella. Erityisesti pyrittiin selvittämään avalanche transistorin korkean kytkentähyötysuhteen (kollektori-emitterin ns. residual-jännitteen käyttäytyminen virrantiheystason mukaan) ja komponentin luotettavuuden välistä riippuvuutta. Luotettavuuteen vaikuttaa olennaisesti komponentin sisäinen, lokalisoitunut lämpötilamaksimi, joka myös riippuu keskeisesti komponentin virrantiheystasosta kytkentäpulssin aikana. Toisaalta virrantiheyteen vaikuttavat juuri komponentin 3-dimensionaaliset dynaamiset prosessit, joten työn käytännöllinen merkitys on suuri. Työn toisen osa käsittelee elektroniikan laboratoriossa äskettäin kehitetyn GaAs-avalanche transistorin luotettavuutta. Tällaisella transistorilla on demonstroitu olevan erityislaatuinen supernopea kytkeytymisefekti, ja se emittoi korkealla tehotasolla sähkömagneettista säteilyä n. 0,1–1 THz taajuusalueella. GaAs-avalanche transistoria voidaan täten potentiaalisesti hyödyntää mm-alueen kuvantamisessa ja tutkissa. Tämän uuden transistorin luotettavuuteen vaikuttaa ratkaisevasti rajoitus, joka aiheutuu ennenaikaisen, GaAs-pn-liitoksen pinnassa vaikuttavasta suuresta pintatilatiheydestä johtuvan läpilyönnin mahdollisuudesta. Työn kaksi keskeistä tulosta ovat: (i) kaikilla GaAs-transistoreilla ilmenevä ns. ”pehmeä”-läpilyönti aiheutuu avalanche ilmiön synnyttämien elektronien loukkuuntumisesta pinta-tiloihin, ja (ii) pinnan passivointi kalkopyriittilasilla estää läpilyönnin kokonaan, koska kalkopyriittilasille luonteenomaiset ”U-tilat” aiheuttavat liitoksen pintaan korkean negatiivisen pintavarauksen.

Acteurs des mécanismes moléculaires de signalisation cellulaire, les espèces réactives de l'oxygène (ROS) et les espèces réactives de l'azote (RNS) agissent comme des molécules signal transférant des informations extracellulaires ou intracellulaires et induisant des réponses spécifiques. Les ROS/RNS agissent principalement via un ensemble de modifications post-traductionnelles réversibles des résidus thiols sur les protéines parmi lesquelles la nitrosylation et la glutathionylation apparaissent comme des éléments jouant un rôle important dans de nombreux processus cellulaires fondamentaux et impliqués dans nombre de maladies humaines. Bien que présents chez les organismes photosynthétiques, ces modifications ont été moins étudiées. Mon projet était d'étudier, in vivo, chez l'algue Chlamydomonas reinhardtii, la dynamique de la nitrosylation et de la glutathionylation, en utilisant une combinaison d'approches multidisciplinaires incluant protéomique, biochimie et biologie moléculaire. En réponse au stress nitrosatif, 492 protéines S-nitrosylées in vivo et 392 sites de nitrosylation ont été identifiés par spectrométrie de masse. Ces protéines participent à un large éventail de processus biologiques tels que la photosynthèse et la réponse au stress. Avec une stratégie similaire, l’analyse de la glutathionylation en réponse à des stresses physiologiques de forte lumière et de choc thermique, a révélé des voies spécifiques de réponse au stress. En parallèle, la dépendance redox des mécanismes moléculaires sous-jacents a été examinée pour la GAPDH cytoplasmique et l’isocitrate lyase, mais aussi la triosephosphate isomérase et la phosphoglycérate kinase chloroplastiques. / Actors of the molecular mechanism of cell signaling, reactive oxygen species (ROS) and reactive nitrogen species (RNS) act as signaling molecules to transfer extracellular or intracellular information and elicit specific responses. ROS/RNS mainly act through a set of reversible post-translational modifications of thiol residues on proteins among which nitrosylation and glutathionylation have emerged as key elements playing a major role in numerous fundamental cell processes and implicated in a broad spectrum of human diseases. Despite ROS and RNS are present in photosynthetic organisms, such modifications have been less studied. My project was to investigate in the green algae Chlamydomonas reinhardtii, the in vivo dynamics of nitrosylation and glutathionylation, using a combination of multidisciplinary approaches including proteomic, biochemistry and molecular biology. In response to nitrosative stress, 492 in vivo s-nitrosylated proteins and 392 sites of nitrosylation were identified by mass spectrometry. These proteins were found to participate in a wide range of biological processes and pathway such as photosynthesis, stress response and carbohydrate metabolism. Employing a similar strategy, analysis of glutathionylation in response to physiological stresses, specifically high light and heat stress revealed specific stress dependent targeted pathways. In a second part, the redox dependence of the underlying molecular mechanisms was examined for the cytoplasmic GAPDH and ICL, but also the chloroplastic TPI and PGK. This work has highlighted the existence of a strong interplay between these redox modifications. a complex redox network

This thesis presents System Identification based On-Line Health Monitoring to analyse the dynamic behaviour of the Switch-Mode Power Converter (SMPC), detect, and diagnose anomalies in passive electronic components. The anomaly detection in this research is determined by examining the change in passive component values due to degradation. Degradation, which is a long-term process, however, is characterised by inserting different component values in the power converter. The novel health-monitoring capability enables accurate detection of passive electronic components despite component variations and uncertainties and is valid for different topologies of the switch-mode power converter. The need for a novel on-line health-monitoring capability is driven by the need to improve unscheduled in-service, logistics, and engineering costs, including the requirement of Integrated Vehicle Health Management (IVHM) for electronic systems and components. The detection and diagnosis of degradations and failures within power converters is of great importance for aircraft electronic manufacturers, such as Thales, where component failures result in equipment downtime and large maintenance costs. The fact that existing techniques, including built-in-self test, use of dedicated sensors, physics-of-failure, and data-driven based health-monitoring, have yet to deliver extensive application in IVHM, provides the motivation for this research ... [cont.].

Ce manuscrit traite de la fiabilité de micro-composants électro-mécaniques que l'on appelle des MEMS (Acronyme anglais signifiant Micro-Electro-Mechanical Systems). Les MEMS sont utilisés dans un grand nombre de domaines et le domaine qui nous concerne est celui des télécommunications. Plus précisément, notre domaine de travail se situe autour des radio-fréquences où les MEMS vont principalement réaliser des fonctions de commutation. On appellera ainsi nos composants des MEMS-RF, RF signifiant Radio-Fréquence. Dans ce domaine, les MEMS sont des candidats à fort potentiel grâce à une faible consommation de puissance, leur performance dans le domaine RF, leur encombrement et leur poids. De plus, en utilisant un procédé de fabrication dérivé de celui des semi-conducteurs, leur coût de production reste relativement faible. Dans ce manuscrit, on s'intéresse à la fiabilité de ces composants car c'est le dernier verrou avant une éventuelle industrialisation. Les principaux mécanismes de défaillance sont abordés dans une première partie, puis ce manuscrit se concentre sur l'étude du fluage mécanique et des facteurs d'accélération de modes de défaillance. On verra notamment l'influence de la température et des conditions de fonctionnement sur la durée de vie des commutateurs. / The thesis deals with reliability of tiny electro-mechanical components called MEMS. MEMS stands for Micro-Electro-Mechanical Systems. These components, designed for switching applications, are suitable candidates for telecommunications due to their low power consumption, Radio-Frequencies (RF) performances, compactness and lightness. A MEMS is fabricated using processes of integrated circuit manufacturing that makes its cost relatively low. Few of these components are commercially available and more are expected to be in the market as soon as reliability issues will be solved. Reliability issues studied in the thesis regard mechanical creep and acceleration factors. The mechanical creep occurs in our suspended structures whilst enduring a constant force, it results in deformation of structures and shift of parameters. Two innovative test benches are developed to assess mechanical creep in RF-MEMS switches. The acceleration factors are keys to conduct accelerated testings and predict lifetime of RF-MEMS switches. Parameters such as bias voltage, input-to-output voltage, temperature are varied to assess lifetime of switches and extract these acceleration factors.

Magister Public Health - MPH / Background: Namibia is one of the Southern African countries hardest hit by the HIV epidemic, with an estimated one out of every five people infected (MoHSS, 2004). Approximately 80,000 of the infected population currently require antiretroviral treatment (ART). In order to prevent the progression of the HIV infection to AIDS, patients are required to take antiretroviral medicines lifelong. This lifelong use exposes patients to toxicities of these medicines and the only available options of managing the toxicities of ARVs are to treat the toxicity or substitute or switch the offending medicines. Aim: The current study aimed to describe the extent and reasons for substituting and switching HAART at the Katutura Intermediate Hospital in Windhoek, Namibia. Methodology: A descriptive retrospective case series study, in which medical records were reviewed to determine the extent and reasons for substituting and switching HAART was conducted. Random sampling was used to draw a sample of 500 from 3477 adult HAART patients who commenced treatment between 1 January 2002 and 31 December 2006. A prepiloted data collection tool was used to collect the data. The following information was collected: baseline CD4 count, weight, initial ARVs, first and second ARV substitutions, ART switch and the reasons for substituting ARVs or switching ART during the indicated period. Epi Info version 6 was used to analyse frequencies, means and medians of all important variables in the data set. Results: The sample was made up of 500 HAART patients; 60% were females. The median age of the sample was 34 years (Inter-quartile range (IQR) 30 – 40) and the median CD4 cell count was 153 cells/mm3 (IQR 96 – 212) at initiation of therapy. The median time on treatment before first substitution was 28 months (IQR 24 – 34), whereas the median time before second substitution was 10 months (IQR 6 – 15) from the time of the first substitution. The median time before switching was 31 months (IQR 24 - 39). A total of 31% of the study subjects underwent a substitution once, whereas 1.8% underwent a second substitution. Only six (1.2%) patients switched to a second line treatment after the modification of the treatment. The most commonly recorded reason for the first substitution was toxicity (19%). As in other studies, stavudine (D4T), nevirapine (NVP) and efavirenz (EFV) were the ARVs associated with most of the recorded toxicities. High viral load (50%) was the most reported reason for switching. In almost half of the substitution cases the reasons for substitution were not stated, and in a third of the switch cases the reasons for switching were not stated. Conclusion: The rate of substitution at 31% was similar to that found in other resource poor settings, however, the rate of switching (1.2%) was much lower than was found in similar settings. The main reason stated for substituting antiretrovirals was “toxicity”. / South Africa

The goal of the research reported in this thesis is to establish the feasibility of a novel optical architecture for an optical route & select circuit switch suitable for implementation as a photonic integrated circuit. The proposed architecture combines Optical Phased Array (OPA) switch elements implemented as multimode interference coupler based Generalised Mach-Zehnder Interferometers (GMZI) with a planar Lüneburg lens-based optical transpose interconnection network implemented using graded metamaterial waveguide slabs. The proposed switch is transparent to signal format and, in principle, can have zero excess insertion loss and scale to large port counts. These switches will enable the low-energy consumption high capacity communications network infrastructure needed to provide environmentally-friendly broadband access to all. The thesis first explains the importance of switch structures in optical communications networks and the difficulties of scaling to a large number of switch ports. The thesis then introduces the Talbot effect, i.e. the self-imaging of periodic field distributions in free space. It elaborates on a new approach to finding the phase relations between pairs of Talbot image planes at carefully selected positions. The free space Talbot effect is mapped to the waveguide Talbot effect which is fundamental to the operation of multimode interference couplers (MMI). Knowledge of the phase relation between the MMI ports is necessary to achieve correct operation of the GMZI OPA switch elements. An outline of the design procedures is given that can be applied to optimise the performance of MMI couplers and, as a consequence, the GMZI OPA switch elements. The Lüneburg Optical Transpose Interconnection System (LOTIS) is introduced as a potential solution to the problem of excessive insertion loss and cross-talk caused by the large number of crossovers in a switch fabric. Finally, the thesis explains how a Lüneburg lens may be implemented in a graded ‘metamaterial’, i.e. a composite material consisting of ‘atoms’ arranged on a regular lattice suspended in a host by nano-structuring of silicon waveguide slabs using a single etch-step. Furthermore, the propagation of light in graded almost-periodic structures is discussed. Detailed consideration is given to the calibration of the local homogenised effective index; in terms of the local parameters of the metamaterial microstructure in the plane and the corrections necessary to accommodate slab waveguide confinement in the normal to the plane. The concept and designs were verified by FDTD simulation. A 4×4 LOTIS structure showed correct routing of light with a low insertion loss of -0.25 dB and crosstalk of -24.12 dB. An -0.45 dB excess loss for 2D analysis and an -0.83 dB insertion excess loss for 3D analysis of two side by side metamaterial Lüneburg lenses with diameter of 15 μm was measured, which suggests that the metamaterial implementation produces minimal additional impairments to the switch.

Le code-switch et les emprunts sont tous les deux des phénomènes linguistiques très courants parmi les communautés multilingues. Malgré le fait qu’il y ait eu beaucoup de recherche à propos de ces phénomènes, il existe deux aspects qui n’ont pas été explorés de manière satisfaisante. Premièrement, la distinction exacte entre le code-switch et l’emprunt, et, deuxièmement, le code-switch parmi les enfants. Plusieurs chercheurs proposent que la différence entre le code-switch et l’emprunt existe dans la phonologie : les emprunts d’une langue à une autre subissent des assimilations phonologiques selon la langue de cible. Si celle-ci est une distinction nécessaire des emprunts, cela ne veut pas dire qu’il est suffisant pour les distinguer du code-switch. Ceci amène plusieurs chercheurs à postuler que la différence cruciale entre le code-switch et l’emprunt est que ce premier est soumis à un ensemble de contraintes. Toutefois, la nature de ces contraintes varie beaucoup parmi les théories. Le code-switch dans les locuteurs bilingues jeunes est un outil idéal pour tester la validité des théories proposées : plusieurs chercheurs proposent qu’il existe un aspect développemental de ces contraintes, qui informe de manière importante sur la nature de l’acquisition du langage bilingue. La cible de ce travail est de répondre à deux questions cruciales. Tout d’abord, s’il existe bel et bien un aspect développemental des contraintes concernant le code-switch, et, deuxièmement, comment le code-switch des enfants peut informer sur l’usage de langues multiples, particulièrement concernant l’acquisition du langage bilingue. / Code-switching and borrowing are both highly common linguistic phenomena in multilingual communities. Whilst much research has been carried out on these phenomena, there are two aspects of them which have not been satisfactorily explored. Firstly, the exact distinction between code-switching and borrowing, and secondly, that of code-switching in children. Many researchers state that the difference between code-switching and borrowing lies in phonology: borrowings from another language assimilate to the phonology of the language in which they have been inserted. Whilst this may be a necessary distinction of borrowing, it may not be sufficient to distinguish it from code-switching. This has led to many researchers to propose that a key difference between code-switching and borrowing is that the former is subject to a set of constraints, though these differ greatly between theories. Code-switching behaviour of young bilingual children is ideal for testing the validity of these theories: many researchers argue that there is a developmental aspect to constraints acting upon children’s code-switching, which provides valuable insight into the nature of bilingual language acquisition. The aim of this thesis is therefore to answer two crucial questions. Firstly, if there does indeed exist a developmental aspect to constraints acting on children’s code-switching, and, secondly, what bilingual children’s code-switching can reveal about multiple language use, particularly with regards to bilingual language acquisition.