Cette thèse présente l’étude théorique et expérimentale de la génération et de la mise en forme d’impulsions térahertz (THz). Dans un premier temps, nous avons étudié la génération d’impulsions THz par redressement optique d’impulsions laser femtosecondes intenses dans des cristaux semiconducteurs de ZnTe. Nous avons mis en évidence une forte dépendance de l'efficacité de ce processus de génération avec l'intensité de l'impulsion laser génératrice. Ceci se traduit en particulier par un décalage progressif du spectre vers les basses fréquences et par une évolution anormale de l'énergie THz avec l'intensité laser. Ces comportements résultent d'une combinaison de trois phénomènes : la déplétion de l’impulsion laser au cours de sa propagation dans le cristal, l’absorption de l'onde THz par les porteurs libres créés par absorption à deux photons et une modification de la condition d’accord de phase. Dans un deuxième temps, nous avons développé une approche analytique permettant de générer des impulsions THz de formes particulièrement intéressantes pour les expériences de spectroscopie cohérente ou de contrôle cohérent. Nous avons notamment généré des paires d'impulsions verrouillées en phase, des trains d'impulsions, ainsi que des impulsions THz accordables de grande finesse spectrale. Cette technique repose sur le redressement optique d’impulsions laser femtosecondes mises en forme à l’aide d’un masque à cristaux liquides placé dans le plan de Fourier d’une ligne à dispersion nulle. Afin de démontrer la validité de notre approche, nous avons également développé un programme de simulation qui donne des résultats en très bon accord avec l'expérience. / This thesis deals with the theoretical and experimental study of the generation and shaping of terahertz (THz) pulses. At first, we have studied the generation of THz pulses by optical rectification of intense femtosecond laser pulses in semiconductor ZnTe crystals. We have demonstrated a strong dependence of the efficiency of the generation process with the intensity of the laser pulse. This is evidenced by a progressive shift of the spectrum towards lower frequencies and an abnormal evolution of the THz energy with laser intensity. These behaviors result from a combination of three phenomena: the depletion of the laser pulse during its propagation in the crystal, the absorption of THz wave by free carriers created by two-photon absorption and a change of the phase matching condition. Secondly, we have developed an analytical approach to generate THz shaped pulses particularly interesting for coherent spectroscopy or coherent control. In particular, we have generated phase-locked THz pulses pairs, pulse trains and tunable narrow-band THz pulses. This technique is based on optical rectification of shaped femtosecond laser pulses generated by a liquid crystal Fourier filter. To demonstrate the validity of our approach, we have also developed a program giving results in very good agreement with experiment.

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Made available in DSpace on 2016-04-28T18:24:02Z (GMT). No. of bitstreams: 1 Maisa Aparecida Requena.pdf: 549716 bytes, checksum: e7b3be3f691c87503a9602bc20bdcfdc (MD5) Previous issue date: 2009-05-07 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / The study of diversities of creative manifestations in Brazilian people has allowed us to find out personages who discovered an alternative of work to face the unemployment: to produce publicity and selling products inside the Metropolitan trains of São Paulo. It is about the discourses produced by the informal worker whose advertising does not appear in magazines, newspaper, pamphlets, outdoors etc., but have the same goals, which are to publicize, spread ideas and, mainly, to sell products. In this sense, this research has as its objective to analyze the discursive mechanism that characterize the speeches of these informal workers. The research conforms to the theoretical field developed by Dominique Maingueneau, more specifically in the conceptions of Interdiscourse, Scenography and Ethos. From the methodological point of view, we have followed these steps: (i) the observation of the work activities of the workers the discourses produced by them, (ii) field notes about the activity in work circumstances and about the discourses transmitted by the workers and (iii) transcription of some of their speech. The analysis has revealed two groups of discourse: the slogan-discourses and the advertisement-discourse. The first one has showed an enunciative scene compatible with the street market conditions, while in the second one, the developed scene was similar to the auction situation. From the scenography analysis, it has emerged the Ethos of the enunciators of both groups. In the slogan-discourse, the presented Ethos is from an agile, discreet and invisible enunciator, while in the advertisement-discourse, the presented Ethos is from a good-tempered, calm, sympathetic, agile and considerate enunciator. Thus, the workers mobilize many mechanisms in order to create a new model of publicity that aims to legitimate its discourses, generating scenographies and presenting an Ethos / A observação das diversas maneiras de manifestações criativas do povo brasileiro nos permitiu localizar pessoas que encontraram um meio diferente de trabalho para enfrentar o problema da falta de emprego: produzir publicidade e vender produtos no interior dos trens metropolitanos de São Paulo. Trata-se de discursos produzidos pelos vendedores informais cuja publicidade não aparece em revistas, jornais, panfletos, outdoors etc., mas que apresentam os mesmos objetivos, o de divulgar, de propagar idéias e, principalmente, o de vender seus produtos. Nesse sentido, a pesquisa tem por objetivo analisar os mecanismos discursivos que caracterizam a fala do vendedor informal. A investigação se enquadra na perspectiva desenvolvida por Dominique Maingueneau, mais precisamente, nas noções de interdiscurso, cenografia e ethos. Do ponto de vista metodológico, foram seguidas as seguintes etapas: (i) observação da atividade de trabalho dos vendedores e dos discursos produzidos por eles, (ii) anotações de campo sobre a atividade em situação de trabalho e sobre os discursos veiculados pelos vendedores e (iii) transcrição de algumas de suas falas. A análise revelou dois grupos de discursos: os discursos-slogans e os discursos-anúncios. Os primeiros apresentam uma cena de enunciação compatível com à de feira livre e os segundos, são semelhantes à cenografia de um leilão. A partir da análise da cenografia, emergiu o ethos dos enunciadores dos dois grupos. No discurso-slogan, o ethos é o de um enunciador ágil, discreto, invisível, enquanto no discursoanúncio, a imagem discursiva é o de um enunciador bem-humorado, calmo, simpático, ágil e atento aos chamados dos clientes

Two important physical aspects that determine the performance of a running train are the total running resistance that acts on the whole train moving forward, and the available adhesion (utilizable wheel-rail-friction) for propulsion and breaking. Using the measured and available signals, online identification of the current running resistance and available adhesion and also prediction of future values for a distance ahead of the train, is desired. With the aim to enhance the precision of those calculations, this thesis investigates the potential of online identification and prediction utilizing the Extended Kalman Filter. The conclusions are that problems with observability and sensitivity arise, which result in a need for sophisticated methods to numerically derive the acceleration from the velocity signal. The smoothing spline approximation is shown to provide the best results for this numerical differentiation. Sensitivity and its need for high accuracy, especially in the acceleration signal, results in a demand of higher sample frequency. A desire for other profound ways of collecting further information, or to enhance the models, arises with possibilities of future work in the field. / Två viktiga fysikaliska aspekter som bestämmer prestandan för ett tåg i drift är det totala gångmotståndet som verkar på hela tåget, samt den tillgängliga adhesionen (användbara hjul-räl-friktionen) för framdrivning och bromsning. Från de tillgängliga signalerna önskas identifiering, samt prediktering, av dessa två storheter, under drift. Med målet att förbättra precisionen av dessa skattningar undersöker detta examensarbete potentialen av skattning och prediktering av gångmotstånd och adhesion med hjälp av Extended KalmanFiltering. Slutsatsen är att problem med observerbarhet och känslighet uppstår, vilket resulterar i ett behov av sofistikerade metoder att numeriskt beräkna acceleration från en hastighetssignal. Metoden smoothing spline approximation visar sig ge de bästa resultaten för denna numeriska derivering. Känsligheten och dess medförda krav på hög precision, speciellt på accelerationssignalen, resulterar i ett behov av högre samplingsfrekvens. Ett behov av andra adekvata metoder att tillföra ytterligare information, eller att förbättra modellerna, ger upphov till möjliga framtida utredningar inom området.

The growth of population and business during the rapid urbanization process in the twentieth century has generated significant demand for transportation. As the demands have grown, road and air transportation are suffering from significant congestion and delays. Continuing expansion of highways and airports has become both expensive and difficult, along with not being able to provide adequate solutions to the growing congestion. One alternative, which is being pursued by many countries, is to invest in efficient high-speed rail networks to meet the pressing demand for mass passenger transportation. This alternative is also one that may have beneficial impacts by reducing energy consumption and alleviating some of the environmental concerns. But to make these infrastructure investments, governments need to make difficult decisions due to the complexity of the industry and technologies involved. This thesis examines decision making by government for such investments. In order to carefully study the industry, we use a two part approach. First, we examine the HSR industry supply-chain. We create a detailed taxonomy of the industry supply-chain and highlight various aspects of the advanced technologies being used, the sophisticated multiproduct nature of the firms, and the diverse international location of the companies. Second, we gather information on all the international HSR contracts between 2001-2011. These contracts enable us to examine business strategies pursued by the major HSR trainset suppliers and component manufacturers, insights into the size of the orders and type of trainsets being delivered, and the formation of partnerships and collaborations to meet the complex demands imposed by Governments when they invite bids for these expensive projects. A detailed examination of the supply-chain shows that the core technologies and competencies are highly concentrated in those countries which historically have had high demand for high-speed rail. Germany, Japan, France, for example, have the highest number of trainset and component suppliers. In more recent years, South Korea and China have emerged as the new frontiers of trainset and components suppliers. This implies that countries who are outside of this group are highly dependent on either importing these technologies and investments or make a concerted effort to develop them via partnerships and technology transfer agreements. Our examination of contracts shows that the size of HSR investment order is important for both business and government strategy. The order size determines the extent of domestic content and production. While many components will inevitably be imported, a larger order size may allow for various components to be manufactured domestically. Order size also appears to influence the nature of partnerships among the firms in the industry. We observe a growing number of HSR investment partnerships among trainset suppliers over time, possibly due to the need to pool risk in these highly complex and uncertain investments, as well as the changing competitive dynamic of HSR markets.

The area of powertrain dynamics has received considerable attention over a number of years. The recent introduction of more stringent emission requirements together with economic pressure has led to a particular focus on increasing powertrain efficiency. This has seen the incorporation of on-board, real-time measurements to predict system behaviour and engine condition. In this domain, accurate models for all powertrain components are important. One strategy to improve accuracy is to evaluate the assumptions made when deriving each model and then to address the simplifications that may introduce large errors. To this end, the aim of the work presented in this dissertation was to investigate the consequences of some of the more common assumptions and simplifications made in low frequency torsional powertrain models, and to propose improved models where appropriate. In particular, the effects of piston-tocylinder friction, crank/gudgeon pin offset, and the torsional behaviour of tyres were studied. Frequency and time domain models were used to investigate system behaviour and model predictions were compared with measurements on a small single cylinder engine. All time domain engine and powertrain models also include a variable inertia function for each reciprocating mechanism. It was found that piston-to-cylinder friction can increase the apparent inertia variation of a single reciprocating engine mechanism. This has implications for the nonlinear behaviour of engines and the drivetrains they are connected to. The effect of crank/gudgeon pin offset also modified the nonlinear behaviour of the mechanism. Though, for typical (small) gudgeon offset values these effects are small. However, for large offset values, achievable practically with crank offset, the modification to the nonlinear behaviour should not be ignored. The low frequency torsional damping properties of a small pneumatic tyre were found to be more accurately represented as hysteretic rather than viscous. Time domain modelling was then used to extend the results to a multi-cylinder engine powertrain and was achieved using the Time Domain Receptance (TDR) method. Various powertrain component TDRs were developed using Laplacians. Powertrain simulations showed that piston-to-cylinder friction can provide additional excitation to the system.

Thesis (MS en S)--Stellenbosch University, 2003. / ENGLISH ABSTRACT: Public participation has already been a point of discussion from as early as 1960, with Arnstein's presentation of eight levels of participation. Various advantages and disadvantages have been published, but theorists agree that the advantages still overshadow the disadvantages. The United States have started much earlier than South Africa with the studies on public participation. It has been realised that public participation forms an integral part of the formal environmental impact assessment which succeeded the formal legislation of 1996. It is generally accepted that public participation is inseparable from the planning process. The purpose of this paper is to investigate the impact of public participation on the planning of the Gautrain project, which is the intended rapid rail link between Johanesburg and Pretoria. It will be investigated whether the consult firm Bohlweki Environmental, that has been appointed to implement the environmental impact assessment of the Gautrain project, complied with the criteria to ensure public participation, and whether the public process made a difference to the planning of the project. It has been apparent that Bohlweki Environmental used various methods of involving the public - inter alia numerous public meetings that have been advertised in the press and elsewhere. From the public inputs changes have been made to the route of the train. These changes however, have made other people discontented. The research concludes with the finding that the public participation process of the environmental impact assessment had a positive influence on the planning of the project, even though everyone, due to the extend and the nature of the project, could not be satisfied, and that the study has been expensive and time consuming. / AFRIKAANSE OPSOMMING: Publieke deelname was reeds 'n besprekingspunt van so vroeg as 1960 met Arnstein se voorstelling van agt deelnemingsvlakke. Oor die jare van navorsing is verskeie voordele en nadele van publieke deelname gepubliseer, maar teoretici is dit eens dat die voordele steeds die nadele oorskadu. In Suid-Afrika is daar veel later as in die Verenigde State studies oor publieke deelname begin. Ook hier is daar uiteindelik besef dat publieke deelname 'n onlosmaakbare deel van die formele omgewingsimpakstudie vorm en het die formele wetgewing in 1996 gevolg. Vandag word algemeen aanvaar dat publieke deelname en die beplanningsproses onafskeidbaar is. Die doel van hierdie werkstuk is om die impak van publieke deelname op die beplanning van die Gautrein projek te ondersoek - dit is die beoogde sneltrein tussen Johannesburg en Pretoria. Die vraag is of die konsultant firma Bohlweki Environmental, wat aangestel is om die omgewingsimpakstudie van die Gautreinprojek te loods, voldoen het aan die kriteria om publieke deelname te verseker, en of die publieke proses 'n verskil gemaak het aan die beplanning van die projek? Uit die analise het dit geblyk dat Bohlweki Environmental van verskeie metodes gebruik gemaak het om die publiek te betrek, onder andere talle publieke vergaderings wat goed geadverteer is in die pers en elders. As gevolg van die groot publieke inset is veranderinge aan die roete van die trein aangebring. Hierdie veranderinge het egter weer ander mense ontevrede gemaak. Die slotsom van die navorsing van hierdie werkstuk is dat die publieke deelname proses van die omgewingsimpakstudie wel 'n betekenisvolle positiewe uitwerking op die beplanning van die projek gehad het, alhoewel almal, uit die aard van die omvang van die projek, nie tevrede gestel kon word nie, en dat die studie duur en tydrowend was.

Cette thèse porte sur la résolution numérique du modèle multi-dimensionnel d'écoulement cisaillé en eau peu profonde. Dans le cas d'un mouvement unidimensionnel, ces équations coïncident avec les équations de la dynamique de gaz pour un choix particulier de l'équation d'état. Dans le cas multi-dimensionnel, le système est complètement différent du modèle de la dynamique de gaz. Il s'agit d'un système EDP hyperbolique 2D non-conservatif qui rappelle un modèle de turbulence barotrope. Le modèle comporte trois types d'ondes correspondant à la propagation des ondes de surface, des ondes de cisaillement et à celle de la discontinuité de contact. Nous présentons dans le cas 2D un schéma numérique basé sur une nouvelle approche de ``splitting" pour les systèmes d'équations non-conservatives. Chaque sous-système ne contient qu'une seule famille d'ondes: ondes de surface ou ondes de cisaillement, et discontinuité de contact. La précision d'une telle approche est testée sur des solutions exactes 2D décrivant l'écoulement lorsque la vitesse est linéaire par rapport aux variables spatiales, ainsi que sur des solutions décrivant des trains de rouleaux 1D. Finalement, nous modélisons un ressaut hydraulique circulaire formé dans un écoulement convergent radial d'eau. Les résultats numériques obtenus sont clairement similaires à ceux obtenus expérimentalement: oscillations du ressaut et son rotation avec formation du point singulier. L'ensemble des validations proposées dans ce manuscrit démontre les aptitudes du modèle et de la méthode numérique pour la résolution des problèmes complexes d'écoulements cisaillés en eau peu profonde multidimensionnels. / This thesis is devoted to the numerical modelling of multi-dimensional shear shallow water flows. In 1D case, the corresponding equations coincide with the equations describing non--isentropic gas flows with a special equation of state. However, in the multi-D case, the system differs significantly from the gas dynamics model. This is a 2D hyperbolic non-conservative system of equations which is reminiscent of a generic Reynolds averaged model of barotropic turbulent flows. The model has three families of characteristics corresponding to the propagation of surface waves, shear waves and average flow (contact characteristics). First, we show the ability of the one-dimensional conservative shear shallow water model to predict the formation of roll-waves from unstable initial data. The stability of roll waves is also studied.Second, we present in 2D case a new numerical scheme based on a splitting approach for non-conservative systems of equations. Each split subsystem contains only one family of waves (either surface or shear waves) and contact characteristics. The accuracy of such an approach is tested on exact 2D solutions describing the flow where the velocity is linear with respect to the space variables, and on the solutions describing 1D roll waves. Finally, we model a circular hydraulic jump formed in a convergent radial flow of water. Obtained numerical results are qualitatively similar to those observed experimentally: oscillation of the hydraulic jump and its rotation with formation of a singular point. These validations demonstrate the capability of the model and numerical method to solve challenging multi--dimensional problems of shear shallow water flows.

Ce mémoire de thèse présente les travaux effectués pour la réalisation de sources optiques fibrées d’impulsions picosecondes cadencées à 40 GHz dans la bande C des télécommunications. Dans une première partie, nous présentons des études numériques et expérimentales mises en place pour la génération d’un train d’impulsions cadencé à 40 GHz par la compression non-linéaire d’un battement sinusoïdal via un processus de mélanges à quatre ondes multiples. Afin d’obtenir des impulsions stables, le battement sinusoïdal initial est obtenu par la modulation en intensité d’un signal continu grâce à un modulateur Mach-Zehnder piloté au point nul de transmission. Nous démontrons également l’amélioration de la qualité des impulsions générées par la suppression de la diffusion Brillouin stimulée grâce à la mise en place d’isolateurs optiques dans la ligne fibrée de la source. Nous présentons ensuite la génération d’impulsions ultra-courtes grâce à un compresseur non-linéaire composé de quatre étages fibrés. Le train d’impulsions obtenu est alors codé puis multiplexé jusqu’à un débit optique de 160 Gbit/s. Dans la dernière partie, nous présentons les démarches mises en place en vue d’un transfert technologique, telles que la réalisation d’un prototype de la source, la recherche d’antériorité et l’étude de marché. / This thesis presents the work carried out on the realization of fibered 40-GHz picosecond optical pulse sources in the telecommunications C-band. In the first part, we present a numerical and experimental study of the generation of 40-GHz pulse trains thanks to the nonlinear compression of an initial beat-signal by multiple Four-Wave Mixing process. Enhanced temporal stability is achieved by generating the sinusoidal beating thanks to a Mach-Zehnder modulator driven at its zero-transmission working point. In order to improve the quality of the generated pulses, we also demonstrate the suppression of stimulated Brillouin back-scattering by inserting several optical isolators into the compression line. In the next part, we present the generation of low duty-cycle pulse trains by using a nonlinear compressor line based on 4 segments of fiber. The generated pulse trains have been encoded and then multiplexed to achieve a high bit rate signal (160 Gb/s). In the last part, we present the technology transfer steps of this optical source, such as creating a prototype of the source, prior art search and market research.

This thesis focuses on the main processes in positive ground flashes and the distant lightning environment for both positive and negative ground flashes. It presents the characteristics of the preliminary breakdown pulses (PBPs), the characteristics of the electric field pulses observed during leader propagation, and the characteristics of the electric fields produced by the first and the subsequent return strokes. It also features the observations of distant positive and negative ground flashes at distances up to 1000 km. The results were based on electric field measurements conducted remotely during summer thunderstorms in Sweden in 2014. We found that the majority of the positive ground flashes were preceded by PBPs. Some were preceded by more than one PBP train, and the parameter values for the subsequent PBP trains were found to be smaller than the values for the first PBP train. Three types of PBPs were also identified. The results suggest that the PBPs in positive ground flashes during summer thunderstorms in Sweden are weak, and the inverted dipole charge cloud configuration is consistent with our observation. A small percentage of these positive ground flashes were observed to be preceded by pronounced leader pulses. The presence of these pulses suggests that the leaders propagate in a stepped manner. We inferred that these pulses were due to the upward-connecting negative leader since their characteristics were similar to those of a negative stepped leader. On the basis of the leader pulses’ time of initiation and the average speed of the leader, we estimated the distance travelled by the leader. One case of positive return stroke preceded by negative leader pulses was also observed, and the occurrence of these pulses was the first in positive ground flashes to be reported. The majority of these positive ground flashes were found to be single-stroke. Comparison between the first and the subsequent return strokes showed that the average durations of the subsequent stroke parameters were smaller than that of the first strokes. The distances reported by the lightning location system suggest that the subsequent strokes probably created new terminations to ground. Two possible reasons were given to explain the reason for the shorter duration of the subsequent return strokes parameters compared to the first strokes. Finally, observations of distant positive and negative ground flashes showed that the electric field waveforms have a typical shape, like a distorted ‘W’ (or distorted ‘M’ for negative ground flashes) followed by small oscillations. These small oscillations were more pronounced in negative ground flashes, especially at a greater distance. The heights of the ionospheric reflections estimated for both ground flashes were found to likely correspond to a D-layer of the ionosphere. Two possible reasons were suggested for the small oscillations observed in the waveforms.