Les flagelles sont des organites essentiels chez la plupart des eucaryotes, y compris chez l’Homme. Ils possèdent une structure cylindrique composée de neuf doublets de microtubules appelée axonème qui est conservée au cours de l’évolution. Ils sont construits par un mécanisme appelé Transport IntraFlagellaire (IFT). Malgré des variations de composition et de longueur entre différents types de cils, la longueur des cils d’un type cellulaire donné est étroitement contrôlée. Toute anomalie de la longueur du flagelle ou de la machinerie IFT peut entraîner de graves dysfonctionnements cellulaires, y compris chez l'homme, où elles sont associées à des maladies génétiques appelées ciliopathies. Au cours de ma thèse, nous avons dans un premier temps étudié le rôle et le fonctionnement de l'IFT chez Trypanosoma brucei, un parasite protozoaire flagellé qui est un excellent modèle pour étudier les cils. En utilisant le FIB-SEM, nous avons démontré que les trains IFT n’étaient présents presque exclusivement que sur deux des neuf doublets microtubules de l'axonème. Puis, l'utilisation de la microscopie à haute résolution nous a permis de démontrer dans des cellules vivantes que ces deux voies sont utilisées pour l’IFT dans les deux sens sur chacun de ces doublets. Nous avons ensuite étudié les mécanismes contrôlant la longueur du flagelle et proposé un nouveau modèle appelé «grow and lock» où le flagelle s'allonge avec un taux de croissance constant jusqu'à ce qu'un signal bloque son élongation ou son raccourcissement. Pour finir nous avons étudié l’implication ce modèle durant le cycle parasitaire, lorsque de la construction de flagelles de très longueurs différentes. / Cilia and flagella are essential organelles in most eukaryotes including humans. They share a canonical cylindrical structure composed of nine doublets of microtubules called the axoneme that is conserved during evolution. They are built by an active mechanism termed Intraflagellar Transport or IFT. Despite some variations in composition and length between different types of cilia, the length for a given cell type is tightly controlled. Any defect in flagellum length or IFT machinery can lead to serious cellular dysfunctions, including in humans where it is associated to genetic diseases called ciliopathies. During my thesis, we have first investigated the role and functioning of IFT in Trypanosoma brucei a flagellated protozoan parasite that is a powerful model to investigate cilia. Using Focus Ion Beam-Scanning Electron Microscopy (FIB-SEM), we have demonstrated that IFT trains are present almost exclusively on only two out of nine microtubules doublets of the axoneme. Then, the use of high-resolution microscopy allowed us to observe in live cells that two tracks are actually used for bidirectional IFT trafficking. We have investigated mechanisms controlling flagellum length and propose a new model named “grow and lock” where the flagellum elongates at a constant growth-rate until a signal blocks further elongation or shortening. Finally this and other models have been investigated during the parasite cycle, when trypanosomes construct flagella with very different lengths.

<p>This master thesis deals with problems in the arc length control in Pulsed MIG/MAG Welding. The main problem is that it is not possible to measure the arc length. In the present solution the voltage over both the electrode and the arc represents the arc length. </p><p>To improve the arc length control a model of the electrode melting has been built. One output from the model is the voltage over the electrode and with this voltage together with the measured voltage it is possible to calculate the voltage over just the arc. Then, having the arc voltage as a value of arc length the arc length control can be improved, which is showed in the end by simulations. Simulations with the present control system are compared with the new one, when the controller is able to control the arc voltage instead of the sum of both the electrode voltage and the arc voltage.</p>

This master thesis deals with problems in the arc length control in Pulsed MIG/MAG Welding. The main problem is that it is not possible to measure the arc length. In the present solution the voltage over both the electrode and the arc represents the arc length. To improve the arc length control a model of the electrode melting has been built. One output from the model is the voltage over the electrode and with this voltage together with the measured voltage it is possible to calculate the voltage over just the arc. Then, having the arc voltage as a value of arc length the arc length control can be improved, which is showed in the end by simulations. Simulations with the present control system are compared with the new one, when the controller is able to control the arc voltage instead of the sum of both the electrode voltage and the arc voltage.

京都大学 / 新制・課程博士 / 博士(工学) / 甲第25017号 / 工博第5194号 / 新制||工||1991(附属図書館) / 京都大学大学院工学研究科化学工学専攻 / (主査)教授 外輪 健一郎, 教授 松坂 修二, 教授 佐野 紀彰 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DFAM