L'objet de la présente étude est d'étudier, de comprendre et de maîtriser les différentes propriétés électriques de contacts électriques constitués de membranes souples en carbone, qui commutent sur des pistes métalliques d'un circuit imprimé. Ces contacts sont de plus en plus utilisés dans l'automobile car ils possèdent des propriétés mécaniques intéressantes vis-à-vis du ressenti de l'utilisateur, tout en permettant une bonne durée de vie. Dans un premier temps, les paramètres électriques et mécaniques de ces contacts sont caractérisés, les phénomènes de commutation sur divers type de charges sont étudiés et l'influence de contaminants et de la corrosion sur la conduction électrique sont examinés. L'évolution des résistances d'isolement en présence d'humidité est quantifiée. Dans un second temps, une approche de fiabilité est réalisée : l'évolution des paramètres électriques et mécaniques de ces contacts est étudiée lorsqu'ils sont soumis à des stress environnementaux, en particulier la chaleur humide. Les principaux modes d'endommagement sont étudiés. Nous montrons en particulier que les défaillances mécaniques proviennent essentiellement du polymère, et les défaillances électriques proviennent plutôt du circuit imprimé. L'influence d'un revêtement doré côté circuit imprimé, pour différentes épaisseurs, est également étudiée. Notre travail se poursuit par une étude un peu plus fondamentale sur les phénomènes de commutation en présence de matériaux en carbone. Au cours de ce travail novateur, les signatures optiques sont examinées lors de la coupure du courant. Un phénomène baptisé « glowing » est mis en évidence ; les limites en courant et en tension entre « glowing » et arcage électrique sont données, et les phénomènes comparés par rapport aux phénomènes de commutation dans les contacts de type métal – métal. L'étude se termine par un bilan synthétique concernant l'utilisation de contacts comprenant une pastille en carbone, avec leurs avantages et leurs limitations. / The purpose of this study is to explore, understand and master the different electrical properties of electrical contacts made of flexible carbon membranes, which switch on metal tracks on a printed circuit board. These contacts are increasingly used in the automobile because they have interesting mechanical properties for the user, while providing a good reliability. At first, the electrical and mechanical parameters of these contacts are characterized, the switching phenomena on various types of loads are studied and the influence of contaminants and corrosion on the electrical conduction is examined. The evolution of insulation resistance in the presence of moisture is quantified. In a second step, an approach to reliability is achieved: the evolution of electrical and mechanical parameters of these contacts is studied when subjected to environmental stresses, especially moist and heat. The main types of damage are considered. We show in particular that mechanical failures come mainly from polymer and electrical failures from the PCB. The influence of a gold-plated printed for different thicknesses system side, is also studied. Our work continues with a slightly more fundamental study on switching phenomena in the presence of carbon materials. In this pioneering work, the optical signatures are discussed at the current break. A phenomenon called "glowing" is highlighted; limits current and voltage between "glowing" and electrical arcing are given, and compared with respect to the phenomena switching phenomena in metal contacts - type metal. The study concludes with a summary review on the use of contacts comprising a carbon pill, with their advantages and limitations.

La mesure cardiaque sans contact réalisée grâce aux méthodes de photopléthysmographie sans contact est un domaine de recherche très actif. Depuis l'introduction en 2010 d'une nouvelle méthode de mesure avec des capteurs optiques d'entrée de gamme (webcam PC), les travaux de recherche se sont multipliés. Ainsi, on observe une plus grande diversité des méthodes proposées afin de réaliser la mesure. Egalement, la précision de la mesure a grandement progressé et les scénarios et possibilités d'usage de la technologie sont aujourd'hui très nombreux. Au cœur de ce processus de mesure, la segmentation dans l'image de la ou les zones d'intérêt est une étape clé. Nous proposons dans cette thèse une méthode innovante afin de réaliser la mesure photoplethysmographique sans contact en identifiant implicitement les zones de peau vivante dans la vidéo. Nous avons montré que notre approche permet d'améliorer la qualité de la mesure en favorisant les zones dans l'image où le signal est de plus grande qualité. Afin de rendre possible l'intégration de notre solution, nous avons proposé une nouvelle méthode de segmentation en superpixels, nommée IBIS, qui permet de réduire la complexité algorithmique de cette étape du traitement. Ce faisant, nous avons démontré la faisabilité de l'intégration de notre solution au sein d'une plateforme embarquée. Les différentes méthodes ont été évaluées au travers de plusieurs expérimentations afin de valider leurs performances. Notre méthode de segmentation en superpixels est comparée aux méthodes de l'état de l'art tandis que nous avons implémenté plusieurs des méthodes de mesure du signal photoplethysmographique afin de discuter de l'impact de notre approche sur la qualité de la mesure photoplethysmographique. Que ce soit pour la segmentation en superpixels ou pour l'estimation du rythme cardiaque sans contact, nous avons montré une importante plus-value de nos méthodes comparées à celles disponibles dans la littérature. Les différents travaux présentés dans ce document ont été valorisés au travers de publications en conférences et revue. / Heart-rate estimation performed with remote photoplethysmography is a very active research field. Since pioneer works in 2010, which demonstrated the feasibility of the measure with low-grade consumers’ camera (webcam), the number of scientific publications have increased significantly in the domain. Hence, we observe a multiplication of the methods in order to retrieve the photoplethysmographic signal which has led to an increased precision and quality of the heart-rate estimation. Region of interest segmentation is a key step of the processing pipeline in order to maximize the quality of the measured signal. We propose a new method to perform remote photoplethysmographic measurement using an implicit living skin identification method. Hence, we have shown that our approach lead to an improvement in both quality of the signal measured and precision of the heart-rate estimation by favoring more contributive area. As we are working with hardware integration constraint, we propose a new superpixels segmentation method which requires significantly less computation power than state of the art methods by reducing the algorithmic complexity of this step. Moreover, we have demonstrated the integration and real time capabilities by implementing our solution to an embedded device. All of our proposed method have been evaluated through different experimentations. Our new segmentation method, called IBIS, have been compared to state of the art methods to quantify the quality of the produced segmentation. To quantify the impact of our approach on the quality of the photoplethysmographic measure, we have implemented and compared state of the art methods with our proposed method. For both the superpixels segmentation and remote heart-rate estimation, our methods have shown great results and advantages compared to state of the art ones. Our works have been reviewed by the scientific community through several conference presentations and journal publications.

La cellule photovoltaïque à porteurs chauds se caractérise par une population électronique hors équilibre thermique avec le réseau, ce qui se traduit par une température électronique supérieure à la température du matériau. Il devient alors possible de récupérer non seulement l'énergie potentielle des porteurs, mais également leur énergie cinétique, et donc d'extraire un surcroît de puissance qui n'est pas exploitée dans des cellules conventionnelles. Cela permet d'atteindre des rendements potentiels proches de la limite thermodynamique. L'extraction des porteurs hors équilibre se fait au moyen de membranes sélectives en énergie afin de limiter les pertes thermiques. Dans cette thèse, l'influence de la sélectivité des contacts sur les performances de la cellule est analysée par des simulations de rendement. Il apparaît que ce paramètre est moins critique qu'annoncé dans la littérature, et que des rendements élevés sont possibles avec des contacts semi-sélectifs, permettant l'extraction de porteurs au dessus d'un seuil d'énergie. De tels contacts sont non seulement beaucoup plus facilement réalisables en pratique que des contacts sélectifs, mais sont également plus compatibles avec les densités de courant élevées qui sont attendues dans de tels dispositifs. Une méthodologie expérimentale est également proposée pour analyser la vitesse de thermalisation des porteurs hors équilibre. Des porteurs sont photogénérés par un laser continu et leur température en régime stationnaire est sondée par photoluminescence en fonction de la densité de puissance excitatrice. Un modèle empirique est obtenu reliant la puissance dissipée par thermalisation à la température électronique. Ce modèle est ensuite utilisé pour simuler le rendement de cellules présentant une thermalisation partielle des porteurs. Enfin, un rendement de cellule réaliste présentant une absorption non idéale, une vitesse de thermalisation mesurée sur des matériaux réels et des contacts semi-sélectifs est calculé. Il ressort qu'une augmentation substantielle de rendement est possible en comparaison d'une simple jonction ayant le même seuil d'absorption, mais que la vitesse de thermalisation observée est néanmoins trop élevée pour permettre de dépasser les records de rendement actuels. Des idées sont proposées afin d'améliorer les performances des structures étudiées.

The internationalization process is usually viewed from an outward- perspective ininternational business literature. In this thesis the focus is put on an outward-inwardinterrelationship perspective. An extensive literature review from literature in internationalbusiness literature, entrepreneurial literature as well as international marketing literature wasconducted in order to extract key variables that affect the process of internationalization of thefirm. The key variables that were examined were: Business Contacts, InternationalExperience, Perceived International Opportunity and Perceived International Uncertainty.A qualitative interview with semi-structured questions was conducted in order to construct amodel that should be used as the basis for a quantitative study of an inward-driveninternationalization process, in order to generalize. The results were in line with thepropositions based on the relationships between the variables. In other words, the constructedmodel and the developed questionnaire were of use when examining the relationship betweenthe variables and seem to be of value when applied to an inward oriented context. Thevariable International Experience received the highest score and seemed to reflect animportant contribution for the internationalization process. Nevertheless, further quantitativeresearch is asked for, in order to support the results and be able to generalize.

Epithelial mesenchymal/-myofibroblast transition (EMT/EMyT) has emerged as one of the central mechanisms in wound healing and tissue fibrosis. The main feature of EMyT is the activation of a myogenic program, leading to the induction of the α-smooth-muscle actin (SMA) gene in the transitioning epithelium. Recent research suggests that intercellular contacts are not merely passive targets, but are active contributors to EMT/EMyT. Indeed, our group showed previously that contact uncoupling or injury is necessary for TGFβ to induce EMyT (two-hit paradigm). Further, our previous work also revealed that Smad3, the main TGFβ-regulated transcription factor, binds to the Myocardin Related Transcription Factor (MRTF), the prime driver of SMA promoter, and inhibits MRTF’s transcriptional activity. During EMyT, Smad3 eventually degrades, which liberates the MRTF-driven myogenic program. However the mechanisms whereby cell contacts regulate the fate of Smad3 and MRTF during EMyT are poorly understood. Accordingly, the central aim of my studies was to explore the role of intercellular contacts, in particular that of Adherens Junction (AJs) in the induction of the myogenic reprogramming of the injured epithelium. This thesis describes two novel molecular mechanisms through which AJs impact EMyT. In the first part, we show β-catenin, an AJs component and transcriptional co-activator counteracts the inhibitory action of Smad3 on MRTF. Moreover we reveal that β-catenin is necessary to maintain MRTF stability via protecting MRTF from proteasomal degradation. Thus, β-catenin is an indispensable permissive factor for SMA expression. In the second part, we demonstrate that contact injury and TGFβ suppress the expression of the phosphatase PTEN. EMyT-related reduction or absence of PTEN potentiates Smad3 degradation. EMyT is associated with enhanced phosphorylation of the T179 residue in Smad3 linker region, and this event is necessary for Smad3 degradation. PTEN silencing increases the stimulatory effect of contact uncoupling and TGFβ on SMA promoter activity and SMA protein expression. Thus, the integrity of intercellular contacts regulates the level of PTEN, which in turn controls Smad3 stability through impacting on T179 phosphorylation. This new knowledge holds promises for targeted therapies and more effective prevention of the currently incurable fibroproliferative and fibrocontractile diseases.

The metal/graphite interface is interesting due to the typically large disparity in the characteristics of the electronic structure (e.g. Fermi wavelength and Fermi energy) and dimensionality (3D in the metal versus quasi-2D in graphite). The goal of this work is to determine how the contact conductance to graphite depends on the metal contact area for nanometer-scale contacts. From this we deduce the effect of electronic screening in the graphite. Three different metals were chosen for this work: Solid Cu and Al, and liquid Ga. Liquid Ga provided a unique opportunity to reduce the effect of mechanical interactions to near zero, while Cu and Al were chosen for their different electronic structures. At the interface between the metal and graphite, the large Fermi wavevector of Al should allow phase matching of Al states to those in graphite, while the Cu Fermi surface lies inside of all available graphite wavevector states.

Abstract The arc behavior during the closing and opening of electrical contacts not only influences the surface morphology, but also causes the erosion of contact material. The mechanical stresses, the molten bridge, and the arc cause this erosion. Consequently, the erosion mechanism is very complex. Therefore, to avoid the influences of mechanical stresses and numerous arc striking, static-gap experiments with a single arc discharge are conducted to investigate the effects of pulse voltage, gap distance, and arc duration on the erosion characteristics and mechanism of silver based contact materials. Moreover, this experimental result is verified by the finding of the dynamic testing of electrical contacts. The results of the erosion characteristics show that the arcing and non-arcing regions have been distinguished at the supply voltage from 32 V to 500 V and the gap distance from 0.2 mm to 40 mm. The empirical formula for the minimum pulse voltage at arc initiation in terms of gap distance is established. When the pulse voltage is smaller than 200 V, the erosion area increases with increasing gap distance due to the action of the metallic-phase arc. However, when the pulse voltage is greater than 200 V, with increasing gap distance, the erosion area increases to a maxim, and finally diminishes due to the increase in the amount of gaseous-phase arc. The results of the erosion mechanism show that the arcing region is classified into three erosion patterns, namely, the molten metal bridge (B), metallic-phase arc (M), and gaseous-phase arc (G). At the gap distance of 0.2 mm, the erosion pattern of anode silver is varied from B, through B+M, and, M, to M+G. According to the electron transfer across triangular potential barrier, the thermionic emission causes the erosion patterns of B, B+M, and M, and mixed thermionic and field emission results in the erosion pattern of M+G. When the pulse voltage is 500 V, with increasing gap distance, the splashing of metallic particles around the anode crater becomes more dispersed, shorter with more silver powder, and finally disappeared with a little silver powder due to the influence of the gaseous-phase arc. The results of the anti-weld ability show that when the pulse voltage is 500 V and the arc energy is grater than 14 J at the static-gap experiments, the critical gap distance to produce welding for Ag-Ni, Ag-CdO, and Ag-SnO2 is 3 mm, 8 mm, and 15 mm, respectively. This indicates Ag-Ni contact possesses the best anti-weld ability. On the other hand, the results of dynamic testing of electrical contacts show that at the arc energy less than 10 J, the anti-erosion, anti-weld ability, and the welding area are seen to increase with contact materials in the following order: Ag-CdO > Ag-SnO2 > Ag-Ni. However, when the arc energy is greater than 10 J, the anti-erosion, anti-weld ability, and the erosion area are seen to increase in the reverse order: Ag-SnO2 < Ag-CdO < Ag-Ni, which are in very good agreement with the results of static-gap experiments. Furthermore, the erosion surface of the silver-based contact materials can be observed and analyzed by using the X-ray diffraction method (XRD), differential thermal analysis (DTA), and gravitation thermal analyzer (GTA). Results show that when the arc energy is greater than 14 J, Ag-CdO and Ag-SnO2 have been decomposed into Ag-Cd and Ag-Sn alloys, respectively, which reduce their anti-weld ability. On the other hand, the welding trend has been reduced due to the dispersion of NiO on the surface of Ag-Ni contact. Consequently, the anti-erosion and anti-weld ability for the Ag-Ni contacts are better than those of the other Ag-MeO contact materials.

Dissertation (Ph.D.)--Auburn University, 2009. / Abstract. Includes bibliographic references (p.139-151).

A Simple way to improve solar cell efficiency is to enhance the absorption of light and reduce the shading losses. One of the main objectives for the photovoltaic roadmap is the reduction of metalized area on the front side of solar cell by fin lines. Industrial solar cell production uses screen-printing of metal pastes with a limit in line width of 70-80 μm. This paper will show a combination of the technique of laser grooved buried contact (LGBC) and Screen-printing is able to improve in fine lines and higher aspect ratio. Laser grooving is a technique to bury the contact into the surface of silicon wafer. Metallization is normally done with electroless or electrolytic plating method, which a high cost. To decrease the relative cost, more complex manufacturing process was needed, therefore in this project the standard process of buried contact solar cells has been optimized in order to gain a laser grooved buried contact solar cell concept with less processing steps. The laser scribing process is set at the first step on raw mono-crystalline silicon wafer. And then the texturing etch; phosphorus diffusion and SiNx passivation process was needed once. While simultaneously optimizing the laser scribing process did to get better results on screen-printing process with fewer difficulties to fill the laser groove. This project has been done to make the whole production of buried contact solar cell with fewer steps and could present a cost effective opportunity to solar cell industries. / <p>In collaboration with Institute for Photovoltaics <strong><em>IPV</em></strong>, University of Stuttgart.</p>

This thesis deals with the tribological and dynamic aspects of tactile perception given by the scanning of the finger on a surface. The attention is focused on a direct analysis of the vibration spectrum characteristics, induced by the surface features that is a relatively new research field. In fact, it is accepted that vibrations activate the tactile afferents and their essential role for the perception of fine textures (duplex theory of tactile texture perception) but it is still unknown the link with the surface texture characteristics and the features of the induced vibration spectra. The work is aimed to contribute to a better understanding of the mechanisms of the tactile sense, that is basilar for manifold different applications: textile quality quantification, ergonomics of everyday objects (which largely affects their commercial competitiveness), identification of surface imperfections, the design of tactile communication devices, the development of artificial tactile sensors for intelligent prostheses or robotic assistants, the development of human-machine interfaces for interaction with virtual realities or teleoperation systems, such as for telediagnosis or microsurgery, reproducing real perception (virtual reality), increasing the human perception (augmented reality), development of tests for evaluation of tactile sensitivity during diagnosis or monitoring process in rehabilitation. The study of a finger that moves on a surface involves different difficulties that are related to the material characteristics and to the measurements themselves. For these reasons, a new experimental set-up, named TriboTouch, has been developed to reproduce the finger/surface scanning phenomena under real values of the contact feature (scanning velocity and amplitude, surface roughness, etc..), avoiding undesired vibrations. The test bench has been designed to guarantee the measurements reproducibility and to perform measurements without introducing external noise. The set-up permits to carry out both measurements of the global dynamics and local ones (at the contact zone) employing a silicone fake finger. In the presented analysis, the behavior of the right hand index finger scanning on the surface sample with periodical and isotropic roughness and on textiles has been investigated for different scanning speed, highlighting the role of fingerprints A simple numerical model have been developed for reproducing the behavior of the induced vibrations when sliding two periodical surfaces and the numerical results have been compared with the experimental ones. The presented work has shown the possibility to obtain objective indexes for the tactile perception characterization, by means of the friction induced vibration spectrum analysis, in agreement with the neurophysiological studies present in literature.