Thèses sur le sujet « Forced proximity »

La spectroscopie électronique basée sur l’effet tunnel donne accès à la densité d’états des électrons (DoS) dans les matériaux conducteurs, et renseigne ainsi en détail sur leurs propriétés électroniques. Au cours de cette thèse, nous avons développé un microscope permettant d’effectuer la spectroscopie tunnel résolue spatialement (10 nm) de nanocircuits individuels, avec une résolution en énergie inégalée (10 µeV). Cet appareil combine les fonctions de Microscopie par Force Atomique (mode AFM) et de spectroscopie Tunnel locale (mode STM), et fonctionne à 30 mK. Dans le mode AFM, la topographie de l’échantillon est imagée grâce à un diapason en quartz piézoélectrique, ce qui permet de repérer les circuits. La spectroscopie tunnel peut ensuite être faite sur les zones conductrices. Avec ce microscope, nous avons mesuré la DoS locale dans une structure hybride Supraconducteur-métal Normal-Supraconducteur (S-N-S). Dans un tel circuit, les propriétés électroniques de N et de S sont modifiées par l’effet de proximité supraconducteur. Notamment, pour des fils N courts, nous avons pu observer -comme prédit- la présence d’un gap dans sa DoS, indépendant de la position dans la structure : le “minigap”. De plus, en modulant la phase supraconductrice entre les deux S, nous avons mesuré la modification de ce gap, et sa disparition lorsque la différence de phase vaut p. Nos résultats expérimentaux pour la DoS, ainsi que ses dépendances en phase, en position, et en longueur de N sont en accord quantitatif avec les prédictions de la théorie quasiclassique de la supraconductivité. Certaines de ces prédictions sont observées pour la première fois.

In this thesis, we address the issue of fully localizing a known object through computer vision, using a monocular camera, what is a central problem in robotics. A particular attention is here paid on space robotics applications, with the aims of providing a unified visual localization system for autonomous navigation purposes for space rendezvous and proximity operations. Two main challenges of the problem are tackled: initially detecting the targeted object and then tracking it frame-by-frame, providing the complete pose between the camera and the object, knowing the 3D CAD model of the object. For detection, the pose estimation process is based on the segmentation of the moving object and on an efficient probabilistic edge-based matching and alignment procedure of a set of synthetic views of the object with a sequence of initial images. For the tracking phase, pose estimation is handled through a 3D model-based tracking algorithm, for which we propose three different types of visual features, pertinently representing the object with its edges, its silhouette and with a set of interest points. The reliability of the localization process is evaluated by propagating the uncertainty from the errors of the visual features. This uncertainty besides feeds a linear Kalman filter on the camera velocity parameters. Qualitative and quantitative experiments have been performed on various synthetic and real data, with challenging imaging conditions, showing the efficiency and the benefits of the different contributions, and their compliance with space rendezvous applications.

Nous étudions la force de Casimir entre deux miroirs métalliques à température non nulle. Nous développons les outils théoriques nécessaires à une évaluation précise de cette force et qui permettent une comparaison de haute précision avec les mesures expérimentales récentes. A partir de la notion de réseau optique, nous caractérisons la diffusion des fluctuations du vide électromagnétique sur une cavité Fabry-Perot et calculons la force de Casimir comme la différence des pressions de radiation exercées par ces fluctuations à l'intérieur et à l'extérieur de la cavité. L'effet de réflexion imparfaite des miroirs est pris en compte en étudiant leur réponse optique, d'abord pour des miroirs diélectriques puis pour des miroirs métalliques. Nous détaillons le rôle des propriétés de causalité, de stabilité et de transparence à haute fréquence des amplitudes de diffusion. Nous calculons également la force de Casimir à température ambiante en évaluant l'effet induit par les fluctuations thermiques du champ. En tenant compte simultanément de cet effet et de l'effet de réflexion imparfaite des miroirs, nous montrons que ces deux effets sont corrélés et que cette corrélation doit être considérée pour une évaluation de haute précision. Dans le cadre de notre formulation, nous résolvons la polémique liée au calcul de la force entre miroirs dissipatifs à température non nulle. Finalement, nous analysons les problèmes de géométrie et de rugosité liés aux expériences. En particulier pour la question de la rugosité de surface des miroirs, nous montrons pour des miroirs parfaits que l'approximation de proximité n'est pas toujours valable. Nous insistons sur les effets de sensibilité liés à la dépendance spectrale de la rugosité.

Les travaux présentés et discutés dans cette thèse ont pour objectif de proposer plusieurs solutions au problème de l’analyse et du clustering de nuages de points en basse dimension. Ces solutions s’appuyent sur l’analyse de triangulations de Delaunay. Deux types d’approches sont présentés et discutés. Le premier type suit une approche en trois-passes classique: 1) la construction d’un graphe de proximité contenant une information topologique, 2) la construction d’une information statistique à partir de ce graphe et 3) la suppression d’éléments inutiles au regard de cette information statistique. L’impact de différentes measures sur le clustering ainsi que sur la reconnaissance de caractères est discuté. Ces mesures s’appuyent sur l’exploitation du complexe simplicial et non pas uniquement sur celle du graphe. Le second type d’approches est composé d’approches en une passe extrayant des clusters en même temps qu’une triangulation de Delaunay est construite
This thesis aims at proposing and discussing several solutions to the problem of low-dimensional point cloudanalysis and clustering. These solutions are based on the analysis of the Delaunay triangulation.Two types of approaches are presented and discussed. The first one follows a classical three steps approach:1) the construction of a proximity graph that embeds topological information, 2) the construction of statisticalinformation out of this graph and 3) the removal of pointless elements regarding this information. The impactof different simplicial complex-based measures, i.e. not only based on a graph, is discussed. Evaluation is madeas regards point cloud clustering quality along with handwritten character recognition rates. The second type ofapproaches consists of one-step approaches that derive clustering along with the construction of the triangulation

Dissertação de Mestrado em Comunicação Social, vertente de Comunicação Estratégica
A evolução da tecnologia lançou novos desafios à comunicação entre as pessoas, o que obrigou as organizações a responderem de igual forma. Os novos canais e espaços onde a comunicação se desenrola, como é o caso dos social media e de outras plataformas digitais, permitem às organizações, através das relações públicas, encetar novas interacções com os seus públicos. As relações entre ambos passam a ser interactivas e participativas e não unidireccionais, como acontece com as mensagens veiculadas nos media tradicionais. As Forças de Segurança, para atingirem os seus objectivos, necessitam de ter uma presença junto da comunidade para a qual recorrem ao policiamento de proximidade. Este, enquanto base de actuação das Forças de Segurança portuguesas, deve adaptar-se à evolução da forma de comunicar, usufruindo das plataformas digitais, que permitem um contacto permanente e eficaz com os seguidores. Partindo deste princípio, pretende-se compreender como podem as ferramentas de comunicação digital contribuir para a promoção de uma política de proximidade nas Forças de Segurança Portuguesas, nomeadamente da PSP e da GNR. Para isso, contou-se com a análise teórica sobre as relações públicas online integradas na estratégia de comunicação das organizações e as mais-valias dos social media para o policiamento de proximidade. Adicionalmente, realizaram-se entrevistas aos responsáveis pelos departamentos de comunicação de cada uma das instituições e foi ainda analisado o conteúdo das suas páginas de Instagram e Facebook, para identificar diferenças e semelhanças entre ambas na linha editorial de conteúdos, assim como as reacções dos seguidores. Desta análise, foi possível concluir sobre o contributo positivo da utilização destas ferramentas na proximidade com os cidadãos, nomeadamente no aumento do número de contactos proactivos com as Forças de Segurança. Estas ferramentas contribuem ainda para aumentar a exposição a conteúdos de prevenção e sensibilização, bem como para diminuir as limitações no contacto dos cidadãos.
The evolution of technology has launched new challenges to communication between people, which has forced organizations to respond in the same way. The new channels and spaces where communication takes place, such as social media and other digital platforms, allow organisations, through public relations, to initiate new interactions with their audiences. The relations between them become interactive and participative and not unidirectional, as happens with the messages conveyed in traditional media. In order to achieve their objectives, the Security Forces need to have a presence in the community for which they resort to proximity policing. This, as a base of action of the Portuguese Security Forces, must adapt to the evolution of the way of communicating, taking advantage of digital platforms, which allow a permanent and effective contact with the followers. Based on this principle, it is entended to understand how digital communication tools can contribute to the promotion of a proximity policy in the Portuguese Security Forces, namely PSP and GNR. To this end, we relied on the theoretical analysis of online public relations integrated into the communication strategy of organisations and the added value of social media for proximity policing. In addition, interviews were conducted with those responsible for the communication departments of each of the institutions and the content of their Instagram and Facebook pages was also analysed to identify differences and similarities between them in the editorial content line, as well as the reactions of the followers. From this analysis, it was possible to conclude on the positive contribution of the use of these tools in proximity with the citizens, namely in the increase of the number of proactive contacts with the Security Forces. These tools also contribute to increasing exposure to prevention and awareness-raising content, as well as to reducing the limitations on citizen contact.
N/A

There is currently a high demand for electric power from renewablesources. One source that remains relatively untapped is the motionof ocean waves. Anders Hagnestål has been developing a uniquelyefficient and simplified design for a point-absorb buoy generator byconverting its linear motion directly into alternating electric power usinga linear PM engine. To test this method, a smaller prototype isbuilt. Its characteristics present some unusual challenges in the designand construction of its winding.Devices of this type typically use relatively low voltage (690V typicallyfor a wind turbine, compared to the 10kV range of traditionalpower plants). To achieve high power, they need high current, whichin turn requires splitting the conductors in the winding into isolatedparallel strands to avoid losses due to eddy currents and current crowding.However, new losses from circulating currents can then arise. Inorder to reduce said losses, the parallel conductors should be transposedin such a way that the aggregate electromotive force the circuitsthat each pair of them forms is minimized.This research and prototyping was performed in absence of advancedindustrial means of construction, with limited space, budget,materials, manpower, know-how, and technology. Manual ingenuityand empirical experimentation were required to find a practical implementationfor: laying the cables, fixing them in place, transferringthem to the machine, stripping their coating at the ends and establishinga reliable connection to the current source.Using theoretical derivations and FEM simulation, a sufficientlygood transposition scheme is proposed for the specific machine thatthe winding is built for. A bobbin replicating the shape of the enginecore is built to lay down the strands.The parallel strands are then organized each into their respectivebobbin, with a bobbin rack and conductor funneling device being designedand constructed to gather them together into a strictly-organizedbundle. An adhesive is found to set the cables in place.Problems with maintaining the orientation and configuration of thecables in the face of repeated torsion are met and solved. A chemicalsolution is used to strip the ends of the conductors, and a reliableconnection is established by crimping the conductors into a bi-metalCu-Al lug.ivIn conclusion, the ideal transposition schemes required to cancelout circulating currents due to magnetic flux leakage are impossibleto put in practice without appropriate technological means. The feasibletransposition scheme turns out to be a simple mirroring of conductors’positions, implemented by building each half of the windingseparately around replicas of the core and then connecting them usingcrimping lugs.
Efterfrågan på el från förnybara källor är hög och inget tyder på att det kommer ändras den närmsta tiden. En källa till förnybar el som än idag står relativt orörd är den där man använder energin från havsvå- gor. Det är denna förnybara källa Anders Hagnestål haft i åtanke när han nu bygger en unikt effektiv generator med syftet att i ett senare skede utvinna el med hjälp av flytande punktabsorberande vågkraft- system. Generatorn är av den linjära typen och omvandlar det punk- tabsorberande systemet rörelse till el. För att testa denna generator- modell så påbörjades bygget av två fullskaliga prototyper 2017. Denna uppsats behandlar specifikt arbetet med generatorlindningen till pro- totyperna och innefattar processen från design till själva byggnatio- nen. Lindingen består av flertalet mindre och isolerade lindningsleda- re med uppgift att bland annat minska skinneffekt och virvelströms- förluster. När man använder denna metod så uppkommer dock ett nytt problem vilket härstammar från att lindningsledarna är samman- kopplade i vardera ända och bildar på så sätt n slutna strömkretsar. Konsekvensen kan vara stora förluster från cirkulerande strömmar på grund av det magnetiska ströflöde som finns runt järnkärnan som lindningen omsluter. Utgångspunkten för att minimera dessa cirkule- rande strömmar är att transponera alla lindningsledare på ett sätt så att den resulterande elektromotoriska spänningen för varje strömkrets blir så liten som möjligt. Med hjälp av förenklade modeller samt FEM simuleringar så bestämdes ett lämpligt sätt att transponera lindningstrådarna utifrån oli- ka kriterier. Lösningen blev att lindningstrådarna endast transponera- des en gång med en så kallad 180 grader transponering. Detta ger en tillräckligt god minimering av de cirkulerande ström- marna, men den stora fördelen med denna lösning är att det är möjligt att linda maskinen med de små resurser projektet hade tillgång till, dock var detta till en stor nackdel då väldigt mycket tid gick till att hitta egna tillvägagångsätt för att utföra byggandet av lindningen på ibland okonventionella sätt.

La spectroscopie électronique basée sur l'effet tunnel donne accès à la densité d'états des électrons (DoS) dans les matériaux conducteurs, et renseigne ainsi en détail sur leurs propriétés électroniques.
Au cours de cette thèse, nous avons développé un microscope permettant d'effectuer la spectroscopie tunnel résolue spatialement (10 nm) de nanocircuits individuels, avec une résolution en énergie inégalée (10 µeV). Cet appareil combine les fonctions de Microscopie par Force Atomique (mode AFM) et de spectroscopie Tunnel locale (mode STM), et fonctionne à 30 mK. Dans le mode AFM, la topographie de l'échantillon est imagée grâce à un diapason en quartz piézoélectrique, ce qui permet de repérer les circuits. La spectroscopie tunnel peut ensuite être faite sur les zones conductrices.
Avec ce microscope, nous avons mesuré la DoS locale dans une structure hybride Supraconducteur-métal Normal-Supraconducteur (S-N-S). Dans un tel circuit, les propriétés électroniques de N et de S sont modifiées par l'effet de proximité supraconducteur. Notamment, pour des fils N courts, nous avons pu observer -comme prédit- la présence d'un gap dans sa DoS, indépendant de la position dans la structure : le “minigap”. De plus, en modulant la phase supraconductrice entre les deux S, nous avons mesuré la modification de ce gap, et sa disparition lorsque la différence de phase vaut π.
Nos résultats expérimentaux pour la DoS, ainsi que ses dépendances en phase, en position, et en longueur de N sont en accord quantitatif avec les prédictions de la théorie quasiclassique de la supraconductivité. Certaines de ces prédictions sont observées pour la première fois.

Dissertação de Mestrado Integrado em Engenharia Mecânica apresentada à Faculdade de Ciências e Tecnologia
A perceção eficaz do ambiente envolvente, assim como a criação de mecan ismos compatíveis são dois objetivos importantes para permitir uma in teração homem-robô (Human-Robot Interaction – HRI) segura e intu itiva. Este trabalho encontra-se dividido em duas partes. Na primeira parte apresentamos um sensor híbrido de força e proximidade, mecanica mente flexível, baseado nos fenómenos de piezoresistividade e capacitân cia. Constituído por materiais e componentes de baixo custo, amplamente disponíveis no mercado, o sensor proposto pode ser fabricado e implemen tado de forma econômica a grande escala, melhorando a perceção senso rial de qualquer instalação robótica. Um sistema de aquisição de dados (Data Acquisition System – DAQ) também foi apresentado, permitindo uma interface conveniente com sensor, por meio de uma conexão série USB (Universal Serial Bus). Resultados demonstraram uma resposta rápida e moderadamente precisa a forças entre 0,5 N e 15 N. A deteção de presença humana foi alcançada a distâncias de até 100 mm, embora com uma resolução espacial relativamente reduzida (~ 50 mm). Na segunda parte deste trabalho apresentamos um atuador flexível baseado no processo de mudança de fase (Phase Change Artificial Muscle – PCAM). Com base em músculos artificiais pneumáticos tradicionais McKibben (Pneumatic Artificial Muscles – PAMs), o atuador proposto explora a ex pansão volumétrica da água em transição de fase líquido-vapor alimen tada por uma fonte de alimentação DC (Direct Current) de baixa tensão. Forças de atuação de 27,5 N foram repetidamente alcançadas com atu adores cuja massa é de apenas 23 g. Alta precisão no controlo de pressão foi alcançada, com o sistema a apresentar-se capaz de seguir comandos de pressão com erros de + - 1 kPa. Vários fenômenos importantes foram explorados e discutidos, incluindo limites para taxas de pressurização, segurança de fluidos e limitações de controlo, estabelecendo uma base sólida para futuro desenvolvimento e implementação.
Insightful perception of the surrounding environment, as well as compliant mechanisms are two important goals to enable safe and intuitive Human-Robot Interaction (HRI). This work is divided into two parts. In Part 1, a mechanically flexible, piezoresistive and self-capacitive hybrid force and proximity sensor is presented. Made of low cost and highly available components, the proposed sensor can be economically made and deployed in large numbers, improving the sensory awareness of any robotic system. A Data Acquisition System (DAQ) was also presented, allowing users to conveniently interface the sensor through a regular Universal Serial Bus (USB) connection. Results show a fast and moderately precise response to forces ranging between 0.5 N and 15 N. Human presence detection was achieved at distances up to 100 mm, but with fairly low spatial resolution (~50 mm). In Part 2 of this work, a compliant Phase Change Artificial Muscle (PCAM) is presented. Based on traditional pneumatic McKibben Pneumatic Artificial Muscles (PAMs), the proposed actuator explores the volumetric expansion of water undergoing liquid-gas phase transition, powered by a low voltage DC power source. Actuation forces of 27.5 N were routinely achieved with actuators weighing just 23 g. High-pressure control precision was achieved, with the system following set pressure commands within +- 1 kPa. Several important phenomena were explored and discussed including limits to pressurization rates, fluid safety and control limitations, laying the foundation for future development and deployment.

Exact analytical solutions for the quasistationary electromagnetic fields in the presence of conducting objects require the field solutions both internal and external to the conductors. Such solutions are limited for certain canonically shaped objects but are useful in testing the accuracy of various approximate models and numerical methods developed to solve complex problems related to real world conducting objects and in calibrating instruments designed to measure various field quantities. Theoretical investigations of quasistationary electromagnetic fields also aid in improving the understanding of the physical phenomena of electromagnetic induction. This thesis presents rigorous analytical expressions derived as benchmark solutions for the quasistationary field quantities both inside and outside, Joule losses and the electromagnetic forces acting upon a conducting spheroid placed in the proximity of a non-uniform field produced by current-carrying turns. These expressions are used to generate numerous numerical results of specified accuracy and selected results are presented in a normalized form for extended ranges of the spheroid axial ratio, the ratio of the depth of penetration to the semi-minor axis and the position of the inducing turns relative to the spheroids. They are intended to constitute reference data to be employed for comprehensive comparisons of results from approximate numerical methods or from boundary impedance models used for real world conductors. Approximate boundary conditions such as the simpler perfect electric conductor model or the Leontovich surface impedance boundary condition model can be used to obtain approximate solutions by only analyzing the field external to the conducting object. The range of validity of these impedance boundary condition models for the analysis of axisymmetric eddy-current problems is thoroughly investigated. While the simpler PEC model can be employed only when the electromagnetic depth of penetration is much smaller than the smallest local radius of curvature, the results obtained using the surface impedance boundary condition model for conducting prolate and oblate spheroids of various axial ratios are in good agreement with the exact results for skin depths of about 1/5 of the semi-minor axis when calculating electromagnetic forces and for skin depths less than 1/20 of the semi-minor axis when calculating Joule losses.