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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
931

Adaptive Eyes

Wege, Claudia 10 April 2015 (has links) (PDF)
Technology pervades our daily living, and is increasingly integrated into the vehicle – directly affecting driving. On the one hand technology such as cell phones provoke driver distraction and inattention, whereas, on the other hand, Advanced Driver Assistance Systems (ADAS) support the driver in the driving task. The question is, can a driver successfully adapt to the ever growing technological advancements? Thus, this thesis aimed at improving safe driver behaviour by understanding the underlying psychological mechanisms that influence behavioural change. Previous research on ADAS and human attention was reviewed in the context of driver behavioural adaptation. Empirical data from multiple data sources such as driving performance data, visual behaviour data, video footage, and subjective data were analyzed to evaluate two ADAS (a brake-capacity forward collision warning system, B-FCW, and a Visual Distraction Alert System, VDA-System). Results from a field operational test (EuroFOT) showed that brake-capacity forward collision warnings lead to immediate attention allocation toward the roadway and drivers hit the brake, yet change their initial response later on by directing their eyes toward the warning source in the instrument cluster. A similar phenomenon of drivers changing initial behaviour was found in a driving simulator study assessing a Visual Distraction Alert System. Analysis showed that a Visual Distraction Alert System successfully assists drivers in redirecting attention to the relevant aspects of the driving task and significantly improves driving performance. The effects are discussed with regard to behavioural adaptation, calibration and system acceptance. Based on these findings a novel assessment for human-machine-interaction (HMI) of ADAS was introduced. Based on the contribution of this thesis and previous best-practices, a holistic safety management model on accident prevention strategies (before, during and after driving) was developed. The DO-IT BEST Feedback Model is a comprehensive feedback strategy including driver feedback at various time scales and therefore is expected to provide an added benefit for distraction and inattention prevention. The central contributions of this work are to advance research in the field of traffic psychology in the context of attention allocation strategies, and to improve the ability to design future safety systems with the human factor in focus. The thesis consists of the introduction of the conducted research, six publications in full text and a comprehensive conclusion of the publications. In brief this thesis intends to improve safe driver behaviour by understanding the underlying psychological mechanisms that influence behavioral change, thereby resulting in more attention allocation to the forward roadway, and improved vehicle control. / Technologie durchdringt unser tägliches Leben und ist zunehmend integriert in Fahrzeuge – das Resultat sind veränderte Anforderungen an Fahrzeugführer. Einerseits besteht die Gefahr, dass er durch die Bedienung innovativer Technologien (z.B. Mobiltelefone) unachtsam wird und visuell abgelenkt ist, andererseits kann die Nutzung von Fahrerassistenzsystemen die den Fahrer bei der Fahraufgabe unterstützten einen wertvollen Beitrag zur Fahrsicherheit bieten. Die steigende Aktualität beider Problematiken wirft die Frage auf: "Kann der Fahrer sich erfolgreich dem ständig wachsenden technologischen Fortschritt anpassen?" Das Ziel der vorliegenden Arbeit ist der Erkenntnisgewinn zur Verbesserung des Fahrverhaltens indem der Verhaltensänderungen zugrunde liegende psychologische Mechanismen untersucht werden. Eine Vielzahl an Literatur zu Fahrerassistenzsystemen und Aufmerksamkeitsverteilung wurde vor dem Hintergrund von Verhaltensanpassung der Fahrer recherchiert. Daten mehrerer empirischer Quellen, z. B. Fahrverhalten, Blickbewegungen, Videomitschnitte und subjektive Daten dienten zur Datenauswertung zweier Fahrerassistenzsysteme. Im Rahmen einer Feldstudie zeigte sich, dass Bremskapazitäts-Kollisionswarnungen zur sofortigen visuellen Aufmerksamkeitsverteilung zur Fahrbahn und zum Bremsen führen, Fahrer allerdings ihre Reaktion anpassen indem sie zur Warnanzeige im Kombinationsinstrument schauen. Ein anderes Phänomen der Verhaltensanpassung wurde in einer Fahrsimulatorstudie zur Untersuchung eines Ablenkungswarnsystems, das dabei hilft die Blicke von Autofahrern stets auf die Straße zu lenken, gefunden. Diese Ergebnisse weisen nach, dass solch ein System unterstützt achtsamer zu sein und sicherer zu fahren. Die vorliegenden Befunde wurden im Zusammenhang zu Vorbefunden zur Verhaltensanpassung zu Fahrerassistenzsystemen, Fahrerkalibrierung und Akzeptanz von Technik diskutiert. Basierend auf den gewonnenen Erkenntnissen wurde ein neues Vorgehen zur Untersuchung von Mensch- Maschine-Interaktion eingeführt. Aufbauend auf den Resultaten der vorliegenden Arbeit wurde ein ganzheitliches Modell zur Fahrsicherheit und -management, das DO-IT BEST Feedback Modell, entwickelt. Das Modell bezieht sich auf multitemporale Fahrer-Feedbackstrategien und soll somit einen entscheidenen Beitrag zur Verkehrssicherheit und dem Umgang mit Fahrerunaufmerksamkeit leisten. Die zentralen Beiträge dieser Arbeit sind die Gewinnung neuer Erkenntnisse in den Bereichen der Angewandten Psychologie und der Verkehrspsychologie in den Kontexten der Aufmerksamkeitsverteilung und der Verbesserung der Gestaltung von Fahrerassistenzsystemen fokusierend auf den Bediener. Die Dissertation besteht aus einem Einleitungsteil, drei empirischen Beiträgen sowie drei Buchkapiteln und einer abschliessenden Zusammenfassung.
932

Etude de lentilles artificielles métalliques et métallo-diélectriques : modélisation par la méthode modale de Fourier et par la méthode des coordonnées curvilignes / Study of artificial metallic and metallo-dilectric lenses : modeling by the Fourier modal method and by the curvilinear coordinate method

Fenniche, Ismail 06 December 2010 (has links)
Nous présentons un modèle théorique et numérique pour simuler la diffraction d’ondes électromagnétiques par des lentilles artificielles métalliques. Le premier chapitre présente les radars anti-collision dans le contexte automobile, le système d’antenne est composé d’une source primaire ponctuelle et d’une lentille artificielle. Cette dernière est réalisée de façon très simple en assemblant des lames métalliques minces sur des morceaux de mousse. Une méthode approchée permet d’obtenir rapidement le champ rayonné à travers une lentille par une source ponctuelle à l’aide des concepts d’optique géométrique et d’optique physique. Dans le second chapitre, deux variantes de la méthode modale sont proposées pour l’étude de la diffraction par des réseaux de lames parfaitement conductrices infiniment minces, une dite classique, décrit le champ à l’intérieur des guides parfaitement conducteurs à l’aide des modes de ces derniers, et l’autre considère que les guides forment un milieu inhomogène par morceaux. Les parois des guides sont vues comme des matériaux d’épaisseur très fine et très conducteurs. Numériquement, cet artifice est possible grâce à la technique de résolution spatiale adaptative aussi appelée formulation paramétrique. Dans le chapitre 3, l’ensemble des techniques présentées précédemment est appliqué aux lentilles. Un modèle numérique et électromagnétique est présenté où la lentille métallique est vue comme un empilement de réseaux lamellaires. Le champ global est obtenu en raccordant les modes de chaque couche. Une autre extension qui permet de modéliser des objets non périodiques est introduite : il s’agit d’un changement de coordonnées complexes qui produit des conditions aux limites absorbantes aux bords du domaine de calcul. Dans le chapitre 4, l’ensemble des techniques numériques développées plus haut est mis en oeuvre sur des cas concrets de lentilles artificielles et des comparaisons avec le modèle simplifié du chapitre 1 sont effectuées. Le chapitre 5 est également consacré à l’étude de lentilles. Cependant le domaine de longueur d’onde envisagé n’est plus le même puisqu’on passe dans le domaine optique. La notion de métal perd le sens qu’on lui donne habituellement. Le métal est caractérisé par une permittivité complexe dont la partie réelle peut être négative. Des modes nouveaux apparaissent. La méthode d’analyse retenue est encore une méthode modale. Pour tenir compte des profils d’entrée et de sortie de la lentille, on effectue un changement de coordonnée grâce auquel ces derniers deviennent des surfaces de coordonnées. / We present a theoretical and numerical model to simulate the scattering of electromagnetic waves by artificial metallic lenses. The first chapter introduces the anti-collision radar in the automotive context. The antenna system is composed of a primary point source and an artificial lens. The latter is achieved very simply by assembling thin metal strips on pieces of foam. The field radiated through a lens by a point source can be quickly obtained using the concepts of geometrical optics and optical physics. In the second chapter, two different modal method are proposed for the study of diffraction by arrays of perfectly conducting infinitely thin blades. The first one describes the field inside the perfectly conducting guides by using their exact modes. The second one considers that the guides are piecewise homogeneous media. The walls of the guides are seen as very thin and highly conducting materials. Numerically, this trick is possible thanks to the technique of adaptive spatial resolution. In chapter 3, all the techniques presented above are applied to lenses. A numerical and electromagnetic model is presented where the lens is seen as a stack of strip gratings. The overall field is obtained by matching the modes of each layer. Another extension that allows to model non-periodic objects is introduced : it consists in a complex change of coordinates that produces absorbing boundary conditions at the edges of the computational domain. In Chapter 4, all the numerical techniques developed above are implemented on specific cases of artificial lenses and comparisons with the approximate model of Chapter 1 are performed. Chapter 5 is devoted to the study of lenses in the optical domain. The concept of metal looses its usual meaning. The metal is characterized by a complex permittivity whose real part can be negative. New modes appear. The analytical method is still a modal method.To account for input and out profile of the lens, a change of coordinates is introduced so that the input and output surface of the lens become surface of coordinates.
933

Study of analytical methods for electron track detection from heavy quark decays generated by sqrt(s)=8TeV pp collisions at ALICE / Estudo de métodos analíticos para detecção de traços de elétrons oriundos do decaimento de quarks pesados por colisões pp a raiz(s)=8TeV no ALICE

Marco Aurelio Luzio 03 May 2017 (has links)
A study of the usage of ALICEs time of flight (TOF), time projection chamber (TPC), and electromagnetic calorimeter (EMCal), aiming at detecting and separating electrons and positrons (e±) originated from different sources, was carried out. To accomplish the objectives of the research, data gathered from the 2012 proton-proton (pp) collision experiment were used. At a center of mass energy of sqrt(s)=8TeV, the collision of the proton beams liberates heavy quarks, charm and bottom, with approximate lifetimes of approximately 10^13s and 10^12s, respectively. The e± generated through weak semileptonic heavy flavor decays are of interest for studying quarks, therefore it served solely as motivation and incentive for the research carried out and described herein. The introduction of carefully selected cuts, with the purpose of separating partial data collected in the three detectors, permitted the understanding of their effect on the results. Furthermore, due to the fact that the TOFs design was not meant to separate e± from the other heavier particles, only the general effects of introducing a simple cut in the beta=v/c values were analyzed. The more specific cuts were only used for the data generated by the events detected by the TPC and the EMCal. A combination of cuts based on the particles energy loss as a function of traveled distance (dE/dx), with the ratio of energy to momentum (E/p) of the particle, was adopted to enable the separation process, thus allowing for the isolation of e± from the other particles, namely pi±, K±, and p/p. The analysis was performed for values of total particle momentum in the range 0<=p<=6GeV/c. A comparison of the raw data with the results obtained by applying this procedure, indicated a substantial increase in the e± yield and efficiency, reaching average values above 90% over the entire momentum range. / Um estudo do uso dos detetores de tempo de voo (TDV), câmara de projeção de tempo (CPT), e calorímetro eletromagnético (CalEM) do ALICE, visando detectar elétrons e pósitrons (e±) originados por diferentes fontes, foi realizado. Para atingir os objetivos da pesquisa, dados coletados durante o experimento de colisões próton-próton em 2012 foram utilizados. Com um nível de enegia do centro de mass igual a raiz(s)=8TeV, a colisão dos feixes de prótons libera quarks pesados, charm e bottom, com tempo de vida de aproximadamente 10^13s e 10^12s, respectivamente. Os e± gerados pelo decaimento fraco semileptônico de sabores pesados é de interesse para o estudo dos quarks, portanto, o conceito serviu somente como motivação e incentivo para a pesquisa realizada e descrita nesta dissertação. A introdução de cortes específicos, com a finalidade de parcialmente separar dados coletados nos três detectores, permitiu adquirir entendimento sobre os efeitos do cortes nos resultados. Adicionalmente, em virtude do projeto do TDV não ter sido feito visando separar e± oriundos do decaimento dos sabores pesados das demais partículas mais massivas, somente os efeitos gerais de introduzir um corte simples nos valores de beta=v/c, foram analisados. Os cortes mais específicos foram somente nos dados detectados pelo CPT e pelo CalEM. Uma combinação de cortes baseados na perda de energia da partícula em função da distância percorrida (dE/dx), com a razão entre a energia e o momento da partícula (E/p), foi adotada para viabilizar o processo de separação, desta forma permitindo a separação dos e± das demais partículas, ou seja, dos pi±, K±, and p/p. A análise foi realizada para valores de momento total das partículas na faixa 0<=p<=6GeV/c. Uma comparação dos dados originais com os resultados obtidos pela aplicação do procedimento, indicou um aumento substancial do rendimento e eficiência dos e±, atingindo valores médios acima de 90% na faixa inteira de momento.
934

Contribution à la réalisation d’un oscillateur push-push 80GHz synchronisé par un signal subharmonique pour des applications radars anticollisions

Ameziane El Hassani, Chama 06 May 2010 (has links)
Ce travail de thèse s’inscrit dans le cadre d’un projet Français « VéLo » qui est une collaboration entre l’industriel STMicroelectronics et plusieurs laboratoires dont les laboratoires IMS-bordeaux et LAAS. Le but du projet est de concevoir un prototype de radar anticollision millimétrique. Dans ce travail un synthétiseur de fréquence est implémenté. Ce dernier sera intégré dans la chaine de réception du démonstrateur. Une étude bibliographique des architectures classiques de système de radiocommunication a été réalisée. Des exemples d’architectures rencontrées dans le domaine millimétrique ont été étudiés.L’objet principal de cette thèse est l’étude des oscillateurs synchronisés par injection ILO. L’objectif est de réaliser un oscillateur verrouillé par injection qui sera piloté par un oscillateur de fréquence plus basse possédant des caractéristiques de stabilité et de bruit meilleures.Dans ce travail de thèse, le mécanisme de verrouillage des oscillateurs par injection a été décrit. Un modèle de synchronisation par injection série, basé sur la théorie de Huntoon Weiss et inspiré du travail de Badets réalisé sur les oscillateurs synchrones verrouillés par injection parallèle, est proposé. La théorie établie a permis d’exprimer la plage de synchronisation en fonction de la topologie utilisée et des composants de la structure. La validité de la théorie a été évaluée par la simulation de la structure. Les résultats présentés montrent une bonne concordance entre la simulation et la théorie et permettent de valider le principe de synchronisation par injection. La faisabilité de l’intégration d’un ILO millimétrique synchronisé par l’harmonique d’un signal de référence de fréquence plus basse a été démontrée expérimentalement. Le synthétiseur de fréquence est réalisé en technologie BiCMOS 130nm pour des applications millimétriques de STMicroelectronics. Ce dernier opère dans une plage de 2GHz autour de la fréquence 82,5GHz. Les performances en bruit du synthétiseur sont satisfaisantes. Le bruit de phase de l’ILO recopie celui du signal injecté. Les équipements de mesures utilisés, le bruit de phase de l’oscillateur atteint des valeurs inférieures à -110dBc/Hz à 1MHz de la porteuse. / This thesis is a part of a French project "VELO". The project is collaboration between STMicroelectronics and several laboratories including IMS-Bordeaux and LAAS laboratories. The aim of this project is to achieve a prototype of millimeter anti-collision radar. In this work a frequency synthesizer is implemented. This circuit will be incorporated in the reception chain of the demonstrator. A bibliographical study of classical architecture was completed. Examples of architectures encountered in the millimeter frequency range have been studied. The purpose of this thesis is to study the phenomena of synchronization in oscillators. The objective is to design an injection locked oscillator ILO driven by another oscillator, the second oscillator operates at lower frequency and offers better stability and noise characteristics.In this thesis, the injection locking mechanism of the oscillators has been described. A model of synchronization by series injection is proposed. The model is based on the theory of Huntoon and Weiss and inspired by Badets’ work performed on parallel injection. The theory expresses the synchronized frequency range depending on the used topology and the values of the components. The validity of the theory was evaluated by simulation. The results show good agreement between simulation and theory and validate the principle of synchronization by injection.The feasibility of a millimeter ILO synchronized by the harmonic of a reference signal operating at lower frequency has been demonstrated experimentally. The synthesizer was implemented in BiCMOS technology for 130nm applications millimeter of STMicroelectronics. The oscillator operates at 82.5 GHz and performs a frequency range of 2GHz. The noise performance of the synthesizer is satisfactory. The phase noise of the ILO depends on the reference phase noise, and reaches values of -110dBc/Hz at 1MHz from the carrier frequency.
935

Analýza chování řidiče při řešení situací spojených s přecházením chodců přes vozovku / Analysis of driver’s conduct during solving of situations associated with pedestrians crossing the road

Maxera, Pavel January 2021 (has links)
The doctoral thesis analyses driver’s conduct while solving situations associated with crossing of pedestrians across the road in cases of various design of pedestrian crossings and at different conditions. The thesis deepens the knowledge of the human factor impact on the occurrence of a traffic accident involved vehicle and pedestrian and thesis also complements knowledge for the needs of the analysis of traffic accidents, especially in solving the pre collision phase and at assessment of possibilities for collision prevention by involved participants. The thesis deals with driver’s conduct, various models of the conduct as well as the thesis focuses on the visual perception, the process of information processing, the driver’s conduct and the reaction time. In terms of the solution suitable types of experiments were designed and implemented. Based on performed measurements a method of processing and evaluating data on drivers’ conduct was found as well as more significant data set was obtained for a detailed analysis of drivers' conduct in different driving situations. The assessed quantities of drivers' conduct were analysed with respect to the dangerousness of driving situations. For these purposes, the categories of the dangerousness of driving situations were defined (situations completely safe, with increased danger, dangerous and critical), into which the analysed driving situations were subsequently included. To enable the quantification of this classification of situations into the categories of the dangerousness, the coefficient of the dangerousness (so called K) was defined. From the detailed analysis of the obtained data, the limit values of this coefficient were determined, and these were subsequently verified using data from the solution of real traffic accidents. Concurrently the analysis verified the suitability of using this hazard coefficient in the analysis of traffic accidents, especially for a detailed assessment of the possibilities of collision prevention.
936

Flight Management System Model / Flight Management System Model

Franěk, Lukáš January 2011 (has links)
Diplomová práce shrnuje nejdůležitější informace o letectví, jako například základní používané termíny, popis letových fází apod. V této práci je popsán flight management system, jeho funkce a schopnosti vytvořit cenově příznivý a současně absolutně spolehlivý letový plán. V další části práce je nastíněna důležitost předpovědi počasí pro bezpečnou a současně cenově příznivou leteckou dopravu. Tato práce je vytvořena v programu Matlab a všechny bloky jsou naprogramovány jako m-funkce. Důležité části kódu jsou z důvodu názornosti zobrazeny jako vývojové diagramy. Praktická část práce je rozdělena do několika podkapitol, kde každá podkapitola popisuje jeden blok z blokového schématu pro výpočet nejistoty odhadované doby příletu. Současně je zde vysvětlena funkce ostatních bloků pro plánování letu, předpověď počasí, kombinování větrů a výpočet odhadnuté doby příletu a její nejistoty.
937

Vybrané způsoby zlepšení orientace řidiče v dopravním prostoru / Selected Methods of Improvement for the Driver's Orientation on the Roads

Černoch, Adam January 2014 (has links)
The aim of this thesis is to find suitable measures which will lead to the improvement of driver orientation in traffic spaceleading to lower the accident rate in the area. The theoretical part describes the traffic surveys that relate to the topic. Furthermore, the work mentioned detectors used for the implementation of automated traffic surveys. The theoretical part also describes methods that can be used to analyze the selected location and then design the ideal modification. At the end gives an overview of the various measures. In the practical part are different methodologies used for the analysis of selected intersections. Firstly, the analysis of observed conflict situations, including making conflicting diagram, under which was designed to measure. Then, the analysis of traffic accidents. Again, the result was a proposal for possible actions. The main objective was to compare and appreciation of both methodologies and proces design measures to improve driver orientation in the selected location.
938

Možnosti kódového zabezpečení stanic s kmitočtovým skákáním / Possibilities of Error Controls in Frequency hopping Stations

Pust, Radim January 2012 (has links)
The doctoral thesis deals with design of coding for frequency hopping stations in band with intensive jamming. In digital modulations erroneous determination of the modulation state occurs due to jam at the receiver side. The result is erroneously transferred symbols of the message. Errors created during the transmission can be eliminated by using error control systems. It is also possible to prevent these errors by using algorithms (techniques) of frequency hopping which select the appropriate channel. Appropriate communication channel is a channel with a lower probability of erroneous symbol in the message. The main contribution of this thesis is to design a new frequency hopping technique with collision avoidance (FH/CA). The station with FH/CA technique measures signal levels in the considered several channels before every jump. Based on the measurements the most appropriate channel with the lowest value of measured signal level is selected. Therefore, it is more probable that a jump to an unoccupied channel with a transmission will occur. Using a mathematical model, the performance of the newly proposed FH/CA technique is compared with the currently used techniques FH and AFH. Comparison criteria are the probability of a collision between an FH/CA communication system and a static (device transmitting continuously at a fixed frequency) or dynamic jammer (i.e. other FH or AFH systems). By comparing the values of the probability of jammed transmission, indisputable theoretical advantages of the new FH/CA technique were found, compared to the currently used FH and AFH techniques. The FH/CA technique always has better or equal results compared with the FH technique in the case of interference by static and dynamic jammers. The FH/CA technique in a band with static and dynamic jammers usually has better results than the AFH technique. A significant contribution of the FH/CA technique can be seen in the case of dynamic jammers. On the other hand, in the case of static jammers the FH/CA technique is in certain situations worse than the AFH technique. The accuracy of the mathematical models were successfully verified on a simulation model that was created as a part of this thesis in the MATLAB environment. Based on the obtained data from the model there was designed coding for frequency hopping stations with the new technique of frequency hopping FH/CA which is designed for small-volume data transfer in a band with intensive jamming.
939

Energy efficient underwater acoustic sensor networks / Réseaux de capteurs acoustiques sous-marins écoénergétiques

Zidi, Chaima 08 March 2018 (has links)
Les réseaux de capteurs acoustiques sous-marins (UW-ASN) sont les plus nouveaux achèvements technologiques en termes de communication. Les UW-ASN visent à observer et à explorer les lacs, les rivières, les mers et les océans. Récemment, ils ont été soumis à une attention particulière en raison de leur grand potentiel en termes d'applications prometteuses dans divers domaines (militaires, environnementaux, scientifiques ...) et aux nouvelles questions scientifiques qu'ils suscitent. Un problème majeur dans les UW-ASN est l'épuisement rapide de l'énergie, car une grande puissance est nécessaire pour la communication acoustique, tandis que le budget de la batterie des capteurs est limité. Par conséquent, les protocoles de communication énergétiques revêtent une importance primordiale pour faire usage judiciaire du budget énergétique disponible. Dans ce contexte, cette thèse vise à étudier les principales caractéristiques des capteurs acoustiques sous-marins difficiles afin de concevoir des protocoles de communication énergétiques, plus spécifiquement au niveau routage et MAC. Tout d'abord, nous abordons le problème des trous énergétiques dans UW-ASN. Le problème du « sink-hole » se produit lorsque les capteurs les plus proches du sink épuisent leur énergie plus rapidement en raison de leur charge plus lourde. En effet, ces capteurs, en particulier ceux qui sont à un seul saut du sinkstatique, agissent comme des relais pour tous les autres capteurs, ce qui leur épuise sévèrement l’énergie.A la couche de routage,en particulier, nous proposons de distribuer la charge transmise par chaque capteur parmi plusieurs voisins potentiels, en supposant que les capteurs peuvent ajuster leur gamme de communication entre deux niveaux lorsqu'ils envoient ou transmettent des données. Plus précisément, nous déterminons pour chaque capteur l'ensemble des prochains sauts avec les poids de charge associés qui entraînent un épuisement équitable d'énergie entre tous les capteurs du réseau. Ensuite, nous étendons notre stratégie de routage équilibrée en supposant que chaque capteur n'est pas seulement capable d'ajuster sa puissance d'émission à 2 niveaux mais aussi jusqu'à n niveaux où n> 2. Par conséquent, à la couche de routage, pour chaque valeur possible de n, nous déterminons pour chaque capteur l'ensemble des éventuels sauts avec les poids de charge associés qui mènent à une consommation d'énergie équitable chez tous les capteurs du réseau. En outre, nous obtenons le nombre optimal de puissances de transmission n qui équilibre la consommation d'énergie de tous les capteurs pour chaque configuration de réseau. En plus de cela, il convient de souligner que notre protocole de routage étendu utilise un modèle de canal à variation de temps plus réaliste qui tient compte de la plupart des caractéristiques fondamentales de la propagation acoustique sous-marine. Les résultats analytiques montrent que notre protocole de routage assure une réduction importante de la consommation d’énergie. Deuxièmement, pour atténuer les impacts de collision spectaculaires gaspillant l’énergie, nous concevons un protocole MAC multicanal (MC-UWMAC) évitant les collisions pour les UW-ASNs. MC-UWMAC fonctionne avec un canal de contrôle (décomposé en créneaux de temps) et un ensemble de canaux de données à bande passante égale. Les créneaux du canal de contrôle sont dédiés à l’échange RTS / CTS permettant à une paire de capteurs communicants de s'accorder sur l'heure de début de la communication sur un canal de données pré-alloué. Dans cette thèse, nous proposons deux nouvelles procédures associées d'allocation des créneaux du canal de contrôle et d'attribution des canaux de données sans nécessiter de frais de négociation supplémentaires. En conséquence, chaque capteur peut initier l'échange RTS / CTS uniquement à son créneau assigné, calculé à l'aide d'une procédure d'allocation basée sur une partition virtuelle de grille de la zone de déploiement. (...) / UnderWaterAcoustic Sensor Networks (UW-ASNs) are the newest technological achievement in terms of communication. Composed of a set of communicating underwater sensors, UW-ASNs are intended to observe and explore lakes, rivers, seas and oceans. Recently, they have been subject to a special attention due to their great potential in terms of promising applications in various domains (military, environmental, scientific...) and to the new scientific issues they raise. A great challenging issue in UW-ASNs is the fast energy depletion since high power is needed for acoustic communication while sensors battery budget is limited. Hence, energy-efficient networking protocols are of a paramount importance to make judicious use of the available energy budget while considering the distinguishing underwater environment characteristics. In this context, this thesis aims at studying the main challenging underwater acoustic sensors characteristics to design energy-efficient communication protocols specifically at the routing and MAC layers. First, we address the problem of energy holes in UW-ASNs. The sink-hole problem occurs when the closest nodes to sink drain their energy faster due to their heavier load. Indeed, those sensors especially the ones that are 1-hop away from the static sink act as relays to it on behalf of all other sensors, thus suffering from severe energy depletion. In particular, at the routing layer, we propose to distribute the transmission load at each sensor among several potential neighbors, assuming that sensors can adjust their communication range among two levels when they send or forward data. Specifically, we determine for each sensor the set of next hops with the associated load weights that lead to a fair energy depletion among all sensors in the network. Then, we extend our balanced routing strategy by assuming that each sensor node is not only able to adjust its transmission power to 2 levels but eventually up to n levels where n > 2. Consequently, at the routing layer, for each possible value of n, we determine for each sensor the set of possible next hops with the associated load weights that lead to a fair energy consumption among all sensors in the network. Moreover, we derive the optimal number of transmission powers n that balances the energy consumption among all sensors for each network configuration. In addition to that, it is worth pointing out that our extended routing protocol uses a more realistic time varying channel model that takes into account most of the fundamental characteristics of the underwater acoustic propagation. Analytical results show that further energy saving is achieved by our extended routing scheme. Second, to mitigate the dramatic collision impacts, we design a collision avoidance energy efficient multichannel MAC protocol (MC-UWMAC) for UW-ASNs. MC-UWMAC operates on single slotted control and a set of equal-bandwidth data channels. Control channel slots are dedicated to RTS/CTS handshaking allowing a communicating node pair to agree on the start time of communication on a pre-allocated data channel. In this thesis, we propose two novel coupled slot assignment and data channels allocation procedures without requiring any extra negotiation overhead. Accordingly, each node can initiate RTS/CTS exchange only at its assigned slot calculated using a slot allocation procedure based on a grid virtual partition of the deployment area. Moreover, for each communicating pair of nodes, one data channel is allocated using a channel allocation procedure based on our newly designed concept of singleton- intersecting quorum. Accordingly, each pair of communicating nodes will have at their disposal a unique 2-hop conflict free data channel. Compared with existing MAC protocol, MC-UWMAC reduces experienced collisions and improves network throughput while minimizing energy consumption.
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Ab-initio molecular dynamics studies of laser- and collision-induced processes in multielectron diatomics, organic molecules and fullerenes

Handt, Jan 18 October 2010 (has links)
This work presents applications of an ab-initio molecular dynamics method, the so-called nonadiabatic quantum molecular dynamics (NA-QMD), for various molecular systems with many electronic and nuclear degrees of freedom. Thereby, the nuclei will be treated classically and the electrons with time-dependent density functional theory (TD-DFT) in basis expansion. Depending on the actual system and physical process, well suited basis sets for the Kohn-Sham orbitals has to be chosen. For the ionization process a novel absorber acting in the energy space as well as additional basis functions will be used depending on the laser frequency. In the first part of the applications, a large variety of different laser-induced molecular processes will be investigated. This concerns, the orientation dependence of the ionization of multielectronic diatomics (N2, O2), the isomerization of organic molecules (N2H2) and the giant excitation of the breathing mode in fullerenes (C60). In the second part, fullerene-fullerene collisions are investigated, for the first time in the whole range of relevant impact velocities concerning the vibrational and electronic energy transfer (\"stopping~power\"). For low energetic (adiabatic) collisions, it is surprisingly found, that a two-dimensional, phenomenological collision model can reproduce (even quantitatively) the basic features of fusion and scattering observed in the fully microscopic calculations as well as in the experiment. For high energetic (nonadiabatic) collisions, the electronic and vibrational excitation regimes are predicted, leading to multifragmentation up to complete atomization.

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