Positive affect is generally associated with improvements in cognitive abilities; however, few studies have addressed positive affect and its relation to specific cognitive control processes. Previous research suggests positive affect conditions are more flexible/distractible states, suggesting cognitive control processes are perhaps decreased in context maintenance and increased in conflict detection/resolution. To measure the cognitive control processes, specific components of the scalp-recorded event-related potentials (ERPs) called the cue slow wave (context maintenance), the N450 (conflict detection), and conflict SP (conflict resolution) were acquired in response to an affective single-trial, cued-Stroop task. Participants were presented with pleasant, neutral, and unpleasant images prior to Stroop instruction (i.e., respond to "color" or "word") and response. Participants had greater accuracy during the pleasant condition when given a longer delay for extra time to process the high conflict task, t(36) = 3.09, p = .004, 95% CI (0.07, 0.02) compared to the unpleasant condition. Additionally, the unpleasant condition resulted in greater context maintenance than pleasant (increased cue-related slow wave amplitude; t(40) = 2.38, p = .02). Unpleasant conditions were associated with greater conflict resolution processes (as measured by the conflict SP) with high conflict trials, t(40) = 2.55, p = .015; whereas pleasant did in congruent trials, t(40) = 2.707, p = .010. Findings suggest negative affective states increase participants' focus on the task in avoidance of the distracting unpleasant picture. Our findings lay the foundation for understanding the differences between state and trait affect on cognitive control processes.

<p>This thesis investigates the crucial problem of collision avoidance for autonomous vehicles.  An anti-collision system for an unmanned aerial vehicle (UAV) is studied in particular. The purpose of this system is to make sure that the own vehicle avoids collision with other aircraft in mid-air. The sensor used to track any possible threat is for a UAV limited basically to a digital video camera. This sensor can only measure the direction to an intruding vehicle, not the range, and is therefore denoted an angle-only sensor. To estimate the position and velocity of the intruder a tracking system, based on an extended Kalman filter, is used. State estimates supplied by this system are very uncertain due to the difficulties of angle-only tracking. Probabilistic methods are therefore required for risk calculation. The risk assessment module is one of the essential parts of the collision avoidance system and has the purpose of continuously evaluating the risk for collision. To do this in a probabilistic way, it is necessary to assume a probability distribution for the tracking system output. A common approach is to assume normality, more out of habit than on actual grounds. This thesis investigates the normality assumption, and it is found that the tracking output rapidly converge towards a good normal distribution approximation. The thesis furthermore investigates the actual risk assessment module to find out how the collision risk should be determined. The traditional way to do this is to focus on a critical time point (time of closest point of approach, time of maximum collision risk etc.). A recently proposed alternative is to evaluate the risk over a horizon of time. The difference between these two concepts is evaluated. An approximate computational method for integrated risk, suitable for real-time implementations, is also validated. It is shown that the risk seen over a horizon of time is much more robust to estimation accuracy than the risk from a critical time point. The integrated risk also gives a more intuitively correct result, which makes it possible to implement the risk assessment module with a direct connection to specified aviation safety rules.</p>

This thesis investigates the crucial problem of collision avoidance for autonomous vehicles.  An anti-collision system for an unmanned aerial vehicle (UAV) is studied in particular. The purpose of this system is to make sure that the own vehicle avoids collision with other aircraft in mid-air. The sensor used to track any possible threat is for a UAV limited basically to a digital video camera. This sensor can only measure the direction to an intruding vehicle, not the range, and is therefore denoted an angle-only sensor. To estimate the position and velocity of the intruder a tracking system, based on an extended Kalman filter, is used. State estimates supplied by this system are very uncertain due to the difficulties of angle-only tracking. Probabilistic methods are therefore required for risk calculation. The risk assessment module is one of the essential parts of the collision avoidance system and has the purpose of continuously evaluating the risk for collision. To do this in a probabilistic way, it is necessary to assume a probability distribution for the tracking system output. A common approach is to assume normality, more out of habit than on actual grounds. This thesis investigates the normality assumption, and it is found that the tracking output rapidly converge towards a good normal distribution approximation. The thesis furthermore investigates the actual risk assessment module to find out how the collision risk should be determined. The traditional way to do this is to focus on a critical time point (time of closest point of approach, time of maximum collision risk etc.). A recently proposed alternative is to evaluate the risk over a horizon of time. The difference between these two concepts is evaluated. An approximate computational method for integrated risk, suitable for real-time implementations, is also validated. It is shown that the risk seen over a horizon of time is much more robust to estimation accuracy than the risk from a critical time point. The integrated risk also gives a more intuitively correct result, which makes it possible to implement the risk assessment module with a direct connection to specified aviation safety rules.

<p>In distributed database systems, immediate global consistency of replicated data can be achieved by distributed commit protocols that are typically unpredictable. If real-time characteristics are necessary, such unpredictability has to be avoided. In a distributed real-time database, optimistic replication can be used to avoid unpredictable delays by allowing transactions to commit locally. The update of other nodes is performed as soon as possible. If optimistic replication is used, conflicts may occur since data can be changed locally without synchronously informing other nodes. To detect these conflicts, this thesis introduces a conflict detection approach for DeeDS, a distributed, active real-time database that supports a dynamic node set. A comparison of existing conflict detection approaches is performed, and it is found that the dynamic version vector approach is the best fitting approach. The main reason is that it can handle a dynamic node set with a minimum of additional conflict detection data. To show the realization of the approach in DeeDS, dynamic version vectors have been implemented. Additionally, conflict management in DeeDS is redesigned to allow separation of conflict detection and conflict resolution. This makes the software architecture more flexible and is a first step towards application specific conflict resolution.</p>

In distributed database systems, immediate global consistency of replicated data can be achieved by distributed commit protocols that are typically unpredictable. If real-time characteristics are necessary, such unpredictability has to be avoided. In a distributed real-time database, optimistic replication can be used to avoid unpredictable delays by allowing transactions to commit locally. The update of other nodes is performed as soon as possible. If optimistic replication is used, conflicts may occur since data can be changed locally without synchronously informing other nodes. To detect these conflicts, this thesis introduces a conflict detection approach for DeeDS, a distributed, active real-time database that supports a dynamic node set. A comparison of existing conflict detection approaches is performed, and it is found that the dynamic version vector approach is the best fitting approach. The main reason is that it can handle a dynamic node set with a minimum of additional conflict detection data. To show the realization of the approach in DeeDS, dynamic version vectors have been implemented. Additionally, conflict management in DeeDS is redesigned to allow separation of conflict detection and conflict resolution. This makes the software architecture more flexible and is a first step towards application specific conflict resolution.

La créativité repose sur la capacité à générer des idées à la fois originales et adaptées aux contraintes de la tâche afin de résoudre des problèmes pour lesquels aucune solution optimale n'est connue. Toutefois, dans ce type de circonstances, les connaissances intuitives des individus ainsi que leurs stratégies habituelles de résolution de problème les conduisent à générer des solutions peu créatives aboutissant à un phénomène de fixation, alors même que d'autres classes de solutions plus originales mais moins aisément accessibles pourraient être explorées. D'après le modèle triadique de la créativité, ces effets de fixations résulteraient de l'activation rapide et spontanée d'un système 1 intuitif et heuristique, alors qu'il serait plus avantageux d'explorer d'autres solutions en utilisant les processus cognitifs d'un système 2 délibératif et analytique. Ce modèle suggère également que le processus d'inhibition cognitive appartenant à un troisième système serait la clef pour diminuer la prégnance de ces effets de fixation créée par le système 1, et augmenter l'exploration d'autres voies plus créatives appartenant au système 2. Ainsi, l'objectif général de cette thèse consistait à apporter des arguments expérimentaux en faveur de ce modèle dans une approche interdisciplinaire allant de la psychologie expérimentale du développement aux neurosciences cognitives. À travers une série de cinq études expérimentales réalisées chez les enfants, les adolescents et les adultes, nous avons démontré 1) que les effets de fixation se développent avec l'âge et sont modulables par l'introduction d'indices comme des exemples de solutions, 2) qu'il est possible de stimuler la créativité des adolescents et des adultes en changeant la représentation qu'ils ont du problème de créativité par l'intermédiaire d'un paradigme d'amorçage, 3) qu'être capable de proposer des solutions créatives en dehors de la fixation implique le processus d'inhibition cognitive et la capacité à détecter que les solutions initialement générées ne sont pas originales, 4) que cette capacité de détection de conflit se développement au cours de l'adolescence et 5) que résister aux effets de fixation implique une modulation de l'activité des réseaux cérébraux au niveau des cortex frontaux et pariétaux sous tendant le contrôle cognitif et les associations sémantiques. / Creativity defined as the ability to think of something original, and adaptive concerning task constraints is crucial during circumstances in which individuals must generate new solutions to solve an unknown problem. In such circumstances, people propose solutions that are built on the most common and accessible knowledge within a specific domain leading to a fixation effects whereas other classes of more creative solutions could be explore. According to our triple systems model of creativity, the difficulty to generate creative ideas results from a specific failure to inhibit intuitive responses leading to fixation effect generated automatically by the intuitive and heuristic System 1 and activate the deliberative and analytic system 2 to explore more creative solutions. This model posits that inhibitory control is a core process to overcoming fixation effects and generating original solutions in a creative task. Therefore, the aim of this thesis was to provide empirical evidences in support of the triple system model of creativity by using an interdisciplinary approach from the field of experimental developmental psychology to the field of cognitive neuroscience. In a series of five experimental studies in children, adolescents and adults, we have demonstrated that 1) fixation effects develop with age and changes with the introduction of external cues such as examples of solutions 2) changing the individuals' representation of the creative task using a priming procedure can stimulate creative ideas generation in adolescents and adults, 3) overcoming fixation to explore creative solutions involves inhibitory control and the ability to detect that initial responses that come quickly to mind are not original, 4) this conflict detection ability develops with age during adolescence and 5) overcoming fixation is related to modulations of brain networks activations within the frontal and the parietal cortex involve in cognitive control and semantic associations respectively.

The modernization of the National Air Traffic Control System is on the horizon, and with it, the possible introduction of autonomous air vehicles into the national airspace. Per the FAA Aerospace Forecast (FAA, 2013), U.S. carrier passenger traffic is expected to average 2.2 percent growth per year over the next 20 years with government statistics indicating that the average domestic load factor for airlines in 2014 was approximately 84.4 percent (US Department of Transportation, 2015). Adding to that demand, the potential introduction of unmanned and autonomous air vehicles motivates reconsideration of control schemes. One of the proposed solutions (Eby, 1994) would involve a decentralized control protocol. Equipping each aircraft with the information necessary to navigate safely through integrated airspace becomes an information sharing problem: how much information about other aircraft is required for a pilot to safely fly the gamut of a heavily populated airspace and what paradigm shifts may be necessary to safely and efficiently utilize available airspace? This thesis describes the development of a tool for testing alternative traffic management systems, centralized or decentralized, in the presence of uncertainty. Applying a computational fluid dynamics-inspired approach to the problem creates a simulation tool to model both the movement of traffic within the airspace and also allows study of the effects of interactions between vehicles. By incorporating a Smoothed Particle Hydrodynamics (SPH) based model, discrete particle aircraft each carry a set of unique deterministic and stochastic properties. With this model, aircraft interaction can be studied to better understand how variations in the nondeterministic properties of the system affect its overall efficiency and safety. The tool is structured to be sufficiently flexible as to allow incorporation of different collision detection and avoidance rules for aircraft traffic management. / Master of Science

Un réseau sans fil mobile est une collection de noeuds mobiles connectés via des liens sans fil. Le noeud mobile peut être une personne portant un terminal mobile, un animal avec une étiquette électronique, un véhicule ou tout autre appareil mobile doté de capacités de communication sans fil. Cette thèse traite deux importants problèmes dans les réseaux sans fil mobiles : la localisation et la détection des conflits. La localisation est l’estimation des positions absolues ou relatives des noeuds mobiles. La détection des conflits est la prédiction des potentiels futurs conflits entre les noeuds mobiles. Un conflit est une situation dans laquelle deux ou plusieurs noeuds mobiles se trouvent à une distance inférieure à une distance minimale requise. La détection des conflits est particulièrement nécessaire dans les réseaux mobiles où les noeuds risquent de trop se rapprocher les uns des autres et se heurter.La première contribution de cette thèse est un nouvel algorithme de localisation pour les réseaux sans fil mobiles. L’algorithme proposé est distribué et nécessite un faible coût de calcul et de communication permettant son utilisation par des noeuds à ressources limitées. En particulier, un petit ensemble de noeuds avec des positions connues, appelés des nœuds ancres, diffusent périodiquement leurs coordonnées. Chaque noeud mobile avec une position inconnue collecte les coordonnées des noeuds ancres, les attribue des poids en fonction de différentes métriques (par exemple, la qualité de la liaison sans fil, le temps de réception) et enfin estime sa position en tant que la moyenne pondérée de toutes les coordonnées collectées. La deuxième contribution de cette thèse consiste en un algorithme de détection de conflit nommé SLIDE. SLIDE est distribué et à faible complexité: chaque noeuds mobile utilise des simples inégalités mathématiques afin de prédire avec précision et en temps opportun les futurs conflits avec les noeuds voisins. En outre, SLIDE abandonne l’hypothèse restrictive des positions et vitesses précises ainsi que des communications non perturbées afin de garantir son efficacité dans les applications du monde réel. La troisième et dernière contribution de cette thèse est un modèle stochastique qui évalue les risques des conflits dans un réseau sans fil mobile où les noeuds mobiles se déplacent dans le même espace partagé. Contrairement à la plupart des modèles stochastiques existants, le modèle proposé est simple, générique et ne nécessite que deux paramètres d’entrée: le nombre de noeuds mobiles et le paramètre λ caractérisant le temps d’inter-contact entre une paire de noeuds mobiles. Le paramètre λ peut être difficile à estimer expérimentalement. Nous proposons donc une expression générique pour λ et puis nous la spécifions pour deux modèles de mobilité couramment utilisés. Toutes les contributions de cette thèse sont validées en utilisant des simulations basées sur le simulateur d’événements discrets OMNeT ++. / A mobile wireless network is a collection of mobile nodes connected via wireless links. The mobile node can be a person carrying a mobile terminal, an animal with an embedded sensor (electronic tag), a vehicle or any other mobile device with wireless communication capabilities. This thesis deals with two fundamental issues in mobile wireless networks: localization and conflict detection. Localization is the estimation of the absolute or relative positions of the mobile nodes. Conflict detection is the prediction of potential future conflicts between the mobile nodes. A conflict is a situation in which two or more mobile nodes are within an unsafe distance from one another. Conflict detection is a crucial requirement for mobile networks where the nodes can get too close to each other and collide.The first contribution of this thesis is a new weighted localization algorithm for mobile wireless networks. The proposed algorithm is distributed and requires low computational and communication overheads enabling its use in resource-limited nodes. In particular, a small set of nodes with known positions, called beacon nodes, are periodically broadcasting their coordinates. A mobile node with an unknown position collects the beacon nodes coordinates, attributes them weights based on different metrics (e.g, link quality, reception time) and finally estimates its position as the weighted average of all the collected coordinates. The second contribution of this thesis consists in a straight line conflict detection algorithm called SLIDE. SLIDE is distributed and lightweight: each mobile node uses simple mathematical inequalities in order to accurately and timely predict future conflicts with the surrounding nodes. Furthermore, SLIDE drops the restrictive assumption of perfect sensing capabilities and perturbation-free environment in order to guarantee its efficiency in real world applications. The third and last contribution of this thesis is a stochastic model that assesses the conflicts risks in a mobile wireless network where the mobile nodes are moving in the same shared space. Unlike most of the existing stochastic models, the proposed model is simple, generic and requires only two input parameters: the number of mobile nodes and the parameter λ characterizing the inter-contact time between a pair of mobile nodes. The parameter λ may be difficult to estimate experimentally. We therefore provide a generic explicit expression for λ and then specify this generic expression for two commonly used mobility models. All the contributions of this thesis are validated through extensive simulations based on the discrete-event simulator OMNeT++.

Present day air traffc control is reaching its operational limits and accommodating future traffic growth will be a challenging task for air traffic service providers and airline operators. Free Flight is a proposed transition from a highly-structured and centrally-controlled air traffic system to a self-optimized and highly-distributed system. In Free Flight, pilots will have the flexibility of real-time trajectory planning and dynamic route optimization given airspace constraints (traffic, weather etc.). A variety of advanced air traffc management (ATM) concepts are proposed as enabling technologies for the realization of Free Flight. Since these concepts can be exposed to unforeseen and challenging scenarios in Free Flight, they need to be validated and evaluated in order to implement the most effective systems in the field. Evaluation of advanced ATM concepts is a challenging task due to the limitations in the existing scenario generation methodologies and limited availability of a common platform (air traffic simulator) where diverse ATM concepts can be modeled and evaluated. Their rigorous evaluation on safety metrics, in a variety of complex scenarios, can provide an insight into their performance, which can help improve upon them while developing new ones. In this thesis, I propose a non-propriety, non-commercial air traffic simulation system, with a novel representation of airspace, which can prototype advanced ATM concepts such as conflict detection and resolution, airborne weather avoidance and cockpit display of traffic information. I then propose a novel evolutionary computation methodology to algorithmically generate a massive number of conflict scenarios of increasing complexity in order to evaluate conflict detection algorithms. I illustrate the methodology in detail by quantitative evaluation of three conflict detection algorithms, from the literature, on safety metrics. I then propose the use of data mining techniques for the discovery of interesting relationships, that may exist implicitly, in the algorithm's performance data. The data mining techniques formulate the conflict characteristics, which may lead to algorithm failure, using if-then rules. Using the rule sets for each algorithm, I propose an ensemble of conflict detection algorithms which uses a switch mechanism to direct the subsequent conflict probes to an algorithm which is less vulnerable to failure in a given conflict scenario. The objective is to form a predictive model for algorithm's vulnerability which can then be included in an ensemble that can minimize the overall vulnerability of the system. In summary, the contributions of this thesis are: 1. A non-propriety, non-commercial air traffic simulation system with a novel representation of airspace for efficient modeling of advanced ATM concepts. 2. An Ant-based dynamic weather avoidance algorithm for traffic-constrained enroute airspace. 3. A novel representation of 4D air traffic scenario that allows the use of an evolutionary computation methodology to evolve complex conflict scenarios for the evaluation of conflict detection algorithms. 4. An evaluation framework where scenario generation, scenario evaluation and scenario evolution processes can be carried out in an integrated manner for rigorous evaluation of advanced ATM concepts. 5. A methodology for forming an intelligent ensemble of conflict detection algorithms by data mining the scenario space.

Afin de pouvoir subvenir aux futurs besoins en matière de transport aérien il est nécessaire d'augmenter la capacité de l'espace aérien. Les contrôleurs aériens, qui occupent une place centrale dans la gestion du trafic, doivent quotidiennement faire face à des situations conflictuelles (conflits) lors desquelles deux vols risquent de violer les normes de séparation en vigueur si aucune modification de trajectoire n'est envisagée. La détection et la résolution des conflits potentiels contribuent à augmenter la charge de travail des contrôleurs et peuvent potentiellement les conduire à diriger les vols vers des zones moins denses de l'espace aérien, induisant a posteriori un retard pour les vols. Le problème de la capacité de l'espace aérien peut donc être abordé en régulant les flux de trafic de façon réduire la quantité de conflits aériens. L'objectif de cette thèse est de mettre au point une méthodologie destinée à minimiser les risques de conflits aériens en modifiant légèrement les vitesses des appareils. Cette approche est principalement motivée par les conclusions du projet ERASMUS portant sur la régulation de vitesse subliminale. Ce type de régulation a été conçu de façon à ne pas perturber les contrôleurs aériens dans leur tâche. En utilisant de faibles modulations de vitesse, imperceptibles par les contrôleurs aériens, les trajectoires des vols peuvent être modifiées pour minimiser la quantité totale de conflits et ainsi faciliter l'écoulement du trafic dans le réseau aérien. La méthode retenue pour mettre en œuvre ce type de régulation est l'optimisation sous contrainte. Dans cette thèse, nous développons un modèle d'optimisation déterministe pour traiter les conflits à deux avions. Ce modèle est par la suite adapté à la résolution de grandes instances de trafic en formulant le modèle comme un Programme Linéaire en Nombres Entiers. Pour reproduire des conditions de trafic réalistes, nous introduisons une perturbation sur la vitesse des vols, destinée à représenter l'impact de l'incertitude en prévision de trajectoire dans la gestion du trafic aérien. Pour valider notre approche, nous utilisons un outil de simulation capable de rejouer des journées entières de trafic au dessus de l'espace aérien européen. Les principaux résultats de ce travail démontrent les performances du modèle de détection et de résolution de conflits et soulignent la robustesse de la formulation face à l'incertitude en prévision de trajectoire. Enfin, l'impact de notre approche est évalué à travers divers indicateurs propres à la gestion du trafic aérien et valide la méthodologie développée. / As global air traffic volume is continuously increasing, it has become a priority to improve air traffic control in order to deal with future air traffic demand. One of the current challenges regarding air traffic management is the airspace capacity problem, which is acknowledged to be correlated to air traffic controllers' workload. Air traffic controllers stand at the core of the traffic monitoring system and one of their main objective is to ensure the separation of aircraft by anticipating potential conflicts. Conflict detection and resolution are likely to increase workload and may lead them to reroute aircrafts to less dense areas, triggering off flight delay. The airspace capacity problem can hence be tackled by regulating air traffic flow in order to reduce the global conflict quantity. The objective of this thesis is to develop a methodology aiming at minimizing potential conflicts quantity by slightly adjusting aircraft speeds in real time. This approach is mainly motivated by conclusions of the ERASMUS project on subliminal speed control, which was designed to keep air traffic controllers unaware of the ongoing regulation process. By focusing on low magnitude speed modulations, aircraft trajectories can be modified to reduce the quantity of conflicts and smoothen air traffic flow in the airspace network. The method used to carry out this type of regulation is constraint optimization. In this thesis, we develop a deterministic optimization model for two-aircraft conflicts which is then adapted to large scale instances using Mixed-Integer Linear Programming. In order to reproduce realistic navigation conditions, uncertainty on aircraft speeds is introduced with the goal of modeling the impact of trajectory prediction uncertainty in air traffic management. To validate our approach, a simulation device capable of simulating real air traffic data over the European airspace is used. Main results of this work reveal a significant conflict quantity reduction and demonstrate the robustness of the developed model to the uncertainty in trajectory prediction. Finally, the impact of our model on air traffic flow is measured through several air traffic management indicators and validates the proposed methodology.