In this thesis, we study self-organized flocking using a swarm of mobile robots. We first present a mobile robot platform having two novel sensing systems developed specifically for swarm robotic studies. We describe its infrared-based short-range sensing system, capable of measuring the range to obstacles and detecting kin robots. In particular, we describe a novel sensing system called the virtual heading sensor (VHS), which combines a digital compass and a wireless communication module to form a scalable method for sensing the relative headings of neighboring robots. We propose a behavior based on heading alignment and proximal control and show that it is capable of generating self-organized ocking in a group of seven robots. Then, we propose a number of metrics to evaluate the quality of flocking and use them to evaluate four main variants of this behavior. We characterize and model the sensing abilities of the robots and develop a physics-based simulator that is verified against the physical robots for flocking in open environments. After showing in simulation that we can achieve flocking in a group of up to 1000 robots in an open environment, we perform experiments to determine the performance of flocking under different controller parameters and characteristics of VHS using the predefined metrics. In the experiments, we vary the three main characteristics of VHS, namely: (1) The amount and nature of noise in heading measurement, (2) The number of neighboring robots that can be &quot / heard&quot / , and (3) the range of wireless communication. Ourresults show that range of communication is the main factor that determines the scale of flocking, and that the behavior is highly robust against the other two characteristics. We extend an existing particle-based model to determine the phase transition characteristics of flocking under different VHS characteristics. An analytical treatment of the model is also presented and verified against the results obtained from experiments in a physics-based simulator.

Nous nous intéressons à l'étude de la dynamique des réseaux composés d'une multitude d'agents. Les motivations de ce travail trouvent leurs sources dans de nombreux domaines et notamment la biologie avec l'étude de l'émergence de comportements collectifs cohérents chez les animaux (vol en formation d'oiseaux migrateurs). Considérons un certain nombre d'agents (animaux) dont le comportement dynamique individuel peut être modélisé par une équation différentielle. Les agents communiquent : les liens sont représentés sous la forme d'un graphe dont les sommets sont les agents du système. Chaque agent a la connaissance de l'état des agents auxquels il est connecté et ajuste sa dynamique à l'aide de cette information. Des comportements collectifs peuvent alors émerger comme par exemple le phénomène de flocking (tous les agents se déplacent dans la même direction). Plusieurs modèles d'interaction ont été proposés, les plus connus étant le modèle de Viscek (1995) ou le modèle de Cucker-Smale (2007). L'étude de ces modèles repose généralement sur des méthodes d'analyse de stabilité des systèmes dynamiques ou des systèmes hybrides, lorsque le graphe de communication évolue dans le temps. Nous souhaitons dans cette thèse évaluer la robustesse de l'émergence de ces comportements collectifs en étudiant l'influence de divers facteurs: paramètres du modèle, topologie du graphe, nombre d'agents, présences de perturbations. Nous nous intéresserons notamment au phénomène de scission du groupe d'agents en plusieurs groupes d'agents coordonnés.

Animal groups often exhibit highly coordinated collective motion in a variety of situations. For example, bird flocks, schools of fish, a flock of sheep being herded by a dog and highly efficient traffic on an ant trail. Although these phenomena can be observed every day all over the world our knowledge of what rules the individual's in such groups use is very limited. Questions of this type has been studied using so called self-propelled particle (SPP) models, most of which assume that collective motion arises from individuals aligning with their neighbors. Here we introduce and analyze a SPP-model based on attraction alone. We find that it produces all the typical groups seen in alignment-based models and some novel ones. In particular, a group that exhibits collective motion coupled with non-trivial internal dynamics. Groups that have this property are rarely seen in SPP-models and we show that even when a repulsion term is added to the attraction only model such groups are still present. These findings suggest that an interplay between attraction and repulsion may be the main driving force in real flocks and that the alignment rule may be superfluous. We then proceed to model two different experiments using the SPP-model approach. The first is a shepherding algorithm constructed primarily to model experiments where a sheepdog is herding a flock of sheep. We find that in addition to modeling the specific experimental situation well the algorithm has some properties which may make it useful in more general shepherding situations. The second is a traffic model for leaf-cutting ants bridges. Based on earlier experiments a set of traffic rules for ants on a very narrow bridge had been suggested. We show that these are sufficient to produce the observed traffic dynamics on the narrow bridge. And that when extended to a wider bridge by replacing 'Stop' with 'Turn' the new rules are sufficient to produce several key characteristics of the dynamics on the wide bridge, in particular three-lane formation.

In this dissertation, we propose and study methods for information transfer within a swarm of mobile robots that coordinately move, or flock, in a common direction. We define information transfer as the process whereby robots share directional information in order to coordinate their heading direction. We identify two paradigms of information transfer: explicit information transfer and implicit information transfer. <p><p>In explicit information transfer, directional information is transferred via communication. Explicit information transfer requires mobile robots equipped with a a communication device. We propose novel communication strategies for explicit information transfer, and we perform flocking experiments in different situations: with one or two desired directions of motion that can be static or change over time. We perform experiments in simulation and with real robots. Furthermore, we show that the same explicit information transfer strategies can also be applied to another collective behavior: collective transport with obstacle avoidance. <p><p>In implicit information transfer, directional information is transferred without communication. We show that a simple motion control method is sufficient to guarantee cohesive and aligned motion without resorting to communication or elaborate<p>sensing. We analyze the motion control method for its capability to achieve flocking with and without a desired direction of motion, both in simulation and using real robots. Furthermore, to better understand its underlying mechanism, we study this<p>method using tools of statistical physics, showing that the process can be explained in terms of non-linear elasticity and energy-cascading dynamics. / Doctorat en Sciences de l'ingénieur / info:eu-repo/semantics/nonPublished

Die enormen Fortschritte und Erkenntnisse der Medizin und der damit einhergehenden gestiegenen mittleren globalen Lebenserwartung von indes knapp 75 Jahren fußen auch auf den medizinischen Entwicklungen des 20. Jahrhunderts, da durch diese z. B. infektiöse und onkologische Erkrankungen, Diabetes, Bluthochdruck, Herzinsuffizienz, Magengeschwüre, Depressionen, Hämophilie und andere Krankheiten erfolgreich therapiert werden können. Die entwickelten Therapiemethoden beruhten im Wesentlichen auf chirurgischen und intensivmedizinischen Neuerungen, chemischen Wirkstoffen, belastungsfähigen Implantaten und extrakorporalen Systemen. Im 21. Jahrhundert hingegen sind medizinische Neuerungen im molekularbiologischen Bereich zu erwarten, wie beispielsweise in der Zellbiologie, DNA-Analyse und -Transfer oder in der regenerativen Medizin. In Letzterer werden autologe regenerative Mechanismen als therapeutisches Prinzip genutzt, um funktionsgestörte Zellen, Gewebe und Organe entweder durch den biologischen Ersatz oder durch die Anregung körpereigener Regenerations- und Reparaturprozesse zu erhalten bzw. wiederherzustellen.

Social behaviour is shaped by complex relationships between evolutionary and ecological processes interacting at different scales. Benefits gained from social associations can range from predator dilution to collective sensing, but little is known about how these can be influenced by social structure and phenotypic composition. In this thesis, I investigated how individual decision-making affects phenotypic social structure, and how this mediates social behaviour through emergent properties of collective group behaviour. First, using mixed-species flocks as a model system, I showed individual tits (Paridae, chapter 2) and thornbills (Acanthizae, chapter 3) varied significantly in their social positions. Within-species variation in network position was as large as between-species variation, sug- gesting that prescribing functional roles at the species level may not sufficiently account for potential differences in fitness operating at the individual level. Rather, this suggested that structure may be driven by phenotypic traits, underpinning network structure (chapter 4). Next, I used an extensive data set of foraging records to explore factors determining the composition, of flocks of great tits (Parus major, chapter 5). For example, assortment by dispersal phenotype (immigration status) was the result of spatial disaggregation, and I showed that this may facilitate social selection for breeding territories (chapter 6). Finally, I investigated how decision-making shaped mixed-species social structure. I found that tits used a common strategy for managing pressures of predation and starvation by shifting from exploration to exploitation at different times of the day (chapter 7). I then found that a very simple interaction rule successfully replicated mixed-species group structure (chapter 8). Strikingly, the same rule was applied to both conspecifics and het- erospecifics, potentially playing an important role in the maintenance of flock structure. Through experimental manipulation of ecological conditions, I found that heightened per- ceived predation resulted in stronger social attraction overall, whereas increased competition led to a reduction in attraction to conspecifics (chapter 9). Simulations suggested this could be one potential mechanism underpinning fission-fusion dynamics in these species. Together, the results in this thesis form a framework linking social behaviour to individ- ual fitness where natural selection is shaped by the social environment. This approach may prove useful for testing whether following common social rules reduces variance in benefits accrued by individuals, and how within-species variation in social behaviour can impact emergent properties of groups.

This work is devoted to the numerical solution of equations describing the dynamics of flocks of birds. Specifically, we pay attention to the Euler equations for compressible flow with a right-hand side correction. This model is based on the work Fornasier et al. (2010). Due to the complexity of the model, we focus only on the one-dimensional case. For the numerical solution we use a semi-implicit discontinuous Galerkin method. Discretization of the right-hand side is chosen so that we preserve the structure of the semi-implicit scheme for the Euler equations presented in the work Feistauer, Kučera (2007). The proposed numerical scheme was implemented and numerical experiments showing the robustness of the scheme were carried out. Powered by TCPDF (www.tcpdf.org)

In this thesis, we study how and to what extent a self-organized mobile robot flock can be guided by informing some of the robots within the flock about a preferred direction of motion. Specifically, we extend a flocking behavior that was shown to maneuver a swarm of mobile robots as a cohesive group in free space, avoiding obstacles. In its original form, this behavior does not have a preferred direction and the flock would wander aimlessly. In this study, we incorporate a preference for a goal direction in some of the robots. These informed robots do not signal that they are informed (a.k.a. unacknowledged leadership) and instead guide the swarm by their tendency to move in the desired direction. Through experimental results with physical and simulated robots we show that the self-organized flocking of a robot swarm can be effectively guided by an informed minority of the flock. We evaluate the system using a number of quantitative metrics: First, we propose to use the mutual information metric from Information Theory as a dynamical measure of the information exchange. Then, we discuss the accuracy metric from directional statistics and size of the largest cluster as the measures of system performance. Using these metrics, we perform analyses from two points of views: In the transient analyses, we demonstrate the information exchange between the robots as the time advances, and the increase in the accuracy of the flock when the conditions are suitable for an adequate amount of information exchange. In the steady state analyses, we investigate the interdependent effects of the size of the flock in terms of the robots in it, the ratio of informed robots in the flock over the total flock size, the weight of the direction preference behavior, and the noise in the system.

Flocktechnologie ist eine im Bereich der Textiltechnik angewandte Methode, bei der kurze Fasern nahezu senkrecht auf ein vorher mit Klebstoff beschichtetes Substrat aufgebracht werden. In der vorliegenden Arbeit wurde die elektrostatische Beflockung als Methode zur Herstellung von porösen, dreidimensionalen Scaffolds für das Tissue Engineering von Knorpel und Knochen etabliert. Dieser neuartige Scaffoldtyp wurde eingehend charakterisiert und in Zellversuchen im Hinblick auf seine Biokompatibilität untersucht. Dabei zeigte sich, dass verschiedene Zellen im Scaffold proliferieren und differenzieren können. Die in der Arbeit beschriebenen Flockscaffolds stellen somit eine vielversprechende Matrix für die Therapie von Gelenkknorpeldefekten dar.

Electroacoustic music is often regarded as not being sufficiently accessible to the general public because of its sound-based abstract quality and the complexity of its language. Live electronic music introduces the figure of the performer as a gestural bodily agent that re-enables our multimodal perception of sound and seems to alleviate the accessibility dilemma. However, live electronic music generally lacks the level of detail found in studio-based fixed media works, and it can hardly be transferred outside the concert hall situation (e.g. as a video recording) without losing most of its fresh, dynamic and unpredictable nature. Recent developments in 3D simulation environments and game audio technologies suggest that alternative approaches to music composition and distribution are possible, presenting an opportunity to address some of these issues. In particular, this Portfolio of Compositions proposes the use of real and virtual space as a new medium for the creation and organisation of sound events via computer-simulated audio-sources. In such a context, the role of the performer is sometimes assumed by the listener itself, through the operation of an interactive-adaptive system, or it is otherwise replaced by a set of automated but flexible procedures. Although all of these works are sonic centric in nature, they often present a visual component that reinforces the multimodal perception of meaningful musical structures, either as real space locations for sonic navigation (locative audio), or live visualisations of physically-informed gestural agents in 3D virtual environments. Consequently, this thesis draws on general game-audio concepts and terminology, such as procedural sound, non-linearity, and generative music; but it also embraces game development tools (game engines) as a new methodological and technological approach to electroacoustic music composition. In such context, space and the real-time generation, control, and manipulation of assets combine to play an important role in broadening the routes of musical expression and the accessibility of the musical language. The portfolio consists of six original compositions. Three of these works–Swirls, Alice - Elegy to the Memory of an Unfortunate Lady, and Alcazabilla–are interactive in nature and they required the creation of custom software solutions (e.g. SonicMaps) in order to deal with open-form musical structures. The last three pieces–Singularity, Apollonian Gasket, and Boids–are based on fractal or emergent behaviour models and algorithms, and they propose a non-interactive linear organisation of sound materials via real-time manipulation of non-conventional 3D virtual instruments. These original instrumental models exhibit strong spatial and kinematic qualities with an abstract and minimal visual representation, resulting in an extremely efficient way to build spatialisation patterns, texture, and musical gesture, while preserving the sonic-centric essence of the pieces.