With the multi-layered flocking system it is possible to simulate flocks that contain different types of agents that can be of various different sizes (variations in bounding radius and height). In the original implementation, the multi-layered flocking system uses a metric distance to find the nearest-neighbours of agents. However, results from real life field studies suggest that animals interact with each other in a flock using a topological distance. The goal of this thesis is therefore to implement a version of the multi-layered flocking system that uses a topological distance for interaction between agents. This is done by adapting two methods that are used to find the k-nearest neighbours (kNN), namely the original spatial partitioning method (OSP method) and the enhanced spatial partitioning method (ESP method), to work with the multi-layered flocking system. The aim is to compare the performance of these methods in terms of query time for four different flocking scenarios (standard, obstacle, follow and steer away). The implementation contains two types of agents of two different sizes. In the standard scenario all agents move together as a flock. The obstacle scenario is similar to the standard scenario with the addition that the simulation space contains stationary obstacles. In the follow scenario the smaller sized agents follow the bigger sized agents, and in the steer away scenario the smaller sized agents steer away from the bigger sized agents. An evaluation of how different numbers of kNN affect the collective motion (polarization, extension and frequency of collisions) of the flock in the four different scenarios is also done. The evaluation was performed by implementing the multi-layered flocking system in the Unity game engine, and running simulations with flocks of different sizes (125-3125 agents) and using different numbers of interacting kNN (k=5,10,15,20) for each of the scenarios. The results show that the ESP method on average is at least twice as fast compared to the OSP method in all four flocking scenarios, and the improvement in performance in query time did not differ much between the scenarios. Moreover, a value of k=10 was shown to be a good compromise between having fast kNN query times for the ESP method, but still having flocks of agents moving in a collective manner. / Med ett flerskiktigt flockningssystem är det möjligt att simulera flockar som innehåller olika typer av agenter som kan vara av olika storlekar (variation i begränsningsradie och längd). I den ursprungliga implementeringen av det flerskiktigt flockningssystem används ett metriskt avstånd för att hitta de närmaste grannarna till agenterna. Resultat från fältstudier tyder dock på att i verkligheten interagerar djur i en flock med varandra genom ett topologiskt avstånd. Målet med denna avhandling är därför att implementera en version av det flerskiktigt flockningssystem som använder ett topologiskt avstånd för att hitta de närmaste grannarna till agenterna. Detta görs genom att anpassa två metoder som kan användas för att hitta en agents k-närmaste grannar till det flerskiktigt flockningssystem. Dessa två metoder kallas den ursprungliga spatiala partitioneringsmetoden (OSP metoden) och den förbättrade spatiala partitioneringsmetoden (ESP metoden). Syftet är att jämföra prestandan mellan dessa två metoder, vilket mäts i tid som det tar att hitta de k-närmaste grannarna för varje metod. Jämförelser genomförs för fyra olika typer av scenarion (standard, hinder, följ och styr ifrån). I standard scenariot rör sig alla agenter tillsammans som en flock. Hinder scenariot liknar standard scenariot med tillägget att simuleringsmiljön består av ett antal stationära hinder. I följ scenariot så följer de mindre agenterna de större agenterna, och i styr ifrån scenariot så försöker de mindre agenterna fly från de större agenterna. Vidare görs en utvärdering av hur olika antal k-närmaste grannar påverkar den totala flockens samlade rörelse (polarisering, förlängning och frekvens av kollisioner) för de olika scenarierna. Utvärderingen görs genom att implementera det flerskiktiga flockningssystemet med de ovan nämnda k-närmaste grannar metoderna i spelmotorn Unity. Ett flertal simuleringar genomförs sedan för de fyra scenarierna och dessa består av olika flockstorlekar (125-3125 agenter) och använder olika värden på k (k=5,10,15,20). Resultaten visar att ESP metoden i genomsnitt är dubbelt så snabb jämfört med OSP metoden. Dessutom visades ett värde på k=10 vara en bra kompromiss mellan att snabbt hitta de k-närmaste grannarna när ESP metoden används, men också ha flockar av agenter som rör sig kollektivt.

Le déplacement cohérent dirigé au sein de troupeaux, d’essaims, de nuées, prend place à toutes les échelles du vivant. En cherchant à rationaliser l’émergence de tels mouvements collectifs, les physiciens ont décrit ces assemblées comme des matériaux actifs. Ces matériaux sont formés de constituants auto-propulsés qui se déplacent spontanément dans une direction commune. Cette thèse expérimentale s’appuie sur la réalisation de troupeaux synthétiques pour explorer les propriétés de la matière active polaire dans des situations défavorables à son auto-organisation : leur dynamique en milieux désordonnés et leur réponse à des perturbations externes. Des rouleurs colloïdaux aux interactions d’alignement sont confinés au sein de dispositifs microfluidiques. Au-delà d’une densité seuil, ils forment un troupeau caractérisé par l’émergence d’un ordre en orientation de longue portée. Ces troupeaux colloïdaux font office de prototypes de la matière active polaire. Nous avons étudié la réponse d’un liquide actif polaire assemblé à partir de rouleurs colloïdaux. Nous avons montré que face à une perturbation longitudinale leur réponse est hystérétique. Nous avons expliqué théoriquement ce comportement non-linéaire et l’avons exploité pour réaliser des oscillateurs microfluidiques autonomes. Nous avons également étudié la dynamique de troupeaux colloïdaux qui se propagent dans des environnements hétérogènes. La présence d’obstacles distribués aléatoirement focalise les troupeaux le long de chemins privilégiés qui forment un réseau épars et tortueux. Augmenter le désordre conduit à la destruction du troupeau. Nous avons démontré que la suppression du mouvement collectif consiste en une transition discontinue, générique à tous les matériaux actifs polaires. / Directed collected motion within herds, swarms and flocks, is a phenomenon that takes place at all scales in living systems. Physicists have rationalized the emergence of such collective behavior. They have described these systems as active materials. These materials are assembled from self-propelled units that spontaneously move in the same direction. By experimentally studying synthetic flocks, this work uncovers some properties of polar active materials in situations that disfavor their self-organization: their dynamics in disordered environments and their response to external perturbations. Colloidal rollers with alignment interactions are confined within microfluidic devices. At high density, they spontaneously form a flock which is characterized by the emergence of orientational long-ranged order. These colloidal flocks are prototypical realizations of polar active matter. We have studied the response of a polar active liquid assembled from colloidal rollers. We have shown that they display a hysteretic response to longitudinal perturbations. We have theoretically accounted for this non-linear behavior. We have used this behavior to realize autonomous microfluidic oscillators. We have also studied the dynamics of colloidal flocks that propagate through heterogeneous environments. Randomly positioned obstacles focalize flocks along favored channels that form a sparse and tortuous network. Increasing disorder leads to the destruction of flocks. We have demonstrated that the suppression of collective motion is a discontinuous transition generic to all polar active materials.

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.

The field of articular cartilage tissue engineering has developed rapidly, and chitosan has become a promising material for scaffold fabrication. For this paper, wet-spun biocompatible chitosan filament yarns were converted into short flock fibers and subsequently electrostatically flocked onto a chitosan substrate, resulting in a pure, highly open, porous, and biodegradable chitosan scaffold. Analyzing the wet-spinning of chitosan revealed its advantages and disadvantages with respect to the fabrication of the fiber-based chitosan scaffolds. The scaffolds were prepared using varying processing parameters and were analyzed in regards to their geometrical and mechanical properties. It was found that the pore sizes were adjustable between 65 and 310 µm, and the compressive strength was in the range 13–57 kPa.

Several of our technological breakthroughs are influenced by types of behavior and structures developed in the natural world, including the emulation of swarm in- telligence and the engineering of artificial synapses that function like the human mind. Much like these breakthroughs, this report examines emerging behaviors across swarms of non-communicating, adaptive units that evade obstacles while find- ing a path, to present a swarming algorithm premised on a class of local rule sets re- sulting in a Unmanned Aerial Vehicle (UAV) group navigating together as a unified swarm. Primarily, this method’s important quality is that its rules are local in nature. Thus, the exponential calculations which can be supposed with growing number of drones, their states, and potential tasks are remedied. To this extent, the study tests the algorithmic rules in experiments to replicate the desired behavior in a bounded virtual space filled with simulated units. Simultaneously, in the adaptation of natural flocking rules the study also introduces the rule sets for goal seeking and uncertainty evasion. In effect, the study succeeds in reaching and displaying the desired goals even as the units avoid unknown before flight obstacles and inter-unit collisions with- out the need for a global centralized command nor a leader based hierarchical system.

No description available.