Perspectives on adaptive dynamical systems

Adaptivity is a dynamical feature that is omnipresent in nature, socio-economics, and technology. For example, adaptive couplings appear in various real-world systems like the power grid, social, and neural networks, and they form the backbone of closed-loop control strategies and machine learning algorithms. In this article, we provide an interdisciplinary perspective on adaptive systems. We reflect on the notion and terminology of adaptivity in different disciplines and discuss which role adaptivity plays for various fields. We highlight common open challenges, and give perspectives on future research directions, looking to inspire interdisciplinary approaches.Comment: 46 pages, 9 figure

Capturing interpersonal coordination processes in association football : from dyads to collectives

Doutoramento em Motricidade Humana, na especialidade de Ciências do DesportoThe purpose of this thesis was to investigate how football performers coordinate their behaviours in different levels of social organisation. We began with a position paper proposing the re-conceptualisation of sport teams as functional integrated superorganisms to frame a deeper understanding of the interpersonal coordination processes emerging between team players. Time-motion analysis procedures and innovative tools were developed and presented in order to capture the superorganismic properties of sports teams and the interpersonal coordination tendencies developed by players. These tendencies were captured and analysed in representative 1vs1 and 3vs3 sub-phases, as well as in the 11-a-side game format. Data showed higher levels of variability at the individual level compared to the team level. This finding suggested that micro-variability may contribute to stabilise the behavioural dynamics at the collective level. Moreover, the specificities of the interpersonal coordination tendencies displayed within attacking-defending dyads demonstrated to have influenced the performance outcome. Attacking players tend to succeed when they were more synchronised in space and time with the defenders, and their interaction were more unpredictable/irregular. Besides, the time-evolving dynamics of the collective behaviours (i.e., at 11-a-side level) during competitive football performance indicated a tendency for an increase in the predictability (i.e., more regularity). These data were interpreted as evidencing co-adaptation processes between opponent players, which suggest that team players may shift from prevalent explorative and irregular behaviours to more predictable behaviours emerging due changes in their functional movement possibilities. However, some game events such as goals scored, halftime and stoppages in play seemed to break this continuum and acted as relevant performance constraints.FCT - Fundação para Ciência e a Tecnologi

Perspectives on adaptive dynamical systems

Adaptivity is a dynamical feature that is omnipresent in nature, socio-economics, and technology. For example, adaptive couplings appear in various real-world systems, such as the power grid, social, and neural networks, and they form the backbone of closed-loop control strategies and machine learning algorithms. In this article, we provide an interdisciplinary perspective on adaptive systems. We reflect on the notion and terminology of adaptivity in different disciplines and discuss which role adaptivity plays for various fields. We highlight common open challenges and give perspectives on future research directions, looking to inspire interdisciplinary approaches

Firefly-Inspired Synchronization in Swarms of Mobile Agents

Synchronization can be a necessary prerequisite to perform coordinated actions or reach consensus in decentralized multi-agent systems, such as robotic swarms and sensor networks. One of the simplest distributed synchronization algorithms is firefly synchronization, also known as pulse-coupled oscillator synchronization. In this framework, each agent possesses an internal oscillator and the completion of oscillation cycles is signaled by means of short pulses, which can be detected by other neighboring agents. This thesis focuses on a realistic mode of interaction for practical implementations, in which agents have a restricted field of view used to detect pulses emitted by other agents. The effect of agent speed on the time required to achieve synchronization is studied. Simulations reveal that synchronization can be fostered or inhibited by tuning the agent (robot) speed, leading to distinct dynamical regimes. These findings are further validated in physical robotic experiments. In addition, an analysis is presented on the effect that the involved system parameters have on the time it takes for the ensemble to synchronize. To assess the effect of noise, the propagation of perturbations over the system is analyzed. The reported findings reveal the conditions for the control of clock or activity synchronization in swarms of mobile agents

Bridging the gap between emotion and joint action

Our daily human life is filled with a myriad of joint action moments, be it children playing, adults working together (i.e., team sports), or strangers navigating through a crowd. Joint action brings individuals (and embodiment of their emotions) together, in space and in time. Yet little is known about how individual emotions propagate through embodied presence in a group, and how joint action changes individual emotion. In fact, the multi-agent component is largely missing from neuroscience-based approaches to emotion, and reversely joint action research has not found a way yet to include emotion as one of the key parameters to model socio-motor interaction. In this review, we first identify the gap and then stockpile evidence showing strong entanglement between emotion and acting together from various branches of sciences. We propose an integrative approach to bridge the gap, highlight five research avenues to do so in behavioral neuroscience and digital sciences, and address some of the key challenges in the area faced by modern societies

A Taxonomy for and Analysis of Anonymous Communications Networks

Any entity operating in cyberspace is susceptible to debilitating attacks. With cyber attacks intended to gather intelligence and disrupt communications rapidly replacing the threat of conventional and nuclear attacks, a new age of warfare is at hand. In 2003, the United States acknowledged that the speed and anonymity of cyber attacks makes distinguishing among the actions of terrorists, criminals, and nation states difficult. Even President Obama’s Cybersecurity Chief-elect recognizes the challenge of increasingly sophisticated cyber attacks. Now through April 2009, the White House is reviewing federal cyber initiatives to protect US citizen privacy rights. Indeed, the rising quantity and ubiquity of new surveillance technologies in cyberspace enables instant, undetectable, and unsolicited information collection about entities. Hence, anonymity and privacy are becoming increasingly important issues. Anonymization enables entities to protect their data and systems from a diverse set of cyber attacks and preserves privacy. This research provides a systematic analysis of anonymity degradation, preservation and elimination in cyberspace to enhance the security of information assets. This includes discovery/obfuscation of identities and actions of/from potential adversaries. First, novel taxonomies are developed for classifying and comparing well-established anonymous networking protocols. These expand the classical definition of anonymity and capture the peer-to-peer and mobile ad hoc anonymous protocol family relationships. Second, a unique synthesis of state-of-the-art anonymity metrics is provided. This significantly aids an entity’s ability to reliably measure changing anonymity levels; thereby, increasing their ability to defend against cyber attacks. Finally, a novel epistemic-based mathematical model is created to characterize how an adversary reasons with knowledge to degrade anonymity. This offers multiple anonymity property representations and well-defined logical proofs to ensure the accuracy and correctness of current and future anonymous network protocol design

On the dichotomic collective behaviors of large populations of pulse-coupled firing oscillators

The study of populations of pulse-coupled firing oscillators is a general and simple paradigm to investigate a wealth of natural phenomena, including the collective behaviors of neurons, the synchronization of cardiac pacemaker cells, or the dynamics of earthquakes. In this framework, the oscillators of the network interact through an instantaneous impulsive coupling: whenever an oscillator fires, it sends out a pulse which instantaneously increments the state of the other oscillators by a constant value. There is an extensive literature on the subject, which investigates various model extensions, but only in the case of leaky integrate-and-fire oscillators. In contrast, the present dissertation addresses the study of other integrate-and-fire dynamics: general monotone integrate-and-fire dynamics and quadratic integrate-and-fire dynamics. The main contribution of the thesis highlights that the populations of oscillators exhibit a dichotomic collective behavior: either the oscillators achieve perfect synchrony (slow firing frequency) or the oscillators converge toward a phase-locked clustering configuration (fast firing frequency). The dichotomic behavior is established both for finite and infinite populations of oscillators, drawing a strong parallel between discrete-time systems in finite-dimensional spaces and continuous-time systems in infinite-dimensional spaces. The first part of the dissertation is dedicated to the study of monotone integrate-and-fire dynamics. We show that the dichotomic behavior of the oscillators results from the monotonicity property of the dynamics: the monotonicity property induces a global contraction property of the network, that forces the dichotomic behavior. Interestingly, the analysis emphasizes that the contraction property is captured through a 1-norm, instead of a (more common) quadratic norm. In the second part of the dissertation, we investigate the collective behavior of quadratic integrate-and-fire oscillators. Although the dynamics is not monotone, an “average” monotonicity property ensures that the collective behavior is still dichotomic. However, a global analysis of the dichotomic behavior is elusive and leads to a standing conjecture. A local stability analysis circumvents this issue and proves the dichotomic behavior in particular situations (small networks, weak coupling, etc.). Surprisingly, the local stability analysis shows that specific integrate-and-fire oscillators exhibit a non-dichotomic behavior, thereby suggesting that the dichotomic behavior is not a general feature of every network of pulse-coupled oscillators. The present thesis investigates the remarkable dichotomic behavior that emerges from networks of pulse-coupled integrate-and-fire oscillators, putting emphasis on the stability properties of these particular networks and developing theoretical results for the analysis of the corresponding dynamical systems.Les populations d’oscillateurs impulsivement couplés constituent un paradigme simple et général pour étudier une multitude de phénomènes naturels, tels que les comportements collectifs des neurones, la synchronisation des cellules pacemaker du coeur, ou encore la dynamique des tremblements de terre. Dans ce contexte, les oscillateurs interagissent au sein du réseau par le biais d’un couplage instantané: quand un oscillateur décharge, il envoie vers les autres oscillateurs une impulsion qui incrémente instantanément leur état par une valeur constante. Diverses extensions du modèle ont été intensément étudiées dans la littérature, mais seulement dans le cas d’oscillateurs leaky integrate-and-fire. Afin de pallier cette restriction, le présent manuscrit traite de l’étude d’autres dynamiques integrate-and-fire: les dynamiques générales integrate-and-fire monotones et les dynamiques integrate-and-fire quadratiques. La contribution principale de la thèse met en évidence le comportement d’ensemble dichotomique selon lequel s’organisent les populations d’oscillateurs: soit les oscillateurs atteignent un état de synchronisation parfaite (taux de décharge lent), soit ils convergent vers une configuration de clustering en blocage de phase (taux de décharge rapide). Ce comportement dichotomique est établi aussi bien pour des populations finies que pour des populations infinies, ce qui démontre un parallèle élégant entre des systèmes en temps-discret dans des espaces de dimension finie et des systèmes en temps-continu dans des espaces de dimension infinie. La première partie du manuscrit se concentre sur l’étude des dynamiques integrate-and-fire monotones. Dans ce cadre, nous montrons que le comportement dichotomique résulte de la propriété de monotonicité des oscillateurs. Cette dernière induit une propriété de contraction globale, elle-même engendrant le comportement dichotomique. En outre, l’analyse révèle que la propriété de contraction est capturée par une norme 1, au lieu d’une norme quadratique (plus usuelle). Dans la seconde partie de la thèse, nous étudions le comportement d’ensemble d’oscillateurs integrate-and-fire quadratiques. Bien que la dynamique ne soit plus monotone, une propriété de monotonicité “en moyenne” implique que le comportement collectif est encore dichotomique. Alors qu’une analyse de stabilité globale s’avère être difficile et conduit à plusieurs conjectures, une analyse locale permet de prouver le comportement dichomique dans certaines situations (réseaux de petite taille, couplage faible, etc.). De plus, l’analyse locale prouve que des oscillateurs integrate-and-fire particuliers ne s’organisent pas suivant un comportement dichotomique, ce qui suggère que ce dernier n’est pas une caractéristique générale de tous les réseaux d’oscillateurs impulsivement couplés. En résumé, la thèse étudie le remarquable comportement dichotomique qui émerge des réseaux d’oscillateurs integrate-and-fire impulsivement couplés, mettant ainsi l’emphase sur les propriétés de stabilité desdits réseaux et développant les résultats théoriques nécessaires à l’étude mathématique des systèmes dynamiques correspondants