Event-triggered control for piecewise affine discrete-time systems

In the present work, we study the problems of stability analysis of piecewise-affine (PWA) discrete-time systems, and trigger-function design for discrete-time event-triggered control systems. We propose a representation for piecewise-affine systems in terms of ramp functions, and we rely on Lyapunov theory for the stability analysis. The proposed implicit piecewise-affine representation prevents the shortcomings of the existing stability analysis approaches of PWA systems. Namely, the need to enumerate regions and allowed transitions of the explicit representations. In this context, we can emphasize two benefits of the proposed approach: first, it makes possible the analysis of uncertainty in the partition and, thus, the transitions. Secondly, it enables the analysis of event-triggered control systems for the class of PWA systems since, for ETC, the transitions cannot be determined as a function of the state variables. The proposed representation, on the other hand, implicitly encodes the partition and the transitions. The stability analysis is performed with Lyapunov theory techniques. We then present conditions for exponential stability. Thanks to the implicit representation, the use of piecewise quadratic Lyapunov functions candidates becomes simple. These conditions can be solved numerically using a linear matrix inequality formulation. The numerical analysis exploits quadratic expressions that describe ramp functions to verify the positiveness of extended quadratic forms. For ETC, a piecewise quadratic trigger function defines the event generator. We find suitable parameters for the trigger function with an optimization procedure. As a result, this function uses the information on the partition to reduce the number of events, achieving better results than the standard quadratic trigger functions found in the literature. We provide numerical examples to illustrate the application of the proposed representation and methods.Ce manuscrit présente des résultats sur l’analyse de stabilité des systèmes affines par morceaux en temps discret et sur le projet de fonctions de déclenchement pour des stratégies de commande par événements. Nous proposons une représentation pour des systèmes affines par morceaux et l’on utilise la théorie de stabilité de Lyapunov pour effectuer l’analyse de stabilité globale de l’origine. La nouvelle représentation implicite que nous proposons rend plus simple l’analyse de stabilité car elle évite l’énumération des régions et des transitions entre régions tel que c’est fait dans le cas des représentations explicites. Dans ce contexte nous pouvons souligner deux avantages principaux, à savoir I) la possibilité de traiter des incertitudes dans la partition qui définit le système et, par conséquent des incertitudes dans les transitions, II) l’analyse des stratégies de commande par événements pour des systèmes affines par morceaux. En effet, dans ces stratégies les transitions ne peuvent pas être définies comme des fonctions des variables d’état. La théorie de stabilité de Lyapunov est utilisée pour établir des conditions pour la stabilité exponentielle de l’origine. Grâce à la représentation implicite des partitions nous utilisons des fonctions de Lyapunov quadratique par morceaux. Ces conditions sont données par des inégalités dont la solution numérique est possible avec une formulation par des inégalités matricielles linéaires. Ces formulations numériques se basent sur des expressions quadratiques décrivant des fonctions rampe. Pour des stratégies par événement, une fonctions quadratique par morceaux est utilisée pour le générateur d’événements. Nous calculons les paramètres de ces fonctions de déclenchement a partir de solutions de problèmes d’optimisation. Cette fonction de déclenchement quadratique par morceaux permet de réduire le nombre de d’événementsen comparaison avec les fonctions quadratiques utilisées dans la littérature. Nous utilisons des exemples numériques pour illustrer les méthodes proposées.No presente trabalho, são estudados os problemas de análise de estabilidade de sistemas afins por partes e o projeto da função de disparo para sistemas de controle baseado em eventos em tempo discreto. É proposta uma representação para sistemas afins por partes em termos de funções rampa, e é utilizada a teoria de Lyapunov para a análise de estabilidade. A representação afim por partes implícita proposta evita algumas das deficiências das abordagens de análise de estabilidade de sistemas afins por partes existentes. Em particular, a necessidade de anumerar regiões e transições admissíveis das representações explícitas. Neste contexto, dois benefícios da abordagem proposta podem ser enfatizados: primeiro, ela torna possível a análise de incertezas na partição, e, assim, nas transições. Segundo, ela permite a análise de sistemas de controle baseado em eventos para a classe de sistemas afins por partes, já que, para o controle baseado em eventos, as transições não podem ser determinadas como uma função das variáveis de estado. A representação proposta, por outro lado, codifica implicitamente a partição e as transições. A análise de estabilidade é realizada com técnicas da teoria de Lyapunov. Condi- ções para a estabilidade exponencial são então apresentadas. Graças à representação implícita, o uso de funções candidatas de Lyapunov se torna simples. Essas condições podem ser resolvidas numéricamente usando uma formulação de desigualdades matriciais lineares. A análise numérica explora expressões quadráticas que descrevem funções de rampa para verificar a postivividade de formas quadráticas extendidas. Para o controle baseado em eventos, uma função de disparo quadrática por partes define o gerador de eventos. Parâmetros adequados para a função de disparo sãoencontrados com um procedimento de otimização. Como resultado, esta função usa informação da partição para reduzir o número de eventos, obtendo resultados melhores do que as funções de disparo quadráticas encontradas na literatura. Exemplos numéricos são fornecidos para ilustrar a aplicação da representação e mé- todos propostos

Formal methods for resilient control

Many systems operate in uncertain, possibly adversarial environments, and their successful operation is contingent upon satisfying specific requirements, optimal performance, and ability to recover from unexpected situations. Examples are prevalent in many engineering disciplines such as transportation, robotics, energy, and biological systems. This thesis studies designing correct, resilient, and optimal controllers for discrete-time complex systems from elaborate, possibly vague, specifications. The first part of the contributions of this thesis is a framework for optimal control of non-deterministic hybrid systems from specifications described by signal temporal logic (STL), which can express a broad spectrum of interesting properties. The method is optimization-based and has several advantages over the existing techniques. When satisfying the specification is impossible, the degree of violation - characterized by STL quantitative semantics - is minimized. The computational limitations are discussed. The focus of second part is on specific types of systems and specifications for which controllers are synthesized efficiently. A class of monotone systems is introduced for which formal synthesis is scalable and almost complete. It is shown that hybrid macroscopic traffic models fall into this class. Novel techniques in modular verification and synthesis are employed for distributed optimal control, and their usefulness is shown for large-scale traffic management. Apart from monotone systems, a method is introduced for robust constrained control of networked linear systems with communication constraints. Case studies on longitudinal control of vehicular platoons are presented. The third part is about learning-based control with formal guarantees. Two approaches are studied. First, a formal perspective on adaptive control is provided in which the model is represented by a parametric transition system, and the specification is captured by an automaton. A correct-by-construction framework is developed such that the controller infers the actual parameters and plans accordingly for all possible future transitions and inferences. The second approach is based on hybrid model identification using input-output data. By assuming some limited knowledge of the range of system behaviors, theoretical performance guarantees are provided on implementing the controller designed for the identified model on the original unknown system

POSSIBLE AND PREFERABLE SCENARIOS OF A SUSTAINABLE FUTURE: TOWARDS 2030 AND BEYOND

Investigating the Future is an established practice for the academy and the world of crafts and industry. From the Chicago Columbian Exhibition of 1893 to the two Worlds Fairs of New York City (1939 and 1965) and so on, the future has been foreseen as filled with technology and amazing architecture but not every vision of the future has described promising scenarios. The four visions of the future proposed by Norman Henchey (1978) are conceptualized in classes – "possible" (any future), "plausible" (future that makes sense), "probable" (highly likely to happen), "preferable" (the best that could happen) – and have been brilliantly described in the ‘Futures Cone’ reinterpreted by Joseph Voros (2003). As we move away from the present, the ‘possible’ tends to ‘preferable’ due to the lack of elements and data on which to base the programming and the planning: in fact, the certainty on the type of technologies and production methods that will be available, on the social structure and user uses, and so on decreases. By 2030, the world will already be different: Thomas L. Friedman (2016) highlights that the three main forces of our Planet – Moore’s Law (technology), the Market (globalization) and Mother Nature (climate change and biodiversity loss) – are all pressing at the same time, with inevitable consequences for the territory, cities, architecture, products and services that will be designed, developed and used in the future. The 17 2030 Sustainable Development Goals presented by the United Nations provide an answer for this time horizon, tracing the path towards a model to achieve a better and more sustainable future for everyone. But will these Goals be able to accelerate sustainable innovation? Paraphrasing Luciano Floridi, philosopher of Information and Technology at the University of Oxford, we ask ourselves if ‘green’ (of natural and artificial environments) and "blue" (of science, technology and therefore the digital world) will succeed in guiding a vision of the future capable of replacing ‘things’ (objects) with "relationships", "individual planning" with "common planning", the "experience economy" (and not consumption) with a "policy of care and relationships" (and not production). A vision of a sustainable future of living, by looking at the two-time horizons of 2030 and 2050, will be played on an increasingly synergistic work aimed at providing answers to many questions. In this regard, the book ‘Possible and Preferable Scenarios of a Sustainable Future – Towards 2030 and Beyond’ collects essays and critical thoughts, research and experimentations on the subject providing some starting points for debate for the international scientific Community

International Conference on Civil Infrastructure and Construction (CIC 2020)

This is the proceedings of the CIC 2020 Conference, which was held under the patronage of His Excellency Sheikh Khalid bin Khalifa bin Abdulaziz Al Thani in Doha, Qatar from 2 to 5 February 2020. The goal of the conference was to provide a platform to discuss next-generation infrastructure and its construction among key players such as researchers, industry professionals and leaders, local government agencies, clients, construction contractors and policymakers. The conference gathered industry and academia to disseminate their research and field experiences in multiple areas of civil engineering. It was also a unique opportunity for companies and organizations to show the most recent advances in the field of civil infrastructure and construction. The conference covered a wide range of timely topics that address the needs of the construction industry all over the world and particularly in Qatar. All papers were peer reviewed by experts in their field and edited for publication. The conference accepted a total number of 127 papers submitted by authors from five different continents under the following four themes: Theme 1: Construction Management and Process Theme 2: Materials and Transportation Engineering Theme 3: Geotechnical, Environmental, and Geo-environmental Engineering Theme 4: Sustainability, Renovation, and Monitoring of Civil InfrastructureThe list of the Sponsors are listed at page 1

Aeronautical Engineering. A continuing bibliography with indexes, supplement 135, May 1981

This bibliography lists 536 reports, articles, and other documents introduced into the NASA scientific and technical information system in April 1981

Explicit fragility margins for PWA control laws of discrete-time linear systems

Print ISBN: 978-3-9524269-1-3International audienceThe paper considers a given discrete-time linear dynamic in closed loop with a piecewise affine control law defined over a bounded polyhedral partition of the state space χ. The objective is to describe the largest error affecting the control law coefficients over each region in the above partition, for which the positive invariance of the set χ is guaranteed with respect to the closed loop dynamics. This subset describes in fact a robust invariance margin with respect to a subset of closed-loop parameters and subsequently represents the explicit fragility margin of the given piecewise affine controller. The fragility characterizes the impact of an error in the implementation of a given controller. It is shown that the largest subset of errors in the state feedback gains is represented by a polyhedral set explicitly constructed with operations over convex domains. A series of remarks on the structure of the numerical problems are discussed and an example is provided for illustration

Sustaining Life During the AIDS Crisis: New Queer Cinema and the Biopic

This dissertation examines the discourses of health, crisis, and personal narrative that coalesced during the AIDS crisis of the 1980s and 1990s, and that shaped the responses of queer artists and activists to the pandemic. More specifically, the sexual politics and biopolitical discourses of that moment explain why queer filmmakers would turn to such a conservative film genre as the biopic as viable terrain. Because film scholars have almost uniformly positioned the biopic as a genre reinscribing Western subject formation, it makes sense that critics like B. Ruby Rich might fail to apprehend queer filmmakers’ biographical films as biopics. Since the biopic has such an enduring history from the early studio era to the present, including queer biographical films as part of the genre precludes the separation of queer filmmakers from dominant film history and cinematic conventions established during studio era Hollywood. The cost of this quarantine is a history in which queer films existed and continue to exist independently from a long line of films that inscribe personhood and personal history. However, the biopic’s interest in recording personal histories made it a particularly salient choice for queer filmmakers during the AIDS crisis when they sought to tell stories of damaged lives lost and lived. Chapter One explores how queer filmmakers John Greyson, Todd Haynes, and Bruce LaBruce responded to the AIDS crisis as precisely a crisis of queer visibility. The case studies of Tom Kalin’s Swoon (1992) and Savage Grace (2007) guide the next chapter’s return to cinema’s biomedical history, as well as psychoanalytic models of suturing, to excavate queer filmmakers’ disruption of normative models of spectatorship. Chapter Three reads Matthew Mishory’s Delphinium (2009) as a new point of entry into Derek Jarman’s cinema in order to understand both filmmakers as part of a queer genealogy. The fourth chapter investigates Elisabeth Subrin’s and Barbara Hammer’s creation and use of queer archives to tell the stories of feminisms—via particular feminists—past. The final chapter discusses the queer biopic’s relationship to People With AIDS (PWA) photography, looking finally to contemporary media practices to reflect upon the current AIDS media landscape

Bibliography of Lewis Research Center Technical Publications announced in 1991

This compilation of abstracts describes and indexes the technical reporting that resulted from the scientific engineering work performed and managed by the Lewis Research Center in 1991. All the publications were announced in the 1991 issues of STAR (Scientific and Technical Aerospace Reports) and/or IAA (International Aerospace Abstracts). Included are research reports, journal articles, conference presentations, patents and patent applications, and theses