Download or read book Conception de lois de commande hautes performances pour l optique adaptative des grands written by Carlos CORREIA and published by . This book was released on 2010 with total page 208 pages. Available in PDF, EPUB and Kindle. Book excerpt: L’optique adaptative (OA) permet de corriger les effets induits par la turbulence atmosphérique, qui dégradent la résolution des télescopes et donc la qualité des images. Introduits dans les années 1990, les systèmes d’OA deviennent désormais tomographiques, permettant l’analyse du volume turbulent pour une correction à grand champ. Ceci s’accompagne d’une forte augmentation de la complexité des OA des futurs grands télescopes. Les nouveaux concepts d’OA souvent à grands nombres de degrés de liberté (GNDL) requièrent des lois de commande innovantes respectant les contraintes temps réel. Plusieurs aspects originaux sont abordés. Pour les GNDL, le point d'entrée est le choix de la base de représentation de la phase. Deux voies sont explorées : avec une formulation zonale, des méthodes Fourier sont étudiées pour la reconstruction statique de front d'onde ; une nouvelle stratégie combinant méthodes Fourier et méthodes itératives est développée pour adapter la commande optimale linéaire quadratique gaussienne (LQG) aux GNDL. On traite ensuite le problème des dynamiques temporelles des grands miroirs déformables. Pour des dynamiques linéaires, la commande optimale minimisant la variance résiduelle est obtenue comme solution d’un problème LQG à temps discret. Ceci permet aussi de quantifier la dégradation de performances pour des commandes sous-optimales. Cette approche est appliquée à la commande des miroirs de basculement destinés aux grands télescopes. On montre que négliger la dynamique conduit à une dégradation significative des performances. Une autre application est traitée : la coordination d’un miroir lent et d’un miroir rapide (concept woofer-tweeter).
Download or read book Validation ciel d une commande haute performance en optique adaptative classique et multi objet sur le d monstrateur CANARY written by Gaetano Sivo and published by . This book was released on 2013 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: L'optique adaptative (OA), qui permet de corriger en temps-réel les déformations du front d'onde induites par la turbulence atmosphérique, connaît une limitation fondamentale : l'anisoplanétisme. Pour y remédier, le concept d'OA grand champ (OAGC) a été proposé. La turbulence est mesurée dans plusieurs directions du champ de vue à l'aide d'étoiles guide naturelles et laser, et son impact corrigé sur les images par une commande basée sur une reconstruction tomographique. L'approche linéaire quadratique gaussienne (LQG) est bien adaptée à la conception de lois de commande en OAGC comme en OA classique. Elle permet d'estimer et de prédire la phase à l'aide d'un filtre de Kalman basé sur des a priori spatiaux et temporels. Les modèles d'état et commandes associées sont détaillés. On présente la première mise en oeuvre sur le ciel d'une commande LQG sur tous les modes, en OA classique et multi-objet, à l'aide du démonstrateur CANARY. Ces résultats sont obtenus avec identification du modèle de tip-tilt et filtrage des vibrations, ce qui constitue la première mise en oeuvre ciel de cette stratégie. Les a priori spatiaux de la phase en volume sont identifiés par la méthode LEARN. Des données issues du profilomètre stereoSCIDAR ont aussi été utilisées. Des comparaisons sont proposées avec une commande intégrateur en OA classique, avec un gain significatif en performances pour le LQG. Les comparaisons avec le reconstructeur statique APPLY (moindres carrés régularisés) en OA multi-objet mettent en évidence un gain du LQG dans certains cas (fort bruit en particulier). L'ensemble des résultats confirme la faisabilité et l'intérêt d'une commande LQG pour un instrument d'OA ou d'OAGC.
Download or read book Commande optimale en optique adaptative classique et multiconjugu e written by Brice Le Roux and published by . This book was released on 2003 with total page 210 pages. Available in PDF, EPUB and Kindle. Book excerpt: La turbulence atmosphérique perturbe la propagation de la lumière provenant d’objets astronomiques. Au foyer du télescope, on observe sur l’image obtenue une perte de résolution angulaire. L’optique adaptative permet de trouver la résolution théorique du télescope. L’Optique Adaptative Multiconjuguée devrait de plus permettre d’élargir le champ isoplanétique en sortie du système. Dans le contexte des futurs systèmes d’Optique Adaptative (à haute dynamique ou à grand champ), la loi de commande du système doit être choisie de façon à optimiser les performances. Elle doit notamment permettre de minimiser l’erreur temporelle ou l’anisoplanétisme résiduel. Nous proposons une commande optimale au sens de la variance de phase résiduelle minimale pour l’Optique Adaptative Classique et l’Optique Adaptative Multiconjuguée. L’approche que nous présentons est basée sur une estimation de la phase turbulente par filtrage de Kalman suivie d’une commande par retour d’état, développés dans un formalisme d’état. Cette approche prend en compte les connaissances a priori disponibles sur le bruit de mesure, le profil de turbulence en altitude, la statistique de Kolmogorov ou encore la vitesse d’évolution de la turbulence. Nous quantifions le gain apporté par cette loi de commande vis-à-vis d’une approche traditionnelle par des simulations numériques en OA classique et multiconjuguée et nous discutons la robustesse des performances approche optimale. Nous présentons également une mise en place d’une validation expérimentale sur le banc BOA de l’Onera.
Download or read book Commande optimale rapide pour l optique adaptative des futurs t lescopes hectom triques written by Clémentine Béchet and published by . This book was released on 2008 with total page 290 pages. Available in PDF, EPUB and Kindle. Book excerpt: Le nombre de degrés de liberté à contrôler dans un système d'optique adaptative (OA) passe de quelques centaines pour les grands télescopes actuels à plusieurs milliers prévus sur les futurs télescopes de 30 à 100 mètres de diamètre. La méthode de commande de cette OA doit être repensée à la fois pour être en adéquation avec les nouveaux critères de performance et pour pouvoir estimer un si grand nombre de paramètres en temps réel. Je montre d'abord qu'il est possible d'améliorer l'estimation de la déformation de la surface d'onde, d'un facteur 2 sur la variance de l'erreur, en tenant compte de connaissances a priori sur la statistique de la turbulence atmosphérique et ce, tout en utilisant un algorithme rapide adapté aux grands systèmes. Ensuite, l'optimisation d'un critère en boucle fermée me conduit à une commande optimale par modèle interne, applicable en temps réel sur un télescope hectométrique grâce à l'algorithme rapide cité précédemment. La robustesse de cette nouvelle méthode de commande a enfin été éprouvée sur un simulateur complet d'OA et ses performances ont été comparées à d'autres approches.
Download or read book Commande Pour L optique Adaptative written by Andrea Abelli and published by . This book was released on 2013 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: His thesis investigates the control aspects of Adaptive Optics applications, a technology used to improve the performance of optical systems by reducing the effect of wavefront distortions, to high angular resolution imaging. The Adaptive Optics control problem is presented through a survey of the literature. Consequently, the design of a feedback controller is addressed, from a modern control point of view, by means of the Linear Quadratic Gaussian control methodology. The proposed approach emphasizes the ability of the adaptive optics loop to reject the atmospheric aberration. We derive a diagonal state-space system representation which clearly separates the dynamics of the plant (deformable mirror and wavefront sensor) from the disturbance dynamics (atmospheric model). This representation facilitates the numerical resolution of the problem. A frequency analysis is carried out to check the performance and robustness specifications of the multiple-input multiple-output feedback system. Moreover, we analyze the performance and the robustness of LQG-based control compared to classic integral control, by means of end-to-end simulations and by considering different levels of wavefront sensor noise. During on-sky observations, the turbulent energy and relative speed of each atmospheric layer can change rapidly degrading the wavefront estimate. For this reason, a numerical model design algorithm guaranteeing satisfactory disturbance rejection performance even in the case of time-varying turbulence's characteristic is derived. Numerical experiments using the Software Package CAOS have been conducted to demonstrate the robustness of every proposed approach. Given the author firm belief that the future of Adaptive Optics also relies on the development of more sophisticated (i.e., nonlinear) models, a substantial amount of work was dedicated to the study of two classes of widespread pattern recognition methods. Namely Support Vector Machines and Kernel Methods, whose regression capabilities are exploited in the solution of the nonlinear optimal tracking problem. Concerning Support Vector Machines, thanks to the singular optimal control theory, constraints are loosened permitting an easier and faster numerical resolution of the optimization problem. So that, in the fully deterministic case the Support Vector controller results simpler to synthesize. With reference to Kernel Methods, an original attempt to bring together their regression strengths with the concept of Adaptive Inverse Control is presented. The Kernel Recursive Least-Square algorithm is used to implement an adaptive inverse controller capable of forcing a suitable nonlinear dynamics to follow a desired output. This very method can also be used to check if a given arbitrary trajectory is an admissible output for the nonlinear system under study. Such an innovative algorithm could be fruitfully applied, in future works, to the control of Tip-Tilt mirrors. Eventually, a first sketch of the theoretical framework supporting the use of Adaptive Inverse Control for the solution of the general tracking problem is given. After introducing the mathematical formulation of the tracking problem and the needed mathematical definitions, sufficient and necessary conditions (linear case) and sufficient (nonlinear case) conditions to the existence of the solution are derived.
Download or read book Flight Vehicle System Identification written by Ravindra V. Jategaonkar and published by AIAA (American Institute of Aeronautics & Astronautics). This book was released on 2006 with total page 568 pages. Available in PDF, EPUB and Kindle. Book excerpt: This valuable volume offers a systematic approach to flight vehicle system identification and exhaustively covers the time domain methodology. It addresses in detail the theoretical and practical aspects of various parameter estimation methods, including those in the stochastic framework and focusing on nonlinear models, cost functions, optimization methods, and residual analysis. A pragmatic and balanced account of pros and cons in each case is provided. The book also presents data gathering and model validation, and covers both large-scale systems and high-fidelity modeling. Real world problems dealing with a variety of flight vehicle applications are addressed and solutions are provided. Examples encompass such problems as estimation of aerodynamics, stability, and control derivatives from flight data, flight path reconstruction, nonlinearities in control surface effectiveness, stall hysteresis, unstable aircraft, and other critical considerations.
Download or read book FiWi Access Networks written by Martin Maier and published by Cambridge University Press. This book was released on 2011-12-15 with total page 276 pages. Available in PDF, EPUB and Kindle. Book excerpt: The evolution of broadband access networks toward bimodal fiber-wireless (FiWi) access networks, described in this book, may be viewed as the endgame of broadband access. After discussing the economic impact of broadband access and current worldwide deployment statistics, all the major legacy wireline and wireless broadband access technologies are reviewed. State-of-the-art GPON and EPON fiber access networks are described, including their migration to next-generation systems such as OCDMA and OFDMA PONs. The latest developments of wireless access networks are covered, including VHT WLAN, Gigabit WiMAX, LTE and WMN. The advantages of FiWi access networks are demonstrated by applying powerful network coding, heterogeneous optical and wireless protection, hierarchical frame aggregation, hybrid routing and QoS continuity techniques across the optical-wireless interface. The book is an essential reference for anyone working on optical fiber access networks, wireless access networks or converged FiWi systems.
Download or read book Artificial Intelligence in Society written by OECD and published by OECD Publishing. This book was released on 2019-06-11 with total page 152 pages. Available in PDF, EPUB and Kindle. Book excerpt: The artificial intelligence (AI) landscape has evolved significantly from 1950 when Alan Turing first posed the question of whether machines can think. Today, AI is transforming societies and economies. It promises to generate productivity gains, improve well-being and help address global challenges, such as climate change, resource scarcity and health crises.
Download or read book Dynamique Non lin aire Et Le Chaos written by and published by . This book was released on 1993 with total page 130 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Cambridge Handbook of Engineering Education Research written by Aditya Johri and published by Cambridge University Press. This book was released on 2014-02-10 with total page 1124 pages. Available in PDF, EPUB and Kindle. Book excerpt: The Cambridge Handbook of Engineering Education Research is the critical reference source for the growing field of engineering education research, featuring the work of world luminaries writing to define and inform this emerging field. The Handbook draws extensively on contemporary research in the learning sciences, examining how technology affects learners and learning environments, and the role of social context in learning. Since a landmark issue of the Journal of Engineering Education (2005), in which senior scholars argued for a stronger theoretical and empirically driven agenda, engineering education has quickly emerged as a research-driven field increasing in both theoretical and empirical work drawing on many social science disciplines, disciplinary engineering knowledge, and computing. The Handbook is based on the research agenda from a series of interdisciplinary colloquia funded by the US National Science Foundation and published in the Journal of Engineering Education in October 2006.
Download or read book Engineering written by Unesco and published by UNESCO. This book was released on 2010-01-01 with total page 392 pages. Available in PDF, EPUB and Kindle. Book excerpt: This report reviews engineering's importance to human, economic, social and cultural development and in addressing the UN Millennium Development Goals. Engineering tends to be viewed as a national issue, but engineering knowledge, companies, conferences and journals, all demonstrate that it is as international as science. The report reviews the role of engineering in development, and covers issues including poverty reduction, sustainable development, climate change mitigation and adaptation. It presents the various fields of engineering around the world and is intended to identify issues and challenges facing engineering, promote better understanding of engineering and its role, and highlight ways of making engineering more attractive to young people, especially women.--Publisher's description.
Download or read book Gharial Conservation in Nepal written by Tirtha Man Maskey and published by . This book was released on 2008 with total page 168 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book The Disappearing Computer written by Norbert Streitz and published by Springer. This book was released on 2007-07-20 with total page 314 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book examines how the computer, as we currently know it, will be replaced by a new generation of technologies, moving computing off the desktop and ultimately integrating it with real world objects and everyday environments. It provides a unique combination of concepts, methods and prototypes of ubiquitous and pervasive computing reflecting the current interest in smart environments and ambient intelligence.
Download or read book Engineering for Sustainable Development written by International Centre for Engineering Education and published by UNESCO Publishing. This book was released on 2021-03-02 with total page 183 pages. Available in PDF, EPUB and Kindle. Book excerpt: The report highlights the crucial role of engineering in achieving each of the 17 SDGs. It shows how equal opportunities for all is key to ensuring an inclusive and gender balanced profession that can better respond to the shortage of engineers for implementing the SDGs. It provides a snapshot of the engineering innovations that are shaping our world, especially emerging technologies such as big data and AI, which are crucial for addressing the pressing challenges facing humankind and the planet. It analyses the transformation of engineering education and capacity-building at the dawn of the Fourth Industrial Revolution that will enable engineers to tackle the challenges ahead. It highlights the global effort needed to address the specific regional disparities, while summarizing the trends of engineering across the different regions of the world.
Download or read book Narratives of fear and safety written by Kaisa Kaukiainen and published by BoD - Books on Demand. This book was released on 2020-09-01 with total page 546 pages. Available in PDF, EPUB and Kindle. Book excerpt: The essays in this edited volume, written in English and French, tackle the intriguing problems of fear and safety by analysing their various meanings and manifestations in literature and other narrative media. The articles bring forth new, cross-cultural interpretations on fear and safety through examining what kinds of genre-specific means of world-making narratives use to express these two affectivities. The articles also show how important it is to study these themes in order to understand challenges in times of global threats, such as the climate crisis. The main themes of the book are approached from various theoretical perspectives as related to their literary and cultural representations. Recent trends in research, such as affect and risk theory, serve as the basis for the discussion. The articles in the volume also draw from disciplines such as gender studies and trauma studies to examine the threats posed by collective fears and aggression on individuals' lives and propose ways of coping with fear. These themes are addressed also in articles analysing new adaptations of old myths that retell stories of the past. Many of the articles in the volume discuss apocalyptic and dystopian narratives that currently permeate the entire cultural landscape. Dystopian narratives do not only deal with future threats, such as totalitarianism, technocracy, or environmental disasters, but also suggest alternative ways of being and new hopes in the form of political resistance.
Download or read book Government at a Glance Southeast Asia 2019 written by OECD and published by OECD Publishing. This book was released on 2019-09-10 with total page 132 pages. Available in PDF, EPUB and Kindle. Book excerpt: Government at a Glance Southeast Asia 2019 is the first edition in the Government at a Glance series for the region. It provides the latest available data on public administrations in the 10 ASEAN member countries: Brunei Darussalam, Cambodia, Indonesia, Lao People’s Democratic Republic, Malaysia, Myanmar, the Philippines, Singapore, Thailand and Viet Nam.
Download or read book American Religion written by Mark A. A. Chaves and published by Princeton University Press. This book was released on 2017-08-29 with total page 172 pages. Available in PDF, EPUB and Kindle. Book excerpt: The most authoritative resource on religious trends in America—now fully updated Most Americans say they believe in God, and more than a third say they attend religious services every week. Yet studies show that people do not really go to church as often as they claim, and it is not always clear what they mean when they tell pollsters they believe in God or pray. American Religion presents the best and most up-to-date information about religious trends in the United States, in a succinct and accessible manner. This sourcebook provides essential information about key developments in American religion since 1972, and is the first major resource of its kind to appear in more than two decades. Mark Chaves looks at trends in diversity, belief, involvement, congregational life, leadership, liberal Protestant decline, and polarization. He draws on two important surveys: the General Social Survey, an ongoing survey of Americans' changing attitudes and behaviors, begun in 1972; and the National Congregations Study, a survey of American religious congregations across the religious spectrum. Chaves finds that American religious life has seen much continuity in recent decades, but also much change. He challenges the popular notion that religion is witnessing a resurgence in the United States—in fact, traditional belief and practice is either stable or declining. Chaves examines why the decline in liberal Protestant denominations has been accompanied by the spread of liberal Protestant attitudes about religious and social tolerance, how confidence in religious institutions has declined more than confidence in secular institutions, and a host of other crucial trends. Now with updated data and a new preface by the author, this revised edition provides essential information about key developments in American religion since 1972, plainly showing that religiosity is declining in America.
