Littérature scientifique sur le sujet « Algorithme du Consensus »
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Articles de revues sur le sujet "Algorithme du Consensus"
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Fermon, Cécile, François-Jérôme Authier, and Laure Gallay. "Les myosites à éosinophiles idiopathiques." Les Cahiers de Myologie, no. 25 (July 2022): 6–9. http://dx.doi.org/10.1051/myolog/202225003.
Texte intégralRésumé :
Les myosites à éosinophiles appartiennent au groupe des myopathies inflammatoires idiopathiques et sont définies par un infiltrat inflammatoire musculaire composé de polynucléaires éosinophiles. Il n’existe pas à ce jour de consensus concernant le diagnostic et le traitement de ces patients. Grâce à une revue exhaustive de la littérature, les principales caractéristiques cliniques et histologiques, ainsi que le traitement et l’évolution des patients, ont été résumés dans cette synthèse. Cette revue a permis de distinguer trois sous-groupes de myosites à éosinophiles : la forme focale, la forme diffuse et les périmyosites à éosinophiles. Un algorithme de traitement et de prise en charge est proposé, et les principaux diagnostics différentiels sont discutés.
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Waardenberg, Ashley J., and Matthew A. Field. "consensusDE: an R package for assessing consensus of multiple RNA-seq algorithms with RUV correction." PeerJ 7 (December 13, 2019): e8206. http://dx.doi.org/10.7717/peerj.8206.
Texte intégralRésumé :
Extensive evaluation of RNA-seq methods have demonstrated that no single algorithm consistently outperforms all others. Removal of unwanted variation (RUV) has also been proposed as a method for stabilizing differential expression (DE) results. Despite this, it remains a challenge to run multiple RNA-seq algorithms to identify significant differences common to multiple algorithms, whilst also integrating and assessing the impact of RUV into all algorithms. consensusDE was developed to automate the process of identifying significant DE by combining the results from multiple algorithms with minimal user input and with the option to automatically integrate RUV. consensusDE only requires a table describing the sample groups, a directory containing BAM files or preprocessed count tables and an optional transcript database for annotation. It supports merging of technical replicates, paired analyses and outputs a compendium of plots to guide the user in subsequent analyses. Herein, we assess the ability of RUV to improve DE stability when combined with multiple algorithms and between algorithms, through application to real and simulated data. We find that, although RUV increased fold change stability between algorithms, it demonstrated improved FDR in a setting of low replication for the intersect, the effect was algorithm specific and diminished with increased replication, reinforcing increased replication for recovery of true DE genes. We finish by offering some rules and considerations for the application of RUV in a consensus-based setting. consensusDE is freely available, implemented in R and available as a Bioconductor package, under the GPL-3 license, along with a comprehensive vignette describing functionality: http://bioconductor.org/packages/consensusDE/.
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Xiong, Huanliang, Muxi Chen, Canghai Wu, Yingding Zhao, and Wenlong Yi. "Research on Progress of Blockchain Consensus Algorithm: A Review on Recent Progress of Blockchain Consensus Algorithms." Future Internet 14, no. 2 (2022): 47. http://dx.doi.org/10.3390/fi14020047.
Texte intégralRésumé :
Blockchain technology can solve the problem of trust in the open network in a decentralized way. It has broad application prospects and has attracted extensive attention from academia and industry. The blockchain consensus algorithm ensures that the nodes in the chain reach consensus in the complex network environment, and the node status ultimately remains the same. The consensus algorithm is one of the core technologies of blockchain and plays a pivotal role in the research of blockchain technology. This article gives the basic concepts of the blockchain, summarizes the key technologies of the blockchain, especially focuses on the research of the blockchain consensus algorithm, expounds the general principles of the consensus process, and classifies the mainstream consensus algorithms. Then, focusing on the improvement of consensus algorithm performance, it reviews the research progress of consensus algorithms in detail, analyzes and compares the characteristics, suitable scenarios, and possible shortcomings of different consensus algorithms, and based on this, studies the future development trend of consensus algorithms for reference.
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Zhong, Weiyu, Ce Yang, Wei Liang, et al. "Byzantine Fault-Tolerant Consensus Algorithms: A Survey." Electronics 12, no. 18 (2023): 3801. http://dx.doi.org/10.3390/electronics12183801.
Texte intégralRésumé :
The emergence of numerous consensus algorithms for distributed systems has resulted from the swift advancement of blockchain and its related technologies. Consensus algorithms play a key role in decentralized distributed systems, because all nodes in the system need to reach a consensus on requests or commands through consensus algorithms. In a distributed system where nodes work together to reach consensus, there may be Byzantine nodes present. The emergence of Byzantine nodes will affect the consensus of nodes in the distributed system. Therefore, tolerating Byzantine nodes in a distributed system and then reaching a consensus is an essential function of a consensus algorithm. So far, many Byzantine fault-tolerant (BFT) consensus algorithms have emerged, and there are correspondingly many methods to improve the performance of these algorithms. In order to allow researchers to have a clearer understanding of the existing methods, this paper systematically investigated and studied the research progress of the current Byzantine fault-tolerant consensus algorithm. The scope of the research ranged from the classic Byzantine consensus algorithm to some of the latest Byzantine consensus algorithms. The articles were classified according to the methods used to improve the Byzantine consensus algorithm. Through classification and centralized analysis and discussion, we achieved a clearer understanding of the development of Byzantine consensus algorithms and, at the same time, clarified the advantages and disadvantages of this type of method and the latest research progress using this method. At the end of this article, an in-depth discussion and analysis is also presented. By analyzing the impact of the use of these methods on the performance of the BFT consensus algorithm, it is proposed that future research can be improved.
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Ge, Lina, Jie Wang, and Guifen Zhang. "Survey of Consensus Algorithms for Proof of Stake in Blockchain." Security and Communication Networks 2022 (May 29, 2022): 1–13. http://dx.doi.org/10.1155/2022/2812526.
Texte intégralRésumé :
As the core of blockchain technology, the consensus algorithm directly affects the security, stability, and decentralisation of the blockchain and numerous other important characteristics. Choosing an appropriate consensus algorithm for different scenarios is currently a challenge in the implementation of blockchain applications. This paper classifies the improvement schemes of proof of stake (PoS) into three categories: PoS-based consensus algorithms, PoS- and PoW-based consensus algorithms, and PoS- and BFT-based consensus algorithms. First, the study introduces the PoS and PoS consensus algorithm variants and then summarises the core ideas, effects, advantages, and disadvantages of these algorithms. Subsequently, the performances of the improved algorithms are compared. Finally, the main improved methods are summarised, and the most common network security attacks are discussed. The study lays a foundation for the main improvement directions of PoS in the future, hoping to provide a reference for researchers to help them select and design consensus algorithms in different application scenarios while also helping the evolution of consensus algorithms and the implementation of blockchain applications.
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Palomares, A., M. Rebollo, and C. Carrascosa. "Supportive consensus." PLOS ONE 15, no. 12 (2020): e0243215. http://dx.doi.org/10.1371/journal.pone.0243215.
Texte intégralRésumé :
The paper is concerned with the consensus problem in a multi-agent system such that each agent has boundary constraints. Classical Olfati-Saber’s consensus algorithm converges to the same value of the consensus variable, and all the agents reach the same value. These algorithms find an equality solution. However, what happens when this equality solution is out of the range of some of the agents? In this case, this solution is not adequate for the proposed problem. In this paper, we propose a new kind of algorithms called supportive consensus where some agents of the network can compensate for the lack of capacity of other agents to reach the average value, and so obtain an acceptable solution for the proposed problem. Supportive consensus finds an equity solution. In the rest of the paper, we define the supportive consensus, analyze and demonstrate the network’s capacity to compensate out of boundaries agents, propose different supportive consensus algorithms, and finally, provide some simulations to show the performance of the proposed algorithms.
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Acharya, Deep Shekhar, and Sudhansu Kumar Mishra. "Optimal Consensus Recovery of Multi-agent System Subjected to Agent Failure." International Journal on Artificial Intelligence Tools 29, no. 06 (2020): 2050017. http://dx.doi.org/10.1142/s0218213020500177.
Texte intégralRésumé :
Multi-Agent Systems are susceptible to external disturbances, sensor failures or collapse of communication channel/media. Such failures disconnect the agent network and thereby hamper the consensus of the system. Quick recovery of consensus is vital to continue the normal operation of an agent-based system. However, only limited works in the past have investigated the problem of recovering the consensus of an agent-based system in the event of a failure. This work proposes a novel algorithmic approach to recover the lost consensus, when an agent-based system is subject to the failure of an agent. The main focus of the algorithm is to reconnect the multi-agent network in a way so as to increase the connectivity of the network, post recovery. The proposed algorithm may be applied to both linear and non-linear continuous-time consensus protocols. To verify the efficiency of the proposed algorithm, it has been applied and tested on two multi-agent networks. The results, thus obtained, have been compared with other state-of-the-art recovery algorithms. Finally, it has been established that the proposed algorithm achieves better connectivity and therefore, faster consensus when compared to the other state-of-the-art.
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Bakhvalova, Ekaterina Alexandrovna, and Vladimir Anatolievich Sudakov. "Research of consensus algorithms for blockchain platforms." Keldysh Institute Preprints, no. 26 (2021): 1–16. http://dx.doi.org/10.20948/prepr-2021-26.
Texte intégralRésumé :
In this paper, several consensus algorithms are investigated, a comparative analysis of these algorithms is made, the results of which are important in the context of the active growth of the cryptocurrency market. In addition, in the context of pandemics, the creation of blockchain technologies for the distributed storage of reliable medical data is relevant. The key properties of consensus algorithms are highlighted, and a detailed analysis of the algorithm of the promising Istanbul BFT algorithm is carried out. Using multi-criterion analysis of alternatives, it is shown how you can select the appropriate consensus algorithm for the needs of specific tasks.
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Hanna, Fouad, Lionel Droz-Bartholet, and Jean-Christophe Lapayre. "Toward a Faster Fault Tolerant Consensus to Maintain Data Consistency in Collaborative Environments." International Journal of Cooperative Information Systems 26, no. 03 (2017): 1750002. http://dx.doi.org/10.1142/s0218843017500022.
Texte intégralRésumé :
The consensus problem has become a key issue in the field of collaborative telemedicine systems because of the need to guarantee the consistency of shared data. In this paper, we focus on the performance of consensus algorithms. First, we studied, in the literature, the most well-known algorithms in the domain. Experiments on these algorithms allowed us to propose a new algorithm that enhances the performance of consensus in different situations. During 2014, we presented our very first initial thoughts to enhance the performance of the consensus algorithms, but the proposed solution gave very moderate results. The goal of this paper is to present a new enhanced consensus algorithm, named Fouad, Lionel and J.-Christophe (FLC). This new algorithm was built on the architecture of the Mostefaoui-Raynal (MR) consensus algorithm and integrates new features and some known techniques in order to enhance the performance of consensus in situations where process crashes are present in the system. The results from our experiments running on the simulation platform Neko show that the FLC algorithm gives the best performance when using a multicast network model on different scenarios: in the first scenario, where there are no process crashes nor wrong suspicion, and even in the second one, where multiple simultaneous process crashes take place in the system.
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Khan, Dr Kashif Mehboob, Muhammad Abdullah Hayat, and Rana Muhammad Ibrahim. "Investigating the Impact of Consensus Algorithm on Scalability in Blockchain Systems." Sir Syed University Research Journal of Engineering & Technology 12, no. 2 (2022): 01–06. http://dx.doi.org/10.33317/ssurj.427.
Texte intégralRésumé :
In the current era, blockchain has emerged as one the best and promising technology. All the cryptocurrencies have also gained a lot of popularity around the globe which are based on blockchain technology. Blockchain provides a distributed architecture, in which transactions are verified by different validators using different algorithms and then are stored in distributed ledger. The verification of transactions is done using consensus algorithms which verifies that incoming transaction is correct and reliable by different distributed nodes working in a peer-to-peer network. Consensus algorithms ensure the integrity and security of blockchain. There are various types of consensus algorithms used in blockchain technology which are used depending on the architecture and usage, some of the consensus algorithms are Proof of Work (PoW), Proof of Stake (PoS) etc. The Proof of Work algorithm is most widely used across the globe by the community. It is used by many popular cryptocurrency networks like Litecoin and Bitcoin. It requires larger computation power while verifying transactions. The selection of a consensus algorithm is one the most important parts of blockchain, as the consensus mechanism is considered to be the core of a network. It is easier to predict and guarantee the security, reliability, fault tolerance, and recoverability of the system if the correct consensus protocol is selected. A single algorithm can never fulfill all the requirements, there is always a tradeoff in the selection of consensus algorithms. Therefore, it is very important to select the best suited consensus algorithm for the network as the consensus mechanism validates transactions without any third-party platform and prevents malicious activities in the network. This paper investigates the comparison among types of consensus algorithms and their effectiveness and viability.
Thèses sur le sujet "Algorithme du Consensus"
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Lavault, Christian. "Algorithmique et complexité distribuées : applications à quelques problèmes fondamentaux de complexité, protocoles distribués à consensus, information globale, problèmes distribués d'élection et de routage." Paris 11, 1987. http://www.theses.fr/1987PA112392.
Texte intégralRésumé :
Présentation d'un cadre général pour l'étude et l'analyse des algorithmes répartis et résolution de plusieurs problèmes de fond relatifs à la complexité dans les systèmes répartis. Développement de divers outils d'analyse en moyenne de la complexite en messages de protocoles généraux à consensus. Résolution par l'analyse mathématique d'un problème ouvert sur les performances comparées des anneaux uni et bidirectionnels pour la complexité en moyenne en messages d'algorithmes d'élection déterministes. Un algorithme probabiliste de construction d'un arbre couvrant sur un système distribué anonyme et quelconque est développé. Deux théorèmes sont proposés qui bornent la faille des messages en fonction de la complexite en messages des algorithmes distribués asynchrones du point de vue de la quantité d'information.
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Hanna, Fouad. "Etude et développement du nouvel algorithme distribué de consensus FLC permfettant de maintenir la cohérence des données partagées et tolérant aux fautess." Thesis, Besançon, 2016. http://www.theses.fr/2016BESA2051.
Texte intégralRésumé :
De nos jours, le travail collaboratif a pris une place très importante dans plusieurs domaines, et notamment dans le domaine du télédiagnostic médical. Et la cohérence des données partagées est un enjeu primordial dans ce type d'application. De plus, pour garantir la cohérence des données, l'utilisation d'un algorithme de consensus est un élément indispensable dans les plateformes collaboratives. Nous présentons ici un nouvel algorithme de consensus, nommé FLC, permettant de garantir la cohérence des données partagées dans les systèmes distribués collaboratifs complètement asynchrones. Notre algorithme est tolérant aux pannes et a pour objectif d'améliorer la performance de consensus et notamment lorsque les processus participants tombent en panne. Ce nouvel algorithme utilise l'oracle leader Omega pour contourner le résultat d'impossibilité du théorème FLP. L'algorithme est décentralisé et adopte le modèle de pannes crash-stop. L'algorithme FLC s'appuie sur deux idées principales. La première propose de réaliser, au début de chaque cycle d'exécution, une phase simple d'élection de processus leader garantissant l'existence d'un seul leader par cycle. La deuxième bénéficie de la stabilité du système et plus particulièrement du fait que le processus leader ne tombe pas en panne d'un consensus à l'autre. Les performances de notre algorithme ont été analysées et comparées à celles des algorithmes les plus connus dans le domaine. Les résultats obtenus par simulation en utilisant la plateforme Neko ont montré que notre algorithme donne les meilleures performances lorsque le réseau utilisé est un réseau multicast et qu'aucun processus ne tombent en panne ainsi que pour les situations dans lesquelles l'algorithme de consensus subit une ou plusieurs pannes de processus coordinateurs/leaders<br>Nowadays, collaborative work took a very important place in many fields and particularly in the medicaltelediagnosis field. The consistency of shared data is a key issue in this type of applications. Moreover, itis essential to use a consensus algorithm to ensure data consistency in collaborative platforms. We presenthere our new consensus algorithm FLC that helps to ensure data consistency in asynchronous collaborativedistributed systems. Our algorithm is fault tolerant and aims to improve the performance of consensus ingeneral and particularly in the case of process crashes. The new algorithm uses the leader oracle tocircumvent the impossibility result of the FLP theorem. It is decentralized and considers the crash-stop failuremodel. The FLC algorithm is based on two main ideas. The first is to perform, at the beginning of eachround, a simple election phase guaranteeing the existence of only one leader per round. The second is totake advantage of system stability and more particularly of the fact that the leader does not crash betweentwo consecutive consensus runs. The performance of our algorithm was analyzed and compared to the mostknown algorithms in the domain. The results obtained by simulation, using the Neko platform, demonstratedthat our algorithm gave the best performance when using a multicast network in the best case scenario and insituations where the algorithm undergoes one or more crashes of coordinators/leaders processes
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Ouattara, Mory. "Développement et mise en place d'une méthode de classification multi-blocs : application aux données de l'OQAI." Phd thesis, Conservatoire national des arts et metiers - CNAM, 2014. http://tel.archives-ouvertes.fr/tel-01062782.
Texte intégralRésumé :
La multiplication des sources d'information et le développement de nouvelles technologies ont engendré des bases données complexes, souvent caractérisées par un nombre de variables relativement élevé par rapport aux individus. En particulier, dans les études environnementales sur la pollution de l'air intérieur, la collecte des informations sur les individus se fait au regard de plusieurs thématiques, engendrant ainsi des données de grande dimension avec une structure multi-blocs définie par les thématiques. L'objectif de ce travail a été de développer des méthodes de classification adaptées à ces jeux de données de grande dimension et structurées en blocs de variables. La première partie de ce travail présente un état de l'art des méthodes de classification en général et dans le cas de la grande dimension. Dans la deuxième partie, trois nouvelles approches de classification d'individus décrits par des variables structurées en blocs ont été proposées. La méthode 2S-SOM (Soft Subspace-Self Organizing Map), une approche de type subspace clustering basée sur une modification de la fonction de coût de l'algorithme des cartes topologiques à travers un double système de poids adaptatifs défini sur les blocs et sur les variables. Nous proposons ensuite des approches CSOM (Consensus SOM) et Rv-CSOM de recherche de consensus de cartes auto-organisées basées sur un système de poids déterminés à partir des partitions initiales. Enfin, la troisième partie présente une application de ces méthodes sur le jeu de données réelles de la campagne nationale logement (CNL) menée par l'OQAI afin de définir une typologie des logements au regard des thématiques : qualité de l'air intérieur, structure du bâtiment, composition des ménages et habitudes des occupants.
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Kyrgyzov, Ivan. "Recherche dans les bases de donnees satellitaires des paysages et application au milieu urbain: clustering, consensus et categorisation." Phd thesis, Télécom ParisTech, 2008. http://pastel.archives-ouvertes.fr/pastel-00004084.
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Les images satellitaires ont trouvées une large application pour l'analyse des ressources naturelles et des activités humaines. Les images à haute résolution, e.g., SPOT5, sont très nombreuses. Ceci donne un grand intérêt afin de développer de nouveaux aspects théoriques et des outils pour la fouille d'images. L'objectif de la thèse est la fouille non-supervisée d'images et inclut trois parties principales. Dans la première partie nous démontrons le contenu d'images à haute résolution. Nous décrivons les zones d'images par les caractéristiques texturelles et géométriques. Les algorithmes de clustering sont présentés dans la deuxième partie. Une étude de critères de validité et de mesures d'information est donnée pour estimer la qualité de clustering. Un nouveau critère basé sur la Longueur de Description Minimale (LDM) est proposé pour estimer le nombre optimal de clusters. Par ailleurs, nous proposons un nouveau algorithme hiérarchique basé sur le critère LDM à noyau. Une nouvelle méthode de ''combinaison de clustering'' est présentée dans la thèse pour profiter de différents algorithmes de clustering. Nous développons un algorithme hiérarchique pour optimiser la fonction objective basée sur une matrice de co-association. Une deuxième méthode est proposée qui converge à une solution globale. Nous prouvons que le minimum global peut être trouvé en utilisant l'algorithme de type ''mean shift''. Les avantages de cette méthode sont une convergence rapide et une complexité linéaire. Dans la troisième partie de la thèse un protocole complet de la fouille d'images est proposé. Différents clusterings sont représentés via les relations sémantiques entre les concepts.
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Belkadi, Adel. "Conception de commande tolérante aux défauts pour les systèmes multi-agents : application au vol en formation d'une flotte de véhicules autonomes aériens." Thesis, Université de Lorraine, 2017. http://www.theses.fr/2017LORR0183/document.
Texte intégralRésumé :
Ces dernières années, l’émergence des nouvelles technologies tels que la miniaturisation des composants, les dispositifs de communication sans fils, l’augmentation de la taille de stockage et les capacités de calcul, a permis la conception de systèmes multi-agents coopératifs de plus en plus complexes. L’un des plus grands axes de recherche dans cette thématique concerne la commande en formation de flottes de véhicules autonomes. Un grand nombre d’applications et de missions, civiles et militaires, telles que l’exploration, la surveillance, et la maintenance, ont alors été développées et réalisées dans des milieux variés (terre, air, eau). Durant l’exécution de ces tâches, les véhicules doivent interagir avec leur environnement et entre eux pour se coordonner. Les outils de communication disponibles disposent souvent d’une portée limitée. La préservation de la connexion au sein du groupe devient alors un des objectifs à satisfaire pour que la tâche puisse être accomplie avec succès. Une des possibilités pour garantir cette contrainte est le déplacement en formation permettant de préserver les distances et la structure géométrique du groupe. Il est toutefois nécessaire de disposer d’outils et de méthodes d’analyse et de commande de ces types de systèmes afin d’exploiter au maximum leurs potentiels. Cette thèse s’inscrit dans cette direction de recherche en présentant une synthèse et une analyse des systèmes dynamiques multi-agents et plus particulièrement la commande en formation de véhicules autonomes. Les lois de commande développées dans la littérature pour la commande en formation permettent d’accomplir un grand nombre de missions avec un niveau de performance élevé. Toutefois, si un défaut/défaillant apparaît dans la formation, ces lois de commandes peuvent s’avérer très limitées, engendrant un comportement instable du système. Le développement de commandes tolérantes aux défauts devient alors primordial pour maintenir les performances de commande en présence de défauts. Cette problématique sera traitée dans ce mémoire de thèse et concernera le développement et la conception de commandes en formation tolérantes au défaut dévolu à une flotte de véhicules autonomes suivant différente configuration/structuration<br>In recent years, the emergence of new technologies such as miniaturization of components, wireless communication devices, increased storage size and computing capabilities have allowed the design of increasingly complex cooperative multi-agent systems. One of the main research axes in this topic concerns the formation control of fleets of autonomous vehicles. Many applications and missions, civilian and military, such as exploration, surveillance, and maintenance, were developed and carried out in various environments. During the execution of these tasks, the vehicles must interact with their environment and among themselves to coordinate. The available communication tools are often limited in scope. The preservation of the connection within the group then becomes one of the objectives to be satisfied in order to carry out the task successfully. One of the possibilities to guarantee this constraint is the training displacement, which makes it possible to preserve the distances and the geometrical structure of the group. However, it is necessary to have tools and methods for analyzing and controlling these types of systems in order to make the most of their potential. This thesis is part of this research direction by presenting a synthesis and analysis of multi-agent dynamical systems and more particularly the formation control of autonomous vehicles. The control laws developed in the literature for formation control allow to carry out a large number of missions with a high level of performance. However, if a fault/failure occurs in the training, these control laws can be very limited, resulting in unstable system behavior. The development of fault tolerant controls becomes paramount to maintaining control performance in the presence of faults. This problem will be dealt with in more detail in this thesis and will concern the development and design of Fault tolerant controls devolved to a fleet of autonomous vehicles according to different configuration/structuring
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Ouattara, Mory. "Développement et mise en place d'une méthode de classification multi-blocs : application aux données de l'OQAI." Electronic Thesis or Diss., Paris, CNAM, 2014. http://www.theses.fr/2014CNAM0914.
Texte intégralRésumé :
La multiplication des sources d'information et le développement de nouvelles technologies ont engendré des bases données complexes, souvent caractérisées par un nombre de variables relativement élevé par rapport aux individus. En particulier, dans les études environnementales sur la pollution de l'air intérieur, la collecte des informations sur les individus se fait au regard de plusieurs thématiques, engendrant ainsi des données de grande dimension avec une structure multi-blocs définie par les thématiques. L'objectif de ce travail a été de développer des méthodes de classification adaptées à ces jeux de données de grande dimension et structurées en blocs de variables. La première partie de ce travail présente un état de l'art des méthodes de classification en général et dans le cas de la grande dimension. Dans la deuxième partie, trois nouvelles approches de classification d'individus décrits par des variables structurées en blocs ont été proposées. La méthode 2S-SOM (Soft Subspace-Self Organizing Map), une approche de type subspace clustering basée sur une modification de la fonction de coût de l'algorithme des cartes topologiques à travers un double système de poids adaptatifs défini sur les blocs et sur les variables. Nous proposons ensuite des approches CSOM (Consensus SOM) et Rv-CSOM de recherche de consensus de cartes auto-organisées basées sur un système de poids déterminés à partir des partitions initiales. Enfin, la troisième partie présente une application de ces méthodes sur le jeu de données réelles de la campagne nationale logement (CNL) menée par l'OQAI afin de définir une typologie des logements au regard des thématiques : qualité de l'air intérieur, structure du bâtiment, composition des ménages et habitudes des occupants<br>The multiplication of information source and the development of news technologies generates complex databases, often characterized by relatively high number of variables compared to individuals. In particular, in the environmental studies on the indoor air quality, the information's collection is done according to several thematic, yielding column partitioned or multi-block data set. However, in case of high dimensional data, classical clustering algorithms are not efficient to find clusters which may exist in subspaces of the original space. The goal of this work is to develop clustering algorithms adapted to high dimensional data sets with multi-block structure. The first part of the work shows the state of art on clustering methods. In the second part, three new methods of clustering: the subspace clustering method 2S-SOM (Soft Subspace-Self Organizing Map)is based on a modified cost function of the Self Organizing Maps method across a double system of weights on the blocks and the variables. Then we propose two approaches to find the consensus of self-organized maps CSOM (Consensus SOM) and Rv-CSOM based on weights determined from initial partitions. The last part presents an application of these methods on the OQAI data to determine a typology of dwellings relatively to the following topics: indoor air quality, dwellings structure, household characteristics and habits of the inhabitants
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van, de Hoef Sebastian. "Extended Consensus Algorithms." Thesis, KTH, Reglerteknik, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-125809.
Texte intégralRésumé :
An extension of the linear consensus protocol for agents moving in the plane is considered. For single integrator agents the use of a vector perpendicular to the standard consensus feedback leads to a large family of trajectories. If the new perpendicular term is applied only sustained oscillations are facilitated. For special congurations the form of the system trajectories is given in form of eigenvalues and {vectors of the system matrix. A proof is given that this additional term does not eect stability. On the other hand it is motivated that robustness against discrete implementation and switching topologies can be decreased. The control strategy is also applied to agents with double integrator dynamics. Stability can be archived with suciently high velocity feedback and the eect of this feedback on the system performance is further discussed. Using the results for single integrators a self{triggered consensus control strategy is proposed based on the assumption of bounded input magnitude of the other agents. Additional communication of the actual input leads to asymptotic convergence. By applying similar reasoning it is shown how local controllers at the agents can avoid circular regions in state{space while moving towards consensus.
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DANCKAERT, PERRUCHOT ANNE. "Traitement informatique des autoradiographies de gels de sequences : conception et mise en oeuvre d'un systeme automatique d'interpretation d'autoradiographies, elaboration d'un algorithme de construction de la sequence consensus a partir de fragments." Paris 7, 1988. http://www.theses.fr/1988PA077045.
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Córdova, Morales David Alexis. "Blockchain Application for Mesh and Mobile Ad Hoc Networks." Electronic Thesis or Diss., Sorbonne université, 2022. https://theses.hal.science/tel-03922843.
Texte intégralRésumé :
La blockchain est une technologie qui permet de maintenir un unique registre d’information de façon décentralisé et distribué tout en garantissant la sécurité des données. Cette technologie, qui est à l’origine de la cryptomonnaie la plus populaire, le Bitcoin, est en train de changer la façon dont nous concevons les registres d’informations dans les systèmes distribués. En effet, l’ensemble des fonctions cryptographiques ainsi que la nature distribuée de la technologie font de la blockchain, un des outils les plus sécurisés de nos jours pour maintenir un registre de l’information. Les premières applications à avoir adopté cette technologie se trouvent dans le domaine des finances, où il est désormais possible de réaliser des transactions directement entre les utilisateurs sans passer par une autorité centrale. Néanmoins, d’autres domaines ont aussi suscité leurs intérêts pour cette technologie, telle que la médecine, pour le partage sécurisé des données médicales ; l’art et la musique, pour le suivi des droits d’auteur et des redevances ; la gouvernance, pour le vote sécurisé, l’IoT, etc. Or, pour bénéficier d’une telle technologie il est nécessaire de compter avec une haute fiabilité et connectivité, telle que fourni par l’Internet. Dans les réseaux mesh et ad hoc mobile, il est souvent nécessaire de déployer sa propre infrastructure et ses propres services là où l’infrastructure des opérateurs ne sont pas disponibles dus à la géographie du site ou à une situation d’exception comme est le cas de désastres naturels, zone de guerre ou le monitorat des zones protégées pour réaliser des missions déterminées. La dynamiste de ces réseaux rend difficile l’utilisation d’une blockchain pour maintenir un registre d’information. En effet, la mobilité des nœuds peut causer des partitions dans le réseau qui peuvent ou pas être désirées ; des nœuds peuvent apparaitre et disparaitre, les partitions peuvent se séparer ou se réunir en fonction de la mobilité des nœuds. Cela pose un problème pour une blockchain traditionnelle, car les partitions dans le réseau entraînent des forks (des chaînes concurrentes) qui sont souvent résolu en choisissant la chaîne la plus longue et en ignorant les autres chaînes concurrentes. Pour les cas d’utilisation des réseaux mesh et ad hoc mobile que nous cherchons à résoudre, les chaînes concurrentes construites par effet des partitions réseaux peuvent être considérés comme des chaînes légitimes portant des informations relatives à une partition réseau déterminé. Il est donc important d’inclure ces chaînes dans le registre d’information. Dans ce manuscrit de thèse, nous proposons le Blockgraph, une technologie semblable à la blockchain capable de faire face aux partitions réseaux pour les réseaux mesh et ad hoc mobiles. Le Blockgraph, prend la forme d’un graph orienté acyclique en fonction de la mobilité de nœuds et hérite de toutes les propriétés de sécurité de la blockchain. De plus, nous proposons C4M, un algorithme de consensus inspiré en RAFT qui a été adapté au Blockgraph et qui également est tolérant aux partitions du réseau. Pour valider nos solutions, nous avons d’abord implémenté le Blockgraph et C4M dans le simulateur à événements discrets, NS-3. Nous avons réalisé une première étude des performances de chaque système, puis nous avons implémenté le Blockgraph dans des vrais routeurs mesh à mode de proof-of-concept pour valider l’efficacité de notre solution. Finalement nous avons réalisé une étude de performances et présenté nos conclusions<br>Blockchain is a technology that maintains a single record of information in a decentralized and distributed manner while ensuring data security. This technology, which is behind the most popular cryptocurrency, Bitcoin, is changing the way we think about information records in distributed systems. Indeed, the cryptographic feature set and the distributed nature of the technology make blockchain one of the most secure tools available today for maintaining a record of information. The first applications to have adopted this technology are in the field of finance, where it is now possible to carry out transactions directly between users without going through a central authority. However, other fields have also shown interest in this technology, such as medicine, for the secure sharing of medical records; art and music, for the tracking of copyrights and royalties; governance, for secure voting, IoT, etc. However, to benefit from such technology it is necessary to count with high reliability and connectivity, as provided by the Internet. In mesh and mobile ad hoc networks, it is often necessary to deploy its own infrastructure and services where the infrastructure of operators are not available due to the geography of the site or to an exceptional situation as is the case of natural disasters, war zones or monitoring of protected areas to achieve specific missions. The dynamism of these networks makes it difficult to use a blockchain to maintain a record of information. Indeed, the mobility of nodes can cause partitions in the network that may or may not be desired; nodes can appear and disappear, partitions can split or reunite depending on the mobility of the nodes. This poses a problem for a traditional blockchain, as partitions in the network lead to forks (competing chains) that are often resolved by choosing the longest chain and ignoring other competing chains. For the use cases of mesh and mobile ad hoc networks that we seek to solve, the concurrent chains constructed by the effect of network partitions can be considered as legitimate chains carrying information related to a given network partition. It is therefore important to include these chains in the information register. In this thesis manuscript, we propose the Blockgraph, a blockchain-like technology capable of dealing with network partitions for mobile mesh and ad hoc networks. The Blockgraph, takes the form of a direct acyclic graph based on node mobility and inherits all the security properties of the blockchain. In addition, we propose C4M, a RAFT-based consensus algorithm that has been adapted to work with the Blockgraph and is also tolerant to network partitions. To validate our solutions, we first implemented the Blockgraph and C4M in the discrete event simulator, NS-3. We performed a first performance study of each system, then we implemented the Blockgraph in real proof-of-concept mesh routers to validate the effectiveness of our solution. Finally, we performed a performance study and presented our conclusions
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Bechihi, Adel. "Joint design of control algorithms and communication protocols for Connected and Automated Vehicles." Electronic Thesis or Diss., université Paris-Saclay, 2023. http://www.theses.fr/2023UPAST203.
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Dans cette thèse, nous nous adressons le problème du contrôle de systèmes multi-agents connectés via des modèles réalistes de systèmes de communication. Nous traitons principalement les systèmes de véhicules connectés et automatisés (CAVs) communiquant via des systèmes de communication 5G qui permettent deux types de communication : la communication directe entre les nœuds, connue sous le nom de communication véhicule-à-véhicule (V2V), et la communication à travers l'infrastructure réseau, qui est la manière traditionnelle de communiquer dans les réseaux cellulaires.La thèse traite de trois problèmes : premièrement, nous analysons les propriétés de stabilité et de convergence de l'algorithme du consensus pour agents d'intégrateurs du premier ordre en utilisant un schéma d'accès multiple par répartition temporelle (TDMA) pour partager les ressources du réseau d'un canal de communication partagé. La stabilité exponentielle du système considéré est démontrée, et une borne explicite dépendant des paramètres du système de communication est fournie pour estimer la vitesse de convergence. Ensuite, nous abordons le problème du contrôle de formation d'un groupe de véhicules connectés dans un contexte de communication 5G. Nous proposons un algorithme d'allocation de ressources pour sélectionner les utilisateurs émetteurs afin d'atteindre la formation souhaitée tout en respectant les contraintes imposées par le couche de communication. Enfin, nous étudions les propriétés de stabilité des filtres de Kalman pour les systèmes hybrides, précisément, des systèmes avec une dynamique en temps continu observée à travers des mesures en temps discret. La stabilité d'entrée-à-état (ISS) est démontrée pour de tels systèmes en utilisant une fonction de Lyapunov appropriée. Ce résultat peut être considéré comme une première étape dans l'analyse de la robustesse du système global, car il permet de prendre en compte les effets des erreurs de communication sur la stabilité du système contrôlé<br>In this thesis, we address the problem of control of multi-agent systems connected over realistic models of communication systems. We mainly focus on systems of connected and automated vehicles (CAVs) that communicate through a 5G communication system, which allows two types of communication: direct communication between nodes, known as Vehicle-to-Vehicle (V2V) communications, and communication through the network infrastructure, which is the traditional way of communication in cellular networks.The thesis discusses three problems: first, we analyze the stability and convergence properties of the consensus algorithm of first-order integrator agents using a time-division multiple access (TDMA) scheme to share the network resources of a broadcast shared communication channel. Exponential stability of the considered system is proved, and an explicit bound depending on the communication system parameters is provided to estimate the convergence rate. Second, we treat the problem of formation control of a float of connected vehicles in a 5G communication context. We propose a resource allocation algorithm to select the transmitting users to achieve the desired formation while satisfying the constraints imposed by the communication system. Finally, we study the stability properties of Kalman filters for hybrid systems, i.e., systems with continuous-time dynamics observed through discrete-time measurements. Input-to-state stability (ISS) is proved for such systems relying on an appropriate Lyapunov function. This result can be considered as a first step in the robustness analysis of the overall system since it allows to treat the effects of communication errors on the controlled system stability
Livres sur le sujet "Algorithme du Consensus"
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W, Beard Randal, ed. Distributed consensus in multi-vehicle cooperative control: Theory and applications. Springer, 2008.
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Semsar-Kazerooni, Elham. Team Cooperation in a Network of Multi-Vehicle Unmanned Systems: Synthesis of Consensus Algorithms. Springer New York, 2013.
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Suter, David, Gerard Medioni, Sven Dickinson, and Tat-Jun Chin. Maximum Consensus Problem: Recent Algorithmic Advances. Morgan & Claypool Publishers, 2017.
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Suter, David, Gerard Medioni, Sven Dickinson, and Tat-Jun Chin. Maximum Consensus Problem: Recent Algorithmic Advances. Morgan & Claypool Publishers, 2017.
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Suter, David, and Tat-Jun Chin. Maximum Consensus Problem: Recent Algorithmic Advances. Springer International Publishing AG, 2017.
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Vukolic, Marko. Quorum Systems: With Applications to Storage and Consensus. Morgan & Claypool Publishers, 2012.
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Vukolic, Marko. Quorum Systems: With Applications to Storage and Consensus. Morgan & Claypool Publishers, 2012.
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Vukolic, Marko. Quorum Systems: With Applications to Storage and Consensus. Springer International Publishing AG, 2012.
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Beard, Randal, and Wei Ren. Distributed Consensus in Multi-Vehicle Cooperative Control: Theory and Applications. Springer London, Limited, 2010.
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Team Cooperation In A Network Of Multivehicle Unmanned Systems Synthesis Of Consensus Algorithms. Springer, 2012.
Trouver le texte intégralChapitres de livres sur le sujet "Algorithme du Consensus"
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Tekriwal, Mohit, Avi Tachna-Fram, Jean-Baptiste Jeannin, Manos Kapritsos, and Dimitra Panagou. "Formally verified asymptotic consensus in robust networks." In Tools and Algorithms for the Construction and Analysis of Systems. Springer Nature Switzerland, 2024. http://dx.doi.org/10.1007/978-3-031-57246-3_14.
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AbstractDistributed architectures are used to improve performance and reliability of various systems. Examples include drone swarms and load-balancing servers. An important capability of a distributed architecture is the ability to reach consensus among all its nodes. Several consensus algorithms have been proposed, and many of these algorithms come with intricate proofs of correctness, that are not mechanically checked. In the controls community, algorithms often achieve consensus asymptotically, e.g., for problems such as the design of human control systems, or the analysis of natural systems like bird flocking. This is in contrast to exact consensus algorithm such as Paxos, which have received much more recent attention in the formal methods community.This paper presents the first formal proof of an asymptotic consensus algorithm, and addresses various challenges in its formalization. Using the Coq proof assistant, we verify the correctness of a widely used consensus algorithm in the distributed controls community, the Weighted-Mean Subsequence Reduced (W-MSR) algorithm. We formalize the necessary and sufficient conditions required to achieve resilient asymptotic consensus under the assumed attacker model. During the formalization, we clarify several imprecisions in the paper proof, including an imprecision on quantifiers in the main theorem.
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Bhardwaj, Rashmi, and Debabrata Datta. "Consensus Algorithm." In Studies in Big Data. Springer International Publishing, 2020. http://dx.doi.org/10.1007/978-3-030-38677-1_5.
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De La Cruz, Livio, Stephen Kobourov, Sergey Pupyrev, Paul S. Shen, and Sankar Veeramoni. "Computing Consensus Curves." In Experimental Algorithms. Springer International Publishing, 2014. http://dx.doi.org/10.1007/978-3-319-07959-2_19.
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Chin, Tat-Jun, and David Suter. "Exact Algorithms." In The Maximum Consensus Problem. Springer International Publishing, 2014. http://dx.doi.org/10.1007/978-3-031-01818-3_3.
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Chin, Tat-Jun, and David Suter. "Approximate Algorithms." In The Maximum Consensus Problem. Springer International Publishing, 2014. http://dx.doi.org/10.1007/978-3-031-01818-3_2.
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Herlihy, Maurice. "Asynchronous Consensus Impossibility." In Encyclopedia of Algorithms. Springer New York, 2016. http://dx.doi.org/10.1007/978-1-4939-2864-4_36.
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Herlihy, Maurice. "Asynchronous Consensus Impossibility." In Encyclopedia of Algorithms. Springer US, 2008. http://dx.doi.org/10.1007/978-0-387-30162-4_36.
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Kao, Ming-Yang. "Wait-Free Consensus." In Encyclopedia of Algorithms. Springer US, 2008. http://dx.doi.org/10.1007/978-0-387-30162-4_468.
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Rehmani, Mubashir Husain. "Blockchain Consensus Algorithms." In Blockchain Systems and Communication Networks: From Concepts to Implementation. Springer International Publishing, 2021. http://dx.doi.org/10.1007/978-3-030-71788-9_4.
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Raynal, Michel. "Consensus Numbers and the Consensus Hierarchy." In Concurrent Programming: Algorithms, Principles, and Foundations. Springer Berlin Heidelberg, 2012. http://dx.doi.org/10.1007/978-3-642-32027-9_16.
Texte intégralActes de conférences sur le sujet "Algorithme du Consensus"
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Bogdanov, A., V. Korkhov, N. Shchegoleva, et al. "COMPARATIVE ANALYSIS AND APPLICABILITY DETERMINATION FOR SEVERAL DLT SOLUTIONS." In 9th International Conference "Distributed Computing and Grid Technologies in Science and Education". Crossref, 2021. http://dx.doi.org/10.54546/mlit.2021.13.56.001.
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Potential benefits of implementation of distributed ledger technology are widely discussedamong different business actors and governmental structures. Within the last decade, with growingpopularity of blockchain-based payment systems and cryptocurrencies, these discussions considerablysharpened. Therefore, an extensive body of research has emerged on this soil. The goal of this study isto attempt to make a comparative analysis of several existing blockchain-based distributed ledgerplatforms. Besides that, authors overview the most commonly used consensus algorithms and designapproaches, as for any blockchain product, consensus algorithm is a crucial part which determines theperformance of the overall system. Choosing the right algorithm would ensure high reliability andthroughput, while the wrong choice could cause fatal malfunctions for the application. A suitablealgorithm usually should be chosen according to the task in consideration, e.g. Nakamoto-styleprotocols could be considered better for public networks, while multiround voting protocols are moresuitable for private and secure systems. The highest attention is paid to consensus algorithms based onthe solution of the Byzantine Fault Tolerance problem (BFT).
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Lunardi, Roben Castagna, and Avelino Francisco Zorzo. "Multi-level consensus algorithm for appendable-block blockchains in IoT Environments." In Simpósio Brasileiro de Segurança da Informação e de Sistemas Computacionais. Sociedade Brasileira de Computação - SBC, 2022. http://dx.doi.org/10.5753/sbseg_estendido.2022.224706.
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Atualmente, existem diversos dispositivos que coletam dados e prestam serviços na Internet. Alguns desses dispositivos colaboram para trocar informacões e usá-las para tomar decisões mais inteligentes em um ambiente chamado Internet das Coisas (IoT). Recentemente, a tecnologia blockchain surgiu como uma possível solução para superar problemas de segurança em IoT. Apesar disso, blockchains tradicionais (como Bitcoin ou Ethereum) nao são adequados para a natureza de capacidade/recursos limitados dos dispositivos IoT. Alem disso, as propostas atuais carecem de uma discussão sobre o comportamento do usuario em diferentes contextos e como ele pode ser adaptado para diferentes algoritmos de consenso. Para superar esses problemas, apresentamos na tese um conjunto de etapas para criar um mecanismo de consenso multinível para diferentes contextos usando uma estrutura blockchain leve chamada appendable-block blockchain. Essa abordagem fornece uma solução que permite usar diferentes configurações ou consensos, de acordo com os requisitos de cada contexto no ambiente IoT. Por fim, a tese mostra que um consenso multinível pode produzir uma alta taxa de transferencia e baixa latência para inserir novas transações em appendable-block blockchains.
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Golab, Wojciech. "The Recoverable Consensus Hierarchy." In SPAA '20: 32nd ACM Symposium on Parallelism in Algorithms and Architectures. ACM, 2020. http://dx.doi.org/10.1145/3350755.3400212.
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Zhang, Xiaojun, Weiyu Zhong, Ce Yang, Lin Chen, Jing Liao, and Naixue Xiong. "BFT Consensus Algorithms." In 2023 IEEE 10th International Conference on Cyber Security and Cloud Computing (CSCloud)/2023 IEEE 9th International Conference on Edge Computing and Scalable Cloud (EdgeCom). IEEE, 2023. http://dx.doi.org/10.1109/cscloud-edgecom58631.2023.00080.
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Mahamuni, Dipti. "A Comparative Framework for Evaluating Consensus Algorithms for Blockchains." In 2nd International Conference on Machine Learning Techniques and NLP (MLNLP 2021). Academy and Industry Research Collaboration Center (AIRCC), 2021. http://dx.doi.org/10.5121/csit.2021.111411.
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The past five years have seen a significant increase in the popularity of Decentralized Ledgers, commonly referred to as Blockchains. Many new protocols have been launched to cater to various applications serving individual consumers and enterprises. While research is conducted on individual consensus mechanisms and comparison against popular protocols, decisionmaking and selection between the protocols is still amorphous. This paper proposes a comprehensive comparative framework to evaluate various consensus algorithms. We hope that such a framework will help evaluate current as well as future consensus algorithms objectively for a given use case. The past five years have seen a significant increase in the popularity of Decentralized Ledgers, commonly referred to as Blockchains. Many new protocols have been launched to cater to various applications serving individual consumers and enterprises. While research is conducted on individual consensus mechanisms and comparison against popular protocols, decisionmaking and selection between the protocols is still amorphous. This paper proposes a comprehensive comparative framework to evaluate various consensus algorithms. We hope that such a framework will help evaluate current as well as future consensus algorithms objectively for a given use case.
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Bassolillo, S. "Target localization with a distributed Kalman filter over a network of UAVs." In Aeronautics and Astronautics. Materials Research Forum LLC, 2023. http://dx.doi.org/10.21741/9781644902813-21.
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Abstract. Unmanned Aerial Vehicles (UAVs) have gained significant usage in various kinds of missions, including reconnaissance, search and rescue, and military operations. In rescue missions, timely detection of missing persons after avalanches is crucial for increasing the chances of saving lives. Using UAVs in such scenarios offers benefits such as reducing risks for rescuers and accelerating search efforts. Employing a formation of multiple drones can effectively cover a larger area and expedite the process. However, the challenge lies in achieving autonomous and scalable systems, as drones are typically operated on a one-to-one basis, requiring a large team of rescuers. To enhance situational awareness and distribute communication load, this paper proposes a decentralized Kalman filtering algorithm that exploits sensor data from multiple drones to estimate target positions and support guidance and control algorithms. The algorithm combines Consensus on Information and Consensus on Measurements techniques. Preliminary validation is conducted through numerical simulations in a sample scenario.
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Afshari, Sina, and Sandipan Mishra. "Decentralized Feedback Control of Smart Lighting Systems." In ASME 2013 Dynamic Systems and Control Conference. American Society of Mechanical Engineers, 2013. http://dx.doi.org/10.1115/dscc2013-3968.
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This paper presents a framework for designing controllers for self-commissioning smart lighting systems with plug-and-play capability. A class of decentralized feedback control methods is proposed for this purpose. Theoretical results for stability and convergence of the proposed algorithms are presented. Further, an automated self-commissioning algorithm is designed to minimize re-identification efforts necessary for the decentralized controller in case of a change in the lighting configuration (e.g. the addition of a new fixture to an existing space). The implementation of this algorithm demonstrates significant reduction in the commissioning effort. Finally, centralized, decentralized and consensus-based control algorithms are implemented on an experimental adaptive lighting testbed. The performance of the decentralized methods is shown to be comparable to that of the centralized controller.
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Becchetti, Luca, Andrea Clementi, Emanuele Natale, Francesco Pasquale, Riccardo Silvestri, and Luca Trevisan. "Simple dynamics for plurality consensus." In SPAA '14: 26th ACM Symposium on Parallelism in Algorithms and Architectures. ACM, 2014. http://dx.doi.org/10.1145/2612669.2612677.
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Becchetti, L., A. Clementi, E. Natale, F. Pasquale, and L. Trevisan. "Stabilizing Consensus with Many Opinions." In Proceedings of the Twenty-Seventh Annual ACM-SIAM Symposium on Discrete Algorithms. Society for Industrial and Applied Mathematics, 2015. http://dx.doi.org/10.1137/1.9781611974331.ch46.
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Jansson, Jesper, Chuanqi Shen, and Wing-Kin Sung. "Improved Algorithms for Constructing Consensus Trees." In Proceedings of the Twenty-Fourth Annual ACM-SIAM Symposium on Discrete Algorithms. Society for Industrial and Applied Mathematics, 2013. http://dx.doi.org/10.1137/1.9781611973105.129.
Texte intégralRapports d'organisations sur le sujet "Algorithme du Consensus"
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Liang, Guanfeng, and Nitin Vaidya. Deterministic Consensus Algorithm with Linear Per-Bit Complexity. Defense Technical Information Center, 2010. http://dx.doi.org/10.21236/ada555082.
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Fox, A., C. Ponce, A. Applegate, M. Nygaard, and N. Duan. Comparison of Distributive Consensus Algorithms for AnomalyDetection on the Power-Grid. Office of Scientific and Technical Information (OSTI), 2018. http://dx.doi.org/10.2172/1490934.
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Matei, Ion, Christoforos Somarakis, and John S. Baras. A Randomized Gossip Consenus Algorithm on Convex Metric Spaces. Defense Technical Information Center, 2012. http://dx.doi.org/10.21236/ada588967.
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Allende López, Marcos, Diego López, Sergio Cerón, et al. Quantum-Resistance in Blockchain Networks. Inter-American Development Bank, 2021. http://dx.doi.org/10.18235/0003313.
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This paper describes the work carried out by the Inter-American Development Bank, the IDB Lab, LACChain, Cambridge Quantum Computing (CQC), and Tecnológico de Monterrey to identify and eliminate quantum threats in blockchain networks. The advent of quantum computing threatens internet protocols and blockchain networks because they utilize non-quantum resistant cryptographic algorithms. When quantum computers become robust enough to run Shor's algorithm on a large scale, the most used asymmetric algorithms, utilized for digital signatures and message encryption, such as RSA, (EC)DSA, and (EC)DH, will be no longer secure. Quantum computers will be able to break them within a short period of time. Similarly, Grover's algorithm concedes a quadratic advantage for mining blocks in certain consensus protocols such as proof of work. Today, there are hundreds of billions of dollars denominated in cryptocurrencies that rely on blockchain ledgers as well as the thousands of blockchain-based applications storing value in blockchain networks. Cryptocurrencies and blockchain-based applications require solutions that guarantee quantum resistance in order to preserve the integrity of data and assets in their public and immutable ledgers. We have designed and developed a layer-two solution to secure the exchange of information between blockchain nodes over the internet and introduced a second signature in transactions using post-quantum keys. Our versatile solution can be applied to any blockchain network. In our implementation, quantum entropy was provided via the IronBridge Platform from CQC and we used LACChain Besu as the blockchain network.
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Dominguez-Garcia, Alejandro D., Christoforos N. Hadjicostis, and Nitin H. Vaidya. Distributed Algorithms for Consensus and Coordination in the Presence of Packet-Dropping Communication Links. Part 1: Statistical Moments Analysis Approach. Defense Technical Information Center, 2011. http://dx.doi.org/10.21236/ada558911.
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Anderson, Gerald L., and Kalman Peleg. Precision Cropping by Remotely Sensed Prorotype Plots and Calibration in the Complex Domain. United States Department of Agriculture, 2002. http://dx.doi.org/10.32747/2002.7585193.bard.
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This research report describes a methodology whereby multi-spectral and hyperspectral imagery from remote sensing, is used for deriving predicted field maps of selected plant growth attributes which are required for precision cropping. A major task in precision cropping is to establish areas of the field that differ from the rest of the field and share a common characteristic. Yield distribution f maps can be prepared by yield monitors, which are available for some harvester types. Other field attributes of interest in precision cropping, e.g. soil properties, leaf Nitrate, biomass etc. are obtained by manual sampling of the filed in a grid pattern. Maps of various field attributes are then prepared from these samples by the "Inverse Distance" interpolation method or by Kriging. An improved interpolation method was developed which is based on minimizing the overall curvature of the resulting map. Such maps are the ground truth reference, used for training the algorithm that generates the predicted field maps from remote sensing imagery. Both the reference and the predicted maps are stratified into "Prototype Plots", e.g. 15xl5 blocks of 2m pixels whereby the block size is 30x30m. This averaging reduces the datasets to manageable size and significantly improves the typically poor repeatability of remote sensing imaging systems. In the first two years of the project we used the Normalized Difference Vegetation Index (NDVI), for generating predicted yield maps of sugar beets and com. The NDVI was computed from image cubes of three spectral bands, generated by an optically filtered three camera video imaging system. A two dimensional FFT based regression model Y=f(X), was used wherein Y was the reference map and X=NDVI was the predictor. The FFT regression method applies the "Wavelet Based", "Pixel Block" and "Image Rotation" transforms to the reference and remote images, prior to the Fast - Fourier Transform (FFT) Regression method with the "Phase Lock" option. A complex domain based map Yfft is derived by least squares minimization between the amplitude matrices of X and Y, via the 2D FFT. For one time predictions, the phase matrix of Y is combined with the amplitude matrix ofYfft, whereby an improved predicted map Yplock is formed. Usually, the residuals of Y plock versus Y are about half of the values of Yfft versus Y. For long term predictions, the phase matrix of a "field mask" is combined with the amplitude matrices of the reference image Y and the predicted image Yfft. The field mask is a binary image of a pre-selected region of interest in X and Y. The resultant maps Ypref and Ypred aremodified versions of Y and Yfft respectively. The residuals of Ypred versus Ypref are even lower than the residuals of Yplock versus Y. The maps, Ypref and Ypred represent a close consensus of two independent imaging methods which "view" the same target. In the last two years of the project our remote sensing capability was expanded by addition of a CASI II airborne hyperspectral imaging system and an ASD hyperspectral radiometer. Unfortunately, the cross-noice and poor repeatability problem we had in multi-spectral imaging was exasperated in hyperspectral imaging. We have been able to overcome this problem by over-flying each field twice in rapid succession and developing the Repeatability Index (RI). The RI quantifies the repeatability of each spectral band in the hyperspectral image cube. Thereby, it is possible to select the bands of higher repeatability for inclusion in the prediction model while bands of low repeatability are excluded. Further segregation of high and low repeatability bands takes place in the prediction model algorithm, which is based on a combination of a "Genetic Algorithm" and Partial Least Squares", (PLS-GA). In summary, modus operandi was developed, for deriving important plant growth attribute maps (yield, leaf nitrate, biomass and sugar percent in beets), from remote sensing imagery, with sufficient accuracy for precision cropping applications. This achievement is remarkable, given the inherently high cross-noice between the reference and remote imagery as well as the highly non-repeatable nature of remote sensing systems. The above methodologies may be readily adopted by commercial companies, which specialize in proving remotely sensed data to farmers.
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Daudelin, Francois, Lina Taing, Lucy Chen, Claudia Abreu Lopes, Adeniyi Francis Fagbamigbe, and Hamid Mehmood. Mapping WASH-related disease risk: A review of risk concepts and methods. United Nations University Institute for Water, Environment and Health, 2021. http://dx.doi.org/10.53328/uxuo4751.
Texte intégralRésumé :
The report provides a review of how risk is conceived of, modelled, and mapped in studies of infectious water, sanitation, and hygiene (WASH) related diseases. It focuses on spatial epidemiology of cholera, malaria and dengue to offer recommendations for the field of WASH-related disease risk mapping. The report notes a lack of consensus on the definition of disease risk in the literature, which limits the interpretability of the resulting analyses and could affect the quality of the design and direction of public health interventions. In addition, existing risk frameworks that consider disease incidence separately from community vulnerability have conceptual overlap in their components and conflate the probability and severity of disease risk into a single component. The report identifies four methods used to develop risk maps, i) observational, ii) index-based, iii) associative modelling and iv) mechanistic modelling. Observational methods are limited by a lack of historical data sets and their assumption that historical outcomes are representative of current and future risks. The more general index-based methods offer a highly flexible approach based on observed and modelled risks and can be used for partially qualitative or difficult-to-measure indicators, such as socioeconomic vulnerability. For multidimensional risk measures, indices representing different dimensions can be aggregated to form a composite index or be considered jointly without aggregation. The latter approach can distinguish between different types of disease risk such as outbreaks of high frequency/low intensity and low frequency/high intensity. Associative models, including machine learning and artificial intelligence (AI), are commonly used to measure current risk, future risk (short-term for early warning systems) or risk in areas with low data availability, but concerns about bias, privacy, trust, and accountability in algorithms can limit their application. In addition, they typically do not account for gender and demographic variables that allow risk analyses for different vulnerable groups. As an alternative, mechanistic models can be used for similar purposes as well as to create spatial measures of disease transmission efficiency or to model risk outcomes from hypothetical scenarios. Mechanistic models, however, are limited by their inability to capture locally specific transmission dynamics. The report recommends that future WASH-related disease risk mapping research: - Conceptualise risk as a function of the probability and severity of a disease risk event. Probability and severity can be disaggregated into sub-components. For outbreak-prone diseases, probability can be represented by a likelihood component while severity can be disaggregated into transmission and sensitivity sub-components, where sensitivity represents factors affecting health and socioeconomic outcomes of infection. -Employ jointly considered unaggregated indices to map multidimensional risk. Individual indices representing multiple dimensions of risk should be developed using a range of methods to take advantage of their relative strengths. -Develop and apply collaborative approaches with public health officials, development organizations and relevant stakeholders to identify appropriate interventions and priority levels for different types of risk, while ensuring the needs and values of users are met in an ethical and socially responsible manner. -Enhance identification of vulnerable populations by further disaggregating risk estimates and accounting for demographic and behavioural variables and using novel data sources such as big data and citizen science. This review is the first to focus solely on WASH-related disease risk mapping and modelling. The recommendations can be used as a guide for developing spatial epidemiology models in tandem with public health officials and to help detect and develop tailored responses to WASH-related disease outbreaks that meet the needs of vulnerable populations. The report’s main target audience is modellers, public health authorities and partners responsible for co-designing and implementing multi-sectoral health interventions, with a particular emphasis on facilitating the integration of health and WASH services delivery contributing to Sustainable Development Goals (SDG) 3 (good health and well-being) and 6 (clean water and sanitation).