1,721,149 research outputs found
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Design, Modeling and Control of a Multi-Drone System for Aerial Manipulation
No full textUn sujet passionnant dans le domaine des véhicules aériens autonomes est l'interaction avec l'environnement par la manipulation en vol, y compris la récupération, le transport et le déploiement, qui dévoile un énorme potentiel vis-à-vis des applications industrielles et de service. À cet égard, cette thèse doctoral se concentre sur la conception et l'étude dynamique basé sur l'énergie d'un système aérien sans pilote à liaisons multiples capable d'effectuer des tâches de manipulation. L'étude de ce système aérien comprend le contrôle du véhicule volant à liaisons multiples par la théorie du contrôle en mode glissant, la conception de contrôleurs basés sur le principe de Lyapunov et, parallèlement, à l'application de filtres de Kalman pour l'estimation de l'état et des perturbations. La dernière partie de la thèse est consacrée à l'examen des effets des retards sur les drones. Des résultats de simulation sont fournis pour prouver l'efficacité de la proposition globale de la thèse.A recent and exciting topic within the field of autonomous aerial vehicles is the interaction with the surrounding environment via in-flight manipulation, including retrieving, transport and deployment, which unveils an enormous potential vis-a-vis industrial and service applications. In this regard, the actual thesis focuses on the conception and energy-based dynamical study of a multi-link unmanned aerial system able to perform manipulation tasks. The study of the aforementioned robotic aerial system includes the control of the flying multi-link vehicle by the sliding mode control theory and the conception of Lyapunov-based controllers alongside the application of Kalman Filters for state and disturbances estimation. The last part of the thesis is devoted to the examination of time-delays effects on unmanned aerial systems. Detailed simulation results are provided to prove the effectiveness of the overall thesis proposal
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Maximizing Prosumer Benefits While Switching Between Dynamic Electricity Contracts Under Regulatory Delays
Full text linkInvestments in decentralized energy systems are shaping the energy demand of the consumers and therefore play an important role in smart grids modeling. In this paper, we present a model aimed at maximizing the benefits for a prosumer who has invested in a decentralized energy system, while being able to choose between dynamic energy contracts offered by several energy suppliers. In our benefits optimization model we take into account the delay due to the regulations governing the process of a prosumer switching between suppliers. The proposed model is applied to a numerical example to determine the optimal benefits and switching sequences at different regulatory delays. The proposed case study reveals that switching between suppliers at regulatory delays does not guarantee maximal prosumer benefits
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Contrôle actif de vibration d'une structure flexible soumise à une saturation d'entrée par contrôleur basé retard et compensateur anti-windup
No full textDans ce travail, on traite le problème du commande actif des vibrations robustes pour une structure mécanique flexible à travers des techniques pour des systèmes à dimensions infinis et finis. Les approches abordées sont réglées pour une commande à retour de sortie basée sur une commande aux actions retardées proportionelles, par une approche basée sur quasipolynomials,et une commande synthétisée par la méthode H∞avec une approche par LMIs. Le but c’est l’analyse de ses capabilités pour amortisser les modes vibratoires dans une bande passante d’intérêt, et éviter les effets dénommés de phénomène “spillover”. Cettes commandes sont sythétisés à travers d’un modèle de dimensions finies,dérivé à partir d’un analyse des dimensions finies des structures mécaniques, combiné avec des methodes de réduction.Les structures flexibles envisagées ici sont, d’abord,une poutre flexible d’aluminium à la configuration Euler-Bernoulli, dont un bout est encastrée et l’autre libre, deuxièmement,une membrane axisymmetrique. Chaque système est instrumenté d’un capteur et d’un actionneur piézoélectrique,ils sont bien soumises à chaque coté des structures et elles sont bien placées. Notre intention est d’examiner les performances susmentionnés par les environnements de simulation numérique et la mise en oeuvre à titre expérimental.In this work, the problem of active vibration control of flexible mechanical structures is addressed through infinite and finite dimensional techniques. The compared approaches are adjusted for an output feedback controller based on delayed proportional actions,through a quasipolynomial-based approach, and an optimalH∞ controller design computed with an LMI approach.They are shown in order to analyze their capabilities to damp some vibrational modes in the frequency band with of interest, and to avoid the so called “spillover”phenomenon. These controllers are synthetized through a finite dimensional model, derived from a finite element analysis of the mechanical structure, combined with some reduction methods.The flexible structures considered here are, firstly, aflexible aluminium beam in the Euler-Bernoulli configuration,and secondly, an axysimmetric membrane. Bothof them are equipped with two piezoelectric patches that are bounded and collocated on each face of the structure.We intend to examine and discuss the aforementioned performances in both simulation and experimental environments
Stability Analysis of Systems with Delay-Dependent Coefficients
No full textDes systèmes avec des coefficients dépendant du retard ont été rencontrés dans diverses applications de la science et de l'ingénierie. Malgré la littérature abondante sur les systèmes de temporisation, il y a peu de résultats concernant l'analyse de stabilité des systèmes avec des coefficients dépendant du retard. Cette thèse est consacrée à l'analyse de stabilité de cette classe de systèmes.Les méthodes d'analyse de la stabilité sont développées à partir de l'équation caractéristique correspondante suivant une approche généralisée tau-décomposition. Étant donné un intervalle d'intérêt de retard, nous sommes capables d'identifier toutes les valeurs de retard critique contenues dans cet intervalle pour lesquelles l'équation caractéristique admet des racines sur l'axe imaginaire du plan complexe. Le critère de direction de croisement des racines sont proposées pour déterminer si ces racines caractéristique se déplacent vers le plan complexe demi-gauche ou demi-droite lorsque le paramètre de retard passe par ces valeurs de retard critique. Le nombre de racines caractéristiques instables pour un retard donné peut ainsi être déterminé. Notre analyse comprend les systèmes avec un seul retard ou des retards proportionnés sous certaines hypothèses. Le critère de direction de croisement des racines développés dans cette thèse peut être appliqués aux multiple racines caractéristiques, ou aux racines caractéristiques dont la position paramétrée par le retard est tangent à l'axe imaginaire. En tant qu'application, il est démontré que les systèmes avec des coefficients dépendant du retard peuvent provenir de schémas de contrôle qui utilisent une sortie retardée pour approcher ses dérivés pour la stabilisation. Les méthodes d'analyse de stabilité développées dans cette thèse sont adaptées et appliquées pour trouver les intervalles de retard qui atteignent un taux de convergence demandé du système en boucle fermée.Systems with delay-dependent coefficients have been encountered in various applications of science and engineering. However, general and systematic stability analysis is rarely reported in the rich literature on time-delay systems. This thesis is committed to the stability analysis of such class of systems.Stability analysis methods are developed based on the corresponding characteristic equation following a generalized tau-decomposition approach. Given a delay interval of interest, we are able to identify all the critical delay values contained in this interval for which the characteristic equation admits roots on the imaginary axis of the complex plane. Various root crossing direction criteria are proposed to determine whether these characteristic roots move toward the left or the right half complex plane as the delay parameter sweeps through these critical delay values. The number of unstable characteristic roots for any given delay can thus be determined. Our analysis covers systems with a single delay or commensurate delays under certain assumptions. The root crossing direction criteria developed in this thesis can be applied to characteristic roots with multiplicity, or characteristic roots whose locus parametrized by the delay is tangent to the imaginary axis. As an application, it is demonstrated that systems with delay-dependent coefficients can arise from control schemes that use delayed output to approximate its derivatives for stabilization. The stability analysis methods developed in this thesis are tailored and applied to find the delay intervals that achieve a demanded convergence rate of the closed-loop system
Amplitude Independent Frequency Synchroniser for a Cubic Planar Polynomial System
Full text linkInternational audienceThe problem of local linearizability of the planar linear center perturbed by cubic non-linearities in all generalities on the system parameters (14 parameters) is far from being solved. Synchronization problem [18, 5] consists in bringing appropriate modifications on a given system to obtain a desired dynamic. The desired phase portrait along this paper contains a compact region around a singular point at the origin in which lies periodic orbits with the same period (independently from the chosen initial conditions). In this paper, starting from a 5-parameters non isochronous Chouikha cubic system [8], we identify all possible monomial perturbations of degree d ∈ {2, 3} insuring local linearizability of the perturbed system.The necessary conditions are obtained by the Normal Forms method. These conditions are real algebraic equations (multivariate polynomials) in the parameters of the studied ordinary differential system. The efficient algorithm FGb [13] for computing the Gröbner basis is used. For the family studied in this paper, an exhaustive list of possible parameters values insuring local linearizability is established. All the found cases are already known in the literature but the contexts is different since our object is the syn-chronisation not the classification. This paper can be seen as a direct continuation of several new works concerned with the hinting of cubic isochronous centers in particular [8, 12, 15, 10, 6, 2, 3], also it can be considered as an adaptation of a qualitative theory method to a synchronization problem. Mathematics Subject Classification (2010). Primary 34C15, 34C25, 34C37
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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