1,721,078 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
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
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
Analogous piezoelectric networks for the design of highly damped metastructures
No full textInternational audienceWhen dealing with thin and lightweight structures, as in aerospace systems, most of the materials offering a good stiffness-to-density ratio have very low intrinsic damping properties. At the level of the whole structure, this generates weakly damped mechanical modes, which can be critical because they often lead to high amplitude vibrations. Such structural vibrations can be reduced by employing piezoelectric material as passive electromechanical transducers able to convert the vibration energy into electrical energy. This concept is behind piezoelectric shunt damping, which consists in connecting a one-port electrical circuit to a piezoelectric transducer for impedance matching and thus optimized energy transfers. Using passive components such as resistors, inductors or capacitors leads to autonomous and inherently stable control solutions. Inductance in the circuit creates an electrical resonance due to the charge exchange with the piezoelectric capacitance. In this case, impedance matching consists in tuning the resonance of the shunt to a natural frequency of the mechanical structure. The equivalent of a tuned mass damper is thus implemented with a vibration absorber that is designed as the electrical counterpart of the mechanical resonance to be controlled. This uni-modal case introduces the interest of electrical analogues for piezoelectric damping. Analogous coupling can actually be extended to broadband vibration mitigation. A multi-resonant electrical network is then required to approximate the modal properties of the mechanical structure. On one hand, the electrical network should exhibit similar modal distributions. Such a spatial coherence condition is met by discretizing the constitutive equations of the continuous mechanical medium, applying an electromechanical analogy, and deriving the electrical connections which are analogous to the considered mechanical boundary conditions. On the other hand, the structure and the developed network should have similar wave propagation properties to meet a frequency coherence condition. Hence, a passive broadband damping can be achieved by coupling a structure to its analogous electrical network. This method was applied to the damping of basic structures such as bars, beams, curved beams and plates. Both numerical and experimental results validate the concept of analogous piezoelectric damping. Application to more complicated geometries can however become difficult when moving away from an assembly of the previously listed simple structures. Furthermore, the method requires a sufficiently fine discretization of the electrical network which often results in a lot of electrical components. More recent techniques introduce modal-based synthesis of multi-port circuits, which reduces the size of the electrical networks to a minimum and thus offers better applicability to complex industrial structures
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
Positionnement optimal de couches minces piézoélectriques dans un objectif de maximisation de couplages modaux
No full textInternational audienc
Optimized placement of piezoelectric patches from a purely mechanical model
No full textInternational audiencePiezoelectric shunt damping can provide passive and robust solutions for vibration control of structures with complex geometries. However, optimal placement of piezoelectric patches is often a critical step as soon as the considered structure deviates from academic geometries. Indeed, the use of a finite element model including piezoelectric elements can quickly lead to prohibitive calculation times in the case of an optimization with many geometric parameters. Despite the possibility of using dedicated algorithms, the complexity of the methods and coupled models remains a barrier for non-specialist users. This work proposes positioning criteria directly applicable after calculation of the modes of a bare structure. It is thus assumed that the addition of thin surface-bonded piezoelectric layers has a negligible influence on the mode shapes. This assumption has already been used by some authors to provide an initial placement before running an optimization algorithm under piezoelectric coupling. Introducing a local criterion directly derived from the stress or strain fields, it becomes possible to define the best area extension of a piezoelectric patch based on the maximization of a modal electromechanical coupling factor. This coupling factor can even be estimated from a purely mechanical finite element model, without the need to model the piezoelectric material. Three criteria of increasing complexity are finally proposed and numerically validated on a benchmark structure which offers a non-standard geometry. Such criteria and methods may have a strong interest in an industrial context where coupled models or specific expertise in piezoelectric coupling are not always available
Amortissement vibratoire multimodal de structures couplées à leurs réseaux piézoélectriques analogues
No full textStructural vibrations can be reduced by benefiting from the electromechanical coupling that is offered by piezoelectric materials. In terms of passive damping, piezoelectric shunts allow converting the vibration energy into electrical energy. Adding an inductor in the circuit creates an electrical resonance due to the charge exchanges with the piezoelectric capacitance. By tuning the resonance of the shunt to the natural frequency of the mechanical structure, the equivalent of a tuned mass damper is implemented. This strategy is extended to the control of a multimodal structure by increasing the number of piezoelectric patches. These are interconnected through an electrical network offering modal properties that approximate the behavior of the structure to control. This multi-resonant network allows the simultaneous control of multiple mechanical modes. An adequate electrical topology is obtained by discretizing the mechanical structure and applying the direct electromechanical analogy. The analogous network shows inductors and transformers, whose numbers and values are chosen according to the frequency band of interest. After focusing on the design of suitable magnetic components, the passive control strategy is applied to the damping of one-dimensional structures as bars or beams. It is then extended to the control of thin plates by implementing a two-dimensional analogous network.L'amplitude vibratoire d'une structure mince peut être réduite grâce au couplage électromécanique qu'offrent les matériaux piézoélectriques. En termes d'amortissement passif, les shunts piézoélectriques permettent une conversion de l'énergie vibratoire en énergie électrique. La présence d'une inductance dans le circuit crée une résonance électrique due à l'échange de charges avec la capacité piézoélectrique. Ainsi, l'ajustement de la fréquence propre de ce shunt résonant à celle de la structure mécanique équivaut à la mise en œuvre d'un amortisseur à masse accordée. Cette stratégie est étendue au contrôle d'une structure multimodale par multiplication du nombre de patchs piézoélectriques. Ceux-ci sont interconnectés via un réseau électrique ayant un comportement modal approximant celui de la structure à contrôler. Ce réseau multi-résonant permet donc le contrôle simultané de plusieurs modes mécaniques. La topologie électrique adéquate est obtenue par discrétisation de la structure mécanique puis par analogie électromécanique directe. Le réseau analogue fait apparaître des inductances et des transformateurs dont le nombre et les valeurs sont choisis en fonction de la bande de fréquences à contrôler. Après s'être penché sur la conception de composants magnétique adaptés, la solution de contrôle passif est appliquée à l'amortissement de structures unidimensionnelles de type barres ou poutres. La stratégie est ensuite étendue au contrôle de plaques minces par mise en œuvre d'un réseau électrique bidimensionnel
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