1,721,005 research outputs found
Gallium Nitride Power Devices in Power Electronics Applications: State of Art and Perspectives
Full text linkHigh-electron-mobility transistors based on gallium nitride technology are the most recently developed power electronics devices involved in power electronics applications. This article critically overviews the advantages and drawbacks of these enhanced, wide-bandgap devices compared with the silicon and silicon carbide MOSFETs used in power converters. High-voltage and low-voltage device applications are discussed to indicate the most suitable area of use for these innovative power switches and to provide perspective for the future. A general survey on the applications of gallium nitride technology in DC-DC and DC-AC converters is carried out, considering the improvements and the issues expected for the higher switching transient speed achievable
Modeling and Experimental Validation of GaN-Based switching leg in Inverter Topology for Motor Drives Applications
No full textThe paper deals with the dead time impact on the reverse conduction of low-voltage GaN FETs in inverter topology for motor control applications. The current variation in AC motor drive leads to a different dead time losses mechanism compared to the DC-DC converter. In the paper, the dead time in the inverter leg is correlated with both current variation and GaN reverse conduction, through an experimental evaluation. Furthermore, a comparison of the GaN FET with a MOSFET with similar parameters in reverse conduction operations is carried out to show the similarities and differences in switching behavior and power losses. Finally, the paper aims to give designers a guideline on the limits and optimum dead time selection in an GaN FET based inverter leg for motor control applications
GaN-Based Low-Voltage Inverter for Electric Scooter Drive System
No full textThe paper deals with the application of the latest generation low voltage (up to 80V) Gallium Nitride (GaN) devices for motor drive applications in the field of electric micro-mobility. A two-level inverter topology oriented to light electric traction (such as electric scooters) with a power rate of 1500W has been considered. An experimental board using two GaN FETs in parallel connection for each switch of an inverter leg has been arranged. The intrinsic parameters spread of the device, as well as the leakage inductances of both the circuit and the PCB, to evaluate the impact on the current share during both the transient phase and in the steady state have been investigated. In the paper, several simulation runs have been carried out and described. Furthermore, the inverter experimental board has been used to evaluate the phase voltages and currents at different load conditions. Finally, the temperature limits versus phase current variation have been evaluated
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
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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