1,720,994 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
Energy Management System for DC Electric Spring with Parallel Topology
No full textDC electric spring (DCES) maintains the voltage stability and improves the power quality in dc microgrid with the inclusion of renewable energy sources. A parallel DCES topology has been recently proposed; it consists of a dc-dc three-port converter and an energy storage system made up of a battery paralleled with the critical load (CL) through a bidirectional buck-boost converter. In this article, an effective energy management system (EMS) is proposed for the parallel DCES topology. After illustrating the DCES operating modes, three functional states are introduced, namely normal, specific time, and emergency, where the normal state refers to the DCES operation under dc microgrid power fluctuations, whereas the specific time and emergency states refer, respectively, to the environment conditions and battery contingent situations. The EMS decides the transitions between the DCES operating modes, changes the operating status of the battery, and realizes multiple charging and discharging mechanism. This gives DCES the capabilities of guaranteeing the voltage stability of CL while keeping the state of charge of the battery within a reasonable range, which extends the lifetime of battery and ensures safe and reliable operation of the whole system. The proposed EMS has been validated by simulation and experimental results
Analysis on boundary conditions of soft switching for DC electric spring with parallel topology
Full text linkThe concept of DC electric spring (DCES) has been introduced some years ago to solve the voltage stabilisation issue caused by the high penetration of intermittent renewable energy sources (RESs) into DC power systems. Recently, a featured DCES topology has been proposed, comprising an isolated three-port DC/DC converter and an embedded energy storage system. The three ports are connected to a DC power system at the supply side, the critical load (CL) and the non-critical load (NCL) at the user side, whilst the energy storage system is paralleled at the CL port. To improve the performance of the topology, this paper investigates the chance of making soft the switching of the DCES converters. After the DCES operation is analysed, equations describing the currents transients during switching have been worked out, from which the boundary conditions for zero-voltage switching (ZVS) to occur are formulated and the resultant ZVS zone is illustrated with the help of visual graphs. The boundary conditions are examined to evaluate how the circuit parameters influence the extension of the ZVS zone. The examination shows that a suitable selection of the parameters widens the ZVS zone notably; its optimal extension is then found for a case study. The effectiveness of the ZVS findings for the featured DCES topology is validated by both simulation and experiment results
Regulation performance of multiple DC electric springs controlled by distributed cooperative system
Full text linkDC electric springs (DCESs) have been recently developed to improve the voltage stability of a DC microgrid. A lately proposed DCES topology is comprised of a DC/DC three port converter (TPC), a bi-directional buck-boost converter (BBC) and a battery, and is arranged as follows: The TPC input port is fed by a renewable energy source (RES) whilst the two TPC output ports supply a non-critical load (NCL) and a critical load (CL) separately; in turn, BBC together with the battery constitutes the DCES energy storage unit (ESU) and is connected in parallel to CL. In this paper, a set of DCESs with such a topology and with their CLs connected to a common DC bus is considered. The control of the DCESs is built up around a distributed cooperative system having two control levels, namely primary and secondary, each of them endowed with algorithms committed to specific tasks. The structure of the control levels is explicated and their parameters are designed. The control system is applied to a DCES set taken as a study-case and tested by simulation. The results of the tests show the excellent performance of the control system in both regulating the CL DC bus voltage and keeping the state-of-charge of the battery within predefined limits
A topology of DC electric springs for DC household applications
No full textThere are two types of existing direct current (DC) electric spring (DCES), of which the one realised by alternative current electric spring has low power density because of the low-pass filter with big volume, another one is realised by DC/DC converters but too complicated. In this study, aiming at households' applications, a novel topology is proposed for DCES, using a three-port DC/DC converter with a bi-directional boost-buck converter (BBC) paralleled at one port. Critical load (CL), noncritical load (NCL) and power source are located at separate port. Besides the isolation electrically, the most important advantage is that the NCL is no longer in series with DCES, which is possibly the first attempt to change the connection type of a visual NCL with an electric spring (ES) from series to normal parallel way. With the proposed DCES, CL power is regulated stable while the fluctuations are transferred to the NCL. Meanwhile, the DCES does not provide nor absorb active power at steady-state. When the battery voltage reaches its lower or upper limits, the protection mechanism will start to ensure safe operations. The effectiveness of the proposed DCES topology and its control has been validated by simulation and experiment results
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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