1,721,251 research outputs found
Power system islands, autonomous microgrids and relevant instrumentation
No full textUnplanned power system islanding is usually seen as a major risky operating condition and specific countermeasures are applied in order to avoid it. However the capability of voluntary disconnection from the external grid and autonomous operation is often a requirement for some industrial power systems and power plants. The panel session at the 2012 IEEE Innovative Smart Grid Technologies Conference on “Power system islands, autonomous microgrids and relevant instrumentation” aims at providing an occasion to exchange ideas and experiences in order to envisage situations in which voluntary power system islanding may be useful and to define the instrumentation required for a reliable operation in islanded conditions. This paper, provided by the organizers, reviews some activities recently carried out on this topic at their institution
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
On dynamic load models for voltage stability studies
No full textAppropriate modelling of dynamic loads is of primary importance in voltage stability studies. The paper deals with the modelling of a load consisting of a static load plus an aggregate of induction motors. The behavior of three simplified models for such a load configuration is compared. The three models are (A) a generic nonlinear dynamic model of the first order as proposed by Karlsson and Hill, (B) a static exponential load plus a dynamic first-order model for the induction motors, and (C) a static exponential load plus a dynamic third-order model for the induction motors. A power system with a longitudinal structure is chosen as the case-study. It is shown that for the same perturbation (tripping of one of two high-voltage parallel lines) the simulation results are quite different from each other and, in certain cases, only the third-order dynamic model correctly predicts the voltage collapse phenomena at the load bus. An interpretation of the different behavior of the various models is give
Dispersed Generators Interfaced with Distribution Systems
No full textThe installation of dispersed generators involves the critical reassessment of the adequacy of network protections, with reference to the relevant standards. The adequacy of the relay design, setting and coordination becomes critical for the proper network operation: that depends on the dynamic interaction among the various types of distributed generators (microturbines, fuel-cells, photovoltaic systems) and the network. Aim of this paper is to analyze the dynamic behavior of different kinds of distributed generators, connected to the network either directly or by means of power electronic interfaces, after the occurrence of faults and typical perturbations. Simplified dynamic models of different types of distributed generation units (microturbines, fuel cells and photovoltaic plants) are given in the paper, and the results of the simulations obtained by using realistic distribution network configurations are presented and discussed, in view of the reassessment of the adequacy and reliability of the power system protections
Lagrangian Heuristics Based on Disaggregated Bundle Methods for Hydrothermal Unit Commitment
No full textThe paper presents a simple and effective Lagrangian relaxation approach for the solution of the optimal short-term unit commitment problem in hydrothermal power-generation systems. The proposed approach, based on a disaggregated Bundle method for the solution of the dual problem, with a new warm-starting procedure, achieves accurate solutions in few iterations. The adoption of a disaggregated Bundle method not only improves the convergence of the proposed approach but also provides information that are suitably exploited for generating a feasible solution of the primal problem and for obtaining an optimal hydro scheduling. A comparison between the proposed Lagrangian approach and other ones, based on subgradient and Bundle methods, is presented for a simple yet reasonable formulation of the Hydrothermal Unit Commitment problem
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