1,720,959 research outputs found
Key Parameters Calibration and Benefits Evaluation of a Closed Loop Performance Monitoring System.
No full textThe paper presents results from field validation of a closed loop performance monitoring system installed on several units of a refinery plant. The system supervises more than 1200 base control loops and evaluates performance periodically, after scheduled data acquisitions followed by off-line analysis. The first point taken into account is a comparison between verdicts issued by the system and indications by control operators: the large number of issued verdicts indicating scarce performance, but considered still acceptable by operators, results practically in False Alarm and forced to revisit the criterion adopted to classify a response as excessively oscillatory. New threshold values for the widely used Hägglund criterion (1995) were found and similar criteria were proposed and compared in order to match operators practical indications. The efficiency of criteria and threshold values depend on the type of loop (i.e. flow, pressure, level or temperature). The second point examined concerns validation of valve stiction diagnosis: indications from the monitoring systems are compared with evidence before and after plant shut down. Results confirm that oscillations in valves indicated as sticky disappeared after the operation, while many valves which underwent the maintenance procedure on the basis of a time schedule did not require it. Therefore, a systematic application of diagnostics tools for maintenance scheduling would be beneficial in order to focus on real needs and avoid unnecessary revision cost
Implementation, Parameters Calibration and Field Validation of a Closed Loop Performance Monitoring System
No full textThe paper illustrates the main features of a performance monitoring system which supervises more than 1200 loops of refinery plants. The system analyses data recorded by the DCS during routine operations and originates verdicts about the performance of control loops; also, indications of low performance causes and different strategies to adopt (retuning, valve maintenance, upstream actions) are given. First, the architecture of the system is illustrated, and characteristics of modules which accomplish different tasks of data acquisition and transfer, system configuration and priority assignment, performance analysis and verdicts emission, database query and operator support, are described. A synthesis of main techniques adopted in the system for stiction detection, process identification and performance evaluation, is also reported. The procedure for calibration of threshold values of key parameters, in order to match verdicts issued automatically by the system with operators evaluations and to avoid false alarms, is also discussed. Examples of results achieved from field validation are then presented, with illustration of loop performance before and after actions suggested by the monitoring system
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Get PDF“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
Get PDFWe 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
Get PDFWe 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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