1,720,963 research outputs found
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
A Novel Testing Methodology to Predict the Endurance of Ball Joints in Absence of Lubrication at High Temperature
No full textThe enhancement of the operational flexibility of axial expanders can be obtained through the implementation of Nozzle Guide Vane (NGV). This design architecture includes moving parts typically sustained by ball joints, whose wear behavior might be important to define the maintenance interval of the expander and define its operational availability. This is especially true when considering challenging loading and temperature conditions. Usually, tribological tests are performed by pin-on disk or similar test methods. However, these techniques neglect important factors as actual sliding zone and contact morphology, which can be fundamental for ball joints.
This work deals with the design of an innovative experimental test procedure for the characterization of the tribological behavior of ball joints considering the actual operating conditions of a NGV at 500°C. The core of the methodology is a customized test bench specifically designed to investigate actual commercial ball joint in field conditions. Details on the design phase and on the commissioning of the experimental set-up are given. The results of the experimental campaign performed on this novel test bench are presented: the chosen test matrix explores a wide spectrum of load and sliding speed. Specimen pre-load and working velocity have been scaled-up to achieve viable testing duration. The test bench was employed on three different kinds of commercial ball joints for high-temperature applications in absence of lubrication. Measurement of diametral clearance and friction in worn conditions were also performed. The results discussion allowed to choose the most suitable solution for a specific design targeting 50000 working hours
Development of Thermo-Mechanical Service-Like Testing for Supercritical CO2 Expanders
No full textThe detailed prediction of the actual life expenditure of expanders operating in power plants has become a common topic of investigation. In the current energy market axial expanders are subjected to frequent load change and to the exposure to higher temperatures. The proper prediction of their life expenditure determines operability and availability improvements through faster start-ups and longer maintenance intervals. A common strategy to achieve this objective has led in the last years towards the development of progressively more and more detailed “service-like” tests aimed at recreating the actual loading conditions in terms of strain and temperature profiles. Recently the need to face the challenge of energy transition through the introduction of advanced cycle employing supercritical carbon dioxide is requiring to further improve this kind of tests by including the effect of environmental attack through corrosion and carburization. This work addresses this topic by presenting the development of customized specimens and of a testing campaign able to evaluate the degradation of creep and fatigue capabilities when high temperature carbon dioxide exposure occurs. After a short introduction on the state of the art, the specimen design will be detailed with FE simulation evaluating stress and temperature distribution in specimens and key insights will be given regarding the design of a proper test matrix and the essential theoretical framework for the interpretation of the results of a testing campaign
Efficient NMPC strategies for thermal stress control of steam turbines
No full textThis paper proposes an advanced control strategy for steam turbines characterized by frequent load variations based on a nonlinear model predictive control (NMPC) algorithm. In this specific scenario, turbines are subject to frequent variations in operating conditions and repeated start-ups that cause significant thermal stress. The main purpose of the developed NMPCs is to effectively regulate the generated electric power while limiting the rotor thermal stress. Collocation methods are adopted to improve the computation time required to solve the optimal control problem and then compared with a standard multiple-shooting approach. The proposed formulation includes time-varying constraints and nonlinear disturbances that vary within the prediction horizon of the dynamic module of the controller
Mechanical Behaviour of Variable Nozzle Guide Vane Systems Based on Full-Scale Testing
No full textA full-scale test bench for the analysis of frictional and modal behavior of Nozzle Guide Vanes (NGV) is an advanced tool enabling high design accuracy for these components equipped in an increasing number of turboexpanders. This subassembly is a key feature enabling operational flexibility for the
expander. Great attention must be paid during the NGV’s design to the natural frequencies of its kinematic chain, which are influenced by internal clearances and by friction. In this paper the results of a testing campaign performed on an NGV assembly employing actual blade geometry are presented together with details concerning the test bench commissioning and set-up procedure. The testing campaign involves three different combinations of blade orientation and pre-load corresponding
to typical design conditions of the expander. In addition, two different bushing clearances values corresponding to worn out conditions were investigated. The measurements of the global friction coefficient based on actuator force detection are summarized. After that, the reconstruction of mode shapes based on experimental modal analysis is explained. The results highlight the importance of loading conditions on the actual value of friction force and their influence on blade natural frequencies. The testing campaign was used to properly validate Finite Element Models to be used for further investigations
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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