1,720,961 research outputs found
Optimization of a sensible heat cascade energy storage by lumped model
No full textIn this study, the concept of exergy is used to analyze and optimize a sensible heat cascade thermal energy storage system which is developed for storing exergy and later using it efficiently. The system is composed of a liquid-gas heat exchanger, an electrical heater, an insulated vessel, a large water bath as a storage liquid and air as the system gas. The units that should be improved are determined by evaluating the irreversibilities caused by viscous losses in the heat exchanger, heat transfer occurring in the storage, electrical heating, removal processes and mixing of the hot gases at the exit of the storage process with ambient air. First and second law efficiencies and irreversibility sources of the system are compared with the thermal energy storage system's having a unique energy resource. Removing time, optimum storage time and the number of transfer units of the heat exchanger are also determined for different operating conditions by minimizing the irreversibilities in the system. (C) 2002 Elsevier Science Ltd. All rights reserved
Review of proton exchange membrane fuel cell models
No full textIn the present study, fuel cell models are described in the light of the open literature. Proton exchange membrane fuel cell (PEMFC) components and its functions are introduced and explained briefly. The state of the art of fuel cell modeling is presented. Comparisons of both modeling and experimental studies are also presented in tables. Governing equations and assumptions are briefly reviewed and presented for PEMFCs. (c) 2005 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved
Entropy generation due to flow across the abrupt contraction of pipe joints
No full textThe flow experiencing the abrupt contraction suffers from the viscous dissipation due to vast change in flow field across the plane of contraction. In the present study, simulation of flow field and entropy generation rate due to viscous dissipation are carried out for different upstream Reynolds numbers. The flow situation is considered to be isothermal to avoid the influence of heat transfer on the entropy generation rate. A control volume approach is introduced when discretizing the governing equations of flow. In order to secure the grid independent solution the grid independent tests are conducted. It is found that overshooting of axial velocity occurs along the symmetry axis across the plane of contraction. Entropy generation rate enhances with increasing Reynolds numbers. The location of maximum entropy generation rate becomes almost identical for all Reynolds numbers considered in the present study. (C) 2008 Elsevier Ltd. All rights reserved
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
Simulation of combustion in a coal-fired boiler with a fixed bed
No full textIn this study, steady-state combustion in boilers with a fixed bed has been investigated. The solution method and the discretization of the governing equations of two-dimensional turbulent reactive flow in the combustion chamber and one-dimensional coal combustion in the fixed bed are explained. Control volume and finite difference methods are used in the discretization of the equations in the combustion chamber and in the fixed bed, respectively. Kinetic calculations are employed in the solution of turbulent reactive flow equations in the combustion chamber The combustion of coal particles in the fixed bed is ruled by the reaction-controlled mechanism. The distributions of temperature and some of the chemical species through the combustion chamber and the fixed bed are presented. Also, the variation of coal particle size with the fixed bed height is given
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
- …
