1,720,966 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
An Optimizer Using the PSO Algorithm to Determine Thermal Parameters of PCM: A case study of grey water heat harnessing
Full text linkThe melting and freezing of Phase Change Materials (PCMs) is categorized as a moving boundary problem. For this reason the mathematical solution to study the behaviour of practical applications is only possible via complex numerical approximations. However for a preliminary design the main concern is to select the optimum thermal characteristics of the PCM storage unit, for both melting and freezing. This is to be done before the detailed design by integrating an optimization algorithm with a numerical simulation. The application of using PCMs to harness the waste heat from non-industrial grey water is investigated as a case of study. For this purpose, the 2-phase analytical solution to the Stefan problem is coupled with the particle swarm optimizer (PSO) to find the best combination of thermal characteristics within the prescribed boundary conditions of this case study. Results show that the optimum phase change temperature lies between 20 and 22 °C, depending on various sets of input parameters. At the same time the ratio of latent to sensible heat transferred by the PCM highly influences this optimum temperature for the combination of both melting and freezing. Similarly results show melting being faster and more intensive in term of latent heat charging compared to a higher sensible heat discharging while freezing
A state of art review on the district heating systems
No full textDistrict heating (DH) has been widely acknowledged as the future for urban heating, as concerns of sustainability and greenhouse gas emissions are pushing, to revamp the heating sector. Although not a new technology, DH has evolved over four different generations, and is now capable of incorporating low temperature distributed renewable heat sources. The ongoing advancements and typical characteristics of a complete grid are researched upon in this paper. The research is extended to link up these characteristics with some of the most interesting DH networks in the world. The technical configurations of these DH grids along with their regulations and policies are explored upon, to understand their evolution and uniqueness. A basic overview of the economics and social aspects are presented as well. The overall trends and results of this study show that, as fossil fuel prices fluctuate and are depleting, there is a unified effort to promote DH, especially for residential heating purposes. The characteristics of modern DH are evolving to cater for distributed renewable technologies with the aim of making the entire system carbon free and sustainable
Experimental study on the thermal performance of a grey water heat harnessing exchanger using Phase Change Materials
Full text linkTo integrate heat extraction and storage into a single unit along with decoupling of demand and supply,\Phase Change Materials (PCMs) can be used to harness heat from grey water (GW). A simple heat\exchanger linking both the GW and incoming mains cold water (CW) in a counter flow arrangement with\a PCM is experimentally tested. To enhance the thermal conductivity of the PCM, metallic copper fins are\placed throughout the cross-section of the pipes.The charging with a GW temperature of 325 K and the discharging with a CW temperature of 285 K, of\the PCM is investigated. The influence of the mass flow rates of both the fluids is investigated by varying\it between discrete values of 0.1 kg/s and 0.05 kg/s. Similarly the operation strategy of the heat exchangeris varied between the solo operation of the GW and CW compared with the simultaneous flows of both.Finally two different PCMs; with a melting temperature of 298 K (RT-25) and 315 K (RT-42) are also\tested.The mass flow rate is proportional to performance with 0.1 kg/s showing the best results but being less\influential for RT-25 as compared to RT-42. In RT-25 most heat is transferred as latent heat with a higher\phase change rate whilst RT-42 transfers sensible heat. The solo operation strategy of non-simultaneousGW and CW flow is more effective as this exchanger is meant to decouple demand and supply. The ability\of RT-25 to retain heat over the long term is also greater compared to RT-42. Ullage issues and corrosion\concerns of the metallic container and pipes are also dominant over the long-term usage of these PCMs
Numerical analysis of rectangular fins in a PCM for low-grade heat harnessing
Full text linkHarnessing waste thermal energy from greywater (GW) in non-industrial buildings is becoming necessary to reduce energy demands, make heating/cooling technologies more efficient and to increase the share of renewables in the consumption. Harnessing this low grade energy to heat incoming cold water (CW) linked with phase change materials (PCMs) would decouple demand and supply along with integrating heat recovery with storage in a single unit, unlike technologies of the past.Radially installed rectangular copper fins around the GW and CW pipes of such heat exchanger (HE) enhance the thermal conductivity of the PCM which is the biggest obstacle in this high-impulse application, with the flow rate being high only for a short duration of time. Initially an experimental test rig is used to validate a numerical model as the basis of a sensitivity analysis to find the optimum geometric parameters of the finned HE for this application. A 40 × 90 mm fin with a 10 mm pitch provides complete phase change for both melting and freezing in the constrained time duration of 900s. Compared to a non-finned geometry this optimized fin configuration enhances the effective thermal conductivity of the PCM by a factor of 1.38 for melting and 4.75 for freezing. Although the development of buoyancy induced natural convection vortices are inhibited by fins the eventual heat transfer is enhanced due to a lower overall thermal resistance compared to a non-finned configuration. The GW to CW energy transfer efficiency is 72.4% with higher fluid flow temperature increments, compared to only 47.3% for a non-finned version
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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