1,721,059 research outputs found
Pulsating flow and heat transfer in a pipe partially filled with a porous medium
No full textA numerical study is made of pulsating flow and heat transfer characteristics in a circular pipe partially filled with a porous medium. The Brinkman-Forchheimer-extended Darcy model is adopted for the porous matrix region, which is attached to the pipe wall. The impacts of the Darcy number Da, the thickness of porous layer S, the ratio of effective thermal conductivity of porous material to fluid, R-k, as well as the pulsating frequency, beta, and the amplitude, A, are investigated. The enhanced longitudinal heat conduction due to pulsating how and the enhanced convective heat transfer from high conducting porous material are examined. The maximum effective thermal diffusivity is found at a critical thickness of porous layer. The effects of pulsating amplitude and frequency on heat transfer are also scrutinized. (C) 1997 Elsevier Science Ltd
Pulsating flow and heat transfer in an annulus partially filled with porous media
No full textA numerical study is made of heat transfer characteristics from pulsating flow in a concentric annulus partially filled with porous media. The unsteady Navier-Stokes equations with the Brinkman-Forchheimer-extended Darcy model in the porous region are solved by using finite volume techniques. Changes in convective heat transfer and in effective axial heat conduction due to pulsation are investigated over broad ranges of the relevant parameters, i.e., the thickness of the porous layer and the frequency and amplitude of pulsation. The results obtained indicate that the effective axial thermal conductivity is substantially increased by pulsation, and this augmentation is more pronounced by partial fillings of porous material
Synthesis of porous carbon electrodes for biological fuel cells
No full textBiological fuel cells potentially offer efficient clean energy conversation from biomass to electricity. One of the critical issues is to develop effective electrode structures for high-capacity and stable loading of biocatalysts (e.g., bacteria and enzymes). Porous carbons are promising if the pore structures can be tailored to maximise the capacity, efficiency and durability, which form the key objectives of this project. In this project, firstly, a 2-part polyurethane foaming system and commercial carbon fibres were used to synthesise porous carbon-fibre foams with high surface area, high electrical conductivity and high mechanical strength. The carbon-fibre foams were impregnated by phenolic resin and then carbonised to improve their electrical conductivity and mechanical strength. Moreover, the foams’ electron transfer capabilities were enhanced by surface modification using electrochemically reduced graphite oxide. To enrich mesopores for enzyme loading, the method of self-assembly of block copolymers was adopted to synthesise mesoporous carbons. Novolac-type phenolic resin was chosen as the carbon precursor and the block copolymers Pluronic P123 and Pluronic F127 were chosen as the structure-directing agents. The synthesised mesoporous carbons had a pore diameter range of 2 – 10 nm and 2 – 5 nm for P123 and F127 respectively. Mesoporous carbons derived from F127 were successfully incorporated into the carbon-fibre foams by solvent impregnation and carbonisation. The resulting hierarchical porous carbons presented meso-/macroporous structures with a much higher surface area (up to 209 m2 g−1) as compared to that of pure carbon-fibre foams (~ 12 m2 g−1). However, myoglobin adsorption tests revealed that these hierarchical porous carbons had low adsorption capacities (up to 0.028 µmol g−1 at room temperature) due to small mesopores (2 – 5 nm in diameter) present in the porous structures. The results are discussed with an aim for further development
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
Multiscale Materials Modelling: Fundamentals and Applications
No full textMultiscale materials modelling offers an integrated approach to modelling material behaviour across a range of scales from the electronic, atomic and microstructural up to the component level. As a result, it provides valuable new insights into complex structures and their properties, opening the way to develop new, multi-functional materials together with improved process and product designs. Multiscale materials modelling summarises some of the key techniques and their applications. The various chapters cover the spectrum of scales in modelling methodologies, including electronic structure calculations, mesoscale and continuum modelling. The book covers such themes as dislocation behaviour and plasticity as well as the modelling of structural materials such as metals, polymers and ceramics. With its distinguished editor and international team of contributors, Multiscale materials modelling is a valuable reference for both the modelling community and those in industry wanting to know more about how multiscale materials modelling can help optimise product and process design. Reviews the principles and applications of mult-scale materials modelling. Covers themes such as dislocation behaviour and plasticity and the modelling of structural materials. Examines the spectrum of scales in modelling methodologies, including electronic structure calculations, mesoscale and continuum modelling. © 2007 Woodhead Publishing Limited. All rights reserved.link_to_subscribed_fulltex
The Deformation and Processing of Structural Materials
No full textHaving a good understanding of a construction materialâ??s performance under different conditions is essential for helping engineers in selecting the right type of material for a job and for setting design specifications. Keeping abreast of the latest research is an important part of this. The deformation and processing of structural materials is divided into eight chapters, each one exploring a materialâ??s processing and deformation behaviour. They also consider how the microstructural composition of materials is affected by processing and what influence this has on its subsequent in situ performance. The materials and behaviours looked at in the chapters include: aluminium and its alloys; magnesium alloys; ferrous alloys; superalloys (Ni-based alloys); semisolid metal (SSM) processing of metallic alloys; plastic deformation of intermetallic alloys; metal matrix composites (MMCs); and fine grain superplasticity in SP materials. The first of its kind to give comprehensive coverage to the subject, The deformation and processing of structural materials is a valuable resource for engineers, researchers in mechanical, civil and structural engineering. © 2005 Woodhead Publishing Limited All rights reserved.link_to_subscribed_fulltex
Cost-effective and durable graphene based oxygen electro-catalysts in alkaline media
Full text linkDevelopment of cost-effective and durable catalysts for sluggish oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is imperative to promote critical energy conversion and storage technologies such as fuel cells and metal-air batteries. Low-cost non-precious metal (NPM) and metal-free (MF) catalysts are promising choices to replace commercial noble metal counterparts. However, there exist crucial challenges in developing such catalysts with comparable or superior performance to the noble metals, while ensuring effective cost reduction. Hence, the primary goal of this thesis is to design and develop low-cost graphene-based ORR / OER electrocatalysts in alkaline media, either in the form of MF catalysts or as a support / co-catalyst to NPMs. Three types of graphene-based systems were designed and evaluated.
The first system involves “MF for ORR” – Intercalated graphene/graphitic carbon nitride (GCN): It was synthesised through intercalation of graphene by GCN to enhance the electrical conductivity while maintain sufficient catalytic sites. Utilisation of hierarchically porous structures can further increase the accessible active sites and improve mass transfer. The optimised structure shows comparable ORR activity and superior durability to commercial Pt/C.
The second system is based on “NPM for ORR” – Maghemite embedded N-doped graphene framework (γ-Fe2O3/N-GF): The hierarchical N-GF substrate was firstly optimised to achieve high pore volume for rapid mass transfer, and then incorporated by an appropriate amount of γ-Fe2O3, via “one-pot” synthesis, to boost reduction potentials without compromising active site accessibility. The optimised structure outperforms Pt/C for ORR, both in activity and durability.
The third system focuses on “MF for bifunctional ORR/OER” – A P,N co-doped graphene framework (PNGF) shows almost identical activity and greater durability than commercial Pt/C for ORR and Ir/C for OER, respectively. Closely coupled first-principle simulations and experiment design show that the OER performance is strongly correlated with P-N bonds, while the ORR activity with N-doped moieties
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
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