1,720,961 research outputs found
Sparce Subspace Learning and Characteristic Based Split for Modelling Artificial Ground Freezing
No full textArtificial Ground Freezing technique is often used to build underground structures, such as urban tunnels. modeling activities are necessary to optimize the design of the freezing process. The paper introduces a numerical solution of the phenomenon of water freezing for various soil types, using the finite element method combined with the model order reduction technique. In particular, the characteristic based split method is used as a base to build a model reduction scheme by means of Sparse Subspace Learning. The aim of this study is to develop a mathematical model able to carry out numerical results with negligible CPU time, by varying three parameters reproducing the characteristics of the soil, i.e. the porosity, the Darcy number and the Rayleigh number. The obtained results show how the soil parameters influence the freezing process and the dimension of ice wall
Proper generalized decomposition for geothermal applications
No full textIn this paper, the proper generalized decomposition (PGD) is presented for the solution of the parametric heat equation for an actual geothermal application. The physical domain is composed by ten geothermal probes inserted in the ground. The temperature profile along the probes is imposed as a parametric Dirichlet condition. The soil properties are parameters difficult to estimate in real life applications, and a parametric analysis is often required. In order to analyse their influence on the geothermal system. Moreover, another problem in modelling geothermal systems is the construction of the 3D mesh near probes. By employing PGD techniques, it is possible to overcome the large computational costs, because PGD is an a priori model reduction method that allow reducing the numerical complexity of the problem through separation of variables and parameters. In addition, the standard PGD strategy fails to converge for the case analysed in this paper, therefore an alternative strategy based on residual minimization idea has been used. In the present work, the authors analyse the effects of the probes presence on the soil temperature, by means of the developed PGD model
A general numerical procedure for solidification and melting in porous media and free fluids
No full textA numerical model of the solid/liquid phase change problem in porous media and free fluids is presented in this paper for the first time by employing a modified version of the generalized porous medium model, in 2D and 3D, solved by means of the Characteristic-Based-Split (CBS) scheme. The proposed procedure is based on the solution of one set of equations to describe different phenomena: natural convection in porous media, solidification and melting both in porous media and in free fluids. The generalized model has been modified to incorporate the apparent heat capacity, source term and pseudo-viscosity methods in order to reproduce phase change phenomena. Two versions of the algorithm, the Semi-Implicit (SI) and the Quasi-Implicit (QI) schemes, have been developed to solve the governing equations, and validated against numerical and experimental data available in the literature. The two schemes have been compared in terms of accuracy and efficiency for the solution of the benchmark problems
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
Effect of Particle Size and Starch Gelatinization on the Mechanical and Metallurgical Performance of Jarosite Plus Blast Furnace Sludge Self-Reducing Briquettes
Full text linkJarosite and blast furnace sludge (BFS) are two of the main wastes from hydrometallurgical zinc production and iron production by blast furnace, respectively. Jarosite is a hazardous material that can, however, be reused in the steel industry after the recovering of the iron contained within it through carbothermal reduction in which BFS is exploited as a reducing agent. Yet, both wastes have a powdery nature that makes it necessary to agglomerate them for industrial use. On the other hand, despite the advantages of producing a self-reducing product, the particle size of the starting powders and the level of gelatinization of the binder could play a crucial role on the mechanical and metallurgical performance and, consequently, on the industrial applicability of the briquettes. Accordingly, two powder particle sizes (very fine sand vs. coarse silt) and three degree of corn starch binder retrogradation (10%, 30% and non-gelatinized starch) were used to produce briquettes, and their influence was studied by experimental and statistical investigation. The results showed that gelatinization plays the main role on the mechanical properties of briquettes, while particle size affects both density and reduction behavior; in particular, although all the mixtures were able to recover iron at 950 °C the most optimal mixture were obtained by using a granulometry of 63–125 μm for jarosite and less than 63 μm for BFS, while the local maximum of mechanical performance was obtained for a 30% starch retrogradation level
Comparison of the reduction behavior through blast furnace sludge of two industrial jarosites
Full text linkJarosite is the main by-product of the zinc hydrometallurgical Roast-Leach-Electrowin (RLE) process and contains 35-50 wt% of iron oxide which can be recovered for low-grade iron production. As a follow-up of the positive experience of an industrial jarosite reduction by using blast furnace sludges, this paper proposes the same procedure applied to another industrial jarosite different in S, Pb, Ca and Zn concentration, with the aim of investigating the effect of the origin of the jarosite on the best BFS/jarosite ratio to be implemented in the production of self-reducing briquettes. Thermogravimetric coupled with differential scanning calorimetry analysis has been conducted in argon atmosphere on three BFS/jarosite/quartz mixes to replicate the same C/Fe2O3 ratio (0.131, 0.261, 0.523) and basicity (0.504) used in the previous investigation. Coherently with the results obtained with the first jarosite (J1), also for the new jarosite (J2), the highest iron oxide reduction was obtained for a C/Fe2O3 ratio of 0.261. Consequently, the reducibility of jarosite plus blast furnace sludge is not affected by the chemical composition of the starting jarosite from the point of view of the overall iron reduction yield
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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