1,721,041 research outputs found
Preliminary investigation of Li4SiO4 pebbles structural performance
No full textOne of the main purposes of a breeder blanket is to remove the heat produced in the blanket by the fusion reaction neutrons, and to breed the tritium required to sustain it. To achieve these requirements, several breeder materials (solid or liquid lithium-bearing ones) have been investigated in the past decades. To date it has not yet been possible to identify a stable material, with high thermal conductivity and melting point. This paper deals with the mechanical characterization of the lithium orthosilicate (Li4SiO4) in form of pebbles, produced at the University of Pisa at room temperature by a drip casting forming technique, starting from an aqueous suspension of Li4SiO4 precursor prepared by a sol-gel synthesis method. To investigate also numerically, by means of FE code, the breeder blanket behaviour, it is of meaningful importance the mechanical characterization of such pebbles. To the purpose, either static or cyclic uniaxial compression tests, without radial constraints, have been performed on several produced pebbles of about 1.5 mm diameter in order to determine the collapse and crushing loads and the stiffness. Moreover, the carried-out post-test SEM examination allowed to evaluate the failure mode and the crack shapes on the contact surface. Results show the influence of the elastic properties and matrix flaw population on the crushing load. The pebbles produced by the sol-gel method showed also a high strength, the value of which is comparable to that of the pebbles obtained by melting process
Feasibility of Li4SiO4 pebbles by drip casting and preliminary characterization
No full textOpen issues for fusion reactor technology are related to the breeder material to be used for the nuclear fusion reaction. Despite in the last decades several studies were carried out, the selection, characterization and reliability of breeder material are still open issues. In this study, the attention is focused on the production of lithium orthosilicate (Li4SiO4) by means of drip casting method. The feasibility of this method was verified using an experimental rig designed and constructed purposely at the Pisa University, Department of Civil and Industrial Engineering (DICI). The green pebbles were produced starting from a suspension of Li4SiO4 precursors (i.e. LiOH and Si(OCH2CH3)4) prepared by sol-gel method. These pebbles were dried at 40 °C for 4 h, and then sintered in air at 900 °C for 10 h. The morphological and physical properties of the obtained pebbles were analyzed by scanning electron microscope (SEM), X-ray and compression tests. The X-ray results showed the main characteristic peaks of Li4SiO4 crystalline phase and small peaks attributable to calcium metasilicate, while the SEM analysis showed a homogeneous and uniform structure of the pebbles. The obtained preliminary results showed the feasibility of dripping at room temperature and provided further useful information for the optimization of the process
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
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
Investigation of Myriophyllum Aquaticum HTC: Reaction Pathways & Compound Identification
No full textHydrothermal Carbonization (HTC) represents a promising green technology for converting various biomass feedstocks into valuable hydrochar and liquid products. In this study, the HTC process of Myriophyllum aquaticum Verd., highly diffused in Tuscany (Italy), was investigated varying the process temperatures and the holding times. Indeed, it is one of the world's most troublesome invasive aquatic weeds, impacting not only the quality of water but also contributing to habitat deterioration; therefore, several management practices are required to address the problem. This research focused on obtaining preliminary experimental data to be further implemented in a lumped kinetic model to elucidate the reaction pathways leading to the formation of primary hydrochar and liquid compounds responsible for secondary hydrochar production. To figure out the HTC liquid phase composition and the organic compounds responsible for secondary hydrochar formation, the High-Performance Liquid Chromatography (HPLC) analytical technique was employed. This technique allowed to identify and quantify some of key chemical components present in the HTC liquid phase, i.e., sugars and furans. Moreover, the future integration of a lumped kinetic model and advanced analytical techniques not only will enhance the understanding of the Myriophyllum aquaticum HTC process but will also provide valuable insights into the optimization of HTC conditions for biomass conversion and resource recovery
Epoxy composites based on low-cost carbon filler derived from hydrothermal carbonization of waste
Full text linkDifferent kinds of composites based on polymer matrix are present on the market. In particular, composites based on epoxy resin are used as high-performance polymers due to their excellent mechanical properties, chemical resistance, thermal stability and low cost production. Recently, in composites production the attention has been focused on the study of materials derived from biomass and organic waste to be used as filler. Hydrochar is a carbonaceous material obtained from hydrothermal carbonization (HTC) of biomasses and organic waste. During HTC biomass is carbonized in an aqueous environment at temperatures of 180-250 °C under saturated pressure (autogenous or provided by a gas) for several hours. For its characteristics, hydrochar can be potentially used as filler in composite materials in view of the growing concern about environmental sustainability. In this work, hydrochar obtained from hydrothermal carbonization of green waste was used as filler for the preparation of diglycidyl ether of bisphenol A-type epoxy composite materials. Two different epoxy matrices were used; the content of hydrochar was varied between 5 and 15 wt%. The resulting samples were characterized by morphologic and mechanical analyses, and electrical properties were evaluated. The addition of hydrochar to epoxy resins resulted in a slight increase of the elastic modulus, although there was a decrease in tensile strength and toughness. Moreover, electrical properties of epoxy resins were not significantly modified by the addition of hydrochar. Therefore, the study provided encouraging results for the production of innovative hydrochar-based epoxy composites, allowing the recycling and re-use of industrial waste
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