1,720,968 research outputs found
Numerical Investigation of AC Losses in Multifilamentary MgB2 Wires
No full textMagnesium diboride (MgB2) is classified as a medium-temperature
superconductor, distinguished by its unique material properties that
render it exceptionally suitable for a diverse array of applications,
including those in industrial, medical, and large-scale scientific (”big
science”) fields. Its critical temperature of 39 K positions it as an
ideal candidate for applications that leverage synergy with liquid
hydrogen, an increasingly pertinent energy carrier in the mid-2020s,
particularly within sectors such as aerospace propulsion, maritime
transport, and energy transmission. However, the escalating de-
mand for superconducting technologies, coupled with the expanding
spectrum of possible alternating current (AC) applications, neces-
sitates a comprehensive optimization of wire performance. Like all
superconducting materials, MgB2 is susceptible to losses induced by
time-varying electromagnetic fields.
This research work addresses these challenges by focusing on two
principal objectives. First, it undertakes an in-depth investigation
of the macroscopic phenomenology of AC losses, aiming to iden-
tify and elucidate the various factors contributing to these losses in
multifilamentary MgB2 wires, particularly those embedded within
resistive and ferromagnetic matrices. A thorough understanding of
these loss mechanisms is essential for mitigating losses in industrial
applications that operate at frequencies exceeding those typically
associated with superconductivity (50-400 Hz). Second, the devel-
opment of robust numerical tools is imperative for facilitating the
analysis and optimization of MgB2 wires, thereby enabling paramet-
ric studies and optimization sweeps aimed at minimizing losses in
AC applications.
Through this comprehensive investigation, three distinct models
have been developed to conduct detailed analyses of AC losses in
MgB2 wires, with particular emphasis on those containing magnetic
stabilizing materials
Membrane adattive in ambito storico: una proposta per la copertura della Rocca Brancaleone a Ravenna
No full textL’articolo riguarda la progettazione di una tensostruttura a membrana in un contesto di valore storico-architettonico. Le tensostrutture si adattano a coprire spazi in ambiti di pregio per il loro ridotto impatto visivo, per la loro efficienza strutturale e per la loro grande funzionalità. Affinché strutture di questo tipo possano essere inserite in modo corretto è necessario tuttavia che la loro conformazione sia attentamente studiata in relazione al contesto in cui si trova. Questo studio si inserisce nella logica dell’adattamento allo spazio esistente e della flessibilità e reversibilità dell’intervento ed evidenzia le potenzialità espressive e funzionali delle membrane mobili, o adattive, ripercorrendo il percorso progettuale dalla ricerca della forma (form finding) alla ideazione del tipo di movimentazione e alla definizione della sagoma di taglio (pattern cutting). Affinché la membrana possa passare dallo stato di ripiegamento a quello di dispiegamento e quindi a quello di esercizio, in cui la superficie deve essere rigida, è necessario applicare un’opportuna deformazione al materiale. Tale deformazione genera lo sforzo di trazione interno che presollecita la tela e le dà una forma stabile. La soluzione trovata per la copertura della Rocca Brancaleone di Ravenna riguarda una forma innovativa a ventaglio, con una movimentazione del tutto originale. Lo sviluppo del progetto con le soluzioni tecniche di dettaglio, benché già definito, non viene mostrato per ragioni di riservatezza, ma ci si sofferma ampiamente sulla concezione preliminare e sui principi che hanno guidato le scelte adottate, in modo che questo lavoro possa fungere da modello per interventi futuri
Mechanical Characterization of Sustainable Mortars with Recycled Aggregates from Construction and Demolition Wastes: An Experimental Investigation
No full textThe use of recycled aggregates in the production of concrete and mortar represents a sustainable way to reintroduce these constituents—which are typically treated as waste and disposed of—in the production chain, providing new value to potentially polluting materials. The effect of recycled aggregates has been widely studied in the production of concrete due to the directions of National Standards in Italy; however, their role in the manufacturing of mortar must be investigated further due to the high variability that can be observed in the literature. In particular, the aim of this paper is the mechanical characterization of sustainable mortars defined by different mix designs and different binders, in which the aggregates are gradually replaced by a recycled sand obtained from the grinding of construction and demolition wastes, which could include old concrete, clay bricks, and minimal amounts of other kinds of residual materials. This investigation is carried out through experimentation, taking into account four different mortar compositions defined by an increasing percentage of recycled constituents. Virgin aggregates are also studied for the sake of comparison. The results, accomplished through a three-point bending test and an unconfined compression test, show that it is still possible to maintain acceptable mechanical properties by using these wastes as aggregates in spite of a decrease in the analyzed values. In general, the mean reductions with respect to the use of natural aggregates are about 30–40% and 35–55%, respectively, for compressive and flexural strengths. It should be highlighted that some experimental sets provide a maximum reduction of 70–80%, but the results are still within the limitations of the standards. This aspect can be considered to be a good compromise since the production of this sustainable construction material can represent a solution that is able to reduce the extreme exploitation of natural resources, the pressure on landfills, and the consumption of energy, which are related to the construction industry
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
Analysis of AC Losses Due to Current Ripple in MgB Wires With Helicoidal Transformation Method
No full textMagnesium diboride (MgB2) presents a promising solution for efficient, reliable, and cost-effective long-distance direct current (DC) power transmission. Its low cost, high critical temperature (39 K), and compatibility with liquid hydrogen cooling are particularly advantageous. However, High Voltage Direct Current (HVDC) superconducting cables face electrodynamic losses due to current ripples from AC/DC conversion, necessitating meticulous cryogenic system design to mitigate these losses. This study employs Finite Element Method (FEM) analysis to investigate the electrodynamic losses in MgB2 wires under varying current conditions, utilizing a 2D Helicoidal Transformation Method-based model and the open-source solver GetDP. The analysis includes the nonlinear ferromagnetic properties of the wire’s Nickel and Monel matrix, revealing that loss dynamics are significantly influenced by the electromagnetic behavior of the stabilizers. By assessing loss contributions across different materials at operational frequencies typical for DC cables, the study provides insights for optimizing MgB2 superconducting wires in DC power transmission applications
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