1,720,964 research outputs found
An investigation on corrosion protection layers in pipelines transporting hydrocarbons
Full text linkChemical reactions between carbon steel, water and chemical species produce corrosion layers
(scales) on the internal surface of pipelines transporting hydrocarbons. Scales act as a diffusion barrier and
prevent the progress of corrosion, a dangerous failure initiator. The protective film (10-100 m thickness) can
be removed locally by the action of the internal flow, or by other mechanisms. Adhesion with the substrate and
the failure modes of the corrosion layer can be tested by indentation. Some results are presented of experiments
performed on specimens with scales grown in a controlled environment
Diametral compression testing of metal matrix composites
No full textFor the design and optimisation of advanced materials, the possibility of reliably testing very small amounts of material or laboratory scale simple shape specimens is particularly interesting. To satisfy such requirements, this work presents a new procedure for mechanical testing of metal matrix composites. The method is essentially a diametral compression test of cylindrical specimens and represents an improvement of the ‘Brazilian’ test. The mechanisms leading to fracture of composites have been investigated via the mechanical behaviour of different metal matrix composites (A354–SiCp A354–A12O3 short fibres) and consideration given to the role of the major parameters involved (both test and material related). The results of the diametral compression test, in terms of rupture strength have been compared with those of conventional tensile tests and characterisation of the microstructure via light and electron microscopy has been carried out. Evaluation of the results led to the conclu..
Evaluation of fluidity in Aluminium alloys
No full textThe knowledge of viscosity of alloys is a key-point for understanding and modelling their behaviour in foundry processes. The lack of experimental data, due to the difficulty in carrying out viscosity tests for metals and alloys, suggests the use of technological tests, such as the measurement of fluidity length. This paper presents the development of a device for the evaluation of fluidity length of casting alloys, and its application to commercially pure (cp) Aluminium and to some Al-Si alloys. The experimental data, obtained in temperature intervals ranging from liquidus to about 800°C, show a good agreement with the behaviour described in literature. Their elaboration, carried out according to an Arrhenius-type approach, allows an estimation of the viscosity of the alloys investigated
Su diagnosi strutturale e caratterizzazione di materiali effettuate mediante prove di indentazione non-distruttive e analisi inverse
No full textLe prove di indentazione (dette in passato di durezza) sono attualmente considerate esperimenti “quasi non distruttivi”, sempre più frequentemente utilizzati nelle analisi di diagnostica strutturale, cioè per la valutazione di parametri che possano quantificare eventuali danni o deterioramenti nel tempo con conseguenti riduzioni dei margini di sicurezza per assegnate condizioni di carico.
Nella presente comunicazione si intendono evidenziare i risultati di recenti ricerche relative a strutture metalliche ed a materiali fragili come il vetro. Tali risultati sono innovativi rispetto all’attuale stato dell’arte e sono caratterizzati dalle seguenti caratteristiche principali.
La prova viene simulata mediante analisi a elementi finiti. Le curve di indentazione rappresentano la sorgente di informazione da utilizzare. Per gli indentatori sono definite nuove forme geometriche , definite mediante procedure di ottimizzazione basate su analisi di sensibilità, cioè: con sezioni “bicircolari” per la determinazione di parametri di frattura fragile; con sezioni “ellittiche” e con indentazioni duplicate dopo rotazione per la valutazione di sforzi residui o per la calibrazione di modelli costitutivi con anisotropia.
L’analisi inversa consiste nella minimizzazione di una “funzione di discrepanza” tra risultati sperimentali e computazionali mediante un noto algoritmo di programmazione matematica (detto “trust region algorithm”) ed è resa veloce ed economica, in vista di applicazioni frequenti e ripetute, mediante una procedura preliminare di riduzione del modello, detta “proper orthogonal decomposition”, e una successiva interpolazione effettuata con “radial basis functions”.
Si utilizzano alcuni esempi per dimostrare potenzialità ed economicità dei procedimenti innovativi proposti e per confrontare l’efficienza pratica del “trust region” e degli algoritmi genetici, anche in considerazione della possibile mancanza di convessità della funzione di discrepanza. Gli effetti dei vari errori sperimentali sui risultati sono stimati mediante un approccio statistico
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
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