1,720,958 research outputs found
Sviluppo di una metodica sperimentale per la valutazione di fenomeni di cementazione
No full textIl presente rapporto illustra i risultati di un primo studio condotto sugli effetti dell’esposizione di un materiale ferroso ad un’atmosfera cementante.
Lo studio ha la finalità di comprendere se ed in che misura prodotti commerciali a base grafite, impiegati come lubrificanti di trafilatura, comportino, a seguito di fenomeni di diffusione del carbonio, una alterazione della microstruttura dell’acciaio con cui vengono a contatto durante il processo produttivo.
I prodotti testati provocano un marcato stato di alterazione della microstruttura del materiale che consiste nella formazione di fasi di differente natura, la cui entità e distribuzione lungo lo spessore del provino è strettamente legata alle condizioni operative di prova e al materiale metallico utilizzato
EPR/ENDOR CHARACTERIZATION OF RADICALS PRODUCED IN THE PHOTOPOLYMERIZATION OF A DIMETHACRYLATE MONOMER
No full textThe formation of trapped, radicals under UV irradiation of ethylene glycol dimethacrylate in the presence of different amounts of photoinitiator, as well as radical decay at different temperatures (90-150-degrees-C) after the end of irradiation, have been studied by electron paramagnetic resonance (EPR) spectroscopy. A fitting procedure of the EPR signals revealed that the nine-line EPR spectrum can be attributed to the propagating radical, undergoing a fast exchange process between two conformations. This radical also gives an ENDOR spectrum even at room temperature, thus suggesting that the polymer structure is essentially solid. At least one different radical species is present in highly photo-cross-linked samples. At temperatures above 100-degrees-C, the hyperfine structure of the nine-line EPR spectrum is partly washed out, owing to a spin-spin exchange phenomenon between radicals. This becomes more evident with increasing degree of polymerization and cross-linking during radical decay kinetic runs and also affects the rate of exchange between the two radical conformations
ELECTRON-PARAMAGNETIC-RESONANCE AND ELECTRON-NUCLEAR DOUBLE-RESONANCE CHARACTERIZATION OF RADICALS IN PHOTOPOLYMERIZED MULTIFUNCTIONAL METHACRYLATES
No full textPropagation radicals generated during the photopolymerization and photo-cross-linking of a trimethacrylate and a vinylmethacrylate monomer have been characterized by EPR and ENDOR spectroscopy at different temperatures. Also, radical decay has been investigated at 363-423 K. The EPR spectral shape reflects a fast exchange process between two radical conformations and is sensitive to the mobility of the polymeric structure surrounding radicals. ENDOR spectra show H-1-matrix lines and a band around 45 MHz, which has been attributed to the interaction of the unpaired electron with the hydrogen nuclei of a freely rotating methyl group. Radical decay and dynamic phenomena involving radicals have been interpreted in the light of a dispersive kinetic model, which allows the evaluation of useful parameters for polymer characterization
Electron paramagnetic resonance spectra of CeO2 catalyst for CO oxidation
No full textThe EPR spectra of freshly prepared CeO2 samples as well as of samples used as a catalyst in the oxidation of CO to CO2 are reported. Attribution of these patterns to oxygen species O-2(-), O-2, O- or to Ce3+ ions is discussed and dynamic phenomena involving these species are described. Bottlenecked systems between conduction electrons and Ce3+ ions are envoked to explain the observation of the Ce3+ EPR spectrum up to temperatures of about 370 K. Oxygen-deficient systems are obtained when the sample is used as a catalyst for CO oxidation in the presence of pyrex or quartz powder as a diluent, showing that the latter can play some role in stabilizing such species
Resistenza a corrosione ad alta temperatura di acciai in presenza di sali fusi di vanadio
No full text
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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