1,721,022 research outputs found
Applications of XAS to Cultural Heritage
No full textX-rays Absorption Spectroscopy (XAS), for its features of high elemental selectivity, spatial resolution and non- destructivity, is a useful tool to study materials that form and decorate art object and to identify different degradation processes that can occur in works of art.In this study, it will be investigated a typical phenomenon of paper alteration called foxing, which appears as spots of variable dimensions generally colored from lemon yellow to dark-brown with sharp or irregular edges. Over the years, in fact, paper undergoes a series of alterations caused both by external and internal factors leading to cellulose degradation. This degradation is one of the greatest problems for the conservation of paper supports such as archival documents, books and artistic works. Degraded papers can show an evident fragility, a general yellowing and the formation of foxing spots that can, in some cases, not only damage the aesthetic of the object, but also compromise the readability of the text or the artistic works. The understanding of the different chemical processes underlying this degradation is of great importance to prevent further damage and to choose the appropriate restoration method. The foxing spots are generated by a complex mechanism based on the oxidation of iron or copper ions (chemical hypothesis) or on micro-organism based processes (microbiological hypothesis). By XAS we have investigated the chemical foxing and in particular the iron oxidation to be able to understand the formation mechanism of foxing. Measurements were performed on ID26 at ESRF on three different kinds of samples: A) Samples prepared and aged at ICPL (Istituto Centrale per la Patologia del Libro)to simulate the foxing spotsB) Samples prepared at ESRF during the experiment to follow the foxing formation mechanism from the beginningC) historical samples to compare the results obtained from the artificially prepared samplesFirst interesting results were obtained by these measurements varying the starting iron solution [Fe(II) and Fe(III) solution were used to simulate the foxing], the solution concentration and the artificial aging process. The foxing mechanism seems to be strongly dependent from the local structure of cellulose. Moreover, these measurements gave us important indications to plan new experiments to understand in depth this complex phenomenon.INFMeeting 2004 – Genova, 8-10 giugno 2004
Interface magnetism and magnetic structure of GdN∕Fe multilayers studied by x-ray magnetic circular dichroism
No full textWe have used the element specificity of x-ray magnetic circular dichroism to separate the contributions of the component layers to the magnetization and local magnetic structure of artificial nanoscale ferrimagnetic multilayers GdN/Fe. The Fe layers, by strong antiferromagnetic interlayer exchange coupling, not only magnetize a narrow interface region in paramagnetic GdN but induce long-range magnetic order in the volume of the GdN layers at temperatures considerably above the Curie temperature of the bare layers (T-C(GdN) approximate to 60 K), in support of a theoretical mean- field prediction. We propose that the effect may be related to the special electronic band structure of GdN, which shows a transition from narrow-gap semiconducting to metallic conduction at T-C(GdN). In an elevated external magnetic field the GdN- and Fe-sublayer magnetic moments adopt a canted configuration. In this state the local magnetization in each GdN layer is highly nonuniform at low temperature. The interior turns its moment into the field direction almost abruptly from one atomic layer to the next in a single block. This indicates weak magnetic coupling between the interfacial and volume magnetizations in GdN. The results are at variance with the much studied "model" multilayer system Gd/Fe, where magnetic order in the Gd-layer volume appears intrinsically only significantly below the Curie temperature of bulk Gd. Furthermore, magnetization reversal in the Gd layers in a magnetic field occurs gradually on a considerably larger length scale, only if they are sufficiently thick. (c) 2006 American Institute of Physics
Extended X-ray absorption fine structure (EXAFS) characterisation of dilute palladium homogeneous catalysts
No full textHighly dilute EXAFS characterisation for the elucidation of species involved in Heck chemistry is demonstrated; the major "monomer" species of Herrmann's acetate-bridged phosphapalladadacycle is characterised and species present during the course of a 50 ppm [Pd] Pd(OAc)(2)/PBu3t catalysed Heck reaction are presented
Element-specific magnetization reversal in Fe/Ce multilayers: a study by X-ray magnetic circular dichroism and the magneto-optic Kerr effect
No full textFe/Ce multilayers are magnetically soft with coercive fields of a few Oersteds. In this artificial system, the itinerant 5d electrons of Ce are magnetically polarized by hybridization with the spin-split 3d states of Fe. To obtain an insight into the magnetization reversal process, the element selectivity of X-ray magnetic circular dichroism was used to measure the magnetization of the Ce-Sd electrons as a function of an applied magnetic field. Comparison with the magnetization curves studied by the magneto-optic Kerr effect, which averages over the whole system, revealed that the coercivity in the hysteresis of the ordered Ce-Sd moments is reduced by 50%. We propose that this is an effect of the magnetically disturbed interface or of the complex non-collinear magnetic structure of the Ce layers detected by recent experiments of X-ray resonant magnetic scattering. The results are compared to the X-ray dichroic and Kerr hysteresis loops of the multilayers Fe/La/Ce/La and Fe/CeH2-delta. These systems are magnetically harder and their coercivities are identical. (C) 2000 Elsevier Science B.V. All rights reserved
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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