1,720,967 research outputs found
A non-invasive spectroscopic study to evaluate both technological features and conservation state of two types of ancient Roman coloured bricks
No full textThe study of both original and decaying compounds is relevant in understanding the chemistry behind the deterioration processes, above all in open museum contexts where environmental stressors affect the artefacts. In this sense, a combination of non-invasive spectroscopy techniques (Raman spectroscopy, μ-X-ray fluorescence and X-ray diffraction) was applied on an ancient Roman building (130 CE), the “Casa di Diana” Mithraeum at Ostia Antica archaeological site. The aim is to study the raw materials, manufacturing and decaying products of the two observed types of Roman fired bricks (red and yellow) that compose the building.
The present study estimates an illite raw material of carbonate-bearing marine clay likely referring to the common deposits of central/southern Italy, which contain calcite as accessory phase and a-plastic fraction constituted by quartz, feldspar and opaques. This clay material was added with volcanic temper characterised by abundant clinopyroxene and analcime (from analcimization of leucite) that are typical of the Roman Province volcanism. The firing would be probably the result of oxidizing conditions, as proved by the hematite presence. Thanks to the existence of specific neoformed mineral phases during firing it was possible to assess different temperatures ranges. In detail, the red/orange bricks, for the existence of gehlenite (formed from calcite and its reaction with silicates), were fired at 800–900 °C range; whereas, the yellow ones are characterised by the lack of gehlenite and the disappearance of illite/muscovite, which indicates firing temperature at over 900 °C.
Regarding the decaying products, the gypsum covers most of the surface of most bricks, both red and the yellow ones, but these latter are more susceptible to environmental stressors (sulphates and carbonates).
Therefore, this work points out how by integrated non-invasive approaches it is possible trace back to original firing temperature, technology of manufacture, interpreting ceramic data
Involvement of microorganisms in the formation of carbonate speleothems in the Cervo Cave (L'Aquila-Italy)
No full textMuch is known about the bacterial precipitation of carbonate
rocks, but comparatively little is known about the involvement of
microbes in the formation of secondary mineral structures in caves.
We hypothesized that bacteria isolated from calcareous stalactites,
which are able to mediate CaCO3 precipitation in vitro, play a role
in the formation of carbonate speleothems.We collected numerous
cultivable calcifying bacteria from calcareous speleothems from
Cervo cave, implying that their presence was not occasional. The
relative abundance of calcifying bacteria among total cultivable
microflora was found to be related to the calcifying activity in
the stalactites. We also determined the δ13C and δ18O values of
the Cervo cave speleothems from which bacteria were isolated and
of the carbonates obtained in vitro to determine whether bacteria
were indeed involved in the formation of secondary mineral structures.
We identified three groups of biological carbonates produced
in vitro at 11◦C on the basis of their carbon isotopic composition:
carbonates with δ13C values (a) slightly more positive, (b) more
negative, and (c) much more negative than those of the stalactite
carbonates. The carbonates belonging to the first group, characterized
by the most similar δ13C values to stalactites, were produced
by the most abundant strains. Most of calcifying isolates belonged
to the genus Kocuria. Scanning electron microscopy showed that
dominant morphologies of the bioliths were sherulithic with fibrous
radiated interiors. We suggest a mechanism of carbonate crystal
formation by bacteria
EVIDENCE FOR CRUSTAL ASSIMILATION, MIXING OF MAGMAS AND A 87sR-RICH UPPER MANTLE. AN OXYGEN AND STRONTIUM ISOTOPE STUDY OF THE M.VULSINI VOLCANIC AREA, CENTRAL ITALY
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
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