1,720,979 research outputs found
Surface weathering of tuffs: Compositional and microstructural changes in the building stones of the medieval castles of hungary
Full text linkVolcanic tuffs have a historical tradition of usage in Northern Hungary as dimension stones for monumental construction, Ottoman architecture, common dwellings, etc., admirable at its best in the medieval castles of Eger and Sirok. This research explores tuff deterioration in the castle walls, dealing with the mineralogical composition, microstructure, trace-element geochemistry, and microporosity of the surface weathering products and the near-surface stone substrate. The classic microscopic and mineralogical techniques–optical microscopy, SEM-EDS, and XRD–were supported by ICP-MS and nitrogen adsorption analyses. The textures and mineral assemblages of the tuffs are partly diverse, and so are the weathering characteristics, although including common features such as secondary crystallization of gypsum, swelling clay minerals, and iron oxides-hydroxides; deposition of airborne pollutants, i.e., carbon particles and heavy metals; formation of crusts and patinas; decreased surface microporosity. Nonetheless, the entity of deterioration varies, in relation to air pollution–involving changing emissions from road and rail transport–and the specific tuff texture, porosity, and durability–affecting pollutant absorption. The studied stone monuments offer the possibility to examine materials with analogue composition and petrogenesis but utilized in different environmental contexts, which allow pointing out the environmental and lithological constraints and cause-effect relationships related to surface weathering
Variability of technical properties and durability in volcanic tuffs from the same quarry region – examples from Northern Hungary
No full textVolcanic tuffs are notoriously very heterogeneous materials exhibiting a recurrent lithological diversity, which, in turn, can be associated with changing petrophysical and mechanical properties. This variability was investigated on a small scale in different Miocene acid tuffs extracted in the same quarry region, within just a few km radius from the town of Eger in Northern Hungary. They have been exploited since the Middle Ages and used for common construction and historical monuments – castles, churches, Ottoman architectures – or excavated and carved for creating wine cellars, cave houses, ritual sites, etc. These pyroclastic rocks are compositionally analogue but turn out to show unexpected major differences in texture and technical properties, which affect their resistance to decay. The rate and intensity of weathering, examined in laboratory conditions by freeze-thaw and salt attack tests, is governed mainly by the following properties: open porosity; relative abundance of pumice, crystals, and groundmass; pore-size distribution; and tensile strength. Nevertheless, open porosity – proportional to water absorption and indirectly related to mechanical performance – is considerably different among the tuff varieties, and this seems to be the most significant factor marking the diverse durability. That is questionable in case of unpredicted textural diversities, e.g., enrichment in pumice and higher concentration of groundmass. Therefore, without rejecting the importance of complementary tests, a basic and fast study involving thin-section examination and open-porosity measurement would be sufficient for providing many indications on the quality of these materials and for the selection of dimension stones for restoration of historical heritage and construction
Underground salt weathering of heritage stone: lithological and environmental constraints on the formation of sulfate efflorescences and crusts
No full textSalt weathering is one of the most damaging processes affecting stone conservation and represents an extensively debated topic in heritage science. The main subject of previous research is the built heritage, whereas other types of assets are often neglected, such as underground cultural heritage. This paper introduces an investigation of stone decay in the subterranean environment focused on salt weathering, its patterns, compositional features, and variability in time and space, aiming at finding its driving forces in the rock properties and environmental setting. Field explorations and the mineralogical analysis of salt efflorescences and crusts were integrated by the petrographic, geochemical, and petrophysical characterization of the rock substrates, a microclimate monitoring, and the chemical analysis of groundwater and rainwater. The subject of study is the underground archaeological-historical site of Yoshimi Hyaku Ana in Japan, a complex of Kofun tombs of the 6th–7th century and galleries of the WWII era. The site is affected by intense salt weathering, involving efflorescences and crusts composed of mixed soluble sulfates, mostly hydrated: gypsum, alunogen, alum-(Na), halotrichite, epsomite, polyhalite, tamarugite, thenardite, and mirabilite. They derive principally from the dissolution of rock-forming minerals and components (pyrite, glass, feldspars, etc.) from the Miocene volcanic tuffs into which the site is excavated. The tuffs show a certain lithological diversity (e.g., glass amount and chemico-mineralogical composition) that controls the space variability of salt composition. Another major influencing factor is the underground microclimate, which also affects the time variability and seasonality of salt weathering. The innermost underground areas have an extremely high relative humidity (~100%) and are essentially salt-free, whereas, nearby the site entrances, the wider fluctuations of air temperature and humidity create conditions for salt crystallization in the dry winter season and deliquescence in summer. Depending on the solubility of each salt phase, cycles of crystallization/dissolution and hydration/dehydration can occur both seasonally and in the short-term, causing severe stresses to the stone and damage
Residui di PCBs, HCB e Pesticidi Organoclorurati in Merluccius merluccius pescati nel Mare Adriatico e nel Mare Ionio
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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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