1,721,086 research outputs found
Calcium phosphates crystallized on Carrara marble after phosphate-based consolidating treatment
Full text linkDiammonium hydrogen phosphate (DAP, (NH4)2HPO4) solutions have been introduced in the conservation field as a new inorganic-mineral treatments to consolidate or protect decayed carbonatic stone materials of historical monuments [1]. The treatment forms calcium phosphates through a dissolution and re-crystallization reaction, which takes place between hydrogen phosphate groups of the reagent and calcium ions of calcite of the substrate. Calcium phosphates nucleate on calcite grains with a pseudomorphic replacement reaction, and form a crystal network able to restore the lost cohesion of the microstructure. Despite the high number of studies on the crystallization of calcium phosphates and their formation on the surface of carbonatic substrates, only a few studies explored the formation of calcium phosphate phases on marbles treated with DAP and using calcite of the substrate as unique source for calcium ions [2-4]. Previous studies revealed a non-stoichiometric reaction that lead to the formation of a mixture of phases, each one characterized by different Ca/P molar ratio, solubility and stability [4]. In this study, we carry out a non-destructive synchrotron radiation grazing incidence X-ray diffraction (SR-GIXRD) investigation on DAP-treated marbles to determine how the mineralogical composition of the stone substrate affects the crystallization of stable and metastable calcium phosphates. The analyses were performed on Carrara marble specimens treated by capillarity by 0.76 M DAP solutions. Our results indicate that the presence of compositional micro-heterogeneity of Carrara marble favours the formation of specific phases. In general, the composition and the localization of the phases directly depend on the availability of free Ca2+ ions. Dicalcium phosphate dihydrate, a calcium phosphate with a low Ca/P molar ratio, is formed on carbonatic phases with a low Ca content, such as dolomite grains and Mg-containing veins. Octacalcium phosphate (OCP, Ca8(HPO4)2·5H2O) and poorly-crystalline partially-substituted hydroxyapatite (HAP, Ca5(PO4)3OH) are the foremost newly-formed phases when the substrate is mainly composed by calcite.
This study shed light on the potentialities of SR-GIXRD as a powerful non-destructive tool for the diagnostic of Cultural Heritage objects, since it allows investigating the conservation history of stone materials with an in depth evaluation of DAP consolidating processes [5].
[1] M. Matteini, S. Rescic, F. Fratini, G. Botticelli Int. J. Archit. Herit. Conserv. Anal. Restor. 2011, 5, 717.
[2] M. Kamiya, J. Hatta, E. Shimada, Y. Ikuma, M. Yoshimura, H. Monma Mater. Sci. Eng. B 2004, 111, 226.
[3] S. Naidu and G. W. Scherer J. Colloid Interface Sci. 2014, 435, 128.
[4] E. Possenti, C. Colombo, D. Bersani, M. Bertasa, A. Botteon, C. Conti, P. P. Lottici, M. Realini Microchem. J. 2016, 127, 79.
[5] E. Possenti, C. Colombo, C. Conti, L. Gigli, M. Merlini, J. R. Plaisier, M. Realini, G. D. Gatta Appl. Phys. A 2018, 124, 383
All’origine dei mestieri: attività professionali e strutture sociali in comunità alto-medievali in Italia. Un’indagine bioarcheologica applicata a due necropoli di cultura longobarda
Full text linkNel periodo dell’Alto Medioevo e, nello specifico per le popolazioni barbariche, le aree funerarie rappresentano una delle maggiori fonti di conoscenza. I dati ricavati dalla contestualizzazione bioarcheologica dei due siti oggetto di studio di questa tesi di dottorato sono descritti nelle pagine seguenti con lo scopo di rispondere ad alcune domane principali: quali sono i possibili limiti e le eventuali risorse offerte dall’indagine bioarcheologica? Quali informazioni si possono aggiungere in merito ai rapporti sociali inter- e intra-popolazionistici? In quali casi e come è possibile indagare le attività occupazionali delle popolazioni umane antiche? La rappresentazione del defunto e il suo ruolo sociale è comune in altri contesti coevi? È possibile, infine, ricreare un modello di ricerca che risponda a queste domande e che possa essere usato anche per altri contesti funerari?
Punto di partenza dell’indagine presentata in questo progetto di dottorato sono le collezioni scheletriche. Il singolo individuo inumato e, quindi, scheletrizzato costituisce il principale e più diretto indicatore della comunità di appartenenza. Le tematiche affrontate partono, quindi, dalla contestualizzazione sociale e dalle attività professionali presenti nelle fonti scritte e nei rinvenimenti archeologici nel periodo post-classico e alto medievale (Capitolo 1). Nel Capitolo 2 vengono presentati i siti in esame: la necropoli di Povegliano Veronese (datata tra la fine VI e gli inizi dell’VIII secolo) e quella di Selvicciola (metà IV – inizi VIII secolo). Nella parte dedicata a questo ultimo sito, la sistemazione della documentazione archeologica e il riesame della collezione scheletrica hanno permesso di dare una lettura aggiornata delle datazioni dell’area funeraria e dei corredi. L’indagine bioarcheologica di questo lavoro parte dallo studio delle due collezioni cimiteriali per un totale di 155 individui. Attraverso l’indagine antropologica si approfondiscono tematiche legate allo stress occupazionale e ai suoi effetti. Il Capitolo 3 ha lo scopo di illustrare gli scopi della metodologia bioarcheologica soffermandosi sulle possibili domande che possono essere poste al fine di indagare le attività occupazionali nelle popolazioni umane antiche, introducendo la metodologia di studio. Quindi, nel Capitolo 4 i risultati delle indagini antropologiche vengono presentati e contestualizzati. Al fine di valutare possibili differenze intra- e inter-popolazionistiche è, quindi, l’integrazione dei dati numerici derivati dalle misurazioni e dalle eventuali paleopatologie con le informazioni archeologiche ed etnografiche. Il primo aspetto ha lo scopo di indagare eventuali differenze negli stili di vita da una popolazione alloctona e una autoctona all’interno della comunità sepolta a Povegliano Veronese. Ugualmente a Selvicciola verranno indagate le differenze sociali tra le sepolture che permettono di identificare una differenza etnico-culturale. È necessario specificare che le differenze tra individui maschili e femminili si concerteranno tra le sepolture identificate sotto l’aspetto cronologico e culturale e che, quindi, possono essere inseriti all’interno di un gruppo verosimilmente distinto da un altro presente nella stessa comunità. Infine, possibili confronti si concentreranno tra le due popolazioni
Crystallography and Cultural Heritage: study of caoxite formed after a conservation treatment
No full textIn Cultural Heritage field, whewellite (CaC2O4•H2O - COM) and weddellite (CaC2O4•(2+x) H2O - COD) play a relevant role for a twofold reason: they are the main components of a particular kind of film found on the surface of many works of art and they also occur in a conservation treatment for carbonatic substrates [1], due to the reaction between ammonium oxalate solution and calcite of the substrate. In order to obtain a more homogeneous and deeper diffusion of the treatment into decayed materials, we focused our experiments on an alternative method using diethyloxalate [(C2H5)2C2O4] which during the hydrolysis transforms calcium carbonate into calcium oxalate [2]. The reaction between diethyloxalate and calcite produces COM, COD and an unexpected relevant amount of caoxite (CaC2O4•3H2O - COT). The crystallization of COT into the treated carbonatic substrate is the main proof of the reaction between diethyloxalate and the decayed stones, thus its identification is essential to monitor the treatment and define its efficacy. Due to the scarce literature data, an extensive investigation of crystallographic, spectroscopic and microscopic features of COT has been performed, including the development of a new method for its synthesis [3]. The experiments clearly highlight the role played by the H2O molecules linked within the structure by different kinds of hydrogen bonds. The vibrational assignment of the infrared and Raman bands is critically proposed. The fact relevant for the work in biomedicine, cultural heritage and crystallography is that a simple examination of the spectra allows quickly to determine the chemical nature of the material in an unknown sample even in a minute quantity or in awkward experimental conditions.
[1] B. Doherty, M. Pamplona, R. Selvaggi, C. Miliani, M. Matteini, A. Sgamellotti, B. Brunetti, Appl. Surf. Sci. 2007, 253, 4477.
[2] C. Conti, I. Aliatis, M. Casati, C. Colombo, M. Matteini, R. Negrotti, M. Realini, G. Zerbi, J. Cult. Herit. 2013, 15, 336.
[3] C. Conti, M. Casati, C. Colombo, E. Possenti, M. Realini, G.D. Gatta, M. Merlini, L. Brambilla, G. Zerbi, Spectrochim. Acta A, 2015, 150, 721
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
La chiesa rupestre di S. Cassiano (Lumignano di Longare - Vicenza)
No full textLe testimonianze epigrafiche conservate nel sito di S. Cassiano costituiscono un piccolo corpus di scritture esposte dai caratteri assai singolari e diversi, con un importante tratto comune, rappresentato dal basso livello di competenze grafiche posseduto da chi ha prodotto questi monumenti scritti, databili fra VII e VIII secolo
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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