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Radiation damage in zircons
No full textMetamictization effects have been investigated in zircons having different uranium and thorium contents and different degrees of metamictization. U and Th contents range from 57 to 2890 ppm and from 27 to 420 ppm, respectively. Parallel to the U and Th increase, density decreases from 4.80 to 4.10 (g/cm(3)) and change in X-ray powder diffraction are noticed. Powder diffraction maxima decrease in intensity, shift to lower 2 theta values, broaden and become asymmetrical with the increment of diffuse-scattering component. Unit cell parameters systematically increase (a = 6.60-6.68 Angstrom, c = 5.97-6.11 Angstrom, V = 260-272 Angstrom(3)) The powder IR spectra show similar variations as X-ray diffraction patterns. There are only minor differences in the two sequences. On the other hand, powder X-ray diffraction patterns and IR spectra give different results during annealing: after heating at 950 degrees C, X-ray diffraction patterns become sharp and well resolved and display a nearly complete structural recovery; IR spectra show that the recovery in the structure in the two metamict zircons is significant, but seems incomplete if compared with the more crystalline samples
Grumiplucite, a new mercury-bismuth sulphosalt from Levigliani mine, Apuan Alps (Tuscany, Italy)
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Dessauite, (Sr,Pb)(Y,U)(Ti,Fe)20O38, a new mineral of the crichtonite group from Buca della Vena mine, Tuscany, Italy
No full textDessauite, a new mineral in the crichtonite group, occurs within cavities in calcite veins as tabular {001} rhombohedral, black, millimeter-sized crystals at Buca della Vena Mine, Apuan Alps (Tuscany, Italy). It is associated with derbylite, hematite, rutile, karelianite, siderite, and calcite. Dessauite is trigonal, space group R3, with a = 9.197(1) Å, alpha = 68.75(2)°. Optically, dessauite is opaque and shows low bireflectance and very weak pleochroism. Electron microprobe analyses led to the following simplified chemical formula: (Sr,Pb)(Y,U)(Ti,Fe3+)20O38. The crystal structure of dessauite was refined from single-crystal X-ray diffraction data to R = 0.065. Dessauite is isostructural with the others members of the crichtonite group; a peculiar structural feature is the presence of additional, partially occupied octahedral sites. A comparison of the crystal-chemical formulas of all the minerals within the crichtonite group is presented. In view of the structural information, the analytical data have been re-arranged on the basis of the crystal-chemical formula ABC18T2O38, rather than AM21O38
Da Argo alla lince. Il ruolo della vista nella cultura scientifica del Seicento
No full textNel periodo che va dal Rinascimento al Barocco le percezioni sensoriali dell’uomo occidentale mutano la gerarchia. A prevalere non è più l’organo dell’udito, dominante nella cultura orale dell’antichità e del Medioevo, ma l’organo della vista, esaltata dalla moderna rivoluzione scientifica e dall’invenzione della stampa. Con il Seicento si viene affermando una civiltà di massa, e questa, come scrive lo storico José Antonio Maravall, si pone degli «obiettivi di diffusione» che favoriscono il ruolo predominante riconosciuto alla «funzione ottica» e lo sviluppo di una «cultura dell’immagine sensibile» perché «è proprio delle società in cui si sviluppa una cultura di massa eterodiretta richiamarsi all’efficacia dell’immagine visiva». Tutto ciò ha delle conseguenze epistemologiche. L’impiego diretto della vista, ovvero l’esame autoptico dei fenomeni, mina alle fondamenta il principio di autorità. Non solo, ma a contare non è più la quantità delle cose osservate, ma il modo penetrante ed ermeneutico con cui valutarle. Alla figura di Argo, il mosdtro dai cento occhi, viene a sostituirsi, con un diverso valore euristico, il simbolo della lince, l’animale dalla vista acutissima. Muta anche la considerazione della curiositas molto diversa rispetto al passato, che la tacciava di hybris, tanto nella cultura greco-romana, quanto nel mondo cristiano dei Padri della Chiesa. Ne è conferma il rovesciamento dei significati di miti come quelli di Prometeo e di Atteone, non più figure eticamente negative ma esempi positivi della volontà di esplorare terre incognite
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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