1,720,965 research outputs found
Thermodynamics and kinetics of cation ordering in natural and synthetic Mg(Al,Fe3+)(2)O-4 spinels from in situ high-temperature X-ray diffraction
No full textOne natural and two synthetic spinels with compositions Ma(Al1-zFez3+)(2)O-4 (with 2z = 0.078, 0.138 and 0.200, respectively) were studied by in situ, high-temperature, single-crystal X-ray diffraction. All samples were heated from room temperature to 1050 degrees C. Thermal expansion was monitored by measuring the cell edge variation. Cation disorder was monitored by measuring the variation of the oxygen positional parameter it, which is closely correlated with the inversion parameter i. All samples showed extensive Al reordering at the M site between 550 and 650 degrees C, followed by an increase of disorder at T > 650 degrees C due to both Mg-Al and Mg-Fe3+ intersite exchanges. The measured cation distributions were compared with those calculated using the general thermodynamic model for spinel binary solid-solutions of O'Neill and Navrotsky (1984). Measured and calculated inversion parameters compare satisfactorily at T > 650 degrees C, i.e. at conditions under which equilibrium was achieved at any temperature. In fact, at T > 650 degrees C, both (IV)Fe(3+)and Al-IV increase with increasing T, following the equilibrium path. The reproducibility of Al-IV occupancies was very high, whereas Fe-IV(3+) occupancies were not satisfactorily matched. The cation distribution relaxation observed between 550 and 650 degrees C was interpreted on the basis of kinetic considerations. In this temperature ran,,e, inversion decreases to a minimum because the amounts of Al that reorder are far more abundant than those of Fe3+ that disorder. The Mg-Fe3+ exchange was confirmed to proceed at a faster rate than the Mg-Al exchange. Moreover, the Mg-Fe3+ exchange wits found to be active at laboratory times at about 550 degrees C, whereas the Mg-Al exchange was hard to monitor below 600 degrees C
Comparative compressibility and structural behavior of spinel MgAl2O4 at high pressures: The independency on the degree of cation order
No full textThe equation of state and the crystal structure evolution with pressure were determined for two single crystals of pure natural MgAl2O4 spinels with different degrees of order. The two samples studied were cut from a larger single crystal and one of them was experimentally disordered at high temperature. The two crystals, showing an inversion parameter x of 0.27 and 0.15 at ambient conditions,
were loaded together in a diamond anvil cell and their unit-cell edge was measured up to about 7.5 GPa at 14 different pressures. The unit-cell volume, V0, the bulk modulus, KT0, and its first pressure derivative, K′, were simultaneously refined using a third-order Birch-Murnaghan equation of state, giving the following coefficients: V0 = 529.32(2) Å3, KT0 = 193(1) GPa, K′ = 5.6(3) for the ordered sample and V0 = 528.39(2) Å3, KT0 = 192(1) GPa, K′ = 5.4(3) for the disordered one. Complete
intensity data were collected at 0, 0.44, 2.92, 7.34, and 8.03 GPa in a separate experiment. For the ordered and disordered samples the oxygen atomic coordinate u remains practically unchanged inside the investigated pressure range with an average value of 0.2633(5) and 0.2614(2), respectively. As a consequence, the polyhedral compressibilities are similar and are not influenced by the Mg/Al distribution over the two crystallographic sites. This also suggests that pressure has little or no influence
on the degree of order in the MgAl2O4 spinel
Lingue in formazione, lingue migranti. Un ricordo di Marina Chini
No full textMarina Chini, docente di Linguistica all’università di Pavia, fedele socia AItLA e assidua e preziosa frequentatrice dei suoi convegni, ci ha lasciati nel luglio 2018, dopo anni di straziante malattia. Noi tutti che l’abbiamo conosciuta la ricordiamo per la dedizione appassionata e sommessamente militante verso il suo lavoro, per la gentilezza delicata e la riservata ironia, per l’instancabile curiosità e apertura verso i colleghi, gli studenti e i giovani studiosi. Nel primo convegno che si è svolto senza la sua partecipazione, abbiamo voluto ricordarla attraverso le parole di quattro colleghe che l’hanno conosciuta in momenti diversi del suo percorso professionale e di vita e si sono qui confrontate con gli ambiti della sua ricerca con cui più intensamente hanno dialogato. Ada Valentini, Patrizia Giuliano, Stefania Scaglione e Silvia Sordella, che ringraziamo per l’affettuoso ricordo che di Marina hanno proposto al convegno, ci presentano nelle pagine che seguono i diversi risvolti della sua ricerca, intrecciando ricerca acquisizionale, sociolinguistica delle migrazioni e riflessione glottodidattica, con aperture su possibili sviluppi del lavoro da lei avviato. L’organizzazione tematica segue una scansione cronologica del progressivo ampliarsi degli interessi di ricerca di Marina: Valentini (§ 1) si concentra sulla ricerca acquisizionale svolta da Marina nei due campi dell’acquisizione della categoria di genere e di strutture e forme della testualità; Giuliano (§ 2) suggerisce possibili sviluppi di questo secondo filone di ricerca nell’ambito dell’acquisizione della lingua materna; Scaglione (§ 3) mette in luce il fondamentale ruolo di Marina negli studi di sociolinguistica delle migrazioni in Italia; Sordella infine (§ 4) richiama i molti spunti di riflessione che emergono dal suo lavoro per la riflessione glottodidattica e la formazione dei docenti. Ne risulta un quadro composito di temi ripresi e ri
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
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
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