1,720,966 research outputs found
Refinement of the crystal structure of anapaite Ca2Fe (PO4)2.4H2O : hydrogen bonding and relationships with the bihydrated phase
No full textThe crystal structure of anapaite from Messel (Hesse), Ca2Fe (PO4)2 • 4H2O, has been refined (R = 0.027) in space group P-1 by 1257 reflections measured on an automatic single-crystal diffractometer (MoKα radiation) ; all the hydrogen atoms have been localized and included in the refinement. The unit-cell parameters are : a = 6.447(1), b = 6.816(1), c = 5.898(1) Å, α = 101.64(3), β = 104.24(3), γ = 70.76(4)° ; Z = 1. Within the framework structure, (100) layers of coordination polyhedra are emphasized in order to describe a plausible crystallochemical path for a phase transition to the bihydrated term (messelite). Bond valence calculations show that Ca is 7 + 1 coordinated and justify the presence of hydrogen bonds which are unusually short for water molecules (2.597 and 2.600 Å).La structure de l'anapaite de Messel (Hesse), Ca2Fe (PO4)2.4H2O, a été affinée (R = 0,027) dans le groupe spatial P-1 par 1 257 réflexions mesurées à l'aide d'un diffractomètre automatique (radiation MoKα) ; tous les atomes d'hydrogène ont été localisés et inclus dans l'affinement. Les paramètres de la maille sont : a = 6,447(1), b = 6,816(1), c = 5,898(1) Å, α = 101,64(3), β = 104,24(3), γ = 70,76(4)° ; Z = 1. Des couches (100) de polyèdres de coordination sont présentes dans la structure, et au moyen d'elles on peut proposer un mécanisme cristallochimique pour la transition à la phase bihydratée (messelite). Des calculs de force de liaison montrent que Ca a une coordination 7 + 1, et expliquent la présence de liaisons hydrogène très courtes (2,597 et 2,600 Å) données par une molécule H2O.Catti Michele, Ferraris Giovanni, Ivaldi Gabriella. Refinement of the crystal structure of anapaite Ca2Fe (PO4)2.4H2O : hydrogen bonding and relationships with the bihydrated phase. In: Bulletin de Minéralogie, volume 102, 4, 1979. pp. 314-318
Hydrogen bonding in the crystalline state. Structure of talmessite, Ca2 (Mg, Co) (As O4)2.2H2O, and crystal chemistry of related minerals
No full textThe crystal structure of a talmessite from Bou-Azzer, Ca₂ (Mg₀,₆₅, Co₀,₃₅) (AsO₄)₂ • 2H₂O, was solved and refined (R = 0.081) in space group P[-1] by 979 reflections measured on an automatic single˗crystal diffractometer (MoKα radiation). The unit˗cell parameters are : a = 5.874 (7), b = 6.943 (11), c = 5.537 (6) Å, α = 97.3 (1), β = 108.7 (1), γ = 108.1 (2)° ; Z = 1. The structure is built up by alternating (110) layers of Ca and Mg coordination polyhedra, and is characterized by two unusually short [2.562 (15) and 2.613 (14) Å] hydrogen bonds donated by the H₂O molecule, which account for the high dehydration temperature (460° C) of this mineral. The triclinic minerals Ca₂Me (XO₄)₂ • 2H₂O (X = P or As), regarded as isostructural, are divided in two subgroups (fairfieldite and messelite ; collinsite, cassidyite, talmessite and β˗roselite) characterized by a closer isostructurality and distinguishable by the cell parameters. Thermal studies were performed on collinsite, fairfieldite and talmessite, showing a dehydration temperature increasing with the strength of hydrogen bonds.La structure cristalline d'une talmessite cobaltifère de Bou-Azzer, Ca₂ (Mg₀,₆₅, Co₀,₃₅) (AsO₄)₂ • 2H₂O, a été résolue et affinée (R = 0,081) dans le groupe spatial P[-1] par 979 réflexions mesurées à l'aide d'un difïractomètre automatique (radiation MoKα). Les paramètres de la maille sont : a = 5,874 (7), b = 6,943 (11), c = 5,537 (6) Å, α = 97,3 (1), β = 108,7 (1), γ = 108,1 (2)° ; Z = 1. La structure est formée de couches ([-1]10) alternée de polyèdres de coordination de Ca et Mg, et montre deux liaisons hydrogène très courtes [2,562 (15) et 2,613 (14) Å], données par la molécule H₂O, qui expliquent la température de déshydratation élevée (460° C) du minéral. Les minéraux tricliniques Ca₂Me (XO₄)₂ • 2H₂O (X = P ou As), considérés isostructuraux, sont divisés en deux groupes (fairfieldite et messélite ; collinsite, cassidyite, talmessite et β˗rosélite) qui sont caractérisés par une isostructuralité plus étroite et peuvent se distinguer par les paramètres de la maille. Des études thermiques sur collinsite, fairfieldite et talmessite ont montré que la température de déshydratation de ces minéraux augmente avec la force des liaisons hydrogène.Catti Michele, Ferraris Giovanni, Ivaldi Gabriella. Hydrogen bonding in the crystalline state. Structure of talmessite, Ca2 (Mg, Co) (As O4)2.2H2O, and crystal chemistry of related minerals. In: Bulletin de la Société française de Minéralogie et de Cristallographie, volume 100, 3-4, 1977. pp. 230-236
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
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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