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Crystal and magnetic structure of the R<sub>15</sub>Si<sub>9</sub>C compounds (R = Ho, Er, Tb)
No full textThe synthesis of the new compounds R15Si9C with R = Sm, Gd-Er, Y and R15Ge9C with R = Ce, Pr and Nd has been recently reported; these compounds crystallize in the hexagonal La 15Ge9Fe structure type, hP50-P63mc, Z = 2 (ordered superstructure of La5Ge3 (Mn5Si 3-type, hP 16-P63/mcm, Z = 2)). Here we report the results of a neutron diffraction investigation that we have performed to study the crystal and magnetic structures of the R15Si9C compounds with R = Tb, Ho and Er. All three compounds see the establishment of commensurate magnetic order with a predominantly ferromagnetic interaction. Details of mixed antiferro-ferromagnetic spin arrangements (κ = [000]) (for Tb15Si9C and Ho15Si9C) or of purely ferromagnetic ordering (Er15Si9C), and of their temperature dependence, are given and linked to the different coordination of the four dissimilar rare earth sites. In the Tb and Ho compounds the thermal evolution of the magnetic moment values strongly differs between the different R sites. The position occupied by the principal carbon has been determined (Wyckoff site 2b) and the existence of a second position available for the interstitial carbon (Wyckoff site 2a) has been revealed for R = Ho, Tb. Moreover, in the Tb and Ho compounds the magnetic moment value of the rare earth site R4, surrounding the second interstitial carbon site, is strongly reduced if compared to the value on the other rare earth sites. The magnetic transition temperatures of all three compounds, i.e. TC = 130, 43 and 45K for Tb15Si9C, Ho15Si9C and Er 15Si9C, are remarkably high compared to those of the parent R5Si3 compounds. The magnetic behaviour of the partly filled Tb5Si3C0.25 is reported
Solid-Phase Synthesis of Optically Active Isocyanides and their Application in the Passerini Multicomponent Reaction
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The Yb2Al1-xMgxSi2 series from a spin fluctuation (x=0) to a magnetically ordered ground state (x=1)
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Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Get PDF“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
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