1,720,956 research outputs found
Synthesis and characterisation of new framework materials
No full textInorganic framework materials, with structures based on arsenate and phosphate, AsO4and PO4, tetrahedra and a variety of octahedral metal units, such as hafnium, niobiumand iron, have been synthesised and fully characterised. These materials have beensynthesised by solvothermal techniques and the principal analytical technique tocharacterise the resulting single crystals has been Single Crystal X-ray Diffraction.Supporting analysis was carried out, using techniques such as Powder and NeutronDiffraction, Thermogravimetric Analysis, Electron Dispersive Spectroscopy andInfrared Spectroscopy.Of the hafnium arsenates and phosphates that have been synthesised, several arefluorinated and one is templated, such as Hf2F2(H(PO4)2)(NH4)2 and[Hf2F8(AsO4)][DABCO-H2](NH4) respectively. Similar layered frameworks have alsobeen characterised and reported for titanium, zirconium and niobium. These structuresall offer ion exchange potential, due to their ammonium cations and/or water molecules.The hydrogen iron phosphates that are discussed include two novel frameworks andone material which offers an improved model for the mineral lipscombite,Fe1.34(PO4)OH0.96. One of the new frameworks presented, (NH4)3Fe3(HPO4)6, offersparticularly interesting potential applications as a high capacity battery material vialithium exchange reactions.The hydrothermal synthesis of two novel hydrated sodium tungstate structures is alsodiscussed. One of these materials was found to contain a very high H : Na ratio,resulting in strong hydrogen bonding and a densely packed framework, which may be ofinterest in the field of high density liquids
Synthesis and crystal structures of iron hydrogen phosphates
No full textThree new iron hydrogen phosphate compositions have been synthesised under hydrothermal conditions; Fe(II)2O(HPO4) ( 1), (NH4)3Fe(III)3(HPO4)6 ( 2) and Fe1.34(III)(PO4)OH0.96 ( 3). 1 and 2 have framework structures constructed from FeO6 octahedra and HPO4/PO4 tetrahedra containing cavities; in the case of 2, these are occupied by ammonium cations while in 1 they are cross linked by hydrogen bonding involving the HPO4 groups. Crystals of 3 grow as 30 m octahedral jackstones and this synthetic material adopts the structure from the Lipscombite solid solution. Thermal decomposition of these materials yields simple iron phosphates and the potential of these compounds and their derivatives, formed for example through Li+-ion exchange of NH4+, for battery applications is discusse
Hydrothermal routes to new sodium polytungstates
No full textThe new acidic sodium polytungstates, Na5[H7W12O42]·20H2O ( 1) and Na2[H10W12O42]·20H2O ( 2), have been synthesised under hydrothermal conditions where variations of pH and temperature allow control of the protonation of the [W12O42]12- cluster in the products. The polytungstate cluster, [HnW12O42](12-n)-, in each compound consists of the well known polyhedral unit based on 12 edge- and corner-sharing WO6 octahedra, though the decoration of this unit with varying levels of protons results in significant changes in the W–O distances. The polytungstate clusters exist in arrays separated by sodium ions and water molecules forming well separated, (polytungstate centre to centre distance of 10.87 Å), rhombohedrally stacked units in 1 and strongly hydrogen bonded and more tightly packed units, (centre to centre distance of 9.34 Å), due to the high H : Na ratio in 2<br/
Controlling dimensionality in templated layer, chain and framework structures by combining metal fluorides with oxotetrahedra
No full textThe use of metal fluorides in hydrothermal reactions with linking phosphate and arsenate groups leads to the synthesis of numerous, frequently non-centrosymmetric, structures of controlled dimensionality
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
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