1,720,993 research outputs found
The morphology and structure of intercalated and pillared clays
No full textThis thesis is submitted in a format of published papers by the candidate. Advanced methods of electron microscopy and X-ray spectroscopy have been used to study the relationship between the pillars and the silicate structure ranging from Al13 and Ga13 complexes to the final products Al- and Ga-pillared clays. The Al13 and Ga13 pillared montmorillonites have been prepared by conventional and ultrasonic methods. The ultrasonic method has been proven to be effective and showed very good catalytically activity. Transmission electron microscopy combined with elemental mapping by EDS showed the distribution of the Ga and Al pillars in the clay structure. The use of gallium allowed the independent observation of the Ga pillar distribution from the Al distribution in the clay structure.\ud
XPS spectra of the Ga13 pillared montmorillonites showed that the pillars has been changed from the original Keggin structure with a 7+ charge to something more stable with a lower charge upon intercalation. No direct evidence of the inverted silicon tetrahedron structure bonding to the pillar structure, as suggested by Plee in his original thesis, was observed. For comparative reasons the major aluminium hydroxide minerals in bauxite (gibbsite, bayerite and (pseudo-) boehmite) were studied. \ud
Detailed information about the Al13 structure was obtained by studying the basic sulphate and nitrate salts with XPS. The XPS results of a set of starting clays in comparison to the pillared clays indicated that small changes in the binding energy could explain the changes in the pillar structure and the formation of chemical bonds to the clay tetrahedral sheets during the calcination leading to the final products
Raman microscopy of selected tungstate minerals
No full textA series of tungstate bearing minerals including scheelite, stolzite ferberite, hübnerite, wolframite, russellite, tungstenian wulfenite and cuprotungstite have been analysed by Raman microscopy. The results of the Raman spectroscopic analysis are compared with published data. These minerals are closely related and often have related paragenesis. Raman microscopy enables the selection of individual crystals of these minerals for spectroscopic analysis even though several of the minerals can be found in the same matrix because of the pargenetic relationships between the minerals. The Raman spectra are assigned according to factor group analysis and related to the structure of the minerals. These minerals have characteristically different Raman spectra. The ￮1(Ag) band is observed at 909 cm-1 and although the corresponding ￮1(Bu) vibration should be inactive a minor band is observed around 894 cm-1. The bands at 790 and 881 cm-1 are associated with the antisymmetric and symmetric Ag modes of terminal WO2. The band at 695 cm-1 is interpreted as an antisymmetric bridging mode associated with the tungstate chain. The ￮4(Eg) band was absent for scheelite. The bands at 353 and 401 cm-1 are assigned as either deformation modes or as r(Bg) and ￤(Ag) modes of terminal WO2. The band at \ud
462 cm-1 has an equivalent band in the infrared at 455 cm-1 assigned as ￤as(Au) of the (W2O4)n chain. The band at 508 cm-1 is assigned as ￮sym(Bg) of the (W2O4)n chain
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
The Distribution Of Ga in Ga-Pillared Montmorillonites: A Transmission Electron Microscopy And Microanalysis Study
No full textThe distribution of Ga in the interlayer of montmorillonite pillared with a Ga polyoxocation complex has been studied by transmission electron microscopy, energy-dispersive X-ray microanalysis (EDX), X-ray mapping and powder X-ray diffraction in combination with N adsorption- desorption. To view the clay layers by TEM, the pillared clay was embedded in Spurrs resin in a preferred orientation, and sectioned with an ultramicrotome perpendicular to the layers. Montmorillonites pillared with Al and AlGa complexes were also prepared for microanalysis in the TEM. The Ga X-ray peaks could be easily distinguished in the EDX spectra, allowing concentrations relative to other elements to be determined. Elemental X-ray maps for Ga, Si and Al in the Ga-pillared clay cross-sections demonstrated that the Ga was homogeneously distributed throughout the crystal thickness. Comparison of the analytical data with that from the Al and AlGa-pillared clays and the starting material suggested that an approximately constant amount of the intercalated species per amount of Si in the clay became incorporated into the structure in each case. Calculation of the formula for the Ga-pillared montmorillonite showed that 0.89 Ga is present per formula unit containing 8 (Si + Al), which is equivalent to 20 silicate rings, each consisting of 6 tetrahedra, for every Ga pillar. The actual dimension of the pillar, based results from the elemental analyses and XRD is 8.7 Å and the mean distance between the pillars is 44.3 Å, which is in good agreement with the average pore size of 39 Å obtained by N adsorption-desorption measurements. This study shows a new approach for obtaining more detailed information on the pillars in pillared clay by combining analytical data from X-ray microanalysis with measurements by XRD and N adsorption-desorption
Microstructure study of early in situ reaction of fly ash geopolymer observed by Environmental Scanning Electron Microscopy (ESEM)
No full textIdentification of mixite minerals – an SEM and Raman spectroscopic analysis
No full textTwo mixites from Boss Tweed Mine, Tintic District, Juab Vounty, Utah and Tin Stope, Majuba Hill, Pershing Co., Nevada have been analysed by SEM with EDX analysis and by Raman spectroscopy. The SEM images show the mixite crystals to be elongated fibres up to 200 μm in length and 2 μm in width. Detailed images of the mixite crystals show the mineral to be composed of bundles of fibres The EDX analyses depend on the crystal studied, however the Majuba mixite gave analyses which matched the formula BiCu6(AsO4)3(OH)6.3H2O). Raman bands observed in the region 880 to 910 cm-1 and in the 867 to 870 cm-1 region are assigned to the AsO stretching vibrations of (HAsO4)2- and (H2AsO4)- units. Whilst bands at 803 and 833 cm-1 are assigned to the stretching vibrations of uncomplexed (AsO4)3- units. Intense bands are observed at 473.7 and 475.4 cm-1 are assigned to the ν4 bending mode of AsO4 units. Bands observed at 386.5, 395.3 and 423.1 cm-1 are assigned to the ν2 bending modes of the HAsO4 (434 and 400 cm-1) and the AsO4 groups (324 cm-1). Raman spectroscopy lends itself to the identification of minerals on host matrices and is especially useful for the identification of mixites
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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