1,720,967 research outputs found
Uniformly dispersed Pr+3 doped silica glass by the sol-gel process
No full textPraseodymia-silica glass samples with high praseodymia content (5 wt%) were prepared by the sol-gel process. Amino alkoxy silane was used to immobilize the Pr+3 cation in the silica (derived from tetraethyl orthosilicate) matrix. The gel to glass transformation was examined by ultraviolet, visible, near infrared and Fourier transform infrared spectroscopy at different stages of drying/densification up to 1000°C. The X-ray microanalysis for praseodymium throughout the bulk glass samples confirmed the homogeneous distribution of the Pr+3 in the matrix
Polymeric foams 3D numerical mechanical modelling
Get PDFOne of the main open issues in the field of polymeric foam materials is the lack of a relationship between the foam geometrical characteristics and its constituent material properties, on one side, and the macroscopic mechanical behavior. This link is an essential ingredient for the development of a predictive numerical model able to fully describe the mechanical behavior of polymeric foams under different loading conditions, which is the ultimate goal of the present work.
In order to build up a systematic and methodological approach to this problem, polymeric structural closed cell foams having different nominal densities (ranging from 60 to 120 kg/m3) were considered. The internal foam structure was investigated throughout micro-Computed Tomography; the acquired stack of images were processed with a home-made algorithm in which Mean Intercept Length method was implemented to compute material volume distribution and the degree of structural anisotropy. The algorithm also allowed the reconstruction of the real geometry using a voxel-based scheme, to perform Finite Element Analysis. With the aim of reducing geometric discontinuities, inherent in the reconstructed voxel mesh, Taubin’s smoothing algorithm was employed to obtain more accurate results. Numerical simulations mimicking experimental quasi-static uniaxial compression test were performed to obtain nominal stress vs. strain curves. To this purpose, suitable mechanical properties were identified for the (equivalent solid) constituent material: the resulting constitutive law highlights the contribution of the material to the macroscopic foam properties. Relevant mechanical parameters such as elastic moduli, buckling strain and plateau stress were then evaluated and related to geometrical features of the real foam
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
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe 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
On the resolution of semiconductor multilayers with a scanning electron microscope
No full textThe main factors affecting the spatial resolution of the scanning electron microscope have been analysed using a suitable inhomogeneous specimen consisting of semiconductor multilayers. Operating in secondary electron as well as in backscattered electron imaging mode, with the support of Monte Carlo simulations of beam-specimen interaction, it has been possible to achieve the following conclusions. All the backscattered or secondary electrons positively contribute to the image formation independently of their trajectories and specimen exit points. The resolution of the backscattered electron images depends only on the beam size and the signal to noise ratio. The generation volume of backscattered electrons affects the contrast but does not represent in itself a limit to the resolution. The contrast of secondary electron images of the semiconductor multilayer has essentially a compositional nature, being linked to the collection of secondary electrons produced by the backscattered ones. Moreover, using a converter of backscattered electrons in secondary electrons located underneath the pole pieces of the microscope objective lens, it has been demonstrated an improvement of the signal that allows a resolution equal to the electron beam size. This resolution cannot be obtained, operating in the same electron optical conditions, without the converter, due to the lower signal level
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe 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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