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Development of new cellular materials by gel-casting technique
No full textIn this PRISMA project new cellular materials will be developed by a gel casting technique.
The process was initially set up to produce dense ceramics, andwill be adapted in a second stage
to the formation of cellular solids with the addition of a pore forming agent (poly(ethylene)),
which decomposes during thermal treatment at high temperature, leaving calibrated porosities.
Commercial ZrO2 powders (Tosoh TZ-3Y and TZ-3YS, 3 mol % Y2O3) as a ceramic material
and gelatine as a gelling agent were employed. Selected powders were preliminary characterised
by Transmission Electron Microscopy (BF and SADP), in order to acquire information about
size distribution and microstructure. The first step of the work was the optimisation of the zirconia
suspension with respect to its stability, because while the gelling process is occurring there
should be no powder sedimentation. The best results were obtained bywith dispersing the powders
in distilled water under natural pH (ca. 4.7) and after 10 minutes of sonication by means
of an u.s. probe, as evidenced by laser granulometry. Then, slurries with varying solid/liquid
ratios and various amounts of gelatine were prepared. The influence of the dispersion method,
of the temperature of gelatine dissolution and of casting, gelation and drying conditions were
studied. In particular, an increase of the viscosity of the suspension was observed with the TZ-
3Y powder, which made the casting very difficult, then this powder was given up. The best
results were reached with a solid content of 50 wt% and a gelatine content of 3 wt.% respect to
the water amount. Knoop micro-hardness technique, performed on a section carefully cut and
polished, was used to investigate the effectiveness of the drying phase: differences in hardness
between surface and core were found, possibly as a consequence of differential drying rate which
involves an internal gradient of density, useful for an effective comparison between different drying
procedures. Density measurements by Archimede’s principle on fired samples at 1400°C for
1 hour indicated that it was possible to reach at least 95% t.d.. Then, poly(ethylene) granules
(125-300 microns) were added to create porosities inside the gel cast pieces (50 vol.%). The
thermal cycle was set up to allow the polymer to decompose, without foam collapsing prior to
high temperature sintering. Dense products were machined to the final standard size of 10x30
mm for cylinders and 4x3x50 mm for prismatic bars, obtaining parallel planar surfaces and
removing surface defects such as voids and irregular profiles.
Samples were tested for mechanical properties by means of Instron 8033 (200 kN) and Zwick
Roell Z010 (10kN) electromechanical testing machines. Uniaxial compressive strength was
measured on cylinders, tensile strength and elastic modulus were measured by four points bending
test on prismatic samples equipped with strain gauges.
Hardness and fracture toughness of bulk samples were finally evaluated by Vickers micro-hardness
testing adopting models available in literature
Dense and porous zirconia prepared by gelatin and agar gel casting: microstructural and mechanical characterization
No full textDense and cellular yttria-tetragonal zirconia polycrystal (Y-TZP) bodies were produced by using a natural gelatine and two different agars as gelling agents, while commercial polyethylene (PE) spheres were added (125 to 300 μm diameter) as a volatile pore forming agent to create 50-65 vol% spherical macro-pores, uniformly distributed in a micro-porous matrix. The microstructure of all dense and cellular ceramics was characterized by FEG-SEM and Focused Ion Beam (FIB) techniques. The mechanical properties of both dense and porous samples were investigated at the microscale by nanoindentation testing, while the influence of microporosity was obtained by the analysis of hardness and modulus depth profiles, coupled with FIB-SEM section observations of selected indentation marks. Mechanical characterization at the macroscale consisted of uniaxial compression tests and four point bending tests.
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
Influence of film thickness on the sensor performance of NdCoO3 and Nd0,8Sr0,2CoO3 towards CO
No full text
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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