1,721,067 research outputs found
A generalised correlation for gas/solid mass transfer coefficients in metallic and ceramic foams
No full textMass transfer characterization of metallic foams as supports for structured catalysts
No full textOpen-celled metal foams have been characterized as supports for structured catalysts, considering
their utilization in gas-solid catalytic processes with short contact times and high reaction rates,
typically controlled by gas-solid diffusional mass transport. Examples of such processes are
found in the field of environmental catalysis, including, e.g., catalytic combustion, selective
catalytic reduction (SCR-DeNOx), and automotive exhaust gas after treatment. In this work,
foams with different cell sizes were coated with a thin layer of palladium-alumina and tested
in a 9-mm inner diameter tubular reactor by performing the catalytic oxidation of CO at empty
tube velocities in the range of 0.8-2.6 m/s. The coated foams exhibited sufficient catalytic activity
to achieve mass-transfer-limited operation in the temperature range of 300-450 °C. Under such
conditions, mass-transfer coefficients were determined according to a simple one-dimensional
model of the test reactor. Adopting the average diameter of the foam struts as the characteristic
length, we obtained a dimensionless correlation for the estimation of mass-transfer coefficients,
which correlates all the data: it closely resembles semitheoretical literature correlations for
heat transfer in flow across banks of tubes at low Reynolds numbers. Pressure drop measurements
across foam samples were also collected for air velocities in the range of 1-16 m/s. The
performances of foams, packed beds of pellets, and honeycomb monoliths as catalyst supports
were compared on the basis of a dimensionless merit index, which accounts for the tradeoff
between pressure drop and mass-transfer properties. Foams are largely superior to packed beds,
because of their high voidage, but perform slightly worse than honeycomb monoliths. On the
other hand, foams can afford marked reductions of reactor volume and weight, with respect to
honeycombs, in fast, diffusion-controlled processes where pressure drop is of minor concern
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
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