1,721,014 research outputs found
The supercooled Stefan problem in radial symmetry
No full textWe prove existence of a Stefan problem even in the threshold case for the initial data beyond which the solution is known to be non-existent. This is done via a novel a priori estimation procedure of the speed of the free boundary
Modelling wax diffusion in crude oils: The cold finger device
Full text linkAbstract In this paper we show how to obtain wax diffusivity and solubility values in crude oils from deposition measurements in the cold finger device with stirring. Providing a rather accurate knowledge of such quantities is of great importance in predicting the wax deposition rate in pipelines. We present a mathematical model in which the physical quantities are assumed to be space-independent in the bulk region of the device, because of agitation, so that mass transport occur in relatively thin boundary layers. As a consequence the deposition phenomenon is accelerated with respect to the static device (see [S. Correra, A. Fasano, L. Fusi, M. Primicerio, F. Rosso. Wax diffusivity under given thermal gradient: a mathematical model, to appear on ZAMM]), shortening the duration of experiments. Comparison with some available laboratory measurements shows a satisfactory agreement and the values obtained are in the range of those usually adopted by practitioners
Numerical simulation of polymer crystallization
No full textWe consider a mathematical model for solidification of
semicrystalline polymers, describing the evolution of
temperature, crystalline volume fraction, number and average
size of crystals. In turn, the model couples a suitable kinetics of
nonisothermal crystallization, taking into account both formation and
growth of nuclei, with the thermal energy balance equation.
We also present a model of secondary crystallization.
The numerical approximation is performed by semiexplicit finite
differences in time and finite elements in space. The fully discrete
scheme amounts to solve, at any time step, a symmetric positive definite
linear system preceded by a elementwise explicit computation.
The computed numerical crystal structures match
qualitatively the experimental ones
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
Models, experiments, and numerical simulation of isothermal crystallization of polymers
No full textWhen a quiescent molten polymer is cooled below the equilibrium melting temperature, crystals (spherulites) appear and keep growing as long as the temperature ranges between the melting temperature and the glass transition temperature. The crystallization process depends upon temperature and crystalline microstructure. In particular, the reduction of the free volume and subsequent impingement between crystals influence both nucleation and growth rates of spherulites. Below the glass transition temperature, the polymer consists of crystal and amorphous phases. In the sequel we discuss a mathematical model for a bidimensional isothermal crystallization process which takes into account the nucleation, growth, and impingement of spherulites
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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