1,720,990 research outputs found
On a diffusion problem arising in nanophased thin films
No full textThe selective-sublimation processing is a technique for deposition
of nanosized thin films aimed at controlling the composition of the film and hence
its properties. The method consists of the deposition of a
solid solution of a mixed-metal oxide with the sublimation
temperature of one of the pure metal oxide being rather low.
Proper thermal treatment allows to selectively sublimate the most
volatile metal oxide.
In this paper we first model the thermal processing undergone by
the films under the assumption that the thickness of the layer is
constant. The problem is formalized as an initial-boundary value
problem for a one-dimensional diffusion equation with fixed
boundary. We construct an explicit solution for the problem
relying on a set of observable physical quantities that can be
profitably used in experiments, i.e., the sublimation rate of the
most volatile oxide and the diffusion coefficient. Conversely, we
discuss the problem of determining such coefficients from an
additional measurement and provide error estimates.
Finally, we propose a more general model taking into account the
thinning of the film due to sublimation. It results in a
free-boundary value problem at the sublimation surface of the
film, which is solved by successive approximations
The amyloid cascade hypothesis and Alzheimer's disease: A mathematical model
Full text linkThe paper presents a conceptual mathematical model for Alzheimer's disease (AD). According to the so-called amyloid cascade hypothesis, we assume that the progression of AD is associated with the presence of soluble toxic oligomers of beta-amyloid. Monomers of this protein are produced normally throughout life, but a change in the metabolism may increase their total production and, through aggregation, ultimately results in a large quantity of highly toxic polymers. The evolution from monomeric amyloid produced by the neurons to senile plaques (long and insoluble polymeric amyloid chains) is modelled by a system of ordinary differential equations (ODEs), in the spirit of the Smoluchowski equation. The basic assumptions of the model are that, at the scale of suitably small representative elementary volumes (REVs) of the brain, the production of monomers depends on the average degradation of the neurons and in turn, at a much slower timescale, the degradation is caused by the number of toxic oligomers. To mimic prion-like diffusion of the disease in the brain, we introduce an interaction among adjacent REVs that can be assumed to be isotropic or to follow given preferential patterns. We display the results of numerical simulations which are obtained under some simplifying assumptions. For instance, the amyloid cascade is modelled by just three ordinary differential equations (ODEs), and the simulations refer to abstract 2D domains, simplifications which can be easily avoided at the price of some additional computational costs. Since the model is suitably flexible to incorporate other mechanisms and geometries, we believe that it can be generalised to describe more realistic situations
Numerical tests on an optimal integration scheme for the von-Mises plasticity model based on exponential maps
No full textWe introduce a reformulation of the time-continuous von-Mises elastoplastic model,
based on the definition of an integration factor and of an augmented relative stress. We present an
integration procedure for the above constitutive model that makes use of exponential maps. The
resulting method shows greater accuracy than other classical integration procedures such as radial
return map methods. Moreover, quadratic accuracy and low error levels can be clearly appreciated
through numerical testing. The new scheme preserves yield consistency along the integration time
interval and is exact in case of zero isotropic hardening as well as for proportional loading
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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