1,721,004 research outputs found
Finite energy weak solutions to the quantum hydrodynamics system
No full textIn this paper we are concerned with the study of the relaxation limit of the 3- hydrodynamic model for semiconductors. We prove the convergence of the weak solutions to the Euler-Poisson system toward the solutions to the drift-diffusion system, as the relaxation time tends to zero
Motion of interfaces for hyperbolic variations of the Allen-Cahn equation
No full textThe Allen-Cahn equation is a (parabolic) reaction-diffusion equation with a balanced bistable reaction term, which describes phase transition processes. It is well-known that when the diffusion coefficient is very small, the solutions exhibit very interesting phenomena. In the one-dimensional case, we have an example of metastable dynamics, while in the multi-dimensional case the Allen-Cahn equation is strictly related to the mean curvature flow. In this paper we discuss such phenomena in the case of some hyperbolic variations of the Allen-Cahn equation. In particular, in the one-dimensional case we focus the attention on the assumptions needed to have metastability and we show some numerical solutions in the case such assumptions are not satisfied
On L1-stability of BV solutions for a model of granular flow
Full text linkWe are concerned with the well-posedness of a model of granular flow that consists of a hyperbolic system of two balance laws in one-space dimension, which is linearly degenerate along two straight lines in the phase plane and genuinely nonlinear in the subdomains confined by such lines. This note provides a survey of recent results on the Lipschitz L1-continuous dependence of the entropy weak solutions on the initial data, with a Lipschitz constant that grows exponentially in time. Our analysis relies on the extension of a Lyapunov like functional and provide the first construction of a Lipschitz semigroup of entropy weak solutions to the regime of hyperbolic systems of balance laws (i) with characteristic families that are neither genuinely nonlinear nor linearly degenerate and (ii) initial data of arbitrarily large total variation
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
On smooth approximations of rough vector fields and the selection of flows
Full text linkIn this work we deal with the selection problem of flows of an irregular vector field. We first summarize an example from [4] of a vector field b and a smooth approximation for which the sequence of flows of has subsequences converging to different flows of the limit vector field b. Furthermore, we give some heuristic ideas on the selection of a subclass of flows in our specific case
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
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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