1,720,971 research outputs found
Numerical solutions of a viscous-hydrodynamic model for semiconductors: the supersonic case
No full textIn this paper, we solve by a finite difference upwinded method an extended
hydrodynamic model for semiconductors, with viscous terms in the momentum equation.
In particular, we consider the simulation of a one-dimensional n+-n -n+ diode, whose solution
exhibits at low temperatures strong discontinuities, and investigate the effect of the momentum
viscosity on the shock waves. Numerical experiments, performed also on a two-dimensional test
case, demonstrate that the numerical scheme, working on non-uniform grids, is suitable to describe
solutions with strong variations in time and space. Well-posedness for the boundary conditions is
discussed, and a linear stability estimate is established for the one-dimensional n+-n -n+ diode
benchmark problem
New substructuring domain decomposition methods for advection-diffusion equations
No full textIn this paper we consider a nonsymmetric elliptic problem and we use the techniques related to the Steklov–Poincare
operators to propose new substructuring iterative procedures. In particular, we propose two methods that generalize the well-known Neumann–Neumann and Dirichlet–Neumann iterative procedures. We prove that our methods, that use symmetric and positive-definite preconditioners, lead to the construction of iterative schemes with optimal convergence properties. Numerical results for the finite element discretization are given
Introduzione al calcolo scientifico: esercizi e problemi risolti con matlab
No full textQuesto testo è espressamente concepito per i corsi brevi del nuovo ordinamento delle Facoltà di Ingegneria e di Scienze. Esso affronta tutti gli argomenti tipici della Matematica Numerica, spaziando dal problema di approssimare una funzione, al calcolo dei suoi zeri, delle sue derivate e del suo integrale definito fino alla risoluzione approssimata di equazioni differenziali ordinarie e di problemi ai limiti. Due capitoli sono inoltre dedicati alla risoluzione di sistemi lineari ed al calcolo degli autovalori di una matrice, mentre un capitolo iniziale conduce lo studente ad un rapido ripasso degli argomenti dell'Analisi Matematica di uso frequente nel volume e ad una introduzione al linguaggio Matlab. I vari argomenti sono volutamente affrontati a livello elementare ed i paragrafi che richiedono maggior impegno sono stati opportunamente contrassegnati. In questa quarta edizione il linguaggio Octave (di distribuzione gratuita) si affianca a MATLAB
Calcolo Scientifico: Esercizi e problemi risolti con MATLAB e Octave
No full textQuesto testo è concepito per i corsi delle Facoltà di Ingegneria e di Scienze. Esso affronta tutti gli argomenti tipici della Matematica Numerica, spaziando dal problema di approssimare una funzione, al calcolo dei suoi zeri, dei suoi minimi, delle sue derivate e del suo integrale definito fino alla risoluzione di sistemi lineari e non lineari, di equazioni differenziali ordinarie e alle derivate parziali con metodi alle differenze finite e agli elementi finiti. Un capitolo iniziale conduce lo studente ad un rapido ripasso degli argomenti dell'Analisi Matematica di uso frequente nel volume e ad una introduzione ai linguaggi MATLAB e Octave. Al fine di rendere maggiormente incisiva la presentazione e fornire un riscontro quantitativo immediato alla teoria vengono implementati in linguaggio MATLAB e Octave tutti gli algoritmi che via via si introducono. Vengono inoltre proposti numerosi esercizi, tutti risolti per esteso, ed esempi, anche con riferimento ad applicazioni negli ambiti piu' svariati
On a viscous-hydrodynamic model for semiconductors: numerical simulation and stability analysis
No full textWe deal with a hydrodynamic model for semiconductors
with a physical viscosity in the momentum/energy equations. The discretization uses a first-order finite difference
scheme with upwinding based on the characteristic
variables. We perform a stability analysis of the numerical
method applied to a linearized incompletely parabolic system
assuming vanishing viscosity in one space dimension
although the analysis can be extended to the two dimensional
case. A thorough numerical parametric study as a function of
the heat conductivity and of the momentum viscosity is carried
out in order to investigate their effect on the development
of shocks in both one and two space dimensions
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Get PDF“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
Get PDFWe 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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