1,720,961 research outputs found
Error estimates of a finite volume method for the compressible Navier--Stokes--Fourier system
Get PDFIn this paper we study the convergence rate of a finite volume approximation
of the compressible Navier--Stokes--Fourier system. To this end we first show
the local existence of a highly regular unique strong solution and analyse its
global extension in time as far as the density and temperature remain bounded.
We make a physically reasonable assumption that the numerical density and
temperature are uniformly bounded from above and below. The relative energy
provides us an elegant way to derive a priori error estimates between finite
volume solutions and the strong solution.Comment: 29 page
Numerical simulation of some viscoelastic fluids
No full textNumerical simulation of the Oldroyd-B type viscoelastic fluids is a very challenging problem. rnThe well-known High Weissenberg Number Problem" has haunted the mathematicians, computer scientists, and rnengineers for more than 40 years. rnWhen the Weissenberg number, which represents the ratio of elasticity to viscosity, rnexceeds some limits, simulations done by standard methods break down exponentially fast in time. rnHowever, some approaches, such as the logarithm transformation technique can significantly improve rnthe limits of the Weissenberg number until which the simulations stay stable. rnrnWe should point out that the global existence of weak solutions for the Oldroyd-B model is still open. rnLet us note that in the evolution equation of the elastic stress tensor the terms describing diffusive rneffects are typically neglected in the modelling due to their smallness. However, when keeping rnthese diffusive terms in the constitutive law the global existence of weak solutions in two-space dimension rncan been shown. rnrnThis main part of the thesis is devoted to the stability study of the Oldroyd-B viscoelastic model. rnFirstly, we show that the free energy of the diffusive Oldroyd-B model as well as its rnlogarithm transformation are dissipative in time. rnFurther, we have developed free energy dissipative schemes based on the characteristic finite element and finite difference framework. rnIn addition, the global linear stability analysis of the diffusive Oldroyd-B model has also be discussed. rnThe next part of the thesis deals with the error estimates of the combined finite element rnand finite volume discretization of a special Oldroyd-B model which covers the limiting rncase of Weissenberg number going to infinity. Theoretical results are confirmed by a series of numerical rnexperiments, which are presented in the thesis, too.Numerische Simulation viskoelastischer Flüssigkeiten vom Oldroyd-B Typ ist ein sehr komplexes Problem. rnTatsächlich beschäftigt das bekannte high Weissenberg number problem” viele Mathematiker, Informatiker und Ingenieure seit längerer Zeit. rnWenn die Weissenberg-Zahl, die das Verhältnis zwischen der Elastizität und der Viskosität rndes Fluides beschreibt, eine gewisse Schranke übersteigt, sind die Standardverfahren instabil und die Lösung exponentiell rnschnell in der Zeit wächst. Anderseits gibt es einige Ansätze, wie, z.B., die logarithmische Transformation, die rneine deutliche Verbesserung der Stabilität des Verfahrens und die Erhöhung der Schranke der Weissenberg-Zahl, für welche die rnnumerischen Simulationen stabil bleiben, erweisen.rn rnWir möchten darauf hinweisen, dass die globale Existenz schwacher Lösungen rnfür das Oldroyd-B Modell noch immer offen bleibt. Bei der Modellierung der Zeitevolution rndes elastischen Spannungstensors werden typischerweise die Diffusionseffekte aufgrund rnihrer Kleinheit vernachlässigt. Werden allerdings diese Diffusionsterme beibehalten, rnkann die globale Existenz schwacher Lösungen in zwei Raumdimension gezeigt werden.rn rnDer Hauptteil dieser Doktorarbeit ist den Stabilitätsuntersuchungen für die viskoelastischen Flüssigkeiten vom rnOldroyd-B Typ gewidmet. Als Erstes wird gezeigt, dass die freie Energie des diffusiven Oldroyd-B Modells sowie die rnlogarithmische-Transformation dissipativ in der Zeit sind. Weiterhin entwickeln wir dissipative numerische Verfahren, rndie auf der charakteristischen Finiten-Elementen-Methode und Finiten-Differenzen-Methode basieren. Darüberrnhinaus wird die lineare Stabilitätsanalyse des diffusiven Oldroyd-B Modells diskutiert.rnDer nächste Teil der Arbeit befasst sich mit den Fehlerschätzungen des kombinierten Finiten-Elementen- und rnFiniten-Volumen-Verfahrens für ein spezielles Oldroyd-B Modell mit der undendlichen Weissenberg-Zahl.rnTheoretische Ergebnisse werden durch eine Reihe von numerischen Experimenten, die in der Arbeit vorgestellt sind, bestätigt
Numerical simulation of some viscoelastic fluids
No full textNumerical simulation of the Oldroyd-B type viscoelastic fluids is a very challenging problem. \r\nThe well-known High Weissenberg Number Problem\" has haunted the mathematicians, computer scientists, and \r\nengineers for more than 40 years. \r\nWhen the Weissenberg number, which represents the ratio of elasticity to viscosity, \r\nexceeds some limits, simulations done by standard methods break down exponentially fast in time. \r\nHowever, some approaches, such as the logarithm transformation technique can significantly improve \r\nthe limits of the Weissenberg number until which the simulations stay stable. \r\n\r\nWe should point out that the global existence of weak solutions for the Oldroyd-B model is still open. \r\nLet us note that in the evolution equation of the elastic stress tensor the terms describing diffusive \r\neffects are typically neglected in the modelling due to their smallness. However, when keeping \r\nthese diffusive terms in the constitutive law the global existence of weak solutions in two-space dimension \r\ncan been shown. \r\n\r\nThis main part of the thesis is devoted to the stability study of the Oldroyd-B viscoelastic model. \r\nFirstly, we show that the free energy of the diffusive Oldroyd-B model as well as its \r\nlogarithm transformation are dissipative in time. \r\nFurther, we have developed free energy dissipative schemes based on the characteristic finite element and finite difference framework. \r\nIn addition, the global linear stability analysis of the diffusive Oldroyd-B model has also be discussed. \r\nThe next part of the thesis deals with the error estimates of the combined finite element \r\nand finite volume discretization of a special Oldroyd-B model which covers the limiting \r\ncase of Weissenberg number going to infinity. Theoretical results are confirmed by a series of numerical \r\nexperiments, which are presented in the thesis, too.Numerische Simulation viskoelastischer Flüssigkeiten vom Oldroyd-B Typ ist ein sehr komplexes Problem. \r\nTatsächlich beschäftigt das bekannte high Weissenberg number problem” viele Mathematiker, Informatiker und Ingenieure seit längerer Zeit. \r\nWenn die Weissenberg-Zahl, die das Verhältnis zwischen der Elastizität und der Viskosität \r\ndes Fluides beschreibt, eine gewisse Schranke übersteigt, sind die Standardverfahren instabil und die Lösung exponentiell \r\nschnell in der Zeit wächst. Anderseits gibt es einige Ansätze, wie, z.B., die logarithmische Transformation, die \r\neine deutliche Verbesserung der Stabilität des Verfahrens und die Erhöhung der Schranke der Weissenberg-Zahl, für welche die \r\nnumerischen Simulationen stabil bleiben, erweisen.\r\n \r\nWir möchten darauf hinweisen, dass die globale Existenz schwacher Lösungen \r\nfür das Oldroyd-B Modell noch immer offen bleibt. Bei der Modellierung der Zeitevolution \r\ndes elastischen Spannungstensors werden typischerweise die Diffusionseffekte aufgrund \r\nihrer Kleinheit vernachlässigt. Werden allerdings diese Diffusionsterme beibehalten, \r\nkann die globale Existenz schwacher Lösungen in zwei Raumdimension gezeigt werden.\r\n \r\nDer Hauptteil dieser Doktorarbeit ist den Stabilitätsuntersuchungen für die viskoelastischen Flüssigkeiten vom \r\nOldroyd-B Typ gewidmet. Als Erstes wird gezeigt, dass die freie Energie des diffusiven Oldroyd-B Modells sowie die \r\nlogarithmische-Transformation dissipativ in der Zeit sind. Weiterhin entwickeln wir dissipative numerische Verfahren, \r\ndie auf der charakteristischen Finiten-Elementen-Methode und Finiten-Differenzen-Methode basieren. Darüber\r\nhinaus wird die lineare Stabilitätsanalyse des diffusiven Oldroyd-B Modells diskutiert.\r\nDer nächste Teil der Arbeit befasst sich mit den Fehlerschätzungen des kombinierten Finiten-Elementen- und \r\nFiniten-Volumen-Verfahrens für ein spezielles Oldroyd-B Modell mit der undendlichen Weissenberg-Zahl.\r\nTheoretische Ergebnisse werden durch eine Reihe von numerischen Experimenten, die in der Arbeit vorgestellt sind, bestätigt
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
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe 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
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
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