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Tertiary patterns in inclined layer convection
No full textConvection in an inclined layer generates various types of spatio-temporal patterns due to interaction of buoyancy and shear. At small angles of incline, the secondary instability of the uniform base state occurs in the form of buoyancy dominated longitudinal rolls. Above a critical angle of incline marking a co-dimension 2 point, shear driven transverse roll instabilities take over as the secondary instabilities. Computing the location of the co-dimension 2 point for varying thermal driving and inclination angle and determining all secondary bifurcations together with the resulting tertiary states allows to characterize the nonlinear phase diagram of inclined layer convection system. The semi-analytically computed phase diagram quantitatively matches experimental observations by Daniels et al. Close to the co-dimension 2 point, a subcritical secondary bifurcation leading to bistability is identified. In the bistable region, heteroclinic cycles generate bursting behavior
Mean flow effects in the electro-hydrodynamic convection in nematic liquid crystals
No full textOn the basis of the weakly nonlinear analysis a set of two coupled amplitude equations is derived, which lead to a better understanding of the electro-hydrodynamic instability in nematic liquid crystals near onset. It is shown that the normal convective patterns are very sensitive against large scale flow (mean flow) modes, which are systematically included. Simulation of the equations shows typically a complex spatio-temporal behavior ("defect turbulence") very similar to the situation often observed in experiments
Structure and dynamics of dislocations in anisotropic pattern-forming systems
No full textThe motion of dislocations in convective roll patterns provides an important wavevector selection mechanism. In this work the structure and velocity of dislocations is calculated near threshold using amplitude equations appropriate for systems with an axial anisotropy. The fact that then the roll pattern has a preferred direction leads to characteristic differences to isotropic systems like Rayleigh-B?nard convection in simple fluids. Furthermore the nucleation process of dislocation pairs is discussed by analyzing the threshold solution that describes the nucleation barrier
Dislocation dynamics in Rayleigh-Bénard convection
No full textTheoretical results on the dynamics of dislocations in Rayleigh-Benard convection are reported both for a Swift-Hohenberg model and the Oberbeck-Boussinesq equations. For intermediate Prandtl numbers the motion of dislocations is found to be driven by the superposition of two independent contributions: (i) the Peach-Koehler force and (ii) an advection force on the dislocation core by its self-generated mean flow. Their competition allows to explain the experimentally observed bound dislocation pairs
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
Invited Lecture. New results on the electrohydrodynamic instability in nematics
No full textWe present theoretical results on the threshold and near-threshold behaviour of electrohydrodynamic convection of planarly aligned nematics under D.C. and A.C. driving. We use the general three dimensional description and include the flexoelectric effect. The experimentally established threshold behaviour is captured in many cases quantitatively, an exception being the extended travelling patterns. Slightly above threshold the observed undulated rolls pose some problems. Defectmediated turbulence can presumably be explained by mean-flow effects
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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