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Saddle-node bifurcations of traveling waves in the asymptotic suction boundary layer flow
No full textThis work aims at investigating three-dimensional finite-amplitude traveling wave solutions of the asymptotic suction boundary layer, as well as their role in state space, based on direct numerical simulations. Using a body forcing and allowing wall-normal perturbations at the wall to be nonzero and linked to the pressure gradient through a wall permeability a, nonlinear invariant solutions of the Navier-Stokes equations are found and continued towards low values of the Reynolds number. The solutions, having a reflect symmetry in the spanwise coordinate, set a new threshold in state space for the onset of exact coherent flow structures. The obtained traveling waves emerge from a saddle-node bifurcation at Re-SN = 225 (based on the displacement thickness) for vanishing wall permeability. Increasing a to small but finite values changes but slightly the value of Re-SN. In all cases, the obtained Re-SN is below the lowest Reynolds number at which sustained turbulence is observed, namely, Re approximate to 270 according to recent works. The corresponding waves in the Blasius boundary layer flow without suction exist from Re-SN = 496, meaning that the asymptotic suction boundary layer might be more nonlinearly unstable (although more linearly stable) than the Blasius one. In the interval of Re studied it is found that the traveling waves occupy a region extending from the wall to the log-law region, with maximum root-mean-square velocities approaching those obtained by direct numerical simulations in the turbulent regime, especially for nonvanishing permeability. These solutions are found to be unstable, with steady leading modes, whose growth rate increases with the permeability and with the Reynolds number. When the trajectory escapes from these traveling waves along their unstable directions, transition to turbulence is observed even at Reynolds number as low as Re = 240, suggesting that these solutions may play an important role in turbulent transition at low Reynolds numbers
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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