1,721,523 research outputs found
Planform changes and overbank flow in meandering rivers: The river Allier
No full textIn this study the river migration model MIANDRAS has been applied to simulations of the planform changes of the river Allier, a tributary of the river Loire in France. The Allier is a very dynamic and natural river system with braided and meandering river sections. Two meandering reaches of the Allier, located between Varennes-sur-Allier and Moulins, have been examined in the present study. MIANDRAS is a numerical model that simulates meandering processes in shallow alluvial rivers with erodible banks. In MIANDRAS the river is schematised as a single meandering channel, as the floodplains are assumed non-conveying. For the prediction of river planform changes, the rate and direction of bank erosion are computed by coupling a steady-state flow and bed topography model with a time-dependent bank erosion model. Sediment gradation, timedependent variations of the bed topography (i.e. migrating bars) and flow exchanges between the main channel and the floodplains are not taken into account. MIANDRAS did not perform satisfactorily in predicting the planform changes of the Allier. The 2(and 3-) dimensional flow processes in flood periods, caused by floodplain constrictions and flow exchange between the main channel and the floodplains, appeared to be an important feature influencing the bank erosion. Therefore, the influence of overbank flow was studied in more detail. The 3-dimensional flow model DELFT3D-FLOW (TRISULA) was used to simulate overbank flow processes in one of the examined reaches of the Allier. The results of the MIANDRAS computations can be explained reasonably well from the results of the overbank flow computations. Near the upstream floodplain constriction, where high bank erosion rates were observed in the prototype river, high velocities occurred in the overbank flow computations. At this location high bank erosion coefficients had to be adopted in the MIANDRAS computations. The relatively low erosion rates at the downstream boundary can be explained by the low velocities occurring in overbank flow. These are due to backwater effects near the downstream floodplain constriction. The small erosion rates at this location resulted in small erodibilities in the MIANDRAS computations. Floodplain bed roughness appears to have a significant influence on velocity directions and magnitudes. The velocity field is correlated to the flow exchange between the main channel and the floodplains. This flow exchange strongly decreases in the case of a higher floodplain bed roughness. These results agree with the results of scale model experiments performed in the Flood Channel Facility at HR Wallingford, England. The results of this study give new indications for the range of applicability of MIANDRAS. Besides the possibility to use MIANDRAS in case of rivers with mainly inbank flow, the model can also be applied to rivers with overbank flow periods, provided that the flow exchange between the main channel and the floodplains is small. A small flow exchange occurs in case of a high floodplain bed roughness, a straight floodplain and main channel, or relatively small flood discharges.Hydraulic EngineeringCivil Engineering and Geoscience
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
Experimental Methodology for Investigating environmental DNA traces Spreading in Rivers
No full textThe biomonitoring of ecosystems is a key operation for evaluating the status of conservation or restauration of biodiversity. Recently, sampling of environmental DNA (eDNA) was evaluated as a promising tool for the future biomonitoring campaigns. For its application many studies have been performed for evaluating the amount of genetic material released by single species and the persistence of this information in static water environments, as ponds or lakes. Here, we demonstrate that more investigations are needed for evaluating the relevance of the transport of eDNA traces over the other parameters. In particular, we believe that the transport is relevant in all environments governed by high Reynolds numbers, because the advection processes will cause the drift of the traces. For this reason, we here publicize an experimental campaign planned for investigating the trace drift and the eventual breaking of the eDNA traces
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
- …
