1,720,965 research outputs found
Analysis of wind-wave induced erosion in the Venice Lagoon in the last four centuries: field observations and modelling
Get PDFTidal systems are subjected to a variety of internal and external drivers whose interplay and feedbacks affect the shape and the morphological evolution of typical tidal landforms such as channel networks, salt marshes and tidal flats. Several studies have been carried out describing the various processes that drive the evolution of tidal landforms (e.g., the hydrodynamic circulation, the consequences of tidal currents and wind waves on sediment dynamics, vertical and horizontal dynamics of salt marshes, sea level rise and human interferences). Understanding the positive feedbacks existing between salt-marsh erosion, tidal-flat widening and deepening and more energetic wave generation by means of observational evidence and numerical models is a critical step to predict the response of tidal landforms to future environmental changes. With this aim we first improved current our knowledge on the ancient configurations of the Venice lagoon through the bathymetric reconstruction of the oldest map, dating back to 1611, providing a realistic representation of its morphological features. This furthermore allowed us to gain new insights on the hydrodynamic changes occurred in the last four centuries. We then compared different existing model approaches, in order to unravel the implications of different assumptions and formulations used to model wave dynamics in shallow tidal basins. Subsequently, we analysed the effects of wave action on marsh boundaries and how the wave field has changed in the last four centuries with the aim of further emphasizing the feedbacks existing between the overall erosion of the Venice Lagoon and the increase in wave power density. Finally, we analysed the bottom shear stress distribution obtained for different configurations of the Venice Lagoon, in order to support the possibility of describing wind-wave induced bottom erosion as a marked Poisson process.
The main results from this work highlighted that: I) the most important mophodynamic changes in the Venice Lagoon have started in the last century and were mainly triggered by human interferences; II) the assumptions adopted in different modelling framework strongly influence the computation of the bottom shear stress induced by waves, in particular when very shallow water depths are considered; III) the salt-marsh erosion rate is linearly related to the mean wave power density; IV) the erosive trend of the Venice Lagoon during the last four centuries can be explained also by the increase in wave power density and by the analysis of bottom shear stress distribution; V) wind-wave induced erosion processes over tidal flats can be described as marked Poisson processes for all the past and current lagoon configurations, thus leading important consequences for the prediction of future scenarios and implications for the long-term morphodynamic modelling of tidal environments
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
Changes in the wind‐wave field and related salt‐marsh lateral erosion: inferences from the evolution of the Venice Lagoon in the last four centuries
No full textSalt marshes are crucially important ecosystems at the boundary between the land and the sea, that are experiencing
significant losses worldwide mainly dictated by the erosion of their margins. Improving our understanding of the mechanisms controlling
marsh edge erosion is a key step to address conservation issues and salt-marsh response to changes in the environmental forcing.
Here we have employed a complete, coupledWind-Wave Tidal Model (WWTM) to analyse the temporal evolution of the wave field,
and in particular of the mean wave-power density, in the Venice Lagoon over the past four centuries (from 1611 to 2012). We have
then related wave-field changes to the observed erosion patterns determined by comparing recent aerial photographs (1978–2010)
and historical bathymetric data. The results of our analyses from the Venice Lagoon show that, while wave-fields did not significantly
change from 1611 to 1901, a rapid increase in wave-power densities occurred in the last century. This is suggested to depend on the
positive feedback between relevant morphological evolutions and changes in the wave field, both influenced by natural forcing and
anthropogenic pressures.We also emphasize the existence of a strong positive linear relationship between the volumetric marsh erosion
rate and mean wave-power density. We thus suggest that relating salt-marsh lateral erosion rates to properly computed mean
wave-power densities provides a valuable tool to address long-term tidal morphodynamics
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
Statistical characterization of erosion and sediment transport mechanics in shallow tidal environments – Part 1: Erosion dynamics
Get PDFReliable descriptions of erosion events are foundational to effective frameworks relevant to the fate of tidal landscape evolution. Besides the rhythmic, predictable action of tidal currents, erosion in shallow tidal environments is strongly influenced by the stochastic wave-induced bottom shear stress (BSS), mainly responsible for sediment resuspension on tidal flats. However, the absence of sufficiently long, measured time series of BSS prevents a direct analysis of the combined tide- and wave-driven erosion dynamics and its proper representation in long-term morphodynamic models. Here we test the hypothesis of describing erosion dynamics in shallow tidal environments as a Poisson process by analysing, with the peak-over-threshold theory, the BSS time series computed using a fully coupled, bi-dimensional numerical model. We perform this analysis on the Venice Lagoon, Italy, taking advantage of several historical surveys done in the last 4 centuries, which allow us to investigate the effects of morphological modifications on spatial and temporal erosion patterns. Our analysis suggests that erosion events on intertidal flats can effectively be modelled as a marked Poisson process in different morphological configurations because the interarrival times, durations, and intensities of the over-threshold exceedances are always well described by exponentially distributed random variables. The resulting statistical characterization allows a straightforward computation of morphological indicators, such as the erosion work, and paves the way for a novel synthetic, yet reliable, approach for the long-term morphodynamic modelling of tidal environments
- …
