1,720,957 research outputs found
Coastal vulnerability: the impact of sea level rise at the physiographic unit scale
Full text linkThe Intergovernmental Panel on Climate Change foresees a significant global sea-level rise (SLR) during the 21st century, which will cause an increase in coastal vulnerability (CV) to erosion and flooding. CV can be estimated at different spatial and time scales ranging from national to local and from tens to hundreds of years, respectively. However, flooding and erosional scenarios need to be calculated at the physiographic unit (PU) and on a decadal scale to plan strategies for defending communities living in the coastal areas and to protect critical infrastructures and natural habitats. We present preliminary results of a study which aims to develop a method for assessing the CV to sea level rise, calculated at the PU scale and on the ten-year time scale. This study is based on: a) the identification of the most significant near-shore marine forcings that control the sediment transport and flooding; b) the prediction of the CV to erosion and flooding under the control of the SLR. We have performed two-dimensional models of wave propagation, sediment transport and morphological changes in the nearshore area and sand/gravel beaches, using the XBeach software. We have integrated grainsize, bathymetric, topographic and wave data (e.g. significant wave height, mean period and average direction of origin of the wave motion). The 18 PU was chosen for testing the method. This area is ~70 km long and extended from Capo Mongerbino and Cefalù (northern Sicily). It is characterized by rocky and low sand/gravel beaches. About 37% of the coastal perimeter suffers from important erosive phenomena resulting in coastal regression with rates that reach the value of 1m/year. Moreover, the coasts are characterized by different orientations and, thus, it is possible to test the influence of different exposure to wind and waves. The expected result is to provide a map of CV to erosion and flooding at the PU scale and on a decadal scale. The method, proposed in this research, allow to understand the synergetic effects of sea level changes and marine forcings affecting the coastal system. Moreover, a fully integrated assessment of CV is useful in supporting policy decision making
Evaluating longshore sediment transport: A comparison between empirical formulas and XBeach 2DH numerical model
Full text linkLongshore sediment transport (LST) is a crucial process shaping coastal environments. As multiple site-specific factors (e.g. wave height, coastal topography) influence the LST, an accurate estimation of LST rate represents a scientific challenge.
This research evaluates the predictive capacity of three widely used empirical formulas (CERC, 1984; Kamphuis, 1991; Van Rijn, 2014) and the XBeach 2DH numerical model for estimating the LST rate by comparing the obtained results with field LST data.
We chose three coastal sites in Malta Island (Għadira Bay, GB) and northern Sicily (Cefalù, CF, and Campofelice di Roccella, CR) based on different sediment grain size, coastal type (open or embayed) and morpho-bathymetry.
For each site, we analysed wave parameters, grain size of the beach and seabed sediments, coastal morphology, and marine vegetation distribution. Furthermore, we used field measurements to calibrate the numerical model's sediment transport and morphological parameters.
The calibrated numerical model provides greater accuracy in LST rate estimation than the empirical formulas. The latter overestimates the LST rates by factors ranging from 435 to 7885, whereas the numerical model overestimates by factors of 1.8 and 1.9 at the CF site and GB, respectively, and underestimates by a factor of 0.5 at the CR site.
The good performance of the numerical model is due to its consideration of site-specific factors. The parameter values for the model calibration can be used successfully in embayed fine/coarse sandy beaches. Moreover, the numerical model, tested so far only for sandy beaches, also works well on gravelly beaches
On the Lowstand System Tracts (LSTs) as paleobathymetric indicators
Full text linkLowstand Systems Tracts (LSTs), formed in the transitional area between the continental shelf and upper slope during the sea level stillstand of the Last Glacial Maximum (LGM), were used to measure the magnitude and rate of Late Pleistocene-Holocene vertical tectonic movements (Casalbore et al., 2017; Fraccascia et al., 2013; Pepe et al., 2014). A literature review shows that different empirical methods have been used to derive the paleo depth of LSTs’ formation. Consequently, the amount and rate of vertical movements calculated for different areas are not comparable. Here, we present the first results of a quantitative analysis of oceanographic and geologic data to estimate the position of the paleo-sea level related to the depth of the LST. The dataset consists of high-resolution reflection seismic profiles, storm wave parameters (e.g., significant wave height, wave period) and grain-size data. The comparison between the theoretical beach equilibrium profile, derived from the Bruun’s method (Bruun, 1954), and the upper bounding surface of LST recognized in the seismic profile provides a depth of about 135 m of the paleo-sea level during the formation of the LST. The obtained value of the paleo-sea level combined with the depth of closure fits with the seaward limit of the active beach profile observed along the seismic section. The results of the quantitative analysis integrated with the Holocene sea-level curves are used to derive the post-LGM vertical tectonic movements along the upper slope of the Southern Tyrrhenian Sea. The present study also provides a vertical tectonic movements chart of the southern Tyrrhenian Sea in the late Quaternary
Method for assessing the coastal vulnerability to erosion and flooding at the physiographic unit scale
Full text linkThe Intergovernmental Panel on Climate Change foresees a significant global sea-level rise (SLR) during the 21st century, which will cause an increase in coastal vulnerability (CV) to erosion and flooding. CV can be estimated at various scales, both in space (from national to local) and time (from tens to hundreds of years). However, flooding and erosional scenarios need to be calculated at the physiographic unit (P.U.) and on a decadal scale to plan strategies for defending communities living in the coastal areas and to protect critical infrastructures and natural habitats. We present preliminary results of a study for assessing the coastal vulnerability to erosion and flooding at the P.U. scale and on the ten-year time scale. This study is based on the analysis of natural marine nearshore factors (e.g., waves, currents) that control the sediment transport and flooding. The method consists of assessing how these factors control the phenomena of erosion and flooding under the influence of the SLR. We have performed two-dimensional models of wave propagation, sediment transport and morphological changes in the nearshore area and sand/gravel beaches using XBeach model. We have integrated grain-size data, bathymetry, meteorological and wave data. The latter derive from the DICCA hindcast database. For testing the method, 18 P.U. were chosen in the coastal zone between Capo Mongerbino and Cefalù (northern Sicily). This area is ~70 km long and is characterized by rocky and low sand/gravel beaches. About 37% of the coastal perimeter suffers from important erosive phenomena resulting in coastal regression with rates that in some cases exceed the value of 1 m/year (Regione Siciliana - Assessorato Territorio E Ambiente, 2006). Moreover, the coasts are characterized by different orientations and, thus, it is possible to test the influence of different exposure to wind and waves. The expected result is a map of CV to erosion and flooding at the physiographic unit scale and on a decadal scale. This study will help to better understand the natural near-shore processes controlling the CV
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
Sviluppo e validazione di un metodo analitico per quantificare i movimenti tettonici verticali attraverso l’uso di cunei progradanti di stazionamento basso
Full text linkI cunei progradanti, che si sono formati durante l’ultima fase di caduta e stazionamento basso del livello del mare (LSTs), sono indicatori paleo-batimetrici utilizzati per calcolare i tassi dei movimenti verticali di aree offshore negli ultimi 20.000 anni. Studi precedenti hanno usato metodi empirici differenti per stimare la paleoprofondità di formazione dei LSTs. Ne consegue che i tassi dei movimenti verticali non sonoconfrontabilitra loro. Questo lavoro presenta i risultati di una ricerca multidisciplinare finalizzata allo sviluppo e alla validazione di un metodo analitico per quantificare i movimenti tettonici verticali di aree offshore. Gli obiettivi sono 1) la stima della profondità di formazione dei LSTs e 2) l’identificazione del punto morfologico dei LSTs da utilizzare come indicatore di paleo-batimetria. Per raggiungere gli obiettivi, è stato analizzato un grid di 65 profili sismici a riflessione ad alta risoluzione, acquisiti lungo il settore offshore tirrenico della Calabria. Inoltre, sono stati utilizzati i parametri delle onde marine, calcolati nel settore offshore di Capo Vaticano (Calabria centro-occidentale), ed i vincoli derivanti dalla profondità di chiusura (DoC). Quest’ultima è una soglia al di sotto della quale termina l’interazione tra le onde e i sedimenti del LST, ed è funzione del clima ondoso dell’area. Pertanto, sono stati stimati i valori dell’altezza d’onda significativa (Hs), del periodo (Ts), e le relative deviazioni standard, per l’intervallo di tempo 1979-2018 nel settore offshore di Capo Vaticano, usando specifici dati di re-analisi (“hindcast”). Per calcolare la DoC è stato adottato il modello proposto da Hallermeier (1981), secondo cui la DoC rappresenta il settore di raccordo tra la zona di transizione e l’offshore. I risultati ottenuti indicano che nell’area di Capo Vaticano il valore medio della DoC è di 8,2 (±1,5) m. I movimenti verticali dell’area di Capo Vaticano negli ultimi 20.000 anni sono stati calcolati utilizzando il valore della DoC e la curva di variazione del livello del mare proposta da Lambeck et al. (2011). I valori ottenuti suggeriscono il verificarsi di movimenti differenziali tra diversi settori dell’area in studio. La comparazione tra i valori dei movimenti verticali ottenuti con il metodo proposto in questo lavoro e quelli presenti in letteratura evidenzia delle differenze legate ad una diversa stima della profondità di formazione del LST. Il metodo sviluppato in questo lavoro fornisce nuovi vincoli per stimare la profondità di formazione dei LSTs, necessaria per quantificare i movimenti verticali di aree offshore negli ultimi 20.000 anni
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
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
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