1,720,981 research outputs found
Stochastic modeling of well head protection zones in highly heterogeneous aquifers
No full textThe assessment of well head protection zones is strongly related to spatial variability of hydrogeological properties. To set up a numerical model for probabilistic wellhead protection zone delineation, field and laboratory scale experiments for subsurface investigation were performed at the “Lauswiesen” site in southern Germany. At this site, spatial variations of hydraulic conductivity mainly dominate flow and transport processes. By means of a multivariate cluster analysis, three different types of aquifer materials (facies) were identified to characterize the heterogeneity of the aquifer lithology. Spatial variability of each material type was separately analysed by a geostatistical procedure based on indicator variography. Three-dimensional recombined distributions of the identified clusters were used to reconstruct the internal aquifer architecture. Then, three-dimensional time related mean well head protection zones and their associated uncertainty were obtained by a Monte Carlo stochastic simulation procedure
A composite medium approach for probabilistic modelling of contaminant travel time distribution to a pumping well in a heterogeneous aquifer
No full textWe analyse the probabilistic nature of the time of travel of conservative solutes to a pumping well operating within a heterogeneous aquifer. The latter is modelled as a three-dimensional, doubly stochastic composite medium, where distributions of geological materials and hydraulic properties are uncertain. The problem is tackled within a numerical Monte Carlo framework. We study the importance of uncertain facies geometry and uncertain hydraulic conductivity and porosity on predictions of solute time of travel to the pumping well by focusing on two special cases in which: (1) the facies distribution is random, but the hydraulic properties of each material are fixed, and (2) both facies geometry and material properties vary
Multivariate geostatistical parameterization approach for 3D transient stochastic modeling of wellhead protection zones in a highly heterogeneous aquifer
No full textHydrogeological parameterization is a key step in modeling well head protection zones in alluvial heterogeneous deposits, often exploited for drinking water needs. We performed field and laboratory scale experiments for subsurface investigation at the “Lauswiesen” site in southern Germany, targeted to set up a numerical model for probabilistic wellhead protection zones assessment. The neighbouring Neckar river is the main boundary condition and strongly impacts the groundwater flow regime. Spatial variations of hydraulic conductivity, K, over several orders of magnitude, mainly dominate flow and transport processes. Sieve analyses performed on undisturbed core samples emphasized a very heterogeneous , highly conductive aquifer. By means of a multivariate cluster analysis, three different types of aquifer materials (clusters / facies) were identified to characterize the heterogeneity of the aquifer lithology. Spatial variability of each material type was separately analysed by a geostatistical procedure based on indicator variography. As a result, 3D recombined spatial distributions of the identified clusters were used to reconstruct the internal aquifer architecture. Since each cluster is completely characterized in terms of its hydraulic and transport parameters, internal variability as well as structural properties, the methodology yields three-dimensional pictures of aquifer parameter distributions, avoiding the usual difficulties of upscaling. The assessment of well head protection zones and their associated uncertainty are then obtained by a Monte Carlo procedure, based on equiprobable realizations of hydraulic conductivity fields. These are embedded within the numerical aquifer model to render the probabilistic well-capture zones distribution, subject to the initial and transient boundary conditions observed at the field site
Caratterizzazione geostatistica delle proprietà idrauliche di un acquifero alluvionale utilizzando dati di prove di emungimento
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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
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
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