1,721,015 research outputs found
Sulla possibilità di definizione della zona di rispetto di un campo-pozzi con riferimento agli effettivi scenari di utilizzo
No full textSimulation of dispersion in heterogeneous porous formations: statistics, first-order theories, convergence of computations
Full text linkThis paper discusses the results of numerical analysis of dispersion of passive solutes in two-dimensional heterogeneous porous formations. Statistics of flow and transport variables, the accuracy and the role of approximations implicit in existing first-order theories, and the convergence of computational results are investigated. The results suggest that quite different rates of convergence with Monte Carlo runs hold for different spatial moments and that over 1000 realizations are required to stabilize second moments even for relatively mild heterogeneity (σY2 < 1.6). This has implications for the extent of the spatial domain for single-realization numerical studies of the same type. A comparison of the variance of plumes with the results of linear theories (0.05 < σY2 < 1.6) shows an unexpectedly broad validity field for the theoretical solution obtained from a suitable linearization of flow and transport. Reformulation of the same problem linearizing in turn the flow or the transport equations shows opposite deviations from the linear theory. The interesting consequence is that the errors induced by linearizations in the flow or the transport equations have different signs, and their effects on the moments of dispersing plumes are compensating, thereby yielding consistent formulations. Unexpected features of the statistics of probability distributions of longitudinal and transverse velocities and travel times are also computed and discussed
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
A comparison between hydrological model predictions and micro-gravity time-lapse distributed surveys
No full textOn the Lagrangian formulations of reactive solute transport in the hydrologic response
No full textWe address Lagrangian dispersion of reactive solutes in the framework of the formulation of transport by travel time distributions, specifically aiming at models of basin-scale, nonpoint transport applicable to complex geomorphological settings. We revisit existing exact solutions of the reactive transport problem derived in the convective stochastic framework and extend them to the case of transport of mass arbitrarily distributed (in time and space) within the immobile phase, a situation which is arguably suited to better describe nonpoint source solute transport driven by the hydrologic response. The initial conditions and, particularly, the mass initially stored in immobile rather than mobile phases bear a pronounced effect on the spatial and temporal moments of the solute plume. We also show that in many nonpoint source cases of interest (typically when heterogeneous conditions prevail) a simpler model of reaction kinetics, where spatial gradients in the immobile concentration are neglected, does well. Such a class of models, termed mass response functions, is known from the literature and has the property, beside being simplified in the mass exchange terms, of embedding unsteady flow forcing of the type typically employed in the theory of the hydrologic response. Thus, in the range of cases where the well-mixed assumption proves meaningful, we suggest a natural extension of current geomorphological models of the hydrologic response to generic transport phenomena
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