1,720,959 research outputs found
Electrical properties of partially saturated sandstones: Novel computational approach with hydrogeophysical applications
No full textElectric and electromagnetic geophysical tools are suitable methods for investigating moisture content, transport, and storage properties of the subsoil with noninvasive surveys. Interpretation of field data is still based on empirical or semiempirical equations, which must be calibrated with complex, time-consuming laboratory measurements. In this paper we develop pore-scale models suitable for computing the effective electric conductivity and the effective permittivity of partially saturated porous media on the basis of simple structural parameters ( grain size distribution and porosity). We compute the electrical conductivity with three approaches that model the conductivity of the shell of coating clay around solid grains of shaly sandstones using different assumptions. We compare the simulated results with experimental data from Sherwood Sandstone (UK) and discuss the effect of these assumptions on the effective conductivity. Simulations performed using a modeling approach that accounts for interaction between volume and surface conduction show an excellent agreement with experimental data. We also model the effective permittivity of the same porous medium at several saturation values and obtain a good match with laboratory measurements
A saline trace test monitored via time-lapse surface electrical resistivity tomography.
No full textA saline tracer test has been performed at an industrial site, located in the Po River delta region (North-Eastern Italy). This tracer test was aimed at identifying possible hydraulic connections between a shallow unconfined aquifer and a deeper confined aquifer. Hydraulic head difference between the two aquifers is maintained via an active hydraulic barrier (pumping wells) screened in the deeper formation. The movement of the tracer in the subsurface has been monitored via electrical resistivity tomography (ERT) from the surface, using a network of twelve 48-electrode lines, for a total time period of about 45 days. This non-invasive geophysical method offers several advantages over direct water sampling from monitoring boreholes: (a) a wide area is investigated in a relatively short time; (b) a 2D picture of the subsurface is produced, in this case to a depth of about 15–20 m; (c) because of the above, it is possible to follow the tracer motion even if the tracer does not reach the few boreholes where water can be sampled. The latter is a major advantage over traditional methods, where it is not uncommon to miss the tracer plume altogether, or sample it only partially. The site is characterized by fairly saline groundwater, and the presence of diffuse silt and clay, that make the system rather conductive. Under such unfavourable conditions, careful inversion of resistance ratios was needed to identify changes in resistivity of as much as 50% with respect to background. The migration of the tracer was successfully monitored and confirmed by direct sampling of water from few boreholes. The results of the time lapse survey confirm that the system is very heterogeneous, and that some downward migration of the tracer through the confining layer can take place over relatively short time periods, maybe through some manmade connections
A saline tracer test monitored via both surface and cross-borehole electrical resistivity tomography: Comparison of time-lapse results
No full textIn contrast to traditional field investigation techniques in hydrogeology, geophysical methods are relatively non-invasive, cost effective and can be performed with a higher spatial sampling. The most commonly applied technique in hydrogeophysics is electrical resistivity tomography (ERT), both from the ground surface and in cross-borehole configurations. To infer reliable results from such a hydrogeophysical application, however, the uncertainty related to the data inversion has to be taken into account and specific attention must be paid to the experimental set-up and design, especially when the main target of the study is a quantitative estimation of some relevant hydrological quantity. The sensitivity and resolving power of ERT depend on the type of acquisition methodology; operating from the ground surface only, for example, could lead to severe limitations in terms of resolution, thus limiting the quantitative utilisation from a hydrogeological perspective. In this work, we present the results of a saline tracer test experiment performed in the saturated zone at the water works facility at Valdobbiadene (Treviso, North-East Italy), where an alluvial phreatic aquifer is heavily exploited for irrigation and drinking water supply. The experiment was monitored by time-lapse ERT acquisitions, using both surface and cross-borehole configurations. We compared the results of the two approaches and conclude that, in general, ERT has excellent imaging capabilities for saline tracer tests, however, significant limitations are inherent in the use of surface electrode configurations only. (C) 2011 Elsevier B.V. All rights reserved
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
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
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
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