1,720,981 research outputs found
Chemico-osmotic coefficients of geosynthetic clay liners under different confinement conditions
No full textCritical issues in the determination of the bentonite cation exchange capacity
Full text linkThe swelling pressure and transport properties of bentonites are controlled by the electric charge density of solid particles, which is commonly estimated from the laboratory measurement of the cation exchange capacity (CEC). However, the standard ammonium displacement method for CEC determination does not take into account the fabric changes that occur in bentonites under exposure to high salt concentration solutions. A series of laboratory tests was conducted to assess the relevance of such a critical issue, by varying the concentration of the extracting KCl solution with respect to that of the standard test. The obtained results show that the release of the adsorbed ammonium cations depends on the bentonite fabric, which is controlled by the KCl concentration. As a consequence, the ammonium displacement method may provide an unrepresentative estimate of the CEC of bentonites. The methylene blue titration method, despite its apparently more limited accuracy, instead seems to provide a more reliable estimation of the CEC, as the bentonite fabric is maintained dispersed during the test
Investigating the Semi-Permeable Membrane Behavior of Geosynthetic Clay Liners by Means of a Novel Apparatus
Full text linkThe paper presents a recently developed rigid-wall diffusion cell and the experimental setup that allows the determination of the coefficient omega, which quantifies the degree of solute restriction in clays or GCLs that exhibit semi-permeable membrane behaviour. In addition, the apparatus allows the monitoring of the total vertical stress acting on the specimen during a chemico-osmotic diffusion test while keeping the vertical deformations at a negligible level (<1%). This improvement of the traditional testing approach allows for the determination of the chemical-osmotic efficiency coefficient, omega, and of the swelling coefficient omega, the main parameters that characterize the chemico-osmotic behaviour of clays and GCLs on the same specimen. The paper also reports on the results of some tests carried out on conventional and enhanced GCLs, with the main purpose of comparing the results obtained by means of the new testing apparatus with literature data. A first application of an advanced existing theoretical model for the description of chemical-osmotic phenomena to the results obtained is also illustrated
Sorption and hydraulic performance of cement-bentonite cutoffs in saline sulphatic solutions
Full text linkThe paper discusses the results of an experimental research on the short and long term hydraulic performance and sorption of cement-bentonite mixtures in saline sulphate solutions. Batch tests at different curing times and permeation tests were performed on three cement-bentonite mixtures with solutions of K2SO4. The results show that permeation can adversely affect the hydraulic performance of cement-bentonite mixtures depending on the sulphate concentration and mixture composition and that the choice of a very low permeable mixture is essential to limit adverse effects of interaction with SO42- on the hydraulic performance. Sorption of K+ was found to be significant, well described by a linear isotherm in a wide range of concentration and nearly constant with curing. Sorption of SO42 was found to decreases with mixture porosity. Since sorption of SO42- means negative interaction, batch tests were found to be useful for a rapid estimation of possible negative effect of SO42- on the hydraulic behaviour in the long term, when selecting a mixture in the design phase. All the results point out the importance of selecting a mixture to be used for cut-off walls with a low hydraulic conductivity already at brief curing and of carefully considering interaction with solute pollutants and sorption capacit
Hydraulic conductivity and sorption capacity of special barrier materials in inorganic solutions
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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
Chemico-osmotic efficiency of geosynthetic clay liners: Testing apparatus and preliminary results
No full textThe membrane behaviour of conventional and enhanced Geosynthetic Clay Liners is regarded with interest for applications in barrier systems as the presence of chemical osmosis improves the GCL containmenty properties. With the purpose of assessing the existence and persistence of chemico-osmotic behavior in GCLs, an apparatus able to perform chemico-osmotic diffusion tests on GCLs and soils has been developed. The paper describes the main features of the systems and preliminary results obtained using conventional and polymer-amended GCLs and a 20 mM KCl solution. The measured osmotic efficiency and solute diffusion coefficients were close to results in the literature on similar GCL materials and similar testing conditions, proving the system reliability
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
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