Relevance of Chemico-Osmotic and Electro-Osmotic Phenomena in Bentonite-Based Barriers

Osmosis is known to play a key role in reducing the transport rate of contaminants through the natural and engineered clay barriers that are used for a number of geoenvironmental applications, such as the lining of landfills and the deep geological disposal of radioactive wastes. Although a significant body of experimental research has focused on the quantification of osmotic phenomena in smectite clays permeated with single-electrolyte solutions, no evidence has been provided about the membrane behaviour of clays in solute mixtures and, specifically, about the so-called osmotic anomalies (i.e. membrane efficiency coefficient outside the 0 to 1 range) that have been documented in the biological and chemical literature for fine-porous charged diaphragms in the presence of two or more electrolytes. In view of the similarities between such fine-porous media and smectite clays, the aim of the paper is to discuss the conditions under which bentonite-based barriers are expected to exhibit the aforementioned osmotic anomalies, which are shown to be caused by the different diffusivities and electrochemical valences of the migrating cations

The role of diffusion induced electro-osmosis in the coupling between hydraulic and ionic fluxes through semipermeable clay soils

Most of the experimental research conducted to date has provided evidence on the semipermeable membrane behaviour of smectite-rich clay soils, the extent of which is typically quantified through the reflection coefficient, when the permeant (electrolyte) solution contains a single monovalent or divalent salt. Under such conditions, the osmotic flow of solution is controlled to a great extent by the different accessibility of ions and water molecules to the soil porosity, which is referred to as the chemico-osmotic effect. However, theoretical simulations of coupled solute and solvent transport suggest that, when two or more cations that diffuse in water at different rates are present simultaneously in the permeant solution, the electro-osmotic effect, which stems from the condition of null electric current density through the porous medium, can be enhanced compared to the case of a single salt to such an extent that it becomes comparable to or even greater than the chemico-osmotic effect. An original closed-form analytical solution to the problem of calculating the diffusion potential, which in turn controls the magnitude of the electro-osmotic effect, is here illustrated, and the relative importance of the aforementioned contributions to multi-electrolyte systems is examined through the interpretation of laboratory test results from the literature pertaining to a bentonite amended clay soil in equilibrium with aqueous mixtures of potassium chloride (KCl) and hydrochloric acid (HCl). The proposed mechanistic model is shown to be able to quantitatively capture the impact of both chemico-osmosis and electro-osmosis on the measured reflection coefficient of smectite clays, thereby breaking new ground in the experimental and theoretical research on the osmotic properties of engineered clay barriers in contact with mixed aqueous electrolyte solutions

From depth-averaging to fully three-dimensional modelling of debris-flow dynamics

Two numerical codes, with fundamental differences in their approaches, are used for modeling the Yu Tung debris flow, which occurred in Hong Kong in 2008. The first code, RASH3D, is based depthaveraged St. Venant equations, solved in an Eulerian framework. The second code, HYBIRD, is fully 3D and based on Lattice-Boltzmann Model (LBM), i.e. the conservation equations are not depth-averaged and therefore multiple velocity measures are available over the depth. The two model output are compared and discussed

Critical issues in the determination of the bentonite cation exchange capacity

The 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

Complete intraperitoneal displacement of a double J stent: a first case.

OBJECTIVES: Ureteral double-J stents are known to migrate proximally and distally within the urinary tract, while perforation and stent displacement are uncommon. Possible mechanisms of displacement are either original malpositioning with ureteral perforation or subsequent fistula and erosion of the excretory system, due to infection or long permanence of the device. We present the unique case of complete intraperitoneal stent migration in a 59-year-old caucasian male without evidence of urinary fistula at the moment of diagnosis, so far an unreported complication. MATERIALS AND METHODS: Eight months after the placement of a double-J stent for lower right ureteral stricture at a district hospital, the patient came at our observation for urosepsis and hydro-uretero-nephrosis. A CT scan demonstrated intraperitoneal migration of the stent outside the urinary tract. Cystoscopy failed to visualize the lower extremity of the stent, a percutaneous nephrostomy was placed to drain the urinary system and the stent was removed through a small abdominal incision on the right lower quadrant. RESULTS: In our case we presume that during the positioning manoeuvre the guide wire perforated simultaneously the lower ureteral wall and the pelvic peritoneum, and that once the upper end of the stent was coiled, the lower extremity was also attracted intraperitoneally. The lack of pain due to the spinal lesion concurred to this unusual complication. CONCLUSIONS: We must be aware that ureteral double J stents may be found displaced even inside the peritoneal cavity, and that the use of retrograde pyelography during placement is of paramount importance to exclude misplacement of an apparently normally coiled upper extremity of the stent

Innovar la educación en ciencias a través de enseñar y aprender acerca de la naturaleza de Ciencia y Tecnología

Esta comunicación contribuye a lema del congreso tratando de mejorar la enseñanza de la ciencia a través de una propuesta innovadora parapromover la comprensión del funcionamiento actual de la ciencia y tecnología en la sociedad (CTS),transformando las propuestas de la investigación didácticaen instrumentos útiles para los profesores en el aula. Describe las líneas básicas de un proyecto de investigación (EANCYT, Enseñanza y aprendizaje de naturaleza de la ciencia y la tecnología, NdCyT) que afronta el problema educativo de enseñar NdCyT con calidad y eficacia en países latinos.Elpropósito central es presentar los aspectos comunesdel proyecto y del simposio, es decir, los fundamentos teóricos y didácticos para enseñarcontenidos de NdCyT, que se apoyan en tres ejes básicos: la investigación sobre NdCyT, sobre secuencias de enseñanza-aprendizaje y las teorías del aprendizaje de la ciencia.Los aspectos innovadores de la comunicación se centran en el diseño de las secuencias de enseñanza aprendizaje (SEA) a aplicar en el aula, los instrumentos de evaluación de la mejora del aprendizaje de los estudiantes y el diseño empírico de la investigación para la verificación de la eficacia de las SEAs

Evaluar para un mundo en transformación : metodología e instrumentos de actitudes aplicados en el proyecto PIEARCTS

La evaluación de las creencias y actitudes de estudiantes y profesorado hacia los temas CTS, como indicadores de alfabetización científica y tecnológica, constituye un problema relevante de la investigación actual. Sin embargo, este diagnóstico no es sencillo por la naturaleza compleja del objeto evaluado y las propias dificultades de validez y fiabilidad de los procedimientos e instrumentos de evaluación. Los instrumentos empíricamente desarrollados como el Cuestionario de Opiniones sobre Ciencia, Tecnología y Sociedad (COCTS) han supuesto un avance para resolver estos problemas. Esta comunicación presenta la metodología de evaluación innovadora, propia, común y contrastada del proyecto de investigación cooperativo internacional (PIEARCTS), objeto del simposio, donde se describen las dos formas de los instrumentos aplicados, los procedimientos, resultados sobre la validez y la fiabilidad

Structural variations, electrochemical properties and computational studies on monomeric and dimeric Fe-Cu carbide clusters, forming copper-based staple arrays

The halide ligands of [Fe4C(CO)12(CuCl)2]2- (1) and [Fe5C(CO)14CuCl]2- (2) can be displaced by N-, P- or S-donors. Beside substitution, the clusters easily undergo structural rearrangements, with loss/gain of metal atoms, and formation of Fe4Cu/Fe4Cu3 metallic frameworks. Thus, the reaction of 1 with excess dppe yielded [{Fe4C(CO)12Cu}2(\uf06d-dppe)]2- (3). [{Fe4C(CO)12Cu}2(\uf06d-pyz)]2- (4) was obtained by reaction of 2 with Ag+ and pyrazine. [Fe4C(CO)12Cu-py]- (5) was formed more directly from [Fe4C(CO)12]2-, [Cu(NCMe)4]+ and pyridine. [Fe4Cu3C(CO)12(\uf06d-S2CNEt2)2]- (6) and [{Fe4Cu3C(CO)12(\uf06d-pz)2}2]2- (7) were prepared by substitution of the halides of 1 with diethyldithiocarbammate and pyrazolate, in the presence of Cu(I) ions. All these products were characterized by X-ray analysis. 3 and 4 and 5 are square based pyramids, with iron in the apical sites, the bridging ligands connect the two copper atoms in 3 and 4. 6 and 7 are octahedral clusters with an additional copper ion held in place by the two bridging anionic ligands, forming a Cu3 triangle with Cu-Cu distances ranging 2.63-3.13 \uc5. In 7, an additional unbridged cuprophilic interaction (2.75 \uc5) is formed between two such cluster units. DFT calculations were able to reproduce the structural deformations of 3-5, and related their differences to the backdonation from the ligand to Cu. Additionally, DFT found that, in solution, the tight ion pair [NEt4]27 is almost isoenergetic with the monomeric form. Thus, 3, 4 and 7 are entities of nanometric size assembled either through conventional metal-ligand bonds, or weaker electrostatic interactions. None of them allows electronic comunication between the two monomeric units, as shown by electrochemistry and spectroelectrochemical studies

Accuracy of a flash glucose monitoring system in cats and determination of the time lag between blood glucose and interstitial glucose concentrations

Background: The FreeStyle Libre (Abbott Laboratories) is a flash glucose monitoring system (FGMS) that measures interstitial glucose concentration (IG). The system is factory-calibrated, easy to use, inexpensive, and could be useful for monitoring diabetic cats. Objectives: To evaluate the analytical and clinical accuracy of the FGMS in cats and establish the lag-time between IG and blood glucose concentration (BG). Animals: Twenty client-owned diabetic cats and 7 purpose-bred healthy cats. Methods: Prospective study. Blood glucose concentration was measured using a portable glucose meter validated for use in cats that served as a reference method for IG, as measured by FGMS. In diabetic cats, data were collected for sensor wearing time with different methods of application and accuracy across glycemic ranges. Accuracy was determined by fulfillment of ISO15197:2013 criteria. In healthy cats, lag-time between IG and BG was established after IV administration of exogenous glucose. Results: Good agreement between IG and BG was obtained (r =.93). Analytical accuracy was not achieved, whereas clinical accuracy was demonstrated with 100% of the results in zones A + B of the Parkes consensus error grid analysis. In the immediate 30 minutes after an IV bolus of glucose, when BG was increasing rapidly (approximately 2%/min), IG increased slowly, resulting in a difference of as much as 579 mg/dL, and no positive correlation between BG and IG was found. Conclusions and Clinical Importance: The FGMS did not fulfill ISO requirements but is sufficiently accurate for glucose monitoring in cats, while considering the lag between IG and BG during periods of rapid changes in BG