Influence du polyéthylène oxyde (PEO) de différentes masses moléculaires sur les propriétés rhéologiques des suspensions d’argile

Le but de ce travail est d’étudier l’effet du polyéthylène oxyde (PEO) (polymère non ionique), utilisé généralement dans la formulation des boues de forage, sur le comportement rhéologique de suspensions debentonite. Des mesures rhéologiques, granulométriques et zétamétriques ont été effectuées sur une suspension de bentonite, des solutions de PEO (polyéthylène oxyde de masse moléculaire de 4.106, 106, 4.105 et 105 g.mol- 1) et des mélanges bentonite-PEO à différentes concentrations de polymères. L’étude a révélé une forte augmentation (d’autant plus importante que la concentration et la masse moléculaire du PEO  augmentent) de la viscosité, de la contrainte seuil et des propriétés viscoélastiques de la suspension argileuse. L’origine de ce changement de comportement a été discutée sur la base de l'étude zétamétrique et granulométrique. Cette dernière a mis en évidence des liaisons pont assurées par les chaînes de polymères entre les particules de bentonite.Mots clés : Boues de forage, bentonite, polyéthylène oxyde

Rheology of high-performance cement pastes: effect of calcined kaolin

The search for a quality of concrete is a major concern in Algeria especially after the 2003 earthquake (East- Algeria). So it's necessary to improve the properties of concrete using fine particles such as mineral additions as a solution. These are currently used in the concrete to develop its performance and reduce consumption of clinker. This reduction will contribute to economic and easy way to solve problems related to the environment. In this work, an experimental rheological investigation was conducted to evaluate the performances of Algerian metakaolin MK on cement pastes. The latter is obtained from calcined natural kaolin found in large amounts in eastern Algeria (Tamazert- Milia). Several rheological tests were carried out by using the stress controlled rheometer AR2000, on the fresh cement pastes incorporating 0%, 5%, 10%, 15% and 20% of MK. The effects of metakaolin on the rheological behaviour of pastes were discussed. The parameters such as shear stress, viscosity, compliance, loss and storage shear modulus were evaluated by means of rheological techniques of both flow test, oscillatory and creep dynamic tests. The study in dynamic mode allow to give information on the evolution of the paste structure related to practically interesting problems such as workability. The results obtained have shown that the metakaolin improves the flowability and exhibits viscous rheological behaviour of cement pastes compared to the elastic behaviour of control paste (0%MK). Moreover, the creep test has shown that MK exhibits a viscoelastic liquid behaviour of cement pastes compared to a viscoelastic solid behaviour of control paste. In addition, it seems that the replacement rate of 10% of MK is an optimum for better rheological behavior of cement pastes. The rheological tests give promising results that encourage the use of metakaolin as component for a high performance concrete designated for industry

Détermination des vitesses de glissement dans un écoulement diphasique par utilisation de la vélocimétrie ultrasonore Doppler pulsée

Il s'agit d'une étude des champs dynamiques d'un écoulement chargé de matières en suspension. L'objectif étant de distinguer le champ des vitesses du fluide porteur de celui des particules transportées et ainsi déduire la vitesse de glissement. La caractérisation des écoulements mixtes de phases solide et liquide reste à l'heure actuelle encore difficile à appréhender. L'étude expérimentale de ce genre d'écoulement mixte nécessite donc la mise en place de méthodes d'investigations adaptées. Une étude effectuée par vélocimétrie ultrasonore Doppler pulsée pour un écoulement diphasique va être présentée. On a vérifié que l'introduction de la phase solide modifie l'allure des profils de vitesse moyenne. Toutefois, une interprétation directe de ce type de profil semble nous apporter peu d'indications quant au comportement dynamique des particules solides. L'étude des histogrammes de vitesse fait apparaître deux pics assez bien identifiés. L'un des pics correspond à la vitesse la plus probable du fluide porteur. Le second pic correspond à la vitesse, plus faible, des particules transportées

Ecoulements de fluides à seuil : suspensions de Bentonite

L'objectif de notre travail est d'apporter un supplément de connaissances quant au comportement mécanique des boues en écoulement (suspensions de bentonite). A partir des mesures de profils de vitesses et de pressions, on étudie l'évolution des paramètres rhéologiques de ces suspensions en écoulement dans une conduite. Nous étudions les profils de vitesse en régime stationnaire et leur évolution au cours du temps ainsi que la variation des coefficients de frottement en fonction du nombre de Reynolds

Optimized testing strategy for the diagnosis of GAA-FGF14 ataxia/spinocerebellar ataxia 27B

Dominantly inherited GAA repeat expansions in FGF14 are a common cause of spinocerebellar ataxia (GAA-FGF14 ataxia; spinocerebellar ataxia 27B). Molecular confirmation of FGF14 GAA repeat expansions has thus far mostly relied on long-read sequencing, a technology that is not yet widely available in clinical laboratories. We developed and validated a strategy to detect FGF14 GAA repeat expansions using long-range PCR, bidirectional repeat-primed PCRs, and Sanger sequencing. We compared this strategy to targeted nanopore sequencing in a cohort of 22 French Canadian patients and next validated it in a cohort of 53 French index patients with unsolved ataxia. Method comparison showed that capillary electrophoresis of long-range PCR amplification products significantly underestimated expansion sizes compared to nanopore sequencing (slope, 0.87 [95% CI, 0.81 to 0.93]; intercept, 14.58 [95% CI, − 2.48 to 31.12]) and gel electrophoresis (slope, 0.84 [95% CI, 0.78 to 0.97]; intercept, 21.34 [95% CI, − 27.66 to 40.22]). The latter techniques yielded similar size estimates. Following calibration with internal controls, expansion size estimates were similar between capillary electrophoresis and nanopore sequencing (slope: 0.98 [95% CI, 0.92 to 1.04]; intercept: 10.62 [95% CI, − 7.49 to 27.71]), and gel electrophoresis (slope: 0.94 [95% CI, 0.88 to 1.09]; intercept: 18.81 [95% CI, − 41.93 to 39.15]). Diagnosis was accurately confirmed for all 22 French Canadian patients using this strategy. We also identified 9 French patients (9/53; 17%) and 2 of their relatives who carried an FGF14 (GAA)≥250 expansion. This novel strategy reliably detected and sized FGF14 GAA expansions, and compared favorably to long-read sequencing

Printability, microstructure, and flow dynamics of phase-separated edible 3D inks

Personalizing the nutrition and sensorial attributes of 3D printed foods primarily requires various multiscale properties to be individually tailored. Herein, multiscale inks are produced by segregative phase separation, a candidate for further 3D inks texture control, of gellan gum (GG), and whey protein isolate (WPI). The inks microstructure, rheological properties, flow dynamics, their impact on printability, and properties-variables interactions are analyzed using experimental design and clustering. The gels are a GG matrix structured with WPI beads or fibers ranging from 100??m in diameter. A straightforward, six-step printability test determines that high-quality prints require increasing viscosity, which is obtained by reducing the size and length of the WPI beads. Also, flow dynamics and rheology models predict the shear stress and extrusion force, according to the print settings and food-inks fluid properties. The phase-separated inks enable printing at high speed (>25/50?mm/s) upon low extrusion forces (<50?N) and low shear stresses (<500?Pa), according to the calculations and model validation. These printability evaluation methodologies and fabrication of phase-separated inks are particularly interesting for 3D food printing, bioprinting, or biomaterials applications.Nanotechnology-based functional solutions project, funded by ERDF and CCDR-N, under the call Norte2020 (Ref. NORTE-01-0145-FEDER-000019) and Enhance Microalgae (High added-value industrial opportunities for microalgae in the Atlantic Area), funded by ERDF, under the Call Interreg Atlantic Area 2014–2020 (Ref. EAPA_338/2016)info:eu-repo/semantics/publishedVersio

Caracterisation rheologique et en ecoulement d'emulsions d'huile de vaseline et d'eau et d'emulsions chargees en solides

SIGLEAvailable from INIST (FR), Document Supply Service, under shelf-number : TD 80830 / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc

Essays on Credit Risk: European studies in the context of the global financial crisis

Given the major role of credit risk in the recent financial crisis, this thesis focuses on analysing different perspectives of credit risk in Europe during the financial crisis. We consider different markets: Credit Default Swap (CDS), options on equities and exchange rates, and finally, the equity markets. We also look at the impact on different entities: corporates, banks and sovereigns however, we focus more on banks