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

Caractérisation rhéologique de la bentonite de maghnia en suspension aqueuse sans et avec additifs anioniques

L'objectif de ce travail est l’étude de l'effet de l’ajout de deux polymères anioniques sur les caractéristiques rhéologiques d'une suspension aqueuse de bentonite algérienne de forage (de Maghnia, Ouest de l’Algérie). Les additifs sont la gomme de xanthane et le carboxymethylcellulose, CMC, utilisés souvent dans la formulation des boues de forage. Dans cet article, nous présentons et discutons des mesures rhéologiques réalisés sur : 1) une suspension aqueuse de bentonite (3%), 2) des polymères en solution aqueuse (le xanthane et le CMC à trois poids moléculaires différentes) et 3) des mélanges eau-bentonite-(xanthane ou CMC) à différentes concentrations de polymère. Ce travail a permis, notamment, de renforcer la conclusion rapportée dans des travaux conduits antérieurement sur la base d’une bentonite de laboratoire, montrant la dominance du comportement rhéologique du CMC et de xanthane sur celui de la suspension de bentonit

Material anisotropy unveiled by random scattering of surface acoustic waves

We consider launching a monochromatic surface acoustic wave packet on a large set of random scatterers. The interference of the multiple scatteredwaves creates a random pattern of ripples on the crystal surface that is recorded by optical interferometry. The Fourier transform of the amplitude and phase data of the measured wave field unveils the complete slowness curve, i.e., the wave-vector as a function of the propagation angle. A simple acoustic speckle model is proposed to explain this observation.Peer reviewe

Theoretical and experimental evidence of level repulsion states and evanescent modes in sonic crystal stubbed waveguides

The complex band structures calculated using the Extended Plane Wave Expansion (EPWE) reveal the presence of evanescent modes in periodic systems, never predicted by the classical \omega(\vec{k}) methods, providing novel interpretations of several phenomena as well as a complete picture of the system. In this work we theoretically and experimentally observe that in the ranges of frequencies where a deaf band is traditionally predicted, an evanescent mode with the excitable symmetry appears changing drastically the interpretation of the transmission properties. On the other hand, the simplicity of the sonic crystals in which only the longitudinal polarization can be excited, is used to interpret, without loss of generality, the level repulsion between symmetric and antisymmetric bands in sonic crystals as the presence of an evanescent mode connecting both repelled bands. These evanescent modes, obtained using EPWE, explain both the attenuation produced in this range of frequencies and the transfer of symmetry from one band to the other in good agreement with both experimental results and multiple scattering predictions. Thus, the evanescent properties of the periodic system have been revealed necessary for the design of new acoustic and electromagnetic applications based on periodicity

The E3 ubiquitin ligase component, Cereblon, is an evolutionarily conserved regulator of Wnt signaling

Immunomodulatory drugs (IMiDs) are important for the treatment of multiple myeloma and myelodysplastic syndrome. Binding of IMiDs to Cereblon (CRBN), the substrate receptor of the CRL4CRBN E3 ubiquitin ligase, induces cancer cell death by targeting key neo-substrates for degradation. Despite this clinical significance, the physiological regulation of CRBN remains largely unknown. Herein we demonstrate that Wnt, the extracellular ligand of an essential signal transduction pathway, promotes the CRBN-dependent degradation of a subset of proteins. These substrates include Casein kinase 1α (CK1α), a negative regulator of Wnt signaling that functions as a key component of the β-Catenin destruction complex. Wnt stimulation induces the interaction of CRBN with CK1α and its resultant ubiquitination, and in contrast with previous reports does so in the absence of an IMiD. Mechanistically, the destruction complex is critical in maintaining CK1α stability in the absence of Wnt, and in recruiting CRBN to target CK1α for degradation in response to Wnt. CRBN is required for physiological Wnt signaling, as modulation of CRBN in zebrafish and Drosophila yields Wnt-driven phenotypes. These studies demonstrate an IMiD-independent, Wnt-driven mechanism of CRBN regulation and provide a means of controlling Wnt pathway activity by CRBN, with relevance for development and disease

In Vitro Antibacterial Activity of Cysteine Protease Inhibitor from Kiwifruit (Actinidia deliciosa)

The need for replacing traditional pesticides with alternative agents for the management of agricultural pathogens is rising worldwide. In this study, a cysteine proteinase inhibitor (CPI), 11 kDa in size, was purified from green kiwifruit to homogeneity. We examined the growth inhibition of three plant pathogenic Gram-negative bacterial strains by kiwi CPI and attempted to elucidate the potential mechanism of the growth inhibition. CPI influenced the growth of phytopathogenic bacteria Agrobacterium tumefaciens (76.2 % growth inhibition using 15 mu M CPI), Burkholderia cepacia (75.6 % growth inhibition) and, to a lesser extent, Erwinia carotovora (44.4 % growth inhibition) by inhibiting proteinases that are excreted by these bacteria. Identification and characterization of natural plant defense molecules is the first step toward creation of improved methods for pest control based on naturally occurring molecules

Conductive Cellulose Composites with Low Percolation Threshold for 3D Printed Electronics

We are reporting a 3D printable composite paste having strong thixotropic rheology. The composite has been designed and investigated with highly conductive silver nanowires. The optimized electrical percolation threshold from both simulation and experiment is shown from 0.7 vol. % of silver nanowires which is significantly lower than other composites using conductive nano-materials. Reliable conductivity of 1.19 × 102 S/cm has been achieved from the demonstrated 3D printable composite with 1.9 vol. % loading of silver nanowires. Utilizing the high conductivity of the printable composites, 3D printing of designed battery electrode pastes is demonstrated. Rheology study shows superior printability of the electrode pastes aided by the cellulose\u27s strong thixotropic rheology. The designed anode, electrolyte, and cathode pastes are sequentially printed to form a three-layered lithium battery for the demonstration of a charging profile. This study opens opportunities of 3D printable conductive materials to create printed electronics with the next generation additive manufacturing process