Utilisation d'un nouveau bio-floculant extrait de cactus marocain dans le traitement des rejets chargés de chrome (VI) par le procédé de coagulation floculation

Dans ce travail, nous avons utilisé un nouveau floculant organique biodégradable extrait de jus de cactus (figuiers de barbarie, voir photo ci-dessous), dans un procédé physico- chimique (coagulation floculation) afin de traiter des rejets liquides chargés en chrome (VI). Ce bio-floculant nous a permis de réduire la turbidité d’un effluent industriel, en passant de 100 NTU à des valeurs au dessous de 2 NTU. L’étude a été réalisée sur des échantillons pseudo-industriels préparés au laboratoire et des échantillons industriels issus d'une unité de traitement de surface (chromage). L’étude comparative entres le floculant organique et le floculant industriel PPRQESTOLR 2515.TR (floculant à base d'acrylamide et acrylate de sodium), a montré que notre biofloculant aboutit à des résultats satisfaisants au niveau du pouvoir de floculation. Une neutralisation et coagulation avec la chaux, suivi par une floculation puis une décantation, pour la solution du chrome (VI) réduit en chrome (III) a montré un effet très significatif sur l’abattement de la turbidité et un pourcentage de rétention de chrome (VI) de plus de 99,5 %. Les résultats obtenus sont très encourageant et incitent notre équipe de recherche à développer cet axe de recherche afin de mettre en place des procédés alternatifs propres pour le traitement des eaux d’une manière générale et qui en même temps permettent la valorisation des ressources naturelles nationales.Mot-clés : Effluent Industriel, chrome (VI), Turbidité, cactus, bio- floculant, Traitement, coagulation floculation

Distribution of aortic mechanical prosthetic valve closure sound model parameters on the surface of chest

Cataloged from PDF version of article.It has been previously proposed that heart valve closure sounds can be modeled by a sum of decaying sinusoids, based on the hypothesis that the heart cavity, heart walls, major vessels, and other structures in the chest constitute a frequency selective linear acoustic system and this system is excited by the rapidly decelerating valve occluder. In this study, distribution of the parameters of this model for the second heart sound is investigated. For this purpose, heart sounds of 10 patients who have a St. Jude-type bileaflet mechanical heart valve prosthesis in aortic position are recorded. Recordings are performed at 12 different locations on the surface of the chest. To reliably assign representative parameters to each recording site, signal averaging, model order selection, and a special filtration technique are employed. The results of the analyses are discussed in relation to the above hypothesis on the heart sound generation mechanism. It is observed that site-to-site variation of frequencies of modes does not exceed the accuracy limit of proposed analysis method, but energies of these modes vary on the surface of the chest, and as a result of statistical analysis, it appears that energy of some modes are significantly different between two recording sites

Hydrodynamic coupling and rotational mobilities near planar elastic membranes

We study theoretically and numerically the coupling and rotational hydrodynamic interactions between spherical particles near a planar elastic membrane that exhibits resistance towards shear and bending. Using a combination of the multipole expansion and Faxen's theorems, we express the frequency-dependent hydrodynamic mobility functions as a power series of the ratio of the particle radius to the distance from the membrane for the self mobilities, and as a power series of the ratio of the radius to the interparticle distance for the pair mobilities. In the quasi-steady limit of zero frequency, we find that the shear- and bending-related contributions to the particle mobilities may have additive or suppressive effects depending on the membrane properties in addition to the geometric configuration of the interacting particles relative to the confining membrane. To elucidate the effect and role of the change of sign observed in the particle self and pair mobilities, we consider an example involving a torque-free doublet of counterrotating particles near an elastic membrane. We find that the induced rotation rate of the doublet around its center of mass may differ in magnitude and direction depending on the membrane shear and bending properties. Near a membrane of only energetic resistance toward shear deformation, such as that of a certain type of elastic capsules, the doublet undergoes rotation of the same sense as observed near a no-slip wall. Near a membrane of only energetic resistance toward bending, such as that of a fluid vesicle, we find a reversed sense of rotation. Our analytical predictions are supplemented and compared with fully resolved boundary integral simulations where a very good agreement is obtained over the whole range of applied frequencies.Comment: 14 pages, 7 figures. Revised manuscript resubmitted to J. Chem. Phy

Model based analysis of the variation in Korotkoff sound onset time during exercise

In this study, a minimal mathematical model of the cardiovascular system is used to study the effects of changes in arterial compliance and cardiac contractility on the onset time of Korotkoff sounds during an auscultatory procedure. The model provides blood pressure waveforms in the ventricle, the aorta and the brachial artery. From these waveforms, pre-ejection time, pulse propagation time and rise time of the blood pressure at the brachial artery can be computed. The time delay between onset time of ECG Q wave and onset time of Korotkoff sound is the sum of these three times. Rise time is zero and the time delay is minimal when the cuff pressure is slightly above the diastolic pressure. This minimum time delay is represented by QKD. Simulation results suggest that during the Bruce exercise protocol QKD decreases to one-third of its pre-exercise value if the cardiac contractility increases threefold. The effect of arterial compliance is not as significant as that of the cardiac contractility. From data recorded during an exercise test, it is observed that QKD decreases considerably as the test load is increased. We show in this study that the amount of decrease in QKD can be used as an index of the amount of increase in cardiac contractility during an exercise ECG test. Use of signal averaging for reducing the effect of motion artifacts during an exercise test is also shown to be very instrumental for making accurate QKD measurements

A reciprocal theorem for the prediction of the normal force induced on a particle translating parallel to an elastic membrane

When an elastic object is dragged through a viscous fluid tangent to a rigid boundary, it experiences a lift force perpendicular to its direction of motion. An analogous lift mechanism occurs when a rigid symmetric object translates parallel to an elastic interface or a soft substrate. The induced lift force is attributed to an elastohydrodynamic coupling that arises from the breaking of the flow reversal symmetry induced by the elastic deformation of the translating object or the interface. Here we derive explicit analytical expressions for the quasi-steady state lift force exerted on a rigid spherical particle translating parallel to a finite-sized membrane exhibiting a resistance toward both shear and bending. Our analytical approach proceeds through the application of the Lorentz reciprocal theorem so as to obtain the solution of the flow problem using a perturbation technique for small deformations of the membrane. We find that the shear-related contribution to the normal force leads to an attractive interaction between the particle and the membrane. This emerging attractive force decreases quadratically with the system size to eventually vanish in the limit of an infinitely-extended membrane. In contrast, membrane bending leads to a repulsive interaction whose effect becomes more pronounced upon increasing the system size, where the lift force is found to diverge logarithmically for an infinitely-large membrane. The unphysical divergence of the bending-induced lift force can be rendered finite by regularizing the solution with a cut-off length beyond which the bending forces become subdominant to an external body force.Comment: 15 pages, 4 figures, 80 references. Under revie

Towards an analytical description of active microswimmers in clean and in surfactant-covered drops

Geometric confinements are frequently encountered in the biological world and strongly affect the stability, topology, and transport properties of active suspensions in viscous flow. Based on a far-field analytical model, the low-Reynolds-number locomotion of a self-propelled microswimmer moving inside a clean viscous drop or a drop covered with a homogeneously distributed surfactant, is theoretically examined. The interfacial viscous stresses induced by the surfactant are described by the well-established Boussinesq-Scriven constitutive rheological model. Moreover, the active agent is represented by a force dipole and the resulting fluid-mediated hydrodynamic couplings between the swimmer and the confining drop are investigated. We find that the presence of the surfactant significantly alters the dynamics of the encapsulated swimmer by enhancing its reorientation. Exact solutions for the velocity images for the Stokeslet and dipolar flow singularities inside the drop are introduced and expressed in terms of infinite series of harmonic components. Our results offer useful insights into guiding principles for the control of confined active matter systems and support the objective of utilizing synthetic microswimmers to drive drops for targeted drug delivery applications.Comment: 19 pages, 7 figures. Regular article contributed to the Topical Issue of the European Physical Journal E entitled "Physics of Motile Active Matter" edited by Gerhard Gompper, Clemens Bechinger, Holger Stark, and Roland G. Winkle

Mobility of an axisymmetric particle near an elastic interface

Using a fully analytical theory, we compute the leading-order corrections to the translational, rotational and translation–rotation coupling mobilities of an arbitrary axisymmetric particle immersed in a Newtonian fluid moving near an elastic cell membrane that exhibits resistance towards stretching and bending. The frequency-dependent mobility corrections are expressed as general relations involving separately the particle’s shape-dependent bulk mobility and the shape-independent parameters such as the membrane–particle distance, the particle orientation and the characteristic frequencies associated with shearing and bending of the membrane. This makes the equations applicable to an arbitrary-shaped axisymmetric particle provided that its bulk mobilities are known, either analytically or numerically. For a spheroidal particle, these general relations reduce to simple expressions in terms of the particle’s eccentricity. We find that the corrections to the translation–rotation coupling mobility are primarily determined by bending, whereas shearing manifests itself in a more pronounced way in the rotational mobility. We demonstrate the validity of the analytical approximations by a detailed comparison with boundary integral simulations of a truly extended spheroidal particle. They are found to be in a good agreement over the whole range of applied frequencies.A.D.-M.-I. and S.G. thank the Volkswagen Foundation for financial support and acknowledge the Gauss Center for Supercomputing e.V. for providing computing time on the GCS Supercomputer SuperMUC at Leibniz Supercomputing Center. This work has been supported by the Ministry of Science and Higher Education of Poland via the Mobility Plus Fellowship awarded to M.L. This article is based upon work from COST Action MP1305, supported by COST (European Cooperation in Science and Technology)