Combination of 13 C/ 113 Cd NMR, potentiometry, and voltammetry in characterizing the interactions between Cd and two models of the main components of soil organic matter

International audienceThis work allowed the characterization of the Cd-binding sites of two compounds taken as models for exudates, the main components of soil organic matter (SOM). The studied compounds were exopolysaccharides (EPS), specifically exudates of roots (polygalacturonic acid) and of soil bacteria (Phytagel). Potentiometric acid– base titrations were performed and fitting of the obtained results indicated the presence of two main classes of acidic sites, defined by their pK a values, for both EPS but of a different nature when comparing the two compounds. The two studied exopolysaccharides presented different acidic/ basic site ratios: 0.15 for Phytagel and 0.76 for polyga-lacturonic acid. Spectroscopic techniques (13 C/ 113 Cd NMR, FTIR) distinguished different Cd surroundings for each of the studied EPS, which is in agreement with the titration results. Furthermore, these analyses indicated the presence of –COOH and –OH groups in various proportions for each exopolysaccharide, which should be linked to their reactiv-ity towards cadmium. Cadmium titrations (voltammetric measurements) also differentiated different binding sites for each compound and allowed the determination of the strength of the Cd-binding site of the EPS. Fitting of the results of such voltammetric measurements was performed using PROSECE (Programme d'Optimisation et de Speci-ation Chimique dans l'Environnement), a software coupling chemical speciation calculation and binding parameter optimization. The fitting, taking into account the Cd 2+ /H

The flow of a very concentrated slurry in a parallel-plate device: influence of gravity

We investigate, both experimentally and theoretically, the fow and structure of a slurry when sheared between 2 horizontal plates. The slurry, otherwise called a "wet granular material", is made of non-Brownian particles immersed in a viscous fluid. The particles are heavier than the fluid, consequently, gravity influences the structure and flow profiles of the sheared material. Experiments are carried out in a plane Couette device, with a model slurry composed of approximately monodisperse spherical PMMA particles in oil, at high average solid concentration (about 58%). Optical observation reveals a typical 2-phase configuration, with a fluidized layer in contact with the upper plate and on top of an amorphous solid phase. We provide data on velocity profiles, wall-slip and shear stress versus the average shear rate. To interpret the data, we propose a model for the ideal case of infinite horizontal flat plates. The model, of mean field type, is based on local constitutive equations for the tangential and normal components of the stress tensor and on expressions relating the material viscometric coefficients (the shear viscosity eta and the normal viscosity psi) with the local concentration (phi) and the local shear rate. 1-,2- and 3-phase configurations are predicted, with non linear flow and concentration profiles. We conclude that the model equations correctly describe the experimental data, provided that appropriate forms are chosen for the divergence of eta and psi near the packing concentration (phi_max), namely a (phi_max-phi)^-1 singularity.Comment: 26 pages, 12 figures ; submitted to Physics of Fluid

Nouvelles données sur la séquence aurignacienne de la grotte d'Isturitz (communes d'Isturitz et de Saint-Martin-d'Arberoue. Pyrénées-Atlantiques)

Isturitz Cave is located in the western Pyrenees in the heart of the zone of passage and contact between the Aquitaine region and the Vasco-Cantabrian ledge. Excavations during the first half of the 20th century yielded a remarkable archaeological sequence covering the Middle Palaeolithic and the entire Upper Palaeolithic. New research conducted in the Saint-Martin chamber has revealed intensive Aurignacian occupations attributed to the archaic and early phases of this techno-complex. In this paper, we present a synthesis of the principal data that make Isturitz a key site in the study of this period.Située dans les Pyrénées occidentales, au coeur de la zone de passage et de contact entre l'Aquitaine et la corniche vasco-cantabrique, la grotte d'Isturitz a fait l'objet, dans la première moitié du XXe siècle, de fouilles qui ont livré un remarquable ensemble archéologique couvrant le Paléolithique moyen et la quasi-totalité du Paléolithique supérieur. De nouvelles recherches menées dans la salle de Saint-Martin ont mis en évidence d'importantes occupations aurignaciennes attribuées aux phases archaïques et anciennes de ce technocomplexe. Nous ferons dans cet article une synthèse des principales données qui font de la grotte d'Isturitz un site clef pour l'étude de celles-ci

Hepatitis C Virus Infection May Lead to Slower Emergence of P. falciparum in Blood

International audienceBACKGROUND: Areas endemic for Plasmodium falciparum, hepatitis B virus (HBV) and hepatitis C virus (HCV) overlap in many parts of sub-Saharan Africa. HBV and HCV infections develop in the liver, where takes place the first development stage of P. falciparum before its further spread in blood. The complex mechanisms involved in the development of hepatitis may potentially influence the development of the liver stage of malaria parasites. Understanding the molecular mechanisms of these interactions could provide new pathophysiological insights for treatment strategies in Malaria. METHODOLOGY: We studied a cohort of 319 individuals living in a village where the three infections are prevalent. The patients were initially given a curative antimalarial treatment and were then monitored for the emergence of asexual P. falciparum forms in blood, fortnightly for one year, by microscopy and polymerase chain reaction. PRINCIPAL FINDINGS: At inclusion, 65 (20.4%) subjects had detectable malaria parasites in blood, 36 (11.3%) were HBV chronic carriers, and 61 (18.9%) were HCV chronic carriers. During follow-up, asexual P. falciparum forms were detected in the blood of 203 patients. The median time to P. falciparum emergence in blood was respectively 140 and 120 days in HBV- and HBV+ individuals, and 135 and 224 days in HCV- and HCV+ individuals. HCV carriage was associated with delayed emergence of asexual P. falciparum forms in blood relative to patients without HCV infection. CONCLUSIONS: This pilot study represents first tentative evidence of a potential epidemiological interaction between HBV, HCV and P. falciparum infections. Age is an important confounding factor in this setting however multivariate analysis points to an interaction between P. falciparum and HCV at the hepatic level with a slower emergence of P. falciparum in HCV chronic carriers. More in depth analysis are necessary to unravel the basis of hepatic interactions between these two pathogens, which could help in identifying new therapeutic approaches against malaria

Black Studies @ Northwestern University

This volume is a compilation of documents related to the history of Black Studies at Northwestern University. The project was the requirement of a course of Afro American Studies Afr0500, core problems in African American Studies by Professor Abdul Alkalimat. Actually, this volume is included in a larger project aiming to build a documentary history of Black studies in Illinois. I will explain how I have proceeded to gather the following documentation.published or submitted for publicatio

Flow and segregation in model granular pastes

Nous étudions les phénomènes de ségrégation par taille dans des suspensions concentréesde particules en écoulement. Les particules sont plus lourdes que le fluide, comme dans laplupart des situations pratiques (boues, bétons, propergols solides. . .). Le matériau modèleest transparent, et nous pouvons mesurer les champs de vitesse et de concentration desespèces sous cisaillement.Dans les deux géométries étudiées (Couette et plan-plan), on observe que l'écoulementprincipal (azimutal) est en général localisé. De plus, nous montrons l'existence systématiqued'une composante non azimutale des trajectoires.Expérimentalement, nous établissons les relations entre figure de ségrégation, écoulementsprimaire et secondaire. Sur cette base, nous discutons les mécanismes possibles dela ségrégation.We study the shear induced segregegation phenomena in non colloidal concentratedsuspensions containing different sizes of particles. Particles are heavier than the fluid,as in most of practical situations (slurries, concrete, solid rocket propellants. . .). In ourexperiments, we use a transparent model material and are able to measure velocity andconcentration fields under shear.In simple shear geometries (Couette cell and parallel-plate), we observe that the main(i.e. azimuthal) flow is generally localized. Besides we demonstrate the systematic existenceof a non-azimuthal component of the trajectories.We experimentally establish the relationship between segregation patterns, primary andsecondary flows. Upon this basis, we discuss the possible mechanisms of segregation

Écoulement et ségrégation dans des pâtes granulaires modèle

We study the shear induced segregegation phenomena in non colloidal concentratedsuspensions containing different sizes of particles. Particles are heavier than the fluid,as in most of practical situations (slurries, concrete, solid rocket propellants. . .). In ourexperiments, we use a transparent model material and are able to measure velocity andconcentration fields under shear.In simple shear geometries (Couette cell and parallel-plate), we observe that the main(i.e. azimuthal) flow is generally localized. Besides we demonstrate the systematic existenceof a non-azimuthal component of the trajectories.We experimentally establish the relationship between segregation patterns, primary andsecondary flows. Upon this basis, we discuss the possible mechanisms of segregation.Nous étudions les phénomènes de ségrégation par taille dans des suspensions concentréesde particules en écoulement. Les particules sont plus lourdes que le fluide, comme dans laplupart des situations pratiques (boues, bétons, propergols solides. . .). Le matériau modèleest transparent, et nous pouvons mesurer les champs de vitesse et de concentration desespèces sous cisaillement.Dans les deux géométries étudiées (Couette et plan-plan), on observe que l'écoulementprincipal (azimutal) est en général localisé. De plus, nous montrons l'existence systématiqued'une composante non azimutale des trajectoires.Expérimentalement, nous établissons les relations entre figure de ségrégation, écoulementsprimaire et secondaire. Sur cette base, nous discutons les mécanismes possibles dela ségrégation

Frankétienne, maître du Chaos

Frankétienne, en tant que poète haïtien, est plongé depuis sa naissance au cœur du chaos politique et social. Il a créé, avec Jean-Claude Fignolé et René Philoctète, un mouvement littéraire capable de représenter la forme même du chaos : le spiralisme. S’inspirant de la théorie scientifique du chaos, les spirales de Frankétienne tendent vers une écriture fractale. Cette esthétique du chaos permet d’opposer aux régimes dictatoriaux qui se sont succédés à Haïti une puissance contestataire, la spirale, véritable « machine désirante » telle que l’ont conceptualisée Deleuze et Guattari dans l’Anti-Œdipe. Ainsi Frankétienne parvient-il à faire corps avec le chaos et d’une certaine façon à le maîtriser.Franketienne, as a Haitian poet, lives in the heart of political and social chaos. He created, with Jean-Claude Fignolé and René Philoctète, a literary movement capable of representing the form of the chaos itself : spiralism. Inspired by scientific chaos theory, the spirals of Frankétienne tend towards fractal writing. This aesthetics of chaos challenged the Haitian dictatorial governments through a contestatory power —the spiral— a real “desiring machine” as conceptualised by Deleuze and Guattari in Anti Oedipus. Eventually, Frankétienne sustains chaos and in a way masters it

Ecoulement et ségrégation dans des pâtes granulaires modèle

Nous étudions les phénomènes de ségrégation par taille dans des suspensions concentrées de particules en écoulement. Les particules sont plus lourdes que le fluide, comme dans la plupart des situations pratiques (boues, bétons, propergols solides). Le matériau modèle est transparent, et nous pouvons mesurer les champs de vitesse et de concentration des espèces sous cisaillement. Dans les deux géométries étudiées (Couette et plan-plan), on observe que 'écoulement principal (azimutal) est en général localisé. De plus, nous montrons l'existence systématique d'une composante non azimutale des trajectoires. Expérimentalement, nous établissons les relations entre figure de ségrégation, écoulements primaire et secondaire. Sur cette base, nous discutons les mécanismes possibles de la ségrégation.BORDEAUX1-BU Sciences-Talence (335222101) / SudocSudocFranceF