Interaction between two spherical bubbles rising in a viscous liquid

The three-dimensional flow around two spherical bubbles moving in a viscous fluid is studied numerically by solving the full Navier-Stokes equations. The study considers the interaction between two bubbles for moderate Reynolds numbers (50 ≤ Re ≤ 500, Re being based on the bubble diameter) and for positions described by the separation S (2.5 ≤ S ≤ 10, S being the distance between the bubble centres normalized by the bubble radius) and the angle θ (0o ≤ θ ≤ 90o ) formed between the line of centre and the direction perpendicular to the direction of the motion. We provide a general description of the interaction extending the results obtained for two bubbles moving side by side (θ = 0o ) by Legendre, Magnaudet & Mougin 2003 (J. Fluid Mech., 497,133-166) and for two bubbles moving in line (θ = 90o ) by Yuan & Prosperetti 1994 (J. Fluid Mech., 278, 325-349). Simple models based on physical arguments are given for the drag and lift forces experienced by each bubble. The interaction is the combination of three effects: a potential effect, a viscous correction (Moore correction) and a significant wake effect observed on both the drag and the transverse force of the second bubble when located in the wake of the first one

Irreducible coupling between physical and biological phenomena: overview of on-line and off-line physical measurements during high cell density cultures of yarrowia lipolytica

During cell cultures in bioreactor, micro-organism physiology closely interacts with physico-chemical parameters (gas and feed flow rates, mixing, temperature, pH, pressure). The specificity of microbial bioreactions in relation with irreducible couplings between heat and mass transfers and fluid mechanics, led into complex (three phases medium) and dynamic (auto-biocatalytic reaction) systems. Our scientific approach aims to investigate, understand and control dynamic interactions between physical and biological systems at different scales (macro, micro and molecular) for molecules, strains and/or bioprocess innovation in a white biotechnology context. Cells (concentration, shape, dimension, physiology) strongly affect physico-chemical properties of broth and the modification of these characteristics interacts with bioprocess performances (specific rates, yields…) with an improvement or, more generally, a decrease of yields. Among these properties, rheological behaviour is a strategy widely used to understand the impact of cells and the modification of bioprocess performances. Our approach rests on physical and physico-chemical on-line and off-line measurements in respect with accurate and stringent conditions imposed by cell culture strategy. This work leads to design and realise an original pilot based on a bioreactor (20L) with a derivation loop including a specific on-line rheometric device as well as additional physical and biological measurements. Y. lipolytica cultures were investigated with a control of growth rate by carbon feed within concentrations ranging from 0.1 up to 60gCDW/L. On-line and off-line measurements are discussed regarding similar or opposite tendencies along culture. If the off-line density could be correlated with cell concentration, on-line measurement exhibit opposite tendancy. On-line and off-line rheological measurements are consistent. Results are discussed in terms of size, morphology, surface properties, concentration, biological activity and compared to scientific literature. On-line rheology highlight about the Non-newtonian rheological behaviour of broths and the gap between on-line and off-line measurements

In-situ and ex-situ rheometry of high density Yarrowia lipolytica broth: determination of critical concentration and impact of yeastmycelial transition

The specificity of microbial bioreactions which give rise to irreducible couplings with hydrodynamics and heat and mass transfers, led into complex (three phases medium) and dynamic (auto-biocatalytic reaction) systems. Cells (concentration, shape, dimension, physiology…) strongly affect physico-chemical properties of broth and the modification of these characteristics interacts with bioprocess performances (specific rates, yields…) with an improvement or, more generally, a decrease of yields

L'expérimentation : un autre agir politique

http://www.csi.ensmp.fr/Items/WorkingPapers/Download/DLWP.php?wp=WP_CSI_013.pdfEssai sur le potentiel de la notion d'expérimentation pour le renouveau du répertoire de la sociologie politique

Impact of cell physiology and densities during oxidative axenic cultures of Yarrowia lipolytica on physico-chemical properties of broth

Impact of cell physiology and densities during oxidative axenic cultures of Yarrowia lipolytica on physico-chemical properties of brot

Hilbert's Tenth Problem in Coq (Extended Version)

We formalise the undecidability of solvability of Diophantine equations, i.e. polynomial equations over natural numbers, in Coq's constructive type theory. To do so, we give the first full mechanisation of the Davis-Putnam-Robinson-Matiyasevich theorem, stating that every recursively enumerable problem -- in our case by a Minsky machine -- is Diophantine. We obtain an elegant and comprehensible proof by using a synthetic approach to computability and by introducing Conway's FRACTRAN language as intermediate layer. Additionally, we prove the reverse direction and show that every Diophantine relation is recognisable by $\mu$-recursive functions and give a certified compiler from $\mu$-recursive functions to Minsky machines.Comment: submitted to LMC

High Conductance Ratio in Molecular Optical Switching of Functionalized Nanoparticle Self-Assembled Nanodevices

Self-assembled functionalized nano particles are at the focus of a number of potential applications, in particular for molecular scale electronics devices. Here we perform experiments of self-assembly of 10 nm Au nano particles (NPs), functionalized by a dense layer of azobenzene-bithiophene (AzBT) molecules, with the aim of building a light-switchable device with memristive properties. We fabricate planar nanodevices consisting of NP self-assembled network (NPSANs) contacted by nanoelectrodes separated by interelectrode gaps ranging from 30 to 100 nm. We demonstrate the light-induced reversible switching of the electrical conductance in these AzBT NPSANs with a record on/off conductance ratio up to 620, an average value of ca. 30 and with 85% of the devices having a ratio above 10. Molecular dynamics simulation of the structure and dynamics of the interface between molecular monolayers chemisorbed on the nano particle surface are performed and compared to the experimental findings. The properties of the contact interface are shown to be strongly correlated to the molecular conformation which in the case of AzBT molecules, can reversibly switched between a cis and a trans form by means of light irradiations of well-defined wavelength. Molecular dynamics simulations provide a microscopic explanation for the experimental observation of the reduction of the on/off current ratio between the two isomers, compared to experiments performed on flat self-assembled monolayers contacted by a conducting cAFM tip.Comment: pdf files : publication and supporting informatio

Mégalithes et météorisation des granites en Bretagne littorale, France du nord-ouest

Les menhirs sont des blocs granitiques de forme allongée qui ont été dressés à la verticale au cours du Néolithique. Ils sont particulièrement nombreux dans deux régions côtières de Bretagne, le Morbihan et le Trégor, et présentent à leur surface deux types de microformes : des vasques et des cannelures qui appartiennent elles-mêmes à deux générations. Certaines sont antérieures à la mise en place des menhirs (formes « prémégalithiques »), d'autres lui sont indiscutablement postérieures (formes « postmégalithiques »). Ainsi, de nombreuses vasques prémégalithiques, initialement formées sur des surfaces rocheuses proches de l'horizontale, s'observent aujourd'hui sur les parois verticales de certains menhirs, tandis que des vasques postmégalithiques, de moindres dimensions, ont été évidées à leur sommet. Les cannelures, quant à elles, ne se développent que sur les faces fortement redressées et ne se prolongent jamais en profondeur dans leur partie enterrée. Elles sont clairement le produit d'une météorisation postmégalithique et, comme les vasques, elles ont été façonnées par des processus subaériens. De telles microformes autorisent une approche de la vitesse de l'érosion puisque l'âge estimé des menhirs est de l'ordre de 5000 ans : si le creusement des cannelures a pu se faire au rythme de quelques dizaines de millimètres par millénaire, la mesure des vasques livre des chiffres plus variables, compris entre 4 et 30 mm/millénaire.Menhirs are elongate granite blocks placed upright, i.e. with the long axis in the vertical, in Neolithic times. Granite menhirs are prominent in the Morbihan and Trégor districts of coastal Brittany. Two minor forms, rock basins (also known as gnammas) and flutings (grooves, Rillen, Karren), are developed on menhirs. Two distinct generations of forms can be distinguished: those that predate the menhirs being placed upright, and those that postdate erection. Several flat-floored basins (or pans) that must have originated on flattish surfaces are now found on steeply inclined surfaces. On the other hand, smaller basins have developed on the summits of the monuments. Several flutings score the steep upper slopes of the blocks. They are deepest where they cut into outwardly convex inclined rock faces. They also diverge over such protuberances and terminate well above ground level. Clearly both the younger generation of basins and the flutings have formed after the monuments had been placed in their present upright positions and by processes active under subaerial or epigene conditions. In this last respect they stand in contrast with similar forms reported from other parts of the world. In Brittany the estimated age of menhirs is about 5000 years. Thus the flutings have deepened at a rate of a few tens mm/1000 years. The implied rate of basin development varies between 4 and 30 mm/1000 years

Contamination par les différentes formes chimiques du Mercure de la composante biologique du barrage hydroélectrique de Petit-Saut et des zones amont/aval du fleuve Sinnamary, an Guyanne française (études in situ et approches expérimentales).

Les recherches menées in situ ont été consacrées à une approche intégrée de la contamination par le mercure de la composante biologique du continuum « fleuve Sinnamary amont – retenue du barrage hydroélectrique de Petit-Saut – fleuve Sinnamary aval », en Guyane française. Ces recherches ont reposé sur la caractérisation écologique de l’ensemble des biocénoses aquatiques (systématique, étude des relations proies/prédateurs par la détermination de la composition isotopique du carbone et de l’azote) et sur une analyse comparative de la bioamplification du métal le long des réseaux trophiques. Des approches expérimentales ont été développées conjointement, afin d’une part, d’étudier le devenir du mercure élémentaire (rejets des activités d’orpaillage) dans les biotopes et d’analyser sa biodisponibilité à l’égard des poissons ; et, d’autre part, d’analyser l’effet d’une exposition au méthylmercure par la voie trophique sur l’expression de 13 gènes dans le cerveau, le foie et le muscle squelettique du poisson-zèbre (Danio rerio).This research consisted of an in situ integrated approach to mercury contamination of the biological component of the “upstream Sinnamary river – hydroelectric Petit-Saut dam – downstream Sinnamary river” continuum in French Guiana. It was based on an ecological analysis of the aquatic biocenoses (systematics, study of prey/predator relationships by determining carbon and nitrogen isotope composition) and a comparative analysis of metal biomagnification along the food webs. Experimental approaches were developed in combination, in order to study first, the chemical fate of elemental mercury (goldmining releases) in the biotopes and its bioavailability to fish; and second, the effect of MeHg trophic exposure on the expression of 13 genes in the brain, liver and skeletal muscle of the zebra fish (Danio rerio)