65 research outputs found

    Coiling Instability of Multilamellar Membrane Tubes with Anchored Polymers

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    We study experimentally a coiling instability of cylindrical multilamellar stacks of phospholipid membranes, induced by polymers with hydrophobic anchors grafted along their hydrophilic backbone. Our system is unique in that coils form in the absence of both twist and adhesion. We interpret our experimental results in terms of a model in which local membrane curvature and polymer concentration are coupled. The model predicts the occurrence of maximally tight coils above a threshold polymer occupancy. A proper comparison between the model and experiment involved imaging of projections from simulated coiled tubes with maximal curvature and complicated torsions.Comment: 11 pages + 7 GIF figures + 10 JPEG figure

    Interactions between Magnetic Nanowires and Living Cells : Uptake, Toxicity and Degradation

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    We report on the uptake, toxicity and degradation of magnetic nanowires by NIH/3T3 mouse fibroblasts. Magnetic nanowires of diameters 200 nm and lengths comprised between 1 {\mu}m and 40 {\mu}m are fabricated by controlled assembly of iron oxide ({\gamma}-Fe2O3) nanoparticles. Using optical and electron microscopy, we show that after 24 h incubation the wires are internalized by the cells and located either in membrane-bound compartments or dispersed in the cytosol. Using fluorescence microscopy, the membrane-bound compartments were identified as late endosomal/lysosomal endosomes labeled with lysosomal associated membrane protein (Lamp1). Toxicity assays evaluating the mitochondrial activity, cell proliferation and production of reactive oxygen species show that the wires do not display acute short-term (< 100 h) toxicity towards the cells. Interestingly, the cells are able to degrade the wires and to transform them into smaller aggregates, even in short time periods (days). This degradation is likely to occur as a consequence of the internal structure of the wires, which is that of a non-covalently bound aggregate. We anticipate that this degradation should prevent long-term asbestos-like toxicity effects related to high aspect ratio morphologies and that these wires represent a promising class of nanomaterials for cell manipulation and microrheology.Comment: 21 pages 12 figure

    Arbitraje entre regiones económicas

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    Arbitraje entre regiones económica

    Le multiplicateur à secteurs multiples et le circuit économique

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    [eng] Economie interrelations and equilibrium can be expressed through the multisectorial multiplier technique which is generalisation of Leontiefs structural analysis The economic system may be devided into sectors caracterised by their marginal propensity to consume the reaction lags of each sectors being different. In such conditions any new expenditure injection leads gener ly to stable situation. It appears also that the notion of equilibrium can only be reached in the frame of dynamical analysis and one is veering gradually form macro-economic full equilibrium to micro-economic general equilibrium There exists in fact for each problem and each type of eco nomic system an optimum degree of dissection But this method is linked with monetary point of view and necessitates study at the same time of quantity and price problems Moreover the dynamisation of the model in imperfect as long as investment expenditures are brought in only as external injections. In both cases progress is beeing made but not yet entirely satisfactory.
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