Twisting and buckling: a new undulation mechanism for artificial swimmers

We present an artificial swimmer consisting in a long cylinder of ferrogel which is polarized transversely and in opposite directions at each extremity. When it is placed on a water film and submitted to a transverse oscillating magnetic field, this artificial worm undulates and swims. Whereas symmetry breaking is due to the field gradient, the undulations of the worm result from a torsional buckling instability as the polarized ends tend to align with the applied magnetic field. The critical magnetic field above which buckling and subsequent swimming is observed may be predicted using elasticity equations including the effect of a magnetic torque. As the length of the worm is varied, several undulation modes are observed which are in good agreement with the bending modes of an elastic rod with free ends

Nager grâce à un mécanisme de torsion/flexion

Nous présentons un nageur artificiel qui progresse grâce à un mécanisme original. Il consiste en un cylindre de ferrogel polarisé transversalement et en sens opposé à ses extrémités. Placé à la surface d'un film d'eau et soumis à un champ magnétique oscillant, le ver ondule et nage. Alors que la brisure de symétrie résulte de l'inhomogénéité du champ magnétique, les ondulations du ver sont dues à une instabilité de torsion/flexion liée à l'alignement des moments magnétiques des extrémités avec le champ appliqué. Les ondes de flexion ainsi excitées régissent alors les modes de nage du ver

Transport of Long Neutral Polymers in the Semidilute Regime through a Protein Nanopore

International audienceWe investigate the entrance of single poly(ethylene glycol) (PEG) chains into an α-Hemolysin channel. We detect the frequency and duration of the current blockades induced by large neutral polymers, where chain radius is larger than pore diameter. In the semi-dilute regime, these chains pass only if the monomer concentration is larger than a well-defined threshold. Experiments are performed in a very large domain of concentration and molecular mass, up to 35% and 200 kDa respectively, previously unexplored. The variation of the dwell time as a function of molecular mass shows that the chains are extracted from the semi-dilute solution in contact with the pore by a reptation mechanism

DNA Unzipping and Protein Unfolding Using Nanopores

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