Biomedical subjects
P G de Gennes
Publications and source records attributed to P G de Gennes.
Passive entry of a DNA molecule into a small pore.
I consider a vesicle with an open pore of small radius rp, exposed to a DNA solution. The crucial moment is the entry, when a chain end faces the pore and enters it. I discuss qualitatively the following three characteristic times: (i) the duration of the entry of one chain end (defining the minimum lifetime of the pore) taue approximately 10(-4) sec, (ii) the transfection time taut (the time required to be sure that one chain has gone in) taut approximately hours, and (iii) the sliding time tauS (the time between entry of one end and entry of the other end) approximately 1 sec. A fortunate feature is that sliding may proceed even if the pore tends to close itself after entry.
Thick surface flows of granular materials: effect of the velocity profile on the avalanche amplitude.
A few years ago, Bouchaud et al. introduced a phenomenological model to describe surface flows of granular materials [J. Phys. I 4, 1383 (1994)]. According to this model, one can distinguish between a static phase and a rolling phase that are able to exchange grains through an erosion or accretion mechanism. Boutreux et al. [Phys. Rev. E 58, 4692 (1998)] proposed a modification of the exchange term in order to describe thicker flows where saturation effects are present. However, these approaches assumed that the downhill convection velocity of the grains is constant inside the rolling phase, a hypothesis that is not verified experimentally. In this article, we therefore modify the above models by introducing a velocity profile in the flow, and study the physical consequences of this modification in the simple situation of an avalanche in an open cell. We present a complete analytical description of the avalanche in the case of a linear velocity profile, and generalize the results for a power-law dependency. We show, in particular, that the amplitude of the avalanche is strongly affected by the velocity profile.
Molecular individualism.
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Statistics of branching and hairpin helices for the dAT copolymer.
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