Electrostatic contribution to twist rigidity of DNA
Physical Review E - Statistical Physics, Plasmas, Fluids, and Related Interdisciplinary Topics 69:6 (2004) 11
Abstract:
The electrostatic contribution to the twist rigidity of DNA is studied, and it is shown that the Coulomb self-energy of the double-helical sugar-phosphate backbone makes a considerable contribution—the electrostatic twist rigidity of DNA is found to be [Formula presented], which makes up about [Formula presented] of its total twist rigidity [Formula presented]. The electrostatic twist rigidity is found, however, to depend only weakly on the salt concentration, because of a competition between two different screening mechanisms: (1) Debye screening by the salt ions in the bulk, and (2) structural screening by the periodic charge distribution along the backbone of the helical polyelectrolyte. It is found that, depending on the parameters, the electrostatic contribution to the twist rigidity could stabilize or destabilize the structure of a helical polyelectrolyte. © 2004 The American Physical Society.Simple swimmer at low Reynolds number: Three linked spheres
Physical Review E - Statistical Physics, Plasmas, Fluids, and Related Interdisciplinary Topics 69:6 (2004) 4
Abstract:
We propose a very simple one-dimensional swimmer consisting of three spheres that are linked by rigid rods whose lengths can change between two values. With a periodic motion in a nonreciprocal fashion, which breaks the time-reversal symmetry as well as the translational symmetry, we show that the model device can swim at low Reynolds number. This model system could be used in constructing molecular-sized machines. © 2004 The American Physical Society.Nonlinear mechanical response of DNA due to anisotropic bending elasticity.
Eur Phys J E Soft Matter 12:4 (2003) 599-604
Abstract:
The response of a short DNA segment to bending is studied, taking into account the anisotropy in the bending rigidities caused by the double-helical structure. It is shown that the anisotropy introduces an effective nonlinear twist-bend coupling that can lead to the formation of kinks and modulations in the curvature and/or in the twist, depending on the values of the elastic constants and the imposed deflection angle. The typical wavelength for the modulations, or the distance between the neighboring kinks is found to be set by half of the DNA pitch.Anomalous Buckling of Charged Rods
ArXiv cond-mat/0308389 (2003)
Abstract:
Unscreened electrostatic interactions exert a profound effect on the onset of the buckling instability of a charged rod. When this interaction is unscreened, the threshold value of the compressional force needed to induce buckling is independent of rod length for sufficiently long rods. In the case of rods of intermediate length, the critical buckling force crosses over from the classic inverse-square length dependence to asymptotic length-independent form with increasing rod length. It is suggested that this effect might lead to the possibility of the ``electromechanical'' stiffening of nanotubes, which would allow relatively long segments of them to be used as atomic force probes.Forces Induced by Non-Equilibrium Fluctuations: The Soret-Casimir Effect
ArXiv cond-mat/0308373 (2003)