Nonlinear dynamic intertwining of rods with self-contact

Twisted marine cables on the sea floor can form highly contorted three-dimensional loops that resemble tangles. Such tangles or hockles are topologically equivalent to the plectomenes that form in supercoiled DNA molecules. The dynamic evolution of these intertwined loops is studied herein using a computational rod model that explicitly accounts for dynamic self-contact. Numerical solutions are presented for an illustrative example of a long rod subjected to increasing twist at one end. The solutions reveal the dynamic evolution of the rod from an initially straight state, through a buckled state in the approximate form of a helix, through the dynamic collapse of this helix into a near-planar loop with one site of self-contact, and the subsequent intertwining of this loop with multiple sites of self-contact. This evolution is controlled by the dynamic conversion of torsional strain energy to bending strain energy or, alternatively by the dynamic conversion of twist (Tw) to writhe (Wr). KEY WORDS Rod Dynamics, Self-contact, Intertwining, DNA Supercoiling, Cable HocklingComment: 35 pages, 9 figures, submitted to Proceedings of the Royal Society A: Mathematical, Physical and Engineering Science

Current-induced phase control in charged-ordered Nd0.5Ca0.5MnO3 and Pr0.6Ca0.4MnO3 crystals

Single crystals of Nd0.5Ca0.5MnO3 and Pr0.6Ca0.4MnO3 show current-induced insulator-metal transitions at low temperatures. In addition, the charge-ordering transition temperature decreases with increasing current. The electroresistive ratio, defined as r0.5/rI where r0.5 is the resistivity at a current of 0.5 mA and rI the resistivity at a given applied current, I, varies markedly with temperature and the value of I. Thermal hysteresis observed in Nd0.5Ca0.5MnO3 and Pr0.6Ca0.4MnO3 at the insulator-metal transition indicates that the transition is first-order. The current-induced changes are comparable to those induced by magnetic fields, and the insulator-metal transition in Pr0.6Ca0.4MnO3 is accordingly associated with a larger drop in resistivity.Comment: 12 pages, 3 figures, first submitted to submitted to J. Phys. D; applied physics on 18th march 200

Configurational Entropy of Self Propelled Glass Formers

The configurational entropy is an indispensable tool to describe super-cooled liquids near the glass transition. Its calculation requires the enumeration of the basins in the potential energy landscape and when available, it reveals a direct connection with the relaxation time of the liquid. While there are several reports on the measurement of configurational entropy in passive liquids, very little is understood about its role in active liquids which have a propensity to undergo a glass transition at low temperatures. In this paper, we report a careful calculation of the configurational entropy in a model glass former where the constituent units are self propelled. We show that unlike passive liquids, the anharmonic contribution to the glass entropy in these self-propelled liquids can be of the same order as the harmonic contribution, and therefore must be included in the calculation of the configurational entropy. Our extracted configurational entropy is in good agreement with the generalized Adam-Gibbs relation predicted by the random first order transition theory enabling us to deduce a scaling relation between the configurational entropy and the point-to-set length scale in these active systems. Our findings could be of great utility in conventional active systems such as self-propelled granules, Janus particles and dense bacterial suspensions, to mention a few