| Summary: | 碩士 === 國立中央大學 === 物理研究所 === 89 === Abstract
In the past decade, advances in experimental techniques using magnetic beads, optical tweezers, or shear flow made it feasible for detailed experimental studies of the conformations of single long molecules, especially in helical double-stranded DNA molecules, so we hope to realize it more theoretically and by simulations. In the thesis, the static properties of a single stiff helical polymer chain under stretching is investigated by Monte Carlo simulations with the bond-fluctuation model. The primary purpose is to describe the change of conformations and the persistence length of a helical chain due to the rigidity of the chain and measure the extension of the chain under an external stretching force. We attempt to employ the measures such as the correlation function of bond vectors, average of the Writhe, radius gyrations, dihedral angles and bending angles to describe the helical structures. At the high scaled temperatures, the chain behaves like a disordered coil chain, however, at low scaled temperatures, the local helical structures emerge. This properties can be verified by the above the measured quantities. As for stretching the helical polymer chain, we focus deformation of the chain on the linear force regime and non-linear Pincus regime mainly because both of the regimes have the universal scaling behaviors. We observed that the width of the regime from the linear to Pincus behaviors for the chain with the rigidity parameter becomes more narrow than one of the flexible chain involving only excluded volume interactions. Finally, our simulation data also show the changes of geometry such as sinθ, sinψ, writhe, and the pitch due to the stretching force.
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