反常压缩动力学和强迫polymer易位
Anomalous zipping dynamics and forced polymer translocation
摘要：
我们通过蒙特卡罗模拟研究了两个聚合物在互补单体间相互吸引作用下的拉链和解拉链动力学。在拉链中，聚合物从高温平衡构型骤冷到低温状态，使得两股通过闭合“Y”叉而拉上拉链。在解链中，聚合物从低温双链构型变为高温，使得两条链分离。模拟结果表明，解链时间，$τ_u$，尺度作为聚合物长度的函数$τ_u \sim L$，而拉链的特点是异常动力学$τ_z \sim L^α$与$α= 1.37(2)$。这个指数是在良好的协议与模拟结果和理论预测的强制聚合物通过一个狭窄的孔的易位时间的缩放。我们发现，指数$α$是强大的参数和温度的变化，而$τ_z$作为驱动力的函数的缩放显示存在两个不同的制度：弱强迫（$τ_z \sim 1/F$）和强强迫（$τ_z$独立于$F$）制度。交叉区域的特点可能是在$F$的非平凡缩放，匹配的预测最近的理论的聚合物易位。虽然几何结构不同，但压缩和移位共享相同类型的异常动力学。这种动态可以通过实验研究的系统是DNA（或RNA）发夹：我们的研究结果意味着一个异常的动态发夹关闭时间，但不是开放时间。
英文摘要：
We investigate by Monte Carlo simulations the zipping and unzipping dynamics of two polymers connected by one end and subject to an attractive interaction between complementary monomers. In zipping, the polymers are quenched from a high temperature equilibrium configuration to a low temperature state, so that the two strands zip up by closing up a "Y"-fork. In unzipping, the polymers are brought from a low temperature double stranded configuration to high temperatures, so that the two strands separate. Simulations show that the unzipping time, $τ_u$, scales as a function of the polymer length as $τ_u \sim L$, while the zipping is characterized by anomalous dynamics $τ_z \sim L^α$ with $α= 1.37(2)$. This exponent is in good agreement with simulation results and theoretical predictions for the scaling of the translocation time of a forced polymer passing through a narrow pore. We find that the exponent $α$ is robust against variations of parameters and temperature, whereas the scaling of $τ_z$ as a function of the driving force shows the existence of two different regimes: the weak forcing ($τ_z \sim 1/F$) and strong forcing ($τ_z$ independent of $F$) regimes. The crossover region is possibly characterized by a non-trivial scaling in $F$, matching the prediction of recent theories of polymer translocation. Although the geometrical setup is different, zipping and translocation share thus the same type of anomalous dynamics. Systems where this dynamics could be experimentally investigated are DNA (or RNA) hairpins: our results imply an anomalous dynamics for the hairpins closing times, but not for the opening times.
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