粗糙势中耦合布朗粒子的定向输运性能

Transport performance of coupled Brownian particles in rough ratchet

研究了粗糙棘轮中耦合粒子的定向输运行为,并进一步讨论了阻尼条件下粗糙棘轮的扰动振幅、扰动波数、粒子间的耦合强度及自由长度等因素对耦合布朗粒子质心平均速度及斯托克斯效率的影响.研究发现,合适的粗糙棘轮扰动振幅和扰动波数能促进耦合布朗粒子的定向输运,同时还能增强其斯托克斯效率.此外,合适的耦合强度和自由长度还能使粗糙棘轮的输运性能达到最强.还发现小扰动振幅条件下,通过改变耦合强度和自由长度能够诱导粗糙棘轮的流反转.通过研究更具实际意义的粗糙棘轮,本文所得结论能为实验上理解分子马达的运动行为提供理论指导,还可为纳米量级分子机器的设计及粒子分离技术的实现提供实验启发.

Molecular motor is a kind of protein macromolecule,which moves along the microfilament or microtubule in cell directionally and participates in all kinds of intracellular life activities fully.In order to study the directional motion of molecular motor,a series of ratchet models have been proposed.However,the potentials used in most of the ratchet models are smooth sawtooth potential or harmonic potential.Recently,the experimental studies show that intracellular impurities,spatial inhomogeneity or the folding process of protein can yield deviation from a smooth ratchet profile.This kind of deviation will roughen the known smooth potential.In fact,the roughness of potential is not only closely related to the properties of protein,but also has an important implication in transition rate.Therefore,the rough ratchet will be used to simulate the interaction between molecular motor and trajectory in this work.In addition,experimental researches show that there is a class of molecular motor that can move directionally without dragging load in organism.According to the theory presented by Wang and Oster(Wang H,Oster G 2002 Europhys.Lett.57134),the directional transport capability of this kind of motor can be investigated by means of Stokes efficiency.The higher the Stokes efficiency of the motor,the stronger the ability of the motor to use external input energy for directional motion.Here in this work,the overdamped Brownian transport of the two harmonically interacting particles is investigated,and the performance of transport is analyzed by studying the mean velocity and Stokes efficiency of the dimer induced by the introduction of roughness into the potential profile.The influences of the amplitude of perturbation,the wavenumber,the coupling strength and the free length of coupled Brownian particles on the directional transport performance are discussed in detail.According to the structure of ratchet,it is found that the roughness can either restrain or enhance the ratchet performance.It is shown that the appropriate amplitude and wavenumber of rough ratchet can promote the directional transport and enhance the Stokes efficiency of coupled Brownian particles.Moreover,one can distinguish between the optimal value of the coupling strength and free length that leads to a local maximum current.In addition,the directional transport of rough ratchet can be reversed by modulating the suitable coupling strength and free length.The conclusions obtained in this paper can provide theoretical guidance for understanding the motion behavior of molecular motor in experiment,and can also provide experimental inspiration for developing the nanometer machines and realizing the particle separation technology.