共查询到17条相似文献,搜索用时 125 毫秒
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研究了反馈耦合布朗棘轮中粒子处于负载力、时变外力及噪声作用下的定向输运问题.详细讨论了外力作用时间的不对称性、外势空间的不对称性及外力周期等对反馈耦合棘轮中粒子输运效率的影响.研究发现,外力的时间不对称度能促进反馈棘轮中粒子的定向输运,随时间不对称度的增大,反馈棘轮中粒子能获得较大的效率.然而,外势空间的不对称度能有效抑制耦合棘轮中粒子的扩散,达到增强耦合粒子定向输运的效果.同时还发现,存在最优的噪声强度能使耦合粒子的输运效率达到最大. 相似文献
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《物理学报》2019,(24)
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. 相似文献
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研究了反馈脉冲棘轮的定向输运及能量转化效率.详细讨论了弹簧自由长度、耦合强度及脉冲相位等参量对耦合布朗粒子定向输运性能的影响.研究发现,一定自由长度和耦合强度都能促进反馈脉冲棘轮的定向输运,并能使耦合粒子拖动负载做功时的能量转化效率达到最大.此外,通过调节脉冲相位能使反馈棘轮在一个演化周期内获得两次流反转,且合适的相位还能增强反馈棘轮的定向输运.所得结论不仅可为实验上设计合适的反馈脉冲作用来优化棘轮的定向输运性能,而且还能为生物医疗上药物的精准投放提供一定的理论参考. 相似文献
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考虑涨落作用下周期驱动的过阻尼分数阶棘轮模型, 通过模型的数值求解, 研究确定性棘轮的混沌特性与噪声的作用对输运行为的影响, 进而讨论过阻尼分数阶分子马达反向输运的机理. 分析表明: 随着势垒高度、 势不对称性与模型记忆性的变化, 随机棘轮的反向输运并不必然地要求确定性棘轮也反向输运; 随着模型阶数的减小, 亦即分数阻尼介质记忆性的增强, 确定性棘轮在反向输运之前会经历一个周期倍化导致的混沌状态, 但在噪声作用下, 反向流的发生会提前, 即混沌状态的确定性棘轮在噪声的作用下即可进行反向输运. 也就是说, 噪声能定性地改变棘轮的输运状态: 从无噪声时的混沌运动到有噪声时的定向输运. 这是过阻尼随机棘轮反向输运的一种机理, 也是噪声在定向输运过程中发挥积极作用的一个体现. 相似文献
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Inertial corrections to the drift velocity of a Brownian particle have been calculated for two main classes of Brownian ratchets operating in the adiabatic regime of fluctuations of the potential energy: first, the stationary periodic potential and dichotomic fluctuations of an external force with zero average value (rocking ratchet) and, second, dichotomic fluctuations of the periodic potential itself. It has been shown that, in contrast to passive transport at which the inertial correction always reduces the effective mobility and diffusion coefficients, inertial corrections for Brownian ratchets can play a constructive role, increasing the drift velocity at least at high temperatures. 相似文献
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A time-delayed feedback ratchet consisting of two Brownian particles interacting through the elastic spring is consid ered. The model describes the directed transport of coupled Brownian particles in an asymmetric two-well ratchet potential which can be calculated theoretically and implemented experimentally. We explore how the centre-of-mass velocity is af fected by the time delay, natural length of the spring, amplitude strength, angular frequency, external force, and the structure of the potential. It is found that the enhancement of the current can be obtained by varying the coupling strength of the delayed feedback system. When the thermal fluctuation and the harmonic potential match appropriately, directed current evolves periodically with the natural length of the spring and can achieve a higher transport coherence. Moreover, the external force and the amplitude strength can enhance the directed transport of coupled Brownian particles under certain conditions. It is expected that the polymer of large biological molecules may demonstrate a variety of novel cooperative effects in real propelling devices. 相似文献
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Brownian motors are nonequilibrium systems that rectify thermal fluctuations to achieve directed motion, using spatial or temporal asymmetry. We provide a tutorial introduction to this basic concept using the well-known example of a flashing ratchet, discussing the micro- to nanoscopic scale on which such motors can operate. Because of the crucial role of thermal noise, the characterization of the performance of Brownian motors must include their fluctuations, and we review suitable performance measures for motor coherency and efficiency. Specifically, we highlight that it is possible to determine the energy efficiency of Brownian motors by measuring their velocity fluctuations, without detailed knowledge of the motor function and its energy input. Finally, we exemplify these concepts using a model for an artificial single-molecule motor with internal degrees of freedom. 相似文献
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Y. Zhang B. H. Lin J. C. Chen 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,53(4):481-485
Brownian particles moving in a spatially asymmetric but periodic
potential (ratchet), with an external load force and connected to an
alternating hot and cold reservoir, are modeled as a microscopic heat
engine, referred to as the Brownian heat engine. The heat flow via both the
potential energy and the kinetic energy of the particles are considered
simultaneously. The forward and backward particle currents are determined
using an Arrhenius' factor. Expressions for the power output and efficiency
are derived analytically. The maximum power output and efficiency are
calculated. It is expounded that the Brownian heat engine is always
irreversible and its efficiency cannot approach the efficiency ηC of
the Carnot heat engine even in quasistatic limit. The influence of the main
parameters such as the load, the barrier height of the potential, the
asymmetry of the potential and the temperature ratio of the heat reservoirs
on the performance of the Brownian heat engine is discussed in detail. It is
found that the Brownian heat engines may be controlled to operate in
different regions through variation of some parameters. 相似文献
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H. Linke T.E. Humphrey P.E. Lindelof A. Löfgren R. Newbury P. Omling A.O. Sushkov R.P. Taylor H. Xu 《Applied Physics A: Materials Science & Processing》2002,75(2):237-246
Quantum ratchets are Brownian motors in which the quantum dynamics of particles induces qualitatively new behavior. We review
a series of experiments in which asymmetric semiconductor devices of sub-micron dimensions are used to study quantum ratchets
for electrons. In rocked quantum-dot ratchets electron-wave interference is used to create a non-linear voltage response, leading to a ratchet effect. The direction of
the net ratchet current in this type of device can be sensitively controlled by changing one of the following experimental
variables: a small external magnetic field, the amplitude of the rocking force, or the Fermi energy. We also describe a tunneling
ratchet in which the current direction depends on temperature. In our discussion of the tunneling ratchet we distinguish between
three contributions to the non-linear current–voltage characteristics that lead to the ratchet effect: thermal excitation
over energy barriers, tunneling through barriers, and wave reflection from barriers. Finally, we discuss the operation of
adiabatically rocked tunneling ratchets as heat pumps.
Received: 8 February 2002 / Accepted: 11 February 2002 / Published online: 22 April 2002 相似文献
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The transport properties of coupled Brownian particles in a two-dimensional rocking ratchet are investigated via Langevin simulation. The results show that the average center-of-mass velocity is multi-peaks function of the frequency of the driving force. Furthermore, in the 2D coupled Brownian motor system there are the collective effect and ratchet behavior, which can switch depending on the frequency of driving force. It turns out that the cooperative effect between the interaction of coupled particles and external rocking driving force facilitates collective directional motion and energy conversion. 相似文献