本文研究了周期对称势中时间非对称外力驱动的布朗粒子输运现象，建立了分数阶布朗马达输运模型。其中外力是零均值的，而分数阶阶数则刻画了客观环境的非均匀性程度。通过将模型离散化进行数值模拟，讨论了分数阶阶数、系统参量和外部参量与定向流之间的依赖关系。研究表明，即使没有倾斜势场的作用，时间非对称外力也可以诱导系统产生定向输运；输运速度随分数阶阶数的增大而单调递增；当阶数固定时，系统的输运速度会随着势垒高度、噪声强度非单调变化，表现出广义随机共振现象。分析指出，分数阶郎之万方程所刻画的输运现象是在整数阶模型基础上的一个推广，进而为输运现象提供了一个可能更为真实的模型。%The directed transport of a Brownian particle in a spatially periodic symmetric field under a temporal asymmetric force is studied. Based on the Caputo’s fractional derivatives theory, we establish a differential aquation for an over-damped fractional Brownian motor as the system’s mathematic model, where the external force is zero-mean and the fractional order is used to describe the inhomogeneity of the real environment. Using the fractional differential algo-rithm, we analyze the relationships between transport velocity and model parameters. It is worth mentioning that the impact of fractional order is discussed in detail. According to the research we find that a temporal asymmetric force can induce a net current without the application of a ratchet potential, even a noise. We also find that the velocity of the current increases monotonically with the increase in fractional order. Moreover with certain fractional orders, a generalized resonance phenomenon is revealed since the velocity of the current varies non-monotonically with the system parameters, such as the height of the potential barrier and the noise strength etc. Research shows that the fractional system is a generalization of the traditional dynamic systems, which could probably give a more reasonable explanation of the directed transport as a consequence.
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