Narrow Results

We study the dynamics of overdamped systems in a symmetric periodic potential against an external load. Using numerical and analytical methods, we show that a symmetric driving signal cannot rectify these systems while an asymmetric one can rectify them, causing its unidirectional rotation. We consider the case where the driving signal is multiharmonic. We find that the mean velocity of the system increases to get the highest value, by appropriate tuning of parameters.

The directed transport of inertial Lévy flights resulting from the superimposed roughness in a corrugated potential is investigated in this paper. The influence of the roughness on the transport is studied by calculating the mean velocity (MV) and the mean first escape time (MFET), with respect to the Lévy index $\mu$ and the asymmetry parameter $q$ which determines the asymmetry of the potential. The results indicate that the particles’ directed transport caused by the asymmetry of the potential will be counteracted by the roughness, which behaves as the absolute value of the MV decreases with roughness $𝜀$ increasing, and the MFET increases with $𝜀$ increasing, correspondingly. Though smaller Lévy index $\mu$ can produce more large jumps, which yield the enhancement of the directed transport, since the roughness superimposed on the corrugated potential supplies the hinder effect, the directed transport is also weakened after the appearance of the roughness.

Little is known about the reliability of postural sway measures in healthy elderly adults. Moreover, there is no standardized balance test protocols such as an efficient number of repeated measurements for older people. Therefore, we investigated test-retest reliability of center of pressure (COP) variables during static balance performance in elderly adults. Twenty-five elderly adults (15 elderly men and 10 elderly women) were asked to perform quiet standing balance test on a self-developed force platform. COP-based variables, i.e., COP mean distance, sway area, mean velocity, mean frequency, maximum frequency, and maximum power amplitude were derived from the COP data. For the test-retest reliability of each COP-based variable, intraclass correlation coefficient (ICC) was assessed in two-trials and three-trials of balance test. Mean velocity showed the highest ICC values in all directions (ICC = 0.832–0.922). Frequency domain variables presented lower reliability than time domain variables. Additionally, elderly adults did not affect the number of repeated measurements in most postural balance variables. These results suggest that time domain variables are more reliable variables than frequency domain variable and that balance test of two trials might be rather effective for elderly adults. These findings can be used to develop an optimal protocol of static balance test and select postural balance variables for elderly adults.

The pulsatile flow of blood in a tapered narrow artery with overlapping time-dependent stenosis is mathematically analyzed, modeling blood as Carreau fluid. Perturbation method is employed for solving the resulting nonlinear system of equations along with the appropriate boundary conditions. The analytic solutions to the pressure gradient, velocity distribution, flow rate, wall shear stress and longitudinal impedance to flow are obtained in the asymptotic form. The variation of the aforesaid flow quantities with respect to various physical parameters such as maximum depth of the stenosis, angle of tapering of the artery, power law index, Reynolds number, pulsatile amplitude of the flow and Weissenberg number is investigated. It is found that the wall shear stress and longitudinal impedance to flow increase with the increase of the angle of tapering of the artery, the maximum depth of the stenosis and pulsatile Reynolds number and these decrease with the increase of the amplitude of the flow, power law index and Weissenberg number. The mean velocity of blood decreases significantly with the increase of the artery radius, maximum depth of the stenosis, angle of tapering of the artery.