Thermodynamic energy exchange in a moving plate capacitor

In this paper we describe an apparent paradox concerning a moving plate capacitor driven by thermal noise from a resistor. The plates are attracted together, but a demon restores the plates of the capacitor to their original position when the voltage across the capacitor is small-hence only small forces are present for the demon to work against. The demon has to work harder than this to avoid the situation of perpetual motion, but the open question is how? This is unsolved, however we explore the concept of a moving plate capacitor by examining the case where it is still excited by thermal noise, but where the restoring force on the capacitor plates is provided by a simple spring rather than some unknown demon. We display simulation results with interesting behavior, particularly where the capacitor plates collide with each other. (c) 2001 American Institute of Physics.B. R. Davis, D. Abbott, and J. M. R. Parrond

A numerical and experimental analysis of flow in a centrifugal pump

Computational fluid dynamics (CFD) analysis has been used to solve the unsteady three-dimensional viscous flow in the entire impeller and volute casing of a centrifugal pump. The results of the calculations are used to predict the impeller/volute interaction and to obtain the unsteady pressure distribution in the impeller and volute casing. The calculated unsteady pressure distribution is used to determine the unsteady blade loading. The calculations at the design point and at two off-design points are carried out with a multiple frame of reference and a sliding mesh technique is applied to consider the impeller/volute interaction

A numerical flow simulation of a mixed flow pump

Mixed flow pumps are primarily axial flow pumps, but they impart some degree of radial and swirling momentum to the pump fluid as it passes through the rotor section. They are popular for pumping water in tight spaces, so are used for residential wells, municipal water works, industrial applications, and even for powering small water craft

Ironwork of Teixois-Taramundi (Asturias) Spain

This paper describes an old ironwork placed in a Spanish village. All parts of it are studied, specially the Air supply and the Hydraulic wheel. The minimum area in the water trump for a correct air flow is calculated. On the other hand, also the power supply by the hydraulic wheel, in normal conditions, to move the hammer with a required frequency is calculated

Closed-loop control strategy with improved current for a flashing ratchet

We show how to switch on and off the ratchet potential of a collective Brownian motor, depending only on the position of the particles, in order to attain a current higher than or at least equal to that induced by any periodic flashing. Maximization of instant velocity turns out to be the optimal protocol for one particle but is nevertheless defeated by a periodic switching when a sufficiently large ensemble of particles is considered. The protocol presented in this article, although not the optimal one, yields approximately the same current as the optimal protocol for one particle and as the optimal periodic switching for an infinite number of them.Comment: 4 pages, 4 figure

Effect of time delay on feedback control of a flashing ratchet

It was recently shown that the use of feedback control can improve the performance of a flashing ratchet. We investigate the effect of a time delay in the implementation of feedback control in a closed-loop collective flashing ratchet, using Langevin dynamics simulations. Surprisingly, for a large ensemble, a well-chosen delay time improves the ratchet performance by allowing the system to synchronize into a quasi-periodic stable mode of oscillation that reproduces the optimal average velocity for a periodically flashing ratchet. For a small ensemble, on the other hand, finite delay times significantly reduce the benefit of feedback control for the time-averaged velocity, because the relevance of information decays on a time scale set by the diffusion time of the particles. Based on these results, we establish that experimental use of feedback control is realistic.Comment: 6 pages, 6 figures, to appear in Europhysics Letter

Deterministic ratchet from stationary light fields

Ratchets are dynamic systems where particle transport is induced by zero-average forces due to the interplay between nonlinearity and asymmetry. Generally, they rely on the effect of a strong external driving. We show that stationary optical lattices can be designed to generate particle flow in one direction while requiring neither noise nor driving. Such optical fields must be arranged to yield a combination of conservative (dipole) and nonconservative (radiation pressure) forces. Under strong friction all paths converge to a discrete set of limit periodic trajectories flowing in the same direction.Comment: 6 pages, 4 figure