Generating power from waves on a breakwater.

Outlines the possibility for wave power generation at artificial islands by construction of a breakwater. Reviews the development of wave energy systems, and describes several wave generators, e.g. the Mauritius lagoon system, the Nodding Duck, the oscillating cylinder, the oscillating water column and the Lancaster Bag. Applications and costs are outlined. (C.J.U.)

High-frequency acousto-electric single-photon source

We propose a single optical photon source for quantum cryptography based on the acoustoelectric effect. Surface acoustic waves (SAWs) propagating through a quasi-one-dimensional channel have been shown to produce packets of electrons that reside in the SAW minima and travel at the velocity of sound. In our scheme, the electron packets are injected into a p-type region, resulting in photon emission. Since the number of electrons in each packet can be controlled down to a single electron, a stream of single- (or N-) photon states, with a creation time strongly correlated with the driving acoustic field, should be generated. ©2000 The American Physical Society.

Reprint of: Flow filtering and the physical sources of aerodynamic sound

The physical sources of sound are expressed in terms of the non-radiating part of the flow. The non-radiating part of the flow can be obtained from convolution filtering, as we demonstrate numerically by using an axi-symmetric jet satisfying the Navier-Stokes equations. Based on the frequency spectrum of the source, we show that the sound sources exhibit more physical behaviour than sound sources based on acoustic analogies. To validate the sources of sound, one needs to let them radiate within the non-radiating flow field. However, our results suggest that the traditional Euler operator linearized about the time-averaged part of the flow should be sufficient to compute the sound field. © 2010 Published by Elsevier Ltd.

Active control of sound radiated by a submarine hull in bending vibration using inertial actuators

Submarines are efficient sources of low frequency radiated noise due to the vibrations induced by the rotation of the propeller in a non uniform wake. In this work the possibility of using inertial actuators to reduce the far field sound pressure is investigated. The submerged vessel is modelled as a cylindrical shell with two conical end caps. Complicating effects such as ring stiffeners, bulkheads and the fluid loading are taken into account. A harmonic radial force is transmitted from the propeller to the hull through the stern end cone and it is tonal at the blade passing frequency (rotational speed of the shaft multiplied by the number of blades). The actuators are attached at the inside of the prow end cone to form a circumferential array. Both Active Vibration Control (AVC) and Active Structural Acoustic Control (ASAC) are analysed and it is shown that the inertial actuators can significantly reduce the far field sound pressure.

Baroclinic waves in an air-filled thermally driven rotating annulus.

In this study an experimental investigation of baroclinic waves in air in a differentially heated rotating annulus is presented. Air has a Prandtl number of 0.707, which falls within a previously unexplored region of parameter space for baroclinic instability. The flow regimes encountered include steady waves, periodic amplitude vacillations, modulated amplitude vacillations, and either monochromatic or mixed wave number weak waves, the latter being characterized by having amplitudes less than 5% of the applied temperature contrast. The distribution of these flow regimes in parameter space are presented in a regime diagram. It was found that the progression of transitions between different regimes is, as predicted by recent numerical modeling results, in the opposite sense to that usually found in experiments with high Prandtl number liquids. No hysteresis in the flow type, with respect to variations in the rotation rate, was found in this investigation.

Synchronization of modulated traveling baroclinic waves in a periodically forced, rotating fluid annulus.

Frequency entrainment and nonlinear synchronization are commonly observed between simple oscillatory systems, but their occurrence and behavior in continuum fluid systems are much less well understood. Motivated by possible applications to geophysical fluid systems, such as in atmospheric circulation and climate dynamics, we have carried out an experimental study of the interaction of fully developed baroclinic instability in a differentially heated, rotating fluid annulus with an externally imposed periodic modulation of the thermal boundary conditions. In quasiperiodic and chaotic amplitude-modulated traveling wave regimes, the results demonstrate a strong interaction between the natural periodic modulation of the wave amplitude and the externally imposed forcing. This leads to partial or complete phase synchronization. Synchronization effects were observed even with very weak amplitudes of forcing, and were found with both 1:1 and 1:2 frequency ratios between forcing and natural oscillations.

Influence of physical parameters of sound on the sensory gating effects of N40 in rats

Sensory gating is the ability of the brain to modulate its sensitivity to incoming stimuli. The N40 component of the auditory evoked potential, evaluated with the paired click paradigm, was used to probe the gating effect in rats. The physical characteris