Energy radiated by a point acoustic dipole that reverses its uniform velocity along its rectilinear path

This work extends a mathematical approach developed recently for monopoles to describe the sound energy radiated by a rectilinearly moving dipole that changes direction along its trajectory. Although the dipole travels with constant speed, it undergoes acceleration by reversing its direction during a finite time interval along its path. This work determines the joint angular and frequency distribution of the radiated energy, its angular distribution, and the total radiated energy output. Results for the radiated energy are systematized by expressing the radiation integrals in terms of hypergeometric functions. This procedure simplifies the evaluations, particularly at low Mach numbers, and permits the comparison of results to the earlier monopole case.     

Tunable infrared generation in KTA and applications

Noncollinear difference frequency mixing of dye laser and Nd:YAG second harmonic (fundamental) radiation from a commercial laser system is employed for the generation of 2.7–5.3 μm (1.6–1.7 μm) radiations in a flux-grown KTiOAsO₁ crystal. The generated radiation is used to scan the methane absorption in the fundamental (v ₃) and its first overtone (2v ₃) band at pressure 90 torr in a laboratory made single pass gas cell of length 33 cm.     

Identification of cavity fillers in elastic solids using the resonance scattering theory

Elastic waves incident on and scattered by fluid-filled (spherical) cavities in solids are usually described by summed scattering amplitudes. These summed amplitudes, when analysed one partial wave at a time, are seen to consist of two interfering contributions. One is a smooth background corresponding to scattering from an empty cavity, and the other is a superimposed set of resonance ‘spikes’ (lines with narrow width) of the filler fluid. We show in this paper how these modal resonances and their widths can be used to identify the material composition of the filler fluid in a way that resembles the spectroscopic methods used to identify chemical elements by means of their optical spectra.     

Working group report: Heavy-ion physics and quark-gluon plasma

This is the report of Heavy Ion Physics and Quark-Gluon Plasma at WHEPP-09 which was part of Working Group-4. Discussion and work on some aspects of quark-gluon plasma believed to have created in heavy-ion collisions and in early Universe are reported.     

Comment on paper entitled, "An inversion of Freedman's 'image pulse' model in air". Acoust. Soc. Am. 119(2), 965-975 (2006)

Echolocation (i.e., perceiving objects using acoustic echoes) is well-known in underwater detection and to a lesser extent in robot guidance and machine perception. The paper by Tsakiris and McKerrow is concerned with machine perception in air using Freedman's asymptotic model, which was originally developed to predict the backscattering multiple-echo effect observed in sonar detection. This effect was subsequently shown to be due to the elastic response of underwater targets. Freedman's model can be used in air because the acoustic target is assumed to be rigid. Also, the model's prediction of multiple echoes can be used to obtain information about the shape of the target. This is the so-called inversion of the Freedman model by Tsakiris and McKerrow. In their paper, various simple bodies are tested in air using ultrasound and it is shown that the model provides relatively poor information about body shape. Several explanations are given. However, one explanation is not considered, namely that the model itself is not satisfactory. First, there is poor agreement with exact backscattering theory. Second, deriving information about target shape from the multiple echoes predicted by the model is a highly questionable procedure. Both these aspects are examined here.     

Comments on ‘Absorption mechanisms for waterborne sound in Alberich anechoic layers’

The vibrational behaviour of Alberich-type absorbers is reviewed once more. Two types of resonance mechanisms are known to be present in such layered configurations. One is due to the radial motion of the hole wall and the other to the drum-like oscillations of the cover layer. The relative importance of these two mechanisms is discussed, and criticisms of an earlier paper of the author are answered, and are placed in proper perspective.     

Sound scattering by bubble clouds near the sea surface

The classical exact formulation required to evaluate the form function (or the scattering cross-section, SCS) of a single, ideal, air bubble in a boundless liquid is briefly recalled. It is then immediately generalized to the case of a round cloud of many possibly interacting such bubbles of known volume concentration, contained within the same boundless medium. This is further generalized to the case when the bubble cloud is near a free surface. The presence of the nearby pressure release surface, assumed flat, substantially alters the cloud's scattering cross-section relative to its value in the absence of boundaries. We then use an earlier technique of ours [i.e., see I.E.E.E. J. Ocean. Eng. 20, 285-293 (1995)] based on the method of images that uses the addition theorem for the spherical wave functions, to relate all the scattered sound fields to a common origin and thus obtain the (modified) SCS of the cloud now near the boundary. This formulation accounts for all orders of multiple scattering and yields an infinite set of coupled algebraic equations for the coupling coefficients. This set is then solved for the coupling coefficients in terms of infinite sums of products of pairs of Wigner 3-j symbols, which are then used to construct and evaluate the form function. We display numerical results in four cases that correspond to geographical sites in which the bubble concentrations within the cloud have been measured along a couple of oblique upward directions, or have been assumed to have increasing (and in a few instances, purposely unrealistically high) values. In all cases considered here the bubble clouds are only a few meters beneath the sea surface and consist of ideal bubbles. The results are also compared to those found in the absence of a boundary in all the cases considered.