Multiple scattering in a reflecting cavity: application to fish counting in a tank.

Classical fisheries acoustics techniques are useless in the presence of multiple scattering or reflecting boundaries. A general technique is developed that provides the number and the scattering strength of scatterers in motion placed inside a highly reflecting cavity. This approach is based on multiple scattering theory. The idea is to measure the average effect of the scatterers on the acoustic echoes of the cavity interfaces. This leads to the measure of the scattering mean free path, a typical length that characterizes the scattering strength of the cloud of scatterers. Numerical results are shown to agree with a simple theoretical analysis. Experiments are performed with fish in a tank at two different scales: ultrasonic frequency (400 kHz) in a 1.4-l beaker with 1-cm-long fish as well as fisheries acoustics frequency (12.8 kHz) in a 30-m3 tank with 35-cm-long fish. These results have interesting applications to fish target strength measurement and fish counting in aquaculture.     

Reply to comment on "Negative refractive index in artificial metamaterials"

The claims of the preceding Comment [Opt. Lett. 32, 1510 (2007)] are discussed. It is shown that Kildishev misread the previously presented method [Opt. Lett. 31, 2483 (2006)] for determining optical constants of nanostructured films. Reasons for a disagreement of the simulations presented in the Comment are also discussed.     

Reply to comment on "Auditory-nerve first-spike latency and auditory absolute threshold: a computer model"

Krisha [J. Acoust. Soc. Am., in press (2006)] has commented that an explanation based on presynaptic calcium accumulation at the inner hair cell is an incorrect explanation for the success of a model of the auditory periphery [Meddis, R., J. Acoustic. Soc. Am. 119, 406-417 (2006)] in explaining data on first-spike auditory nerve latency. This reply accepts the criticism and accepts the strength of an alternative explanation based on expected latencies in random sequences of low-probability events. This reply also goes on briefly to explore the application of this argument to other phenomena, including the dependence of absolute auditory threshold on the duration of the stimulus. This has wide-ranging implications for the concept of "temporal integration" in psychophysics.     

Reply to the comment from Mamedov

Here, I present the reply to the comments from Mamedov regarding numerical solution of Bloch–Gruneisen function to determine the contribution of electron–phonon interaction in polycrystalline superconductor. Reply to the comments from Mamedov is discussed one by one.     

Reply to Lemke's comment on a paper by Gonzalez-Gascon

The distortions introduced in a recent paper (for v > 1) are unavoidable and the “experimentally measured distortions” quoted by Lemke are not distortions at all.     

Multiple scattering of ultrasound in weakly inhomogeneous media: application to human soft tissues

Waves scattered by a weakly inhomogeneous random medium contain a predominant single-scattering contribution as well as a multiple-scattering contribution which is usually neglected, especially for imaging purposes. A method based on random matrix theory is proposed to separate the single- and multiple-scattering contributions. The experimental setup uses an array of sources/receivers placed in front of the medium. The impulse responses between every couple of transducers are measured and form a matrix. Single-scattering contributions are shown to exhibit a deterministic coherence along the antidiagonals of the array response matrix, whatever the distribution of inhomogeneities. This property is taken advantage of to discriminate single- from multiple-scattered waves. This allows one to evaluate the absorption losses and the scattering losses separately, by comparing the multiple-scattering intensity with a radiative transfer model. Moreover, the relative contribution of multiple scattering in the backscattered wave can be estimated, which serves as a validity test for the Born approximation. Experimental results are presented with ultrasonic waves in the megahertz range, on a synthetic sample (agar-gelatine gel) as well as on breast tissues. Interestingly, the multiple-scattering contribution is found to be far from negligible in the breast around 4.3 MHz.     

Reply to comment on 'Molecular arrangement in water: random but not quite'

In a recent paper (Petkov?V,?Ren?Y and Suchomel?M?2012?J.?Phys.:?Condens.?Matter 24?155102) we confirmed the presence of fine features in the molecular distribution function of water and showed that these features can be explained in terms of a simple model featuring water molecules forming tetrahedral units of different perfection and/or participating in rings of different sizes. In this reply we reaffirm our findings.     

Acoustic transmission analysis on cavity resonance sound in a cylindrical cavity system: application to a Korean bell

This paper presents an analytical model for acoustic transmission characteristics of a cylindrical cavity system representing the acoustic resonance conditions of a Korean bell. The cylindrical cavity system consists of an internal cavity, a gap, an auxiliary cavity, and a rigid base. Since the internal cavity is connected to the external field through a gap, determination of the acoustic transmission characteristics becomes a coupling problem between the internal cavity and external field. The acoustic field of the internal cavity is considered by expanding the solution method of the mixed boundary problem, and the external field is addressed by modifying the radiation impedance model of a finite cylinder. The analytical model is validated by comparison with both experiment and a boundary element method. Using the analytical model, the resonance conditions are determined to maximize the resonance effect. Thus, the resonance frequencies of the bell cavity system are investigated according to the gap size and auxiliary cavity depth. By adjusting gap size or auxiliary cavity depth, the cavity resonance frequency is tuned to resonate partial tones of the bell sound. Finally, the optimal combination of gap size and auxiliary cavity depth is determined.     

Reply to the comment by P. Markoš

We present another interpretation of the data by P. Marko? and give numerous new illustrations of our conception. All the existing numerical data look perfectly compatible with predictions of the self-consistent theory of localization.     

Reply to Comment on 'X-ray scattering from a randomly rough surface'

In a recent paper in this journal, the authors have presented a small-contrast perturbation theory of the coherent and incoherent scattering of x-rays from a randomly rough surface. In a Comment on our work, de Boer compares its predictions with those of earlier theories of such scattering. In this reply we argue that several of his comments and conclusions are incorrect owing to an insufficiently careful estimation of certain integrals that occur in our theory.     

Nonlocal and spontaneous material responses: Reply to comment on "Rigorous solution for transient propagation of electromagnetic waves through a medium: causality plus diffraction in time"

I reply to the Comment by Weiglhofer and Lakhtakia on Opt. Lett. 25, 995 (2000). I agree with the comment to such an extent that it is generally known that nonlocal effects and material response time have to be considered in using collective macroscopic material response parameters. However, I believe that the Comment is incomplete and bears no special connection with the study that I reported in the original Letter.