Depth-dependent target strengths of gadoids by the boundary-element method

Author Posting. © Acoustical Society of America, 2003. This article is posted here by permission of Acoustical Society of America for personal use, not for redistribution. The definitive version was published in Journal of the Acoustical Society of America 114 (2003): 3136-3146, doi:10.1121/1.1619982.The depth dependence of fish target strength has mostly eluded experimental investigation because of the need to distinguish it from depth-dependent behavioral effects, which may change the orientation distribution. The boundary-element method (BEM) offers an avenue of approach. Based on detailed morphometric data on 15 gadoid swimbladders, the BEM has been exercised to determine how the orientation dependence of target strength changes with pressure under the assumption that the fish swimbladder remains constant in shape and volume. The backscattering cross section has been computed at a nominal frequency of 38 kHz as a function of orientation for each of three pressures: 1, 11, and 51 atm. Increased variability in target strength and more abundant and stronger resonances are both observed with increasing depth. The respective backscattering cross sections have been averaged with respect to each of four normal distributions of tilt angle, and the corresponding target strengths have been regressed on the logarithm of fish length. The tilt-angle-averaged backscattering cross sections at the highest pressure have also been averaged with respect to frequency over a 2-kHz band for representative conditions of insonification. For all averaging methods, the mean target strength changes only slightly with depth.This work began with sponsorship by the European Commission through its RTD-program, Contract No. MAS3-CT95-0031 (BASS), and was completed with support by the Office of Naval Research, Contract No. N000140310368

Calibration of broadband active acoustic systems using a single standard spherical target

Author Posting. © Acoustical Society of America, 2008. This article is posted here by permission of Acoustical Society of America for personal use, not for redistribution. The definitive version was published in Journal of the Acoustical Society of America 124 (2008): 128-136, doi:10.1121/1.2917387.When calibrating a broadband active acoustic system with a single standard target such as a sphere, the inherent resonances associated with the scattering by the sphere pose a significant challenge. In this paper, a method is developed which completely eliminates the source of resonances through isolating and exploiting the echo from the front interface of a sphere. This echo is relatively insensitive to frequency over a wide range of frequencies, lacking resonances, and is relatively insensitive to small changes in material properties and, in the case of spherical shells, shell thickness. The research builds upon the concept of using this echo for calibration in the work of Dragonette et al. [J. Acoust. Soc. Am. 69, 1186–1189 (1981)]. This current work generalizes that of Dragonette by (1) incorporating a pulse compression technique to significantly improve the ability to resolve the echo, and (2) rigorously accounting for the scattering physics of the echo so that the technique is applicable over a wide range of frequencies and material properties of the sphere. The utility of the new approach is illustrated through application to data collected at sea with an air-filled aluminum spherical shell and long broadband chirp signals (30–105 kHz).This work was supported by the U.S. Office of Naval Research Grant Nos. N00014-04-1-0475 and N00014- 04-1-0440 and the J. Seward Johnson Chair at WHOI

Protocols for calibrating multibeam sonar

Author Posting. © Acoustical Society of America, 2005. This article is posted here by permission of Acoustical Society of America for personal use, not for redistribution. The definitive version was published in Journal of the Acoustical Society of America 117 (2005): 2013-2027, doi:10.1121/1.1869073.Development of protocols for calibrating multibeam sonar by means of the standard-target method is documented. Particular systems used in the development work included three that provide the water-column signals, namely the SIMRAD SM2000/90- and 200-kHz sonars and RESON SeaBat 8101 sonar, with operating frequency of 240 kHz. Two facilities were instrumented specifically for the work: a sea well at the Woods Hole Oceanographic Institution and a large, indoor freshwater tank at the University of New Hampshire. Methods for measuring the transfer characteristics of each sonar, with transducers attached, are described and illustrated with measurement results. The principal results, however, are the protocols themselves. These are elaborated for positioning the target, choosing the receiver gain function, quantifying the system stability, mapping the directionality in the plane of the receiving array and in the plane normal to the central axis, measuring the directionality of individual beams, and measuring the nearfield response. General preparations for calibrating multibeam sonars and a method for measuring the receiver response electronically are outlined. Advantages of multibeam sonar calibration and outstanding problems, such as that of validation of the performance of multibeam sonars as configured for use, are mentioned.Support by the National Science Foundation through Award No. OCE-0002664, NOAA through Grant No. NA97OG0241, and the Cooperative Institute for Climate and Ocean Research (CICOR) through NOAA Contract No. NA17RJ1223 is acknowledged

Size differentiation of a continuous stream of particles using acoustic emissions

Procter and Gamble (P&G) requires an online system that can monitor the particle size distribution of their washing powder mixing process. This would enable the process to take a closed loop form which would enable process optimization to take place in real time. Acoustic emission (AE) was selected as the sensing method due to its non-invasive nature and primary sensitivity to frequencies which particle events emanate. This work details the results of the first experiment carried out in this research project. The first experiment involved the use of AE to distinguish sieved particle which ranged from 53 to 250 microns and were dispensed on a target plate using a funnel. By conducting a threshold analysis of the peaks in the signal, the sizes of the particles could be distinguished and a signal feature was found which could be directly linked to the sizes of the particles

Generalized iterated wreath products of cyclic groups and rooted trees correspondence

Consider the generalized iterated wreath product $\mathbb{Z}_{r_1}\wr \mathbb{Z}_{r_2}\wr \ldots \wr \mathbb{Z}_{r_k}$ where $r_i \in \mathbb{N}$. We prove that the irreducible representations for this class of groups are indexed by a certain type of rooted trees. This provides a Bratteli diagram for the generalized iterated wreath product, a simple recursion formula for the number of irreducible representations, and a strategy to calculate the dimension of each irreducible representation. We calculate explicitly fast Fourier transforms (FFT) for this class of groups, giving literature's fastest FFT upper bound estimate.Comment: 15 pages, to appear in Advances in the Mathematical Science

Muddled Boundaries of Digital Shrines

International audienceBased on an online ethnography study of 274 YouTube videos posted during the Virginia Tech or the Newtown massacres, this article discusses how users resort to participatory media during such mediatized events to create a digital spontaneous shrine. The assemblage of this sanctuary on a website hosting billions of user-generated contents is made possible by means of folksonomy and website architecture, and a two-fold social dynamic based on participatory commitment and the institutionalization of a collective entity. Unlike “physical” spontaneous shrines erected in public spaces, these digital shrines connect the bereaved with provocative or outrageous contributions, notably tributes from school shooting fans using participatory media to commemorate the killer’s memory. This side effect, generated by the technical properties of the platform, compromises the tranquility of the memorial and muddles the boundaries and the contents of such sanctuaries

Generalized iterated wreath products of symmetric groups and generalized rooted trees correspondence

Consider the generalized iterated wreath product $S_{r_1}\wr \ldots \wr S_{r_k}$ of symmetric groups. We give a complete description of the traversal for the generalized iterated wreath product. We also prove an existence of a bijection between the equivalence classes of ordinary irreducible representations of the generalized iterated wreath product and orbits of labels on certain rooted trees. We find a recursion for the number of these labels and the degrees of irreducible representations of the generalized iterated wreath product. Finally, we give rough upper bound estimates for fast Fourier transforms.Comment: 18 pages, to appear in Advances in the Mathematical Sciences. arXiv admin note: text overlap with arXiv:1409.060

A seven-octave-bandwidth echo sounding system for application to fish and zooplankton

Abstract only. Journal home page: http://scitation.aip.org/jasa

Simple, nonoptimal, real-time classifiers for euphausiid and copepod numerical density estimation

Abstract only. journal home page: http://scitation.aip.org/jasa