bluuebunny/crossref_metadata_2025 huggingface dataset:
Sonoporation and ultrasound transfection assisted by contrast agents
Authors: Wu Junru
Published: July 2012

Gene therapy provides potentially effective treatment of a wide variety of diseases. Generally speaking, all gene therapy protocols require introduction of foreign nucleic acids, most often DNA, into the target cells and tissue, where gene expression is induced. However, low permeability of tissue and cells causes efficient barriers to entry of foreign DNA. Therefore, gene therapy requires transfection techniques that promote the uptake and expression of foreign DNA by a cell. There are two types of transfection techniques—viral and nonviral. Among the nonviral transfection methods, sonoporation and ultrasound-induced transfection are relatively new methods. Recent in vitro studies [Bao et al., Ultrasound Med. Biol. 23, 953–959 (1997); Greenleaf et al., ibid. 24, 587–595 (1998); Ward et al., J. Acoust. Soc. Am. 105, 2951–2957 (1999)] have shown that the presence of contrast agents dramatically enhances the efficiency of the transfection and also reduces the required acoustic pressure. This presentation will focus on reviewing the recent publications of sonoporation and ultrasound transfection using contrast agents. The possible physical mechanisms involved and main advantages of this technique will be discussed.
Qualifying a reverberation room for sound absorption measurements
Authors: Warnock Alf
Published: July 2012

ASTM C423, the standard method for measuring sound absorption in a reverberation room, was recently revised extensively and now includes tests to verify that the room has acceptable acoustical properties. Further changes are planned by the ASTM task group. This paper will present sets of measurements made in the reverberation rooms at the National Research Council Canada illustrating the effects of some physical factors, such as number of loudspeakers, number of microphones, the need for rotating diffusers, and the number of specimen positions that should be used for different specimens. Practical problems facing laboratory operators will be discussed. The precision required for measurement in a room will be determined to some extent by the reproducibility of the test method. There is little point in reducing the precision of the measurement in individual rooms once it is significantly less than the test reproducibility. Further changes that might be made to C423 will be presented.
Experiences with anechoic chamber qualification per ISO 3745 and ASA/ANSI S12.35
Authors: Cunefare Kenneth A.
Published: July 2012

ISO 3745 and ASA/ANSI S12.35 contain recommended procedures for the performance qualification of anechoic and semianechoic rooms. This paper presents experience with a number of different methodologies and analyses used in a series of tests configured to comply with these specifications. The methods include discrete measurements at fixed separation distances with multiple microphones, measurements taken with a single microphone repositioned between each measurement, and a computer-controlled continuous traverse system. Experience with different instrumentation chains will be briefly addressed. Also, a comparison of test results using pure tone and pink noise excitation will be presented. Finally, an algorithm will be described which, for a given continuous traverse test data set, determines the best acoustic source center and source offset distance to minimize the deviation from the permissible bounds contained within the specifications.
On sound power determination: The uncertainty in sound power determined in a reverberation room based on a round-robin
Authors: Peppin Richard J.
Published: July 2012

In this paper I will present the results of an extensive round-robin sponsored under the NIST National Voluntary Laboratory Accreditation Program for Acoustics. The round-robin tested the interlaboratory variability of sound power measured using the reverberation room sound power standards ANSI S12.31-33 and ISO 3741-3743. Also I will discuss the ramifications of uncertainty on sound-pressure estimation.
Noise and vibration isolation design for a vibration testing laboratory
Authors: Nelson David A. , Stewart Thomas
Published: July 2012

Cisco Systems new Engineering Approvals Center provides an example of the successful application of noise and vibration control principles in a mixed-use building. The Vibration Laboratory portion of the building is designed for maximum throughput and comprises a number of powerful noise and vibration sources, including four hydraulic shaker tables with hydraulic pumps, an electrodynamic shaker table, two drop shock tables, and a package drop area. Because office spaces, conference facilities and sensitive high-performance EMC chambers are located directly above and adjacent to the Vibration Laboratory, a considerable degree of isolation was designed into the structure to preserve an officelike environment in these areas. Design and installed performance of critical building elements will be discussed, including the isolated slab and vibration breaks, noise-isolating control room, walls, windows, doors and ceiling.
Noise labeling for consumer products
Authors: Schomer Paul
Published: July 2012

Currently, ISO 4871-1996 (Acoustics–Declaration and verification of noise emission values of machinery and equipment) uses A-weighted or spectral sound power levels as metrics of choice for noise labeling. Also included is a measure of the likely variations in levels that result from machine to machine variability, measurement to measurement variability, and site to site variability. This labeling scheme is adequate to label machinery for use in commercial or industrial settings. Here, plant engineers or audiologists, etc., can readily interpret and use data. But a two-number label using the sound power level in decibels is not optimum for conveying information to the consumer. This paper suggests an alternate form for the data. Sound power is still the physical quantity measured, and, as suggested by others, a one-number system is used. The statistical variation is included by reporting the value that will not be exceeded in 19 out of 20 measurements. But the metric reported is one that is roughly proportional to judgments of loudness, and, as such, should provide greater meaning and clarity to the user. Hopefully, with comprehensible noise labeling, the consumer will be able to include noise in his/her choice of products.
Computer sound quality: Masking, loudness and prominence
Authors: Nelson David A.
Published: July 2012

Computers and business equipment were one of the first applications for standardized sound quality metrics. Various product specifications (emanating primarily from Europe) defined criteria for A-weighted sound pressure and sound power levels as well as the absence of prominent tones and impulsive noise. Standards such as ISO 7779, ANSI S12.10 and ECMA 74 have provided the means for assessing these quantities. Of particular interest at the moment is the prominent tone, for which there are two accepted metrics: tone-to-noise ratio and prominence ratio. Experience has shown that both metrics occasionally fail to track listeners perception of the prominence of tones or tonal complexes. An alternate prominence analysis is constructed based on psychoacoustical factors, using a method proposed by Zwicker for identifying the loudness of any sound masked by another. The accepted metrics are compared and contrasted with the masked loudness method using carefully selected test cases.
Sound quality of contemporary personal-computers
Authors: Chou Ya-Wen , Cheng Ming-San
Published: July 2012

Development of sound quality analysis in product design and marketing has drawn much attention in recent years. Many makers nowadays would like to know their products sound quality and to improve them instead of just reducing the overall sound pressure level. The noise of personal-computers is characterized as either rumble or containing pure tone components, while sound quality analysis may reveal additional information on the market acceptance and the noise influence to customers. The prevailing industrial test standards for product rating of these products, however, have not yet included the concept of sound quality. To investigate the possibility and appropriateness of adopting sound quality analysis in the test standard to rate product noise, we used many personal-computers in accordance with prevailing test standards such as ISO 7779. The results were then analyzed and indexes of sensory pleasantness were calculated by sound quality parameters of loudness, sharpness, roughness and tonality as suggested by Zwicker and Fastl. Comparison between sensory pleasantness values and sound power level indicates a large discrepancy in terms of product rating. It is suggested that the rating of these products by sensory pleasantness may be considered in the future.
International space station acoustics
Authors: Goodman Jerry R.
Published: July 2012

Control of acoustics is important in the International Space Station (ISS) because of the long-term crew exposure to noise and their confinement. ISS requirements cover modules, government furnished equipment, and payloads. The current status of compliance to these requirements will be described, including examples of where acoustics efforts have aided compliance and where difficulties were experienced. Concerns with obsolete requirements, and lack of acoustic experience and rigor to achieve compliance, will be discussed.
Community noise at Del Mar, California, during two four-day helicopter noise studies
Authors: Young Robert W.
Published: July 2012

Monday, 30 August 1999, was the first day of a four-day Marine Corps demonstration of noise of helicopters flying north and south along the coast at Del Mar, California. The second four-day demonstration was 26–29 October 1999. A Computer Engineering Limited automatic noise monitor operated continuously at 421 Ocean View Ave. or at 12839 Via Grimaldi. Helicopters flew 0.5- to 5-mile intervals offshore, at altitudes 500 or 2000 feet above sea level. On 2 September 1999, at 421 Ocean View Ave., from midnight to 0800, the one-hour average sound level was less than 41 dB. From 0800 until 0951, helicopter sound levels exceeded an 80-dB threshold 15 times. During the hour ending at 1000, helicopter one-hour average sound level was 72 dB. The maximum fast A-weighted sound level MXFA was 94 dB. The A-weighted sound exposure level ASEL was 103 dB. The 421 Ocean View site is 300 feet east of the shoreline and about 200 feet above sea level. Thus when a helicopter flies 0.5 miles offshore and altitude 500 feet above sea level, it is only 300 feet above and 3500 feet distant from the monitor at 421 Ocean View Ave.
Noise produced by religious pilgrimages in Monterrey, Mexico
Authors: Elizondo-Garza Fernando J. , de J. Villalobos-Luna Jose
Published: July 2012

In this paper are shown the result of measurements of the noise produced by religious pilgrimage in the context of the traditional ‘‘Virgin of Guadalupe’’ Christian celebration in the city of Monterrey, Mexico. The noise implications are discussed and conclusions are presented.
Regulation of amplified sound sources
Authors: Zwerling Eric
Published: July 2012

Few sources of noise generate more complaints than amplified music, which can present a difficult enforcement profile if the appropriate approach is not employed. Highly amplified vehicular sound systems are a nuisance increasing in both occurrence and intensity, requiring an enforcement standard that is objective, content-neutral and easily employed by an officer in a police cruiser. A ‘‘plainly audible’’ standard meets these criteria and has withstood court challenges. The specific language for inclusion into an ordinance is presented. The regulation, enforcement and curtailment of low-frequency nuisances arising from fixed sources such as bars or parties may prove intractable for performance codes setting A-scale permissible sound level limits. One possible approach, octave band regulation, is not cost-effective and technically feasible for most enforcement agencies which desire efficiently rapid response. An effective approach is a C-scale regulatory protocol prohibiting an amplified sound reproduction device from raising total sound levels within the dwelling of a complainant by specific time-indexed levels. There are technical and evidentiary benefits to taking these measurements within the residence, and not at the property line. This new approach has been recently adopted by St. Augustine, FL and Lafayette, LA. The ordinance language is presented.
Verification of sound levels inside discotheques and public show sites
Authors: de Leo Alberto , Giuliani Franco , Fabozzi Concetta , Tommasi Renzo
Published: July 2012

In 1997 a decree was issued in Italy with the aim of defining the limits of noise sources inside discotheques and public show sites. ANPA (Italian Agency for Environmental Protection) has started research on about 30 sites in order to know the real levels of exposures to noise inside different types of public show sites and, after, carry out a first verification on proposed limits and methods, and also evaluate the possibility of using the automatic control systems stated by the rules. Such campaigns enable us to obtain elements that are very useful for the development of sectoral rules and for the planning of interventions.
Active noise control studies using the Rayleigh–Ritz method
Authors: Gopinathan Senthil V. , Varadan Vasundara V. , Varadan Vijay K.
Published: July 2012

The Rayleigh–Ritz method is used to model a smart composite plate and the piezoelectric patches attached to it. Classical plate theory is used to model the composite plate and electroelastic theory is used to model the segmented piezoelectric patches. Eigenfunctions of a clamped–clamped beam are used as the Ritz functions for the panel and the rigid cavity modes are used to model the acoustic cavity. The dynamic equations of motion for the coupled smart panel-cavity system are derived using Hamilton’s principle. The forcing term due to the cavity acoustic pressure is determined by using virtual work considerations. Five collocated pairs of actuator/sensor pairs are attached to the plate at a predetermined placement scheme. A (multi-input–multi-output) MIMO controller is designed for the coupled vibroacoustic system. The output feedback controller is then employed to emulate the optimal controller by solving the Riccati equations. The performance of the control system in reducing the vibration and the noise transmitted into the enclosure is studied. It is shown that the Rayleigh–Ritz procedure can be used more efficiently than the finite-element method for cabin noise control problems.
Noise reduction in a launch vehicle fairing using actively tuned loudspeakers
Authors: Kemp Jonathan D. , Clark Robert L.
Published: July 2012

Loudspeakers tuned as optimal acoustic absorbers can significantly reduce damaging, low-frequency, reverberant noise in a full-scale launch vehicle fairing. Irregular geometry, changing payloads, and the compliant nature of the fairing hinder effective implementation of a passively tuned loudspeaker. A method of tuning the loudspeaker dynamics in real time is required to meet the application requirements. Through system identification, the dynamics of the enclosure can be identified and used to tune the dynamics of the loudspeaker for passive dissipation of targeted, high-intensity, low-frequency modes that dominate the acoustic response in the fairing. A loudspeaker model with desired dynamics serves as the reference model in a control law designed to tune the dynamics of a nonideal loudspeaker to act as an optimal tuned absorber. Experimental results indicate that a tuned loudspeaker placed in the nose cone of the fairing dissipates significant acoustic energy, up to 12 dB at the targeted modes, and verifies results calculated from the simulation. [Work supported by AFOSR F49620-98-1-0383 under the supervision of Dr. Daniel J. Segalman.]
Passive vibration suppression using nonlinear electromechanical coupling
Authors: Anderson Tony J. , Anderson Michael J. , Hocut Christopher , Zornik William , Blotter Jonathan D.
Published: July 2012

The development of a new class of passive vibration and acoustic suppression systems is presented. The approach is to transfer the energy from one mechanical system to another using reversible piezoelectric transducers connected with a passive electric circuit. Response of the first system is suppressed while exciting the response of the second system. The two mechanical systems can be physically separated structures, or different mechanical modes of a single structure. The passive electric circuit is a network containing diodes and/or transistors switched from the piezoelectric voltages. Reductions of 25% in the response of the directly excited system have been shown. This approach is an improvement over a passive shunt technique in that the typically heavy inductor in the electrical shunt is replaced with an existing system mechanical impedance. It also has the advantage over active control techniques in that an external power source is not required and there is no possibility to add energy to the system from the controller.
The segmental representation of consonant clusters: Constituents, cohabitants, or unitary clusters
Authors: Measer Kathleen M. , Sawusch James R.
Published: July 2012

What is the form of the segmental representation that underlies auditory word recognition? In spoken word recognition, different segmental representations have been proposed for words. Most models of word recognition assume some form of phonetic representation. In a phonetic representation, consonant clusters such as the /spl/ in ‘‘splash’’ are treated as a sequence of separate, discrete elements. However, the precise nature of this representation is unknown. Clusters could be composed of abstract phonemes, context-sensitive allophones, or some other unit. A form-based priming paradigm was used with naming, lexical decision, and A–X name matching tasks to investigate the representation of syllable initial clusters. Primes that differ from the targets in the number and order of consonants (in syllable initial clusters) were presented to listeners. For example, primes such as /skrav/, /skav/, /krav/, /sav/, /kav/, /rav/, and /bav/ (control) were used with the target /skrem/. If clusters are composed from their constituent phonemes, the number of phonemes in common between prime and target should determine the magnitude of priming. The results will be discussed in terms of their implications for the segmental representation of speech. [Work supported by NIDCD Grant R01DC00219 to the Univ. at Buffalo.]
12-month-olds show evidence of a possible-word constraint
Authors: Johnson Elizabeth K. , Jusczyk Peter W. , Cutler Anne , Norris Dennis
Published: July 2012

The possible-word constraint (PWC) limits the number of lexical candidates considered for a given input by stipulating that the input should be parsed into a string of feasible words [Norris et al., Cogn. Sci. 34, 191–243 (1997)]. Any segmentation resulting in impossible word candidates (i.e., an isolated single consonant) is disfavored. Four experiments using the head-turn preference procedure investigated whether 12-month-olds observe the PWC to aid them in word recognition. In the first two experiments, infants were familiarized with lists of words (e.g, ‘‘rush’’), then tested on lists of nonsense items containing these words in ‘‘possible’’ or ‘‘impossible’’ positions [e.g., ‘‘niprush’’ (nip+rush—possible) or ‘‘prush’’ (p+rush—impossible)]. In the other experiments, 12-month-olds were similarly familiarized with lists of words, but test items occurred in sentential contexts; this condition more readily taxed online segmentation abilities. In the first two experiments, 12-month-olds listened significantly longer to targets in ‘‘possible’’ versus ‘‘impossible’’ contexts when targets occurred at the end of nonsense items, but not when they occurred at the beginning. In experiments 3 and 4, infants listened significantly longer to words in the ‘‘possible’’ condition regardless of target location. These results suggest that 12-month-olds, like adults, use the PWC during online word recognition.
Speech perception and production as evidence for the role of phonological representation in the development of phonological awareness
Authors: Mann Virginia A. , Foy Judith G.
Published: July 2012

Previous research has shown a clear relationship between phonological awareness and early reading ability. The factors underlying the development of phonological awareness are not well understood; both exposure to literacy and the adequacy of underlying phonological representations are cited as antecedents. To test the hypothesis that phonological awareness associates with strength of phonological representations, this study examined speech perception, production, and phonological awareness in 40 four- to six-year-old children attending private preschools. An extensive questionnaire was administered as a probe to home literacy environment; vocabulary letter knowledge and reading ability were also determined. The data indicate that both literacy environment and the adequacy of phonological representation are factors in phonological awareness. They further suggest that strength of phonological representations may be more closely associated with the awareness of onset-rime than with true phoneme awareness. Children with a less developed sense of rhyme had less mature speech perceptual skills and a less mature pattern of articulation independent of age, vocabulary, and letter knowledge. Children with weaker phoneme awareness also showed less mature speech perception and articulation than children with strong abilities, but this appeared to turn on age, letter knowledge, and vocabulary knowledge.
The role of the time-reversal processor in acoustical signal processing
Authors: Candy James , Chambers David
Published: July 2012

Time-reversal (T/R) processing of noisy ultrasonic sensor array measurements is an established technique for focusing energy in both homogeneous and inhomogeneous media. It can effectively be used to detect flaws or scatterers by utilizing its primary attribute, the ability to focus on the strongest scatterer. In this paper, temporal techniques are discussed that exploit this focusing property to construct signal processing algorithms. First, the underlying theory is briefly discussed illustrating the focusing property and then the discussion of a technique to detect when the T/R processor has focused on the dominant scatterer or flaw follows. Once focus detection is accomplished, that particular scatterer is removed from the measured data enabling a recursive detection of the next scatterer until all have been detected and removed. Next the localization problem is attacked using the dominant scatterer focusing property of the T/R processor. Here a simple nonparametric model of the wave-front is matched with the measured by varying the assumed flaw (scatterer) location until the best match occurs.
Real-time noise canceling based on spectral minimum detection and diffusive gain factors
Authors: Kim Hyoung-Gook , Obermayer Klaus , Bode Mathias , Ruwisch Dietmar
Published: July 2012

In this paper, we propose a very simple but highly effective psychoacoustically motivated real-time approach on the basis of spectral minimum detection and diffusive gain factors without a speech activity detector. The first processing step is the calculation of the short-time power spectrum of the noisy speech signal. Estimating the background noise, the system calculates diffusive gain values in real time being obtained in a two-layer structure: Each node of a layer is responsible for a single mode of the power spectrum. The first layer, called the ‘‘minimum detection layer,’’ holds the present noise level derived from the minimum of the input power spectrum which is detected within frames smaller than the FFT window. The minimum is transformed into a gain factor function using a signal-to-noise ratio control parameter. The diffusive gain factor interaction of neighboring modes is performed in the second layer, called the ‘‘diffusion layer,’’ in order to avoid ‘‘musical tones.’’ In the frequency domain, a filtering operation is performed by multiplying the noisy speech power spectrum by the diffusive gain factors to yield the filtered signal spectrum. This latter is transformed to the time domain by an inverse Fourier transform with original noisy phase.
Standard-target calibration of broadband sonars
Authors: Foote Kenneth G.
Published: July 2012

The object of a standard-target calibration is specification of the overall frequency response function of the system. In terms of the transmit and receive signal spectra ST and SR, standard-target far-field form function F, and two-way acoustic path loss P for an on-axis far-field calibration; the frequency response function is H=SR/(STFP), where each of the displayed functions is frequency-dependent. In practice, a broadband calibration may be hindered by (1) a vanishing denominator value, causing a divergence in H, or (2) a small numerator value or large denominator value, effectively amplifying the influence of noise. The general solution to these problems is to use multiple dissimilar targets to be able to avoid extrema in F, change the transmit signal waveform to avoid nulls in ST, and ensure that the signal-to-noise ratio is high over the frequency band of interest. The near-field case can be addressed by adjusting the target range. Given these measures, the standard-target technique demonstrated by Dragonette et al. [J. Acoust. Soc. Am. 69, 1186–1189 (1981)] for scattering measurements may be rendered into general practice for active broadband sonars.
Experimental validation of numerical models of 3-D target scattering and reverberation in very shallow water
Authors: Veljkovic Irena , Schmidt Henrik
Published: July 2012

OASES 3-D, a wave theory model of seabed insonification, three-dimensional target scattering, and rough seabed reverberation, has been developed to investigate characteristics of multistatic scattering and reverberation from rippled shallow-water seabeds with buried targets. The model combines a scattering theory based on the method of small perturbations with a seismoacoustic propagation model, allowing for field simulations in arbitrarily stratified ocean environments. The validation of this new modeling framework was a major objective of the GOATS’98 experiment carried out in 12–15-m deep water at Elba in May 1998. Spherical and cylindrical targets were buried at different depths within a 10×10 m area of sandy bottom and insonified by a parametric source. The unique dataset provided by the experiment has been used for both experimental validation of numerical models and identification of features of the 3-D acoustics which distinguish targets from reverberation. The methodology used for estimating the bistatic scattering strength of the targets and the background seabed reverberation from data collected by a moving AUV platform will be described. The performance of the model for predicting scattering from proud and buried targets will be discussed and illustrated by examples including both isotropic and aspect-dependent targets. [Work supported by ONR and SACLANTCEN.]
The Fermi pseudo-potential and acoustical scattering
Authors: Dacol Dalcio K. , Roy Dilip G.
Published: July 2012

The Fermi pseudo-potential was introduced in quantum mechanics as a means of simplifying problems involving scattering by a multicentered potential including applications to many-body problems. As such, it has direct applications in acoustics. It also provides a physically intuitive basis for discussing scattering by complex objects. In this presentation the pseudo-potential concept is briefly reviewed. Then, applications to scattering by complex objects and to acoustic scattering by multiple objects are discussed. The case of multiple object scattering in an oceanic waveguide will also be discussed in detail. [Work supported by ONR.]
Extinction theorem for object scattering in a stratified medium
Authors: Ratilal Purnima , Makris Nicholas C.
Published: July 2012

A simple relation for the rate at which energy is extinguished from the incident wave of a far-field point source by an obstacle of arbitrary size and shape in a stratified medium is derived from wave theory. This relation generalizes the classical extinction theorem, or optical theorem, that was originally derived for plane wave scattering in free space and greatly facilitates extinction calculations by eliminating the need to integrate energy flux about the obstacle. The total extinction is shown to be a linear sum of the extinction of each waveguide mode. Each modal extinction involves a sum over all incident modes that are scattered into the extinguished mode and is expressed in terms of the object’s plane wave scatter function in the forward azimuth and equivalent plane wave amplitudes of the modes. The only assumptions are that multiple scattering between the object and waveguide boundaries is negligible, and the object lies within a constant sound-speed layer. Calculations for a shallow-water waveguide show that the extinction cross section is highly dependent on measurement geometry, and medium stratification, as well as the scattering properties of the object and may be significantly modified by the presence of absorption in the medium.
A spectral formulation for the Doppler-shifted field scattered by an object moving in a stratified medium
Authors: Lai Yisan , Makris Nicholas C.
Published: July 2012

A spectral formulation for the 3-D field scattered by an object moving in a stratified medium is derived using full-field wave theory. The derivation is based on Green’s theorem for the time-domain scalar wave equation and accounts for Doppler effects induced by target motion as well as source and receiver motion. The formulation is valid when multiple scattering between the object and waveguide boundaries can be neglected and the scattered field can be expressed as a linear function of the object’s plane wave scattering function. A normal mode formulation that is more computationally efficient but less general is also derived from first principles. The advantage of the spectral representation is that it incorporates the entire wave number spectrum, including evanescent waves, and so can potentially be used at much closer ranges to the target than the modal formulation. The Doppler effects are illustrated through a number of canonical examples.
On scattering effects due to the proximity and relative position of two bubbles in a sound field
Authors: Kapodistrias George , Dahl Peter H.
Published: July 2012

Recently the authors published results from a theoretical and experimental investigation on scattering of sound from two bubbles symmetrically arranged about the combined beam axis of a set of transducers [J. Acoust. Soc. Am. 107, 3006–3017 (2000)]. In this presentation the investigation is extended to two additional geometries, with the two bubble array placed at angles of 0° and 45° from the combined beam axis. For each angle, the half interbubble distance d is varied such that the dimensionless variable kd ranges from 0.2–5 (for the 0° case) and 0.2–10 (for the 45° case), where k is the acoustic wave number. Modeling is accomplished by using a closed-form solution derived from the multiple scattering series, with the bubble scattering function expressed in terms of spherical harmonics. Experimental data are obtained by symmetrically arranging two bubbles, each of radius a≊425 μm, on a fine nylon thread, with the bubbles insonified by tone bursts with a center frequency of 120 kHz. The data closely agree with the simulations, and it is verified that, regardless of the geometry, for kd≤1 the response of the two bubble array drastically departs from the one due to single scattering. This departure is attributed to multiple scattering and is manifested as a reduction in backscattered radiation.
Rough sea surface limitations on high-frequency SAS imaging
Authors: Chang Enson , Chatham Ralph E. , Marx David S. , Nelson Matthew A. , Putney Angela , Warman L. Kieffer
Published: July 2012

It is a long-held notion that medium-induced signal fluctuations render long-range synthetic aperture sonar (SAS) imaging unfeasible. Recent experimental results in shallow water, however, indicate that near-theoretical SAS performance can be achieved with the aid of (sonar data driven) motion compensation and autofocus algorithms, even for surface- and bottom-reflected paths. This study examined in detail the role of these adaptive compensation algorithms in overcoming rough surface scattering-induced phase errors. Imaging and compensation algorithms were applied to sonar data that was numerically modeled for moderate to severe surface conditions. We report here the predicted imaging performance as a function of surface conditions and grazing angles. [Work supported by the Office of Naval Research.]
Modal conversion by rough surface scattering: The key to the T-phase
Authors: Odom Robert I. , Park Minkyu , Soukup Darin J.
Published: July 2012

The amplitudes of the propagating acoustic modes associated with T-waves decay exponentially below their ray equivalent turning points, and cannot be excited directly by an earthquake. The modal decomposition for a T-wave producing earthquake that occurred near the western tip of the Blanco TFZ has been computed. The directly excited higher order modes are characterized by relatively large amplitudes in the ocean crust, significant water-borne components, and often strong interface components at the ocean-bottom boundary. Employing the modal scattering theory of Park and Odom (1999), it is found that energy has been transferred from higher order modes to the Stoneley fundamental and the lower order modes have significant amplitude at the water-bottom interface. Scattering from irregular ocean bottom bathymetry is the mechanism for the energy transfer. The lowest order acoustic modes, modes 1 and 2, are only very weakly excited because they have very small amplitudes at the bottom. This is consistent with the interpretation of de Groot-Hedlin and Orcutt (1999). [Work supported by the NOPP Program and ONR.]
Virtual musical instruments
Authors: Smith Julius O.
Published: July 2012

Virtual musical instruments are interesting from multiple points of view. The listener may, or may not, know that the music is computer generated. The composer can use the computer to produce sonorities that cannot be obtained in a real environment, such as strings many meters long, or instruments that gradually change form. The performer can benefit from virtual instruments because they are usually easier to play than real instruments. The scientists, being able to reproduce the sonority of a particular instrument, show that the physics of the instrument itself has been understood. For these reasons and more, virtual musical instruments based on mathematical acoustics have been successful for many years in the computer music research community. In this tutorial we will cover some of the more effective virtual instrument algorithms, and how they can be played and varied in real time. Examples will be described and sound examples played. Starting from the simplest cases of plucked and struck strings, we will show how simple configurations of delay lines, digital filters, and nonlinear elements can be used to synthesize realistic sounding musical instruments. Examples will work up to bowed strings and other ‘‘self-sustained oscillators’’ such as in the flute and clarinet. The richness and breadth of the timbral spaces offered by these models will be illustrated.
Acoustic investigation of the Hawaiian mesopelagic boundary community
Authors: Benoit Bird Kelly , Au Whitlow
Published: July 2012

A 200 kHz echosounder modified to sample directly into a computer was used to survey the mesopelagic boundary community (MBC) in waters off the leeward coasts of three Hawaiian Islands from dusk to dawn. The target strengths of individual mesopelagic organisms captured in Isaacs-Kidd midwater trawls were measured with the echosounder in a shipboard seawater tank for use in echo-energy integration calculations. Acoustic survey data were mapped in ArcView, allowing analysis of spatial structure. The MBC is spatially heterogeneous both horizontally and vertically. The parameters of patch structure vary significantly throughout a night and between islands. The density of mesopelagic organisms was consistently higher off the coasts of Oahu and Lanai than the coast of Hawaii. However, the density of organisms observed in all locations was high, reaching a maximum of 1800 organisms/m3 off Oahu and 700 organisms/m3 off Hawaii. Patterns in density were significantly affected by the location’s distance from the shoreline, but not by its depth. Patterns in density suggest that the MBC undergoes a significant diel horizontal migration in addition to its well-documented vertical migration. Due to this predictable and conserved horizontal migration, the MBC is found much closer to shore than previously reported.
Acoustical study of the prey field and supporting food web for whales in the Ligurian Sea north of Corsica
Authors: McGehee Duncan E. , Demer David A.
Published: July 2012

The Sound, Oceanography, and Living Marine Resources (SOLMAR) program is a study coordinated by the NATO SACLANT Undersea Research Centre to develop ways of mitigating risks to whales from anthropogenic sound sources. One objective of the SOLMAR program is to examine the correlation between the distribution of whales in parts of the Mediterranean Sea and that of their prey, lower trophic levels, and basic oceanographic parameters. A multiship field study was conducted in the Ligurian Sea north of Corsica in August 1999, as will be a follow-up study in August 2000. The primary role of the R/V Ammiraglio Magnaghi is to map basic physical oceanographic parameters with a CTD; phytoplankton with a fluorometer; small zoo-plankton (copepods and smaller) with a six-frequency TAPS (Tracor Acoustic Profiling System) and small plankton net; and large zooplankton (euphausiids and larger) with a 120-kHz split-beam echosounder. Measurements in 1999 were consistent with a counterclockwise circulation in the basin causing Ekman pumping of nutrients in the center. Phytoplankton were concentrated in the center, small zooplankton were around the periphery, and larger zooplankton were associated with the shelf break and basin center. Results from the two field seasons will be discussed and compared.
Biophysical interactions at the Almeria–Oran front
Authors: Fielding Sophie , Crisp Nick , Mustard Alex
Published: July 2012

The Almeria–Oran front forms where Atlantic origin waters meet Mediterranean surface waters at the eastern end of the Alboran Sea. Following a multidisciplinary cruise on RRS Discovery in December 1996, analysis of temperature and salinity on density surfaces at the front showed that periodic subduction of Mediterranean surface waters (MSW) influenced the distribution of phytoplankton and zooplankton in the frontal region. A layer of fluorescence coincident with the subducted MSW indicated that phytoplankton were drawn down and along isopycnals to depths of 200 m. The study of scattering layers, identified with acoustic backscatter data from the shipboard ADCP and a SIMRAD EK500 echosounder, revealed that a layer of zooplankton was also found coincident with the drawn-down phytoplankton. This layer persisted during and despite diel vertical migration. Smaller zooplankton, not undertaking diel vertical migration, were concentrated in the fast-flowing frontal jet as seen in high-resolution OPC data. EK500 target-strength data indicate that the subducted communities may constitute different size classes to those in the surrounding waters. Samples from Longhurst Hardy plankton recorder tows across the front provide additional ground truthing for our acoustic observations. [Work supported by EU MAST, NERC, and DERA.]
Changes in volume reverberation from deep to shallow water in the Gulf of Mexico
Authors: Love Richard H. , Thompson Charles H. , Nero Redwood W.
Published: July 2012

Volume reverberation at frequencies below 10 kHz is caused primarily by resonance scattering from swimbladders of dispersed fish. Since fish populations change from deep to shallow water, the character of volume reverberation should likewise change. However, there are few data available from shelf and slope waters to document expected changes. Therefore, the Naval Research Laboratory conducted a short experiment to examine volume reverberation in deep, slope, and shelf waters of the eastern Gulf of Mexico. Day and night measurements at frequencies from 1 to 10 kHz were made with shallow explosive sources and downward-looking receivers in water depths of 200, 450, and over 3000 m. Reverberation at the deep location was typical of that caused by small mesopelagic fishes of the ‘‘deep scattering layer;’’ scattering strengths increased rapidly with frequency up to about 5 kHz and were relatively constant at higher frequencies. At the shelf location, scattering strengths were low during the day and increased by 20 dB at 10 kHz to 40 dB below 2 kHz, as larger fishes rose off bottom at night. Reverberation over the slope combined characteristics of the deep and shelf locations. [Work supported by ONR.]
Monitoring fish movement using an ADCP
Authors: Patro Ranjan , Zedel Len , Spanu-Tollefsen Cristina
Published: July 2012

An Acoustic Doppler Current Profiler, ADCP, can detect the presence of fish in water using the backscatter intensity. The Doppler profiler does not, however, make a point measurement; rather, measurement is made by averaging multiple beams and assuming that the current velocity is uniform between the distinct sample locations. As a result, individual fish speed cannot be measured. However, data are presented that demonstrate that the ADCP can measure the swimming speed of large fish schools. Fish speed and direction were measured for Norwegian spring herring. Observed speeds were 0–40 cm sec−1. Diel vertical migrations were observed with Norwegian herring ascending to the surface at dusk, and descending to greater depth at dawn. The accuracy and precision of an ADCP is a complex function of many variables (i.e., frequency, pulse length, transducer characteristics, backscatter strength, type and distribution of scatters). The other problems to be considered are sampling criteria and calibration. These sampling problems are explored for the case of ADCP measurements of fish movement. [Work supported by the Natural Sciences and Engineering Research Council of Canada and an Atlantic Canada Opportunities Agency Infrastructure grant.]
Comparison and evaluation of methods for distinguishing among several functional classes of zooplankton and fish using acoustic backscatter data at four frequencies
Authors: Swartzman Gordon L. , Holliday D. Van , Coyle Kenneth O. , Napp Jeffrey M.
Published: July 2012

Zooplankton net samples data were collected at 30 locations near the Pribilof Islands, Alaska in September 1999 using a MOCNESS. Simultaneous volume backscatter data were collected with an HTI echosounder system at: 43, 120, 200, and 420 kHz. Three algorithms were compared for their ability to classify acoustic data into the dominant zooplankton functional/size groups (euphausiids, copepods, and ostra cods) and separating them from fish. The algorithms tested include: (1) combining morphological image processing and image differences to identify patches in different size ranges, and using the forward problem calibrated to plankton found in MOCNESS hauls to ascribe size/functional groups to the different patches; (2) application of canonical correlation between acoustics (backscatter volume and target strengths) and plankton biomass captured by the MOCNESS; and (3) application of inverse techniques to estimate the number of individuals in set size classes using multiple theoretical models of backscatter volume compared to plankton biomass captured by a net. Knowledge of the strengths and weaknesses of each technique allows us to better interpret broad-scale acoustic survey results from the same cruise, thus providing a synoptic view of the fish and their plankton prey which are in the size and density range to be acoustically detected.
Measurement of oceanic bubble populations using broadband acoustics
Authors: Terrill Eric J.
Published: July 2012

The size distribution of bubbles in the ocean will evolve with a number of different temporal and spatial scales as a result of both the physics which govern their formation (breaking wind waves, breaking waves in the surf zone, or ship wakes) and the physical processes which control their lifetimes: turbulent mixing, bubble rise speed, and gas dissolution. A broadband acoustic bubble sizing technique that is suitable for deployment in the rigors of the ocean environment has been developed and deployed on a number of occasions to study the physics of the bubble field and their implications to underwater sound propagation (Terrill and Melville, 2000). The technique is based upon inversions of direct acoustic attenuation and sound-speed measurements at frequencies ranging from approximately 2–200 kHz using broadband pulse transmissions at ping rates up to 25 Hz across short path lengths of O (0.1–1) m. The accuracy of the measured bubble size distributions has been confirmed with both internal consistency checks based on the complex dispersion relationship as well as laboratory comparisons with independent optical techniques. A review of the development of the bubble sizing instrumentation will be presented and results from a number of different field deployments discussed.
On bubble-mediated scattering from the sea surface: Modeling, and field and laboratory measurements
Authors: Dahl Peter H.
Published: July 2012

Bubbles, located just below the air–sea interface, contribute significantly to the observed level of acoustic scattering originating from the sea surface, in contrast, for example, to microwave scattering. Typically, such bubbles are the result of breaking wind-generated waves, and thus their concentration is closely linked to wind speed. In this paper we discuss scattering from bubbles located within the proximity of the sea surface, with emphasis on the effects of the nearby reflecting surface, which gives rise to multiple paths from source to bubble to receiver. The effects of scattering geometry, e.g., as in bistatic forward scattering and monostatic backscattering, are illustrated using field data taken at a frequency of 30 kHz. An interpretive model for the contribution of near-surface bubbles to the apparent scattering cross section per unit area of sea surface is also discussed. This model has both a monostatic and a bistatic form, and, somewhat paradoxically, the bistatic form does not reduce to the monostatic form in the limit of source and receiver co-location. The issue is clarified, however, by examining the constituent pressures associated with the multiple paths, and by well-controlled laboratory measurements that include rough surface effects. These confirm both monostatic and bistatic forms of the model.