bluuebunny/crossref_metadata_2025 huggingface dataset:
Analysis of structural damping performance in passenger vehicles chasis.
Authors: Furukava Marcio , Gerges Samir , Neves Miguel M. , Coelho Bento J. L.
Published: October 2009

Viscoelastic material is commonly used in the passive treatment of structural vibration of the vehicle structure, to introduce damping and reduce vibration level at resonance frequencies. The effectiveness of such damping treatment depends on design parameters such as location, area, thickness, and choice of the type of the damping material. This paper describes the experimental proceeds to evaluate two different layer damping material performances, when they are applied to a passenger vehicle chassis.
Characterizing energy dissipation in singlewalled carbon nanotube polycarbonate composites.
Authors: Koratkar Nikhil A. , Suhr Jonghwan , Joshi Amit , Kane Ravi S. , Schadler Linda S. , Ajayan Pulickel M. , Bartolucci Steve
Published: October 2009

In this study, singlewalled carbon nanotube and bisphenol-A-polycarbonate composite beams were fabricated by a solution mixing process and dynamic (cyclic) load tests were performed to characterize energy dissipation. We report up to an order of magnitude (>1000%) increase in loss modulus of the polycarbonate system with the addition of 2% weight fraction of oxidized singlewalled nanotube fillers. We show that the increase in damping is derived from frictional sliding at the nanotube-polymer interfaces. The nanoscale dimensions of the tubes not only results in large interfacial contact area, thereby generating high damping efficiency, but also enables seamless integration of the filler materials into the composite structure.
Temperature activated interfacial friction damping in carbon nanotube polymer composites.
Authors: Suhr Jonghwan , Zhang Wei , Ajayan Pulickel M. , Koratkar Nikhil A.
Published: October 2009

Effect of temperature on interfacial sliding in single-walled carbon nanotube polycarbonate composites is investigated experimentally. We show that interfacial slip at the tube-polymer interfaces can be activated at relatively low dynamic strain levels (∼0.35%) by raising temperature to ∼90°C. We attribute this to increased mobility of the polymer chain backbones at elevated temperatures and thermal relaxation of the radial compressive stresses at the tube-polymer interfaces. These results show the potential of polymer nano-composites as high temperature damping materials for vibration and acoustic suppression in a variety of dynamic systems.
Nonlinear sensitivity of capacitive micromachined ultrasonic Lamb wave transducers.
Authors: Ge Li-Feng
Published: October 2009

A capacitive micromachined Lamb wave transducer using the second-order bending mode of high-aspect rectangular diaphragms to excite and receive Lamb waves in a silicon plate was presented [L. Ge, Proc. SPIE 6358, 1 (2006)]. Thus, the width of the diaphragm is made equal to the wavelength of the A0 wave, and all the transducer parameters can be determined by the TDK model for CMUTs with high-aspect rectangular diaphragms. The sensitivity, i.e., a ratio of the relative frequency shift to the change in mass loading of the plate, is derived and is a nonlinear function, which is the same as that for capacitive ultrasonic mass resonators [L. Ge, IEEE IUS, 1034 (2008)]. Also, it is a general nonlinear sensitivity expression available for both capacitive and piezoelectric gravimetric sensors. The area density increment, caused by the adsorbed or bound molecules or the fluid loading, is usually comparable with the area density of the silicon plate. Therefore, it is significant to use the nonlinear expression for determining the sensitivity accurately. The capacitive Lamb wave transducers are very attractive as gravimetric sensors for chemical and biological sensing since they have much simple structure and high sensitivity. [Work supported by NSFC (60774053).]
A piezoelectric microelectromechanical systems ultrasonic radiator.
Authors: Griffin Benjamin A. , Williams Matthew D. , Sheplak Mark
Published: October 2009

The development of a piezoelectric micromachined ultrasonic radiator is presented. The transmitter is formed by a radially non-uniform circular composite diaphragm. The diaphragm consists of a layer of piezoelectric material with annular electrodes. Transduction of the diaphragm occurs when an electric field is induced between annular electrodes across the piezoelectric material creating mechanical strain in the annular region. The strain couples into force and moment resultants that generate diaphragm deflection. A time varying electric field induces vibrations of the diaphragm which in turn generates acoustic waves. Included in the overall systems design of the transmitter is a unique package with back cavity depth control. A systems model incorporates electrical, mechanical, and acoustic components using composite plate mechanics, lumped element modeling, and acoustic theory. Comparison to experimental results is conducted through mechanical and acoustic characterizations. A laser vibrometer system measures diaphragm velocity from which the fundamental mode shape and resonant frequency are extracted. Farfield acoustic measurements are compared to the extrapolation of vibrometer measurements via Rayleigh’s integral. The characterization results show mismatch between devices as well as the equivalent circuit model. Experimental results of the variable back cavity depth show a qualitative match to the systems model.
Diffraction based optical microelectromechanical systems microphone and its application to the measurement of sound intensity.
Authors: Bicen Baris , Cui Weili , Su Quang , Miles Ronald , Degertekin Levent
Published: October 2009

Diffraction based optical MEMS microphones and force feedback capabilities of these microphones are presented earlier [Bicen et al., J. Acoust. Soc. Am. 123, 3230 (2008)]. Further investigation is done in order to see the capabilities of these optical microphones in measuring the sound intensity. The biomimetic diaphragms of these microphones are designed for responding to pressure gradient which can be used for extracting the particle velocity required to measure the sound intensity. In order to show the velocity measuring capability of these microphones, an impedance tube method is used because the velocity and pressure at each point in the impedance tube can be found accurately. The comparison of the measured velocities and sound intensities with the optical microphone and commercially available sound intensity probes is presented. Model results are discussed in order to show the effect of the different mode shapes on the accuracy of the pressure gradient measurements. Optimization of these biomimetic diaphragms will result in the measurement of the sound intensity in a larger bandwidth without using any spacers and additional microphone adapters like in commercial sound intensity probes. [Work supported by National Institutes of Health (NIH) and the Catalyst Foundation.]
How listeners represent dialectal variation.
Authors: Kraljic Tanya
Published: October 2009

Successful speech recognition requires that listeners map acoustically variant pronunciations onto the same meaningful interpretation. As listeners are exposed to a talker’s speech, they learn the relevant mapping, and their perception shifts to accommodate the talker’s pronunciations. Recent work on the perceptual learning of idiolectal variation has made it possible to investigate precisely what it is that changes in perceptual processing as listeners adapt to speakers. These studies suggest that phonemic representations themselves are rapidly modified to reflect the idiolectal variants produced by a talker. However, dialectal variation appears to be handled differently. Several studies will be presented that address the representation of dialectal forms, including a recent experiment that directly compared learning of a dialectal variant to learning of an idiolectal variant with the same acoustic properties. Listeners adjust to talkers’ dialects, but unlike with idiolectal variation, such adjustments do not reflect an underlying modification of the phonemic representations of the canonical counterparts. The implication of these results for dialect representation, as well as for the perceptual learning process, will be discussed. [This work was supported by NIH NRSA Award No. 7 F32 HD052342-03.]
Perceptual learning of non-native speech sounds: The importance of features from an attention to dimensions perspective.
Authors: Francis Alexander, L.
Published: October 2009

Research on the acquisition of non-native speech sounds is frequently conducted within the framework of theories that were originally developed to account for aspects of cross-language speech perception (e.g., PAM, NLM, and the SLM). Such theories typically focus on the influence of native phonetic categories on the perception of non-native speech, and second language learning researchers may tend to adopt this category-focused view although these theories make few strong predictions about learning. Interestingly, despite their focus on the role of categories, all of these theories incorporate the same assumption: That learning (of both first- and second-language contrasts) progresses by reweighting of phonetic features. This talk presents an overview of results from a series of studies that support this core assumption, suggesting that features, not categories, should play the central role in structuring our understanding of phonetic learning, especially with respect to such short-term adult learning as may be obtained in the laboratory or classroom. Taking such a perspective facilitates connections between theories of linguistic and non-linguistic perceptual learning, reduces dependence on category-based models of speech perception and production, and may provide a more principled basis for making predictions about what non-native contrasts should be easy or difficult to learn.
Surface and deep ducting of sound parallel to strong nonlinear internal wave fronts.
Authors: Lin Ying-Tsong , Duda Timothy F. , Reeder D. Benjamin
Published: October 2009

Acoustic ducting effects observed in a nonlinear internal wave field on the shelf of the South China Sea northeast of Tung-Sha Island (water depth of ∼120 m) are investigated. Environmental measurements from stationary instruments in the area show that the nonlinear internal waves have large amplitudes (over 40 m) and strong curvature. A principal component interpolation method is used to reconstruct the time-dependent three-dimensional internal wave field. A three-dimensional parabolic equation model is then employed to simulate monochromatic 400-Hz acoustic propagation parallel to the internal wave fronts for comparison to field data. The passing internal waves alternately elevate and depress the thermocline to form strong three-dimensional near-bottom acoustic ducts between the wave troughs and strong surface ducts of mixed layer water in the wave troughs. These alternating, depth-dependent acoustic ducts create asynchronous, vertically-bifurcated sweeping beams of ducted acoustic energy. The three-dimensional acoustic propagation modeling results are shown to mimic the field observations to a strong degree and elucidate the propagation physics in this highly complex environment.
Empirical dependence of acoustic transmission scintillation statistics on bandwidth, frequency, and range in the Gulf of Maine.
Authors: Andrews Mark , Ratilal Purnima
Published: October 2009

The scintillation statistics of broadband acoustic transmissions are determined as a function of signal bandwidth B, center frequency fc, and range with experimental data in Georges basin in the Gulf of Maine. The received signal intensity is shown to follow the gamma distribution implying that the central limit theorem has led to a fully saturated field from independent multi-modal propagation contributions. The gamma distribution depends on the mean intensity and the number of independent statistical fluctuations or coherent cells in the received signal. The latter is calculated for the matched filter, the Parseval sum, and the band-passed center frequency, all of which are standard ocean acoustic receivers. The number of fluctuations in the received signal is found to be an order of magnitude smaller than the time-bandwidth product TB of the transmitted signal, and to increase monotonically with relative bandwidth B/fc. A computationally efficient numerical approach is developed to predict the mean intensity and the corresponding broadband transmission loss of a fluctuating, range-dependent ocean waveguide by range and depth averaging the output of a time-harmonic stochastic propagation model. This model enables efficient and accurate estimation of transmission loss over wide areas, which has become essential in wide-area sonar imaging applications.
Accounting for spatiotemporal variability of shallow water waveguides in the geoacoustic inverse problem.
Authors: Becker Kyle M.
Published: October 2009

Reliable acoustic field predictions are essential for sonar performance modeling and matched field processing, particularly related to the geoacoustic inverse problem. On continental shelves and slopes, properties of the water column can vary widely in both time and space, while the seabed can be heterogeneous over scales of only a few kilometers and sometimes less. This combined spatiotemporal variability of the acoustic waveguide was a hallmark of the Shallow Water Experiment 2006 (SW06). This is illustrated using data collected during SW06 for an acoustic field measured on a fixed receiver array for a source towed along a radial track and repeated several times. In these experiments, the large degree of variability in the observed acoustic fields was attributed to large-scale changes in the water column that occurred over the course of a day. Properly accounting for this variability proved to be essential for obtaining robust geoacoustic inversion results for the seabed. Specifically, the spatiotemporal properties of the water column had to be accounted for in the forward models from which objective functions were derived. Methods for capturing the observed water-column variability are discussed as used in the inverse problem as well as for the more general problem of model-data comparison.
Temporal coherence of normal modes in an ocean waveguide.
Authors: Yang T. C.
Published: October 2009

Temporal coherence is a measure of sound correlation in time, and the temporal coherence time refers to the time it takes for the signal to become uncorrelated. Over 20 experiments have been conducted over the past 40 years to measure the temporal coherence of sound propagation to a long distance. The experimental results in shallow and deep water were recently analyzed by Yang [J. Acoust. Soc. Am. 120, 2595–2614 (2006); J. Acoust. Soc. Am. 124, 113–127 (2008); J. Acoust. Soc. Am. 125, 1247 (2009)]. A theoretical treatment is given in this paper for the temporal coherence of normal modes using the path integral approach and also the perturbation expansion of the coupled normal-mode equation to the first order of sound-speed-perturbation squared. For a typical shallow water and deep water environment with internal waves present, the coherence time of the acoustic field (averaged over the source and receiver depths) decreases as −3/2 power of frequency due to mode coupling, as is observed in data. Not including mode-coupling, the coherence time of the acoustic field decreases as −1 power of frequency, same as that predicted for acoustic rays. The coherence time decreases as −1/2 power of range in all cases. (Work supported by the Office of Naval Research.)
Statistics of acoustic intensity fluctuations caused by non-linear internal waves of elevation in shallow water in the South China Sea.
Authors: Reeder D. Benjamin
Published: October 2009

In April 2007, a 6-day long field experiment was conducted to measure internal waves and their acoustic effects at the edge of the continental shelf in the Northern South China Sea. Very large internal solitary waves of depression originating in the Luzon Strait generate trains of internal elevation waves as they encounter a subaqueous bluff at the shelf edge in 120-m water depth. The acoustic transect, from the moored acoustic source transmitting 400-Hz m-sequences to two vertical line arrays moored at 3- and 6-km ranges, was oriented roughly parallel to the crests of the passing internal elevation waves, so as to observe the strong horizontal refraction effects which occur under such conditions. Statistics of and correlations between the internal wave characteristics and their associated effects on acoustic propagation are presented. [Work supported by ONR.]
The effects of surface variability on received signal statistics.
Authors: Joseph Jeremy M. , Culver R. Lee. , Sell Alex W.
Published: October 2009

Acoustic propagation through the ocean can result in significant variability in the received signal. The degree of variability depends on the signal frequency and source-receiver range as well as medium variability along the propagation path. Our overall research goal is to develop the capability to classify passive sonar signals using the statistics of the received signal, and to support this goal, we require the capability to simulate statistically-valid signals. When the propagation path interacts with a rough ocean surface, the received signal will vary with time. We have employed the rough surface RAM parabolic wave equation code (Rosenberg, J. Acoust. Soc. Am. 105, 1999) to predict the statistics of low-frequency received signals that interact with the surface (such as in a shallow ocean channel) in order to calculate the effects of the time-varying rough surface scattering on frequency and amplitude statistics. Using a temporally-evolving rough surface, frequency and amplitude statistics are calculated for several ranges and depths. Received signal parameter statistics are compared with published analytical and empirical models. [Work sponsored by ONR Undersea Signal Processing.]
Analysis of a Schroeder diffusor using the Biot–Tolstoy theory.
Authors: Ramírez Nicolás , Raveau Maria Paz , Ramírez Osvaldo , Feuillade Christopher
Published: October 2009

The Biot–Tolstoy (BT) theory for the impulse response of a point source to a rigid wedge [J. Acoust. Soc. Am. 29, 381–391 (1957)] has been used to investigate the scattering properties of a QRD Schroeder acoustic diffusor. The BT is a fully three dimensional time-domain method, which facilitates individual identification and evaluation of the three components which give rise to the diffused field: reflections from the faces of the diffusor, diffractions from the edges of the wells, and “reflection-diffractions,” which combine the previous two phenomena. The computed impulse response readily enables frequency analysis over a broad frequency band with an upper limit determined by the signal sampling rate. Comparisons with published theoretical results for a diffusor at long range, obtained using a boundary element technique, show very good agreement, both for the diffusion coefficient and the polar scattering patterns as a function of frequency. Comparisons of the results of experimental measurements, with BT predictions, for short range diffusor configurations also show promising agreement. The results of both of these tests of the BT method will be presented, and the overall performance assessed.
Optimizing scattering from stage canopy arrays: determining density, size, shape and position.
Authors: D’Antonio Peter , Cox Trevor J.
Published: October 2009

The reflecting surfaces around a stage area play an important part in enabling ensemble among musicians. Energy must be reflected back to the stage to enable musicians to hear themselves and others and so achieve the correct rhythm, intonation, balance, and timbre. Gade summarized the current understanding of stage acoustic requirements; in particular, when stage reflections should arrive and how loud they should be. The study presented in this paper concentrates on the design of overhead canopy arrays, in particular, investigating effects of density, size, shape, and position. This aspect has surprisingly been little researched, although work by Rindel investigated similar questions to those being posed here. The advent of modern computer processing power allows stage canopy arrays and towers to be optimized using iterative algorithms, based on wave-based acoustic prediction models. A shape optimization program has been developed to optimize both the shape and tilt of overhead canopy arrays. Previously, the height and density have been specified based on experimental evidence and lighting/scenery considerations. The program has recently been updated to address the question of optimal canopy density and size, and some results from this work are presented below.
Determining the directional scattering coefficient from polar responses.
Authors: D’Antonio Peter
Published: October 2009

A method to measure the random incidence scattering coefficient has been described in ISO 17497-1. The method involves averaging the impulse responses for the sample in different orientations to isolate the specular component of the scattering. As such, the method does not distinguish between samples in which there is depth variation in only one direction, as in a cylinder, and textured surfaces with depth variation in many directions. Since computer model algorithms currently do not distinguish between these two types of surfaces, this may be an acceptable approximation. However, as computer models evolve to distinguish between these types of surfaces, directional scattering coefficients will be required. It is possible to calculate or measure the directional scattering coefficient from scattered polar responses, using either the correlation scattering coefficient described by Mommertz, in which the polar responses of a scattering sample and a flat surface are correlated, or the ratio of the energy in the specular zone and the total energy. Examples of calculated and measured directional scattering coefficients will be presented and discussed.
Deconstructing the interaural cross-correlation function.
Authors: Hartmann William M. , Rakerd Brad
Published: October 2009

Because it is a measure of the similarity of signals in a listener’s left and right ears, the long-term interaural cross-correlation (IACC) function within one-third octave bands provides an estimate of auditory envelopment as well as a guide to the ability to localize a sound. The peak height of the IACC, known as the coherence, is particularly relevant. The IACC can be written mathematically in terms of the amplitudes of spectral components in the left and right ears and in terms of the interaural differences in the component phases. The ensemble-average IACC, as measured with an artificial head in real rooms, can be further analyzed in terms of the amplitudes—their statistical distributions and their interaural correlations—and in terms of the interaural phases—their distributions and correlations with amplitudes. The nature of these statistical relationships depends on the frequency range through the ratio of a characteristic wavelength to the head radius. Analysis of this kind helps solve the long-wavelength problem. In the long-wavelength limit, the IACC must be large, but that does not mean that sound localization is good. [Work supported by the NIDCD Grant DC00181.]
A comparison study between the transport equation model and diffusion equation model for room-acoustic predictions in long spaces.
Authors: Jing Yun , Xiang Ning , Larsen Edward
Published: October 2009

This paper compares two numerical models: diffusion equation model and transport equation model, for room-acoustic predications in long spaces. Mathematically, the diffusion equation is the asymptotic approximation to the transport equation, therefore is expected to be less accurate. In addition, the transport equation intrinsically includes the direct sound field while the diffusion equation does not. However, due to its simple form of the diffusion equation, it has certain computational advantages over the transport equation model, e.g., it is less computationally expensive. When comparing the two models with the ray-tracing based method, the transport equation is shown to be more precise, especially when the walls are highly absorptive. Nevertheless, the diffusion equation model performs fairly well provided that the absorption on the walls is low. In this case, the diffusion equation model might be preferred over the transport equation model due to a low computational load.
Auditory scene analysis in fish.
Authors: Fay Richard
Published: October 2009

Auditory scene analysis (ASA) is a capacity of auditory perception that results in the hearing out or segregating of sound sources as individual objects or events when heard in the presence of other, simultaneous sources. Fish, humans, starlings, and nonhuman primates have been shown to have this capacity. I argue that any animal that hears probably has this capacity, and that it is not restricted to large-brained animals, nor to the perception of species-specific communication sounds. The demonstrations of ASA in goldfish include the capacity to hear out the frequency of pure tones when heard as a mixture of tones, and the hearing out of two, simultaneous pulse trains based on temporal and spectral differences, analagous to hearing out different musical instruments playing the same note. So far, harmonicity has been ruled out as a factor in ASA in goldfish, and spectral resolution has been shown to be necessary. ASA is a powerful phenomenon of human and animal hearing, and probably determines what we mean by “hearing.” ASA probably evolved very early as a fundamental feature of the sense of hearing.
Processing of clustered sensory signals in gray treefrogs (Hyla versicolor): Behavioral responses in the laboratory and field.
Authors: Christie Kevin W. , Schul Johannes , Feng Albert S.
Published: October 2009

Anuran mating choruses may consist of hundreds of sympatric and conspecific males calling in addition to other biotic and abiotic noise, representing a complex auditory scene whose characteristics change with distance. Detecting and localizing individual males in the chorus poses a challenge to the female, especially at long ranges. We carried out a series of recordings and behavioral experiments that are aimed at determining the distance at which female treefrogs (Hyla versicolor) use the chorus as an acoustic cue for their orienting responses. We analyzed natural choruses recorded at distances of 1–100 m and used these to create stimuli for phonotaxis experiments evaluating how the chorus attracts and provides cues for localization by females. In addition, we performed phonotaxis tests in the field near natural choruses to compare the frog’s behavior under laboratory and field conditions. We found that females utilize acoustic cues for orientation toward choruses at a distance up to 50 m, but additional cues may be used to ensure orientation in the field at distances >50 m. Additional experiments revealed that temporal coherence of the male call, as opposed to a general reduction in stimulus intensity, was the most important factor in female phonotactic behavior.
Dendritic mechanisms of auditory stream segregation in an insect.
Authors: Schul Johannes
Published: October 2009

Auditory stream segregation (AudSS) is the process of grouping the auditory scene into coherent perceptual objects. We recently described AudSS in an insect: In Neoconocephalus katydids, a first-order auditory interneuron (TN-1) segregates bat cries with slow pulse rates from conspecific communication signals with fast pulse rates. This insect system provides a powerful opportunity to study neuronal mechanisms of AudSS in an identified neuron with testable behavioral function. TN-1 adapts rapidly to fast pulse rates and responses are completely suppressed. However, if a slow pulse rate of sufficiently different carrier frequency is presented simultaneously, TN-1 responds reliably to the slow rate pulses. The suppression of the fast pulse rate on TN-1, i.e., the critical component of AudSS, is caused by two dendritic processes intrinsic to TN-1. The first mechanism is transient and likely calcium mediated, while the second mechanism is sustained throughout the stimulation and likely sodium mediated. TN-1 responses to slow pulse rates, occurred when the slow and fast pulse rate were transmitted by different groups of receptor cells, which project onto different regions of the TN-1 dendrite. Based on these results, we propose a mechanism of dynamic dendritic compartmentalization to underlie AudSS in the katydid TN-1.
Acoustic and perceptual categories for vocal signals in budgerigars (Melopsittacus undulatus).
Authors: Tu Hsiao-Wei , Osmanski Michael S. , Dooling Robert J.
Published: October 2009

The budgerigar has an extraordinarily complex, learned, vocal repertoire consisting of both long rambling warble and a number of shorter calls produced as single utterances. The contact call is the most frequently produced vocalization by budgerigars, and it bears a strong resemblance to short (about 150-ms), frequency-modulated elements that make up 25% of the sounds of warble. Using signal processing and psychophysical techniques we examined whether these two vocalizations represent different phonological systems or whether contact calls are used in two different situations. Warble call elements and contact calls were recorded from four male budgerigars. For each bird, contact calls produced as single utterances were different from contact call-like warble elements on a number of acoustic dimensions. Psychophysical tests showed that contact calls and call-like warble elements represent distinct perceptual categories. Finally, comparison of percent correct and response latencies across tests indicates that birds perceive the similarity between contact calls and call-like warble elements produced by the same bird. In sum, these birds show perceptual categories that correspond to acoustic categories in these complex vocalizations and they perceive the similarity in vocalizations from different acoustic categories produced by the same bird. [Work supported by NIH/NIDCD R01DC000198 to R.J.D.]
Effect of multiple scattering and modal dispersion on population density imagery of Atlantic herring shoals with ocean acoustic waveguide remote sensing.
Authors: Andrews Mark
Published: October 2009

Wide area sonar such as ocean acoustic waveguide remote sensing (OAWRS) has been shown to be a useful tool for instantaneously imaging large shoals of fish distributed over continental shelf regions. Here, we show that the population density of fish groups can be accurately estimated by using incoherent averaging of the matched filtered returns. Numerical Monte-Carlo models are applied to simulate the active imaging system and determine the statistics of the received matched filtered intensity scattered off Atlantic herring shoals in the Gulf of Maine. The model includes multiple scattering of the dense fish groups and uses a range-dependent acoustic model to simulate modal dispersion in the fluctuating ocean environment. We illustrate the effects of modal dispersion on the sonar imagery for various seafloor types. We determine the conditions for when multiple scattering is significant for Atlantic herring shoals, which depends on the fish density, imaging frequency, and mean target strength. Results of the model are compared to OAWRS sonar imagery collected during the 2006 Gulf of Maine Experiment.
Scattering and radiation force of helicoidal Bessel beams incident on spheres and the movable rigid sphere case.
Authors: Marston Philip L.
Published: October 2009

Understanding the scattering properties and coupling to modes of spheres in beams gives insight into several issues. Beam parameters may be selected to suppress or highlight the coupling to specific modes. When considering the radiation force on spheres by acoustic beams, it is also helpful to remember that while the axial wave-vector component has similarities to propagating waves, the transverse components may have similarities to standing waves. The present work examines the scattering and radiation force for the simplest Bessel beam having an axial null [P. L. Marston, J. Acoust. Soc. Am. 125, 3539–3547 (2009); F. G. Mitri, J. Phys. A: Math. Theor. 42, 245202 (2009)]. This is an acoustic vortex beam having a unit magnitude topological charge m. For some elastic and fluid spheres such beams allow conditions giving negative as well as positive axial forces. Negative forces are found to be correlated with reduced backward hemisphere scattering (as previously reported in the m=0 case). A noteworthy example is the case of a movable rigid sphere since for low ka the scattering properties are similar to metallic objects in water and the elastic modulus only weakly affects the scattering and radiation force. [Work partially supported by ONR.]
The Rubens tube.
Authors: Gee Kent L.
Published: October 2009

In 1905, Heinrich Rubens and Otto Krigar-Menzel published a paper describing a unique acoustics teaching apparatus. They developed a flammable gas-filled tube with holes in the top that revealed the acoustic standing wave behavior inside the pipe via the height of flames above the pipe. Interestingly, their article holds the distinction of being printed immediately following Einstein’s Nobel-prize winning paper on the photoelectric effect. From that auspicious beginning, the “Rubens tube” has been used for over a century in the teaching of acoustical resonance behavior. This paper will describe the tube’s operation, examples of its use, and commentary on and investigations involving the flame tube found in the literature.
Ultrasonic diffraction grating spectroscopy: Variables affecting the penetration depth.
Authors: Greenwood Margaret S.
Published: October 2009

Initial measurements of the penetration depth were presented at the ASA meeting in Portland. The grating unit is in contact with a slurry and send and receive transducer fastened to the back surfaces, as described previously [M. S. Greenwood, POMA 4, 045017 (2008)]. At the critical frequency, a peak appears in the signal to the receive transducer. Attenuation is observed by comparing the peak height for the slurry with that for water. The penetration depth is defined as the perpendicular distance from the diffraction grating where the attenuation occurs. The measurement uses a vessel in which the grating surface is in a horizontal plane and in contact with a slurry of polystyrene spheres. When the mixer is turned off, the particles start to fall and the peak in the receive transducer increases until it has the same size as for water. By recording the time for the change in signal and determining the terminal speed, the penetration depth is determined. Data will be presented to show how the frequency and the number of grooves insonified affect the penetration depth. Results will be compared with the theory for the interference of N wavelets from N grooves.
Monitoring stress in materials using diffuse ultrasonic backscatter.
Authors: Kube Chris , Ghoshal Goutam , Turner Joseph A.
Published: October 2009

Monitoring stress in structures is very important for various safety reasons. One of the challenging problems is to estimate stress non-destructively in various structural components due to changes in loading conditions so that accurate maintenance can be taken before failure. In this presentation, a non-destructive method of monitoring and measuring uniaxial tensile stress in metals using diffuse ultrasonic backscatter is discussed with a focus on the experimental implementation. Ultrasonic backscatter occurs when incident ultrasonic energy is scattered from heterogeneities (in this case grain boundaries) in the material. When an applied load is introduced, third-order elastic behavior of the grains results in changes to the received backscattered energy. Uniaxial loading experiments on samples of steel, aluminum, and a magnesium alloy highlight the utility of this approach for monitoring structural components under stress. Different scattering modes are shown to have different sensitivities to the applied load. Specific application of this technology for quantification of rail stress is also discussed. These results are anticipated to impact ultrasonic nondestructive evaluation of heterogeneous media under stress. [Work supported by US FRA.]
Granite rock acoustic measurements of nonlinearity and slow dynamics recovery.
Authors: Hedberg Claes , Haller Kristian
Published: October 2009

Through monitoring the resonance frequency of a granite bar, the nonlinearity and the slow recovery dynamics have been investigated. Nonlinearity was measured through a constant strain protocol, and slow dynamics was measured through a conditioning and relaxation cycle protocol. It is noteworthy that both tests show the same behavior—an increase in resonance frequency with strain for low amplitudes, which at higher strains turns into the normally expected decrease with strain.
Experimental results of a two-dimensional sonic device.
Authors: Bock Daniel M. , Kim Keehoon , Lopez Martin , Molina Bryan
Published: October 2009

The authors present the design and experimental results of a meta-material multilayered structure in a two-dimensional (2-D) matrix described by Torrent and Sánchez-Dehesa (2007) which can be applied to the fabrication of acoustic lenses and cloaks by tailoring the material anisotropy. The structure consists of a 2-D matrix made of two isotropic materials (low-density foam and aluminum) that are evenly spaced in air with varying diameters in order to control the acoustic impedance. We simulated a 2-D matrix in order to design an acoustic lens with a focal length of 18 cm and a gain of 13 dB in a finite element analysis program. Based on these simulation results, we designed and fabricated a 2-D acoustic lens. We measured the properties of the acoustic lens, having a focal length of 17 cm and a focal point gain of 14 dB (re 20 μPa). The excellent agreement between the simulation and experimental results supports the use of a 2-D meta-material structure for the control of acoustic signals in any arbitrary application and can be used for the design of more complex structures in the future.
Acoustic radiation of a vibrating wall covered by a porous layer: Transfer impedance concept and effect of compression.
Authors: Dauchez Nicolas , Doutres Olivier , Genevaux Jean-Michel
Published: October 2009

The acoustic radiation of a vibrating wall covered by a porous layer is investigated. The porous layer is described by the one-dimensional Biot model: it accounts for the propagation of the two longitudinal waves in the porous layer within its thickness. The transfer impedance concept [Doutres et al., J. Acoust. Soc. Am. 121, 206–213 (2007)] allows to determine the effect of the porous layer on the acoustic radiation of the vibrating wall. This impedance differs from the surface impedance that can be measured in a plane wave impedance tube. It is shown that the radiation efficiency of the structure increases in the vicinity of the first resonance of the skeleton in its thickness and decreases for higher frequencies. Experimental validation is performed with a baffled piston covered by a foam or a fibrous layer. Only the radiation model using the transfer impedance shows close agreement with experimental data. Finally, effect of compression of the porous layer is investigated by both analytical and experimental approaches, in the case of fibrous materials used in aeronautical applications.
Modeling porous-elastic materials in periodically mount connected double panel partitions.
Authors: Legault Julien , Atalla Noureddine
Published: October 2009

In aeronautic double panel partitions, the trim panel (interior panel) is usually attached to the ring frames that are ribbed to the skin panel (exterior panel) with periodically spaced resilient mounts. Moreover, porous-elastic materials are inserted in the cavity between these panels to provide absorption. Due to their periodic nature, these partitions allow the use of space-harmonic expansion formulations for their vibration and sound transmission analysis. This paper shows how equivalent fluid and porous-elastic models can be incorporated in such formulations to assess the influence of sound absorbing materials. The equations of the model are derived and simulation results are presented for materials providing different absorptions. Application is focused on the relative effects of absorption versus the mounts’ resilience on the transmission loss of the system.
Perceptual constancy, reverberation, and grouping: Within-band effects.
Authors: Watkins Anthony , Makin Simon , Raimond Andrew
Published: October 2009

Perceptual constancy effects are observed when differing amounts of reverberation are applied to a context sentence and a test-word embedded in it. Adding reverberation to members of a “sir”-“stir” test-word continuum causes temporal-envelope distortion, which has the effect of eliciting more sir responses from listeners. If the same amount of reverberation is also applied to the context sentence, the number of sir responses decreases again, indicating an “extrinsic” compensation for the effects of reverberation. Such a mechanism would effect perceptual constancy of phonetic perception when temporal envelopes vary in reverberation. This experiment asks whether such effects precede or follow grouping. Eight auditory-filter shaped noise-bands were modulated with the temporal envelopes that arise when speech is played through these filters. The resulting “gestalt” percept is the appropriate speech rather than the sound of noise-bands, presumably due to across-channel “grouping.” These sounds were played to listeners in “matched” conditions, where reverberation was present in the same bands in both context and test-word, and in “mismatched” conditions, where the bands in which reverberation was added differed between context and test-word. Constancy effects were obtained in matched conditions, but not in mismatched conditions, indicating that this type of constancy in hearing precedes across-channel grouping.
Listener’s variation in phoneme category boundary as a source of sound change: A case of /u/-fronting.
Authors: Kataoka Reiko
Published: October 2009

Previous work examined listeners’ recognition of a vowel in a series of [dVt] and [bVp] syllables varying perceptually from /CiC/ to /CuC/ in four different conditions (without precursor phrase, with precursor phrase, and in fast, medium, and slow speech), and found that ambiguous vowel stimuli were more often heard as /u/ in the [dt] context as opposed to the [bp] context (compensation for coarticulation). This paper reports the results of further analysis of the data and shows that although listeners varied in their /i/-/u/ category boundaries, their perceptual responses were systematic so that a group of listeners who had the category boundary closer to the /i/-end than the rest of the listeners in the “no-precursor” condition consistently had it this way in other conditions as well. This study also investigated the listeners’ response in vowel repetition task, where the listeners were asked to listen to the same [CVC] stimuli as used in the vowel recognition task and to repeat only the vowel. Results of this part of the study will be presented and the implications for a listener-based theory of sound change will be discussed.
Predicting perceptual outcomes from acoustic measures of vowels in dysarthria: A classification analysis.
Authors: Lansford Kaitlin L. , Liss Julie M.
Published: October 2009

Reductions in vowel space presumably obscure the distinctiveness of vowels produced by individuals with dysarthria. This represents a source of intelligibility decrement to the extent that more ambiguous vowels influence access of correct lexical items. The present study sought to examine (1) whether vowel formant frequencies predict perceptual decisions through classification analysis and (2) whether different forms of dysarthria are associated with different classification outcomes. Productions of phrases containing the target vowels /i/, /ɪ/, /ε/, /æ/, /u/, /o/, /ɑ/, and /ʌ/ in strong syllables were obtained from patients whose speech was affected by one of four neurological impairments: Parkinson disease, Huntington disease, amyotrophic lateral sclerosis, or cerebellar degeneration. The first two formant frequencies of each vowel were measured at its midpoint and then subjected to a classification analysis. Classification rules based on the acoustic measurements were used to classify each token as one of the eight target vowels. For each speaker group, the performance patterns obtained by the classification analysis were compared to those made by 15 listeners in an open transcription task. The ability of the classification analysis to predict perceptual outcomes specific to each dysarthric speaker group will be discussed. [Work supported by NIH/NIDCD.]
Phonological reduction in spoken word recognition.
Authors: Viebahn Malte C. , Luce Paul A.
Published: October 2009

In casual speech, speakers often produce reduced phonological variants of the intended spoken words. Although these reductions are not obligatory, they occur in a regular way and only in certain phonological environments. Nasal tapping is one of these allophonic processes. During nasal tapping words such as “center” are pronounced as “cenner.” Recent studies suggest that the recognition of word forms that have undergone nasal tapping is associated with substantial processing costs. The present set of experiments explores potential causes that may contribute to this effect. It is suggested that the perception of allophonic variants depends on the phonetic conditions under which they are produced and encountered.
At which processing level does extrinsic speaker information influence vowel perception?
Authors: Sjerps Matthias J. , Mitterer Holger , McQueen James M.
Published: October 2009

The interpretation of vowel sounds depends on perceived characteristics of the speaker [e.g., average first formant (F1) frequency]. A vowel between /ɪ/ and /ε/ is more likely to be perceived as /ɪ/ if a precursor sentence indicates that the speaker has a relatively high average F1. Behavioral and electrophysiological experiments investigating the locus of this extrinsic vowel normalization are reported. The normalization effect with a categorization task was first replicated. More vowels on an /ɪ/-/ε/ continuum followed by a /papu/ context were categorized as /ɪ/ with a high-F1 context than with a low-F1 context. Two experiments then examined this context effect in a 4I-oddity discrimination task. Ambiguous vowels were more difficult to distinguish from the /ɪ/-endpoint if the context /papu/ had a high F1 than if it had a low F1 (and vice versa for discrimination of ambiguous vowels from the /ε/-endpoint). Furthermore, between-category discriminations were no easier than within-category discriminations. Together, these results suggest that the normalization mechanism operates largely at an auditory processing level. The mismatch negativity (an automatically evoked brain potential) arising from the same stimuli is being measured, to investigate whether extrinsic normalization takes place in the absence of an explicit decision task.