bluuebunny/crossref_metadata_2025 huggingface dataset:
Techniques for active classification of underwater structures
Authors: Gaunaurd G. C. , Strifors H. C. , Moore P. W. B. , Huang H.
Published: July 2002

Various techniques for the detailed classification of submerged shells insonified by short pulses from either an active sonar or a small explosion are discussed [Ultrasonics 33, 147–153 (1995)]. The returned shell echoes in several signal domains are examined. These included the frequency, the time, and particularly the joint time-frequency domain. The use of Wigner-type distributions was most informative in the latter case. Selected features in these echo-displays which provided information about a certain specific target characteristic were identified. The achieved ‘‘in situ’’ classification is rapid, unambiguous, and accurate. Examples dealing with short pulses simultaneously scattered by one, two, or more elastic shells will be shown. Theoretical predictions and measurements show good agreement. This novel analysis in the above domains determines the size, shape, wall thickness, material composition of the shell(s), and their possible filler substance(s), as well as the number of shells involved, and their ranges from the projector. The basis of this technique has been proposed as a possible explanation of how echolocating dolphins successfully identify submerged structures [J. Acoust. Soc. Am. 100, 2820 (1996)].
Novel formalism for resonance scattering of acoustic and elastic waves
Authors: Rhee Huinam , Park Youngjin
Published: July 2002

A novel formalism is proposed for the exact isolation of resonances from scattered waves for acoustic wave scattering from elastic or liquid bodies. The resonance scattering function (RSF) consisting of purely resonance information is proposed. Both magnitudes and phases of isolated resonances can be correctly obtained by using the proposed formalism while previous works based on the conventional resonance scattering theory (RST) can produce only magnitude correctly. The reason why previous works using RST could obtain correct magnitude information of resonances for the case of acoustic wave scattering is explained. Acoustic wave scattering from a variety of submerged bodies is analyzed by utilizing the RSF and the isolated resonances were compared with previously published studies. The exact π-phase shift through resonances and at the anti-resonances caused by the interaction between adjacent resonances, which has never been obtained by using RST, shows that the proposed formalism properly extracts the resonances from scattered waves. Due to the differences in phases, the novel formalism and the conventional RST generate different resonance spectrum. For elastic wave scattering, even magnitudes of resonances isolated by the proposed formalism will be different from those obtained by the conventional RST. a)Also at Dept. of Mech. Eng., KOPEC, 150 Duckjin-Dong, Yusung-ku, Taejon, 305-353 Korea.
Analytical study of the acoustic scattering from a submerged stiffened cylindrical shell with two endplates
Authors: Harari Azriel , Boisvert Jeffrey E.
Published: July 2002

A mathematical model is described for the sound scattering from a finite cylindrical shell with two endplates submerged in a fluid, subjected to an incident wave impinging on the shell from a source in an arbitrary direction. The effect of structural damping and rib-stiffeners on the monostatic scattered response of the structure is considered for a full range of incident wave angles over the nondimensional frequency range ka=0.1–30.
Phonological variation in spoken word recognition
Authors: Deelman Thomas , Lang Brian , Connine Cynthia M.
Published: July 2002

A common form of phonological variation in American English is flapping. For example, the word ‘‘pretty’’ may be pronounced as [prIDi] or [prIti]. A phonological priming experiment was conducted where a lexical decision was made on a flap or canonical target. The target was preceded by itself (repetition condition), by its variant (form condition), or by a phonologically unrelated word (control). The results showed that priming for a canonical variant was comparable in the repetition and form condition. In contrast, priming for flaps was reduced in the form condition compared to the repetition condition. These findings suggest that the underlying voiceless stop is recovered when processing a flapped variant. The results are discussed in terms of surface versus underlying representations as the currency of lexical activation.
A new imaging science test object for performance measurements of ultrasonic imaging systems
Authors: Phillips Daniel , McAleavey Stephen , Parker Kevin J.
Published: July 2002

A novel test object for ultrasound imaging has been developed. The test object, or phantom, is manufactured with thin film techniques allowing precise placement of ‘‘digital scatterers’’ which can produce sophisticated test targets, similar to those that are widely used in imaging science to evaluate displays, printers, and electronic imaging systems. This type of test object can be used to determine parameters such as the MTF and resolution limits, and can facilitate the detection of imaging phenomena and artifacts such as spatial warping and spatial frequency aliasing. These test objects can be used in conjunction with standard performance evaluation methods and devices to augment and enhance their capabilities and range of application. In addition, by imparting an appropriate motion to the target, it is possible to provide unique test stimuli for pulsed and continuous wave as well as color flow and color energy Doppler ultrasound systems. Results are presented which demonstrate how the ability to make precise line targets allowed the assessment of direction related resolution and spatial frequency response by inspection, thus facilitating the implementation of a simple evaluation procedure.
Atmospheric propagation modelling
Authors: Noble John M.
Published: July 2002

With the developments in modeling the propagation of sound through the atmosphere, it is now possible to merge these models with sensor models to determine the impact of the atmosphere on acoustic sensor performance. Early numerical models such as the Fast-Field Program (FFP) allowed users to predict the effects of refraction, geometric spreading, diffraction, and complex ground impedance on sound propagation in the atmosphere. Coupling these numerical models with models for acoustic arrays, gave researchers the ability to predict the effects of the mean atmosphere on array performance. The newer numerical models like the Parabolic Equation (PE) and Green’s Function PE (GFPE) have allowed researchers to incorporate homogeneous and isotropic turbulence and complex terrain into propagation models. These new capabilities will lead to determining the effects of turbulence and terrain on acoustic arrays. With the development of high-speed/low-power/low-cost microcomputers, it is now possible to even integrate simple propagation models into an acoustic array processor. This will allow the development of smart acoustic arrays which can determine the impact of the atmosphere on their performance and possibly modify how the array processes the data.
The prehistory of synthetic aperture sonar
Authors: Parvelescu Antares
Published: July 2002

It is necessary to go back to 1958 (A.D.) and the summer of 1959. The concept of using recorded data obtained from a single moving element to provide a ‘‘memorized array’’ instead of the multiple-element physical array, was offered to ONR (Aubrey Pryce), whose reaction will be described. The years 1960–68 saw slow (mini-funded) progress at Hudson Labs of Columbia University. Two algorithms were conceived and (mini-)tested; a 6-m towed ‘‘fish’’ was built, then progress slowed further at the Hawaii Inst. of Geophysics. Graduate students wrote theses and bootlegged computer time; names will be named and credit will be given. The unquenched urge to ‘‘see’’ acoustically the seabed in two or three dimensions is at least almost here, as the next few papers show. Some formerly classified reports may have been released by the time of this meeting.
Test results for a synthetic aperture sonar (SAS)
Authors: Neudorfer Mark L. , Garrood Dennis , Luk Tony , Nelson Matt
Published: July 2002

A special purpose synthetic aperture sonar (SAS) system has been developed and built by Hughes Aircraft Co. and Dynamics Technology, Inc. The main features of the system are a 3.2-m-long, 32-element linear array, and a data acquisition system capable of recording the elemental data in real time while preserving the phase and amplitude fidelity required by SAS processing. High-resolution, large (1002 m2) and small (32 m2) SAS images of various objects will be presented that demonstrate resolutions of 20 cm at 1000 m. The innovation of the work is that resolution achievable only with short-range, high-frequency sonar has been demonstrated at ranges obtainable only with a low-frequency sonar. [Work supported by DARPA.]
Medium effects on high-frequency propagation: A recent experiment
Authors: Williams Kevin , Henyey Frank , Ewart Terry , Grochocinski Jim , Reynolds Steve , Rouseff Daniel
Published: July 2002

In August 1996 an experiment was performed southeast of Long Island, NY (40 30.16 N, 70 30.58 W) to examine water column effects on synthetic aperture sonar (SAS). Both the experiment and the pre-experimental modeling that guided the experiment will be presented. Salient features of the experimental equipment and procedure include the use of bottom mounted towers for stability, transmission frequencies of 6, 20, 75, and 129 kHz, reciprocal tower-to-tower transmissions, and receivers spaced over a 10-m horizontal and 6-m vertical aperture. First look results will be presented for a 24-h period that included a solibore event. Large variations in propagation conditions over time scales of minutes are evident in the data. The SAS relevant quantities to be extracted from this data set will be discussed. [Work supported by ONR.]
An approximation theoretic approach to synthetic aperture processing
Authors: Fitzgerald Raymond
Published: July 2002

An algorithm for synthetic aperture processing derived using approximation theory is presented. Improvements offered by this approximation theoretic algorithm and the analytic relationships between the algorithm and other algorithms are described. The approximation theoretic approach is shown to provide a unified formalism for comparing and evaluating existing and proposed algorithms as well as a method for generalizing and improving them.
Three-dimensional modal mapping in shallow water using simulated acoustic field data
Authors: Becker Kyle M. , Frisk George V. , Connor Laurence N. , Doust Barry J.
Published: July 2002

It is well known that the acoustic field propagated through a shallow- water waveguide is sensitive to the properties of the waveguide and its boundaries. Through adiabatic mode theory, it is understood that the modal eigenfunctions and eigenvalues adapt to the local environment and changing boundary conditions. It has been proposed that modal tracking may be employed in a laterally varying waveguide to infer properties of the normal-mode field and the environment. In support of a three-dimensional modal mapping experiment, synthetic three-dimensional acoustic fields are generated to simulate propagation in a shallow-water region in the vicinity of the East Coast strataform site. Synthetic fields are computed using normal-mode and parabolic equation codes and transformed to the wavenumber domain to obtain estimates of the spatially varying spectral content of the modal field. The resulting modal maps are discussed for several experimental regions. [Work supported by ONR and ARL Penn State Univ.]
Low-frequency signaling behavior in mysticete whales
Authors: Clark Christopher W. , Ellison William T.
Published: July 2002

Mysticete whales produce a variety of low-frequency sounds. These range from the highly labile song of the humpback whale (Megaptera novaeangliae) to the infrasonic sounds of the blue (Balaenoptera musculus) and fin (Balaenoptera physalus) whales. Biological functions of these sounds remain largely untested, the most common being that sounds are a male reproductive display for social communication. Recent access to fixed arrays of bottom-mounted hydrophones and towed arrays has provided a novel mechanism for documenting low-frequency whale sounds throughout large ocean areas in relation to season, bathymetric features, and ocean conditions. Ocean sound propagation conditions impose severe constraints and offer dramatic opportunities for acoustic transmission for whales. The bioacoustic data in combination with sound propagation models provide novel insights into the possible biological functions for low-frequency whale sounds, and offer testable predictions. Improved understanding of low-frequency whale bioacoustics is critical for knowing the potential impact of human-made low-frequency sounds on whales, and offers insights into improved signal design. Biological functions will be presented in conjunction with empirical evidence to support, for example, that blue and fin whales navigate using reverberation and bistatics, and humpback males should prefer deep rather than shallow water singing habitat.
Comparison of the low-frequency response of the peripheral auditory organs in the goldfish and oscar
Authors: Derenburger Corrie , Finneran James J. , Hastings Mardi C.
Published: July 2002

A noninvasive ultrasonic measurement system was used to measure the amplitude and phase response of the peripheral auditory organs of the goldfish, considered auditory specialists, and the oscar, having an auditory threshold noticeably higher than that of the goldfish. The fish were excited with an underwater acoustic source at frequencies ranging from 12.5–3000 Hz. For frequencies between 12.5–400 Hz, tests were performed in a 14-m acoustic waveguide. For tests above 400 Hz, a 2.43-m-diam pool with a depth of 0.4 m was used. The response of the goldfish swimbladders, Weberian ossicles, and otoliths were measured. In addition, the swimbladders were deflated and measurements were made of the Weberian ossicles and the otoliths. Similar measurements were obtained for the auditory organs of the oscars, which vary from the goldfish in that they contain only one swimbladder and lack the Weberian apparatus. Comparisons within and between species are presented based on these four groups of data. [Work supported by ONR Grant No. N00014-94-1-0337.]
Psychometric functions for detecting an increment added to a continuous or gated pedestal
Authors: Dai Huanping , Neff Donna L.
Published: July 2002

Green et al. [J. Acoust. Soc. Am. 66, 1051–1056 (1979)] reported that a psychometric function for detecting a 1000-Hz increment was two to three times steeper with a continuous rather than with a gated pedestal. Intrigued by their finding, the observations to frequencies of 250 and 4000 Hz were extended, and to signal types including tone in noise and noise in noise. Psychometric functions of three normal-hearing listeners were constructed from 2IFC adaptive tracks and fitted with a Gaussian function: pc=Φ(d′/√2), where d′=(x/α)β, x is the signal level, α is the threshold, and β is the slope. In all conditions, slopes obtained with continuous pedestals were steeper than those obtained with gated pedestals. For tone-in-tone conditions [x=10 log(1+ΔI/I)], slopes differed by a factor of 2 at 250 and 1000 Hz, and by a factor of 4 at 4000 Hz. For tone-in-noise conditions [x=E/N0], slopes differed by a factor of 2 across the three frequencies. For noise-in-noise conditions [x=10 log(1+S0/N0)], the slopes differed by a factor of 1.5. Implications of these data for existing models of intensity coding will be discussed. [Work supported by NIH/NIDCD.]
Masking of pure tones by sinusoidally amplitude-modulated tonal maskers
Authors: Gregan Melanie J. , Bacon Sid P. , Lee Jungmee
Published: July 2002

In experiment 1, masking patterns were obtained with an 80-dB SPL, 500-ms sinusoidally amplitude-modulated (SAM) masker (m=1.0). The 30-ms signal was centered at a masker peak or masker valley. Masker frequency (fm) was 750, 1350, or 2430 Hz; signal frequency (fs) was 0.8, 0.9, 0.95, 1.0, 1.2, 1.44, or 1.62 fm. Thresholds were generally higher for a signal at masker peak. The magnitude of this effect was governed by fs/fm, rather than by fs. In experiment 2, growth-of-masking functions (fm=1350 Hz, fs=1.44 fm) were measured for a SAM masker (m=0.5, 0.75, or 1.0). These thresholds were compared with those obtained with unmodulated maskers in forward or simultaneous masking. The comparisons suggest that thresholds for a signal at a peak of a SAM masker are due to simultaneous masking, while those in a valley are due primarily to forward masking when m=1.0 or simultaneous masking when m=0.5 or 0.75. Finally, the slope of the masking functions in simultaneous masking (unmodulated masker or signal at peak of SAM masker) changed from a slope greater than 2.0 to a slope of 1.0 at the highest levels; this will be discussed in terms of basilar membrane nonlinearity. [Work supported by NIDCD.]
Influence of masker phase structure on tone detection by normal-hearing and hearing-impaired listeners
Authors: Summers Van , Leek Marjorie R.
Published: July 2002

For normal-hearing listeners, harmonic complexes with equivalent power spectra but which differ in temporal waveform shape (i.e., in phase spectra) may also differ in their effectiveness as maskers. Summing harmonic components in positive-Schroeder phase generally produces a less effective masker than a negative-Schroeder complex [Kohlrausch and Sander, J. Acoust. Soc. Am. 97, 1817–1829 (1995)]. This influence of phase structure on masking effectiveness may reflect nonlinear compressive processing in a healthy cochlea [Carlyon and Datta, J. Acoust. Soc. Am. 99, 2542 (1996)]. This study measured detection thresholds of normal-hearing and hearing-impaired listeners for tones masked by complexes in positive- and negative-Schroeder phase. Masker stimuli contained all harmonics between 200 and 5000 Hz of a 100-Hz fundamental with harmonics set equal in amplitude. Three probe frequencies (1000, 2000, and 4000 Hz) and three probe levels (60, 70, and 80 dB SPL) were tested. For normal-hearing listeners, positive-Schroeder stimuli were consistently less effective maskers than negative-Schroeder complexes, particularly at the 60-dB probe level. Differences in masker phase structure had less effect at high presentation levels and for hearing-impaired listeners. The results are consistent with nonlinear compressive auditory processing by normal-hearing listeners which is reduced at high presentation levels and in the presence of sensorineural hearing loss. [Work supported by NIH.]
Effects of timbre manipulations on melody perception
Authors: Acker Barbara E. , Pastore Richard E.
Published: July 2002

The effects of timbre on melody perception were explored in three-voice homophonic (H) and polyphonic (P) pieces. Musically trained subjects learned a 12-note melody in isolation, then listened to H and P pieces that contained the melody in either the high, middle, or low spectral positions. Three timbre conditions were created: (1) homogeneous, where all three voices were in the same timbre; (2) enhanced, where the melody was presented in a timbre distinct from the other two voices; and (3) inconsistent, where each of the three timbres formed distinct patterns which were independent of the melody (H pieces only). In a discrimination task, subjects responded to errors only in the melody, although errors could occur in the other two voices. Several patterns of results occurred which were dependent on the type of timbre manipulation and the musical context employed. Thus the results demonstrate important aspects of how principles from music cognition (melody memory, timbre manipulations) and music theory (H and P pieces) can interact. [Work supported by AFOSR.]
The role of timbre, pitch, and loudness changes in determining perceived metrical structure
Authors: Singh Punita
Published: July 2002

The role of differences in pitch, loudness, and timbre as determinants of metrical structures was investigated. A repeated sequence of 12 pure tones was systematically partitioned into 4 groups of 3 tones or 3 groups of 4 tones by introducing changes in F0, intensity, and spectral complexity between sounds at serial positions 1, 4, 7, 10 or 1, 5, 9, respectively. Listeners used a rating scale to indicate if a triple, quadruple, or ambiguous meter was perceived. For changes in only one parameter at a time, perception of rhythmic structure followed the physical markers. When changes in more than one parameter were made concurrently, multiple cues for triple or quadruple meter were available. Coincident changes led to reinforcement of the rhythm demarcated by the points of change. Conflicting changes led to different outcomes: Timbre and pitch changes dominated over a loudness-based accent structure. Pitch versus timbre stimuli were rated as having ambiguous meter. A combination of any two parameters versus the third dominated in determining the metrical structure. The results raise questions about the role of timbre in rhythm perception in general and as a tool for marking metrical units in particular.
The interaction of pitch and loudness in dynamic stimuli: Beyond the Doppler illusion
Authors: Neuhoff John G. , McBeath Michael K.
Published: July 2002

Listeners tend to experience rising pitch even though frequency falls as a sound source approaches. The phenomenon, called the Doppler illusion [J. G. Neuhoff and M. K. McBeath, J. Exp. Psychol. Hum. Percept. Perform. 22, 970–985 (1996)], shows that dynamic intensity change influences perceived pitch in a way that is qualitatively different from discrete static intensity change. Two new studies show a dynamic influence of intensity change on perceived pitch and a dynamic influence of frequency change on perceived loudness. Listeners were presented with square wave tones of either rising, falling, or constant intensity that either rose, fell, or remained constant in frequency for 6 s. Listeners responded in real time to either changes in pitch or loudness by moving a response wheel. It was found that dynamic intensity sweeps contribute to the perception of dynamic pitch change in the direction of the intensity sweep. In addition, dynamic frequency sweeps contribute to the perception of perceived loudness change in the direction of the frequency sweep. The results imply that pitch and loudness perception interact under dynamic conditions in a way that cannot be predicted by perceptual models derived from the presentation of discrete static tones.
Discrimination thresholds for glides in frequency as a function of transition span, duration, and direction
Authors: Madden John P.
Published: July 2002

The study measured discrimination thresholds for glides in frequency as a function of magnitude of transition span, duration, and direction. The purpose was to determine whether the Weber fraction is constant across a range of transition spans, as suggested by an earlier study [J. P. Madden and K. M. Fire, J. Acoust. Soc. Am. 100, 3754–3760 (1996)]. Subjects were asked to distinguish between a comparison glide with a fixed transition span and a target glide with a greater transition span. Comparison signal frequency transition spans were 0.5, 1, 2, 4, and 8 times the ERB of the auditory filter at the signal center frequency. The nominal center frequency of the glides was 1.8 kHz, but the actual signals were roved over a range of center frequencies. Both up- and down-glides were used; signal durations were 50 ms and 400 ms. The results indicate that the Weber fraction is essentially constant for transition spans of 1–8 ERBs, but increases below 1 ERB. The effects of duration and direction were small. [Work supported by Research Grant No. 1 R15 DC 02662-01 from the National Institute on Deafness and Other Communication Disorders, National Institutes of Health.]
Visible speech revisited: An acoustically driven model of lip and tongue motion
Authors: Moody Jay T. , Stone Maureen
Published: July 2002

A method is presented for converting acoustic speech data into a ‘‘speech readable’’ movie of a canonical talking face using a neural network. Target values for the network are created by finding the principal components of a set of video frames, with each frame consisting of side-by-side images of the face and tongue of a single speaker. Tongue contours are extracted from mid-sagittal ultrasound images. Input to the network consists of a set of cepstral parameters and their derivatives calculated over 22-ms windows (overlapping by 11 ms). Two such input frames are matched to each video frame (33 ms). Recurrent (backward) connections in the network encourage it to learn not only the acoustic-articulatory pairings, but also articulatory trajectories (expectations of the next articulatory state based on recent articulatory states). It is hypothesized that this supplemental trajectory information helps to alleviate the uncertainties inherent in the vocal tract inverse mapping. After training, the network is presented with new (untrained) tokens (audio only) of utterances from the training corpus and the network’s video output is recorded. The network’s output is compared to the actual recorded video. [Work supported by US Dept. of Education and NIH.]
Temporal relationships of the articulatory, acoustic, and perceptual effects of fricative–vowel coarticulation
Authors: Xu Ying
Published: July 2002

Anticipatory coarticulation has been extensively studied as part of the general phenomenon of coarticulation. However, the temporal relationships of the articulatory, acoustic, and perceptual effects of this particular type of coarticulation have not received much attention. The purpose of this study was to systematically examine lip protrusion gestures, acoustic and perceptual effects in fricative–vowel contexts, and explore the temporal relationships among these three effects. The onset of lip protrusion and acoustic effects as obtained and compared by employing a minimal contrast technique. The results showed that the onset of lip protrusion was much more consistent in a relative timeframe than in an absolute timeframe, and it was much earlier than, but independent of, the onset of traceable changes in formant frequencies. A reliable effect of anticipatory coarticulation on perception was also observed and the onset of this perceptual effect occurs tens of milliseconds later than the onset of the acoustic effect.
Investigation of a smart trigger for an acoustic deterrent device
Authors: Huang Dehua , Christensen Steve G. , Boucher Stephen G. , Tancrell Roger H.
Published: July 2002

Attacks of pinnipeds on fish pens cause considerable destruction to the fish farming industry. An acoustic deterrent device (ADD) operated at 10–16 kHz with a source level around 200 dB re: 1 μPa at 1 m is an effective way of predation deterrence. The present technique is to operate the ADD system on a continuous basis. This constant insonification could lead to predator habituation and could create serious man-made acoustic noise. In this paper, techniques for creating a device to trigger the existing ADD system are investigated. The trigger will turn on the ADD system only when the fish pens are threatened. Field tests were conducted by applying both passive hydrophone and active Doppler methods to detect the presence of marauding pinnipeds. During the test, acoustic devices were located inside the fish pen or outside the fish cage, and the observation objects were fish in the pen or predators in the open sea. Design concept for the trigger devices, related DSP technique and pattern recognition, along with data collected in the field will be presented and discussed. [The principal investigator, Dr. Huang, acknowledges the funding from USDA/NRAC (Project No. 5555506).]
Nonlinear time-domain analysis of electrostrictive materials by the finite element method
Authors: Coutte-Dubois Jocelyne F. , Debus Jean-Claude , Dubus Bertrand , Bossut Regis
Published: July 2002

Lead magnesium niobate ceramics (PMN) are promising materials for applications in the field of underwater acoustic projectors. A finite element procedure has been developed in the ATILA code to model the static deformation of these materialss [J. C. Debus et al., J. Acoust. Soc. Am. 100, 2584(A) (1996)]. Two different elements are available according to whether or not the saturation of polarization is included. An extension of this model to nonlinear transient analysis is presented in this paper. The procedure is derived for time stepping by finite difference, using a central difference scheme. This new capability is demonstrated by analyzing the transient response of an electrostrictive bar submitted to different electrical excitations (voltage step, charge step, continuous sine). The validation of the model is carried out by comparing the results obtained with the analytical results for a lumped constants model. The validity of commonly used transducer characteristics is discussed to describe electrostrictive transducers. [Work supported by ONR contract and DRET/DCN grant.]
Sensitivity of a spherically focused transducer to focal length and aperture
Authors: Manley Martin
Published: July 2002

A method is presented to calculate the impulse respone of a spherically focused transducer which generates a signal and then receives the reflection of the signal from a rigid surface. Results of calculations are shown in order to illustrate the effects of varying the focal length and the aperture. These results suggest a method for empirical determination of effective values of the governing parameters of the transducer impulse response.
Comb transducer design for optimal guided wave performance
Authors: Pelts Semyen P. , Rose Joseph L. , Quarry Michael J.
Published: July 2002

Benefits of a comb transducer for producing guided waves in a structure include an ability to produce specific guided waves of choice in a low modulus material as well as good flexibility in mode choice and generation. As a result, excellent sensitivity and penetration power can be obtained by optimal mode choice. The comb transducer design for effective excitation of guided waves in an isotropic elastic plate is therefore considered in this study. The design involves optimizing geometrical and mechanical parameters of the transducer such as number of elements, element width, comb sizing, and frequency bandwidth. The mathematical model is necessary to provide framework for this design. The impulse excitation in an elastic plate is studied by applying a double Fourier transform in the wave-number and frequency domains. The method of residues and numerical integration are used to evaluate the solution of the boundary value problem. The solution demonstrates how various parameters affect the transmission of energy in the elastic plate. Experimental results are obtained on the basis of this model. [Work supported by the Office of Naval Research.]
A method of health hazard assessment for human exposure to repeated mechanical shocks
Authors: Morrison James , Nicol Jordan , Robinson Daniel , Roddan George , Springer Julie , Martin Steven , Albano John
Published: July 2002

This study describes a health hazard assessment (HHA) method for evaluating human exposures to repeated shocks in tactical ground vehicles. The method predicts the risk of injury to the occupants of a vehicle from the accelerations measured at the seat. The HHA will identify both acute and chronic health risks resulting from either a single exposure, or from multiple exposures to travel over rough terrain. The HHA is based on existing models, human injury data, and experimental data obtained from volunteers subjected to a range of shock profiles and to prolonged repeated shock exposures. The HHA consists of three components: (1) dynamic response models which predict seat-to-spine transmission of acceleration; (2) a dose model for exposure to repeated shocks based on fatigue failure theory and subjective tolerance data; and (3) an injury risk model based on the cumulative probability of failure. A biomechanical model is also described which analyzes spinal compression forces in response to shock. This model uses human experimental data to provide an independent evaluation of the HHA. The components of the HHA are outlined and some test results are presented. [Work supported by US Army Med. Res. & Dev. Command, Contract No. DAMD17-91-C-1115.]
Process monitoring of 2-D carbon–carbon composites with passive ultrasonics and mass spectroscopy
Authors: Yen C. Eric , Tittmann Bernhard R.
Published: July 2002

2-D woven carbon–carbon composites are a class of advanced structure composite materials which can maintain good mechanical property and high stiffness constants at elevated temperatures. The high failure rate during the initial charring process has been the major obstacle in attaining increased popularity of these materials. This paper reports the use of passive ultrasonics and mass spectroscopy techniques to monitor the charring process of 2-D woven carbon–carbon composites in order to accurately and sensitively detect in situ the development of macro-porosity. The passive ultrasonic technique with high-temperature waveguide sensors is demonstrated to effectively detect the acoustic emission (AE) associated with the microcracking events during the charring process. The mass spectrometry (MS) technique together with a unique ‘‘sniffing’’ tube is shown to detect major gas evolution, such as water, methane, and hydrogen during the initial pyrolysis. The gas information is important to understand the nature of catastrophic delamination. Post-process material characterizations, such as thickness shrinkage, weight loss, and microscopic characterization, were conducted to provide information about the physical changes due to the carbonization process and proved to correlate well with the AE and MS data.
W. Dixon Ward—A personal retrospective
Authors: Hirsh Ira J.
Published: July 2002

‘‘Dix’’ Ward’s professional career began about 50 years ago, when he was an undergraduate majoring in physics and practicing a life-long interest in music, both as a student and as pianist and singer. Encouraged by one of his college teachers, W. A. Rosenblith, he pursued graduate work at Harvard in the Psychoacoustic Laboratory, under S. S. Stevens. A disseration on subjective musical pitch and experimental study of the recovery of hearing after acoustic stimulation set him on a double course which continued his musical interests (first with D. W. Martin) and the study of hearing damage following noise exposure (with H. Davis and A. Glorig). Those interests were to continue as he reached his final and long-lasting appointments at the University of Minnesota. His scientific contributions have been empirical, not theoretical. He focused on finding out what is demonstrably true. His contributions as a scientific citizen were many—in the Acoustical Society, in national and international standards, in the International Society of Audiology, in CHABA, and in related government activities related to noise and noise damage.
Acoustic radiation in light fluid of a vibrating beam with uncertain material properties
Authors: Genot Jean-Sébastien S. , Charron François , Atalla Noureddine
Published: July 2002

Engineers are aware of the need to account for uncertainties in their predictions in knowledge of the material and cross-section properties (e.g., Young’s modulus, damping factor, section area). Furthermore, acousticians are often interested in the prediction of the maximum sound power that could be radiated by a given structure. But they face a numerical challenge due to the amount of input parameter combinations they must solve to compute the maximum response. In this context, a simple case of acoustic radiation in two dimensions—a simply supported beam in light fluid—is a good way to investigate the sensitivity of the acoustic power to the uncertainties of the input parameters. To study this case, an analytical method with a perturbation scheme up to the second order has been intensively used, and compared with a Monte Carlo method. In this presentation, it will be shown that the acoustic power is very sensitive to the variations of the structural parameters in the neighborhood of the beam eigenfrequencies, and that second-order perturbation techniques are not sufficient. Consequently, a hybrid method is proposed to improve the results locally.
Influence of partial coatings on the acoustic radiation from a fluid-loaded structure
Authors: Cuschieri Joseph M. , Feit David
Published: July 2002

In general, an acoustic coating is applied uniformly on the surface of a fluid-loaded structure to minimize acoustic radiation and scattering. There are, however, some inherent advantages to optimize the distribution of the coating around areas from which the acoustic radiation appears to emanate. This would be analogous to the application of damping treatment in areas of a vibrating structure which have high vibration levels. In the case of the acoustic radiation the problem is more complex because of the coupling between the acoustic fluid and the structure. In this paper, the acoustic radiation from a partially coated fluid-loaded structure, of infinite extent and excited by a point or line force, is examined by developing an analytic/numeric solution. The solution follows along some of the procedures that the authors developed in previous work related to the scattering from fluid-loaded plates and shells. The coating is assumed to provide mainly a decoupling layer between the acoustic medium and the structure; that is, it does not add mass or stiffness to the base structure. The influence of added mass or stiffness of the coating can be included as an added inhomogeneity and treated separately in the solution. [Work sponsored by NSWC-CD.]
A novel acceleration method for the variational boundary element approach based on multipole expansions
Authors: Tournour Michel , Atalla Noureddine
Published: July 2002

The acoustic radiation of general structures with Neumann’s boundary condition using the variational boundary element method (VBEM) is considered. The classical numerical implementation of the VBEM suffers from the computation cost associated with double surface integrals. To circumvent this limitation a novel acceleration method is proposed. It is based on the expansion of the cross influence matrices in terms of multipoles using the expansion of the Green’s function in terms of spherical Bessel functions. Since the resulting multipoles are not dependent on the elements locations, the technique results in large computation time savings for homogeneous meshes. The theory behind the approach, its convergence, and its numerical implementation in a VBEM code will be presented. It will be shown that by accounting for the monopole, dipole, and quadrupole terms in the multipoles expansion, the classical convergence criteria usually used for quadratic element hold. Numerical applications to acoustic radiation from plates, open cylinders, and closed boxes will be presented to demonstrate the accuracy and efficiency of the method.
Accent, stress, and spectral tilt
Authors: Campbell Nick , Beckman Mary E.
Published: July 2002

In English and Dutch, pitch accents occur only on lexically prominent syllables. Such syllables are not always accented in longer utterances, however, and traditional descriptions differentiated ‘‘stress’’ proper as a local increase in loudness, although the intonational event is the most salient cue to prominence, far outweighing any differences in overall rms amplitude. Recent work by Sluijter and colleagues [J. Acoust. Soc. Am. 101, 503–513 (1997)] indicates that stressed syllables in Dutch are associated with differentially increased energy at frequencies well above the fundamental, and that these spectral tilt differences are a robust cue to relative syllable prominence — whether or not the word is in focal prominence. Because accents are not necessarily associated with focused words, however, their experiments do not tell us whether spectral tilt differentiates lexically stressed from unstressed syllables in the absence of an associated intonational prominence. The current study examines five acoustic measures, including spectral tilt and open quotient, for accented, unaccented but stressed, and unstressed syllables in a corpus of utterances produced by four speakers of American English. Results confirm that spectral tilt is affected by accent independent of F0 increase, and that it is affected (to a lesser extent) by stress in the absence of accent.
Simultaneous effects on the duration of syllable nuclei: A covariance structure analysis approach
Authors: Erickson Mary L.
Published: July 2002

Using covariance structure anaysis, two linear models of vowel duration were tested. The first model, the Direct Effects Only model, tested the direct effects on vowel duration of intrinsic duration, following consonant voicing, stress, position in utterance, change in fundamental frequency, and final lengthening. The second model, the Direct and Indirect Effects model, tested all of the above direct effects on duration, plus the indirect effects of stress and phrase final position on vowel duration via their effects on fundamental frequency change. Model goodness of fit was estimated by three fit indices: the Normed Fit Index (NFI), the Nonnormed Fit Index (NNFI), and the Comparative Fit Index (CFI). The Direct Effects Only model yielded the following fit indices: NFI=0.810, NNFI=0.788, and CFI=0.821. The Direct and Indirect Effects model yielded slightly higher fit indices: NFI=0.822, NNFI=0.802, and CFI=0.833. Position in syllable, position in phrase, intrinsic duration, phrase final position, stress, and change in frequency were significant predictors of duration in both models. In the Direct and Indirect Effects model, phrase final position had an indirect effect on vowel duration via a significant effect on change in frequency; stress did not.
The effect of an absorptive bottom on the propagation of the coherence function in a shallow-water channel
Authors: Barnard T. , Beran M. J.
Published: July 2002

When a transverse plane wave propagates through a shallow-water channel with random sound-speed fluctuations, the waveforms at different transverse separations no longer correlate perfectly. The associated coherence falls as the in-line propagation distance and the transverse separation increase. In the (lossless) rigid-bottom case, when the waveforms are represented as a summation of normal modes, the multimodal coherence vector obeys a first-order matrix differential equation with in-line propagation distance as the independent variable. The scattering matrix in this differential equation is a function of transverse separation. As the in-line propagation distance approaches infinity, the coherence vector approaches a constant vector times a scalar Dirac delta function centered at zero transverse separation. If the bottom is absorptive rather than rigid, an additional diffusion term appears in the matrix partial differential equation governing the coherence. Diffusion along the transverse separation axis then prevents the creation of a Dirac delta function as the in-line propagation distance increases without limit. This diffusion occurs whenever the imaginary part of the horizontal wave-number component for a particular mode is nonzero. Some graphical outputs depicting the coherence propagation for an absorptive bottom are presented in this paper. [Work supported by ONR Code 321.]
Mode excitation for a source on a rough, elastic, sloping bottom
Authors: Baggeroer Arthur B. , Schmidt Henrik , Sperry Brian
Published: July 2002

In the ATOC program, the source was sited on a slope at a depth of the SOFAR axis so that the signal would excite the axial modes efficiently for long-range propagation. One of the important issues was the elevation of the source off the seafloor. Buoying it on a mooring into the water column presented significantly more engineering challenges than simply resting it on a platform on the seafloor. Here, the impact upon the mode excitation spectrum of the source depth on a rough, elastic, sloping bottom is examined using the new range-dependent OASES code. This code matches vertical wave numbers across range-independent sectors, which may include interface roughness, as it steps out in range. It has been very successful in modeling the related problem of the effect of epicenter depth for T-phase excitation on a sloping bottom [Sperry et al., J. Acoust. Soc. Am. 100, 2641(A) (1996)]. A Munk sound-speed profile is assumed with a minimum at 1000 m and a sloping bottom out to a range of 30 km after which the bottom depth is constant. The field is projected onto the depth-dependent modes to determine their excitation. Also, the group delays are examined to determine the impact on travel times. Initial results suggest that even a modest (100 m) elevation concentrates the power in the low-order modes. In addition to the source elevation, the slope gradient and roughness and the elastic properties of the bottom are important parameters. [Work supported by ONR.]
Normal-mode analysis for signal fluctuations in the Yellow Sea
Authors: Zhang Renhe , Sun Zhenge , Sha Liewei , Lei Liangying , Hao Longsheng , Sun Nan , Li Fenghua , Zhou Ji-Xun , Rogers Peter H. , Caille Gary W.
Published: July 2002

This paper presents a normal mode approach for analyzing signal fluctuation in shallow water with a thermocline which fluctuates due to tides and internal waves. In the Yellow Sea 1996 experiment, variations of thermocline structure and internal waves were observed by CTD and thermistor chains. The cw and FM acoustic signals were measured over a 12-h period with two 16-hydrophone vertical arrays deployed 3.11 and 10.32 km from the source. The cw pulses were used to observe fluctuation at four specified frequencies. Amplitude fluctuations of more than 20 dB were observed. The FM signals were used to isolate individual normal modes by pulse compression and mode filtering. The influence of internal waves on the normal-mode structure and signal fluctuation was examined. It was found that the variation of the thermocline was significant in determining acoustic signal fluctuation. The normal-mode structure and dispersion relations in the channel depend strongly on the thermocline. Variation of the thermocline thus causes phase and group velocity to become variable. This leads to signal fluctuation, since the amplitude of the received signal is determined by interference between arriving modes. The study also showed that the amplitude fluctuation is weaker at shorter range.
The perception of tonal closure by skilled musicians
Authors: Marvin Elizabeth W. , Brinkman Alexander R.
Published: July 2002

This study arises in response to Cook (1987) and Karno and Konecni (1992), who call into question the ability of listeners to perceive tonal closure in the tonic key, a primary structural principle of tonal composition. Participants in their experiments heard unaltered compositions and variants that destroyed the compositions’ tonal structure by transposing the second half to a new key or by reordering formal units. Neither study found a correlation between the listeners aesthetic preferences and the tonal closure of the original compositions. The blurred distinction between aesthetic response and music-structural judgments in these designs is misleading; the experiment reported here asks the music-structural question explicitly. Our stimuli consisted of 12 unaltered excerpts from classical CD recordings in three categories: nonmodulating, modulating to the dominant, modulating to a key other than the dominant. For each excerpt, 36 students at a professional music school answered six questions, one of which asked whether the concluding key was the same as the initial key. Participants’ accuracy was significantly above chance in this task. Musicians in scholarly disciplines and performers discriminated tonal closure equally well, although there was a significant effect for number of years of theory training.