bluuebunny/crossref_metadata_2025 huggingface dataset:
Recognition of digit strings in noisy speech with limited resources
Authors: O’Shaughnessy Douglas , Gabrea Marcel
Published: July 2002

Automatic recognition of sequences of spoken digits (e.g., telephone or credit card numbers) can be accomplished with excellent accuracy, even in speaker-independent applications over telephone links. However, even such relatively simple recognition tasks suffer decreased performance in adverse conditions, such as significant background noise or fading on portable telephone channels. If one further imposes significant limitations on the computing resources to be dedicated to a recognition task, then robust, limited-resource speech recognition remains a suitable challenge, even for a vocabulary as simple as the digits. Since connected-digit recognition over telephone lines is a very practical application, the amount of computer resources needed for a given level of recognition accuracy was investigated for different levels and types of acoustic noise. Rather than use a traditional hidden Markov model approach with cepstral analysis, which is computationally intensive and does not always work well under adverse acoustic conditions, simpler spectral analysis was used, combined with a segmental approach. The limited nature of the vocabulary (i.e., ten digits) allows this simpler approach. High recognition accuracy is maintained despite a massive decrease (versus traditional methods) in both memory and computation.
Quantization errors in formant estimation
Authors: Vallabha Gautam K. , Tuller Betty
Published: July 2002

The locations of formants in a speech signal are usually estimated by computing the linear predictive coefficients (LPC) over a sliding window and estimating the peaks in the spectrum of the resulting all-pole LPC filter. The peaks are estimated either by solving for the roots of the LPC polynomial or by computing its DFT and finding the peaks in the magnitude spectrum. Three different sources of errors in this analysis were investigated using synthesized vowels: (1) F0 quantization: In addition to the expected result that error increases with F0, it was found that the absolute error decreases with higher formant frequencies. (2) LPC+root solving: The location and bandwidth of a peak are usually estimated from the location of a pole on the z plane. It was found that this approximation is invalid if the formants have high bandwidths or if they are either too close or too far from each other. (3) LPC+DFT: In order to compensate for the quantization error introduced by the short-term DFT, a three-point parabolic interpolation scheme is usually employed for better estimation of peak locations. It was found that this compensation scheme is effective only for high-bandwidth formants. [Work supported by NIMH.]
The perceived pitch of synthesized vowels with alternate pulse cycles
Authors: Sun Xuejing
Published: July 2002

Speech with alternate pulse cycles (APC), also known as diplophonia, double pulsing, etc., often brings problems to pitch determination algorithms. Although this phenomenon has been studied in light of nonlinear theory recently, to date, no study has been done to measure the perceived pitch of speech with APC. In the present study, a perception experiment was conducted to investigate the perceived pitch of speech with APC. Two synthetic vowels, /a/ and /i/, with fundamental frequencies at 140 and 220 Hz, both amplitude and frequency modulated, respectively, were used as stimuli. The modulation levels ranged from 0 to 0.9. The subjects were asked to judge the pitch of modulated vowels in reference to the synthetic vowels without modulation. The results show that the modulation level affects the perceived pitch in a nonlinear manner, and frequency modulation seems to have greater effects on the perceived pitch than amplitude modulation. In addition, different fundamental frequencies have different effects on the perceived pitch across modulation levels, whereas different vowel types appear to make no significant differences. Based on these results, a pitch determination algorithm was developed, and the performance of the algorithm appeared promising.
A review of matched field processing and moving sources
Authors: Tolstoy A.
Published: July 2002

Over the past two decades or so there has been considerable work devoted to matched field processing (MFP), with particular emphasis on source localization. Most of that work has assumed a stationary source, a simpler problem in many ways. However, there has also been work done to investigate and even take advantage of source motion. Examples include: early work by Song (1990) and Song and Baggeroer (1990) based partially on research by Shan et al. (1985); work by Zala and Ozard (1991) generalized the Linear and Capon processors for source motion; Tran and Hodgkiss (1991) analyzed 200-Hz data for low speed sources. Alternately, one might consider the source to be fixed while the array moves, introducing synthetic aperture techniques as seen in Stergiopoulos and Sullivan (1989). MFP for a moving source can be a more challenging problem than for the fixed source but also offers new and different techniques with much promise. [Work supported by ONR.]
Tracking performance of least-squares algorithms in time-varying ocean channels
Authors: Preisig James C.
Published: July 2002

Adaptive least-squares algorithms are widely used to estimate the state of or compensate for the effects of time-varying acoustic channels in the ocean environment. A special case of such time-varying channels is those through which the signals emitted by moving sources propagate. Current methods of characterizing the tracking behavior of these adaptive algorithms are limited to cases where the algorithm accurately models the time-varying behavior of the channel or for which this behavior has a particularly simple form. A new technique is presented which allows the performance of adaptive least-squares algorithms to be characterized for more general classes of channel fluctuations. The technique shows that the performance can be interpreted in terms of model mismatch. New applications enabled by the technique are presented. [Work supported by ONR.]
Motion compensation for a synthetic aperture sonar
Authors: Piper John E.
Published: July 2002

Synthetic aperture sonar is capable of producing high-resolution images. The method typically requires many small corrections to the timing of the data to compensate for motion perturbations. A redundant phase center approach is used to calculate these corrections. This approach uses channels that spatially overlap between pings. This allows construction of a correlation function that can be used to estimate motion-induced time lag differences. To improve the accuracy of this method the correlation function is fit to a quadratic function to find its maximum. Experimental data from a variety of at-sea tests is used in this analysis. Results indicate that significant improvements to the image resolution can be gained with this approach.
Behavior characteristics of silicon micromachined electrostatic ultrasonic transducers
Authors: Ge Li-Feng , Shao Jingping
Published: July 2002

The plate-on-air-spring model for electrostatic ultrasonic transducers with grooved backplates [L.-F. Ge, IEEE Trans. UFFC 46, 1120–1127 (1999); Sci. China, Ser. A 42, 1308–1315 (1999)] is applied to simulate the behavior of silicon micromachined transducers with pit-array-textured backplates. Thus a subdiaphragm on an individual cavity is treated as a circular or square tensile plate supported by an elastic medium. A program is developed for simulating the physical model. The calculated results reveal that such transducers possess the same basic behavior characteristics as grooved transducers, i.e., multipeaked or multimode responses. The fundamental mode is determined by the air-gap spring stiffness and the electrostatic negative stiffness produced by the electrostatic attraction, and higher modes (i.e., bending modes) mainly by the bending stiffness of the diaphragm and the tension in it. Therefore, the useful operation modes for such transducers have two single modes (i.e., the fundamental mode and the first bending mode), and a compound mode including the two single modes simultaneously. The analytical results well agree with the experimental observations. [Work supported by NNSF (♯69974001), NCP, ANSF, and AU211F.]
Focusing of shock waves at smooth caustics
Authors: Auger Thierry , Coulouvrat Francois
Published: July 2002

Focusing of weak shock waves at smooth caustics is investigated both theoretically and numerically. The pioneering works of Buchal and Keller (1960) and Ludwig (1966) about geometrical theory of diffraction are extended to take into account 3D heterogeneity and fluid motion, along with nonlinear effects. We thus recover the nonlinear Tricomi equation derived by Guiraud (1965) and Hayes (1968). In most situations, nonlinear effects are shown to be negligible for incoming smooth signals. However, for incoming weak shock waves, the linear theory predicts an unphysical, infinite amplification of the signal discontinuity. To recover finite amplitudes, it is necessary to take into account nonlinearities. The resulting equation to be solved is the so-called nonlinear Tricomi equation, similar to a transonic equation. To solve it, an iterative algorithm is based on an unsteady version of the equation. The algorithm is a modification of the pseudospectral code used for solving the KZ equation of nonlinear acoustics. Convergence of the method is analyzed. The results are illustrated by simulations performed in various situations, and the application to sonic boom is discussed.
Specificity of learning for the discrimination of sinusoidal-amplitude-modulation rate
Authors: Fitzgerald Matthew B. , Wright Beverly A.
Published: July 2002

There is evidence that the learning of tonal-frequency discrimination is specific to the trained frequency. This study examined whether learning of the discrimination of sinusoidal-amplitude-modulation (SAM) rate was also specific to the trained rate, and whether that learning was specific to the trained task. SAM-rate-discrimination thresholds of six listeners trained 1 h per day for 6 days with a 150-Hz rate improved from 24 Hz before to 12 Hz after training. Comparisons between proportional improvements of trained and control listeners revealed that trained listeners learned substantially more than controls on the trained task, but learned only slightly or no more than controls on: (1) the SAM-rate task at two untrained rates (30 and 300 Hz) and (2) three untrained tasks (tonal-frequency discrimination, ripple-noise discrimination, modulation detection) at the trained rate/frequency. Thus, as with tonal-frequency discrimination, learning of SAM-rate discrimination is specific to the trained rate. However, the mechanism(s) underlying this discrimination are probably separate from those governing tonal-frequency discrimination and other related discrimination or detection tasks. These results enhance our understanding of perceptual learning, the processing of amplitude modulation, and the perception of pitch. [Work supported by NIDCD.]
Bistatic reverberation in range-independent waveguides
Authors: LePage Kevin D.
Published: July 2002

The basis for predictions of the temporal evolution of bistatic reverberation in range-independent waveguides is obtained under a modal framework using the narrow-band approximation. Approximate expressions for the field incident on the bottom at any given time are obtained as a function of modal group speed, dispersion, bandwidth, and azimuthal Fourier order. These functions, combined with the range-dependent spatial correlation functions of Gaussian distributed scatterers, which are also approximated as a function of Fourier order, provide the basis for the prediction of reverberation intensity and three-dimensional spatial coherence as a function of time after shot in multipath environments. The predicted characteristics of the reverberation are shown for several scenarios, emphasizing the differences caused by frequency, bandwidth, waveguide parameters, and receiver aperture characteristics.
Critical comparisons of the measured forward scattering from a clay bottom and a sand bottom
Authors: Yamamoto Tokuo , Sun Hua
Published: July 2002

Low grazing angle, medium frequency (3 to 15 kHz) forward scattering from a clay bottom off the coast of Gulf Port, Mississippi was measured using a 32-channel bilinear array and a broadband acoustic source. The clay bottom has a sharp velocity gradient with the sound speed at the interface slightly less than that of sound speed in water. The forward scattering was also measured at a sand-bottom site on the Florida Atlantic coastal shelf. The sound speed of the sand bed was roughly 1700 m/s. The measured bottom scattering-strength patterns are very similar both in magnitudes (−60 to −20 dB) and the distributions (roughly elliptical with the source and receiver being the foci). The apparent similarity, however, results from two different physical mechanisms. The waveform and time analyses show that acoustic energy penetrates deep into the clay bottom and scattered within the sediment volume, whereas acoustic energy is scattered at the surface of the sand bottom. In the clay bed, the sound waves are upward refracted due to the velocity gradient, showing a caustic-like phase shift by 0 to 90 deg. [Work supported by ONR Ocean Acoustics Program.]
Continuous P-SV coupling and strongly dispersive surface waves in soft marine sediments
Authors: Godin Oleg A. , Chapman David M. F.
Published: July 2002

In the upper tens to few hundred meters of clay and silt marine sediments with high porosity, the shear wave velocity is much smaller than the compressional wave velocity. The shear velocity has very large gradients close to the ocean floor leading to strong P-SV coupling in such ‘‘soft’’ sediments. A theory of elastic wave propagation in continuously stratified soft sediments is developed that fully accounts for the coupling. Elastic waves in soft sediments consist of ‘‘fast’’ waves propagating with velocities close to the compressional velocity and ‘‘slow’’ waves propagating with velocities on the order of the shear velocity. For the slow waves, the theory predicts existence of surface waves at the ocean/sediment boundary. An explicit, exact solution is obtained for the surface waves in the case of linear increase of shear rigidity with depth. Asymptotic and perturbation techniques are used to extend the result to more general environments. Velocity of vertically polarized interface waves is sensitive to sediment density and shear rigidity. Theoretical dispersion relations agree well with available experimental data and are shown to lead to a simple and robust inversion of interface waves travel times for shear-velocity profiles in the sediment.
Simple vocal identification method of porpoise sonar signals using an acoustic data logger and a time depth recorder
Authors: Akamatsu Tomonari , Wang Ding , Wang Kexiong , Naito Yasuhiko
Published: July 2002

Individual identification is needed for the standard behavioral observation. However, the vocal identification of cetacean sound is difficult even using an acoustic data logger attached to the animal, because it is hard to exclude the sounds from a nearby conspecific. This paper shows that simultaneous measurement of echolocation signals and the dive depth of a free-ranging finless porpoise (Neophocaena phocaenoides) enables vocal identification. Echolocation signals of a juvenile finless porpoise were observed with an acoustic data logger attached to the upper posterior side of the pectoral fin by a suction cup. The acoustic data logger had 4.8-kHz sampling frequency and recorded each event of pulse, processed by an amplitude peak hold circuit. Dive depth and swim speed of the porpoise were recorded by another data logger every 1 s. Surface reflection of echolocation signals was clearly detected during shallow dives less than 2 m in depth. The delay time of the reflected signal corresponded with the two-way transmission time from the animal dive depth to the surface. This shows that the signals were from the animal wearing the data loggers.
Acoustical techniques for observing the processes that control the formation of ocean bottom geology
Authors: Traykovski Peter
Published: July 2002

While acoustical methods provide useful techniques for surveying geological properties of the seafloor, acoustical techniques are also useful for examining the processes which create the observable geological properties. The dynamic processes which control sediment deposition and erosion are complex, and understanding these processes requires knowledge of the interactions of the seafloor topography with the hydrodynamics just above the seafloor and the subsequent sediment erosion, transport, and deposition. Observing these interactions requires multi-dimensional systems with high resolution in both space and time. This mini-tutorial talk will review some of the acoustic techniques for observing sediment transport processes which are currently being used. These techniques include acoustic backscatter measurements of suspended sediment concentration, acoustic imaging techniques such as rotary sidescan sonars and rotary pencil beam sonars, and the latest advances in high-resolution Doppler current profiling. Examples of data from these techniques will also be presented to give an overview of the transport processes including sediment transport due to the combined action of both waves and mean currents, sediment transport due to gravitational flows, and the relation between bedform migration and bedload transport.
The predictibility of broadband sound propagation in shallow water and geoacoustic inversion
Authors: Knobles David P. , Thompson Lewis A. , Koch Robert A. , Focke Karl C.
Published: July 2002

An experiment was performed in a shallow-water region in the Gulf of Mexico to collect data for testing the performance of geoacoustic inversion algorithms using acoustic propagation measurements. Previous geophysical and acoustic measurements, along with inversions for seabed parameters in the general area, provide an excellent standard for validating several acoustic data inversion techniques. Continuous wave acoustic signals at multiple frequencies from a towed source, broadband impulsive source signals, and broadband signals generated by a moving surface ship were recorded on an advanced system that included a horizontal line array. Simulated annealing is used in conjunction with a normal-mode description of the propagation and various types of broadband matched-field cost functions to invert for a geoacoustic representation of the seabed. Consistent inversion results are obtained using all three types of acoustic data and are in general agreement with the reported physical measurements. The nature of the soft seabed results in a unique acoustic signature in the pressure time series from impulsive sources and the interference patterns in the transmission loss as a function of source-receiver range. The results indicate that the use of surface ships of opportunity can be successfully employed for geoacoustic inversion.
Fundamental frequency signal cancellation for tissue harmonic imaging
Authors: Ucar Fatma N. , Yamakoshi Yoshiki
Published: July 2002

An alternative method for tissue harmonic imaging is proposed. An adaptive filter (AF) is applied for each receiving RF signal acquired by the ultrasonic (US) transducer array. The technique uses single transmit pulse but cancels out the fundamental frequency (FF) of the received signal by appropriately changing the delay terms of the AF’s. The resultant signal is slightly improved at second harmonic frequency. The M-tap-delay AF processing can be illustrated for N-element transducer array as below:
Vibration of thin and thick annular plates
Authors: Xiang Yan , Brown David A. , Reinhart Lawrence , Aronov Boris
Published: July 2002

This work is on the determination of the resonant frequency and mode shapes of thin and thick annular plates. We summarize an extensive experimental and theoretical investigation on the vibration of annular plates driven symmetrically with a center post. Experimental data for the thin plates agree well with theory. We also present the energy analysis method to describe thick plates and obtain an equivalent equation for mode shape as predicted by Mindlin’s theory. Several sets of polycarbonate plates with inner radius to outer radius ratio range from 0.1–0.5 and thickness to outer radius ratio range from 0.1–0.5 were fabricated and tested using a noncontact photonic sensor. The resonance frequency, mode shape, and surface stress distribution were investigated. These results are useful in the design of acoustical accelerometers and pressure gradient hydrophone designs. [This work was supported in part by the University of Massachusetts Dartmouth and ONR, Code 321.]
Beams with large depth of field
Authors: Gori Paola , Cincotti Gabriella , Pappalardo Massimo
Published: July 2002

Acoustic bullets, also known as limited diffraction beams, are solutions of the scalar wave equation with the property of maintaining their shape upon propagation, without spreading in space and in time. A necessary and sufficient condition for the generation of acoustic bullets is presented. In particular, it is proved that a necessary condition for acoustic bullets is that all the wave vectors characterizing the beam are disposed over a cone with a given vertex angle. Impulse responses for the case of axial symmetry, and for the situation in which axial symmetry is lacking, are then given. The results obtained for acoustic bullets are then contrasted with those of other types of beams with large depth of field recently presented in literature (an example is the so-called ‘‘sinc wave’’). Finally, the topic of the realization of practical approximation of these kind of beams, which, in principle, requires infinite apertures, is addressed. Numerical simulations are presented in order to analyze the departures from the ideal case when using a finite-dimension aperture.
Electronic architecture: Issues of use and acceptance in the musical community
Authors: Scarbrough Paul H. , Robb David W. , Jaffe J. Christopher
Published: July 2002

Electronic architecture has become a mature technology in recent years, particularly through the wide application of digital signal processing to the problem of creating uniform, stable acoustical enhancement. Despite vast improvements in the impact and stability of such systems, a considerable segment of the musical community continues to express reservations about the use of this technology in the concert hall or opera house. It is clear that some musicians and music critics fail to understand how such systems function as well as the capabilities and limitations of the technology. This paper will outline the degree to which current state-of-the-art systems do indeed succeed in producing measurable acoustical improvements and discuss the varying degrees of acceptance such systems are receiving in different parts of the world.
Masked underwater audiogram for a Pacific white-sided dolphin
Authors: Thomas Jeanette , Ramirez Ken , Jalili Mersedeh , Grimm K. Kristine
Published: July 2002

Little is known about abilities of odontocetes to hear in a noisy environment. Using a descending staircase method and go/no-go response, underwater hearing of a female, Pacific white-sided dolphin masked by two levels of white noise (30 dB apart) was measured. The same dolphin had an unmasked audiogram [Tremel et al. (1998)]. Frequencies were tested in octaves between 500 Hz and 64 kHz, with 15 to 30 trials/frequency. Masked thresholds at maximum noise were similar to those on a bottlenose dolphin [Moore and Au (1982)], a beluga [Johnson et al. (1989)], and a false killer whale [Thomas et al. (1990)]. At 8 kHz, masked thresholds were more sensitive than unmasked thresholds, perhaps because masking and pool noise were similar levels. The highest critical ratio (43) was at 500 Hz and the lowest critical ratio (14) at 8 kHz. Critical ratios at 8 kHz or higher were comparable to other species. However, critical ratios at 500 Hz (43) and at 1 kHz (40) were higher than in the beluga (20 and 18, respectively). [The authors are grateful for support by the marine mammal staff at the Shedd Aquarium and financial support by ONR.]
Pressure and pressure-gradient sensitivity of the tadpole medulla
Authors: Simmons Andrea M. , Coombs Sheryl
Published: July 2002

The dorsal medulla of anuran tadpoles undergoes significant anatomical reorganization over metamorphic development. To examine how functional properties alter in response to anatomical changes, we recorded single and multiple unit activity in the medulla of bullfrog tadpoles to a sinusoidal-oscillating dipole source that traversed the length of the animal’s body. This dipole stimulus has been used previously to distinguish between pressure-sensitive auditory responses in the saccular nerve of the goldfish and pressure-gradient lateral line responses in the lateral line nerves of goldfish and other teleost fish. Recording sites in the developing dorsal lateral nucleus showed pressure-type responses to dipole stimulation near the animal’s head and lung. Evidence for the role of the bronchial columella and the air-filled lungs acting as a sound pressure transducer in mediating these responses was equivocal. Recording sites in the lateral line nucleus and surrounding neuropil showed pressure-gradient-type responses to stimulation near identified lines of superficial neuromasts on the body or tail. These data show that dipole stimulation is effective in eliciting responses from the medulla, and can be used to elucidate changes in function as the lateral line system degenerates and an auditory system adapted to hearing airborne sounds develops.
Noise in the news: What is and is not being covered by the media
Authors: Blomberg Les D.
Published: July 2002

More than 100 newspapers were monitored for 4 years for articles concerning noise. A database of more than 7000 newspaper articles concerning noise was created. The articles were summarized and categorized by noise source and area of interest. The data provided a unique overview of what the public has been reading about noise in print media. Coverage of noise was seen to follow hot-button issues. Aircraft noise, airport noise, and airport expansion dominated news coverage. Some very important noise issues, such as occupational noise, received almost no coverage. And, some emerging trends and issues such as environmental justice and noise-related violence were observed. Finally, conclusions regarding media coverage and the role of the media in educating the public about noise were discussed.
Experimental study of a heat-driven/solar thermoacoustic refrigerator
Authors: Holmberg David G. , Chen G. H. , Wo Andrew M. , Lin H. T.
Published: July 2002

This work reports the design and testing of a prototype thermoacoustic refrigerator optimized by the code DeltaE. The key functional feature of this quarter-wavelength resonator is its dual power input capability electric heating elements and the sun. These can be utilized independently or complimentarily to benefit all-weather operation. The machine operates near 270 Hz with helium (60%)–argon (40%) mixture at two bars mean pressure. Heat from either heat source is transported from the high-temperature end to the prime mover stack via thin copper plates that also serve as the hot-end heat exchanger. Both stacks utilize an uncoated automobile catalytic converter ceramic structure with 1.3-mm cell-to-cell square openings and 74% porosity. The ceramic structure provides a strong and easy-to-implement stack with minimal heat conduction. Both middle- and cold-end heat exchangers use simple copper fin design, with the middle heat exchanger using circulating water cooling. DeltaE results predict a 30°C temperature drop across the heat pump stack at no-load condition with 30 W heating, 363°C  across the prime mover stack (work=4.0 W) and pressure fluctuation level equal to 6.2%. Results from the effects of working fluid, changing pressure, heating temperature, and cooling load will be discussed.
Traveling-wave heat pumping in stack-spaced pores
Authors: Wakeland Ray Scott , Keolian Robert M.
Published: July 2002

Both standing and traveling waves cause heat flow near surfaces. Thermoacoustic refrigerators are based on two well-studied types of acoustically induced heat flow: (1) heat pumping concentrated about a thermal penetration depth from a surface due to a standing wave, and (2) heat pumping much closer to the surface due to a traveling wave. This talk examines another thermoacoustic pumping mechanism, induced by a traveling wave but occurring mostly a thermal penetration depth from the surface. This sort of heat pumping, therefore, is greatest for pore sizes typical of stacks rather than regenerators. Unlike ‘‘Stirling pumping’’ (traveling-wave heat pumping that occurs very close to a surface), which is independent of surface temperature gradient, this mechanism is proportional to temperature gradient. It pumps heat down the temperature gradient, and is thus a sort of ‘‘thermoacoustic short circuit,’’ detrimental to all types of working thermoacoustic devices. It appears to set an upper limit on the pore size of the regenerator in a thermoacoustic Stirling-type refrigerator that depends on temperature gradient. Analytical and graphical results will be presented, along with a Lagrangian ‘‘moving-parcel picture’’ that explains the results on physical grounds. [Work supported by ONR and NSF.]
High-PACE: A high performance acoustics computing environment
Authors: Tuttle Brian C. , Sparrow Victor W. , Dennis Brian H.
Published: July 2002

In physical acoustics it is now possible to solve some large problems via direct simulation on parallel computers due to the emergence of relatively inexpensive Beowulf class clusters of commodity personal computers. In this brief talk, an overview of the performance characteristics and initial calculation results from such a cluster will be provided. Called High-PACE, for high performance acoustics computing environment, the new machine has 32 Pentium III processors at 450 MHz, 8.5 GB of RAM, over 200 GB of disk storage, and is interconnected by a Myrinet (Myricom, Arcadia, CA) 1.28 gigabit/s interface. The machine uses the Linux operating system and is programmed with fortran 90 and the message passing interface, MPI. Initial work is focused on a deep understanding of nonlinear acoustic streaming for thermoacoustics applications. [Work supported by ONR.]
Accurate nonreflecting boundary conditions for time- dependent acoustic scattering
Authors: Thompson Lonny L. , Huan Runnong , He Dantong
Published: July 2002

Accurate radiation boundary conditions for the time-dependent wave equation are formulated in the finite-element method as an auxiliary problem for each radial harmonic on a spherical boundary. The method is based on residuals of an asymptotic expansion for the time-dependent radial harmonics. A decomposition into orthogonal transverse modes on the spherical boundary is used so that the residual functions may be computed efficiently and concurrently without altering the local/sparse character of the finite-element equations. The method has the ability to vary separately, and up to any desired order, the radial and transverse modal orders of the radition boundary condition. With the number of equations in the auxiliary Cauchy problem equal to the transverse mode number, the conditions are exact. If fewer equations are used, then the boundary conditions form high-order accurate asymptotic approximations to the exact condition, with corresponding reduction in work and memory. Numerical studies are performed to assess the accuracy and convergence properties of the radiation boundary conditions. The results demonstrate dramatically improved accuracy for time-domain simulations compared to standard boundary treatments and improved efficiency over the exact condition. [Work supported by NSF PECASE.]
Exact radiation conditions on spheroidal boundaries with sparse iterative methods for efficient computation of exterior structural acoustics
Authors: Thompson Lonny L. , Ianculescu Cristian
Published: July 2002

Exact radiation boundary conditions are derived from harmonic expansions in spheroidal coordinates and formulated in a finite-element method for the Helmholtz equation in unbounded domains. The use of spheroidal boundaries enables the efficient solution of scattering from elongated objects. Extending the ideas of Malhotra for the exact Dirichlet-to-Neumann (DtN) map defined on a sphere, a matrix-free implementation of the nonlocal DtN map for spheroidal boundaries, suitable for iterative solution of the resulting complex–symmetric system, is described. Efficient SSOR preconditioners together with Eisenstat’s trick based on the sparse matrix partition associated with the interior mesh and local part of the radiation boundary operator are used to accelerate convergence of Krylov-subspace iterative solution methods. Numerical examples are computed to demonstrate the efficiency and accuracy of the boundary treatments for high-frequency scattering from elongated structures. [Work supported by NSF PECASE.]
The effect of immersion on Japanese listeners’ labeling of American English vowels
Authors: Stack Janet W. , Kubo Rieko , Pruitt John S.
Published: July 2002

A set of 118 synthetic stimuli was presented twice to three groups of listeners to be labeled as American English (AE) vowels. The stimuli were generated through a Klatt cascade formant synthesizer, where first (F1) and second (F2) formant frequencies were varied factorially. F1 ranged from 200–700 Hz in 50-Hz steps. F2 ranged from 600–2600 Hz in 200-Hz steps. The labeling of 11 AE vowels was compared for AE listeners, Japanese listeners living in the United States (immersed), and Japanese listeners living in Japan (nonimmersed). In addition to labeling, all listeners judged the goodness of the stimuli on a 1–7 rating scale. The modal responses of the immersed Japanese listeners were significantly more similar to those of the AE listeners than were those of the nonimmersed Japanese. The immersed Japanese also had higher ratings than the nonimmersed Japanese listeners, showing greater confidence in their labeling of AE vowels. As an additional task, the nonimmersed Japanese also labeled the stimuli as the five Japanese vowels, and demonstrated that Japanese vowel identities largely differed from AE vowels on F1−F2. This difference may be a factor in Japanese listeners’ difficulty in perceiving and producing AE vowels.
Does early speaking experience in Korean help adult relearners?
Authors: Oh Janet S. , Jun Sun-Ah , Au Terry K.
Published: July 2002

Research indicates that early linguistic input is crucial for acquiring native-like phonology and morphosyntax. This study investigates whether early discontinued linguistic experience helps adult relearners master the phonology of a language. Students from first-year Korean classes were classified into three groups: no/minimal speaking experience, childhood speaking experience (until about age 5), and native speakers. Native speakers not enrolled in Korean classes also participated. Participants produced sentences that included words utilizing the three-way contrast in Korean stop consonants (lenis, tense, and aspirated). Measurements of stop closure duration indicate that only the two native speaker groups were differentially producing lenis and tense consonants. Measurements of VOT indicate that only the childhood and the native speaker groups were differentially producing the three consonants. Furthermore, the childhood speakers’ general pattern of closure duration and VOT for the three consonants was similar to those of the native speakers (this was not true for the no/minimal experience group). Results indicate that even early discontinued speaking experience can provide an advantage in relearning a language as an adult. [Work supported by an NIMH Developmental Cognitive Science Training Grant awarded to Janet Oh, and by NIMH Grant MH56118 and a UCLA Academic Senate Grant awarded to Terry Au.]
Effect of childhood language experience on pronunciation in adulthood
Authors: Knightly Leah M. , Au Terry Kitfong , España Laura E.
Published: July 2002

This study examined the effect of childhood experience with Spanish on Spanish pronunciation in adulthood. Twenty-eight native speakers of Spanish were asked to rate the pronunciation of Spanish consonants /p, t, k/ and /b, d, g/ produced by five groups of English-speaking adults: (1) Eighteen native Spanish speakers, (2) nine childhood Spanish speakers who had spoken Spanish fluently during childhood for at least three years, (3) six addressees who had regularly been addressed in Spanish during childhood but had spoken Spanish minimally, (4) sixteen overhearers who had overheard Spanish regularly as children but had spoken Spanish minimally, (5) seventeen late learners who had no experience with Spanish until high-school Spanish class. Childhood speakers, addressees, and overhearers all received reliably better accent ratings than those who first learned Spanish in high school [by HSD, ps<0.05]. Addressees obtained accent ratings comparable to native speakers for voiceless stops. However, only childhood speakers received accent ratings comparable to native speakers for both voiced and voiceless stops. Acoustical analyses revealed that those speakers who received more native-like ratings had shorter voice-onset time for /p, t, k/ and a higher percentage of lenited intervocalic /b, d, g/ [rs>0.76, ps<0.0001].
Reevaluating the effect of length of residence (LOR) on adults’ performance in a second language
Authors: Flege James E. , Liu Serena
Published: July 2002

Previous work has shown that children but not adults make regular progress in a second language (L2) as length of residence (LOR) in an L2-speaking country increases. These findings might be interpreted to mean that adults’ ability to learn an L2 is severely constrained. The present study examined the effect of LOR in a more controlled fashion than previous studies. Experiment 1 assessed the identification of word-final English consonants. Experiment 2 examined the scores on a 144-item grammaticality judgment test. Experiment 3 examined the scores on a 45-item listening comprehension test. Adult Chinese participants were assigned to one of four groups of 15 each based on LOR in the United States and academic status (students versus nonstudents). In all three experiments, significantly higher scores were obtained for students with a relatively long LOR than students with a shorter LOR. However, the difference between nonstudents differing in LOR was nonsignificant in every instance. When taken together, these results suggested that the negative findings for LOR that were obtained in previous studies might have been due to sampling error. Adults’ performance in an L2 seems to improve measurably as LOR increases, but only if they receive a substantial amount of native-speaker input. [Work supported by NIH.]
Neural activation patterns during discrimination of a native versus non-native contrast by Japanese speakers
Authors: Doeleman Tobey L. , Kuhl Patricia K. , Conley Ryan J. , Stevens Erica B.
Published: July 2002

Discrimination of a native versus a non-native consonantal contrast was investigated using two experimental paradigms in a functional magnetic resonance imaging (fMRI) examination of neural activation patterns. Native Japanese speakers were tested on both a /b/–/d/ (native) contrast and an /r/–/l/ (nonnative) contrast in same–different and AXB conditions. All consonant tokens were paired with vowels [a, i, u, e] in two different phonological environments, syllable initial and intervocalic, and discrimination was measured behaviorally both in and out of the scanner. Stimuli in the same–different task consisted of VCV syllables, while CV syllables were presented in the AXB task. The use of different syllable structures in the two tasks ensured that the activation patterns common to both conditions were in fact due to processing of the abstract phoneme representations. Activation during discrimination was calculated as those voxels were significantly more active than both baseline and recovery periods on two independent runs. A comparison of patterns for the native versus non-native contrast reveals differences in processing characteristics such as location and extent of activation.
On the noncategorical perception of Cantonese level tones
Authors: Francis Alexander L. , Ng Brenda K. C. , Ciocca Valter
Published: July 2002

Previous research provides conflicting evidence about the categorical nature of lexical tone perception. Chan et al. [J. Acoust. Soc. Am. 58, 119 (1975)] found that an f0 continuum between a Mandarin level tone (high level) and a contour tone (high rising) was perceived categorically. In contrast, Abramson [J. Acoust. Soc. Am. 33, 842(A) (1961)] found that a Thai level tone continuum ranging in f0 from low level to high level was not perceived categorically. The present study examined whether level lexical tones are perceived categorically in Cantonese. Native Cantonese speakers were asked to identify and discriminate stimuli consisting of Klatt-synthesized Cantonese syllables ranging in f0 from low level to high level in nine equal mel steps. For identification, syllables were presented medially in (synthesized) sentential context to facilitate talker-dependent pitch processing [P. Wong and R. Diehl, J. Acoust. Soc. Am. 104, 1834 (1998)]. For discrimination, adjacent steps were presented in isolated pairs with 250 msec ISI. Although the identification function showed boundaries typical of categorically perceived continua, discrimination was poor across the continuum. These results suggest that Cantonese level tones are not perceived categorically. Results and implications for theories of tone perception will be discussed.
A study of vowel length in Thai
Authors: Roengpitya Rungpat
Published: July 2002

In Thai, vowel length is contrastive (e.g., [cìp] ‘‘to sip’’–[ciìp] ‘‘to pleat’’). The main cue to distinguish short-long vowels in Thai is vowel duration [Abramson, 1962]. However, in some literature, there are other cues for vowel length in Thai, such as final nasal duration. This paper was aimed to see how important vowel duration and final nasal duration are as perceptual cues for Thai listeners. A perceptual experiment was conducted. Eighteen (near-) minimal pairs of Thai words were used, consisting of initial voiceless unaspirated stop [p], nine pairs of Thai vowels, a final voiceless velar stop [k] or an alveolar final nasal [n]. Short vowels were lengthened and long vowels were shortened at 10–30-ms steps, using LPC analysis and resynthesis. The same procedure was done for short and long final nasals at 10-ms steps. All 1148 tokens were put into a Thai frame sentence and randomized. Forty native Thai listeners listened to these tokens and judged whether each token had a short or a long vowel. The results are that vowel duration is the main perceptual cue to distinguish short and long vowels in Thai.
Topograhical image reconstruction via differential geometry in the ultrasonic tactile sensing system
Authors: Teramoto Kenbu
Published: July 2002

This paper describes a topographic image reconstruction via differential geometry using a proposed acoustical tactile sensing probe. The proposed tactile sensing system has an ability to identify the principal curvatures of the object surface by detecting reflected wave fronts. Two major difficulties, however, exist in the principal curvature identification. The first reason is that the wave front reflected by the paraboloidal surface cannot be described in the combination of the plane waves nor the spherical waves strictly. The second is that the principal curvature identification process becomes ill-posed due to the nonlinear relationship between the principal curvatures and propagation time of flight. Avoiding these difficulties, the proposed sensing system seeks the unique point over the manifold which satisfies the Snell’s law. After the principal curvature estimation at several points over the object surface, the topographic image of the surface can be reconstructed via geometrical connection. Connecting identified principal curvatures and principal direction, the differential geometrical method then provides a smooth surface description and discrimination following plane and paraboloidal surfaces: (1) plane, (2) paraboloid, (3) elliptic paraboloid, (4) hyperbolic paraboloid. Further, several acoustical experiments show that the tactile sensor can identify the principal direction and curvatures of the paraboloidal surfaces.
Passive acoustic thermotomography—Correlation and noncorrelation variants
Authors: Passechnik Victor I. , Anosov Andrej A. , Bograchev Konstantin M.
Published: July 2002

Passive thermoacoustic tomography is a method for reconstructing temperature, 2D and 3D distributions inside objects, using the intensity of ultrasonic thermal acoustic radiation emitted from within the object. This radiation can be measured by piezotransducers (PT) both in noncorrelation and correlation mode. For noncorrelation mode, a priori information about ultrasound absorption coefficient distribution is needed for reconstruction. In this case, the methods for the reconstruction of temperature distributions were analyzed by computer simulation. The standard error of reconstruction did not exceed 0.25 K (for about 300 measurements and fluctuation error of every measurement, 0.1 K). The physical experiments confirmed the predictions of the theory. In correlation mode, two spatial distributions—of the temperature and of the absorption coefficient—could be potentially reconstructed. The spatial correlation function of sound pressure from a source of thermal acoustic radiation was measured experimentally by a two-probe acoustic interferometer. The acoustic blackbody made from a narrow strip of a material with a large absorption coefficient served as the source of radiation. The spatial correlation function was computed; this function turned to be in good agreement with experimental data. [Work supported by Russian Basic Research Foundation Grant No. 98-01-00100.]
Travel time and pulse dispersion in range-dependent waveguides
Authors: LePage Kevin D.
Published: July 2002

The evolution of time series through range-dependent ocean media is of substantial interest for a variety of reasons. Here the group speed and pulse dispersion of range-dependent modes is obtained under the narrow-band approximation. The results for range-dependent group speed show that in most cases the adiabatic approximation fails to capture even the most fundamental characteristics of individual mode travel time in range-dependent environments. Instead it is seen the group speed is strongly controlled by the balance of amplitudes in the modes and the way in which this balance is changed by bathymetry and sound speed fluctuations. In up-slope situations, as evanescent modes are locally energized by the cutoff and penetration of propagating modes, the local group speed of these modes becomes effectively equivalent to the group speed of the cutoff mode. In down-slope situations, where the adiabatic approximation fails entirely to assign a group speed to newly propagating modes, the current approach gives a physically justified basis for assigning a value. Time series computed using the new range-dependent narrow-band approximation are compared to Fourier synthesized results for a variety of scenarios.