bluuebunny/crossref_metadata_2025 huggingface dataset:
Speech synthesis by glottal excited linear prediction
Authors: Childers D. G. , Hu H. T.
Published: October 2005

This paper describes a linear predictive (LP) speech synthesis procedure that resynthesizes speech using a 6th-order polynomial waveform to model the glottal excitation. The coefficients of the polynomial model form a vector that represents the glottal excitation waveform for one pitch period. A glottal excitation code book with 32 entries for voiced excitation is designed and trained using two sentences spoken by different speakers. The purpose for using this approach is to demonstrate that quantization of the glottal excitation waveform does not significantly degrade the quality of speech synthesized with a glottal excitation linear predictive (GELP) synthesizer. This implementation of the LP synthesizer is patterned after both a pitch-excited LP speech synthesizer and a code excited linear predictive (CELP) speech coder. In addition to the glottal excitation codebook, we use a stochastic codebook with 256 entries for unvoiced noise excitation. Analysis techniques are described for constructing both codebooks. The GELP synthesizer, which resynthesizes speech with high quality, provides the speech scientist a simple speech synthesis procedure that uses established analysis techniques, that is able to reproduce all speed sounds, and yet also has an excitation model waveform that is related to the derivative of the glottal flow and the integral of the residue. It is conjectured that the glottal excitation codebook approach could provide a mechanism for quantitatively comparing the differences in glottal excitation codebooks for male and female speakers and for speakers with vocal disorders and for speakers with different voice types such as breathy and vocal fry voices. Conceivably, one could also convert the voice of a speaker with one voice type, e.g., breathy, to the voice of a speaker with another voice type, e.g., vocal fry, by synthesizing speech using the vocal tract LP parameters for the speaker with the breathy voice excited by the glottal excitation codebook trained for vocal fry.
Low-frequency acoustic emissions in fresh and salt water
Authors: Kolaini Ali R. , Roy Ronald A. , Gardner David L.
Published: October 2005

The impact of a jet of water onto a still water surface results in the entrainment of large amounts of air and the eventual formation of a bubble plume. Densely populated bubble plumes are generated by dropping a fixed volume of water, held in a cylindrical container, onto a still-water surface. The detached bubble plume, which is roughly spherical in shape, then undergoes volume pulsation and radiates relatively large-amplitude, low-frequency sound. The results of a laboratory study of the noise produced by this process were reported previously by Kolaini et al. [J. Acoust. Soc. Am. 94, 2809–2820 (1993)]. In this paper we report the results of a field study of noise produced by this process in both fresh water (Lake Washington, WA) and salt water (Puget Sound, WA). Studies of acoustic emissions from transient bubble plumes as a function of cylinder parameters are described, with specific attention devoted to a comparison of the results obtained in salt and fresh water. The measurements, which exhibit good agreement with laboratory study, indicate that there is a correlation between the acoustic intensity radiated from bubble plumes and the total potential energy of the water jet.
Viseme classifications of Dutch consonants and vowels
Authors: van Son Nic , Huiskamp Tirtsa M. I. , Bosman Arjan J. , Smoorenburg Guido F.
Published: October 2005

Videotaped lists of meaningless Dutch syllables were presented in quiet to four subject groups, differing with respect to their knowledge of and experience with lipreading (lipreading expertise). Syllables consisted of all Dutch consonants within three vowel contexts, and of all Dutch vowels within four consonant contexts. Three speakers pronounced all syllable lists. The aim of the research was (1) to establish viseme classifications of Dutch vowels and consonants; (2) to interpret the visual-perceptual dimensions underlying this classification and relate them to acoustic-phonetic parameters; (3) to establish the effect of lipreading expertise on the classification of visually similar phonemes (visemes). In general, viseme classification proved very constant with different subject groups: Lipreading expertise is not related to viseme recognition. Important visual features in consonant lipreading are lip articulation, degree of oral cavity opening, and place of articulation, leading to the following viseme classification: /p,b,m/, /f,v,υ/, /s,z,■/, and /t,d,n,j,l,k,x,r,■,h/. In the acoustic domain, these features may be related to spectral differences. Vowel features in lipreading are lip rounding, degree of lip opening, and vowel duration, yielding the following visemes: /i,■,e,ε,εi,a,■/, /u,y,œ,■/, /o/,o/, and /au,œy/. In the acoustic domain, lip rounding may roughly be related to the second formant, lip opening to the first formant.
Wideband processing of acoustic signals using wavelet transforms. Part II. Efficient implementation and examples
Authors: Weiss L. G.
Published: October 2005

In Part I [J. Acoust. Soc. Am. 96, 850–856 (1994)], a theoretical derivation for processing wideband signals to localize sources was presented. This was first done for the active case of a single sensor illuminating the environment. It was then done for the passive case of three receivers sensing the environment. In both cases, the processing was formulated as a deconvolution. This part presents a new and efficient technique for coherently processing signals received at three or more passive sensors, and therefore implementing the wideband passive deconvolution to estimate the wideband spreading function. The technique is first described for the case of three receivers passively sensing an environment; it is then generalized to N passive sensors. The issue of additive noise on the received signals is then addressed. The noisy received signals are processed with the new implementation of the deconvolution. An expression relating the signal-to-noise ratio (SNR) of the estimate of the wideband spreading function to the SNRs of the received signals is also derived. The results show that the wideband deconvolution robustly operates on signals that have been contaminated with noise. Examples are provided.
Internal-wave effects on 1000-km oceanic acoustic pulse propagation: Simulation and comparison with experiment
Authors: Colosi John A. , Flatté Stanley M. , Bracher Charles
Published: October 2005

A recent 1000-km acoustic pulse transmission experiment in the Pacific revealed unexpected fluctuations on received wavefronts, including a dominant rapid variation, called the broadband fluctuation, with time scales less than 10 minutes and spatial scales of less than 60 m; a distinct breakdown of the geometrical optics wavefront pattern and broadening of the wavefront near the transmission finalé; and a coherent wavefront motion with a timescale near the semi-diurnal tidal period. Parabolic-equation numerical simulations have been carried out which utilize environmental data and which take into account internal-wave-induced sound-speed perturbations obeying the Garrett–Munk (GM) spectral model. It is shown that the effects of internal waves can account for the broadband fluctuations, the breakdown of the geometrical optics pattern, and the wavefront broadening. The sensitivity of these fluctuations to internal-wave energy and modal content is examined. The spectral energy in the GM model at tidal periods proves insufficient to explain the tidal period coherent fluctuations, strongly suggesting the influence of an internal tide during the experiment. The simulations allow the estimation of the average travel-time bias caused by internal waves. The simulation results for travel-time wander and bias are compared with analytic calculations based on the path-integral technique.
Extension of Biot’s theory of wave propagation to frozen porous media
Authors: Leclaire Ph. , Cohen-Ténoudji F. , Aguirre-Puente J.
Published: October 2005

An extension of Biot’s theory is proposed for frozen porous media where the solid substrate, ice particles, and unfrozen water can coexist. Elastic, kinetic, and dissipation energy densities are written using the results of continuum mechanics, then the equations of propagation are deduced with the help of Lagrange’s equations and Hamilton’s least-action principle. The ice parameters are introduced in the model in addition to those used in Biot’s theory. It appears that only the percolation theory is able to describe the transition of the ice matrix between the continuous state and the discontinuous state during a freezing or a thawing process. The resolution of the equations of propagation lead to the existence of three longitudinal and two transverse modes. Their velocities and attenuations are calculated as functions of the physical parameters of the medium. Independently, a thermodynamical argument is developed which allows the mechanical properties to be related to temperature. Experimental results are briefly presented to confirm the theoretical predictions.
Trans-Arctic propagation effects of changes in ice morphology
Authors: Schmidt Henrik , Tracey Brian
Published: October 2005

The objective of the Trans-Arctic Propagation (TAP) experiment carried out in the spring of 1994 was to investigate the feasibility of using acoustic thermometry for inferring changes in the Arctic climate [P. Mikhalevsky, J. Acoust. Soc. Am. 94, 1760(A) (1993)]. An important issue is which acoustic property will provide the strongest climate change signature. The sensitivity of various properties of the acoustic field to changes in ice volume was investigated theoretically. A perturbation formulation for 3-D scattering from rough ice has been combined with the kraken normal-mode code to provide a model of the second-order statistics of the acoustic field. Such a hybrid model has been shown to provide excellent agreement with historical Arctic transmission loss data [LePage and Schmidt, J. Acoust. Soc. Am. 96, 1783–1795 (1994)]. We use this model to investigate the sensitivity of deterministic properties of the coherent field, such as modal loss, and modal phase and group velocity, to change in ice thickness and roughness statistics. In addition, the model has been use to investigate the sensitivity to changes in the ice cover of the higher-order statistics such as cross-modal correlation, and spatial correlation in general. Comparing these theoretical sensitivity measures, we discuss the potential performance of both deterministic and statistic acoustic thermometry in the Arctic.
Perceptual centers in Japanese disyllables
Authors: Bell Alan , Morishima Yasunori
Published: October 2005

Most research on perceptual centers has been based on monosyllables in languages with stress; indeed the term ‘‘stress beat’’ is sometimes used for the same phenomenon. Accent in Japanese is mainly realized by pitch; amplitude and duration are relatively unimportant. Perceptual centers in disyllabic words perceived by four Japanese were used to investigate the characteristics of perceptual centers in the context of pitch accent. Perceptual centers occur later in disyllables with longer consonant onsets, by a magnitude comparable to that found for stressed monosyllables [e.g., Cooper etal., Percept. Psychophys. 39, 187–196 (1986)] and for Japanese monosyllables [Hoequist, Lang. Speech 26, 367–376 (1983)]. The effect of lengthening the tail (the portion following the initial consonant) of disyllables also corresponded in magnitude to that found previously. Accent placement had little or no effect. The same effect of onset duration was found for initially accented and finally accented disyllables whose duration and amplitude contour were held constant. A small accent difference with respect to the effect of tail duration was found in words of the same duration but retaining differences in amplitude contour. The results are consonant with the greater prominence effects found for amplitude and duration than for pitch in rhythmic perception.
Wave packet synthesis via the wavelet transform
Authors: Drumheller David M. , Hughes David H. , O’Connor Brian , Gaumond Charles F.
Published: October 2005

A wavelet transform is used to synthesize distinct contributions from the monostatic form function for a randomly ribbed, complex end-capped, finite cylindrical shell. In order to achieve satisfactory wave packets, as measured by their cross-correlation with the original impulse response, two wavelet transforms are used, a temporal wavelet transform and a spectral wavelet transform. This is in contrast to synthesizing wave packets from the Wigner distribution where just one two-dimensional surface was necessary. However, interference terms between components in the Wigner distribution, which is quadratic in the underlying signal, are absent in the linear wavelet transform. This allows for a more facile synthesis of the acoustic excitations. The interference terms in the Wigner distribution can sometimes fall at points in the time-frequency plane where a signal component exists, making it difficult to synthesize that component without corruption caused by the presence of other compounds in the form function.
Exploring the relationship of breath intake to utterance duration
Authors: Whalen D. H. , Kinsella-Shaw J. M.
Published: October 2005

Previous work has indicated that there may be a positive relationship between the duration and extent of breath intake and the length of an upcoming utterance. However, none of that work has been free of alternative interpretations. An attempt was made to avoid some of those by forcing subjects to utter single sentences ranging in length from 5 to 82 syllables (mean of 27), after inspiring fully and then expiring down to a set level before uttering the sentence. For three subjects, there was a significant positive relationship between breath intake and utterance length (0.65, 0.50, and 0.29 individually). This was still true without those utterances containing a secondary breath (0.53, 0.54, and 0.29). The two subjects with the higher correlations also exhaled more quickly for the shorter sentences than longer ones. The other subject had no correlation with exhalation rate: He might have been selecting a point within a rather large range of starting lung volumes, with only the longest sentences requiring that the range’s lower part be avoided. The individual differences need further investigation, but there is a correlation between the duration of the sentence to be said and the breath before it. [Work supported by NIH Grant No. HD-01994.]
Voice pitch as an aid to speechreading in young children
Authors: Fagg Joanna D.
Published: October 2005

The speechreading ability of a group of young children with normal hearing was assessed using a simple, closed-set, single word identification task. The speechreading test was devised such that the accurate identification of half of the test items would be expected to be facilitated by the ability to perceive voicing contrasts. All of the subjects performed the task twice, once with visual speech information only and once with visual information supplemented by a voice pitch signal, derived using an electrolaryngograph. Subjects were found to be able to identify familiar words through speechreading, both in the silent condition and with the addition voice pitch signal. No significant overall improvement was found to result from the provision of voice pitch information. However, subjects were found to significantly improve in their ability to identify those test items which required the discrimination of voicing contrasts. Conclusions were drawn about the normal speech perceptual processes of young children and about the possible benefits of providing simple speech pattern information, such as the voice pitch signal, for children with profound hearing losses.
Exploiting source dynamics in matched-field processing
Authors: Michalopoulou Zoi-Heleni , Porter Michael B.
Published: October 2005

Matched-field processing is typically considered as a static problem of locating a fixed, narrow-band source. However, the source does not randomly jump from point to point during the course of time and much can be gained by exploiting this extra information. Various schemes have been proposed in the past for treating source motion. A key problem is that even when the source motion is uniform the source may appear to have a nonuniform speed due to environmental mismatch. We show that by allowing for these random perturbations in source motion, an improvement in the localization results is obtained.
Temporal model of high-frequency seafloor acoustic backscatter
Authors: de Moustier Christian , Sternlicht Daniel
Published: October 2005

A monostatic temporal model of seafloor acoustic backscatter has been developed to investigate the relative contributions of interface roughness and inhomogeneities in the sediment volume for measurements made at various angles of incidence. The model takes into account sonar parameters such as acoustic wavelength, beam pattern, pulse length, and angle of incidence, and it includes a theoretical angular dependence of seafloor scattering strength that is controlled by the roughness statistics of the surface insonified, by its refraction index, and by a volume reverberation term. Simulations have been carried over angles of incidence from 0° to 60°, and at acoustic frequencies ranging from 10 to 100 kHz for various types of substrates. The theoretical angular dependence predicts that the contribution from the sediment volume becomes noticeable for angles of incidence greater than about 6°; however, in the temporal model it is shown that this contribution can be detected closer to normal incidence for small beamwidths (e.g., 2°). When applied to a multi-narrow-beam sonar geometry this temporal model shows greater potential for bottom classification than the angular dependence function of acoustic backscatter obtained by integrating the returns received in each beam. [Work supported by ONR.]
Measurement of three-dimensional transient motion of surfaces by optical vibrometry
Authors: Vignola Joseph , Simpson Harry , Houston Brian H.
Published: October 2005

A three-dimensional laser vibrometer for measuring simultaneously the three components of vibration induced displacement on a surface has been constructed and tested [Vignola and Houston, J. Acoust. Soc. Am. 94, 1853(A) (1993) and ASME Winter Meeting, 93-WA/NCA-10 (11/93)]. The device, which is fully submersible, was developed for structural acoustic studies where measurements of full three-dimensional motion can provide insight into the analysis of the sound radiated by a structure. This presentation is principally concerned with the methodology and design of the signal processing schemes for the detection of transient events. Some preliminary data are shown together with an analysis of the sensitivity, noise sources, and other performance characteristics of the system. The data presented has been collected from both a test structure (a piezoelectric cylinder with three accelerometers for comparison) and in a water tank half-filled with filtered sand (mean diameter of 140 μm). In the sand experiment the motion of the water-saturated sand interface was monitored.
The perception of vowel height in Castilian Spanish: Effects of varying F1−F0 Bark distance
Authors: Fahey Richard P. , Lopez-Bascuas Luis E.
Published: October 2005

Analyzing American English vowels, Syrdal and Gopal [J. Acoust. Soc. Am. 79, 1086–1100] found that F1−F0 Bark distance was highly correlated with vowel height. The [±high] distinction could be based on a boundary at 3–3.5 Bark F1−F0 distance. This corresponds to the distance under which the center of gravity effect is thought to occur [Chistovich and Lublinskaya, Hear. Res. 1, 185–195]. Since a feature distinction with an auditory basis is a good candidate for a phonetic universal, one would expect the [±high] boundary to be at 3–3.5 Bark F1−F0 distance in many languages. This is true of the [±high] distinction in American English, for both front vowels [Hoemeke and Diehl, J. Acoust. Soc. Am. 93, 2422(A) (1993)] and back vowels [Fahey, J. Acoust. Soc. Am. 95, 2978(A) (1994)]. In the current study, native Castilian Spanish speakers identified synthetic vowel height series ranging between /i/ and /e/ or /u/ and /o/. Within each set, F0 and formant pattern varied orthogonally. Data were analyzed to determine (1) whether F1−F0 distance is a correlate of perceived vowel height, and (2) whether the [±high] boundary is at 3–3.5 Bark F1−F0 distance.
Scale model experiments on the diffraction and scattering of sound by a partially rough curved surface
Authors: Chambers James P. , Berthelot Yves H. , Stone T. Shane
Published: October 2005

Scale model experiments have been conducted to study the propagation of sound over a curved surface partially covered with rigid random roughness elements in the high-frequency diffraction/low-frequency scattering regime. The effects of roughness are found by comparing the sound field with that obtained with a fully smooth curved surface. Experiments indicate that roughness in the shadow zone acts to tunnel more sound into the shadow zone of the partially rough surface, relative to the curved smooth surface, via a ‘‘creeping boundary wave.’’ This wave qualitatively follows the trends of both creeping waves due to diffraction and Tolstoy-type ‘‘boundary waves’’ due to coherent scattering. However, roughness in the bright zone causes less sound to propagate into the shadow zone of the partially rough surface, relative to the curved smooth surface, because of incoherent scattering. [This work is supported by a Fannie and John Hertz Fellowship.] a)Current address: National Center for Physical Acoustics, University, MS 38677.
Sound isolation criteria for Cornell University Music Department
Authors: Foulkes Timothy J. , Cavanaugh William J.
Published: October 2005

A detailed case study in sound isolation criteria for a new music education facility at a major university is presented. Part of the department is to be housed in an existing, historic building with wood floor structures. Part of the new facility will be an addition (new construction).
Consistent geoacoustic models in the frequency range 50–5000 Hz
Authors: Holland Charles W. , Neumann Peter , Muncill Greg
Published: October 2005

The process of creating a geoacoustic model begins with the process of defining the dominant mechanisms that control bottom interaction for the frequency range and application of interest. For example, a geoacoustic model that treats the seafloor reflection process might be much simpler than a geoacoustic model which treats bottom interaction (i.e., general bi-static scattering including reflection and backscattering as special cases). The following step is to determine values for the parameters that describe those physical mechanisms of importance. This is typically approached by a combination of direct measurements (e.g., core data), empirical modeling {e.g., Hamilton relations [E. L. Hamilton, J. Acoust. Soc. Am. 68, 1313–1340 (1980)]}, or by inversion the acoustic data. The result can be tested by comparing the geoacoustic model predictions (used as primary inputs to an acoustic model) against measured acoustic data. Geoacoustic model predictions and comparisons with acoustic data and are given for a variety of marine environments. A geoacoustic model that is successfully employed for both seafloor reflection and scattering is demonstrated. [Work supported by the ONR/AEAS Program.]
Effect of ambient pressure on sonoluminescence from a single bubble
Authors: Barber Bradley P.
Published: October 2005

The dynamic sound field pressure Pa required to generate sonoluminescence (SL) from a single trapped bubble is a little higher than the ambient pressure P0 (e.g., Pa≊1.2P0). Since the acoustic energy density is proportional to the square of Pa observation of SL at lower drive levels would imply that even greater degrees of energy concentration accompany the transduction of sound into light. Motivated by this perspective, the dependence of SL on ambient pressure is being measured. Light emission at P0=0.3 Atm has already been achieved. Pressures higher than an atmosphere are also being investigated, especially with attempts to find single bubble SL in liquids other than water. [Work supported by the U.S. DOE Division of Advanced Energy Projects.]
Continuous wave and M-sequence transmissions across the Arctic
Authors: Mikhalevsky Peter N. , Baggeroer Arthur B. , Gavrilov Alexander , Slavinsky Mark
Published: October 2005

In the spring of 1994 a series of cw and maximal length sequences (M sequences) were transmitted 2600 km across the Arctic Ocean. The transmissions were centered at 19.6 Hz from a Russian source located 300 km north of the Svalbard Archipelago. The transmissions were received in the Lincoln Sea (900-km range) on a 32-element vertical line array and in the Beaufort Sea (2600-km range) on a 32-element vertical line array and a 32-element horizontal planar array. Analysis of the transmission loss, phase stability, array gain, and pulse compression gain are being used to develop an acoustic monitoring strategy in the Arctic for climate studies. The exceptional stability of the Arctic sound channel first noted in the early 1980s [P. N. Mikhalevsky, J. Acoust. Soc. Am. 70, 1717 (1981)] make acoustic thermometry potentially a very sensitive indicator of Arctic Ocean temperature and ice changes.
Predictions of the acoustic response of free-methane bubbles in muddy sediments
Authors: Lyons Anthony P. , Duncan Michael E. , Hawkins James A. , Anderson Aubrey L.
Published: October 2005

The response of the sediments of Eckernfoerde Bay, Germany to acoustic remote sensing has been attributed to gas features found within the sediment. The existence of features as small as 0.5 mm equivalent spherical radius has been confirmed by x-ray computed tomography of cores taken and scanned under insitu pressures. The interaction of an acoustic pulse from the Acoustic Sediment Classification System (ASCS) with this type of gassy sediment was modeled. The bubble scattering response included the effects of shear modulus and nonspherical bubbles. Model predictions made using the observed gas feature distribution and normal incidence ASCS data agree and show extended returns (greater than a pulse length) from the seafloor bubble layers as well as high attenuation within the bubble layers. These results show that the acoustic returns from the gas bubble layers are probably due to scattering and that differences in level of return can be attributed to random variations in the distributions of scatterers.
Weak Anderson localization and enhanced backscatter in reverberation rooms and quantum dots
Authors: Weaver Richard L. , Burkhardt John
Published: October 2005

Enhanced backscatter is studied in closed finite systems which have ballistic internal propagation and diffuse scattering at rough boundaries. Weak localization arguments indicate that the mean-square response at the source should be twice as large as it is at other points. It is argued, however, that the actual ratio is three. Numerical solutions are found to agree with a more detailed theory and to show that the enhanced return factor is two at moderate times, but three at late times comparable to the modal density.
Mode coupling in solid/liquid/solid trilayers
Authors: Laperre J. , Thys W.
Published: October 2005

This paper deals with elastic wave dispersion in trilayers composed of two solid plates (glass or aluminum) separated by a thin water layer. Two symmetrical (identical top and bottom layers) and two asymmetrical trilayers are investigated. It is shown that the dispersion curves of a trilayer can be analyzed in terms of the dispersion in the decoupled constituent layers, provided that the appropriate boundary conditions are used and that mode coupling between the modes of the decoupled layers is taken into account. The experimental data obtained by means of a double transmission immersion technique confirm this analysis. The main conclusions reached are (i) that the normal propagation modes of the decoupled constituents determine the asymptotic behavior of the trilayer modes; and (ii) that successive mode coupling is responsible for the course of the trilayer modes. Further, numerical and experimental evidence is found that doublets are formed around the modes of the decoupled solid plates in symmetrical but not in asymmetrical trilayers. It will be shown that mode coupling between two identical modes of the top and bottom layer is responsible for these doublets. Plots of the modulus and the phase of the reflection coefficient of the trilayers, as a function of frequency, further elucidate the analysis.
A novel approach to feedforward higher-harmonic control
Authors: Clark Robert L. , Gibbs Gary P.
Published: October 2005

A novel adaptive filter structure is proposed for the control of systems characterized by higher harmonic response. The control approach has been designated the higher harmonic least-mean squares (HLMS) algorithm to differentiate it from the standard multifrequency filtered-x version of the least-mean squares approach. In the HLMS algorithm, a single frequency reference at that of the fundamental is all that is required to implement the controller. The remaining harmonics are generated internally based upon simple trigonometric relationships. The filtered-x LMS algorithm is implemented in parallel for each frequency to be controlled, minimizing or totally eliminating the contribution of the time-varying terms during the convergence process and increasing the rate of convergence for the higher harmonic control application. Results from the simulation demonstrate that the HLMS approach is far superior to the standard multifrequency, filtered-x LMS algorithm in adaptive, feedforward, higher-harmonic control.
Approximate ray synthesis of the surface fields of a submerged elastic cylindrical shell with hemispherical endcaps
Authors: Ho Jin-Meng , Couchman Luise S.
Published: October 2005

Combining the available ray acoustic algorithms descriptive of submerged cylindrical and spherical shells, this paper formulates the pressure and velocity distributions on a hemispherically capped cylindrical shell which is immersed in an acoustic fluid and insonified by an obliquely incident plane wave. As the first ray acoustic model for a noncanonical (nonseparable) shell geometry of considerable current interest, it neglects wave coupling and diffraction due to curvature discontinuities at the junctures as well as contributions from the leaky waves excited through the endcaps. Nevertheless, by matching the surface wave vectors along the joints, due account is taken of leaky wave propagation on, and radiation from, the hemispheres. The total pressure or velocity on the cylinder—their ray constituents are related to each other by appropriate impedances—is then synthesized by a modified geometrical acoustics field, as developed recently, and a supersonic membrane wave field. The latter is contributed by the surface leaky rays successively traveling to the observer along helical trajectories and great circles on the cylinder and hemispheres; such rays are excited through phase matching by a series of incident rays, which are in turn identified by reciprocal ray tracing so as to quantify the leaky wave contribution. Numerical implementation is also performed here. The results are compared with the reference solution generated at the Naval Research Laboratory (NRL) by boundary element/finite element codes.
Model experiments related to outdoor propagation over an earth berm
Authors: Rasmussen Karsten Bo
Published: October 2005

A series of scale model experiments related to outdoor propagation over an earth berm is described. The measurements are performed with a triggered spark source. The results are compared with data from an existing calculation model based upon uniform diffraction theory. Comparisons are made in the frequency domain as well as in the time domain and good agreement is obtained.
Frequency independence property of radiation spatial filters
Authors: Borgiotti Giorgio V. , Jones Kenneth E.
Published: October 2005

It is known that a time harmonic boundary normal velocity field of a radiating object immersed in an acoustic fluid can be decomposed into a (efficiently) radiating and a non (efficiently) radiating components, belonging to two orthogonal ‘‘radiating’’ and ‘‘evanescent’’ subspaces. Numerical results show the validity for a capped cylinder of the conjecture that the ‘‘radiating’’ subspace at a certain frequency f1 is a subspace of the radiating subspace at frequency f2≳f1. The implications are (a) from the output of a bank of spatial filters designed for the max frequency of operation the far field can be identified over the entire frequency band, and, perhaps more importantly, (b) if in an active control scheme the outputs of the filters are driven to zero, broadband cancellation of the radiating noise is achieved.
Remote sensing of sheet metal texture in aluminum alloys
Authors: Min Shermann , Peng Lawrence , Lu Wei-yang , Hughes Darcy
Published: October 2005

Metal forming operations such as deep drawing, stretching, bending, hemming, etc. are all significantly influenced by the degree of crystallographic anisotropy (texture) present within the workpiece. An effort is underway at Sandia National Laboratories/CA to develop two noncontact ultrasonic systems for the measurement of texture in aluminum sheets. Although the effect of stress wave velocities on elastic anisotropy is well known, its ability to predict plastic behavior has yet to be firmly established. Ultrasonic measurements, which hold the potential for remote, in-process screening, will be shown to exhibit a high degree of correlation with current techniques for measuring texture, which are off-line, destructive, and often inaccurate. Results from an electromagnetic acoustic transducer (EMAT) system are used as a baseline comparison for a more promising noncontact technique involving the optical generation and detection of ultrasound, commonly referred to as laser ultrasonics (LU). In addition to displaying the level of anisotropy, slowness curves obtained from these systems suggest the ability to distinguish between different types of texture, as predicted from theory.
Theoretical evaluation of flow-induced noise in hull-mounted sonar arrays
Authors: Dubus Bertrand , Giangreco Christian
Published: October 2005

Future hull-mounted sonar arrays are likely to be limited by the effects of flow-induced acoustic noise on the sensors. These arrays are usually constituted by extended sensors embedded in an elastomer layer acting as outer decoupler (OD) mounted on a structural support plate (SSP). Predictive models of flow-induced noise are obtained by assuming specific mechanisms: (i) The direct path results from the detection by the sensors of the fluctuating pressures from the turbulent boundary layer after propagation through the OD [Ko etal., J. Acoust. Soc. Am. 85, 1469 (1989)]; (ii) the flexural noise is associated with the flexure of the extended sensors via their lateral sensitivity [Montgomery etal., J. Acoust. Soc. Am. 94, 1688 (1993)]; (iii) The vibrating SSP radiates acoustic pressures in the near field which are sensed by the array. The OD and SSP are assumed of infinite extent for the direct path and of finite extent otherwise. This paper presents an analytical model for the later path. Results are displayed in terms of wave-number-frequency spectrum of the radiated pressure and of frequency spectral density. The relative contribution of the different paths and the effect of various parameters of the array are discussed.
Bistatic reverberation from an ocean ridge
Authors: Makris Nicholas C. , Avelino Lilimar , Menis Richard
Published: October 2005

Bistatic reverberation from a highly lineated ridge in the mid-Atlantic was measured by two research vessels during the ARSRP Main Acoustics Experiment of 1993. Each vessel used a vertical source array and a horizontal receiving array to collect bistatic and monostatic data over a full range of incident and scattered angles with respect to the ridge axis. High-resolution bathymetry reveals that the ridge protrudes above conjugate depth for roughly 50 km, and is characterized by a number of extended scarps running parallel to the ridge axis. Sufficient excess depth exists around the ridge to isolate it with waterborne propagation paths from 1/2 convergence zone (CZ) range (∼33 km) where low-frequency returns register precisely with steep scarps. Significant variations in received level from a given scarp occur as a function of incident and scattered angle. The most prominent returns register with scarps facing the receiving array. Registration between returns from high-resolution waveforms (∼10 m in range) and fine-scale bathymetry is used to elucidate the fundamental scattering process. Comparisons with monostatic measurements of the same ridge from 1/2 CZ and 2 1/2 CZ indicate how fine-scale structure from a given scarp is smeared in long-range reverberation.
1–3 Piezocomposite transducer materials for commercial underwater applications
Authors: Murray Victor
Published: October 2005

Fugro-UDI Limited has gained several years experience in developing piezo-composite materials for use in underwater imaging sonars operating in the frequency range 100–500 kHz. A substantial amount of this work has concentrated on multielement arrays for military applications such as mine counter measures. The low mechanical quality factor (Qm) and high electro-mechanical coupling coefficient (Kt) of the material has provided wideband and efficient transducer materials. These parameters and others such as dielectric constant and electrical impedance can be tailored by varying the type and quality of both the ceramic material and polymer phase within the piezocomposite device. This has contributed to reducing the development and manufacturing costs of piezocomposite transducers. This presentation will discuss the various transducers developed by Fugro-UDI for commercial applications ranging from simple echo-sounder transducers, to sidescan transducers, through to multielement arrays for electronically scanned sonars. Sensitivities and beam patterns for piezocomposite devices will be compared with their ceramic counterparts. Other important transducer parameters such as pressure and temperature dependence of the piezocomposite materials will be presented.
Broadband source localization in a shallow-water environment with a small bottom slope
Authors: Knobles David P. , Koch Robert A.
Published: October 2005

Results from an analysis of matched-field source localization in range and depth for a range-dependent shallow-water ocean environment are presented. The matched-field localization is based on a broadband cross-correlation technique. The measured data are the time series of acoustic arrivals that propagated to a bottom mounted array from small omnisources at a location 0.5–30 km downslope. Over these ranges the water depth was 125–180 m. The measured data contain many strong multipaths because the acoustic environment was a downward refracting water column and a seafloor with a thin sand-silt sediment over a thick limestone layer. Matching fields for the localization of the sources in the measured data were computed with a broadband adiabatic normal-mode model in the 100–500-Hz band. The presentation also includes a comparison of the measured and modeled time series as a validation of the environmental and propagation descriptions. [Work supported by the Office of Naval Research (Code 322). The data measurements were sponsored by ARPA.]
Measurements of ultrasonic attenuation and sound velocity in a single crystal of (La1−xSrx)2CuO4
Authors: Zhang Hong , McKenna M. J. , Sarma Bimal K. , Levy Moises , Kimura T. , Kishio K. , Kitazawa K.
Published: October 2005

Measurements of the ultrasonic attenuation and sound velocity were made at frequencies of 32 and 87 MHz in a large single crystal of (La0.925Sr0.075)2CuO4 (∼4×4×4 mm3), which exhibits a sharp (ΔT∼1 K) superconducting transition at 37 K. For longitudinal waves propagating along the c axis, the sound velocity shows a sharp softening, Δv/v∼100 ppm, concurrent with the sharp superconducting transition in the susceptibility measurements. Following this transition, the susceptibility exhibits a small tail extending to 27 K, where a smaller softening, Δv/v∼20 ppm, has been observed in the velocity measurements. Accompanying the ∼100-ppm velocity drop, there is a signature in the attenuation; following this feature, the attenuation changes as the temperature is decreased further, with a small kink in the attenuation at 27 K. Additional results of the dependence of the attenuation and sound velocity in external magnetic fields, orientated in the a-b plane, will be presented. [Work supported by ONR.]
Simplified model for the study of nonlinear processes in thermoacoustic engines
Authors: Prosperetti A. , Watanabe M.
Published: October 2005

Upon integrating the governing equations over the cross section of a thermoacoustic device, a simplified one-dimensional model is obtained. While only approximate, this model renders the study of nonlinear effects very amenable to analysis. In particular, for a thermoacoustic prime mover, the stability limits are calculated and the steady-state amplitude is estimated on the basis of a weakly nonlinear theory. For larger amplitudes, numerical results are presented. The marked propensity of the system to develop shock waves is found to be a very strong factor limiting its efficiency. [Work supported by the Office of Naval Research.]
Shear-wave induced transmission loss in a fluid–solid medium
Authors: Ivansson Sven
Published: October 2005

Formulas are derived for decomposition of power and energy within a wave field, a modal wave field in particular, into bulk and shear parts. It is noted that the complex bulk and shear moduli must be restricted to the fourth quadrant if a harmonic time dependence e−iωt with ω≳0 is assumed. An example case with frequency-dependent transmission loss is studied. The power decomposition results turn out to be very useful for demonstrating that shear losses in the sediment form the major cause of the narrow stop bands that occur. Furthermore, these losses have a resonance character which is illustrated very clearly by showing how the bulk and shear losses are distributed within the sediment layer.
Repulsion of phase-velocity dispersion curves and the nature of plate vibrations
Authors: Überall H. , Hosten B. , Deschamps M. , Gérard A.
Published: October 2005

The Lamb waves propagating in an elastic plate in vacuo generate compressional (L) and shear-type (T) plate vibrations which are coupled due to the boundary conditions. Without such coupling, their phase-velocity dispersion curves would form two intersecting families, which at high frequency, tend toward the elastic-wave speeds CL and CT, respectively. It is shown that the coupling causes a repulsion of the dispersion curves similar to that encountered in atomic physics for the energy levels of atoms combining into molecules, which prevents their intersection and at the same time exchanges the nature (L⇆T) of the underlying vibrations. However, in the repulsion regions a succession of dispersion curves combines to asymptotically approach the uncoupled L or T dispersion curves, respectively. For the case of a plate bounded by fluid on one side, and vacuum on the other, the dispersion curves of the fluid-borne (Stoneley–Scholte-type) wave which is known from the studies of Grabowska and Talmant to be present in this case, and of the usual A0 Lamb wave exhibit a similar repulsion phenomenon.
Regenerating the spectral shapes of [s] and [∫] from a limited set of articulatory parameters
Authors: Nguyen Noël , Hoole Philip , Marchal Alain
Published: October 2005

This work was aimed at exploring articulatory-acoustic relationships in the production of French fricatives. More precisely, an attempt was made to find out whether the spectral shapes of [s] and [■] can be regenerated from the x and y coordinates of three electromagnetic transducers affixed to the tongue in the midsagittal plane. The corpus was composed of the two fricatives /s/ and /■/ combined with the vowels /a/ and /i/ in sequences of the type /Vs■V/ and /V■sV/, and was read by one male native speaker of French. The spectrum regeneration was based on a statistical procedure which consisted of estimating the factors explaining the main part of the acoustic variance from the position of the transducers, by means of multiple linear regression. The articulatory-acoustic correlations were high and allowed us to regenerate the fricative spectra with a good accuracy. The way in which the acoustic parameters varied as a function of the articulatory ones in the statistical model was in good agreement with data reported in previous works. The results support the idea that the tongue has relatively few degrees of freedom in the production of [s] and [■].
Correlation between amplitude and frequency fluctuations of spontaneous otoacoustic emissions
Authors: van Dijk Pim , Wit Hero P. , Tubis Arnold , Talmadge Carrick L. , Long Glenis R.
Published: October 2005

The normalized cross-correlation function between the amplitude and frequency fluctuations of 11 spontaneous otoacoustic emissions was measured. A significant correlation was found in seven subjects. The correlation coefficient ranged from −0.37 to +0.65 across subjects. In four subjects, the amplitude fluctuation lagged the frequency fluctuation. The time lag was between 1.6 and 5.5 ms. The results were interpreted using a noise-perturbed limit-cycle oscillator with nonlinear (Duffing) stiffness as a model for a spontaneous emission. The data show that the relative increase of the nonlinear stiffness in this model was between −0.010 and +0.015. This indicates that an even-order nonlinear stiffness plays a minor role in the emission generator.
Frequency modulation versus amplitude modulation discrimination: Evidence for a second frequency modulation encoding mechanism
Authors: Edwards Brent W. , Viemeister Neal F.
Published: October 2005

The encoding mechanisms for amplitude modulation (AM) and frequency modulation (FM) were investigated using AM–FM discrimination tasks. In the first experiment, AM and FM were set at equally detectable levels within a trial, and discrimination thresholds were obtained adaptively in a 3IFC task. Here, AM–FM discrimination thresholds were considerably larger than both AM and FM detection thresholds. This is consistent with an encoding system whereby AM and FM are partially encoded by the same mechanism. In the second experiment, performance on AM–FM discrimination is measured with a fixed-level procedure. Psychometric functions obtained for a constant modulation depth of AM were nonmonotonic with FMs modulation index β and each displayed a single minimum. The nonmonotonic nature of the functions is consistent with a model in which FM is encoded primarily with the same mechanism that encodes AM but also with a second mechanism, probably related to changes in instantaneous frequency, that is independent of the mechanism that extracts AM. The fact that minima in the discrimination psychometric functions increase from d′=0 as β increases indicates that the information encoded by the second mechanism becomes more detectable with increasing β.