bluuebunny/crossref_metadata_2025 huggingface dataset:
Noise levels and hearing thresholds in the drop forging industry
Authors: Taylor William , Lempert Barry , Pelmear Peter , Hemstock Ian , Kershaw Jeffrey
Published: October 2005

A-weighted equivalent continuous noise levels for hammer and press operations in a drop-forging industry were determined using both tape recordings of the noise and personal noise dosimeters. The results indicated average A-weighted Leq values of 108 dB for hammer operators and 99 dB for press operators. Comparison of hearing level statistics for 716 hammer and press operators and 293 control subjects indicated the severe hazard to hearing of impact noise exposures. For mean exposure times of less than 10 years, hearing levels for the press (99 dB) and hammer (108 dB) operator age groups are nearly identical, and in the latter case are less than those predicted for exposure to equivalent continuous noise. For long-term exposures of 10 years or more, the results of this study indicate that hearing losses resulting from impact noise in the drop-forging industry are as great or greater than those resulting from continuous noise.
Scattering in glass beads: Effects of frame and pore fluid compressibilities
Authors: Winkler Kenneth W. , Murphy William F.
Published: October 2005

Ultrasonic compressional wave phase velocities and attenuation have been measured as functions of frequency in packings of unconsolidated glass beads. External confining pressure was varied so as to modify the physical interactions between grains. Samples were studied when vacuum dry and when saturated with different pore fluids. Pressure/pore fluid combinations were chosen so as to minimize nonscattering loss mechanisms. In each experiment, phase velocity exhibited negative dispersion and attenuation was proportional to the fourth power of frequency. Increasing confining pressure (to 15 MPa) significantly reduced the scattering losses (by an order of magnitude at a given frequency in dry glass beads). Decreasing pore fluid compressibility produced a corresponding decrease in the scattering losses. This work shows that theoretical models based on suspensions are not adequate when the grains are interacting to form a solid frame. The present data, along with previous data for fused glass beads, suggest that the scattering strength is related to the contrast between the acoustic properties of the composite and of the grains, rather than to pore/grain or pore/composite contrasts.
Iterative extended boundary condition method for scattering by objects of high aspect ratios
Authors: Lakhtakia Akhlesh , Varadan Vijay K. , Varadan Vasundara V.
Published: October 2005

The limitations of the T-matrix procedure or the extended boundary condition method (EBCM) for wave scattering problems, when used for long slender objects, are due to the shrinking volume over which the incident field is extinguished. The resulting ill-conditioning of the matrices involved makes it impossible to invert them. For nondissipative objects only, we observe that the Reinforced Modified Gram–Schmidt (RMGS) orthogonalization procedure works best of all such unitary approaches investigated, but information about the surface and the internal fields is lost in the process. An alternate approach, called the iterative EBCM (IEBCM) is more general in its scope since it provides convergent surface and internal field values and can also work for dissipative targets. This success of the IEBCM results because it extends the interior volume over which the incident field is extinguished.
Impedance profile recovery from transmission data
Authors: Carroll Robert , Santosa Fadil
Published: October 2005

We consider the problem of reconstructing the impedance profile from transmitted data. The problem (which arises for example in one-dimensional tomography) is quite different from the problem in reflection seismology where the excitation and measurements are made at the surface. In our previous investigations, we used transmutation techniques to relate the transmitted data for time 0<t<∞ to the reflection data. This allows the use of the Gelfand–Levitan theory to recover the profile. In the present work, we consider the more difficult situation in which the transmitted data are given only up to a finite time. We study various maps and show that we can pose a fixed point problem to solve for the unknown profile. A new way of characterizing the Gelfand–Levitan theory for this problem based on minimization procedures is also presented.
Frequency discrimination in quiet and in noise for signals with triangular spectral envelopes
Authors: Horst J. W. , Ritsma R. J. , Wit H. P.
Published: October 2005

The just-noticeable-difference in frequency (jndf) for complex signals with triangular spectral envelopes is found to depend on the envelope slope. For shallow slopes (<140 dB/oct), jndf increases with decreasing slope. Addition of noise also impairs frequency discrimination within a region of about 20 dB above masked threshold. This is found for both maskers used: a wideband noise and a narrow-band masker which is below the signal in frequency. When wideband noise is used, frequency discrimination of complex signals with shallow slopes deteriorates more rapidly with decreasing signal-to-noise ratio than it does when the signals have steep spectral slopes.
Spontaneous narrow-band oto-acoustic signals emitted by human ears: A replication
Authors: Wier Craig C. , Norton Susan J. , Kincaid Gail E.
Published: October 2005

The presence of continuous, narrow-band acoustic signals (oto-acoustic emissions) in recordings made from the ear canals of human subjects has been reported by several authors. We report here the results of our attempt to detect such emissions from a series of 92 normally hearing ears from 47 adult subjects. Our results were quite similar to those reported by Zurek [J. Acoust. Soc. Am. 69, 514–523 (1981)]. Emissions were found in 38% of the people and 27% of the ears tested. The distributions of the recorded emissions were also very similar to the results of Zurek’s study.
Evidence for a reappraisal of the psychophysical selective adaptation paradigm
Authors: Moody David B. , Cole Dorothy , Davidson Linda M. , Stebbins William C.
Published: October 2005

The human psychophysical adaptation literature infers the existence of channels in the auditory system sensitive to frequency modulation (FM) from selective increases in FM detection thresholds following adaptation with FM stimuli. Using this psychophysical paradigm to characterize the attributes of feature-sensitive channels requires knowledge of the phenomenon’s stability over repeated testing. In this study FM detection thresholds were measured in human subjects with continued testing over numerous sessions. During adapting intervals within the sessions either FM upsweeps or silence was presented. Exposure to FM upsweeps initially resulted in an increase in FM detection thresholds by a factor of 2 to 3 relative to those measured following silence. These initial threshold elevations decreased markedly with repeated testing (more than five 30-min experimental sessions). Final threshold differences between adapted and nonadapted conditions approached zero. In one subject, such asymptotic threshold values were regained in a single session, after a 4-month hiatus. The findings suggest multiple determinants of the selective adaptation function, as well as a reevaluation of inferred mechanisms.
Predicting the subjective response to nonsteady vibration based on the summation of subjective magnitude
Authors: Hiramatsu Kozo , Griffin Michael J.
Published: October 2005

A purpose of this study was to determine the values of exponents of psychophysical functions for the discomfort produced by whole-body vertical vibration. In addition, the applicability of a method of predicting the average stimulus intensity of a stimulus the intensity of which varies with time was investigated. The first experiment investigated the effect on discomfort of the duration of vibration (for durations of 2, 5, 10, 20, and 50 s) and of the vibration acceleration magnitude [for 0.5, 0.75, 1.11, 1.67, and 2.5 ms−2 (rms) at 8 Hz]. The magnitude estimation method was used. The results show that the logarithm of the magnitude estimates is in linear proportion to both the logarithm of the acceleration and the logarithm of the duration. The values of exponents for acceleration and duration were 0.96 and 0.56, respectively. In the second experiment, the point of subjective equality of each of 16 nonsteady vibrations was measured and compared with the stimulus intensity predicted by means of the method proposed by the authors. Good agreement was found between the measured and predicted stimulus intensity and it was confirmed that the predicting method could be applied to vibration as well as to noise.
Nonlinear King integral for arbitrary axisymmetric sound beams at finite amplitude. II. Derivation of uniformly accurate expressions
Authors: Ginsberg Jerry H.
Published: October 2005

The first part of this investigation [J. Acoust. Soc. Am. 76, 1201–1207 (1984)] derived a perturbation representation of the velocity potential for an axisymmetric, monochromatic sound beam in the form of a complex function. That result, which used Hankel transforms to describe the dependence on transverse position, lacked uniform validity in the corresponding wavenumber, as well as the distance from the transducer. Expressions for the state variables derived from the potential have the same behavior. The example of a planar wave is used to adapt the singular perturbation method of renormalization to the case where the potential is in complex form. The resulting technique is used to obtain a coordinate straining transformation that makes the state variables uniformly accurate. The expression for the pressure is similar to the King integral in linear theory, except that the integrand is a function of the strained coordinates. Comparison of the predicted waveform properties with experimental data [Gallego-Juarez and Gaete-Garreton, J. Acoust. Soc. Am. 73, 761–765 (1983)] shows good correlation. Further evaluations disclose some new features of the distortion phenomena in both the time and frequency domains.
On the uniqueness of solution for all wavenumbers in acoustic radiation
Authors: Brod K.
Published: October 2005

The integral relations equivalent to Helmholtz’s equation with closed-boundary conditions possess nonunique exterior solutions at eigenwavenumbers of the corresponding interior problems. If the Green’s function for Helmholtz’s equation can be expanded into a series of orthogonal functions, then an infinite set of integral equations at the boundary results. These ‘‘null-field’’ equations are shown to possess unique solutions for all wavenumbers. Furthermore, these solutions can be used to represent the solutions in the exterior domain as algebraic series.
Radiation coupling between two coaxial disks of different diameter: An exact solution and detailed experimental verification
Authors: Harrison Jonathan A. , Cook-Martin Geoffrey N. , Challis Richard E.
Published: October 2005

The impulse response for the acoustic radiation coupling between two disks has been found in a closed analytic form for the case of a transmitter larger in diameter than a coaxially aligned receiver. In order to verify experimentally the derived expression piezoelectric transducers were used as transmitters and receivers. An analysis of piezoelectric transduction is presented in order to account for transduction effects in the experimental system. Discrete time models of the transmitter and receiver processes valid for times less than one reverberation period are formed based on Redwood’s equivalent circuits adapted by z-transform techniques. Recurrence relationships are derived and used in the manner of digital filters to calculate the transducer output due to any type of input. In the case of the transmitter, the force acting on the front face is calculated for any applied electrical waveform, whereas the receiver model calculates the voltage generated across the device due to any force function acting on the receiver face. The transducer models are used in conjunction with the disk to disk impulse response to calculate the voltage generated across the receiver due to any electrical waveform applied to the transmitter. Responses measured experimentally in water are presented and compared with predicted waveforms; receiver amplifier insertion characteristics are included in the model and a correction is made to take into account ultrasonic absorption by water. Good agreement is shown between the predicted and measured waveforms.
Measurement of the acoustic nonlinearity parameter B/A in human tissues by a thermodynamic method
Authors: Sehgal Chandra M. , Bahn Robert C. , Greenleaf James F.
Published: October 2005

A thermodynamic method for measuring the acoustic nonlinearity parameter B/A in tissues is presented. It is based on the measurement of change in phase velocity as a function of time as the hydrostatic pressure of the sample is quickly reduced from a known value. This technique circumvents the effect of the attenuation in the medium and does not require a prior knowledge of the thermodynamic parameters of the tissues. The method is used to estimate nonlinearity parameters for normal and malignant tissues in the temperature range 20° to 37 °C. The values and the temperature dependence of these parameters are found to vary with the nature of the tissues.
The timing of articulatory gestures: Evidence for relational invariants
Authors: Tuller Betty , Kelso J. A. Scott
Published: October 2005

In this article, we examine the effects of changing speaking rate and syllable stress on the space–time structure of articulatory gestures. Lip and jaw movements of four subjects were monitored during production of selected bisyllabic utterances in which stress and rate were orthogonally varied. Analysis of the relative timing of articulatory movements revealed that the time of onset of gestures specific to consonant articulation was tightly linked to the timing of gestures specific to the flanking vowels. The observed temporal stability was independent of large variations in displacement, duration, and velocity of individual gestures. The kinematic results are in close agreement with our previously reported EMG finding [B. Tuller et al., J. Exp. Psychol.: HPP 8, 460–472 (1982a)] and together provide evidence for relational invariants in articulation.
Range and frequency dependence of transfer function phase
Authors: Lyon Richard H.
Published: October 2005

The phase trend in multi-degree-of-freedom systems can be determined by an algorithm that tracks the relative signs of adjacent resonances in a modal expansion of transfer functions. This algorithm is expressed in analytical form for two-dimensional systems. The analytical expression shows the transition from input function phase to the reverberant phase limit. The phase trend for two-dimensional systems greatly exceeds that of the average response of such systems and the reason for this difference is analyzed.
Effects of noncollinear interaction on parametric acoustic arrays in dispersive fluids
Authors: Hamilton Mark F.
Published: October 2005

The effect of noncollinear interaction on radiation of the difference-frequency signal from a parametric array is analyzed for small angles of intersection formed by two primary beams radiated from the same source. Although variations in the angle of intersection affect the phasing of the array, it is shown that for no practical situations can noncollinear interaction be used to offset detrimental effects due to dispersion. Instead, reduction in length of the interaction region as a result of noncollinear interaction adversely affects the farfield radiation. Length reduction is avoided when one primary beam completely overlaps the other, which is the situation encountered with the parametric receiving array.
Scattering of elastic waves by a cylindrical obstacle embedded in a multilayered medium
Authors: Franssens G. R. , Lagasse P. E.
Published: October 2005

A numerical method is presented for the computation of reflection, transmission, and mode conversion coefficients, for the scattering of both SH and P–SV waves by a cylindrical obstacle embedded in a multilayered medium. In this method the scatterer and the surrounding medium are modeled by means of finite elements. On the boundary of the finite element mesh an integral representation boundary condition (IRBC) is imposed. This condition is derived from the elastodynamic reciprocity relation and contains the Green’s tensor of the undisturbed layered medium. The size of the finite element mesh is limited to roughly that of the cross section of the scatterer. The displacements over the finite element mesh are then obtained using a Galerkin error criterion. Numerical results are presented for geometries occurring in underground seismic surveys of coal layers and in the design of surface acoustic wave devices.
Effects of air loading on timpani membrane vibrations
Authors: Christian Richard S. , Davis Robert E. , Tubis Arnold , Anderson Craig A. , Mills Ronald I. , Rossing Thomas D.
Published: October 2005

Measurements and theoretical calculations of timpani modal frequencies and decay times are made for the cases of no kettle enclosure and kettle enclosures of varying volume. For the calculations, the timpani membrane is assumed to be ideal and the kettle is assumed to be a rigid cylinder which is volume equivalent to the actual kettle. A Green function method is used for calculating the effects of air loading. The calculated modal frequencies and decay times are generally in good agreement with the experimental measurements. In particular, for typical kettle enclosures, the frequency ratios f11 : f21 : f31 ; f41 are found to be close to the harmonic ratios 2 : 3 : 4 : 5 over the normal playing range 100 Hz≲f11≲175 Hz.
Vocal cues to speaker affect: Testing two models
Authors: Scherer Klaus R. , Ladd D. Robert , Silverman Kim E. A.
Published: October 2005

We identified certain assumptions implicit in two divergent approaches to studying vocal affect signaling. The ‘‘covariance’’ model assumes that nonverbal cues function independently of verbal content, and that relevant acoustic parameters covary with the strength of the affect conveyed. The ‘‘configuration’’ model assumes that both verbal and nonverbal cues exhibit categorical linguistic structure, and that different affective messages are conveyed by different configurations of category variables. We tested these assumptions in a series of two judgment experiments in which subjects rated recorded utterances, written transcripts, and three different acoustically masked versions of the utterances. Comparison of the different conditions showed that voice quality and F0 level can convey affective information independently of the verbal context. However, judgments of the unaltered recordings also showed that intonational categories (contour types) conveyed affective information only in interaction with grammatical features of the text. It appears necessary to distinguish between linguistic features of intonation and other (paralinguistic) nonverbal cues and to design research methods appropriate to the type of cues under study.
Tomographic observation of flow in a water tank
Authors: Sato Takuso , Shiraki Makoto
Published: October 2005

A tomographic method flow distribution estimation from the data of time of flight of pulsed sound waves among fixed stations is examined for the case of plane flow detection in a water tank. The errors due to the limited number of stations and the effects of the use of a pseudoinverse method are examined under practical conditions. Experimental results showed the usefulness of the method in these cases.
Transient fields radiated by curved surfaces—Application to focusing
Authors: Guyomar Daniel , Powers John
Published: October 2005

A theoretical model is presented for computing the transient radiated field (potential or pressure) resulting from a curved surface having an arbitrary velocity distribution. The method is a generalization of the angular spectrum theory giving the time impulse response for a given shaped surface. The technique leads to a systems theory interpretation of the radiation and diffraction effects. General expressions for arbitrary surfaces are given but important simplifications occur for radially symmetric geometries. For this case, simple expressions for the wave location may be obtained without requiring solution of the wave. Numerical simulations for common focused waves are given using computationally efficient FFT algorithms.
Radial extrapolation of wave fields by spectral methods
Authors: Candel Sébastien M. , Chassaignon Christian
Published: October 2005

Wave extrapolation methods are of considerable technological interest. When the wave field is axisymmetric or contains lower order azimuthal components, extrapolation may be performed in the radial direction from data recorded on a single sideline. This yields important reductions in the data acquisition and computation processes. This paper provides a theoretical basis for spectral-domain radial extrapolation and describes numerical simulations and an experimental application.
The T-matrix approach for scattering by a traction-free periodic rough surface
Authors: Lakhtakia A. , Varadan V. K. , Varadan V. V. , Wall D. J. N.
Published: October 2005

A T matrix is formulated to characterize scattering by a traction-free periodic rough surface and numerical results for several surface profiles are presented. The normalized reflected intensities are computed, for the cases of longitudinal (P) as well as shear (SV) wave incidence, as functions of the angle of incidence and frequency of the incident wave. The anomalous behavior of the reflected waves are explained in terms of their conversion from evanescent to propagating waves, as well as in terms of Rayleigh surface waves. Hybridization of the T-matrix scheme with a point-matching procedure is also discussed.
Coherent response to a point source irradiating a rough plane
Authors: Lucas R. J. , Twersky V.
Published: October 2005

We consider a point source above a rough surface, and write the coherent response as the Sommerfeld–Weyl–Noether integral in terms of the coherent plane-wave reflection coefficient R for correlated distributions of bosses on rigid or free planes. The uniform asymptotic development of the integral (a generalization of the original Sommerfeld approximation based on the error function complement) is applied to near-grazing for a rigid base, and graphical results and simple analytical approximations are presented to exhibit the essentials for data inversion programs. The coefficient R and the associated angle-dependent impedance (determined by the ensemble-averaged multiple scattering amplitude for one fixed boss) are specified by the single scattered amplitude and the statistical-mechanics pair distribution function. Low-frequency illustrations for rigid bosses delineate multipole-coupling and packing effects on propagation and on attenuation arising from incoherent scattering, as functions of the packing fraction and of the shapes of the bosses and their exclusion regions.
On the drag and virtual mass coefficients in Biot’s equations
Authors: Bedford A. , Costley R. D. , Stern M.
Published: October 2005

If the solid constituent of a fluid saturated porous medium is assumed to be subjected to a uniform oscillatory motion, Biot’s equations can be solved for the drag and virtual mass coefficients in terms of the resulting oscillatory motion of the fluid. The determination of these coefficients is therefore reduced to the solution of a boundary value problem for a viscous, compressible fluid. As an example, the pores have been assumed to be cylindrical. The motion of the fluid has been determined theoretically by subjecting the wall of a cylinder of viscous compressible fluid to a uniform oscillatory motion and averaging the resulting fluid displacement over the volume of the cylinder. Motions parallel to and normal to the axis of the cylinder have been considered. In the case of motion parallel to the cylinder axis, the obtained coefficients are equivalent to those obtained by Biot and by Hovem and Ingram. By superimposing the parallel and normal cases, the coefficients for cylindrical pores at an arbitrary angle to the propagation direction have been obtained. Then by averaging with respect to the angle, the coefficients have been determined for a material containing pores of random orientation.
A reconsideration of acoustic invariance for place of articulation in diffuse stop consonants: Evidence from a cross-language study
Authors: Lahiri Aditi , Gewirth Letitia , Blumstein Sheila E.
Published: October 2005

This study explored the claim that invariant acoustic properties corresponding to phonetic features generalize across languages. Experiment I examined whether the same invariant properties can characterize diffuse stop consonants in Malayalam, French, and English. Results showed that, contrary to theoretical predictions, we could not distinguish labials from dentals, nor could we classify dentals and alveolars together in terms of the same invariant properties. We developed an alternative metric based on the change in the distribution of spectral energy from the burst onset to the onset of voicing. This metric classified over 91% of the stops in Malayalam, French, and English. In experiment II, we investigated whether the invariant properties defined by the metric are used by English-speaking listeners in making phonetic decisions for place of articulation. Prototype CV syllables—[b d] in the context of [i e a o u]—were synthesized. The gross shape of the spectrum was manipulated first at the burst onset, then at the onset of voicing, such that the stimulus configuration had the spectral properties prescribed by our metric for labial and dental consonants, while the formant frequencies and transitions were appropriate to the contrasting place of articulation. Results of identification tests showed that listeners were able to perceive place of articulation as a function of the relative distribution of spectral energy specified by the metric.
Interaction of cortical evoked potentials to electric and acoustic stimuli
Authors: Lusted Hugh S. , Simmons F. Blair
Published: October 2005

Evoked potentials to a dichotic stimulus composed of either (1) two binaurally presented tone pips or (2) one tone pip and an electrical pulse to the auditory nerve are recorded from the primary auditory cortex of barbiturate anesthetized cats. The composite stimulus is delivered as a time delayed pair where the interstimulus interval (25 ms) is within the relative refractory period of the evoked potential to either stimulus alone. The amplitude of the cortical potential to the trailing stimulus is compared with its single stimulus amplitude as the frequency of the trailing tone pip is changed from 250 Hz through 40 kHz. There is an optimal frequency range over which the trailing stimulus is suppressed and this range appears directly related to the current of a preceding electrical pulse. The frequency of maximum suppression shifts according to the position of the electrode in the nerve. In some experiments secondary maxima develop, suggesting stimulus current spread from fibers of one cochlear turn into fibers from another turn.
Single beam synthesis from thinned arrays
Authors: Kaiser Julius A.
Published: October 2005

A readily steerable, ambiguity-free beam is formed in real time from a receive aperture containing a sparsely populated array of transducer elements with selected spacings. The system approach utilizes multiple phase-matched local oscillators in the process of producing at an IF a full set of synthetic spatial frequencies which are similar to the actual spatial frequencies associated with all conventional apertures. A summation of these synthetic spatial frequencies produces the scannable beam with at least as much resolution and freedom from interference as that obtainable from the same size aperture fully filled with closely spaced elements. Beam formation is accomplished either within the system by using a beam forming network or externally by applying the synthesized spatial frequencies to a fully filled transmit array of elements (an autonomous retrodirective system). Experimental measurements at a rf demonstrate that the principles are valid. Superdirectivity, circular arrays (for cylindrical coverage), self-steering arrays, real-time holography, passive distance measurement, and frequency/phase modulation recovery from incident carriers are possible extensions of the system approach.
Some gas flow and acoustic pressure measurements inside a concentric-tube resonator
Authors: Sullivan Joseph W.
Published: October 2005

The one-dimensional model of the concentric-tube resonator [J. W. Sullivan and M. J. Crocker, J. Acoust Soc. Am. 64, 207–215 (1978)] assumes that (1) the impedance of the perforation is constant along the length of the flow tube and (2) spatial variations of acoustic pressure in the transverse direction of either tube or cavity are small. Some recent measurements on long resonators have indicated that when mean flow is present, net flow in the cavity, although small relative to that in the tube, affects the impedance in a bidirectional manner resulting in violation of assumption 1. Experiments using microphone probes have demonstrated the validity of assumption 2 provided the tube is perforated axisymmetrically and uniformly. When this is not the case, a circumferential cross mode can be induced which invalidates the one-dimensional model.
Measurement of normal surface displacements for the characterization of rectangular acoustic array elements
Authors: Jungerman R. L. , Bennett P. , Selfridge A. R. , Khuri-Yakub B. T. , Kino G. S.
Published: October 2005

The performance of elements in transducer arrays is evaluated, at various stages of construction, using an interferometric optical probe that is capable of measuring acoustic displacements of the order of 3 × 10−4 Å. The vertical displacement is first measured on a single piezoelectric strip without matching layers or backing, and is compared with variational calculations of the surface displacement for both the open- and short-circuit modes. Good agreement is obtained between experiment and theory. The measurement is repeated after a matching layer is added, then after a backing is added, and finally with the array water loaded after final completion. Our experimental results are in excellent agreement with theory, where theoretical predictions are available. Laser probe measurements are used to evaluate the cross-coupling between array elements and predict the farfield illumination pattern of the array elements.
Three models of global ocean noise
Authors: Dashen Roger , Munk Walter
Published: October 2005

The vertical directionality of ambient low-frequency (shipping) noise at midlatitudes has been measured by Wales and Diachok [S. C. Wales and O. I. Diachok, J. Acoust. Soc. Am. 70, 577–582 (1981)] in the Atlantic and by Williams and Fisher (R. B. Williams, personal communication. The measurements were taken in October 1979) in the Pacific. At the sound axis the angular distribution in intensity is flat from 0° (horizontal) up to the inclination of the surface-limited rays. The intensity falls off sharply for steeper rays (which are associated with lossy bottom reflections). This observed flat angular distribution is in contrast with the bimodal distribution (peaked near the inclinations of surface-limited rays and zero for flat rays) which is expected from surface sources in a range-independent environment. A flat angular distribution is equivalent to an equal partition of energy among modes; once such equipartition is attained, the distribution remains unaltered with propagation (or scattering) in a lossless channel. The simplest model consists of surface sources generating rays of steep axial inclination, which are then scattered into flat rays by internal waves throughout the ocean volume. The model fails because of the weakness of the scatterers, requiring 104 km for equipartition. There are two regions for the noise energy to couple directly into flat (near-axial) rays: (i) at high latitudes where the rising sound axis intersects the surface, and (ii) at the continental slope where the sound axis intersects the rising bottom. The second model consists of sources in the high latitude duct (where the sound axis is essentially at the surface), with energy broadly partitioned among modes from the very start (dipole sources in a linear sound speed gradient give precisely equipartition). Subsequently, the energy is ducted downward along the axis into midlatitudes, preserving equipartition. This model fails because of the low density of shipping at high latitudes. In the third model, the steeply descending rays from coastal shipping are bounced into flat near-axial rays over the continental slope, as proposed by Wales and Diachok. Although there is some mystery as to how this will lead to the observed high degree of mode equipartition, we conclude (reluctantly) that reflections at the continental slope are probably the dominant mechanism for getting energy into the flat rays.
Converging uniaxial strain shock waves in nonlinearly locking solids under loading–unloading blasts. I: Wave characteristics formulation and permanent strain boundary formation
Authors: Ziv M.
Published: October 2005

A formulation is derived in Eulerian description governing finite amplitude compressible motion of uniaxial strain in an elastic-plastic locking half-space under an abrupt loading–unloading blast. For the material flow during the deformation phase, a wave characteristics formulation is presented valid for large strains but restricted to unloading stages which are moderate in comparison to linear elasticity. A method is also presented by which the permanent strain boundary is located in the space–time solution domain upon the termination of the unloading process. Finally, a scheme is given for the determination of the rigid body motion that takes place behind the permanent strain boundary.
Effects of background noise level on detection of tone glides
Authors: Collins M. Jane , Cullen John K.
Published: October 2005

Detection thresholds were obtained for short duration rising tone glides and falling tone glides for normal hearing listeners in quiet and with varied levels of background, broadband noise. For signal durations 50 ms, or greater, pure tones were detectable at lower levels than were rising and falling tone glides; no level effects were observed. For signal durations less than 50 ms an interaction between background noise level, signal duration, and signal class was observed. The previously reported tendency for short duration rising glides to be detected at lower sound pressures than pure tones or falling tone glides appears to be unique to a limited range of noise levels (40–75 dB).
Vowel-to-vowel coarticulation in Catalan VCV sequences
Authors: Recasens Daniel
Published: October 2005

Electropalatographic and acoustical data on vowel-to-vowel (V-to-V) coarticulatory effects were obtained for Catalan VCV sequences, with the consonants representing different degrees of tongue-dorsum contact (dorsopalatal approximant [j], alveolo-palatal nasal [ν], alveolo-palatal lateral [Y], and alveolar nasal [n]). Results show that the degree of V-to-V coarticulation in linguopalatal fronting and F2 frequency varies monotonically and inversely with the degree of tongue-dorsum contact, carryover effects being larger than anticipatory effects. The temporal extent of coarticulation also varies with the degree of tongue-dorsum contact, much more so for anticipatory effects than for carryover effects. Overall, results indicate that V-to-V coarticulation in VCV sequences is dependent on the mechanical constraints imposed on the tongue dorsum to achieve dorsopalatal closure during the production of the intervening consonant. Moreover, anticipatory effects, but not carryover effects, involve articulatory preprogramming.
Signaling along elastic plates with wideband acoustic pulses
Authors: Barger James E.
Published: October 2005

High data-rate signaling with acoustic pulses along an elastic plate is made difficult by the conversion of a transmitted pulse into many component pulses that arrive separately during a time span that can exceed the travel time of the first component pulse to arrive. In addition, the amplitude of the received signals fluctuates widely with changes in pulse center frequency. But to obtain high data-rate signaling, many pulses with different center frequencies must be transmitted at closely spaced time intervals. It is important in these circumstances to understand the principal features of the component pulses that originate from a single transmitted pulse. This paper derives analytical expressions for the arrival times, the peak envelope amplitudes, and the center frequencies of the arriving component pulses that are transmitted by wideband line forces acting normal to the plate surface. Each component pulse is the manifestation of a different mode of propagation. By carefully picking the bandwidth and center frequency of the launching pulse, the number of its component pulses (or, alternatively, excited modes) that have significant amplitude can be minimized, if the pulse center frequency is low enough. If the frequency is high enough, so that more than about six propagating modes can exist, then the number of arrivals cannot be reduced significantly. At higher frequencies, several of the modes merge to form the Rayleigh wave, which is centered within both earlier and later modes. A series of photographs show how transmitted Gaussian pulses look when the pulse center frequency is picked to illustrate three regimes; where the Rayleigh wave is not formed; where it is partially formed; and where it is fully formed.
Reconstructing spatially incoherent random sources in the nearfield: Exact inversion formulas for circular and spherical arrays
Authors: Norton Stephen J. , Linzer Melvin
Published: October 2005

We consider the inverse problem for a two-dimensional, spatially incoherent random source. Under these assumptions, we show that an exact inversion formula can be derived for recovering the source spectral intensity, as a function of position, from nearfield measurements of the emitted radiation recorded on the circumference of a circle enclosing the source region. Although solutions to the inverse random source problem have been reported in the past, these results have almost always employed farfield approximations. After deriving the inversion formula in two dimensions, we discuss an efficient method for numerically evaluating this formula using the fast Fourier transform algorithm. Finally, a generalization of the inverse problem to a three-dimensional source enclosed by a spherical recording surface is given.
The propagation of sound through a gas with an overpopulation of excited states
Authors: Shields F. Douglas
Published: October 2005

Calculations have been made which predict sound amplification under certain conditions when propagated through a gas with an overpopulation of vibrationally excited states. Three metastable states have been analyzed, where the vibrational temperature is varying slowly on the scale of the sound period. The first is that of a long-lived vibrational mode in a diatomic gas. Calculations were made for N2, CO, O2, and Cl2. The second is that of a fast v–v exchange followed by a slow v–t. Calculations were made for CD4 as an example of this situation. And the third is that of a slow v–v followed by a fast v–t. Calculations were made for a mixture of N2/CO2/He as an example of this situation. Some of the difficulties in experimentally observing the gain are discussed.
An assessment of second-order perturbation theory for scattering of sound by hard, statistically rough surfaces
Authors: Tolstoy A. , Berman D. , Diachok O. , Tolstoy I.
Published: October 2005

Perturbation theory and boss models for rough surface scattering are compared for the case of a surface bossed with oblate hemispheroids (height a≤radius b). In particular, the surface consists of identical, hard, hemispheroidal bosses sparsely and independently distributed on a hard plane by means of a uniform probability law. To apply perturbation theory we compute the surface correlation function, operate on that function, and compute an effective boundary admittance. Finally, we compare that admittance with (farfield) near-exact results for hemispherical bosses and for oblate hemispheroidal bosses. Calculations of the magnitude of the reflection coefficient ‖R‖ are presented showing that for low frequencies, i.e., kb=0.1, the discrepancy is approximately 70% for a=b but less than 10% for a/b=0.1. In general, the error decreases as grazing angle increases and decreases as a→0. Thus, at low frequencies perturbation theory is shown to give excellent results for ‖R‖ when a/b≪1, despite the discontinuous and infinite slope in the surface where the bosses meet the base plane. We also examine the effects of increasing frequency for hemispherically bossed surfaces, and in particular, we see errors as large as 3 dB for sparse, hemispherical bosses with a=b=5 m and frequencies less than 60 Hz. We conclude that perturbation theory is excellent in the case of oblate hemispheroids, shows significant percentage errors for hemispheres and should not be used for prolate hemispheroids.
Resonance response of submerged, acoustically excited thick and thin shells
Authors: Gaunaurd G. C. , Werby M. F.
Published: October 2005

We study the elastodynamic spectral response of thick and thin shells in water when they undergo resonance scattering caused by the incidence of sound waves that impinge upon them at selected aspects. All the shells considered are elastic, air-filled, and of cylindrical and prolate spheroidal shapes. Their thickness is intentionally varied three orders of magnitude from very thick (i.e., h≡1−b/a=90%) to very thin (i.e., h=0.1%), so that the effects of shell stiffness on their scattering behavior can be quantitatively analyzed and understood. The quantities a and b are the outer and inner shell radii, respectively. Material composition effects are studied by comparing various metals such as steel and aluminum. The shell motions are described by the exact equations of elastodynamics in all cases, so that comparisons may be drawn concerning the regions of applicability of pertinent shell theories. For the spheroidal shells no exact solution is possible, thus, we have presented results based on an extended T-matrix method that still makes use of the exact 3-D equations of elastodynamics to describe the shell vibrations.

For a wide range of shell thicknesses and compositions, we have computed the positions of the poles of the scattering amplitudes, in the complex frequency plane x1. Here, x1 is k1a, where k1=ω/c1, ω is the angular frequency of the incident wave, c1 is the sound speed in the outer medium, and a is the shell’s outer radius. These poles group themselves in certain families and give rise to surface waves that circumnavigate the shell, either in the water side (Franz or SEM-type poles or waves) or inside the shell metal (Rayleigh/whispering gallery waves for solid bodies, or Lamb momentless and flexural waves for shells). This latter set of waves is the least attenuated and the most dominant. We have shown how the pole families affect the spectral shape of the form function, and that of it’s partial waves, with their interacting modal backgrounds and resonances. As the shells become thinner, only one-pole family is shown to remain within the displayed boundary of the complex x1 plane. This single-pole family becomes responsible for the generation of the first-order set of symmetric/antisymmetric Lamb waves in the shell. All these concepts are illustrated with many examples which show the crucial importance of the pole-position diagrams to understand the spectral behavior of the form function, and the way it reveals information about the shell and the types of waves it supports on its surfaces. A transition from the rigid to the soft background is observed as the shells become very thin, and it is used to properly isolate the resonances of very thin shells. Extensions of these spectral results to the time domain are forthcoming.
Sound transmission loss: Comparison of conventional techniques with sound intensity techniques
Authors: Halliwell R. E. , Warnock A. C. C.
Published: October 2005

Sound transmission losses for a single layer wall are measured in a reverberation room facility using conventional methods (ASTM E90) and the more recently introduced sound intensity method. The specimen is placed in five positions in the tunnel between the two reverberation rooms and measurements are made for four different absorptive conditions in the smaller room. Significant differences between the two measurement techniques are found at low frequencies and at high frequencies. Low-frequency differences are attributed partly to the increase in sound energy close to the surfaces of the receiving room (the Waterhouse effect) and the lack of any consideration of this in standard test methods. Inclusion of the Waterhouse term in the conventional transmission loss formula improves the agreement between the conventional and the sound intensity measurement technique at low frequencies. High-frequency differences are not explained.
Intonation in text-to-speech synthesis: Evaluation of algorithms
Authors: Akers Glenn , Lennig Matthew
Published: October 2005

Two algorithms, termed schematic and naturalistic, for generating intonation contours in an English text-to-speech system are compared by eliciting preference judgments from a total of 21 subjects. The major problem for both algorithms, but especially for the schematic algorithm, has to do with accent assignment and with the determination of the intonation phrase rather than with the phonetic realization of accent through manipulation of F0. Due to parser errors, phrase boundaries are incorrectly identified in 30% of the sentences used in the three experiments. Moreover, the naturalistic algorithm uses a grammatical part-of-speech hierarchy which ranks nouns higher than verbs. Therefore, incorrect classification of verbs as nouns (the major classification error) results in an unintended accent. The results indicate that accent assignment and phrase determination are the primary areas requiring improvement in order to further increase the naturalness of synthetic speech intonation.
An open tube technique for the measurement of acoustic parameters of porous absorbing materials
Authors: Dunlop John I.
Published: October 2005

A new method of measuring the acoustic parameters of porous materials is described. The method is based on the measurement of radiation impedance at the end of an open flanged pipe placed against a sample. Five samples of polystyrene foam of differing porosities have been used to assess the usefulness of the method. The acoustic characteristics of the samples were first determined using a conventional acoustic impedance tube with rigid end cap. Estimates of the acoustic parameters of the samples—sound speed and attenuation constant—were then obtained by applying various acoustic models to match the measured characteristics. Open tube measurements were then made on the samples and these impedance characteristics compared with those predicted by application of acoustic models. Moderately good agreement was obtained between measured and predicted impedance although the values of acoustic parameters derived deviated from those obtained from the closed tube measurements. The results confirm the potential of the method to be developed into an alternative method of measurement of acoustic absorptivity.