bluuebunny/crossref_metadata_2025 huggingface dataset:
Spectrum of delay fluctuations in single-path underwater transmission over a range of 43 nmi
Authors: Gant E. H. , Worley R. D.
Published: October 2005

Two single-path transmission experiments were performed, one at 450 Hz and one at 400 Hz, to measure the spectrum of the fluctuations in acoustic travel-time difference between two receivers. In the first, a source on the ocean bottom 15 000 ft deep transmitted a pulsed cw signal to two bottomed receivers spaced 4300 ft in line with the source 19 nmi away. Large low-frequency fluctuations were found in the arrival-time difference between the two receivers. The energy in the spectrum of these fluctuations peaked around 0.2 to 0.7 cycles/h; it corresponded to a rms fluctuation in relative delay of about 1 ft. The second experiment used the same receivers to examine more rapid fluctuations, with a source suspended at 1200 ft depth 43 nmi away. In this case the results showed an additional peak in the fluctuation spectrum around 0.1 Hz. The energy in these fluctuations corresponded to a rms variation in acoustic path length difference of 0.11 ft. The faster fluctuations are ascribed to reflections from the undulating ocean surface. The slower ones are believed due to slow changes in the sound-speed profile.
Average excess attenuation during sound propagation from an isotropic source above grassland
Authors: Soom Andres , Gu Ron–Ren
Published: October 2005

Measurements of sound attenuation from an isotropic source have been made over a meadow at propagation ranges between 15 to 300 m and for source and receiver heights within 3 m of the ground. Approximately 750 measurements were made at more than 70 source–receiver geometries under essentially constant ground conditions. The sound source was driven by a pseudo-random binary sequence signal giving a discrete spectrum in the 100- to 2500-Hz frequency range. The received signal was analyzed and averaged using Fast Fourier Transform techniques in narrow bands of 3 Hz. A separate measurement of the free-field source levels allowed excess attenuation to be relatively unambiguously calculated from the measured data. The surface used in the tests appears to have a boundary impedance different from grasslands studied by previous investigators. However, the interference phenomenon between direct and ground-reflected waves, as modified by meteorological factors remains a major feature of the results, often producing excess attenuations of 20 to 30 dB. The effects of propagation range, source height, receiver height, and vector wind in determining excess attenuation are presented in detail. It is evident from the data that the theory of a simple source radiating into a quiescent, isothermal medium above an impedance plane often cannot be used to accurately predict average attenuation to distances much beyond 50 m from the source. Finally, it is shown that the method of averaging propagation data can significantly alter the apparent results.
Cylindrical waves in transversely isotropic media
Authors: White J. E. , Tongtaow Chalermkiat
Published: October 2005

Because of fine layering, many sedimentary rocks can be characterized as transversely isotropic, possessing an axis of symmetry perpendicular to the layering. The many kinds of measurements made in fluid-filled holes drilled parallel to this axis prompted this study of axisymmetric cylindrical waves. The literature shows how such waves in an isotropic solid can be expressed in terms of a compressional potential or a shear potential. This paper shows that in a transversely isotropic medium, particular combinations of these potentials are needed simultaneously, yielding either a quasi-compressional wave or a quasi-shear wave. The expressions are used to compute the transient response of an acoustic logging tool. The speeds of refracted compressional and shear waves agree with the speeds of plane waves traveling along the axis of symmetry. Dispersive waves in the fluid annulus yield further information about the elastic constants of the solid. The potentials also portray the radiation of elastic waves from a point force or from a transducer on the surface.
Diffraction by a hard–soft barrier
Authors: Kendig Robert P. , Hayek Sabih I.
Published: October 2005

An analytical solution for the diffraction by a half-plane is given for a plane-wave incidence and a point source. One surface of the half-plane has a hard impedance (rigid) and the other has a soft impedance (pressure release). The solution is obtained by function theoretic methods and has a simple form in marked contrast to those obtained by the Wiener–Hopf technique. A null in the diffracted field was shown to exist as a function of the source location. In general, the diffracted field tended to resemble that of a soft–soft half-plane in the half-space adjacent to the soft face and resembles that of a hard–hard half-plane in the other half-space.
Acoustic transients from planar axisymmetric vibrators using the impulse response approach
Authors: Stepanishen Peter R.
Published: October 2005

A generalized impulse response approach is developed to evaluate the transient pressures which result from a general time dependent axisymmetric velocity of a planar vibrator, e.g., a membrane, plate, or disk transducer. The approach, which is based on expressing the velocity distribution in terms of a set of radial orthonormal functions, leads to the pressure being expressed as a sum of convolution integrals which involve the time dependent coefficients of the orthonormal functions and generalized impulse responses. As a specific case of interest and importance, the generalized impulse response is developed for a radiator in which the orthonormal functions are zeroth-order Bessel functions of the first kind. A series representation for the impulse response as a function of an arbitrary spatial wavenumber is obtained via the use of the addition theorem for Bessel functions. Finally, some numerical results are presented to illustrate the effect of a nonuniform spatial velocity on the on-axis nearfield pressures of a pulsed radiator.
Auditory filter shapes derived in simultaneous and forward masking
Authors: Moore Brian C. J. , Glasberg Brian R.
Published: October 2005

In this paper we describe a method for comparing frequency selectivity in simultaneous and forward masking. The method is designed to eliminate off-frequency listening, which may have had a confounding influence in earlier studies. Thresholds for 1-kHz sinusoidal signals were measured as a function of the width of a spectral notch, centered at 1 kHz, in a noise masker. In experiment I thresholds were measured in forward masking for signal durations of 5, 15, and 45 ms, with a noise spectrum level of 40 dB SPL/Hz. Thresholds decreased with increasing notch width for all signal durations. However, the change was more gradual at longer signal durations. This is consistent with a model in which the process of decay of masking follows the auditory filter. For each signal duration, threshold was also measured as a function of the level of a noise without a spectral notch. Each signal threshold for the notch-noise condition was then expressed as the level of a flat-spectrum noise which would give the same masking. When transformed in this way, the data for the three signal durations coincide, and can be interpreted in terms of the same auditory filter. In experiment II the 5-ms signal, whose level was fixed, followed the masker with delays of 5, 15, or 25 ms. The noise spectrum level was varied to find threshold. The change in threshold with notch width was independent of signal delay, confirming that the process of decay of masking follows the auditory filter. Experiment III showed that short-term spectral changes produced by differences in the shapes of the envelopes of signal and masker did not influence the results. In experiment IV thresholds for a 5-ms signal were measured in simultaneous and forward masking, both for a fixed noise level and for a fixed signal level. The derived auditory filters are similar for the two types of measure for each type of masking. However, the auditory filters derived in forward masking have bandwidths 17% smaller and slopes 48% greater than those in simultaneous masking. The differences between simultaneous and forward masking are interpreted in terms of suppression.
Measurement of the acoustic input immittance of the human ear
Authors: Rabinowitz William M.
Published: October 2005

A method is presented for measuring acoustic immittance (admittance or impedance) in the human ear canal and its validity is demonstrated for frequencies from 62 Hz to 4 kHz. Special attention is given to estimating the residual ear-canal space between the eardrum and the tip of the measuring device; estimates were determined, in part, using immittances measured with static pressures applied in the ear canal. Immittance estimates at the eardrum are reported for four normal subjects. Below 500 Hz, the immittance is compliance dominated. Our averaged compliance equivalent to 0.70 cc agrees with that reported by others. From 1 to 4 kHz, the immittance is resistance dominated. Our resistance values exceed those generally reported previously; they are, however, similar to those of Mehrgardt and Mellert [J. Acoust. Soc. Am. 61, 1567–1576 (1977)] and to values suggested from analysis of other acoustical measurements on the external ear.
Physiological and psychophysical measures from humans with temporary threshold shift
Authors: Klein Alan J. , Mills John H.
Published: October 2005

Tuning curves and amplitude–intensity functions on wave I and wave V of the auditory-evoked brain stem response and psychophysical tuning curves were obtained from human subjects (N = 5) with noise-induced temporary threshold shift (TTS). All tuning curves were measured with the same stimuli. Maskers were pure tones presented simultaneously with the signal which was a 3.6-kHz tone pip. TTS was produced by a narrow-band noise centered at 2.6 kHz and presented at 86 dB SPL for 8 h. The maximum mean TTS was 28 dB and occurred at 3.5 kHz. Although intersubject variability of TTS was small, individual differences in other measurements were substantial. In some subjects, amplitudes of waves I and V decreased following the noise exposure with wave I typically being more affected, while in other subjects, little or no change in amplitude occurred. All tuning curves had wider response areas following noise exposure. In a given subject, changes in psychophysical and wave V tuning curves were similar and were less than changes measured for wave I. Recovery of tuning curves (low- and high-frequency side) to pre-exposure values required between 7 and 41 h depending upon the individual and preceded complete recovery of TTS.
Discrimination of voice onset time in infancy
Authors: Eilers Rebecca E. , Morse Philip A. , Gavin William J. , Oller D. Kimbrough
Published: October 2005

In an effort to determine whether infants can discriminate speech sounds on the basis of a single acoustic cue, timing onset of periodic voicing, two experiments were conducted employing synthetic speech sounds. Naturally produced syllable pairs were also used for comparison. In the first experiment infants evidenced discrimination of a naturally produced /ba/ versus /pa/ pair and a naturally produced /du/ versus /tu/ pair. In addition, infants discriminated a synthetic /ba/ versus /pa/ contrast that was cued by several acoustic differences in addition to timing onset of periodic voicing but failed to evidence an ability to discriminate a synthetic /du/ versus /tu/ contrast that contained flat first formants and differed only in timing onset of periodic voicing. A second experiment was conducted in which infants once again evidenced discrimination of naturally produced /du/ versus /tu/ stimuli but not of synthetic /du/ versus /tu/ stimuli containing slight first-formant transitions. These results suggest that timing onset of periodic voicing alone may not be a sufficient cue for infant discrimination of English voicing contrasts.
Recognition of vowels from information in fricatives: Perceptual evidence of fricative-vowel coarticulation
Authors: Yeni–Komshian Grace H. , Soli Sigfrid D.
Published: October 2005

Four studies investigated the perceptual effects of spectral variations in fricatives produced in different vowel contexts. The alveolar and palatal fricatives, [s, z, ℱ, z], were produced by two talkers in the context of the vowels [a, i, u], generating 12 fricative–vowel combinations. A computer-controlled editing procedure was used to excise fricative segments of 150-ms duration, as measured back from vowel onset. These excised segments were used as test stimuli in the four experiments. In the first experiment, fricative identification was highly accurate, especially for segments produced in the [a] context. The results of the subsequent three vowel identification experiments, revealed that the high vowels [i] and [u] were identified 60%–80% of the time in all fricative contexts, with the exception of [i] produced in the context of [ℱ]. In contrast, identification scores for [a] were close to chance in all fricative contexts. Acoustic analyses of the stimuli revealed that the fricative segments with high vowel identification scores exhibited clear evidence of spectral changes associated with the vowels, while those segments with the highest fricative identification scores exhibited spectra most similar to fricatives produced in isolation. These results, in combination with more extensive acoustic analyses [S. D. Soli, J. Acoust. Soc. Am. 70, 976–984 (1981)] are discussed in terms of variations in the articulatory compatibility of tongue movements required to produce fricative–vowel sequences.
Some results on lateral suppression obtained in a partial-masking lateralization paradigm
Authors: Bezemer A. W.
Published: October 2005

Results were reported of psychophysical forward-masking experiments using a lateralization method. A general interpretation of masking was given, considering masking to be the combined result of three different mechanisms: the overlap mechanism, the adaptation mechanism, and the suppression mechanism. The aim of this study was to demonstrate the use of the lateralization method in a masking experiment. Masking was measured in a band-widening experiment using a test tone frequency of 3 kHz, which is the center frequency of the masking noise. It was found that the effect of the suppression mechanism depends in a complex way on the difference between masker level and test tone level, as does the bandwidth at which maximum masking occurs. These level effects could be described qualitatively by means of nonlinear excitation patterns.
Asymptotic behavior of the N-wave solution of Burgers’ generalized equation for cylindrical acoustic waves
Authors: Enflo B. O.
Published: October 2005

Asymptotic solutions for large distances and for long times are found of Burgers’ generalized equation for a cylindrical wave when the boundary condition is an N-shaped (in the time variable) disturbance at a cylindrical surface. The solution is found to have a tail as in the case of linear waves. The amplitude of the faraway solution is determined by the condition that it should be consistent with a long-time solution, which matches a Taylor shock solution.
Effective lengths of parametric acoustic sources
Authors: Moffett Mark B. , Mellen Robert H.
Published: October 2005

Computations of effective virtual-source array lengths for parametric acoustic sources are presented. The effective length is defined as the distance from the primary projector where the difference-frequency source level is 1 dB different from (it may be greater or less than) the farfield value. For absorption-limited (i.e., low primary level) sources, the parameter, 2αreff (where α is the primary absorption coefficient and reff is the effective length), is plotted as a function of the single variable, 2αR0f0/f (where R0 is the Rayleigh length, f0 the primary frequency, and f the difference frequency). For 2αR0f0/f≲1, 2αreff∠1/2. For 2αR0f0/f≳1, 2αreff increases by an order of magnitude. As the primary level is increased, the parametric source becomes saturation-limited, and no such simple scaling exists. Results covering a range of useful cases are presented for reff/R0.
Elastic wave propagation in hexagonal honeycombs: I. Method of analysis and low-frequency characteristics
Authors: Park S. K. , Bertoni H. L.
Published: October 2005

Elastic waves propagating in honeycomb panels may be used to inspect for defects induced during manufacture or during use. In order to develop techniques for rapid inspection, it is necessary to know the properties of waves propagating in the honeycomb itself. Physically the wave consists of vibrations of the cell walls of the honeycomb, assuming the cells to be empty. Sensitive inspection would require the use of high frequencies where the wavelength is on the order of cell diameter. At high frequencies the periodic nature of the honeycomb must be accounted for. In this paper we develop a method for analytically finding the properties of Bloch waves propagating in a hexagonal honeycomb. Results presented here show that the honeycomb acts as an elastic continuum of hexagonal symmetry at low frequencies. Results showing the dispersive character of the propagation are given in a companion paper.
Refractive and other acoustic effects produced by a prism-shaped network of rigid strips
Authors: Amram Maurice , Stern Richard
Published: October 2005

We have investigated, on a scale model, the efficiency of an open, prism-shaped network of rigid strips to deflect long wavelength sounds incident normally, or at a slight angle, on the structure. Our experimental results, particularly at the low-frequency end of the noise spectrum, are well explained by a general theory, developed for microwave lenses, modified for acoustics, and extended to a larger domain of frequencies. Finally it is suggested that this prismatic array offers some possibilities as an obstacle to redirect low-frequency noises in directions harmless for populations.
Acoustic scattering from fluid spheres: Diffraction and interference near the critical scattering angle
Authors: Marston Philip L. , Kingsbury Dwight L.
Published: October 2005

We consider the scattering of plane waves from an inviscid fluid sphere of sound speed ci and density ρi imbedded in a fluid with a sound speed c0<ci and a density ρ0≊ρi. Naive application of ray acoustics predicts that the derivative of the modulus of the form function f has an unphysical divergence as the scattering angle φ approaches a critical scattering angle φc and that with φ<φc, the surface reflectivity is unimodular with a phase advancement. A divergence-free model is given here which is analogous to the physical-optics approximation in ’’Scattering by a bubble in water near the critical angle: Interference effects’’ [P. L. Marston and D. L. Kingsbury, J. Opt. Soc. Am. 71, 192–196 (1981)]. The model uses rays to construct virtual waves at the scatterer; the waves diffract to the farfield. To test the model, a modified algorithm for Mie scattering summed the exact series for f with ka as large as 10 000 (a = sphere radius, k = 2π/λ, λ = wavelength). When φ<φc, interference and diffraction cause a coarse structure in the scattering with a quasi-period ≲(λ/a)1/2; the main features of this structure in the exact result are described by the model provided ka≳25. There is also a fine structure of quasi-period ≊λ/a rad. Some effects of attenuation and tunneling are described.
Continuous waves generated by focused radiators
Authors: Madsen Ernest L. , Goodsitt Mitchell M. , Zagzebski James A.
Published: October 2005

A single integration technique for calculating the pressure distribution in the field of a focused sinusoidally oscillating radiator is described. This technique involves the direct closed form integration of one of the integrals in the Rayleigh formula; the latter formula itself contains a double integral corresponding to integration over the area of the source transducer face. Precise experimental measurements of a hydrophone’s response to the pressure field generated by a focused medical diagnostic transducer are also reported, and comparison between experiment and theory is made. Very good agreement between theory and experiment is demonstrated with respect to both amplitude and phase for lateral beam profiles at six different distances from the source transducer. At a seventh distance (about 1 cm from the source transducer) much more violent fluctuations in the response are observed than result from the theory.
A limiting form for the nearfield of the baffled piston
Authors: New Ronald , Becker Ronald I. , Wilhelmij Paul
Published: October 2005

Formulations for the circular piston on the plane, infinite, rigid baffle, and the pulsating sphere are fundamental (if not classic) problems in acoustic radiation theory. Those who work in the area of radiation and scattering are very familiar with the solutions to these two problems. The solution to a somewhat more difficult problem—the radially vibrating polar cap on an otherwise rigid sphere—is also available, and is well documented. Although it is mathematically difficult to prove, the general solution to the polar cap problem reduces to that of the pulsating sphere in one limiting form, and to that of the piston on the baffle in another. This notion—that the solution to the polar cap problem subsumes the solutions to the two classic radiation problems of linear acoustics—is instructive and useful. Its significance is in the use of the general solution of the polar cap problem to generate a convergent infinite series solution for the nearfield of the piston on the baffle. Extensive computations have been performed in limiting cases to demonstrate this convergence.
Effects of stimulus level on perception of two acoustic cues in speech
Authors: Van Tasell Dianne J. , Crump Elizabeth S. A.
Published: October 2005

Normal-hearing subjects identified tokens from two synthetic syllable continua in terms of stop consonant voicing and place of articulation. Each continuum was presented at both 60 and 100 dB SPL. Different effects of stimulus level were observed for the two sets of stimuli. For the voicing continuum, the phonetic boundary shifted to indicate more ’’voiceless’’ responses at the higher levels. For the place series, all syllables were identified less consistently at the higher level. Implications are discussed for comparing the speech-cue identification performance of normal versus hearing-impaired subjects who must listen at high levels.
More notes on reflection from a corrugated surface
Authors: LaCasce E. O.
Published: October 2005

Some comments are made on the experiments of LaCasce and Tamarkin. Some data at 20° is made available.
A scheme to predict the sound pressure radiated from an automotive exhaust system
Authors: Prasad M. G. , Crocker Malcolm J.
Published: October 2005

A general scheme to predict the sound pressure radiated from an automotive exhaust system is presented. The scheme is demonstrated with a step-wise computational procedure on a model system comprised of an electroacoustic driver source, an expansion chamber muffler, and a tailpipe radiating to free space. The predicted sound pressure level spectra agree well with the corresponding measured spectra for various test cases with zero mean flow. Also, studies are made of the theoretical effects of variations of the source impedance on the sound pressure radiated from the model system.
Random Rayleigh waves in viscoelastic media
Authors: Beltzer A. I.
Published: October 2005

The basic equations are derived which govern the propagation of random Rayleigh waves in isotropic viscoelastic solids. The particular cases of elastic and low-loss media are also considered. Since such wave sources as earthquakes or an evolution of material defects are random or incompletely known events, the results may have applications in seismology and nondestructive evaluation of materials.
Detection of spatially nonuniform ultrasonic radiation with phase sensitive (piezoelectric) and phase insensitive (acoustoelectric) receivers
Authors: Busse L.J. , Miller J.G.
Published: October 2005

An analysis is presented of the responses of a phase sensitive and a phase insensitive ultrasound receiver detecting a spatially nonuniform pressure distribution. The predicted output of each type of receiver is obtained numerically using a model of wave propagation based upon diffraction theory. Experimental verification of these predictions is obtained using a piezoelectric and an acoustoelectric receiver as a phase sensitive and a phase insensitive detector, respectively. Results are illustrated for transmission measurements of the frequency-dependent attenuation of an irregular plastic plate and for scattering measurements of the observed angular and spatial dependence of scattering from a pair of brass rods.
Calculation of the phase-structure function density from oceanic internal waves
Authors: Esswein Robert , Flatté Stanley M.
Published: October 2005

The phase-structure function is of importance in understanding statistical behavior of oceanic acoustic transmission, particularly temporal and spatial coherence. Techniques for calculating the contribution to the phase-structure function density from a spectrum of oceanic internal waves are presented. Methods employed include power series expansion, asymptotic expansion, and global approximations.
Noise attenuation characteristics for supra-aural audiometric headsets using the models MX–41/AR and 51 earphone cushions
Authors: Michael Paul L. , Bienvenue Gordon R.
Published: October 2005

Continuing problems with the consistency of the MX–41/AR earphone cushion’s physical and acoustical characteristics have led to the development of a one-piece cushion (model 51) by the Telephonics Corporation. The attenuation characteristics of this one-piece cushion have been measured according to ASA Standard 1–1975 (ANSI S3.19–1974) and are reported herein. The attenuation characteristics provided for the wearer by the model 51 cushions tend to be slightly greater than those of the MX–41/AR cushion but the differences are not generally significant, with α = 0.05.
Experiments on the intelligibility of low-frequency speech codes
Authors: Allen Donald R. , Strong William J. , Palmer E. Paul
Published: October 2005

The intelligibility of unprocessed and of low-pass filtered speech was compared to that of speech processed using three versions of an all-harmonic code consisting of many harmonic sinusoids, a largest harmonic code consisting of four harmonic sinusoids closest to the formants, and a formant code consisting of three sinusoids scaled from the formant frequencies. Fundamental frequency and formant frequencies were scaled down in frequency by different amounts in the various codes. Normal-hearing subjects were tested on three different types of tests. The Diagnostic Rhyme Test (DRT) was used on the two speech varieties and on codes that were not frequency lowered, a Diagnostic Discrimination Test (DDT) was used on frequency-lowered speech codes, and a prosodic test was run on all versions of the speech and speech codes. Results of each test are presented and compared for the various talker, speech, and speech-code combination; they show that the low-pass-filtered speech was always more intelligible than any low-frequency speech code tested.
Identification of vowels in and out of context
Authors: Howell Peter
Published: October 2005

Vowels presented in consonant context are identified better than vowels presented in isolation. This finding has been interpreted as evidence that articulatory knowledge is used during the perception of speech. To test this interpretation the accuracy of identification of three synthetic stimulus sets was measured: diphthongs in isolation, in consonant context, and in a tonal context. Diphthongs were selected because they could be synthesized with identical F1 and F2 onset frequencies so that formant transitions would be the same for both diphthongs and would not provide differential information about how the sound would be articulated. Tones were used because they provide no information about articulation. Whether the contextual material preceded or followed, diphthongs in context were identified better than in isolation. In a third experiment the tone context also improved performance with real speech stimuli. It is concluded that differences in the accuracy of vowel identification with and without an acoustic context do not provide evidence that articulatory knowledge is used during vowel perception.
Dependence of level and phase of the (2f1−f2)-cancellation tone on frequency range, frequency difference, level of primaries, and subject
Authors: Zwicker Eberhard
Published: October 2005

From the comparison of competing methods, it is confirmed that the cancellation method yields meaningful and interpretable results. Using this method cancellation level and phase have been measured with up to six subjects as functions of the following variables: level L1 and L2 of the primaries, frequency difference Δf of the primaries, and frequency f1 of the lower primary for f1 = 540 and 1620 Hz, 4,8, and 10 kHz. For comparison with the literature additional data were obtained at f2 = 1 kHz. Using all the data several characteristic rules of the behavior of the cancellation tone can be extracted.
Reduction of individual sampling rates by generalizing quadrature methods of separate interpolation
Authors: Figueiras–Vidal Aníbal R. , Mariño–Acebal José B. , Lagunas–Hernández Miguel A. , García–Gómez Ramón
Published: October 2005

The limitations of sampling a bandpass signal at the (on the average) Nyquist rate and the possibility of equivalent low pass processing have stimulated research toward obtaining a separate interpolation for the in-phase and quadrature components of the signal. Known results are to sample at a half the Nyquist rate of these in-phase and quadrature components, or, under Brown’s condition, ω0 = kσ/2 (where ω0 and σ are the center angular frequency and the angular bandwidth of the signal, respectively, and k is an integer), to sample at the same rate the signal and its Hilbert transform or the signal and the signal delayed π/2ω0. Grace and Pitt [J. Acoust. Soc. Am. 44, 1453 (1968)] and Brown [IEEE Trans. Aerosp. Electron. Syst. AES–15, 366 (1979); J. Acoust. Soc. Am. 67, 1959 (1980)] have worked in the last direction, that has been generalized by the authors [Proc. First European Conf. Signal Proc., 197, Lausanne (1980)] to consider two general linear functionals of the signal. In this paper, the possibility of a further reduction of the sampling rate of the functionals maintaining a separate interpolation is shown: if we consider 2N linear functionals (with a certain restriction) and ω0 = kσ/2N (generalized Brown’s condition), an interpolation is possible from samples taken at 1/2N the Nyquist rate, and separation is obtained when N functionals have identically zero quadrature components of their impulse responses and the impulse responses of the other N functionals do not show in-phase components. Minimum oversampling rates required when generalized Brown’s condition fails are also discussed.
Optimum frequencies for noise-limited active sonar detection
Authors: Stewart James L. , Westerfield Everett C. , Brandon Marshall K.
Published: October 2005

The curves of optimum frequencies versus maximum range for active sonar detection under specific sets of assumptions are presented for the more recent expressions for attenuation given by Lovett [J. Acoust. Soc. Am. 58, 620–625 (1975)] for the eastern North Pacific and Thorp [J. Acoust. Soc. Am. 42, 270 (1967)] for the western North Atlantic as corrected at low frequencies by Kibblewhite et al. [J. Acoust. Soc. Am. 60, 1040–1047 (1976)].
Insertion loss studies on models of automotive exhaust systems
Authors: Prasad M. G. , Crocker Malcolm J.
Published: October 2005

Transmission loss, noise reduction, and insertion loss are the three main characteristics used to describe the performance of a muffler in an automotive exhaust system. Of these characteristics, insertion loss is the most useful. Unlike transmission loss and noise reduction, insertion loss is dependent on both source and radiation impedances. In this paper, source and radiation impedances were measured. The insertion loss of exhaust systems was predicted using theoretical values of radiation impedance and measured values of source impedance. Comparisons of predicted and measured insertion loss are given for various source and radiation conditions. So far the investigations are confined to an electroacoustic driver source and an expansion chamber muffler.
Analysis of an echo signal reflected from a weakly scattering volume by a discrete model of the medium
Authors: Ueda Mitsuhiro , Ichikawa Hiroshi
Published: October 2005

An echo signal reflected from a weakly scattering volume is analyzed by using the wave equation for an inhomogeneous medium and a discrete model of the medium. The discrete model means that the medium is represented by a pile of small cubes which have uniform density and sound velocity, and the size of the cubes is assumed to be much smaller than the wavelength of ultrasonic waves. By adopting the discrete model, simple and understandable relations are obtained from the wave equation for an inhomogeneous medium. The analysis shows that the difference between echo signals scattered by density and velocity fluctuations becomes appreciable when the distance between the scatterer and a transducer is less than a radius of the transducer. The difference was detected experimentally and shows rather good agreement with the theory. Furthermore, relations are obtained which describe echo signals resulting from an arbitrary incident wave in terms of the fluctuation of specific acoustic impedance of medium. These relations are valid in a region a little larger than a radius of the transducer from the transducer. Waveforms of the echo signal reflected from a rod made of silicone rubber are estimated by using the relations and are compared with experimentally obtained echo signals.
Comments on ’’Very low frequency (VLF) wind-generated noise produced by turbulent pressure fluctuations in the atmosphere near the ocean surface’’ [J. Acoust. Soc. Am. 66, 1499–1507 (1979)]
Authors: Cato Douglas H.
Published: October 2005

In a recent paper, Wilson claims to have corrected errors in the theory by Isakovich and Kur’yanov [Sov. Phys. Acoust. 16, 49–58 (1970)] of underwater noise from wind turbulence and to have used improved models of the sea surface waves, resulting in substantially different predictions of noise level. In fact, Wilson’s corrections appear to contain errors, mainly in the evaluation of an integral. While not commenting on the validity or otherwise of the assumptions used in the theories it is pointed out that a correct evaluation of the integral results in Wilson’s method predicting noise levels about 20 dB higher than actually presented by Wilson. Over the frequency range for which the surface wave models apply, the corrected predictions of Wilson are then much closer to those of Isakovich and Kur’yanov, and substantially higher than measurements presented by Wilson.
Rebuttal to ’’Comments on ’Very low frequency (VLF) wind-generated noise produced by turbulent pressure fluctuations in the atmosphere near the ocean surface’ ’’ by Douglas H. Cato
Authors: Wilson James H.
Published: October 2005

The author takes this opportunity to reply to Douglas H. Cato [J. Acoust. Soc. Am. 70, 1783–1784 (1981)].
Reply to comments by Filippi and Habault
Authors: Cole J. E. , Garrelick J. M.
Published: October 2005

The authors take this opportunity to reply to Filippi and Habault [J. Acoust. Soc. Am. 70, 1786–1788 (1981)].
An excitation-pattern model for intensity discrimination
Authors: Florentine Mary , Buus So/ren
Published: October 2005

This paper evaluates two different versions of Zwicker [Acustica 6, 365–381 (1956)] and Maiwald’s [Acustica 18, 193–207 (1967)] excitation-pattern model for intensity discrimination. The single-band version is that originally used by Zwicker and Maiwald. They assumed that performance was determined by the critical band in which the excitation grows most rapidly with increasing level of the stimulus. The multiband version forms an optimum decision based on information in all critical bands. Predictions from the two versions of the model are compared to data for intensity discrimination of tones as a function of level and frequency, for partially masked tones and for white noise. In general, the single-band version yields predictions in qualitative agreement, but not in quantitative agreement with the intensity-resolution data for pulsed tones. The multiband version yields predictions in good qualitative as well as quantitative agreement with the data, except at high frequencies.
Recognition of the Spanish fricatives /s/ and /f/
Authors: Gurlekian Jorge A.
Published: October 2005

The present work examines the role played by the amplitude of a fricative noise relative to the vowel /a/ in the identification of the fricatives /f/ and /s/. Synthetic fricative–vowel syllables were generated in which the fricative portion consisted of bandpass noise with a center frequency of 4500 Hz and a bandwidth of 500 Hz. The amplitude of the noise was varied through a set of ten values relative to a fixed vowel amplitude. Spanish and American speaking listeners identified syllables with low amplitude fricative noise as /fa/ and those with high amplitude as /sa/. In a second experiment, subjects were tested on the same stimuli at three different overall sound pressure levels for the vowels: 40, 60, and 80 dB SPL re 0.0002 dyn/cm2. At the 40- and 80-dB levels, subjects identified more sounds as /f/ than at the 60-dB level. The responses obtained at 80 dB SPL may be due to a differential masking effect of the vowel at different amplitudes.
Approximate formula of the averaged sound energy decay curve in a rectangular reverberant room
Authors: Tohyama Mikio , Yoshikawa Shokichiro
Published: October 2005

An approximate formula of the space and ensemble averaged reverberation decay curve in a rectangular reverberant room is derived here theoretically. This approximate decay curve is written by the summation of the decay curve in three (oblique, tangential, and axial) types of diffuse fields. This formula contains not only the averaged sound absorption coefficient of the walls but the number of resonance wave modes excited in a rectangular reverberant room. The sound energy distribution rate of three types of diffuse fields at the steady state is determined by the ratio of the number of resonance wave modes constituting each type of diffuse field.
Ultrasonic attenuation in single crystals of bismuth germanium oxide at low temperatures
Authors: Omotoso Elias A. , McCarthy Kathryn A.
Published: October 2005

The ultrasonic attenuation of longitudinal acoustic waves in single crystals of bismuth germanium oxide has been measured over a temperature range from 4.2° to 78 °K, using the pulse-echo technique. The frequency range of the impressed phonons was from 10 to 70 MHz. Measurements have been made for phonons propagated along the [100], [110], and [111] crystallographic axes of the specimens. Analysis of the experimental results indicates that the attenuation can be accounted for entirely by the relaxation interaction of mobile charge carriers with the longitudinal electric fields of piezoelectric origin, which accompany the stress waves in the crystal. Based on this analysis, the electromechanical coupling constants obtained from the attenuation data are an order of magnitude smaller than the previously reported values.
The acoustic environment of ring BOB
Authors: Vastano Andrew C. , Olson Donald B. , Vastano John A.
Published: October 2005

The sound-speed distribution in ring BOB present during cruise 011 of r/vendeavor (July–August 1977) has been examined on the basis of CTD and XBT observations. Sound-speed values for the XBTs have been computed utilizing a regression analysis for salinity on the hydrographic data and Wilson’s sound-speed formula. In addition to the characteristic low sound-speed lens associated with the ring core, the resolution obtained with the XBT observations has revealed a near-surface high sound-speed halo, surrounding the core, in the region of the encircling Gulf Stream remnant. The halo is present between the depths of 50 to 150 m and represents a deviation of approximately 20 m/s relative to ring center at 100 m. The azimuthal deviations of sound speed from circular symmetry are presented in terms of observations taken on cruise 008 of r/vendeavor (May 1977). These perturbations are related to quasi-geostrophic wave structures within the ring which may be stationary or rotate around the ring. The high sound-speed halo, low speed lens, shape perturbations, and translation generate a complex acoustic environment within cyclonic rings.
An example of ocean acoustic multipath identification at long range using both travel time and vertical arrival angle
Authors: Worcester Peter F.
Published: October 2005

A phase-coded signal with 62.5-ms time resolution was transmitted for a 22-day period between an acoustic source moored at 1375-m depth and an autonomous acoustic receiver moored at 1333-m depth and at 215-km range. The receiver consisted of a four-element vertical array with 1.5 wavelengths between elements. Three strong arrivals were observed. Excellent agreement was obtained between measured and predicted arrival patterns, including both arrival times and arrival angles. The first two arrivals were predicted by geometric ray theory; the third arrival was nongeometric and associated with a caustic 400 m above the receiver.
Thermodynamic corrections to the velocity of propagation in a bubbly medium
Authors: Floyd Edward R.
Published: October 2005

Corrections due to two additional thermodynamic degrees of freedom innate to bubbles are determined and applied to Wood’s equation for the velocity of propagation in a bubbly medium.
Application of the
Synechococcus nirA
Promoter To Establish an Inducible Expression System for Engineering the
Synechocystis
Tocopherol Pathway
Authors: Qi Qungang , Hao Ming , Ng Wing-on , Slater Steven C. , Baszis Susan R. , Weiss James D. , Valentin Henry E.
Published: October 2005

Tocopherols are important antioxidants in lipophilic environments. They are synthesized by plants and some photosynthetic bacteria. Recent efforts to analyze and engineer tocopherol biosynthesis led to the identification of
Synechocystis
sp. strain PCC 6803 as a well-characterized model system. To facilitate the identification of the rate-limiting step(s) in the tocopherol biosynthetic pathway through the modulation of transgene expression, we established an inducible expression system in
Synechocystis
sp. strain PCC 6803. The
nirA
promoter from
Synechococcus
sp. strain PCC 7942, which is repressed by ammonium and induced by nitrite (S.-I. Maeda et al., J. Bacteriol. 180:4080-4088, 1998), was chosen to drive the expression of
Arabidopsis thaliana p-
hydroxyphenylpyruvate dioxygenase. The enzyme catalyzes the formation of homogentisic acid from
p-
hydroxyphenylpyruvate. Expression of this gene under inducing conditions resulted in up to a fivefold increase in total tocopherol levels with up to 20% of tocopherols being accumulated as tocotrienols. The culture supernatant of these cultures exhibited a brown coloration, a finding indicative of homogentisic acid excretion. Enzyme assays, functional complementation, reverse transcription-PCR, and Western blot analysis confirmed transgene expression under inducing conditions only. These data demonstrate that the
nirA
promoter can be used to control transgene expression in
Synechocystis
and that homogentisic acid is a limiting factor for tocopherol synthesis in
Synechocystis
sp. strain PCC 6803.
Mycobacterial Ecology of the Rio Grande
Authors: Bland Christopher S. , Ireland Jamie M. , Lozano Eduardo , Alvarez Maria E. , Primm Todd P.
Published: October 2005

This is the first study to characterize the environmental conditions which contribute to the presence and proliferation of environmental mycobacteria in a major freshwater river. Over 20 different species of environmental mycobacteria were isolated, including the pathogenic
M. avium
and
M. kansasii
. Species of the rapidly growing
M. fortuitum
complex were the most commonly isolated mycobacteria, and one-third of all isolates were not identified at the species level, even by 16S sequencing. PCR restriction analysis of the
hsp65
gene was more accurate and rapid than biochemical tests and as accurate as yet less expensive than 16S sequencing, showing great promise as a new tool for species identification of environmentally isolated mycobacteria. Total environmental mycobacteria counts positively correlated with coliform and
Escherichia coli
counts and negatively correlated with chemical toxicity and water temperature. Environmental mycobacteria can survive in the alkaline conditions of the river despite previous reports that especially acidic conditions favor their presence. A representative river isolate (
M. fortuitum
) survived better than
E. coli
O157:H7 at pHs below 7 and above 8 in nutrient broth. The river strain also retained viability at 8 ppm of free chlorine, while
E. coli
was eliminated at 2 ppm and above. Thus, in vitro studies support environmental observations that a variety of extreme conditions favor the hardy environmental mycobacteria.
Directed Evolution of a Thermostable Phosphite Dehydrogenase for NAD(P)H Regeneration
Authors: Johannes Tyler W. , Woodyer Ryan D. , Zhao Huimin
Published: October 2005

NAD(P)H-dependent oxidoreductases are valuable tools for synthesis of chiral compounds. The expense of the cofactors, however, requires in situ cofactor regeneration for preparative applications. We have attempted to develop an enzymatic system based on phosphite dehydrogenase (PTDH) from
Pseudomonas stutzeri
to regenerate the reduced nicotinamide cofactors NADH and NADPH. Here we report the use of directed evolution to address one of the main limitations with the wild-type PTDH enzyme, its low stability. After three rounds of random mutagenesis and high-throughput screening, 12 thermostabilizing amino acid substitutions were identified. These 12 mutations were combined by site-directed mutagenesis, resulting in a mutant whose
T
50
is 20°C higher and half-life of thermal inactivation at 45°C is >7,000-fold greater than that of the parent PTDH. The engineered PTDH has a half-life at 50°C that is 2.4-fold greater than the
Candida boidinii
formate dehydrogenase, an enzyme widely used for NADH regeneration. In addition, its catalytic efficiency is slightly higher than that of the parent PTDH. Various mechanisms of thermostabilization were identified using molecular modeling. The improved stability and effectiveness of the final mutant were shown using the industrially important bioconversion of trimethylpyruvate to
l
-
tert
-leucine. The engineered PTDH will be useful in NAD(P)H regeneration for industrial biocatalysis.
Integrated Recombinant Protein Expression and Purification Platform Based on
Ralstonia eutropha
Authors: Barnard Gavin C. , McCool Jesse D. , Wood David W. , Gerngross Tillman U.
Published: October 2005

Protein purification of recombinant proteins constitutes a significant cost of biomanufacturing and various efforts have been directed at developing more efficient purification methods. We describe a protein purification scheme wherein
Ralstonia eutropha
is used to produce its own “affinity matrix,” thereby eliminating the need for external chromatographic purification steps. This approach is based on the specific interaction of phasin proteins with granules of the intracellular polymer polyhydroxybutyrate (PHB). By creating in-frame fusions of phasins and green fluorescent protein (GFP) as a model protein, we demonstrated that GFP can be efficiently sequestered to the surface of PHB granules. In a second step, we generated a phasin-intein-GFP fusion, wherein the self-cleaving intein can be activated by the addition of thiols. This construct allowed for the controlled binding and release of essentially pure GFP in a single separation step. Finally, pure, active β-galactosidase was obtained in a single step using the above described method.