bluuebunny/crossref_metadata_2025 huggingface dataset:
Bearing Errors Inherent in the Use of Passive Sonar Arrays
Authors: Nitsche J. R. , Waters J. F.
Published: October 2005

Bearing errors associated with passive sonar systems are identified and estimated. Bearing errors due to horizontal sound speed gradients, nonhorizontal incidence of acoustic rays at the receiver, quantization of measured bearings, and uncertainties in receiver headings are considered. Bearing errors due to nonhorizontal angles of incidence are found to be most serious. A statistical analysis is performed to determine the likelihood of receiving an acoustic ray from a sonar target at a particular vertical (depression/elevation) angle of incidence. Several acoustic propagation models are used in conjunction with the derived probability density distribution of received vertical angles to determine typical values of the acoustic ray depression/elevation angles incident on the sonar receiver. Depending on the assumed sound speed profile, the vertical angles of incidence range from 6° to 13°. The sonar bearing errors due to these vertical angles of incidence range from 1° for a target at an actual relative bearing of 60° (or 120°), to 15° for a target at an actual relative bearing of 0° (or 180°). Finally, a method whereby these bearing errors can be eliminated by making deliberate changes in the heading of the sonar array is described.
Application of Love Waves to Object Location and Measurement in the Sea Bottom
Authors: Hudimac A. A. , Welsh R. , Koopmann G.
Published: October 2005

A suitable stratified ocean bottom will propagate a Love wave. Bemuse it is a pure shear wave with particle motion parallel to the surface of the bottom, very little acoustic energy leaks into the water in the case of uniform strata. If an object is buried in the bottom, some of the scattered waves are coupled to the water; a hydrophone towed in the sea can thus localize the position of the object. Tests with a laboratory model will be described which demonstrated the validity of this concept. Dispersion curves were also measured experimentally. A least-squares technique was used to fit the theoretical dispersion curve (for the given model) to the data, thus determining the constitutive parameters of the model. This technique can be used for making in situ measurements of the properties of the sea bottom, particularly the shear modulus. [This work was supported under contracts.]
Measurement of the Dynamic Stiffness and Loss Factor of Elastic Mounts as a Function of Static Load
Authors: Ver I. L.
Published: October 2005

The dynamic stiffness of a number of elastic mounts commonly used in floating floor applications was measured as a function of the static load. The paper reports on the measurement method and on the measured data obtained. The measurements indicated that the dynamic stiffness for cork, neoprene, and precompressed glass fiber mounts increases with increasing static load. The dynamic stiffness was found to be independent of frequency in the region of from 20 Hz to 2 kHz. An inspection of the static-load deflection curves indicated that the tangent of the static-load deflection curves does not agree with the measured dynamic stiffness, the latter being 2 to 3 times larger. [The work was supported by the Korfund Dynamics Corporation.]
Response of a Cylindrical Shell to Localized Direct Radiation
Authors: Khabbaz Ghassan R.
Published: October 2005

During high-velocity motion of a space vehicle, oscillating shock waves may form in regions of structural discontinuities, such as at flares. These oscillating shock waves cause high intensity pressure regions. Acoustic horns placed circumferentially around the shroud at a fixed axial location are used to produce a high pressure region simulating the effect of oscillating shock waves. The shroud is modeled as a circular cylindrical shell. The horns are placed at one end of the cylinder and are evenly spaced around the circumference. One-third octave power spectral densities for the radial deflection and acceleration have been derived in a closed form. A computer program has been developed and the following points investigated: (1) effect of longitudinal size of the horns on the radial acceleration; (2) effect of circumferential size of the horns on the radial acceleration; and (3) longitudinal variation of the radial acceleration with frequency and the size of the horns. The results are presented in a series of curves.
Separation of Multipath Energy in Dispersive Media
Authors: Weiss Robert
Published: October 2005

The usefulness of determining the noise path of flexural waves by means of cross-correlation techniques is demonstrated. In particular, this paper presents theoretical and experimental results which demonstrate that if the cross-power spectral density function is transformed by use of a Fourier transform in terms of Tf (where T is the time lag and f is the frequency), a near-correlation function is generated, which, when applied to transmission path studies in dispersive media, will have analogous properties to the standard cross-correlation function when applied to nondispersive media. The theoretical results were checked for both single- and multipath cases. The experimental setups consisted of 18 in.×1 in. aluminum beams, which were excited by white noise using an electromagnetic shaker. The response at two points was measured with accelerometers and their output recorded on magnetic tape. This information was digitized and processed on the Univac 1107 computer.
A Method for the Calculation of the Normal-Mode Frequencies in Irregular Rooms
Authors: Slusser Ronald A.
Published: October 2005

This paper will present a method to solve for the normal-mode frequencies (standing-wave frequencies) in rooms of irregular shape. Since, in general, a direct solution of this problem is not possible, a numerical approximation procedure is presented. The theoretical derivation and solution for the normal-mode frequencies in an irregularly shaped room is done by using forward and backward difference formulas in approximating the second partial space derivatives in the acoustic wave equation. An alternative derivation, using Stirling's interpolation formula, will be presented. Boundary conditions (walls) are applied with an approximation of the image technique. A computer program will be shown that was written to calculate the lowest-mode wavelength constant k in a specified irregularly shaped room. Results of computer calculations for a cubic and pentagonal room will also be shown.
Effects of Large Panels on Eigenvalues of Rectangular Rooms
Authors: Ingalls D. J.
Published: October 2005

The effects of a large, stationary flat panel in lowering the eigenvalues of a small reverberant chamber are experimentally investigated for panels of different surface density. The observed shifts of frequencies downward depend on panel orientation and surface density with the heaviest materials exhibiting the greatest frequency shift. The experimental results show good agreement with the theoretical predictions of Morse and Fesbach, Methods of Theoretical Physics (McGraw-Hill Book Co., New York, 1953) on the distortion of a standing wave by a strip.
Superposition of Time-Interval Pitch Percepts
Authors: Rosenburg A. E.
Published: October 2005

Time-interval or repetition pitch may be considered to be the pitch percept associated with the interval between repeated portions of a stimulus waveform. A simple stimulus evoking this percept is a single, equal amplitude pulse pair. The pitch corresponds to the reciprocal of the interval between pulses. Repetition of the pulse pair, not necessarily periodic, increases the strength of the percept. Substitution of another waveform for each of the pulses can be expected to produce a similar percept. For example, wide-band noise delayed and added to itself produces a continuous stream of waveform segments correlated at the interval of the delay. Consider a stimulus consisting of wide-band noise that is multiply delayed and added to itself. Suppose that in general the delays are unequal. As a hypothesis, it is proposed that the over-all pitch percept is a superposition of time-interval pitch percepts associated with individual delays and combinations of delays. That is, the individual pitch percepts are apparent in the over-all percept. A series of pitch-matching and discrimination experiments has been undertaken, which strongly supports this hypothesis. More fundamentally, the results are consistent with a temporal rather than a spectral processing of pitch information for these stimuli.
Direct Measure of Duration Discrimination
Authors: Rochester S. R.
Published: October 2005

Observers (O's) were presented with a two-alternative forced-choice (2AFC) duration-discrimination task. In separate experimental runs, O's were asked to choose either the longer of two increments or the longer of two decrements from a continuous white noise background. Direct determinations of the increase in duration (ΔT) necessary for 75% and for 90% correct response were made at each of four base durations (T = 10, 25, 50, and 100 msec). These measurements were possible through the use of Delta, a combination of the PEST (parameter estimation by sequential testing) technique with ΔT as dependent variable. To establish whether Delta yielded results comparable to the more traditional 2AFC measurement of per cent correct, psychometric functions for the same observers were obtained for the same base durations. From these functions, the value of ΔT needed by an observer to achieve 75% and 90% correct discrimination was found for each T. In general, the estimated values of ΔT did not differ from those obtained directly by the Delta technique. [Supported by the National Research Council of Canada.]
Frequency Glides—Their Spectra and Pitch Perception
Authors: Nabelek I. , Nabelek A.
Published: October 2005

The spectra of tone bursts with linearly changing frequency as calculated on the LINC computer are shown. The conditions for which different numbers of maxima occur in the spectrum are compared with some results of measurement of perception of pitch of such acoustic bursts. Those spectra that contain only one or two peaks correspond to tone bursts likely to be evaluated as having one quite distinct pitch. When the spectra show many maxima, the corresponding pitch character of the burst becomes less clear and the matched frequencies may be spread over the whole swept frequency range or are equal to the final frequency.
Noise Encountered in Rotary-Wing Aircraft
Authors: Gasaway D. C.
Published: October 2005

The acoustic environment encountered within rotary-wing aircraft constitutes a mixture of several noise-generating mechanisms. Primary and secondary noise-producing mechanisms that are associated with the ground and airborne operation of rotary-wing aircraft are identified, described, and illustrated. Some of the noise sources studied include main rotor(s), antitorque rotor, main and secondary transmission and gear-shaft distribution systems, and auxiliary power units. In addition to reporting specific noise generators, composite noise envelopes are provided, which illustrate typical noise environs found within rotary-wing vehicles with different configurations of rotor-power plant matings. Alterations in internal noise that occur during conditions of hover and forward flight are described, and aeromedical factors such as speech interference and potential auditory risk are identified.
Effects of Shear Flow on Sound Propagation in Ducts
Authors: Catton I. , Hersh Alan S. , Bies David Alan
Published: October 2005

The effects of velocity gradients (shear) on upstream and downstream acoustic propagation in rigid ducts have been analytically investigated. The results are compared, for the downstream case, with the earlier work of Pridmore-Brown [J. Fluid Mech. 4, 393–406 (1958)]. The results show that the sound is channeled towards the duct wall. Thus, the trends but not the magnitudes predicted by Pridmore-Brown have been verified. The upstream results show the opposite effect that the sound is channeled towards the middle of the duct. The investigation extends from very narrow to very wide ducts and from zero to high shear flows.
Low-Frequency Ground Attenuation in Outdoor Noise Measurements
Authors: Oncley P. B.
Published: October 2005

Outdoor acoustic measurements often show severe attenuation of frequencies on the order of several hundred hertz. It is shown that this apparently anomalous loss can be explained in terms of the conventional interference analysis if allowance is made for the phase delay of the reflected wave. The amplitude and phase of the reflected wave are computed following the approach given by Rudnick. Although accurate impedances and propagation-constant data have not been available for comparison of calculations with actual field measurements, estimates based on measurements at other places and data on porous insulating board have been used to calculate excess ground attenuation curves. These curves are shown to be similar to those obtained from actual jet-engine noise spectra obtained at Boeing test sites and by other investigators. Applications to jet-noise testing from this analysis and the comparison paper by Panko are presented.
Target Detection Using Echo-to-Echo Cross Covariance
Authors: Cosgrove Michael A.
Published: October 2005

Traditional signal-processing techniques such as replica correlation and narrow-band filtering are ineffective for noise rejection when one uses a wide-band source in an active sonar system. Some signal processors such as cross-covariance and integrated-square-law detectors, however, can take advantage of the available high time-bandwidth products for noise rejection. Output statistics for such devices are well known for the case of identical signals in uncorrelated noise fields. But this is an optimistic case for sonar applications where the signals are consecutive target echoes that will decorrelate with target aspect and multipath changes, and where the noises may be fairly stable and, therefore, correlated reverberation. Output statistics were developed, which included the effects of signal and noise correlation. Detection thresholds were then calculated from the output statistics.
Testing for Isotropy
Authors: Scharf L. L. , Schmid C. E.
Published: October 2005

The presence of acoustic targets in the ocean produces an anisotropic field. Hence a hypothesis test for detection of these targets is formulated as H0 (isotropic noise field) versus H1 (anisotropic field). The outputs of N hydrophones are available. Two logical approaches become apparent, namely (1) to test the estimated element cross covariance matrix or equivalently the N×N cross-spectral matrices and (2)to test the power of the M beams formed from the N elements. The latter approach, although less direct, leads to an asymptotically uniformly most powerful invariant test providing that the beam powers are independent through design or suitable transformation. The test is to decide upon H0 if the spatial variance of the power does not exceed a threshold, and decide upon H1 if the variance does exceed that threshold. The test is written as where ∑ i=1M (Pi−P̄i)2≷H0H1 THRESHOLD, where P̄i= 1M  ∑ i=1MPi, and Pi is the measured power (in decibels) in the ith beam. False alarm and miss probabilities are determined through the introduction of targets with various strengths into selected beams.
Signal Waveform Design for a Correlation Echo Sounder
Authors: Bartram James F. , Pitassi David A.
Published: October 2005

There are two basic types of consideration involved in the signal-design task for the correlation echo sounder: linear and nonlinear. The linear factors include those encountered in general signal-design procedures and also the less frequently considered effect of linear filtering on the peak-to-average power ratio. The nonlinear factor is the effect of amplitude quantization, including the extreme case of hard clipping. Of particular concern is the ability to resolve multiple bottom-layer returns. It is found that when a linear FM slide is used, together with hard clipping at the receiver input, the bottom returns tend to interfere destructively with each other. It is further found that it is possible to design a signal waveform that will permit the use of hard clipping without the destructive interference.
Doppler Dispersion Losses in the Reduced Averaging Processor for the Linear Swept FM Pulse
Authors: Lee S. P.
Published: October 2005

Reduced averaging processing of the linear swept FM pulse signal has been studied by the technique of using one common reference signal with one common set of step oscillators for multiple acoustic channels. Doppler dispersion effects versus the doppler resolution accuracy in both point and a special type of extended target are considered. Under the matched echo and reference signal slopes, the stated processing technique acts as the matched filter processor for both point and extended targets. Under the mismatched echo and reference signal slopes for the point target case, the Doppler dispersion loss is negligible and the stated processing technique does not degrade the resolution performance from the system that provides more than one reference signal. When the target is extended and both echo and reference signal slopes are mismatched, the stated processing technique indicates the serious dispersion loss; therefore, the resolution accuracy is jeopardized. In other words, it is necessary to have multiple reference signals for the specified resolution accuracy.
Signal Processing for an Acoustic Homing System
Authors: Noiseux D. U. , Horwath T. G. , Maidanik G.
Published: October 2005

An acoustic sensing system as a unit of a homing system is described. The elemental acoustic sensing system embodies two pressure transducers each consisting of a flush-mounted porous plate backed by a cavity. The function of the acoustic sensing system is described in terms of its filtering action and the form of the signal processing adopted to extract the information relating to the location of an acoustic source—the target. This information can be employed to actuate a control system that would guide a vehicle toward the target. It is shown that the angular location of the target is related to the time delay between the signals received by the two pressure transducers. Phase detection is selected as the process by which the time delay is extracted. The normalized gain of the signal processor as a function of the signal-to-noise ratio of the response of the acoustic sensing system is discussed. A typical relationship between the normalized gain and the signal-to-noise level is presented. [This work was initiated and sponsored by Systems Application Division, MERDC, Fort Belvoir, Virginia 20060.]
Operational Signal-to-Noise Level for Gravitationally Propelled Acoustic Homing
Authors: Horwath T. G. , Maidanik G. , Noiseux D. U.
Published: October 2005

The signal-to-noise level of the acoustic sensing system on a gravitationally propelled vehicle homing on a trajectory toward a localized acoustic source—the target—is modeled. The speed of the vehicle as a function of the trajectory is derived in terms of the apogee and the terminal speed of the vehicle. On the basis of a simple exponent relationship between the speed of the vehicle and the noise in the response of the acoustic sensing system, the noise is determined as a function of the trajectory. The signal in the response of the acoustic sensing system is determined as a function of the trajectory on the basis of the geometrical spreading of the acoustic pressure field generated by the target. From a combination of these determinations, a nomograph is constructed so that the signal-to-noise level of the acoustic sensing system as a function of the trajectory can be read once the following items of information are specified: (a) the noise level at a specific speed [e.g., at 200 ft/sec] of the vehicle; (b) the signal level at a specific distance [e.g., at 100 ft] from the target; (c) the terminal speed of the vehicle; and (d) the apogee. From knowledge of the gain of the signal processor as a function of the signal-to-noise level, one can ascertain the necessary operational requirement on the four stated items to prevent a range in the trajectory where guidance may be ineffective. [This work was initiated and sponsored by Systems Application Division, MERDC, Fort Belvoir, Virginia 22060.]
Results of Television Data Transmitted Acoustically via a Water Medium
Authors: Guthals D. L.
Published: October 2005

Slow-scan television pictures were acoustically transmitted by FM modulation from depths ranging from 200 to 15 000 feet. Photographs taken of the TV-monitor display during two field operations were examined for distortion resulting from acoustic propagation effects with laboratory data serving as a control. The distortion was displayed in the form of ghost images, waviness, line sync irregularities, and granulation. It appears that the primary interference was due to the bottom-reflected signal. Reverberation effects appeared to be minimal during the two field trials.
Parameter Variations in Linear Memories
Authors: Roberts R. A.
Published: October 2005

In signal-processing models, one often stores and updates variables or functions successively in time as new data are received. This is done in the processor's memory. If one considers the memory as a system, under what conditions is this system (memory) linear? Assuming these conditions are fulfilled so that a linear memory is a sufficient memory for the problem of interest, what is the effect of parameter variations in the linear memory system? These questions can be answered in the specific case of estimating a fixed but unknown vector in added white Gaussian noise. [Work supported by NSF grant.]
Computer Programs for Sonically Induced Vibration of Structures
Authors: Lee Tsin N. , Liu C. K.
Published: October 2005

Formulations were derived and computer programs were written to calculate responses of rectangular cylindrical panels that are cross reinforced with stiffeners subjected to the excitation of acoustic pressures. The input spectral density or 3-oct pressure level of the acoustic pressure of any spectrum shape may be read in any discrete frequencies. The frequency equations are incorporated in the programs. The input data include only the geometric dimensions and material properties of the panel. The formulations are according to the normal mode approach. The responses are calculated as the acceleration, displacement, and stress spectral densities, and the rms values. The results are tabulated and plotted. New expressions for the joint acceptance of all mode combinations for different correlation functions are derived. Both the main and the cross terms are taken into account to obtain the response. Up to 625 terms are summed to obtain the spectral density at one data point. More than 1000 data points are calculated for each spectrum. Both the local responses at any point and the average responses over the complete panel are calculated. The program can be used to investigate the contribution of the principal terms and the cross terms. Comparison of calculated results with test data shows good agreement.
Free Vibrations of Spherical Sandwich Shells
Authors: Mirza S. , Doige A. G.
Published: October 2005

In the present study, the problem of axisymmetric vibrations of spherical sandwich shells is considered. In obtaining the governing differential equations, the longitudinal inertia terms u,it and v,it can be neglected. This makes possible the introduction of a stress function F similar to the one in elastostatic problems. The differential equations are written in terms of an arbitrary deformation function φ and the stress function F. For simplicity in the final results, the face sheets and core are considered to be isotropic elastic and of uniform thickness t and c, respectively. In some applications, the core material acts as a heat shield and an insulator. In this paper, the effect of the thermal gradient along the thickness of the sandwich is not considered. Since the core filler is of honeycomb thermoplastic or aluminum foam having low values of shearing modulus, an order analysis of various terms in the differential equations establishes that the problem can be studied in two parts. This results in two sets of differential equations, which are applied in accordance with the physical parameters of the core geometry and material. The final frequency equation |aij| = 0; i, j = 1, ⋯4 and the results are given for two types of boundary conditions (fixed and simply supported). The solution of the frequency equation degenerates to the classical solution for vibration of shallow shells and to that of two layered shells.
Comparative Intelligibility of Monosyllabic Word Lists
Authors: Coleman R. F. , Hollien Harry
Published: October 2005

Two experiments are reported in which the underwater intelligibility scores of four standard word lists were compared. As would be expected, closed-set lists produced higher scores than open-ended tests. Alternate forms of two tests were compared and the results indicated that lists which are equated for difficulty in normal environments were also sufficiently equated for underwater use. A preliminary analysis of phoneme type distortion was derived from one closed-set test, and appeared to demonstrate that, for these experiments, the most common type of phoneme error was in specification of place of production, with fricative phonemes most affected.
Auditory Discrimination of Speech Altered by a Frequency-Transposition Process
Authors: Ling Daniel , Ely William G.
Published: October 2005

A single-channel transposing instrument that uses a sample-and-hold process to accomplish multiple transpositions of input frequencies was compared with a conventional (linear) amplifier. The purpose of the experiment was to determine whether transposition could improve the consonant discrimination of 12 profoundly deaf children, aged 8–18 yr. Subjects were presented with a series of paired syllables and asked to indicate by pressing one of two buttons on a response device whether each pair was the same (e.g./sɛ-sɛ/) or different (e.g./tɛ-sɛ/). Consonants were paired to represent differences ranging from zero to five distinctive features. An equal number of same and different pairs, constructed from 15 consonants and two vowels /ɔ/ and /ε/ were presented under each of three conditions: conventional amplification, transposition sampling at 1500 Hz, and transposition sampling at 3000 Hz. Analysis of over-all results for pairs judged different showed that discrimination between consonants under all three amplification conditions was similar [F(22.2) = 0.03], but consonant discrimination for pairs employing the vowel /ɛ/ was better with both conventional amplification and with transposition. In only three instances were specific pairs judged more accurately under one condition than another. These were /h-∂/, /v-k/ and /θ-p/, and in each case conventional amplification yielded superior scores to transposition.
Measurement and Operant Conditioning of the Vocalization of Preschool Deaf Children
Authors: Asp Carl W. , Lawrence Connie
Published: October 2005

A voice-operated relay, a throat microphone, and an electromechanical counter were utilized to record automatically the rate of vocalization of 20 deaf and 28 normal hearing, preschool children. The mean rate of vocalization of each child served as the criterion measure. The results of a t test indicated a significant difference between the groups with regard to vocalization. For the operant conditioning of 13 deaf children, the eyes and nameplate of a stuffed animal were modified and electrically connected to the apparatus to illuminate when the child vocalized. To avoid extinction, candy, peanuts, and charms were utilized as secondary reinforcers. In addition, each vocalization was picked up by a concealed microphone, amplified and presented to the child via a set of earphones. At the outset, a continuous reinforcement schedule was employed, but a variable schedule with increasing mean values of 2.5, 3.5, and 4.5 was implemented to strengthen the reinforcement. The mean vocalization increased 25/mm during conditioning. After an extinction period, spontaneous recovery was observed. [Supported by NIH Biomedical Sciences Support Grant.]
Further Results on the Development of Voicing in Stop Consonants in Young Children
Authors: Preston Malcolm S. , Port Diane K.
Published: October 2005

This paper reports further results on a research project that was designed to examine the development of stop consonants occurring in initial position in the vocalizations of children primarily during the second year of life. A previous paper [M. Preston, G. Yeni-Komshian, R. Stark, and D. Port, “Certain Aspects of the Development of Speech Production and Perception in Children,” J. Acoust. Soc. Amer. 46, 102 (A) (1969)] presented results for apical stops. This report deals with the results for labial and velar stops over the same time period. The principal measure employed in the analysis is voice onset time (VOT), a perceptually and productively relevant measure, which can be easily obtained from spectrograms. In addition, a more complete analysis of apical stops comparing VOT distributions of adults with children between 2 and 212 yr is presented. [Research supported in part by the National Institute of Child Health and Human Development.]
A Concert Grand Electropiano
Authors: Martin Daniel W.
Published: October 2005

The purpose was to extend the musical scope of the concert grand piano without losing present inherent tonal and dynamic capabilities. The inherent acoustical problems were (1) to reduce greatly the direct tonal radiation without affecting adversely the string-vibration properties; {2) to transduce successfully the string vibrations into electrical waves; (3) to transduce successfully the amplified electrical waves into tone radiated realistically from the instrument. Control of the sound level and equalization of the over-all tone spectrum improve adaptability to concerts in different acoustical conditions. Additional pedals increase the dynamic range of expression and permit new timbre-loudness combinations. Electronic controls provide new timbres for special effects. Benioff and Martin-Ziegler patents are cited.
GRooVE—a Computer Program for Real-Time Music and Sound Synthesis
Authors: Mathews M. V. , Moore F. R.
Published: October 2005

A program for controlling an electronic sound synthesizer is described. The program logic is based on procedures for creating, storing, reproducing, and editing functions of time. Multiple functions (up to 14) may be produced for long periods of time (up to several hours) at sufficiently high sampling rates to describe fast human actions (up to 200 samples/sec). In addition to sound synthesizers, these functions could be used for controlling machine tools, real-time experiments, or anything a person normally controls. The program operates on a small computer (DDP 224). Functions are stored on a disk unit. Functions may be created by real-time human inputs, which interact with previously stored and/or computed functions. Real-time feedback from the sound synthesizer is an important link in the system. The environment for effective man-machine interaction has been carefully nurtured.
Computer Display of Array Characteristics
Authors: Byram G. W. , Olds G. V.
Published: October 2005

The calculated response of a linear array of isotropic point sensors to a plane wavefront has been displayed in three-dimensional computer plots. These plots display beamformer output as a function of signal angle and a third variable selected from frequency, beam angle, and array shading. Sidelobes appear as sharp ridges that curve across the baseplane of the plot. Changes and shifts in sidelobe structure as a function of the third variable are readily visible. General equations for contours of constant amplitude in the signal-angle, beam-angle, and signal-angle frequency planes are derived. Plots of these equations can be used to extrapolate one known beam pattern to other beam angles and frequencies.
Acoustic Radiation from Fluid-Loaded Rectangular Plates
Authors: Davies Huw G.
Published: October 2005

The acoustic radiation into a fluid-filled infinite half-space from a randomly excited, thin rectangular plate inserted in an infinite baffle is discussed. The analysis is based on the in vacuo modes of the plate. The modal coupling coefficients are evaluated approximately at both low and high (but below acoustic critical) frequencies. An approximate solution of the resulting infinite set of linear simultaneous equations for the plate modal velocity amplitudes is obtained in terms of modal admittances of the plate-fluid system. These admittances describe the important modal coupling due to both fluid inertia and radiation damping effects. The effective amount of coupling, and hence the effective radiation damping acting on a mode, depends on the relative magnitudes of the structural damping—i.e., on the widths of the modal resonance peaks and on the frequency spacing of the resonances. Expressions are obtained for the spectral density of the radiated acoustic power for the particular case of excitation by a turbulent boundary layer. [Work supported by the Office of Naval Research.]
Resonance-Enhanced Brillouin Scattering in Crystals
Authors: Ito R. , Burstein E. , Pinczuk A. , Shand M. L.
Published: October 2005

The Brillouin scattering intensity exhibits resonance enhancement as the frequency of the incident radiation approaches exciton absorption bands and the interband absorption edge. A theory of resonance-enhanced Brillouin scattering that is analogous to that of resonance-enhanced Raman scattering [E. Burstein, D. L. Mills, A. Pinczuk, and S. Ushioda, Phys. Rev. Lett. 22, 348 (1969)] is presented in terms of the scattering of polaritons by acoustic phonons via the exciton and continuum electron-hole pair excitation parts of the polaritons. The theory also provides a basis for the enhancement of the electro-optic and elasto-optic coefficients, which is observed in II–VI compounds near the absorption edge. Two mechanisms are taken into account, that of the deformation potential coupling arising from the strain field, which gives rises to the piezo-optic effect and, in the case of piezoelectric crystals, that of the Frölich interaction arising from the macroscopic electric field, which gives rise to the electro-optic effect. Experimental results are presented for ZnSe and CdS. [Research supported in part by the Army Research Office—Durham and the Advanced Research Projects Agency.]
Phonon Instabilities and Interactions near Solid-State Phase Transitions
Authors: Fleury Paul A.
Published: October 2005

The rôle of phonon instabilities (soft modes) in several types of solid-state structural phase transitions has recently been demonstrated by inelastic light-scattering experiments. The symmetry of the soft phonon mode relates the crystal structures above and below Tc, and the temperature dependence of its frequency is associated with various crystal properties near Tc. Examples of both Brillouin zone-center (q = 0) and zone-boundary (q≠0) soft modes are presented. The interactions between optic and acoustic phonons respOnsible for sound-velocity anomalies near Tc are discussed for several classes of phase transitions (ferroelectric, order-disorder, etc.). While emphasis is placed on phase transitions in crystals of the perovskite structure (e.g., SrTiO3), some attention is also given to interesting transitions in other types of crystals.
The Glottal Stop as a Junctural Correlate in English
Authors: Allen Jonathan
Published: October 2005

The fundamental-frequency contours of English sentences have been thought to be affected by sobglottal pressure, laryngeal tension, vowel height, changes in transglottal air pressure, stress placement, and coarticulation effects. In this study, fundamental-frequency contours in vowel-vowel transitions have been studied for varying constituent structures, phonemic environments, and stress patterns. Transitions within words, at formative boundaries within words (re-enter), at word boundaries, and at phrase boundaries were studied, and the fundamental-frequency contours for these transitions were recorded. It was found that many speakers use the glottal stop to indicate juncture, and that this usage is conditioned by the position of the transition in the formative structure of the utterance. Thus the changes in fundamental frequency in vowel-vowel transitions serve as junctural cues. Models that describe the variations in fundamental frequency in English sentences must, therefore, make provision for this effect.
Temporal Structure in Speech Production
Authors: Allen George
Published: October 2005

Temporal sequential dependencies in speech can be realized as negative correlations between the variations in duration of successive articulations; for example, if the consonant in a consonant-vowel syllable is articulated overlong, the following vowel will often be overshort, making the syllable less variable in duration than the sum of the variabilities of its parts. Temporal dependencies in an articulatory interval may be measured by the interval's relative variance (RV), i.e., the variance of the interval's duration divided by its length. Under an hypothesis of no sequential dependency between articulations, RV is approximately constant for all intervals. As sequential dependencies increase, RV decreases; units of articulation then emerge as speech segments with low RV. RV also separates two kinds of dependencies. Since RV, unlike relative error, is sensitive to changes of scale, tempo variations in repetitions of an utterance will artificially inflate the RV of tempo-related intervals (e.g., rhythmic phrases), leaving unchanged the RV of segments whose durations derive more from peripheral constraints (e.g., aspiration). The RVs of some longer intervals drop dramatically when tempo effects are removed, showing clearly the presence of rhythmic constraints in speech.
Spectrographic Speech Patterns of Identical Twins
Authors: Kersta L. G. , Colangelo J. A.
Published: October 2005

It has previously been reported that speakers are identifiable on the basis of a voiceprint or spectrographic analyses of their voices. This study applies the same techniques to the voices of identical twins to demonstrate that there are invariant qualities of the voice that are unique to the individual even when vocal-tract physiology may be expected to be identical and when environmental effects have familial similarities. The tests were first performed by two scientifically näive high school girls whose training consisted initially of voiceprint matching of unrelated individuals, followed by matching tasks on thirty pairs of fraternal twins. In the testing procedure, the panel was presented with two spectrograms of one pair of identical twins. Each twin had uttered a phrase containing the words “were you.” The panel was then presented with a third spectrogram containing the words “you were” and asked which of the first two speakers was the same as the third. In 60 attempts, they were able to correctly identify 52 of the twins based on two words spoken in common. The tests were then repeated using a more skilled technician, who successfully identified 59 of the 60 speakers.
The Effect of Some Neurally Active Drugs on the Cochlear Afterpotential
Authors: Stopp Phyllis E. , Panayiotopoulos C. P. , Whitfield I. C.
Published: October 2005

At the termination of a tone burst of more than 10–20 msec duration, an afterpotential immediately succeeding the microphonic/summating potential complex can be recorded from the cochlea [Stopp, Nature 215, 1400 (1967)]. This potential is negative-going relative to an indifferent extracochlear electrode, and is of spatially different origin from the microphonic, since its polarity is the same in both scala tympani and scala vestibuli. Like the afterpotential seen following repetitive neuronal stimulation, it is abolished by perfusing the cochlea with fluid in which Na+ has been replaced by Li+, or which contains DNP. A number of other drugs that act on membrane-excitation processes have been found to abolish the afterpotential in a reversible manner by perfusing scala tympani when they are added to Ringer's solution. Among these are tetrodotoxin, TEA, strychnine, GABA, and glutamate. None of these substances affects the cochlear microphonic when administered in this way. All these drugs simultaneously reduce or abolish the N1 response in doses that abolish the afterpotential, tetrodotoxin being the most effective in this respect. The spatial and pharmacological differential between the microphonic and the afterpotential suggests that the afterpotential may be closely connected with the hair-cell synaptic mechanism, rather than with the hair-bearing end of the cell.
Temporal Position of Discharges in Single Auditory Nerve Fibers within the Cycle of a Sine-Wave Stimulus
Authors: Anderson D. J. , Rose J. E. , Hind J. E. , Brugge J. F.
Published: October 2005

Period histograms, which display the distribution of spikes throughout the cycle of the sinusoidal stimulus, were computed for discharges recorded from single auditory nerve fibers of the squirrel monkey when low-frequency tones were employed. For each histogram, an average phase angle was determined, which constitutes a measure of central tendency for the spike distribution. For frequencies up to 4 kHz, where phase locking is observed, the average phase angle was tracked as frequency was varied in small steps from low to high. To the first approximation, the cumulative shift in average phase angle is a linear function of frequency, as would be anticipated for a constant-propagation delay. A more detailed examination revealed that average phase angle is also sensitive to intensity, depending upon the relation of the stimulating frequency to the best frequency. For stimulating frequencies below best frequency, discharges tend to occur progressively later in the cycle as intensity increases. Above best frequency, an opposite tendency often prevails. At or near best frequency, little change in average phase angle is noted as intensity varies.
Inhibitory and Excitatory Synaptic Events in Cat Cochlear Nucleus
Authors: Starr A. , Britt R.
Published: October 2005

Intracellular recordings were made from 58 cells in dorsal cochlear nucleus of pentobarbital-anesthetized cats in response to tone bursts (0.5–22.0 kHz, −20–90 dB SPL). Depolarizing shifts (EPSPs) almost invariably accompanied tonal signals increasing discharge rates (43 of 49 cells), whereas hyperpolarizing shifts (IPSPs) were detected in only 16 of the 29 cells in which tones suppressed discharges. Cell discharges evoked by passage of intracellular depolarizing currents were decreased in rate whenever tones in the inhibitory surround were concomitantly presented independent of whether or not the tone also evoked an IPSP. These results suggest (1) that inhibitory surround in cochlear nucleus is due to postsynaptic inhibition and (2) that the inhibitory synapses must have a restricted spatial distribution on the cell, rendering the detection of IPSPs difficult. [Supported by two grants from NIH.]
Low-Frequency Characteristics of the Auditory Periphery
Authors: Dallos Peter , Cheatham Mary Ann , Schoeny Zahrl G.
Published: October 2005

There is considerable controversy in the literature concerning the low-frequency slope of the cochlear microphonic/sound-pressure transfer function. In order to clarify this matter, we measured both magnitude and phase of this transfer function for four species with identical experimental techniques. The species were the cat, guinea pig, chinchilla, and kangaroo rat. Our results were dichotomized in that cats and chinchillas had similar functions, while guinea pigs and kangaroo rats demonstrated a radically different type of magnitude and phase pattern. In the former two animals, the low-frequency slope was 12 dB/oct, accompanied by a low-frequency phase of 180° lead; in contrast, the latter two animals had transfer functions with a low-frequency slope of 6 dB/oct, and 90° phase lead. It is argued that the stapes velocity/sound-pressure transfer function is similar in all four species and that the observed differences in the cochlear microphonic/sound-pressure functions are the consequences of differing cochlear input impedance. The cochlear input impedance is apparently influenced by the gross physical structure of the cochlea, most specifically by the number of turns. [Work supported by the National Institute of Neurological Diseases and Stroke.]
Function of the Tympanic Membrane
Authors: Tonndorf Juergen , Khanna Shyam M.
Published: October 2005

Vibrational holography was performed on tympanic membranes (TM) in human temporal bones obtained immediately after death. Displacement patterns at the first mode (and also at higher modes) were essentially the same as those found in cats (Khanna et al., 1969). Findings in both species can best be reconciled with the catenary concept of Helmholtz (1868). Owing to the curvature of the TM's surface, a force transformation is brought about between the membrane (larger displacement/lesser force) and the malleus (lesser displacement/larger force). Point-by-point comparisons of displacement amplitudes along the manubrium with those in adjacent regions of the posterior quadrant suggested that forces exerted upon the manubrium decrease with distance from the ossicular rotational axis so that FORCE×FORCE ARM≅CONSTANT. The amplitude differences between TM quadrants (Khanna et al., 1969) are explained by the fact that the manubrium and the ossicular rotational axis form an acute angle, open anteriorly (Bárány, 1938). Thus, the manubrium appear to rotate around two axes. With frequency, the efficiency of the system varied in a manner resembling the middle-ear impedance curve. [Supported by NIH grants.]
Measurement of the Amplitude and Phase of Vibration of the Basilar Membrane Using the Mössbauer Effect
Authors: Rhode W. S. , Geisler C. D.
Published: October 2005

The Mössbauer effect has been applied to the measurement of the amplitude and phase of the motion of the basilar membrane of the squirrel monkey's cochlea (in vivo). Measurements were taken every 200–300 Hz from 200 to 12 000 Hz in the 6- to 9-kHz region of the cochlea. Measurements of the umbo or incus motion were also taken. Umbo motion was measured at 100–110 dB SPL and was linear over the range of SPLs used. Results of the basilar membrane measurements indicate that the low-frequency portion of basilar membrane-incus transfer characteristic increases at 5–10 dB/oct, while the high-frequency region drops off at a slope of 90–150 dB/oct. The phase difference between the basilar membrane and incus is a linear function of frequency except at low frequencies, where the basilar membrane leads the incus vibration by 90°. The velocity of the traveling wave over this region of the cochlea is 15–20 m/sec. The basilar-membrane measurements were taken at 80–120 dB SPL. The peak excursions of the membrane were on the order of 0.05–0.1 at 5 kHz for 90 dB SPL.