bluuebunny/crossref_metadata_2025 huggingface dataset:
Unsteady supersonic inlet cascade aerodynamics—a schlieren study
Authors: Fleeter S. , McClure R. B. , Sinner G. T. , Holtman R. L.
Published: October 2005

The fundamental mechanism of many aerodynamic-vibration problem areas currently being investigated with regard to the development of advanced fan and compressor components is directly related to unsteady cascade aerodynamic phenomena. Such problem areas include: discrete frequency noise generation; forced vibration phenomena due to wakes from upstream obstructions, inlet distortion, or turbulence; and self-excited vibrations, in particular, supersonic inlet torsional flutter. This paper describes the flow visualization of a unique unsteady supersonic inlet two-dimensional cascade experiment wherein five flattened double-wedge-shaped airfoils are cantilevered and mounted in a mirrored sidewall. This mirrored sidewall serves as a tunnel wall as well as a reflective surface in the double-pass schlieren system, thereby providing flow visualization. The cascade was tuned to and excited at a torsional frequency of approximately 100 Hz. Over a Mach number range of 1.4–1.67, the cascade was excited, the excitation stopped, and the resulting dynamic stability observed and recorded. High-speed color schlieren movies (5000 frames per second) of the unsteady cascade phenomena including the effect of interblade vibratory phasing angle and shock wave-airfoil interaction were made and are presented. [This work was supported, in part, by the Power Program, Office of Naval Research, under Contract N00014-72-C-0351.]
Investigation of acoustic radiation from supersonic turbulent jets by double-pulse holographic interferometry
Authors: Ozkul Ahmet
Published: October 2005

A new experimental method was used to investigate optically the acoustical radiation field and the related fluctuating turbulent field from supersonic air jets. The method utilizes double exposure of a supersonic jet using a pulse ruby laser. The jet remains on during both exposures eliminating the no-flow exposure. The time separtion between the pulses can be varied, depending on the spectral component of the radiation and flow field to be observed. Optical records were obtained for supersonic jets with exit Mach number ranging from 1.0–3.0. It was found that high-frequency acoustic radiation mainly originates from the regions near the nozzle exit, 1–3 nozzle diameters, whereas the low-frequency noise is generated from regions of 8–10 diameters downstream. (The resulting three-dimensional optical data also reveal information on the relative intensity of the observed spectral component.) These findings are consistent with the acoustic data obtained by other investigators. The other experimental details on the acoustic radiation from supersonic jets and potential applications of this technique to other aeroacoustics problems are also discussed.
Effects of upstream turbulent wakes on rotor noise
Authors: Abdelhamid A. N.
Published: October 2005

Inflow mean and fluctuating velocity components produced by the wake of a body upstream of a subsonic rotor are described in terms of spatial modes of time-varying amplitude. The unsteady loads on the rotor blades and on the rotor disk are presented in terms of wake mean velocity distribution and the spectrum and coherence characteristics of the random velocity fluctuations. The analysis includes the important case of turbulence spectrum at frequencies between rotor shaft frequency and blade passage frequency. Noise generated by a ducted rotor interacting with the wake is described through coupling factors between the turbulence and acoustic spatial modes. In addition to blade passage frequency and its harmonics, the noise spectrum is shown to contain the turbulence frequencies and the translation of these frequencies by some harmonics of the rotor shaft frequency. If the rotor is not in the very near velocity field of the upstream body and for wakes in which the turbulence intensity is of the same order of magnitude as the deficit in the mean velocity, the unsteady velocity distortion effects become dominant particularly if the eddy size results in the generation of significant acoustic modes at frequencies above duct cutoff.
Threshold shift produced by continuous noise exposure in the parakeet (Melopsittacus undulatus)
Authors: Dooling Robert J. , Saunders James C.
Published: October 2005

Parakeets were trained for behavioral audiometry and then exposed to an 86-dB-SPL 13-octave band of noise centered at 2.0 kHz for three days. Thresholds were periodically measured during this time and, after 72 hours, the noise was terminated and the decay of threshold shift was followed in a similar manner until recovery was observed. This procedure was then repeated at three additional levels (76, 96, and 106 dB) of the 13-octave band of noise centered at 2.0 kHz. The threshold shift measured at frequencies exhibiting the greatest loss (2.0 kHz) appears to reach an asymptote (ATS4) after 9–12 hours of noise exposure. The level of ATS4 also increased with the level of the 13-octave band of noise. The decay of TS was related to the level of the noise, and, thus, the amount of ATS4. For exposures of 76 and 86 dB, the decay of TS was complete after 9–12 hours in the quiet. The exposure at 96 dB required three to five days for complete recovery, while that at 106 dB was slower and not complete with an average value of PTS of about 8 dB.
“Quasiphysiological” tongue model
Authors: Perkell J. S.
Published: October 2005

A quasiphysiological dynamic model of the tongue has been devised and implemented in a discrete simulation. The model changes shape only in the saggital plane. Its thickness in the dimension perpendicular to this plane is fixed; consequently, areas in the midsaggital plane correspond to volumes of the tongue. The model consists of 16 mass-bearing fleshpoints, which are connected to one another and to bony attachments by 38 active muscle elements and 47 passive connective-tissue elements. A simple submodel accounts for the behavior of each element type, and the muscle model develops tension in response to an input stimulation. The tongue muscles are represented by anatomical groupings of these tension-developing elements which are arranged to enclose 14 quadrilateral areas. These “volumes” have limited compressibility to allow for the transmission of compression forces and conservation of volume. In addition to tensile and volume-conserving forces, sliding-friction and hard-structure impenetrability forces act on the fleshpoints in the model to determine their movement. The model's behavior is compared with EMG and cineradiographic data, and it will become a component of an overall articulatory model which is intended to guide experimentation and evaluation of data on the physical and physiological properties of the vocal tract. [Research supported by an NIH grant.]
Laryngeal activity accompanying the moment of stuttering: a preliminary report of EMG investigations
Authors: Freeman Frances J. , Ushijima Tatsujiro
Published: October 2005

The existence of a laryngeal component in the stuttering block has long been a subject of speculation. In this investigation, one adult male stutterer and two normally fluent adults served as subjects. Electromyographic recordings were taken from five intrinsic laryngeal muscles and four upper-tract articulators. Comparisons were made of the stuttering subjects' fluent and stuttered utterances of the same words. Similar comparisons were made of the two normal subjects' fluent and “faked” stuttered utterances. Results indicate that fluent utterance is characterized by precise balance and timing of laryngeal abductor and adductor forces. In fluent utterance abductor and adductor forces act reciprocally, whereas, in stuttered utterance, this reciprocity is disrupted. In many stuttered utterances the lateral cricoarytenoid—generally presumed to be an adductor, with the specific function of medial compression—achieved abnormally high levels of activity. Stuttered utterances involving prolongations of vocalic segments were typically characterized by activity of the laryngeal abductor, the posterior cricoarytenoid. These patterns did not occur in normal fluent utterance. [Supported by the National Institute of Dental Research, Grant DE01774.]
Palatographic observation of VCV articulations in Japanese
Authors: Miyawaki K. , Kiritani S. , Tatsumi I. F. , Fujimura O.
Published: October 2005

Tongue gestures during speech utterances were studied by use of computerized dynamic palatography [O. Fujimura, I. F. Tatsumi, and R. Kagaya, J. Phonetics 1, 47–54 (1972)]. An artificial palate with 64 independent electrodes was used to record the palato-lingual contact patterns at a rate of 100 frames per second. Some computer programs have been developed for recording a large number of speech samples, to display contact patterns as viewed from two different angles for visual examination and to compute the number of the electrodes in contact with the tongue within specific portions of the palate as a function of time. A number of utterances of various V1CV2- and V1V2-type nonsense words have been examined, and some characteristics of the coarticulartory effects, including the palatalization of consonants when succeeded by/i/, are discussed with physiological interpretations.
On the interaction of a vibrating plate with an acoustic medium
Authors: Mixson J. S. , Koval L. R.
Published: October 2005

In this analysis, a vibrating plate is coupled to the medium via the acoustic pressure exerted on the plate by the medium. This interaction is manifested on the plate equation of motion as a term which is mass-like and another which is damping-like (called “radiation damping”). The emphasis is on the vibrating plate, rather than on the radiation of energy in the acoustic medium. Solution is by a finite-difference scheme, and the corresponding matrix equation is then numerically solved to give the coupled-plate response. Both the free plate vibrations (neglecting radiation damping) and the forced response are investigated for a wide range of fluid-plate mass ratios. Numerical results for the first five modes of a specific plate show that as the fluid-plate mass ratio increases, the natural frequencies decrease. The radiation damping is expressed as an equivalent viscous friction and it is shown that the equivalent viscous damping can be as large as 25% for the fundamental mode. The resonant mode shape under forced vibration was found to be affected by the acoustic medium, and there was some evidence that the distribution pattern of the excitation had some influence on the forced-vibration coupled mode shape.
Response characteristics of neurons in the cochlear nuclei to sinusoidal and vowel-sound stimulation
Authors: Caspary D. M. , Rupert A. L. , Moushegian G.
Published: October 2005

The response characteristics of neurons in the dorsal (DCN) and ventral (VCN) cochlear nuclei of kangaroo rat (D. spectabilis) to sinusoids and trains of vowel segments are described. Synchronization coefficients, response areas, post-stimulus-time histograms, interval histograms, and period histograms are all used to compare functional features of neurons in the cochlear nuclei. Pauser and chopper-type neurons of DCN exhibited low discharge rates to vowel-segment sounds. Low-frequency DCN neurons which had low synchronization coefficients did not follow closely the vowel segment waveforms. The responses of VCN neurons with low best frequencies but high coefficients of synchronization occurred in temporal sequences which were closely related to the waveform within each vowel segment. This paper relates the subnuclear cytoarchitectonics of the cochlear nuclei and stimulus coding. [Supported by Air Force Office of Scientific Research.]
Responses of single traits in the inferior colliculus of the rat to binaural stimuli
Authors: Flammino F. , Clopton B. M.
Published: October 2005

The activity of single units in the inferior colliculus of the albino rat was recorded while clicks, tones, or noise bursts were presented with various interaural time and intensity differences. The range of time and intensity differences used approximated those which occur naturally in the rat. Overall firing rate, probability of firing, and initial latency were measured. For many cells, firing rate and probability of firing increased and latency decreased when the contralateral ear was stimulated earlier in time or more intensely than the ipsilateral ear. While plots of firing rate versus interaural time or intensity differences for these cells exhibited maxima and minima, the peaks were often outside the range of time and intensity differences naturally encountered. Many showed multiple peaks or broad plateaus extending over a wide range of time and intensity differences. For some cells, the location of the peaks was not consistent for the various kinds of stimuli used. When probability of a response and latency were plotted, the cells gave a more consistent differential response and steeper functions. The data suggest that a characteristic delay or place mode[ of auditory localization is inappropriate for the rat. Rather, it seems that the rat relies on some statistical property of a population of cells or on the difference in latencies between single cells or groups of cells as a mechanism to localize the source of a sound. [Supported in part by NINDS Grant NS09551 and a General Research Grant, U.C. Academic Senate.]
Verbal transformation effect: effect of context on subjects' reported verbal transformations
Authors: Lass Norman J. , Silvis Kathryn N. , Settle Susan A.
Published: October 2005

Continued listening to recorded repetitions of a stimulus has been found to produce perceptual illusory changes in normal listeners. This phenomenon was discovered and labeled by Warren [Brit. J. Psychol. 52, 249–258 (1961)] as the verbal transformation effect. According to Warren, verbal information is normally stored and later confirmed on the basis of contextual cues in speech. Thus, the listener uses the context to help in correctly perceiving what he has heard indistinctly in the normally noisy environment. However, when the preliminary organization of speech sounds into words is not confirmed by subsequent context, verbal reorganization takes place. Warren asserts that verbal transformations represent skilled reorganizational mechanisms which are employed in speech perception. The purpose of the present investigation was to explore Warren's hypothesis by determining what effect the context in which a word appears has on the nature of subjects' reported verbal transformations. A total of 12 two-word phrases, six meaningful and six meaningless, were repeatedly presented to each of 20 adult listeners. The same 12 words were employed in both meaningful and meaningless phrases. Results of subjects' responses to the repeating stimuli indicate that there are only slight differences between meaningful and meaningless phrases in number of elicited forms and transitions. In addition, the listeners reported the same types of transformations for both meaningful and meaningless phrases. Implications of these findings for the proposed theory that verbal transformations reflect skilled reorganizational mechanisms aiding in speech perception are discussed.
Learned speech intelligibility as a function of training duration
Authors: Tobias Jerry V.
Published: October 2005

Each of 30 subjects, trained in shadowing (simultaneously repeating) clear, undistorted speech, was given experience in listening to badly distorted speech. The distortion, a kind of pulse modulation, deteriorated the signal enough that first-minute intelligibility scores averaged about 35%. The subjects were divided into five groups of six: one group was permitted 2 min of listening practice, another group 4, another 8, another 16, and the other 32. When called back a week or more after this training, these groups showed improvement in the ability to understand speech as a function of the number of minutes of previous experience up to 16.
Parallel processing of auditory and phonetic information in speech perception. II. Application of a probabilistic model
Authors: Wood Charles C.
Published: October 2005

At the last meeting of the Society I presented data suggesting that auditory and phonetic information in a speech signal can be processed in parallel. In that experiment, subjects identified either an auditory dimension (fundamental frequency) or a phonetic dimension (place of articulation of the consonant) of synthetic consonant-vowel syllables. Reaction times (RTs) were significantly shorter when the two dimensions varied in a completely correlated manner (correlated condition) than when each dimension varied alone (control condition). The purpose of this paper is to apply a simple probabilistic model to these results. The model makes two assumptions: (a) the component processes for auditory and phonetic dimensions can operate simultaneously, with the durations of each component process distributed statistically over trials; and (b) the subject's response on each trial in the correlated condition is based upon whichever component process is completed first on that trial. Equations based on this model accurately predict both the magnitude of the improvement and the form of the RT distributions in the correlated condition from the empirical RT distributions in the control conditions. In addition, the model makes precise quantitative predictions concerning the effects of (a) varying the relative discriminability of the two dimensions, and (b) adding additional redundant dimensions. The empirical validity of these additional predictions is currently under investigation.
Behavior of the basilar membrane with pure-tone excitation
Authors: Steele C. R.
Published: October 2005

Three successively more elaborate models for the fluid-elastic interaction in the cochlea are analyzed by asymptotic methods, with which an a priori assumption of “long” or “short” wavelengths is not necessary. Appropriate stiffnesses are estimated from Békésy's static-point and pressure-load measurements. The last model admits an independent motion of the arches of Corti and the remaining portion of the basilar membrane. Results indicate that the maximum arch displacement does occur about 5 mm closer to the stapes than the maximum basilar-membrane displacement, which seems to provide an explanation for the difference in “place” according to Békésy's observation and damage evidence. Furthermore, the calculated results for the phase agree remarkably with Békésy's observation for low frequency and with the recent observations by Rhode for high frequency.
Tactile perception of computer-derived formant patterns from voiced speech
Authors: Kirman Jacob H.
Published: October 2005

An experimental arrangement is described which is capable of utilizing the output of a variety of computer programs for the analysis of the acoustic speech signal and assigning the extracted parameters to a tactile display in a flexible manner. A study is reported which investigated the tactile presentation of the frequencies of the two lowest formants of vowels and vowel-like speech sounds on a matrix of 15-by-15 point stimulators. Six subjects learned two pronunciations of 15 words to an average accuracy of 83% and 70%. Generalization tests to unfamiliar pronunciations by the same speaker resulted in an accuracy of 54%, and tests to three different speakers yielded a score of 35% correct responses. Analysis of the errors indicated the same phonemic confusions accounted for a large proportion of the errors in all pronunciations, suggesting some specific limitations of this two-formant tactile display.
Critical-Point Ultrasonic Attenuation and Velocity Behavior
Authors: Leisure R. G. , Moss R. W.
Published: October 2005

Ultrasonic attenuation and velocity measurements exhibit anomalous peaks in the region of critical-point transformations. Measurements near the Neél point (67.3°K) in MnF2 show such anomalous behavior with temperature. A large peak in the attenuation is observed over about a 2°–3°K temperature range with its maximum occurring at the Neél point. This peak has been studied over a frequency range from 10–150 MHz. The attenuation maximum is not seen with shear waves. Recently, we have been able to observe a similar anomaly in the velocity behavior of this material using a sensitive mechanical resonance technique. Both the attenuation and velocity data show anisotropy with the change in the (001) direction about 3 times that in the (110). These measurements, as well as results from other investigators, are discussed in terms of current theories.
Development of a Low-Noise, Low-Turbulence Free Jet Wind Tunnel
Authors: Shulman Arnold L.
Published: October 2005

A small-scale free jet wind-tunnel facility for aerodynamic noise studies has been fabricated and installed in the anechoic chamber of the Rye Canyon Acoustics Laboratory of the Lockheed-California Company Research Center. Using wind-tunnel supply air at flow rates up to 20 lb/see, the facility operates at Mach numbers up to 0.4 and Reynolds numbers up to 3×106/ft with a test section whose dimensions are 4×20 in. A unique multiple-jet pressure reducer/muffler has been incorporated into the initial duct section and widespread use made of compressed polyurethane foam for acoustical treatment of duct walls and turning vanes. Damping screens and a honeycomb of soda straws are incorporated in the final settling chamber to reduce turbulence and flow noise. Preliminary measurements have been made of velocity profile at the nozzle exit plane, as well as background noise levels in the settling chamber, at nozzle sidewall, and in the free field of the jet. At M=0.41, variations in velocity profile were less than 0.2% in the core of the jet. Aeolian tones generated by a 12 in. diam. rod in the potential core and in the turbulent mixing region of the jet gave a signal/noise ratio of approximately 10–15 dB, clearly indicating the adequacy of the facility for the study of vortex shedding noise.
Transmission of Pyrotechnic Shock in a Missile Section and Its Measurement
Authors: Wang Paul
Published: October 2005

In a space vehicle or a missile system, two sections are sometimes connected together in such a way that a pyrotechnic device is incorporated, either continuously along a circumference or at several discrete locations. At a specific and controlled instant, the pyrotechnic charge is fired and the vehicular sections are separated. The initial forces of separation are explosive in nature. Because the time interval is extremely short, being microseconds in duration, a shock phenomenon is invariably created. The magnitude of this shock is usually quite difficult to measure. Often times, accelerometers are located near the interfaces to serve as transducers for the observation of the same phenomenon. The accelerometer outputs are, however, not always congruent with the original pressure rise. Even though the results are transformed in shock-spectrum terms, the true shock-impulse history is seldom reproduced accurately. However, an illustration is given that utilizes the accelerometer outputs at many monitor stations along with the characteristics in the transmitted responses to deduce the initial shock intensity. It is further demonstrated that in complex structures such as space-system components, the specification based on rigid-body dynamics of shock may be rendered equally applicable if the transmitted shock is so identified at a selected location.
Model for Generating On-Off Speech Patterns in Two-Way Conversation
Authors: Brandy Paul T.
Published: October 2005

This study presents a model which will generate on-off patterns representative of those obtained in measurements of experimental two-way telephone conversations. The model assumes a conversant to occupy one of three speaking or one of three silent states. Transitions among the states are Markovion, except during certain brief times during which the speaker is forced to remain in his state. Thus, six parameters (one for each state) are required to represent a sneaker. The validity of the model is tested by comparing the patterns generated by the model computer simulation of 16 conversations with patterns obtained from 16 real conversations. Cumulative distribution functions are compared for ten events (such as talkspurts, pauses, mutual silences, etc.) defined on the speech patterns. The model yields good fits to all events except that when an interruption occurs, a model speaker tends to interrupt the other's talkspurt later than a real speaker does. Possible applications of the model include studying people's motivations to talk and fall silent on different circuits, and predicting statistical behavior of voice-operated devices on the circuits.
Determination of Vocal Tract Shape from Acoustical Measurements
Authors: Gopinath B. , Sondhi M. M.
Published: October 2005

A direct noniterative method is described for determining the shape of the vocal tract from a specification of the acoustical driving point impedance at the lips. One way of specifying the impedance at the lips is to specify the volume velocity at the lips (as a function of time) due to an impulse of pressure. If this “impulse response” can be accurately determined, the length of the tube and the glottal boundary condition need not be known. Another way is to specify all the poles and residues (or poles and zeros) of the impedance. As is well known [see, for example, M. R. Schroeder, J. Acoust. Soc. Amer. 41, 1002 (1967) and P. Mermelstein, J. Acoust. Soc. Amer. 41, 1283 (1967)], either of these specifications gives a unique shape. In cases where only a finite number of poles and residues can be measured, rationales are presented for specifying the remaining ones.
Evidence for Quantal Vowel Articulations
Authors: Stevens K. N.
Published: October 2005

The articulation of different vowels is often represented by points located in multidimensional “articulatory space,” where the dimensions represent the coordinates of tongue and lip positions. Data are presented to show that the relations between vowel articulatory positions and properties of the acoustic output (e.g., the formant frequencies) are highly nonlinear. In some regions of articulatory space, the properties of the acoustic signal are relatively uninfluenced by perturbations in articulation, and these are separated by other regions in which the acoustic output is quite sensitive to articulatory perturbations. The former group of regions represent configurations appropriate for vowels in language since the requirements on articulatory precision are minimal. It can be argued that there are six basic quantal vowel articulations, corresponding to /i e æ ɑ o u/, and that the vowels in any language are always selected from these regions. Additional vowels are actualized by superposing on these basic vowels changes in additional articulatory “dimensions” such as rounding, nasality, tongue-root widening, duration, and fundamental frequency. [Work supported in part by the Air Force Cambridge Research Laboratories and in part by the National Institutes of Health.]
Peripheral and Central Mechanisms of Olivocochlear Bundle
Authors: Nieder P. , Nieder I.
Published: October 2005

Effects of electrical stimulation and sectioning of cochlear efferents have been studied using the two-tone stimulation technique. In the cat, under pentobarbital sodium anaesthesia, electrical stimulation of the crossed component of the OCB at rates from 50 to 400 pulses/sec (pps) enhances the microphonic modulation effect produced with bitonal stimulation—the enhancement increasing with rate up to about 400 pps. This modulation enhancement is similar to that produced in both cat and guinea pig by short periods of continued bitonal stimulation at modulation levels; the effect is ordinarily greater in guinea pig with comparable—pentobarbital sodium—anaesthesia. In acute experiments with guinea pigs, lesions in the floor of the fourth ventrical interrupting crossed OCB fibers produce no immediate effect on the modulation response. Changes developing slowly postlesion include a reduction in percent simple modulation, a trend towards equalization of double-modulation peaks, and a reduction in the modulation enhancement produced by continuous sound stimulation. These results imply both central and peripheral reflex mechanisms for OCB action. [Research supported in part by NIH grant.]
Analog Description and Simulation of Acoustic Target Echoes from Scattering Bodies
Authors: Ettenhofer K. L.
Published: October 2005

The mechanism for the formation of an acoustic echo developed by Freedman [Acustica 12, 10–21 (1962)] for rigid bodies has been expanded to other than rigid bodies. The expanded mechanism for the formation of acoustic echoes has made possible the development of an analog-active target simulator that will simulate the scattering of sound from generally convex bodies in the actual operating medium. Empirical methods have been developed that allow calculation of short and long pulse-echo envelopes when the exact relation of a body to the source are not known, and a theory is presented on the character of the amplitude and phase of the scattered radiation from small irregularities in body surface. Solutions have been found for some of the practical problems associated with real-time simulation in the medium. The analog-active target simulator has demonstrated its usefulness in testing new signal-processing techniques in sonors, and other uses in sonar and ultrasonic systems are possible.
Scattering of Acoustic Waves by a Rough, Pressure-Release Surface
Authors: Horton C. W. , Melton D. R.
Published: October 2005

Four rough surfaces 32 in. by 32 in. in size were made of a pressure-release material. The amplitude and phase of a pulsed wave scattered in the specular direction were measured at a frequency of 95.8 kHz for grazing angles from 6° to 80°. The theoretical approach of Gulin [Sov. Phys.—Acoust. 8, 228–234, (1963)] was used successfully in the Fresnel approximation to predict the observed amplitude and phase fluctuations for a Rayleigh parameter less than 0.6. Experimental measurements were extended to a Rayleigh parameter of 7.4. The observed fluctuations in the amplitude reached a maximum at a Rayleigh parameter of 2.5 and fluctuated about this value as the parameter increased to 7.4.
Effect of Shadowing on Acoustic Scattering from the Sea Surface
Authors: Gardner R. R.
Published: October 2005

Scattering from the sea surface was studied using a displacement hydrophone in order to observe the effect of surface-wave shadowing. The displacement hydrophone, able to receive the acoustic field at or near the sea surface, is particularly suitable for observing the effect of shadowing. A stable platform at sea was provided by the use of the NUWC Oceanographic Tower off San Diego. Comparison of preliminary results with Wagner's geometrical shadowing function indicates that the observed shadowing is less than would be expected theoretically. For example, with a wind speed of 20 kt the surface appears acoustically to be only 20% shadowed at 4° grazing angle, whereas geometrically 40% would be in shadow. This suggests that corrections to the scattering function using the geometrical approximation to shadowing may not be applicable. [The author received support under the Advanced Study Program from Naval Undersea Warfare Centers, San Diego, California.]
Volume Scattering of Acoustic Waves in the N. E. Pacific Ocean
Authors: Scrimger J. A. , Turner R. G.
Published: October 2005

Two types of scattering strength measurements have been obtained in the N. E. Pacific Ocean in deep water approximately 100 NM west of the entrance to the Strait of Juan de Fuca. The first type is obtained using surface venting explosive charges with the listening hydrophone suspended near the surface (i.e. depth <50 ft) to measure the backscattered acoustic energy. Levels of the intensity time curves so observed yield the scattering strength integrated to the depth corresponding to the time coordinate on the decay curve i.e., ∫ z−dz−Omr (z) dz, while the decay rates yield information on the scattering distribution in the medium. The second type of scattering measurement obtained is the scattering strength profile. Such profiles are obtained using near monostatic fired charge and receiver placed at various depths. Observation of the close-in scattered returns permits adequate resolution to plot scattering profiles through most layers [i.e., mv(z), z=0+d]. Both sets of measurements show the diurnal migration of the scattering layers as well as the frequency characteristics. However, the technique of measuring the scattering strength profile is the more direct and yields a better picture of layer distributions and the depth dependence of the scattering spectra.
Near-Surface Ocean Bubble Distributions Measured in Situ by Acoustic Techniques
Authors: Medwin Herman
Published: October 2005

An in situ acoustic measurement is highly specific for the detection of bubbles in water because of the very large values of their resonant cross sections for sound absorption and scatter. A pulse-echo “bubble spectrometer” has been used to depths of 50 ft in shallow water during sea states 1 and 2. The pulse-echo oscillograms have been analyzed both for excess attenuation (relative to clean water calibration) and backscatter between echoes (relative to a rigid reflector) to provide data over the frequency range 20 to 200 kHz (inferred bubble radius 200 to 18 μ). The number of sea-level bubbles (of radius between R and R+1 μ) per unit volume shows the peak at approximately R=60 to 80 μ, as observed by Glotov et al. for wind-agitated waves in a labortory tank. In addition, there is strong evidence of a significant distribution of very small bubbles (R<40 μ) whose number per unit volume, being proportional to R−1, will play an important part in high-frequency attenuation in well-mixed shallow ocean waters. It is postulated that the surfaces of these small bubbles are so encumbered by soluble organic matter and detritus, that their numbers are determined more by buoyancy and turblent entrainment than by rate of gas diffusion across the bubble walls. (This analysis is based on data collected by S. Buxcey, RCN, James E. McNeil, RCAF, and Robert H. Marks, Jr., USN.) [Support was obtained from the Office of Naval Research.]
Binaural Detection of Low-Frequency Tones as a Function of Noise Level
Authors: Wilbanks W. A. , Cornelius P. T.
Published: October 2005

Wilbanks and Whitmore [J. Acoust. Soc. Amer. 43, 785–797 (1968)] have reported that any sizeable binaural assistance in detecting signals in correlated noise of moderate intensity is confined to signal frequencies between 225 and 1200 Hz. They suggest that their failure to obtain substantial MLD's with signals below 200 Hz was due to the low noise level employed. The present work shows this to be the case. With correlated noise, MLD's for 150-Hz monaural and binaural signals increase from 0 and 4 dB, respectively, to 9 and 15 dB as the spectrum level of the masker is raised from +10 to +55 dB. Several hypotheses as to why the size of the binaural advantage for detection depends upon the level the masking noise will be discussed. [Research supported by National Science Foundation and Office of General Research, University of Georgia.]
NASA Duct Lining Research Program
Authors: Lowry John G.
Published: October 2005

Because of the rapidly increasing noise pollution in the vicinity of large commercial airports, the government established an interagency panel in October 1965 to develop recommendations concerning the implementation of a coordinated noise-abatement program. A part of NASA's contribution to this program resulted in the awarding of contracts to The Boeing Company and the McDonnell Douglas Corporation in May 1967, directed toward reducing the noise under the flight path of the current large four-engine fan-jet commercial transports. This paper is a brief review of the background of these contracts to study and develop nacelle modifications to minimize fan-compressor noise radiation. The goals and scope of the contracts is discussed and the current status presented.
Application of Duct-Lining Technology to Jet Aircraft
Authors: Marsh A. H.
Published: October 2005

Design studies have been conducted of various acoustically treated inlet and fan-exhaust ducts for the JT3D turbofan engine installation on DC-8 airplanes. These design studies resulted in selection of two configurations of treated engine inlets and one configuration of treated fan-exhaust ducts for full-scale fabrication. On the basis of ground-runup test results, a configuration was chosen for subsequent flyover noise and cruise performance testing. This paper discusses some of the results of design studies, the full-scale testing, and also presents predictions of the reduction in flyover perceived-noise level owing to installation of treated nacelles on DC-8-50/61 airplanes.
Ultrasonic Examination of Proton-Transfer Reactions in Amino Acid Solutions
Authors: Hussey Matthew , Edmonds Peter D.
Published: October 2005

Ultrasonic velocity and attenuation at frequencies 3–130 MHz were measured in aqueous solutions of glycine, lysine, and arginine at concentrations 0.25, 0.5, and 1.0 M and temperatures 22°, 30°, and 37°C. Values of pH were selected to permit study of the hydrolysis of α-COOH and α-NH3+ of glycine, ε-NH3+ of lysine and guanidino −NH2+ of arginine. An analysis utilizing activity coefficients yielded the following rate constants of the reactions of glycine: α-COOH: 10−10k12=0.87 M−1 sec−1 and 10−5k21′=0.20 sec−1 at 22°C, 10−10k12=0.63 M−1 sec−1 and 10−5k21′=0.12 sec−1 at 37°C; α-NH3+: 10−10k12=4.9 M−1 sec−1 and 10−5k21′= 30 sec−1 at 22°C, 10−10k12=3.5 M−1 sec−1 and 10−5k21′=23 sec−1 at 37°C. In solutions of lysine at pH 11.4–11.5 and arginine at pH 12.2–12.4, contributions from both the reactions at α-NH3+ and the side chain groups were superposed. We therefore conclude that the results of Busse [thesis, Braunschweig (1967)] for lysine solutions at pH≃11 refer in fact to the reaction at α-NH3+ instead of ε-NH3+. [This work supported by two NIH grants.]
Feasibility of Supplying High-Frequency Speech Information Via Visual Channels
Authors: Rosenstein Milton
Published: October 2005

Hearing impairment arising from sensorineural causes is characterized by pure-tone audiograms that fall off sharply with increasing frequency and result in deterioration in discrimination for plosives, affricates, and fricatives. The feasibility of supplying such missing high-frequency information visually is investigated and discrimination improvement measured when such information supplements residual hearing. The high-frequency speech information is derived from an audio band-shaping filter cascaded with a zero-crossing frequency discriminator. This system is adjusted to select the most significant frequency in an upward sloping band between 2500 and 10 000 Hz and to present, on an oscilloscope, a real-time plot of significant frequency versus time. This permitted the the separation of: (1) plosives, affricates, and fricatives on the basis of duration, (2) /s/ from /∫/ and both from /f/ and /θ/ on the basis of frequency, (3) /t/ from /p/ and /k/ on the basis of frequency, (4) voiced from unvoiced on the basis of shape. Discrimination scores using PB word lists were measured through filters that simulated severe high-frequency hearing loss both with and without visual feedback. Scores without feedback averaged 28%, improving to 48% with visual feedback.
Excitation of Transient Vibrations of Idealized Ship Models by Underwater Explosions
Authors: Chertock George
Published: October 2005

The bending or whipping vibrations of shiplike structures are easily excited by underwater explosions, particularly if the explosion bubble period approximately synchronizes with a period of flexural vibration. We first summarize the theoretical analysis [G. Chertock, Symp. on Naval Hydrodynamics, 4th, Office of Naval Res., ACR 92, (Aug. 1962)], which shows how the transient motions are related to the principal vibration modes of the structure and to the distribution and history of the applied pressures, the latter depending on the size, depth, and relative position of the explosive. We then describe experiments on small, idealized ship and submarine models, varying the weight, depth, and position of the explosive, and measuring the instantaneous deformations of the model with strain gauges connected into special bridge circuits to yield the normal coordinates associated with the principal bending vibration modes. Comparison of the theory and experiments verifies the theory as applied to the fundamental whipping mode and, with less precision, as applied to the higher whipping modes. The principal mode patterns and the history of the explosion bubble are verified by independent experiments.
Application of Noise-Exposure Forecast Contours to Noise-Reduction Tradeoff Studies
Authors: Bishop Dwight E. , Horonjeff Richard
Published: October 2005

Noise Exposure Forecast (NEF) procedures were developed to depict areas near airports having different degrees of noise exposure and differing impact upon land use. The NEF procedures represent a refinement of earlier airport land use planning procedures based upon the Composite Noise Rating (CNR). The NEF procedures have recently been applied to study the differences in total noise exposure resulting from various proposed modifications of current jet-transport aircraft-noise characteristics and changes in takeoff and landing profiles. Preliminary results are available based upon consideration of two different mixes of aircraft types operating from a hypothetical single-runway airport. Changes in noise exposure are summarized in terms of the percentage of land areas falling within NEF 30 and NEF 40 contours. [Work supported by the Federal Aviation Administration under contract.]
First Branch Dispersion of Torsional Waves in Bimaterial Rods
Authors: Reuter Robert C.
Published: October 2005

Torsional wave propagation is investigated for a rod consisting of two concentric, circular cylinders of dissimilar materials, perfectly bonded at the interface. Dispersion curves for the first branch of propagation are obtained from the frequency equation, which is derived through a solution satisfying the equations of linear elasticity. These dispersion curves are presented in dimensionless form with the ratio of constituent cylinder radii and ratios of like material properties as parameters. Only parameter values for which ρ2/ρ1>μ2/μ1 are considered. An expression for the first branch torsional wave velocity limit, as wavelength becomes infinite, is obtained from the exact frequency equation.
Absolute Thresholds for Continuous and Interrupted Pure Tones
Authors: Ehmer Richard H. , Ehmer Barbara J.
Published: October 2005

It has often been reported that interrupted tones give lower thresholds than continuous tones, especially at high frequencies like 4 kHz. This finding is paradoxical in that interrupted tones give lower thresholds the longer their duration. It would be expected, then, that as the duration of interrupted tones is increased their thresholds should approach those of continuous tones as asymptotic values. A study was performed in which the threshold was measured for a wide variety of durations, repetition rates, and rise-fall times of pure tones and compared with the threshold for continuous tones. The tones covered 100–10 000 Hz and were presented by a Békésy audiometer. In contrast to other reports, findings conformed to expectation: The threshold was highest for the shortest tones and reached the continuous-tone threshold, but not below, for the longest durations. A reconciliation of the differences among the various reports is attempted. [Supported by a grant from the National Institute of Neurological Diseases and Blindness.]
Binaural Loudness Summation for Tones and Noise
Authors: Fishken D. , Scharf B.
Published: October 2005

The relation between binaural and monaural loudness was measured by magnitude estimation and magnitude production for a 1000-Hz tone and for a white noise. Four types of stimuli—monaural and binaural tone, monaural and binaural noise—were presented together, at eight levels, in mixed, randomly selected sequences. Subjects were instructed to rate or adjust the four stimuli according to a single loudness scale. The loudness of the monaural and binaural tones was a power function of sound pressure with an exponent near 0.5. The loudness of the noise increased more rapidly at low levels than that of the tone; at high levels, it increased more slowly. The bow shape of the noise function would be predicted from loudness matches between wide-band and narrow-band stimuli. A binaural sound was 1.3 to 1.7 times louder than a monaural sound at the same SPL. The results of these direct loudness estimations agreed almost perfectly with earlier results from another group of subjects who made loudness matches between binaural and monaural stimuli. [Research supported by a grant from the National Institute of Neurological Diseases and Blindness.]
Segment-Synchronization Problem in Speech Recognition
Authors: Reddy D. Raj
Published: October 2005

Procedures for the segmentation of acoustic continuum of speech cannot usually guarantee that two utterances of the same phrase by the same speaker will always result in the same number of segments even under ideal conditions. To match the segmental parameters of an utterance against known parameters of the same phrase, one must determine correspondences between the segments of the two utterances. A solution to this synchronization problem that requires no time normalization can be based on the possibility labeling the segments at least in terms of phoneme groups. Segments of unvoiced fricatives and vowels can usually be more reliably detected than others. Therefore, the synchronization procedure first maps vowel to vowel and fricative to fricative. The few unmapped segments between any two pairs can then be mapped using segment labels such as nasal or stop, or on the basis of similarity of segmental parameters. This scheme is much faster than correlation-based schemes and has been used successfully in a real time recognition program. It took 4 (15) sec/recognition for a 50-(500)-word vocabulary to achieve 98% correct recognition.
Experimental Conversational Computer System
Authors: Neely Richard B.
Published: October 2005

This paper describes an experimental system with speech input and output providing a problem domain for speech analysis and synthesis research. Speech input to the computer is provided using a system developed at Stanford (Reddy and Vicens, “Spoken Message Recognition by a Computer,” to be published). Time-domain compressed speech [D. R. Reddy, J. Acoust. Soc. Amer. 44, 391(A) (1968)] is used for voice response from the computer. If a query is not one of the 25 or so messages the system can recognize, it responds with “Please repeat,” or some such. If the input is recognized, then the response is a random but relevant message chosen from about 100 messages. This system was developed not so much to talk to machines but rather to study some aspects of man-machine voice communication such as the effect of (a) a delayed reply on a human speaker, (b) intonationless speech that can result from concatenating isolated words to form a sentence, (c) the increase of vocabulary on computer speed and storage requirements, and (d) improvements to the analysis or synthesis algorithms on the over-all performance of the system.
Some Typical Sound-Pressure Levels of Recorded “Classical” Music in Home Environments”
Authors: Crabtree John B. , Coles James J.
Published: October 2005

The sound levels produced by residential high-fidelity sound systems are of considerable importance in architectural acoustics. For example, partitions between quality apartments should provide sufficient acoustical separation so that neighbors are not annoyed even when listeners to serious music play their systems as loudly as they wish. Also, designers of auditoriums should be concerned if listeners to recorded music are becoming accustomed to sound levels significantly different from those experienced in typical concert halls. We have determined the statistical distribution of the sound levels of serious music that several listeners with high-quality disk-playback equipment considered “normal” for their tastes. The measured values are presented and their implications discussed.