bluuebunny/crossref_metadata_2025 huggingface dataset:
Temperature effects on the auditory system: An amphibian case history
Authors: Narins Peter M.
Published: July 2002

The inner ear of anurans is unique in that it contains three organs specialized for sound reception. The amphibian papilla (AP), the basilar papilla (BP), and the saccule (S) are anatomically distinct, spatially separate organs each with its own complement of sensory hair cells and overlying tectorial structure. The BP and portions of the AP respond exclusively to airborne sounds, whereas other portions of the AP and the S exhibit sensitivity both to airborne sounds and to substrate-borne vibrations. Measurements from the auditory periphery of Rana pipiens pipiens suggest that in contrast to BP fibers, AP fiber tuning is highly temperature-dependent. Moreover, hair cells from the rostral AP and S exhibit a clear temperature dependence in their intracellular current step response, unlike caudally located AP and BP cells. Finally, spontaneous otoacoustic emissions, which presumably reflect hair cell motility, are highly temperature-dependent despite the fact that the upper portion of the emission frequency range (600–1600 Hz) corresponds to the domain of the BP. A model is presented that attempts to reconcile these disparate results. [Work supported by NIDCD Grant No. DC-00222.]
Lateral inhibition in frequency tuning of central auditory neurons
Authors: Jen Philip H.-S.
Published: July 2002

Previous studies have shown that frequency tuning curves (FTCs) of auditory neurons in the inferior colliculus (IC) are composed of an excitatory area that is either neighbored by an inhibitory area on one flank or is sandwiched by two inhibitory areas. Neurons that are responsible for excitatory and inhibitory areas are likely neighboring neurons. Whereas this neural lateral inhibition sharpens frequency tuning and provides a means to reduce ambiguity in encoding frequency at high stimulus intensities, neurons with two-flank lateral inhibitory areas have larger Qn values and smaller excitatory areas than neurons with one-flank inhibitory areas. The closer the inhibitory area is to the excitatory area, the sharper the frequency tuning becomes. The Qn values of IC neurons tend to increase with the ratio of inhibitory area to excitatory area. Application of bicuculline and/or strychnine broadens FTCs of many IC neurons and completely or partially abolishes the inhibitory areas. Corticofugal pathways sharpen the FTC by narrowing the excitotory area and broadening the lateral inhibitory areas. [Work supported by NSF.]
Measurement of impulse noise-induced temporary threshold shift in endangered and protected animals—Two case studies
Authors: Bowles Ann E. , Wolski Larry , Berg Erik , Yochem Pamela K.
Published: July 2002

Sonic booms at levels typical for supersonic airlines (<3 psf) are considered harmless to hearing based on laboratory studies. However, data on laboratory animals are difficult to generalize to other species. Wildlife present a particular problem because experimental efforts to induce permanent threshold shift (PTS) cannot be conducted for ethical or management reasons. Instead, ‘‘significant’’ temporary threshold shift (TTS) has been proposed as a conservative damage risk criterion (DRC). With this in mind, two series of experiments were conducted using simulated N waves at levels up to 6 psf, rise time down to 0.4 ms, and 100- or 300-ms duration—one on seals and sea lions and a second on the desert tortoise. Level of the least-detectable auditory brainstem response (ABR) was used to estimate best sensitivity before and after exposure. Small immediate threshold shifts (∼5 dB) were detected in pinnipeds and larger (∼20 dB) shifts in desert tortoises. The greater impact on desert tortoises may be explained by their greater best sensitivity at low frequencies. No PTS was detected. Thresholds for TTS were therefore detected in both species and may be useful in establishing DRCs for animals. [Work supported by NASA, Contract No. NAS1-20101 and USAF, Contract No. F33615-89-D-4003.]
Creating virtual surround using dipole and monopole pressure fields
Authors: Norris John W.
Published: July 2002

The objective of virtual 3-D sound technology is to convey to the listener an accurate impression of an acoustic environment. This is accomplished by conveying a realistic directional impression of sounds. Most of the successful techniques for doing this are based on the head-related transfer function (HRTF). In this paper a new method that creates the desired pressure field using dipole and monopole pressure fields will be presented. The object is to recreate locally the pressure field an actual sound source would produce, in a neighborhood of the listener’s ears. One of the drawbacks of using HRTF’s is that they have the pinna characteristics of the ears used to make the measurement, and so introduce the associated notches and peaks into the transfer function. The listener then has to ‘‘in effect’’ listen through these ears. And as pinna characteristics vary widely between individuals, the introduced notches and peaks associated with the measured pinnas may not correlate with the listener’s. Thus by approximating the pressure field in the neighborhood of the ears, it is no longer necessary to create artifical peaks and notches in the transfer functions.
Algorithm for the design of broadband, constant-beamwidth, point-element linear arrays with constant sidelobe level
Authors: Gaalaas Joseph B. , Hixson Elmer L.
Published: July 2002

An algorithm has been designed that allows one to calculate the individual element weights, as a function of frequency, required to achieve specified values of sidelobe level and half-power beamwidth. The arrays considered had linear geometry and an odd number of evenly spaced, point elements. The input parameters are the sidelobe level, half-power beamwidth, and the number of elements. For different values of the input parameters, the bandwidth that produced realizable solutions was determined numerically. Upon choosing values for the input parameters that yield realizable solutions, the weighting functions for each element are determined by an explicit calculation. An array may be combined with a scaled version of itself to increase the bandwidth. The element weights for an octave bandwidth broadside array were calculated using this algorithm and this array was combined with a scaled version of itself to extend the bandwidth to two octaves. Microphone and loudspeaker arrays based on these calculated weights were implemented with a digital signal processor. Measurements of the directivity patterns in an anechoic room were compared to the desired directivity patterns to assess the design procedure. [Work supported by NSF Graduate Research Fellowship and Uniden Endowed Thrust 2000 Fellowship.]
A proposal to adopt Maxwell distribution as a measure of acoustic field diffuseness in a reverberation room
Authors: Han Matias , Budhiantho W. , Hixson Elmer L.
Published: July 2002

The existence of an acoustic velocity vector resultant field which follows Maxwell distribution in a reverberation room indicates 3-D diffuseness of the field. Therefore, Maxwell distribution is a better measure for the sound-field diffuseness than Gaussian distribution given by the acoustic pressure in the same room that does not have a directional information. A Gaussian distributed pressure field does not always give a satisfactory diffuseness. The acoustic velocity vector resultant was measured using total energy density sensor. Theoretical and experimental investigations are given to support this proposal.
A Rayleigh wave model for the lip reed: Qualitative aspects
Authors: Ayers R. Dean , Birkemeier Richard P. , Eliason Lowell J.
Published: July 2002

The stroboscopic technique of Daniel W. Martin [J. Acoust. Soc. Am. 13, 305–308 (1942)] has been updated by using a video camera. Improved magnification and resolution show that the upper lip’s motion is complicated: a Rayleigh wave propagates downstream in a thin, passive layer of flesh. Muscles of the embouchure are used to adjust the tension and dimensions of that layer. The lips of accomplished performers show a wide range of detailed behaviors, due in some cases to asymmetry in the lip structure. The fact that players must find their own particular techniques for efficient control of the Rayleigh wave is significant for brass pedagogy. Seeing their lips in motion may help beginning players to advance more rapidly. Results of a preliminary survey among accomplished performers and beginners will be presented. [Work supported in part by the Scholarly and Creative Activities Committee and the College of Natural Sciences and Mathematics at CSULB.]
Self-excitation in woodwinds: From a particular model to a generic model
Authors: Barjau Ana , Gibiat Vincent
Published: July 2002

The process of sound production in a double-reed woodwind is based upon two mechanisms: the Bernoulli mechanism, which is associated only with the reed and air dynamics, and the coupling mechanism, which represents the interaction between the bore and the reed. A realistic model, close to the physical reality of the system, leads to satisfactory simulated results compared to experimental measures. However, the great number of parameters and variables appearing in the mathematical formulation makes it difficult to predict the final behavior of the system. In this paper, the realistic model is presented, and progressive simplifications are done to reduce the formulation to a single equation containing a few control parameters and a single variable. The progressive models are discussed and applied to simulate the internal pressure at the input section of the instrument. Different behaviors are then evident: from more traditional ones (periodic states) to quasiperiodic and chaotic signals.
Swiss horns and their harmonicity
Authors: Fehlmann Rolphe F.
Published: July 2002

Earlier it has been shown that there exists an optimal curved waveguide for musical purposes exhibiting a sequence of harmonic resonance modes [R. F. Fehlmann, in Intl. Congress on Acoustics, III (1995), pp. 417–421]. The radiation of some ekmelic overtones even consists of elliptical waves [R. F. Fehlmann, J. Acoust. Soc. Am. 103, 2774 (A) (1998)]. According to the hypothesis of Risset/Mathews [J.-C. Risset and M. V. Mathews, Phys. Today 22(2), 23–30 (1969)], the ‘‘warmth’’ of a sound source is due to the inharmonicity of the musical tones. However, in this paper, it is shown that this is not the case for the well-known ‘‘warm and melancholic’’ sound of the Swiss horns and thus questions the reasoning of Risset/Mathews.
A simulation model for urban traffic noise
Authors: Di Giulio A. , Mancosu F. , Nucci C. , Zocchi L.
Published: July 2002

Urban traffic noise is studied by a simulation model whose main features are the following: effects of traffic lights, speed limit, possibility of vehicles overtaking, and driving styles. In the model there is a basic assumption about driver’s behavior (‘‘follow the leader’’), considering the case of straight and level road with two lanes for every carriageway, and two traffic lights. Three driving styles are considered: A (‘‘quiet driver’’): change of gear at 60% of engine speed corresponding to maximum torque, B (‘‘normal driver’’): at 80%, C (‘‘fast driver’’): at 100%. The behavior rules provide for: keeping of safety distance, overtaking if there are vehicles at different speeds, deceleration and stop at traffic lights with red, synchronization of two traffic lights, if requested. From the kinematic side, the model was validated by comparison with acceleration distribution of a real vehicle’s flow, while the acoustic one was by the comparison with noise levels measured along urban streets. The simulation model lets one take into account the following factors concerning the traffic noise emission: main noise sources of vehicle (tires, engine, intake and exhaust system), traffic flow and maximum speed allowed, traffic mix as regards different driving styles.
Influence of the frequency-range broadening for the value of the acoustic vibrational relaxation time
Authors: Linde Bogumil B. J. , Lezhnev Nikolaj B.
Published: July 2002

This paper deals with the many acoustical investigations, provided by some scientists (Rapuano et al.), in two liquid compounds: benzene C6H6 and carbon disulfide CS2. These compounds are typical liquids where one can observe the acoustical relaxation combined with Kneser processes—energy transfer between translational and vibrational degrees of freedom. Acoustical values, a characteristic of the compounds, were different in many papers and the goal was to try to explain these discrepancies and show how it is possible to avoid these mistakes. The main problem in experimentally determining the relaxation time from the dependence of absorption and frequencies was the narrow frequency range.
Dislocations in the wave front of acoustic waves propagating through thermal turbulent fields
Authors: Blanc-Benon Ph. , Juvé D.
Published: July 2002

Acoustic waves traversing a turbulent medium develop random changes in phase and amplitude. Here the wavefront distortions of a spherical wave that traverses a medium exhibiting temperature fluctuations are investigated under well controlled laboratory conditions. A heated grid in air is placed horizontally in a large anechoic room and the mixing of the free convected plumes above the grid generates an homogeneous isotropic thermal turbulent field. By varying the frequency of the ultrasonic source and the distance of propagation, all the regimes from weak scattering to strong scattering can be explored. The presentation will concentrate on the measurements of phase variations along a linear array of microphones. Measurements of these phase differences demonstrate the limitation of the Rytov’s method for remote sensing techniques due to the existence of phase jumps between neighboring elements of the array. Numerical simulations based on a wide-angle parabolic equation are used to explain these rapid phase variations in terms of random caustics and phase dislocations.
Acoustoelectric sensing and actuating of physicochemical processes by SAW
Authors: Giriuniene R. , Garshka E.
Published: July 2002

The purpose of the paper is to present the studies of the influence of SAW in cw mode on catalyst properties of semiconductive catalyst surface and of the peculiarities of the control of chemical processes on this surface with the help of the SAW. Also, the studies of this structure when the surface of the semiconductor is covered with ion-selective membrane and the gap is filled with electrolyte are presented. It is found that SAW in pulse mode presents a very effective tool for monitoring catalytic and sorption processes on this surface and in the electrolyte itself. It allows the determination of a nature and limited stage of the reaction. The change of acoustoelectric parameters reflects the electronic processes which take place on the catalyst surface during the reaction. The activation energy of the processes on the real surface of the catalyst is determined by acoustoelectric method too. The acousto-electrocatalytic effect is investigated. It is found that SAW in cw mode changes the catalyic activity on the semiconductive catalyst surface and in some cases the catalytic selectivity of the surface.
Transmission-line modeling (TLM) of an elastic wave propagation in two dimensions
Authors: Kagawa Y. , Fujitani T. , Tsuchiya T.
Published: July 2002

Transmission-line matrix modeling (TLM) provides a simulation approach to the wave propagation for which the Huygens’ principle is discretely realized on computer. The TLM modeling is primarily developed for the electromagnetic wave propagation simulation in time domain and its application has been widely practiced. The application to acoustic field problems is the easy extension as it is of scalar field, while the elastic wave is of vectorial field like the electromagnetic wave so that a special TLM node must be developed. The formulation of the elastic wave problems are well established, which can be expressed in terms of the two separate potential waves. The two waves can independently be present, whereas is experienced in seismic wave observation, the elastic wave consists of the longitudinal and shear waves. They, however, couple at the boundaries to satisfy the boundary condition at which mode conversion is said to take place. The present paper proposes the two potential wave approach. The two scalar waves using simple regular TLM nodes are simulated to propagate independently under the boundary conditions which should properly be devised. The expression is discussed for a two-dimensional homogeneous elastic field and some examples are demonstrated, compared with the solutions of another approach, such as the finite difference.
Accurate noncontact measurement of elastic properties of ceramics using acoustic microsopy and laser ultrasonics
Authors: Flannery C. M. , Crean G. M.
Published: July 2002

Accurate measurement of elastic properties of advanced materials is of considerable importance for the further development of such materials and their applications. For many materials, data for elastic properties are not available or are unreliable. Noncontact, nondestructive techniques are of particular interest as being suitable for process control and hostile environments. Acoustic microscopy and laser ultrasonic techniques can measure bulk acoustic wave velocities (longitudinal and shear), from which elastic properties may be extracted, but there are many problems with measuring shear wave velocity with acoustic microscopy and with generating and detecting bulk acoustic wave modes using laser ultrasonics. In this work, a dual-probe beam laser interferometer setup is used to measure the velocity of laser-generated surface acoustic waves on materials; these results are combined with measurements of longitudinal velocity obtained with a standard 50-MHz point-focus-beam acoustic microscope. The technique is illustrated and applied to a set of ceramic samples (silicon nitride, silicon carbide, alumina, zirconia). Results are compared to available data and it is shown that elastic properties of isotropic materials (Young’s modulus, Poisson’s ratio) can be measured by this noncontact, nondestructive method to accuracies of 1% or better. This compares very well to other noncontact measurement methods.
Prediction of post-operative profits in cochlear implanted people using electrical stimulation test results
Authors: Skarzynski Henryk , Czyzewski Andrzej , Kostek Bozena
Published: July 2002

There are few techniques adequate for assessing the remaining sensitivity of a hearing nerve in deaf people or those with a severe hearing loss. The procedures developed at the Institute of Physiology and Pathology of Hearing in Warsaw allow the determination of some vital characteristics of the hearing sense that help to make decisions regarding the cochlear implantation. The post-operative profits evaluation is also very important in the case of cochlea implanted persons. Apart from standard preexamination procedures, a test based on the electrical stimulation via the external auditory canal filled with saline can be performed. In order to evaluate the test results, both the dynamics range defined by the auditory threshold and the uncomfortable loudness level and the time difference limen test are considered. However, usually the results of electrical stimulation tests are highly diversified, depending on a patient’s age and condition, thus there was a need to create a database allowing one to find and to study the correlation between obtained test results and patients’ ability to receive and understand sounds. In this way, the interpretation of the electrical stimulation test results for the new diagnosed cases was made more reliable. [Work supported by KBN, Poland, Grant No. 4 P05C 082 12.]
Communication problems in noisy workplaces for normal hearing and hearing-impaired employees
Authors: Franck Bas A. , Dreschler Wouter A. , Pastoors Alexandra D. , Kiessling Juergen
Published: July 2002

Although much is known about hearing impairment, there is a real lack in knowledge about the relation between unfavorable listening conditions and the individual hearing capacities of normal-hearing and hearing-impaired listeners. Moreover, occupational communication problems are hardly exploited. Therefore, a suitable questionnaire has been developed that is based on studies of Gatehouse (1994), Kapteyn and Kramer (1997), and Boermans (1997). The questionnaire was completed by four different subgroups that cover hearing-impaired subjects with and without hearing aids and normal-hearing subjects that work in soft or loud background noise. It appears that most hearing-impaired employees mainly suffer from speech-related soft noises, especially in communicative tasks. Loud noises are annoying for all subgroups, whereas reverberation causes only problems in high noise levels. Localization and identification appear to be strongly related and are only problematic for a subset of the hearing-impaired subjects, without hearing aids. Interindividual differences between subjects suggest a need for flexible communication devices. These devices should combine functions of selective amplification, protection, recognition of warning sounds, and reduction of noise and reverberation. [Work supported by TAP.]
On the acoustical properties of cylindrical shells and pipe sleeves
Authors: Gužas D.
Published: July 2002

Acoustical properties of cylindrical shells and pipes differ greatly from plane sound insulation properties. Sometimes opposite results are achieved, especially at low frequencies. The report presents these differences and causes that have been proved theoretically. The sound permeability through sleeves has not been fully investigated as yet. Here analysis and comments of the works performed are presented.
Application of active control techniques to the turbomachine fan noise reduction
Authors: Julliard J. , Lozachmeur Ch. , Berge D.
Published: July 2002

Fan noise is a dominant source in future high-bypass engines with a lower and more extended frequency signature. The reduced efficiency of passive liners with thinner and shorter nacelles leading to a more severe noise legislation requires work on active technologies in order to reduce even better the fan noise radiation (especially tones) in the near and far fields. This paper deals with active noise control (ANC) applied to the reduction of fan tones. The described investigation is an experimental study performed on a fan model installed in an anechoic chamber. Error sensors are successively located in the near-field radiation and flush mounted in the forward and aft duct fan. Loudspeakers are used as actuators to generate a secondary acoustic field. A moving antenna in the far field measures the noise radiation and the zones of silence. A new multi-channel controller, highly efficient in terms of frequency and channel number, is used. Transfer functions between actuator and sensors are analyzed and numerical simulation calculations are achieved for optimization of the number and location of error sensors and actuators. Fundamental tone of the fan is controlled with reductions up to 10–15 dB.
Comparison of two algorithms for modal active control of fan noise in a duct
Authors: Tardy Laurent , Gonneau Eric , Guilhot Jean-Pierre
Published: July 2002

The reduction of fan noise in circular ducts has been realized using active control. Preliminary modal decomposition has allowed the determination of preponderant acoustical modes. The comparison of two methods has been executed both in simulation and experimentation. First, the x-filtered LMS algorithm has been tested. The second algorithm, based on a harmonic controller specially adapted for tonal noise, was composed of multiple in-phase and quadrature weights; it only needs two complex coefficients per frequency and per mode. Simulations have been first performed to evaluate filter lengths and step sizes. In an initial experiment, the fundamental has been reduced by 15 dB thanks to a SISO environment acting on the (1,0) mode. Then, with a MIMO controller, the (0,0) and the (1,0) modes could have been cancelled simultaneously at the fundamental frequency and the first harmonic. The test bed is composed of an axial fan whose fundamental frequency is 2150 Hz and a 0.1-m-diam duct; the actuators and sensors are, respectively, crowns of four loudspeakers and four error microphones mounted on the wall. With regard to these experimental results, both control methods have been compared, looking at efficiency, stability, and speed, in accordance with computational complexity.
Analysis of voiced speech using harmonic models
Authors: Stylianou Yannis
Published: July 2002

It is very common to consider voiced speech as a periodic or quasiperiodic signal. Therefore, harmonic models are usually proposed for the modeling of this part of speech. This paper focuses on the harmonic analysis of speech. Three models are presented and compared. The first model is the simplest among the three models and it supposes that the speech signal is a stationary signal. The second model does not make the hypothesis of the stationarity of the speech signal; however, it is an harmonic model. The third model does not consider speech as a stationary signal, and even though the fact that it uses the fundamental frequency as the basic frequency of the signal, it is not an harmonic model. The analysis presented here has as a goal to clarify the harmonic analysis of speech signals. From an application point of view, the first simple model seems to be quite good for low bit rate speech coding. The other two models are more complicated and they need more parameters to represent the speech signal. However, these models are more efficient in modeling the speech signal and they give us more insight about speech that can be used on applications like speech analysis and synthesis.
Crime-detection automatic speaker verification and identification (CASVI) system
Authors: Gorban Igor I. , Gorban Nick I. , Klimenko Anatoly V.
Published: July 2002

The crime-detection automatic speaker verification and identification (CASVI) system, using a new spectral and cepstral analysis technique, is described. Robust speaker recognition algorithms, the operation modes, the control windows, the testing methodology, and the testing results of the system are presented. Research of the system has shown it can efficiently work with strongly corrupted utterances, while the corruption of the utterances being compared may be considerably different. For any utterances, permissible frequency distortions are 35 dB in the operating band and the permissible signal-to-noise ratio of additive noise is 12 dB. In these conditions, the CASVI system using 12-s speech utterances demonstrates the possibility to verify and identify persons on the level of 90% of correct acceptance when the false-alarm rate is 10%. The verification and identification time by the system takes some minutes. The CASVI system does not require high qualification of an expert. The system has a very simple interface that allows working in full automatic mode and forming reports without any special schooling. The CASVI system is a software product installed on a Pentium-based PC running with Windows 95.
Effects of lip protrusion on measurements of lip aperture
Authors: Whalen D. H. , Gick Bryan , Lofqvist Anders
Published: July 2002

Lip movement during speech has been measured by many techniques. One common class of methods uses one marker for each lip, usually located midsagittally at the vermilion border. However, equating the distance between markers with the distance between the lips is problematic. Westbury and Hashi [J. Phonet. 25, 405–419 (1997)] found that compression of the lips during stop closure precluded using a single value for the minimum distance when the lips were together. Thus lip trajectories alone cannot determine the point of closure nor estimate lip aperture during vowels. The present experiment used video images collected simultaneously from front and side views of phonemes varying in lip shape (three vowels, two fricatives). The distance between the vermilion borders (i.e., typical marker locations) was about 3 mm larger than the actual aperture for /u/ relative to /a/ and /i/ and for the palatal fricative relative to /s/. This difference correlated best with the degree of upper lip protrusion. Outward curling of the lips, bringing the inner margins closer during rounding, seems the likeliest explanation. Predicting the actual aperture from marker locations must consider both the vertical separation and the degree of protrusion. [Work supported by NIH Grant No. DC-02717.]
MM and the music world
Authors: Ramone Phil
Published: July 2002

Creating music for the new and old media, for example: DVD standard, downloading, compression, and watermarking. The future of music production minus picture or a full bandwidth audio with high-quality pictures, including documentary. In general, the new frontierlike canvas of 1999 into the new millenium.
Vibration characteristics of microphone membranes
Authors: Pastille Holger
Published: July 2002

Using laser scanners, the vibration pictures of the condenser microphone diaphragms were taken. In order to be monofrequent, the microphone was in an impedance tube. Standard microphones were used. The behavior of the vibrations can be well observed in the animated pictures. Besides the fundamental component, the nonlinear parts are also of special interest. Coherence between the sound-pressure level and the distortion of the microphone cap is seen. Seen also is the motion of the diaphragm itself. Results are shown for two studio microphones and a measuring microphone, each for three selected sound-pressure levels.
Development of a multiprocessor system (HUGO) for acoustic applications
Authors: Kleber Jochen
Published: July 2002

For research in acoustics, audio signals must often be subjected to a complex processing. For listening tests, a real-time processing becomes desired in practice, in order to be able to switch between different situations. A free programmable device was implemented with up to eight channels with analogous and digital inputs and outputs. On four DSP’s with a computing power of in total 160 MIPS, applications can be implemented. During design of hardware and software, it was considered to highest audio quality. In future this device can be used for other interesting developments, such as multichannel front ends with an A/D dynamics of 125 dB. In the paper, two applications will be presented more closely: crosstalk cancellation and binaural mixing console.
Low-pass filter for the DFT process and its application to impulse response of sound-field and ultrasonic B-mode echo simulator
Authors: Lawu Tjundewo , Ueda Mitsuhiro
Published: July 2002

Convolution and correlation are closely related operations that are basic to many areas of signal processing. To obtain the frequency component of the signals using discrete Fourier transform (DFT), the continuous signals must first be sampled. A low-pass antialiasing filter which is simple to implement is proposed. The low-pass filter has equally good frequency response characteristics and can be used to eliminate possible aliasing effects by ensuring that the signal to be sampled is limited in the spectral content. The impulse response of the sound field was calculated by using the proposed low-pass antialiasing filter and compared with the rigorous solution to verify the realizability of the filter. The filter was also applied to construct the ultrasonic B-mode image of a 3-D phantom model.
Numerical simulation of time domain ocean acoustic propagation
Authors: Boisson Cedric , Piraux Joel
Published: July 2002

The time domain parabolic equation is studied for ocean acoustic long-range propagation, including wide-angle propagation, without involving Fourier synthesis. Instead of solving the wave equation with boundary conditions in the whole ocean domain, the governing equations are written in a moving coordinate system. Since the studied frame is moving with acoustic perturbations, dependent variables evolve more gradually, which increases time integration accuracy. The number of space points and thus CPU time are greatly reduced because the pulse occupies a narrow range window. Numerical tests were made to study first the headwave problem by handling discontinuities of sound speed and density at a layer interface. Media with continuously variable celerity profile were also studied: there was a particular interest in studying wave propagation in media with multiple deep sound channels. Results were compared with those worked out with other codes based on Bessel–Fourier analysis (SPARC developed by M. B. Porter), requiring much CPU time. An excellent agreement was observed. The originality of the interactive program developed is to display a movie of wave propagation. It is an efficient tool to solve the direct problem and consider the inverse problem.
Internal wave imprint in the oceanic ambient noise
Authors: Furduev Alexandr V. , Serebryany Andrey N.
Published: July 2002

Investigations of dependencies between the characteristics of ambient noise field and different types of hydrophysical inhomogeneities in the ocean had revealed the possibility of realization of passive acoustic tomography methods (without transmitting signal and only on the basis of a noise field). Internal gravity waves are one of such inhomogeneities. They are manifested in the ambient noise field by modulation of noise level due to variation of sound-speed profile and by noise of ‘‘suloy’’ created on the sea surface by intense internal waves. The results of complex field experiments on synchronous measurements of internal waves and ambient noises are presented and analyzed. The observations were carried out near the Mascarene Ridge in the Indian Ocean, the region of generation of large-amplitude internal waves. The interrelation between fluctuations of noise field (received by vertical array of hydrophones) and vertical displacements of thermocline caused by internal waves had confirmed the possibility of practical realization of the acoustical system for internal wave observation. It was shown that amplitudes, periods, number of modes and directions of internal wave propagation can be determined on the basis of measuring of noise fluctuations. [Work supported by Russian Foundation for Basic Research.]
First results from an acoustic-communication transmission model using 3D Gaussian beams and quadrature detection
Authors: Baxley Paul A. , Bucker Homer , Rice Joseph
Published: July 2002

Analysis of shallow-water, acoustic-communication channels must account for the joint phenomena of multipath spread and Doppler spread. A physics-based, numerical propagation model is being developed to reproduce these effects via the combined use of three-dimensional Gaussian beams and quadrature detection for finite-duration tones. Closely spaced microbeams are traced in three spatial dimensions to properly incorporate out-of-plane boundary effects from rough boundaries and a sloping sea- floor. Refraction, absorption, reflection, scattering, and Doppler-shifts influence the individual beams according to our best understanding of these physical processes. At an arbitrarily located quadrature-detector receiver, signal contributions are accumulated with coherent treatment of the travel-time, phase, and Doppler shifts associated with each microbeam. This approach supports the analysis of the spatio-temporal dispersion associated with the significant multipath arrivals. Fluctuation and coherence statistics may be analyzed via the specification of source/receiver motion or time-varying boundaries. Simulations of the quadrature response for measured shallow-water channels (<200 m) near San Diego, California will be presented. For these first case studies, sea-surface roughness is neglected, but scattering from a rough bottom is considered and Doppler spread is assumed to arise solely from source/receiver motion. [Work supported by the SPAWARSYSCEN San Diego Independent Research Program.]
Improved reliability and data rates for AUV acoustic communications
Authors: Kilfoyle Daniel
Published: July 2002

The availability of parallel channels in a point-to-point communication system may be exploited to increase data rate and reliability, without additional power, beyond that possible with a single channel. The severe power and bandwidth constraints imposed on an autonomous underwater vehicle acoustic telemetry link motivate the use of spatial modulation techniques to achieve these benefits, particularly for missions requiring real time sensor data transmission. Theoretical performance improvements for coherent modulation schemes yielding the equivalent of 6 dB or greater signal-to-noise ratio gain are shown. Experimental results from an underwater range near the Bahama Islands are given. Inclusion of a modest horizontal line array on the vehicle and a remote transceiver on the surface are the sole additional requirements beyond a conventional telemetry system.
Three-dimensional auditory display of passive sonar data
Authors: Richardson Suzanne , Loeffler Charles
Published: July 2002

Submarine sonar operators typically use visual and monaural audio outputs to locate obstacles, ships, and animals in the surrounding ocean. Recently, the effectiveness of using 3-D, rather than monaural, sonar audio outputs was investigated. A multi-channel signal processing system has been developed that converts sonar signals collected by elements of a hydrophone array into binaural signals for the left and right ears, which provide accurate 3-D aural imaging of an underwater acoustical environment. An operator who listens to the binaural signals via stereo headphones will perceive that he is immersed in the underwater acoustical environment. The system incorporates two banks of FIR filters (one for the left ear and one for the right ear) to process the sonar data. The FIR filters simultaneously beamform the hydrophone data and filter the data with head-related transfer functions in order to create binaural signals that provide 3-D sound. [Work supported by Applied Research Laboratories: U. T. Internal Research and Development.]
Fluctuation of room acoustical parameters on small spatial intervals
Authors: de Vries Diemer , Baan Jan
Published: July 2002

The Delft Acoustics group has introduced array technology in room acoustic measurement practice: instead of at a limited number of ‘‘representative’’ places, impulse responses are measured along an array of closely sampled microphone positions. By displaying the responses as a visual entity, the wave character of the sound field is clearly revealed. The data form a base for further processing, enabling the separation and analyzing of the different wave-field components. The sound fields in several concert halls have been measured this way. From impulse responses recorded with 0.05-m spatial separation, the common room acoustical parameters have been determined. It appears that, even between the ten positions in front of one and the same seat, unexpected fluctuations occur, e.g., when measured in octave bands, the clarity index varies over 1 dB on this interval, the lateral energy fraction 0.2 (i.e., between 0.1 and 0.3). For the broadband versions, these variations are approximately halved, still being significant. These results explain why the predictive value of these parameters for the perceptual quality of the acoustics on a (group of) seat(s) is limited. Instead of at one point, the values at several adjacent points should be considered.
Enhancement of fibrinolysis by low-intensity c.w. ultrasound
Authors: Francis Charles W. , Suchkova Valentina , Everbach E. Carr
Published: July 2002

Continuous-wave ultrasound at intensities below 4 W/cm2 (SATA) and frequencies around 1 MHz has been shown to accelerate enzymatic fibrinolysis in vitro and in some animal models. The mechanism for this ultrasound accelerated thrombolysis (UAT) is unknown, although heating is unlikely. Hyperbaric studies have shown that approximately half of the acceleration is removed with overpressures of 3 atm or more, implicating cavitational mechanisms as dominant contributors to UAT, if not the sole ones. Detection of bubbles and cavitational activity in UAT via passive and active detectors corroborates this view. Recent studies using 40-kHz cw ultrasound at intensities as low as 0.25 W/cm2 show promise for eventual clinical applications, including insonification through bone without significant heating. [Work supported by NIH.]
Multi-purpose apparatus for evaluation of noise transmitted through air ducts
Authors: Di Bella Antonino , Zecchin Roberto
Published: July 2002

The noise generated in HVAC systems by fans or air turbulence is propagated along ducts and, through duct walls, can be irradiated in rooms; moreover duct lines can easily transmit the sound produced in noisy environments from one room to another, vanishing the sound insulation of walls which they are passing through. The knowledge of sound insulating properties of duct walls is fundamental for a good system design, including unitary attenuators and active noise control devices. In this work a multi-purpose apparatus for evaluation of noise transmitted through air ducts in a reverberant room is presented. This apparatus allows one to measure, with the same equipment, the sound power level emitted from a short length ducts specimen in a reverberant room, as well as linear sound attenuation and break-in and break-out transmission loss. A further application of the same apparatus is the measurement of sound insulation and normal incidence impedance of small plane elements of isotropic or composite materials.
Hybrid discrete vortex method (DVM)/boundary element method (BEM) calculations for cavity acoustics
Authors: Epstein Ronald J. , Leonard Anthony , Cain Alan B.
Published: July 2002

A hybrid computational methodology has been developed for cavity acoustics applications. The method utilizes a discrete vortex method coupled to an acoustic boundary element calculation. The discrete vortex method uses a Lagrangian evolution in time and space of a field of Gaussian distributed vortex blobs to simulate a two-dimensional, time-dependent, vorticity dominated shear layer. The method yields accurate and fast unsteady solutions to the time-dependent nonlinear flow equations. The cavity acoustics is modeled using acoustic boundary elements which are distributed on the surface of the cavity geometry. The vortex simulation of the shear layer is coupled to the boundary element calculation through Neumann boundary conditions imposed on the cavity surface. The hybrid method simulates a shear layer interacting with a cavity at low Mach number. In example calculations, acoustic radiation and far-field directivity patterns are calculated for the two-dimensional cavity/shear layer system.
Acoustic pulse sounding of the atmospheric boundary layer
Authors: Chunchuzov Igor P.
Published: July 2002

The method of acoustic pulse sounding of the atmospheric boundary layer is used to study spatial coherence and frequency spectra of the pulse travel time fluctuations between the pulse source and the triangular set of receivers 2.5 km apart from each other. The wind speed fluctuations were measured up to 200–300 m with the use of SODAR and the anemometers placed on the mast of 56-m height. The maximum coherence between the wind speed and pulse travel time fluctuations was obtained for the period of 8 min. This period is thought to be associated with the ducted internal waves in the troposphere. The use of the pulse sounding for the acoustic tomography of the atmospheric boundary layer is proposed.
Investigation of the effects of acoustic refraction on Doppler measurements caused by wind- and temperature profiles
Authors: Schomburg Annette , Englich Detlef , Mellert Volker
Published: July 2002

The subject of this investigation is the errors appearing in Doppler SODAR measurements due to wind and temperature profiles. Usually the wind velocity is calculated from the measured Doppler shift under the assumption of straight line propagation. Wind and temperature profiles cause a deviation of the rays from the straight path which is given by the choice of geometry between transmitting antenna, receiving microphone and scattering volume. The appearing errors in the magnitude of the Doppler shift because of the displacement of the scattering volume, changes of scattering angle, and scattering vector have been investigated. Results from simulations, where the exact position of the scatterer, as well as the ray deformation, has been taken into account, show that upwind and downwind errors are symmetrical. This leads to a new method of measuring wind profiles. Outdoor measurements performed with a new SODAR configuration will be presented. Four receivers allow a construction in which each receiver pair builds a plane to measure down- and upwind components. The resulting two wind profiles describe the horizontal wind component. With a fifth receiver near the source, the vertical component should be measurable, so that the complete wind vector and even the temperature profile could be determined.
The Radar-RASS spaced-antenna windprofiler, a tool to measure atmospheric turbulence
Authors: Hirsch Lutz
Published: July 2002

Recently a Radar-RASS spaced-antenna wind profiling system with four receiving antennas has been developed. The system was designed to use the RASS-signal for radar-interferometry measurements of high-resolution time-series of the 3-D wind vector. The use of the deterministic RASS-backscatter signal which is insensitive to clutter interferences from the ground or elevated targets makes this system a useful tool for turbulence observation in the atmospheric boundary layer. The well-known problem of overestimating the horizontal velocity using simple correlation algorithms, caused by decaying refraction pattern, had to be addressed carefully. Multiple published approaches to find the correct horizontal velocity in the frequency domain using power and cross spectra as well as in the time-domain using correlation-functions were compared to each other. Based on these comparisons the implementation of the most suitable algorithm for the present system together with problems like noise suppression or system constants estimation will be discussed. Results of field measurements will be presented and the performance of the system to derive high-resolution time series of the 3-D wind vector will be demonstrated. Average quantities will be compared with the results of a SODAR operated next to the RASS.
On the frequency effect and the solvent effect in sonochemistry
Authors: Bartik Kristin , Segebarth Nicolas , Vandercammen Juliana , Reisse Jacques
Published: July 2002

The frequency effect in sonochemistry remains an open question. On the basis of data reported in the literature it seems that sonochemistry in water is faster in the high-frequency range (between 500 kHz and 1 MHz) than in the low-frequency range (between 20 and 100 kHz). This work is devoted to the study of the frequency effect in various solvents. The study of a frequency effect is far from trivial. Indeed, a systematic study would require that all the other parameters of the system be kept constant. This condition is never fully fulfilled. Heat dissipation and electrical energy consumption were used to characterize the ultrasound intensity even if criticisms can be formulated against these very indirect methods of measuring the ultrasound intensity. Various sonochemical reactions were studied. The frequency change (with all that it encompasses) clearly has an effect, and this effect is different in water, organic solvents, and emulsions. An interpretation of these observations will be proposed.