bluuebunny/crossref_metadata_2025 huggingface dataset:
An indirect method for computing troublesome coefficients in the boundary integral equation method
Authors: Kessel Ronald T.
Published: July 2002

The boundary integral equation (BIE) method is ideal for modeling scattering of waves from arbitrarily shaped objects embedded in unbounded domains. Its singular or ‘‘self’’-coefficients require special numerical treatment because the kernel of the integral equation exhibits the singularity of the Green’s function for a fundamental point source. Regularization for direct numerical integration is particularly complicated for elastic waves in layered media where the Green’s function is a tensor whose elements cannot be written in closed form. Here the singular coefficients are computed indirectly, by inferring their values from a family of related propagation scenarios whose solutions are known in advance by virtue of Huygens’ principle. The method can be applied quite generally to compute other potentially troublesome coefficients, which may occur in thin platelike objects, for example, when one boundary element lies close and parallel to another on the opposite face, or in horizontally stratified media when one element lies directly above another, making the Green’s function poorly convergent. The method is verified here for scattering from elastic spheres (low to moderate ka), and is demonstrated for scattering from an ice keel in floating sea ice, and for a sphere half-buried in seafloor sediments.
Background speaker noise removal using combined EM sensor/acoustic signals
Authors: Ng Lawrence C. , Holzrichter John F. , Burnett Gregory C. , Gable Todd J.
Published: July 2002

Recently, very low-power EM radarlike sensors have been used to measure the macro- and micro-motions of human speech articulators as human speech is produced [see Holzrichter et al., J. Acoust. Soc. Am. 103, 622 (1998)]. These sensors can measure tracheal wall motions, associated with the air pressure build up and fall as the vocal folds open and close, leading to a voiced speech excitation function. In addition, they provide generalized motion measurements of vocal tract articulator gestures that lead to speech formation. For example, tongue, jaw, lips, velum, and pharynx motions have been measured as speech is produced. Since the EM sensor information is independent of acoustic air pressure waves, it is independent of the state of the acoustic background noise spectrum surrounding the speaker. By correlating the two streams of information together, from a microphone and (one or more) EM sensor signals, to characterize a speaker’s speech signal, much of the background speaker noise can be eliminated in real time. This paper presents several algorithms to demonstrate the added noise suppression capability of the glottal EM sensors (GEMS). [Work supported by NSF and DOE.]
Transmission loss since Urick
Authors: Spofford Charles W.
Published: July 2002

Advances in understanding propagation of ‘‘underwater sound’’ are traced from the view expressed in Urick’s 1967 landmark text to our current state through two remarkable transitions. First, propagation in 1967 was an arcane phenomenon with annoying, questionably modelable ‘‘anomalies’’ from spherical spreading which forced extensive global measurements. It is now known to be a stable, well-understood property of the ocean whose predictability is limited only by our knowledge of the controlling environmental inputs. In fact, models are now being used to deduce that environment through inversions. Second, the ‘‘TL’’ term in the sonar equation has expanded to include coherence measures inextricably coupled to the ‘‘gain’’ terms. These are being routinely modeled, again limited mainly by our knowledge of the environmental inputs. The variety of approaches to modeling propagation hinted at in Urick has blossomed to form a powerful set of tools for designing and analyzing a wide range of sonars. Geo-political ASW concerns gave birth to ‘‘underwater sound’’ for engineering sonar systems of ever increasing complexity and challenged us in 1967 to understand the physics of deep-water propagation. In 1999 our challenge is to extrapolate that physics to the world’s enormously variable shallow-water areas.
Bob Urick and ambient sea noise
Authors: Cavanagh Raymond C.
Published: July 2002

Selected highlights of progress in the measurement and understanding of ambient sea noise are presented, from the time of publication of the first edition of Urick’s pioneering textbook (1967) through his noise monograph (1984) and beyond. Urick’s presentation of the fundamentals became the primer for a generation of ocean acousticians and the basis for many of today’s theories and predictive capabilities. Valuable insights were derived from his direct involvement in the measurement and interpretation of noise data, dating to the early 1950’s. His treatments of arctic and shallow-water noise anticipated research initiatives of the 1980’s and 1990’s, as did his framework for noise fluctuations. Some notable advances since Urick’s publications are discussed, including: mechanisms for wind-wave noise sources, predictive models for ship-generated noise properties, the noise ‘‘floor’’ and noise increases over time, directionality, and the effects of coastal sources. His attention to the details of metrics and units for ocean acoustic quantities is acknowledged as a special contribution to the field.
Detection threshold
Authors: Cox Henry
Published: July 2002

Detection threshold or recognition differential is defined as the signal-to-noise ratio at the beamformer output required for detection. An introduction to this topic is provided in Uricks’ Principles of Underwater Sound. The subject is frequently a source of confusion due to the multiple possible definitions of signal-to-noise ratio, the effects of nonlinearities in the signal processing, and the overall complexity of the sonar operators job of signal recognition in real-world clutter. In this paper, a review of the basic theory of mathematical relationships are provided, followed by a discussion of practical limitations in applying simple formulas to performance predictions. The relationships of detection threshold to the signal-processing approach and background-noise statistics are discussed. Active sonars in both noise and reverberation, as well as passive sonars involving energy detection, spectral analysis, and cross correlators are discussed.
A robotic platform for investigating the usage of acoustic flow in cf-bats
Authors: Carmena Jose M. , Hallam John C. T.
Published: July 2002

In this work, a biomimetic sonarhead mounted on a mobile robot is used as a platform with which to test the type of acoustic flow in cf-bats considered by Muller [R. Muller and H.-U. Schnitzler, J. Acoust. Soc. Am. (submitted)]. Such acoustic flow, based on changes in Doppler shift and echo amplitude, provides crude localization information which suffices for tasks like obstacle avoidance in which high accuracy is not needed. Previous results with the biomimetic sonarhead [V. A. Walker, H. Peremans, and J. C. T. Hallam, J. Acoust. Soc. Am. 104, 569–579 (1998)] showed the availability of dynamic cues in the form of frequency and amplitude modulations obtained by pinnae motion. Kuc’s sensorimotor model for the fm bat [R. Kuc, J. Acoust. Soc. Am. 94, 1965–1978 (1994)] has been adapted to the cf bat and implemented in the robot. Appropriate experiments, composed of a prey capture task during which obstacle avoidance by means of acoustic flow is performed, have been designed to exclude trivial static cues such as the echo delay correspondent to the closest reflector. The results of this on-going work will be included in the final abstract if accepted.
Noninvasive ultrasonic interruption of contrast agents for monitoring flow in hepatic vasculature
Authors: Rhee Richard , Fowlkes J. Brian , Rubin Jonathan , Carson Paul
Published: July 2002

An experimental setup has been designed to assess differential liver perfusion due to the hepatic artery (HA) and the portal vein (PV) using continuous intravenous infusion of ultrasound contrast agents (CA) and transcutaneous ultrasound applied to target selected vessels. A perfluorocarbon-based CA was continuously infused intravenously in the ear vein of New Zealand White rabbits. A 1-in.-diam single element medical ultrasound transducer was applied transcutaneously to interrupt the CA in the abdominal aorta. Real-time feedback from the ultrasound scanner showing the clearing of CA in the target vessel indicated successful positioning of the interruption transducer. The clearing of all CA from the hepatic vasculature was accomplished by a sufficiently long pulsed insonification of the interruption transducer. The interruption transducer was turned off, producing a sharp bolus of CA. Rapid bolus rise times on the order of 0.1 s were observed in the abdominal aorta. Sharp demarcations in vascular response between the HA and PV to the applied CA bolus was observed. Differential arrival times of the bolus between the HA and PV on the order of 7 s was measured by analysis of spectral Doppler images. Through this technique, liver perfusion due to HA and PV may be discriminated.
Control of cavitation in lithotripsy by waveform shaping
Authors: Davenny Benjamin C. , Cleveland Robin O.
Published: July 2002

Cavitation has been proposed as a possible mechanism in lithotripsy. Results presented by Bailey et al. [J. Acoust. Soc. Am. 104, 2517–2524 (1998)] using an electrohydraulic lithotripter indicate that cavitation field created by a lithotripsy shock wave can be dramatically affected by the shape of the incident pressure waveform. We consider a piezoelectric lithotripter with 170 elements which allows for great flexibility in creating pressure waveforms. Pressure pulses are constructed from both predicted and measured waveforms. The Gilmore–Akulichev formulation is used to model the response of a cavitation bubble to the pressure waveforms. Preliminary numerical results have been obtained using single pulses and multiple pulse sequences. Results from the bubble dynamics model indicate that careful construction of the pressure pulse can lead to either enhanced or diminished collapse of cavitation bubbles. [Work supported by NIH-DK43881.]
Integrated diffusion and ultrasound therapy unit, for membrane transport studies
Authors: Bond Leonard J. , Diaz Aaron A. , Judd Kayte M. , Ng Lawrence K-Y.
Published: July 2002

The application of ultrasound has been shown to enhance transport through a variety of membranes. This paper will present the design, calibration and initial results for a custom integrated ultrasound therapy and diffusion cell for use with a system that is a model for the blood brain barrier. The unit is designed to operate at frequencies between 300 kHz and 35 MHz, with initial trials and data taken at 1 MHz. Power levels are comparable with those commonly used in physical therapy (0.5–10 W/cm2). Unit calibration has included ultrasound field and point measurement, and both thermal and electrical measurements to calibrate power delivered. The unit is designed to hold standard snap-well cell culture supports, which are used with a cell culture system that consists of primary cultures of bovine microvessel endothelial cells. Preliminary data with a prototype-cell provide an enhancement in diffusion of up to a factor of 3. This paper will present new data, for the new cell, which has significantly improved acoustic characteristics.
Aerodynamic sound from a high-speed transitory wave by Rayleigh’s formula
Authors: Powell Alan
Published: July 2002

Lighthill’s theory of aerodynamic sound generation and the vortex theory are not well-suited for application to high-speed periodic flows. Another method, used for very low Mach number flows, employs Helmholtz’s formula, for which the very near-field (incompressible) perturbations on the enclosing boundary can be determined by any useful method, vortex or otherwise. This notion is carried over to a screeching supersonic jet, for which Schlieren photographs show evanescent waves that appear to be the source region: they extend far beyond the jet boundary into the ambient fluid. For rectangular jets, Rayleigh’s formula can be reduced to a line integral through the evanescent field just exterior to the jet. The jet instability can be represented by a convecting sinuous transitory wave in the jet boundary that grows and then decays spatially according to some envelope function. The establishment and the decay of the associated evanescent field result in radiation. Because of very effective cancellation, the radiation is very weak except at convective Mach numbers approaching unity, when a single downstream maximum occurs. The intensity is insensitive to the envelope shape and does not follow any simple power law. Plausible assumptions lead to realistic intensity estimates.
Teaching acoustics courses on the Internet
Authors: Wheeler Paul A.
Published: July 2002

This paper describes a general education course in acoustics taught over the internet. This makes the course available to colleges and universities not currently teaching courses in acoustics. The paper discusses challenges faced in offering on-line courses, such as homework, labs, and exams. This course uses a software package called webct, which provides an administrative backbone for the course. The backbone includes: web navigation, exam base, threaded discussions, and tools to track students. Exam questions include formula-based questions for which each student receives a different input variable which is automatically calculated and compared to the student’s answer. One difficulty in creating a web-based course is providing a hands-on lab experience. Traditional labs were converted into web activities and home activities. Web activities use the internet to supplement information found in the text. Home activities allow students to perform experiments at home which are later submitted through the web. All submissions and grading is done on the web, including homework, exams, web and home activities. The course works well for handling the large number of students commonly found in general education courses while providing access to nonconventional students taking the course through distance education.
Development of computer-based interactivities in hearing science
Authors: Zurek Patrick M. , Durlach Nathaniel I.
Published: July 2002

Work is underway to develop a CD-ROM collection of interactivities to supplement undergraduate and graduate instruction in hearing science. No attempt is made to provide complete coverage of hearing science in a stand-alone course. Rather, the approach emphasizes and exploits those features that can make multimedia computer-based presentation so valuable as a teaching adjunct: animation, audio output, and interactivity. With these capabilities, moving graphical images can represent physical or conceptual objects to help convey ideas and relationships that are difficult to illustrate with static images. In addition, the student is given extensive opportunity to hear the stimuli and experience the relevant psychoacoustic phenomena directly. Most important, in the current approach, unlike what can be achieved simply with prerecorded materials, students are given sufficient control over the signals, parameters, and procedures, to conduct a wide variety of experiments. To a significant degree, the materials provide each student with a personal laboratory. The CD-ROM now being developed, which includes interactivities in basic auditory anatomy, physiology, and perception, will be useful both for classroom demonstrations by an instructor and for work by individual students. [Work supported by NIDCD.]
Dan Martin and musical acoustics
Authors: Keefe Douglas H.
Published: July 2002

Dan Martin published research findings on musical acoustics in the Journal of the Acoustical Society of America in the years 1941–1983. Among the areas of inquiry were the acoustics of musical instruments including the brass wind instruments, piano, organ and electroacoustic instruments, subjective musical acoustics, and the complex interactions between the instrument, the concert hall and the listener. A retrospective examination of these publications highlights the progress made in musical acoustics as well as questions that remain the concern of current and future research.
An examination of the acoustic characteristics of four churches
Authors: Marshall L. Gerald
Published: July 2002

For over 15 centuries, the axial-plan basilica church and its cruciform derivative have comprised the dominant architectural forms employed for Christian churches. The author has selected four churches with which he is intimately familiar, ranging in size from ‘‘cathedral’’ to ‘‘meeting-house,’’ to illustrate acoustic attributes and differences associated with specific geometric qualities, including choir/organ placement. Personal experience with the buildings includes participation as a congregant, as a performing musician in concerts, and/or as an acoustic consultant. Measured data include RT, C50 for speech intelligibility, C80 for music clarity, and organ/choir sound distrubtion.
Guidelines for the measurements and assessment of low-level ambient noise
Authors: Fleming Gregg G.
Published: July 2002

The Federal Aviation Administration’s Office of Environment and Energy (FAA/AEE) with support from the Acoustics Facility at the John A. Volpe National Transportation Systems Center has developed a detailed methodology for characterizing ambient noise in low-level environments such as the National Parks. The presentation will include a general overview of the method, along with a brief historical perspective. Specific details of characterizing a study area’s ambient noise will be outlined, including measurement site selection, instrumentation, and general field measurement procedures. Particular attention will be given to the data reduction and analysis methodology, including guidance on assigning actual measured ambient noise to specific locations within a study area. In addition, several examples of how this methodology has actually been utilized in a practical field measurement application will also be discussed.
Measurement of the natural soundscapes in south Florida National Parks
Authors: Downing Micah , Hobbs Christopher , Stusnick Eric
Published: July 2002

The National Park Service is in the process of developing noise management plans for one or more of its parks in south Florida—Everglades National Park, Biscayne National Park, and Big Cypress National Preserve. A central concept is the definition of the natural (ambient) soundscapes as a resource to be managed as authorized by the NPS Organic Act of 1916 and other relevant mandates. The key to this concept is the development of a credible and defensible description of that resource. Previous studies have involved sound level monitoring with manned observations over relatively short time periods of 1–3 h in which all natural and intruding sounds were identified. This study evaluated the use of unmanned monitors to extend the measurement of the natural soundscapes to time periods of several days duration. Results from unmanned measurements will be compared to previous manned studies and methods for quantifying the natural soundscape and the effect of intrusions will be discussed. [Work supported by The National Park Service.]
Analysis of surface instability in an elastic anisotropic cone by the use of surface waves of weak discontinuity
Authors: Shitikova Marina V. , Rossikhin Yuriy A.
Published: July 2002

The problem of surface instability of a right circular hexagonal cone is investigated. The surface of the cone is free from stresses, but in the near-surface layer initial constant tensile or compressive stresses act in the hoop direction and in the direction of the cone’s generators. Surface instability is analyzed by the use of weak nonstationary disturbances which propagate along the conic surface in the form of the nonstationary Rayleigh wave polarized in the sagittal plane and the nonstationary wave of the ‘‘whispering gallery’’ type polarized perpendicular to the sagittal plane. The analysis is carried out using the theory of discontinuities based on the conditions of compatibility; in so doing the velocities of surface wave propagation and their intensities have been obtained. It has been found that the characteristics of nonstationary Rayleigh waves and surface waves of the ‘‘whispering gallery’’ type are very sensitive to the level of the tensile or compressive stresses in the near-surface layer of an elastic cone. These properties allow one to use these types of surface waves for the analysis of surface instability of elastic bodies and for nondestructive testing of residual stresses in the vicinity of surfaces of different bodies. [Work supported by RFBR.]
A cortical map for tempo
Authors: Drake Carolyn , Adenier Matthieu , Brochard Renaud , Ducorps Antoine , Ragot Richard
Published: July 2002

Tonotopy is a well-known property of the brain which consists of a linearly organized representation of the tonal frequencies on the auditory cortex. A similar organization for the rate of auditory events (tempo) is demonstrated. Subjects listened to isochronous, isotonic sequences of pure tones varying in tempo (100-, 200-, 250-, 300-, 400-, 800-, and 1600-ms IOI) and frequency (400, 1000, and 2500 Hz). Brain magnetic activity (MEG) was recorded over the whole skull with a 150-sensor array. For slow tempi (above 300-ms IOI), sources of brain magnetic activity occurring 100 ms after stimulus onset (M100) were localized in the auditory cortex of both hemispheres. Source position varied systematically as a function of tempo and frequency: (1) on a transverse line for different tempi, more laterally in both hemispheres for the slower tempi (‘‘tempotopy’’), and (2) on an anteroposterior line for different frequencies, more anterior for the higher frequencies (tonotopy). For fast tempi, the main observed MEG response occurred at 70 ms. The presence of these two distinct neural activation patterns corroborates previous psychophysical data.
Loudness functions of older people for pure tones and broadband noises
Authors: Kurakata Kenji , Kuchinomachi Yasuo
Published: July 2002

Loudness functions for pure tones and low-pass filtered noises were obtained by the magnitude estimation to develop a method for evaluating loudness of older people. The subjects were young adults in their twenties with normal hearing and old adults of 60 and over with age-related hearing loss. The results of the measurements are as follows: (1) There is no significant difference in the slope of loudness functions for pure tones between both age groups, suggesting most of the older subjects do not have large loudness recruitment. (2) The loudness of filtered noises judged by the older subjects decreases as the cutoff frequency of the noises increases. Considering the audiograms of the subjects, the declined ability of hearing at higher frequencies seems to be the cause of the decrease of loudness. (3) The decrease of loudness may be corrected by taking into account the amount of hearing loss of older people because they have no significant loudness recruitment.
Frequency-discrimination performance using place-domain techniques
Authors: Thongprasirt Rachod , Wilson Timothy A.
Published: July 2002

A classic analysis [W. M. Siebert, Proc. IEEE 58, 723–730 (1970)] of performance in frequency discrimination tasks used a Poisson-process model for auditory neuron firings in a simple model of the auditory periphery to infer that frequency-discrimination performance can be explained by place mechanisms (or, alternatively, that periodicity information, if used, is used inefficiently). The analysis consisted of determining the variance of the maximum-likelihood estimate of sinusoidal frequency for a single neuron, using the firings over the duration of the stimulus, then averaging those estimates over the independent neurons. An alternative approach is to consider the pattern of auditory nerve firings in the place-time plane first as a function of place, then averaging over time. To that end, the frequency-discrimination performance of a computational model of the auditory periphery was examined by determining maximum-likelihood frequency estimates from the spatial pattern of firings at an instant, then averaging over the duration of the stimulus. Those results, and likelihood-ratio ones, are compared to the analytical results mentioned above, to computational implementation of the Siebert approach, and to psychophysical observations.
A new system of environmental noise identification and subjective evaluation
Authors: Sakai Hiroyuki , Sato Shin-ichi , Ando Yoichi
Published: July 2002

A new system of environmental noise identification including aircraft noise or traffic noise and its subjective evaluation based on the model of the human auditory-brain system [Y. Ando, Architectural Acoustics—Blending sound sources, sound fields, and listeners (AIP Press/ Springer-Verlag, New York, 1998)] is proposed. In order to discuss the subjective effects of environmental noise, following factors are calculated by use of the autocorrelation function (ACF) and interaural crosscorrelation function (IACF) of binaural signals; From the ACF analysis: (1) energy represented at the origin of the delay, Φ(0); (2) effective duration of the envelope of the normalized ACF, τe; (3) the delay time of the first peak, τ1; and (4) its amplitude, φ1 are extracted. From the IACF analysis: (5) IACC; (6) interaural delay time at which the IACC is defined, τIACC; and (7) width of the IACF at the τIACC, WIACC are extracted. For example, loudness is related with Φ(0) and τe, and directional information may be obtained from τIACC. Especially, a noise source may be identified by the all ACF factors are timbre. [Work was partially supported by the Research and Development Applying Advanced Computational Science and Technology, Japan, Science and Technology Corporation (ACT-JST), 1999.]
Analysis of periodically varying gear systems with Coulomb friction using Floquet theory
Authors: Vaishya Manish , Singh Rajendra
Published: July 2002

Realistic gear pairs may undergo significant time-varying mesh stiffness and damping changes during one mesh cycle. The instantaneous number of teeth in contact governs the load distribution and sliding resistance acting on individual teeth. The geared system responds to a combined excitation of transmission error due to profile deviations, periodic variations in system parameters, and time-varying sliding friction. Such complexities have led prior researchers to adopt numerical approaches or approximate analyses, with many modeling simplifications. This article presents a new analytical model of a gear mesh with spatially varying mesh stiffness and viscous damping parameters. Unlike previous models, the excitation consists of two separate terms, namely the unloaded transmission error and the periodically varying Coulomb friction force. Hill’s equation with nonproportional damping is employed to determine the forced system response. Exact integrals are calculated for the state transition matrix, instead of using Fourier series expansion, thus eliminating the mode truncation errors. Floquet theory provides an efficient analytical tool for such time-varying systems, especially for the dynamic response over long time intervals.
Theoretical treatment and design of vibration damping constructions in the upper path structure for underground railways
Authors: Rybak Samuil A. , Kostarev Stanislav A.
Published: July 2002

Perspective vibration damping devices, applicable for underground conditions, are considered. The physical model of elastic damping designs for the upper structure of a railway is formulated and on its base the numerical analysis of their effectiveness for underground railways conditions is carried out. The possible realizations of a design as continuous elastic mats and separate elements (shock absorbers) are considered. In the second case, the arrangement of the damping elements under a ballast stratum and under the carrying elements of a rail path (cross ties, concrete blocks, etc.) is possible. General conclusions are following: the most critical frequency band for underground railways’ practice is an octave with mean geometric frequency 31.5 Hz; for correct choice of the vibration isolating measure a simulation of multi-unit oscillation system is needed; usually a two-unit system is more efficient than one-unit both for low and high frequencies; the most efficient mechanism for vibration reducing in 31–63-Hz frequency bands is elastic coefficient lowering and mass enhancing of a unit with maximal vibration levels; damping coefficient increase leads to vibration level reduction for the resonant frequency and weak influence on the amplitude far from the resonant frequency.
Using signal processing techniques to improve finite element modeling
Authors: Burnett Gregory C. , Clark Gregory A. , Candy James V.
Published: July 2002

The use of signal processing parameter identification techniques to systematically improve finite element (FE) models of extended structures will be presented. FE models have been used with success for many years to simulate the response of structures, and work has recently been undertaken at LLNL to use FE models to model extended structures such as the Oakland/San Francisco Bay Bridge. At present, there is no way to systematically improve the FE models using measured displacements of the structures. Standard signal processing parameter identification techniques adapted for large order models have proven useful in both refining FE models given measured displacement and acceleration data as well as indicating points of failure for structures after damaging events such as simulated earthquakes. These abilities could prove useful in improving current FE models as well as speeding repair time for damaged structures. The presentation will identify the strengths and weaknesses of specific parameter identification algorithms and include illustrative examples of improvements to FE models.
Atmospheric lidar extinction and multiple scattering in haze, plumes, and clouds as analogues to ocean acoustic sounding
Authors: Eberhard Wynn L.
Published: July 2002

Sonar probing of fish schools, black-smoker plumes, and bubble clouds can experience attenuation (or ‘‘shadowing’’) and multiple scatter. Similar kinds of effects are typical during atmospheric lidar (light detection and ranging) observations of turbid media, such as haze, smoke plumes, and clouds. Researchers have developed a variety of techniques to account for these effects on atmospheric lidar in different situations. Some of these methods might be adapted by ocean scientists with comparable problems. In order to be clear about the analogues, the physical conditions for the atmospheric problem will be listed. For example, scattering particles are usually assumed to be point targets randomly positioned in the air. Also, pertinent characteristics of the instrument will be specified, including the difference between ‘‘photon-bucket’’ detection (the common type of lidar) and ‘‘diffraction-limited’’ detection (more like sonar). The types of mathematical approaches for solving attenuation and multiple scattering problems in atmospheric lidar will be summarized. Some common atmospheric examples and the corresponding methods to correct the lidar data will be described.
Backscattering from a large planar array of bubbles
Authors: Nero Redwood W. , Thompson Charles H. , Feuillade Christopher , Love Richard H.
Published: July 2002

Backscattering measurements were obtained from a large planar array of bubbles located near the sea surface during preliminary tests of a towed midfrequency volume scattering measurement system. The planar array consisted of sheets of ‘‘bubble wrap’’ packing material suspended between the sea surface and 3 m depth. The array was originally intended as an approximation of a fish school to provide a strongly reflecting target at midfrequency for a field test of the towed system. Favorable at-sea conditions and successful operation of the towed system provided an opportunity to make additional measurements from the target using cw pulses at frequencies approaching the resonance expected from a single bubble. Weston’s multiple scattering theory for large planar arrays of small bubbles [J. Acoust. Soc. Am. 39, 316–322 (1965)], and Feuillade et al.’s school scattering model [J. Acoust. Soc. Am. 99, 196–208 (1996)] suggest that the resonance of a single bubble is suppressed and that the planar array should show a generally flat response over the frequency range of 1200 to 5000 Hz. Experimental results are presented and compared with theory and in addition, demonstrate the confounding effects of Lloyd’s mirror. [Work supported by ONR.]
Experimentally validated statistical energy analysis models of wood and metal frame walls
Authors: Godfrey Richard D.
Published: July 2002

Statistical energy analysis models were developed, using commercially available programs, for insulated and uninsulated wood and metal frame walls with various gypsum configurations. Material properties were taken from the literature. The 1/3 octave band results over the frequency range from 100 to 6300 Hz were compared with measured data from tests conducted in accordance with ASTM E 90. The predicted sound transmission losses were found to compare favorably with the measured data. The predicted power flows gave some insight into which paths were most significant, and the opportunity to alter them with changes in material properties.
Neural circuitry and neutrotransmitters that mediate the acoustic startle reflex in the rat
Authors: Davis Michael
Published: July 2002

Because the acoustic startle reflex has such a short latency (e.g., 5 ms measured electromyographically in the neck, 8 ms in the hindleg), it must be mediated by a relatively simple neural pathway. We believe that the acoustic startle pathway is mediated by three synapses. These include auditory nerve inputs onto cochlear root neurons, which are cells embedded in the auditory nerve that receive the first afferent information in the auditory system. They send exceedingly thick axons (e.g., 7 μm in diameter) to cells in the nucleus reticularis pontis caudalis which in turn project directly to motoneurons in the facial motor nucleus (pinna reflex) or spinal cord (whole body startle). Chemical lesions of cochlear root neurons or of cells in the ventral lateral nucleus reticularis pontis caudalis eliminate startle. Local infusion of either NMDA or non-NMDA antagonists into either the nucleus reticularis pontis caudalis or the spinal cord, via intrathecal infusion, markedly depress acoustic startle, suggesting that both of these glutamate receptor subtypes may mediate the acoustic startle reflex.
Electroacoustic measurements on cellular telephones
Authors: Bareham John R.
Published: July 2002

The fundamental electroacoustic frequency response measurements on cellular telephones are send, receive, sidetone, and echo. Loudness ratings are calculated from these measurements. Measurements can be made by using a test instrument incorporating a vocoder, a reference base station, a digital audio interface, an actual telephone call, or by testing the phone in loopback mode. In each case, the measurement is calibrated in terms which relate to the public telephone network. Selection of test signals such as sine wave, pink noise, or artificial speech can influence the results. The ear simulator used to measure the receiver can be a sealed complex cavity, sealed but including a defined leak, or a complex cavity plus an anthropomorphic pinna. The choice of ear simulator dramatically influences the results of receiver measurements. Send response is usually measured in close proximity to a standard mouth simulator, but can also be measured in a diffuse sound field to assess pickup of room noise. Hands-free kits pose special measurement challenges which will be briefly reviewed. Key national and international standards associated with electroacoustic measurements on cellular telephones will be cited.
Voice quality in new telephony systems
Authors: Quinlan Dan
Published: July 2002

During the development of the wired analog network, engineering teams recognized from the start that voice quality was a primary design driver. As such, projects aimed at understanding speech mechanisms and the human auditory system were a key component of the telephony research executed in the first half of this century. The recent migration from analog to digital (and wired to wireless) voice communication systems has given rise to a new set of signal degradations, and these impairments can have severe perceptual effects. While the ideal system would transmit voice at high bit-rates and with no signal degradation, voice-over-data (VODN) and wireless systems require the use of signal compression in the edge equipment, and the transmission paths are far from ideal. With regard to voice transmission, mainstream communications systems can no longer be thought of as linear and time invariant. The development community is struggling to systematically evaluate the effects of these new impairments, and is beginning to understand that a connection must be made between objective specifications and subjective response. The talk will present a broad overview of the key issues, and will present some thoughts regarding how the communications industry is responding to these interesting problems.
Using experimental design to choose an acoustical model for a hands-free telephone
Authors: Brun-Berthet Joris , Laville Frédéric , Dedieu Stéphane
Published: July 2002

In full duplex speakerphones sound quality is aversely affected by the coupling between the speaker and the microphone. In addition to signal processing, this problem needs to be addressed by a better physical design of the telephone set. This requires the development of a computational model of the telephone acoustics. Due to the complexity of the geometry, the coupling between various systems and the rather large frequency band (150 Hz–7 kHz in wideband telephony), several complementary modeling approaches such as BEM/FEM, SEA, analytical or empirical methods are required. A determination of the best modeling technique for each phenomenon in each frequency band is needed. Instead of a classical one-factor-at-a-time method, an experimental design approach was used. This method goes beyond the qualitative interpretation of the experimental results and gives a statistical significance to the observed effects of each factor and their interactions. Although this approach is widely used in engineering, no reference was found in the literature of its proposed use to help with acoustical model selection. The method and its application using telephone set prototypes will be presented. [The support of MITEL, Inc. and NSERC is gratefully acknowledged.] a)Presently at MITEL, Inc., Kanata, Ontario.
An effective modal analysis of an acoustic waveguide in the presence of a fine-scale heterogeneity
Authors: McCoy John J. , Steinberg Ben Z.
Published: July 2002

A fine-scale heterogeneity refers to one that can be observed using a scale that is 50 to 100 times, or more, finer than that for observing the depth of the waveguide. At issue are the effects of this heterogeneity on the lower-order, say the first 10 to 20 modes, and their corresponding modal wave numbers. A multiresolution approach to the homogenization of the Sturm–Liouville eigenfunction/eigenvalue problem that determines these modes/wave numbers is used to obtain a self-consistent formulation. The fine-scale layering is described ‘‘effectively’’ in this formulation, by a spatial structure that is much less detailed that the actual structure. Demonstrated is an equality that applies to the eigenvalues of the ‘‘lower-order’’ modes for the given and the homogenized Sturm–Liouville problems, and a precisely described relationship between the corresponding eigenfunctions. The demonstration is given both analytically and numerically. The ‘‘distortion’’ in the prediction of large-scale heterogeneity of an ocean waveguide, which would obtain as a result of an unrecognized, localized fine-scale layering is described and demonstrated.
Attenuation and dispersion in pulse propagation over an elastic sediment
Authors: Jerzak Wayne , Kulkarni Rahul S. , Collins Michael D.
Published: July 2002

The parabolic equation method is used to model pulse propagation in an ocean overlying a lossy and dispersive elastic sediment. As for a fluid sediment [Kulkarni et al., J. Acoust. Soc. Am. 104, 1356–1362], loss and dispersion are included in the frequency domain propagation, and Fourier synthesis is used to recover the broadband signal. Loss is known to depend linearly on frequency in many materials. This is evidently because there are no relevant attenuation length scales in such materials. Lossy materials must also be dispersive in order to keep the waves causal, and the dispersive correction is a Hilbert transform of the attenuation as a consequence of the Kramers–Krönig relationship. In particular, the wave speed depends logarithmically on frequency when loss depends linearly on frequency. Examples are presented to illustrate the effects of dispersion on signals in shallow water environments. [Work supported by ONR.]
Experimental research on adaptive match of ocean sound channel
Authors: Chen Geng
Published: July 2002

Ocean sound channel is a time-space-variant channel. Due to weighting of the channel’s transfer function, acoustic signals are often distorted after they propagated, and with distorted results the receiver using correlation processing can not get its theoretical gain. In this paper based on the study of time-variant characteristics of the channel, the channel response function is found by adaptive filtering. A transversal filter with adaptive weights is used to simulate a time-variant multipath channel. The key problem is how to increase the convergent speed of adaptive match algorithm. For this purpose, first the equation of adaptive filtering is solved by using the method of modified adaptive equation with adaptive step size factor. Second, by implementing adaptive filtering in the frequency domain, the calculation time is reduced. Third, by rational selecting the weight number and deterring the time relation among the weights, convergent speed increased greatly. Finally, convergent weights of the transversal filter are obtained as a response function of the channel and it can be used for channel match. The result of experiment shows that under the condition of rational selection of weight parameters a complicated response function of the channel can be expressed by very limited weight.
Acoustics of ancient theatrical buildings in China
Authors: Wang Ji-qing
Published: July 2002

The performing arts in China could be traced back to a long history and had well developed during the Song and Yuan Dynasties, 11th–14th centuries. A unique form of pavilion stage, opened on three sides and thrust into the audience area, was then the most popular for the open-air theatres, the courtyard theatres, and the indoor theatres. As the traditional Chinese opera, Beijing opera and a variety of local opera, was performed in an abstract sense, no stage sets were used. Therefore, it was possible that the low stage ceiling and back wall of a pavilion stage could function as the reflective shell, which increased the early reflections and also the intensity of the sound to the audience, and meanwhile provided sufficient support to the singer. The measured reverberation times of these halls were around 1.0 s at major frequency bands that were optimal for occupied halls of moderate size. Such a stage house provided the performers a desirable sense that the auditorium was responsive to their effort. Illustrations of acoustical features in different types of stage house will be provided during presentation.
Sonoporation of monolayer cells by diagnostic ultrasound activation of contrast-agent gas bodies
Authors: Miller Douglas L. , Quddus Jawaid
Published: July 2002

Fluorescent dextran (500 kD) uptake by sonoporation was observed after 1-min ultrasound exposure of human (A431 epidermoid carcinoma) and mouse (strain L connective tissue) cell monolayers in the presence of 1% Optison ultrasound contrast agent (Mallinckrodt, Inc.). Ultrasound exposure was provided by a 3.5-MHz array (Acoustic Imaging model 5200B, Dornier Medical Systems) operated in the spectral Doppler mode (5-s pulses, 4.4-kHz PRF). The array was mounted in a 37°C water bath and aimed upward 7 cm away at a 1-mm-thick chamber with the monolayer grown on the upper 5-m-thick mylar window. For a water path, up to about 10% of the cells in a rectangular 0.37-mm2 observation area (smaller than the −3 dB beam width) exhibited fluorescent dextran uptake for the high-power setting. For exposure with a 6-cm tissue-mimicking phantom, which approximated a −0.3 dB/cm/MHz derating factor, some fluorescent cells were noted even for low power (0.25 MPa p-, 0.13 MI) increasing to about 4%–8% at high power. These results indicate that activation of contrast agent gas bodies by diagnostic ultrasound can be biologically effective at the cellular level. [Work supported by NIH CA42947.]
Analysis of ultrasonic nondestructive evaluation data using singular value decomposition of the Hankel data matrix
Authors: Hanshaw Timothy C. , Hsu Chin S. , Anderson Michael J.
Published: July 2002

A method is presented for processing data from ultrasonic nondestructive evaluation (NDE) tests of material specimens by performing a singular value decomposition of the Hankel data matrix. The singular vectors and singular values of the Hankel data matrix correspond roughly to modal shapes and amplitudes in the ultrasonic waveform. A great deal of information about the specimen being tested can thus be conveyed with relatively little data; one approach which has been explored is to generate a colormap in which the intensity of the RGB components are determined by selected singular values. This approach was applied to simulated test data for both nominal and flawed specimens and the resulting colormap has been compared to a gray scale based on the rms value of the response data. The color map provides more information about the flaw than the gray scale in two ways: the intensity of the color components increases monotonically with increasing flaw severity, and the color map provides information about the flaw location.
Identification and localization of sound sources in the median sagittal plane
Authors: Rakerd Brad , Hartmann William M. , McCaskey Timothy L.
Published: July 2002

The ability of human listeners to identify broadband noises having different spectral structures was studied for multiple sound-source locations in the median sagittal plane. The purpose of the study was to understand how sound identification is affected by spectral variations caused by directionally dependent head-related transfer functions. It was found that listeners could accurately identify noises with different spectral peaks and valleys when the source location was fixed. Listeners could also identify noises when the source location was roved in the median sagittal plane when the relevant spectral features were at low frequency. Listeners failed to identify noises with roved location when the spectral structure was at high frequency, presumably because the spectral structure was confused with the spectral variations caused by different locations. Parallel experiments on source localization showed that listeners can localize noises that they cannot identify. The combination of identification and localization experiments leads to the conclusion that listeners cannot compensate for directionally dependent filtering by their own heads when they try to identify sounds. [Work supported by the NIDCD.]