bluuebunny/crossref_metadata_2025 huggingface dataset:
Deployment of biosonar in diverse tasks by FM echolocating bats
Authors: Simmons James A. , Eastman Kyler M. , O’Farrell Michael J.
Published: July 2002

Using an infrared body-heat-imaging video camera and a microphone array, we made field recordings of FM echolocating bats (Eptesicus, Myotis, Pipistrellus) while they deployed their sonar alone or in company with other bats. We observed cruising flights of bats in transit from roosts to feeding areas, bats flying low over water for drinking or hunting, and aerial interception maneuvers in open areas (larger insects were visible, too). However, we also recorded frequent captures of insects on or near the ground, flights into vegetation to capture beetles, and groups of bats flying in close proximity while drinking or making aerial captures of insects. Bat-to-bat dogfights were common, some involving two or more bats diving and violently maneuvering close to the ground or near vegetation. For single bats or several bats not very close to each other, we recorded typical interception maneuvers with pursuit sequences consisting of search-, approach- (tracking-), and terminal-stage signals. By reconstruction of flight and emission patterns, we found that bats flying in close proximity alternated their broadcasts, and large aggregations of bats feeding close together perpetually emitted sounds characteristic of the mid-approach stage, with short durations, high repetition rates, and no discernible terminal stages.
Increasing field of view of high frame rate ultrasonic imaging
Authors: Lu Jian-yu , He Shiping
Published: July 2002

A high frame rate imaging method has been developed recently based on the theory of limited diffraction beams for medical diagnosis. This method constructs images in a direction normal to the transducer surface. In this report, the high frame rate method is extended so that it will not only construct images in the normal direction, but also in any oblique directions. This increases the image construction area because images from several oblique angles can be combined. A new equation has been derived for this extension. A computer simulation was performed. Results show that the field of view of images constructed with the extended method is increased from about 15.74 deg to about 96.57 deg with a linear array of a width (foot print) of about 18.288 mm after combining images from only seven angles (the depth of the images is assumed to be 66.12 mm). This work is significant because a large field of view with a small transducer footprint is desirable for high frame rate heart imaging. [Work supported in part by Grant No. HL60301 from NIH.]
Helical focus wave modes and helical nondiffracting beams
Authors: Overfelt Pamela L.
Published: July 2002

A number of years ago Durnin and colleagues considered the possibility of nondiffracting beams, beams defined to be nonsingular free space exact solutions of the scalar wave equation having the same intensity distribution in every plane normal to the axis of propagation [J. Durnin, J. Opt. Soc. Am. A 4, 651–655 (1987)]. Assuming harmonic time dependence and cylindrical coordinates, i.e., a Fourier decomposition of the time and space coordinates, the Bessel function mode solutions of the scalar Helmholtz equation were pointed out as a class of diffraction-free solutions. Similarly, using a nonorthogonal helical coordinate system, helical mode solutions of the scalar Helmholtz equation that are nondiffracting in the same sense as the Bessel beams can be determined [P. L. Overfelt, Phys. Rev. A 46, 3516–3522 (1992)]. In this paper, when a bidirectional plane wave decomposition [I. M. Besieris et al., J. Math. Phys. 30, 1254–1269 (1989)] is assumed, this same helical coordinate system can be used to obtain helical focus wave mode (FWM) solutions to the scalar wave equation. The fundamental Gaussian FWM can be decomposed into two oppositely polarized helical FWMs. Many relationships between the helical and cylindrical FWMs and their beam solution counterparts will be shown.
Masked hearing thresholds for a bottlenose dolphin (Tursiops truncatus) and white whale (Delphinapterus leucas) in the far field and hydrodynamic near field
Authors: Finneran James J. , Ridgway Sam H.
Published: July 2002

A behavioral response paradigm was used to measure masked underwater hearing thresholds in a bottlenose dolphin (Tursiops truncatus) and white whale (Delphinapterus leucas) within the far field and hydrodynamic near field of an underwater sound projector. Masked hearing thresholds at 100 and 300 Hz were measured at source distances of 1, 2, and 4 m; over these distances the specific acoustic impedance ratio varied from approximately −10 to 0 dB at 100 Hz and −3 to 0 dB at 300 Hz. Individual hearing test trials consisted of a 3.5-s noise burst alone (N) or a noise burst along with a 1-s tone (S+N). Subjects were trained to produce an audible whistle in response to S+N trials and to remain silent for N trials. Thresholds were estimated using an up–down staircase procedure. Preliminary results indicate no significant differences between thresholds measured at the three different source distances for either test subject. [Work supported by ONR.]
Effects of underwater noise on auditory sensitivity of a cyprinid fish
Authors: Scholik Amy R. , Yan Hong Y.
Published: July 2002

The ability of a fish to interpret acoustic information in its environment is essential for survival. Thus it is important to understand how underwater noise, from anthropogenic sources such as boats, affects fish hearing. In this study, the fathead minnow, Pimephales promelas, was used to examine the following: (1) the immediate effects of white-noise exposure (300–4000 Hz, 142 dB re: 1 μPa) on auditory thresholds; (2) recovery time of hearing ability after exposure; and (3) the effects of noise exposure, from a small boat engine recorded in the field, on hearing thresholds. Audiograms were measured using the auditory brainstem response (ABR) protocol and compared to fathead minnows not exposed to noise. Immediately after exposure to white noise, five out of the eight frequencies tested showed a significantly higher threshold compared to the control fish. Recovery was found to depend on both duration of noise exposure and auditory frequency. Boat engine noise, peak frequency of 1292 Hz, also elevated thresholds in the fathead’s most sensitive hearing range (1000–2500 Hz). These results support the hypothesis that auditory thresholds can be altered by noise in the environment and provide evidence to show that these effects can be long term (>14 days). [Work supported by the Kentucky Academy of Science.]
Ultrasonic scattering from blood as a means of measuring hemolysis
Authors: Coussios Constantin C. , Ffowcs Williams John E.
Published: July 2002

The need for a method that would permit the on-line monitoring of hemolysis (the destruction of red blood cells) as blood flows through artificial circuits is becoming increasingly important, as new techniques in transplantation surgery and organ preservation aim at longer periods of extra-corporeal support. It has already been demonstrated experimentally that ultrasonic scattering from blood is a function of the hematocrit (red cell concentration), the cell size, and the degree of red cell aggregation. This paper investigates whether ultrasonic scattering might be used, not only to obtain on-line measurements of the hematocrit, but also to assess the degree of hemolysis and to detect malformed populations of cells. The study involves a reexamination of existing models of ultrasonic scattering from blood, in which red cells have been traditionally modeled as spheres (Rayleigh scattering), and their extension to consider the effect on scattering of disk-shaped particles.
Effects of static pressure on ultrasound-mediated transdermal delivery of tagging compounds into migratory fish
Authors: Young Jane A. , Clark Joseph A. , Frenkel Victor , Zohar Yonathan
Published: July 2002

Research is currently being conducted with the US Fish and Wildlife Service investigating the use of ultrasound to enhance the transdermal delivery of tagging compounds into migratory fish. There is a need for noninvasive, low-cost, and efficient methods of tagging large numbers of fish in order to follow their migratory patterns. Current methods require long periods of immersion that can create health problems and are limited in the amount of uptake of the compound. Previously reported research [J. A. Clark et al., J. Acoust. Soc. Am. 101, 3138(A) (1997)] showed cavitation levels of ultrasound (2–3 W/cm2) at 71 kHz significantly enhanced the transdermal delivery of the tagging compound calcein (fluorexon) into rainbow trout (Salmo gairdneri) yoke-sac larvae. However, attempts to repeat the experiment at higher altitudes revealed that static pressure critically affected the results. A further investigation into the effect of static pressure on the enhanced delivery of calcein by ultrasound into rainbow trout is reported here. A system for generating controlled doses of cavitation level ultrasound at various levels of ambient pressure will be described. The effect of static pressure on calcein uptake will be shown via fluorescent microscopy.
Eyes ’n ears: A system of attentive teleconferencing
Authors: Kapralos Bill , Jenkin Michael , Tsotsos John , Milios Evangelos
Published: July 2002

Various teleconferencing systems exist, including systems intended for multiple speakers where a speaker must be localized. Although many sound-localization systems are available, not only are they expensive and nonportable, most require extensive audio arrays resulting in substantial computational processing. A simple, economical, and compact method of sound localization for use in a teleconferencing system is being investigated. In order to localize a sound source, this system relies solely on ITD measurements between microphone pairs, which allows the sound source to be determined as one of many possible locations on the surface of a cone. By taking the intersection of a sufficient number of cones, the location of a sound source in three-dimensional space may be determined. Our goal is to overcome the problems associated with the sound-localization systems currently available. In particular, this work seeks to develop an affordable, limited maintenance and compact sound-localization system for use with a teleconferencing system capable of locating and tracking a speaker in a multiple speaker setting.
Active source location and beamforming
Authors: Duraiswami Ramani , Zotkin Dmitry , Borovikov Eugene A. , Davis Larry S.
Published: July 2002

A fundamental problem in designing user interfaces that incorporate speech and vision is locating the user(s) and enhancing the quality of their speech. We present a novel algorithm for actively doing this. Two complementary coarse-to-fine strategies that divide both the space being searched and the received signal in the frequency domain are used to arrive at an efficient dynamic search algorithm that is capable of both locating and beamforming multiple sources distributed in space. The algorithm makes no assumptions on noise statistics, and has a deterministic performance bound. It is able to make use of prior information on the possible location of sources obtained via means such as video. The algorithm is particularly applicable to locating speech sources in rooms of regular size, and is thus suitable for videoconferencing and user-interface applications. The algorithm and details are presented. [Support from the W. M. Keck Foundation and ONR Contract No. N000149510521 is gratefully acknowledged.]
Modeling and control parameters of percussive sounds
Authors: Chaigne Antoine J.
Published: July 2002

The sounds of percussive instruments are essentially the result of free oscillations of a structure subjected to impact. For a given impact, their qualities depend on both the geometry and material of the structure. One efficient strategy for simulating such sound sources consists of modeling the propagation of elastic and acoustic waves in the various parts of the instruments. This yields a great variety of sounds governed by a relatively small number of parameters. The realism of the simulation is linked to the degree of refinement in the modeling. Current challenging points in such an approach are due to the difficulties in measuring the physical parameters of the model, including the action of the player, and in the modeling of complicating factors, such as the various causes of inhomogeneities in the vibrating structure. In this paper, some aspects of the mathematical and physical connections between the geometry, the material properties, and the spectral parameters of simple and complex sound sources will be presented. The question of the appropriate ‘‘refinement’’ of the modeling will be addressed with regard to the practical use of the modeling: physics, instrument making, and experiments in psychoacoustics.
The importance of community involvement in a successful construction noise control program
Authors: Thalheimer Erich
Published: July 2002

The Central Artery/Tunnel Project in Boston is generally recognized as the largest and most ambitious urban reconstruction project ever undertaken in the United States. The most politically charged of the required mitigation programs is to successfully control construction noise. Toward this end, the importance of the Project’s active interaction and relationship-building with the affected communities cannot be overstated. The CA/T Project’s construction noise control program attempts wherever possible to be proactive to avoid noise complaints. Part of the proactive strategy is to fully inform the affected neighborhoods through regularly scheduled community meetings. These meetings are organized by the Project’s Community Liaison Group, with support from applicable technical staff. All interested parties are encouraged to attend. A statistical analysis has been performed for all noise-related complaints received by the Project for the time period of May 1994 through November 1999. The trends show that the ‘‘rate’’ of noise complaints has remained relatively steady even though construction activities have increased some fourfold over this time period. The good news is that through the lessons learned and precedents set by the CA/T Project, large-scale urban construction projects can be advanced and noise can be successfully mitigated to the extent necessary to satisfy the affected communities
Thin film photoacoustics: From the laboratory to the real world and back
Authors: Rogers John A. , Maznev Alexei A. , Nelson Keith A.
Published: July 2002

Characterization of thin film anisotropic elastic moduli, thermal diffusivities, thickness, delamination, cure kinetics, residual stress, and other properties through impulsive stimulated thermal scattering (ISTS), a noncontact, nondestructive photoacoustic method, was demonstrated in the 1990s. The method, which involves two crossed ‘‘excitation’’ laser pulses used for generation of acoustic waves, a probe laser beam, and a diffracted signal beam whose time-dependent intensity is measured to reveal acoustic oscillations and damping as well as thermal diffusion, originally required large-frame lasers and painstaking optical alignment. A series of refinements resulted in a compact ISTS system including only miniaturized diode and diode-pumped lasers, using only wallplug electrical power, with automated tuning of the acoustic wavelength and frequency, and with no user-adjusted optical elements. Commercially available ISTS systems are now used routinely in the microelectronics industry for metal film thickness measurement, yielding angstrom precision with 1-s data acquisition times. The ISTS method will be reviewed. Several new advances in methodology and new applications and thin films and bulk materials will be discussed. Finally, the connection between ISTS and related time-resolved measurements of collective vibrations will be illustrated.
Generation of photoacoustic sound for gases in an open environment
Authors: Yönak Serdar H. , Dowling David R.
Published: July 2002

Photoacoustics is the generation of acoustic waves due to unsteady heating from a light source. It was discovered over 119 years ago and is commonly used for trace gas detection and molecular spectroscopy when the photoactive gas or gas mixture is contained in a chamber. However, photoacoustic phenomena are less well characterized in an open environment. In this presentation, scaling laws for radiated photoacoustic sound pressure are developed from dimensional analysis and verified with experiments using a carbon dioxide laser tuned to 10.6 μm and small plumes of sulfur hexafluoride, a photoactive tracer gas. In addition, a forced wave equation that includes laser-gas heating is developed to predict the generation and propagation of photoacoustic sound. Using this forced wave equation, the shape and amplitude of photoacoustic sound pulses are determined based on the shape of the tracer-gas plume and the extent of laser-beam absorption through the Lambert–Beer law. The model results are compared to measured photoacoustic signal pulses and show favorable agreement. [Work supported by Ford Motor Company.]
Age-related differences in temporal processing and speech perception in noise
Authors: Snell Karen B. , Frisina D. Robert
Published: July 2002

Studies of age-related changes in speech perception have shown that older adults experience more problems understanding everyday speech, and require more favorable signal-to-noise ratios when compared with younger adults. Similarly, other studies suggest older adults show poorer temporal processing, especially when the complexity of the signal, the background, or the task is increased. While many age-related differences can be predicted by hearing loss, our studies of older subjects with essentially normal audiometric thresholds suggest that some age-related differences in temporal processing and speech perception in noise persist even in the absence of hearing loss. In addition, it appears that declines in speech perception in noise may follow changes in temporal processing that begin decades earlier. Results from studies of middle-aged subjects will be discussed that suggest age-related changes in auditory processing occur over many decades. [Work supported by NIA-NIH, and the International Center for Hearing and Speech Research, Rochester, NY.]
Active noise control on a large-scale ducted fan with inlet wave-number sensing
Authors: Smith Jerome P. , Burdisso Ricardo A. , Sutliff Daniel L. , Heidelberg Laurence J.
Published: July 2002

Active noise-control (ANC) methods for reduction of turbofan inlet noise have been previously demonstrated on a business-sized turbofan engine. The potential of ANC is investigated here on a large 4-ft-diameter ducted fan which has a geometry and tone frequencies which are more characteristic of current and future large production engines. The control inputs are implemented with a single circumferential array of acoustic drivers constructed with rare-earth magnets. Both far-field pressure transducers and an inlet wave-number sensing technique are investigated as error-sensing strategies to reduce the 2BPF tone of the ducted fan (approximately 1000 Hz.) The wave-number sensing strategy involves filtering and combination of inlet-mounted microphone signals to result in the observation of a particular wave number propagating axially out of the inlet. The ducted fan is equipped with a rotating microphone array in the inlet, which allows for modal analysis of the inlet acoustic field before and after control. The in-duct mode measurements provide insight into the control mechanisms. The test facility is also equipped for making far-field pressure measurements. Experimental results for a single circumferential control source array in conjunction with far-field pressure and inlet wave-number sensing techniques will be presented and discussed. [Work supported by NASA Langley Research Center.]
An adaptive active noise control system in ducts
Authors: Peng Shimin
Published: July 2002

The active noise control (ANC) technique is used to cancel original noise by actively generating a secondary sound signal. Actually it is a method using the interference effect of sound waves. The first part of this paper will introduce and discuss the ANC technique, including the basic concepts and principles, history, current development, and application. Some application examples of ANC technique in duct noise control are given here. The second part will introduce the necessary digital signal processing knowledge and system identification technique which is used in this noise control system. The mathematic model of the sound feedback channel and error signal channel is established by using the system identification technique. The third part of this paper will introduce the ANC experiment results in an air-duct, and an important conclusion is given. Many factors related to ANC are investigated; these factors include the position of the microphones in the duct, the vibration of the shells of the duct, the reflection of the sound waves from the end of the duct, .... Very excellent results were achieved by using this system; it reduces the wide-band noise in the range of 0–800 Hz effectively; 30-dB reduction of sound power level was obtained to the white noise of 250 Hz oct.
The effect of neutral tone on the f0 peak alignment in Standard Chinese
Authors: Li Zhiqiang
Published: July 2002

The f0 peaks sometimes are realized after the right-hand boundary of their host syllables when followed by syllables that carry one of the four tones in Standard Chinese. Further, tone 1 (H) and tone 2 (R) exhibit different peak alignment patterns. This study investigates the effect of neutral tone on the alignment of f0 peaks with their host syllables in tone 1 and tone 2 at normal speaking rate. When a syllable is unstressed, it does not carry any of the four tones, but is said to be in the neutral tone. The greatest amount of peak delay was found on tone 2 when it was followed by one or two neutral tone syllables. The f0 peaks were aligned pretty close to the C−V boundary of the following syllable, and in many cases even across it. The peak on tone 1 was delayed the most in the context of two neutral tone syllables, always being realized after the right-hand boundary of its host syllable, and the least before a full tone syllable. The different alignment patterns are attributable to the inherent tonal properties of tone 1 and tone 2, and the phonological analysis of neutral tone.
Diffraction tomography in acoustical imaging: Theoretical development, signal processing techniques, and applications
Authors: Lee Hua
Published: July 2002

Diffraction tomography has been playing a crucial role in acoustical imaging. In many applications, it has advanced far beyond the classical concept of tomography with narrow-beam illumination and intensity-mapping schemes to the level of multiple-angle multiple-frequency systems with monostatic and bistatic data acquisition configurations. In this presentation, in addition to an overview of the fundamental concepts and theoretical development of diffraction tomography in acoustical imaging, the practical signal processing techniques associated with image reconstruction will be discussed in detail. Furthermore, important subjects such as resolution limit, trade-off analysis between aperture span and signal bandwidth, and computation complexity will be fully analyzed. Responding to various physical constraints, the data acquisition process of a diffraction tomographic system can be achieved by using linear or circular receiver arrays. This presentation will also include the algorithm structures of the image formation algorithms for both linear and circular array systems to illustrate the commonalities and differences of these modalities. Results from various applications in microscopy, underwater sonar sensing, and medical imaging will be included.
Precise acoustic measurements of seafloor transponder and towed-vehicle positions
Authors: Sweeney Aaron D. , Chadwell Carl D. , Hildebrand John A. , Spiess Fred N.
Published: July 2002

We describe a project using acoustic techniques to determine the pattern of seafloor deformation between annual measurements. Using cross-correlation between transmitted and received signals, round-trip travel times precise to a few microseconds were achieved between a towed vehicle and seafloor transponders. The technique is sensitive to sound-speed changes as small as 0.01 m/s. The positions of the transponders and towed vehicle are calculated in a least-squares sense from a ray-trace model, providing relative positions for seafloor transponders with an accuracy of a few centimeters. Two experimental sites were surveyed. The first is in the interior of the Juan de Fuca plate, where the temporal variability of the near-bottom sound speed was 0.05 m/s, with little range dependence. Deformation at the few-centimenter level was neither observed nor expected due to remoteness from plate boundaries. The second site straddled the Juan de Fuca spreading center. Measurements at this site suggest temporal sound-speed variations of about 0.15 m/s, and range dependence due to the presence of localized hydrothermal vents. These measurements are also consistent with little or no deformation over a 2-year interval, in agreement with other measurements, although the spatio–temporal sound speed changes create larger overall error in position determination.
On ray trajectory instability in a range-dependent waveguide
Authors: Zaslavsky George , Virovlyansky Anatoly L.
Published: July 2002

The sensitivity of ray trajectories to initial conditions in a deep ocean environment, including internal wave-induced inhomogeneities, is considered. It is known from a numerical simulation [Simmen et al., J. Acoust. Soc. Am. 102, 239–255 (1997)] that for a given realization of inhomogeneities there is a strong dependence of ray sensitivity on average (unperturbed) sound-speed profile. So, there are ‘‘stable’’ and ‘‘unstable’’ waveguides. Besides, for a given perturbed profile there are ‘‘stable’’ (typically steep) and ‘‘unstable’’ (axial) ray trajectories. We discuss a mechanism of ray instability due to overlapping of nonlinear ray-medium resonances. In an environment with a periodic range-dependence, this mechanism plays a crucial role in the emergence of ray chaos. Approximating a real nonperiodic sound-speed perturbation by one with a finite number of spatial frequencies we study overlapping of ray-medium resonances. This approach allows one to get a quantitative description showing how the sensitivity to initial conditions depends on the propagation conditions. [Work supported by U.S. Navy, Grant N00014-97-1-0426.]
Chaotic ray motion manifestation in mode amplitude range dependencies
Authors: Virovlyansky Anatoly L. , Zaslavsky George
Published: July 2002

An analytical ray-based description of normal mode amplitude range variations has been obtained by projecting the wave field taken in the geometrical optics approximation onto eigenfunctions of the boundary value problem. The mode amplitude at the given range is presented as a sum of contributions from several rays (which can be called eigenrays for the mode) with values of action variables equal to that of the mode. Under the condition of ray chaos, the number of rays contributing to a particular mode should grow exponentially with range, leading to complicated range variations of modal structure. This approach provides a convenient way to study how chaotic behavior of ray trajectories reveals itself in a range dependence of mode amplitudes, and, hence, in wave phenomena. An analog to nonlinear ray-medium resonance for normal modes has been investigated and the impact of this phenomenon on modal structure is discussed. It is argued that overlapping of different mode-medium resonances causes a complicated range dependence of mode amplitude in almost the same manner as the overlapping of ray-medium resonances leads to ray chaos. [Work supported by U.S. Navy, Grant N00014-97-1-0426.]
RT60 and speech intelligibility comparisons in stadia with movable roof systems
Authors: Marsh David E.
Published: July 2002

Open-air stadia are usually less reverberant than enclosed ones and they provide the possibility of natural turf for sporting events, which is generally preferred over synthetic turf. However, enclosed stadia have the financial advantage of year-round event bookings with heating or air-conditioning as appropriate. In recent years, a number of stadia with movable roof systems have been built, providing the best of both worlds. Reverberation time (RT60) measurements and speech-intelligibility measurements were made in some of these facilities and the results were compared for the two conditions of ‘‘roof open’’ and ‘‘roof closed.’’
Estimating echo-delay acuity from timing of neural responses in echolocating bats
Authors: Simmons James A. , Sanderson Mark I. , Eastman Kyler M.
Published: July 2002

Big brown bats resolve delays of overlapping FM biosonar echoes down to 2–4 μs. They must use a time-frequency representation because integration time is ∼350 μs. The bat may have ∼25000 auditory-nerve fibers from ∼1000 inner hair cells tuned to frequencies from 10 to 100 kHz. If auditory-nerve latency jitters of 50–100 us are averaged across frequencies, estimated timing accuracy could be as good as ∼0.5 μs. Monaural timing pathways to the inferior colliculus have jitters no worse than the auditory nerve and also could convey a timing accuracy as good as ∼0.5 us. In the inferior colliculus, frequency-domain responses to interference notches register delay separations down to 5–6 μs for two-point resolution. Time-domain latency jitter for tone bursts increases sharply in the IC, but over half of the cells respond to FM pulses and echoes in synthetic pursuit sequences with latency jitters of only 100–500 μs. This ∼2–5x increase in intrinsic jitter in the IC is accompanied by a disproportionate increase in the number of active cells, thus preserving a physiologically plausible acuity of ∼0.5–1 μs. Moreover, if the whole time-frequency representation in the IC is taken into account, delay changes of ∼0.05–0.1 us might be detectable.
Cellular models of coincidence detection
Authors: Simon Jonathan Z. , Parameshwaran Suchitra , Carr Catherine E.
Published: July 2002

The avian brainstem contains a circuit for detection of interaural time differences (ITDs). Bilateral projections from the cochlear nucleus magnocellularis (NM) form maps of ITD in the nucleus laminaris (NL). A computational model of a NL neuron investigates the cell’s ability to detect coincidences between ipsilateral and contralateral inputs. The model, constructed in the NEURON programming environment, is biophysically detailed and includes recent information on the distribution of high threshold potassium conductances in NL neurons. The role of dendritic processing is explored and emphasized, including the effects of dendrite size on postsynaptic potentials, parallel (multiple) dendritic processing, and the benefits of having dendrites at all. The model makes several predictions, some of which confirm those of a previous model [H. Agmon-Snir, C. E. Carr, and J. Rinzel, Nature 393, 268–272 (1998)]. Active potassium channels greatly increase the ability to detect coincidences at high frequencies. Rate-coded output is much more robust than vector-strength-coded output at distinguishing coincidences from partial coincidences. There is an optimal number of dendrites for a given stimulus frequency, dendritic length, and number of synaptic inputs. The most efficient dendritic length decreases with best frequency.
Correlations between UCA-destruction-induced bioeffects and inertial cavitation dose
Authors: Chen Wen-Shiang , Chang Peter P. , Matula Thomas J. , Crum Lawrence A.
Published: July 2002

Certain therapeutic applications of ultrasound may be enhanced by the use of ultrasound contrast agents, whose controlled destruction may produce a desired bioeffect. It is therefore important to understand the mechanisms of microbubble destruction, and to quantify the relationship between bioeffects and the acoustical signature of these agents. In previous studies, we found two distinct thresholds for the ultrasonic destruction of shelled microbubbles: a fragmentation threshold (P1) at which the microbubble shell is disrupted, creating smaller bubbles, and an inertial cavitation [IC] threshold (P2) for sustained, vigorous IC activity. The inertial cavitation dose (ICD) was used to monitor continuous changes in IC activity. The samples, containing mixtures of Optison with either a buffer solution or whole blood, were insonified with a 1.1-MHz focused transducer (up to 4.4 MPa peak-to-peak). Below P2, the ICD increased slowly with increasing pressure amplitude; hemolysis accumulated more rapidly. Above P2, the ICD decreased. Increased hemolysis was observed between P1 and P2, and was associated with short bursts of IC activity. At fixed PRF, or fixed total ‘‘on’’ time (by adjustment of pulse length and PRF), a pulse length threshold existed for the ICD and hemolysis measurements. [Work supported by WTC and EKOS Corp.]
Pulse combustion
Authors: Jagoda Jechiel I.
Published: July 2002

Pulse combustion has been gaining increased interest because of its potential for higher combustion efficiency, greater combustion intensity, and lower pollutant emissions. Unsteady combustion causes increased mass, momentum, and heat transfer. As a result, reactants mix faster, heat release is accelerated, and heat transfer is enhanced in unsteady reacting flows. Many of these phenomena were discovered long ago by engineers looking for the cause of often detrimental combustion instabilities. Much more recently some of these enhanced transfer properties have been used to design efficient and compact pulse combustors. Although, to date, successful commercialization on a large scale has been limited to home heating units (e.g., the Lenox Pulse Furnace) highly efficient pulse spray dryers (Bepex Unison Dryer), pulse calciners, and pulse waste incinerators have been designed. Pulsations have also been applied to carbon black fluidized bed gasifiers. Not all these designs will become economically viable. However, the development of tunable pulse combustors that can be acoustically matched to the changing resonance frequency of these pulse processes have made many of them more promising. Recent findings that pulsation can enhance burning even in turbulent flows lend further encouragement to the developers of novel pulse combustion devices.
Physical and perceptual modeling of sound-source radiation
Authors: Warusfel Olivier , Misdariis Nicolas , Caussé René
Published: July 2002

Radiation characteristics of sound sources are now considered important when reproducing the signal of a musical instrument or, more generally, when controlling a virtual auditory scene. Both applications have raised the need for analyzing, modeling, and synthesizing the radiation behavior of sound sources. The first part describes a general method for the reproduction of arbitrary radiation patterns with digitally controlled loudspeakers arranged to form a three-dimensional array. In order to evaluate the performance of the synthesis method, this section presents possible definitions of similarity criteria based either on a physical or a perceptual approach. In the second part, perceptual features are investigated based on the analysis of musical instruments or listening tests conducted with elementary radiation patterns such as the first spherical harmonics. The perceptual analysis is conducted first with the help of classical acoustic cues used in room acoustics, and second by analyzing the possible consequences of directivity characteristics on stream segregation mechanisms involved in auditory scene perception. The final part presents ongoing research on the reproduction of salient directivity cues of different musical instruments, as well as the voice.
Knowledge acquisition by listeners in a source learning task using physical models
Authors: Scavone Gary P. , Lakatos Stephen , Cook Perry R.
Published: July 2002

Two experiments examined listeners’ ability to learn about the acoustic properties of physical models by varying the amount of structured information listeners received about the models. In experiment 1, 60 listeners participated in a repeated learning-testing paradigm, using a graphical interface to permit listeners to manipulate three acoustic properties for each of eight simulated percussive instruments. Information about the properties of the instruments varied across six conditions, ranging from highly structured (e.g., pictures of instruments, description of physical properties, sliders grouped by instrument with properties labeled) to weakly structured (e.g., unlabeled sliders arranged randomly without reference to instruments). Performance on discrimination and memory tasks suggests that learning can occur even with weakly structured acoustic information. To determine whether learning can occur even when acoustic information is obtained ‘‘passively,’’ 30 listeners in experiment 2 were yoked to listeners in three conditions of experiment 1. These former listeners heard sounds produced by the manipulations of listeners in experiment 1, but were unaware of the nature of the information in the physical model interface. Both experiments suggest that mechanisms associated with acquiring knowledge about acoustic properties may be largely automatic.
Automatic identification of musical woodwind instruments using pattern recognition
Authors: Brown Judith C.
Published: July 2002

Computer recognition of musical instruments is a relatively unexplored and potentially very important research problem for its promise to liberate humans from time consuming searches on the Internet and the sequential identification of audio material on archival tapes. Pattern recognition with a cluster-based Gaussian mixture model has been used to identify a statistically significant number of short sounds from commercial recordings representing four musical classes. These are the oboe, flute, saxophone, and clarinet, all members of the woodwind family of instruments, and which share similar excitation and resonators. Features explored include cepstral coefficients, constant Q coefficients, spectral centroid, autocorrelation coefficients, and moments of the time wave. The most successful features for classification gave correct results in the range of 79%–84%. These were cepstral coefficients, bin-to-bin differences of the constant Q coefficients, and autocorrelation coefficients. The latter have not been explored previously in either speaker or instrument identification studies. Overall our results show great promise for automatic classification of musical sounds.
Acoustics of two-phase fluids
Authors: Nigmatulin Robert I.
Published: July 2002

Wave propagation in two-phase fluids is accompanied by a great variety of inter- and intraphase hydromechanical and thermophysical processes. These processes are initiated by a wave and, in turn, influence wave propagation strongly. Specific and anomalous features of the waves are the following: (1) Relaxation nonequilibrium processes need some relaxation time and space to transfer one equilibrium state in front of the wave to another equilibrium state behind. That is why the thickness of the wave or its relaxation zone may be large. (2) Attenuation of the wave is governed by nonlinear dispersion of disturbances and by dissipation because of the viscous friction between the carrier and dispersed phases and thermal dissipation, which is strongly dependent on phase transition possibility. (3) Bubbly liquid may show not only the attenuation, but even amplification of the shock wave. (4) For gas-drop mixtures with two-component carrier gas (noncondensable gas and vapor) it is possible to see an anomalous nonmonotonous effect of the mass drop content on the attenuation of the harmonic forced oscillation wave. (5) The breakdown of drops and bubbles has a strong influence on the wave propagation. It intensifies the interface force, heat, and mass transfer interactions. Sometimes it may appear as a ‘‘vapor explosion.’’
Design and characterization of a system for acoustophoresis
Authors: Brooks Todd L. , Apfel Robert E.
Published: July 2002

The manipulation of particles using acoustic forces is a basis for a potentially valuable continuous separation method. The method is unique in that particles can be distinguished based on their relative compressibilities, as well as on mass density and size. An acoustic standing wave is oriented perpendicular to the fluid flow direction which enables an incoming particle mixture to be separated into different streams at the fluid output. Effects which cause mixing such as heat convection and acoustic streaming must be minimized through careful design. An imaging system has been implemented to record the trajectories of individual particles as they flow through the separation cell. Trajectories of various types of particles ranging from 5 to 55 microns are compared to theoretical estimates of separation effectiveness, with a particular emphasis on the role of secondary inter-particle acoustic forces. [Work supported by NASA through Grant No. NAG8-1351.]
On a novel application of the Helmholtz integral in the development of a noiseless sonar
Authors: Romano Anthony J. , Bucaro Joseph A. , Houston Brian H. , Williams Earl G.
Published: July 2002

A novel application of the Helmholtz integral is presented in the development of a noiseless sonar. Given total pressure and normal velocity information over the surface of a structure which has been excited both by an incident field as well as interior noise sources, when the field point resulting from the Helmholtz integral is evaluated inside the surface of the structure, only the incident field remains. Therefore, it is possible to integrate out the effects of both self-noise (due to interior noise sources) and scattering (due to incident excitation) throughout a ‘‘virtual’’ volumetric sensor array projected within the structure. This approach will be discussed and demonstrated using numerical results based on finite element simulations. [Work supported by ONR.]
Backscattering enhancements associated with mode conversion in thin tilted circular plates in water: Observations and Gaussian beam model
Authors: Hefner Brian T. , Marston Philip L.
Published: July 2002

When a thin tilted circular plate is illuminated with high-frequency sound, a significant enhancement occurs when the angle of incidence corresponds to the extensional wave coupling angle. It has been found that there are two mechanisms responsible for this enhancement. The largest response is due to the extensional leaky wave which travels along the diameter and reflects from the plate edge. This can be modeled in the thin-plate limit using a Gaussian beam model which was first developed for the reflection of leaky Rayleigh waves on tilted truncated cylinders [K. Gipson and P. L. Marston, J. Acoust. Soc. Am. 107, 112–117 (2000)]. The second response is due to extensional waves traveling along off-diameter paths. When these waves strike the plate edge, they mode-convert into shear waves. These shear waves cross the diameter to strike the opposite edge and mode-convert into extensional waves which then reradiate back towards the source. Since the shear waves do not leak energy into the water, this enhancement has a relatively slow decay as the waves undergo multiple reflections around the plate edge. The Gaussian beam model has been extended to quantitatively model this enhancement in the thin-plate limit. [Work supported by ONR.]
Radiation impedance matrix of a rectangular aperture, with arbitrary vibration, in a rigid baffle
Authors: Pierce Allan D. , Cleveland Robin O.
Published: July 2002

The present paper shows that multidimensional integrals associated with radiation from a rectangular surface in a plane rigid baffle can be reduced to one-dimensional integrals. If the vibrational excitation is expanded into a summation over a set of basis functions, the surface pressure and velocity may be related by an infinite matrix. Each element of the matrix is expressed as a quadruple integral. The numerical evaluation of such integrals, although possible, is prohibitively time consuming for many practical applications. However, for some choices of the basis functions, each quadruple integral may be reduced analytically to single integrals. Explicit expressions are given for square surfaces and with the basis functions taken as products (or sums of products) of trigonometric functions. Numerical results agree well with previous results published in the literature for the pressure distribution over a surface when the vibration is uniform.
A general acoustic background for evacuated and water-filled submerged shells
Authors: Werby Michael F. , Uberall Herbert
Published: July 2002

Historically, the acoustic background for elastic solids dates back to the early 1980s to the work of Flax, Uberall, and Dragonette. Werby extended this concept in 1991 to evacuated elastic shells by employing the concept of entrained mass. Here we extend the concept to one valid for a water-filled shell. The new background is equally valid even for the limit of an evacuated shell. We derive the equations used in the method and illustrate its use for a variety of problems.
Free-field and virtual studies of the precedence effect in the median–sagittal plane: Duration effects
Authors: Ng Gerald , Dizon Roberto , Litovsky Ruth , Colburn H. Steven
Published: July 2002

The study of precedence in the median–sagittal plane is made difficult by poor localization ability in this plane, as well as by front–back confusions. We report on both free-field and virtual localization studies in which a source and simulated reflection are presented from two speakers chosen from an array of six, all of which are in the frontal median–sagittal plane. Subjects perform a forced-choice identification of which speaker emitted the combined stimulus. Stimuli consisted of lead–lag pairs of 1-, 10-, 25-, or 50-ms broadband noise bursts, where the onset of the reflection lags that of the source by 2 ms. Single-source cases were presented intermixed with the lead–lag paired stimuli. In the free-field condition, identification accuracy increased with duration for the single-source stimuli. For the precedence stimuli, a majority of responses is biased towards the elevation of the leading stimulus. However, details of individual performance show some evidence of response bias towards certain elevations, bimodal distributions, and perceptual averaging of lead and lag locations. Virtually presented stimuli using individualized HRTFs yielded localization judgments comparable to free-field stimuli for single-source conditions, but not for lead–lag pairs. [Work supported by NIH (DC02696 and DC00100) and ONR-MURI (Z883401).]