bluuebunny/crossref_metadata_2025 huggingface dataset:
Quality assurance in stereotactic space. A system test for verifying the accuracy of aim in radiosurgery
Authors: Mack A. , Czempiel Heinz , Kreiner Hans‐Jürg , Dürr Gerhard , Wowra Berndt
Published: July 2002

A detailed quality assurance (QA) program is essential for high precision single dose irradiations. The accuracy of stereotactic radiosurgery is limited by the errors of each step in the chain for optimal treatment beginning with the diagnostic imaging and target localization leading to the dose planning and ending up with the treatment of the patient. Two main goals were followed on the way to finding a concept for a suitable and sufficient quality assurance routine. First, the chain of items in terms of a complete patient simulation should be followed and second, the stereotactic MR image data should be verified against a reference in our case stereotactic radiographic projection images. Target point verifications were performed using the so‐called, unknown target method based on MRI, CT, and stereotactic projection images. A marked radiochromic film, embedded between inserts of the phantom is fixed parallel to either the xy or the xz plane of the stereotactic coordinate system. After imaging and planning, the phantom is adjusted and irradiated. At the end, the film, dyed by the radiation field around the premarked cross, is evaluated. The measured distance between the unit center point (shadow) and the localization of the marked film leads to the deviation to be minimized. This is referred to as the displacement vector. The results, evaluating 170 system tests within 5 years, show that the mean displacement vector of the complete system is Factors having a significant influence on the overall accuracy are associated with MRI parameters. Test results based on axial images (xy plane; are significantly superior to coronal images (xz plane; Further on, the 3D‐mpr sequence is significantly superior to the T1 weighted SE sequences Given the high mechanical accuracy of the Leksell gamma knife, the most sensitive technical factor having an influence on the overall precision of radiosurgery is the MRI study. However, using the appropriate imaging sequences and parameters the dislocation error inferred by MRI can be kept very low and restricted to the rare patient inherent distortion factors. With these precautions in mind, MRI is recommended as the imaging method of choice in radiosurgery.
Multiple local minima in radiotherapy optimization problems with dose–volume constraints
Authors: Deasy J. O.
Published: July 2002

The cause of multiple local minima in beam weight optimization problems subject to dose–volume constraints is analyzed. Three objective functions were considered: (a) maximization of tumor control probability (TCP), (b) maximization of the minimum target dose, and (c) minimization of the mean‐squared‐deviation of the target dose from the prescription dose. It is shown that: (a) TCP models generally result in strongly quasiconvex objective functions; (b) maximization of the minimum target dose results in a strongly quasiconvex objective function; and (c) minimizing the root‐mean‐square dose deviation results in a convex objective function. Dose–volume constraints are considered such that, for each region at risk (RAR), the volume of tissue whose dose exceeds a certain tolerance dose is kept equal to or below a given fractional level If all RARs lack a “volume effect” (i.e., for all RARs) then there is a single local minimum. But if volume effects are present, then the feasible space is possibly nonconvex and therefore possibly leads to multiple local minima. These conclusions hold for all three objective functions. Hence, possible local minima come not from the nonlinear nature of the objective functions considered, but from the “either this volume or that volume but not both” nature of the volume effect. These observations imply that optimization algorithms for dose‐volume constraint types of problems should have effective strategies for dealing with multiple local minima.
In‐phantom dosimetry and spectrometry of photoneutrons from an 18 MV linear accelerator
Authors: d'Errico Francesco , Nath Ravinder , Tana Luigi , Curzio Giorgio , Alberts Wolfgang G.
Published: July 2002

A combination of three superheated drop detectors with different neutron energy responses was developed to evaluate dose‐equivalent and energy distributions of photoneutrons in a phantom irradiated by radiotherapy high‐energy x‐ray beams. One of the three detectors measures the total neutron dose equivalent and the other two measure the contributions from fast neutrons above 1 and 5.5 MeV, respectively. In order to test the new method, the neutron field produced by the 10 cm × 10 cm x‐ray beam of an 18 MV radiotherapy accelerator was studied. Measurements were performed inside a tissue‐equivalent liquid phantom, at depths of 1, 5, 10 and 15 cm and at lateral distances of 0, 10, and 20 cm from the central axis. These data were used to calculate the average integral dose to the radiotherapy patient from direct neutrons as well as from neutrons transmitted through the accelerator head. The characteristics of the dosimeters were confirmed by results in excellent agreement with those of prior studies. Track etch detectors were also used and provided an independent verification of the validity of this new technique. Within the primary beam, we measured a neutron entrance dose equivalent of 4.5 mSv per Gy of photons. It was observed that fast neutrons above 1 MeV deliver most of the total neutron dose along the beam axis. Their relative contribution increases with depth, from about 60% at the entrance to over 90% at a depth of 10 cm. Thus, the average energy increases with depth in the phantom as neutron spectra harden.
A pulsed jumping ring apparatus for demonstration of Lenz’s law
Authors: Tanner Paul , Loebach Jeff , Cook James , Hallen H. D.
Published: July 2002

Lenz’s law is often demonstrated in classrooms by the use of Elihu Thomson’s jumping ring. However, it is ironic that a thorough analysis of the physics of the ac jumping ring reveals that the operation is due mainly to a phase difference, not Lenz’s law. A complete analysis of the physics behind the ac jumping ring is difficult for the introductory student. We present a design for a pulsed jumping ring which can be fully described by the application of Lenz’s law. Other advantages of this system are that it lends itself to a rigorous analysis of the force balances and energy flow. The simple jumping ring apparatus closely resembles Thomson’s, but is powered by a capacitor bank. The jump heights were measured for several rings as a function of energy stored in the capacitors. A simple model describes the data well. Currents in both the drive coil and ring are measured and that of the drive coil modeled to illuminate some properties of the capacitors. An analysis of the energy flow in the system explains the higher jump heights, to 2 m, when the ring is cooled.
Classical Casimir effect for beads on a string
Authors: Griffiths David J. , Ho Elan
Published: July 2002

Two small beads are situated at distance a apart on an otherwise uniform taut string. A transverse wave of angular frequency ω is incident from one side, exerting longitudinal forces F1 and F2, respectively, on the beads. The effective “force of attraction” between the beads, FC=(F1−F2)/2, is the simplest classical analog to the Casimir effect. We find that FC can be positive or negative, depending on the values of a and ω. For a broad spectrum of incident “noise,” however, the net “Casimir” force is zero.
An easy to perform but often counterintuitive demonstration of gas expansion
Authors: Baker Brad
Published: July 2002

During their thermodynamics courses, students learn that the temperature of an ideal gas will drop during an adiabatic reversible expansion. They also usually learn that no change of temperature occurs as a result of a certain free expansion. These results often become intuitively connected with gas expansion. However when air expands freely into an evacuated chamber from a constant pressure atmosphere, its temperature increases. This can be easily demonstrated using only simple equipment and makes for a memorable lesson on the importance of identifying what exactly is the system and then simply applying the first law of thermodynamics.
Multiple-prism arrays in laser optics
Authors: Duarte F. J.
Published: July 2002

At present, multiple-prism arrays play an important and pervasive role in laser optics. From intracavity beam expansion to pulse compression these integrated optical elements have given a new and expanded meaning to the word prism. In this article we offer a pedagogical introduction to the physics and mathematics of practical multiple-prism arrays.
Curve fits in the presence of random and systematic error
Authors: Bechhoefer John
Published: July 2002

From the autocovariance function of residual errors in least-square curve fits, one can estimate the random error present in experimental data, along with the relative proportion of systematic to statistical error. The methods outlined here have important implications for teaching error analysis.
Symmetry, extinctions, and band sticking
Authors: König Anja , Mermin N. David
Published: July 2002

The space-group symmetry of a crystal has a simple form in Fourier space, which provides a natural language for the basic facts about x-ray extinctions and band sticking in nonsymmorphic crystals.
Providing low- and mid-frequency speech information to listeners with sensorineural hearing loss
Authors: Turner Christopher W. , Brus Shea L.
Published: July 2002

The present study examined the benefits of providing amplified speech to the low- and mid-frequency regions of listeners with various degrees of sensorineural hearing loss. Nonsense syllables were low-pass filtered at various cutoff frequencies and consonant recognition was measured as the bandwidth of the signal was increased. In addition, error patterns were analyzed to determine the types of speech cues that were, or were not, transmitted to the listeners. For speech frequencies of 2800 Hz and below, a positive benefit of amplified speech was observed in every case, although the benefit provided was very often less than that observed in normal-hearing listeners who received the same increase in speech audibility. There was no dependence of this benefit upon the degree of hearing loss. Error patterns suggested that the primary difficulty that hearing-impaired individuals have in using amplified speech is due to their poor ability to perceive the place of articulation of consonants, followed by a reduced ability to perceive manner information.
Transient flexural waves in a disk and square plate from off-center impact
Authors: El-Raheb Michael , Wagner Paul
Published: July 2002

Flexural waves in a disk and square plate produced by off-center impact are analyzed. The effects on maximum transient stress σmax of boundary shape, edge constraint, thickness, side of square plate or diameter of disk, and eccentricity of center of impact are studied. While prior analytical work has been confined to disks for simplicity, ballistic experiments were performed using square plates for practical reasons. The two geometries agree better for central impact or edges that are simply supported or clamped. Analytical results show some intensification as center of impact approaches the edge, but this is insufficient to explain the measured rise in residual projectile kinetic energy after penetrating a ceramic tile. This reveals the inadequacy of the crack initiation mechanism as the primary model of defeating the projectile by ceramic tiles.
Masked threshold difference due to masker harmonicity: Uniform modulation rates of auditory filter outputs versus periodicity in waveform fine structure
Authors: Treurniet William C. , Boucher Darcy R.
Published: July 2002

In a previous paper [Treurniet and Boucher, J. Acoust. Soc. Am. 109, 306–320 (2001)], a model was presented which successfully accounted for the lower threshold obtained using a harmonic masker instead of a similar inharmonic masker. For the harmonic masker, the frequencies of partials were equally spaced, so the envelope modulation rates of auditory filter outputs were invariant across filters. However, for the inharmonic masker, the intervals between adjacent partials were not equal and this resulted in a decreased uniformity of modulation rates across filters. The model proposed that the lower uniformity interferes with detection of a probe-induced change in the modulation rates, thus accounting for the masked threshold difference. This paper shows that an inharmonic masker yields thresholds similar to a harmonic masker provided that the modulation rates are uniform across the auditory filters involved in processing the masker and probe. Thus, the lowered threshold associated with a harmonic masker appears to arise from uniform modulation rates across auditory filters, and does not require periodicity in the fine structure of the waveform produced by partial frequencies that are integer multiples of a fundamental.
A comparative assessment of speech sound discrimination in the Mongolian gerbil
Authors: Sinnott Joan M. , Mosteller Kelly W.
Published: July 2002

The Mongolian gerbil is a small rodent with human-like absolute auditory sensitivity in the speech range below 4 kHz. Here, gerbil “speech DLs” (difference limens) are measured along several synthetic speech continua and compared with human data. Results show that gerbils are similar to humans in that they discriminate “within-category” information more easily for vowels than for consonants. However, gerbils are less sensitive to all the speech stimuli, with DLs about 2–3 times higher. Interestingly, gerbil speech DLs are not accurately predicted by their pure-tone frequency DL, which is 36 times that of the human at 1 kHz. Thus, gerbils are actually much more similar to humans in speech sound discrimination than in pure-tone discrimination. It is concluded that the gerbil offers a promising “small-mammal” model for the processing of spectral cues in human speech sounds.
Some aspects of sound extinction by zooplankton
Authors: Gorska N. , Chu D.
Published: July 2002

To address the importance of sound extinction (or the shadowing effect) in the presence of a densely aggregated zooplankton layer, acoustic scattering by weakly scattering fluid objects is studied theoretically. An analytical expression for the extinction cross section is obtained based on the forward scattering theorem and the analytical formula for the forward scattering amplitude is derived from the Modal Based–Deformed Cylinder Model (MB–DCM). The validity of the MB–DCM solution for the forward scattering amplitude and its sensitivity to geometrical and physical parameters is studied. Comparison with the PC–DWBA (Phase-Compensated–Distorted Wave Born Approximation) shows a reasonable agreement between the two models. The extinction cross section is shown to be proportional to (ka)2 and the induced attenuation is predicted for various species of zooplankton over a wide frequency range. It is shown that, under certain realistic conditions, such as the presence of a swarm of aggregated krill, sound extinction by zooplankton could influence the acoustic measurements significantly, as much as an 85% reduction in acoustic intensity for Euphausia superba with n=5000 ind./m3 over a range of 50 m.
Modeling the influence of inherent envelope fluctuations in simultaneous masking experiments
Authors: Verhey Jesko L.
Published: July 2002

Masked thresholds are measured and simulated for bandpass-noise signals ranging in bandwidth from 4 to 256 Hz in the presence of a masking bandpass noise also ranging in bandwidth from 4 to 256 Hz. Signal and masker are centered at 2 kHz. To investigate the role of temporal processing in simultaneous masking, simulations were performed with the modulation-filterbank model by Dau et al. [J. Acoust. Soc Am. 102, 2906–2919 (1997)]. For a fixed masker bandwidth, thresholds are independent of the signal bandwidth as long as the signal bandwidth does not exceed the masker bandwidth and thresholds decrease with increasing masker bandwidth in those conditions. A simple modulation-low-pass filter (energy integrator) would be sufficient to describe the experimental results in those conditions. In contrast, the processing by a modulation filterbank is necessary to account for the conditions of “asymmetry of masking,” where thresholds for signals with bandwidths larger than the masker bandwidth are much lower than those for the reversed condition. In those conditions, the modulation-filterbank model is able to use the inherent higher modulation frequencies of the signal as an additional cue.
Scattering from impedance gratings and surface wave formation
Authors: Zhu Wenhao , Stinson Michael R. , Daigle Gilles A.
Published: July 2002

The scattering problem of acoustic plane waves from comb-like impedance gratings on a rigid surface has been investigated in this paper. A rigorous analytic approach for homogeneous plane-wave incidence is presented based on the periodicity of the grating structure, in which the problem was solved as a mixed boundary value problem and the scattered field was represented by the tangent velocity difference across a partition wall of the grating. A singular integral equation has been derived for the tangent velocity difference, which can directly be solved with the Gauss–Chebyshev procedure. The resulting solution consists of a series of Bloch–Floquet waves (plane bulk wave and surface wave modes) with explicit expressions for the expansion coefficients. When the grating period is much less than the incident wavelength (ka≪1), the grating structure is equivalent to a plane impedance surface and no surface waves can be excited with homogeneous plane-wave incidence. When the grating period is comparable to the incident wavelength, resonance phenomena are predicted under certain conditions and surface waves can form, even with homogeneous plane-wave incidence. The dispersion relation for surface waves has also been examined. The impedance effects of the grating on the reflection and diffraction waves as well as on the dispersion and formation of surface waves have been studied, with the acoustically hard grating being the special case of the general impedance grating.
Structural wave reflection coefficients of cylindrical shell terminations: Numerical extraction and reciprocity constraints
Authors: Smith P. W. , McDaniel J. Gregory , LePage Kevin D. , Barile Robert
Published: July 2002

A fluid-loaded cylindrical shell guides vibratory energy along its axial direction in the form of a finite set of distinct traveling wave types. On a finite shell, the energy incident upon a termination is redirected into reflected waves of all types and into sound radiated into the farfield. (The total field near the termination also includes various evanescent components.) Reflection coefficients relate the amplitudes of individual reflected wave types to the amplitudes of individual incident wave types. In this paper, values for the reflection coefficients of several terminations have been extracted from results of finite element analysis for the forced response of a finite structure excited by a variety of different sources. The numerical results exhibit good agreement with the analytical constraints consequent to the principle of reciprocity. The constraints are developed here by an analysis adaptable to other multimodal waveguides by appropriate modification of detail.
Understanding the periodic driving pressure in the Rayleigh–Plesset equation
Authors: Moss William C.
Published: July 2002

The Rayleigh–Plesset equation is the basis of most theoretical analyses of bubble dynamics. Surprisingly, experiment and theory do not agree on the spatial location and the value of the periodic driving pressure. In the experiment the driving pressure is located near the bubble, whereas, the theory assumes that the driving pressure is far from the bubble. The paradox is resolved by deriving a modified equation that is valid for compressible flows in a finite spherical geometry. The modified equation is identical to the incompressible Rayleigh–Plesset equation with the driving pressure at infinity replaced by the actual driving pressure, which is located within 25 bubble radii of the bubble. We show that a hydrophone at the center of the flask measures this driving pressure, which is why the theory and experiment agree when an incompressible Rayleigh–Plesset equation is used to describe compressible flows.
A hybrid split-step/finite-difference PE algorithm for variable-density media
Authors: Yevick David , Thomson David J.
Published: July 2002

Although variations in the density, ρ, are naturally incorporated into finite-difference parabolic equation (PE) solvers, split-step PE algorithms traditionally account for density changes by adding to the refractive index terms containing derivatives of ρ. As a consequence, geoacoustic density profiles that contain step discontinuities at layer interfaces must be smoothed appropriately before these extra terms can be evaluated. In this paper, a new hybrid method is proposed for treating density inhomogeneities in the split-step PE. This approach involves splitting the differential operator into density-independent and density-dependent components. While the former terms may be evaluated with the split-step Fourier technique, the influence of density changes is handled through a finite-difference procedure. Such an algorithm can be easily implemented in recently proposed hybrid split-step/finite-difference and split-step/Lanczos PE solvers. [J. Acoust. Soc. Am. 96, 396–405 (1994)].
Can acoustic multipath explain finback (B. physalus) 20-Hz doublets in shallow water?
Authors: Premus V. , Spiesberger J. L.
Published: July 2002

A broadband acoustic propagation code is combined with an empirically derived geoacoustic seafloor model for the purpose of interpreting finback doublet sequences recorded in the northern Gulf of California by Thompson et al. in 1987 [Thompson et al., J. Acoust. Soc. Am. 92, 3051–3057 (1992)]. The result is that for ranges less than 30 km, it is plausible to explain the appearance of the finback doublet in this environment in terms of multipath propagation through the water column and the seafloor. For a channel depth as shallow as 50 m, the detection range of the subbottom arrival may exceed that of the water-borne arrival. This result may have important implications for the accuracy of hyperbolic localization algorithms which assume a sound speed consistent with a water-borne propagation path. When doublet propagation is supported, the interpulse delay is demonstrated to be strongly range dependent. With prior knowledge of the geoacoustic environment, the interpulse delay may provide a practical tool for the real-time passive ranging of finbacks using only a single hydrophone or sensor array. Scientists might consider the impact the multipath-induced doublet has on long distance communication between whales based on temporal cues encoded in patterned 20-Hz pulse sequences.
Source localization in noisy and uncertain ocean environments
Authors: Fialkowski Laurie T. , Collins Michael D. , Perkins John S. , Kuperman W. A.
Published: July 2002

Interference from noise and uncertainties in the environmental parameters are arguably the two most serious limitations in matched-field processing (MFP). Among the techniques that have been developed for handling these difficulties are the noise-canceling processor [M. D. Collins, N. C. Makris, and L. T. Fialkowski, “Noise cancellation and source localization,” J. Acoust. Soc. Am. 96, 1773–1776 (1994)] and focalization [M. D. Collins and W. A. Kuperman, “Focalization: Environmental focusing and source localization,” J. Acoust. Soc. Am. 90, 1410–1422 (1991)]. The noise-canceling processor is a generalization of the Bartlett processor that is based on matching the covariance matrix of the data with replica covariance matrices of the signal and the noise. Simulations are presented to illustrate the performance of the noise-canceling processor when there are errors in the noise replica. Focalization is a generalization of MFP in which environmental parameters are included along with source parameters in the search space. An implementation of this approach that is suitable for applications is developed and tested. The noise-canceling processor and focalization are used to simulate the localization of a source buried in noise in an uncertain environment.
Variation of measured nitrogen sound speed with temperature and pressure
Authors: Wong George S. K. , Wu Lixue
Published: July 2002

Based on nitrogen sound speeds measured by Younglove and McCarty in 1980 [J. Chem. Thermodynam. 12, 1121–1128 (1980)], a multicolumn coefficient fitting method is used to derive an empirical equation for the computation of sound speed at temperatures from 150 to 330 K and pressures from 0.028 75 to 1.506 85 MPa. The maximum deviation between the measured sound speeds and those computed with the empirical equation is less than 380 ppm.
High-resolution analysis of the complex wave spectrum in a cylindrical shell containing a viscoelastic medium. Part II. Experimental results versus theory
Authors: Vollmann Johannes , Breu Roger , Dual Jürg
Published: July 2002

The complex frequency spectrum of axisymmetric wave modes in a circular cylindrical shell containing various viscoelastic media is measured. A new measurement technique has been developed for this purpose by combining a high-resolution laser interferometer with modern spectrum estimation methods. To decompose the complex wave-number dependence, a complex spectrum estimation method has been implemented. Up to 40 dispersion curves of traveling, axisymmetric modes are decomposed simultaneously in a frequency range between 1 kHz and 2 MHz. The guided structural waves are excited by piezoelectric transducers. Linear elasticity can be considered as an extreme case of viscoelasticity (long relaxation times compared with the deformation periods). To ascertain the validity of the theory, dispersion curves are calculated for a shell containing a viscoelastic material behaving like the elastic shell and are compared with the measured curves of an isotropic aluminium rod. The phenomenon of “backward wave propagation,” in which the group velocity and the phase velocity of one mode have opposite signs, is clearly measured. Excellent agreement between experimental and theoretical results, which are also presented in a corresponding paper [J. Vollmann and J. Dual, J. Acoust. Soc. Am. 102, 896–908 (1997)], is found over a wide parameter range, including the case of a linear elastic rod.
Growth rate of simultaneous masking in cat auditory-nerve fibers: Relationship to the growth of basilar-membrane motion and the origin of two-tone suppression
Authors: Pang Xiao Dong , Guinan John J.
Published: July 2002

Although many aspects of the mechanisms by which low-frequency sounds exert their powerful masking on responses to high-frequency sounds are well documented and understood, there are few data on the growth of masking for signal frequencies near, but not necessarily at, auditory-nerve-fiber characteristic frequency (CF). Masking of responses to 6- or 8-kHz tones by a continuous 300-Hz band of noise centered at 500 Hz was measured in single auditory-nerve fibers with various CFs. The growth rate of maskings averaged approximately 2 dB/dB, was typically largest for tones about 10% above fiber CF, and decreased at higher and lower frequencies. This pattern of masking versus frequency relative to CF resembles the pattern of compression of the growth of basilar membrane motion versus frequency at a fixed cochlear place. This correspondence supports the hypothesis that the high growth rate of masking by low-frequency sounds is due to the same mechanisms which produce the compression in the growth of basilar membrane motion.
Sound generation and air entrainment by breaking waves in the surf zone
Authors: Deane Grant B.
Published: July 2002

This paper presents the results of acoustic and optical measurements of individual breaking waves in the surf zone. Two hydrophones, horizontally separated and deployed in 2 m of water off La Jolla Shores beach, California, were used to measure the source spectrum of breaking surf, and characterize propagation through the surf zone over length scales of order 10 m. The acoustic data show an acoustically active region within a wave which propagates shoreward. The production of sound within the active region is associated with the formation of bubble plumes. Above 500 Hz, the sound is consistent with the radiation from individual bubble oscillations. Pictures were taken of the bubble plumes formed beneath the breaking surf, providing estimates of the plume size, and bubble size distribution and void fraction within a plume. The density of bubbles scales as a−2.5 for a<1 mm and a−4.5 for a>1 mm, where a is bubble radius, and total void fractions of 0.3–0.4 were measured. Theoretical calculations show that radiation from bubbles within a plume is strongly damped, and only a thin shell of bubbles on the exterior of the plume contributes to the wave noise. A “moving bubble sheet” source model for the wave noise is presented which shows fair agreement with the acoustic measurements.
Rhythmic masking release: A paradigm to investigate auditory grouping resulting from the integration of time-varying intensity levels across frequency and across ears
Authors: Turgeon Martine , Bregman Albert S.
Published: July 2002

The perceptual organization of sequences of short-duration 200-Hz-wide modulated noise bands was investigated. Sequences with one of two possible rhythms were presented over headphones or in a semi-circular array of 13 speakers. The ‘‘rhythm’’ was embedded in an irregular sequence of ‘‘maskers’’ with the same frequencies and energy. Adding ‘‘flankers’’ in other critical bands, synchronous with the irregular maskers released the rhythm from masking. RMR as measured by the correct identification of the rhythm and its perceived clarity was assumed to be contingent upon the perceptual grouping of the maskers and flankers. Using a 2-AFC procedure with a four-point clarity rating for each alternative, the effect of the following relations between the maskers and flankers on their simultaneous grouping was investigated: stimulus onset asynchrony (SOA), frequency separation (ΔF), commonality of microstructure, and angular separation of their sources (Δθ). RMR decreased significantly with SOA, Δθ, differences in microstructure and with ΔF for spatially separated maskers and flankers. RMR will be compared to other paradigms which have been claimed to result from a cross-spectral binaural analysis of the temporal envelope, such as dichotic CMR and/or of the fine temporal structure such as BMLD [Hall et al., J. Acoust. Soc. Am. 83, 1839–1845 (1988)].
Ear canal reflectance in the presence of spontaneous otoacoustic emissions. I. Limit-cycle oscillator model
Authors: Tubis Arnold , Talmadge Carrick L.
Published: July 2002

Allen et al. [Abstract in Eighteenth Midwinter Research Meeting of the Association for Research in Otolaryngology, Des Moines, IA (1995)] have found that the ear canal reflectance passes through a minimum around the frequency of a spontaneous otoacoustic emission (SOAE). They considered this result to constitute evidence against active nonlinear cochlear function as the basis for SOAEs. In order to investigate theoretically the expected behavior of ear canal reflectance in the neighborhood of a SOAE associated with an active-nonlinear cochlea, we use a simplified model in which the ear drum end of the ear canal is effectively terminated by a nonlinear-active element. Under the influence of a sinusoidal driver at the entrance of the ear canal, this element will, to a good approximation, either (1) oscillate at both the frequency of the driver (at which the reflectance is determined) and the SOAE (at a suppressed level, corresponding to nonentrainment), or (2) be entrained and only oscillate at the driving frequency. The magnitude of the nonlinear ear canal reflectance is found to exceed unity only at sufficiently low stimulus levels, and occurs under conditions of entrainment and nonentrainment of the spontaneous emission. Otherwise, the reflectance is less than unity and, as a function of frequency, has a minimum around the SOAE frequency.
Temporal versus spectral cues in AM detection
Authors: Rickert Martin E. , Viemeister Neal F.
Published: July 2002

Several recent studies have shown that modulation thresholds for detecting sinusoidal AM are approximately constant out to much higher modulation frequencies for tonal carriers than for broadband noise carriers. It has been suggested that with tonal carriers there is a range of modulation frequencies for which both temporal (envelope) cues and spectral cues are used for detection. The present study attempts to assess the relative importance of these cues. Modulation thresholds for AM, quasifrequency modulation (QFM), and beats were measured for modulation frequencies of 8–512 Hz and carrier frequencies of 2 and 5 kHz. The results indicate that at intermediate modulation frequencies, AM thresholds are approximately constant while those for QFM and for beats decrease with increasing modulation frequency. This indicates that the detection of AM is not based solely on temporal cues. The implications of these findings for envelope detection and modulation filter-bank models will be discussed. [Work supported by NIDCD Grant No. DC00683.]
Underwater sound localization: Role of interaural time and intensity differences
Authors: Bovet Pierre , Drake Carolyn , Bernaschina François , Savel Sohpie
Published: July 2002

In theory, underwater sound localization is very limited compared with that in air. Most cues are greatly reduced underwater: Interaural time differences are divided by four (due to faster sound propogation in water) and intensity differences are greatly reduced because signal conduction to the inner ear mainly occurs through skull bone condition, making the head transparent. However, preliminary studies indicate some localization abilities in scuba divers. An azimuth identification task was conducted in Lake Leman. At a depth of 10 m, 14 divers indicated which of eight transducers located every 45 was generating a sound (400 Hz, 6 kHz, or white noise). Results indicate: (a) correct estimates were highest for lateral positions (left and right) and poor for median positions (front and back), (b) performance was high for 400 Hz and white noise but low for 6-kHz signals, and (c) head movements did not appear to facilitate localization. Thus the best localization abilities were observed in positions with highest interaural time differences, suggesting that, contrary to theoretical predictions, temporal binaural cues must be at least partially functional. However, the fact that localization was poor for high-frequency signals suggests that interaural intensity differences do not play a significant role.
A new in situ method for the acoustic performance of road traffic noise reducing devices
Authors: Clairbois Jean-Pierre , Beaumont Jacques , Garai Massimo , Schupp Gerold
Published: July 2002

When they drew the European standards for ‘‘road traffic noise reducing devices’’ (NRD), the members of CEN/TC226 (road equipments)/WG6 (antinoise devices) found problems in using ISO 354 and ISO140 for characterizing sound absorption and airborne sound insulation of NRD. The problems are due to the fact that these standards have been drawn for building products, used inside buildings. The measurement of the sound absorption under a reverberant field does not reflect the real absorption coefficient found with road traffic. In addition, many road administrations wish to get a field test method for testing installed products. A European funded research (‘‘ADRIENNE’’) has been started in January 1995 and finished in December 1997 with the objectives to be able to measure the in-situ sound absorption and airborne sound insulation of NRD for the widest range of existing products (i.e., flat and nonflat ones). This paper shall present the results of the research, which is based on the combination of MLS signal and signal analysis, a substraction technique to enlarge the lowest reliable frequency limit, and a specific window. The fundamental method has been developed with three laboratories, and initial validation with eight laboratories shows promising results for a future standard.
The influence of stimulus envelope and fine structure on the binaural masking level difference
Authors: Eddins David A. , Barber Laura E.
Published: July 2002

A masking level difference (MLD) paradigm was used to investigate the influence of stimulus envelope and stimulus fine-structure characteristics on monaural and binaural hearing. The degree of masker envelope fluctuation was manipulated by selecting narrow-band noises (50 Hz) on a continuum of values of the normalized fourth moment of the envelope. The noises were specified as low-noise noise (LNN), medium-noise noise (MNN), and high-noise noise (HNN). Fine-structure cues were studied by measuring thresholds at 500 and 4000 Hz, regions in which the availability of such cues to the auditory system differ substantially. In addition, thresholds were measured for Gaussian noise maskers (GN) and for maskers having a flat magnitude spectrum, termed equal-magnitude noise (EMN) maskers. The results indicated lower NoSo thresholds for LNN than for the other four masker types. Furthermore, there were no differences in threshold for maskers having moderate and high degrees of envelope fluctuation (MNN and HNN). The NoSπ thresholds were not significantly different across masker type and were characterized by large individual differences among the seven listeners. The results are considered in relation to models of monaural and binaural processing. Consistent with previous reports, the results indicate that binaural detection depends on interaural differences in the stimulus envelope and fine structure at low frequencies and changes in the envelope at high frequencies.
Simplified expressions for the displacements and stresses produced by the Rayleigh wave
Authors: Hassan Waled , Nagy Peter B.
Published: July 2002

In many cases involving Rayleigh wave propagation along the free surface of a solid, the ratio between the normal and transverse displacement components, i.e., the aspect ratio of the elliptical particle trajectory on the surface, is of great importance. Surprisingly, this aspect ratio is exactly the same as the ratio between the vector and scalar displacement potential amplitudes. More importantly, the aspect ratio is also identically the same as the ratio between the shear and normal stresses in any plane parallel to the surface at any depth, i.e., exactly the same ratio also shows up between two fundamental physical quantities. It is shown that the identical amplitude ratio, which apparently has not been pointed out in the otherwise very comprehensive literature on Rayleigh wave propagation, is a direct result of the requirement that just below the surface even the oscillating power, i.e., the imaginary component of the Poynting vector, be parallel to the surface (of course, the average power, i.e., the real component of the Poynting vector is everywhere parallel to the surface).
Effects of amplitude nonlinearity on phoneme recognition by cochlear implant users and normal-hearing listeners
Authors: Fu Qian-Jie , Shannon Robert V.
Published: July 2002

It is widely assumed that the proper transformation of acoustic amplitude to electric amplitude is a critical factor affecting speech recognition in cochlear implant users. The goal of this study was to investigate the effects of instantaneous nonlinear amplitude mapping on vowel and consonant recognition in both cochlear implant users and normal-hearing listeners. A four-channel noise-band speech processor was implemented, reducing spectral information to four bands. A power-law transformation was applied to the amplitude mapping stage in the speech processor design, and the exponent of the power function varied from a strongly compressive (p=0.05) to a weakly compressive value (p=0.75) for implant listeners and from 0.3 to 3.0 for acoustic listeners. Results for implants showed that best performance was achieved with an exponent of about 0.2, and performance gradually deteriorated when either more compressive or less compressive exponents were applied. The loudness growth functions of the four activated electrodes in each subject were measured and those data were well fit by a power function with a mean exponent of 2.72. The results indicated that best performance was achieved when the normal loudness growth was restored. For acoustic listeners, results were similar to those observed with cochlear implant listeners, except that best performance was achieved with no amplitude nonlinearity (p=1.0). The similarity of results in both acoustic and electric stimulation indicated that the performance deterioration observed for extreme nonlinearity was due to similar perceptual effects. The function relating amplitude mapping exponent and performance was relatively flat, indicating that phoneme recognition was only mildly affected by amplitude nonlinearity.
Active removal of wind noise from outdoor microphones using local velocity measurements
Authors: Shust Michael R. , Rogers James C.
Published: July 2002

Wind noise in outdoor microphone measurements can significantly degrade acoustic data. An outdoor active windscreen based upon four local anemometer velocity measurements applied to an unscreened microphone is demonstrated. A simple relationship, developed from the Bernoulli equation, is used to transform hot-film anemometer wind velocity measurements into microphone wind pressure estimates. Measurements performed outdoors on a horizontally positioned microphone demonstrate that a major part of unscreened microphone wind noise is flow noise caused by interaction between the microphone and adjacent air flow. These measurements also indicate that the dominant source of wind noise in a passively screened microphone are local pressure fluctuations that are not correlated with local velocity fluctuations. This important observation indicates that the active windscreen is unlikely to significantly quiet a microphone that has conventional passive screening and that the active windscreen applied to an unscreened microphone is unlikely to surpass the performance of a passive windscreen. Wind energy reduction performance of the active windscreen is shown to be approximately 12 dB for frequencies below 200 Hz and decreases smoothly to approximately 5 dB at 500 Hz. In addition, the active system transfer functions are observed to possess significant stability of over periods of hours. a)Currently at Texas Instruments. b)Currently at California Maritime Academy.
Enhancement of electrically evoked oto-acoustic emissions associated with low-frequency stimulus bias of the basilar membrane towards scala vestibuli
Authors: Kirk Desmond L. , Yates Graeme K.
Published: July 2002

Electrically evoked oto-acoustic emissions (EEOAEs) are sounds present in the ear canal when ac current is passed into the cochlea. EEOAEs are attributed to the activation of fast electromotile responses in outer hair cells (OHCs). An interesting property of EEOAEs is the phenomenon of “acoustic enhancement,” where the emission amplitude is increased by moderate-level sound [D. C. Mountain and A. E. Hubbard, Hear. Res. 42, 195–202 (1989)]. In this report a form of enhancement is described which occurs with displacements of the basilar membrane toward scala vestibuli, during amplitude modulation of the EEOAE waveform by low-frequency tones. This “SV-bias enhancement” possibly consists of two components: (i) a low-level component induced by sound at levels which produce nonlinear growth of the cochlear microphonic and which may be equivalent to the “acoustic enhancement” described previously, and (ii) a high-level component which occurs at sound levels well above those which cause saturation of the cochlear microphonic. The low-level component could be explained by either an increased access of the extrinsically applied current to a membrane-based source of OHC motility, perhaps coupled with a reduction in negative feedback, or an increase in electromotile output during scala vestibuli displacements, but the origin of the high-level component is obscure.
Frequency-weighting functions for broadband speech as estimated by a correlational method
Authors: Turner Christopher W. , Kwon Bom Jun , Tanaka Chiemi , Knapp Jennifer , Hubbartt Jodi L. , Doherty Karen A.
Published: July 2002

The relative contributions of various regions of the frequency spectrum to speech recognition were assessed with a correlational method [K. A. Doherty and C. W. Turner, J. Acoust. Soc. Am. 100, 3769–3773 (1996)]. The speech materials employed were the 258-item set of the Nonsense Syllable Test. The speech was filtered into four frequency bands and a random level of noise was added to each band on each trial. A point biserial correlation was computed between the signal-to-noise ratio in each band on the trials and the listener’s responses, and these correlations were then taken as estimates of the relative weights for each frequency band. When the four bands were presented separately, the correlations for each band were approximately equal; however, when the four bands were presented in combination, the correlations were quite different from one another, implying that in the broadband case listeners relied much more on some bands than on others. It is hypothesized that these differences reflect the way in which listeners combine and attend to speech information across various frequency regions. The frequency-weighting functions as determined by this method were highly similar across all subjects, suggesting that normal-hearing listeners use similar frequency-weighting strategies in recognizing speech.
Research on a sonic boom evaluation and low-boom and low-drag design
Authors: Inagaki Kenjiro , Yamamoto Ayano , Ogoshi Hirokage , Hayama Kenji , Sakai Kenji
Published: July 2002

Kawasaki Heavy Industries, Ltd. has been researching on a sonic boom since 1990 toward the development of the next-generation SST (super sonic transport). A small chamber where a similar-sonic-boom could be created was made in 1993, and over 200 tests were carried out to see the reaction of people inside the chamber. As the result, it was found that A-weighted sound-pressure level (ASEL) and Stevens’ Mark VII perceived level (PL) were good metrics for boom evaluation, and the intolerable levels of ASEL and PL were studied. At the same time, an aerodynamic design technique was developed, which was produced by combining the low-boom theory of Darden (NASA) with the low-drag design method of super sonic aircraft. The validity of the design technique was verified by computational fluid dynamics (CFD) and wind tunnel testing. The effect of trim characteristics on a sonic boom has also been studied for more practical investigations. A boom propagation has also been calculated recently by using Hayes’ program for more understanding. The effects of weight, altitude, and Mach number on a propagating boom were investigated by parametric studies using the next-generation SST configurations in Japan.