bluuebunny/crossref_metadata_2025 huggingface dataset:
The coupling of anisotropy and radial dose functions for and for use with a commercial treatment planning system
Authors: Prete James J. , Bice William S. , Dubois Donald F. , Prestidge Bradley R.
Published: July 2002

Many commercial treatment planning systems available today employ traditional dose calculation formulae in their interstitial brachytherapy source calculation algorithms. The 1995 AAPM report on interstitial brachytherapy source dosimetry recommended a new dose calculational formalism and presented a technique for adopting it on systems which embody traditional formalism. In order to comply with these recommendations on our system, the transformations for implementing a one dimensional isotropic point source model were modified by coupling the published anisotropy and radial dose corrections and fitting them to a fifth order polynomial. Using this approach, a more accurate dose calculation is obtained.
Dose outside the irradiated volume in radiotherapy
Authors: van der Giessen Piet‐Hein
Published: July 2002

This thesis presents data that enable an estimation of the dose to organs outside the irradiated volume in radiotherapy, often called the peripheral dose (PD). This can be of interest when young or pregnant patients have to be treated with radiation and an evaluation is required of the benefits and risks. Using a large water phantom, the PD was measured as a function of field size, distance, depth, and patient thickness from cobalt‐60 gamma radiation to 25 MV x rays, for perpendicularly as well as tangentially incident beams. PDs were also determined by recalculating and averaging published data for different treatment machines. The spread of these averaged data of about 30% is adequate for risk assessment. Physicists in The Netherlands provided data on leakage and collimator scatter for their treatment machines showing that the variation for different types of machines from different manufacturers is small. Therefore, two sets of data are sufficient for PD estimates, one for cobalt‐60 gamma radiation and one for 4–25 MV x rays. The accuracy of the model was checked under clinical conditions by measuring the dose at the location of the perineum in patients treated for various tumor types. The dose at large distances from brachytherapy sources including Co‐60, Cs‐137, and Ir‐192 was also measured.
A new Diamentor for measuring kerma‐area product and air‐kerma simultaneously
Authors: Gfirtner Hans , Stieve Friedrich‐Ernst , Wild Johannes
Published: July 2002

The new M4KDK Diamentor (PTW‐Freiburg) for measuring the air‐kerma‐area product (KAP) and air kerma (AK) simultaneously was evaluated. The special design of the Diamentor chamber influences the variation of the calibration factor with respect to the field size somewhat differently to what is the case with the classic Diamentor. It is therefore recommended that calibration be performed for a larger field size. If the M4KDK Diamentor is calibrated for a field size of (at the chamber), an uncertainty in the KAP value of better than 15% for all field sizes used in practice, and an uncertainty in the AK value of better than 15% for a field size larger than the calibration field, can be expected. The influence of backscattered radiation on the calibration factor is equivalent to that for the classic Diamentor chamber. The variation in response in accordance with tube potential, is also comparable with that of the classic Diamentor. Dramatic changes in response have to be expected if additional filters are introduced in close proximity to the Diamentor chamber.
Electron transport in photon and electron beam modeling
Authors: Keall Paul
Published: July 2002

To address the deficiencies of currently available dose calculation algorithms for radiotherapy planning, two dose calculation methods have been devised. The first method incorporates Fermi–Eyges multiple scattering theory into the primary dose calculation of the superposition method for external x‐ray beam radiotherapy. The inclusion of scattering theory into the superposition technique accounts for the density distribution between the primary photon interaction and energy deposition sites. The second method developed is the super‐Monte Carlo (SMC) method. SMC calculates dose by a superposition of pregenerated Monte Carlo electron track kernels. For x‐ray beams, the primary dose is calculated by transporting pregenerated (in water) Monte Carlo electron tracks from each primary photon interaction site. The length of each electron step is scaled by the inverse of the density of the medium at the beginning of the step. The scatter dose is calculated by superposition. SMC can also be applied to electron beam dose calculation. Pregenerated electron tracks are transported through media of varying density and atomic number. The perturbation of the electron fluence due to each material encountered by the electrons is explicitly accounted for. Dose distributions in a variety of phantoms show good agreement with Monte Carlo results. SMC is an accurate, three‐dimensional unified photon/electron dose calculation algorithm.
Automated lung segmentation in digital posteroanterior and lateral chest radiographs: Applications in diagnostic radiology and nuclear medicine
Authors: Armato Samuel G.
Published: July 2002

Automated segmentation of anatomic regions in digital radiographs is a key element of computer‐aided diagnostic (CAD) methods. Computerized methods for automatically segmenting the aerated lung fields from digital posteroanterior (PA) and lateral chest radiographs have been developed. The methods are based on gray‐level thresholding techniques, including iterative global gray‐level thresholding and local gray‐level thresholding, thus reducing the need for a priori assumptions regarding overall lung morphology. Consequently, this method is particularly applicable to the detection of abnormal asymmetry in PA radiographs, where pathological processes may produce gross alterations in the appearance of radiographic lung anatomy. An anatomic region of particular interest is the costophrenic angle. The method described lends itself to the automated assessment of costophrenic angle blunting, for which a technique has been developed. Another application of this method crosses into the field of nuclear medicine. Radionuclide lung scans are typically used in conjunction with chest radiographs for diagnostic purposes. An automated method for registering digital PA and lateral chest radiographs with the perfusion and ventilation images of a lung scan has been developed. These computerized techniques may be incorporated into future CAD schemes and may potentially aid radiologists in the interpretation and assessment of medical images.
Quality assurance for dynamic multileaf collimator modulated fields using a fast beam imaging system
Authors: Ma Lijun , Geis Paul B. , Boyer Arthur L.
Published: July 2002

A quality assurance procedure was developed for x‐ray beam intensity modulated conformal radiotherapy (IMCRT) using dynamic multileaf collimators (MLC). The procedure verifies a prescribed intensity modulated x‐ray beam pattern in the beam eye's view (BEV) before the treatment procedure is applied to a patient. It verifies that (a) the leaf sequencing computer files were transferred correctly to the linac control computer; (b) the treatment can be correctly executed without machine faults. A fast beam imaging system (BIS) consisting of a scintillation screen, a charge‐coupled device (CCD) camera, and a portable personal computer (Wellhöfer Dosimetrie, Schwarzenbruck, Germany) was commissioned for this purpose. Measurements for the BIS performance are presented in this work. Reference images were derived from MLC leaf sequencing files that were used to drive a dynamic MLC system (Varian Oncology Systems, Palo Alto, CA). A correlation method was developed to compare the BIS measurements with the calculated reference images. A correlation coefficient calculated using 26 correct intensity modulated fields was shown to be a reliable threshold to identify inaccurate treatment delivery files. The study has demonstrated the feasibility of using the BIS and the correlation method to carry out on‐line quality assurance tasks for IMCRT treatment fields in the BEV.
Designing an optical distance indicator for a radiation therapy accelerator
Authors: Maughan Richard L.
Published: July 2002

The computational aspects of the design of an optical distance indicator (ODI) for use with a radiation therapy accelerator are discussed. The specifics of the optical and mechanical design of an ODI for use with a superconducting cyclotron used for fast neutron therapy are presented.
Spatial resolution of imaging with diffusing light: Edge spread function measurements on a realistic tissue phantom
Authors: Cubeddu Rinaldo , Pifferi Antonio , Taroni Paola , Torricelli Alessandro , Valentini Gianluca
Published: July 2002

A realistic tissue phantom was used to study the spatial resolution of time‐resolved transmittance imaging techniques based on time gating and on the plot of the optical coefficients obtained from the fit to a theoretical model. Time‐resolved transmittance curves were collected along a line across a sharp transition between two regions of different, but realistic, optical properties. The effect of scattering and absorption edges were examined to get a deeper insight into the problem of imaging both scattering and absorption inhomogeneities. For both the fitted optical parameters and the integrated intensity, the edge spread function was evaluated and fitted to an error function, providing quantitative information on both spatial resolution and edge location. The plot of the fitted scattering coefficient and the intensity integrated within an early gate have similar resolution, while the performance of the fitted absorption coefficient is definitely worse. The edge location is more sensitive to the optical contrast with the fitted scattering than with the integrated intensity.
Direct measurement of mammographic x‐ray spectra using a CdZnTe detector
Authors: Matsumoto Masao , Yamamoto Akihide , Honda Ikuko , Taniguchi Akira , Kanamori Hitoshi
Published: July 2002

Our purpose is to directly measure mammographic x‐ray spectra with collimators and a low‐efficiency CdZnTe detector developed recently and to find out the best fit response function of CdZnTe detector to correct the measured spectra. Photon spectra (target Mo or Rh) produced by a mammographic x‐ray unit at 25–32 kV and 240 mAs (=3 times of 80 mAs) and transmitted through 0.03 mm Mo or 0.025 mm Rh filter and object (0.1 mm Al to 0.8 mm Al phantoms) have been analyzed. Since detected spectra were distorted by the response of CdZnTe detector and did not present the true photon spectra, the correction was applied by the stripping procedure. The response function of detector used in this procedure has been determined by the evaluation of interactions (K‐escape, coherent scattering, and Compton scattering processes) and incomplete charge collection calculated using the Monte Carlo method. We have used radiations of Cd, Zn, and Te, respectively and have used the weight function for the incomplete charge collection and have considered Compton scattering. The Monte Carlo simulations were continued by changing the important factors (mean path length of hole dead layer of the CZT crystal and weight factor of incomplete charge collection until the best fit response function was found out. Corrected photon spectra were compared with the mammographic x‐ray spectral data of Bureau of Radiological Health (BRH) measured using a Ge detector. Attenuation curves of aluminum for 25–32 kV were calculated from the corrected photon spectra and compared with the attenuation curves measured using an ionization chamber. These results obtained using the CdZnTe detector agreed with the mammographic x‐ray spectral data of BRH and attenuation curves obtained by the ionization chamber.
Student understanding of quantum mechanics
Authors: Singh Chandralekha
Published: July 2002

We investigate the difficulties of advanced undergraduate students toward the end of a full year upper-level quantum mechanics course with concepts related to quantum measurements and time development. Our analysis is based upon a test administered to 89 students from six universities and interviews with 9 students. Strikingly, most students shared the same difficulties despite variations in background, teaching styles, and textbooks. Concepts related to stationary states, eigenstates, and time dependence of expectation values were found to be particularly difficult. An analysis of written tests and interviews suggests that widespread misconceptions originate from an inability to discriminate between related concepts and a tendency to overgeneralize.
Relation of acoustical parameters with and without audiences in concert halls and a simple method for simulating the occupied state
Authors: Hidaka Takayuki , Nishihara Noriko , Beranek Leo L.
Published: July 2002

Five acoustical parameters—reverberation time RT, early decay time EDT, clarity C80, strength G, and interaural cross-correlation coefficient IACC—were measured using identical procedures with and without audiences in six concert and opera halls. Reverberation times without audiences were measured in 15 additional halls using the same measuring techniques as for the six halls above, but for full occupancy the data were taken from musical stop chords at symphonic concerts. This paper shows that in all halls (1) the occupied RT can be predicted from the unoccupied RT using a linear regression equation, y=a−b exp(x), within acceptable limits, at low- and mid-frequencies. It is also shown for the six halls that (2) occupied C80’s are predicted accurately from unoccupied values by the newly proposed equation; (3) G’s with and without audiences are highly correlated by a first degree linear regression equation; and (4) IACCs have nearly the same value in both occupied and unoccupied halls. As a separate subject, the successful use of a cloth covering for seats in a concert or opera hall to simulate the occupied condition has been developed.
The acoustic features of human laughter
Authors: Bachorowski Jo-Anne , Smoski Moria J. , Owren Michael J.
Published: July 2002

Remarkably little is known about the acoustic features of laughter. Here, acoustic outcomes are reported for 1024 naturally produced laugh bouts recorded from 97 young adults as they watched funny video clips. Analyses focused on temporal features, production modes, source- and filter-related effects, and indexical cues to laugher sex and individual identity. Although a number of researchers have previously emphasized stereotypy in laughter, its acoustics were found now to be variable and complex. Among the variety of findings reported, evident diversity in production modes, remarkable variability in fundamental frequency characteristics, and consistent lack of articulation effects in supralaryngeal filtering are of particular interest. In addition, formant-related filtering effects were found to be disproportionately important as acoustic correlates of laugher sex and individual identity. These outcomes are examined in light of existing data concerning laugh acoustics, as well as a number of hypotheses and conjectures previously advanced about this species-typical vocal signal.
Scattering from a ribbed finite cylindrical shell
Authors: Tran-Van-Nhieu Michel
Published: July 2002

Scattering from a ribbed finite cylindrical shell is investigated with a theoretical formalism valid for long cylinders. An analytic expression is derived for the scattered pressure and it is shown that the scattered far field can be expressed as the sum of three components associated with specular reflection, scattering from helical waves, and Bloch–Floquet waves. Approximate solutions are proposed to reduce the computation load and resonance scattering is analyzed from the derived formulas leading to a relatively simple equation for the calculation of the Bloch–Floquet dispersion curves. Simple equations are proposed to determine the locations of the Bloch–Floquet waves for weak interactions of the ribs and the surface elastic waves. In the first Brillouin zone, it is found that the maximum level of Bloch–Floquet wave scattering depends only on the length of the cylinder as for the resonant modes of uniform cylindrical shells. Finally the relevancy of the method is examined by comparing numerical results to experimental data available in the published literature.
Effects of draining cochlear fluids on stapes displacement in human middle-ear models
Authors: Lord Richard M. , Abel Eric W. , Wang Zhigang , Mills Robert P.
Published: July 2002

Displacement-frequency characteristics of the stapes footplate were measured in five human temporal bones before and after draining the vestibule. Measurements were made in the 0.125–8 kHz range at 80 dB input sound pressure level, using a laser Doppler vibrometer. A circuit model was also used to predict stapes displacement. The temporal bone studies show a slight decrease in stapes footplate displacement at low frequency, and little change above 1 kHz. The displacement change is not as great as that found by other investigators or predicted by the model. There is little difference in stapes motion in temporal bones when the inner ear is intact or drained.
Radiation impedance matrices for rectangular interfaces within rigid baffles: Calculation methodology and applications
Authors: Pierce Allan D. , Cleveland Robin O. , Zampolli Mario
Published: July 2002

The coupling of sound fields through a finite-sized aperture in a plane rigid baffle where the region (half-space) on one side is unbounded can be described by an integral equation which constitutes a boundary condition for the field on the other side of the aperture. Such a boundary condition, when the pressure and the normal velocity are expanded in basis functions defined over the aperture, can be recast into a matrix form relating the coefficients of the basis functions in the expansions, the principal feature being a matrix of fourfold (double-area) integrals analogous to those encountered in studies of radiation from flexible pistons in rigid baffles. A substantial analytical reduction to sums of single nonsingular integrals is derived for the elements of this radiation impedance matrix when the aperture is rectangular and the basis functions are expressible as a sum of products of exponential functions of the Cartesian coordinates of the aperture plane, with the exponential coefficients being arbitrary complex numbers. The validity of the result is substantiated by its reduction to previously published results for less general cases. Its utility is demonstrated with the example of diffraction by a square hole in a screen.
Solving the background mystery in acoustical resonance scattering theory (RST)
Authors: Huang Changzheng
Published: July 2002

The acoustical resonance scattering theory (RST) aims to solving inverse scattering problems by decomposing the backscattering echoes into a background part and a resonance part. The former contains scatterers shape information, and the latter contains the material composition information. RST assumes the existence of an intermediate background for general scatterer and surrounding combinations. However, despite the efforts taken in the 1970s through 80s, such a background still remains elusive. This long-standing difficult problem is re-investigated in this study. It is concluded here that an intermediate background or alike is not needed for the purpose of solving inverse scattering problems. The simplest rigid or soft background is sufficient for the extraction of resonance information for any type of scatterer and surrounding combinations. In other words, the missing background problem is not a problem at all. Another new finding of this study is that a rational expression for the backscattering echoes is better suited to convey the resonance information than the additive decomposition expression as in RST. Explicit and concise relations exist between the rational expression and the acoustical properties of any scatterer, which is important for applications such as underwater target identification. This presentation will be illustrated by animation movies.
Investigation of reverberation synthesized by electro-acoustic enhancement systems, from a subjective and physical acoustic standpoint
Authors: Shimizu Yasushi
Published: July 2002

Current electro-acoustic enhancement technology enables wide control over concert hall acoustics. The goal of sound field synthesis in anechoic space is to reconstruct a specific sound field. However, applying acoustic enhancement technology to existing reverberant spaces is a less developed research direction. This presentation demonstrates a methodology of electro-acoustic enhancement using regenerative reverberation through SAAF (spatially averaged acoustic feedback), an acceptable variation of RT and SPL in enhanced acoustical conditions. That was presented by YAMAHA Acoustic Research Laboratories. SAAF technology can flatten amplitude peaks at the howling frequency of acoustical feedback loops by using time variant finite impulse response filters. Therefore it enables regeneration of reverberated sound by wide band feedback in frequency without coloration. This system has been applied to ‘‘negative absorption control’’ and loudness equalization of under-balcony seats in current concert halls, to optimize concert hall acoustics electronically instead of architecturally. Adjusted reverberation time in enhanced condition should be between 1.5 and 2.0 times higher than the natural RT (ex. RTon/Rtoff=1.8). The SPL increases about 1 dB to 3 dB based on measured results of more than 30 performing halls integrated with acoustic enhancement system in Japan. Examples of the major Japanese concert halls with acoustic enhancement systems are presented.
Interrupted traffic noise
Authors: Kokowski Piotr , Makarewicz Rufin
Published: July 2002

A one-parameter model (ξ) for stop-and-go noise is developed. The physics of the phenomenon is based on the idea of the linear density of radiated energy. The methodology of ξ determination has been worked out and illustrated. The noise interaction with the surface of the ground is considered to be the only wave phenomenon that disturbs geometrical spreading. The model makes possible the calculation of the correction term in the time-average sound level, LAT, as an adjustment to the constant speed model of traffic noise.
Wavelet-based denoising of underwater acoustic signals
Authors: Weiss L. G. , Dixon T. L.
Published: July 2002

Underwater environmental measurements of the ocean require signals that are free from unwanted backscatter and clutter. Removing these unwanted signal components usually amounts to applying some form of filtering technique such as a high pass filter, a bandpass filter, a Wiener filter, etc. These approaches however are limited in their abilities to remove acoustic returns that vary spectrally. This paper presents a multiresolution approach to removing unwanted backscatter from high-frequency underwater acoustic signals and compares it to high pass filtering of the same signals. The filtering approach presented applies wavelet transforms for signal recovery and denoising of high-frequency acoustic signals. It is shown that by computing a wavelet transform of the returned signals, applying a denoising technique, and then reconstructing the signal, additional unwanted backscatter can be removed.
Materials for guitar back plates made from sustainable forest resources
Authors: Yano Hiroyuki , Furuta Yuuzoh , Nakagawa Hiroyuki
Published: July 2002

A new type of wood-based material for guitar back plates as a substitute for Brazilian rosewood was produced based on Japanese cedar logs with a small diameter, of which the utilization is limited despite its availability. The sapwood portion of logs with a diameter of 20 cm was processed to veneers of 2 mm thickness using a rotary lathing machine. The veneers were impregnated with a low-molecular-weight phenolic resin, laminated in parallel, and compressed perpendicular to their plane. When the veneers were treated with a 3% or 5% aqueous solution and compressed to a density of 0.8 without adhesives, the specific dynamic Young’s modulus (E/γ, ratio of stiffness to specific gravity) and tan δ (damping) of the materials became almost the same as those of Brazilian rosewood in the lower-frequency range, not only in the longitudinal direction but also across the longitudinal direction. However, the frequency dependencies of the specific Young’s modulus and tan δ of the materials differed from those of Brazilian rosewood, which may be partially related to the higher values of E/G of laminated compressed wood as a result of the increased density induced by deformation of the cell walls.
On the Duifhuis pitch effect
Authors: Lin Jian-Yu , Hartmann William M.
Published: July 2002

An effect discovered by Duifhuis [J. Acoust. Soc. Am. 48, 888–893 (1970)], wherein an omitted high harmonic of a periodic complex tone is found to have an audible pitch, is extended to a variety of new broadband signal conditions. The effect is found to exist for flat spectra and spectra decreasing at 6 dB/octave, independent of phases as long as they are constant. The effect exists for alternating phases and Schroeder phases. It can generate a missing-fundamental pitch. Pitch and loudness matching experiments support the status of the omitted harmonic as an objective tone in the signal. Further experiments using narrower bands challenge the traditional explanation for the effect, which attributes it to short-term frequency analysis by peripheral auditory filters. Instead, the experiments suggest that different peripheral channels must be combined, maintaining some phase information, to generate the effect.
Adaptive IIR filtered-v algorithms for active noise control
Authors: Crawford David H. , Stewart Robert W.
Published: July 2002

This paper reports on the development of “full-gradient” and “simplified-gradient” versions of the filtered-u algorithm for active noise control. After discussing the general principles of active noise control, the paper presents full mathematical derivations of the full-gradient, simplified-gradient, and Feintuch-based versions of the filtered-u algorithm, clearly showing the various levels of simplifying assumptions that are made along the way. Finally, some illustrative simulation results are presented.
The acoustic features of vowel-like grunt calls in chacma baboons (Papio cyncephalus ursinus): Implications for production processes and functions
Authors: Owren Michael J. , Seyfarth Robert M. , Cheney Dorothy L.
Published: July 2002

The acoustic features of 216 baboon grunts were investigated through analysis of field-recorded calls produced by identified females in known contexts. Analyses addressed two distinct questions: whether the acoustic features of these tonal sounds could be characterized using a source-filter approach and whether the acoustic features of grunts varied by individual caller and social context. Converging evidence indicated that grunts were produced through a combination of periodic laryngeal vibration and a stable vocal tract filter. Their acoustic properties closely resembled those of prototypical human vowel sounds. In general, variation in the acoustic features of the grunts was more strongly related to caller identity than to the social contexts of calling. However, two acoustic parameters, second formant frequency and overall spectral tilt, did vary consistently depending on whether the caller was interacting with an infant or participating in a group move. Nonetheless, in accordance with the general view that identity cueing is a compelling function in animal communication, it can be concluded that much of the observed variability in grunt acoustics is likely to be related to this aspect of signaling. Further, cues related to vocal tract filtering appear particularly likely to play an important role in identifying individual calling animals.
Annoyance caused by sounds of wheeled and tracked vehicles
Authors: Versfeld Niek J. , Vos Joos
Published: July 2002

In a laboratory experiment, the relationship between the annoyance caused by sounds of tracked and wheeled vehicles was investigated. Sounds of various vehicles, ranging from a main battle tank (MBT) to a passenger car, were recorded at several distances. Subjects were presented with these sounds and were asked to judge the annoyance if they were exposed to them at home on a regular basis. Overall, sounds emanated from military tracked vehicles were judged to be less annoying than civil passenger cars, provided that the indoor A-weighted sound-exposure levels (ASELs) were the same. It should be noted that receiver distance and operating conditions were not specifically matched for military and civil vehicles but were chosen to represent typical ranges of values found in practice. For steady-speed conditions, the sounds were judged to be equally annoying if the (indoor) ASELs of the tracked armored personnel carrier (APC) and the MBT exceeded that of a passenger car by 5 and 10 dB, respectively. In specific driving conditions such as alternate accelerations and decelerations, however, these differences were smaller. For ASELs below 55 dB, passenger cars were found to be more annoying than heavier wheeled vehicles, such as a bus or a truck with a trailer. The data indicate that the difference between the high-frequency part and the low-frequency part of the spectrum might play a role in the annoyance. With respect to noise-zoning procedures it is highly interesting that the outdoor ASEL could predict the annoyance, as rated indoors, better than could any indoor noise measure. The 5- and 10-dB bonuses to the indoor level of the APC and the MBT, respectively, were reduced to 1 and 3 dB if the dose was measured outdoors.
Detection of silent intervals between noises activating different perceptual channels: Some properties of “central” auditory gap detection
Authors: Phillips D. P. , Taylor T. L. , Hall S. E. , Carr M. M. , Mossop J. E.
Published: July 2002

This article describes four experiments on gap detection by normal listeners, with the general goal being to examine the consequences of using noises in different perceptual channels to delimit a silent temporal gap to be detected. In experiment 1, subjects were presented with pairs of narrow-band noise sequences. The leading element in each pair had a center frequency of 2 kHz and the trailing element’s center frequency was parametrically varied. Gap detection thresholds became increasingly poor, sometimes by up to an order of magnitude, as the spectral disparity was increased between the noise bursts that marked the gap. These data suggested that gap-detection performance is impoverished when the underlying perceptual timing operation requires a comparison of activity in different perceptual channels rather than a discontinuity detection within a given channel. In experiment 2, we assessed the effect of leading-element duration in within-channel and between-channel gap detection tasks. Gap detection thresholds rose when the duration of the leading element was less than about 30 ms, but only in the between-channel case. In experiment 3, the gap-detection stimulus was redesigned so that we could probe the perceptual mechanisms that might be involved in stop consonant discrimination. The leading element was a wideband noise burst, and the trailing element was a 300-ms bandpassed noise centered on 1.0 kHz. The independent variable was the duration of the leading element, and the dependent variable was the smallest detectable gap between the elements. When the leading element was short in duration (5–10 ms), gap thresholds were close to 30 ms, which is close to the voice onset time that parses some voiced from unvoiced stop consonants. In experiment 4, the generality of the leading-element duration effect in between-channel gap detection was examined. Spectrally identical noises defining the leading and trailing edges of the gap were presented to the same or to different ears. There was a leading-element duration effect only for the between channel case. The mean gap threshold was again close to 30 ms for short leading-element durations. Taken together, the data suggest that gap detection requiring a temporal correlation of activity in different perceptual channels is a fundamentally different task to the discontinuity detection used to execute gap detection performance in the traditional, within-channel paradigm.
A time domain binaural model based on spatial feature extraction for the head-related transfer function
Authors: Wu Zhenyang , Chan Francis H. Y. , Lam F. K. , Chan Joseph C. K.
Published: July 2002

A complex-valued head-related transfer function (HRTF) can be represented as a real-valued head-related impulse response (HRIR). The interaural time and level cues of HRIRs are extracted to derive the binaural model and also to normalize each measured HRIR. Using the Karhunen–Loeve expansion, normalized HRIRs are modeled as a weighted combination of a set of basis functions in a low-dimensional subspace. The basis functions and the space samples of the weights are obtained from the measured HRIR. A simple linear interpolation algorithm is employed to obtain the modeled binaural HRIRs. The modeled HRIRs are nearly identical to the measured HRIRs from an anesthetized live cat. Typical mean-square errors and cross-correlation coefficients between the 1816 measured and modeled HRIRs are 1% and 0.99, respectively. The real-valued operations and linear interpolating in the model are very effective for speeding up the model computation in real-time implementation. This approach has made it possible to simulate real free-field signals at the two eardrums of a cat via earphones and to study the neuronal responses to such a virtual acoustic space (VAR).
Measurements of newly defined intensimetric quantities and their physical interpretation
Authors: Stanzial Domenico , Prodi Nicola
Published: July 2002

This paper deals with the measurement and physical interpretation of the quantities a and r introduced in a previous paper [D. Stanzial, N. Prodi, and G. Schiffrer, “Reactive intensity for general fields and energy polarization,” J. Acoust. Soc. Am. 99, 1868–1876 (1996)]. The quantity a, which has the same time dependence as the squared acoustic pressure and the same direction as the time averaged sound intensity 〈j〉, will be called here “radiating” intensity, while r which has zero average, will be called “oscillating” intensity. A coherent picture of the energy transfer process in steady sound fields based on the decomposition j=a+r of the instantaneous sound intensity will be sketched and discussed. Furthermore, a direct experimental comparison between a and r and the real and imaginary parts of the complex intensity is presented for some field conditions.
Interpretation of distortion product otoacoustic emission measurements. II. Estimating tuning characteristics using three stimulus tones
Authors: Mills David M.
Published: July 2002

The simple model introduced in Part I [J. Acoust. Soc. Am. 102, 413–429 (1997)] is used to simulate the response of the cochlea to three stimulus tones. The focus is on “emission suppression tuning curves” constructed using a third tone to suppress the cubic distortion tone emission (CDT, 2 f1−f2) generated by two primary tones at frequencies f1 and f2 (intensities L1 and L2). A criterion decrease (here, 5 dB) of the CDT emission amplitude defines the 2 f1−f2 emission suppression tuning curve. Applying traditional tuning curve measures to emission suppression tuning curves appears ineffective in determining the underlying cochlear amplifier characteristics. However, it is shown that there are three characteristics of emission suppression tuning curves which are particularly useful: (1) the “f2 threshold” which is the level of the third tone, L3, required for the criterion CDT amplitude decrease, under the condition that the third tone frequency, f3, is approximately equal to f2; (2) the “shoulder threshold” similarly defined for f3≪f2; and (3) the “tuning width,” w40. The tuning width is defined to be the distance (in octaves) from the frequency f2 to the upper f3 frequency for which there is a criterion CDT decrease, in this case using the L3 level which is 40 dB above the f2 threshold. Model calculations appropriate to gerbils show that these measures are most accurately related to the underlying cochlear amplifier characteristics for parameters where the primary stimulus amplitudes satisfy L1/L2>20 dB and for which L1 is 25 dB or more below the sharp “notch” seen in the two tone input–output function. In this parameter region, the cochlear amplifier characteristics are related to measured quantities by the relationships wr≅w40 and Ga≅TE+w40gp. Here, Ga is the gain (dB) of the cochlear amplifier, defined as the total increase in cochlear response over the passive response, wr is the distance (octaves) over which the active cochlear response rises to a maximum, and gp is the passive increase (dB/octave) of the traveling wave along the basilar membrane. The measured quantities are TE, the difference (dB) between the shoulder threshold and the f2 threshold, and the tuning width, w40 (octaves), defined above. Model predictions are confirmed by measurements in adult gerbils.
Jimi Hendrix’ use of distortion to extend the performance vocabulary of the electric guitar
Authors: Fricke James J.
Published: July 2002

Experience Music Project is an interactive music museum scheduled to open in Seattle in 1999. Sound Lab, the hands-on portion of the museum, will use a variety of exhibit techniques to lead the visitor to explore music composition and performance, the technology of popular music making, and the physical principles involved in sound production and reproduction. The role of acoustics and signal processing in the development and realization of these exhibits is discussed. Jimi Hendrix, who pioneered the use of electronic effects in extending the expressive vocabulary of the electric guitar, is central to one planned exhibit. Hendrix’ ‘‘Drivin’ South’’ guitar solo from 1967 is presented as an example of the extended expressive possibilities afforded by a highly overdriven, amplified electric guitar. This use of distortion for artistic effect is analyzed, and the performance is compared to an undistorted performance of the same piece. The electronic means for achieving the distorted guitar sound is presented using artifacts from EMP’s Jimi Hendrix collection, and the resulting signal modification is demonstrated and analyzed.
Modeling and simulating finite-amplitude propagation through time-varying inhomogeneous absorbing media
Authors: Hallaj Ibrahim M. , Cleveland Robin O. , Kargl Steven G.
Published: July 2002

A model equation is derived for three-dimensional wave propagation through an inhomogeneous, time-varying medium. The model equation accounts for arbitrary inhomogeneities, finite-amplitude distortion, and absorption. The effect of time dependence of the background medium parameters is included in the equation. An ordering scheme based on the characteristic time of the evolution of each parameter allows one to evaluate their relative importance. A two-dimensional version of the wave equation is solved in the time-domain using finite-difference methods. Explicit, implicit, and operator splitting techniques were used in the solution to overcome numerical instabilities. Results from the code are compared to known solutions for some simple geometries in homogeneous and step indexed media. Various modeling and numerical schemes for treating the absorption on the computational domain interior and at the boundaries of the domain will be presented. [Work supported by ONR and DARPA.]
A multiple microphone recording technique for the generation of virtual acoustic images
Authors: Kahana Yuvi , Nelson Philip A. , Kirkeby Ole , Hamada Hareo
Published: July 2002

A new recording technique based on multichannel digital signal processing is suggested. The system uses a dummy-head that is modeled as a rigid sphere with two pairs of microphones mounted on opposite sides of the sphere in the horizontal plane. Reversals—front back confusion, is a well-known phenomenon when localizing virtual acoustic images produced by either headphones or loudspeakers. Reproduction with two loudspeakers to the front of the listener causes rear virtual acoustic images to be perceived primarily at “mirrored” angles in the frontal hemisphere. The problem is tackled here by using a multichannel signal processing technique rather than by mimicking accurately the acoustomechanical properties of a human head. The acoustic signals which are recorded at the microphones are filtered by a 4×4 matrix of digital filters before being transmitted via four loudspeakers. The performance of the system is investigated by means of computer simulations, objective measurements, and also by subjective experiments in an anechoic environment, where the listeners are asked to localize the perceived angle of the signals which were prerecorded with the sphere dummy-head. Successful discrimination of reversals is achieved primarily due to the dominant role of the interaural time delay (ITD) for localization at low frequencies, but the accuracy with which listeners can localize virtual acoustic images is reduced in comparison to a conventional two-ear dummy-head (e.g., KEMAR) with a two-loudspeaker arrangement. The system is robust with respect to head rotations—virtual acoustic images do not disappear and localization ability improves when listeners use small head rotations.
Actively created quiet zones for broadband noise using multiple control sources and error microphones
Authors: Guo Jingnan , Pan Jie
Published: July 2002

Previous research on the quiet zones created in the free space, using multiple control sources and error microphones equally located in two parallel lines or in two parallel planes, demonstrated that there exists a range of optimal spacing for the control sources and error microphones. With the optimal arrangement, the largest area of quiet zone can be created with the least increase of total power output. This range for the optimal spacing is related to the configuration of the control system and the wavelength of the noise. The effectiveness of the optimally arranged control system to broadband noise is investigated in this paper. The results from both numerical simulation and experiment show that a control system optimally arranged for a particular frequency will be effective not only to the noise at the frequency, but also to that within a frequency band specified in this paper.
A binaural analog of gap detection
Authors: Akeroyd Michael A. , Summerfield A. Quentin
Published: July 2002

The temporal resolution of the binaural auditory system was measured using a binaural analog of gap detection. A binaural “gap” was defined as a burst of interaurally uncorrelated noise (Nu) placed between two bursts of interaurally correlated noise (N0). The Nu burst creates a dip in the output of a binaural temporal window integrating interaural correlation, analogous to the dip created by a silent gap in the output of a monaural temporal window integrating intensity. The equivalent rectangular duration (ERD) of the binaural window was used as an index of binaural temporal resolution. In order to derive the ERD, both the shortest-detectable binaural gap and the jnd for a reduction in interaural correlation from unity were measured. In experiment 1, binaural-gap thresholds were measured using narrow-band noise carriers as a function of center frequency from 250 to 2000 Hz (fixed 100-Hz bandwidth) and as a function of lower-cutoff frequency from 100 to 400 Hz (fixed 500-Hz upper-cutoff frequency). Binaural-gap thresholds (1) increased significantly with increasing frequency in both tasks, and (2) at frequencies below 500 Hz, were shorter than corresponding silent-gap thresholds measured with the same N0 noises. In experiment 2, interaural-correlation jnd’s were measured for the same conditions. The jnd’s also increased significantly with increasing frequency. The results were analyzed using a temporal window integrating the output of a computational model of binaural processing. The ERD of the window varied widely across listeners, with a mean value of 140 ms, and did not significantly depend on frequency. This duration is about an order of magnitude longer than the ERD of the monaural temporal window and is, therefore, consistent with “binaural sluggishness.”
Detection and censusing of blue whale vocalizations along the central California coast using a former SOSUS array
Authors: Chiu Ching-Sang , Miller Christopher W. , Moore Therese C. , Collins Curtis A.
Published: July 2002

To investigate the feasibility of automating the detection and censusing of blue whale vocalizations over a large coastal region using the Naval Postgraduate School (NPS) Ocean Acoustic Observatory (OAO), a four-day experiment was conducted along Central California in the summer of 1997. During the experiment, array data were archived continuously at the NPS OAO, a former SOSUS array. In addition to shore-based acoustic monitoring, an aircraft was assigned to locate blue whales in the Monterey Bay National Marine Sanctuary, and a research vessel, manned with observers and instrumented with a towed hydrophone array, was used to confirm locations of the blue whales and classify the vocalized near-field signals. The shipboard measurements were required to provide a means to separate the source signal characteristics from their multipath signatures. The towed array data were deverberated, source level and characteristics were estimated, and call-to-call variability was studied. Based on robust signal parameters, two simple autodetection correlation filters for the ‘‘A’’ and ‘‘B’’ blue whale calls were constructed, respectively. By applying the autodetection filters to the OAO data, the number of blue whale calls for the summer of 1998 was tallied. [Research supported by SERDP/ONR.]
Geographic variations of the Hawai’ian spinner dolphin (Stenella longirostris) whistle repertoire: Do they exist?
Authors: Bazua-Duran Carmen , Au Whitlow W. L.
Published: July 2002

In the present work, groups of spinner dolphins (Stenella longirostris) off four of the main Hawai’ian islands (Hawai’i, Lana’i, Maui, and O’ahu) have been studied. The whistle repertoire of dolphin groups from each island will be compared to search for geographic variations. In addition, behavioral, ecological, and acoustical variables have been quantified in order to correlate the dolphin whistle repertoire with specific behavioral and ecological factors. Geographic variations in the whistle repertoire of coastal bottlenose dolphins (Tursiops truncatus) from the Gulf of Mexico have been found. The differences were not attributable to different behavioral states, but were related to group structure (group size and contacts established between groups) and coastal habitat. These findings on the whistle repertoire of coastal bottlenose dolphins support the hypothesis that delphinid whistles serve to coordinate group behavior. Preliminary results on group structure of spinner dolphin groups off Hawai’i suggest that geographic variations should exist. Gulf of Mexico bottlenose and Hawai’ian spinner dolphin societies share several characteristics. Thus, it is expected that the Hawai’ian spinner dolphin whistle repertoire will show variations as does the bottlenose dolphin whistle repertoire. [This work was supported by a Leonida Memorial Scholarship and Seed Money Grant from the University of Hawai’i.]