bluuebunny/crossref_metadata_2025 huggingface dataset:
A multiresolution restoration method for cardiac SPECT imaging
Authors: Franquiz Juan M. , Shukla Shailendra
Published: July 2002

In this study we present a multiresolution based method for restoring cardiac SPECT projections. Original projections were decomposed into a set of sub‐band frequency images by using analyzing functions localized in both the space and frequency domain. This representation allows a simple denoising and restoration procedure by discarding high‐frequency channels and performing inversion only in low frequencies. The method was evaluated in bull's eye reconstructions of a realistic cardiac chest phantom with a custom‐made liver insert and liver‐to‐heart activity ratios (LHAR) of 0:1, 1.5:1, 2.5:1, and 3.5:1. The cardiac phantom in free air was used as the reference standard. Reconstructions were performed by filtered backprojection using (1) no correction; (2) restoration without attenuation correction; (3) attenuation correction without restoration; and (4) restoration and attenuation correction. The attenuation correction was carried out with the Chang's method for one iteration. Results were compared with those obtained using an optimized prereconstruction Metz filter. Quantitative analysis was performed by calculating the normalized chi‐square measure and of bull's eye counts. In reconstructions with high liver activity attenuation correction without restoration severely distorted the polar maps due to the spillover of liver activity into the inferior myocardial wall. Both restoration methods when combined with an attenuation correction compensated this artifact and yielded uniform polar maps similar to that of the standard reference. There was no visual or quantitative difference between the performance of Metz filtering and multiresolution restoration. However, the main advantage of the multiresolution method is that it states a more concise and straightforward approach to the restoration problem. Multiresolution based methods does not require information about the object image or optimization processes, such as in conventional nuclear medicine restoration filters. In addition, the method is easy to implement using DFT techniques and potentially can be extended to noniterative spatially shift‐invariant restorations in SPECT.
Reduced partial volume artifacts using spiral computed tomography and an integrating interpolator
Authors: Heuscher D. J. , Vembar M.
Published: July 2002

A technique is described for obtaining computed tomography (CT) head images with significantly reduced partial volume artifacts while retaining excellent low contrast resolution. Partial volume artifacts could be reduced by narrowing the collimation and summing thin slices. However, in axial scans, the acquisition and reconstruction time required for generating all the thin slices would prove clinically impractical. In addition, image artifacts could occur due to patient motion during the scans, particularly in trauma cases. In the case of spiral CT, a narrow collimation along with a small pitch can be used to reduce partial volume artifacts. However, the time required to reconstruct and sum the thin slices is still prohibitive. In this paper, we present a spiral technique using an integrating spiral interpolator (ISI) that allows a head study to be performed in less time without the partial volume artifacts normally seen. Using this interpolator, thick slices can be prospectively reconstructed from a spiral scan with a narrow collimation. The slice sensitivity profile for this interpolator was obtained and the full width at half‐maximum and full width at tenth‐maximum values were compared with both axial and predicted values. Noise values were also measured and compared to axial and theoretical predictions. Using this ISI interpolator, high quality head images were obtained with significantly reduced partial volume artifacts compared to standard axial and spiral scans. Total acquisition time is less than that of standard contiguous axial head scans.
A Gaussian approach for the calculation of the accuracy of stereotactic frame systems
Authors: Zylka Waldemar , Sabczynski Jörg , Schmitz Georg
Published: July 2002

Stereotactic frame systems are widely used in neurosurgery. The accuracy of frame devices is considered as a gold standard to which the accuracy of new frameless stereotactic navigation systems is compared. The purpose of this study is to develop a general approach for the prediction of the application accuracy of stereotactic systems. The approach will be applied to the frame‐based biopsy performed with three frame devices: Leksell G, Cosman–Roberts–Wells (CRW), and Brown–Roberts–Wells (BRW). A work‐flow analysis will be carried out demonstrating that the accuracy relevant for a clinical application comprises several error sources including imaging, target and entry point selection, image to frame coordinates registration, and the setting of mechanical parameters of the frame. These error sources will be postulated to obey a Gaussian distribution probability density. The linear, i.e., Gaussian, error propagation, will be used to link all error contributions thus to calculate the cumulative accuracy of the frame used in the application. Although the Gaussian approach is an approximation, it allows for an analytical treatment of the accuracy. Both the accuracy at the target point and the accuracy of the probe needle guidance along the planned trajectory have been investigated. Of great significance is the relationship found between accuracy, pixel dimension, and image slice thickness, the latter being the dominant factor for slices of more than 1.5 mm thickness, yielding inaccuracies larger than 1.5 mm. For target points the predictions for the application accuracy have been compared to the results of measurements, showing good agreement with the experimental data.
Time‐gated imaging in planar and tomographic x‐ray imaging
Authors: Grätz Matthias , Kiernan Laurence , Herrlin Kristian
Published: July 2002

Time‐gated imaging is a new technique for scatter suppression in radiological imaging, based on the use of ultrashort x‐ray pulses in combination with a fast gatable detector. We demonstrate scatter suppression in both planar and computed tomography (CT) radiography in an experimental model using x rays from a laser‐produced plasma. The scatter‐suppression efficiency of time‐gated imaging is found to be similar to existing standard techniques. Furthermore, it allows for a potential decrease in patient dose. Monte‐Carlo simulations confirm these results. We present an overview including theoretical simulations, experimental studies and comparisons to established techniques. The current technical limitations are evaluated and possible future applications in volumetric CT imaging are discussed.
Modeling of scintillation camera systems
Authors: Woldeselassie Tilahun
Published: July 2002

Despite their widespread use, the satisfactory modeling of scintillation camera systems has remained difficult. Although the resolving time and deadtime T of a nonparalyzable counter are identical and also invariable, a distinction needs to be made between the fixed resolving time and the variable deadtime τ of a paralyzable counter. It is shown here that where is the normalized input rate and N the absolute input rate. The normalized output rate, where R is the absolute output rate, has a maximum value at the input rate where It is also shown that the response of a system of nonparalyzable and paralyzable components at all input rates is determined by just the dominant nonparalyzable and paralyzable components in the system, the response at any particular input rate being that of the component with the higher of the two deadtimes T or τ. A system can be purely paralyzable combined paralyzable/nonparalyzable or essentially nonparalyzable the combined paralyzable/nonparalyzable system having a lower nonparalyzable and an upper paralyzable operating range separated by a threshold input rate at which A highly accurate and explicit expression for has also been derived. In the essentially nonparalyzable case, the system operates as nonparalyzable all the way up to the system's peak response point, which may occur at or above A two‐component system with can also be described mathematically as nonparalyzable using where for and for or as paralyzable using with for and for These alternative descriptions will be of considerable importance in the measurement of T and for such systems. The model described is able to account fully for the three different operating modes possible with scintillation camera systems.
Subunity coordinate translation with Fourier transform to achieve efficient and quality three‐dimensional medical image interpolation
Authors: Chen Qin‐Sheng , Crownover Richard , Weinhous Martin S.
Published: July 2002

A new approach to the interpolation of three‐dimensional (3D) medical images is presented. Instead of going through the conventional interpolation scheme where the continuous function is first reconstructed from the discrete data set and then resampled, the interpolation is achieved with a subunity coordinate translation technique. The original image is first transformed into the spatial‐frequency domain. The phase of the transform is then modified with linear phase terms in the axial direction to achieve subunity coordinate translations with a distance where n is an interpolation ratio, following the phase shift theorem of Fourier transformation. All the translated images after inverse Fourier transformation are then interspersed in turn into the original image. Since windowing plays an important role in the process, different window functions have been studied and a proper recommendation is provided. The interpolation quality produced with the present method is as good as that with the sampling (sinc) function, while the efficiency, thanks to the fast Fourier transformation, is very much improved. The approach has been validated with both computed tomography (CT) and magnetic resonance (MR) images. The interpolations of 3D CT and MR images are demonstrated.
Characterization of a fluoroscopic imaging system for kV and MV radiography
Authors: Drake D. G. , Jaffray D. A. , Wong J. W.
Published: July 2002

An on‐line kilovoltage (kV) imaging system has been implemented on a medical linear accelerator to verify radiotherapy field placement. A kV x‐ray tube is mounted on the accelerator at 90° to the megavoltage (MV) source and shares the same isocenter. Nearly identical CCD‐based fluoroscopic imagers are mounted opposite the two x‐ray sources. These systems are being used in a clinical study of patient setup error that examines the advantage of kV imaging for on‐line localization. In the investigation reported here, the imaging performance of the kV and MV systems are characterized to provide support to the conclusions of the studies of setup error. A spatial‐frequency‐dependent linear systems model is used to predict the detective quantum efficiencies (DQEs) of the two systems. Each is divided into a series of gain and spreading stages. The parameters of each stage are either measured or obtained from the literature. The model predicts the system gain to within 7% of the measured gain for the MV system and to within 10% for the kV system. The systems' noise power spectra (NPSs) and modulation transfer functions (MTFs) are measured to construct the measured DQEs. X‐ray fluences are calculated using modeled polyenergetic spectra. Measured DQEs agree well with those predicted by the model. The model reveals that the MV system is well optimized, and is x‐ray quantum noise limited at low spatial frequencies. The kV system is suboptimal, but for purposes of patient positioning yields images superior to those produced by the MV system. This is attributed to the kV system's higher DQE and to the inherently higher contrasts present at kV energies.
Using light sensitometry to evaluate mammography film performance
Authors: West Michael S. , Spelic David C.
Published: July 2002

The performance of commercially available light sensitometers was compared with two other methods of x‐ray sensitometry to determine whether commercially available sensitometers are viable for evaluating clinical performance of mammography film. X‐ray sensitometry was performed using mammography screens that were modified to accommodate a graded optical step tablet (screen sensitometry). Finally, a means for performing intensity‐scale x‐ray sensitometry was configured (inverse‐square sensitometry). Clinical mammography x‐ray exposure conditions were used and film processing quality was closely monitored during the study. Statistical results for chi‐square probabilities on the resulting contrast curves yielded good agreement for most of the configurations investigated. Comparison of film gradient versus optical density curves showed good agreement for maximum contrast values and the corresponding optical density for maximum contrast for three of the four screen–film combinations used when comparing light sensitometry to screen sensitometry. A similar comparison of light sensitometers to inverse‐square sensitometry showed good agreement for maximum contrast, but less agreement for the corresponding optical density of maximum contrast. Based on these results, the authors concluded that commercially available sensitometers could be used to estimate clinical film performance for the screen–film systems tested. In particular they can be used to determine the range of optical densities that provide optimal film contrast.
Comparison of dosimetry calibration factors at the NRCC and the NIST
Authors: Shortt Ken , Shobe Jileen , Domen Steve
Published: July 2002

In early 1998, three transfer ionization chambers were used to compare the air‐kerma and absorbed‐dose‐to‐water calibration factors measured by the National Research Council of Canada (NRCC) and the National Institute of Standards and Technology (NIST). The ratios between the NRCC and NIST calibration factors are 0.9950 and 1.0061 in the case of the absorbed‐dose‐to‐water and air‐kerma standards, respectively. In the case of the standard of absorbed dose to water, the combined uncertainty of the ratio between the standards of the two laboratories is about 0.6% and consequently, the observed difference of 0.5% is not significant at the one sigma level. In the case of the standard of air kerma, the combined uncertainty of the ratio between the standards of the two laboratories is about 0.4%, and so the observed difference of 0.61% is significant at the one sigma level. However, this discrepancy is due to the known differences in the methods of assessing the wall correction factor at the two laboratories. Taking into account changes implemented in the standards that form the basis of the calibrations, the present results are consistent with those of the previous comparison done in 1990/91. As a direct result of these differences in the calibration factors, changing from an air‐kerma based protocol following TG‐21 to an absorbed‐dose‐to‐water based protocol following TG‐51, would alter the relationship between clinical dosimetry in Canada and the United States by about 1%. For clinical reference dosimetry, the change from TG‐21 to TG‐51 could result in an increase of up to 2% depending upon the ion chamber used, the details of the protocol followed and the source of traceability, either NRCC or NIST.
Steering in bicycles and motorcycles
Authors: Fajans J.
Published: July 2002

Steering a motorcycle or bicycle is counterintuitive; to turn right, you must steer left initially, and vice versa. You can execute this initially counter-directed turn by turning the handlebars explicitly (called counter-steering) or by throwing your hips to the side. Contrary to common belief, gyroscopic forces play only a limited role in balancing and steering [D. E. H. Jones, Phys. Today 23 (4), 34–40 (1970)].
Tests of some common assumptions of ear-canal acoustics in cats
Authors: Huang Gregory T. , Rosowski John J. , Puria Sunil , Peake William T.
Published: July 2002

The accuracy of ear-canal admittance and reflectance as measures of the ear’s properties depends on the acoustic effects of the canal. Here, measurements of acoustic admittance at different canal locations in domestic cats are used to test three common assumptions. (1) Can a uniform-tube model of the canal represent spatial variations in admittance? Data from cats support this assumption for frequencies below 3 kHz, where the admittance inferred at the tympanic membrane (TM) based on a uniform-tube model differs by less than 3 dB in magnitude and 0.07 periods in angle from the admittance measured at the TM; for higher frequencies greater differences occur. (2) Do large static air pressures in the canal make the middle ear rigid without affecting the properties of the canal space? The measurements reported indicate that large negative static pressures reduce the low-frequency compliance of the cat middle ear to about 10% of the compliance of the canal air volume. Static displacements of the acoustic probe, TM, and canal walls with static pressure may affect estimates of the canal volume and middle-ear compliance by as much as 15% to 20%. (3) Is the acoustic-reflectance magnitude constant with position along the canal? Reflectance data from cat ear canals generally support this idea, except within a frequency region near 0.5 kHz for which there is evidence of energy loss. These results demonstrate that noninvasive measurements in the canal describe middle-ear acoustic properties to within tolerances that depend on the effects of the canal.
Active control design for acoustic radiation using mixed-norm optimization
Authors: Clark Robert L. , Cox David E.
Published: July 2002

Linear matrix inequalities were applied to design a mixed H2/H∞ feedback control compensator for a structural acoustic system. The compensator was designed to minimize the H2 norm of radiation filters while constraining the H∞ norm through the control path to be less than unity. A trade-off between minimizing sound power radiated and maximum rms gain in the control path resulted in a reliable and robust means of designing compensators for structural acoustic control.
Low-grazing-angle monostatic acoustic reverberation from rough and heterogeneous seafloors
Authors: Greaves Robert J. , Stephen Ralph A.
Published: July 2002

Numerical wavefield modeling, based on time domain finite difference solutions to the full elastic wave equation, is used to quantitatively predict the sensitivity of monostatic backscatter to variations in geological properties of the seabed. This article addresses the hypothesis that observed backscatter signals from the seafloor are produced by a combination of seafloor (interface) and subseafloor (volume) scattering from structures having variations at scale lengths comparable to the wavelength of the insonifying acoustic field. Wavelength-scale seafloor roughness and subseafloor volume heterogeneity parameters are defined using stochastic spatial probability functions having Gaussian autocorrelations. The range of the variations in these parameters is constrained to realistic values based on estimates derived from seafloor bathymetry and other geologic data. Modeling results show that backscattering from rough, basaltic (hard) bottoms, in the absence of large-scale seafloor slope, is dominated by rough surface scattering with little contribution from volume scattering. Contrary to this, sediment (soft) bottoms with subseafloor volume heterogeneity, with or without seafloor roughness, produce significant backscattering signals compared to a homogeneous sediment bottom.
On the spectral periodicity of transient-evoked otoacoustic emissions from normal and damaged cochleas
Authors: Avan Paul , Wit Hero P. , Guitton Matthieu , Mom Thierry , Bonfils Pierre
Published: July 2002

The spectral quasi-periodicity of transient-evoked otoacoustic emissions (TEOAE) is well acknowledged since Zwicker described a preferred spacing of 0.4 bark between consecutive peaks in the spectrum of otoacoustic emissions from normal ears. While there is scarce evidence of any anatomical reason for this regularity, several functional models of the cochlea have predicted that the structure of emission spectra reflects important characteristics of cochlear filters. In an attempt to check such predictions, the average regularity of TEOAE spectra was studied in three groups of human subjects, normally hearing adults, healthy neonates, and adults suffering from noise-induced hearing loss. Significant differences in emission periodicities were found. Around 1 kHz, the preferred spacing was close to 130 Hz in normally hearing adult ears and neonates. In contrast, no clear periodicity was found in the group of damaged ears, even though they had clinically normal pure-tone audiometry below 2 kHz. Around 4 kHz, the preferred spacing was close to 240 Hz in normal adults and neonates, whereas TEOAEs were absent in many impaired ears. A phenomenological model assuming that TEOAEs stem from the responses of a slightly disarrayed bank of highly tuned filters predicts that the filter width would be the same in healthy young adults and neonates. In contrast, ears suffering from high-frequency hearing loss could exhibit early damaged filters. The proposed method might provide an objective assessment of parameters otherwise difficult to evaluate, especially in neonatal cochleas.
On the relationships between the fixed-f1, fixed-f2, and fixed-ratio phase derivatives of the 2f1–f2 distortion product otoacoustic emission
Authors: Tubis Arnold , Talmadge Carrick L. , Tong Christopher , Dhar Sumit
Published: July 2002

For primary frequency ratios, f2/f1, in the range 1.1–1.3, the fixed-f1 (“f2-sweep”) phase derivative of the 2f1–f2 distortion product otoacoustic emission (DPOAE) is larger than the fixed-f2 (“f1-sweep”) one. It has been proposed by some researchers that part or all of the difference between these delays may be attributed to the so-called cochlear filter “build-up” or response time in the DPOAE generation region around the f2 tonotopic site. The analysis of an approximate theoretical expression for the DPOAE signal [Talmadge et al., J. Acoust. Soc. Am. 104, 1517–1543 (1998)] shows that the contributions to the phase derivatives associated with the cochlear filter response is small. It is also shown that the difference between the phase derivatives can be qualitatively accounted for by assuming the approximate scale invariance of cochlear mechanics. The effects of DPOAE fine structure on the phase derivative are also explored, and it is found that the interpretation of the phase derivative in terms of the phase variation of a single DPOAE component can be quite problematic.
Effects of relative phase and frequency spacing on the detection of three-component amplitude modulation
Authors: Moore Brian C. J. , Sek Aleksander
Published: July 2002

These experiments explored the effect of relative modulator phase on the detection of a three-component modulator applied to a 4000-Hz sinusoidal carrier with a level of 70 dB SPL. The central modulator component had a frequency of 50 Hz, and the two other components had frequencies of 50±5, 10, 25, 40, or 45 Hz. Thus, the modulator waveform was always periodic. Each modulator component had the same modulation index, m. The relative phases of the components were chosen to give a variety of modulation waveforms differing in the ratio of maximum to minimum value (max–min) and in crest factor. In experiment 1, modulation detection thresholds were measured by varying m, using an adaptive two-interval forced-choice procedure. Thresholds were found to be independent of relative modulator phase and of the frequency spacing of the components. In experiment 2, detectability (d′) of the modulation was measured for several fixed values of m. Detectability was found to be independent of relative modulator phase and of the frequency spacing of the components. The results are not consistent with the idea that modulation detection thresholds are determined by the max–min value or crest factor of the envelope. The results are consistent with a model which assumes that the stimuli are subjected to a nonlinearity, and thresholds are determined by the root-mean-square value (or the mean square value) of the ac component of the envelope, following this nonlinearity. The nonlinearity may partly reflect compression on the basilar membrane, but other nonlinearities may be involved. This model can also explain some aspects of earlier results on the sensitivity to relative modulator phase [E. A. Strickland and N. F. Viemeister, J. Acoust. Soc. Am. 99, 3638–3646 (1996)].
Measurement of the acoustic nonlinearity parameter B/A in solvents: Dependence on chain length and sound velocity
Authors: Banchet J. , Cheeke J. D. N.
Published: July 2002

This work consists of a systematic study of the acoustic nonlinearity parameter (B/A) in 1-alkanols from methanol to 1-decanol, ketones from acetone to methyl hexyl ketone, and alkyl acetates from ethyl to octyl acetate. By focusing a 14-MHz tone burst through a spherical quartz lens in each solvent, the second harmonic is generated and measured by a 28-MHz transducer at various distances from the focus. This provides the point of maximum second harmonic power, and enables the computation of the nonlinear parameter using a simple model. The B/A values thus obtained are in reasonable agreement with these available in the literature. The B/A values are found to increase with chain length and sound velocity, this increase being in contradiction with Ballou’s rule. Moreover, a hybrid model based on Schaaffs’ formula for sound velocity fits the experimental results, questioning the validity of Ballou’s rule for solvents within a single chemical family.
Complex Padé approximants for wide-angle acoustic propagators
Authors: Yevick David , Thomson David J.
Published: July 2002

Procedures for constructing wide-angle propagators that attenuate evanescent modes in parabolic equation (PE) models of underwater sound propagation are examined. In this context, two new split-step Padé approximations to exponentiated square-root operators are proposed. The first method involves a propagator derived from a Padé approximant of a square-root operator that has been rotated in the complex plane while the propagator of the second method is obtained from a complex coefficient rational approximation of the square-root operator. Numerical evidence confirms that these proposed methods yield improved behavior compared to previously suggested techniques in selected areas of the spectral domain.
Effects of flanking component spectral position and modulation pattern on thresholds for signals presented in the peaks of a modulated tonal masker
Authors: Delahaye Roel , Fantini Deborah A. , Meddis Ray
Published: July 2002

Detection of signals added solely to the peaks of an on-frequency modulated masker has never been found to improve after adding flanking components (FCs) at remote frequencies. However, according to theories underlying comodulation masking release (CMR), adding comodulated FCs could provide cues that improve signal detection for signal-peak placement. A reason masking release was not found with peak placement might be because of processes underlying modulation detection interference (MDI). This possibility was further investigated by using FCs that could diminish MDI but still provide signal detection cues associated with theories of CMR. It seemed that a peripheral within-channel and a central across-channel mechanism underlying MDI could hinder signal detection for signal peak placement.
Monaural masking release in random-phase and low-noise noise
Authors: Eddins David A.
Published: July 2002

Two masking-release paradigms thought to involve across-channel processing are comodulation masking release (CMR) and profile analysis. Similarities between these two paradigms were explored by comparing signal detection in maskers that varied only in degree of envelope fluctuation. The narrow-band-noise maskers were 10 Hz wide and their envelope fluctuations were manipulated using the low-noise noise algorithm of Pumplin [J. Acoust. Soc. Am. 78, 100–104 (1985)]. Masking conditions included the classic CMR conditions of an on-frequency band, multiple (five) incoherent bands, or multiple coherent bands. Detection was compared using both random-phase noise (RPN) and low-noise noise (LNN) maskers. In one set of conditions, the signal was identical to the on-frequency masker, yielding an intensity discrimination task. Conditions that included RPN maskers and tonal signals resembled the classic CMR paradigm, whereas conditions including LNN and noise signals more closely resembled the classic profile analysis paradigm. Other conditions may be considered hybrids. This combination of conditions provided a wide variety of within- and across-channel cues for detection. The results suggest that CMR and profile analysis could be based upon the same set of stimulus cues and perhaps the same perceptual processes.
Weak nonlinear propagation of sound in a finite exponential horn
Authors: Béquin Philippe , Morfey Christopher L.
Published: July 2002

This article presents an approximate solution for weak nonlinear standing waves in the interior of an exponential acoustic horn. An analytical approach is chosen assuming one-dimensional plane-wave propagation in a lossless fluid within an exponential horn. The model developed for the propagation of finite-amplitude waves includes linear reflections at the throat and at the mouth of the horn, and neglects boundary layer effects. Starting from the one-dimensional continuity and momentum equations and an isentropic pressure–density relation in Eulerian coordinates, a perturbation analysis is used to obtain a hierarchy of wave equations with nonlinear source terms. Green’s theorem is used to obtain a formal solution of the inhomogeneous equation which takes into account linear reflections at the ends of the horn, and the solution is applied to the nonlinear horn problem to yield the acoustic pressure for each order, first in the frequency and then in the time domain. In order to validate the model, an experimental setup for measuring fundamental and second harmonic pressures inside the horn has been developed. For an imposed throat fundamental level, good agreement is obtained between predicted and measured levels (fundamental and second harmonic) at the mouth of the horn.
The prediction of façade effects from a point source above an impedance ground
Authors: Tang Siu Hong , Li Kai Ming
Published: July 2002

In many environmental noise prediction schemes, an empirical correction factor of 2.5 or 3.0 dB is normally added for the calculation of noise levels 1 meter in front of a reflecting façade. In this paper, theoretical and experimental studies have been conducted to examine the validity and accuracy of such approximations for a point source. The theoretical analysis involves the extension of the classical Weyl–van der Pol formula to include the effect of a reflecting façade. Experimental measurements have been conducted in an anechoic chamber to validate the theoretical predictions. It has been demonstrated that the simple empirical correction factor is adequate in cases for the assessment of the façade noise levels near the ground. However, this correction factor is not sufficient to predict the noise levels high above the ground. Some adjustments of the correction factor are required for a better estimation of sound fields in front of a reflecting façade above an impedance ground.
Effects of asynchrony and ear of presentation on the pitch of mistuned partials in harmonic and frequency-shifted complex tones
Authors: Brunstrom Jeffrey M. , Roberts Brian
Published: July 2002

When a partial of a periodic complex is mistuned, its change in pitch is greater than expected. Two experiments examined whether these partial-pitch shifts are related to the computation of global pitch. In experiment 1, stimuli were either harmonic or frequency-shifted (25% of F0) complexes. One partial was mistuned by ±4% and played with leading and lagging portions of 500 ms each, relative to the other components (1 s), in both monaural and dichotic contexts. Subjects indicated whether the mistuned partial was higher or lower in pitch when concurrent with the other components. Responses were positively correlated with the direction of mistuning in all conditions. In experiment 2, stimuli from each condition were compared with synchronous equivalents. Subjects matched a pure tone to the pitch of the mistuned partial (component 4). The results showed that partial-pitch shifts are not reduced in size by asynchrony. Similar asynchronies are known to produce a near-exclusion of a mistuned partial from the global-pitch computation. This mismatch indicates that global and partial pitch are derived from different processes. The similarity of the partial-pitch shifts observed for harmonic and frequency-shifted stimuli suggests that they arise from a grouping mechanism that is sensitive to spectral regularity.
A hybrid BIE/FFP scheme for predicting barrier efficiency outdoors
Authors: Taherzadeh Shahram , Li Kai Ming , Attenborough Keith
Published: July 2002

To assess the acoustical performance of noise screens in the presence of an arbitrary sound speed profile, a numerical scheme based on a combination of the boundary integral and fast field program methods is developed. The Green’s function required in the boundary integral is evaluated by a fast field formulation. The procedure is validated by comparing its predictions with other numerical results for simple cases and with measurements for indoor model experiments simulating downward refracting conditions. It is predicted that the performance of a noise screen placed 50 m from the source is reduced considerably by moderate downwind conditions.
k-omega beamforming on non-equally spaced line arrays
Authors: Breed B. R.
Published: July 2002

It is not generally known that k-omega beamforming can be applied to nonuniform line arrays. The concept is that each of the nonuniform array signals is deemed to come from the nearest array element on a fictitious uniform array spatially sampled at a high-enough density that location errors are negligible. The k-omega approach can mimic the time delay and sum approach to an arbitrary degree of accuracy. Interpolating weights are derived and applied to a center-tapered logarithmic array as an example. Benefits of this beamforming approach over the direct approach are discussed.
Modifying modal characteristics of sound fields by state feedback control
Authors: Samejima Toshiya
Published: July 2002

State feedback control of a sound field is investigated for improving the irregular distribution of the natural frequencies at low frequencies. A state-space description of a sound field is derived from an inhomogeneous wave equation using the finite element method. The feedback control system is realized as a feedback filter between sensor microphones and control sources using a state estimator for a linear dynamic system. Pole allocation is employed for calculating the state feedback gain vector, such that the roots of the closed-loop system have the desired modal distribution. Computer simulations are performed to demonstrate the control achieved by distributing the lowest undamped natural frequencies in a uniform manner. As a result, the transfer functions with the state feedback control are modified so as to have peaks at identical intervals for the frequency range of interest. A control experiment in an enclosure is carried out with the same objective of control as modeled in the simulations. The experiment verifies that the desired modal distribution can be achieved by introducing the proposed state feedback control into a sound field.
Underwater measurements and modeling of a sonic boom
Authors: Desharnais Francine , Chapman David M. F.
Published: July 2002

During a sea trial on the Scotian Shelf, acoustic signals from a sonic boom were recorded on 11 hydrophones of a vertical array. The array spanned the lower 50 m of the water column above a sand bank at 76 m water depth. The source of the sonic boom was deduced to be a Concorde supersonic airliner traveling at about Mach 2. The waterborne waveform was observed to decay as an evanescent wave below the sea surface, as expected. The calm weather (sea state 1) resulted in low ambient noise and low self-noise at the hydrophones, and good signal-to-noise ratio on the upper hydrophones; however, the decreased signal amplitude is more difficult to detect towards the lower part of the water column. The period of the observed waveform is of the order 0.23 s, corresponding to a peak frequency of about 3 Hz. The shape of the measured waveform differs noticeably from the theoretical N-shape waveform predicted with Sawyers’ theory [J. Acoust. Soc. Am. 44, 523–524 (1968)]. A simple shallow-ocean geoacoustic model suggests that this effect may be caused in part by seismo–acoustic interaction of the infrasonic waves with the elastic sediments that form the seabed.
Instantaneous frequency and short term Fourier transforms: Application to piano sounds
Authors: Rossi L. , Girolami G.
Published: July 2002

For more than 30 years and until nowadays, development of a system reproducing the functioning of human hearing has remained an aim difficult to reach. Recent methods for identification of the fundamental frequency of musical sounds obtain good results using information about the temporal evolution of the amplitude and frequency of individual sound partials. Piano sounds and polyphonic sounds, which can have several partials that are closely spaced in the frequency domain, have not been extensively tested by these procedures. In this paper, the Instantaneous Frequency (IF), as defined by the Hilbert transform, is used to obtain the frequency variations of piano sounds partials. The result implies that, for these sounds, the IF may contain modulations resulting in the separation of an apparent single sinusoid signal into two or more sinusoidal components at various times in the analysis process, which makes it impossible to use the temporal evolution of the frequency of partials for the procedure of note identification. The separation phenomenon also appears when the short term Fourier transform is used and can induce the detection of short-lived parasitic spectral peaks that must be taken into account by any note identification procedure based on the use of spectral information.
Mechanism of sound absorption by seated audience in halls
Authors: Nishihara Noriko , Hidaka Takayuki , Beranek Leo L.
Published: July 2002

Four methods are explored for predicting the reverberation times in fully occupied halls for music as related to the sound absorption by their audiences. The methods for providing audience absorptions include two that use reverberation chambers, namely, the ISO 354 method (and other similar standards) (ISO) and Kath and Kuhl’s method (K & K) [Acustica 15, 127–131 (1965)], and two that use average data from halls, i.e., Beranek’s method (COH) [Concert and Opera Halls: How They Sound (Acoustical Society of America, Melville, NY, 1996)], and the average audience power-per-seat absorption which in practice is multiplied by the number of seats (ΔA). These methods are applied to the calculation of reverberation times in six existing halls, fully occupied, and the results were compared with actual measurements. The COH method was best for predictions over the entire frequency range. The K & K method showed the highest accuracy at mid-frequencies. Both the ISO and the K & K methods yielded wide differences for the measurements in the 125- and 250-Hz bands. The ΔA method was as good as the COH method when the measurements for the six halls were averaged, but showed a wide spread in the predictions around the average because it does not consider the degree of upholstering of the seats. It was hypothecated by the authors that the principal reasons for the ISO and K & K discrepancies at low frequencies were (a) differences between the degree of sound diffusion in actual halls and that in reverberation chambers, and (b) lack of information on the mechanisms of absorption of sound by people seated side-by-side in rows, particularly for near-grazing incidence sound fields. First, this article explores the sound diffusivity in a reverberation chamber and in the halls using CAD models. A probability density function of the incident angles of the sound rays that impinge on the audiences is defined and was measured for each case. Using a unique method, the sound absorption coefficient of each portion of the body and chair in a seated audience was determined in an anechoic chamber as a function of the incident angle of a sound wave. With adjustments from these findings, the K & K method can be made to equal the COH method in accuracy at all frequencies. Its forte is that it can be used for the determination of the sound absorption of occupied chairs from measurements of a limited number in a reverberation chamber.
Comment on “Eigenmode analysis of arbitrarily shaped two-dimensional cavities by the method of point matching” [J. Acoust. Soc. Am. 107, 1153 (2000)]
Authors: Chen J. T. , Chang M. H. , Chung I. L. , Cheng Y. C.
Published: July 2002

The method of point matching proposed by Kang and Lee [J. Acoust. Soc. Am. 107, 1153–1160 (2000)] is revisited. This method can be seen as a single-layer potential approach from the viewpoint of imaginary-part dual BEM developed by Chen et al. [J. Chin. Inst. Eng. 12, 729–739 (1999)]. Based on the concept of double-layer potential, an innovative method is proposed to deal with the problem of spurious eigensolution for the Neumann problem. Also, the acoustic mode is analytically derived for the circular cavity. Both the analytical study for a circular case and numerical result for a square cavity show the validity of the proposed formulation.
The effect of a coastline on the underwater penetration of sonic booms
Authors: Garrelick Joel
Published: July 2002

A simplified analysis is presented for the underwater noise levels from a steady supersonic flight traversing a coastline. The effect of the coast is to introduce a propagating noise component that does not exhibit the classic evanescent attenuation with depth for flights subsonic in water. Expressions are given to estimate the boundary of, and levels within, the coastal region where this component dominates. An illustrative example is presented.
Acoustical design of Benaroya Hall, Seattle
Authors: Harris Cyril M.
Published: July 2002

Benaroya Hall in Seattle, Washington, was inaugurated on September 12, 1998. This 2500-seat concert hall has a rectangular plan, follows the traditional “shoebox” form, and has a volume of 680 000 ft3 (19 244 m3). To obtain excellent diffusion over a wide frequency range requires surface irregularities of different sizes and shapes; to obtain excellent diffusion at very low frequencies requires scattering surfaces of very large dimensions. These considerations were essential to the acoustical design of Benaroya Hall. The two principal reasons for providing a high degree of diffusion across the frequency range were (1) to increase the uniformity of the distribution of sound throughout the concert hall, and (2) to smooth out significant variations in the rate of growth and the rate of decay in the hall. The values of reverberation time, at all measured frequencies, for fully occupied Benaroya Hall are within 0.1 sec of the corresponding values in the Grossermusikvereinssaal in Vienna. Noise is inaudible throughout the auditorium, having a measured value of between NC-10 and NC-15 with air conditioning systems in operation.
Variational method for estimating the effects of continuously varying lenses in HIFU, sonography, and sonography-based cross-correlation methods
Authors: Alaniz Alex , Kallel Faouzi , Hungerford Ed , Ophir Jonathan
Published: July 2002

The effects of high intensity focused ultrasound (HIFU)-induced continuously varying thermal gradients on sound ray propagation were modeled theoretically. This modeling was based on Fermat’s variational principle of least time for rays propagating in a continuously varying thermal gradient described by a radially symmetric heat equation. Such thermal lenses dynamically affect HIFU beam focusing, and simultaneously create ultrasonic geometric and intensity distortions and artifacts in monitoring devices. Techniques which are based upon ultrasonic cross-correlation methods, such as elastography and two-dimensional temperature estimation, also suffer distortion effects and generate artifacts.
Refracted arrival waves in a zone of silence from a finite thickness mixing layer
Authors: Suzuki Takao , Lele Sanjiva K.
Published: July 2002

Refracted arrival waves which propagate in the zone of silence of a finite thickness mixing layer are analyzed using geometrical acoustics in two dimensions. Here, two simplifying assumptions are made: (i) the mean flow field is transversely sheared, and (ii) the mean velocity and temperature profiles approach the free-stream conditions exponentially. Under these assumptions, ray trajectories are analytically solved, and a formula for acoustic pressure amplitude in the far field is derived in the high-frequency limit. This formula is compared with the existing theory based on a vortex sheet corresponding to the low-frequency limit. The analysis covers the dependence on the Mach number as well as on the temperature ratio. The results show that both limits have some qualitative similarities, but the amplitude in the zone of silence at high frequencies is proportional to ω−1/2, while that at low frequencies is proportional to ω−3/2, ω being the angular frequency of the source.
Hydrodynamic acoustic absorption at the fluid/solid transition of suspensions
Authors: Esquivel-Sirvent R. , Green D. H.
Published: July 2002

A theoretical calculation of the excess acoustic attenuation due to hydrodynamic interactions in colloidal suspensions, when the suspended particles are spheres or plates, is presented. Our model is based on the fluid flow shearing between suspended particles during the passage of a longitudinal acoustic wave. To incorporate the many-body effects of the system, the nearest-neighbor distribution function for finite-size particles is introduced. The results of the modeling are compared to available experimental results. The main features of the experimental curves (e.g., attenuation maxima as a function of concentration and an increase in attenuation with frequency) are reproduced and it is shown that the attenuation due to hydrodynamic effects is a significant contribution to wave damping in high-concentration suspensions.
Analysis of noise barrier overlap gaps
Authors: Herman Lloyd A. , Clum Craig M.
Published: July 2002

Sound propagation through the gap produced by two parallel vertical barriers with overlapped ends is formulated for traffic noise sources. The analysis identifies both source and receiver regions according to the mechanisms that influence noise propagation in the vicinity of an overlap gap. A method to account for the contributions from the various source regions for a given receiver location is described. The derived method can be implemented using various equations for sound propagation. The results of using equations approved by the United States Federal Highway Administration for traffic noise propagation are given. Uncalibrated predictions are compared with field measurements for up to 30 receiver positions from each of four overlap gaps. The relative importance of contributions from reflected rays to the noise levels at receiver positions is given. The analysis confirms the initial hypothesis that a commonly used strategy of overlapping barriers by an amount equal to two or three times the overlap width is useful for controlling line-of-sight propagation but ignores the substantial effect of reflections.