bluuebunny/crossref_metadata_2025 huggingface dataset:
Sensitivity of megavoltage photon beam Monte Carlo simulations to electron beam and other parameters
Authors: Sheikh‐Bagheri Daryoush , Rogers D. W. O.
Published: July 2002

The BEAM code is used to simulate nine photon beams from three major manufacturers of medical linear accelerators (Varian, Elekta, and Siemens), to derive and evaluate estimates for the parameters of the electron beam incident on the target, and to study the effects of some mechanical parameters like target width, primary collimator opening, flattening filter material and density. The mean energy and the FWHM of the incident electron beam intensity distributions (assumed Gaussian and cylindrically symmetric) are derived by matching calculated percentage depth‐dose curves past the depth of maximum dose (within 1% of maximum dose) and off‐axis factors (within 2σ at 1% statistics or less) with measured data from the AAPM RTC TG‐46 compilation. The off‐axis factors are found to be very sensitive to the mean energy of the electron beam, the FWHM of its intensity distribution, its angle of incidence, the dimensions of the upper opening of the primary collimator, the material of the flattening filter and its density. The off‐axis factors are relatively insensitive to the FWHM of the electron beam energy distribution, its divergence and the lateral dimensions of the target. The depth‐dose curves are sensitive to the electron beam energy, and to its energy distribution, but they show no sensitivity to the FWHM of the electron beam intensity distribution. The electron beam incident energy can be estimated within 0.2 MeV when matching either the measured off‐axis factors or the central‐axis depth‐dose curves when the calculated uncertainties are about 0.7% at the 1 σ level. The derived FWHM (±0.1 mm) of the electron beam intensity distributions all fall within 1 mm of the manufacturer specifications except in one case where the difference is 1.2 mm.
Comparisons of point and average organ dose within an anthropomorphic physical phantom and a computational model of the newborn patient
Authors: Sessions J. B. , Roshau J. N. , Tressler M. A. , Hintenlang D. E. , Arreola M. M. , Williams J. L. , Bouchet L. G. , Bolch W. E.
Published: July 2002

Pediatric radiographic examinations yield medical benefits and/or diagnostic information that must be balanced against potential risk from patient radiation exposure. Consequently, clinical tools for measuring internal organ dose are needed for medical risk assessment. In this study, a physical phantom and Monte Carlo simulation model of the newborn patient were developed based upon their stylized mathematical expressions (ORNL and MIRD model series). The physical phantom was constructed using tissue equivalent substitutes for soft tissue, lung, and skeleton. Twenty metal–oxide–semiconductor field effect transistor (MOSFET) dosimeters were then inserted at three‐dimensional positions representing the centroids of organs assigned in the ICRP's definition of the effective dose. MOSFET‐derived point estimates of organ dose were shown to be in reasonable agreement with Monte Carlo estimates for representative newborn head, chest, and abdomen radiographic exams. Ratios of average organ dose assessed via MCNP simulations to the MOSFET‐derived point doses (point‐to‐organ dose scaling factors,are tabulated for subsequent use in clinical irradiations of the newborn phantom/MOSFET system. Values ofindicate that MOSFET measurements of point dose for in‐field exposures need to be adjusted only to within 10% to report volume‐averaged organ dose. Larger adjustments to point doses are noted for organs out‐of‐field. For walled organs, point estimates of organ dose at the content centroid are shown to underestimate the average wall dose when the organ is within the primary field:of 1.19 for the stomach (AP chest exam), andof 1.15 for the urinary bladder (AP abdomen exam).
Performance evaluation of a diode array for enhanced dynamic wedge dosimetry
Authors: Zhu T. C. , Ding L. , Liu C. R. , Palta J. R. , Simon W. E. , Shi J.
Published: July 2002

The performance of a diode array (Profiler) was evaluated by comparing its enhanced dynamic wedge (EDW) profiles measured at various depths with point measurements using a ionization chamber on a commercial linear accelerator. The Profiler, which covers a 22.5 cm width, was used to measure larger field widths by concatenating three data sets into a larger field. An innovative wide‐field calibration technique developed by the manufacturer of the device was used to calibrate the individual diode sensitivity, which can vary by more than 10%. Profiles of EDW measured with this device at several depths were used to construct isodose curves using the percentage depth dose curve measured by the ionization chamber. These isodose curves were used to check those generated by a commercial treatment planning system. The profiles measured with the diode array for both 8 and 18 MV photon beams agreed with those of the ionization chamber within a standard deviation of 0.4% in the field (defined as 80% of the field width) and within a maximum shift of less than 2 mm in the penumbra region. The percentage depth dose generally agreed to within 2% except in the buildup region. The Profiler was extremely useful as a quality assurance tool for EDW and as a dosimetry measurement device with tremendous savings in data acquisition time.
A multiresolution approach for contour extraction from brain images
Authors: Soltanian‐Zadeh Hamid , Windham Joe P.
Published: July 2002

Many image registration methods use head surface, brain surface, or inner/outer surface of the skull to estimate rotation and translation parameters. The inner surface of the skull is also used for intracranial volume segmentation which is considered the first step in segmentation and analysis of brain images. The surface is usually characterized by a set of edge or contour points extracted from cross‐sectional images. Automatic extraction of contour points is complicated by discontinuity of edges in the back of the eyes and ears and sometimes by a previous surgery or an inadequate field of view. We have developed an automated method for contour extraction that connects discontinuities using a multiresolution pyramid. Steps of the method are: (1) Contour points are found by an edge‐tracking algorithm; (2) A multiresolution pyramid of contour points is constructed; (3) Contour points of reduced images are found; (4) From the continuous contour found at the lowest resolution, contour points at a higher resolution are found; (5) Step 4 is repeated until contour points at the highest resolution (original image) are found. The method runs fast and has been successful in extracting contours from MRI and CT images. We illustrate the method and its performance using MRI and CT images of the human brain.
Determination of 3D positions of pacemaker leads from biplane angiographic sequences
Authors: Hoffmann Kenneth R. , Williams Benjamin B. , Esthappan Jacqueline , Chen Shiuh‐Yung J. , Carroll John D. , Harauchi Hajime , Doerr Vince , Kay G. Neal , Eberhardt Allen , Overland Mary
Published: July 2002

In vitroandin vivoanalyses of stress on pacemaker leads and their components during the heart cycle have become especially important because of incidences of failure of some of these mechanical components. For stress analyses, the three‐dimensional (3D) position, shape, and motion of the pacemaker leads must be known accurately at each time point during the cardiac cycle. We have developed a method for determination of thein vivo3D positions of pacemaker leads during the entire heart cycle. Sequences of biplane images of patients with pacemakers were obtained at 30 frames/s for each projection. The sequences usually included at least two heart cycles. After patient imaging, biplane images of a calibration object were obtained from which the biplane imaging geometry was determined. The centerlines of the leads and unique, identifiable points on the attached electrodes were indicated manually for all acquired images. Temporal interpolation of the lead and electrode data was performed so that the temporal nonsynchronicity of the image acquisition was overcome. Epipolar lines, generated from the calculated geometry, were employed to identify corresponding points along the leads in the pairs of biplane images for each time point. The 3D positions of the lead and electrodes were calculated from the known geometry and from the identified corresponding points in the images. Using multiple image sets obtained with the calibration object at various orientations, the precision of the calculated rotation matrix and of the translation vector defining the imaging geometry was found to be approximately 0.7° and 1%, respectively. The 3D positions were reproducible to within 2 mm, with the error lying primarily along the axis between the focal spot and the imaging plane. Using data obtained by temporally downsampling to 15 frames/s, the interpolated data were found to lie within approximately 2 mm of the true position for most of the heart cycle. These results indicate that, with this technique, one can reliably determine pacemaker lead positions throughout the heart cycle, and thereby it will provide the basis for stress analysis on pacemaker leads.
Review and evaluation of MRI nonuniformity corrections for brain tumor response measurements
Authors: Velthuizen Robert P. , Heine John J. , Cantor Alan B. , Lin Hongbo , Fletcher Lynn M. , Clarke Laurence P.
Published: July 2002

Current MRI nonuniformity correction techniques are reviewed and investigated. Many approaches are used to remedy this artifact, but it is not clear which method is the most appropriate in a given situation, as the applications have been with different MRI coils and different clinical applications. In this work four widely used nonuniformity correction techniques are investigated in order to assess the effect on tumor response measurements (change in tumor volume over time): a phantom correction method, an image smoothing technique, homomorphic filtering, and surface fitting approach. Six brain tumor cases with baseline and follow‐up MRIs after treatment with varying degrees of difficulty of segmentation were analyzed without and with each of the nonuniformity corrections. Different methods give significantly different correction images, indicating that rf nonuniformity correction is not yet well understood. No improvement in tumor segmentation or in tumor growth/shrinkage assessment was achieved using any of the evaluated corrections.
Computerized analysis of mammographic microcalcifications in morphological and texture feature spaces
Authors: Chan Heang‐Ping , Sahiner Berkman , Lam Kwok Leung , Petrick Nicholas , Helvie Mark A. , Goodsitt Mitchell M. , Adler Dorit D.
Published: July 2002

We are developing computerized feature extraction and classification methods to analyze malignant and benign microcalcifications on digitized mammograms. Morphological features that described the size, contrast, and shape of microcalcifications and their variations within a cluster were designed to characterize microcalcifications segmented from the mammographic background. Texture features were derived from the spatial gray‐level dependence (SGLD) matrices constructed at multiple distances and directions from tissue regions containing microcalcifications. A genetic algorithm (GA) based feature selection technique was used to select the best feature subset from the multi‐dimensional feature spaces. The GA‐based method was compared to the commonly used feature selection method based on the stepwise linear discriminant analysis (LDA) procedure. Linear discriminant classifiers using the selected features as input predictor variables were formulated for the classification task. The discriminant scores output from the classifiers were analyzed by receiver operating characteristic (ROC) methodology and the classification accuracy was quantified by the area, under the ROC curve. We analyzed a data set of 145 mammographic microcalcification clusters in this study. It was found that the feature subsets selected by the GA‐based method are comparable to or slightly better than those selected by the stepwise LDA method. The texture features were more effective than morphological features in distinguishing malignant and benign microcalcifications. The highest classification accuracy was obtained in the combined texture and morphological feature space. The improvement was statistically significant in comparison to classification in either the morphological or the texture feature space alone. The classifier using the best feature subset from the combined feature space and an appropriate decision threshold could correctly identify 35% of the benign clusters without missing a malignant cluster. When the average discriminant score from all views of the same cluster was used for classification, the value increased to 0.93 and the classifier could identify 50% of the benign clusters at 100% sensitivity for malignancy. Alternatively, if the minimum discriminant score from all views of the same cluster was used, the value would be 0.90 and a specificity of 32% would be obtained at 100% sensitivity. The results of this study indicate the potential of using combined morphological and texture features for computer‐aided classification of microcalcifications.
Signal formation and decay in CdTe x‐ray detectors under intense irradiation
Authors: Jahnke A. , Matz R.
Published: July 2002

The response of Cd(Zn)Te Schottky and resistive detectors to intense x‐rays is investigated in a commercial computed tomography (CT) system to assess their potential for medical diagnostics. To describe their signal height, responsivity, signal‐to‐noise ratio (SNR), and detective quantum efficiency the devices are modeled as solid‐state ionization chambers with spatially varying electric field and charge collection efficiency. The thicknesses and pixel areas of the discrete detector elements are 0.5–2 mm and a few mm2, respectively. The incident spectrum extends from 26 to 120 keV and comprisesIt photogenerates a carrier concentration in the semiconductor that is two to three orders of magnitude above the intrinsic concentration, but remains to a similar extent below the charge densities on the device electrodes. Stable linear operation is achieved with the Schottky‐type devices under high bias. Their behavior can be modeled well if negatively charged near‐midgap bulk defects with a concentration ofare assumed. The bulk defects explain the amount and time constant (about 100 ms) of the detrapping current measured after x‐ray pulses (afterglow). To avoid screening by the trapped space charge the bias voltage should exceedDark currents are of the order of the generation‐recombination current, i.e., 300 pA/mm3detector volume. With proper device design the signal height approaches the theoretical maximum of 0.2 A/W. This high responsivity, however, is not exploited in CT since the SNR is determined here by the incident quantum noise. As a consequence of the detrapping current, the response speed does not meet CT requirements. A medium‐term effort for crystal growth appears necessary to achieve the required reduction of the trap density by an order of magnitude. Scintillation based detectors are, therefore, still preferred in fast operating medical diagnostic systems.
Quantitative evaluation of vessel tracking techniques on coronary angiograms
Authors: Sen Anindya , Lan Li , Doi Kunio , Hoffmann Kenneth R.
Published: July 2002

Accurate, automated determination of vessel center lines is essential for two‐ and three‐dimensional analysis of the coronary vascular tree. Therefore, we have been developing techniques for vessel tracking and for evaluating their accuracy and precision in clinical images. After points in vessels are manually indicated, the vessels are tracked automatically by means of a modified sector‐search approach. The perimeters of sectors centered on previous tracking points are searched for the pixels with the maximum contrast. The sector size and radius are automatically adjusted based on local vessel tortuosity. The performance of the tracking technique in regions of high‐intensity background is improved by application of a nonlinear adaptive filtering technique in which the vessel signal is effectively removed prior to background estimation. The tracking results were evaluated visually and by calculation of distances between the tracked and user‐indicated centerlines, which were used as the “truth.” Two hundred and fifty‐six coronary vessels were tracked in 32 angiograms. Vessels as small as 0.6 mm in diameter were tracked accurately. This technique correctly tracked 255/256 (>99%) vessels based on an average of 2–3 indicated points per vessel. The one incorrect tracking result was due to a low signal‐to‐noise ratioThe distance between the tracked and the “true” centerlines ranged from 0.4 to 1.8 pixels, with an average of 0.8 pixels. These results indicate that this technique can provide a reliable basis for 2D and 3D vascular analysis.
AnEGS4Monte Carlo examination of the response of a PTW‐diamond radiation detector in megavoltage electron beams
Authors: Mobit Paul N. , Sandison George A.
Published: July 2002

TheEGS4Monte Carlo code has been used to investigate the response of a PTW/diamond detector irradiated in both clinical and monoenergetic megavoltage electron beams ranging in energy from 5 to 20 MeV. The sensitive volume of the PTW/diamond detector simulated has a thickness of 0.4 mm and a diameter of 4.4 mm. Irradiation was simulated at various depths in a water phantom. The results show that the PTW/diamond detector has a constant response (within 1.0%) in electron beams if irradiated at depths closed toand its response is almost independent of irradiation depth or incident electron energy (within 3%). A detailed examination of the average detector dose shows that the sensitive volume of the PTW/diamond detector acts as a Spencer–Attix cavity within 1%. The encapsulation of the bare diamond detector with low‐Zepoxy and polystyrene wall material does not affect its response in electron beams. The difference in response between the unencapsulated (TLD) and the encapsulated form of the detector is less than 0.5% for all depths over electron energy range investigated.
Comparison of low contrast detectability between a digital amorphous silicon and a screen‐film based imaging system for thoracic radiography
Authors: Aufrichtig Richard
Published: July 2002

Low contrast threshold detectability is investigated theoretically and experimentally for an amorphous silicon x‐ray detector designed for digital radiography and for a standard thoracic screen‐film combination. A theoretical signal‐to‐noise ratio is described with a human observer signal detection model. It is calculated using the detective quantum efficiency (DQE) and the modulation transfer function of the imaging system, as well as a spatial response function for the human visual system. Using a four‐alternative forced choice observer perception study, the threshold contrasts of disk shaped objects ranging in size from 0.3 to 4.0 mm are determined. Significantly better contrast detectability is obtained from the digital detector, which is attributed to its higher DQE. On average, the disk shaped objects can be detected at 45% less contrast than required for screen‐film. With no free parameters the experimental data agree well with those predicted by the observer model. Based upon the data, the model predicts that x‐ray exposure for the detector only needs to be 30% of the exposure required to perform equally well on the contrast‐detail detectability task using screen‐film.
Radial dose distribution, dose to water and dose rate constant for monoenergetic photon point sources from 10 keV to 2 MeV: EGS4 Monte Carlo model calculation
Authors: Luxton Gary , Jozsef Gabor
Published: July 2002

A comprehensive set of dose distributions from monoenergetic photon‐emitting isotropic point sources in a medium can be used as a reference database for the dosimetry of photon emitter sources in that medium. Data of this type for water over the photon energy range from 15 keV to 2 MeV have been published based on calculations using a one‐dimensional photon transport model. The present work, based on a previously publishedEGS4Monte Carlo code, updates the classic data set of Berger and provides more extensive calculations than previously available. Air kerma strength per unit photon emission rate from an isotropic point emitter is obtained as a function of energy using published data for mass energy absorption coefficients. The TG‐43 dose rate constant for water as a function of energy is calculated for monoenergetic photon emitters as the ratio of dose rate to water at 1 cm to air kerma strength for unit photon emission rate. Results for the radial dose distribution agree well with the data of Berger between 40 and 400 keV. For energies ⩾500 keV, a previously undescribed buildup region for the radial dose function is identified. Thickness of the buildup region ranges from 1 mm at 500 keV to 8 mm at 2 MeV. Between 15 and 30 keV, the radial dose function within a few millimeters of the emitter is calculated to be 4%–5% higher than values derived from Berger's data. The maximum dose rate constant for monoenergetic photon emitters occurs at an energy of 60 keV, and has the value 1.355 cGy h−1U−1, where U is the unit of air kerma strength, 1 μGy m2h−1. This would correspond to the maximum hypothetical dose rate constant for a brachytherapy photon source emitting photons of energy ⩽2 MeV.
Thermal and SAR characterization of multielement dual concentric conductor microwave applicators for hyperthermia, a theoretical investigation
Authors: Rossetto F. , Diederich C. J. , Stauffer P. R.
Published: July 2002

Six aperture array dual concentric conductor (DCO) microwave hyperthermia applicators were studied using theoretical models to characterize power deposition (SAR) and steady state temperature distributions in perfused tissue. SAR patterns were calculated using the finite difference time domain (FDTD) numerical method, and were used as input to a finite difference thermal modeling program based on the Pennes Bio‐Heat Equation in order to calculate corresponding temperature distributions. Numerous array configurations were investigated including the use of different size DCC apertures (2, 3, and 4 cm), different spacing between apertures (1.0–2.0 cm), and different water bolus thicknesses (5–15 mm). Thermal simulations were repeated using blood perfusion values ranging from 0.5 to 5 kg/m3s. Results demonstrate the ability of DCC array applicators to effectively and uniformly heat tissue down to a depth of 7.5–10 mm below the skin surface for a large number of different combinations of DCC element size, spacing, and water bolus thickness. Results also reveal the close correlation between SAR patterns and corresponding temperature distributions, verifying that design studies of the applicator can be performed confidently by analysis of SAR, from which the thermal behavior can be estimated. These simulations are useful in the design optimization of large microwave DCC array applicators for superficial tissue heating and for identifying appropriate aperture spacing and bolus thickness parameters for different size DCC aperture arrays and tissue blood perfusion conditions.
Waves in locally periodic media
Authors: Griffiths David J. , Steinke Carl A.
Published: July 2002

We review the theory of wave propagation in one dimension through a medium consisting of N identical “cells.” Surprisingly, exact closed-form results can be obtained for arbitrary N. Examples include the vibration of weighted strings, the acoustics of corrugated tubes, the optics of photonic crystals, and, of course, electron wave functions in the quantum theory of solids. As N increases, the band structure characteristic of waves in infinite periodic media emerges.
Measurement of the relativistic potential difference across a rotating magnetic dielectric cylinder
Authors: Hertzberg J. B. , Bickman S. R. , Hummon M. T. , Krause D. , Peck S. K. , Hunter L. R.
Published: July 2002

According to the Special Theory of Relativity, a rotating magnetic dielectric cylinder in an axial magnetic field should exhibit a contribution to the radial electric potential that is associated with the motion of the material’s magnetic dipoles. In 1913 Wilson and Wilson reported a measurement of the potential difference across a magnetic dielectric constructed from wax and steel balls. Their measurement has long been regarded as a verification of this prediction. In 1995 Pelligrini and Swift questioned the theoretical basis of the experiment. In particular, they pointed out that it is not obvious that a rotating medium may be treated as if each point in the medium is locally inertial. They calculated the effect in the rotating frame and predicted a potential different from both the Wilsons’ theory and experiment. Subsequent analysis of the experiment suggests that the Wilsons’ experiment does not distinguish between the two predictions due to the fact that their composite steel–wax cylinder is conductive in the regions of magnetization. We report measurements of the radial voltage difference across various rotating dielectric cylinders, including a homogeneous magnetic dielectric material (YIG), to unambiguously test the competing calculations. Our results are compatible with the traditional treatment of the effect using a co-moving locally inertial reference frame, and are incompatible with predictions based on the model of Pelligrini and Swift.
Nine formulations of quantum mechanics
Authors: Styer Daniel F. , Balkin Miranda S. , Becker Kathryn M. , Burns Matthew R. , Dudley Christopher E. , Forth Scott T. , Gaumer Jeremy S. , Kramer Mark A. , Oertel David C. , Park Leonard H. , Rinkoski Marie T. , Smith Clait T. , Wotherspoon Timothy D.
Published: July 2002

Nine formulations of nonrelativistic quantum mechanics are reviewed. These are the wavefunction, matrix, path integral, phase space, density matrix, second quantization, variational, pilot wave, and Hamilton–Jacobi formulations. Also mentioned are the many-worlds and transactional interpretations. The various formulations differ dramatically in mathematical and conceptual overview, yet each one makes identical predictions for all experimental results.
Nonlinear laser spectroscopy and magneto-optics
Authors: Budker Dmitry , Orlando Donald J. , Yashchuk Valeriy
Published: July 2002

An experiment on nonlinear laser spectroscopy and magneto-optics at the Advanced Undergraduate Laboratory at Berkeley is described. The experiment consists of three parts. In the first part, students learn to operate a diode laser system and characterize its performance using a Fabry–Perot spectrum analyzer. In the second part, Doppler-broadened laser-induced fluorescence and Doppler-free saturated absorption spectra of the rubidium D2 line (780 nm) are recorded and analyzed. Finally, in the third part of the experiment, which we describe in greater detail, the near-resonant magneto-optical rotation is investigated. Nonlinear light-atom interaction leads to spectacular manifestations of the resonant Faraday effect—polarization plane rotation in a magnetic field applied along the direction of light propagation radically different from the linear case. In particular, narrow (∼30 Hz) effective line widths are observed in this experiment corresponding to a rotation enhancement by some seven orders of magnitude compared to the linear Faraday rotation.
Criterion for existence of a bound state in one dimension
Authors: Brownstein K. R.
Published: July 2002

Let V(x)≢0 be a one-dimensional potential which vanishes outside some interval. A well-known fact is that a bound state must exist if V(x)⩽0 for all x or even if V(x) satisfies the weaker condition ∫V(x)dx<0. Previously, Simon has shown that a bound state must exist if V(x) satisfies the even weaker condition ∫V(x)dx⩽0 [including the interesting case ∫V(x)dx=0]. In the present paper, using a simple trial function, we obtain a criterion for the existence of a bound state in one dimension, a special case of which gives the Simon result ∫V(x)dx⩽0.
Acoustic field variability induced by time evolving internal wave fields
Authors: Finette Steven , Orr Marshall H. , Turgut Altan , Apel John R. , Badiey Mohsen , Chiu Ching-sang , Headrick Robert H. , Kemp John N. , Lynch James F. , Newhall Arthur E. , von der Heydt Keith , Pasewark Bruce , Wolf Stephen N. , Tielbuerger Dirk
Published: July 2002

A space- and time-dependent internal wave model was developed for a shallow water area on the New Jersey continental shelf and combined with a propagation algorithm to perform numerical simulations of acoustic field variability. This data-constrained environmental model links the oceanographic field, dominated by internal waves, to the random sound speed distribution that drives acoustic field fluctuations in this region. Working with a suite of environmental measurements along a 42-km track, a parameter set was developed that characterized the influence of the internal wave field on sound speed perturbations in the water column. The acoustic propagation environment was reconstructed from this set in conjunction with bottom parameters extracted by use of acoustic inversion techniques. The resulting space- and time-varying sound speed field was synthesized from an internal wave field composed of both a spatially diffuse (linear) contribution and a spatially localized (nonlinear) component, the latter consisting of solitary waves propagating with the internal tide. Acoustic simulation results at 224 and 400 Hz were obtained from a solution to an elastic parabolic equation and are presented as examples of propagation through this evolving environment. Modal decomposition of the acoustic field received at a vertical line array was used to clarify the effects of both internal wave contributions to the complex structure of the received signals.
The effect of the physical properties of the tube wall on the attenuation of sound in evaporating and condensing gas–vapor mixtures
Authors: Slaton William V. , Raspet Richard , Hickey Craig J.
Published: July 2002

An investigation of sound propagation in an air–water vapor mixture contained in a cylindrical tube with wet walls was recently completed [Hickey et al., J. Acoust. Soc. Am. 107, 1126–1130 (2000)]. A generalization to include the heat flux at the tube wall is presented here. The attenuation of sound in air–water vapor mixtures can be affected by the thermal properties of the tube wall. The controlling parameter is εs, which is a proportionality constant that relates the heat flux per degree Kelvin for the substrate to that of the gas mixture. For a given amount of heat, provided by expansion and rarefaction of the working fluid, different substrates will undergo different temperature excursions. These temperature swings at the boundary change the vapor pressure of the condensate and thus reduce the diffusion of vapor to and from the boundary resulting in a reduction of the attenuation.
Feature dependence in the automatic identification of musical woodwind instruments
Authors: Brown Judith C. , Houix Olivier , McAdams Stephen
Published: July 2002

The automatic identification of musical instruments is a relatively unexplored and potentially very important field for its promise to free humans from time-consuming searches on the Internet and indexing of audio material. Speaker identification techniques have been used in this paper to determine the properties (features) which are most effective in identifying a statistically significant number of sounds representing four classes of musical instruments (oboe, sax, clarinet, flute) excerpted from actual performances. Features examined include cepstral coefficients, constant-Q coefficients, spectral centroid, autocorrelation coefficients, and moments of the time wave. The number of these coefficients was varied, and in the case of cepstral coefficients, ten coefficients were sufficient for identification. Correct identifications of 79%–84% were obtained with cepstral coefficients, bin-to-bin differences of the constant-Q coefficients, and autocorrelation coefficients; the latter have not been used previously in either speaker or instrument identification work. These results depended on the training sounds chosen and the number of clusters used in the calculation. Comparison to a human perception experiment with sounds produced by the same instruments indicates that, under these conditions, computers do as well as humans in identifying woodwind instruments.
A computational sensorimotor model of bat echolocation
Authors: Erwin Harry R. , Wilson Willard W. , Moss Cynthia F.
Published: July 2002

A computational sensorimotor model of target capture behavior by the echolocating bat, Eptesicus fuscus, was developed to understand the detection, localization, tracking, and interception of insect prey in a biological sonar system. This model incorporated acoustics, target localization processes, flight aerodynamics, and target capture planning to produce model trajectories replicating those observed in behavioral insect capture trials. Estimates of target range were based on echo delay, azimuth on the relative intensity of the echo at the two ears, and elevation on the spectral pattern of the sonar return in a match/mismatch process. Flapping flight aerodynamics was used to produce realistic model trajectories. Localization in all three spatial dimensions proved necessary to control target tracking and interception for an adequate model of insect capture behavior by echolocating bats. Target capture using maneuvering flight was generally successful when the model’s path was controlled by a planning process that made use of an anticipatory internal simulation, while simple homing was successful only for targets directly ahead of the model bat.
An examination of the parameters that govern the acoustic behavior of sea bed sediments containing gas bubbles
Authors: Gardner T. N. , Sills G. C.
Published: July 2002

The acoustic properties of sea bed sediments containing occluded gas are dominated by the volume of gas contained in bubbles, the size of bubbles, and the elastic properties of the soil matrix. This study evaluated current theory developed by Anderson and Hampton to determine the sound speed and resonance frequency of gassy soils, and the models they used to determine the elastic properties of the soils. It compared calculated sound speeds, based on material properties simulated by the models, with measured sound speeds on “large bubble” laboratory soils produced in a similar manner to natural sea bed gassy soils. There was some evidence that the Anderson and Hampton equations accurately predicted sound speed at lower frequencies of bubbles resonance and below, but results were sensitive to inappropriate values for the elastic and damping properties of the soil. The bounds of sound speed based on the elastic properties of models that simulate “compressible fluid” or “suspension” behavior were grossly misleading when applied to large bubble soils. Conversely, sound speed based on models that correctly simulate the “bulk” or “matrix” properties of large bubble soils, at strain magnitudes and strain rates equivalent to acoustic signals, agreed well with measured data.
Exact solutions for modeling sound propagation through a combustion zone
Authors: Sujith R. I.
Published: July 2002

Exact analytical solutions for one-dimensional sound propagation through a combustion zone, taking the effects of mean temperature gradient and oscillatory heat release into account, are presented in this paper. The wave equation is derived starting from the momentum and energy equations. Using appropriate transformations, solutions are derived for the case of an exponential mean temperature gradient in terms of Bessel functions. For the case of a linear mean temperature profile, solutions are derived in terms of confluent hypergeometric functions. Example calculations show that the accuracy in modeling combustion–acoustics interactions can be significantly increased by the use of these solutions.
Water as a standard in the measurements of speed of sound in liquids
Authors: Marczak Wojciech
Published: July 2002

The speeds of sound in water measured by Del Grosso and Mader [J. Acoust. Soc. Am. 52, 1442–1446 (1972)], Kroebel and Mahrt [Acustica 35, 154–164 (1976)], and Fujii and Masui [J. Acoust. Soc. Am. 93, 276–282 (1993)] were compared. A fairly good agreement was found. A new fifth-order polynomial describing the dependence of the speed of sound in water on temperature (ITS-90) within the limits 0–95 °C was proposed. The importance of the effect of impurities of water on the systematic errors of the measurement results was pointed out. The accuracy of the relative measurements of speed of sound in liquids was discussed in the context of the proper choice of a standard (“true”) value of the speed in water.
Transmission line method for the measurement of the acoustic nonlinearity parameter in biological liquids at very high frequencies
Authors: Kushibiki J. , Ishibashi M. , Akashi N. , Sannomiya T. , Chubachi N. , Dunn F.
Published: July 2002

Nonlinear wave propagation in a system consisting of a liquid specimen held between two SiO2 buffer rods is studied as a new method of determining the acoustic nonlinearity parameter of liquids at very high frequencies. Since the sign of the nonlinearity parameter of SiO2 is opposite that for liquids, the system can be viewed as a transmission line containing regions of both positive and negative nonlinearity. The nonlinear characterization curve is employed in which the second harmonic component output of the receiving transducer is plotted as a function of propagation distance in liquids between the two SiO2 buffer rods. The nonlinearity parameter is determined by measuring the dip position at which the transducer output becomes zero in the curve. Measurements are reported for water and aqueous solutions of dextrose and dextran in the fundamental frequency range 100–200 MHz.
Mean-square responses in a plate with sprung masses, energy flow and diffusion
Authors: Weaver Richard L.
Published: July 2002

Diagrammatic multiple-scattering theory is applied to the calculation of ensemble average square responses in an infinite homogeneous plate in flexure attached to a random distribution of undamped sprung masses. This system is a prototypical example of a wave-bearing master structure with a locally reacting “fuzzy” substructure. Results for mean fields were obtained in an earlier work. Here it is found that fluctuations away from the mean are weak if the spectral and areal number density of sprung masses is great. A radiative transfer equation is found to govern the flow of energy on time scales greater than the inverse of the frequency, and a diffusion equation is found to govern the flow of energy at times greater than the dwell time of energy in the substructure. The diffusion rate is very slow if the dwell time in the substructure is long. The effect of true damping on these results is discussed.
Double monopole resonance of a gas-filled, spherical cavity in a sediment
Authors: Kargl Steven G. , Williams Kevin L. , Lim Raymond
Published: July 2002

The monopole response of a gas-filled, spherical cavity in a sediment is investigated. The sediment is either a fluid, elastic solid, or saturated poroelastic medium. The present method entails the scattering of an incident displacement field that preferentially excites the monopole resonance of the cavity. The main result demonstrates that a gas-filled, spherical cavity in a saturated poroelastic medium can exhibit two distinct monopole resonances. These resonances arise from the two distinct longitudinal modes of propagation in saturated poroelastic medium as described by Biot’s theory.
Target scattering calculations with the parabolic equation method
Authors: Levy Mireille F. , Zaporozhets Andrew A.
Published: July 2002

The parabolic equation technique is used to solve the Helmholtz equation in the presence of scatterers of arbitrary shape, in two and three dimensions. The scattered field is computed directly, using non-homogeneous boundary conditions on the scattering object to represent the incident field. Effectively this decouples the PE paraxial direction from the direction of incidence. For convex objects the whole range of scattering angles can be covered with a small number of narrow-angle calculations. Finite-difference implementations involve tridiagonal matrices in two dimensions and more general sparse matrices in three dimensions. The resulting codes can be used to solve scattering problems for objects ranging in size from a few wavelengths to hundreds of wavelengths. The method has been tested against analytical solutions for soft and rigid circular cylinders in 2D and soft and rigid spheres in 3D, showing good agreement at all scattering angles.
Resonator frequency shift due to ultrasonically induced microparticle migration in an aqueous suspension: Observations and model for the maximum frequency shift
Authors: Kwiatkowski Christopher S. , Marston Philip L.
Published: July 2002

Aqueous suspensions of plastic and hollow-glass microspheres are subjected to the radiation pressure of an ultrasonic standing wave. It is well known that the particles are attracted to the pressure nodes of the standing wave for the particle and host properties considered. We demonstrated that the radiation pressure induced migration of particles leads to a significant shift in the resonant frequency of a suitably designed chamber. This shift is easily resolved with a phase-locked loop even if the particle volume fraction is as small as 0.001. For sufficient ultrasonic amplitudes, the shift is found to saturate at a limiting value. To approximate the limiting frequency shift, the principle of adiabatic invariance is first applied to the case of a single compressible sphere in a standing wave and then superposition is used to give the collective shift for the suspension. The measured limiting shifts are typically within 25% of the calculated value and this method may have application to the characterization of dilute suspensions since the shift is proportional to the volume fraction and to a material contrast factor. The applicability of adiabatic invariance is confirmed by comparing frequency shifts for certain cases of idealized particle spatial distributions with results based on transfer matrix eigenvalues combined with an effective-medium approximation.
Measurement and prediction of typical speech and background-noise levels in university classrooms during lectures
Authors: Hodgson Murray , Rempel Rod , Kennedy Susan
Published: July 2002

A method has been developed for determining typical long-term speech and background-noise levels during lectures. Lectures are recorded and the recordings digitized and processed to obtain sound-pressure-level frequency distributions to which three normal-distribution curves are fit. The maximum values of these curves are associated with long-term sound-pressure levels associated with speech, ventilation noise, and student-activity noise. Recordings made during 18 university lectures in 11 classrooms have been analyzed. Average (standard deviation) A-weighted levels for the various sound components were determined as follows: ventilation noise, 40.9 (3.9) dB; student-activity noise, 41.9 (4.0) dB; total background noise, 44.4 (3.5) dB; and received speech-signal, 50.8 (3.9) dB. The average (standard deviation) A-weighted speech-signal to background-noise ratio was 7.9 (3.1) dB. That of the instructor sound-power level was 64.5 (4.2) dB. Empirical models have been developed to predict the room-average A-weighted results using multivariable regression analysis. Further analysis in the 63- to 8000-Hz octave bands confirmed the spectra of ventilation noise and of speech, and determined the spectrum of student-activity noise and of the speech-signal to background-noise ratio.
Interarticulator programming in VCV sequences: Lip and tongue movements
Authors: Löfqvist Anders , Gracco Vincent L.
Published: July 2002

This study examined the temporal phasing of tongue and lip movements in vowel–consonant–vowel sequences where the consonant is a bilabial stop consonant /p, b/ and the vowels one of /i, a, u/; only asymmetrical vowel contexts were included in the analysis. Four subjects participated. Articulatory movements were recorded using a magnetometer system. The onset of the tongue movement from the first to the second vowel almost always occurred before the oral closure. Most of the tongue movement trajectory from the first to the second vowel took place during the oral closure for the stop. For all subjects, the onset of the tongue movement occurred earlier with respect to the onset of the lip closing movement as the tongue movement trajectory increased. The influence of consonant voicing and vowel context on interarticulator timing and tongue movement kinematics varied across subjects. Overall, the results are compatible with the hypothesis that there is a temporal window before the oral closure for the stop during which the tongue movement can start. A very early onset of the tongue movement relative to the stop closure together with an extensive movement before the closure would most likely produce an extra vowel sound before the closure.
Morphology and development of the human vocal tract: A study using magnetic resonance imaging
Authors: Fitch W. Tecumseh , Giedd Jay
Published: July 2002

Magnetic resonance imaging was used to quantify the vocal tract morphology of 129 normal humans, aged 2–25 years. Morphometric data, including midsagittal vocal tract length, shape, and proportions, were collected using computer graphic techniques. There was a significant positive correlation between vocal tract length and body size (either height or weight). The data also reveal clear differences in male and female vocal tract morphology, including changes in overall vocal tract length and the relative proportions of the oral and pharyngeal cavity. These sex differences are not evident in children, but arise at puberty, suggesting that they are part of the vocal remodeling process that occurs during puberty in males. These findings have implications for speech recognition, speech forensics, and the evolution of the human speech production system, and provide a normative standard for future studies of human vocal tract morphology and development.
Effect of vocal effort on spectral properties of vowels
Authors: Liénard Jean-Sylvain , Di Benedetto Maria-Gabriella
Published: July 2002

The effects of variations in vocal effort corresponding to common conversation situations on spectral properties of vowels were investigated. A database in which three degrees of vocal effort were suggested to the speakers by varying the distance to their interlocutor in three steps (close—0.4 m, normal—1.5 m, and far—6 m) was recorded. The speech materials consisted of isolated French vowels, uttered by ten naive speakers in a quiet furnished room. Manual measurements of fundamental frequency F0, frequencies, and amplitudes of the first three formants (F1, F2, F3, A1, A2, and A3), and on total amplitude were carried out. The speech materials were perceptually validated in three respects: identity of the vowel, gender of the speaker, and vocal effort. Results indicated that the speech materials were appropriate for the study. Acoustic analysis showed that F0 and F1 were highly correlated with vocal effort and varied at rates close to 5 Hz/dB for F0 and 3.5 Hz/dB for F1. Statistically F2 and F3 did not vary significantly with vocal effort. Formant amplitudes A1, A2, and A3 increased significantly; The amplitudes in the high-frequency range increased more than those in the lower part of the spectrum, revealing a change in spectral tilt. On the average, when the overall amplitude is increased by 10 dB, A1, A2, and A3 are increased by 11, 12.4, and 13 dB, respectively. Using “auditory” dimensions, such as the F1–F0 difference, and a “spectral center of gravity” between adjacent formants for representing vowel features did not reveal a better constancy of these parameters with respect to the variations of vocal effort and speaker. Thus a global view is evoked, in which all of the aspects of the signal should be processed simultaneously.