bluuebunny/crossref_metadata_2025 huggingface dataset:
Graphical treatment simulation and automated collision detection for conformal and stereotactic radiotherapy treatment planning
Authors: Tsiakalos Miltiadis F. , Schrebmann Eduard , Theodorou Kiki , Kappas Constantin
Published: July 2002

The purpose of this work is to develop a “room's eye view” graphical simulation program with an automated collision detection option, to assist a treatment planning user to visualize the treatment setup checking at the same time the feasibility of his plan. The program simulates the treatment process using accurate three‐dimensional graphical models of the gantry, table, and that of an average patient. This allows the use of any mechanical movement concerning the radiotherapy unit. The simulation of the mechanical movements and their limitations are according to IEC standards and thus compatible with any radiotherapy machine. Graphical methods for collision detection between the models guarantee speed and accuracy. The module simulates the treatment setup with accuracy better than 2° for any tested case. When a collision takes place a warning message is displayed. In this paper a software tool is developed that can be used as a stand‐alone program or embedded in any treatment planning system. The visualization of the treatment fields prior to treatment permits the geometric feasibility of the plan, thus adding one more step toward the automation of the treatment process.
The use of an inexpensive red acetate filter to improve the sensitivity of GAFChromic dosimetry
Authors: Odero D. O. , Gluckman G. R. , Welsh K. , Wlodarczyk R. A. , Reinstein L. E.
Published: July 2002

The sensitivity of GAFChromic dosimetry using a conventional broad band light source densitometer has significantly been improved twofold using an inexpensive red acetate filter overlay during the densitometric measurements. This thin sheet of red acetate enhances the dosimetric analysis of radiochromic blue image distributions recorded on GAFChromic films. The combination provides higher sensitivity in the optical density measurements than the more expensive He–Ne laser‐scanning densitometers.
Monte Carlo‐aided dosimetry of the new Bebig IsoSeed® Interstitial Brachytherapy Seed
Authors: Daskalov George M. , Williamson J. F.
Published: July 2002

A new model interstitial brachytherapy source, the IsoSeed® was recently introduced by Bebig Isotopentechnik und Umweltdiagnostik GmbH for permanent implant applications. This study presents the first quantitative theoretical study of the seed's dosimetric quantities. Monte Carlo photon transport (MCPT) simulation techniques have been used to evaluate the dose‐rate distributions around the model IsoSeed® source in liquid water and air phantoms. These results have been used to calculate and tabulate the anisotropy function, radial dose function, and anisotropy factors, and dose‐rate constant as defined by AAPM Task Group 43 (TG‐43) Report. Cartesian “away” and “along” tables, giving the dose rates per unit air‐kerma strength in water in the range 0.1–3 cm distance around the seed have also been tabulated. The dose‐rate constant, Λ, was evaluated by simulating the wide‐angle, free‐air chamber (WAFAC) calibration geometry recently implemented by NIST (National Institute of Standards and Technology) to realize the primary standard of air‐kerma strength for low‐energy photon‐emitting brachytherapy sources. The dose‐rate constant has been found to be Λ=0.660±0.017 in units of dose‐rate per unit air‐kerma strength (cGy⋅h−1⋅U−1).
Reference dosimetry in clinical high‐energy electron beams: Comparison of the AAPM TG‐51 and AAPM TG‐21 dosimetry protocols
Authors: Huq M. Saiful , Song Haijun , Andreo Pedro , Houser Chris J.
Published: July 2002

A comparison of the determination of absorbed dose to water in reference conditions with high‐energy electron beams of 6, 8, 10, 12, 15, and 18 MeV) following the recommendations given in the AAPM TG‐51 and in the original TG‐21 dosimetry protocols has been made. Six different ionization chamber types have been used, two Farmer‐type cylindrical (PTW 30001, PMMA wall; NE 2571, graphite wall) and four plane parallel (PTW Markus, and Scanditronix‐Wellhöfer NACP, PPC‐05 and Roos PPC‐40). Depending upon the cylindrical chamber type used and the beam energy, the doses at determined with TG‐51 were higher than with TG‐21 by about 1%–3%. Approximately 1% of this difference is due to the differences in the data given in the two protocols; another 1.1%–1.2% difference is due to the change of standards, from air‐kerma to absorbed dose to water. For plane‐parallel chambers, absorbed doses were determined by using two chamber calibration methods: (i) direct use of the ADCL calibration factors and for each chamber type in the appropriate equations for dose determination recommended by each protocol, and (ii) cross‐calibration techniques in a high‐energy electron beam, as recommended by TG‐21, TG‐39, and TG‐51. Depending upon the plane‐parallel chamber type used and the beam energy, the doses at determined with TG‐51 were higher than with TG‐21 by about 0.7%–2.9% for the direct calibration procedures and by 0.8%–3.2% for the cross‐calibration techniques. Measured values of photon‐electron conversion for the NACP and Markus chambers were found to be 0.3% higher and 1.7% lower than the corresponding values given in TG‐51. For the PPC‐05 and PPC‐40 (Roos) chamber types, the values of were measured to be 0.889 and 0.893, respectively. The uncertainty for the entire calibration chain, starting from the calibration of the ionization chamber in the standards laboratory to the determination of absorbed dose to water in the user beam, has been analyzed for the two formalisms. For cylindrical chambers, the observed differences between the two protocols are within the estimated combined uncertainty of the ratios of absorbed doses for 6 and 8 MeV; however, at higher energies (10⩽E⩽18 MeV), the differences are larger than the estimated combined uncertainties by about 1%. For plane‐parallel chambers, the observed differences are within the estimated combined uncertainties for the direct calibration technique; for the cross‐calibration technique the differences are within the uncertainty estimates at low energies whereas they are comparable to the uncertainty estimates at higher energies. A detailed analysis of the reasons for the discrepancies is made which includes comparing the formalisms, correction factors, and quantities in the two protocols, as well as the influence of the implementation of the different standards for chamber calibration.
CT and MRI derived source localization error in a custom prostate phantom using automated image coregistration
Authors: Dubois Donald F. , Bice William S. , Prestige Bradley R.
Published: July 2002

Dosimetric evaluation of completed brachytherapy implant procedures is crucial in developing proper technique. Additionally, accurate dosimetry may be useful in predicting the success of an implant. Accurate definition of the prostate gland and localization of the implanted radioactive sources are critical to attain meaningful dosimetric data. MRI is recognized as a superior imaging modality in delineating the prostate gland. More importantly, MRI can be used for source localization in postimplant prostates. However, the MRI derived source localization error bears further investigation. We present a useful tool in determining the source localization error as well as permitting the fusion, or coregistration, of selected data from multiple imaging modalities. We constructed a custom prostate phantom of hydrocolloid material precisely implanted with I‐125 seeds. We obtained CT, the accepted modality, and MRI scans of the phantom. Subsequently, we developed an automated algorithm that employs a sequential translation of data sets to initially maximize coregistration and minimize error between data sets. This was followed by a noniterative solution for the necessary rotation transformation matrix using the Orthogonal Procrustes Solution. We applied this algorithm to CT and MRI scans of the custom phantom. CT derived source locations had source localization errors of MRI derived source locations produced similar results These errors may be attributed to the image digitization process.
Evaluation of layer decomposition for multiframe quantitative coronary angiography
Authors: Close Robert A. , Abbey Craig K. , Morioka Craig A. , Whiting James S.
Published: July 2002

Multiframe quantitative coronary angiography is typically performed by averaging measurements of artery diameter over multiple frames. This approach reduces errors attributable to random noise but may not reduce systematic errors caused by background structures, nonlinear system response, and motion blur. We attempt to reduce these sources of error by decomposing the image sequence into moving layers, one of which includes the artery. We embed simulated arteries into clinical angiographic sequences so that the true vessel dimensions are known accurately. The measurement tasks are minimum diameter, geometric percent stenosis, and densitometric percent stenosis. We compare measurements for single and multiple raw images, single images with fixed mask subtraction, single and multiple images with layered background subtraction, and time‐averaged layer images. We find that both multiframe averaging and layer decomposition significantly improve geometric and densitometric accuracy compared with single‐frame measurements. The best results were obtained by averaging measurements from multiple frames of layered background‐subtracted images.
Development of a portal imager and of tools for radiation treatment verification
Authors: Wang Hui
Published: July 2002

A prototype electrostatic imager has been developed for megavoltage protal imaging in radiation therapy.\sThe imager utilizes amorphous selenium (a‐Se) with a front metal plate as the image receptor and a high resolution voltmeter probe for imager readout.\sImaging characteristics of a‐Se have been investigated theoretically through Monte Carlo simultions, and experimentally by measuring radiation discharging curves and phantom tests.\sThe results of this study have shown that the prototype imager has high sensitivity, good spatial resolution, and low noise level.\sOur study also reveals the potential of electrostatic imaging with metal/ in megavoltage imaging.\sTwo computer algorithms have also been developed for automatic segmentation and contrast enhancement of digital portal images, and for radiation field shape verification.\sBased on a priori knowledge of the properties of portal images, the segmentation and contrast‐enhancement algorithm employs multiple criteria and dynamic reasoning to achieve optimal segmentation of individual images, and has been proved to be accurate, robust, and fast.\sThe algorithm for radiation field shape verification is an adapatation of the chamfer matching technique to a specific application:\smatching closed contours.\sBy incorporating geometric features of the radiation field and using a simple minimization method which is more specific to this task, the algorithm appears to be able to improve the matching results of the standard method.
Energy‐dependent polarity correction factors for four commercial ionization chambers used in electron dosimetry
Authors: Williams Janelle A. , Agarwal Suresh K.
Published: July 2002

The polarity effects of four commercially available ionization chambers were characterized and correction factors as a function of mean energy at depth were tabulated. These included a Farmer‐type chamber, two parallel plate chambers, and one cylindrical chamber used in a scanning water phantom dosimetry system. Polarity effects were measured at representative depths along the depth dose curves of 6, 9, 12, 16, and 20 MeV electron beams. The term “polarity error” is introduced and is defined as the error which is introduced if polarity effects are ignored. Polarity errors for the four ionization chambers studied were shown to monotonically decrease with increasing mean energy at depth and were largely independent of the energy of the incident electron beam. Only at very low energies, that is, very near the end of the practical range, did the correction factors for beams of different incident energy diverge. Three of the four chambers studied had correction factors which were independent of field size, to within ±%. One chamber showed an increase in correction factor with increasing field size which was shown to be mainly due to stem and cable irradiation.
Characterization of a positron emitting V48 nitinol stent for intracoronary brachytherapy
Authors: Li Alexander N. , Eigler Neal L. , Litvack Frank , Whiting James S.
Published: July 2002

Percutaneous transluminal coronary angioplasty (PTCA) is currently one of the most common treatments for obstructive coronary artery disease. The long term success of the treatment, however, is severely limited by restenosis. Recently, different investigators have begun to study the possibility of radiation therapy in restenosis prevention and have shown promising results. However, an optimal radiation delivery device for delivering a highly localized radiation dose to the arterial medial layer while preserving the viability of the artery has yet to be established. In this article, we discuss the development of a unique mixed gamma/beta brachytherapy source capable of delivering high radiation dose to a 0.5 mm thick vessel wall by proton‐beam activating an existing nickel titanium stent to produce vanadium‐48. The dose distribution of the activated stent is determined by computer simulation using MCNP Monte Carlo code and is verified by radiochromic film measurement.
Two‐effective‐source method for the calculation of in‐air output at various source‐to‐detector distances in wedged fields
Authors: Kim Siyong , Liu Chihray , Chen Cody , Palta Jatinder R.
Published: July 2002

A simple algorithm was developed for calculation of the in‐air output at various source‐to‐detector distances (SDDs) on the central axis for wedged fields. In the algorithm we dealt independently with two effective sources, one for head scatter and the other for wedge scatter. Varian 2100C with 18 and 8 MV photon beams was used to examine this algorithm. The effective source position for head scatter for wedged fields was assumed to be the same as that for open fields, and the effective source position for wedge scatter was assumed to be a certain distance upstream from the physical location of the wedge. The shift of the effective source for wedge scatter, w, was found to be independent of field size. Moreover, we observed no systematic dependency of w on wedge angle or beam energy. One value, cm, provided less than 1% difference in in‐air outputs through the whole experimental range, i.e., to field size for 60° wedge), 15°–60° wedge angle, 80–130 cm SDD, and both 18 and 8 MV photon beams. This algorithm can handle the case in which use of a tertiary collimator with an external wedge makes the field size for the determination of wedge scatter different from that for head scatter. In this case, without the two‐effective‐source method, the maximum of 4.7% and 2.6% difference can be given by the inverse square method and one‐effective‐source method in a 45° wedged field with 18 MV. Differences can be larger for thicker wedges. Enhanced dynamic wedge (EDW) fields were also examined. It was found that no second effective source is required for EDW fields.
Theoretical considerations of monitor unit calculations for intensity modulated beam treatment planning
Authors: Boyer A. , Xing L. , Ma C‐M. , Curran B. , Hill R. , Kania A. , Bleier A.
Published: July 2002

A treatment planning system to compute intensity modulated radiotherapy (IMRT) treatments using inverse planning was investigated. The system was designed to optimize the intensity patterns required to treat a specified target volume with specified normal structure constraints. A beam model that uses the convolution of pencil beams was used to compute the dose distributions. A multileaf collimator leaf‐setting sequence intended to produce the intensity pattern was computed along with the monitor units required to deliver each of a number of fixed‐gantry modulated fields. Computer calculations are commonly verified using an independent manual procedure. It is difficult to calculate treatment delivery monitor units for this variant of IMRT using manual methods. Since manual calculations are not feasible, it is important both to understand and to verify the calculation of treatment monitor units by the planning system algorithm. A formal analysis was made of the dose calculation model and the monitor unit calculation embedded in the algorithm. Experimental verification of the dose delivered by plans computed with the methodology demonstrated an agreement of better than 4% between the dose model and measurements.
Characterization of the reciprocity law failure in three mammography screen–film systems
Authors: de Almeida Adelaide , Sobol Wlad T. , Barnes Gary T.
Published: July 2002

The purpose of this project was to quantify reciprocity law failure (RLF) for mammography screen–film systems. Three widely used screen–film systems were evaluated: the Kodak MinR 2000 system, Fuji UM Mammo Fine screen and Fuji UM MA HC film, and Agfa MR Detail screen and Agfa Mammoray MR5 film. The logit algorithm that linearizes logistic curve shapes was utilized to characterize film sensitometric response. Different values of mammographic phantom thickness, tube current, and kVp were used to vary screen–film exposure rates. RLF was quantified by examining the dependence of logit parameters (maximum and minimum film density, curve shift, and slope) on exposure rate. The shift of the logit curve was found to be a good indicator of the screen–film system speed, while the slope of the logit curve is affected by the RLF. RLF leads to changes in film contrast as well as speed. For the range of exposure rates measured (50‐fold), screen–film contrast and speed varied by factors of 2 and 3.5, respectively. Film contrast decreased as exposure rate increased. The greatest changes were observed with the Kodak MinR 2000 screen–film system.
Comparison of superheated drop detector with phosphorous pentoxide powder for the detection of neutrons in 18 MV x rays
Authors: Loye T. , Sidhu N. P. S. , Sandison G. A.
Published: July 2002

Neutron dose equivalent measurements were performed in and around an 18 MV x‐ray beam using superheated drop detectors (SDD) and phosphorous pentoxide powder. The neutron dose equivalent profiles for various field sizes of and were measured. The results measured with the were checked for any gross systematic errors by comparing with the published results computed by using Monte Carlo calculations. A comparison was then made between the neutron dose equivalent profiles measured with the and the SDD. The results of this comparison show that the neutron dose equivalents measured with the two types of detectors agree with each other for measurements about 20 cm away from the beam edges. However, in and near the beam edges the SDD measurements are upto 50% less than the neutron dose equivalents measured using for the 18 MV x‐ray beam.
Correlated histogram representation of Monte Carlo derived medical accelerator photon‐output phase space
Authors: Schach von Wittenau A. E. , Cox L. J. , Bergstrom P. M. , Chandler W. P. , Siantar C. L. Hartmann , Mohan R.
Published: July 2002

We present a method for condensing the photon energy and angular distributions obtained from Monte Carlo simulations of medical accelerators. This method represents the output as a series of correlated histograms and as such is well‐suited for inclusion as the photon‐source package for Monte Carlo codes used to determine the dose distributions in photon teletherapy. The method accounts for the isocenter‐plane variations of the photon energy spectral distributions with increasing distance from the beam central axis for radiation produced in the bremsstrahlung target as well as for radiation scattered by the various treatment machine components within the accelerator head. Comparison of the isocenter energy fluence computed by this algorithm with that of the underlying full‐physics Monte Carlo photon phase space indicates that energy fluence errors are less than 1% of the maximum energy fluence for a range of open‐field sizes. Comparison of jaw‐edge penumbrae shows that the angular distributions of the photons are accurately reproduced. The Monte Carlo sampling efficiency (the fraction of generated photons which clear the collimator jaws) of the algorithm is approximately 83% for an open 10×10 field, rising to approximately 96% for an open 40×40 field. Data file sizes for a typical medical accelerator, at a given energy, are approximately 150 kB, compared to the 1 GB size of the underlying full‐physics phase space file.
Fission converter and metal–oxide–semiconductor field effect transistor study of thermal neutron flux distribution in an epithermal neutron therapy beam
Authors: Kaplan Greg I. , Rosenfeld Anatoly B. , Allen Barry J. , Coderre Jeffrey A. , Liu Hungyan B.
Published: July 2002

The depth distribution of the thermal neutron flux is a major factor in boron neutron capture therapy (BNCT) in determining the efficiency of cell sterilization. In this paper the fission detector method is developed and applied to measure the in‐phantom thermal neutron flux depth distribution. Advantages of the fission detector include small size, direct measurement of thermal neutron flux in a mixed radiation field of BNCT beam, self‐calibration, and the possibility of on‐line measurement. The measurements were performed at epithermal a BNCT facility. The experimental results were compared with the thermal neutron flux calculated by the Monte Carlo method and found to be in good agreement.
Application of radiosurgery principles to a target in the breast: A dosimetric study
Authors: Jozsef Gabor , Luxton Gary , Formenti Silvia C.
Published: July 2002

Purpose: To investigate the technical and physical feasibility of using a radiosurgery‐like technique to irradiate a small target within the breast with a single fraction. Material and Methods: During diagnostic biopsy, a tantalum surgical clip is placed in the lesion identified at mammography. Transverse CT scans over the entire breast are obtained, as the patient lies prone on a special table that allows the breast to hang down. The clip is used as a reference point to define the isocenter of the radiation treatment. Results: The clip is visible on port films taken with a 4 MV beam, allowing the isocenter to be set to its planned location. No movement of the hanging breast is visually detected. The possible beam directions are enclosed by a 220° vertical angular interval. Dosimetry of two “radiosurgical” examples, (A) seven fixed horizontal beams and (B) six 45° arcs and a 90° sagittal arc using a 4 MV x‐ray beam with a 32 mm diameter collimator, are discussed. Both field arrangements produce adequate tumor coverage: the minimum target dose is 83% of the dose maximum in the fixed beam arrangement and 86% in the multiarc setup. In arrangement A the lung and other tissues external to the breast receive dose only from scattered radiation. In arrangement B the maximum lung dose is less than 5% of the dose to isocenter. Conclusion: From a dosimetric point of view both described techniques are feasible, and the radiosurgery‐like treatment is executable.
The self-force and radiation reaction
Authors: Rohrlich F.
Published: July 2002

In view of the confusion in the literature, the nomenclature of “self-force” and “radiation reaction” is clarified. The difference in their physical meaning and their characteristic form permits one to obtain the total rate of radiation emission (both its momentum rate and its energy rate) from knowledge of the self-force. This can be done without knowledge of the asymptotic form of the radiation field. The electromagnetic case is the main topic, but the method is also applied to the emission of gravitational radiation in the linear approximation to general relativity.
Least-squares Legendre spectral element solutions to sound propagation problems
Authors: Lin Wen H.
Published: July 2002

This paper presents a novel algorithm and numerical results of sound wave propagation. The method is based on a least-squares Legendre spectral element approach for spatial discretization and the Crank–Nicolson [Proc. Cambridge Philos. Soc. 43, 50–67 (1947)] and Adams–Bashforth [D. Gottlieb and S. A. Orszag, Numerical Analysis of Spectral Methods: Theory and Applications (CBMS-NSF Monograph, Siam 1977)] schemes for temporal discretization to solve the linearized acoustic field equations for sound propagation. Two types of NASA Computational Aeroacoustics (CAA) Workshop benchmark problems [ICASE/LaRC Workshop on Benchmark Problems in Computational Aeroacoustics, edited by J. C. Hardin, J. R. Ristorcelli, and C. K. W. Tam, NASA Conference Publication 3300, 1995a] are considered: a narrow Gaussian sound wave propagating in a one-dimensional space without flows, and the reflection of a two-dimensional acoustic pulse off a rigid wall in the presence of a uniform flow of Mach 0.5 in a semi-infinite space. The first problem was used to examine the numerical dispersion and dissipation characteristics of the proposed algorithm. The second problem was to demonstrate the capability of the algorithm in treating sound propagation in a flow. Comparisons were made of the computed results with analytical results and results obtained by other methods. It is shown that all results computed by the present method are in good agreement with the analytical solutions and results of the first problem agree very well with those predicted by other schemes.
Spectral shapes of forward and reverse transfer functions between ear canal and cochlea estimated using DPOAE input/output functions
Authors: Keefe Douglas H.
Published: July 2002

It is widely assumed that the distortion characteristics of the cochlea are uniform across its length, or at least across some portion of its length. For each distortion product otoacoustic emission (DPOAE) input/output (I/O) function across frequency, there is a corresponding cochlear I/O function defined over the cochlear source region. An assumption of distortion invariance is adopted such that these cochlear I/O functions are identical across tonotopic place, which is testable in the sense that a single nonlinear function should adequately describe the set of DPOAE I/O functions across frequency. If so, the differences in measured DPOAE I/O functions across frequency are produced by differences in the forward stimulus transmission to the generation site, and reverse DP transmission back to the ear canal. The absolute transfer-function magnitude is not determined by this technique, but the spectral shapes across frequency and between ears are determined. The role of middle-ear functioning is implicit in the I/O functions because of its controlling influence on these transfer functions. Results have been obtained using the average DPOAE I/O functions measured in a population of healthy ears [Gorga et al., J. Acoust. Soc. Am. 107, 2128–2135 (2000)], and support the hypothesis of cochlear-distortion invariance. The measured forward and reverse transfer functions have a general bandpass characteristic, and a more narrow-band structure with similarities to the behavioral threshold curve.
The relationship between the intelligibility of time-compressed speech and speech in noise in young and elderly listeners
Authors: Versfeld Niek J. , Dreschler Wouter A.
Published: July 2002

A conventional measure to determine the ability to understand speech in noisy backgrounds is the so-called speech reception threshold (SRT) for sentences. It yields the signal-to-noise ratio (in dB) for which half of the sentences are correctly perceived. The SRT defines to what degree speech must be audible to a listener in order to become just intelligible. There are indications that elderly listeners have greater difficulty in understanding speech in adverse listening conditions than young listeners. This may be partly due to the differences in hearing sensitivity (presbycusis), hence audibility, but other factors, such as temporal acuity, may also play a significant role. A potential measure for the temporal acuity may be the threshold to which speech can be accelerated, or compressed in time. A new test is introduced where the speech rate is varied adaptively. In analogy to the SRT, the time-compression threshold (or TCT) then is defined as the speech rate (expressed in syllables per second) for which half of the sentences are correctly perceived. In experiment I, the TCT test is introduced and normative data are provided. In experiment II, four groups of subjects (young and elderly normal-hearing and hearing-impaired subjects) participated, and the SRT’s in stationary and fluctuating speech-shaped noise were determined, as well as the TCT. The results show that the SRT in fluctuating noise and the TCT are highly correlated. All tests indicate that, even after correction for the hearing loss, elderly normal-hearing subjects perform worse than young normal-hearing subjects. The results indicate that the use of the TCT test or the SRT test in fluctuating noise is preferred over the SRT test in stationary noise.
Grazing instabilities and post-bifurcation behavior in an impacting string
Authors: Murphy K. D. , Morrison T. M.
Published: July 2002

A theoretical and experimental investigation of the nonlinear dynamic response of a periodically excited string subject to a knife-edge amplitude restraint is presented. The amplitude restraint creates an impact condition as the amplitude of the response grows. The focus of this work is on the influence of a grazing instability; this zero-velocity impact event leads to complicated, post-bifurcation behavior ranging from multifrequency, periodic motion to chaos. In addition to looking at the response numerically, parameter combinations leading to an incidence of grazing are clearly identified in the excitation force excitation frequency parameter space using a multiple scales perturbation analysis. Modeling issues, numerical difficulties, and experimental limitations are also discussed.
Transformation of external-ear spectral cues into perceived delays by the big brown bat, Eptesicus fuscus
Authors: Simmons James A. , Wotton Janine M. , Ferragamo Michael J. , Moss Cynthia F.
Published: July 2002

The external-ear transfer function for big brown bats (Eptesicus fuscus) contains two prominent notches that vary from 30 to 55 kHz and from 70 to 100 kHz, respectively, as sound-source elevation moves from −40 to +10 degrees. These notches resemble a higher-frequency version of external-ear cues for vertical localization in humans and other mammals. However, they also resemble interference notches created in echoes when reflected sounds overlap at short time separations of 30–50 μs. Psychophysical experiments have shown that bats actually perceive small time separations from interference notches, and here we used the same technique to test whether external-ear notches are recognized as a corresponding time separation, too. The bats’ performance reveals the elevation dependence of a time-separation estimate at 25–45 μs in perceived delay. Convergence of target-shape and external-ear cues onto echo spectra creates ambiguity about whether a particular notch relates to the object or to its location, which the bat could resolve by ignoring the presence of notches at external-ear frequencies. Instead, the bat registers the frequencies of notches caused by the external ear along with notches caused by the target’s structure and employs spectrogram correlation and transformation (SCAT) to convert them all into a family of delay estimates that includes elevation.
Responses to cochlear normalized speech stimuli in the auditory nerve of cat
Authors: Recio Alberto , Rhode William S. , Kiefte Michael , Kluender Keith R.
Published: July 2002

Previous studies of auditory-nerve fiber (ANF) representation of vowels in cats and rodents (chinchillas and guinea pigs) have shown that, at amplitudes typical for conversational speech (60–70 dB), neuronal firing rate as a function of characteristic frequency alone provides a poor representation of spectral prominences (e.g., formants) of speech sounds. However, ANF rate representations may not be as inadequate as they appear. Here, it is investigated whether some of this apparent inadequacy owes to the mismatch between animal and human cochlear characteristics. For all animal models tested in earlier studies, the basilar membrane is shorter and encompasses a broader range of frequencies than that of humans. In this study, a customized speech synthesizer was used to create a rendition of the vowel [ɛ] with formant spacing and bandwidths that fit the cat cochlea in proportion to the human cochlea. In these vowels, the spectral envelope is matched to cochlear distance rather than to frequency. Recordings of responses to this cochlear normalized [ɛ] in auditory-nerve fibers of cats demonstrate that rate-based encoding of vowel sounds is capable of distinguishing spectral prominences even at 70–80-dB SPL. When cochlear dimensions are taken into account, rate encoding in ANF appears more informative than was previously believed.
Effect of duration on amplitude-modulation masking
Authors: Millman Rebecca E. , Lorenzi Christian , Apoux Frédéric , Füllgrabe Christian , Green Gary G. R. , Bacon Sid P.
Published: July 2002

Detection thresholds for a signal sinusoidal amplitude modulation (SAM) were measured in the presence of an additional, masking SAM. Signal and masker modulations were applied synchronously to a gated white noise carrier. The masker modulation frequency was fixed at 16 Hz and the signal modulation frequency ranged from 2 to 256 Hz. Modulation masking patterns were measured in three listeners for stimulus durations of 500, 1000, and 2000 ms. The results showed that modulation masking was reduced or abolished at signal modulation frequencies of 2, 14, and 18 Hz when stimulus duration was increased from 500 to 2000 ms. The effect at 2 Hz suggests that fringe effects in modulation masking previously reported by Bacon and Grantham [S. P. Bacon and D. W. Grantham, J. Acoust. Soc. Am. 91, 3451–3455 (1992)] were at least partly due to an increase in masker modulation duration. The reduction in modulation masking observed at signal modulation frequencies of 14 and 18 Hz was similar to that at 2 Hz, suggesting that listeners use a low-frequency temporal envelope beat cue (in this case at 2 Hz) when the distance between the signal and masker modulations is small.
Benefit of modulated maskers for speech recognition by younger and older adults with normal hearing
Authors: Dubno Judy R. , Horwitz Amy R. , Ahlstrom Jayne B.
Published: July 2002

To assess age-related differences in benefit from masker modulation, younger and older adults with normal hearing but not identical audiograms listened to nonsense syllables in each of two maskers: (1) a steady-state noise shaped to match the long-term spectrum of the speech, and (2) this same noise modulated by a 10-Hz square wave, resulting in an interrupted noise. An additional low-level broadband noise was always present which was shaped to produce equivalent masked thresholds for all subjects. This minimized differences in speech audibility due to differences in quiet thresholds among subjects. An additional goal was to determine if age-related differences in benefit from modulation could be explained by differences in thresholds measured in simultaneous and forward maskers. Accordingly, thresholds for 350-ms pure tones were measured in quiet and in each masker; thresholds for 20-ms signals in forward and simultaneous masking were also measured at selected signal frequencies. To determine if benefit from modulated maskers varied with masker spectrum and to provide a comparison with previous studies, a subgroup of younger subjects also listened in steady-state and interrupted noise that was not spectrally shaped. Articulation index (AI) values were computed and speech-recognition scores were predicted for steady-state and interrupted noise; predicted benefit from modulation was also determined. Masked thresholds of older subjects were slightly higher than those of younger subjects; larger age-related threshold differences were observed for short-duration than for long-duration signals. In steady-state noise, speech recognition for older subjects was poorer than for younger subjects, which was partially attributable to older subjects’ slightly higher thresholds in these maskers. In interrupted noise, although predicted benefit was larger for older than younger subjects, scores improved more for younger than for older subjects, particularly at the higher noise level. This may be related to age-related increases in thresholds in steady-state noise and in forward masking, especially at higher frequencies. Benefit of interrupted maskers was larger for unshaped than for speech-shaped noise, consistent with AI predictions.
Classification by multiple-resolution statistical analysis with application to automated recognition of marine mammal sounds
Authors: Hayward Thomas J.
Published: July 2002

A multiple-resolution statistical pattern recognition technique for classification by supervised learning is developed and then applied to automated recognition of marine mammal sounds. The data to be classified may be either unprocessed or transformed, e.g., time series or time-frequency distributions of acoustic transients. Training data consist of samples previously grouped by a human expert into labeled sets; these sets are presumed to be associated with different “classes.” The labeled sets are then characterized by occupancy statistics associated with a multiple-resolution, binary partition of the (unreduced) sample space. Classification of a new sample is performed by calculating a posteriori probabilities of membership of the new sample in each class, computed by Bayesian inference from the occupancy statistics of the associated labeled set. These a posteriori probabilities are calculated by a recursive algorithm that progresses from coarse to fine resolution in the sample space. The algorithm is implemented in a simple, highly efficient computer program. Automated classification of both time series and time-frequency distributions of marine-mammal vocalizations is demonstrated using a small number of labeled samples (approximately ten samples per class).
High-frequency scattering from an acoustic cavity
Authors: Garrelick Joel
Published: July 2002

High-frequency reradiation, or scattering, from a plate covered acoustic cavity is analyzed by assuming that the cavity geometry is sufficiently complex to produce a diffuse field. The plate is taken to be effectively infinite and the cavity baffled. For an illustrative example the cavity is shown to smear the return relative to the backscattered directivity pattern for the equivalent rigid plate alone, that is reduce the peak and fill in the nulls. Also, the effect of the plating above its flexural coincidence frequency is shown to redirect the peak return from normal incidence at lower frequencies to the vicinity of the coincidence angle.
Influence of an inclusion on the phase of a Stoneley wave
Authors: Briers R. , Leroy O. , Shkerdin G. N.
Published: July 2002

The propagation of a Stoneley wave through an inclusion near a liquid/solid interface is investigated on the basis of mode theory [Briers et al., J. Acoust. Soc. Am. 95, 1953–1966, 1967–1976 (1994)]. An expression for the phase and amplitude changes of the Stoneley wave is derived and analyzed in the case of a thin (kd≪1) and of a thick (kd≫1) inclusion of arbitrary length (kd is the multiplication of the liquid wave number with the thickness of the inclusion).
Radiation from finite phased and focused linear array including interaction
Authors: Assaad Jamal , Bruneel Christian
Published: July 2002

Resultant pressure of linear arrays, consisting of N elementary transducers, are in general computed with the help of simplified assumptions for the displacement field of the transducer radiating surface. Moreover, interactions between neighboring elements are not included in most of the numerical approaches. In this paper, a new calculation scheme is proposed to compute the resultant pressure of such arrays, including interactions. For this purpose, using the finite element method (FEM), the far-field directivity pattern of a part of the array is computed using dipolar dampers and a previously described extrapolation algorithm [J. Assaad et al., J. Acoust. Soc. Am. 94, 562–573 (1993)]. This part is constituted of an active elementary transducer (electrically driven) mounted between 2Q passives (electrically grounded) neighboring transducers. Then, the resultant pressure of a finite phased and focused array can be obtained by summing up the far-field directivity patterns of the 2Q+1 transducers sets weighted by the classical term which takes into account the geometrical and electrical phase shifts. This new calculation scheme is then used to compute the resultant pressure of a lithium niobate linear array. It will be shown that mechanical interaction must be taken into account for high frequency arrays.
Solving ray acoustic problems with a DNA computer
Authors: Yang Yang , Li Yuling , Couchman Luise S.
Published: July 2002

A computational scheme that integrates the advantages of both the electronic computer and DNA computer (DNA experiment) is proposed to solve the ray acoustic problems at high frequencies. More explicitly, a conventional electronic computer is used to perform most of the sequential operations, such as solving differential equations, designing the DNA experiment, and verifying the final experimental solutions; whereas DNA annealing reaction is used to provide huge parallel operations to assemble the solutions to the scattered field for all the specified incident directions. To illustrate this idea, an example is given where the DNA reaction, rather than carrying out experimentally, is tested and simulated on an electronic computer.
Modeling the environmental influence on the vertical directionality of ambient noise in shallow water
Authors: Yang T. C. , Yoo Kwang
Published: July 2002

The vertical directionality of acoustic ambient noise has been a subject of much interest in the past. It is a well-defined physical quantity that can be measured experimentally with a vertical array. It possesses certain deterministic features that can be modeled theoretically with environmental acoustic and source data. Ambient noise in shallow waters, including its vertical directionality, is not very well known and is also difficult to model/predict. This is because the acoustic environment varies with time and is location dependent. Thus arises the question, how does the vertical directionality of the ambient noise depend on the acoustic environments (found in typical coastal waters)? Due to the shallow water depth, it is noted that sound (noise) propagation can be significantly influenced by the bottom. The degree of bottom interaction will depend on the sound-speed profile in the water column: whether it is downward refractive or not. Bottom attenuation will in turn determine how far the sound will propagate in the water column. Using a modal representation, a closed-form expression is obtained which can be used to interpret and predict the distant noise vertical directionality as a function of the environmental acoustic parameters. The nearby (overhead) noise is separately modeled and is found less sensitive to environmental changes as the propagation distance is short. As the deterministic features of the noise vertical directionality is controlled by the sound propagation in the channel, it could be used as an acoustic indicator of the acoustic environment in the area. Time variations of the noise directionality will also be discussed.
Numerical simulations with horizontal-refraction-modal tomography. Part I. Adiabatic propagation
Authors: Voronovich A. G. , Shang E. C.
Published: July 2002

Numerical simulations on retrieving the 3-D structure of the sound-speed inhomogeneities based on data on the horizontal refraction angle (HRA) of acoustic modes have been performed. The inversion proceeds in two stages. At the first stage the values of propagation constants of different acoustic modes at the nodes of a horizontal grid are calculated. The corresponding procedure represents a linear 2-D problem which is solved for different modes independently. At the second stage the coefficients of the expansion of the variation of the sound-speed profile with respect to some set of empirical orthogonal functions are calculated based on already determined values of propagation constants. This stage represents a 1-D nonlinear problem which is solved for different nodes of the horizontal grid independently. When error-free HRA data were used in the numerical simulations, the 3-D sound-speed field was retrieved perfectly. Then the HRA data were artificially distorted with random errors. It was found that the relative error of the retrieved values of the propagation constant of modes is proportional to the error in HRA (expressed in radians). Corresponding relative error in retrieved values of sound speed is in its turn proportional to the relative error in propagation constants. When the level of HRA error has been chosen according to the level arising from distortions caused by internal waves, the rms error in the retrieved sound-speed values for the situation considered appeared to be about 0.7 m/s.
Some hot topics in animal bioacoustics
Authors: Au Whitlow W. L.
Published: July 2002

This paper is derived from a “Hot Topics in Animal Bioacoustics” presentation at the 130th meeting of the Acoustical Society of America in St. Louis, Missouri. Six bioacoustics studies on a wide variety of species are discussed. Two of the studies are concerned with insects, the parasitoid fly, and cotton bollworms. The remaining bioacoustics studies are on aquatic animals including the West Indian manatee, elephant seals, and dolphins.
Modeling of piezoelectric ceramic vibrators including thermal effects. Part III. Bond graph model for one-dimensional heat conduction
Authors: Moon Won-kyu , Busch-Vishniac Ilene J.
Published: July 2002

A new bond graph model for conduction heat transfer is developed, and applied to thermal energy balance in the piezoelectric thickness vibrator. In formulation of the heat conduction model, the mechanical and electrical effects are included. Hence, it can be directly applied to the temperature-dependent thickness vibrator. For the purpose of evaluation of the new method, one-dimensional heat conduction excluding other variable effects is compared with the results of the analytic solutions in simple cases. The simulation illustrates the validity and the accuracy of the model. Although the model is applied to the one-dimensional case only, the method can be easily used for general heat conduction problems.
New phenomena on King integral with dissipation
Authors: Too Gee-Pinn James
Published: July 2002

Sound beams generated by an arbitrary baffled projector are considered. A wave equation which considers thermoviscous effects is derived in terms of nondimensional velocity potential. Then, an improved King integral solution that includes the thermoviscous effect is developed here. The solution shows an interesting phenomenon: that the dissipation effect contributes exponential decay in the propagation spectrum. In addition, the effect also contributes a propagation mode in the evanescent spectrum. The dissipation effects on sound beams are investigated numerically on axis and off axis with propagation spectrum and evanescent spectrum, respectively.