bluuebunny/crossref_metadata_2025 huggingface dataset:
Development of a portal dose image prediction algorithm for arbitrary detector systems
Authors: McCurdy Boyd M. C.
Published: July 2002

This thesis presents the development of a two‐step model that predicts dose deposition in arbitrary portal image detectors. The algorithm requires patient computed tomographic data, source‐detector distance, and knowledge of the incident photon beam fluence. The first step predicts the photon fluence entering a portal imaging detector located behind the patient. Primary fluence is obtained through simple ray tracing techniques, while scatter fluence prediction requires a library of scatter fluence kernels generated by Monte Carlo simulation. These kernels allow prediction of basic radiation transport parameters characterizing the scattered photons, including fluence and energy. The second step of the algorithm involves a superposition of Monte Carlo‐generated pencil beam kernels, describing dose deposition in a specific detector, with the predicted incident fluence of primary and scattered photons. The algorithm is tested on a variety of simple slab and anthropomorphic phantoms. Clinical parameters were varied over a wide range of interest, including 6, 18, and 23 MV photon beam spectra and 10–80 cm air gap between phantom and portal imaging detector. Both low and high atomic number detectors were used to verify the algorithm, including a linear array of fluid ionization chambers and a solid state, amorphous silicon detector. Agreement between predicted and measured portal dose is better than 5% in areas of low dose gradient (<30%/cm) and better than 5 mm in areas of high dose gradient (>30%/cm) for the variety of situations tested here. It is concluded that this portal dose prediction algorithm is fast, accurate, allows separation of primary and scatter dose, and can model dose image formation in arbitrary detector systems.
Comparison of eye position versus computer identified microcalcification clusters on mammograms
Authors: Krupinski Elizabeth A. , Nishikawa Robert M.
Published: July 2002

The purpose of this study was to compare identifications of microcalcification clusters on mammograms by a computerized detection scheme and by human observers having their eye position recorded. Eighty digitized mammograms (half with a subtle microcalcification cluster) were analyzed by a computerized detection scheme and then were read from laser‐printed films by six mammographers while eye position was recorded. The computer had 83% true positives with a false‐positive rate of 0.5 per image. The true positives of the radiologists ranged from 78% to 90%, with false‐positive rates ranging from 0.03 to 0.20. Locations of true and false positives identified by computer and by the human were compared. All but 5% of the true clusters were identified by either the computer, human, or by both. Here 10% of the clusters were detected by only the computer, and 11% were missed by the computer but detected by at least one radiologist. False positives were of three types: identified by computer only, by the human reader only, or by both. Eye‐position data indicated significant differences in dwell time between both true‐positive and false‐positive locations reported by the radiologist versus the computer detections. A follow‐up analysis indicated that microcalcification clusters and false positives were judged to have more identifiable characteristics of true calcifications and were associated with longer gaze durations than those with fewer microcalcification characteristics. In general, the computer was able to detect clusters judged to have few or no features that the radiologists were not able to detect. Comparison of computer versus human identification of microcalcification clusters may be useful for improving computerized detection schemes to serve as clinical aids to mammographers, and for understanding what image features lead to false‐positive decisions for both the computer and the human reader.
The investigation of 32P wire for catheter‐based endovascular irradiation
Authors: Xu Zhigang , Reinstein L. E. , Yang Guozhen , Pai S. , Gluckman G. , Almond P. R.
Published: July 2002

The dose distribution from a source has been measured and calculated in order to evaluate its application in endovascular irradiation. The source dimension was 27 mm in length and 0.3 mm in diameter and was embedded in the end of a Ni–Ti wire. Dose measurements were performed using radiochromic film in several specially designed tissue equivalent phantoms. Loevinger's point dose kernel was used for the calculation. The approximate dose rate at a radial distance of 1.5 mm from the center of the source was found to be 6.75 cGy/s per GBq (0.25 cGy/s per mCi), which allows the delivery of a therapeutic dose in a short time interval with a satisfactory homogeneity without stepping the source. However, the dose rate falls off almost exponentially along the radial distance. Therefore it may not be suitable for treating large diameter vessel from a centrally located source. The effect of a curved wire source on the radial dose distribution was also investigated. The results showed that for a maximum bend of 180° the dose rate was increased by as much as 20% along the inner radial distance but decreased by as much as 20% along the outer radial distance compared to the dose along a straight wire. However, for curvatures normally encountered in a clinical situation, the dose rate was changed less than 5%.
A system for nonradiographic source localization and real‐time planning of intraoperative high dose rate brachytherapy
Authors: Watanabe Yoichi , Anderson Lowell L.
Published: July 2002

We have developed a system for source localization and real‐time planning of interstitial volume implants for intraoperative radiation therapy (IORT) using high dose rate remote afterloading techniques. Source localization is realized by using an electromagnetic tracking device, which consists of a transmitter coil, a receiver coil, and a signal processing unit, to generate the coordinates and orientation of the receiver. A drawback of the device is its sensitivity to adjacent metallic objects. Localization accuracy was evaluated in an operating room environment, where the metallic objects closest to the receiver are surgical retractors (that, incidentally, preclude radiographic localization). For achievable separation distances, we found an rms error of 0.7 mm in determining the distance between points 2 cm apart, thereby demonstrating the feasibility of the method. The receiver is mounted on a plastic block from which projects a long stylet and the transmitter is located at about 50 cm from the receiver. The stylet is inserted sequentially into source catheters to obtain the location and orientation data that serve as input to treatment planning software. The planning program optimizes source dwell time to make calculated dose conform to the dose prescribed on an ellipsoidal surface to an extent consistent with a certain level of dose uniformity inside the target volume. A least squares method is used that involves minimizing the objective function by a matrix method (nonnegative least squares). We have demonstrated that dwell time optimization can be performed in a short time and that the approach is adequate for the IORT application.
Composite x‐ray image assembly for large‐field digital mammography with one‐ and two‐dimensional positioning of a focal plane array
Authors: Halama Gary , McAdoo James , Liu Hong
Published: July 2002

To demonstrate the feasibility of a novel large‐field digital mammography technique, a Loral charge‐coupled device (CCD) focal plane array (FPA) was positioned in a mammographic field with one‐ and two‐dimensional scan sequences to obtain and composite images, respectively. These experiments verify that precise positioning of FPAs produced seamless composites and that the CCD mosaic concept has potential for high‐resolution, large‐field imaging. The proposed CCD mosaic concept resembles a checkerboard pattern with spacing left between the CCDs for the driver and readout electronics. To obtain a complete x‐ray image, the mosaic must be repositioned four times, with an x‐ray exposure at each position. To reduce the patient dose, a lead shield with appropriately patterned holes is placed between the x‐ray source and the patient. The high‐precision motorized translation stages and the fiber‐coupled‐scintillating‐screen–CCD sensor assembly were placed in the position usually occupied by the film cassette. Because of the high mechanical precision, seamless composites were constructed from the subimages. This paper discusses the positioning, image alignment procedure, and composite image results. The paper only addresses the formation of a seamless composite image from subimages and will not consider the effects of the lead shield, multiple CCDs, or the speed of motion.
Scatter and attenuation measurements at distances greater than 10 cm from an source
Authors: Mauceri T. , Biggs P. , Beatty J. , Flynn D.
Published: July 2002

Most algorithms developed by various investigators for use in brachytherapy treatment planning have typically been designed to calculate the dose within a 10 cm range of a radiation source. These algorithms predict the dose well at distances <10 cm from the source but were not developed and should not be utilized to predict the dose at distances >10 cm. On the contrary, treatment planning systems and manual calculations will produce erroneous results when dose points >10 cm are calculated using these algorithms. The spread in the data generated by the above algorithms is 16% at 15 cm and 42% at 20 cm. Physical measurements were performed at distances between 5 and 50 cm from a high activity source in water. The measured data correlated well with the predicted data from 5 to 10 cm, which had a 5% spread. Beyond 10 cm the measured data fell central to the range of the predicted data, with the spread of the predicted data increasing from 5% to 80% with increasing distance from the source. The measured data was fitted with a model incorporating a buildup factor and an attenuation factor. The best fit values are in reasonable agreement with those obtained by two of the investigators, Thomason and Tripathi.
Quality assurance for the Leksell gamma unit: Considering magnetic resonance image‐distortion and delineation failure in the targeting of the internal auditory canal
Authors: Ertl Adolf , Saringer Walter , Heimberger Karl , Kindl Peter
Published: July 2002

Our aim in this study was to distinguish quantitatively between the localization accuracy of a commercially available stereotactic fixation device as claimed by the manufacturer and the target accuracy as measured by a user, applying neuroradiologic imaging in Gamma Knife planning and phantom irradiation. Missing the target is the most serious possible failure in Gamma Knife and Linac therapy. To reduce this risk, we developed a quality control algorithm and designed a phantom. To evaluate the accuracy of the targeting procedure with a Leksell Gamma unit, and to experience the possible errors in all procedural steps, irradiations of phantoms were performed, using the so‐called “unknown” targeting method. Accuracy is defined by the extent of spatial deviation of the irradiated target from the calculated target. Digital imaging was used for therapy planning. GafChromic films, which had been irradiated while affixed to a specially developed phantom, were used for measuring the precision of the radiation unit. A series of MR images (in two plains: transverse and coronal) was acquired sequentially to image the three‐dimensional (3‐D) volume of the phantom. The results obtained for isocentric accuracy of the Leksell Gamma unit, model B, were in good agreement to the calculated position. The observed spatial deviations between calculated and irradiated targets is less than 1 mm. The newly designed phantom and quality control algorithm are useful in quality assurance measurements of stereotactic radiation therapy.
Setup verification in linac‐based radiosurgery
Authors: Falco T. , Lachaine M. , Poffenbarger B. , Podgorsak E. B. , Fallone B. G.
Published: July 2002

A semi‐automatic technique for the direct setup alignment of radiosurgical circular fields from an isocentric linac to treatment room laser cross‐hairs is described. Alignment is achieved by acquiring images of the treatment room positioning laser cross‐hairs superimposed on the radiosurgical circular field image. An alignment algorithm calculates the center of the radiosurgical field image as well as the intersection of the laser cross‐hairs. This determines any alignment deviations and the information is then used to translate the radiosurgical collimator to its correct aligned position. Two detectors, each being sensitive to the lasers and ionizing radiation, were used to acquire the radiation/laser images. The first detector consists of a 0.3‐mm‐thick layer of photoconducting a‐Se deposited on a 1.5‐mm‐thick copper plate and the second is film. The algorithm and detector system can detect deviations with a precision of ∼0.04 mm. A device with gyroscopic degrees of freedom was built in order to firmly hold the detector at any orientation perpendicular to the radiosurgical beam axis. This device was used in conjunction with our alignment algorithm to quantify the isocentric sphere relative to the treatment room lasers over all gantry and couch angles used in dynamic stereotactic radiosurgery.
Finding mechanisms responsible for the spectral distribution of electron beams produced by a linear accelerator
Authors: Kok J. G. M. , Welleweerd J.
Published: July 2002

The measured electron spectra of linear accelerators from several manufacturers differ in comparison to the spectral form and width. As part of our investigations of linac performance and stability, we analyzed the electron spectra of our linacs. After building a spectrometer the electron spectra were measured. The measured spectral widths were comparable with the results published in the literature. It appeared that the phase of the recycled radio pulse in combination with the limited bandwidth of the bending magnet are responsible for unusual (multipeak) electron spectra. The scatter filters only have a relatively small widening effect on the spectrum. There was no indication that multipeak or wide spectra are related to linac instabilities.
Automatic on‐line electronic portal image analysis with a wavelet‐based edge detector
Authors: Petrascu O. , Bel A. , Linthout N. , Verellen D. , Soete G. , Storme G.
Published: July 2002

A fully automatic method for on‐line electronic portal image analysis is proposed. The method uses multiscale edge detection with wavelets for both the field outline and the anatomical structures. An algorithm to extract and combine the information from different scales has been developed. The edges from the portal image are aligned with the edges from the reference image using chamfer matching. The reference is the first portal image of each treatment. The matching is applied first to the field and subsequently to the anatomy. The setup deviations are quantified as the displacement of the anatomical structures relative to the radiation beam boundaries. The performance of the algorithm was investigated for portal images with different contrast and noise level. The automatic analysis was used first to detect simulated displacements. Then the automatic procedure was tested on anterior–posterior and lateral portal images of a pelvic phantom. In both sets of tests the differences between the measured and the actual shifts were used to quantify the performance. Finally we applied the automatic procedure to clinical images of pelvic and lung regions. The output of the procedure was compared with the results of a manual match performed by a trained operator. The errors for the phantom tests were small: average standard deviation of 0.39 mm and 0.26 degrees and absolute mean error of 0.31 mm and 0.2 degrees were obtained. In the clinical cases average standard deviations of 1.32 mm and 0.6 degrees were found. The average absolute mean errors were 1.09 mm and 0.39 degrees. Failures were registered in 2% of the phantom tests and in 3% of the clinical cases. The algorithm execution is approximately 5 s on a 168 MHz Sun Ultra 2 workstation. The automatic analysis tool is considered to be a very useful tool for on‐line setup corrections.
Digital mammography image simulation using Monte Carlo
Authors: Peplow Douglas E. , Verghese Kuruvilla
Published: July 2002

Monte Carlo simulations of digital images of the contrast detail phantom and the ACR phantom are presented for two different x‐ray digital mammography modalities: a synchrotron mammography system and a next‐generation scanning slot clinical system. A combination of variance reduction methods made it possible to simulate accurate images using real pixel dimensions within reasonable computation times. The complete method of image simulation, including a simple detector response model, a simple noise model, and the incorporation of system effects (MTF), is presented. The simulated images of the phantoms show good agreement with images measured on the two systems.
Computational validation of the stereology principle applied to the microdosimetry of boron neutron capture therapy
Authors: Yam C. S. , Zamenhof R. G.
Published: July 2002

High resolution quantitative autoradiography (HRQAR) is a novel technique that has been developed in our laboratory and applied to the microdosimetry of boron neutron capture therapy (BNCT). High resolution quantitative autoradiography is employed to define the microdistribution of boron‐10 atoms within a 1–2 μm frozen tissue section. This microdistribution is used as input to a novel two‐dimensional Monte Carlo charged particle transport calculation that computes various microdosimetric parameters, such as the number of nuclear “hits,” energy absorbed in the nuclei, etc., within the environment of actual tissue morphology (i.e., cell nuclei, cytoplasm, and intracellular space). Stereological transformation is then implemented to transform the two‐dimensional calculations into effectively three‐dimensional results. In the present study no seek to demonstrate the validity of the surrogate two‐dimensional 2‐D computation as being quantitatively equivalent to a hypothetical full 3‐D calculation. The results show that within the limitations of the test parameters used the surrogate 2‐D and 3‐D results are completely equivalent within the statistical constraints of the Monte Carlo calculations. Limitations of this approach also are evaluated, including a Monte Carlo calculation of the influence of the thickness of the histological tissue section and the track detector and the influence of and particle lateral and range straggling.
Statistical estimation of π using random vectors
Authors: Bloch S. C. , Dressler R.
Published: July 2002

We present a simple application of a spreadsheet to estimate π using random vector ensembles. The worksheet, combining elements of the works of Archimedes, Liu Hui, and Buffon, can be used as a brief introductory tutorial on the Monte Carlo method, random number generators, and the logical IF function. Complete instructions are given for composing the worksheet.
Chinese dialect identification using segmental and prosodic features
Authors: Chang Wen-Whei , Tsai Wuei-He
Published: July 2002

Several approaches to Chinese dialect identification based on segmental and prosodic features of speech are described in this paper. When using segmental information only, the system performs phonotactic analysis after speech utterances have been tokenized into sequences of broad phonetic classes. The second scheme comprises prosodic models which are trained to capture tone sequence information for individual dialects. Also proposed is a novel approach that examines differences between Chinese dialects at broad phonetic and prosodic levels. These algorithms were evaluated via a multispeaker read-speech mode. Simulation results indicate that the combined use of segmental and prosodic features allows the proposed system to discriminate among three major Chinese dialects spoken in Taiwan with 93.0% accuracy.
A masking level difference due to harmonicity
Authors: Treurniet William C. , Boucher Darcy R.
Published: July 2002

The role of harmonicity in masking was studied by comparing the effect of harmonic and inharmonic maskers on the masked thresholds of noise probes using a three-alternative, forced-choice method. Harmonic maskers were created by selecting sets of partials from a harmonic series with an 88-Hz fundamental and 45 consecutive partials. Inharmonic maskers differed in that the partial frequencies were perturbed to nearby values that were not integer multiples of the fundamental frequency. Average simultaneous-masked thresholds were as much as 10 dB lower with the harmonic masker than with the inharmonic masker, and this difference was unaffected by masker level. It was reduced or eliminated when the harmonic partials were separated by more than 176 Hz, suggesting that the effect is related to the extent to which the harmonics are resolved by auditory filters. The threshold difference was not observed in a forward-masking experiment. Finally, an across-channel mechanism was implicated when the threshold difference was found between a harmonic masker flanked by harmonic bands and a harmonic masker flanked by inharmonic bands. A model developed to explain the observed difference recognizes that an auditory filter output envelope is modulated when the filter passes two or more sinusoids, and that the modulation rate depends on the differences among the input frequencies. For a harmonic masker, the frequency differences of adjacent partials are identical, and all auditory filters have the same dominant modulation rate. For an inharmonic masker, however, the frequency differences are not constant and the envelope modulation rate varies across filters. The model proposes that a lower variability facilitates detection of a probe-induced change in the variability, thus accounting for the masked threshold difference. The model was supported by significantly improved predictions of observed thresholds when the predictor variables included envelope modulation rate variance measured using simulated auditory filters.
Active control of the volume acquisition noise in functional magnetic resonance imaging: Method and psychoacoustical evaluation
Authors: Chambers John , Akeroyd Michael A. , Summerfield A. Quentin , Palmer Alan R.
Published: July 2002

Functional magnetic resonance imaging (fMRI) provides a noninvasive tool for observing correlates of neural activity in the brain while a subject listens to sound. However, intense acoustic noise is generated in the process of capturing MR images. This noise stimulates the auditory nervous system, limiting the dynamic range available for displaying stimulus-driven activity. The noise is potentially damaging to hearing and is distracting for the subject. In an active noise control (ANC) system, a reference sample of a noise is processed to form a sound which adds destructively with the noise at the listener’s ear. We describe an implementation of ANC in the electromagnetically hostile and physically compact MRI scanning environment. First, a prototype system was evaluated psychoacoustically in the laboratory, using the electrical drive to a noise-generating loudspeaker as the reference. This system produced 10–20 dB of subjective noise-reduction between 250 Hz and 1 kHz, and smaller amounts at higher frequencies. The system was modified to operate in a real MR scanner where the reference was obtained by recording the acoustic scanner noise. Objective reduction by 30–40 dB of the most intense component in scanner noises was realized between 500 Hz and 3500 Hz, and subjective reduction of 12 dB and 5 dB in tests at frequencies of 600 Hz and at 1.9 kHz, respectively. Although the benefit of ANC is limited by transmission paths to the cochlea other than air-conduction routes from the auditory meatus, ANC achieves worthwhile attenuation even in the frequency range of maximum bone conduction (1.5–2 kHz). ANC should, therefore, be generally useful during auditory fMRI.
Directional dependence of nonlinear surface acoustic waves in the (001) plane of cubic crystals
Authors: Kumon R. E. , Hamilton M. F.
Published: July 2002

Spectral evolution equations are used to perform analytical and numerical studies of nonlinear surface acoustic waves in the (001) plane of a variety of nonpiezoelectric cubic crystals. The basic theory underlying the model equations is outlined, and quasilinear solutions of the equations are presented. Expressions are also developed for a characteristic length scale for nonlinear distortion and a nonlinearity coefficient. A time-domain equation corresponding to the spectral equations is derived. Numerical calculations based on measured second- and third-order elastic constants taken from the literature are performed to predict the evolution of initially monofrequency surface waves. Nonlinearity matrix elements that indicate the coupling strength of harmonic interactions are shown to provide a useful tool for characterizing waveform distortion. The formation of compression or rarefaction shocks can be strongly dependent on the direction of propagation, and harmonic generation is suppressed or increased in certain directions.
One source for distortion product otoacoustic emissions generated by low- and high-level primaries
Authors: Lukashkin Andrei N. , Lukashkina Victoria A. , Russell Ian J.
Published: July 2002

Distortion product otoacoustic emissions (DPOAE) elicited by tones below 60–70 dB sound pressure level (SPL) are significantly more sensitive to cochlear insults. The vulnerable, low-level DPOAE have been associated with the postulated active cochlear process, whereas the relatively robust high-level DPOAE component has been attributed to the passive, nonlinear macromechanical properties of the cochlea. However, it is proposed that the differences in the vulnerability of DPOAEs to high and low SPLs is a natural consequence of the way the cochlea responds to high and low SPLs. An active process boosts the basilar membrane (BM) vibrations, which are attenuated when the active process is impaired. However, at high SPLs the contribution of the active process to BM vibration is small compared with the dominating passive mechanical properties of the BM. Consequently, reduction of active cochlear amplification will have greatest effect on BM vibrations and DPOAEs at low SPLs. To distinguish between the “two sources” and the “single source” hypotheses we analyzed the level dependence of the notch and corresponding phase discontinuity in plots of DPOAE magnitude and phase as functions of the level of the primaries. In experiments where furosemide was used to reduce cochlear amplification, an upward shift of the notch supports the conclusion that both the low- and high-level DPOAEs are generated by a single source, namely a nonlinear amplifier with saturating I/O characteristic.
Transient vibratory response of fluid-loaded shells using convolution integral equations
Authors: Stepanishen Peter R.
Published: July 2002

A general time-domain approach is presented to address the transient vibratory response of fluid-loaded shells of arbitrary shape when subjected to specified mechanical and/or acoustical excitations. The approach is based on utilizing an in vacuo eigenvector expansion with time-dependent coefficients to describe the velocity field of the shell. Fluid loading on the shells is described via the use of convolution integrals involving the modal velocity coefficients and mode-dependent acoustic radiation impulse responses. Time domain methods are used to develop a set of universal coupled convolution integral equations for the time-dependent modal velocity coefficients of the shell. Special cases which include a finite plate and an arbitrary shell of revolution are then addressed using the general approach. A reduced set of the coupled convolution integral equations for the time-dependent modal velocity coefficients is obtained for the plate and sets of similar equations are also obtained for the shell.
The mechanical waveform of the basilar membrane. I. Frequency modulations (“glides”) in impulse responses and cross-correlation functions
Authors: de Boer Egbert , Nuttall Alfred L.
Published: July 2002

The purpose of this investigation is to present evidence from experimental as well as model results on temporal variations of the frequency of oscillation in the basilar membrane’s impulse response. Stimuli were either clicks leading to a direct estimate of the impulse response, or bands of pseudo-random noise (one or two octaves wide) which lead to an indirect estimate of the impulse response via a cross-correlation procedure. The noise bands were centered at the best frequency of the BM location under observation. Responses were obtained from the basal turn of the guinea-pig cochlea, from a location with a best frequency (for the weakest stimuli) between 17.0 and 18.5 kHz. Data acquisition was done with a sample frequency of 208 kHz. Input–output cross-correlation functions were found to share with impulse responses the property that the initial oscillations have a noticeably lower frequency than the later ones. During the impulse response the frequency of oscillation increases gradually. This increase occurs and continues to beyond the time that the oscillations reach the largest amplitude. This frequency variation is called a “glide.” Using the “analytic signal” method the frequency of oscillation is found to increase continually throughout the duration of the main lobe of oscillation, even at the lowest tested stimulus intensities (about 20 dB SPL). At high stimulus intensity both the direct and indirect impulse response change their appearance drastically but the glide retains its basic form. In the case of the direct impulse response estimate the glide can be attributed to temporal variation of the degree of nonlinearity. For the indirect impulse response this is not true, because with a constant level noise stimulus there is no regular temporal variation of nonlinearity. In this case the glide should be interpreted as an intrinsic property of the cochlear system. From our and others’ data the glide was found to exist over a topographic frequency range of best frequencies of at least from 1.76 to 18 kHz. Two examples of present-day models of the cochlea are discussed of which one is found to demonstrate the glide phenomenon in its response, and the other one does not.
The characteristics of voicing in syllable-initial fricatives in American English
Authors: Pirello Karen , Blumstein Sheila E. , Kurowski Kathleen
Published: July 2002

This study investigated the acoustic characteristics of voicing in the production of fricative consonants. The fricatives [f v s z] were used in combination with the vowels [i e a o u] to create CV syllables, which were produced by four subjects both in a context condition (following voiced and voiceless velar stops) and in isolation. Analyses were conducted of the time course of glottal excitation during the fricative noise interval in the voiced and voiceless fricative stimuli. Results showed that the patterns of voicing in the fricative noise interval were influenced by the voicing characteristics of preceding stop consonants. Nonetheless, these carryover coarticulatory effects were short-lived, influencing only the first 10’s of ms of the following segment. Despite the influence of phonetic context on the patterns of voicing, an acoustic measure relating to the presence or absence of glottal excitation at the acoustic boundaries of the fricative noise reliably classified a majority (93%) of the fricative consonants in terms of the phonetic category of voicing. Thus, while phonetic context affected the patterns of glottal excitation in the fricative noise interval, it did not affect the criterial attribute associated with the phonetic category of voicing.
Effects of electrode configuration on psychophysical strength-duration functions for single biphasic electrical stimuli in cats
Authors: Smith David W. , Finley Charles C.
Published: July 2002

The interface between electrode and neural target tissue is thought to influence certain characteristics of neural and behavioral responses to electrical stimulation of the auditory system. At present, the biophysical properties of this interface are not well understood. Here the effects of biphasic phase duration and electrode configuration on psychophysical threshold in response to electrical stimulation in cats are described. Five cats were trained to respond to acoustic stimuli using food as a reward in an operant reinforcement paradigm. After training, the animals were unilaterally deafened and implanted with a multicontact intracochlear electrode array. Thresholds for single presentations of biphasic current pulses were measured as a function of phase duration and electrode arrangement. Statistical analyses of the data indicated that strength-duration function slopes between 200 and 1600 μs/phase were significantly different for the different electrode configurations and, overall, were unrelated to the absolute level of the strength-duration function (i.e., were independent of absolute threshold). For all subjects, the slope of this function for intermediate pulse durations was dependent on electrode configuration and most shallow for radial-bipolar configurations (−3.4 dB/doubling), was steepest for monopolar arrangements (−5.9 dB/doubling), and was intermediate for longitudinal-bipolar pairings (−4.4 dB/doubling). Slopes for both shorter and longer phase duration stimuli were not significantly different. The underlying mechanisms for these effects may include, or be a combination of altered electrical field patterns, integrated activity across multiple fibers, and stochastic behavior of individual auditory neurons to electrical stimulation.
Perception of the American English liquid /ra–la/ contrast by humans and monkeys
Authors: Sinnott Joan M. , Brown Charles H.
Published: July 2002

Human and monkey perception of the American English liquid /ra–la/ contrast was compared using various synthetic continua in which the normal spectral and temporal cues were either complete, partial, or altered in various ways. Two experiments compared human and monkey discrimination of the various continua using a low-uncertainty repeating-standard procedure. Results showed that, while human sensitivity was best at the human phoneme boundary, monkey sensitivity was best inside the /ra/ category. Also, while humans were more sensitive than monkeys to temporal variation in the stimuli, monkeys were more sensitive than humans to spectral variation, particularly for stimuli inside the /ra/ category. Two additional experiments compared human and monkey identification of the /ra–la/ continua using a higher-uncertainty go/nogo identification procedure. Monkeys performed as accurately as humans (including one native Spanish and one native Hindi listener) in identifying the stimuli. However, human and monkey “phoneme boundaries” were in different places, with monkey boundaries shifted more toward /ra/ than human boundaries. These results suggest that human boundaries may be based on some sort of specific linguistic knowledge. Despite these boundary differences, monkeys showed a trading relation comparable to that of humans, indicating that the /ra–la/ trading relation has a psychoacoustic basis and that linguistic knowledge is not a necessary prerequisite for it to occur.
New methods to characterize radially polarized piezoelectric ceramic cylindrical shells of finite length
Authors: Ebenezer D. D. , Sujatha A. J.
Published: July 2002

New methods to experimentally determine the electroelastic coefficients of radially polarized piezoelectric ceramic cylindrical shells (RPPCCSs) of arbitrary length to radius ratio are presented. The real parts of ε33T, s11E, s12E, and g31 are explicitly expressed in terms of quantities which can be easily measured. The quantities can be obtained from the measured frequency-dependent input electrical admittances (IEAs) of RPPCCSs with free ends. The theoretical IEA based on the two-dimensional equations of state and the membrane approximation is used to derive the explicit expressions. Some methods cannot be used when the resonance frequencies, which are required as inputs, cannot be identified. This occurs when there are several resonances in a narrow frequency band or losses are high. However, the other methods can be used. The methods are validated by using simulated data. The required input data are computed using the theoretical expression for the IEA and an assumed set of complex electroelastic coefficients. It is then shown that the real parts of the coefficients of RPPCCSs with a small or large length to radius ratio and low or high mechanical losses can be accurately determined by using the input data. The effect of measurement errors on the overall accuracy of the experimentally determined values is also discussed. The methods are further validated by the good agreement over a wide frequency range between measured IEAs and the IEAs computed using the experimentally determined values of coefficients.
Models and measurements of sound propagation from a point source over mixed impedance ground
Authors: Boulanger Patrice , Waters-Fuller Tim , Attenborough Keith , Li Kai Ming
Published: July 2002

Measurements of the excess attenuation of sound from a point source over mixed impedance ground in an anechoic chamber are compared with predictions obtained from models based on (a) the semiempirical theory due to De Jong, (b) Nyberg’s theory, (c) a Fresnel-zone approximation, and (d) a boundary element code. The impedance discontinuities studied in this work are perpendicular to the source–receiver line. When there is a single discontinuity between acoustically hard and finite impedance surfaces, the De Jong semiempirical model, the Fresnel-zone model and boundary element code are found to give satisfactory agreement with measured data. The frequency of the first maximum in attenuation is found to be highest at approximately 70% hard surface cover rather than at the 100% expected. It is argued that this is a result of edge diffraction. When extended to multiple impedance discontinuities, the De Jong semiempirical model performs poorly. However, both Nyberg’s theory and the boundary element code give good agreement with measured results, and the Fresnel-zone model gives qualitative agreement with the measured data. The measurements confirm that, under certain constraints given by Nyberg’s theory, the ground effect due to mixed impedance may be determined from that predicted by using the area-average impedance.
Lamb waves as thickness vibrations superimposed on a membrane carrier wave
Authors: Achenbach J. D.
Published: July 2002

Classical Lamb waves in an homogeneous, isotropic linearly elastic plate are reconsidered. The displacement components are obtained in terms of thickness motions superimposed on a membrane carrier wave which defines the propagation along the plate. The carrier wave can be any solution of the reduced wave equation for a membrane. The analysis of the thickness motions results in the usual Rayleigh–Lamb frequency equation. A number of special cases for the carrier wave are considered.
Ejectives in Tanana Athabaskan
Authors: Tuttle Siri G.
Published: July 2002

Ejectives in Athabaskan languages have been investigated phonetically by Lindau (1984), McDonough and Ladefoged (1993), in Navajo, and by Davis and Hargus (1994, 1996) in Babine/Witsuwit’en. In the latter two investigations, three different types of production were found associated with glottal consonants, only one of which showed the classic ejective pattern with a silent period. Examination of samples of Tanana Athabaskan recorded in 1961, 1962, 1974, and the early 1990s found similar variation in samples of this Alaskan Athabaskan language. There appeared, however, to be no examples of ejectives without silent periods in the oldest samples (1961 and 1962). This suggests the hypothesis that the ejective without silent period is an innovation in the last generation of Tanana speakers. Recordings analyzed include a set of standardized word lists recorded by McKennan in 1962 with speakers of Minto, Chena, and Salcha dialects; texts of Teddy Charlie (Minto) recorded by Michael Krauss in 1962; and 3keywords2 recordings of Isabel Charlie (Minto) and Eva Moffit (Salcha) recorded by James Kari and Siri Tuttle in 1991. [This work has been supported by NSF.]
Determination of acoustic center correction values for type LS2aP microphones at normal incidence
Authors: Wagner Randall P. , Nedzelnitsky Victor
Published: July 2002

Frequency-dependent acoustic center correction values are required to obtain accurate microphone calibrations in the free-field by the reciprocity technique. These values were determined for IEC type LS2aP microphones at normal incidence by utilizing the theoretical inverse relationship between the sound pressure amplitude at the acoustic center of a receiver and the distance between acoustic centers of source and receiver. A dynamic signal analyzer was used to measure the gain factor between the amplified output voltage of the receiver and the source input voltage at 500-Hz intervals in the extended frequency range 2–50 kHz. This procedure allowed all the data for a microphone pair to be gathered within several hours for microphone diaphragm separations from 101–311 mm at 10-mm intervals. At each frequency, the reciprocal of this gain factor as a function of microphone diaphragm separation was fit to a straight line after correction for atmospheric effects, including attenuation of sound caused by atmospheric absorption. Mean acoustic center correction values (from four microphones combined in six pairs) were calculated using the parameters obtained from the fit and found to be in good agreement with published values calculated by the boundary element method, as well as with values predicted by scaling published values of the acoustic center correction for microphones with a geometrical configuration similar to that of IEC type LS1P microphones.
Temporal integration of loudness under partial masking
Authors: Florentine Mary , Buus So/ren , Robinson Monica
Published: July 2002

This paper tests the hypothesis that the loudness ratio between equal-SPL tones with different durations is the same at all SPLs. Detection thresholds and levels required to produce equal loudness for 5- and 200-ms tones presented in quiet or in broadband noise were measured using adaptive, two-interval, two-alternative forced-choice procedures. Tone levels ranged from 5 dB SL to 90 dB SPL for the long tones and about 100 dB SPL for the short tones. Results from six listeners with normal hearing show that the amount of temporal integration, defined as the level difference between equally loud 5- and 200-ms tones, varies nonmonotonically with level and is greatest at moderate levels. The average amount of temporal integration in quiet is about 15 dB near threshold, increases to a peak of 27 dB when the 5-ms tone is about 58 dB SPL, and decreases to about 15 dB near 100 dB SPL. For masker levels of 40, 60, and 80 dB SPL, the amount of temporal integration near masked threshold remains near 15 dB. The maximum amount of temporal integration decreases as masker level increases and occurs at progressively higher levels. At high levels, the amount of temporal integration is nearly the same as in the quiet for all masker levels. Loudness functions derived by applying the equal-loudness-ratio hypothesis to the data yield excellent predictions of loudness matches between tones in the quiet and partially masked tones with the 40- and 60-dB maskers. For the 80-dB masker, clear deviations are present. These results support the equal-loudness-ratio hypothesis, but suggest that intense masking may alter the loudness ratio between 200- and 5-ms tones.
The role of excitation-pattern cues and temporal cues in the frequency and modulation-rate discrimination of amplitude-modulated tones
Authors: Micheyl Christophe , Moore Brian C. J. , Carlyon Robert P.
Published: July 2002

These experiments examine the influence of excitation-pattern cues and temporal-fine-structure cues on frequency difference limens (FDLs) measured as a function of duration. In the first three conditions, listeners were required to detect a change in carrier frequency from a baseline of 250 or 2000 Hz, for stimuli with half-amplitude durations ranging from 5 to 320 ms. In the “steady” condition, duration was manipulated by increasing the steady-state portion of the envelope between two 5-ms linear onset and offset ramps. This resulted in spectra and excitation patterns that broadened with decreasing duration. In the “modulated” condition, the carrier was amplitude modulated with a triangle function (period 10 ms) and duration was manipulated by varying the number of cycles of the modulator. In this case, the spectral envelope did not vary with duration, but the width of individual spectral lobes broadened with decreasing duration. The “low-peak-constant” condition was similar to the modulated condition, except that an increase in carrier frequency was accompanied by a decrease in the period of the modulator, so as to hold constant the frequency of the spectral lobe located roughly 100 Hz below the carrier frequency. In this condition, changes in carrier frequency resulted in minimal changes in excitation level on the low-frequency side of the excitation pattern, but changes on the high-frequency side were larger than for the first two conditions. Both the values of the FDLs, and their variation with frequency and duration, were similar in these three conditions. The fourth, “modulator varying,” condition differed in that the carrier frequency was held constant and listeners were required to detect a change in modulator frequency. Thresholds were expressed as the change in frequency of the spectral side lobes adjacent to the carrier frequency (“equivalent” FDLs). Excitation-pattern cues in this condition were at least as large as in the first three conditions. However, equivalent FDLs were significantly higher than for the other three conditions. The higher FDLs are attributed to the lack of temporal fine-structure cues related to the carrier frequency. Overall, the results suggest that FDLs in the first three conditions were determined by temporal cues rather than by excitation-pattern cues. The increase of the FDLs with decreasing duration did not arise from increasing spectral splatter.
Numerical and experimental study of finite-amplitude standing waves in a tube at high sonic frequencies
Authors: Elvira-Segura L. , Riera-Franco de Sarabia E.
Published: July 2002

Finite-amplitude standing waves in an air-filled tube are studied numerically and experimentally. The standing wave is excited at one end of the rigid-walled tube and a rigid cap is assumed at the other end. The one-dimensional nonlinear second order wave equation is solved numerically using a finite element algorithm based on the Bubnov–Galerkin method. Viscous and thermal losses at the walls of the tube are taken into account. An experimental setup is developed for the study of standing waves at high sonic frequencies. The acoustic field is measured along the tube axis with a fine calibrated probe. Experimental data of pressure distributions for the fundamental frequency (9.5 kHz) and the second harmonic (19 kHz) are compared with the numerical results, as a function of the tube length.