bluuebunny/crossref_metadata_2025 huggingface dataset:
Aberration-corrected time-domain ultrasound diffraction tomography
Authors: Mast T. Douglas
Published: February 2014

The inverse scattering problem of reconstructing a spatially dependent sound speed variation from far-field time-domain acoustic scattering measurements is considered. Such reconstructions are quantitative images with applications including ultrasonic mammography. Although the linearized time-domain inverse scattering problem is shown to have no general solution for finite signal bandwidth, an approximate solution to the linearized problem is constructed using a simple delay-and-sum method analogous to ‘‘gold standard’’ ultrasonic beamforming. The form of this solution suggests that the full nonlinear inverse scattering problem can be approximated by applying appropriate angle- and space-dependent time shifts to the time-domain scattering data; this analogy leads to a general approach to aberration correction. Two related methods for aberration correction are presented: one in which delays are computed from estimates of the medium using an efficient straight-ray approximation, and one in which delays are applied directly to a time-dependent linearized reconstruction. Numerical results indicate that these correction methods achieve substantial quality improvments for imaging of large scatterers. [Work supported by the Breast Cancer Research Program of the U.S. Army Medical Research and Materiel Command.]
Theoretical considerations for the use of microbubbles as point targets for phase aberration correction
Authors: Psychoudakis Dimitris , Fowlkes J. Brian , Volakis John L. , Kripfgans Oliver D. , Carson Paul L.
Published: February 2014

Bubbles can be produced by vaporization of perfluorocarbon droplets of a few μm diameter. These bubbles can reach up to 100 μm in diameter and their backscatter is calculated to be more than 10 dB above that of several organ tissues. At these sizes and for diagnostic frequencies (2–8 MHz), bubbles can be approximated by the nonrigid sphere scattering solution employed here. This presentation concerns the bubble size and its implications on the backscatter amplitude and the phase error introduced in diagnostic ultrasound when assuming that the bubble acts as a point target for phase aberration correction. The phase error is the difference between the phase at each location along the receiving aperture relative to that at the aperture center, compared with the same relative phase for a perfect point target. Evaluations were made of the phase error with respect to a range of transducer f-numbers (0.5–2.0) for a specific bubble size (30 μm radius) and at certain frequencies (2–8 MHz). For example, at 5 MHz the phase error introduced by the point target assumption is maximally 5 deg, while the phase error of breast tissue scattering is around 160 deg. [Work supported by PHS Grant No. R01HL54201 from the National Heart, Lung, and Blood Institute.]
Measurements of the spatial coherence of the fundamental and second-harmonic beams for a clinical imaging system
Authors: Fedewa Russell J. , Wallace Kirk D. , Holland Mark R. , Jago James R. , Ng Gary C. , Rielly Matthew R. , Robinson Brent S. , Miller James G.
Published: February 2014

Spatial coherence of backscattered signals underlies correlation-based phase aberration corrections. The van Cittert–Zernike theorem relates frequency-independent spatial coherence to the autocorrelation of the transmit apodization. Previous studies suggest that the mainlobe of the nonlinearly generated harmonic beam is wider and exhibits lower sidelobes than a beam linearly generated at the harmonic frequency. The objective of this study was to measure the spatial coherence associated with fundamental and nonlinearly generated harmonic beams. Using data experimentally acquired from a clinical scanner (ATL HDI5000), two independent methods were employed to measure the spatial coherence. One approach measured the spatial coherence of backscatter from a tissue-mimicking phantom using rf signals from individual elements of a linear array. In the second approach, the effective apodization was determined by a linear angular spectrum backpropagation of hydrophone-sampled data from a transverse plane in the focal zone. The results show that the effective apodization of the nonlinearly generated harmonic beam is more aggressive than the actual transmit apodization. The spatial coherence associated with the second-harmonic beam differs from the spatial coherence of the fundamental beam, but is predicted by the effective apodization. [Supported in part by NIHHL40302 & ATL.]
Efficient computation of field of 2-D array with limited diffraction array beams
Authors: Lu Jian-yu , Cheng Jiqi
Published: February 2014

Two-dimensional (2-D) arrays are useful for improving quality of three-dimensional (3-D) medical imaging in ultrasound. Beams produced with a 2-D array are usually simulated with the Rayleigh–Sommerfeld diffraction formula (RSDF). In general, the RSDF requires a 2-D integration for each field point in space and thus is very time consuming. Fresnel approximation may reduce the 2-D integration to 1-D but will not yield satisfactory results near the transducer surface or for field at a large angle from the beam axis. In this work, limited diffraction array beams are used to synthesize beams produced with a 2-D array [J.-Y. Lu, Int. J. Imaging Syst. Technol. 8, 126–136 (1997)]. In this method, the 2-D integration is replaced with a 2-D summation leading to a much faster computation. The method is accurate even if the field to be evaluated is very close to the surface of a transducer. Results of Bessel beams, X waves, and focused Gaussian beams will be shown and compared with those obtained with the RSDF and the experiments. [This work was supported in part by Grant No. HL60301 from the National Institutes of Health of the U.S.A.]
Modulated piezoresistive sensor for airborne infrasound
Authors: Gabrielson Thomas B.
Published: February 2014

This paper will describe the design, construction, and testing of a piezoresistive sensor for airborne acoustics in the frequency range 0.005–100 Hz. Intended as a candidate for many-element infrasound arrays where element cost is critical, the sensor was designed around an inexpensive silicon-membrane chip with an implanted piezoresistive bridge. The prototype has a measured self-noise below one millipascal per root hertz at 1 Hz with a 1/f power spectrum to 0.005 Hz, the designed low-frequency rolloff. The responsivity is nominally 20 mV/Pa with a linear signal range to 150 Pa. When the bridge is operated with high-frequency drive and synchronous detection, the self-noise is within a factor of 2 of the intrinisic Johnson noise of the resistive bridge. This self-noise level is well below ambient levels in the microbarometric region from 0.2 to 0.7 Hz. Basic sensor-element limitations will be discussed along with the electronics and package design. In addition, the techniques for calibration and self-noise evaluation will be presented. [Work sponsored by the U.S. Army Space and Missile Defense Command.]
The determination of the depth to the liquid-gas interface in a producing well
Authors: Hixson Elmer L. , Podio Augasto L. , Garcia-Osuno Fernando
Published: February 2014

Many oil wells use electrically driven pumps at the bottom of the well to pump oil to the surface. If the oil-gas interface falls below the pump, gas is pumped, the pump overheats and usually fails. A passive acoustic system is described here that uses the annulus between the production tubing and the cemented steel casing as a closed end gas filled tube. Pump noise excites many longitudinal resonant modes. These modes occur at n-half wavelengths of the tube length. The depth is then related to the sound speed in the gas and the difference frequency between modes as measured by a microphone at the top of the well and a sprectum analyzer. When the depth falls below a critical value as indicated by a minimum frequency, the pump is turned off.
A new hand-held meter for measuring the occlusion effect produced by, and leakage around, earmolds
Authors: Killion Mead C. , Goldberg Jack
Published: February 2014

Three of the most common complaints by hearing aid wearers are (a) difficulty hearing in noise, (b) the occlusion effect (hollow voice sound), and (c) feedback. The latter two can be largely controlled by earmold construction. What has been lacking is a simple way to measure earmold performance with regard to those two properties. A new hand-held occlusion effect meter using a 0.4-mm-thick crescent-shaped probe tube will be described.
Research into the comfortable volume control curve of TV in Korean style apartments
Authors: Kim Ki Duk , Kim Chul Whan , Choi Hoon Ki , Ryu Dong Su
Published: February 2014

We occasionally experience anger because of unsuitable TV volume for comfortable and clear listening. We do not concentrate on TV while annoyed that we are not tuned in at the desired sound volume. Therefore, we made the preference volume width in watching TV with consideration of age, sex, time periods, variety of broadcasting programs, and watching space structure. We determined the variable sound volume control step based on jnd (just noticeable difference). On the basis of the data obtained, this paper is the research into the preferential sound while watching TV and the optimum TV volume curve.
Audio analysis method of a car stereo
Authors: Kim Ki Duk , Kim Chul Whan , Choi Hoon Ki , Ryu Dong Su , Kim Chul Whan , Choi Hoon Ki , Ryu Dong Su
Published: February 2014

Presently, a car stereo system plays an important part in choosing a car, as people spend more time in their cars and pursue comfortable space, including audio. Thus, the sound quality analysis of a car becomes more conspicuous. We made an analysis of acoustic characteristics with 4-channel loudspeakers of three car types and carried out a subjective listening test with a test reference CD based on sound factors using a scale of seven. This paper proposes how the sound reproduction characteristics are changed according to position of loudspeakers, interior space of the cars, and the characteristics of sound reproduction equipment, in particular, a delay time and frequency response. Moreover, we examined the relation between measurement data and human listening sense.
Evaluation of relative sensitivity of hydrophone with varying hydrostatic pressure employing high pressure tube assembly
Authors: Singh Janardan
Published: February 2014

The high pressure tube assembly employing active impedance termination method has been found most suited to calibrate deep submergence underwater transducers of low frequencies which cannot be calibrated using conventional anechoic tanks because of fabrication engineering problems as well as multiplying factors of cost. A high pressure tube assembly (12.5 cm internal diameter and 200 cm length) has been employed for the measurements of relative sensitivity of hydrophones with varying hydrostatic pressure. The suitable reference projectors were fabricated which were placed at the end of tube assembly as termination transducers. Four hydrophones as probe hydrophone and Kjaer hydrophone (B&K-8103) for the relative sensitivity measurement have been suitably rigged in the transducer carriage. Free field condition is created with active impedance termination method which is achieved by precise adjustment of amplitudes as well as phases of termination transducers. A method of achieving the free field condition has been evolved which minimizes hit and trial procedure. The variations of the relative sensitivity of a hydrophone (B&K-8103) with hydrostatic pressure up to pressure of 1000 psi have been measured and the values were found close to the values specified (up to 400 meters of ocean depth) by Bruel and Kjaer.
Implementation of loudness in a digital instrument
Authors: Kaper Hans G. , Tipei Sever
Published: February 2014

Loudness is a psychological term used to describe the magnitude of an auditory sensation. The loudness of a sound depends not only on the intensity of the sound and its physical composition (the partials in the sound and their amplitudes and frequencies), but also on the subjective conditions of the listener. In this talk, we discuss the algorithms implemented in DISCO to compute the loudness of a synthesized sound. DISCO (Digital Instrument for Sonification and Composition) is an additive synthesis program that produces sound files from score files. Score files are generated by an editor, which implements the composer’s specifications of a piece. DISCO, written in C++, is being developed jointly by the authors at the University of Illinois at Urbana-Champaign (Computer Music Project) and Argonne National Laboratory (Mathematics and Computer Science Division). The program can be used for music composition, as well as for the auditory display of complex data sets—for example, in scientific computing (scientific sonification). The loudness routines in DISCO enable the user to design complex sounds to specified loudness. Additional routines are designed to prevent overflow in the sound file, which would cause ‘‘clipping’’ upon playing, while preserving the relative loudness of all sounds.
Vowel representation and synthesis of singer identity
Authors: Mellody Maureen , Bartsch Mark A. , Herseth Freda , Shirley George I. , Wakefield Gregory H.
Published: February 2014

Professional singers shape the acoustical attributes of their vocal production to create the perceptual impression of a single instrument spanning a variety of vowel timbres over a wide range of pitch. Samples of the five Italian vowels over a two-octave range were analyzed using the modal distribution to yield a time-frequency image of the signal. From such images (high-order) representations of the composite transfer function of the signal were extracted. These representations provide little evidence for the existence of an acoustic ‘‘signature’’ that is invariant over the singer’s entire range of production. Rather, the data, along with results from a perceptual study, suggest that singers create the impression of a single instrument by smoothly transitioning from one local region of invariance to the next. By identifying these regions, low-order, perceptually robust approximations are constructed which bear the identity of the singer when used to synthesize new instances of sung vowels. These low-order representations also serve as endpoints for interpolating between two different singers, as well as boundary points for extrapolating a singer from chest to head modes of production. [Work supported by the MusEn Project at the University of Michigan.]
Noise from aircraft at a condominium complex near Logan
Authors: Timmerman Nancy S. , Iacovino Frank N.
Published: February 2014

Massport undertook an aircraft noise survey at a condominium complex which is less than two miles from one of Logan International Airport’s departure runways. The study took place from September 28 to October 19, 2000, at a time of year when the runway is commonly used. Aircraft operational and flight track information were obtained from Massport’s Noise Monitoring System. Noise data collected at the survey location, which included both statistical and event data, were compared with two permanent monitors from that system. Results at this complex were consistent with the other data.
Development of a high bandwidth Hartmann–Whistle type actuator
Authors: Khanafseh Samer , Raman Ganesh , Cain Alan
Published: February 2014

There is current interest in using Hartmann–Whistle type powered resonance tube actuators for aeroacoustic control. Previous experiments (Raman et al. (2000, 2001) AIAA 2000-1930; Stanek et al. (2000) AIAA 2000-1905) have shown that such actuators with no moving parts are very effective in the suppression of flow impingement and cavity noise. However, fixed geometry actuators can only produce effective actuation over a small range of frequencies. Our idea is to use a variable depth powered resonance tube actuator where the depth of the resonance tube and the distance between the supply jet and the resonance tube can be controlled actively during the experiment. The experimental setup consists of a 1/4′′ diameter jet facing the open end of the resonance tube that is closed at the other end. The tube depth is changed by a computer controlled piston fitted inside the tube. Microphone and pressure sensors located at various locations in the vicinity of actuation were used to measure the frequency and amplitude of the fluctuations produced by this device. Due to the high amplitudes of pressure within the resonance tube the linear eigenfrequencies do not predict the measured frequencies. [Work supported by AFOSR.]
Admixture of traveling wave and standing wave components in a miniature thermoacoustic heat engine
Authors: Kwon Young , Symko Orest G. , Emmi Matt
Published: February 2014

Because of the importance of the thermoacoustic prime mover for all sorts of applications, we have investigated its performance at different operating conditions. Of special interest is the onset of oscillation temperature difference and its dependence on the geometry of the device. This was investigated in miniature heat engines, with resonant frequencies of 2 – 5 kHz, with temperature differences where one end of the device was below room temperature and also when the other end was above room temperature. All the devices were operated with air at 1 atm in the wave resonator configuration. The onset temperature ratios depended strongly on geometry, stack, heat exchangers, and on the degree of traveling wave admixture to the standing wave produced by the resonator.
Thermoacoustic–Stirling model refrigerator
Authors: Poese Matthew E. , Garrett Steven L.
Published: February 2014

The design and performance of a model refrigerator that uses a stainless-steel woven regenerator (4.1 cm diameter, 5.0 mm thick) and an unconventional Helmholtz resonator to provide proper phasing for the regenerator are described. Cooling is produced in air at atmospheric pressure with sound pressures in excess of 6 kPa in a transparent 60 cm long standing wave tube. The sound power is generated using an inexpensive 5 in loudspeaker enclosed in standard PVC plumbing hardware. The resonance frequency of the Helmholtz resonator, and thereby the refrigerator’s cooling capacity, can be tuned by adjusting the volume between the hot end of the regenerator and the end of the tube. As described in Swift et al. [J. Acoust. Soc. Am. 105, 711 (1999)], performance is improved significantly by the addition of a latex diaphragm to suppress streaming. Due to its low cost and flexibility, this device is useful as both a lecture demonstration and for the measurements that will be presented and compared with theoretical performance. [Work supported by ONR and the PSU Applied Research Laboratory. Donation of the regenerator material by N. V. Bekaert S.A. of Belgium and discussions with R. M. Keolian, R. W. Smith, and R. S. Wakeland are gratefully acknowledged.]
Numerical simulation of minor losses in thermoacoustic devices
Authors: Shieh Chingwei M. , Morris Philip J. , Sparrow Victor W.
Published: February 2014

As thermoacoustic devices become more efficient, minor losses through sudden expansions or contractions in such acoustic resonators become more important. To further improve the efficiency of thermoacoustic devices it is necessary to understand in detail the fluid dynamic mechanisms involved in these minor losses. In the present study, a parallel numerical simulation of a three-dimensional acoustic resonator, typical of a thermoacoustic device, is presented. A computational aeroacoustic (CAA) approach is used. The Navier–Stokes equations are discretized in space with the fourth-order dispersion-relation-preserving (DRP) scheme of Tam and Webb and are integrated in time with a fourth-order Runge–Kutta scheme. In the attached regions of the flow the Spalart–Allmaras one-equation turbulence model is used. For separated flow regions this transitions automatically to a detached eddy simulation (DES). In the present study a high amplitude standing wave is generated in a resonator with a sudden change in cross-sectional area. Numerical results for the flow field and minor losses are presented and initial results are compared with experimental data. [Work supported by ONR.]
Thermoviscous functions of wire mesh and RVC stacks
Authors: Muehleisen Ralph T. , Beamer C. Walter
Published: February 2014

Thermoacoustic stacks made of stacked wire mesh elements or reticulated vitreous carbon (RVC) are becoming popular because of their performance, cost, and ease of construction. The thermoviscous Rott functions fν and fκ [related to the porous media function F(λ)] have been measured for wire mesh and RVC stacks of 20, 30, 45, 60, 80, and 100 pores-per-inch. The thermoviscous functions were determined from measurements of the characteristic impedance and propagating wave number of the stacks using the 4 microphone method of Song and Bolton. The measurements were then used to develop empirical models for the stacks. The measurement technique, measurement results, and emprical models are presented. [Work supported by ONR.]
Numerical model of heat exchangers in oscillating flow with oscillating pressure
Authors: Wakeland Ray Scott , Keolian Robert M.
Published: February 2014

Results are presented from a numerical model of heat transfer between two heat exchangers in oscillating flow and with pressure oscillations of the type expected in a standing-wave-based thermoacoustic device. The model assumes that each parcel of gas undergoes adiabatic compression/expansion when outside the exchangers; when inside an exchanger, the parcel temperature change ΔT in each small time step Δt is taken to be a superposition of the change that would have occurred for adiabatic pressure change Δp plus a change due to thermal relaxation toward the exchanger temperature Thx. That is, ΔT=[(γ−1)/γ](T/p)Δp−α(T−Thx)Δt, where γ is the polytropic coefficient and α is an arbitrary relaxation time constant characterizing the exchanger. The pressure p fluctuates as p/p0=(x/x0)−γ, where x is the distance from the parcel to the pressure antinode (hard end) and subscripts zero indicate equilibrium values. This relation is expected to hold close to pressure antinodes, where heat exchangers operate in thermoacoustic devices. After iteration, the model results in a closed cycle of parcel temperature as a function of time, allowing calculation of cycle work and cycle thermal efficiency. [Work supported by ONR and the Pennsylvania Space Grant Consortium.]
Thermodynamics of open cycle thermoacoustic engines
Authors: Weiland Nathan T. , Zinn Ben T.
Published: February 2014

Recent advances in thermoacoustics have included the design, fabrication, and testing of an open cycle thermoacoustic refrigerator where the cold heat exchanger can be replaced by a slowly flowing gas which is cooled as it passes through the stack [R. S. Reid and G. W. Swift, J. Acoust. Soc. Am. 108, 2835–2842 (2000)]. In addition to removing the irreversibilities associated with the cold heat exchanger, an important thermodynamic advantage is provided by cooling the working fluid as it flows through the stack, because the removal of heat from the fluid at higher temperatures increases the efficiency of the refrigeration process. This work investigates the possibility of similar efficiency improvements in open cycle thermoacoustic engines and heat pumps, where a steady flow is superimposed on the working fluid. The benefits of adding mean flow to a thermoacoustic engine rely heavily on the chosen method of heat transfer to the hot side of the stack or regenerator. Ideal and nonideal heat transfer from flow-based and electric-based heat exchangers will be analyzed and compared to an open cycle thermoacoustic engine driven by a steady flow of hot gas through its stack or regenerator.
Sound refraction characteristics near the ground based on turbulence similarity theory
Authors: Wilson D. Keith
Published: February 2014

Sound refraction in the near-ground atmosphere over uniform terrain is systematically addressed with the Monin–Obukhov turbulence similarity theory. The gradient of the effective sound speed (actual sound speed plus the component of the wind vector in the propagation direction) is parametrized with two nondimensional ratios, one proportional to the height and the other representing the magnitude of sound-speed fluctuations relative to wind-speed fluctuations. Based on these parameters, three distinct propagation regimes (with transitions) can be identified: (1) strongly unstable atmospheric stratification where refraction is upward at all propagation angles relative to the mean wind, (2) strongly stable atmospheric stratification where refraction is downward for all angles, and (3) neutral atmospheric stratification where refraction is determined by the wind direction for small values of the nondimensional height ratio and is upward for greater heights. The relative contributions of temperature and humidity to the sound-speed gradient are found to depend on the Bowen ratio, defined as the ratio of the sensible and latent heat fluxes at the surface. Weather conditions appropriate for measuring sound-pressure levels are discussed in connection with the specifications in ANSI S12.18-1994.
Optimization of time-reversal focusing in a multiple scattering environment
Authors: Derode Arnaud , Tourin Arnaud , Fink Mathias
Published: February 2014

We present new experimental results about the limits of time-reversal focusing through a two-dimensional multiple scattering medium. In a weakly heterogeneous medium, the quality of focusing is limited by the array aperture and bandwidth. It gets better in the presence of high-order multiple scattering: the long-lasting scattered signals are recompressed to form a high-power pulse, and the spatial resolution becomes practically independent from the array’s aperture. With a 16-element 3-MHz array, the resolution was found to be 30 times thinner than in a homogeneous medium and resolutions of the order of the wavelength were attained. Therefore one could think that the more multiple scattering, the better. Experimental results show that this is not true. As the order of scattering is progressively increased, the system first takes advantage of multiple scattering, then reaches a limit; for higher orders of scattering, the focusing is degraded both spatially and temporally. The origin and consequences of this phenomenon are shown and discussed in relation with the transport parameters of the medium. There is therefore an optimal amount of multiple scattering. This is of high importance for applications of time-reversal focusing in a scattering or reverberating environment, whether for imaging or communication purposes.
Backscattering of acoustic waves in a cavity
Authors: Beran Mark J. , Frankenthal Shimshon
Published: February 2014

We discuss here the transmission of an acoustic signal in a cavity with random fluctuations in the sound speed. We consider pulse transmission in the single-mode case which consists of one forward and one backward propagating wave and cw signals in cavities with two propagating forward and backward waves. We begin by reviewing the cw single-mode case which has been treated in depth by a number of authors. For the pulse propagating in a single-mode cavity we then show how the cw results may be used to obtain useful information. Finally, we extend the governing equations to the two-mode case and consider possible methods of solution.
Physiological and behavioral assessments of an auditory pathway for processing spectral cues for sound localization
Authors: May Brad
Published: February 2014

Many species, including humans and cats, have head-related transfer functions (HRTFs) that introduce sharp features to the amplitude spectrum of broadband sounds as auditory stimuli propagate to the eardrum. Our behavioral results indicate that HRTF-based spectral cues, in particular mid-frequency spectral notches, are crucial for accurate spatial hearing in cats. This talk will summarize a series of physiological and behavioral assessments that follow the neural encoding of biologically relevant spectral information from a distributed representation in the auditory nerve to notch-selective neurons in the inferior colliculus. Just as anatomically defined pathways have been described for binaural directional cues, our results support the existence of a functionally segregated auditory pathway that is specialized for the processing of spectral cues for sound localization. [Work supported by NIDCD Grant No. DC00954.]
Psychophysical and physiological studies of the precedence effect and echo threshold in the inferior colliculus of the behaving cat
Authors: Tollin Daniel J. , Populin Luis C. , Yin Tom C. T.
Published: February 2014

We are studying the relationship between single-unit responses in the inferior colliculus (IC) of behaving cats and their perception of spatial location using stimuli evoking the precedence effect (PE), an illusion where the perceived location of two similar sounds delivered from different locations but separated by a time delay approximates the perceived location of only the leading sound. Psychophysically, our cats experienced the PE: for 1–15-ms delays, they localized paired transients to nearly the same location as the leading sound alone. For delays greater than 15–20 ms, they often localized the leading and/or lagging location, an indication of echo threshold. Physiologically, for the delays that the cats experienced the PE the IC responses to the lag were reduced relative to the responses to the lag presented alone but with little effect on the response to the lead. The responses of these cells correlate with the behavioral perception of location: for delays encompassing the PE the cats’ spatial perception of the sound is similar in the presence or absence of the lag, while at echo threshold the IC responses to the lag are nearly fully recovered to the response obtained in the lag presented in isolation. [Work supported by DC00116, DC02840, and DC00376.]
Spectral and temporal integration in the auditory cortex of alert primates
Authors: Wang Xiaoqin
Published: February 2014

Lesion studies in humans and primates have shown that the auditory cortex is necessary for the perception of spectrally and temporally complex sounds. Our knowledge on signal processing mechanisms in this cortical area, however, has been largely based on experimental observations obtained under anesthetized conditions. Anesthetics have long been known to have severe side effects on auditory cortical responses. We have systematically studied single-unit activities in the auditory cortex of alert primates using a wide range of spectrally and temporally complex sounds. In the spectral domain, our results showed that neurons in the auditory cortex integrate inputs as far away as several octaves from their central excitatory receptive fields. Such spectral integration appears to be supported by an extensive network of long-range horizontal connections. In the temporal domain, we showed that stimulus-synchronized discharges are on average limited to 20–30 ms inter-stimulus intervals in the unanesthetized cortex. Acoustic transients occurring at shorter time scales are integrated by cortical neurons and transformed into discharge-rate based representations. These findings suggest that (1) processing of acoustic signals by individual cortical neurons is modulated by spectral context and (2) time-varying signals are represented in nonisomorphic forms in the auditory cortex.
Auditory spatial resolution in the barn owl under echoic and anechoic conditions
Authors: Takahashi Terry T. , Spitzer Matthew W. , Bala Avinash
Published: February 2014

Experiments were designed to allow direct comparison of auditory spatial resolution, measured behaviorally, with that of single space-specific neurons in the barn owl’s midbrain. Behavioral measurements of spatial discrimination were obtained using habituation and recovery of the pupillary dilation response (PDR). The acoustically evoked PDR habituates to repeated presentation of a sound, and recovers if the location changes. Thus, the difference in magnitudes of PDRs evoked by a sequence of test and habituating stimuli can be quantified using signal detection theory to provide a measure of discrimination [‘‘p(c),’’ computed from empirical ROC curves]. The minimum audible angles (MAAs) for single sound sources separated in azimuth and elevation were 3° and 9°, respectively. Under simulated echoic conditions, MAAs increased by a factor of 2 for direct sources, and 4 for simulated reflections. Neuronal discrimination was similarly quantified using ROC curves to calculate p(c) for spike discharges evoked by sources at different virtual locations. Preliminary analysis of neuronal data from anesthetized owls suggests that MAAs of the most sensitive neurons are similar to behavioral MAAs. Simultaneous measurement of neuronal and behavioral performance in awake owls is currently underway. [Work supported by the McKnight Foundation, NIH DC03925 and DC00448.]
An energy formulation for high-frequency radiation into an unbounded acoustic medium
Authors: Wang Aimin , Vlahopoulos Nickolas , Wu Kuangcheng
Published: February 2014

A new energy formulation for computing high-frequency radiation from structures into an unbounded acoustic medium is presented. The outer surface of the radiating structure is divided into elements. Surface intensity values on each element comprise the boundary conditions. Similar to the panel method [J. L. Hess and A. M. O. Smith, Calculation of Potential Flow About Arbitrary Bodies, Progress in Aeronautical Sciences Vol. 8, edited by D. Kuchemann (Pergamon, New York, 1967)] a distribution of fictitious energy sources and sinks is considered over the surface of the model. Appropriate strengths are computed for the sources and the sinks in order to satisfy the intensity boundary conditions. Once the distribution of the surface sources/sinks has been completed, the acoustic energy density and the acoustic intensity can be evaluated at any point on the surface of the radiating object, or at any field point within the acoustic medium. The new development does not require one to define damping properties for the infinite fluid and no assumptions are made about representing the radiated acoustic field as reverberant. The new developments are validated through comparisons of numerical results to analytical solutions. [Research supported by ONR, Contract No. N00014-00-I-0382.]
Determination of the frequency response functions of complex systems using spectral-based inverse substructuring approach
Authors: Lim Teik C.
Published: February 2014

The structural-acoustic response of discretely connected complex structures, such as a motor vehicle, are determined by inverting the spectral-based substructuring matrix equation in dynamic compliance form, which is classically used to compute coupled system response in terms of the dynamic characteristics of free substructures. The resulting formulation backs out the response spectra of the free substructures and the dynamic stiffness matrix representing the coupling elements. This provides a useful way to dissect a fairly complex system into two or more substructures. When analyzing the dynamic interaction between two adjacent substructures, the proposed theory can be conveniently used to express the transmissibility and path contribution functions directly as measurable coupled system response functions. Therefore, critical elements of a complex system can be identified easily without having to physically disconnect the substructures. The salient features of this approach are demonstrated using a motor vehicle example. The study specifically addresses the road noise problem by examining the sensitivity of the motor vehicle structure response to tire patch excitation. In the analysis, the body structural-acoustic functions, and excitation transfer functions between the spindle and chassis mounts are determined. [Work supported by CAVT and Ford.]
On the emergence of the Green’s function in the correlations of a diffuse field
Authors: L. Weaver Richard , I. Lobkis Oleg
Published: February 2014

It is shown that a diffuse field is not devoid of phase information, but has a correlation function equal to the Green’s function. More specifically, the cross correlation between diffuse signals in two transducers is very nearly equal to the direct response of one transducer to an impulse applied to the other. Plausibility arguments for this assertion are followed by a detailed proof. Estimates are constructed for the amount of averaging necessary before clear convergence can be expected. The assertion is then confirmed in laboratory experiments using a single impulsive ultrasonic point source to generate the diffuse field. The correlation function is constructed by averaging over the long ring down time of the resulting diffuse field. Comparison with direct responses shows that the correlation function reveals the strongest features, but smaller features do not emerge above the grain noise. The convergence is found to further improve with additional averaging over source position. [Work supported by NSF.]
Research and education program in machinery monitoring and prognosis at the University of Tennessee
Authors: Byerley Tom , Upadhyaya Belle
Published: February 2014

An effective strategy for modern plant operation and maintenance requires the integration of plant monitoring, incipient detection and isolation of faults in critical equipment, and life prediction or prognosis to enable plant personnel in making decisions about maintenance scheduling and equipment replacement. This paper presents some of the recent techniques being developed for equipment prognosis and their implementation. Examples of current techniques include data-driven modeling, wavelet analysis, and generalized trending techniques. Applications to vibration signature trending, steam generator tubing degradation trending, accelerated aging of induction motors and their prognostics will be presented, demonstrating that the tools may be used effectively in minimizing unscheduled plant downtime. In addition, the paper will discuss how The University of Tennessee (UT), through its Maintenance and Reliability Center (MRC), is developing both the above-mentioned cutting edge tools and the personnel qualified to implement them in plant operations. UT and the MRC have created additional curriculum and a certification program at the BS, MS and PhD levels in order to prepare engineering graduates with knowledge and experience in the use of these emerging techniques and tools. The MRC also performs research to further develop these new health monitoring/life prediction systems.
Geometrical deformation of the canine vocal fold induced by formalin fixation
Authors: Kimura Miwako , Tayama Niro , Chan Roger W. , Titze Ingo R.
Published: February 2014

Many existing data on vocal fold geometry are based on anatomical measurements made on histologically prepared vocal fold tissues, commonly by formalin fixation. However, the reliability and validity of these geometrical data are questionable because of the potentially significant tissue deformation associated with histological fixation. As we have shown that reliable geometrical data may be obtained on tissue samples quickly frozen with liquid nitrogen [Tayama et al., Ann. Otol. Rhinol. Laryngol. (in press)], this study attempted to quantify the geometrical deformation of vocal fold tissues fixed with formalin with respect to quick-frozen tissues. Excised canine larynges were divided into two halves along the sagittal plane, one of which was quickly frozen and the other was fixed with formalin. Coronal sections of the frozen halves were thawed and histological slides were prepared from the fixed halves. Measurements of vocal fold geometry (depth and thickness) were made on images of midmembranous coronal sections of the samples. Results showed that significant shrinkage of the vocal fold body (thyroarytenoid muscle) and considerable distortion of the vocal fold cover (free edge) were associated with formalin fixation. These artifacts should be carefully considered when any geometrical data based on histologically fixed tissues are used for laryngeal biomechanical modeling.
Finite-element analysis of passive vocal fold posturing using nonlinear muscle responses
Authors: Hunter Eric J. , Titze Ingo R. , Alipour Fariborz
Published: February 2014

A finite-element model of the passive properties of laryngeal muscles was created, based on nonlinear stress–strain responses of laryngeal muscular tissue [E. J. Hunter and I. Titze, J. Acoust. Soc. Am. 108, 2531 (2000)]. Using this finite-element muscle model as a building block, groups of muscles are used to construct a 3-D tissue model of vocal fold posturing. Vocal fold configurations were studied with assumed muscle stresses applied to the adductor–abductor muscles. Results comply, in the linear region, with earlier results on a 2-D linear model that had constant thickness [E. J. Hunter, J. Acoust. Soc. Am. 106, 2540 (1999)], but now take into account more accurately the high strains. [Work supported by NIDCD.]
Wavelet analysis of turbulence in the glottal jet flow
Authors: Alipour Fariborz
Published: February 2014

Airflow from the lungs drives the vocal folds into oscillation and exits the glottis as a turbulent jet, even though laminar flow is documented entering the glottis. Incomplete glottal closure may result in air leakage that becomes turbulent. This turbulence is thought to be the main source of breathiness in the voice. Few studies have measured degree of turbulent noise in the glottis. This turbulent noise adds significant amounts of energy to the voice signal and cannot be extracted easily without changing the voice. In this study, the turbulent jet was investigated in an excised canine larynx model with simultaneous recordings of air particle velocity, subglottal pressure, airflow rate, and EGG signal for various conditions of phonation. The velocity was measured with a constant-temperature hot-wire anemometer system. To separate the turbulence from the periodic component of the velocity signal, the technique of wavelet denoising was employed. In this method, unlike the Fourier transform which decomposes the signal into periodic components, wavelet denoising uses template matching transform to approximate the signal with different resolution or scale. Results indicate that the high resolution part contains the turbulent noise. [Work supported by NIDCD Grant No. R01 DC03566.]
Effects of syllable position on F0 and duration in Mandarin disyllabic words
Authors: Xu Ching X. , Xu Yi
Published: February 2014

In a previous attempt to fit a pitch target approximation model for F0 contours in Mandarin disyllabic words [Xu et al. (1999)], it was found that the implementation of tonal targets required two sets of values for the model parameters, one for each of the two syllable positions. This suggests that syllable position may have an effect on the production of the syllable. The present study is designed to further examine this position effect. One-hundred-eleven disyllabic words with various tonal combinations were read by native Mandarin speakers with two carrier sentences. Duration and F0 analyses were performed. Preliminary results indicate that a syllable has longer duration, higher F0, and closer-to-ideal F0 shape when it is in the first position than in the second position. These results agree with previous acoustic-phonetics findings about Mandarin disyllabic words, and together they seem to suggest that the first syllable in a disyllabic word is more stressed than the second one. Interestingly, this appears to be at odds with current phonological theories about Mandarin prosody, which maintain that the second syllable carries greater weight than the first in a disyllabic foot. Possible causes for this discrepancy will be discussed.
Experiment on pitch target approximation model for generating Mandarin F0 contour
Authors: Sun Xuejing , Xu Ching X. , Xu Yi
Published: February 2014

In the present study, an experiment was conducted to generate F0 contours for Mandarin with a pitch target approximation model proposed in Xu, Xu and Luo (1999). In this model, F0 contours in speech are assumed to be resulting from asymptotic approximation to underlying pitch targets that are either static or dynamic. The model parameters were estimated through nonlinear regression using the Levenberg–Marquardt algorithm. The speech corpus consisted of sentences from Voice of America broadcasting news. After the regression analysis, sentences were re-synthesized with the generated F0 using the TD-PSOLA technique. Preliminary results indicate that F0 contours generated by the model are close to the original both numerically and perceptually. Furthermore, most underlying pitch targets obtained through the regression analysis seem to match the models basic assumptions. However, it is also apparent that information about both higher-level linguistic functionality and additional low-level articulatory constraints is needed to account for the numerical variations in the estimated parameters. In general, the results are encouraging as they show that the model can generate close-fitting F0 contours even with strong linguistic assumptions. This suggests that it has the potential to evolve into a system with the predictive power desirable for intonation modeling.
Effects of semantic focus on Taiwanese intonation in spontaneous and read speech
Authors: Peng Shu-hui
Published: February 2014

Previous studies on prosodic effects of semantic focus indicated that sentences produced with narrow semantic focus had different intonation patterns from sentences produced with broad semantic focus. Theses effects include expansion of the pitch range for the focused words and compression of the pitch range for unfocused words in sentences produced with narrow focus. The present study examined the prosodic effects of semantic focus on the intonation patterns of Taiwanese by comparing pragmatically controlled spontaneous speech with read speech. Spontaneous speech was obtained from the dialogue between pairs of speakers participating in a game. The same speakers were asked to read scripts prepared from the original dialogues. Both the read and spontaneous versions were analyzed to show prosodic phrasing and global pitch shapes for different types of sentences. Sentences produced with a narrow focus in the spontaneous version were compared with their read counterparts produced with a broad focus for expansion and compression of pitch range and other tonal features.
A comparison of conversational and clear speech versions of three Green Mong tones
Authors: Andruski Jean E. , Turner Scott
Published: February 2014

Green Mong has a phonological tone system that incorporates both fundamental frequency (F0) and phonation-type distinctions. Previous work using discriminant analyses examined three tones which have similar F0 contours, but which are characterized by the distinctive use of breathy, creaky and modal phonation [Andruski and Ratliff, JIPA (in press)]. Results indicated that the relative amplitude of lower and higher harmonics (measured as the H1–H2 amplitude difference) most reliably discriminates productions of these three tones. The contributions of jitter, duration, F0 and shimmer were also significant. This study compares the same three tones in one male speaker’s clear speech and conversational speech productions. Clear speech is typically more intelligible than conversational speech. The increase in intelligibility appears to result from exaggeration of acoustic cues that contribute to phonological distinctions in the language. The question explored here is the extent to which cues relating to phonation type are exaggerated in these three tones, as compared to F0 and F0 contour cues. Results of acoustic analyses of clear and conversational speech tokens will be presented, as well as results of a discriminant analysis using the discriminant functions generated in the previous study from the productions of six other speakers.