bluuebunny/crossref_metadata_2025 huggingface dataset:
Relativistically expanding spherical emitters
Authors: Eriksen Erik , Gro/n O/yvind
Published: July 2002

We demonstrate several relativistic effects associated with expanding spherical sources of light. We show that if the surface lights up for say a month, it may be seen for a few seconds only if it expands sufficiently fast. Also it is demonstrated how the observed properties of the light source are modified by aberration and the Doppler effect. The apparent luminosity as a function of time is calculated and shown graphically. Modifications due to the motion of the light source away from the observer are calculated.
Energy spectrum of a confined two-dimensional particle in an external magnetic field
Authors: Rosas R. , Riera R. , Marı́n J. L. , León H.
Published: July 2002

The energy spectrum of a particle confined within a circle in the presence of an external magnetic field perpendicular to the plane of confinement is studied both exactly and approximately by the quasiclassical formalism (Wentzel–Kramers–Brillouin). For pure spatial confinement (without magnetic field) the energy spectrum for states other than the ground state is twofold degenerate, while in the case of pure magnetic confinement the spectrum shows the infinite-fold degeneration, typical of Landau states. For both types of confinement, the latter infinite-fold degeneration is lifted due to spatial confinement. Interestingly enough, for a given ratio between spatial and magnetic confining lengths, the magnetic flux is quantized. The conditions for the quantization of the flux are established; the nature and peculiarity of the energy spectrum are also discussed.
Electromagnetic interaction momentum and simultaneity
Authors: Coı̈sson R. , Guidi G.
Published: July 2002

Using a simple example of two interacting electric charges, we show that different observers see a different distribution of momentum between the particles and the electromagnetic field, and we discuss how this is related to the relativity of simultaneity (which has to be taken into account even if it seems that we are in a “nonrelativistic” approximation).
Monte Carlo image representation
Authors: de Aquino Verı́ssimo M. , Aguilera-Navarro Valdir C. , Goto Mario , Iwamoto Hiromi
Published: July 2002

A simple method for representing probabilistic systems visually based on a Monte Carlo approach is discussed. Applications are given for the hydrogen atom and the propagation of wave functions associated with tunneling through a potential barrier.
Tight-binding-like expressions for the continuous-space electromagnetic coupling Hamiltonian
Authors: Boykin Timothy B.
Published: July 2002

In quantum mechanics texts one sometimes encounters the unqualified (and generally untrue) assertion that the solution of the Schrödinger equation for a charged particle in the presence of an externally applied vector potential can be found from that in the absence of the vector potential simply via multiplication with an r-dependent phase factor. The confusion caused by this assertion is only increased when one examines the expression for the matrix elements of the Hamiltonian including electromagnetic interactions (via the vector potential) appropriate for a tight-binding model, for this expression indeed takes a different form from that of the usual minimal coupling Hamiltonian in continuous space. Motivated by the tight-binding (i.e., discretized) result, we derive its continuous-space analog. We show that the aforementioned perplexing assertion actually arises from a confusion between the wavefunction and the matrix elements of the continuous-space Hamiltonian in the position basis and discuss both the tight-binding and continuous-space expressions.
Photorefractive polymers: Materials science, thin-film fabrication, and experiments in volume holography
Authors: McGee David J. , Matlin Mark D.
Published: July 2002

When exposed to low power laser light, photorefractive materials can function as dynamic diffraction gratings, making them attractive for applications in holography and optical image processing. Conventional crystalline photorefractive materials are useful in demonstrations of basic nonlinear optical phenomena at the advanced undergraduate level, although the fabrication of such crystals is beyond the reach of most undergraduate facilities. Within the last five years, however, polymeric photorefractive materials have been developed that can be fabricated by collaborative teams of undergraduate physics and chemistry students. We have found that the study of photorefractive polymers provides an excellent framework to emphasize connections among optics, chemistry, and materials science at a level accessible to undergraduates. We provide an overview of photorefractive polymers, describe the fabrication of a typical photorefractive polymeric system, and discuss experiments in volume holography.
Note on solving for the dynamics of the Universe
Authors: Sales Lima José Ademir
Published: July 2002

In a recent article, Faraoni proposed an alternative procedure to solve the Friedman–Lemaître–Robertson–Walker cosmological equations. The basic result of that paper was obtained long ago through a different approach, which seems to be little known and deserves closer attention due to its pedagogical interest. The broad importance of this method is readily recognized by examining some additional cases not considered by Faraoni. Its instructive potential for introductory courses on cosmology has been positively verified by the author in many lectures during the last decade.
The calculated photon: Visualization of a quantum field
Authors: Ligare Martin , Oliveri Ryan
Published: July 2002

We calculate spatial localization and phase properties of spontaneously emitted photons. Our model is simple yet fully quantized: the emitting atom is a two-level atom located in a one-dimensional multimode optical cavity. Although the photon state vector does not have a position-space representation, the expectation value of the square of the electric field operator (intensity) is spatially localized and this pattern shifts at the speed of light. The emitted photon exhibits classical-like phase properties in the intensity expectation value when it “interferes with itself” after reflection. The phase properties of the emitted radiation are also evident at times sufficiently long for the radiation to have returned to the emitting atom before the decay of excited atomic state is complete.
Relativity of representations in quantum mechanics
Authors: de la Torre A. C.
Published: July 2002

Only the position representation is used in introductory quantum mechanics and the momentum representation is not usually presented until advanced undergraduate courses. To emphasize the relativity of the representations of the abstract formulation of quantum mechanics, two examples of representations related to the operators αX+(1−α)P and 12(XP+PX) are presented.
Electrons, Stern–Gerlach magnets, and quantum mechanical propagation
Authors: Batelaan H.
Published: July 2002

Quantum corrections to Newton’s equations are obtained and used to illustrate that classical dynamics is embedded explicitly in quantum dynamics. Originally, the resultant set of dynamical equations has been used to shed light on quantum chaos. We show that the method can provide insight into the dynamics of free particles and the harmonic oscillator. We then use it to determine whether Stern–Gerlach magnets can be constructed for free electrons.
Resource Letter: RA-1: Risk analysis
Authors: Wilson Richard
Published: July 2002

This Resource Letter provides an introduction to the literature on risk analysis. It starts with a discussion of how risks are calculated with roughly decreasing reliability: from historical data; new risks calculated by an understanding of engineering processes and new risks calculated by analogies with other processes. The Resource Letter then lists journals and books and discusses how risks are perceived, uncertainty, risks at low doses, major public misconceptions, the costs to reduce hazards, and the way the courts handle issues of risk.
An invertibility paradox
Authors: Binder P.-M. , Pedraza J. M. , Garzón S.
Published: July 2002

The chaotic volume-preserving standard map is used to illustrate the invertibility paradox, which is related to the reversibility paradox of the microscopic foundations of thermodynamics. The new paradox, whose resolution relies exclusively on phase-space arguments, gives insight into Boltzmann’s original resolution of the reversibility paradox.
Phase-plane analysis of perihelion precession and Schwarzschild orbital dynamics
Authors: Dean Bruce
Published: July 2002

A calculation of perihelion precession is presented that utilizes a phase-plane analysis of the general relativistic equations of motion. The equations of motion are reviewed in addition to the phase-plane analysis required for the calculation. “Exact” phase planes for orbital dynamics in the Schwarzschild geometry are discussed, and bifurcations are identified as a dimensionless parameter involving the angular momentum is varied.
“Now Boarding: The Flight from Physics” David Goodstein’s acceptance speech for the 1999 Oersted Medal presented by the American Association of Physics Teachers, 11 January 1999
Authors: Goodstein David
Published: July 2002

All across the country, the number of students majoring in physics is said to be at its lowest point since Sputnik, 40 years ago. The most important role of the college physics course today seems to be to weed out a few poor souls who might otherwise make it to medical school or some other kind of quasi-scientific training. If the profession of teaching physics were a business, we would be filing for bankruptcy. On the other hand, our assets include nothing less than the wisdom of the ages, the most important part of the body of human knowledge. Mastery of that knowledge, a fundamental grasp of how the world works, ought to be the best possible preparation for the coming century. Rather than being an endangered species, the physics major should be the wave of the future, but it isn’t, at least not yet. This talk will analyze how we got ourselves into this fix, and suggest what is needed to get ourselves out of it.
A video technique for the quantitative analysis of the Poisson spot and other diffraction patterns
Authors: Wein G. Robert
Published: July 2002

A new approach is presented for the observation and analysis of diffraction phenomena. Using the discussed procedures, direct comparison between measured light intensity and theoretical predictions is possible. A modified version of a Poisson spot experiment where the resulting diffraction pattern is recorded by a Sanyo vidicon camera is presented. A double slit experiment is also discussed, demonstrating the quantitative possibilities while addressing detector linearity. A video signal is connected directly to a computer and analyzed using public domain software. This is an excellent arrangement for demonstrations, student labs, or a more general diffraction experiment.
Radiation reaction and runaway solutions in acoustics
Authors: Templin Jacques D.
Published: July 2002

A solution is given to the acoustical field equations when the source of the field is a sphere undergoing radial pulsations. This solution, which is exact within the usual linear approximation, is used to investigate two topics of interest in electrodynamics. The first is the indirect calculation of the radiation reaction. An alternative to the usual method is presented which does not involve equating the average radiated power to the average work done by the source. It is also shown that the acoustic field separates into two, a radiating field and a nonradiating retarded field, with the latter field possessing some interesting properties. The second topic is the demonstration that runaway solutions can occur when the acoustic source is mechanically coupled to the acoustic field. Using the exact solution, it is shown that this is an artifact arising from the inappropriate use of perturbation theory. The paper also discusses possible applications to electrodynamics.
Paraxial imaging: Gaussian beams versus paraxial-spherical waves
Authors: Almeida A. M. , Nogueira E. , Belsley M.
Published: July 2002

The features of Gaussian beam imaging are not generally well appreciated. Here we suggest that it is convenient to view a Gaussian beam as a generalization of a paraxial-spherical source with a complex source location. This approach allows one to show that the modification of the geometric optics thin lens equations necessary to adequately describe the imaging of a Gaussian beam is due to the latter being a coherent source of finite extent. An experiment is outlined which highlights the differences between simple geometric and Gaussian beam imaging. Our approach gives students a firm conceptual foundation from which to discuss the concept of spatial coherence in laser beams.
The flight of a balsa glider
Authors: Waltham Chris
Published: July 2002

A simple analysis is performed on the flight of a small balsa toy glider. All the basic features of flight have to be included in the calculation. Key differences between the flight of small objects like the glider, and full-sized aircraft, are examined. Good agreement with experimental data is obtained when only one parameter, the drag coefficient, is allowed to vary. The experimental drag coefficient is found to be within a factor of 2 of that obtained using the theory of ideal flat plates.
Short proof of Jacobi’s identity for Poisson brackets
Authors: Lemos Nivaldo A.
Published: July 2002

Making use of the theory of infinitesimal canonical transformations, a concise proof is given of Jacobi’s identity for Poisson brackets.
The loop-gas approach to Bose–Einstein condensation for trapped particles
Authors: Mullin William J.
Published: July 2002

We examine Bose–Einstein condensation (BEC) for particles trapped in a harmonic potential by considering it as a transition in the length of permutation cycles that arise from wave-function symmetry. This “loop-gas” approach was originally developed by Feynman in his path-integral study of BEC for a homogeneous gas in a box. For the harmonic oscillator potential it is possible to treat the ideal gas exactly so that one can easily see how standard approximations become more accurate in the thermodynamic limit (TDL). One clearly sees that the condensate is made up of very long permutation loops whose length fluctuates ever more widely as the number of particles increases. In the TDL, the Wentzel–Kramers–Brillouin approximation, equivalent to the standard approach to BEC, becomes precise for the noncondensate; however, this approximation neglects completely the long cycles that make up the condensate. We examine the exact form for the density matrix for the system and show how it describes the condensate and behaves in the TDL.
Resource Letter BD-1: Bubble dynamics
Authors: Godwin R. P. , Chapyak E. J.
Published: July 2002

This Resource Letter provides a tutorial on bubble and cavitation dynamics and an introduction to its extensive literature.
Photon polarization measurements without the quantum Zeno effect
Authors: Kidambi V. , Widom A. , Lerner C. , Srivastava Y. N.
Published: July 2002

We consider a photon beam incident on a stack of polarizers as an example of a von Neumann projective measurement, theoretically leading to the quantum Zeno effect. The Maxwell theory (which is equivalent to the single-photon Schrödinger equation) describes measured polarization phenomena, but without recourse to the notion of a projective measurement.
Bound states of a uniform spherical charge distribution—revisited!
Authors: Tiburzi Brian C. , Holstein Barry R.
Published: July 2002

In this note, we revisit modeling the nucleus as a uniformly charged sphere in order to examine finite nuclear size effects on atomic binding energies. We use nonrelativistic quantum mechanics to extract binding energies of a negatively charged lepton bound by a uniform-sphere potential. Energies are determined by using MATHEMATICA to match interior and exterior solutions at the nuclear radius. Muonic lead and tin binding energies are found, as are their fine-structure transition energies, and compared with experimental data. In the course of our reinvestigation of this problem, we came upon several subtle features of using infinite (especially asymptotic) series for numerical evaluation. Effective handling of these features is made practical both by using certain analytic transformations and the powerful computer programs currently available. We believe that these technical observations are of value to a wider class of problems beyond the ones considered in detail in this paper.
Modeling piezoceramic transducer hysteresis in the structural vibration control problem
Authors: Lee S.-H. , Royston T. J.
Published: July 2002

To appropriately assess, compensate for and/or potentially utilize piezoceramic transducer nonlinearities, reversible and irreversible, in the structural vibration control problem, a suitable theoretical framework is needed. In this study such a framework is developed and experimentally evaluated for a basic pedagogical structural vibration control system, the simply supported beam with a monolithic piezoceramic wafer bonded to it that can be both electrically shunted and/or driven by an external electric source. A constitutive model for the piezoceramic (PZT) wafer by itself is formulated that incorporates reversible (higher order polynomial) and irreversible (hysteretic) dielectric nonlinearity. An identification scheme for the model is validated experimentally. The nonlinear PZT model is then integrated into the coupled dynamic equations of the overall system consisting of the simply supported beam and the electrically shunted PZT wafer bonded to the beam. The theoretical system model is then evaluated by comparing its predictions to experimental results. Energy loss and transduction mechanisms in the integrated structural system are investigated.
The feasibility of maximum length sequences to reduce acquisition time of the middle latency response
Authors: Bell S. L. , Allen R. , Lutman M. E.
Published: July 2002

Maximum length sequences (MLS) have been used to improve the signal-to-noise ratio (SNR) of otoacoustic emissions [Thornton, J. Acoust. Soc. Am. 94, 132–136 (1993)] and the auditory brainstem response [Thornton and Slaven, Br. J. Audiol. 27, 205–210 (1993)]. By implication, a shorter recording time would be required to give equal signal-to-noise ratio (SNR). This study aimed to establish whether it is also possible to improve the SNR of the auditory-evoked potential termed the middle latency response (MLR) using maximum length sequences (MLS). Recordings of 180 s each were made using a conventional recording rate and MLS rates of 42, 89, and 185 clicks/s. Three different stimulus intensities were used in the range 30 to 70 dB nHL. The rate of 89 clicks/s was found to produce most improvement in SNR for both the Na–Pa region of the MLR and the Na–Pb region. This improvement in SNR using MLS implies that an MLS rate of 89 clicks/s would produce a fourfold reduction in recording time for equal SNR over conventional recording for the Pa–Nb region of the MLR at a stimulus intensity of 70 dB nHL. The latency of the Nb wave was found to reduce significantly using MLS. An MLR could not be recorded from every subject in this study, but more subjects had an identifiable response for MLS than for conventional recordings. Use of MLS to record the MLR appears to offer the potential for reduction in test time and better wave identification.
Elevation localization and head-related transfer function analysis at low frequencies
Authors: Algazi V. Ralph , Avendano Carlos , Duda Richard O.
Published: July 2002

Monaural spectral features due to pinna diffraction are the primary cues for elevation. Because these features appear above 3 kHz where the wavelength becomes comparable to pinna size, it is generally believed that accurate elevation estimation requires wideband sources. However, psychoacoustic tests show that subjects can estimate elevation for low-frequency sources. In the experiments reported, random noise bursts low-pass filtered to 3 kHz were processed with individualized head-related transfer functions (HRTFs), and six subjects were asked to report the elevation angle around four cones of confusion. The accuracy in estimating elevation was degraded when compared to a baseline test with wideband stimuli. The reduction in performance was a function of azimuth and was highest in the median plane. However, when the source was located away from the median plane, subjects were able to estimate elevation, often with surprisingly good accuracy. Analysis of the HRTFs reveals the existence of elevation-dependent features at low frequencies. The physical origin of the low-frequency features is attributed primarily to head diffraction and torso reflections. It is shown that simple geometrical approximations and models of the head and torso explain these low-frequency features and the corresponding elevations cues.
Orthogonal acoustical factors of a sound field in a bamboo forest
Authors: Sakai Hiroyuki , Shibata Shozo , Ando Yoichi
Published: July 2002

To investigate the acoustical quality of a sound field in a bamboo forest, acoustical measurements were conducted to obtain orthogonal acoustical factors of the sound field. These results are compared with previous results for a sound field in an ordinary forest [H. Sakai, S. Sato, and Y. Ando, J. Acoust. Soc. Am. 104, 1491–1497 (1998)]. The IACC, which is defined as a maximum value of the normalized interaural cross-correlation function between signals at the ears, was 0.07 (4 kHz) and 0.16 (2 kHz) at positions 20 and 40 m from the source, respectively. These values are much better than those in the previously investigated forest. The measured subsequent reverberation time Tsub was up to 1.5 s in the frequency range above 1 kHz at the position 40 m from the source. For certain music sources with higher frequency components, therefore, sound fields in a bamboo forest have excellent acoustic properties.
Ultrasonic properties of random media under uniaxial loading
Authors: Insana M. F. , Hall T. J. , Chaturvedi P. , Kargel Ch.
Published: July 2002

Acoustic properties of two types of soft tissue-like media were measured as a function of compressive strain. Samples were subjected to uniaxial strains up to 40% along the axis of the transducer beam. Measurements were analyzed to test a common assumption made when using pulse-echo waveforms to track motion in soft tissues—that local properties of wave propagation and scattering are invariant under deformation. Violations of this assumption have implications for elasticity imaging procedures and could provide new opportunities for identifying the sources of backscatter in biological media such as breast parenchyma. We measured speeds of sound, attenuation coefficients, and echo spectra in compressed phantoms containing randomly positioned scatterers either stiffer or softer than the surrounding gelatin. Only the echo spectra of gel media with soft scatterers varied significantly during compression. Centroids of the echo spectra were found to be shifted to higher frequencies in proportion to the applied strain up to 10%, and increased monotonically up to 40% at a rate depending on the scatterer size. Centroid measurements were accurately modeled by assuming incoherent scattering from oblate spheroids with an eccentricity that increases with strain. While spectral shifts can be accurately modeled, recovery of lost echo coherence does not seem possible. Consequently, spectral variance during compression may ultimately limit the amount of strain that can be applied between two data fields in heterogeneous media such as lipid-filled tissues. It also appears to partially explain why strain images often produce greater echo decorrelation in tissues than in commonly used graphite–gelatin test phantoms.
Effects of frequency-shifted auditory feedback on voice F0 contours in syllables
Authors: Donath Thomas M. , Natke Ulrich , Kalveram Karl Th.
Published: July 2002

Previous studies have shown that, during continuous vocalization, voice fundamental frequency (voice F0) is modified by frequency-shifted auditory feedback. In this study, the effects of frequency-shifted auditory feedback on voice F0 contours were determined for the first two syllables of the nonsense word [tatatas]. Results show that voice F0 is auditorily controlled with a long latency and responses are not interrupted by the onset and offset of phonation itself. Furthermore, after-effects were found in voice F0 in trials after the termination of the frequency shift, which indicates that the response persists for several seconds. It is argued that the purpose of the auditory-vocal system is not to control voice F0 precisely within single syllables, but rather on a supra-segmental level in the context of prosody.
Monaural sound localization revisited
Authors: Wightman Frederic L. , Kistler Doris J.
Published: July 2002

Research reported during the past few decades has revealed the importance for human sound localization of the so-called “monaural spectral cues.” These cues are the result of the direction-dependent filtering of incoming sound waves accomplished by the pinnae. One point of view about how these cues are extracted places great emphasis on the spectrum of the received sound at each ear individually. This leads to the suggestion that an effective way of studying the influence of these cues is to measure the ability of listeners to localize sounds when one of their ears is plugged. Numerous studies have appeared using this monaural localization paradigm. Three experiments are described here which are intended to clarify the results of the previous monaural localization studies and provide new data on how monaural spectral cues might be processed. Virtual sound sources are used in the experiments in order to manipulate and control the stimuli independently at the two ears. Two of the experiments deal with the consequences of the incomplete monauralization that may have contaminated previous work. The results suggest that even very low sound levels in the occluded ear provide access to interaural localization cues. The presence of these cues complicates the interpretation of the results of nominally monaural localization studies. The third experiment concerns the role of prior knowledge of the source spectrum, which is required if monaural cues are to be useful. The results of this last experiment demonstrate that extraction of monaural spectral cues can be severely disrupted by trial-to-trial fluctuations in the source spectrum. The general conclusion of the experiments is that, while monaural spectral cues are important, the monaural localization paradigm may not be the most appropriate way to study their role.
Computing effective reflection coefficients in layered media
Authors: Berman David H.
Published: July 2002

Computations are presented which show that the effective reflection and transmission coefficients for a rough interface embedded in a layered medium can differ significantly from the mean reflection and transmission coefficients computed for the same rough interface when it separates two homogeneous half-spaces. These differences are large when the correlation length of the roughness is long compared to the skip distance of rays associated with normal modes in the layered medium. Otherwise, these differences may be generally neglected. However, increasing the rms roughness decreases the ratio of correlation length to skip distance at which the effect of the layering is important. The case of a Pekeris waveguide with a rough fluid–fluid interface and the case of a rough Dirichlet surface bounding an upwardly refracting medium are considered.
Structural and acoustical wave interaction at a wedge-shaped junction of fluid-loaded plates
Authors: Norris A. N. , Osipov A. V.
Published: July 2002

Two semi-infinite elastic plates are joined along a line forming a wedge structure with unilateral fluid loading in the outer sector of the two plates. The structure is modeled using thin plate theory, allowing freely propagating flexural and longitudinal waves. The junction is mechanically connected with an applied force and moment acting there to simulate a possible internal connection. The general two-dimensional solution is described for incidence of time harmonic structural or acoustical waves. The total pressure is expressed as a Sommerfeld integral, the integrand comprising Malyuzhinets functions and particular solutions of certain difference equations. The junction conditions reduce to a system of four linear equations. Numerical examples indicate the coupling between the modes for welded steel plates in water. Acoustic plane-wave incidence on the flattest junction considered is converted almost equally, in terms of energy, among diffracted flexural and longitudinal waves. The coupling to flexural energy increases with the angle of the water wedge sector, at the expense of the longitudinal energy which vanishes in the limit as the water occupies the entire domain except for a strip comprising the two plates. An incident longitudinal wave generates relatively little acoustic sound for all wedge angles considered, with most of its energy redistributed among structural modes. The acoustical diffraction is generally greater for flexural incidence. Comparison with the dry structural diffraction coefficients indicates that the fluid loading effects for steel and water configurations can be significant for frequencies less than one-fifth of the coincidence frequency, but are small for higher frequencies.
A study on beam optimizing of wideband stagger-tuned array
Authors: Chen Qimin , Bao Shanhui , Zang Xiaofei , Wei Wei , Guo Jianzhong
Published: July 2002

A new method is presented for designing the wideband stagger-tuned array (WSTA) which was first put forward by Zhang et al. [Chin. J. Med. Instrum. 9(3), 5–10 (1985)]. Based on the beam-equivalence principle and the sampling-composing law, this method is simple in calculation and good in precision. An optimized array scheme and expected beam pattern can be obtained by simulating a given beam pattern. Within ±20°, the simulative error is below 1%. The experiment was conducted and the results showed excellent agreement with simulation and calculation for the major-lobe scope.
The frequency response of the ER-2 speaker at the eardrum
Authors: Whitehead M. L. , Simons I. , Stagner B. B. , Martin G. K.
Published: July 2002

Distortion-product otoacoustic emissions are often measured using ER-2 speakers and the ER-10B microphone probe (Etymotic Research). The frequency response at the eardrum of the ER-2 speaker used in this configuration has not been described. An indirect estimate of the average eardrum frequency response of the ER-2 speaker used with the ER-10B probe has been obtained. The average eardrum frequency response varies less than ±5 dB from 0.3 to 10 kHz.
An adiabatic normal mode solution for the benchmark wedge
Authors: Tindle C. T. , Zhang Z. Y.
Published: July 2002

An adiabatic normal mode solution for the benchmark wedge is described for both fluid and solid attenuating ocean bottoms. The continuous mode contribution is treated as a sum of leaky modes. Each trapped mode changes smoothly into a leaky mode as the water depth decreases. The Pekeris branch line integral can be ignored if an approximate mode normalization is used when the normal mode pole approaches the branch point.
Pitch and loudness estimation for single and multiple pulse per period electric pulse rates by cochlear implant patients
Authors: Busby P. A. , Clark G. M.
Published: July 2002

Numerical estimates of loudness and pitch for electric pulse rates were obtained from 14 patients using the 22 electrode cochlear implant manufactured by Cochlear Limited. Six patients were postlinguistically deafened adults, and eight patients were adults and children who became deaf very early in life. Comparisons were made between two types of pulse rate patterns. The SPP pulse pattern presented a single pulse every period, the inverse of the pulse rate. The MPP pulse pattern presented multiple pulses in the first half of the period, using a rate of 1000 pulses/s, with no stimulation in the second half of the period. The pulse rates used for the SPP and MPP pulse patterns were 71.4–500 pulses/s, which corresponded to periods of 14–2 ms. For the SPP pulse pattern, the total number of pulses over the duration of the stimulus increased with increases in pulse rate, while for the MPP pulse pattern, the total number of pulses remained constant. Pitch and loudness estimates were obtained from the postlinguistically deafened patients for the SPP and MPP pulse patterns, and from the early-deafened patients for the MPP pulse pattern. Loudness estimates for the SPP pulse pattern increased with increases in pulse rate for all postlinguistically deafened patients. Loudness estimates for the MPP pulse pattern decreased with increases in pulse rate for three of the six postlinguistically deafened patients and for six of the eight early-deafened patients. For the other patients (three postlinguistically deafened and two early-deafened), loudness estimates marginally increased with increases in pulse rate. Pitch estimates for the SPP and MPP pulse patterns increased with increases in pulse rate for the six postlinguistically deafened patients. For the early-deafened patients, pitch estimates for the MPP pulse patterns increased with increases in pulse rate for only five of the eight patients. For the other three early-deafened patients, pitch estimates were similar to the loudness estimates and decreased with increases in pulse rate.
Activity of primary auditory neurons in the cochlear ganglion of the emu Dromaius novaehollandiae: Spontaneous discharge, frequency tuning, and phase locking
Authors: Manley Geoffrey A. , Köppl Christine , Yates Graeme K.
Published: July 2002

The spontaneous and pure-tone sound-driven activity of primary auditory units was recorded in the cochlear ganglion of emu chicks aged between post-hatching days 1 and 14. Spontaneous activity tended to increase both with the chick’s age and as a function of the unit’s characteristic frequency (CF). The CF of 887 units ranged from 0.04 to 4 kHz, the thresholds down to 0 dB SPL. Although the CF range did not change, the thresholds improved with age during the first two weeks after hatching, by up to 18 dB at the highest frequencies. The threshold spread between units of similar CF in single animals was up to 60 dB. Rate-threshold tuning-curve symmetry varied with CF. In low-frequency units, the slope of the low-frequency tuning-curve flank was on average steeper than the high-frequency flank, whereas for high-frequency units, the reverse was true. Units of CF >0.5 kHz generally showed low-frequency “tails” similar to those seen in mammalian primary auditory fibers. The mean tuning-curve frequency selectivity increased with CF. For units of CF >0.2 kHz, thresholds were moderately correlated with tuning-curve frequency selectivity. Significant phase locking was observed up to about 4 kHz, the corner frequency of phase locking being at 1.15 kHz.
Prediction of sound-pressure level in an occupied enclosure
Authors: Tang S. K. , Chan Daniel W. T. , Chan K. C.
Published: July 2002

In a room with inadequate sound absorption, occupants may suffer from low speech intelligibility due to the high noise level resulting from human activities. For effective communication, they tend to raise their voices. In the present study, a method which takes into account the effect of raising voices is derived to predict the variation of A-weighted sound level inside an enclosure in which the number of occupants changes with time. Site measurements are also performed in a canteen of capacity around 250. The model predicts the variations of A-weighted sound levels with a number of occupants with sufficient accuracy for engineering applications.
In-car noise reduction for a newly developed home elevator
Authors: Zhou Y-Q.
Published: July 2002

A serious in-car noise problem was found for our newly developed home elevator, which was designed using low-cost and light-weight material for its cab panels. After a series of real-run measurements, the main source for in-car noise was identified to be the car panel vibration. Numerical analysis using the FEM method has also been performed for understanding the panel dynamic behaviors. The cab panels were redesigned based on measurement and numerical analysis results. The newly designed cab gives a nearly 9-dB in-car noise reduction, which enables that type of home elevator to be sold in the Japanese market as a Nippon Otis product. [See NOISE-CON Proceedings for full paper.]
Transient waves in a periodic stack: Experiments and comparison with analysis
Authors: El-Raheb Michael , Tham Reinhard
Published: July 2002

Transient waves were initiated by allowing a thick PMMA disk to strike a periodic stack of ceramic layers bonded by thin weak silicone rubber layers. Pressure at interfaces of ceramic and bond layers was measured by carbon gauges along the centerline of the stack. Comparison of experimental histories with those from a 1-D analysis [J. Acoust. Soc. Am. 94, 172–184 (1993)] and a 2-D axisymmetric analysis [J. Acoust. Soc. Am. 99, 3513–3527 (1996)] reveals that waves propagate two-dimensionally and that flexure of the ceramic layers controls attenuation and shape of compressive wave of first arrival. Viscoelasticity of the bond material sharply reduces tensile stresses.
Identification of multidimensional stimuli containing speech cues and the effects of training
Authors: Christensen Laurel A. , Humes Larry E.
Published: July 2002

The purpose of this study was to determine how listeners with normal hearing make use of cues from multiple, independent stimulus dimensions when classifying synthesized stimuli containing acoustic cues found in speech. Listeners classified synthesized stimuli that differed on three independent and discriminable dimensions. The three dimensions of the stimuli included: (1) the fricative spectrum center frequency; (2) the slope of the frequency transition; and (3) the duration of the temporal gap. Each of the three dimensions could take on one of three possible values. Twenty-seven stimuli were synthesized using all possible combinations of the values on the three dimensions. Multidimensional scaling of paired-comparison similarity judgments confirmed the existence of three perceptual dimensions. Listeners were then trained to classify three exemplar stimuli as “circle,” “triangle,” and “square,” respectively. Following this training, subjects classified all 27 stimuli as “circle,” “triangle,” and “square.” From this it was determined how each listener’s attention was distributed among the dimensions. Results indicated the listeners did not pay equal attention to the three stimulus dimensions. In addition, it was demonstrated that it was possible to train a listener to attend to a dimension that was not previously used to classify the stimuli.
Acoustical characterization of absorbing porous materials through transmission measurements in a free field
Authors: Amédin Celse K. , Champoux Yvan , Berry Alain
Published: July 2002

Various results are presented to experimentally validate the theoretical modeling of the acoustic radiation of a circular piston through a thin layer of porous absorbing material, as worked out by Amédin et al. [J. Acoust. Soc. Am. 98, 1757–1766 (1995)]. This theoretical modeling is subsequently exploited for the development of an acoustical characterization method for porous absorbing materials. The method is based on acoustical pressure measurements taken at two different positions in an open baffled tube radiating into the material to be characterized and at a given point above the material, and on an iterative process of numerical resolution. The reliability of the method is evaluated by means of numerical simulations and by comparisons using the two-layer method in an impedance tube [J. Acoust. Soc. Am. 74, 1577–1582 (1983)]. The preliminary tests show that the new method can be used to experimentally characterize the specific acoustic impedance and the propagation constant of porous absorbing materials. Its use will be possible for the acoustical characterization of porous absorbing materials in situ.
Surface wave formation at an impedance discontinuity
Authors: Stinson Michael R. , Daigle Gilles A.
Published: July 2002

The formation of air-coupled acoustic surface waves over an impedance plane has been studied in a series of model experiments. Surface waves were generated at an impedance discontinuity on a flat surface, one section of the surface being acoustically hard, and the other composed of an array of small cavities with an effective impedance suitable for surface wave propagation. A point source of sound (800 Hz–2 kHz) was located on the hard surface and the vertical sound pressure distribution measured over the impedance plane, at various distances. The formation, propagation, and decay of the surface waves were clearly observed. The measured pressure distributions are consistent with the theoretical formulation of Rasmussen [J. Sound Vib. 84, 598–602 (1982)] for propagation of sound over an impedance jump. An alternative formulation for the case of plane waves incident at grazing angles to a surface has been described by McAninch and Myers [AIAA 26th Aerospace Sciences Meeting, paper AIAA-88-0179 (1988)]. This simpler formulation has been found to be consistent with our measurements, and with the Rasmussen theory, when the distance between source and impedance discontinuity is sufficiently large.
Comodulation masking release: The effect of the characteristics of noise bands presented before and after a signal
Authors: Mendoza Lee , Hall Joseph W. , Grose John H.
Published: July 2002

CMR was measured as a function of masker duration in three conditions. In the first condition, a 400-ms pure-tone signal was presented in the temporal center of comodulated masking bands ranging in duration from 400 to 1200 ms. No effect of masker duration was observed: CMR was equivalent to that found in continuous maskers. In the second condition, continuous independent bands identical in spectra to the comodulated bands were gated off before, and on following, the comodulated bands. The presence of the independent bands reduced CMR considerably. Increasing the duration of the comodulated bands increased CMR somewhat; however, CMR was still substantially smaller than that observed without the independent bands. In the third condition, band limited noise spanning the same range as the comodulated bands was substituted for the independent bands. The bandlimited noise had little effect on CMR. In a second experiment, independent bands were gated on for various durations preceding spectrally identical 400-ms comodulated bands masking a 400-ms signal. As the duration of the independent bands increased, CMR decreased. Based on these results, it appears that CMR is not entirely the result of processing only information concurrent with the signal. [Work supported by NIH-NIDCD and Louisiana Board of Regents.]
Observation of the brass player’s lips in motion
Authors: Ayers R. Dean
Published: July 2002

Mouthpieces with flat windows are used to examine the lip reed’s motion during the steady parts of notes played on brass instruments. Magnified stroboscopic images show different parts of the upper lip moving out of phase with each other. Sighting directly along the channel between the lips, one can observe a Rayleigh wave propagating downstream in the flesh of the upper lip. Downward crests of this disturbance reach maximum amplitude at the downstream end of the channel, where they provide most of the valving action on the air flow. The lower lip moves more as a lumped element, and mostly in the longitudinal direction. A computer model for this behavior will be complicated and may not show much improvement over the two-dimensional model of Adachi and Sato [J. Acoust. Soc. Am. 99, 1200–1209 (1996)]. Of potentially greater value is a more accurate mental image for performers. Muscles controlling the embouchure just establish the boundary conditions for the motion of a thin, passive layer of flesh. This knowledge may help beginners to avoid such practices as jamming the mouthpiece against the lips and tensing muscles against each other unnecessarily.
A finite element analysis of an interferometric optical fiber hydrophone
Authors: Im Jong-in , Roh Yong-rae
Published: July 2002

This paper investigates the influence of structural parameters on the performance of an optical fiber wound mandrel hydrophone by using the finite element method (FEM). A hydrophone should exhibit the highest possible sensitivity, the widest possible flat frequency response, and an omni-directional sensitivity pattern within the frequency range. The parameters studied included the mandrel geometry, the thickness of the molding coated over the fiber, and the material properties of the constituent parts of the hydrophone. The analysis results showed that the pressure sensitivity of a hydrophone increases in relation to the length of the mandrel and the thickness of the molding. A higher pressure-sensitivity also requires a mandrel or molding material with a relatively low Young’s modulus and Poisson’s ratio. On the other hand, the flat frequency response of a hydrophone increases when either the mandrel length is shortened or the mandrel material is hardened. The omni-directional characteristic is also improved with a shorter mandrel. Therefore, a hydrophone with the best performance must balance the tradeoff between the geometrical and material parameters. The analysis discussion is focused on a representative specification of a frequency range of up to 5 kHz.
The pitch of a mistuned harmonic: Evidence for a template model
Authors: Lin Jian-Yu , Hartmann William M.
Published: July 2002

A harmonic of a periodic complex tone can be heard out as a separate entity if the harmonic is slightly mistuned from its correct frequency. Pitch matching experiments show that the pitch of such a mistuned harmonic differs systematically from its frequency. The shift in pitch is found to be an exaggeration of the frequency mistuning. This article considers two classes of model for the pitch shift. In the first class are tonotopically local interaction models which attribute the pitch shift to interactions between the mistuned harmonic and neighboring harmonics, where the neighborhood is established by peripheral filtering. The second class of model attributes the pitch shift to a contrast between the mistuned harmonic and a broadband harmonic template. This article describes six pitch matching experiments using complex tones having spectral gaps, strategically chosen to compare local interaction and template models. The results show that when a competition is set up between local interactions and a template, the template proves to be dominant. A parallel between the pitch shifts of mistuned harmonics and periodicity pitch, also attributed to a harmonic template, is seen as the frequency range of the mistuned harmonic is changed. Tonotopically local influences are evident in several experiments, but they are of secondary importance.
Wave propagation in range-dependent poro-acoustic waveguides
Authors: Lingevitch Joseph F. , Collins Michael D.
Published: July 2002

The parabolic equation method is extended to handle range-dependent poro-acoustic waveguides. A poro-acoustic medium is the limiting case of a poro-elastic medium in which the shear wave speed vanishes. Recent experiments indicate that this is a relevant limit [Chotiros, “Biot model of sound propagation in water-saturated sand,” J. Acoust. Soc. Am. 97, 199–214 (1995)]. Energy-conserving and single-scattering techniques are developed for handling vertical interfaces. The single-scattering solution is extended to problems involving fluid layers above poro-acoustic sediments. Improved rational function approximations are developed by rotating the branch cut [Milinazzo et al., “Rational square-root approximations for parabolic equation algorithms,” J. Acoust. Soc. Am. 101, 760–766 (1997)].