bluuebunny/crossref_metadata_2025 huggingface dataset:
Reverberation: Urick and beyond
Authors: Holliday D. V.
Published: July 2002

In his classic textbook, Principles of Underwater Sound for Engineers, Urick dedicated more space to reverberation, than to any other subject except propagation loss. His characterizations of reverberation were practical, easily understood, and remarkably complete for the era in which they were written. The chapter on scattering, especially the references, was an invaluable starting point for both students and practicing designers of active sonars. Urick, the sonar designer, pragmatically asserted that reverberation was a ‘‘particularly obnoxious’’ phenomenon. However, Urick, the scientist, demonstrated an unbridled curiosity about the underlying causes of the phenomena that he observed in the sea. Near the end of his active career in acoustics, the patterns of research into sound scattering changed dramatically. Urick personally encouraged young scientists to pursue a detailed understanding of the causes of scattering. Reverberation, which clearly had been a part of the ‘‘noise’’ in the sea became a ‘‘signal’’ which could be used to study and describe the sea surface, the seabed, and the various particles, animals, and bubbles found in the water column. This paradigm shift and some of its consequences, e.g., the extension of measurements to both higher and lower frequencies will be examined. [Work supported by ONR Code 322BC.]
Array signal-gain measurements in shallow-water
Authors: Carey William M. , Cable Peter G.
Published: July 2002

Shallow-water transverse coherence lengths can be estimated by the measurement of the narrow-band coherence function, broadband correlation function, or the signal gain either from a direct measurement with a filled aperture or the steered beam response of a sparsely filled aperture. Signal-gain measurements with an array of sensors have a larger number of degrees of freedom, spatial filtering of unwanted noise sources, and higher signal-to-noise ratios. Given a Gaussian coherence function, the coherence length may be estimated from these gain measurements. This paper discusses signal-gain measurements performed in five shallow-water sandy-bottomed areas with known environmental conditions using horizontal-bottomed arrays, omnidirectional explosives, and continuous sources between 100 and 600 Hz to ranges of 40 km. The coherence lengths determined by using a Gaussian coherence function yield a consistent representative value of approximately 30 wavelengths at a range of 40 km and a frequency of 400 Hz, which decreases with an increase in frequency. Comparisons show these lengths are consistent with previous measurements. Analytical considerations indicate these lengths are due to the combined effects of the water column variability and bottom. Implications for shallow-water array processing are discussed.
Application of a new post-processing method for predicting acoustic radiation when using incompressible, viscous computational fluid dynamics
Authors: Grace Sheryl M. , Curtis Caroline K.
Published: July 2002

A new framework is being developed for post-processing results from computational models of incompressible, viscous flows. The post-processor is a computational scheme focused on producing acoustic predictions using the incompressible flow quantities as inputs. The post-processing method has three distinguishing features: it is applicable to any flow field; it allows for the computation of the acoustic pressure within complex flow regions; and it extends the applicability of existing CFD codes in a manner easily implemented by those with CFD experience. The method is based on the classical splitting of a field into three components; vortical, acoustic, and entropy modes; and the method accounts for viscous and thermal dissipation. When simplified, the method reduces to solving Lighthill’s equation computationally with the source term supplied by the incompressible CFD calculation. Here, the new method is applied to the problem of a two-dimensional cavity subject to grazing flow. The incompressible, viscous results are calculated using fluent. The subsequent acoustic predictions are then compared to experimental and computational results found in the literature and are shown to agree well.
Acoustic radiation impedance of rectangular pistons on prolate spheroids
Authors: Boisvert J. E. , Van Buren A. L.
Published: July 2002

The self- and mutual impedances for rectangular piston(s) arbitrarily located on a rigid prolate spheroidal baffle are formulated. The pistons are assumed to vibrate with uniform normal velocity and the solution is expressed in terms of a modal series representation in spheroidal eigenfunctions. The prolate spheroidal wavefunctions are obtained using computer programs that have been recently modified to provide accurate values of the wavefunctions at high frequencies. Results of the normalized self- and mutual radiation resistance and reactance are presented over a wide frequency range at various locations for several different sizes of pistons and spheroidal baffles. [Work supported by ONR Code 321 and NUWC ILIR program.]
Ultrasonic investigation of acoustic lenses
Authors: Petculescu Petre
Published: July 2002

In order to be efficient, acoustic lenses must meet the following requirements: the lens material must have low-ultrasound attenuation and be defect-free and the concave focusing surface must be as smooth as possible to minimize abberations. In this paper, we analyzed two types of plane-concave lenses by using the immersion C-scan method. To acquire and process the data, we used a last-generation ultrasonic flaw detector interfaced with a computer which also drives the mechanical immersion scanning setup. The software also enabled us to perform B-scans on the lens for depth visualization and analysis. Thus we were able to realize both depth and profile maps of the lenses with considerable precision.
National park service noise issues
Authors: Henry Wesley R. , Schmidt William B. , Ernenwein Rick
Published: July 2002

The National Park Service (NPS) is an agency established, in part, to protect the resources and values associated with the properties assigned to its care. The NPS has found itself increasingly involved in responding to and dealing with human-caused noise and its impacts on the parks. This paper traces some of the more significant developments in the recent NPS past related to noise and discusses the current NPS issues related to noise.
Educating national park users on preserving natural soundscapes
Authors: Ernenwein Rick , Henry Wesley R. , Schmidt William B.
Published: July 2002

The National Park Service (NPS) is the custodian of both some of the sites tied intimately to the history of powered flight and some of the quietest places in this country. Recognizing the need to both educate its personnel and the public about the sounds of nature and to properly deal with visitor opportunities like air tours that generate noise that masks the sounds of nature, the NPS has put together an educational package. This presentation will use many of those materials to show how the NPS is dealing with the protection of the sounds of nature, the natural soundscape of the parks.
Ipsilateral acoustic reflex detection using wideband acoustic reflectance, admittance, and power measurements
Authors: Keefe Douglas H. , Feeney M. Patrick
Published: July 2002

Progress has been achieved in measuring contralateral acoustic reflex shifts to tonal and noise activators in wideband reflectance, admittance, and power [Feeney and Keefe, J. Speech, Language, and Hearing Research (in press)], but no measurements have been made of the corresponding ipsilateral reflex shifts. Because the thresholds of these wideband contralateral reflex shifts were at least 8 dB lower than those obtained using standard clinical techniques, and because clinical research requires the use of both contralateral and ipsilateral testing, it is of interest to formulate a wideband technique to measure the ipsilateral reflex. Such an ipsilateral technique has been developed based on the observation that the major component of the contralateral reflex is below 1.6 kHz. Probe signals were designed with bandwidths from 0.25 kHz up to 1.6 or 2 kHz, and calibrated to measure reflectance (and related responses). The reflex activator signals consisted of tonal stimuli in the range from 2–4 kHz, with levels varied to measure reflex input–output functions. Ipsilateral reflex shifts have been detected using this technique. Work is in progress to compare ipsilateral and contralateral reflexes measured using the same probe and activator signals. [Work supported by NIDCD.]
Gap detection for similar and dissimilar gap markers
Authors: Grose John H. , Hall Joseph W. , Buss Emily , Hatch Deb
Published: July 2002

Gap detection for acoustic stimuli is most acute for iso-frequency gap markers and becomes poorer when the two markers are shifted apart in frequency. Gap detection for electrical stimuli presented on a single (iso-frequency) electrode channel in cochlear implant users is most acute when the two markers of the gap are perceptually similar and becomes poorer for perceptually dissimilar markers [M. Chatterjee, Q. Fu, and R. V. Shannon, J. Acoust. Soc. Am. 103, 2515–2519 (1998)]. This raises the question of whether the decline in performance for acoustic stimuli with disparate frequencies reflects poor across-frequency temporal processing or the effects of a perceptual discontinuity between the two markers. To test this, gap detection was measured in a group of normal-hearing listeners using markers that were either perceptually similar or dissimilar. The types of markers were pure tones, am tones, and fm tones. The two markers bounding a gap were either the same or differed in type, frequency, and/or modulation rate. Results indicated that gap detection performance declined for frequency-disparate markers but did not uniformly deteriorate for perceptually dissimilar markers. [Work supported by NIH NIDCD R01-DC01507.]
The effect of internal point masses on the radiation of a ribbed cylindrical shell
Authors: Marcus Martin H. , Houston Brian H.
Published: July 2002

The radiation associated with complexity is examined by use of finite element–infinite element models of framed fluid loaded shells for frequencies up to ka=10. The vibro-acoustic response of the shell with no internal complexity is compared to an identical structure with point masses attached to the frames. The simple ribbed shell is seen to have pass and stop band structure with radiation physics that is dominated by supersonic components. The addition of point masses to the structure gives rise to major changes in the response that include a coupling of radiating and otherwise nonradiating circumferential orders, resulting in a significant increase in radiation (about 10 dB) over a broad frequency range. These results are in general agreement with nearfield acoustical holography (NAH) experimental results. [Work supported by ONR.]
Modeling and compensation of hysteresis in piezoceramic actuators for vibration control
Authors: Lee Soon-Hong , Royston Thomas J. , Friedman Gary
Published: July 2002

It has been established that the Maxwell resistive capacitor (MRC) hysteresis model accurately represents hysteretic behavior in the dielectric domain of PZT-based piezoceramics. Methods for MRC and inverse MRC online model identification have been developed along with an MRC-based framework for calculating continuous hysteretic energy loss for arbitrary loading histories. Building on these developments, an adaptive feedforward compensation technique for attenuating the effect of hysteresis in vibration control applications is proposed and evaluated experimentally via studies on a 1–3 piezoceramic composite. Also, indirect electrical excitation is compared to direct voltage drive of PZT devices for reduced hysteretic behavior in vibration control applications. [Work supported by the Office of Naval Research.]
Damage detection for enhanced evaluation of structures
Authors: Clark Gregory A. , Burnett Gregory C.
Published: July 2002

Monumental structures consist of public and private buildings, bridges and other transportation structures, dams, key industrial and scientific buildings and many special structures. Most of these structures are key to our social, commercial and technical infrastructure. All are vulnerable to damage or failure when stressed by abrupt, large-scale extreme events, the most common of which are earthquakes and wind. Forward reaching simulations, structural dynamic analysis techniques, innovative sensing, signal processing and remote communication form the core of this effort. Here we discuss our solutions to the structural damage detection problem. We take a model-based signal processing approach. This means that we exploit prior knowledge from first principle models for the structure to construct signal processing algorithms. Assuming that the models are representative of the actual structure, the model based approach offers significant performance improvement over algorithms based on measured data alone. Here we discuss the processor performance on both simulated and experimental data of a five-story structure.
Pre-differentiated M-sequences for laser Doppler-based identification of vibrational systems
Authors: Xiang Ning , Sabatier James
Published: July 2002

A laser Doppler vibrometer (LDV) can be used to measure the surface velocity of a vibrating object in a noncontacting manner. One of basic components in the LDV for sensing surface velocity is frequency demodulation where inevitable phase noise can impair sensing precision of the LDV. Owing to high-noise immunity and computational efficiency the fast M-sequence transform technique has received wide acceptance in various scientific and engineering fields. In the present work, pre-differentiated M-sequences have been employed as excitation signals for system identifications using a laser Doppler vibrometer. Along with inherent cross-correlation mechanism of the fast M-sequence transform, further improvement of phase noise immunity can be achieved. [The work is supported by U. S. Army Communications-Electronics Command.]
Low-frequency multiple scattering in fish schools: The self-consistent method for strongly coupled resonators
Authors: Feuillade C.
Published: July 2002

Low-frequency acoustic scattering from fish is typically dominated by the swimbladder resonance response. Schools of fish frequently consist of closely spaced individuals of similar size and, at resonance frequencies, this can cause multiple scattering processes between the fish to become significant and complex. The acoustic wavelength at the swimbladder resonance frequency is generally many times the length of the fish, and frequently greater than the dimensions of a small school. Since schooling fish often arrange themselves so that they are about one fish length apart, the scattered wave fields from neighboring fish will interact coherently. This feature must also be incorporated to realistically describe scattering from fish schools. An effective methodology is available through the application of self-consistent multiple scattering techniques, and a school scattering model based on this approach has recently been developed and used successfully to analyze data [J. Acoust. Soc. Am. 99, 196–208 (1996)]. Swimbladders are physically similar to bubbles, and the same approach may be used to develop a theory of multiple scattering in bubbly water which applies to strongly resonating scatterers and high-volume fractions. [Work supported by ONR.]
Noise effects in learning experiments
Authors: McDonald Louise M.
Published: July 2002

The effects of noise in learning experiments vary considerably, depending on the characteristics and duration of the noise, and the behavior through which learning is being measured. There can also be considerable individual differences in animals’ responses to noise, even between members of the same species. Acute, mild noise is typically no more than a distractor. As noise intensity increases, behavioral effects increase, ranging from increased rates of responding in lever-pressing experiments to freezing in radial-maze tasks. Some paradigms are relatively unaffected by noise, including purely appetitive tasks, such as solving mazes for food reward, and tasks such as the water maze, where the aversive properties of water immersion outweigh the aversive effects of noise. Individual differences in animals’ responsiveness to noise can predict learning performance, with stronger responses to noise being associated with more effective learning. Research using rats in our own laboratory shows that chronic exposure to mild but unpredictable noise can attenuate latent inhibition, the capacity to ignore a stimulus that has previously been conditioned to be irrelevant.
A low-cost sound level meter based on personal computer
Authors: de Arcas Guillermo , Lopez Juan M. , Recuero Manuel , Martin Alberto
Published: July 2002

In this abstract a low-cost sound level meter is developed with the help of digital signal processing techniques and an integrated programming environment. The instrument is based on the use of a general purpose data acquisition PC card to acquire the signal and a powerful digital signal processing algorithm based on digital filters to compute a one-third octave band analysis conforming to ANSI S1.11-1986 in real time. The objective is made possible thanks to the use of optimized signal processing routines from Intel Signal Processing Library. The use of this library and an instrumentation specific integrated programming environment such as LabWindows/CVI (National Instruments) makes it possible to design a low-cost instrument in a very short time. The algorithm is a multirate filter bank implementation of the standard. The discussion is completed with several simulations and benchmarks are presented for different design situations. Execution time is also compared to that obtained with a popular digital signal processor (TMS820C30 from Texas Instruments). [For Engineering Acoustics Best Student Paper Award.]
Problems associated with driving an efficient Tonpilz transducer with broadband signals
Authors: Lubell Alan H.
Published: July 2002

A symmetrical piezoceramic-stack-driven Tonpilz makes a very efficient underwater loudspeaker for use in any body of water where human activity takes place. The large variation of impedance with frequency makes driving this type of transducer a unique problem. Transformer leakage inductance together with stack capacitance causes excessive current to be drawn at the series resonant frequency, which must be controlled with an appropriately sized series resistor. This paper presents measured and computed frequency responses and impedance magnitude versus frequency graphs for several of Lubell Labs.’ underwater acoustic transducers. Included are recent calibrations made at the USN Dodge Pond facility. These are used to determine suitable values of leakage inductance and series resistance. A reasonable size series resistance is one that will not cause excessive loss at the fundamental transducer resonance. Excessive leakage inductance must be avoided because of its effect on high frequency response. An expression for the current drawn when the transducer is driven with bandlimited pink noise has been derived by the author and will be given herein.
Perception of rhythm by children in multitimbral, multimetric contexts
Authors: Singh Punita G.
Published: July 2002

Perception of meter by children aged 6 to 12 was studied using sequences of 12 tones as stimuli. Either no accents, or physical accents at positions implying triple, quadruple, or both meters were provided by changing the spectral locus of four harmonics n, n+1, n+2, n=3, of tones Ln (where n=2 or 6) or the rise/decay times of their temporal envelopes (95+5 ms, vs 5+95 ms). Listeners reported if they perceived a triple, quadruple, or ambiguous meter, or no accents at all. Children were easily able to perceive the metrical structure of sequences with accents on triple or quadruple meter positions alone. Mixed meters were hard to parse in a single-timbre context. In mixed sequences with accents provided by different timbre features at quadruple and triple meter positions, listeners tended to follow the meter implied by tones L2 rather than L6. Temporal envelope variables were not effective in facilitating parsing of mixed meters. Results indicate that young listeners are similar to adults in using timbral information to parse complex meters. Lower harmonics seemed to be more effective carriers of accents than higher harmonics. Spectral resolving power may thus be an important aspect of not just pitch, but rhythm perception as well.
Timing relationships in rhythmic tapping and music performance with delayed auditory feedback
Authors: Finney Steven A.
Published: July 2002

Delayed auditory feedback (DAF) disrupts performance in speech, music, and rhythmic tapping, with a characteristic symptom in all domains being insertions or repetitions of material (resembling stuttering). One recent attempt to explain DAF impairment, the Node Structure Theory [D. G. MacKay, The Organization of Perception and Action (Springer, New York, 1987)] has proposed that such repetitions are due to the auditory feedback causing reactivation of the node which produced that feedback, i.e., the sound is a stimulus which precedes (and causes) the repetition. The current research investigated the effects of various auditory delays on tapping simple rhythms, and analyzed the precise temporal relationships between sounds and taps. For the delays causing the most impairment, sound onset was found to follow rather than precede the onset of inserted taps, counter to the requirements of the Node Structure Theory. DAF impairment in a previous experiment in musical performance [S. A. Finney, Music Perception 15, 153–174 (1977)] was reanalyzed from this perspective, and alternative explanations of the repetition behavior are discussed.
Progress on a rating system for hearing protector attenuation
Authors: Murphy William J. , Franks John R.
Published: July 2002

The cumulative distribution of A-weighted noise reduction (CDNRA) has been proposed as an alternative to the noise reduction rating for hearing protectors [W. J. Murphy and J. R. Franks, J. Acoust. Soc. Am. 105, 1131 (1999)]. Individuals’ REAT data were A-weighted and summed across frequencies to determine the statistical distribution. The cumulative distribution of REAT data was fit to a combination of two logistic curves to capture the features of well-fit and poorly-fit hearing protectors. Previously, the CDNRA model was shown to yield Pearson’s correlation coefficients of 0.99 or better. In this paper, the CDNRA theory will be reviewed and the method will be applied to the subject-fit data from six HPDs. The Bilsom UF-1 earmuff was rated at 23-dB attenuation. The V-51R was rated at 6-dB attenuation. The EP100 was rated at 7-dB attenuation. And the EAR Classic was rated at 23-dB attenuation. Subject-fit data from the EAR Express and Howard Leight Max earplugs will be presented as well.
Time-of-flight measurements on high-frequency surface acoustic phonons in silicon
Authors: Photiadis D. M. , Ding J.
Published: July 2002

Results from time-of-flight measurements of high-frequency surface acoustic phonons (50–500 GHz) in (001) silicon wafers at low temperatures are reported. Pulsed laser excitation is used for the generation of the high-frequency surface acoustic phonons and aluminum edge bolometers are used as detectors. The times defined by the fast initial response of the edge bolometer correspond to surface acoustic delays in silicon. Late time responses consistant with echoes from the back face of the wafer were also observed. These results and the accompanying analysis will be discussed. [This research was supported by the Office of Naval Research.]
Wave-number solution for a string with distributed mass properties
Authors: Pierucci Mauro
Published: July 2002

A structure with spatially variable properties when excited at a single frequency will excite many wave numbers. In this paper the vibration of a string with a mass distribution m(x) given by a Fourier series expansion is analyzed. The equation governing the wave-number solution w(k) for the string displacement is obtained via Fourier transform. The final result is a finite-difference equation. The finite-difference equation relates all of the displacement wave numbers to each other. The solution to this equation is obtained by rewriting it as a system of simultaneous equations that are then solved by standard linear algebra techniques. Wave-number spectral solutions are obtained for different mass distribution. In one case the mass distribution is assumed to vary in a discontinuous manner between adjacent bays, in another case the mass is assumed to vary in a ‘‘triangular’’ manner. The wave-number solutions are presented in 3-D graphs so that the magnitude of the displacement can be seen as a function of the wave number and either the magnitude of the additional mass, the area over which the mass is distributed, or the length of the bay. In the limiting case as the mass distribution becomes very concentrated, the classical pass/stop band, familiar with periodic structures, is recovered.
Assessment of intelligibility of digitized speech by young adults under different listening conditions
Authors: Bettagere Ramesh N.
Published: July 2002

The present study evaluated the intelligibility of tape-recorded speech sentences and digitized speech sentences digitized at low (4 kHz), moderate (8 kHz), and high (16 kHz) sampling rates by young adults under different listening conditions (quiet versus noise). Twenty-four young adults participated as subjects. The tape-recorded speech sentences and digitized speech sentences were presented to each subject in quiet and in the presence of background speech babble at a signal-to-noise ratio of 0 dB. The subjects were instructed to immediately write down each sentence soon after they heard it. A 4×2 analysis of variance with repeated measures was performed to assess the effects of mode of speech and listening conditions on total number of words correctly transcribed. Results showed that the main effects for mode of speech and listening condition were statistically significant. The interaction effects of mode of speech by listening condition were also statistically significant. Pairwise comparisons showed that significantly more words were transcribed in the quiet condition than in the corresponding noise condition for all the modes of speech except for the digitized speech at high sampling rate (16 kHz). The implications of the results are discussed.
A spread spectrum technique for studying sound propagation in forested areas
Authors: Swearingen Michelle E. , Swanson David C.
Published: July 2002

Spread spectrum methods are relatively new to acoustics, but have been shown to be quite useful, especially in determining the path taken by a particular sound pulse. Because of this property, spread spectrum signals should give a rough picture of the scattering off tree boles that occurs in a forest. The arrival times will determine the path taken, and the level changes will determine how much attenuation that path contributes. The experimental setup and preliminary data will be presented.
What is a neighbor in a neighborhood effect? Items that mismatch on the first phoneme still produce neighborhood effects
Authors: Newman Rochelle S. , Sawusch James R. , Luce Paul A. , Healy Alicia
Published: July 2002

Previously, we presented results suggesting that neighborhood density could influence perception in phoneme identification tasks. In a typical task demonstrating this effect, subjects might hear two series, one ranging from beysh to peysh, while the other varied from beyth to peyth, where beyth is similar to more real words than peyth, and peysh is similar to more real words than beysh. Subjects were more likely to classify the ambiguous stimuli from each series as members of the category which makes it more wordlike. In the present series, similar series were created where the only neighbors for the endpoints were ones that differed in their initial consonant. We created two pairs of series: in the first, ∫oif–t∫oif and ∫of–t∫of, the neighbors which drove the bias were all ones which matched on the initial phoneme (e.g, choke). In the second series, zU∫–zUt∫ and zE∫–zEt∫, the only neighbors for the items were ones that mismatched on the initial phoneme (e.g., push, mesh, fetch, etc.). Similar neighborhood effects were found for both series, suggesting that words in memory which do not match the beginning of a perceived item are still activated and can still influence perception.
Perspectives on teaching: A tribute to Bob Urick
Authors: Etter Paul C.
Published: July 2002

Based on 5 years of teaching short courses with Bob Urick, an assessment is made of his teaching style and elements of content. Urick’s influence on the underwater-acoustics community is exemplified by the popularity of his books and short courses. The fact that much of Urick’s nomenclature became institutionalized within the international community provides further evidence of his authoritative command of the technical literature and his lucid conveyance of fundamental concepts. Specific examples are drawn from personal experience to demonstrate the effective aspects of his instructional methods, including both style and content.A synthesis of Urick’s methods can instruct and inform contemporary educators in the field of underwater acoustics and related disciplines.His equally important, but less tangible, impact on the professional development of emerging sonar engineers is also discussed from the dual perspective of a co-instructor and former student. Finally, Urick’s conception of the complementary roles of field measurements and numerical modeling is reviewed to characterize the proper relationship between measurements and modeling in modern ocean-acoustics research.
Development of a velocity gradient underwater acoustic intensity sensor
Authors: Bastyr Kevin J. , Lauchle Gerald C. , McConnell James A.
Published: July 2002

A neutrally buoyant, underwater acoustic intensity probe is constructed and tested. This sensor measures the acoustic particle velocity at two closely spaced locations, hence it is denoted a “u-u” intensity probe. A new theoretical derivation infers the acoustic pressure from this one-dimensional velocity gradient, permitting the computation of one component of acoustic intensity. A calibration device, which produces a planar standing-wave field, is constructed and tested. In this calibrator, the performance of the u-u intensity probe compares favorably to that of an acoustic intensity probe which measures both pressure and velocity directly.
A boundary that sustains a negligible specular reflection coefficient over a wide frequency band
Authors: Maidanik G. , Dickey J.
Published: July 2002

In a previous paper the authors analyzed and discussed the specular reflection coefficient of a plane boundary comprised of a plate, a compliant layer, and a fluid. The analysis showed that a negligible specular reflection coefficient may be derived provided specific resonance conditions are met. The resonance of concern is that between the surface mass of the plate and the surface stiffness of the compliant layer. The conditions of resonance included the value that must be assigned to the loss factor in the compliant layer. In the present paper, an attempt is made to determine the conditions that must be placed on the surface stiffness of the compliant layer in order to increase the frequency range over which a negligible specular reflection coefficient may be maintained. The tolerances in these conditions are also estimated.
Acoustic mechanisms that determine the ear-canal sound pressures generated by earphones
Authors: Voss Susan E. , Rosowski John J. , Shera Christopher A. , Peake William T.
Published: July 2002

In clinical measurements of hearing sensitivity, a given earphone is assumed to produce essentially the same sound-pressure level in all ears. However, recent measurements [Voss et al., Ear and Hearing (in press)] show that with some middle-ear pathologies, ear-canal sound pressures can deviate by as much as 35 dB from the normal-ear value; the deviations depend on the earphone, the middle-ear pathology, and frequency. These pressure variations cause errors in the results of hearing tests. Models developed here identify acoustic mechanisms that cause pressure variations in certain pathological conditions. The models combine measurement-based Thévenin equivalents for insert and supra-aural earphones with lumped-element models for both the normal ear and ears with pathologies that alter the ear’s impedance (mastoid bowl, tympanostomy tube, tympanic-membrane perforation, and a “high-impedance” ear). Comparison of the earphones’ Thévenin impedances to the ear’s input impedance with these middle-ear conditions shows that neither class of earphone acts as an ideal pressure source; with some middle-ear pathologies, the ear’s input impedance deviates substantially from normal and thereby causes abnormal ear-canal pressure levels. In general, for the three conditions that make the ear’s impedance magnitude lower than normal, the model predicts a reduced ear-canal pressure (as much as 35 dB), with a greater pressure reduction with an insert earphone than with a supra-aural earphone. In contrast, the model predicts that ear-canal pressure levels increase only a few dB when the ear has an increased impedance magnitude; the compliance of the air–space between the tympanic membrane and the earphone determines an upper limit on the effect of the middle-ear’s impedance increase. Acoustic leaks at the earphone-to-ear connection can also cause uncontrolled pressure variations during hearing tests. From measurements at the supra-aural earphone-to-ear connection, we conclude that it is unusual for the connection between the earphone cushion and the pinna to seal effectively for frequencies below 250 Hz. The models developed here explain the measured pressure variations with several pathologic ears. Understanding these mechanisms should inform the design of more accurate audiometric systems which might include a microphone that monitors the ear-canal pressure and corrects deviations from normal.
Characteristics of efferent mediated enhancement of distortion-product otoacoustic emissions
Authors: Sun Xiao-Ming , Dolan David F.
Published: July 2002

Efferent stimulation can enhance distortion-product otoacoustic emissions (DPOAEs) (Siegel and Kim, 1982), but the stimulus conditions in which enhancement occurs have not been clearly described. To clarify the efferent mediated enhancement of cochlear active process, 2f1–f2 DPOAE I/O function was measured in pigmented guinea pigs. For f2/f1=1.20, the crossed olivocochlear bundle (COCB) stimulation suppressed the DPOAE evoked by low primary levels, the rapid growth portion of an I/O function. It enhanced it in the saturating portion evoked by moderate levels, 45 to 65 dB SPL when L1−L2=0 to 20 dB, and suppressed it with further increase in stimulus level. For f2/f1=1.08, enhancement appeared only when L1=75 dB SPL and L1−L2=30 to 40 dB. For f2/f1=1.45, enhancement appeared when L1=45 to 55 dB SPL and L1−L2=-10 to -20 dB. COCB stimulation tends to alter the DPOAE I/O function toward linear growth. Both suppression and enhancement were significantly reduced by strychnine. The results suggest that effect of efferent activation on evoked OHC activity is not a simple suppression, but a modulation of the nonlinearity of its growth function. [Work supported by grants: NIH/NIDCD PO1−DC00078 and T32−DC00011.]
Control performance and robustness of an active noise control system for uncertain primary sound fields
Authors: Yoon Doo-Byung , Kim Yang-Hann
Published: July 2002

In this work, the control performance and robustness of an active noise control system subjected to uncertain primary sound fields are investigated. For this purpose, the performance index, residual potential energy in a desired quiet zone, is derived as a function of sound field variables, quiet zone variables, and control system variables. In the presence of uncertainty, typical measures of the robustness and performance of a control system, maximum, minimum, mean, and variance of the performance index are derived theoretically. In addition, based on the least-squares orthogonality principle, the condition for implementing the best-oriented control system, which is robust and can maximize the control performance by using a given number of control sources and sensors, is investigated. Finally, numerical simulations are carried out to illustrate and verify the proposed theory.
An inexpensive passive acoustic system for recording and localizing wild animal sounds
Authors: Hayes Sean A. , Mellinger David K. , Croll Donald A. , Costa Daniel P. , Borsani J. Fabrizio
Published: July 2002

An inexpensive animal recording and tracking system was designed, which uses sound-recording buoys deployed at several locations simultaneously in a passive hydrophone array. Each buoy contains a global positioning system (GPS) Location logger, a stereo digital audio tape (DAT) recorder with a hydrophone connected to one channel, and a VHF radio signal for time synchronization connected to the second channel. In a calibration test, three buoys were deployed in triangle formation at 1.8-km spacing. Light bulb implosions were localized to an accuracy of 60 m at the array center. These buoys are far less expensive than most marine acoustic tracking systems. The instrument package can be used for drift, moored, or terrestrial applications.
Transient Development of Velocity Profiles During Shear Flow of a Viscoelastic Fluid
Authors: Okeson J. K. , Emery A. H.
Published: July 2002

A solution is presented to the boundary value problem for the transient development of the velocity profile in a viscoelastic fluid subjected to the sudden onset of shearing in an idealized viscometer. A differential Oldroyd type of constitutive equation is used to describe the mechanical behavior of the fluid. The results indicate that the elastic nature of the fluid significantly increases the length of time required for the steady-state velocity profile to be established. A solution is also presented for the drainage of a viscoelastic fluid off a vertical plate. The predicted initial elastic overshoot or rapid drainage of the fluid is in qualitative agreement with reported experimental results.
Quantitative analyses of complex pharmaceutical mixtures by the Rietveld method
Authors: Iyengar Sampath S. , Phadnis Neelima V. , Suryanarayanan Raj
Published: July 2002

The object was to perform simultaneous quantitative analyses of complex pharmaceutical solid mixtures by the Rietveld method. Mixtures consisting of anhydrous β-carbamazepine, anhydrous α-carbamazepine, and carbamazepine dihydrate were chosen as the model system. Lithium fluoride was used as the internal standard. Mixtures of various compositions were prepared and subjected to X-ray powder diffractometry (XRD). The XRD pattern of each mixture was analyzed by the Rietveld method and at the end of the refinement, the goodness of fit was evaluated. When the analyte concentration was high (≥20%), the relative error in the determination was <±5%. The detection of analyte was possible even when its concentration was low (<1% w/w). A unique advantage of the method is that it enables simultaneous quantitative analyses of multiple phases without the requirement of “standard curves.” © 2001 International Centre for Diffraction Data.
Structure determination of anhydrous acid strontium oxalate by conventional X-ray powder diffraction
Authors: Vanhoyland G. , Van Bael M. K. , Mullens J. , Van Poucke L. C.
Published: July 2002

The anhydrous acid strontium oxalate Sr(HC2O4)⋅½(C2O4) was obtained by thermal decomposition of the hydrated acid strontium oxalate Sr(HC2O4)⋅½(C2O4)⋅H2O. This non-hygroscopic compound crystallizes in the space group P 21/c (No. 14) with unit cell parameters: a=0.796 61(7) nm, b=0.9205(1) nm, c=0.731 98(8) nm, and β=102.104(8)°. Final refinement of the X-ray powder data yielded RB=3.2% and Rwp=11.1% (background-corrected data). In this structure, Sr is eight-fold coordinated by O. These polyhedra are connected together by edge-sharing to form two-dimensional (2D) layers along the bc-plane, which means that there is an increased dimensionality from 1D to 2D with decreasing water content of the acid oxalates.
A powder diffraction study of MIBaIn2(PO4)3 (MI=Na, K, Cs) with a langbeinite-type structure
Authors: Louër D. , Moise V. , Liégeois-Duyckaerts M. , Rulmont A.
Published: July 2002

Three phosphates, MIBaIn2(PO4)3 with MI=Na, K, Cs, isostructural to the langbeinite structure, have been studied from powder diffraction data collected with monochromatic radiation obtained from a conventional X-ray source. Precise powder data are reported, as well as cell parameters, i.e., a=10.026 08(9) Å, a=10.121 57(13) Å and a=10.226 94(9) Å for MI=Na, K and Cs, respectively. A Rietveld refinement has been carried out (space group P213), with final RF factors, 0.061, 0.041 and 0.027, and Rwp factors, 0.196, 0.142 and 0.129, for MI=Na, K and Cs, respectively. There are two octahedrally coordinated In3+ ions in the asymmetric unit and the final refinements suggest disorder on the two sites of the MI/Ba sublattice.
Association of Medicaid Expansion With Postpartum Depression Treatment in Arkansas
Authors: Steenland Maria W. , Trivedi Amal N.
Published: February 2023

Importance

Postpartum depression affects approximately 1 in every 8 postpartum individuals in the US. Antidepressant medication can effectively treat postpartum depression. However, gaps in postpartum insurance coverage after the end of Medicaid pregnancy coverage at 60 days postpartum may limit treatment uptake and decrease continuity of postpartum depression treatment.

Objective

To examine the association of Medicaid expansion in Arkansas with postpartum antidepressant prescription fills and antidepressant continuation and supply during the first 6 months postpartum.

Design, Setting, and Participants

Cohort study with a difference-in-differences analysis comparing persons with Medicaid and commercially financed childbirth using Arkansas’ All-Payer Claims Database (2013-2016). Analysis was completed between July 2021 and June 2022.

Exposures

Medicaid-paid childbirth after January 1, 2014.

Main Outcomes and Measures

Antidepressant medication prescription fills and the number of days of antidepressant supply in the early (first 60 days after childbirth) and the late (61 days to 6 months after childbirth) postpartum periods.

Results

In this cohort study with a difference-in-differences analysis of 60 990 childbirths (mean [SD] birthing parent’s age, 27 [5.3] years; 22% Black, 7% Hispanic, 67% White individuals), 72% of births were paid for by Medicaid and 28% were paid for by a commercial payer. Before expansion, 4.2% of people with a Medicaid-paid birth filled an antidepressant prescription in the later postpartum period. Medicaid expansion was associated with a 4.6 percentage point (95% CI, 2.9-6.3) increase in the likelihood, or a relative change of 110%, in this outcome. Before expansion, among people with postpartum depression in the early postpartum period with a Medicaid-paid birth, 32.7% filled an antidepressant prescription in the later postpartum period, and had an average of 23 days of antidepressant prescription supply during the later postpartum period. Among people with early postpartum depression, Medicaid expansion increased the continuity of antidepressant treatment by 20.5 percentage points (95% CI, 14.1-26.9) and the number of days with antidepressant supply in the later postpartum period by 14.1 days (95% CI, 7.2-20.9).

Conclusions and Relevance

Medicaid expansion in Arkansas was associated with an increase in postpartum antidepressant prescription fills, and an increase in antidepressant treatment continuity and medication supply in the period after Medicaid pregnancy-related eligibility ended.
US Medical School Admissions Leaders’ Experiences With Barriers to and Advancements in Diversity, Equity, and Inclusion
Authors: Ko Michelle , Henderson Mark C. , Fancher Tonya L. , London Maya R. , Simon Mark , Hardeman Rachel R.
Published: February 2023

Importance

Despite decades-long calls for increasing racial and ethnic diversity, the medical profession continues to exclude members of Black or African American, Hispanic or Latinx, and Indigenous groups.

Objective

To describe US medical school admissions leaders’ experiences with barriers to and advances in diversity, equity, and inclusion.

Design, Setting, and Participants

This qualitative study involved key-informant interviews of 39 deans and directors of admission from 37 US allopathic medical schools across the range of student body racial and ethnic composition. Interviews were conducted in person and online from October 16, 2019, to March 27, 2020, and analyzed from October 2019 to March 2021.

Main Outcomes and Measures

Participant experiences with barriers to and advances in diversity, equity, and inclusion.

Results

Among 39 participants from 37 medical schools, admissions experience ranged from 1 to 40 years. Overall, 56.4% of participants identified as women, 10.3% as Asian American, 25.6% as Black or African American, 5.1% as Hispanic or Latinx, and 61.5% as White (participants could report >1 race and/or ethnicity). Participants characterized diversity broadly, with limited attention to racial injustice. Barriers to advancing racial and ethnic diversity included lack of leadership commitment; pressure from faculty and administrators to overemphasize academic scores and school rankings; and political and social influences, such as donors and alumni. Accreditation requirements, holistic review initiatives, and local policy motivated reforms but may also have inadvertently lowered expectations and accountability. Strategies to overcome challenges included narrative change and revision of school leadership structure, admissions goals, practices, and committee membership.

Conclusions and Relevance

In this qualitative study, admissions leaders characterized the ways in which entrenched beliefs, practices, and power structures in medical schools may perpetuate institutional racism, with far-reaching implications for health equity. Participants offered insights on how to remove inequitable structures and implement process changes. Without such action, calls for racial justice will likely remain performative, and racism across health care institutions will continue.